COBISS: 1.01 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA NENAVADNO MINERALOGENO JAMSKO OKOLJE V MEHIKI: PODROÈJE CUATRO CIÉNEGAS Paolo fORTI1, Ermanno GALLI2, Antonio ROSSI Abstract UDC 552.54:551.44(72) Paolo Forti & Ermanno Galli & Antonio Rossi: Peculiar minerogenetic cave environments ofMexico: the Cuatro Cié-negas area Te karst area of Quatro Ciénegas (Coahuila, Mexico) repre-sents an ideal site to study cave mineralogy, because it hosts caves of diferent age and genesis (karst, thermal, mine caves). Among the speleothems studied is worth to mention a nest of aragonite cave pearls found deep inside the Reforma mine char-acterized by the total absence of growing layers inside them. Despite only few studied caves (8), some 32 diferent cave min-erals have been detected, one of which is new for the cavern en-vironment (kingsmountite) and another one, still under study, which probably will result new for science. Due to the scientifc interest of their chemical deposits it should be very important to protect in the future the natural cavities of the karst systems of Cuatro Ciénegas in order to preserve a scientifc patrimony actually only partially known. keywords: cave minerals, guano minerals, minerogenetic mechanisms, climate, Cuatro Ciénegas desert, Mexico. Izvleèek UDK 552.54:551.44(72) Paolo Forti & Ermanno Galli & Antonio Rossi: Nenavadno mineralogeno jamsko okolje v Mehiki: podroèje Cuatro Cié-negas Kraško ozemlje Quatro Ciénegas (Coahuila, Mehika) predstavlja idealno obmoèje za preuèevanje jamske mineralogije, saj so tam jame razliène starosti in razliènega nastanka (kraške, termalne, jamski rudniki). Med preuèevanimi kapniki je vredno omeniti gnezdo aragonitnih jamskih biserov globoko v rudniku Reforma, za katere je znaèilna popolna odsotnost rastnih plasti (»letnic«). Kljub majhnemu številu preuèevanih jam (8) je bilo odkritih 32 razliènih jamskih mineralov, eden izmed njih nov za jamsko okolje (kingsmountite), drugi pa, ki je še v preuèevanju, bo najbrž novo znanstveno odkritje. Zaradi znanstvenega pomena kemijskih odkladnin bi bilo zelo pomembno naravne jame kraškega sistema Quatro Ciénegas zašèititi, da bi s tem ohranili znanstveno dedišèino, za zdaj šele deloma poznano. kljuène besede: jamski minerali, minerali guana, mineralogeni mehanizmi, podnebje, pušèava Quatro Ciénegas, Mehika. INTRODUCTION Te natural caves are the seats of complex minerogenetic posits in caves. forti (1996) stated that the hyperkarstic processes controlled by peculiar conditions existing in evolution occurs according to two chemical and physi- every single cave (Hill & forti, 1997): hosting rock, cave cal contemporary processes: the corrosion/dissolution sediments and circulating fuids are the most important of pre-existing rocks and the deposition of speleothems factors controlling the development of the chemical de- with an extremely variable chemical composition. 1 Istituto Italiano di Speleologia, Universita di Bologna & La Venta Exploring Team, forti@geomin.unibo.it 2 Dipartimento di Scienze della Terra, Universita di Modena e Reggio Emilia Received / Prejeto: 29.11.2005 ACTA CARSOLOGICA 35/1, 79–98, LJUBLJANA 2006 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI Recent researches, performed on internal cave de-posits of European and extra-European locations, have brought to the identifcation of particular and extremely rare mineral phases, whose crystalline nature and chemi-cal composition are strictly related to geological, clima-tological, lithological and hydrogeological continuously changing parametres (frau et al, 1998; Lattanzi et al, 1998). Some very diferent minerogenetical mechanisms may induce the deposition of crystalline and/or amor-phous phases, that are stable as long as the environmental conditions remain constant. Tese “products” can easi-ly change or slightly modify if the genetical conditions change (Benedetto et al, 1998; forti et al, 1999, 2000, 2001). In this framework the thermal caves, which have been characterised at least once during their evolution by the presence of fuids with complex chemistry, are extremely interesting, permitting the evolution of poly- genetic complex chemical deposits, mostly, although not always, correlated to the “Sulphur cycle” (forti, 1989; frau & Sabelli 2000). Another peculiar class of natural cavities is repre-sented by the “mine caves”, cavities without any natural entrance, which have been intersected by mine galleries or other artifcial tunnels: their minerogenetic interest comes from the possible interaction between karst fuids and ore bodies (forti 2005, De Waele & Naseddu 2005). Te karst area of Quatro Ciénegas (Coahuila, Mexi-co) represents an ideal site to study cave mineralogy, be-cause it hosts caves of diferent age and genesis (karst, thermal, mine caves) and therefore the chemical deposits developed inside them should result quite diferent from cave to cave, allowing the detection of many simultane -ous and/or subsequent minerogenetic mechanisms. In the present paper the observed speleothems are de-scribed and the related minerogenetic mechanisms are discussed in detail. THE KARST Of CUATRO CIÉNEGAS Cuatro Ciénegas plain is a Natural Protected Area since 1994; it is located in the state of Coahuila, Mexico, in the Sierra Madre Oriental at the eastern edge of the Chihua-hua desert (fig. 1). moist air coming from the cyclones developing in the Mexican Gulf Te rainiest period is September, with an average of 35 mm; anyway some years, particularly strong events Fig. 1: location map and a general view of the Cuatro Ciénegas desert. Tis desert is characterized by a single period of may cause the fall of over 5 mm in a few hours, thus trans-rain, which normally consists of short but strong rain- forming the depressions in swallow ephemeral lakes. storms in the summer period: they are caused by the 80 ACTA CARSOLOGICA 35/1 – 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA Long rectilinear anticline ridges characterize the landscape of Cuatro Ciénegas whereas major valleys cor-respond to synclines. Te most inclined slopes of major structures, mostly facing SW, ofen display vertical or overburden beds. Along them, deep transversal and longitudinal valleys form a typical trellis drainage pat-tern. In the pedemontane areas, several coalescent fuvial fans form a wide regular surface gently inclined, where streams display a disrupted and irregular pattern. Runof is quite absent in these areas. Te plains behave as endo-reic basins where major storms form shallow lakes and ponds, the evaporation of which causes the formation of sulphates deposits. Eolian gypsum dunes occur in these areas. Some of the major caves in the area of Cuatro Cié-negas are hypogenic in origin, created by rising thermal water. Te best example is the Cueva Rancho Guadalupe, in the NE of Sierra la fragua. Tis cave has a typical den-dritic pattern and consists of maze conduits and spheri-cal rooms (Bernabei et al., 2002). Tough it receives little rain, the Cuatro Ciénegas valley has abundant subterranean water, which creates hundreds of small pools, marshes, rivers, lakes (large, saline lakes locally called lagunas or playas), and canals with a unique biota of great interest to the international scientifc community and at risk of extinction (fig. 2). A peculiar characteristics of the pools is the presence of living stromatolithes, which act as local primary agents of the food chain. Despite the relevant ecological interest of the aqua-tic environment of Cuatro Ciénegas only in 2000 La Ven-ta Exploring Team started a hydrogeological study of the pools and of high surrounding mountains proving that most of the pool recharge comes from karst structures; during this research over 60 caves were explored and mapped (forti et al, 2003). Te karst of Cuatro Ciénegas underwent a complex evolution over a very long span of time, which may be evaluated of several tens of millions years. Actually most of the karst systems show a rather inactive evolution, even if corrosion and/or depositional processes are still going on somewhere. Te speleogenetic mechanisms were very difer-ent among each other and therefore produced peculiar forms, which now allow reconstruction at least the mean steps of the complex evolution the caves of Quatro Ciénegas underwent. Tis evolution may be subdivided into four princi-pal types (forti et al. 2003), which may be also regarded as subsequent stages being rather in chronological order even if some overlap occurred: 1. Te genesis of mine caves (hyperkarst phenomenon) 2. Te genesis of thermal caves (hyperkarst phenomenon) 3. Te genesis of meteoric caves (karst phenomenon) 4. Te development of biogenic forms inside previously formed caves (hyperkarst phenomenon) Te frst two mechanisms are related to the uplifing of deep hot fuids, the third to the seepage of meteoric (rain) waters, the forth to the presence of huge bat com-munities, which colonized mainly the caves of the third type. Te study on the speleothems of the Cuatro Ciénegas caves, started in 2001, and it is far to be completed, Fig. 2: Aerial view of the pools of the Cuatro Ciénegas desert ACTA CARSOLOGICA 35/1 – 2006 81 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI but on the basis of the achieved results it is evident that this karst region can be considered as one of the most interesting in the world from the point of view of the hosted cave minerals. Tis uncommon richness of mineralogical phases, most of which phosphates, is the direct consequence of the complex karst evolution this area underwent. More-over, some of the “normal” karst caves became in the past (since several years ago) shelter for huge colonies of bats, thus allowing the accumulation of widespread guano de-posits up to several metres thick inside which microbio-logical reactions gave rise to an extraordinary variety of minerals. finally the karst springs are fed by mineralized wa-ters uplifing from rather deep circuits and the peculiar climatic conditions of the desert of Cuatro Ciénegas inducing strong evaporations creating a “sabkha” type environment thus allowing the deposition of even very soluble minerals. Te scarcity of available time for the cave explo-ration and for mineral sampling obliged to restrict the mineralogical study to a rather small number of natural cavities. Anyway they have been selected to represent all the diferent environmental and minerogenetic conditions existing in Cuatro Ciénegas. Among the analyzed caves there are mine caves (Reforma Mine), thermal caves (Cueva Rancho Guadalupe), karst cavities with bat colonies (Cueva Rossillo) and Cueva de los Murcielagos. ExPERIMENTAL METHODS A detailed analysis of all the samples by the stereoscopic microscope was performed to distinguish and to separate the diferent mineralogical phases present in each sam-ple. Ten the single phases were analysed by a powder difractometre (Philips PW 1050/25), when the material was quantitatively enough and homogeneous, or by a Gandolf camera (O: 114.6 mm, exposition: 24/48 hrs), when the material was scarce or inhomogeneous. Always the experimental conditions were: 40Kv e 20 mA tube, CuK? Ni fltered radiation (? = 1.5418 A). Te analyses of the clay minerals were done not only over the natural samples but also afer a glycerine treatment. Almost all the samples analyzed by Gandolf camera were later used to obtain images and chemical quali-tative analyses through an electron scanning microscope (SEM Philips xL40) with an electronic microprobe (EDS-EDAx 9900) at the C.I.G.S. (Centro Interdiparti-mentale Grandi Strumenti) of the Modena and Reggio Emilia University THE MINE CAVES AND THEIR MINEROGENETIC MECHANISMS Te speleological interest of the mining areas around Cuatro Ciénegas is represented by the existence of “mine caves” (De Waele & Naseddu 2005, De Waele et al, 1999, 2001; forti et al, 1999), karst cavities without any natural connection with the surface, which has been intersected by the mine galleries. Te oldest actually known karst (paleokarst) phe-nomena of the Cuatro Ciénegas area (forti et al., 2003) are those connected with the formation of the metallic sulphides ore bodies, mainly consisting of lead, zinc and, in a lesser extent, of silver, extensively mined in the past (De Vivo & forti 2002). Te area of Cuatro Ciénegas was one of the very frst Mexican regions in which mining activities started since the frst half of the 14th century Tese activities lasted until 1958, when the most important mine (the Reforma mine) was defnitively closed because the reached depth, 82 ACTA CARSOLOGICA 35/1 – 2006 far below the water table, made the production costs higher than the exploitation profts. Te ore bodies consist of sulphides with some su-pergenic minerals, most of which carbonates, dispersed within a carbonate breccia or flling karst cavities (Vargas et al, 1993). Te fuids fowing inside the carbonate rocks developed caves along the bedding planes and the major discontinuities, mainly where the rock was highly fractured and therefore more permeable. Tese fuids simultaneously, or just afer the development of the caves, flled them with lead and zinc sulphides as in the case of the Reforma Mine. Due to the progressive cool-ing down and loosing pressure of the thermal fuids, at the end of the mineral deposition, euhedral (middle thermality) quartz and fnally low thermality calcite was formed. PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA In the frst hypothesis (MVTOD) the caves flled by ore bodies should testify an old karst stage, partially connected to the seepage of meteoric waters, in a Creta-ceous carbonate platform environment; in the second hy-pothesis the caves developed due to the uplifing of high temperature and pressure fuids, formed by the strong volcanic activity which took place in the Upper Miocene (about 10-15 Myr BP). Tis type of caves are practically never directly ac-cessible and, even when intersected by mine galleries, they are hardly recognizable if completely deprived of the hosted ore bodies. Teir dimensions normally are of a few metres, but sometimes they are larger than ten metres. Tey exhibit an irregular shape without structural control; ofen they are rounded cavities elongated perpendicularly with re-spect to bedding. Good examples of such caves are visible inside the still accessible galleries of the Reforma Mine. Tese cavities are relatively rare worldwide and extremely important from the minerogenetic point of view: for ex-ample in Italy the mine caves of the Iglesiente (Sardinia) are the most known (De Waele et al. 1999, 2001). Peculiar low-enthalpy reaction normally takes place inside such cavities, thus allowing the evolution of inte-resting and ofen rare speleothems and cave minerals. In the area of Cuatro Ciénegas the mine caves are surely widespread even if they are actually very scarcely known. Tis study took into consideration only a few cavities intersected by the main galleries inside the Refor- CUEVA DE L It is a large cavity over 70 metres high and 100 long, developed along the big fault which controlled the depo-sition of the Pb/Zn sulphide ore bodies. Eight samples were taken from the wall of this cave where the primary minerals have been transformed to give rise to alteration compounds (fig. 4). Te 6 detected minerals were: Calcite: vitreous transparent euhedral rombohedral crystals up to 1 cm in size developed over iron hydrox-ides or as milky white to pale pink crusts; Fig. 3: Te 30 metres high pit giving access to the Cueva de los Cristales inside the Reforma mine. ma Mine: among them only the Cueva de los Cristales (fig. 3) has a dimension of some tens of metres. CRISTALES Chlorite: it is an Mg, f fllosilicate; it consists of grains of diferent size with the same characteristics of the antigorite to which is always strictly associated; goethite: it is present as earthy from yellow to pale brown grains of diferent size; gypsum: it is present as thin dark grey layers cover-ing the walls of small holes within the calcite crystals; hematite: it gave rise to a) small earthy reddish speleothems over sub-spherical hemi-transparent calcite grains or b) hard grains the powder of which has the typi-cal bloody red colour. ACTA CARSOLOGICA 35/1 – 2006 83 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI Fig. 4: Cueva de los Cristales: transparent calcite crystals with hematite (A), illite (B) and goethite (C) within a broken speleothem. LEVEL 12 A few more samples were collected in small karst cavi-ties the “Level 12” gallery of the same mine, from 300 to 600 m from the entrance and at the end of this gallery. Tey consist of heterogeneous materials characterized by the presence of diferent mineral phases. Te 6 detected minerals were: Calcite: orange-yellow globular masses; goethite: it is present as earthy from yellow to pale brown grains of diferent size; gypsum: it is present as small lens-shaped aggre-gates of vitreous pale to dark grey crystals; hematite: it is strictly related to calcite and goethite; Illite: this K fllosilicate is the major constituent of a clay and it consists of very small pale green-grey spheres over a black lithoid substratum; Quartz: small euhedral transparent crystals. Te total number of the cave minerals found inside these mine caves (8) is by far lower than expected: in fact no lead or zinc compounds have been observed, while it is sure that such kind of minerals should be anyway present inside the karst cavities developed within the ore bodies. In fact in a previous paper (Vargas et al., 1993) ce-russite, anglesite, smithsonite, hemimorphite, hydrozi-ncite, hematite and limonite are reported as common supergene minerals of this mine. All of them have been well documented in the mine caves of Iglesiente (Hill & forti, 1997), which are characterized by ore bodies and structural-lithological conditions very similar to those of Cuatro Ciénegas. Terefore it is logical to suppose that these minerals developed also inside the natural cavities of this mine. But the principal ore body is actually completely fooded and therefore it is impossible to be reached; this fact is probably the main reason why these minerals have not been observed during the present study which has been focused only over the few mine caves existing in the upper part of the mine. THE ARAGONITE CAVE PEARLS One of the most important fndings from the scientifc the internal growing layers were completely lacking point of view is a nest of aragonite cave pearls in which (forti, 2004). 84 ACTA CARSOLOGICA 35/1 - 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA Along the tunnel at the foot of the 170 m pit of the Reforma mine, several cave pearls nests were found lined with ultra-white pearls ranging from 1-2 mm to 2 cm in diameter (fig. 5 lef). Tis tunnel was used by miners until just 50 years ago which would suggest that these speleothems only be-gan to grow once the mine was abandoned, thus dating these formations at just half a century. Te largest pearls have a diameter of about 14 mm and the average size of their nuclei is 3 mm, therefore the average growth of those spleothems has been approxi-mately 0.1 mm/year. Such a growth rate is considered ave-rage-average/fast for a carbonate speleothem in general and for a cave pearl in particular (Hill & forti 1997). Some of the pearls were found to have a caulifower-shaped morphology, as a consequence of the coalescence of several single smaller pearls. Tis allows to state that the water supply to the nest should have been variable with periods of fast dripping followed by slow dripping or even completely dry periods, during which the origi-nally insulated pearls cemented together. In fact cemen-tation of diferent pearls may occur only if any kind of vibrations (induced by dripping) is completely avoided (forti, 1983). Anyway, since composite pearls are quite rare, this would suggest that completely dry periods were far less frequent than the wet ones. A mineral analysis by x-rays powder difractions of the pearls has shown that the pearls consist of pure aragonite, the deposition of which is favoured when ions such as magnesium, lead and zinc, etc. are present in the feeding water (lead and zinc were originally extracted in the mine). Te cave pearls found in the Reforma Mine are ex-tremely interesting because they completely lack growing layers (fig 5, right), which would be of 0,1 mm/year if annual (Backer et al., 1993). However, the Cuatro Cié-negas climate (dry/hot) would eventually have caused the development of many layers/year. In fact in such a climatic conditions, the relative long periods in between two subsequent rains surely avoid permanent dripping of infltration water over the pearls nest, thus the development of the external layer would result stopped. If so, each rainfall or each series of close rainfalls would cause the development of one specifc layer (Piancastelli & forti, 1997). Terefore the absence of concentric structure in the pearls of the Reforma mine is the result of very peculiar climatic conditions: • Pearls must have a rather constant water supply during its growing. • Te chemical composition of the water supply must re-main unchanged (irrespective of seasonal changes). Tese seemingly simple conditions are in practice extremely difcult to be ftted in nature, which would ex-plain why speleothems with no internal layers have been observed for the frst time in the world here. Te Cuatro Ciénegas climate could hold the key to the evolution of these speleothems. Its aridity prevents most vegetal growth and soil covering, which in any case get quickly swept away by the regular strong winds. Terefore the infltration water undergoes little or even none of the usual soil processes. But this is not enough to explain the presence of the cave pearls in the Reforma Mine. Te low rainfalls, high evaporation-transpiration, poor permeability around the mine could never guarantee a low but constant wa-ter supply in the tunnels. Terefore the water dripping into the pearl nests only occasionally may partially result from the rare rainfalls. Te constant presence of water in the depths of the mine is due to the daily temperature extremes typical of the Cuatro Ciénegas semi-arid climate and to the many man-made, interlinking tunnels on many diferent lev-els within the mountain, which in turn has a very stable temperature. Tese conditions allow for condensation, which would account for the constant presence of a few but continuously dripping water deep within the mountain. Fig. 5: Te pearls nest of the Reforma mine (lef) and a polished section of a cave pearl lacking of growing layers (right). ACTA CARSOLOGICA 35/1 – 2006 85 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI Tis condensation also explains the lack of any cy-clicity in the depositional mechanism and, therefore, the absence of any (annual) growing layers. In fact the car-bon dioxide content in condensation water is maintained stable due to CO2 rather constant partial pressure within the mine over the year and the scarcity of meteoric wa-ter. Some of the most interesting cavities of the Cuatro Cienegas belong to this group; their genesis is linked to the uplifing of deep hot and chemically aggressive waters, which easily dissolve the rock during their slow movement toward the topographic surface. Tese waters were depleted of the heavy metals and of the other low solubility salts but represented the fnal stage of the pro-cesses, which gave rise to the mine caves. Te thermal caves, as well as the mine ones, are commonly called hypogenic, because they are generated by fuids coming from the depth (forti, 1996). Tey nor-mally lack of a natural entrance on the surface and when it is present, ofen it is the result of the demolition of the hosting outcrops by meteoric degradation. Te “pure” thermal caves are those whose develop-ment is exclusively controlled by the efect of thermal water uplifing, they are normally referred to as “mono-genic”: this kind of cavity is rare enough in the world and they have been described in details rather exclusively in the area of Budapest (Muller & Sarvary, 1977). A “monogenic” cave is characterized by the pre-sence of a reservoir of the thermal water (the equivalent of the magmatic chamber for a volcano), which consists of a huge “basal” chamber; several splitting and/or anas-tomized spherical cavities develop from the roof of such a chamber giving rise to a peculiar “branched tree” struc-ture. Te thermal caves of Cuatro Cienegas belong to this category; therefore their importance exceeds the local interest (fig. 6). Te Rancho Guadalupe cave, which is located just at the foot of the Sierra La fragua, represents the best example of monogenic thermal cave. It is a classical 3D maze cave with a net of con-duits interconnecting large chambers all characterized by typical thermal corrosion forms. Due to the pres-ence of some strange speleothems observed during the frst visit, nine samples have been taken for an accurate mineralogical study, during the frst exploration of this cave. Later, due to the peculiarity evidenced by the one sampled on top of an organic deposit rich in vegetal f-bres up to 1 cm long, bird droppings and other animals for these reasons the pearls found in the Reforma Mine has more far-reaching consequences. Tey have provided a method, based on the growth layers within a speleothem, for evaluating both qualitatively, as well as maybe quantitatively, the predominance of condensation over climatic-controlled water infltration. excreta 4 more samples have been selected by the same deposit. Te study of the sampled speleothems confrmed the extraordinary importance of the secondary chemical de-posits hosted in the Rancho Guadalupe cave (forti et al., 2004). Inside this cavity 18 diferent cave minerals have been observed (Tab. 1). Anyway the origin of only a few of them is directly related to the thermal processes which gave rise to the cave itself, others begun to grow afer the thermal fuids defnitively abandoned the cave and the meteoric waters entered the cave and fnally some others were originated by the mineralization of some organic remains which were accumulated inside by small animals (mainly rodents) which use the cave as a shelter (fig. 7). Fig. 7: Cueva Rancho guadalupe: a general view of a rodent shelter in a side passage close to the entrance of the cave where, beside whewellite, ardealite and sepiolite, a new still undefned mineralogical phase has been found. Te detected minerals are: Aragonite: this polymorph of calcite is not common and it forms small milky-white to pale hazel-brown sphe-roidal grains; Calcite: very common it is present as: a) radial aggre-gates of elongated (30x5 mm) vitreous, semitransparent, THE THERMAL CAVES AND THEIR MINEROGENETIC MECHANISMS 86 ACTA CARSOLOGICA 35/1 – 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA prismatic crystals which are ofen part of speleothems (fowstones); b) pale pink to brick-red hard material; or c) saccaroidal to powdery incoherent material; Carnotite: this very rare uranil vanadate is present as small aggregates of canary-yellow small tabular crystals (SEM images in fig. 8a,b); Chlorapatite: it forms hard dark hazel-brown mi-crocrystalline aggregates. Te presence of Cl was con-frmed by EDAx analyses; Dolomite: it is present as aggregates of opaque, milky grains associated with sepiolite within the thick cave rafs deposit covering the whole foor of the thermal basal chamber; Fluorite: it has been identifed in a single sample: it consists of earthy and/or saccaroidal milky white grains within a speleothem (fowstone) on the wall of a small side bell shaped cavity; Fig. 6: Sketch for the evolution of the Rancho guadalupe cave. A: due to the thickness and the low fracturation degree of the limestone, the uplifing of the thermal waters induces the development of a huge hydrothermal chamber in which they accumulates. B: Te convective motions develop the upward evolution of a dendritic series of cohalescent subspherical voids. C: when part of the cave becomes partially unsaturated, the difusion of CO2 in the cave atmosphere allows for the development of some epiphreatic speleothems (cave cloud in black in the sketch) and the sedimentation over the cave foor of cave rafs, developed at the water-atmosphere interface; at the same time the meteoric seeping water starts the normal karst process in the unsaturated zone. D: the progressive erosion of the surface connects the cave to the exterior; the cave is then abandoned by the thermal waters. All the thermal forms and/or deposits are therefore fossilised, and meteoric seeping waters develop gravitational speleolothems (stalactites, stalagmites, fowstones…). gypsum: it is present as: a) vitreous, milky crystals within a crust over a corrosion pocket of the wall; b) aggregates of small vitreous semitransparent dark-grey prismatic crystals; hydromagnesite: it gives rise very small spheroidal silky shining white aggregates of microcrystals. It is nor-mally associated with monohydrocalcite (SEM image in fig. 8c); monohydrocalcite: it normally consists of a earthy dust consisting of cream-white to pale hazel-brown mi-cro spheres; sometimes it gives rise thin crusts and aggregates of small and fragile silky-lustre bladed crystals over the vegetable fbres (SEM images in fig. 8d); Niter: it presents: a) ofen as small eforesces of aggregates of thin transparent silky tabular crystals, often with a radial structure to simulate “an open book”; ACTA CARSOLOGICA 35/1 - 2006 87 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI Tab. 1: Minerals identifed in the karst systems of Cuatro Ciénegas: G – Cueva Rancho Guadalupe; L – Leona; M – Cueva de San Vicente (or de los Murciélagos); P – Cueva de Las Pinturas; R – Cueva Rosillo; Re – Reforma Mine; T – Tanche Nuevo; V – Vibora karst mineral Chemical formula * System Figure no. References hAlIDES G fluorite Sylvite Caf2 KCl Cubic Cubic Anthony et al. (1997), vol. III, 205 G 9a Anthony et al. (1997), vol. III, 545 OXIDES R Asbolane 0.5[(Ni,Co)(OH)2][MnO · nH2O] Z Hexagonal Anthony et al. (1997), vol. III, 26 R, Re Goethite ?-feOOH Orthorhombic Anthony et al. (1997), vol. III, 223 Re Hematite fe2O3 Trigonal Anthony et al. (1997), vol. III, 239 R Lepidocrocite ?-feOOH Orthorhombic 9f Anthony et al. (1997), vol. III, 312 G Opal-CT SiO2 ? nH2O 8e Smith (1998) G, M, R, Re Quartz SiO2 Trigonal Anthony et al. (1995), vol. II, 672 CARBONAtES AND NItRAtES G, Re Aragonite Ca[CO3] Orthorhombic Anthony et al. (2003), vol. V, 31 G,L,R,Re,T,V Calcite Ca[CO3] Trigonal Anthony et al. (2003), vol. V, 101 G, Re Dolomite CaMg[CO 3]2 Trigonal Anthony et al. (2003), vol. V, 191 G Hydromagnesite Mg(OH)|CO)] · 4H2O 5[2 3 4 Monoclinic 8c Anthony et al. (2003), vol. V, 310 G Monohydrocalcite Ca[CO3] ? H2O Hexagonal 8d Anthony et al. (2003), vol. V, 465 G Niter K[NO3] Orthorhombic Anthony et al. (2003), vol. V, 497 SUlFAtES G, L, R, Re, T Gypsum Ca[SO] ? 2H2O 4 Monoclinic Anthony et al. (2003), vol. V, 271 PhOSPhAtES AND vANADAtES M, P, R Apatite group Ca5[(f,OH,Cl,O)|(PO4,CO3)3] Hexagonal 15d,e Pau & fleet (2002) R Ardealite CaH[SO| PO4 ]·4H2O 2 4 Monoclinic 12c Anthony et al. (2000), vol. IV, 23 L, R, T Brushite CaH[PO] ? 2H2O 4 Monoclinic 9c,d Anthony et al. (2000), vol. IV, 83 G Carnotite K[UO|VO,l, ? 3H2O 22 4 Z Monoclinic 8a,b Anthony et al. (2000), vol. IV, 96 G Chlorapatite CaCl|(PO) 5[ 43] Hexagonal Anthony et al. (2000), vol. IV, 111 R Crandallite CaAl[(OH)|POOH|PO] 36 3 4 Trigonal Anthony et al. (2000), vol. IV, 130 R Kingsmountite Ca4feAl4[(OH)2|(PO4)3]2. 12H2O Monoclinic 15a,b Anthony et al. (2000), vol. IV, 282 R Montgomeryite Ca4MgAl4[(OH)2|(PO4)3]2. 12H2O Monoclinic Anthony et al. (2000), vol. IV, 387 R Taranakite K3Al5[(PO3OH6)3|(PO4)2] ? 18H2O Trigonal 15c Anthony et al. (2000), vol. IV, 581 M, R Variscite Al[PO4]. 2H2O Orthorhombic Anthony et al. (2000), vol. IV, 621 M, P, R Whitlockite Ca9(Mg,fe)[PO3OH|(PO4)6] Trigonal 15d,e,f Anthony et al. (2000), vol. IV, 653 SIlICAtES Re Illite (K,H3O)Al2[(H2O,OH)2|(Si,Al)4 O10] Monoclinic Brigatti & Guggenheim (2002) G Sepiolite Mg8 [(OH)2|Si6O15] ? 12H2O Orthorhombic 8e,f Anthony et al. (1995), vol. II, 722 ORgANIC COmPOUNDS R Bitumen nC H x y R Guanine C5H3(NH2)N4O Monoclinic 9e Anthony et al. (2003), vol. V 265 G Whewellite CaC2O4.H2O Monoclinic 9b Anthony et al. (2003), vol. V 755 NEW mINERAl( ?) G Unknown Mg hydrated carbonate (?) *Classifcation and chemical formulae afer Strunz & Nickel, 2001. 88 ACTA CARSOLOGICA 35/1 – 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA b d Fig. 8: SEm images of minerals from Cueva Rancho guadalupe: a) inclusion of platy crystals of carnotite in tabular gypsum; b) magnifcation of a); c) aggregate of tabular crystal of hydromagnesite; d) fan like aggregate of platy crystals of monohydrocalcite; e) microspheres di opale-Ct with fbrous sepiolite; f) fbrous sepiolite. ACTA CARSOLOGICA 35/1 – 2006 89 c PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI b d Fig. 9: SEm images of cave minerals from Cueva Rancho guadalupe (a, b) and Cueva Rossillo (c, d, e, f): a) net of irregular fbres of sylvite; b) spheroidal aggregate of prismatic crystal of whewellite; c) aggregate of triangular plate crystals of brushite; d) close view of brushite crystals; e) aggregate of microspheres of guanine; f) star-like aggregates of lepidocrocite crystals. 90 ACTA CARSOLOGICA 35/1 – 2006 c PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA b) sometimes as transparent crusts over the organic material; Opal-Ct: detected as incoherent milky white sof material like sawdust (SEM images in fig. 8e); Quartz: identifed only by x-ray difraction analyses within a thin gypsum-calcite speleothem; Sepiolite: it gives rise to small hard milky white ag-gregates associated with dolomite within the cave rafs deposit covering the whole foor of the thermal basal chamber (SEM images in fig. 8e,f); Sylvite: observed as tufs of vitreous, transparent bended flaments inside small pockets in the cave walls (SEM images in fig. 9a); Whewellite: this calcium oxalate monohydrate is present as small spherical aggregates of euhedral greasy semitransparent prismatic crystals grown inside the cop-rolites (SEM images in fig. 9b). Anyway the uncommon richness and variety of the hosted cave minerals is not the principal reason of interest of this cave: in fact its importance from the mineralogical point of view depends on a mineral deposit, which has never been observed before in nature and which seems to be completely new for science. It is a highly crystalline magnesium compound, probably a hydrated carbonate, which is presently under examination to defne univo-cally its structure and chemical formula. It occurs as ex-tremely small (a few microns in diameter) milky white sof earthy spheroidal aggregates of tabular crystals inside organic materials (mainly vegetable fbres). THE KARST CAVES AND THEIR MINEROGENETIC MECHANISMS Te most widespread karst phenomena are surely those connected with the seepage of meteoric water. Te karst forms induced by the difuse and/or con-centrated seepage are quite absent: in fact, even if the nature of the rock is carbonate and the fracturation degree is high, deep karst phenomena are normally scarcely de-veloped and concentrated in very restricted areas. Most of the known cavities are sub-horizontal: they started as small interbedded conduits, which later have been widened by physical degradation starting from the en-trance. Ofen they host plenty of speleothems even of huge dimension. Sometimes the caves are fragment of old huge drain-age tubes. Many of the cavities in the Sierra San Vincente and in the Canon el Pedregoso are relict of old phreatic galleries developed in a period in which the rainfalls were by far higher than actually. Often the karst caves do not host speleothems and/or cave minerals of interest: usually only cal-cite speleothems (stalactites, stalagmites, flowstones, etc…) are present, often with evident corrosion fea-tures induced by condensation processes. Among the cave minerals the crust and crystal aggregates of gyp-sum are fairly common: most of them are related to the dissolution of the discontinuous layers of this mineral present within the carbonate sequence, but some are generated by the oxidation of the sulphides associated to the ore bodies. Normally the karst caves have scarce minerogenetic importance, but those, which have been and/or still are shelter for huge colonies of bats may exhibit a wide vari-ety of secondary cave deposits. In fact actually the most active minerogenetic processes are related to the presence of guano deposits. Several thousand of years ago millions of bats colonized some caves, mostly of meteoric origin, afer the active water fow stopped inside, thus allowing the development of widespread deposits of an incredible amount of guano (fig. 10). Fig. 10: Cueva Rossillo: one of the widespread large guano deposits. Te oxidation and mineralization processes of guano are strongly exothermic and release high quantity of H2O and CO2 thus inducing strong convective move-ments within the cave atmosphere, and producing a dis-crete amount of strong acids: mainly nitric (HNO3), sul-phuric (H2SO4) and phosphoric (H3PO4). Tese processes may have strong morphologic con-sequences (fig. 11), causing the development of peculiar condensation-corrosion forms like megascallops on the protruding walls and huge spherical domes in the cei- ACTA CARSOLOGICA 35/1 – 2006 91 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI lings or allowing for the evolution of corrosion furrows and/or holes in the cave foor. Te condensation water reacts with the carbonate rock, the other minerals eventually dispersed inside, the clay and sand deposits giving rise to many second-ary minerals, among which the phosphates are the most widespread and may develop even as huge speleothems (fig. 12). CUEVA ROSILLO It is a classical karst cave which has been deeply modi-fied by the presence of an extremely large bat colony over a long time interval. The cave consists of a single Fig. 11: Sketch of the morphological and mineralogical efect induced by guano deposits (Forti et al., 2004). huge gallery (average size 10 x 10 metres) some 1 km long. Its origin is related to important karst drainage below the groundwater level in a period in which the climate must be by far more humid than actually. The widespread presence of domes in the ceiling, mega-scallops in the walls and sponge-works on the floor is the direct consequence of the still occurring strong acid aggression due to the presence of huge fossil Fig. 12: Cueva Rossillo: a) a thick phosphate fowstone developed in the fnal part of the cave; b) layers diferent in colour and/or texture are evident in a polished cross section; c) microsphere of pale yellow ardealite in a small void of the speleothem; d) the diferent layers observed with a polarizing microscope with crossed nicols. and/or actual guano deposits. The main cave gallery present on the floor a 5-7 m deep canyon developed when the lowering of the groundwater lever allowed for an epiphreatic to unsaturated evolution. Later 92 ACTA CARSOLOGICA 35/1 – 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA the canyon was rather completely filled by sediments (mainly guano and its by-products): in the last century these sediments were intensely mined to produce fer-tilizers (fig. 13). Fig. 13: One of the many tunnels dug by guano miners in the foor of the main gallery of the Cueva Rossilo. Where the guano leaking seeped along the limestone beds then gave rise to huge speleothems with inside layer of diferent thickness and colours, which ofen presented small cavities flled sometimes by pale vitreous crystals or dusty hazel-brown to pale pink grey material. In one case, the seepage of organics leached by guano in the upper series of the cave developed small black stalactites, the colour of which was due to the presence of bitumen within the diferent growing layers of the speleothems (fig. 14). A total of 15 samples have been taken from sediments on the cave foor and from speleothems; the ob-served minerals are: Apatite group: this generic name was given to hy-droxylapatite, carbonate-hydroxylapatite, carbonate-fu-orapatite and fuorapatite because it was rather impos-sible to discriminate among these phosphates. Tey are the most frequent phases in both the sampled sediments and speleothems. Teir morphology resulted extremely variable: a) hard microcrystalline china-ware material, Fig. 14: Cueva Rossillo: polished section (lef) of the black stalactite and a thin section (right) of it showing thin bitumen flms adsorbed over calcite layers. sometime layered with colours ranging from ivory to ha-zel brown, from pale brown to dark brown due to the dispersed presence of carbon rich phases; b) plastic light greasy pale pink powder, which sometime gives rise to small spheres, which in turn may be insulated or aggre-gated to form thin crusts; c) tufs of radial aggregates of thin vitreous colourless to white acicular crystals; d) ir-regular grains of hard orange-red material (SEM images in fig. 15d,e); Ardealite: vary rare, it has been observed only in one sample where it was associated to gypsum within a small sphere of greasy pale lemon-yellow microcrystalline material (SEM image in fig. 12c); Bitumen: this organic compound is responsible for the pigmentation of the growing layers of a small dark brown calcite stalactite (5 x 2 cm) collected already bro-ken close to the cave entrance. Te concentration of this compound was high enough to allow a strong H2S smell while crushing the sample; Asbolane: this Ni and Mn hydroxide is rare for the cave environment and in 4C was identifed only in a couple of samples. It consists of small black earthy and spongy spheres within an earthy white material; Brushite: common mineral which has been observed in several forms: a) thin crusts of vitreous, semitrans-parent milky white to pale greenish tabular crystals; b) aggregates of transparent lance shaped crystals; c) tufs of thin elongated fairly bended crystals; d) aggregates of sof earthy grains, of small prismatic tabular crystals and of pale hazel-brown larger crystals; e) earthy milky white irregular grains; f) lens shaped aggregates of shin-ing crystals within the earthy milky white material (SEM images in fig. 9c,d); Calcite: it is by far the most common mineral and consequently it is present in very diferent forms: a) in sub-spherical aggregates of radial elongated (30 x 5 mm) semitransparent vitreous prismatic crystals, similar to those observed inside some speleothems in a side cor- ACTA CARSOLOGICA 35/1 – 2006 93 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI b c d Fig. 15: SEm images of cave minerals from Cueva Rossillo (a, b, c) and Cueva de los murcielagos (d, e, f): rose-like aggregates of tabular crystals of kingsmountite; b) tabular subparallel crystals of kingsmountite; c) prismatic ditrigonal crystals of taranakite; d) radial aggregates of fbrous crystals of apatite with rombohedral whitlockite; e) magnifcation of d) to put in evidence an overgrow of whitlockite; f) aggregate of euhedral rombohedral, sometime twinned, whitlockite crystals. 94 ACTA CARSOLOGICA 35/1 - 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA ridor; b) hard pale pink to brick-red microcrystalline material; c) as incoherent ochre-yellow sandy to dusty sediment; Crandallite: extremely rare; it has been observed only in a single sample as thin irregular vitreous crust partially covering a yellow grain; goethite: it is present as earthy lemon-yellow to ochre-yellow grains; guanine: this rare organic compound gave rise to small black partially hard grains (SEM image in fig. 9e); gypsum: rather common; it is present as: a) aggre-gates of fbrous silky-lustre micro crystals; b) vitreous lustre, transparent slightly grained, tabular prismatic crystal with a pseudo-square base; Kingsmountite: it is always associated with mont-gomeryite and whitlockite; it is present as: a) thin small pale pink crusts or spheroidal aggregates of silky lustre, silver shining scaled crystals, which cover the walls of some cavities within the milky white material; b) aggregates of radial (open book) extremely thin silky blades over the surface of a single milky white grain (SEM ima-ges in fig. 15a,b); lepidocrocite: this polymorph of goethite is fairly rare; it has been observed only in the alteration crust de-veloped over an iron art craf (a small vessel or a cup) probably lef by guano miners some tens of years ago and now found some 50 cm inside the fresh guano. Te alteration crust consists of a millimetric layer of empty ochre-yellow to ruby red micro-spheres; at large magnifcation prismatic structures seem to be present over their surface. In this crust lepidocrocite is strictly associated with goethite, apatite and gypsum (SEM image in fig. 9f); montgomeryite: it gave rise to small (O < 2.5 mm) pale yellow partially empty spheres, which consist of silky tabular radial crystals arranged in concentric layers; Quartz: it has been found as cave mineral a single time over a sub-spherical grain of variscite. It consists of a hard thin transparent crust; taranachite: spherical sof aggregates of saccaroidal vitreous milky white micro-crystals (SEM image in fig. 15c); variscite: very rare observed in a single sample where it is the nucleus of a rounded grain with the outer part made by quartz. It consists of lemon yellow micro-crystalline material; Whitlockite: semitransparent thin hard crusts with the outer surface smooth or consisting of semi-spheres of colourless or pale yellow to pale brown, vitreous, some-times silky shining crystals covering the walls of some small empty voids within a china-ware material (SEM images in fig. 15d,e,f). CUEVA DE LOS MURCIELAGOS (BATS CAVE) Tis cave has been drastically modifed by guano miners, who lef inside most of their art crafs like wood ladders and leaching structures: for this reason the cave is know also with the name of San Vincente mine. Anyway it is a classical karst cave, partially modifed by the hyperkarst reactions connected with guano digestion. Seven samples have been collected in this cave: three consist of fragments of small calcite stalactites, three of which consist of fragments of broken calcite stalactites (soda straw) and/or stalagmites; some pieces of fow-stones consisting of honey yellow calcite are also present. Most of these samples are covered by a thin whitish powder. Te other four samples are globular yellowish speleothems (up to 15 mm in diameter) the structure of which consists partially of pale yellow fbrous radial crys-tals and of a hard layered material with plenty of small cavities, sometimes covered by a thin semi-transparent calcite layer. Beside calcite, the other observed minerals are: Apatite: the phosphates hydroxylapatite, carbon-ate-hydroxylapatite, carbonate-fuorapatite and fuor-apatite are grouped under this generic name, due to the difculty to discriminate among them. Tey occur as: 1) small aggregates of fbrous pale-yellow material; b) vitreous semi-transparent layers over the fbrous material; c) crusts consisting of small milky white to cream yellow spheres; Kingsmountite: this Ca, fe, Al phosphate is eas-ily recognized even at naked eye; it consist of: a) bladed millimetric bladed crystals with easy cleavage b) small crusts made by perfectly rounded shining yellow grains dispersed inside in an earthy whitish material; Quartz: hard thin transparent crust in association with variscite; variscite: semitransparent thin hard crusts with smooth outer surface. A few other karst caves have been sampled during the study (Leona, Las Pinturas, Tanche Nuevo, and Vi-bora) but they resulted of scarce mineralogical interest hosting only very common cave minerals (calcite, gyp-sum, hydroxilapatite and whitlockite) and therefore they will not be described here. Anyway their hosted chemical deposits are summarized together with those of all the other caves in the Tab. 1. ACTA CARSOLOGICA 35/1 – 2006 95 PAOLO fORTI, ERMANNO GALLI, ANTONIO ROSSI fINAL REMARKS Te mineralogical study of the secondary chemical de-posits developed within the karst systems of Cuatro Ciénegas put in evidence the great variety of mineroge-netic processes which were and/or are still active in this area: this is the reason why the number of observed cave minerals (Tab. 1) is very high in comparison to that nor-mally present in a single karst area. Moreover, the study of some of the caves in the area, even if not exhaustive, confrmed their extraordi-nary mineralogical interest: in fact in two natural cavities (Cueva Rossillo and Cueva Rancho Guadalupe) over 15 diferent cave minerals have been found, number which puts them among the most interesting caves of the world as for variety and richness of hosted mineralogical spe-cies. Some of the 32 identifed minerals (ardealite, as-bolan, carnotite, crandallite, monohydrocalcite, mont-gomeryite, niter, sepiolite, sylvite, variscite, whitlockite) must be considered “rare” in the cave environment (Hill & forti, 1997), while one Al, fe, Ca hydrated phosphate (kingsmountite) has been cited for the fst time as cave mineral from Rossillo cave. Previously this mineral was described by Dunn et al. (1979) from the Mine foote, near Kings Mountain town, North Caroline (USA): the kingsmountite of Rossillo cave has the same morphology of the olotype, occur-ring as bladed tiny crystals, usually in radial hemispheri-cal aggregates up to 1 mm in diameter. Kingsmountite is isostructural and therefore with an x-ray powder pat-tern similar to that of montgomeryite, but it may only be discriminate on the basis of chemical analyses because kingsmountite lacks of signifcative amounts of Mg. While phosphate largely prevails in Rossillo cave due to the large amount of guano deposits, oxides and carbonates are the main cave minerals in the Rancho Guadalupe cave. In this cave it is worth of mention the presence of carnotite as small aggregates of bright, green-ish-yellow plate crystals < 50 µm in length, as inclusion in tabular gypsum (fig. 8 alb); this occurrence seems to be very similar to that of the Horsethief Cave, Wyoming (USA) (Mosh & Polyak, 1996). In the Rancho Guadalupe cave there are several different silicate minerals: quartz, sequences of aligned mi- cro-spheres (up to 15 µm in diameter) of opal-CT (fig. 8e), and sepiolite (fig. 8f), the origin of which should be related to diagenetic processes involving opal in an Mg-rich environment ( the simultaneous presence of dolomite supports this hypothesis). Among the organic compounds the guanine of Cueva Rossillo and wewellite of Cueva Rancho Guadalupe are worth of mention. Te frst of these compounds (fig. 9e) gave rise to micro-spheres up to 20 µm in size and it is extremely rare for the cavern environment and up to present it was reported only from a few caves where it de-rived directly from bat guano mineralization. Whewellite of Rancho Guadalupe forms sub spherical aggregates of prismatic crystals (fig. 9b): its origin is related to animal excreta (Martini et al, 1990). finally the magnesium carbonate from Cueva Rancho Guadalupe, still under study, is highly probably to become not only a new cave mineral but probably new for science. Beside this ongoing research, the mineralogical studies in the karst systems of Cuatro Ciénegas cannot be considered concluded, mostly those related to the mine caves. As already written in the relative paragraph, the cave minerals observed in these caves are far to represent if not the totality at least a signifcant portion of those which should have developed in this environment: future research shall be surely addressed toward this topic. Anyway the mine environment has already proved to be of noticeable interest and scientifc importance: in fact a completely new kind of cave pearls has been observed in the Reforma mine. It is thank to these cave pearls to be possible to re-alize a new method to defne the relative ratio between condensation and seeping waters feeding a speleothem. Due to the peculiarity and noticeable scientifc interest of the secondary cave minerals of the karst systems of Cuatro Ciénegas it should be important that the natural cavities of such an area would be protected in the near future, in order to preserve their very high scientifc pat-rimony, which actually is only partially known. ACKNOWLEDGMENTS Te authors thank “La Venta Exploring Team”: without years of explorations in the Cuatro Ciénegas area this re-its efort in preparing, organizing and carrying out the 3 search would not be possible. Moreover they are grateful 96 ACTA CARSOLOGICA 35/1 - 2006 PECULIAR MINEROGENETIC CAVE ENVIRONMENTS Of MExICO: THE CUATRO CIÉNEGAS AREA to Área de Protección de flora y fauna Cuatro Ciénegas, Instituto Coahuilense de Ecologia, Semarnap, Conabio and Pronatura Noreste A.C., for allowing feld research. finally, the authors are indebted with all the partici-pants to “Cuatro Ciénegas” Project for their help in the feld and logistic support and to Drs. 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