Low-temperature Hydrothermal Systems Research Articles

Unraveling the Genesis of the Geothermal System at the Northeastern Edge of the Pamir Plateau

High-temperature geothermal systems hold promise for sustainable and environmentally friendly power generation. However, China’s geothermal power capacity significantly underutilizes its abundant resources. This study focuses on the geothermal potential of the Pamir Plateau, particularly its northeastern edge, where complex tectonic forces converge. We aim to unveil the mechanisms driving the emergence of high-temperature geothermal reservoirs in this unique geological setting. Hydrogeochemical analysis reveals diverse profiles in geothermal water, primarily derived from atmospheric precipitation. Estimation of reservoir temperatures and simulation of geotherms unveil distinct geothermal systems. Kongur exhibits a medium–low-temperature hydrothermal system and Tashkurgan demonstrates high-temperature hydrothermal system characteristics, while the Pamir’s northeastern edge hints at a potential high-temperature dry geothermal system where there might not be a fault. These findings have important implications for sustainable energy development and future geothermal exploration.

The mechanism of high salinity geothermal water formed in karst low-temperature hydrothermal system

The mechanism of high salinity geothermal water formed in karst low-temperature hydrothermal system

Assessment of possibility of finding geothermal energy resources around Mount Meru in northern Tanzania using classical solute geothermometry

This study uses classical solute geothermometry analysis to estimate the temperature and circulation depth of the geothermal reservoir around Mount Meru. Five springs affected by magmatic gases from a deep magmatic heat source are investigated; these include two hydrothermal springs. Results from silica geothermometers show that estimated reservoir temperatures range from 70 to 110 °C; this corresponds to a low-temperature hydrothermal system. Since Mount Meru is an active volcano, one would expect a high-temperature hydrothermal system; the low temperatures are ascribed to the mixing of hydrothermal and cold recharge waters. The geothermal reservoir is estimated to be about 1.3–1.4 km deep. Thus, the study shows that a low-temperature geothermal energy resource can be found on the eastern flank of Mount Meru.

Mineral textures, mineral chemistry and S isotopes of sulphides from the Tianbaoshan Pb–Zn–Cu deposit in the Sichuan–Yunnan–Guizhou triangle: implications for mineralization process

AbstractThe carbonate-hosted Pb–Zn deposits in the Sichuan–Yunnan–Guizhou (SYG) triangle region are important Indosinian deposits in South China. The Tianbaoshan deposit is a typical large Pb–Zn deposit in the SYG area and occurs as pipe-like type, hosted by Sinian dolostone. It contains ∼26 Mt Zn–Pb ore (7.76–10.09 % Zn, 1.28–1.50 % Pb and 93.6 g t−1 Ag) and >0.1 Mt Cu ore (2.55 % Cu). In this study, the detailed mineral textures, mineral chemical and sulphur isotopic compositions of the various sulphides have been analysed to constrain the abnormal enrichment mechanism and mineralization relationship. Four mineralization stages have been recognized: Stage 1, minor early pyrite (Py1) with relics and infill of intergranular dolomite or quartz grains; Stage 2, Cu mineralization with coarse-grained, elliptical crystal chalcopyrite (Cp1); (3) Stage 3, Zn mineralization with dark fine-grained sphalerite (Sph1) and light coarse-grained sphalerite (Sph2); and (4) Stage 4, as represented by a quartz–calcite assemblage with galena, minor pyrite (Py2) and chalcopyrite (Cp2). The petrography of the sulphide minerals (Py1, Cp1, Sph1 and Sph2) demonstrates a mutual inclusion relationship. The nature of this relationship from core to rim and their similar sulphur isotope values (5.5–8.3 ‰) indicates a single sulphur source, suggesting that the different mineralization types are the result of different stages of a continuous hydrothermal system. Sphalerite geothermometer study suggests that sphalerite in the Tianbaoshan deposit formed in a low-temperature (<200 °C) hydrothermal system. The low concentrations of Mn and In, low In/Ge ratios and high Fe/Cd ratios in the sphalerite are consistent with those of Mississippi Valley-type (MVT) deposits, but different from those of magmatism-related deposits (e.g. epithermal, skarn and VMS deposits). The positive δ34S values for Py1 (5.1–7.9 ‰), Cp1 (5.1–7.2 ‰), Sph1 (4.7–7.4 ‰), Sph2 (3.9–8.7 ‰), Py2 (4.4–9.3 ‰) and Cp2 (5.0–6.8 ‰) indicate a sulphur source from thermochemical reduction of coeval seawater sulphate. Widely developed dissolved textures (caverns and breccias) with massive sulphide infillings and deformed host rock remnants suggest that replacement of host dolostones by ore fluids was volumetrically significant and the ore formed nearly simultaneously with the cavities. The Tianbaoshan deposit is a typical MVT deposit, which resulted from mixing of a H2S-rich fluid and a metal-rich fluid, with thermochemical sulphate reduction occurring before ore precipitation rather than during ore precipitation.

Tin mineralization in the giant Shuangjianzishan Ag-Pb-Zn deposit, Inner Mongolia

The newly discovered Shuangjianzishan giant Ag-Pb-Zn deposit which located in the Southern segment of the Great Xing’an Range (SGXR), has controlled more than 18 000 t reserves of Ag, 1.9 Mt reserves of Zn, and 3.3 Mt reserves of Pb. Previous research has shown that Shuangjianzishan is a typical epithermal Ag-Pb-Zn deposit, however, mid- to high-temperature Cu-Sn (-W) mineralization are few studies. In this paper, a detailed mineralogical study reveals that a remarkable Cu-Sn (-W) mineralization is observed both in the upper tunnel and the deeper drill core samples. In the shallow ore-bodies, tin dominantly occurs as canfieldite in Pb-Zn-rich ores, minor as cassiterite-quartz veinlets. In the deep drill cores, tin occurs as cassiterite in the Cu-rich ores with the assemblage of quartz-arsenopyrite-chalcopyrite-stannite-(wolframite). Four primary paragenetic stages have been recognized. Stage I: cassiterite-quartz-arsenopyrite-chalcopyrite, including two sub-stage: cassiterite-arsenopyrite-pyrrhotite-quartz (stage I1) and sphalerite-chalcopyrite-galena-pyrite (stage I2); Stage II: galena-sphalerite-silver minerals; Stage III: Quartz-silver minerals, and stage IV: pyrite-carbonate.Electron probe micro-analysis (EPMA) show that the early mineralization (stage I) is characterized by Fe-rich sphalerite, Co-rich pyrite, Se-rich canfieldite, and Se-Bi-rich galena, while the later mineralization (stage II-IV) contains Fe-depleted sphalerite, As-rich pyrite, and Sb-bearing silver minerals. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis show that cassiterite has high contents of W, Fe, Sb, and Ti and depleted in Nb and Ta. Mineral associations and compositions implies a cassiterite-sulfide type tin mineralization in the Shuangjianzishan Ag-Pb-Zn deposit.A concealed granite porphyry intrusion was exposed in deep drill cores in the northwest part of the ore-field, with zircon U-Pb ages of (137.8 ± 1.1) Ma and (136.8 ± 1.0) Ma for fine- and coarse-grains granite, respectively. Bulk analysis shows that concealed granites are characterized by a highly fractionated, relatively reduced, and high K-calc-alkaline to alkaline, which belongs to A-type granites, and the remnant of Sn-bearing titanite suggests that it has the potential to provide the source of tin. Zircon U-Pb age (138–130 Ma) is well coupled with the previous data (ore-forming age, 136–129 Ma) of Shuangjianzishan, suggesting a close temporal and genetic relationship between tin mineralization and emplacement of the granite. This contribution implies that the Shuangjianzishan deposit may exist a middle- to high-temperature Cu-Sn (-W) mineralization center rather than a simple low-temperature hydrothermal system, and shows there is significant Sn-Cu mineralization potential in the peripheral and root zone of ore district.

The Origin of Synchysite-(Ce) and Sources of Rare Earth Elements in the Rožná Uranium Deposit, Czech Republic

Synchysite was identified in the Rožná uranium deposit in a quartz–carbonate–sulfide vein, which is a part of the late (post-uranium and, post-Variscan) stage of the development of the hydrothermal system. The synchysite forms needles or lamellae, which are almost exclusively bound to the quartz filling of the veins. The structure of the quartz vein-filling, i.e., the preserved tubular syneresis crack pattern, Liesegang bands formed by hematite, chaotic grain size distribution of quartz grains, and ribbons of fibrous SiO2 grains, indicate that the synchysite crystallized in a silica gel. Its formation may be explained by the reaction of hydrothermal acid fluids rich in Fe2+ and rare earth elements (REEs) with alkaline Ca2+ HCO3− and F-rich fluids expelled from the gel during syneresis, or by its ageing. The subsequent recrystallization of the gel to form euhedral quartz grains was accompanied by the deformation of previously formed Liesegang rings, and the development of quartz rosettes. The study of fluid inclusions indicated that the silica gel originated at a very low temperature. The temperatures of the homogenization of two-phase inclusions in carbonate and quartz vein-filling varied between 38 and 74 °C, and the salinity ranged between 4 and 10 wt.% NaCl equiv. The δ13C carbonate values (from −4.65 to −5.21‰, PDB) indicate the deep-seated source of CO2, and δ18O values (from 14.76 to 18.22‰, SMOW) show that the source of the hydrothermal fluids was mainly surface water, with a possible admixture of fossil saline brines. The main sources of REEs are thought to have predominantly been uranium minerals (coffinitized uraninite and coffinite) that form a part of the breccia fragments embedded in the vein filling. The results illustrate the significant mobility of REEs in the late, low-temperature hydrothermal system, and they indicate the multiple remobilizations of REEs in the uranium deposits in general.

The effect of granite fracture network on silica-enriched groundwater formation and geothermometers in low-temperature hydrothermal system

Silica-enriched mineral groundwater has important commercial and health value and is most common in volcanic areas and high-temperature geothermal areas. But we found abundant silica-enriched mineral groundwater (dissolved SiO2 up to 51.57 mg/L) exposed from the granite fracture network in Suining, South China, where is no volcanoes and high-temperature hydrothermal system. Pumping test and hydrogeochemistry were employed to investigate the formation mechanism of silica-enriched mineral groundwater in granite fracture network. It is HCO3-Ca type and high content of dissolved silica, formed warm groundwater on the F86-1 fault and recharged by meteoric water with a close distance of 3.90 km. Pumping test results indicate that the hydraulic conductivity decreases from top to bottom in the granite fracture network (in order of 2.27 × 10−1 m/d, 5.42 × 10−2 m/d, 7.04 × 10−4 m/d), and they are much smaller than that of the F86-1 fault zone (0.751 m/d). The flow framework constructed by water chemistry suggest the groundwater has experienced the maximum temperature of 68–75 °C and reached the maximum depth of 1.93 km. And the average seepage velocity is about 2.8 × 10−3 m/d and 1.5 × 10−3 m/d in the horizontal and vertical directions, respectively. Water-rock interaction confirms that the granite fracture network provides long-term and sufficient water-rock interaction and dominantly contributes the formation of silica-enriched mineral groundwater because of the weatherability of granite. But the temperature of SiO2-geothermometer will be slightly underestimated for the deep warm groundwater continuously mixing with the shallow groundwater in the granite fracture network.

Microporphyritic and microspherulitic melt grains, Hiawatha crater, Northwest Greenland: Implications for post-impact cooling rates, hydration, and the cratering environment

Abstract Sand-sized impactite melt grains hand-picked from a glaciofluvial sample proximal to the Hiawatha impact crater in Northwest Greenland contain new information about the crystallization and cooling history of this impact structure, which is concealed by the Greenland Ice Sheet. Of course, the original locations of the individual sand grains are unknown, but this is offset by the substantial number and wide variety of impactite grains available for study. A detailed investigation of 16 melt grains shows that post-cratering crystallization took place under very variable conditions of strong undercooling with temperatures that dropped rapidly from high above their solidus to far below. A distinct event of near-isochemical hydration at above or ~250 °C is recorded by intense perlitic fracturing and the growth of closely packed mordenite spherulites only 1–3 μm across in felsic melt grains, which was followed by lower temperature hydrothermal alteration along the pre-existing perlitic fractures. The formation of abundant mordenite microspherulites appears to be very rare or not previously recorded in impactite melts and suggests the rapid infilling of the Hiawatha crater by a hydrous source. The infilling did not occur immediately after the impact as in submarine impacts, but soon thereafter, and before the establishment of a low-temperature hydrothermal alteration system common to the waning stage of cooling in many impact structures. These observations and previous documentation of terrestrial organic matter in the impactites are consistent with an impact into a water-rich terrestrial environment, such as through the Greenland Ice Sheet or into a forested, lacustrine–fluvial region.

Formation mechanism of a carbonate geothermal system and calculation of the reservoir temperature under complex conditions

Carbonate geothermal systems are widely distributed and have huge mining potential. They have complex and diverse mechanisms for their genesis and strong regional characteristics. Therefore, the detailed description of the mechanisms for the genesis of carbonate geothermal systems is not only an important scientific issue but also a practical issue for the scientific and sustainable exploitation of geothermal resources. Based on the analysis of hydrochemical characteristics and isotopic characteristics of different types of water and hydrogeological characteristics of the study area, the geothermal water source, temperature distribution and water flow channels are described in detail. The accuracy of estimates of temperature has been increased and the geological model of the geothermal system has been well determined. The results show that the Tangshan area is mainly composed of a mid to low temperature hydrothermal carbonate convective geothermal system. Geothermal water is replenished from atmospheric precipitation, flow down and then, under the influence of terrestrial heat flow, it moves upward along multiple sets of structural channels and forms geothermal resources in the groundwater drainage belts on the eastern and western sides of Tangshan. The zoning characteristics of the heat storage temperature are shown by the high temperature area where the reservoir temperature is approximately 84 °C and the low temperature area where it is only 40 °C. This research provides some evidence for determining the conditions controlling the formation of carbonate geothermal systems and provides a theoretical basis for the scientific and sustainable exploitation of geothermal resources in the future.

Kaolinite-to-Chlorite Conversion from Si,Al-Rich Fluid-Origin Veins/Fe-Rich Carboniferous Shale Interaction

The kaolinite-to-chlorite conversion is one of the chloritization processes that occurs in low temperature diagenetic and hydrothermal systems. The mechanism of this mineralogical transformation is still under discussion, since direct transformation, conversion via berthierine as intermediate phase or direct formation of berthierine/chlorite mix, either by dissolution-crystallization or by solid state transformation (or a combination of both), are all hypotheses put forward. In this context, each description of a kaolinite-to-chlorite conversion occurrence becomes an opportunity to shed new light and to renew this debate. Studying Carboniferous shale–crosscut by large quartz-kaolinite veins–from the mining basin of the North of France, we report therefore an uncommon kaolinite-Fe-rich chlorite assemblage. This assemblage appears as a chlorite fringe 20 µm wide along the interfaces between the shale and the quartz-kaolinite veins. All petrographical, mineralogical and chemical data suggest that the Fe-chlorite results from the interaction between the shale, providing the Fe,Mg supply, and the Si,Al-rich veins, leading to the chloritization of the kaolinite at a small scale via at least one dissolution-recrystallisation step. High-resolution observations highlight that neoformed Fe-rich chlorite contains some 7Å isochemical layers, as relict of berthierine. Therefore, we advance that the conversion takes place either through the precipitation of berthierine following by a second step involving solid state berthierine-chlorite conversion, or through the direct precipitation of a chlorite-rich/berthierine-poor mix driven by the Fe/(Fe + Mg) ratio, at low temperature and in reducing conditions. The comparison of our data with the recent literature allows to prefer the second hypothesis.

Минеральные ассоциации жил с кварцем типа «диаманты Донбасса» Селезневского угленосного района (cкладчатый Донбасс)

The authors have established quartz and quartz-carbonate veins, the formation of which is associated with a low-temperature hydrothermal system of methane-water composition within the Seleznevsky coal-bearing region of the Folded Donbass. The article considers the features of localization of hydrothermal mineralization containing quartz with inclusions of hydrocarbons, and its potential ore content. It is established that the vein bodies are localized mainly in the near-hinge parts of the third-order brachianticlines in the central and marginal parts of the Seleznevskaya syncline. These veins form systems associated with the fracturing of the inter-layer stratification or intersecting the layers. Interplastic veins are subdivided into plate-like massive and vein-like bodies with a druze texture. The veins of the second type contain quartz crystals with hydrocarbon inclusions, referred to as "diamonds of Donbass". They form a paragenetic association with dickite. In addition, calcite in the form of short-prismatic crystals is a typical associated mineral in the vein bodies among limestone strata. In the veins among the sandstone layers, the association with goethite, oxides and hydroxides of manganese is developed. Two morphological types of cinnabar were found in the vein bodies on the basis of HMS sampling, the largest number is confined to the brachianticlines of the marginal parts of the Seleznevskaya syncline. The analysis of the results indicates the prospects for identifying mercury mineralization with quartz-dickite-cinnabar type of mineralization.

An experimental study of basalt–seawater–CO2 interaction at 130 °C

Over millions of years, the interaction of marine basalt with percolating seawater in low-temperature ocean floor hydrothermal systems leads to the formation of calcite and aragonite. The presence of these minerals in marine basalts provides evidence for substantial CO2 fixation in these rocks. Here, we report on laboratory experiments to study this process under enhanced CO2 partial pressures (pCO2) at 130 °C. Mid-ocean-ridge-basalt (MORB) glass was reacted with North Atlantic Seawater charged with CO2 in batch experiments lasting up to 7 months. For experiments initiated with seawater charged with ~2.5 bar pCO2, calcite and aragonite are the first carbonate minerals to form, later followed by only aragonite (±siderite and ankerite). For experiments initiated with seawater charged with ~16 bar pCO2, magnesite was the only carbonate mineral observed to form. In total, approximately 20% of the initial CO2 in the reactors was mineralized within five months. This carbonation rate is similar to corresponding rates observed in freshwater-basalt-CO2 interaction experiments and during field experiments of the carbonation of basalts in response to CO2-charged freshwater injections in SW-Iceland. Our experiments thus suggest that CO2-charged seawater injected into submarine basalts will lead to rapid CO2 mineralization. Notably, at pCO2 of tens of bars, magnesite will form, limiting the formation of Mg-rich clays, which might otherwise compete for the Mg cation and pore-space in the submarine basaltic crust. This suggests that the injection of CO2-charged seawater into subsurface basalts can be an efficient and effective approach to the long-term safe mineral storage of anthropogenic carbon.

Formation and origin of Fe–Si oxyhydroxide deposits at the ultra-slow spreading Southwest Indian Ridge

Low-temperature hydrothermal systems are generally dominated by Fe–Si oxyhydroxide deposits. However, the formation process and mechanism of modern hydrothermal Fe–Si oxyhydroxides at ultra-slow spreading centers remain poorly understood. This study focused on six Fe–Si oxyhydroxide deposits collected from different sites at a typical ultra-slow spreading center, the Southwest Indian Ridge (SWIR). The mineralogical and geochemical evidence showed significant characteristics of a low-temperature hydrothermal origin. Sr and Nd isotope compositions of Fe–Si oxyhydroxide deposits at the SWIR probably reflected a combined signature of the hydrothermal fluids and seawater. Pb in the Fe–Si oxyhydroxides exhibited a close association with the substrate rocks and seawater. The Mössbauer spectra and iron speciation data further provided insights into iron-bearing phases in all deposits. Two different types of biomineralized forms were also discovered in these deposits by scanning electron microscopy (SEM) analysis. Energy-dispersive X-ray spectroscopy (EDS) and nanoscale secondary ion mass spectrometry (nanoSIMS) revealed that distinct biogenic structures were mainly composed of Fe, Si, and O, together with some trace elements. Based on these findings, we propose that microbial activity plays a significant role in the formation of Fe–Si oxyhydroxides at the ultra-slow spreading SWIR.

Caldelas and Gerês hydrothermal systems (NW Portugal): a comparative study based on geochemical and isotopic signatures

A study based on geochemical and environmental isotope data was performed in two low-temperature hydrothermal systems in NW Portugal (Caldelas and Geres hydrothermal systems). This study aims to demonstrate the role of integrated hydrogeological tools for developing conceptual models of groundwater circulation. The studied hydrothermal systems are ascribed to groundwater circulation in fractured calc-alkaline/alkaline granitic contexts, responsible for different groundwater geochemical types. Caldelas hydrothermal system is dominated by Ca/Na-HCO3 waters, while at Geres, the hydrothermal system is characterized by Na-HCO3-type waters. The isotopic signatures indicate that the preferential recharge areas are located at very different altitudes (Caldelas around 171 m a.s.l. and Geres between 912 and 1118 m a.s.l.). The thermomineral waters issue with a mean temperature of 27 °C (Caldelas) and 43 °C (Geres). Several geothermometers were used to estimate the reservoir temperature and the corresponding depth reached by the hydrothermal systems. At Caldelas, the mean estimated reservoir temperature was 42 ± 6 °C, using only the chalcedony and K2/Mg geothermometers, which suggests depths around 0.93 km. In the Geres thermal area, the chalcedony, K2/Mg, and Na/K/Ca (β = 4/3) geothermometers gave a mean estimated reservoir temperature of 96 ± 5 °C, suggesting depths close to 2.8 km. In both case studies, conceptual circulation models are proposed, based on: geological heterogeneities, geochemical and isotopic signatures, mean preferential recharge altitudes, groundwater circulation paths, and mean residence time.

The nature and age of basement host rocks and fissure fills in the Lancaster field fractured reservoir, West of Shetland

Hosting up to 3.3 billion barrels of oil in place, the upfaulted Precambrian crystalline rocks of the Lancaster field, offshore west of Shetland, give key insights into how fractured hydrocarbon reservoirs can form in such old rocks. The Neoarchean (c. 2700–2740 Ma) charnockitic basement is cut by deeply penetrating oil-, mineral- and sediment-filled fissure systems seen in geophysical and production logs and thin sections of core. Mineral textures and fluid inclusion geothermometry suggest that a low-temperature (<200°C) near-surface hydrothermal system is associated with these fissures. The fills help to permanently prop open fissures in the basement, permitting the ingress of hydrocarbons into extensive well-connected oil-saturated fracture networks. U–Pb dating of calcite mineral fills constrains the onset of mineralization and contemporaneous oil charge to the mid-Cretaceous and later from Jurassic source rocks flanking the upfaulted ridge. Late Cretaceous subsidence and deposition of mudstones sealed the ridge, and was followed by buoyancy-driven migration of oil into the pre-existing propped fracture systems. These new observations provide an explanation for the preservation of intra-reservoir fractures (‘joints’) with effective apertures of 2 m or more, thereby highlighting a new mechanism for generating and preserving fracture permeability in sub-unconformity fractured basement reservoirs worldwide.Supplementary material: Analytical methods and isotopic compositions and ages are available at https://doi.org/10.6084/m9.figshare.c.4763237Thematic Collection: This article is part of the Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

Integrated U–Pb, Lu–Hf and (U–Th)/He analysis of zircon from the Banxi Sb deposit and its implications for the low-temperature mineralization in South China

Low-temperature Sb (Au–Hg) deposits in South China account for more than 50% of the world’s Sb reserves, however, their genesis remains controversial. Here we report the first study that integrates U–Pb and Lu–Hf analysis by LA-(MC)-ICPMS and conventional (U–Th)/He analysis, all applied to single zircon crystals, in an attempt to constrain the origin and timing of world-class Sb (Au–Hg) deposits in Banxi (South China). Zircon separated from a quartz-stibnite ore and an altered country rock samples revealed similar U–Pb age spectra defining two major populations – Paleoproterozoic (~1900–2500 ​Ma) and Neoproterozoic (~770 ​Ma), which are characterized by variable εHf(t) values (–10.7 to 9.1 and –16.5 to 11.2, respectively) and Hf crustal model ages (TDMC) (2.48 to 3.24 ​Ga and 0.97 to 2.71 ​Ga, respectively). The U–Pb age and Hf isotopic features of the zircons are consistent with the Banxi Group in the region, indicating that the zircons involved in the low-temperature hydrothermal system were originally from the Banxi Group country rocks. Thirty-three mineralization-related zircon crystals yielded a mean (U–Th)/He age of 123.8 ​± ​3.8 ​Ma, which is interpreted to represent the timing of the latest low-temperature mineralization stage of the Banxi Sb deposit. The combined U–Pb, Lu–Hf and (U–Th)/He data suggest that Precambrian basement rocks were the major contributors to the low-temperature mineralization, and that Early Cretaceous (130–120 ​Ma) could be the most important ore-forming epoch for the Sb deposits in South China. This study also demonstrates the analytical feasibility of integrated U–Pb - Lu–Hf - (U–Th)/He “triple-dating”, all applied to single zircon crystals. This approach reveals the full evolution of zircon, from its origin of the magmatic source, through its crystallization and low-temperature cooling. Although this study demonstrates the usefulness of this integrated approach in dating low-temperature mineralization, it has great potential for zircon provenance and other studies that may benefit from the large amount of information that can be extracted from single zircon crystals.

Carbon cycling in low temperature hydrothermal systems: The Dorado Outcrop

Carbon cycling in low temperature hydrothermal systems: The Dorado Outcrop

Physico-chemical conditions of existence of early Cambrian chemotrophic microbiota in zone of influence of ore-forming hydrothermal solutions

Complex researches of the pyrite Early Cambrian Kyzyl-Tashtyg deposit (East Tuva) have allowed to reconstruct paleohydrothermal systems, to find out physical and chemical conditions of hydrothermal processes, and also to establish features of existence of ancient hydrothermal biota in the operating zone of the solutions, participating at all stages of formation of ore-bearing structures, since influence of postmagmatic fluids and finishing low temperature hydrotherms. The representative data on biota has been received at studying of the objects, which were in a zone of influence of rather low temperature hydrothermal systems. In one cases findings of microorganisms are dated for basalt complexes, containing ore body, and in other cases the found fauna is connected with ferruginous-siliceous sediments. It has been found out that microorganisms in the tonsil cavities of basalts evolved at the temperatures nearby 110-140°С under the influence of hydrothermal solutions. Much lower temperatures (to 100 °С) existed at development of micro-fossils in the quartz-hematite hydrothermal constructions of Kyzyl-Tashtyg deposit.

Physicochemical Conditions of the Existence of Early Cambrian Chemotrophic Microbiota in the Zone of Influence of Sulfide Ore-Forming Hydrothermal Solutions

Complex studies of the Early Cambrian Kyzyl-Tashtyg pyrite deposit (East Tuva) allowed us to reconstruct the paleohydrothermal systems, to understand the physicochemical conditions of hydrothermal processes, and to study the patterns of existence of ancient hydrothermal biota in the zone of activity of solutions participating at all stages of the formation of ore-bearing structures starting from the influence of postmagmatic fluids and up to low-temperature hydrotherms. The data on the biota reported were obtained during study of the objects occurring in the zone of influence of relatively low-temperature hydrothermal systems. In some cases, microorganisms were found in basaltic complexes hosting ore bodies; in other cases, fauna was related to the ferrous–siliceous deposits. It was found that microorganisms in basaltic amygdules were formed at temperatures of ~110–140°C under the influence of hydrothermal solutions of the Kyzyl-Tashtyg deposit. Much lower temperatures (up to 100°C) existed during the evolution of microfossils in the quartz–hematite hydrothermal structures of the Kyzyl-Tashtyg deposit.

Major and trace elements and sulfur isotopes in two stages of sphalerite from the world-class Angouran Zn–Pb deposit, Iran: Implications for mineralization conditions and type

The Angouran deposit is the second-largest Zn–Pb deposit in Iran with 4.7 Mt sulfide ore (27.7% Zn, 2.4% Pb, and 110 g/t Ag) and 14.6 Mt nonsulfide ore (28.1% Zn, 4.4% Pb). Various models have been proposed to explain the genesis of sulfide ore in this deposit. Moreover, the mineralization type of its primary sulfide ores remains controversial. The major and trace element concentrations and sulfur isotopic composition of the two stages of sphalerite have been analyzed to constrain mineralization conditions and the genesis. The Angouran deposit, which contains discordant orebodies, is hosted in a Neoproterozoic/Cambrian schist-marble sequence. Two stages of sphalerite have been distinguished: early-stage (S1) red-brown sphalerite and late-stage (S2) honey-yellow sphalerite. Our result shows that, relative to the S2 sphalerite, the S1 sphalerite has higher contents of Fe, Mn, Co, Cu, Ag, Sn, Ga, Sb and In, but lower contents of As and Tl. Time-resolved depth profiles in these sphalerites determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Fe, Cd, Co, Hg, Mn, Ge, and In are mainly present in solid solution and that Ag, Cu, Pb, As, Ni, Ga, Tl, Sb, and Sn are present in both solid solution and mineral inclusions. Correlation analyses reveal the occurrence of direct substitution mechanisms, such as Zn2+ ↔ (Fe2+, Cd2+) and 2Zn2+ ↔ Ge4++□ (vacancy) as well as coupled substitutions, such as 2Zn2+ ↔ Cu+ + Ga3+, 2Zn2+ ↔ (Cu+, Ag+) + Sb3+, 3Zn2+ ↔ Pb2+ + Tl+ + As3+, 4Zn2+ ↔ Pb2+ + 2As3++□(vacancy) or (Zn2+, Pb2+) ↔ Tl+ + As3+, and 4Zn2+ ↔ Cu+ + (Ga3+, In3+) + Sn4++□(vacancy). Geothermometer studies suggest that sphalerite in the Angouran deposit precipitated from a low-temperature (<200 °C) hydrothermal system. Trace element concentrations also reveal that the estimated average temperature of ore-forming fluid decreases gradually and becomes relatively oxidized from early stage to late stage. The low contents of Mn, and In and Zn/Cd ratios and high contents of Cd and Ge in sphalerite are consistent with those of MVT deposits but are different than that of magmatism-related deposits (e.g., epithermal, skarn, carbonate-replacement, and volcanogenic massive sulfide deposits). Meanwhile, the δ34SV-CDT values of the S1 and S2 sphalerites, which range from 5.1‰ to 10.9‰, are atypical of magma-derived sulfur isotopic compositions. Therefore, the Angouran deposit was formed in a low-temperature (<200 °C) fluid system and can be classified as a Mississippi Valley-type (MVT) deposit.