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Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

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That fracture spring is see spring, fracture.?

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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for precambrian (Keyword) returned 43 results for the whole karstbase:
Showing 16 to 30 of 43
The Postmasburg Mn/Fe-ores occur exclusively in dolomitic Precambrian sinkhole structures with siliceous breccias and shales as hostrocks. The main manganese minerals are braunite and bixbyite, apart from secondary alteration products of the psilomelane-manganomelane family. Various generations of ore minerals could be identified. The ore mineralization is subdivided into three different genetic types. They are classified either as pure karst deposits or as combined formations of karst origin and shallow marine sedimentation due to the transgression of the Banded Iron Formation (BIF) sea. Post-sedimentary metamorphism is identified as very low grade. The development of the different ore types is illustrated schematically

Gypsum karst in the United States., 1996, Johnson Kenneth S.
Gypsum is one of the most soluble of common rocks; it is dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirements for gypsum karst to develop are: (1) a deposit of gypsum; (2) water, unsaturated with CaSO4 (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Gypsum deposits are present in 32 of the 48 conterminous United States, and they underlie about 35-40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quaternary. Gypsum karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by gypsum, and commonly extends down to depths of at least 30 m below the land surface. The most widespread and pronounced examples of gypsum karst are in the Permian basin of southwestern United States, but many other areas also are significant. Human activities may also cause, or accelerate, development of gypsum karst.

Phnomnes karstiques et pseudo-karstiques dans des quartzites au Burundi, 1997, Peyrot, Bernard
Central Africa, underground karstic caves are to be found in precambrian carbonated series, but also in quartzite as in the case of Burundi. The arenisation process which took place during very wet periods of intense biological activity may explain the origin of these caves and of karstic landforms such as pavements and pinnacles.

Evaporite karst in the United States, 1997, Johnson K. S. ,
Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirements for evaporite karst to develop are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO4 or NaCl; (3) an outlet for escape of dissolving water; and(4) energy to cause water to now through the system Evaporites are present in 32 of the 48 contiguous states, and they underlie about 35-40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quatemary. Evaporite karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites. The most widespread and pronounced examples of both gypsum and salt karst are in the Permian basin of the southwestern United States, but many other areas are also significant. Human activities have caused some evaporite-karst development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to now through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse

Fault and stratigraphic controls on volcanogenic massive sulphide deposits in the Strelley Belt, Pilbara Craton, Western Australia, 1998, Vearncombe S. , Vearncombe J. R. , Barley M. E. ,
Early Archaean, Fe-Zn-Cu volcanogenic massive sulphide deposits of the Strelley Belt, Pilbara Craton. occur at the top of a volcanic dominated sequence, at the interface of felsic volcanic rucks and siliceous laminites, beneath an unconformity overlain by elastic sedimentary rocks. The structure of the Sulphur Springs and Kangaroo Caves VMS deposits is relatively simple, with the present morphology reflecting original deposition rather than significant structural modification. The rocks have been tilted giving an oblique cross-sectional view of discordant high-angle, deep penetrating faults in the footwall, which splay close to the zones of voltcanogenic massive sulphide mineralization. Faults do not extend far into the overlying sedimentary cover, indicating their syn-volcanic and syn-mineralization timing. Both the Sulphur Springs and Kangaroo Caves sulphide deposits are located within elevated grabens in a setting similar to massive sulphide mineralization in modern back-are environments. Mineralization at Sulphur Springs and Kangaroo Caves is located at the edge of the grabens, at the site of intersecting syn-volcanic extensional faults.

Hydrogeology of Kartchner Caverns State Park, Arizona, 1999, Graf, C. G.
Three distinct hydrogeologic systems occur within Kartchner Caverns State Park, Arizona, each in fault contact with the other two. The southeastern corner and eastern edge of the park is part of the large graben that formed the San Pedro Valley during Miocene Basin and Range faulting. A thick alluvial sequence fills this graben and contains a regional aquifer covering 1000 km. One well in the park penetrates this aquifer. The groundwater level measured in this well was 226 m below land surface (1167 m msl), which is 233 m lower than the lowest measured point inside of Kartchner Caverns (1400 m msl). A pediment occupies a small part of the southwestern corner of the park. Structurally, this feature is part of the Whetstone Mountains horst rising above the park to the west. The pediment consists of a bedrock surface of Precambrian Pinal Schist overlain by a few tens of meters of granite wash sediments. Groundwater occurs at depths of 4-18 m below land surface in wells tapping the granite wash sediments. Data from these wells indicate that the zones of saturation within the granite wash sediments are probably of limited lateral extent and yield little water to wells. At the boundary between the pediment and the carbonate ridge containing Kartchner Caverns, the water table in the granite wash aquifer is 20 m higher than the bottom of the nearest known cave passage, located about 200 m to the east.The arid carbonate hills occupying the northwestern part of the park are the erosional remnants of a fault block (the Kartchner Block) that was displaced downward with respect to the Whetstone Mountains horst to the west. Kartchner Caverns is wholly contained in a ridge of highly faulted Mississippian Escabrosa Limestone and cuts conspicuously across Escabrosa beds dipping 10-40 to the southwest and west. Meteoric water enters the Kartchner Block and Kartchner Caverns from infiltration of runoff in washes that border the block and from overhead infiltration of precipitation. A small amount of groundwater also may flow into the Kartchner Block from the schist pediment to the south. Response in the cave to these fluxes is slow. As calculated from past records, the probability of flooding in the cave in any one year is about 57%.

Paleokarsts in late Precambrian and Ordovician carbonates, Kalpin-Shaya uplift zone, Tarim basin, China, 1999, Cao Hs, Yang Jd, Wang Dn,
The reservoir properties in the Kalpin-Shaya uplift zone, Tarim basin, are a common concern with regards to petroleum exploration and reservoir evaluation alike. Dissolution and paleokarst have a positive impact on the porosity as well as the storage capacity of carbonate reservoirs because the secondary porosity related to dissolution and paleokarst serves as excellent traps for migrating hydrocarbons. In order to evaluate the reservoir characteristics reasonably in the late Precambrian and Ordovician carbonate rocks, the secondary porosity, which was produced by dissolution and paleokarstification in late diagenetic stage. should be studied because the primary pores were mostly destroyed during the early-middle diagenesis due to serious compaction and multi-cementation. Carbonate rocks ate among the most important collectors of oil and gas accumulations in the world Important oil and gas reservoirs in paleokarst-containing carbonate rocks are known worldwide because micropores and megapores, such as solution openings, solution fissures, funnels, sinkholes. and caves, serve as the fundamentally important secondary porosity in those rocks. Several wells revealed that the Kalpin-Shaya region is a prospective target for oil and gas exploration. The reservoir carbonates of the Kalpin-Shaya uplift zone in the northern Tarim include dolomites and limestones. The best dolomite reservoirs are in the late Precambrian Qigebulake Formation (Z(2)(2)), the lower Qiulitage Group (is an element of(2-3)), the upper Qiulitage Group (O-1(1)), smd the Xiaoerbulake Formation (is an element of(1)), whereas limestone reservoirs are in the middle-upper formations of the upper Qiulitage Group (O-1(2-3)). On the basis of the study of petrology, paleontology, and stratigraphy from field work and well core data, the pore spaces within the Precambrian and Ordovician carbonate reservoirs are studied with the aim of proving that all secondary pores are controlled by dissolution and paleokarst

Karst-like landforms and hydrology in quartzites of the Venezuelan Guyana shield: Pseudokarst or 'real' karst?, 1999, Doerr Sh,
The surfaces of table mountains (Tepuis) in southeastern Venezuela display well-developed karst topography including caves, sinkholes and karren-features. Although the rock (orthoquartzite of the Precambrian Roraima Formation) has a very low solubility, active cave systems are present with passages more than one kilometre in length, descending to more than 300 metres depth. These dimensions are greater than any so far reported in quartzitic rocks. There is strong evidence that corrosive rather than erosive processes are responsible for the karstification. Thin-sections of rock samples show dissolution not only of the amorphous silica cement, but also of the crystalline quartz grains themselves. Together with field observations in and near an active cave system on the Kukenan Tepui, this indicates a close similarity between the processes active on the Venezuelan table mountains and karstification processes in rocks of greater solubility. A combination of factors including high precipitation (4000-7000 mm/year), rock of very high purity (98 % silica) and the absence of other significant geomorphological processes prevailing for at least several million years are thought to have enabled a spectacular karst landscape to evolve in a rock that in the past has been regarded as almost immune to chemical weathering

La grotte et le karst de Cango (Afrique du Sud), 2000, Martini, J. E. J.
The author describes a small karst area in the extreme south of the African Continent, with special reference to the Cango Cave, which is a major tourist attraction. Compared with the other karsts of Southern Africa, this area is unique. The karst is typically exogenic, with caves forming by stream disappearance into swallow holes, where the thalweg intersects steeply dipping Precambrian limestone. Wet caves are vadose, with only short phreatic segments and exhibit rectilinear, longitudinal sections. Passages are low, but wide with bevelled ceilings, often terraced. This peculiar morphology is typical of the caves developing exactly on the water-table and seems to be controlled by the abundance of sediments introduced from the swallow holes. If one excepts a short active lower level, Cango is a dry cave of the same type than the wet ones. It is practically linear in plan and in profile, with a length of 2.6 km from entrance to end for a total of 5.2 km of passages. The age of the speleogenesis has been estimated as early Pleistocene from the entrance elevation, which is in between the altitude of the actual thalweg and the one of the Post African I erosion surface, which started to be eroded during the Upper Pliocene. This relatively young age is in contrast with a Miocene model, which was accepted by most of the previous authors. Cango is well adorned with speleothems, in particular with outstanding abundant shields, monocrystalline stalagmites and pools coated with calcite crystals. In the first chambers from entrance, the speleothems have been deeply corroded by bat guano, with deposition of hydroxylapatite. Previously this corrosion was attributed to resolution due to several rises of the paleowater-table. The meteorology is discussed, in particular the high carbon dioxide, which indicates that the cave is poorly ventilated and which constitutes a problem for management and conservation.

Carbonate platform systems: components and interactions -- an introduction, 2000, Insalaco Enzo, Skelton Peter, Palmer Tim J. ,
Carbonate platforms are open systems with natural boundaries in space and time. Across their spatial boundaries there are fluxes of energy (e.g. light, chemical energy in compounds, and kinetic energy in currents and mass flows) and matter (e.g. nutrients, dissolved gases such as CO2, and sediment -- especially, of course, carbonates). Internally, these fluxes are regulated by myriads of interactions and feedbacks (Masse 1995), and the residue is consigned to the geological record. The most distinctive aspect of carbonate platforms is the predominant role of organisms in producing, processing and/or trapping carbonate sediment, even in Precambrian examples. Because of evolutionary changes in this strong biotic input, it is harder to generalize about carbonate platforms than about most other sedimentary systems. Evolution has altered both the constructive and destructive effects of platform-dwelling organisms on carbonate fabrics, with profound consequences for facies development. Moreover, changing patterns in the provision of accommodation space (e.g. between greenhouse and icehouse climatic regimes) have also left their stamp on facies geometries, in turn feeding back to the evolution of the platform biotas. Hence simplistic analogies between modern and ancient platforms may give rise to misleading interpretations of what the latter were like and how they formed. Although a number of carbonate platform and reef specialists have warned of the dangers of such misplaced uniformitarianism (e.g. Braithwaite 1973; Gili et al. 1995; Wood 1999), it remains depressingly commonplace in the literature on ancient carbonate platforms. The endless quest in the literature for an allpurpose definition of reefs' ... This 250-word extract was created in the absence of an abstract

Quartzite caves in southern Africa, 2000, Martini J. E. J.
A number of karst systems occur in lower Precambrian and in Ordovician quartzite in Southern Africa. They are developed only in high rainfall areas. At the surface pinnacle fields and lapiaz are common, but the drainage remains surficial, except in very localized areas where dolines, swallow-holes, stream caves and resurgences occur. The underground channels seldom extend more than a kilometers upstream from the resurgences, and generally much less. Caves over 2 km in total passage length have been mapped. The speleogenesis is by initial weathering of the quartzite, which is transformed into crumbly material and then removed by piping, thus forming caves. Other types of caves have developed by the erosion of deeply weathered diabase sills intrusive into quartzite. Some caves were initiated by gravity rifting in quartzite and then enlarged by stream action.

Stable isotope variations in the Neoproterozoic Beck Spring Dolomite and Mesoproterozoic Mescal Limestone paleokarst: Implications for life on land in the Precambrian, 2001, Kenny Ray, Knauth L. Paul,
Proterozoic karst events lowered {delta}13C values by as much as 11{per thousand} for the 800 Ma Beck Spring Dolomite, California, and as much as 8.5{per thousand} for the 1.1 Ga Mescal Limestone, central Arizona, relative to the originally deposited carbonate. The 13C changes are attributed to input of 13C-depleted organic CO2 derived from photosynthetic organisms that colonized the ancient land surface. The large isotopic shift and its presence at two separate localities suggest that Proterozoic karst surfaces were colonized by significant photosynthetic communities with phytomasses possibly approaching those of today

Existence of karsts into silicated non-carbonated crystalline rocks in Sahelian and Equatorial Africa, hydrogeological implications, 2002, Willems Luc, Pouclet Andre, Vicat Jean Paul,
Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized caves resulted from generalized dissolution of silicate formations in spite of their low solubility. Karstification is produced by deep hydrous transfer along lithological discontinuities and fracture net works. The existence of such caves has major implications in geomorphology, under either Sahelian and Equatorial climate, and in hydrogeology and water supply, particularly in the Sahel area. Introduction. - Since a few decades, several karst-like morphologies are described in non-carbonated rocks (sandstones, quartzites, schistes, gneisses...) [Wray, 1997 ; Vicat and Willems, 1998 ; Willems, 2000]. The cave of Guessedoundou in West Niger seems to be due to a large dissolution of metagabbros. The cave of Mfoula, South Cameroon, attests for the same process in gneisses. This forms proof that big holes may exist deeper in the substratum even of non-carbonated silicate rocks. Their size and number could mainly influence the landscape and the hydrogeology, especially in the Sahelian areas. Guessedoundou, a cave into metagabbros in West Niger. - The site of Guessedoundou is located 70 km south-west of Niamey (fig. 1). The cave is opened at the top of a small hill, inside in NNE-SSW elongated pit (fig. 2 ; pl. I A). The hole, 3 to 4 m deep and 20 m large, has vertical walls and contains numerous sub-metric angular blocks. A cave, a few meters deep, comes out the south wall. Bedrocks consist of metagabbros of the Makalondi greenstone belt, a belt of the Palaeoproterozoic Birimian Formations of the West Africa craton [Pouclet et al., 1990]. The rock has a common granular texture with plagioclases, partly converted in albite and clinozoisite, and pyroxenes pseudomorphosed in actinote and chlorite. It is rather fairly altered. Chemical composition is mafic and poorly alkaline (tabl. I). A weak E-W schistosity generated with the epizonal thermometamorphism. The site depression was created along a N010o shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation. The absence of human activity traces and the disposition of the angular blocks attest that the pit is natural and was due to the collapse of the roof of a vast cavity whose current cave is only the residual prolongation. To the vertical walls of the depression and at the cave entry, pluridecimetric hemispheric hollows are observed (pl. I B). Smooth morphology and position of these hollows sheltered within the depression dismiss the assumptions of formation by mechanical erosion. In return, these features are typical shape of dissolution processes observed into limestone karstic caves. That kind of process must be invoked to explain the opening of the Guessedoundou cave, in the total lack of desagregation materials. Dissolution of metagabbro occurred during hydrous transfer, which was probably guided by numerous fractures of the shear zone. Additional observations have been done in the Sirba Valley, where similar metabasite rocks constitute the substratum, with sudden sinking of doline-like depressions and evidence of deep cavities by core logging [Willems et al., 1993, 1996]. It is concluded that karstic phenomena may exist even in silica-aluminous rocks of crystalline terrains, such as the greenstones of a Precambrian craton. Mfoula a cave into gneisses in South Cameroon. - The cave of Mfoula is located 80 km north-east of Yaounde (fig. 3). It is the second largest cave of Cameroon, more than 5,000 m3, with a large opening in the lower flank of a deep valley (pl. I C). The cavity is about 60 m long, 30 m large and 5 to 12 m high (fig. 4; pl. I D). It is hollowed in orthogneisses belonging to the Pan-African Yaounde nappe. Rocks exhibit subhorizontal foliation in two superposed lithological facies: the lower part is made of amphibole- and garnet-bearing layered gneisses, and the upper part, of more massive granulitic gneisses. Average composition is silico-aluminous and moderately alkaline (tabl. I). The cave is made of different chambers separated by sub-cylindrical pillars. The ceiling of the main chamber, 6 m in diameter, is dome-shaped with a smooth surface (D, fig. 4). The walls have also a smooth aspect decorated with many hemispherical hollows. The floor is flat according to the rock foliation. They are very few rock debris and detrital fragments and no traces of mechanical erosion and transport. The general inner morphology is amazingly similar to that of a limestone cave. The only way to generate such a cavity is to dissolve the rock by water transfer. To test the effect of the dissolution process, we analysed a clayey residual sampled in an horizontal fracture of the floor (tabl. I). Alteration begins by plagioclases in producing clay minerals and in disagregating the rock. However, there is no more clay and sand material. That means all the silicate minerals must have been eliminated. Dissolution of silicates is a known process in sandstone and quartzite caves. It may work as well in gneisses. To fasten the chemical action, we may consider an additional microbial chemolitotrophe activity. The activity of bacteria colonies is known in various rocks and depths, mainly in the aquifer [Sinclair and Ghiorse, 1989 ; Stevens and McKinley, 1995]. The formation of the Mfoula cave is summarized as follow (fig. 5). Meteoric water is drained down along sub-vertical fractures and then along horizontal discontinuities of the foliation, particularly in case of lithological variations. Chemical and biological dissolution is working. Lateral transfers linked to the aquifer oscillations caused widening of the caves. Dissolved products are transported by the vertical drains. Regressive erosion of the valley, linked to the epeirogenic upwelling due to the volcano-tectonic activity of the Cameroon Line, makes the cavities come into sight at the valley flanks. Discussion and conclusion. - The two examples of the Guessedoundou and Mfoula caves evidence the reality of the karsts in non-carbonated silicated rocks. The karst term is used to design >> any features of the classical karst morphology (caves, dolines, lapies...) where dissolution plays the main genetical action >> [Willems, 2000]. Our observations indicate that (i) the karst genesis may have occurred into any kind of rocks, and (ii) the cave formation is not directly dependent of the present climate. These facts have major consequences to hydrogeological investigations, especially for water supply in Sahelian and sub-desertic countries. Some measurements of water transfer speed across either sedimentary pelitic strata of the Continental terminal or igneous rocks of the substratum in West Niger [Esteves and Lenoir, 1996 ; Ousmane et al., 1984] proved that supplying of aquifers in these silico-aluminous rocks may be as fast as in a karstic limestone. That means the West Niger substratum is highly invaded by a karstic net and may hidden a lot of discontinuous aquifers. The existence of this karst system can be easily shown by morphological observations, the same that are done in karstic limestone regions (abnormally suspended dry valleys, collapses, dolines...). Clearly, this must be the guide for any search of water, even in desertic areas where limestones are absent

Evaporite karst and resultant geohazards in China, 2002, Lu Y. R. , Zhang F. E. , Qi J. X. , Xu J. M. , Guo X. H. ,
The main kinds of evaporite karst, both sulphate karst and halide karst, are widely distributed in China. Gypsum karst is especially widespread, because China contains the largest gypsum resources in the world. These gypsum deposits range in age from Precambrian to Quaternary, and they were deposited in many environments, including marine, lacustrine, thermal process, metamorphic, and also as secondary deposits. Halide karst is developed in rock salt and salt-water lakes, the latter related to more than 300 salt-water lakes distributed in the Qinghai Plateau of Xizang (Tibet) province. Gypsum and halite are easily dissolved; therefore, development of evaporite karst is somewhat different when compared with carbonate karst, which has developed many typical features in China. This paper discusses the mechanism and development of evaporite karst in sulphate rocks and in halides, and makes comparisons between evaporite karst and carbonate karst based upon field investigations and new tests in the laboratory. The geohazards of evaporite karst usually are triggered by natural karst processes, but often they are exaggerated by artificial (human) actions and engineering impacts that cause flesh groundwater or surface water to come in contact with the evaporite rocks. Some examples of evaporite-karst geohazards are described in this paper; they are present in Shandong, Sichuan, and Guizhou Provinces, and in the Qinghai Plateau of China

Permo-Mesozoic multiple fluid flow and ore deposits in Sardinia: a comparison with post-Variscan mineralization of Western Europe, 2002, Boni M, Muchez P, Schneider J,
The post-Variscan hydrothermal activity and mineralization in Sardinia (Italy) is reviewed in the framework of the geological and metallogenic evolution of Western Europe. The deposits can be grouped into (a) skarn, (b) high- to low-temperature veins and (c) low-temperature palaeokarst. The structural, stratigraphical and geochemical data are discussed. The results suggest three hydrologically, spatially, and possibly temporally, distinct fluid systems. System 1 (precipitating skarn and high-temperature veins) is characterized by magmatic and/or (?) magmatically heated, meteoric fluids of low-salinity. The source of metals was in the Variscan magmatites, or in the Palaeozoic/Precambrian basement. System 2 (low-temperature veins and palaeokarst) is represented by highly saline, Ca-rich (formation or modified meteoric) fluids. Sources of the metals were the pre-Variscan ores and carbonate rocks. System 3 is characterized by low-temperature, low-salinity fluids of meteoric origin. The hydrothermal deposits related to Systems 1 and 2 can be framed in a crustal-scale hydrothermal palaeofield', characterizing most of the post-orogenic mineralization in Variscan regions of Western and Southern Europe, allowing for local age differences of each single ore district and background effects. The suggested timing for the hydrothermal events in Sardinia is: (1) Mid-Permian (270 Ma), (2) Triassic-Jurassic. It is suggested that the Mesozoic events were related to the onset of Tethys spreading

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