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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. ...

Did you know?

That cascading water is in reference to wells, ground water which trickles or pours down the casing or uncased borehole above the water level in the well through cracks or perforations [22].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms


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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 brine (Keyword) returned 57 results for the whole karstbase:
Showing 16 to 30 of 57
The role of evaporites in the genesis of base metal sulphide mineralisation in the Northern Platform of the Pan-African Damara Belt, Namibia: geochemical and fluid inclusion evidence from carbonate wa, 2000,
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Chetty D, Frimmel He,
The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association? stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging, trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established. Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits. Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation. Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high salinity (17-33 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370-405 degrees C) with early sulphide remobilisation in Tsumeb at 275 degrees C, whereas they are lower at Berg Aukas (up to 255 degrees C). Fluid inclusion leachate analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct

Geochemical study of calcite veins in the Silurian and Devonian of the Barrandian Basin (Czech Republic): evidence for widespread post-Variscan fluid flow in the central part of the Bohemian Massif, 2000,
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Suchy V. , Heijlen W. , Sykorova I. , Muchez Ph. , Dobes P. , Hladikova J. , Jackova I. , Safanda J. , Zeman A.

Carbonate fracture cements in limestones have been investigated by fluid inclusion and stable isotope analysis to provide insight into fluid evolution and deformation conditions of the Barrandian Basin (Silurian–Devonian) of the Czech Republic. The fractures strike generally north–south and appear to postdate major Variscan deformation. The most common fracture cement is calcite that is locally accompanied by quartz, natural bitumen, dolomite, Mn-oxides and fluorite. Three successive generations of fracture-filling calcite cements are distinguished based on their petrographical and geochemical characteristics. The oldest calcite cements (Stage 1) are moderate to dull brown cathodoluminescent, Fe-rich and exhibit intense cleavage, subgrain development and other features characteristic of tectonic deformation. Less tectonically deformed, variable luminescent Fe-poor calcite corresponds to a paragenetically younger Stage 2 cement. First melting temperatures, Te, of two-phase aqueous inclusions in Stages 1 and 2 calcites are often around 2208C, suggesting that precipitation of the cements occurred from H2O–NaCl fluids. The melting temperature, Tm, has values between 0 and 25.88C, corresponding to a low salinity between 0 and 8.9 eq. wt% NaCl. Homogenization temperatures, Th, from calcite cements are interpreted to indicate precipitation at about 708C or less. No distinction could be made between the calcite of Stages 1 and 2 based on their fluid inclusion characteristics. In some Stage 2 cements, inclusions of highly saline (up to 23 eq. wt% NaCl) brines appear to coexist with low-salinity inclusions. The low salinity fluid possibly contains Na-, K-, Mg- and Ca-chlorides. The high salinity fluid has a H2O–NaCl–CaCl2 composition. Blue-to-yellow-green fluorescing hydrocarbon inclusions composed of medium to higher API gravity oils are also identified in some Stages 1 and 2 calcite cements. Stage 1 and 2 calcites have d 18O values between 213.2‰ and 27.2‰ PDB. The lower range of the calculated d 18O values of the ambient fluids (23.5‰ to 1 2.7‰ SMOW) indicate precipitation of these cements from deeply circulating meteoric waters. The presence of petroleum hydrocarbon inclusions in some samples is interpreted to reflect partial mixing with deeper basinal fluids. The paragenetically youngest Stage 3 calcite cement has only been encountered in a fewveins.These calcites are characterised by an intensely zoned luminescence pattern, with bright yellow and non-luminescent zones. Inclusions of Mn-oxides and siliceous sinters are commonly associated with Stage 3 calcite, which is interpreted to have precipitated from shallower meteoric waters. Regional structural analysis revealed that the calcite veins of the Barrandian basin belong to a large-scale system of north–south-trending lineaments that run through the territory of the Czech Republic. The veins probably reflect episodes of fluid migration that occurred along these lineaments during late stages of the Variscan orogeny


Origin of iron-rich Mississippi Valley-type deposits, 2001,
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Marie James St, Kesler Stephen E. , Allen Cameron R. ,
The abundance of iron in Mississippi Valley-type lead-zinc deposits and districts varies greatly; some deposits contain large amounts and others are almost free of iron. Iron in Mississippi Valley-type deposits is largely paragenetically early pyrite or marcasite that was replaced by sphalerite and galena, often in the central part of the deposit or district. Sedimentary exhalative and Irish-type base metal deposits, which also form from basinal brines, have similar variations in iron content. Calculated metal contents of brines in equilibrium with galena, sphalerite, and pyrite show that iron is significantly more abundant than lead and zinc in high-temperature (>200 {degrees}C), relatively acid brines with low sulfur contents, whereas zinc dominates under most other conditions, including brines with high temperatures and high sulfur contents. These results suggest that iron-rich Mississippi Valley-type deposits form from brines expelled from the deepest, hottest parts of sedimentary basins

Environmental problems caused by gypsum karst and salt karst in Great Britain., 2001,
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Cooper A. H.
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 m; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground.

Environmental problems caused by gypsum karst and salt karst in Great Britain, 2002,
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Cooper Ah,
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 in; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground

Origin and Significance of Postore Dissolution Collapse Breccias Cemented with Calcite and Barite at the Meikle Gold Deposit, Northern Carlin Trend, Nevada, 2003,
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Emsbo P, Hofstra Ah,
The final event in a complicated hydrothermal history at the Meikle gold deposit was gold deficient but caused extensive postore dissolution of carbonate, collapse brecciation, and precipitation of calcite and barite crystals in the resulting cavities. Although previously interpreted to be part of the Carlin-type hydrothermal system, crosscutting relationships and U-Th-Pb geochronology constrain this hydrothermal event to late Pliocene time (ca. 2 Ma), nearly 36 Ma after ore formation. Mineralogic, fluid inclusion, and stable isotope data indicate that postore hydrothermal fluids were reduced, H2S-rich, unevolved meteoric waters ({delta}18O = -17{per thousand}) of low temperature (ca. 65{degrees}C). The{delta} 18O values of barite and calcite indicate that these minerals were in isotopic equilibrium, requiring that barite SO4 was derived from the oxidation of reduced sulfur; however, preexisting sulfides in breccia cavities were not oxidized. The{delta} 34S (15{per thousand}) values of barite are higher than those of local bulk sulfide and supergene alunite indicating that SO4 was not derived from supergene oxidation of local sulfide minerals. The 15 per mil {delta}34S value suggests that the H2S in the fluids may have been leached from sulfur-rich organic matter in the local carbonaceous sedimentary rocks. A reduced H2S-rich fluid is also supported by the bright cathodoluminescence of calcite which indicates that it is Mn rich and Fe poor. Calcite has a narrow range of {delta}13C values (0.3-1.8{per thousand}) that are indistinguishable from those of the host Bootstrap limestone, indicating that CO2 in the fluid was from dissolution of the local limestone. These data suggest that dissolution and brecciation of the Bootstrap limestone occurred where H2S-rich fluids encountered more oxidizing fluids and formed sulfuric acid (H2SO4). Intense fracturing in the mine area by previous structural and hydrothermal events probably provided conduits for the descent of oxidized surface water which mixed with the underlying H2S-rich waters to form the dissolving acid. The surface-derived fluid apparently contained sufficient oxygen to produce H2SO4 from H2S but not enough to alter pyrite to Fe oxide. Although H2S is an important gold-transporting ligand, the temperature was too low to transport a significant amount of gold. The presence of analogous calcite- and barite-lined cavities in other Carlin-type deposits suggests that the generation (and oxidation) of H2S-rich meteoric waters was a common phenomenon in north-central Nevada. Previous sulfur isotope studies have also shown that the Paleozoic sedimentary rocks were the principal source of H2S in Devonian sedimentary exhalative-type, Jurassic intrusion-related, Eocene Carlin-type, and Miocene low-sulfidation gold deposits in the region. The similar sulfur source in all of these systems suggests that basin brines, magmatic fluids, and meteoric waters all evolved to be H2S-rich ore fluids by circulation through Paleozoic sedimentary rocks. Thus, although not directly related to gold mineralization, the recent hydrologic history of the deposit provides important clues to earlier ore-forming processes that were responsible for gold mineralization

Carbonate-Hosted Zn-Pb Deposits in Upper Silesia, Poland: Origin and Evolution of Mineralizing Fluids and Constraints on Genetic Models, 2003,
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Heijlen Wouter, Muchez Philippe, Banks David A. , Schneider Jens, Kucha Henryk, Keppens Eddy,
Microthermometric and crush-leach analyses of fluid inclusions in ore and gangue minerals of the Upper Silesian Zn-Pb deposits, Poland, along with first results of Rb-Sr geochronology on sulfides, provide important constraints on the paleohydrogeologic and metallogenetic models for the origin of these ores. The analyzed samples comprise two generations of dolomite, two generations of sphalerite, galena, and late calcite. The two dolomite generations and the late calcite were also analyzed for their oxygen and carbon isotope compositions, allowing a characterization of the mineralizing fluids. The ore-forming fluids represent highly saline (20-23 wt % CaCl2 equiv) Na-Ca-Cl brines, episodically introduced into the Triassic host carbonates. They had an oxygen isotope composition of ~0 per mil V-SMOW. Their Na-Cl-Br content (molar Na/Br and Cl/Br ratios between 99 and 337 and between 248 and 560, respectively) suggests that they originated by evaporation of seawater, which most likely occurred in the Permian-Triassic. The relative concentrations of potassium (molar K/Cl between 0.0147 and 0.0746) and lithium (molar Li/Cl between 0.0004 and 0.0031) further indicate that the fluids significantly interacted with siliciclastic rocks. The ionic and calculated oxygen isotope compositions of the fluids indicate that they were more evolved than present-day brines in the Upper Silesian coal basin, and the present-day brines show more extensive mixing with low-salinity fluids. The first results of direct Rb-Sr dating of ore-stage sulfides yield an isochron model age of 135 {} 4 Ma for the mineralizing event. This is consistent with hydrothermal activity and ore formation in Upper Silesia occurring in response to Early Cretaceous crustal extension preceding the opening of the northern Atlantic Ocean. The data presented support a model in which bittern brines migrated down into the deep subsurface and evolved into mineralizing fluids owing to extensive water-rock interaction. They were episodically expelled along deeply penetrating faults during the Early Cretaceous to form Zn-Pb deposits in the overlying Mesozoic carbonate rocks

Geology and Geochemistry of the Reocin Zinc-Lead Deposit, Basque-Cantabrian Basin, Northern Spain, 2003,
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Velasco Francisco, Herrero Jose Miguel, Yusta Inaki, Alonso Jose Antonio, Seebold Ignacio, Leach David,
The Reocin Zn-Pb deposit, 30 km southwest of Santander, Spain, occurs within Lower Cretaceous dolomitized Urgonian limestones on the southern flank of the Santillana syncline. The Reocin deposit is one of the largest known strata-bound, carbonate-hosted, zinc-lead deposits in Europe. The total metal endowment of the deposit, including past production and remaining reserves, is 62 Mt of ore grading 8.7 percent Zn and 1.0 percent Pb. The epigenetic mineralization consists of sphalerite and galena, with lesser marcasite and trace pyrite with dolomite as gangue. Microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron (up to 14 mol % of FeCO3). Replacement of host dolomite, open-space filling of fractures, and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence. Detailed cross-section mapping indicates a stratigraphic and structural control on the deposit. A stratiform morphology is present in the western part of the orebody (Capa Sur), whereas mineralization in the eastern part is highly discordant but strata bound (Barrendera). Stratigraphic studies demonstrate that synsedimentary tectonic activity, related to the rifting of the North Atlantic (Bay of Biscay), was responsible for variation in sedimentation, presence of unconformities (including paleokarsts), local platform emergence and dolomitization along the N60 fault trend. In the Reocin area, two stages of dolomitization are recognized. The first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the Aptian and the complete Albian sequence. The second dolomitization event occurred after erosion and was controlled by karstic cavities. This later dolomitization was accompanied by ore deposition and, locally, filling of dolomite sands and clastic sediments in karstic cavities. The circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous, indicating a post-Albian age. Vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100{degrees}C. Carbon and oxygen isotopic data from samples of regional limestone, host-rock dolostone and ore-stage dolomite suggest an early hydrothermal alteration of limestone to dolostone. This initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal-rich fluids with local modified seawater. Both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines. The{delta} 34S values of sulfides are between -1.8 and .5 per mil, which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur. Galena lead isotope compositions are among the most radiogenic values reported for Zn-Pb occurrences in Europe, and they are distinct from values reported for galena from other Basque-Cantabrian deposits. This suggests that a significant part of the lead was scavenged from the local underlying Asturian sediments. The stratigraphic and structural setting, timing of epigenetic mineralization, mineralogy, and isotopic geochemistry of sulfide and gangue minerals of the Reocin deposit are consistent with the features of most of Mississippi Valley-type ore deposits

Concepts and models of dolomitization: a critical reappraisal, 2004,
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Machel Hans G. ,
Despite intensive research over more than 200 years, the origin of dolomite, the mineral and the rock, remains subject to considerable controversy. This is partly because some of the chemical and/or hydrological conditions of dolomite formation are poorly understood, and because petrographic and geochemical data commonly permit more than one genetic interpretation. This paper is a summary and critical appraisal of the state of the art in dolomite research, highlighting its major advances and controversies, especially over the last 20-25 years. The thermodynamic conditions of dolomite formation have been known quite well since the 1970s, and the latest experimental studies essentially confirm earlier results. The kinetics of dolomite formation are still relatively poorly understood, however. The role of sulphate as an inhibitor to dolomite formation has been overrated. Sulphate appears to be an inhibitor only in relatively low-sulphate aqueous solutions, and probably only indirectly. In sulphate-rich solutions it may actually promote dolomite formation. Mass-balance calculations show that large water/rock ratios are required for extensive dolomitization and the formation of massive dolostones. This constraint necessitates advection, which is why all models for the genesis of massive dolostones are essentially hydrological models. The exceptions are environments where carbonate muds or limestones can be dolomitized via diffusion of magnesium from seawater rather than by advection. Replacement of shallow-water limestones, the most common form of dolomitization, results in a series of distinctive textures that form in a sequential manner with progressive degrees of dolomitization, i.e. matrix-selective replacement, overdolomitization, formation of vugs and moulds, emplacement of up to 20 vol% calcium sulphate in the case of seawater dolomitization, formation of two dolomite populations, and -- in the case of advanced burial -- formation of saddle dolomite. In addition, dolomite dissolution, including karstification, is to be expected in cases of influx of formation waters that are dilute, acidic, or both. Many dolostones, especially at greater depths, have higher porosities than limestones, and this may be the result of several processes, i.e. mole-per-mole replacement, dissolution of unreplaced calcite as part of the dolomitization process, dissolution of dolomite due to acidification of the pore waters, fluid mixing (mischungskorrosion), and thermochemical sulphate reduction. There also are several processes that destroy porosity, most commonly dolomite and calcium sulphate cementation. These processes vary in importance from place to place. For this reason, generalizations about the porosity and permeability development of dolostones are difficult, and these parameters have to be investigated on a case-by-case basis. A wide range of geochemical methods may be used to characterize dolomites and dolostones, and to decipher their origin. The most widely used methods are the analysis and interpretation of stable isotopes (O, C), Sr isotopes, trace elements, and fluid inclusions. Under favourable circumstances some of these parameters can be used to determine the direction of fluid flow during dolomitization. The extent of recrystallization in dolomites and dolostones is much disputed, yet extremely important for geochemical interpretations. Dolomites that originally form very close to the surface and from evaporitic brines tend to recrystallize with time and during burial. Those dolomites that originally form at several hundred to a few thousand metres depth commonly show little or no evidence of recrystallization. Traditionally, dolomitization models in near-surface and shallow diagenetic settings are defined and/or based on water chemistry, but on hydrology in burial diagenetic settings. In this paper, however, the various dolomite models are placed into appropriate diagenetic settings. Penecontemporaneous dolomites form almost syndepositionally as a normal consequence of the geochemical conditions prevailing in the environment of deposition. There are many such settings, and most commonly they form only a few per cent of microcrystalline dolomite(s). Many, if not most, penecontemporaneous dolomites appear to have formed through the mediation of microbes. Virtually all volumetrically large, replacive dolostone bodies are post-depositional and formed during some degree of burial. The viability of the many models for dolomitization in such settings is variable. Massive dolomitization by freshwater-seawater mixing is a myth. Mixing zones tend to form caves without or, at best, with very small amounts of dolomite. The role of coastal mixing zones with respect to dolomitization may be that of a hydrological pump for seawater dolomitization. Reflux dolomitization, most commonly by mesohaline brines that originated from seawater evaporation, is capable of pervasively dolomitizing entire carbonate platforms. However, the extent of dolomitization varies strongly with the extent and duration of evaporation and flooding, and with the subsurface permeability distribution. Complete dolomitization of carbonate platforms appears possible only under favourable circumstances. Similarly, thermal convection in open half-cells (Kohout convection), most commonly by seawater or slightly modified seawater, can form massive dolostones under favourable circumstances, whereas thermal convection in closed cells cannot. Compaction flow cannot form massive dolostones, unless it is funnelled, which may be more common than generally recognized. Neither topography driven flow nor tectonically induced ( squeegee-type') flow is likely to form massive dolostones, except under unusual circumstances. Hydrothermal dolomitization may occur in a variety of subsurface diagenetic settings, but has been significantly overrated. It commonly forms massive dolostones that are localized around faults, but regional or basin-wide dolomitization is not hydrothermal. The regionally extensive dolostones of the Bahamas (Cenozoic), western Canada and Ireland (Palaeozoic), and Israel (Mesozoic) probably formed from seawater that was pumped' through these sequences by thermal convection, reflux, funnelled compaction, or a combination thereof. For such platform settings flushed with seawater, geochemical data and numerical modelling suggest that most dolomites form(ed) at temperatures around 50-80 {degrees}C commensurate with depths of 500 to a maximum of 2000 m. The resulting dolostones can be classified both as seawater dolomites and as burial dolomites. This ambiguity is a consequence of the historical evolution of dolomite research

Hydrothermal mixing, carbonate dissolution and sulfide precipitation in Mississippi Valley-type deposits, 2004,
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Corbella M, Ayora C, Cardellach E,
A large number of Mississippi Valley-Type (MVT) deposits are located within dissolution zones in carbonate host rocks. Some genetic models propose the existence of cavities generated by an earlier event such as a shallow karstification, that were subsequently filled with hydrothermal minerals. Alternative models propose carbonate dissolution caused by the simultaneous precipitation of sulfides. These models fail to explain either the deep geological setting of the cavities, or the observational features which suggest that the dissolution of carbonates and the precipitation of minerals filling the cavities are not strictly coeval. We present a genetic model inspired by the textural characteristics of MVT deposits that accounts for both the dissolution of carbonate and precipitation of sulfides and later carbonates in variable volumes. The model is based on the mixing of two hydrothermal fluids with a different chemistry. Depending on the proportion of the end members, the mixture dissolves and precipitates carbonates even though the two mixing solutions are both independently saturated in carbonates. We perform reactive transport simulations of mixing of a regional groundwater and brine ascending through a fracture, both saturated in calcite, but with different overall chemistries (Ca and carbonate concentrations, pH, etc). As a result of the intrinsic effects of chemical mixing, a carbonate dissolution zone, which is enhanced by acid brines, appears above the fracture, and another zone of calcite precipitation builds up between the cavity and the surrounding rock. Sulfide forms near the fracture and occupies a volume smaller than the cavity. A decline of the fluid flux in the fracture would cause the precipitation of calcite within the previously formed cavities. Therefore, dissolution of carbonate host rock, sulfide precipitation within the forming cavity, and later filling by carbonates may be part of the same overall process of mixing of fluids in the carbonate host rock

Geochemical simulation of the formation of brine and salt minerals based on Pitzer model in Caka Salt Lake, 2004,
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Liu X. Q. , Cai K. Q. , Yu S. S. ,
The geochemical simulation of the formation of brine and salt minerals based on Pitzer model was made in Caka Salt Lake. The evolution of the mixed surface-water and the mineral sequences were calculated and compared with the hydrochemical compositions of the brine and the salt minerals of the deposit in Caka Salt Lake. The results show that the formation temperature of the lake is between 0degreesC and 5degreesC, which is well identical with other studies. The mixing of salt-karst water with the surface waters, neglected by the former researchers, is very important to the formation of the lake, indicating that the initial waters resulting in the formation of the lake are multi-source. It is the first time to use Pitzer model in China for making geochemical simulation of the formation and evolution of inland salt lake and satisfactory results have been achieved

'Sour gas' hydrothermal jarosite: ancient to modem acid-sulfate mineralization in the southern Rio Grande Rift, 2005,
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Lueth V. W. , Rye R. O. , Peters L. ,
As many as 29 mining districts along the Rio Grande Rift in southern New Mexico contain Rio Grande Rift-type (RGR) deposits consisting of fluorite-barite sulfide-jarosite, and additional RGR deposits occur to the south in the Basin and Range province near Chihuahua, Mexico. Jarosite occurs in many of these deposits as a late-stage hydrothermal mineral coprecipitated with fluorite, or in veinlets that crosscut barite. In these deposits, many of which are limestone-hosted, jarosite is followed by natrojarosite and is nested within silicified or argillized wallrock and a sequence of fluorite-barite sulfide and late hematite-gypsum. These deposits range in age from similar to 10 to 0.4 Ma on the basis of Ar-40/Ar-39 dating of jarosite. There is a crude north-south distribution of ages, with older deposits concentrated toward the south. Recent deposits also occur in the south, but are confined to the central axis of the rift and are associated with modem geothermal systems. The duration of hydrothermal jarosite mineralization in one of the deposits was approximately 1.0 my. Most Delta(18)O(SO4)-OH values indicate that jarosite precipitated between 80 and 240 degrees C, which is consistent with the range of filling temperatures of fluid inclusions in late fluorite throughout the rift, and in jarosite (180 degrees C) from Pena Blanca, Chihuahua, Mexico. These temperatures, along with mineral occurrence, require that the jarosite have had a hydrothermal origin in a shallow steam-heated environment wherein the low pH necessary for the precipitation of jarosite was achieved by the oxidation of H2S derived from deeper hydrothermal fluids. The jarosite also has high trace-element contents (notably As and F), and the jarosite parental fluids have calculated isotopic signatures similar to those of modem geothermal waters along the southern rift; isotopic values range from those typical of meteoric water to those of deep brine that has been shown to form from the dissolution of Permian evaporite by deeply circulating meteoric water. Jarosite delta(34)S values range from -24 parts per thousand to 5 parts per thousand, overlapping the values for barite and gypsum at the high end of the range and for sulfides at the low end. Most delta(34)S values for barite are 10.6 parts per thousand to 13.1 parts per thousand and many delta(34)S values for gypsum range from 13.1 parts per thousand to 13.9 parts per thousand indicating that a component of aqueous sulfate was derived from Permian evaporites (delta(34)S = 12 2 parts per thousand). The requisite H2SO4 for jarosite formation was derived from oxidation of H2S which was likely largely sour gas derived from the thermochemical reduction of Permian sulfate. The low delta(34)S values for the precursor H2S probably resulted from exchange deeper in the basin with the more abundant Permian SO42-- at similar to 150 to 200 degrees C. Jarosite formed at shallow levels after the PH buffering capacity of the host rock (typically limestone) was neutralized by precipitation of earlier minerals. Some limestone-hosted deposits contain caves that may have been caused by the low pH of the deep basin fluids due to the addition of deep-seated HF and other magmatic gases during periods of renewed rifting. Caves in other deposits may be due to sulfuric acid speleogenesis as a result of H2S incursion into oxygenated groundwaters. The isotopic data in these 'sour gas' jarosite occurrences encode a recod of episodic tectonic or hydrologic processes that have operated in the rift over the last 10 my. (c) 2004 Elsevier B.V. All rights reserved

Magmatic and Hydrothermal Chronology of the Giant Rio Blanco Porphyry Copper Deposit, Central Chile: Implications of an Integrated U-Pb and 40Ar/39Ar Database, 2005,
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Deckart K, Clark Ah, Celso Aa, Ricardo Vr, Bertens An, Mortensen Jk, Fanning M,
The history of hypabyssal intrusion and hydrothermal activity in the northeastern and central parts of the be-hemothian (sensu Clark, 1993) Rio Blanco-Los Bronces porphyry copper-molybdenum deposit is clarified on the basis of integrated U-Pb and 40Ar/39Ar geochronology. Isotope dilution thermal ion mass spectrometry (ID-TIMS) U-Pb dates for zircon separates and ID-TIMS and sensitive high resolution ion microprobe (SHRIMP) dates for single zircon grains in pre-, syn- and late-mineralization volcanic and intrusive host rocks in the Rio Blanco, Don Luis, and Sur-Sur mining sectors provide a temporal framework for interpretation of incremental-heating and spot-fusion 40Ar/39Ar dates for, respectively, magmatic biotite and hydrothermal biotite, muscovite, and orthoclase. The ore deposit is hosted in part by 16.77 {} 0.25 to 17.20 {} 0.05 (2{sigma}) Ma andesitic volcanic strata of the Farellones Formation, but the major host rocks are units of the San Francisco batholith, including the 11.96 {} 0.40 Ma Rio Blanco granodiorite (mine terminology), the 8.40 {} 0.23 Ma Cascada granodiorite, and the 8.16 {} 0.45 Ma diorite. Hypabyssal dacitic intrusions (late porphyries) emplaced into the batholith yield 206Pb/238U ID-TIMS dates ranging from 6.32 {} 0.09 Ma (quartz monzonite porphyry), through 5.84 {} 0.03 Ma (feldspar porphyry) to 5.23 {} 0.07 Ma (Don Luis porphyry). The late-mineralization Rio Blanco dacite plug yields a SHRIMP zircon age of 4.92 {} 0.09 Ma. The 40Ar/39Ar plateau ages for phenocrystic biotites in quartz monzonite porphyry, feldspar porphyry, and Don Luis porphyry, as well as the preore diorite, range only from 5.12 {} 0.07 to 4.57 {} 0.06 Ma. All are significantly younger than the corresponding zircons and exhibit no correlation with intrusive sequence. The 40Ar/39Ar ages for hydrothermal biotite and orthoclase veins within the San Francisco batholith units fall in a narrow interval from 5.32 {} 0.27 to 4.59 {} 0.11 Ma. Hydrothermal sericites (muscovite), one associated with chalcopyrite, yielded spot-fusion ages of 4.40 {} 0.15 Ma (Rio Blanco granodiorite hosted) and 4.37 {} 0.06 Ma (Don Luis porphyry hosted). Comparison with the ID-TIMS and SHRIMP zircon ages indicates that most of the 40Ar/39Ar ages, even 95 percent plateaus, do not record initial magmatic cooling or hydrothermal alteration-mineralization events, evidence for quasipervasive reheating to at least 300{degrees}C by successive intrusions. Published Re-Os ages for two molybdenite samples range from 5.4 to 6.3 Ma and overlap extensively with the zircon U-Pb ages for the late porphyries. They imply that Cu-Mo mineralization overlapped temporally with the emplacement of, at least, quartz monzonite porphyry and feldspar porphyry units of the late porphyry suite and was, therefore, contemporaneous with the rise of dacitic melts to subvolcanic levels. Hydrothermal activity is inferred to have continued until 4.37 {} 0.06 Ma, following intrusion of the Don Luis porphyry and the early stages of emplacement of the Rio Blanco dacite plug complex. Hypogene Cu-Mo mineralization therefore probably persisted for 2 m.y. The geochronologic data do not resolve whether ore formation was continuous or episodic, but the observed crosscutting relationships between intensely altered and mineralized country rocks and less altered and mineralized late porphyry bodies support a model in which the ascent of metal-rich brines from an unexposed zone of the parental magma chamber was periodically stimulated by magma perturbation and hypabyssal intrusion

Hypogene and supergene alteration of the Late Palaeozoic Ratburi Limestone during the Mesozoic and Cenozoic (Thailand, Surat Thani Province). Implications for the concentration of mineral commodities, 2005,
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Dill H. G. , Botz R. , Luppold F. W. , Henjeskunst F.
An interdisciplinary study of the Upper Carboniferous to Middle Permian Ratburi Group, Peninsular Thailand, is presented. The investigation involved sedimentary petrography, inorganic geochemistry, Sr, C, O isotope analyses, micropalaeontology as well as radio-carbon age dating. Emphasis was placed on the post-depositional evolution of the Ratburi Limestone in the Surat Thani Province. The Holocene chemical residues and the various calcite and dolomite minerals which have formed since the Late Palaeozoic in the Ratburi Limestone are the product of a complex, multistage alteration which is called supergene and hypogene karstifications, respectively. Sedimentation took place in a shelf environment with some reefs evolving during the late Murgabian at the shelf margin. There was no pre-concentration of elements, except for Ca and F during sedimentation. Diagenetic neomorphism and cementation under marine and freshwater conditions caused the Ratburi Limestone to convert into a marble-like rock. Fabric-selective dolomitization is of local scale and has impacted only on part of the Ratburi Limestone during the Lower to Upper Permian. A significant enhancement of pore space and better conduits were generated during the Late Cretaceous epithermal alteration. The most favorable conditions for the accumulation of metals were provided during the high-temperature stage of epithermal alteration when a low-metal concentration with As, Zn, Sb, U, Co and Pb existed. Unlike the other elements, Sb was subject to a multiphase concentration, giving rise to a considerable Sb deposit in the region. The most recent stage of karstification produced numerous caves, dripstones, tufa terraces and encrustations around brine pools in the study area. This alteration originated from per descensum and per ascensum processes which may be traced back to 15,000 years before present. The alteration of the Ratburi Limestone may be subdivided into two parts. The prograde post-depositional alteration, beginning with diagenesis, reached its temperature climax during epithermal subsurface alteration I. The retrograde branch of alteration lasted until the most recent times. The initial stages deposition and diagenesis took place under more or less closed-system conditions relative to the succeeding stages of the prograde alteration which saw the strongest influx of metal-bearing brine during the epithermal stage I. The retrograde branch of alteration is element-conservative.

The geochemistry of fluids from an active shallow submarine hydrothermal system: Milos island, Hellenic Volcanic Arc, 2005,
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Valsamijones E. , Baltatzis E. , Bailey E. H. , Boyce A. J. , Alexander J. L. , Magganas A. , Anderson L. , Waldron S. , Ragnarsdottir K. V. ,
Geothermal activity in the Aegean island of Milos (Greece), associated with island-arc volcanism, is abundant both on-and off-shore. Hydrothermal fluids venting from several sites, mainly shallow submarine (up to 10 m), but also just above seawater level in one locality, were sampled over four summer field seasons. Some of the discharging fluids are associated with the formation of hydrothermal edifices. Overall, the main characteristics of the hydrothermal fluids are low pH and variable chlorinity. The lowest recorded pH was 1.7, and chlorinity ranged from 0.1 to 2.5 times that of seawater. The highest fluid temperatures recorded on site were 115 degrees C. Two main types of fluids were identified: low-chlorinity fluids containing low concentrations of alkalis (potassium, lithium, sodium) and calcium, and high concentrations of silica and sulphate; and high-chlorinity fluids containing high concentrations of alkalis and calcium, and lower concentrations of silica and sulphate. The type locality of the high-chlorinity fluids is shallow submarine in Palaeochori, near the cast end of the south coast of the island, whereas the type locality of the low-chlorinity fluids is a cave to the west of Palaeochori. The two fluid types are therefore often referred to as 'submarine' and 'cave' fluids respectively. Both fluid types had low magnesium and high metal concentrations but were otherwise consistently different from each other. The low-chlorinity fluids had the highest cobalt, nickel, aluminium, iron and chromium (up to 1.6 mu M, 3.6 mu M, 1586 mu M, 936 mu M and 3.0 mu M, respectively) and the high-chlorinity fluids had the highest zinc, cadmium, manganese and lead (up to 4.1 mu M, 1.0 mu M, 230 mu M and 32 mu M, respectively). Geochemical modelling suggests that metals in the former are likely to have been transported as sulphate species or free ions and in the latter as chloride species or free ions. Isotopic values for both water types range between delta D -12 to 33 parts per thousand and delta(18)O 1.2 to 4.6 parts per thousand. The range of fluid compositions and isotopic contents indicates a complex history of evolution for the system. Both types of fluids appear to be derived from seawater and thus are likely to represent end members of a single fluid phase that underwent phase separation at depth. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved

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