Table of Contents Kazalo Review paperPregledni papir Študij rudarstva in geotehnologije na Univerzi v Ljubljani od leta 1919 do danes Željko Vukelic 211 Original scientific paperIzvirni znanstveni clanki Removal of Na2SO4 from a Filter Ash Odstranjevanje Na2SO4 iz filtrskega prahu Blaž Janc, Damjan Hann 215 Hydrocarbon-Generating Potential of Eocene Source Rocks in the Abakaliki Fold Belt, NigeriaPotencial za nastanek oglikovodikov v eocenskih izvornih kamninah nariva Abakaliki O.A. Oluwajana, A.O. Opatola, O.B. Ogbe, T.D. Johnson 223 Assessment and Analysis of Precambrian Basement Soil Deposits Using Grain Size Distribution Ocena in analiza predkambrijskih nahajališc zemljin z uporabo porazdelitve velikosti zrn Gideon Layade, Charles Ogunkoya, Victor Makinde, Kehinde Ajayi 235 Spatial Resistivity Mapping of Ureje Dam Floor, Southwestern NigeriaProstorsko upornostno kartiranje dna jezu Ureje, JZ Nigerija Fatoba J.O., Eluwole A.B., Sanuade O.A., Aroyehun M.T. 245 Historical Review Zgodovinski pregled Instructions to Authors Navodila avtorjem Historical Review More than 90 years have passed since the University Lju­bljana in Slovenia was founded in 1919. Technical fields were united in the School of Engineering that included the Geologic and Mining Division, while the Metallurgy Divi­sion was established only in 1939. Today, the Departments of Geology, Mining and Geotechnology, Materials and Met­allurgy are all part of the Faculty of Natural Sciences and Engineering, University of Ljubljana. Before World War II, the members of the Mining Section together with the Association of Yugoslav Mining and Met­allurgy Engineers began to publish the summaries of their research and studies in their technical periodical Rudarski zbornik (Mining Proceedings). Three volumes of Rudarski zbornik (1937, 1938 and 1939) were published. The War interrupted the publication and it was not until 1952 that the first issue of the new journal Rudarsko-metalurški zbornik – RMZ (Mining and Metallurgy Quarterly) was published by the Division of Mining and Metallurgy, Uni­versity of Ljubljana. Today, the journal is regularly pub­lished quarterly. RMZ – M&G is co-issued and co-financed by the Faculty of Natural Sciences and Engineering Ljublja­na, the Institute for Mining, Geotechnology and Environ­ment Ljubljana, and the Velenje Coal Mine. In addition, it is partly funded by the Ministry of Education, Science and Sport of Slovenia. During the meeting of the Advisory and the Editorial Board on May 22, 1998, Rudarsko-metalurški zbornik was renamed into “RMZ – Materials and Geoenvironment (RMZ – Materiali in Geookolje)” or shortly RMZ – M&G. RMZ – M&G is managed by an advisory and international editorial board and is exchanged with other world-known periodicals. All the papers submitted to the RMZ – M&G undergoes the course of the peer-review process. RMZ – M&G is the only scientific and professional periodi­cal in Slovenia which has been published in the same form for 60 years. It incorporates the scientific and professional topics on geology, mining, geotechnology, materials and metallurgy. In the year 2013, the Editorial Board decided to modernize the journal’s format. A wide range of topics on geosciences are welcome to be published in the RMZ – Materials and Geoenvironment. Research results in geology, hydrogeology, mining, geo-technology, materials, metallurgy, natural and anthropo­genic pollution of environment, biogeochemistry are the proposed fields of work which the journal will handle. Editor-in-Chief Zgodovinski pregled Že vec kot 90 let je minilo od ustanovitve Univerze v Lju­bljani leta1919. Tehnicne stroke sose združile v Tehniški visoki šoli, ki sta jo sestavljala oddelka za geologijo in ru­darstvo, medtem ko je bil oddelek za metalurgijo ustano­vljen leta 1939. Danes oddelki za geologijo, rudarstvo in geotehnologijo ter materiale in metalurgijo delujejo v sklo­pu Naravoslovnotehniške fakultete Univerze v Ljubljani. Pred 2. svetovno vojno so clani rudarske sekcije skupaj zZdruženjem jugoslovanskih inženirjev rudarstva in me-talurgije zaceli izdajanje povzetkov njihovega raziskoval­nega dela v Rudarskem zborniku. Izšli so trije letniki zbor­nika (1937, 1938 in 1939). Vojna je prekinila izdajanje zbornika vse do leta 1952, ko je izšel prvi letnik nove revi­je Rudarsko-metalurški zbornik – RMZ v izdaji odsekov za rudarstvo in metalurgijo Univerze v Ljubljani. Danes revija izhaja štirikrat letno. RMZ – M&G izdajajo in financirajo Naravoslovnotehniška fakulteta v Ljubljani, Inštitut za ru­darstvo, geotehnologijo in okolje ter Premogovnik Velenje. Prav tako izdajo revije financira Ministrstvo za izobraževa­nje, znanost in šport. Na seji izdajateljskega sveta in uredniškega odbora je bilo 22. maja 1998 sklenjeno, da se Rudarsko-metalurški zbornik preimenuje v RMZ – Materiali in geookolje (RMZ – Materials and Geoenvironment) ali skrajšano RMZ – M&G. Revijo RMZ – M&G upravljata izdajateljski svet in medna­ rodni uredniški odbor. Revija je vkljucena v mednarodno izmenjavo svetovno znanih publikacij. Vsi clanki so pod­vrženi recenzijskemu postopku. RMZ – M&G je edina strokovno-znanstvena revija v Slo­ veniji, ki izhaja v nespremenjeni obliki že 60 let. Združuje podrocja geologije, rudarstva, geotehnologije, materialov in metalurgije. Uredniški odbor je leta 2013 sklenil, da po­sodobi obliko revije. Za objavo v reviji RMZ – Materiali in geookolje so dobrodo­ šli tudi prispevki s širokega podrocja geoznanosti, kot so: geologija, hidrologija, rudarstvo, geotehnologija, materiali, metalurgija, onesnaževanje okolja in biokemija. Glavni urednik Review paper Received: Jan 28, 2020 Accepted: Feb 04, 2020 DOI: RMZMAG-D-20-00004 Študij rudarstva in geotehnologije na Univerzi v Ljubljani od leta 1919 do danes Željko Vukelic Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geotehnologijo, rudarstvo in okolje, Aškerceva 12, Ljubljana, Slovenija *zeljko.vukelic@ntf.uni-lj.si Zgodovinski podatki o razvoju slovenske uni­ verze prikazujejo veliko željo za ustanovitev visoke šole na slovenskih tleh. Iz podatkov je razvidno, da sože davno premišljevali o uvedbi študija tehnicnih predmetov, kot sta mehanika in jamomerstvo. Ta zahteva se pojavi s strani Kranjskih deželnih stanov v letih 1786–1787, ki so se sklicevalina rudnike živega srebra v Idriji, rudnike železove rude in na tovarne v Sloveni­ji, da bi tehnicno osebje v rudnikih in tovarnah opravljalo svoje delo zadovoljivo. Zahtevo so podprli z ustanovitvijo prve rudarske akademi­je na svetu leta 1765 v Freibergu na Saškem.S prihodom Francozov v Ljubljano, ki so na tleh province Ilirije leta 1810 ustanovili Centralno šolo, je bilo omogoceno študirati inženirsko stroko. Študij naj bi trajal 4 leta, vendar ni ni- hce študija dokoncal, ker je nova uredba ukinila študij za inženirje. Kljub veckratnim ponovnim poskusom, da bi Slovenija dobila univerzo, so se Slovencem te želje izpolnile šele po prvi svetovni vojni z razpadom Avstro-Ogrske monarhije. V 19. stoletju je bilo rudarstvo v Sloveniji že precej razvito. Ob kovinskih rudnikih (Idrija, Mežica in drugi manjši), je imela Slovenija že pomembne premogovnike Senovo, Zagorje, Trbovlje, Hrastnik in Laško. Konec 19. stoletja pa se je pricela tudi proizvodnja lignita v Ve­lenju. Strokovno osebje za te rudnike se je šo­lalo predvsem na avstrijski rudarski akademiji vLeobnu, vendar je bilo na domacih tleh slov­enskih inženirjev sorazmerno malo. Z ustanovitvijo Univerze v Ljubljani leta 1919, je zaživela tudi Tehniška fakulteta, ki je imela 5 oddelkov. Eden od teh je bil Rudarski odd-elek. Slovenske narodnosti je bil samo en pro-fesor in sicer dr. Karel Hinterlechner, ki je bil hkrati eden od ustanoviteljev ljubljanske uni­verze in prvi dekan Tehniške fakultete. Ostali ucitelji so bili pretežno profesorji ruske narod­nosti, ki so emigrirali iz Sovjetske zveze in so pred tem poucevali na rudarskih visokih šolah v Rusiji. Za ustanovitev Rudarskega oddelka v Ljubljani ima pomembne zasluge rudarski gla-var Vinko Strgar. Na Tehniško fakulteto se je vpisalo 50 slušateljev, od tega 6 slušateljev za študij rudarstva. Vse do leta 1939 je bil Rudar-ski oddelek edini v tedanji Jugoslaviji in tudi na Balkanu. Leta 1939 so ustanovili Rudarski odd-elek v Zagrebu, po drugi svetovni vojni pa še ru­darske oddelke oziroma fakultete v Beogradu, Tuzli in Boru. Tik pred drugosvetovno vojno je pricel Rudar-ski oddelek zidati stavbo. Uspeli so dokoncati železobetonsko skeletno konstrukcijo do stre-he. Gradnja je bila med vojno prekinjena. Stav­ba v kateri danes domuje Oddelek za geoteh­ nologijo, rudarstvo in okolje na Aškercevi 12 vLjubljani je bila dokoncana leta 1950. Znano je, da je bil študij rudarstva od nekdaj heterogen. Razen povsem rudarskih predme­ tov kot so bili: tehnicno rudarstvo, bogatenje mineralnih surovin, globinsko vrtanje, rudar­sko merjenje in geofizika, transport in izvažan­je v rudnikih, je zajemal študij še geološke predmete, naravoslovne predmete in predmete s podrocja strojništva in elektrotehnike. Sprico take pestrosti študijske snovi, marsikateri slušatelj ni uspel koncati študija prej kot v pe- Open Access. © 2019 Željko Vukelic, published bySciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. tih letih, za vecino pa je veljalo, da so porabili veccasa. Do leta 1931 je imel tedanji Rudarski oddelek dve rudarski organizacijski enoti – inštituta: . Inštitut za rudarstvo, . Inštitut za rudarska merjenje in geofizikalna raziskovanja. V naslednjih letih se je Inštitut za rudarstvo re-organiziral v tri enote in tako so nastali štirje inštituti znotraj oddelka za rudarstvo in sicer: .Inštitut za tehnicno rudarstvo, . Inštitut za separiranje in briketiranje rud in premoga ter za rudarsko gospodarstvo, . Inštitut za rudarsko strojništvo, . Inštitut za rudarska merjenje in geofizikalna raziskovanja. Imena in naslovi teh enot so se veckrat menja­vali in tako zasledimo tudi naslove: stolica, za­vod in katedra. Po drugi svetovni vojni so zavo­di dobili ime katedra, ki se je ohranilo do danes.Vse do šolskega leta 1949/50 je bil Rudarski oddelek v sestavu Tehniške fakultete Univerze v Ljubljani. Ko je bila leta 1950 ustanovljena Tehniška visoka šola, je Rudarski oddelek postal oddelek na Fakulteti za rudarstvo in metalurgi­ jo. Tehniška visoka šola je združevala 6fakultet. V tem obdobju se je prešlo na 10 semestrski študij. Sledilo je kar nekaj reorganizacij vi-sokošolskega študija. V šolskem letu 1957/58 je Oddelek za rudarstvo prešel v sestavo Fakultete za rudarstvo, metalurgijo in kemijsko tehnologijo (FRMKT), s šolskim letom 1959/60 pa je oddelek prevzel ime Oddelka za montan­istiko. Šolsko leto 1960/61 je prineslo bistvene novosti v študij rudarske stroke. Predvidene so bile tri stopnje študija, katerih vsaka posebej je trajala 4 semestre. Študenti prve stopnje so dobili naziv inženir rudarstva, druge stopnje diplomirani inženir rudarstva in tretje stopnje magister rudarske stroke. Obenem je prišlo do reorganizacije fakultete in nastala je Fakulteta za naravoslovje in tehnologijo (FNT). Vse do šolskega leta 1965/66 se študijski program ni spreminjal. S tem letom se je znova prešlo na štiri semestrski študij I. in II. stopnje in na tri usmeritve v II. stopnji: eksploatacija, bogatenje in merstvo z geofiziko. Z letom 1968/69 je bila prva stopnja študija ukinjena in prešlo se je na osem semestrski študij z navedenimi tremi os­novnimi usmeritvami. Zanimivo je, da je Odd-elek za rudarstvo deloval znotraj Fakultete za naravoslovje in tehnologijo (FNT) vse do leta 1995, ko je bila ustanovljena Naravoslovnoteh­ niška fakulteta (NTF), ki je združevala: . Oddelek za geotehnologijo in rudarstvo, . Oddelek za geologijo, . Oddelek za materiale in metalurgijo, . Oddelek za tekstilstvo, .Oddelek za kemijsko izobraževanje in infor­matiko. V obdobju med leti 1966 in 1995 ni prišlo do bistvenih sprememb v študijskem programu. Oddelek je imel v sestavi 4 katedre in sicer: .Katedra za tehnicno rudarstvo, . Katedra za bogatenje mineralnih surovin, . Katedra za rudarsko strojništvo, transport in elektrotehniko, . Katedra za rudarsko merjenje in geofizikalno raziskovanje. Študenti višjih letnikov so imeli možnost iz­brati tri že omenjene osnovne usmeritve: ek­sploatacijo, bogatenje in merstvo z geofiziko. Zaradi vse vecjega zanimanja stroke in gos-podarstva na podrocjih podzemnih gradenj, ravnanjem z industrijskimi in komunalnimi odpadki, recikliranjem in izrabo alternativnih virov energije so na Oddelku za rudarstvo priceli izvajati nov študijski program GEOTEH­NOLOGIJA v šolskem letu 1993/94. Oddelek se je preimenoval v Oddelek za geotehnologijo in rudarstvo ter smiselno in vsebinsko preob­ likoval štiri katedre: .Katedra za tehnicno rudarstvo in geotehniko, . Katedra za mehansko procesno tehniko in bogatenje mineralnih in sekundarnih suro­vin, . Katedra za rudarsko strojništvo, transport, elektrotehniko in racunalništvo, . Katedra za rudarsko merjenje in geofizikalno raziskovanje. Univerzitetni študij geotehnologije in rudarst­va je trajal 8. semestrov in sezakljuci z izdela­vo diplomske naloge v 9. semestru. Diplomanti so po uspešnokoncanem študijo pridobili na­ziv univerzitetni diplomirani inženir geoteh­nologije in rudarstva. V šolskem letu 1997/98 se je pricel izvajati Visokošolski strokovni pro- gram geotehnologije in rudarstva, ki je bistve-no bolj usmerjen v pridobivanje aplikativnih znanj spodrocja stroke. Diplomanti po uspešno koncanem študijo pridobijo naziv diplomirani inženir geotehnologije in rudarstva. Z vstopom Slovenije v Evropsko skupnost, je Slovenija morala izvesti reforme na podrocju visokega šolstva. Univerza v Ljubljani je pricela reformo visokega šolstva na podlagi Bolonjske deklaracije iz septembra 2003. Na Oddelku za geotehnologijo in rudarstvo je bil v letu 2005 prenovljen študijski program v skladu z bolon­jskimi smernicami in Merili za akreditacijo študijskih programov. Program je pripravljen po sistemu 3+2+3: l stopnja (univerzitetni trajanje: 3 leta dodiplomski študij) 2 stopnja (univerzitetni trajanje: 2 leti podiplomski študij, magisterij) 3 stopnja (doktorski študij) trajanje: 4 leta Program smo pripravili po Merilih za akred­itacijo visokošolskih zavodov in študijskih pro-gramov, ki jih je sprejel Svet za visoko šolstvo Republike Slovenije (Uradni list RS, št. 63/04, 10.09.2004). Študijski program Geotehnologi­ja in rudarstvo daje naravoslovno in tehniško izobrazbo, ki sledi razvoju v okviru strok geoznanosti. Vedno bolj pa se v tem okviru izka­zuje potreba tudi po drugih znanjih, na primer iz ekonomike in informacijsko komunikacijske tehnologije (IKT). Program daje študentom potrebna teoreticna in prakticna znanja za reševanje konkretnih strokovnih problemov v praksi, hkrati pa jih uvaja tudi v osnove raziskovanja, ki so potrebne za nadaljevanje študija na naslednjih stopnjah.S programom študenti pridobijo kompetence za neposrednozaposlitev na najširšem podroc­ju pridobivanja mineralnih surovin, primarne predelave, podzemnih gradenj, vrtalne tehnike, dela za izvajanje merjenj in sledenj v naravi, dela za vrednotenje in izvajanje posegov v nar­avi, sanacije degradiranih površin, ravnanje z okoljem, trdnimi odpadnimi snovmi, itn.Pridobljena znanja in sposobnosti omogoca­jo uspešno delo na zahtevnejših strokovnih in tudi vodstvenih delovnih mestih tako v javnih kot tudi v zasebnih podjetjih. Vsebina programa je prilagojena vsebinsko pri­merljivim študijskim programom s podrocja ge­otehnologije, geotehnike in rudarstva. Podobne študijske programe izvajajo na Montanisticni univerzi v Leobnu – Avstrija, na Politehniki v To-rinu – Italija, na Rudarski akademiji v Freibergu in Tehniški visoki šoli v Clausthalu – Nemcija. Poudarek je na študiju raznovrstnih aktivnosti, ki se odvijajo v zemeljski skorji z vkljucevan­jem tehnicnih in naravoslovnih znanstvenih polj. Težišca študijskega programa omogocajo mednarodno sodelovanje na interdisciplin­arnih podrocjih, ki pokrivajo tehnicno obravna­vo gradnje podzemnih objektov, geotehnicne gradnje, gospodarjenje z odpadki z vsemi pri­ padajocimi sklopi s podrocja okoljevarstvenega inženirstva, upravljanja podjetij in gospodar­skih družb v zaokroženi celoti. Leta 2015 se je oddelek zaradi vsebin poucevan­ja preimenoval v Oddelek za geotehnologijo, ru­darstvo in okolje.Danes je Oddelek za geotehnologijo, rudarstvo in okolje organiziran znotraj dveh kateder: .Katedra za tehnicno rudarstvo, geotehniko, geotermijo in urbano rudarjenje, . Katedra za rudarsko merjenje in geofizikalno raziskovanje. Do 31. decembra 2018 je na Oddelku za geoteh­ nologijo, rudarstvo in okolje uspešno zakljucilo študij naslednje število diplomantov: ŠTEVILO STOPNJA ŠTUDIJA DIPLOMANTOV Univerzitetni študij 785 Študij I. stopnje 31 Visokošolski strokovni študij 77 Podiplomski študij, magisterij 62 Geotehnologija in rudarstvo 17 VS - 1. stopnja Geotehnologija in okolje 40 UN - 1. stopnja Geotehnologija – 2. stopnja 25 Doktorski študij 29 Original scientific paper Received: Jan 27, 2020 Accepted: Jan 29, 2020 DOI: 10.2478/rmzmag-2019-0020 Removal of Na2SO4 from a Filter Ash Odstranjevanje Na2SO4 iz filtrskega prahu Blaž Janc*, Damjan Hann University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geotechnology, Mining and Environment, Aškerceva 12, Ljubljana, Slovenia * blaz.janc@ntf.uni-lj.si Abstract In this paper, research on the possibilities of sodium sulphate (Na2SO4) separation from other substances in the filter ash sample is presented. The research materi­al contains six components that differ in chemical com­position and density. The possibilities of Na2SO4 sepa­ration using dry and wet methods were studied. The dry method was based on separation with a centrifugal air classifier at four cut size limits. The wet method was based on the dissolution of water-soluble components, filtration of insoluble components, and drying the products. The sulphur content of the individual prod­ucts was determined using both methods. The aim of the research was to determine which method is more suitable for separation of the material in a way that most of the material would contain as little sulphur as possible and the rest of the material would contain con­centrated sulphur. The wet method proved to be more successful. The product with mass fraction 33.1% of the total mass, obtained from the aqueous solution, contained 8.39% sulphur after filtration and drying. The water-insoluble component, with mass fraction 66.9% of the total mass, contained 0.56% sulphur. The dry method with the centrifugal air classifier proved to be less successful in comparison with the wet method. The particles containing Na2SO4 are very similar in size and density to the other components of the material, so the separation to the desired extent was not achieved. Keywords: sulphur, centrifugal air classifier, filtration, filter ash, waste material. Povzetek V clanku je predstavljena raziskava možnosti locenja Na2SO4 od ostalih snovi v vzorcu filtrskega prahu. Prei­skovan material vsebuje šest komponent, ki se med se­ boj razlikujejo po kemijski sestavi in gostoti. Preucevali smo možnost locenja Na2SO4 s suhim in mokrim po­stopkom. Suh postopek je temeljil na locevanju scen­trifugalnim zracnim klasifikatorjem pri štirih mejah lo­cenja. Mokri postopek je temeljil na raztapljanju vvodi topnih komponent, filtraciji netopnih komponent in sušenju produktov. Po obeh izvedenih metodah smo dolocili vsebnost žvepla v posameznih produktih. Cilj raziskave je bilo ugotavljanje, s katero metodo doseci locenje materiala tako, da bi vecina materiala vsebova-la cim manj žvepla, preostanek materiala pa bi vseboval koncentrirano žveplo. Kot bolj uspešna se je pokazala metoda z mokrim postopkom. Produkt z masnim de­ ležem 33.1% od celote, pridobljen iz vodne raztopine, je po filtraciji in sušenju vseboval 8.39% žvepla. V vodi netopna frakcija, katere delež je bil 66.9% od celote, je vsebovala 0.56%žvepla. Suhi postopek z zracnim klasi­fikatorjem se je izkazal kot manj uspešen. Delci Na2SO4 so namrec po velikosti in gostoti dokaj podobni ostalim komponentam materiala, zato nismo dosegli locenja vželenem obsegu. Kljucne besede: žveplo, centrifugalni zracni klasifika-tor, filtracija, filtrski prah, odpadne snovi. Open Access. © 2019 Janc B., Hann D., published bySciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. Introduction The construction industry in Slovenia is cur­rently in expansion. Major repairs, reconstruc­tions and renovations of residential, public and industrial buildings are underway. In connec­tion with the increased number of buildings under construction, the production of con­struction materials is also increasing. Due to the demolition and reconstruction of buildings, the amount of construction waste is increasing, most of which have the potential of secondary use [1]. In the circular economy concept, waste is considered as raw material and could be re­used in the production process. This avoids waste disposal and the associated environmen­tal problems and reduces the need for new raw materials, in which sources are limited. The composition of construction waste has changed over the years. The construction waste whose use has spread in recent decades is increasing. Dry prefabricated materials such as gypsum boards and insulating materials which are the result of the energy efficiency concept and the introduction of new building materials and con­struction methods are included in this group.In the European Union, 40.9 million tons of waste materials were generated in the field of construction and demolition in 2016, rep­resenting 36.4% of all waste, compared with 10.3% of industrial waste. The construction sector is thus the largest producer of waste in comparison with other economic sectors [2].The European Commission Waste Directive also addresses waste hierarchy, which makes prevention of the top waste management prior­ity, followed by preparation for reuse, recycling, recovery and landfill [3]. As a result, industrial companies are looking for new approaches to the waste management which are consistent with the environmental, social and economic sustainability [4].As with most production processes, the pro­duction of building materials, whether using exclusively primary raw materials or adding secondary raw materials into the process, waste materials are produced as a by-product. Their quantity and composition depend on the type of technological process.In the case of thermal treatment of materials, flue gases are mainly produced as by-products, carrying dusty ash particles with them. Mass fraction of heat treatment by-products may be significant in the intense production process. Products are frequently waste materials but can represent the potential for reuse in case of providing technological and environmental re­quirements. Some of these materials have one or more hazardous properties and may repre­sent an environmental risk. If the material is characterised as hazardous waste, it represents a much higher cost to the waste producer or the payer to properly treat it than if the waste were considered to be a non-hazardous waste. Such materials may be prepared by mechanical and/or other processes to the extent that they are environmental friendly and reusable.This study presents some methods for minimis­ing sulphur content with mechanical processes in handling thermal treatment products, more specifically when handling filter ash containing a certain content of sulphur. By minimising the sulphur content, it is possible to achieve the removal of hazardous properties from waste which transforms waste from hazardous to non-hazardous type, thereby opening the pos­sibilities of reuse or at least significantly reduc­ing the cost of waste disposal. Materials and Methods The filter ash that is a subject of this research is a mixture of: . Sodium bicarbonate (NaHCO3), . Sodium sulphate (Na2SO4), . Coke, . Limestone, . Basalt (rock wool fibres), . Ash. In order to minimise the sulphur content of the filter ash, the aim of the research was to sep­arate Na2SO4 from the other components or to concentrate sodium sulphate. One option was to perform the dry process separation us­ing a centrifugal air classifier. Considering the fact that the research deals with the particu­late matter, which was extracted from the flue gas by filters, it is logical that the maximum particle size in the sample taken was limited to about 50µm. If the particles of the Na2SO4 component were present in a specific granu­lometric interval, there exists a possibility of separation with the centrifugal air classifier. Al­ternatively, a wet process could be performed in which the water-soluble Na2SO4 is separated from the other components by dissolving, fil­tration of insoluble components and drying the products.A centrifugal air classifier is a device for sep­arating particles according to their size and density. During the classification operation, the particles are under the influence of centrif­ugal force (Fc), drag force (Fd) and gravity (Fg) force. The centrifugal force field is generated by a rotor, which accelerates the particles to­wards the periphery of the classification zone where a coarse fraction is deposited. The air enters the classification zone tangentially, flows through the middle of the classification zone and removes finer particles on which the drag force of the air resistance is greater than the centrifugal force. The fine particles carried by the air stream are separated from the gas phase in the air cyclone. The material enters the clas­sifier using a uniform dosing mechanism (dos­ing screw). The device principle is explained in Figure 1.The definitions of the forces acting on particles are as follows [5]: Table 1. Density measurements with a pycnometer Test no. Density (kg/m3) 1 2,445.8 2 2,579.5 3 2,539.5 ................ = 4 3·p ·................3 ·................ ·........2 ........ (1) ................ = 2 2 ·................................ ·........·p ·........................ (2) ........ = .... ·(........ -....)·.... (3) where r is particle radius, . is particle density, pp v is the peripheral velocity of the rotor, r is rotor radius, cD is drag coefficient, . is the air density, m is mass of particle and g is gravitational con­stant. The cut size of the classifier is the particle size limit at which the material is separated into a fine and coarse fractions. It depends on the rotor revolutions per minute (RPM), which cre­ates the centrifugal field, and on the air volume flow through the classification zone. The re­quired rotor RPM and the airflow for the select­ed cut size are determined from the diagram provided by the classifier manufacturer.For the purpose of determining the operating conditions of the centrifugal air classifier, the sample density was measured using a pycnom­eter method. Since two components of the ma­terial (NaHCO3 and Na2SO4) are water-soluble, in order to determine the density, we used iso­propanol in which those components are insol­uble or slightly soluble. First, we determined the density of isopropanol with a pycnome­ter (. = 784.8 kg/m3). Following this, we per­formed three measurements of sample density, which are presented in Table 1.The calculated mean density of the sample was 2,521.6 kg/m3. In the next step, four different cut sizes were selected, namely 10, 20, 30 and 40 µm. For each cut size, the required rotor RPM and airflow quantity in accordance with Table 2. Determination of operating conditions for the centrifugal air classifier using the operating diagram of the classifier Cut size dTV RPM n Airflow Q (mm) (min-1) (m3/h) 10 8,900 46.1 20 5,200 49.8 30 4,100 50.9 40 3,500 51.5 the operating diagram of the device were deter­mined (Table 2).Na2SO4 is soluble in water, so it is possible to re­move it from insoluble components by mixing the material in water at the appropriate tem­perature, and then filtration process is used to remove the insoluble residue, which is followed by the elimination of water-soluble substances, including Na2SO4, for which drying or a reverse osmosis process may be used.Of the components contained in the input ma­terial, NaHCO3 is also soluble in water, whose solubility at 35°C is approximately 120 g/L. The solubility of sodium sulphate in the water rises to 32.4°C (497 g/L), and decreases slightly at higher temperatures [6]. Sampling of Material The material was sampled with a spoon. It was poured on a flat surface; a rectangle 1–2 cm high was formed and 5 × 6 even squares were drawn into it. Next, we took a spoonful of ma­terial from each quadrant to get four samples with about 250 g each for classification purpos­es. Sampling is shown schematically in Figure 2. The sulphur content of the samples was mea­sured with an X-ray fluorescence (XRF) spec­trometer and S = 3.38% for the initial sample. Results and Discussion Removal of Sulphur from Filter Dust by a Dry Process with Classification The classification of the sample was performed four times, for each cut size individually. After each classification, the weight of the material of the coarse and fine fraction was determined by weighing. The data are presented in Tables 3–6.Classification of sample 1 at the cut size of 10 mm yielded 21.8% fine fraction and 78.2% coarse fraction. This means that by weight 21.8% of the particles are smaller than 10 mm and 78.2% are larger than 10 mm. When classifying sample 2 at the cut size of 20 mm, we found that about half of the particles were smaller than 20 mm and half were larger than 20 mm. Classification of sample 3 at the cut size of 30 mm yielded 75.1% fine and 24.9% coarse fraction. When classifying sample 4 at the cut size of 40 mm, the share of the fine fraction was 78.3% and the share of the coarse fraction was 21.7%. The mean particle size of Na2SO4 can be, accord­ing to the sulphur content results, estimated to be around 20 mm. The most favourable result with air classification was obtained at a cut size of 10 mm, where the sulphur content in the fine fraction was 0.55%, but the mass share of the fine fraction was only 22.4% at this separation size. In all other cases, the sulphur content was not minimised. The particles of the Na2SO4 component are quite dispersed in size and at the same time they are not significantly different in density from the other components in such a way that they can Table 3. Classification at a cut size of 10 µm Sample 1 (S1) Mass (g) 258.4 Mass per cent (%) 100.0 Sulphur content (%) 3.38 Fine fraction (1F) 56.3 21.8 0.55 Coarse fraction (1C) 202.1 78.2 4.19 Table 4. Classification at a cut size of 20 µm Sample 2 (S2) Mass (g) 251.7 Mass per cent (%) 100.0 Sulphur content (%) 3.38 Fine fraction (2F) 128.9 51.2 3.30 Coarse fraction (2C) 122.8 48.8 3.44 Table 5. Classification at a cut size of 30 µm Sample 3 (S3) Mass (g) 260.2 Mass per cent (%) 100.0 Sulphur content (%) 3.38 Fine fraction (3F) 195.4 75.1 3.71 Coarse fraction (3C) 64.8 24.9 2.32 Table 6. Classification at a cut size of 40 µm Sample 4 (S4) Mass (g) 254.0 Mass per cent (%) 100.0 Sulphur content (%) 3.38 Fine fraction (4F) 198.8 78.3 3.49 Coarse fraction (4C) 55.2 21.7 2.81 be successfully separated from the other com­ponents by the air classifier. Removal of Sulphur from Filter Dust by Wet Process Approximately 100 g of sample was mixed with 800 mL of water. The suspension was stirred with a magnetic stirrer for 30 min, while it was heated to a temperature of about 35°C. The sus­pension was then poured into a Sartorius filtra­ tion cell equipped with a 0.2µm aperture filter. The filtration was initially carried out at atmo­spheric pressure. The remaining fluid from the filtration cell was obtained using compressed air. The residue of the solid phase in the filtra­tion cell (filter cake) was dried in an oven at 105°C until dry. The solution containing Na2SO4was also processed to dryness in the oven. The process is schematically shown in Figure 3. Af­ter drying, both masses were determined. The weight of the filter cake of the water-insoluble solid phase was 72.5 g, while the mass in the water-soluble material was 35.9 g. The mea­sured sulphur content of both samples is given in Table 7. Table 7 shows that the sulphur content of the insoluble material is 0.56%. Figure 3. Dissolution, filtration and drying of material. Table 7. Results of an attempt to remove sulphur from filter ash by the wet procedure Sample 5 (S5) Mass (g) 108.4 Mass per cent (%) 100.0 Sulphur content (%) 3.38 Insoluble material (5I) 72.5 66.9 0.56 Soluble material (5S) 35.9 33.1 8.39 In this case, it is the majority of the material (66.9%). Sulphur is concentrated in dissolved material, in which the sulphur content in­creased to 8.39%. Figure 4 shows that only the 5I and 1F samples represent the minimisation of sulphur content, with the 5I sample having a much larger mass fraction than the 1F sample, which means that the separation using wet process is more opti­mal. Conclusions This article presents dry and wet methods of minimising the sulphur content in filter dust.A dry method of sulphur minimisation would be a faster and more cost-effective method of sulphur removal in the industry but attempting to classify it at different cut sizes did not pro­duce adequate results. With respect to the sul­phur content, only a classification at the cut size of 10 mm would be appropriate, where the sul­phur content in the fine fraction S = 0.55% was measured, but the share of this fraction was only 21.8%. The mass content of sulphur in the coarse fraction at this cut size was S = 4.19%. In the case of all other cut sizes (20, 30 and 40 mm), the sulphur-containing particles are approximately evenly distributed between the fine and coarse fractions so that the sulphur content in both the fine and coarse fractions does not deviate significantly from the sulphur content of the starting sample.Better results were obtained from the wet sul­phur content minimisation process. In this part of the study, the sample was mixed with a suf­ficient amount of water, and the suspension was heated to the temperature necessary for maximum solubility of sodium sulphate in wa­ter. The water-soluble material, together with the insoluble residue, was filtered on a 0.2 mm aperture filter and then dried, and the sulphur content in the insoluble and water-soluble ma­terial was measured. The insoluble material represented about two-third of the total sample and had a sulphur content of S = 0.56%, while the measured sulphur content in the rest of the material was S = 8.39%. Considering that a lot of energy is consumed in drying the material, a suitable solution for the industrial removal of Na2SO4 would include mixing of water and material while heating at 35°C, separation of the solid and liquid phase by filtration, elimination of Na2SO4 from the liq­uid phase by reverse osmosis and drying of the products.By using reverse osmosis, drying volumes and energy consumption would be greatly reduced. References [1] Aleksanin, A. (2019): Development of construction waste management. In: XXII International Scientific Conference on Advanced In Civil Engineering, Tash­kent, Uzbekistan, Volkov, A., Pustovgar, A., Sultanov, T., Adamtsevich, A. (eds.). E3S Web of Conferences. [2] Eurostat [online]. European Commission [cited 1/15/2020]. Available on: https://ec.europa.eu/eu-rostat/statistics-explained/index.php?title=Waste_ statistics#Total_waste_generation. [3] DIRECTIVE 2008/98/EC (2008). Directive 2008/98/EC of the European Parliament and Council of 19 November 2008 on Waste and Repealing Cerain Directives. European Parliament. Official Journal of the European Union, pp. 3–30. [4] Shahbazi, S., Kurdve, M., Bjelkemyr, M., Jsson, C., Wiktorsson, M. (2013): Industrial waste manage­ment within manufacturing: A comparative study of tools, policies, visions and concepts. In: Proceedings of the 11th International Conference on Manufactur­ing Research (ICMR2013), Shehab, E., Ball, P., Tjahjo- no, B. (eds.). Cranfield University: Cranfield, UK, pp. 637–642. [5] Altun, O., Toprak, A., Benzer, H., Darilmaz, O. (2016): Multi component modelling of an air classifier. Min­erals Engineering, 93, pp. 50–56. DOI:10.1016/j.mi­neng.2016.04.014. [6] Bharmoria, P., Gehlot, P.S., Gupta, H., Kumar, A. (2014): Temperature-Dependent Solubility Transition of Na­2SO4 in Water and Effect of NaCl Therein: Solution Structures and Salt Water Dynamics. The journal of physical chemistry B, 118, pp. 12734–12742. DOI: 10.1021/jp507949h. [7] Stražišar, J., Knez, S. (2001): Vaje in racunski primeri iz mehanske procesne tehnike. Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geoteh­ nologijo in rudarstvo: Ljubljana, 176 p. Original scientific paper Received: Sep 28, 2019 Accepted: Nov 22, 2019 DOI: 10.2478/rmzmag-2019-0014 Hydrocarbon-Generating Potential of Eocene Source Rocks in the Abakaliki Fold Belt, Nigeria Potencial za nastanek oglikovodikov v eocenskih izvornih kamninah nariva Abakaliki O.A. Oluwajana1,*, A.O. Opatola2, O.B. Ogbe3, T.D. Johnson1 1 Department of Earth Sciences, Adekunle Ajasin University, Akungba-Akoko, Nigeria 2 Department of Geosciences, University of Lagos, Lagos, Nigeria 3 Department of Earth Sciences, Federal University of Petroleum Resources, Effurun, Nigeria * afolabi.oladotun@gmail.com, oladotun.oluwajana@aaua.edu.ng Abstract Subsurface information on source rock potential of the Eocene shale unit of the Abakaliki Fold Belt is limited and has not been widely discussed. The total organic carbon (TOC) content and results of rock-eval pyroly­sis for nine shale samples, as well as the one-dimen­sional (1D) geochemical model, from an exploration well in the Abakaliki Fold Belt were used to evaluate the source rock potentials and timing of hydrocarbon generation of Lower Eocene source rocks. The TOC content values of all the samples exceeded the mini­mum threshold value of 0.5 wt.% required for potential source rocks. A pseudo-Van Krevelen plot for the shale samples indicated Type II–III organic matter capable of generating gaseous hydrocarbon at thermally mature subsurface levels. The 1D burial model suggests that the Eocene source rock is capable of generating oil and gas at the present time. The modelled transformation ratio trend indicates that a fair amount of hydrocarbon has been expelled from the source rocks. The results of this study indicate that the Eocene source units may have charged the overlying thin Eocene sand bodies of the Abakaliki Fold Belt. Key words: Abakaliki Fold Belt, generation, Eocene, basin modelling, hydrocarbon Povzetek Pod-površinske informacije o potencialu izvornih ka­ mnin na obmocju eocenske enote nariva Abakaliki so omejene in niso bile predmet široke razprave. Za oceno potenciala izvornih kamnin in cas nastanka oglikovodi­kov nižjiheocenskih izvornih kamnin so bile uporablje­ne naslednje preiskave: skupni organski ogljik (TOC), rezultati pirolize Rock-Eval za devet vzorcev skrilavcev in 1Dgeokemicnimodel iz raziskovalne vrtine. Vredno­sti TOC so pri vseh vzorcih presegale minimalne mejne vrednosti 0.5 ut.%. Pseudo-Van Krevelen graf za vzorce skrilavcev nakazuje Tip II­III organske snovi, zmožne generiranja plinastega oglikovodika pod nivojem zrelo­sti organske snovi. 1D modeli predlagajo, da so eocen­ ske izvorne kamnine zmožne generiranja nafte in plina v sedanjem casu. Modeliran trend transformacijskega razmerja nakazuje, da je neka kolicina ogljikovodikov ušla iz izvornih kamnin. Rezultati raziskave prikazuje­jo, da so eocenske izvorne enote lahko napolnile prekri­ vajoce tanke eocenske peske na narivu Abakaliki. Kljucne besede: nariv Abakaliki, nastanek, Eocen, mo-deliranje bazena, ogljikovodik Open Access. © 2019 Oluwajana O.A., Opatola A.O., Ogbe O.B., Johnson T.D., published bySciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. Introduction Petroleum exploration companies had drilled some wells in the Abakaliki Fold Belt in the 1950s and ’60s but had abandoned these be­cause it was thought that magmatic intrusion in the belt did not favour hydrocarbon accumula­tion. However, in recent times, there has been a resurgence of interest in the search for petro­leum in the belt [1]. The discovery of oil shale and indications of hydrocarbon in the Abakaliki Fold Belt (Figure 1) have shown that the basin has significant hydrocarbon potential [2, 3]. The Cretaceous source facies of the Abakaliki Fold Belt have, over the years, been considered as viable source units capable of generating hy­drocarbons [1, 4].Recent studies have shown that Eocene source rocks are immature with respect to hydrocar­bon generation at the present outcrop level; but they have a fair-to-moderate potential to gen­erate gaseous hydrocarbons at mature levels in the subsurface [5, 6]. Published works on deep­ly buried Eocene source rocks of the Abakaliki Fold Belt are rare. This study attempts to de­termine whether deeply buried Eocene source rock is responsible for charging the overlying Lower Eocene sandy facies of an exploration well (Ihuo-1 well) drilled in the Abakaliki Fold Belt by evaluation of the Lower Eocene source rocks (organic richness and kerogen type) and reconstruction of one-dimensional (1D) ba­sin models. Modelling of the results allows for the assessment of Lower Eocene Bende/Ame­ki source rock in the Abakaliki Fold Belt, which will give a new perspective on the source po­tential and generative potential of the deeply buried Eocene source unit. Figure 1: Location of the study area showing the position of the Ihuo-1 well and other wells in the Abakaliki Fold Belt and the Calabar Flank. Insert: Map of Nigeria showing the location of the Abakaliki Fold Belt (marked by a red box), Southeastern Nigeria. Geological Settings the Santonian, the Abakaliki region was one of the most important depocentres in the Lower The Abakaliki Fold Belt consists of Creta-Benue Trough, with marine sediments ranging ceous-to-Neogene sediments (Figure 2). Before in age from Albian to Coniacian. The second Figure 2: A simplified regional section of the Cretaceous and Cenozoic stratigraphy of Anambra Basin, Abakaliki Fold Belt and Calabar Flank, with time stratigraphy and tectonic events [9–10]. sedimentary phase occurred between the Up­per Cenomanian and Middle Turonian and was associated with the deposition of Eze-Aku Shale and its lateral equivalents, namely the Amasiri and Makurdi sandstones [7]. The Lower Turo­nian Eze-Aku Shale in the Abakaliki Fold Belt underlies the Coniacian Awgu Shale [8].The Campanian–Maastrichtian Nkporo Group overlies the Awgu Shale (Abakaliki Fold Belt) unconformably, above which are the Palaeo-gene–Neogene marine shales and regressive sandstones [11]. The Albian–to-Coniacian sed­iments were deposited before the Santonian compressional tectonic phase, which is re­flected by basic volcanism and a disconformi­ty [2]. It then implies that after the Santonian thermo-tectonic event, most of the source rock deposited earlier might have been overcooked due to high thermal effects; hence, the search for suitable hydrocarbon source rock in the Abakaliki Fold Belt should be in the subsurface post-Santonian (Eocene) sediments. The Nige­rian Eocene sediments are well-dated marine deposits [12]. Eocene rocks that outcropped in Southeastern Nigeria constitute the subsurface Agbada Formation, which – according to previ­ous research [13] – have been identified as the major source rock of petroleum in the Niger Delta Basin. Materials and Methods A total of nine ditch-cutting samples from shale interval depths ranging from 2204 m to 2557 m of the Ihuo-1 well, drilled by the Shell Petroleum Development Company (SPDC), lo­cated in the Abakaliki Fold Belt, were used in Table 1: Geochemical results of rock-eval/TOC analyses of Eocene samples in Ihuo-1 well Rock-eval pyrolysis Depth TOC (m) (wt.%) S1 S2 OI HI PI + S2 T (mgHC/gTOC) (mgHC/gTOC) S1max (mgHC/gTOC) (mgHC/gTOC) (mgHC/gTOC) 2204 0.8 2.7 2.58 5.28 442 171 323 0.51 2265 1.8 3.91 2.88 6.79 441 158 160 0.58 2320 1.5 3.70 2.40 6.10 439 156 150 0.61 2355 0.8 2.56 1.45 4.01 466 129 181 0.64 2375 0.7 6.52 3.28 9.80 455 557 469 0.67 2415 1.1 4.14 2.03 6.17 476 177 185 0.67 2510 0.9 1.60 0.83 2.43 469 17 92 0.66 2520 1.0 5.03 2.18 7.21 478 353 218 0.7 2557 0.8 2.53 1.21 3.74 480 116 151 0.88 Table 2: Input for 1D basin modelling of the Ihuo-1 well as used in the present study. Deposition Erosion Modelled Depth Thickness Modelled HI Layer name period period TOC range (m) (m) (gHC/gTOC) (Ma) (Ma) (wt.%) Overburden 0–28 28 0.2–0 Mio-Oligocene (Coastal plain sands) 28–584 556 27–0.2 Oligocene shaly sands 584–1328 744 28–27 Upper Eocene 1328–1426 98 37.6–34 34–28 (Bende/Ameki Formation) Mid-Eocene (Bende/Ameki Formation) 1426–1862 436 41.2–39 39–37.6 Lower Eocene (Bende/Ameki Formation) 1862–2655 793 49–41.2 1 214 Lower Eocene (Bende/Ameki Formation) 2655–2710 55 54–49 Lower Eocene (Bende/Ameki Formation) 2710–2863 153 56–54 Palaeocene (Imo Shale) 2863–3228 365 66–56 Maastrichtian (Nkporo Shale) 3228–3450 222 71.2–66 Table 3: Measured vitrinite reflectance values of Eocene stratigraphic levels in Ihuo-1 well. Well Depth (m) Vitrinite reflectance values Ihuo-1 2204 0.80 Ihuo-1 2265 0.78 Ihuo-1 2375 1.03 Ihuo-1 2557 1.48 the study. This work utilized the total organic carbon (TOC) content and rock-eval pyrolysis results (Table 1), in addition to the well data, of the Lower Eocene shale samples that were pro­vided by the SPDC.The sedimentation history of the basin is subdi­vided into a series of events of specified age and duration [14]. Accordingly, 1D basin modelling was carried out using Petromod 1-DExpress to de­termine the maturation and timing of hydrocar­bon generation of the Lower Eocene source unit. The input data for the stratigraphic modelling included thicknesses, durations of deposition, ages and lithologies of the different sedimen­tary layers (Figure 3, Table 2). Palaeobathym­etry values were obtained from the proprietary SPDC chart. The modelled vitrinite reflectance was correlated with the measured data in order to calibrate the hydrocarbon generation levels (Table 3). The source rock parameters, i.e. TOC content and hydrogen index (HI), used in the construction of the 1D models, were obtained from the well report (Tables 1 and 2). Average values of 1.00 wt.% TOC and HI of 214 mgHC (milligram hydrocarbon)/gTOC were applied during the modelling. The 1D model of the ex­ploration well was simulated and the results are presented visually. Results Quality and Quantity of Organic Matter The organic richness (i.e. TOC%) is a key pa­rameter for the assessment of source rock po­tential. The data obtained from Table 1 shows that the TOC content of the Eocene shale unit ranges from 0.8 wt.% to 1.8 wt.% (mean value of 1.0 wt.%). The TOC values of all the sam­ples exceeded the minimum threshold value of 0.5 wt.% required for potential source rocks [15]. A cross-plot of S1 against TOC can be used to distinguish between allochthonous and au­tochthonous hydrocarbons (Figure 4), which shows that the analysed rock samples of the Eocene source rocks contain allochthonous (non-indigenous) hydrocarbons. Generation Potential (GP) Based on rock-eval pyrolysis, the hydrocarbon GP of a source rock can be estimated. The GP of a source rock is the summation of the S1 and S2 values. The GP of source rocks can be classi­fied as poor, fair, good and very good with GP values <2, from 2 to 5, from 5 to 10, and >10, respectively [17]. A cross-plot of the GP (i.e. S1 + S2) against TOC suggests that the Eocene source rocks have fair-to-good source potential (Figure 5). In addition, the cross-plot of the HI against TOC shows that the source rocks are fair oil source rocks. Figure 6: Van Krevelen diagram for kerogen typing of Eocene shale samples in Ihuo-1 well [16], used to determine the kerogen types of the shale samples. The red dots represent the analysed Kerogen Type of the Organic Matter samples. The original kerogen type of a source rock is a key element that aids in the forecast of oil and gas potential. HI values <150 mgHC/gTOC indicate potential for gas generation (chief­ly Type III); HI values ranging from 150 to 300 mgHC/gTOC indicate potential for gener­ation of mixed gas and oil (Type III and II, re­spectively), with mainly gas being generated. Kerogen with HI > 300 mgHC/gTOC has poten­tial for more oil generation, with minor levels of gas (Type II); HI >600 mgHC/gTOC indicates Type I kerogen, which has the highest potential to generate oil [18].Based on the data obtained in Table 1, the ker­ogen type was classified using the key param­eters, such as HI, oxygen index (OI), and Tmax. A cross-plot of HI against OI was used to con­struct a Van Krevelen diagram for the categori­sation of kerogen types. The results obtained suggest that the rock samples of the Eocene shale unit are of kerogen Type II–III (i.e. po­tential for generating mixed oil and gas, with more gas being generated than oil) (Figure 6). A pseudo-Van Krevelen diagram was also con­structed with a cross-plot of HI against Tmax(Figure 7), which suggests a Type II–III organ­ic matter type. The shale unit in Ihuo-1 well is characterised by average S1 + S2 yields of about up to 5.7 mgHC/gTOC rock and rather low aver-rock (Table 1), thus indicating lower percentag-age present-day HI value of <250 mgHC/gTOC es of autochthonous organic matter [19]. Heat Flow and Thermal History The reconstruction of thermal histories of sedimentary basins is always simplified and calibrated against maturity profile indicators such as vitrinite reflectance [21]. The heat flow values were determined based on the tecton­ic history of the basins and were defined by streaming modelled and measured thermal data (Figure 8).Elevated heat flow values (Figure 9) were cal­ibrated for Aptian-to-early Albian times be­cause of the rifting associated with intensive magmatic activity, uplift and erosion [22] in the Abakaliki Fold Belt. Heat flow values (Fig­ure 9) were reduced during the Cenomanian to account for the period of cooling following ces­sation of mantle upwelling [3]. High heat flow values were modelled for early-to-middle Turo­nian times to indicate extensional movements caused by the reactivation of mantle upwelling, accompanied by well documented rifting event in the Abakaliki Fold Belt [23–24]. Late Turoni-an to Santonian times were marked by indica­tion of active tectonic phase of folding, faulting Figure 8: Boundary condition used to model the most probable scenario for hydrocarbon generation in the Abakaliki Fold Belt. The figure indicates the heat flow trend for the Lower Eocene source rock. Figure 9: Correlation of measured and modelled vitrinite reflectance data for Ihuo-1 well. The heat flow values were determined based on the tectonic history of the basins and were defined by streaming modelled and measured thermal data. and uplifting [25]. Thick series of hydrother-Terminal tectonic event during late Maastrich­mally altered Late Turonian-Coniacian basaltic tian had been reported [9, 27], where rifting, sediment in the Abakaliki Fold Belt suggested deformation and high heat flow from magmatic an extrusive, rather than an intrusive, charac-activity played an important role [28]. Thermal ter, in which the volcanic activity occurred [26].heat flow peak for Eocene tectonism was mod-Santonian tectonism was followed by loss of elled based on intensive erosion [9] during the thermal momentum associated with final ces-period. sation of mantle upwelling during Campanian to Palaeocene in the Abakaliki Fold Belt [3, 25]. Hydrocarbon Generation The 1D charge modelling of the Ihuo-1 well used the [29] kinetic model to establish the hy­drocarbon GP of the Eocene organic-rich shale bed. The top of the wet gas window was iden­tified at about 2592 m, and this suggests that the Eocene shale unit is presently in the oil–wet gas generation phase. The maturity model (Figure 10) assumes that the source bed began hydrocarbon generation during Eocene times (40.58 Ma) and continues till date. The areas of crustal extension are commonly characterised by high heat flow (> 90 mWm-2), volcanic activ­ity and related thermal fluid circulation [30]. Elevated heat flow would have contributed to the maturation of the source unit (wet gas win­dow) in the Abakaliki Fold Belt, as observed on the measured Tmax. Transformation Ratio The modelled present-day transformation ra­tio value of the deeply buried Lower Eocene source samples in the exploration (Ihuo-1) well ranges from 25% to 59% (Figure 11). This suggests that a fair quantity of hydrocarbon has been expelled. The source rock intervals may have contributed to the charging of the Lower Eocene sand bodies in the Ihuo-1 well. Discussion The hydrocarbon source potential of the Low­er Eocene (Bende/Ameki) shale is uncertain even with some oil and gas indications in the Abakaliki Fold Belt. Shales of the Cretaceous age (Turonian-Maastrichtian) have been pre­viously considered as the major source rocks for the Abakaliki Fold Belt [1, 31, 32]. Although the Lower Eocene (Bende/Ameki) source rocks are of moderate-to-good quality, the source rocks must have generated and expelled hydro­carbon. This hydrocarbon source potential is attributed to the depth of burial of the Lower Eocene source rock. The herein-studied well, Ihuo-1 well, has the thickest sedimentary suc­cession and source rock burial in the Abakali­ki Fold Belt [9, 26]. More than 3000 m of sed­iment pile was deposited and Eocene source rock burial depth of >1800 m was observed in Ihuo-1 well. The Lower Eocene (Bende/Ameki) source rocks have the required depth of source rock burial for maturation. The initial hydrocarbon generation phase com­menced during the Eocene age with the gener­ation of liquid hydrocarbon. The major phase of generation and expulsion of hydrocarbon start­ed in the Oligocene age. The thermal maturity of Lower Eocene source rock is moderate to high, as observed in vitrinite reflectance data, suggesting that it is thermally mature for hy­drocarbon generation. The thermal maturation of Lower Eocene source bed in the Ihuo-1 well may have been strongly affected by elevated heat flow (Figure 9). The areas of crustal exten­sion are commonly characterised by high heat flow (>90 mWm-2), volcanic activity and relatedthermal fluid circulation [30]. Rifting associat­ed with intensive magmatic activity, uplift and erosion in the Abakaliki Fold Belt are more pro­nounced during the Cretaceous [22].Strong indication of gas was found in Ihuo-1 well during drilling [9]. The origin of the gas in­dication in Ihuo-1 well is speculative, hence the need to carry out isotope geochemical analysis. The occurrence of gas within the thin Eocene reservoir is thought to have been sourced part­ly from Eocene organic-rich shales or deeply buried Cretaceous organic-rich intervals. Eo­cene-sourced oil and gas have been discovered in the Northern Delta depobelt [10]. The North­ern Delta is the oldest mega-structure of the Niger Delta Basin and represents the transition depobelt between the Cretaceous succession of the Abakaliki Fold (including Anambra Basin) and the Niger Delta Basin. Conclusions Subsurface information on source rock poten­tial of the Eocene shale unit of the Abakaliki Fold Belt is limited and has not been widely discussed. This study used results of rock–eval analysis and 1D basin models to evaluate Eo­cene shale samples from an exploration well (Ihuo-1 well) to evaluate the quantity and qual­ity of the source rock, as well as reconstruct the timing of hydrocarbon generation.TOC values and results of rock-eval pyroly­sis for nine shale samples, as well as the geo­chemical model of Eocene Formation, from an exploration well in the Abakaliki Fold Belt, Nigeria, were used to evaluate and determine the source rock potentials and timing of hydro­carbon generation of Eocene source rocks. The TOC content values of all the samples exceeded the minimum threshold value of 0.5 wt.% re­quired for potential source rock. The relation­ship between (S1+ S2) and TOC suggested that the Eocene samples could be regarded as hav­ing fair-to-good source potential. Van Krevelen plot for shale samples indicated Type II–III or­ganic matter and showed that it can generate mixed oil and gas (with more of gas) hydrocar­bon at thermally mature subsurface levels. This hydrocarbon source potential is attributed to the depth of burial of the Lower Eocene source rock. The 1D burial model suggests that the Eocene source rock entered peak oil maturity in the Eocene, late oil maturity in the Oligocene and wet gas maturity during the Miocene age. The shale unit is capable of generating oil and gas at the present time. With transformation ra­tio ranging from 25% to 59% (with increasing depth), the shale unit has expelled fair amounts of hydrocarbon. The results of this study indi­cate that the Eocene source units may have fair­ly charged the thin Eocene sand bodies of the Ihuo-1 well. Acknowledgements We appreciate the management of Shell Pe­troleum Development Company (SPDC), Port Harcourt, Nigeria, for the PhD internship op­portunity granted to the first three authors and for providing the well-related information and geochemical data used for the source rock evaluation. The manuscript benefitted from critical commentary by an anonymous review­er of the journal. Thanks to Osasona Ojuoluwa of Sub-surface Geoscience workstation, Univer­sity of Lagos, for his technical assistance. Digi­tal topography has been provided by Olushola Olayinka of Zobeten Petroleum Nigeria Limit­ed, Lagos, Nigeria. References [1] Ekweozor, C.M. (1982): Petroleum Geochemistry: Application to petroleum exploration in Nigeria’s Lower Benue Trough. In: 20th Anniversary proceed­ing, Nigeria Mining and Geosciences Society, Oluyide, P. O., Mbonu, W. C., Onuogu, S. A., 19(1), pp. 122–129. [2] Ehinola, O.A., Sonibare, O.O., Akanbi, O.A. (2005): Economic evaluation, recovery techniques, and en­vironmental implications of the oil shale deposits in the Abakaliki Fold Belt, Southeastern, Nigeria. Oil Shale, 22(1), pp. 1–15. [3] Oluwajana O.A., Ehinola O.A. (2018): Potential shale resource plays in southeastern Nigeria: Petroleum system modeling and microfabric perspectives. Journal of African Earth Sciences, 138, pp. 247–257. [4] Unomah G.I., Ekweozor, C.M. (1990): First discov­ery of oil shale in the Benue Trough, Nigeria. FUEL, 69(4), pp. 502–508. [5] Olajubaje, T.A., Akande S.O., Adeoye, J.A., Adekeye, O.A., Friedrich, C. (2018): Depositional Environ­ments and Geochemical Assessments of the Bende Ameki Formation Potential as Petroleum Source Rocks in the Ogbunike Quarry, South-Eastern Nige­ria. European Scientific Journal, 14, pp. 157–175. [6] Nzekwe, I.E., Okoro, A.U. (2016): Organic and Trace Element Geochemistry of the Ameki Formation, South Eastern Nigeria: Implicationsand Hydrocar­bon Generating Potential. Journal of Applied Geology and Geophysics, 4(4), pp. 12–20. [7] Ehinola, O.A. (2002): Depositional Environment and Hydrocarbon Potential of the Oil Shale Deposit from the Abakaliki Fold Belt, Southeastern Nigeria. Ph. D. Thesis. University of Ibadan: Ibadan, 240 p. [8] Petters, S.W., Ekweozor, C.M. (1982): Petroleum geology of Benue Trough and southeastern Chad basin, Nigeria. Am. Assoc. Petrol. Geol. Bull, 66, pp. 1141–1149. [9] Murat, R.C. (1969): Geological Data Book of Southern Nigeria, Unpublished Report of Exploration Depart­ment of Shell-BP.C Nigeria, 26 p. [10] Oluwajana, O.A., Ehinola, O.A., Okeugo, C.G., Adegoke O. (2017): Modelling hydrocarbon generation po­tentials of Eocene source rocks in the Agbada For­mation, Northern Delta Depobelt, Niger Delta Basin, Nigeria. Journal of Petroleum Exploration and Pro­duction Technology, 7(2), pp. 379–388. [11] Ehinola, O.A., Sonibare, O.O., Javie, D.M., Oluwole, E.A. (2008): Geochemical appraisal of organic mat­ter in the mid-cretaceous sediments of the Calabar Flank, Southeastern Nigeria. Eur. J. Sci. Res., 4(23), pp. 567–577. [12] Reyment, R.A. (1965): Aspects of the Geology of Ni­geria. Am. Assoc. Petrol. Geol. Bull, 66, p. 1141. [13] Short, K.C., Stauble, A.J. (1967): Outline of Geology of Niger Delta. The American Association of Petroleum Geologists Bulletin, 51, pp. 761–779. [14] Underdown, R., Redfern, J. (2008): Petroleum gen­eration and migration in the Ghadames Basin, North Africa: a two­dimensional basin­modeling study. The American Association of Petroleum Geologists Bulletin, 92(1), pp. 53–76. [15] Tissot, G.P., Welte, D.H. (1984): Petroleum Formation and occurrence, 2nd edition, Springer: Berlin, 702 p. [16] El Nady, M.M. Ramadan, F.S., Hammad, M.M., Lotfy, N.M. (2015): Evaluation of organic matters, hydro­carbon potential and thermal maturity of source rocks based on geochemical and statistical methods: Case study of source rocks in Ras Gharib oilfield, central Gulf of Suez, Egypt. Egyptian Journal of Pe­troleum, 24, pp. 203–211. [17] Hunt, J. (1996): Petroleum Geochemistry and Geolo­gy, 2nd edition, W.H. Freeman and Company. [18] Waples, D. (1985): Geochemistry in Petroleum Ex­ploration. Inter. Human Resources and Develop. Co.: Boston, 232 p. [19] Bustin, R.M. (1988): Sedimentology and character­istics of dispersed organic matter in Tertiary Niger Delta: Origin of source rocks in a deltaic environ­ment: The American Association of Petroleum Geol­ogists Bulletin, 72, pp. 277–298. [20] Amer, A.M., Che, A.A. (2009): Characterization of the Black Shales of the Temburong Formation in West Sabah, East Malaysia. European Journal of Scientific Research, 30(1), pp. 79–98. [21] Yahi, N., Schaefer, R.G., Littke, R. (2001): Petroleum generation and accumulation in the Berkine basin, eastern Algeria. The American Association of Petro­leum Geologists Bulletin, 85(8), pp. 1439–1467. [22] Benkhelil, J., Guiraud, M., Ponsard, J. F., Saugy, F. (1989): The Bornu Benue Trough, the Niger Del­ta and its Offshore: Tectono­sedimentary Recon­struction during the Cretaceous and Tertiary from Geophysical Data and Geology. In: Geology of Nige­ria, Kogbe, C.A. (ed.). Elizabethan Publ. Co.: Lagos, pp. 277–309. [23] Olade, M.A. (1975): Evolution of Nigeria’s Benue Trough (Aulacogen): A tectonic model. Geological Magazine, 112(6), pp. 575–583. [24] Nwachukwu, J.I. (1985): Petroleum prospects of the Benue Trough, Nigeria. The American Association of Petroleum Geologists Bulletin, 69(4), pp. 601–609. [25] Kogbe, C.A., (1989): Paleogeographic History of Nigeria from Albian Times. Geology of Nigeria, pp. 257–274. [26] Baggelaar, H., Van Morkhoven, F.P.C.N., Gutjahr, C.M. (1954): Owerri Geological Report No 116 Compila­tion Paleontological and Biostratigraphical Results, Southern Nigeria. Unpublished Shell Internal Re­port, 35 p. [27] Odigi, M.I., Amajor, L.C. (2009): Brittle deformation of the Afikpo Basin, Southeastern Nigeria: evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough. China J. Geochem., 28(4), pp. 369–376. [28] Odigi, M.I. (2011): Diagenesis and reservoir qual­ity of Cretaceous sandstones of Nkporo Formation (Campanian) southeastern Benue trough, Nigeria. J. Geol. Min. Res, 3(10), pp. 265–280. [29] Sweeney, J.J., Burnham, A.K. (1990): Evaluation of a simple model of vitrinite reflectance based on chemical kinetics. The American Association of Pe­troleum Geologists Bulletin, 74, pp. 1559–1570. [30] ÇiftÇi B., Temel, R., Iztan, Y. (2010): Hydrocarbon occurrences in the western Anatolian (Aegean) gra­bens, Turkey: Is there a working petroleum system? The American Association of Petroleum Geologists Bulletin, 94(12), pp. 1827–1857. [31] Agagu, O.K., Fayose, E.A., Peters S.W. (1985): Stratig­raphy and sedimentology of the Senonian Anambra Basin of eastern Nigeria Nig. Journ. Min. Geol., 22, pp. 25–36. [32] Ekine, A.S., Onuoha, K.M. (2010): Seismic Geohisto­ry and Differential Interformational Velocity Analy­sis in the Anambra Basin, Nigeria. Earth Sci. Res. J., 14(1), pp. 88–99. Original scientific paper Received: Nov 20, 2019 Accepted: Dec 12, 2019 DOI: 10.2478/rmzmag-2019-0019 Assessment and Analysis of Precambrian Basement Soil Deposits Using Grain Size Distribution Ocena in analiza predkambrijskih nahajališc zemljin z uporabo porazdelitve velikosti zrn Gideon Layade*, Charles Ogunkoya, Victor Makinde, Kehinde Ajayi Department of Physics, Federal University of Agriculture, Abeokuta, Nigeria * layadeoluyinka018@gmail.com Abstract The article presents the grain size distribution of soil samples from the Precambrian basement within the purview of the textural properties, deduced transpor­tation history and the numerical assessments using sta­tistical parameters. The fourteen soil samples collected from the study area were subjected to sieve analysis in the laboratory for the determination of their grain size distribution. The statistical parameters’ study includes the graphic mean, skewness, sorting and kurtosis. The result of the analysis of the soil samples ranged from coarse to fine-grained samples, moderately and poorly sorted, positively and negatively skewed and the kurto­sis also shows leptokurtic as the most dominant which suggests the samples poorly distributed and moder­ately sorted at the centre of the grain size distribution. These results also suggest the geological environment of the soil samples could be responsible for the poorly and moderately sorted exhibited by the samples depos­ited in the location. Key words: Deposition, Grain size analysis, Kurtosis, Skewness, Provenance Povzetek Clanek predstavlja porazdelitev velikosti delcev vzor­cev zemljine iz predkambrijske osnove znotraj na­ mena proucevanja teksturnih znacilnosti, zgodovine transporta in numericne ocene z uporabo statisticnih parametrov. Na štirinajsti vzorcev zemljine iz preisko­vanega obmocja je bila opravljenalaboratorijska sejal­na analiza z namenom dolocitve porazdelitve velikosti delcev. Statisticna parametricna raziskava vkljucuje: graficno srednjo vrednost, asimetrijo, razvršcanje in splošcenost. Rezultati granulometricne analize kažejo na grobe do fine vzorce zemljin, ki so srednje do slabo sortirane. Vzorci imajo pozitivno in negativno asime­ trijo. Splošcenost kaže na najbolj pogosto konicasto porazdelitev, ki predlaga slabo porazdeljene in srednje sortirane vzorce v sredini porazdelitve velikosti delcev. Rezultati prav tako kažejo, da je geološko okolje vzor­cev zemljine lahko razlog za slabo in srednjo sortira­nost. Kljucne besede: odlaganje, preiskava velikosti delcev, splošcenost, asimetrija, poreklo Open Access. © 2019 Layade G., Ogunkoya C., Makinde V., Ajayi K., published bySciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. Introduction The grain size analysis is one of the tests that can be performed to determine the percentage of different grain size contained within the soil. It provides very useful information on the clas­sification of sedimentary environment and the transportation of the sediments. The grain size distribution provides good quantification for soil studies and reveals the weathering char­acteristics of sedimentary processes and prov­enance [1–4]. The results of Abuodha [5] have helped to clarify the sedimentary environment and its transport dynamism.The benefits of mathematical representation of grain size analysis cannot be overemphasised which include the soil classification using the best-fit parameters. Second, the mathematical equation can be used as the basis for analysis related to estimating the soil–water character­istic curve. Third, a mathematical equation pro­vides a method of representing the entire curve between the measured data points [6]. Repre­senting the soil as a mathematical function also provides increased the flexibility in searching for similar soils in the database. The development of computerized data analysis has enhanced the knowledge of the calculation of different statistical parameters to determine the transportation history of the sediments as in the kurtosis, the average size of grain, sorting and skewness. They are designated by different methods and characterised the particle-size distribution in sediments [7–9]. Various re­searchers [10–18] have established different formulae for the statistical parameters but the most widely used among the formulae are those proposed by Folk and Ward [19].The measures of quartile, phi scale among oth­ers are some of the frequently used statistical measures of grain size distribution. Seven dif­ferent points on the cumulative frequency curve are directly selected (at 5, 16, 25, 50, 75, 84 and 95 percentiles) for the computation of the para­metric statistics [20]. Sediment transportation is the movement of organic or inorganic parti­cles (sediments) by water, the sediments can also be carried by gravity, glaciers and fluid in which the sediment is entrained. Most miner­al sediments are as a result of weathering and erosion [21]. Transportation of sediments was often responsible for the intermixing of geolog­ic features by carrying mineral particles away from their origin [22].According to Adegoke and Layade [23], a geo­physical investigation had been carried out within Gbede, the study area which revealed the proximity of the iron ore in form of magne­tite and hematite to the ground surface. Vents, supposedly the ore source, were also identified in the area which shows the presence of the ore in the area as a result of sediment transporta­tion that took place for years irrespective of the geological constituent of the area. This research is aimed at analyzing the grain size of the soil samples collected from the study area in other to classify the samples based on their textural properties and determine the transportation history of the samples. Geology and Description of the Study Area The study area is located in Gbede of Surulere L.G.A of Oyo State, Southwest Nigeria. It is ac­cessible through Ogbomoso – Gambari – Ilorin road, and is about 30 km from Ilorin Airport. The area is bounded within latitudes 8°17’37.7” and 8°17’49.8’’ North and between longitudes 4°20’45.9’’ and 4°20’58.8’’ East. It has an undu­lating topography with an average elevation of 370 m above the mean sea level. Past studies [24–25] have identified the hydrogeology of Sub-Saharan African as represented in Nigeria into four provinces; the Precambrian basement rocks, volcanic rocks, unconsolidated sediments and consolidated sedimentary rocks. Howev­er, the province of the Precambrian basement is located on the study area, and it comprises crystalline and metamorphic rocks. Materials and Method Sample Collection Grain size analysis can be determined using var­ious analytical techniques among which were sieving methods adopted for this research. The low investment, ease of handling and high accu­racy make the sieve analysis a commonly used procedure to determine the soil texture. Four-teen fresh samples were collected at different locations using Soil Auger. This Auger used at a different point was properly rinsed before and after each sample collection for good analy­sis. A small polythene bag was used to transport the samples to the laboratory to begin the siev­ing procedure and further analysis. For proper identification, each polythene bag was labelled GB1 to GB14 (GB means Gbede, while the fig­ures represent the number of strata being sam­pled). Sieve Analysis A weighing balance was used to weigh 100 g of each sample already arranged according to their depth. Since collected samples were fresh at the point of collection, it was then oven-dried at 70oC so that it will be free from trace mois­ture and thereafter passed through the me­chanical sieving process using the Ro-tap shak­er. The result of this sieving was tabulated and analysed. From the histogram chart, the cumu­lative frequency weight percent plotted against grain size (Phi) were generated and statistical parameters such as graphic mean, standard deviation skewness were computed from the graph. Seven points were identified as percen­tiles (5, 16, 25, 50, 75, 84 and 95 percentiles) and the results presented in Tables 1–6, respec­tively. The trend of grain size distribution was then determined from the total average value of each computed parameter. Appendices 1 and 2 represent the histogram and cumulative arith­metic curve plotted together from each sample. Results and Discussion Graphic Mean Graphic mean is one of the statistical parame­ters to understand the transport history of the sediments. It depends on the size of available sediments and the amount of energy impacted to the sediments. The result of the classification of samples with graphic mean is presented in Table 1 while Figure 1 shows the variogram of the mean for the soil samples. Ř16+50+84 ........= (1) 3 Table 1: Classification of the graphic mean. Graphic mean Classification Ř – 1 to Ř 0 Very coarse sand Ř 0 to Ř 1 Coarse sand Ř 1 to Ř 2 Medium sand Ř 2 to Ř 3 Fine sand Ř 3 to Ř 4 Very fine sand On the basis of the classification of as given different researchers [26–28] and using Equa­tion (1), the range from 1.09 to 2.33 was ob­tained and the average value for the distribution within the analysed samples was 1.61. The two sediments category identified from the study area were coarse-grained and fine-grained sed­iments. The range values of the coarse grained are from 0.6 to 1.0, which suggests the samples were transported farther than other groups, while the value of fine-grained samples is greater than 2 which is a result of low energy of transportation that is associated with coarse conglomeratic of soil [29]. Sorting (Standard Deviation) Sorting indicates how effective the deposition-al medium in separating different classes of grains. The expression for graphic standard de­viation is given in Equation (2) followed by its interpretation as shown in Table 2. According to [30], the various ranges of sorting in sand­stones indicate the various environments of the sand. Ř(84-16)+ Ř(95-5) ....1= (2) 4 6.6 Table 2: Graphic Standard deviation with classes of sorting. Graphic Standard Classes of Sorting Deviation Ř 0.35 to Ř 0.50 well sorted moderately well Ř 0.50 to Ř 0.71 sorted Ř 0.71 to Ř 1.00 moderately sorted Ř 1.00 to Ř 2.00 poorly sorted Figure 2 shows the range of sorted values lies between 0.54 and 1.42. This statistical calcula­tion revealed two different categories, namely moderately sorted and poorly sorted. But mod­erately sorted is the most dominant, suggest­ing the samples were transferred farther away from the point of collection. From the result, the classification class of 0.71–1.0 represented the moderately sorted grain, while the latter cate­gory is within the range of 1.0–2.0. The ener­gy and transportation of sediment distance are all functions of the distance of sorting values; therefore, the more the sediment is transferred from the source, the more the sample is moder­ately sorted and the closer the sediments to the source, the poor the samples sorted. Skewness Another parameter for the transportation history of sediments is Skewness and its de­termined using Equation (3) with the results presented in Table 3. It simply determines or measures symmetry in the scatter of distribu­tion as well as degree of lopsidedness of a curve Table 3: Classification scale describing the skewness. Classification scale Skewness Ř 0.1 to Ř 0.3 Fine skewed Ř -0.1 to Ř 0.1 Near symmetrical Ř -0.3 to Ř -0.1 Coarse-skewed (Figure 3). Skewness is directly related to the fine and coarse tails of the size distribution, and hence suggestive of energy of deposition. (Ř16+Ř84-2Ř50) ........1= 2(Ř84-Ř16) (Ř5+Ř95-2Ř50) + (3) 2(Ř95-Ř5) On the basis of the result of this parameter cal­culated, all the sediments are positively and negatively skewed. The values ranged from -0.01 to 0.26. The most significant classifica­tions identified are near symmetrically skewed (from -0.1 to 0.1) and finely skewed samples ranged from 0.1 to 0.3. This is an indication that samples are transported from various sources. The positive and negative values are the confir­mation that the sediments were transported to and away from the source. Kurtosis The kurtosis is the peakedness of the distribu­tion and measures the ratio between the sort- Figure 4: Variogram of Kurtosis of sample location. Table 4: Classification scale and description of Kurtosis. Classification scale Kurtosis <Ř 0.67 Very Platykurtic Ř 0.67 to Ř 0.90 Platykurtic Ř 0.90 to Ř 1.11 Mesokurtic Ř 1.11 to Ř 1.50 Leptokurtic Ř 1.50 to Ř 3.00 Very leptokurtic ing in the tails and central portion of the curve as given by Equation (4). The result of the clas­sification scale for kurtosis is presented in Ta­ble 4 while the range of Kurtosis is 0.58–1.72 as shown in Figure 4. From the classifications (platykurtic, leptokurtic, very leptokurtic and mesokurtic), the classes of leptokurtic are the most predominant in the study area with 50% of the samples. This implies the central por­tions are better sorted at the tails and strongly suggests that the samples are located at the wa­ter concentrated zone. (Ř95-Ř5) ........= (4) 2.44(Ř75-Ř25) The Cross Plot Analysis A graph of graphic mean values versus standard deviation, skewness against standard deviation as shown in Figures 5 and 6 respectively was used to determine the paleoenvironment of deposition of the soil samples from grain size analysis. Therefore, the graphical plots depict that all the samples analysed from the study Figure 5: Cross Plot of mean against standard deviation [30]. Figure 6: Cross Plot of Skewness against standard deviation. Table 5: Comparative result of the Grain Size Analysis for soil samples in phi (F). Sample Mean STD Skewness Kurtosis GB1 1.46 1.01 -0.05 1.35 GB2 1.55 0.54 -0.12 1.36 GB3 1.96 0.64 -0.13 1.50 GB4 1.29 0.95 0.18 1.03 GB5 1.09 1.26 0.03 1.17 GB6 1.19 0.91 0.06 1.72 GB7 2.06 1.20 -0.25 1.66 GB8 1.50 1.26 0.01 0.97 GB9 2.33 0.84 -0.08 1.21 GB10 1.69 0.42 0.20 1.40 GB11 2.03 0.57 0.26 0.58 GB12 1.37 0.87 0.02 1.66 GB13 1.94 0.62 -0.13 1.67 GB14 1.19 0.91 0.06 1.72 Average 1.62 0.95 4.3E-3 1.36 Table 6: Description of the Soil samples with Grain Size Analysis. Sample points Descriptions GB1 Medium sand, poorly sorted, ear symmetrical and leptokurtic. GB2 Medium sand, moderately well sorted, coarse-skewed and leptokurtic. GB3 Medium sand, moderately well sorted, coarse-skewed and leptokurtic. GB4 Medium sand, moderately sorted, fine skewed and mesokurtic. GB5 Medium sand, poorly sorted, near symmetrical and leptokurtic. GB6 Medium sand, moderately sorted, near symmetrical and very leptokurtic. GB7 Fine sand, poorly sorted, coarse-skewed and very leptokurtic. GB8 Medium sand, poorly sorted, near symmetrical and mesokurtic. GB9 Fine sand, moderately sorted, near symmetrical and leptokurtic. GB10 Medium sand, moderately sorted, fine skewed and leptokurtic GB11 Medium sand, moderately sorted, near symmetrical and leptokurtic GB12 Medium sand, moderately sorted, near symmetrical and very leptokurtic. GB13 Medium sand, moderately well sorted, coarse skewed and very leptokurtic. GB14 Medium sand, moderately sorted, near symmetrical and very leptokurtic. Average Medium sand, moderately sorted, near symmetrical and leptokurtic area were deposited by the transitional envi­ronment of geological effects [31]. The multiple directional patters of the paleoenvironment of deposition of soil samples were suggested to be responsible for the moderately sorted impact on the soil samples. Conclusion The transportation history of the soil deposit of the Gbede area has been assessed and analysed using grain size distribution through statistical parameters of mean, standard deviation, skew­ness, kurtosis and cross plot analysis, respec­tively. The geological environment of the soil samples could be responsible for the poorly and moderately sorted characteristics, and near symmetrical and leptokurtic nature exhibited by the samples deposited in the location [32]. All locations are characterised by soil samples input from a mineral source. Acknowledgement The authors acknowledge and appreciate the technical input of Mr. Akhihiero-Atta Samuel Oje of the Department of Geology, University of Ibadan Nigeria where the analysis was car­ried out. References [1] Kranck, K., Milligan, T.G. (1985): Origin of grain size spectra of suspension deposited sediment. Geo-Mari Letter, 5, pp. 61–66. [2] Kranck, K., Smith, P.C., Milligan, T.G. (1996a): Grain­size characteristics of fine-grained unflocculated sediments I: “one round” distributions. Sedimentol­ogy, 43, pp. 589–96. [3] Lĺng, L.O., Stevens, R.L. (1999): Source, transport and weathering influences upon grain-size and heavy mineral trends in glacial deposits of south­western Sweden. GFF, 121(2), pp. 45–53. [4] Kranck, K., Smith, P.C., Milligan, T.G. (1996b): Grain­size characteristics of fine-grained unflocculated sediments II: “multi round” distributions. Sedimen­tology, 43, pp. 597–606. [5] Abuodha, J.O.Z. (2003): Grain Size Distribution and Composition of Modern Dune and Beach Sediments, Malindi Bay Coast, Kenya. Journal of African Earth Sciences, 36, pp 41–54. [6] McLaren, P. (1981): An interpretation of trends in grain size measures. Journal of Sedimentary Petrol­ogy, 51, pp. 611–624. [7] Folk, R.L. (1966): A review of grain­size parameters. Sedimentology, 6, pp. 3–93. [8] Grzegorczyk, M. (1970):Metodyprzedstawianiauziar­nieniaosadw [Methods of presentation of grain size distribution of sediments]. PraceKomisji-Geograficzno-Geologicznej, 10(2), pp. 38–40. [9] Racinowski, R., Szczypek, T., Wach, J. (2001): Prez­entacja i interpretacja wyników badan uziarnienia [Presentation and interpretation of the grain-size distribution of Quaternary sediments]. University of Silesia Press, Katowice, 146 pp. [10] Trask, P.D. (1932): Hydrological investigative work by petroleum companies. Transactions, Ameri­can Geophysical Union, 13(1), pp. 306–307, doi: 10.1029/TR013i001p00306. [11] Krumbein, W.C., Pettijohn, F.J. (1938): Manual of Sedi­mentary Petrography. Appleton Century Crofts: New York, 549 p. [12] [12] Otto, G.H. (1939): A modified logarithmic prob­ability graph for the interpretation of mechanical an­alyzes of sediments. Journal Sedimentary Petrology, 9, pp. 62–72. [13] Dudley, R.J. (1977): The Particle SizeAnalysis of Soils and its Use in Forensic Science - The Determination of Particle size Distribution within the Silt and Sand Fractions. Journal of the Forensic Science Society, 16, pp. 219–229. [14] Inman, D.L. (1952): Measures for describing size of sediments. Journal of Sedimentary Petrology, 19, pp. 51–70. [15] McCammon, R.B. (1962): Efficiencies of percentile measures for describing the mean size and sorting of sedimentary particles. Journal of Geology, 70, pp. 453–465. [16] Kane, W.T., Hubert, J.F. (1962): FORTRAN program for the calculation of grain-size textural parame­ters on the IBM 1620 computer. Sedimentology, 2, pp. 87–90. [17] Sawyer, M.B. (1977): Computer program for the calculation of grain-size statistics by the method of moments: U.S. Geological Survey Open­File Report 77–580, 15 p. [18] Gupta, S.C., Larson, W.E. (1979b): A model for pre­dicting packing Density of soils using particle-size distribution. Soil Science Society of America Journal, 43, pp. 758–764. [19] Folk, R.L., Ward, W.C. (1957): Brazos River bar: a study in the significance of grain size parameters. Journal of Sedimentary Petrology, 27, pp. 3–26. [20] Folk, R.L. (1974): The petrology of sedimentary rocks. Hemphill Publishing Co.: Austin, Texas, 182 p. [21] Nichols, G. (1999): Sedimentology and Stratigraphy. Blackwell Science Ltd.: Oxford. 355 p. [22] Czuba, J.A., Magirl, C.S., Czuba, C.R., Grossman, E.E., Curran, C.A., Gendaszek, A.S., Dinicola, R.S. (2011): Sediment load from major rivers into Puget Sound and its adjacent waters: U.S. Geological Survey Fact Sheet 2011–3083, 4 p. [23] Adegoke, J.A., Layade, G.O. (2019): Compara­tive depth estimation of iron-ore deposit using the Data-Coordinate Interpolation Technique for airborne and ground magnetic survey vari­ation. African Journal of Science, Technology, In­novation and Development, 11(5), 663–669, doi: 10.1080/20421338.2019.1572702. [24] Alagbe, O.A. (2005): Integration of Electrical Resis­tivity Techniques and Lineament analysis in Hydro-geological investigation of parts of Ogbomoso, South – Western Nigeria. M. Tech Thesis. Ladoke Akintola University of Technology, Ogbomoso, Nigeria. [25] MacDonald, A.M., Davies, J. (2000): A brief review of groundwater for rural water supply in Sub-Saharan Africa. B.G.S. Technical Report. W.C./00/33. [26] Udden, J.A. (1914): Mechanical composition of clas-tic sediments. Bulletin of the Geological Society of America, 25, pp. 655–744. [27] Brown, A.G., (1985): Traditional and multivariate techniques in the interpretation of floodplain sedi­ment grain size variations. Earth Surface Processes and Landforms, 10, pp. 281–291. [28] Wentworth, C.K. (1922): A scale ofgrade and class terms for clastic sediments. Journal of Geology, 30, pp. 377–392. [29] Murray, R.C., Solebello, L.P. (2002). In: Forensic Sci­ence Handbook (volume I), Saferstein R. (ed.). Pren- tice­Hall: Upper Saddle River, New Jersey. [30] Friedman, G.M. (1962): On sorting, sorting coeffi­cients, and lognormality of the grain size distribution of sandstone. Journal of Geology, 70, pp. 737–756. [31] Gupta, S.C., Larson, W.E. (1979a): Estimating soil­wa­ter retention Characteristic from particles size dis­tribution, of organic matter percent, and bulk densi­ty. Water Resources Research, 15(6), pp. 1633–1635. [32] Passega, R. (1964): Grain size representation by CM patterns as a geological tool. Journal of Sedimentary Petrology, 34, p 4. APPENDIX 1: Typical result of sieve analyzes for sample points GB1 and GB2. APPENDIX 2: Typical results of histogram and frequency cumulative curve of different points. Figure 1: Histogram and frequency Cummulative curve for sample GB1. Figure 2: Histogram and frequency Cumulative curve for sample GB2. Figure 3: Histogram and frequency Cumulative curve for sample GB3. Original scientific paper Received: Jun 22, 2019 Accepted: Dec 18, 2019 DOI: 10.2478/rmzmag-2019-0025 Spatial Resistivity Mapping of Ureje Dam Floor, Southwestern Nigeria Prostorsko upornostno kartiranje dna jezu Ureje, JZ Nigerija Fatoba J.O.1,*, Eluwole A.B.1, Sanuade O.A.2, Aroyehun M.T.1 1 Dept. of Geophysics, Federal University Oye-Ekiti, Nigeria 2 King Fahd University of Petroleum and Minerals * julius.fatoba@fuoye.edu.ng Abstract Ureje Dam, Ado-Ekiti has witnessed drastic reduction in the water storage capacity of its reservoir. It be­came imperative to determine the possible cause(s) of the reduction in storage capacity. Geophysical in­vestigation involving the vertical electrical sounding technique of the electrical resistivity method was con­ducted in the upstream part of the dam. Five lithologic units that include the mud/suspended materials, such as sandy clay, clay, weathered/fractured bedrock and fresh bedrock, were delineated. The respective resistiv­ity and thickness range of the units are 2–19 ohm-m; 147–206 ohm-m, 2–38 ohm-m; 47–236 ohm-m and 455–1516 ohm-m and 0.4–1.9 m; 0.5–2.5 m; 1.0–12.2 m; 7.3–16.4 m and 8. The thicknessof suspended mate­rials, resistivity/thickness of weathered layer and the presence of near-surface impervious layer were used as the main indices for the spatial demarcation of the dam axis in terms of vulnerability to loss of impounded water. Using the cumulative response of the indices, the study concluded that the eastern to southeastern parts of the dam axis showed the highest indications of vul­nerability to loss of impounded water. Key words: Drastic reduction, vulnerability, spatial de­marcation, impounded water. Povzetek Jez Ureje na obmocju Ado­Ekiti se sooca z drasticnim zmanjšanjem kapacitete zadrževanja vode. Dolocitev mogocih vzrokov za zmanjšanje kapacitete zadrževa­nja je postalo nujno. V gor-vodnem delu jezu so bile izvedene geofizikalne preiskave z navpicnim elektric­nim sondiranjem. Razmejenih je bilo pet litoloških enot, ki so vkljucevale blato/suspendirane materiale; pešceno glino; glino; preperelo/razpokano podlago in svežo podlago. Pripadajoce upornosti in debeline plasti za omenjene enote so 2–19 ohm-m; 147–206 ohm-m, 2–38 ohm-m; 47–236 ohm-m in 455–1516 ohm-m ter 0.4–1.9 m; 0.5–2.5 m; 1.0–12.2 m; 7.3–16.4 m in 8. De-belina suspendiranih materialov, upornost/debelina preperele plasti in prisotnost neprepustne plasti blizu površine so bili uporabljeni kot glavni indeksi za pro-storsko razmejitev osi jezu v smislu ranljivosti glede izgube zajezene vode. Z uporabo kumulativnih odzivov indeksov preiskava zakljucuje, da vzhodni do jugovzho­dni deli osi jezu kažejo najvišje znake ranljivosti na iz­gubo zajezene vode. Kljucne besede: drasticno znižanje, ranljivost, pro-storska razmejitev, zajezena voda. Open Access. © 2019 Fatoba J.O., Eluwole A.B., Sanuade O.A., Aroyehun M.T., published bySciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. Introduction Ureje dam, Ado-Ekiti was constructed over 50 years ago with the sole aim of providing po­table water for the populace of Ado-Ekiti and its environs. At construction, the dam lake had an initial production capacity of 10,000 m3 volume of water per day. The production capacity has, however, dwindled over the years and has re­duced abysmally in recent times. This research aims to investigate the possible cause(s) for the reduction in reservoir water, which has nega­tive impact on the living standard of the people.Dam lake floors are susceptible to the accumu­lation of sediments after several years of con­struction. This is due to the transportation of sediments through the streams and rivers that serve as feeders to the lake. The volume of sedi­ments deposited is a function of the rate of flow of the streams and the progressive deposition increases the volume of sediments in the dam lake floor [1].The initial storage capacity and functions of the dam reservoir have been compromised by the increase in the volume of sediments with the attendant reduction in the production ca­pacity of the dam. Unpublished reports from local fishermen at the Ureje dam site indicate that there has been a rise in the level of the dam floor in some portions of the dam lake. This rise in the level of the dam floor could be attribut­ed to the appreciable deposition of sediments. Apart from the accumulation of sediments, the nature of subsurface materials and anomalous seepages may contribute to the loss of dam res­ervoir water [2–4]. Subsurface geologic struc­tures such as faults, fracture zones, basement depressions, and so on, if present beneath, a dam reservoir floor may also inhibit the stor­age capacity of the dam reservoir [5–8].Geophysical methods, especially the electrical resistivity (ER) method, have been used in dam site investigation [2, 3, 9, 10, 11]. ER method is a non-destructive technique that is capable of detecting internal erosion processes and de­tection of anomalous seepage [12–14] during pre-construction feasibility studies, post-con­struction integrity assessment and post-failure investigations. ER method has proven its per­formance and adequacy in the characterization of the potential paths of water seepage from dams [10, 12]. For example, [15] successfully carried out geophysical surveys at the Marathon Dam site near Athens, Greece, to detect possible degraded areas that are potentially liable to wa­ter infiltration or leakage. They also evaluated the dynamic properties of the subsurface ma­terials and evaluated the quality of the concrete in the dam interior using this technique. [16] employed geoelectrical measurement to iden­tify seepages through embankments and dams. [17] successfully used electrical resistivity to­mography (ERT) technique at Abu Baara earth dam in northwestern Syria to delineate poten­tial pathways of leakage that occur through the subsurface structure close to the body of the dam. [18] investigated water seepage of earth dams in Cordeirolis, Săo Paulo in Brazil using the direct current ERT technique with Wenner electrode array configuration.This study, therefore, aims at investigating the upstream part of the Ureje dam floor to unravel the subsurface features that may be undermin­ing the production capacity of the dam. Location, Geology and Geomorphology Ureje Earth Dam is located in Ado-Ekiti, Ado Local Government Area of Ekiti State, South­western Nigeria. The geographic coordinates of the dam site are between latitude 7o 35.74' and 7o 36.26' N of the equator and longitude 5o 12.45' and 5o 13.01' E of the Greenwich me­ridian (Figure 1).Geologically, the dam site lies on charnockite (Figure 2), a member of the Precambrian Base­ment Complex rocks of Southwestern Nigeria. Although the rock is concealed within the im­mediate vicinity of the dam, charnockites are classified in terms of structures as gneissic charnockites, foliated charnockites and coarse-grained charnockites [19].The topography at the site is gently undulat­ing with elevation above mean sea level vary­ing between 400 m and 418 m. The surround­ing hills roll towards the dam artificial lake. The area surrounding the dam site is covered with thick vegetation typical of the tropical rain forest vegetation belt of Nigeria. Two sea­sons occur in the area, namely the wet season Figure 1: Location Map of the Study Area. Figure 2: Geological Map of the Area Around Ado-Ekiti Showing the Ureje Dam site (After [20]). (April–October) and the dry season (Novem­ber–March). Methodology The ER method of geophysical prospecting was used in this study. The vertical electrical sound­ing (VES) technique, which involved the use of the Schlumberger electrode array, was adopt­ed. Twenty-five (25) VES stations were occu-pied (Figure 3) and the half current electrode spacing (AB/2) varied from 1 to 50 m. The geo­graphic coordinates of the VES locations were taken using the Garmin® Global Positioning System (GPS). All measurements were taken on the dam floor with the aid of three wood­en canoes on which measuring apparatus was related. The same parameters were also spa­tially interpolated, and relevant maps were generated. Results and Discussion Depth Sounding Curves The interpreted depth sounding curves (Fig­ure 4a–d) in the dam lake shows that they are characterised by 3–5 geoelectric layers. The lithology is generally made up of mud/sus­pended materials, sandy clay, clay, weathered/fractured bedrock and fresh bedrock. The curve types include A, K, KH and KHA with A–type Figure 4: Typical Depth Sounding Curves. (a) A – Type, (b) K – Type, (c) KH – Type and (d) KHA – Type. Table 1: Colour Chart of the Distribution of the Depth Sounding Curves. VES LOCATIONS KEY 1 10 19 p1 > p2 > p3 = A-Type Curve 2 11 20 p1 < p2 > p3 = K-Type Curve 3 12 21 p1 < p2 > p3 p4 = KH-Type Curve 4 13 22 p1 < p2 > p3 < p4 < p5 = KHA-Type Curve 5 14 23 6 15 24 7 16 25 8 17 9 18 curve being the dominant curve. The summary Geoelectric Sections of the VES type-curves and their distribution The geoelectric sections (Figure 5a–c) gen-within the 25 sounded positions are presented erated from approximately linearly existing in Table 1. VES locations show that there are a maximum Figure 5: Geoelectric Sections Beneath the Dam Floor (a) Section A – B (b) Section C – D, (c) Section E – F. of five (5) geoelectric units beneath the Ureje logic units were identified. The lithologic units, dam lake. The geoelectric units were calibrated in order of their occurrence, include mud/sus-in terms of apparent resistivity and five litho-pended materials, sandy clay, clay, weathered/ fractured bedrock and fresh bedrock. Each of the lithologic units has their implication(s) on the overall storage capacity of the dam reser­voir. The mud/suspended materials is char-acterised by resistivity values generally less than 20 ohm-m and its thickness varies from 0.4–1.9 m. An increase in the cumulative vol­ume of the mud/suspended materials could in­hibit the storage capacity of the reservoir.The sandy clay layer with resistivity values greater than 100 ohm-m present in VES 12, 14 and 15 (Figure 5a) and VES1 and 5 (Figure 5c) constitutes a liability to the reservoir. This is because the relatively high porosity associat­ed with sandy clay materials can enhance the seepage of impounded water into the subsur­face. On the other hand, the clay unit where sig­nificantly thick, (Figure 5a and 5b) is advanta­geous to the dam reservoir as it will inhibit the percolation of water into the subsurface due to very poor permeability characteristics of the clay materials.The weathered/fractured bedrock unit is a threat to any engineering structure/facility due to its incompetent nature. The threat becomes greater when it is near the surface and is not overlain by any impervious medium as found in Figure 5c and some portions of Figure 5b. Also, the weathered/fractured bedrock is an aquif­erous unit in a typical Basement Complex envi­ronment, and as such, the Ureje dam lake may be losing water to the groundwater in zones associated with near-surface weathered/frac­tured bedrock and without overlying impervi­ous layers.The fresh bedrock is a relatively resistive layer with impervious characteristics. The bedrock ordinarily has the capacity to support the foun­dation of any engineering structure especially containment facilities such as dams. However, the potential could be inhibited if it is deeply seated and with undulating topography – most especially depressions. The basement bedrock beneath the Ureje dam as seen in Figure 5a to 5c is generally deeply seated with exceptions of VES 18 and VES 23. The depth of occurrence of the bedrock varies between 7 m and 18 m and as such has minimal importance as far as the containment of impounded water is con­cerned. Spatial Vulnerability Indices The general vulnerability of the Ureje dam lake to reduction in volume/loss of impounded water was assessed using three main indices [9, 10] which include: i. the thickness of suspended materials, ii. the resistivity of weathered layer, iii.the presence of near-surface impervious (clay) layer. The dam lake was demarcated based on the thickness of suspended materials, such that ar­eas having thicknesses less than the mean thick­ness (0.77 m) of suspended materials under the bluish colour band in Figure 6 are classified as having a low vulnerability to the reduction in volume/loss of impounded water. Areas having thickness values greater than 0.77 m (identified by the reddish colour band) are classified to be highly vulnerable to loss of impounded water.As shown in Figure 7, areas within the dam lake characterised by weathered layer resistivity values greater than 100 ohm-m are classified to have a higher vulnerability to the loss of im­pounded water due to the sandy nature of the weathered materials inferred from the resistiv­ity values. However, areas under the greenish colour band associated with relatively low re­sistivity values possess low vulnerability to loss of impounded water.As mentioned earlier, the presence of a near-surface impervious (clay) layer beneath a dam lake has the potential to inhibit the perco­lation of impounded water into the subsurface. Zones devoid of clay substratum (purple colour band) in Figure 8 are classified to possess high vulnerability. Other areas are potentially less prone to loss of impounded water due to the presence of clay. Cumulative Spatial Vulnerability Assessment The indices earlier discussed were spatially overlaid to generate the cumulative index map (Figure 9) of the dam lake to assess its general vulnerability to loss of impounded water. The map shows that the eastern to southeastern portions of the dam lake constitute zones with the highest indications of high vulnerability to loss of impounded water. Such zones are also present in other locations within the lake. It is interesting to note that the zones are mainly as­ Figure 6: Spatial Vulnerability Assessment from Thickness of Suspended Materials. Figure 7: Spatial Vulnerability Assessment from Resistivity of Weathered Layer. Figure 8: Spatial Vulnerability Assessment from Presence of Near-surface Clay Substratum. Figure 9: Cumulative Spatial Vulnerability Map. sociated with the boundaries of the lake with resent zones adjudged to be less prone to the most occurring around the water intake section loss of impounded water as far as the indices through which the river straddles. On the other deployed are concerned. hand, areas under the bluish colour band rep­ Conclusions The cause of the drastic drop in the quantity of impounded water in the Ureje dam lake in Ado-Ekiti southwestern Nigeria has been in­vestigated using the ER method of geophysical prospecting. The VES field technique was de­ployed via the Schlumberger electrode array. Twenty-five locations were depth sounded within the dam lake, and three geoelectric sec­tions were constructed to cut across a sizeable number of VES locations for correlating their resistivity parameters. Five subsurface geo-electric layers were delineated within the lake. These include the mud/suspended materials, sandy clay, clay, weathered/fractured bedrock and the fresh bedrock. The thickness of the sus­pended materials, weathered layer resistivity and the presence of near-surface clay substra­tum were used as the main indices for the loss/reduction in the volume of impounded water. Areas classified as having high vulnerability to the loss of impounded water are those having attributes such as the thickness of suspended materials greater than the mean thickness of 0.77 m; weathered layer resistivity greater than 100 ohm-m and absence of near-surface clay substratum. On the other hand, zones charac­terised by a thickness of suspended materials less than the mean thickness of 0.77 m; low re­sistivity values and presence of clay substratum were considered to be less prone to the loss of impounded water. The general characteristics of the vulnerability indices indicated that the eastern–southeastern axis and some localised zones of the dam lake possess the highest cu­mulative vulnerability to the loss/reduction in the quantity of impounded water. Conclusively, therefore, the Ureje dam lake may have been losing most of its impounded water in the east­ern–southeastern areas of the dam lake. References [1] Snyder, N.P., Rubin D.M., Alpers C.N., Childs J.R., Cur­ tis J.A., Flint L.E., Wright S.A. (2004): Estimating accumulation rates and physical properties of sed­iment behind a dam: Englebright Lake, Yuba Riv­er, northern California. Water Resources Research, 40(11), W11301, doi:10.1029/2004WR003279. [2] Aina, A., Olorunfemi, M.O., Ojo, J.S. (1996): An Inter­pretation of Aeromagnetic and Electrical Resistivi­ty Methods in Dam Site Investigation. Geophysics, 61(2), pp. 349–356. [3] Eluwole, A.B., Olorunfemi, M.O. (2012): Time­Lapsed Geophysical Investigation of the Mokuro Earth Dam Embankment, Southwestern Nigeria, for Anomalous Seepages. Pacific Journal of Science and Technology, 13(1), pp. 604–614. [4] Olorunfemi, M.O., Idornigie, A.I., Fagunloye, H.O., Ogun, O.A. (2004): Assessment of Anomalous Seep­age Conditions in the Ope Dam Embankment, Ile-Ife, Southwestrn Nigeria. Global Journal of Geological Sciences, 2(2), pp. 191–198. [5] Johri M., Zoback M.D., Hennings P. (2014): A scaling law to characterize fault-damage zones at reservoir depths. AAPG Bulletin, 98(10), pp. 2057–2079. [6] Mansour K., Omar K., Ali K., Zaher M.A. (2018): Geo­physical characterization of the role of fault and fracture systems for recharging groundwater aqui­fers from surface water of Lake Nasser. NRIAG Jour­nal of Astronomy and Geophysics, 7(1), pp. 99–106. [7] Song S., Feng X., Rao H., Zheng H. (2013): Treatment design of geological defects in dam foundation of Jin-ping I hydropower station. Journal of Rock Mechan­ics and Geotechnical Engineering, 5, pp. 342–349. [8] Wieland M., Brenner R.P., Bozovic A. (2008): Poten­tially active faults in the foundations of large dams part i: vulnerability of dams to seismic movements in dam foundation. In: The 14th World Conference on Earthquake Engineering, Beijing, China. [9] Ajayi, O., Olorunfemi, M.O., Ojo, J.S., Adegoke-Antho­ny, C.W. (2006): Integrated geophysical and geotech­nical investigation of a damsite on River Mayo Ini, Adamawa State, Northern Nigeria. Africa Geoscience Review, 12 (3), pp. 179–188. [10] Olorunfemi, M.O., Ojo, J S., Sonuga, F.A., Ajayi, O., Ol­adapo, M.I. (2000): Geoelectric and Electromagnet­ic Investigation of the Failed Koza and Nassarawa Dams Around Katsina, Northern Nigeria. Journal of Mining and Geology, 36 (1), pp. 51–56. [11] Sjodahl, P., Dahlin, T., Johansson, S. (2003): Resis­tivity Monitoring for Leakage Detection at Hallby Embankment Dam. In: 9th Meeting of Environmental and Engineering Geophysics, Prague, Czech Republic. [12] Cho I.K., Yeom J.Y. (2007): Cross line resistivity to­mography for the delineation of anomalous seep­age pathways in an embankment dam. Geophysics, 72(2), pp. G31–G38, doi: 10.1190/1.2435200. [13] Lin C.P., Hung Y.C., Wu P.L., Yu Z.H.(2014): Perfor­mance of 2-D ERT in investigation of abnormal seepage: a case study at the Hsin­Shan earth dam in Taiwan. Journal of Environmental and Engineering Geophysics, 19(2), pp. 101–112. [14] Sjödahl P., Dahlin T., Johansson S. (2010): Using the resistivity method for leakage detection in a blind test at the Rsvatn embankment dam test facility in Norway. Bulletin of Engineering Geology and Envi­ronment, 69(4), pp. 643–658. [15] Karastathis V.K., Karmis P.N., Drakatos G., Stavraka­ kis G. (2002): Geophysical methods contributing to the testing of concrete dams. Application at the Marathon Dam. Journal of Applied Geophysics, 50, pp. 247–260. [16] Benes, V., Tesar M., Boukalova, Z. (2011). Repeated geophysical measurement—The basic principle of the GMS methodology used to inspect the condition of flood control dikes. Trans. Ecol. Environ.,146, pp. 105–115. [17] Al-Fares W. (2014). Application of Electrical Resis­tivity Tomography Technique for Characterizing Leakage Problem in Abu Baara Earth Dam, Syria. International Journal of Geophysics, 2014, 9 pages, doi:10.1155/2014/368128. [18] Camarero P.L., Moreira C.A. (2017): Geophysical in­vestigation of earth dam using the electrical tomog­raphy resistivity technique. REM: Int. Eng. J., Ouro Preto, 70(1), pp. 47–52. [19] Rahaman, M. (1988): Recent Advances in the Study of the Basement Complex of Nigeria. Precambrian Geology of Nigeria, pp. 11–41. [20] Talabi, A., Tijani, M. (2013): Hydrochemical and Stable Isotropic Characterization of Shallow Groun-water System in the Crystalline Basement Complex Terrain of Ekiti Area, Southwestern Nigeria. Applied Water Science, 3(1), pp. 229–245. Instructions for Authors About the Journal RMZ – Materials and Geoenvironment (RMZ – Materiali in geookolje) is a periodical publication with four issues per year. It was established in 1952 and renamed to RMZ – M&G in 1998). The main topics of Journal are Mining, Geotechnology, Metallurgy, Materials, Geology and Geoenvironment. RMZ – M&G publishes original scientific papers, review papers, preliminary notes and professional papers in Eng­lish. Only professional papers will exceptionally be published in Slovene. In addition, evaluations of other publica­tions (books, monographs, etc.), in memoriam, presentation of a scientific or a professional event, short commu­nications, professional remarks and reviews published in RMZ – M&G can be written in English or Slovene. These contributions should be short and clear. . Original scientific papers represent unpublished results of original research. . Review papers summarize previously published scientific, research and/or expertise articles on a new scientific level and can contain other cited sources which are not mainly the result of the author(s). . Preliminary notes represent preliminary research findings, which should be published rapidly (up to 7 pages). . Professional papers are the result of technological research achievements, application research results and in­formation on achievements in practice and industry. . Publication notes contain the author’s opinion on newly published books, monographs, textbooks, etc. (up to 2 pages). A figure of the cover page is expected, as well as a short citation of basic data. . In memoriam (up to 2 pages), a photo is expected. . Discussion of papers (Comments) where only professional disagreements of the articles published in previous issue of RMZ – M&G can be discussed. Normally the source author(s) reply to the remarks in the same issue. . Event notes in which descriptions of an scientific or a professional event are given (up to 2 pages). Form of the Manuscript Basic Requirements for Manuscript . Optimal number of pages is 7 to 15; longer articles should be discussed with the Editor-in-Chief prior to submission. . Text of the manuscript should be written in Times New Roman font with 12-point size and 1.5 line spacing. . Figures, tables and formulas should be included in the text of the manuscript. . Headings should be written in Arial bold font (12-point size) and should not be numbered. . Subheadings should be written in Arial italic font (12-point size). . The electronic version of the manuscript should be simple, without complex formatting. For highlighting, only bold and italic types should be used. . The manuscript should be submitted in Microsoft Word via the online system. Composition of the Manuscript The manuscript should have the following composition: Title The title of the article should be precise, informative and not longer than 100 characters. The author should also in­dicate the short version of the title. The title should be written in English and for Slovenian authors also in Slovene. Author’s Information Author’s information should include name and surname of the authors, the address of the institution and the e-mail address of the corresponding author. Abstract An Abstract presents the purpose of the article and the main results and conclusions. It should not exceed 180 words. It should be written in English and for Slovenian authors also in Slovene. Keywords A list of up to 5 key words (3 to 5) that will be useful for indexing or searching. They should be written in English and for Slovenian authors also in Slovene. Introduction An Introduction should provide a review of recent literature and sufficient background information to allow the results of the article to be understood and evaluated. Materials and methods The Materials and method section details the theoretical or experimental methods and materials used to obtain the results. Results and discussion The result section should clearly and concisely present the data, using figures and tables where appropriate. The Discussion section should describe the relationships shown by results and discuss the significance of the results, making comparison with previously published work. Conclusions A Conclusions section should present one or more conclusions that have been made from the results and discus­sion. Acknowledgements Acknowledgement (optional) of collaboration or preparation assistance may be included. If the research was fund­ed, please note the source of funding. References A references section includes a list of references, which comprises all the references cited in the text. Units and Abbreviations Only standard SI symbols and abbreviations should be used in the text, tables and figures. Symbols for physical quantities in the text should be written in italics (e.g. m, l, v, T). Symbols for units that consist of letters should be in plain text with spaces after number (e.g. 10 m, 5.2 kg/s, 2 s-1, 50 kPa). All abbreviations should be spelt out in full on first appearance. A period/full stop is used as the decimal point (3.14 and not 3,14). Figures Figures must be cited in consecutive numerical order in the text and referred to in both the text and the captions as Figure 1, Figure 2, etc. Figures should be originals, made in an electronic form (Microsoft Excel, Adobe Illustra­tor, Inkscape, AutoCAD, CorelDraw, etc.) and saved in .eps, .tiff or .jpg format with a resolution of at least 300 dpi. The width of the figures should be at least 152 mm. Figures should be named the same as in the article (Figure 1, Figure 2, etc.). Letters and numbers should be readable, with equal sizes and fonts in all figures. Figures should also be submitted as a separate document, i.e. separated from the text in the article. Tables Tables must be cited in consecutive numerical order in the text and referred to in both the text and the caption as Table 1, Table 2, etc. Tables should be prepared using a table editor and not inserted as a graphic. Equations Equations should be numbered in consecutive numerical order with the use of round brackets on its right side and referred in the text as Equation (1), Equation (2), etc. The equations should be written using equation editor. References The references should be cited in the same order as they appear in the article. Where possible the DOI for the refer­ence should be included at the end of the reference. They should be numbered in square brackets. Any references cited in the article must be given in full. Unpublished results and personal communications are not recommended in the reference list, but may be mentioned in the text, if necessary. Please use examples in Appendix as a guide. Manuscript Submission Please submit your article via RMZ – M&G Editorial Manager System. You can find it on the address http://edmgr.editool.com/rmzmag/default.htm Log in as an author and submit your article. Note that the manuscript should be submitted in Microsoft Word for­mat. High resolution figures should be included in the text and also submitted as a separate document. You can follow the status of your submission in the Editorial Manager System and your e-mail. Review Process All manuscripts will be supervised in a review process. The reviewers evaluate the manuscript and can ask the authors to change particular segments, and propose to the Editor-in-Chief the acceptability of the submitted arti­cles. Authors are requested to identify three reviewers and may also exclude specific individuals from reviewing their manuscript. The Editor-in-Chief has the right to choose other reviewers. The name of the reviewer remains anonymous. The technical corrections will also be done and the authors can be asked to correct the missing items. The final decision on the publication of the manuscript is made by the Editor-in-Chief. Production Process After composing PDF document and language editing, author receive document for proofreading. If author have any comments, mark them and write a comment in the same PDF document. Comments in another document or scanned and corrected document are inappropriate. Upload PDF document in Editorial Manager System under the different name. If author do not cooperate in production process, manuscript can be rejected, despite of receiving letter of acceptance. Appendix: citing of references Journal article: Surname 1, Initials, Surname 2, Initials (year): Title. Journal, volume(number), page range, DOI code. Journal title should be complete and not abbreviated. Note that Journal Title is italicized. [1] Malej, S., Tercelj, M., Peruš, I., Kugler, G. (2016): Influence of cooling mode in relation to casting and extrusion parameters on mechanical properties of AA6082. Materials and Geoenvironment, 64(1), pp. 11–19, DOI:10.1515/ rmzmag-2016-0022. Book: Surname 1, Initials, Surname 2, Initials (year): Title. Publisher: placeof publication, number of pages. Note that the Title of the book is italicized. [2] Reynolds, J.M. (2011): An introduction to applied and environmental geophysics. Wiley­Blackwell: Chichester, 710 p. Chapter in an Edited Book: Surname 1, Initials, Surname 2, Initials (year): Chapter title. In: Book title, Editor Surname 1, Initials, Editor Sur­name 2, Initials (ed(s).). Publisher: place of publication, page range. Note that the Book title is italicized. [3] Blindow, N., Eisenburger, D., Illich, B., Petzold, H., Richer, T. (2007): Ground Penetrating Radar. In: Environmen­tal Geology – Handbook of Field Methods and Case Studies, Knödel, K., Lange, G., Voigt, H.J. (eds.). Springer: Berlin, pp. 283–335. Proceeding Paper: Surname 1, Initials, Surname 2, Initials (year): Paper title. In: Proceedings title, place of symposium/conference, Editor Surname 1, Initials, Editor Surname 2, Initials (ed(s).). Publisher: place of publication, page range. Note that the Proceedings title is italicized. [4] Benac, C., Gržancic, Ž., Šišic, S., Ružic, I. (2008): Submerged Karst Phenomena in the Kvarner Area. In: Proceedings of the 5th International ProGEO Symposium on Conversation of the Geological Heritage, Rab, Croatia, Marjanac, T. (ed.). Pro GEO Croatia: Zagreb, pp. 12–13. Master Thesis or Ph. D. Thesis: Surname, Initials (year): Title. Type of document (Master Thesis or Ph. D. Thesis). Publisher: place of publication, number of pages. Note that the Title is italicized. [5] Rošer, J. (2010): Study of the effects of sediments on seismic ground motion in the city of Ljubljana using the micro-tremor survey method. Ph. D. Thesis. University of Ljubljana, Faculty of Natural Sciences and Engineering, Depart­ ment of Geotechnology, Mining and Environment: Ljubljana, 278 p. Standard: Standard-Code (year). Title of the Standard. Organisation: place. Note that the Title of the Standard is italicized. [6] ISO/ICS 17892­10:2018. Geotechnical investigation and testing – Laboratory testing of soils – Part 10: Direct shear tests. International Organization for Standardization: Genova. Electronic source: Title [online]. Surname, Initials or Company name, renewed (date) [cited (date)]. Available on: http://address. Note that the www address is italicized. [7] CASREACT – Chemical reactions database [online]. Chemical Abstracts Service, renewed 2/15/2000 [cited 2/25/2000]. Available on: http://www.cas.org/casreact.html. These instructions are valid from February 2020.