Geochemical Evolution of Hydrothermal Fluids at the Daejang Cu–Zn–Pb Vein Deposit, Korea

Abstract: The Daejang mine is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into four stages (stages I, II, III and IV) by major tectonic fracturing. Stages I, III and IV are economically barren. Stage II, at which the precipitation of major ore minerals occurred, is further divided into three substages with paragenetic time based on minor fractures and discernible mineral assemblages: substage IIa, marked by deposition of quartz and Fe–sulfides; substage IIb, by introduction of base-metal sulfides within carbonates and some quartz; substage IIc, by quartz and carbonates with various sulfosalts. Fluid inclusion data indicate a complex geochemical evolution of hydrothermal fluids. Both CO₂–rich and H₂O–rich fluids were trapped in fluid inclusions at stage I and substage IIa. It is suggested that a compositionally heterogeneous fluid was formed by fluid boiling and CO₂ immiscibility at temperatures of about 400° to 300°C. Composite lodes of base-metal sul–fides, carbonates and quartz at substage IIb were deposited in open spaces created by fracturing. The fracturing event prompted rapid decreases in pressure and temperature of residual fluids and resulted in retrograde fluid boiling at about 200 bars and 300°–250°C during substage IIb. The progressive loss of CO₂ by CO₂ effervescence and retrograde boiling from substage IIa and IIb fluids resulted in pH increase and related increase in carbonate activity, causing deposition of abundant carbonates. The change in pH also caused the decrease of stability of hydrogen sulfide with Cu, Zn and Pb chloride complexes (as main transporting agents at Daejang) and resulted in the pricipitation of base-metal minerals. Deposition of Ag– and Sb-bearing sul–fides and sulfosalts of substage IIc occurred at temperatures of about 250° to 150°C from a dominantly aqueous fluid with low salinity (down to 3. 0 equiv. wt % NaCl). At this substage, aqueous fluid formed by mixing with cooler and less saline meteoric groundwater. There is a systematic decrease in caculated δ¹⁸O_water values with the mineralization stage (and decreasing temperature) in the Daejang hydrothermal system, from values of about 11% for stage I, through about 4% for stages II and III, to about –3 per mil for stage IV. The result of stable isotope and fluid inclusion studies are interpreted to indicate progressive less evolved and/or unexchanged meteoric water influx of an early hydrothermal system formed by highly evolved meteoric waters.     

Fluid Inclusions,Stable Isotopes,and Geochronology of the Haobugao Lead‐Zinc Deposit,Inner Mongolia,China

The Haobugao deposit, located in the southern segment of the Great Xing'an Range, is a famous skarn‐related Pb‐Zn‐(Cu)‐(Fe) deposit in northern China. The results of our fluid inclusion research indicate that garnets of the early stage (I skarn stage) contain three types of fluid inclusions (consistent with the Mesozoic granites): vapor‐rich inclusions (type LV, with V_H2O/(V_H2O + L_H2O) < 50 vol %, and the majority are 5–25 vol %), liquid‐rich two‐phase aqueous inclusions (type VL, with V_H2O/(V_H2O + L_H2O) > 50 vol %, the majority are 60–80 vol %), and halite‐bearing multiphase inclusions (type SL). These different types of fluid inclusions are totally homogenized at similar temperatures (around 320–420°C), indicating that the ore‐forming fluids of the early mineralization stage may belong to a boiling fluid system. The hydrothermal fluids of the middle mineralization stage (II, magnetite‐quartz) are characterized by liquid‐rich two‐phase aqueous inclusions (type VL, homogenization temperatures of 309–439°C and salinities of 9.5–14.9 wt % NaCl eqv.) that coexist with vapor‐rich inclusions (type LV, homogenization temperatures of 284–365°C and salinities of 5.2–10.4 wt % NaCl eqv.). Minerals of the late mineralization stage (III sulfide‐quartz stage and IV sulfide‐calcite stage) only contain liquid‐rich aqueous inclusions (type VL). These inclusions are totally homogenized at temperatures of 145–240°C, and the calculated salinities range from 2.0 to 12.6 wt % NaCl eqv. Therefore, the ore‐forming fluids of the late stage are NaCl‐H₂O‐type hydrothermal solutions of low to medium temperature and low salinity. The δD values and calculated δ¹⁸O_SMOW values of ore‐forming fluids of the deposit are in the range of ?4.8 to 2.65‰ and ?127.3‰ to ?144.1‰, respectively, indicating that ore‐forming fluids of the Haobugao deposit originated from the mixing of magmatic fluid and meteoric water. The S‐Pb isotopic compositions of sulfides indicate that the ore‐forming materials are mainly derived from underlying magma. Zircon grains from the mineralization‐related granite in the mining area yield a weighted ²⁰⁶Pb/²³⁸U mean age of 144.8 ±0.8 Ma, which is consistent with a molybdenite Re‐Os model age (140.3 ±3.4 Ma). Therefore, the Haobugao deposit formed in the Early Cretaceous, and it is the product of a magmatic hydrothermal system.     

Ore-Forming Fluids of Vein-Type Fluorite Deposits of the Cerro Aspero Batholith,Southern Cordoba Province,Argentina

Vein-type fluorite deposits in the southern part of the Sierras Pampeanas, Córdoba Province, Argentina, occur mainly hosted by calc-alkaline porphyritic biotite granites, which belong to the Paleozoic, post-tectonic Cerro Aspero batholith. The fluorite veins, of Cretaceous age, occupy steeply dipping, strike-slip regional fault zones, and are composed of fluorite and chalcedony, locally with subordinate amounts of pyrite and, in some cases, coffinite and pitchblende. These veins show typical open-space-filling textures and are closely related to pervasive silicic and argillic alteration of the host granite.

Three successive stages of mineralization were distinguished on the basis of vein chronology, REE data, and fluid-inclusion study in fluorite ores. These stages generally display slightly fractionated REE patterns (La/Yb = 1.4 to 14), with REE behavior given by a relatively stronger LREE fractionation with respect to HREE. The REE composition of the fluids responsible for fluorite deposition was largely controlled by differential mobility of the REE during the silicic or argillic alteration of the host granite. Preferential leaching of HREE over LREE occurred during both alteration types, but in the argillic alteration the LREE were practically not removed. The total homogenization of primary-like aqueous inclusions took place invariably in the liquid phase at temperatures ranging from 187°C to 103°C, with concentrations of values around 160°C, 136°C, and 116°C (stages I, II, and III, respectively), defining a clear trend of fluid cooling. This cooling is accompanied by large changes in the fO₂ of the fluid, from oxidizing to reducing, as inferred from the Eu/Eu? ratios and the mineral assemblage (pyrite, pitchblende, and coffinite).

The three stages of fluorite deposition exhibit temperatures of ice melting within the interval from ?0.3°C to +0.4° C, indicating that the mineralizing fluids were exclusively aqueous and highly dilute. No evidence of fluid mixing or boiling was found. The fluid-inclusion data suggest that the proposed three stages of mineralization probably were the result of a single hydrothermal event, and strongly support a single, uniform fluid reservoir for the ore-forming solutions; evidently, the latter were heated meteoric waters rather than fluids generated in deep-seated environments within the crust.     

Genesis of the Jinding Zn-Pb deposit,northwest Yunnan Province,China: Constraints from rare earth elements and noble gas isotopes

The giant sediment-hosted Jinding zinc-lead deposit is located in the Lanping Basin, northwestern Yunnan Province, China. The genesis of the deposit has long been debated and the sources of the ore-forming fluids and metals are controversial. This study presents rare earth element (REE) and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation. The early-stage sulfides are enriched in light REEs and have high ∑REE values (30.8–94.8 ppm) and weakly negative Eu (δEu 0.85–0.89) and Ce anomalies (δCe 0.84–0.95), suggesting that the fluids were likely derived from dissolution of Upper Triassic marine carbonates with input of REEs from aluminosilicate rocks in the basin. In contrast, the late-stage sulfides have irregular REE patterns, generally low ∑REE values (0.24–10.8 ppm) and positive Eu (δEu 1.22–10.9) and weakly negative Ce anomalies (δCe 0.53–0.90), which suggest that the ore-forming fluids interacted with evaporite minerals. The ³He/⁴He (0.01–0.04 R_a) and ⁴⁰Ar/³⁶Ar values (301–340) of the ore-forming fluids indicate crustal and atmospheric origins for these noble gases. These findings are in agreement with the published fluid inclusion microthermometry data and the results of H, O, C, S, Pb and Sr isotope studies. Our data, in combination with published results, support a two-stage hydrothermal mineralization model, involving early-stage basinal brines and late-stage meteoric water that acquired metals and heat from crustal sources.     

Hydrothermal Fluid Sources of the Fengjia Barite–fluorite Deposit in Southeast Sichuan,China: Evidence from Fluid Inclusions and Hydrogen and Oxygen Isotopes

The Fengjia barite–fluorite deposit in southeast Sichuan is a stratabound ore deposit which occurs mainly in Lower Ordovician carbonate rocks. Here we present results from fluid inclusion and oxygen and hydrogen isotope studies to determine the nature and origin of the hydrothermal fluids that generated the deposit. The temperature of the ore‐forming fluid shows a range of 86 to 302 °C. Our detailed microthermometric data show that the temperature during mineralization of the fluorite and barite in the early ore‐forming stage was higher than that during the formation of the calcite in the late ore‐forming stage. The salinity varied substantially from 0.18% to 21.19% NaCl eqv., whereas the density was around 1.00 g/cm³. The fluid composition was mainly H₂O (>91.33%), followed by CO₂, CH₄ and traces of C₂H₆, CO, Ar, and H₂S. The dominant cation was Na⁺ and the dominant anion Cl^‐, followed by Ca²⁺, SO₄^2‐, K⁺, and Mg²⁺, indicating a mid–low‐temperature, mid‐low‐salinity, low‐density NaCl–H₂O system. Our results demonstrate that the temperature decreased during the ore‐forming process and the fluid system changed from a closed reducing environment to an open oxidizing environment. The hydrogen and oxygen isotope data demonstrate that the hydrothermal fluids in the study area had multiple sources, primarily formation water, as well as meteoric water and metamorphic water. Combined with the geological setting and mineralization features we infer that the stratabound barite–fluorite deposits originated from mid–low‐temperature hydrothermal fluids and formed vein filling in the fault zone.     

Geochemical characteristics and source of ore-forming fluid of Duolanasayi gold deposit,Xinjiang

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Geological and Geophysical Studies of Sulfide Copper Mineralization in the Dochileh Area: An Example of Manto‐Type Deposit in the Sabzevar Zone,Iran

The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rock displays two hydrothermal events: zeolite–carbonate alteration that is a stratigraphic–lithologic feature and chlorite and chlorite/ferruginous alterations in the local mineralized structures. Ore formation is related to both hydrothermal events and occurs in both stratiform and vein mineralization types. Mineralization consists of main chalcocite with variable amounts of bornite, chalcopyrite, native copper, malachite, and cuprite minerals, which occur as hydrothermal breccias, and disseminated, vein, and veinlet forms. Geophysical field studies using resistivity and induction polarization (IP) methods were conducted along nine survey lines in the area. As a result of modeling and interpretation of the acquired geophysical data, high values of IP and resistivity corresponding to mineralization were observed at two depth levels: 0–20 m and more than 40 m. Based on these geological and geophysical investigations, six locations for drilling exploration boreholes were proposed. Drilling data confirmed the mineralization containing high copper values in the two depth levels: the vein‐type mineralization in the surface and shallow depth level, and the stratiform mineralization at the deeper level. Fluid inclusion studies in calcite and quartz from stratiform‐ and vein‐type mineralization show the evidence of mixing, and a linear dilution trend during the ore formation occurred at a wide range of temperatures: 121–308°C and 80–284°C, respectively, and varying salinities of between 3.2–16.8 and 0.8–22 wt% NaCl equivalents. The stable isotope composition of δ³⁴S that falls in a range of ?2.4 to +25.0‰ could be considered biogenetic sulfur from bacterial sulfate reduction and leaching of sulfur from hosting basalt. The δ¹³C values of calcite vary between ?0.6 and ?7.6‰, suggesting a major contribution of marine carbonates associated with igneous carbonates, and the δ¹⁸O_SMOW values of calcite are between +15.2 and +19.9‰, suggesting a contribution of δ¹⁸O‐rich sedimentary rocks and δ¹⁸O‐poor meteoric water. Copper and sulfide‐rich hydrothermal fluid have flowed upward through the local faults and permeable interbeds within the Eocene volcanic sequence and have formed the mineralized veins and horizons. The geophysical results have detected the local faults as the channel ways for mineralization.     

Characteristic Features of REE and Pb–Zn–Ag Mineralizations in the Na Son Deposit,Northeastern Vietnam

The Na Son deposit is a small‐scale Pb–ZnPb–Zn–Ag deposit in northeast Vietnam and consists of biotite–chlorite schist, reddish altered rocks, quartz veins and syenite. The biotite–chlorite schist is intruded by syenite. Reddish altered rocks occur as an alteration halo between the biotite–allanite‐bearing quartz veins and the biotite–chlorite schist. Allanite occurs in the biotite–allanite‐bearing quartz veins and in the proximal reddish altered rocks. Rare earth element (REE) fluorocarbonate minerals occur along fractures or at rim of allanite crystals. The later horizontal aggregates of sulfide veins and veinlets cut the earlier reddish altered rocks. The earlier Pb–Zn veins consist of a large amount of galena and lesser amounts of sphalerite, pyrite and molybdenite. The later Cu veins cutting the Pb–Zn veins include chalcopyrite and lesser amounts of tetrahedrite and pyrite. The occurrences of two‐phase H₂O–CO₂ fluid inclusions in quartz from biotite–allanite‐bearing quartz veins and REE‐bearing fluorocarbonate minerals in allanite suggest the presence of CO₂ and F in the hydrothermal fluid. The oxygen isotopic ratios of the reddish altered rocks, biotite–chlorite schist, and syenite range from +13.9 to +14.9 ‰, +11.5 to +13.3 ‰, and +10.1 to +11.6 ‰, respectively. Assuming an isotopic equilibrium between quartz (+14.6 to +15.8 ‰) and biotite (+8.6 ‰) in the biotite–allanite‐bearing quartz vein, formation temperature was estimated to be 400°C. At 400°C, δ¹⁸O values of the hydrothermal fluid in equilibrium with quartz and biotite range from +10.5 to +11.7 ‰. These δ¹⁸O values are consistent with fluid that is derived from metamorphism. Assuming an isotopic equilibrium between galena (+1.5 to +1.7 ‰) and chalcopyrite (+3.4 ‰), the formation temperature was estimated to be approximately 300°C. The formation temperature of the Na Son deposit decreased with the progress of mineralization. Based on the geological data, occurrence of REE‐bearing minerals and oxygen isotopic ratios, the REE mineralization is thought to result from interaction between biotite–chlorite schist and REE‐, CO₂‐ and F‐bearing metamorphic fluid at 400°C under a rock‐dominant condition.     

Geology,geochemistry, sulfur isotope composition,and fluid inclusion data of Farsesh barite deposit,Lorestan Province,Iran

Farsesh barite in the central part of Iranian Sanandaj-Sirjan zone is a sample of epigenetic hydrothermal mineralization in dolomitized limestone, which provides appropriate chemicophysical conditions making the passage of mineral-bearing fluids possible. Barite veins may range from a few centimeters to 2 m in thickness that increases downward. The microthermometry measurements obtained from more than 30 fluid inclusions show relative homogenization temperatures ranging from 125 to 200 °C with an average of 110 °C for Farsesh barite deposits. The mean salinity measured proves 16 times as much as weight percentage of NaCl for barite. Coexistence of liquid- and vapor-rich fluid inclusions in barite minerals may provide an evidence of boiling in ore veins. Moreover, occurrence of bladed calcite, high-grade ore zones, and presence of hydrothermal breccia are all consistent with boiling. Thermometric studies indicate that homogenization temperatures (Th) for primary and pseudosecondary fluid inclusions in barite range from 125 to 200 °C with an average of 1,100 °C. The δ³⁴S values of barite also lie between 8.88 and 16.6 %. The relatively narrow spread in δ³⁴S values may suggest uniform environmental conditions throughout the mineralization field. Thus, δ³⁴S values are lower than those of contemporaneous seawater, which indicates a contribution of magmatic sulfur to the ore-forming solution. Barite is marked by total amounts of rare Earth elements (REEs) (6.25–17.39 ppm). Moreover, chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (i.e., LREEs) from La to Sm, similar to those for barite from different origins. The La_CN/Lu_CN ratios and chondrite-normalized REE patterns reveal that barite in Farsesh deposit is enriched in LREEs compared with heavy rare Earth elements (HREEs). Similarity between Ce/La ratios in barite samples and those found in deep-sea barite supports its marine origin. Lanthanum and Gd exhibit positive anomalies, which are common features of chemical marine sediments. Cerium shows a negative anomaly in most samples inherited from the negative Ce anomaly of hydrothermal fluid that is mixed with seawater at barite precipitation. The available data including tectonic setting, host rock characteristics, REE geochemistry, and sulfur isotopic compositions may support a hydrothermal submarine origin for Farsesh barite deposit.     

A fluid inclusion and light element stable isotope study of the gold-bearing quartz vein system,Falun, Sweden

The Falun gold quartz vein mineralization is located ca 230 km NW of Stockholm, Sweden, within the Early Proterozoic volcano-sedimentary sequence of Bergslagen. The mineralization consists of a system with subparallel quartz veins that crosscut the alteration zone to the Falun massive sulphide deposit. Early barren and late gold-bearing quartz veins follow tectonic structures postdating the formation of the massive sulphide ore. Both generations of veins are epigenetic to the massive sulphide ore and were formed by hydrothermal processes. Fluid inclusion study of the gold-bearing quartz veins indicates a low-moderately saline fluid (0.3 to 17.4 equiv wt% NaCl). Heterogeneous trapping is indicated by coexisting inclusions showing a variable CO₂ content from 100% CO₂ ± CH₄ to 100% aqueous fluid. Temperatures of total homogenization also show a wide spread from 116–350°C with a slightly bimodal distribution with peaks at ca 180°C and 280°C. MeasuredδD values — 69 to — 63%0 (SMOW), of inclusion fluid and calculatedδ ¹⁸O values of hydrothermal fluids — 7.5 to — 1.4%0 (SMOW), strongly suggest a meteoric origin for the fluids. The quite consistentδD values and the range inδ ¹⁸O values indicate that major water-rock interaction led to the evolution inδ18O of the hydrothermal fluids.     

Geochemistry,fluid inclusion and stable isotope constraints (C and O) of the Sivrikaya Fe-skarn mineralization (Rize,NE Turkey)

The Sivrikaya Fe-skarn mineralization is hosted by dolomitic limestone layers of Late Cretaceous volcano-sedimentary unit, comprised of andesite, basalt and their pyroclastites, including, sandstone, shale and dolomitic limestone layers. Intrusion of the Late Cretaceous–Eocene İkizdere Granitoid in the volcano–sedimentary unit resulted in skarn mineralization along the granitoid–dolomitic limestone contact. The ore is associated with exoskarns, and mineralization is characterized by early anhydrous garnet and pyroxene with late hydrous minerals, such as epidote, tremolite, actinolite and chlorite. The ore minerals are mainly magnetite and hematite, with minor amounts of pyrite and chalcopyrite. The composition of garnet and pyroxene in the exoskarn is Adr_{79.45−99.03}Grs_0−17.9Prs_0.97−2.65 and Di_69.1−77.1Hd_22.2−29.8Jhn_0.6−1.4, respectively, and abundances of magnetite in the ore suggest that the Fe-skarn mineralization formed under relatively oxidized conditions.Homogenization temperatures (T_h) of all fluid inclusions and calculated salinity content are in the range of 166 °C–462 °C and 0.35–14.3 wt% NaCl equ., respectively. Well-defined positive correlation between Th and salinity values indicates that meteoric water was involved in the hydrothermal solutions. Eutectic temperatures (Te) between −40.8 °C and −53.6 °C correspond to the presence of CaCl₂ in the early stage of fluid inclusions. On the other hand, the Te temperatures of later-stage fluid inclusions, in the range of −38 °C and −21.2 °C, correspond to the presence of MgCl₂, FeCl₂, KCl and NaCl type salt combinations. None of the fluid inclusions were found to contain separated gas phases in microscopy observations. However, a limited amount of dissolved CH₄ was identified in the early stage, high temperature fluid inclusions using Raman spectroscopic studies.Δ¹⁸O values in both dolomitic limestone (10.8–12.5‰) and skarn calcite (7.6–9.8‰) were highly depleted compared to the typical δ¹⁸O values of marine limestones. Decreases in δ¹⁸O values are accepted as an indication of dilution by meteoric water because retrograde brecciation of garnet, magnetite and breccia filling epidote and quartz in volcanic host rocks are an indication of increasing permeability, allowing infiltration of meteoric water. Highly depleted δ¹³C isotopes (up to −6.5‰) of dolomitic limestone, indicate that organic matter in carbonates had an effect on the decreasing isotopic ratios. The presence of CH₄ and CH₂ in fluid inclusions can be explained by the thermal degradation of these organic materials.     

Hydrochemical,isotopic, and reservoir characterization of the Pasinler (Erzurum) geothermal field,eastern Turkey

The reservoir temperature and conceptual model of the Pasinler geothermal area, which is one of the most important geothermal areas in Eastern Anatolia, are determined by considering its hydrogeochemical and isotope properties. The geothermal waters have a temperature of 51 °C in the geothermal wells and are of Na–Cl–HCO₃ type. The isotope contents of geothermal waters indicate that they are of meteoric origin and that they recharge on higher elevations than cold waters. The geothermal waters are of immature water class and their reservoir temperatures are calculated as 122–155 °C, and their cold water mixture rate is calculated as 32%. According to the δ¹³C_VPDB values, the carbon in the geothermal waters originated from the dissolved carbon in the groundwaters and mantle-based CO₂ gases. According to the δ³⁴S_CDT values, the sources of sulfur in the geothermal waters are volcanic sulfur, oil and coal, and limestones. The sources of the major ions (Na⁺, Ca²⁺, Mg²⁺, Cl^?, and HCO₃ ^?) in the geothermal waters are ion exchange and plagioclase and silicate weathering. It is determined that the volcanic rocks in the area have effects on the water chemistry and elements like Zn, Rb, Sr, and Ba originated from the rhyolite, rhyolitic tuff, and basalts. The rare earth element (REE) content of the geothermal waters is low, and according to the normalized REE diagrams, the light REE are getting depleted and heavy REE are getting enriched. The positive Eu and negative Ce anomalies of waters indicate oxygen-rich environments.     

The Laal-Kan fluorite deposit,Zanjan Province,NW Iran: constraints on REE geochemistry and fluid inclusions

The Laal-Kan fluorite deposit (west of Zanjan city, NW Iran) mainly occurred as some open-space filling and vein/veinlet in the schist of the Paleozoic age. Mineralogically, calcite, fluorite types (white, smoky, and violet), and quartz are the principal constituents accompanied by a number of minor accessory minerals such as hemimorphite, hematite, barite, and clays. Based on chemical analyses, fluorites of various colors were found to have low rare earth element (REE) concentrations (4.16–25.67 ppm). The chondrite-normalized REE patterns indicated that early fluorites were enriched in LREE, relative to HREE, whereas late fluorites were enriched in HREE relative to LREE. This study, therefore, indicated that fugacity of oxygen likely played a significant role in the occurrence of positive Ce and negative anomaly in the late fluorite. Furthermore, the Gd behavior of the fluorite samples could be attributed to the Gd-F complex in ore-forming fluids. On the other hand, low pH hydrothermal fluids under alkaline conditions were probably the main mechanism responsible for the deposition of the early fluorites in this district. Fluorite-hosted fluid inclusion analyses also indicated that fluorite-forming fluids consisted of NaCl, MgCl₂, CaCl₂, and LiCl with a narrow T_H (118–151 °C) and high salinities (18.96–23.47 wt.% NaCl equiv.). Further, the diagram of Tb/La-Tb/Ca ratios revealed that fluorites were predominantly deposited in the hydrothermal environment and the late stage fluorites could be considered as the product of the secondary mineralization of the early fluorites due to the interaction of the fluid with the early fluorites.     

Fluid Inclusion,H-O,S, Pb and noble gas isotope studies of the Aerhada Pb-Zn-Ag deposit,Inner Mongolia,NE China

The Aerhada Pb-Zn-Ag deposit is located in the western segment of the Great Hinggan Range Ag-Pb-Zn-Cu-Mo-Au-Fe metallogenic belt in NE China. Orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate. Three stages of primary mineralization, including an early arsenopyrite-pyrite-quartz, a middle polymetallic and silver sulfides-quartz and a late sphalerite-pyrite-calcite-fluorite are recognized. Four types of fluid inclusions have been identified in the ore-bearing quartz and fluorite veins, i.e., liquid-rich, gas-rich, three-phase CO₂ aqueous inclusions, and pure gas or liquid aqueous inclusions. Microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253° to 430 °C, 195° to 394 °C and 133° to 207 °C, respectively. Fluid salinities range from 2.9 to 14.0 wt.% NaCl equiv. The vapor composition of the ore fluid is dominated by H₂O, CO₂ and CH₄, with minor proportions of N₂. The fluid δ¹⁸O_H2O and δD_H2O values vary from +1.6 to +9.3‰ and −122 to −56‰, respectively, and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization, respectively. The calculated δ³⁴S_H2S values of hydrothermal fluids in equilibrium with sulfides range from +5.2 to +7.1‰, suggesting a mixed source for sulfur, i.e., the local magmatic and sedimentary rocks. The Pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks, implying that lead and possibly silver relate to these sources. The noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore-forming fluids were dominantly derived from a deep mantle source. Fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition. The Aerhada Pb-Zn-Ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit.     

Fluid Inclusions and Metallization of the Kendekeke Polymetallic Deposit in Qinghai Province,China

The Kendekeke polymetallic deposit, located in the middle part of the magmatic arc belt of Qimantag on the southwestern margin of the Qaidam Basin, is a polygenetic compound deposit in the Qimantag metallogenic belt of Qinghai Province. Multi-periodic ore-forming processes occurred in this deposit, including early-stage iron mineralization and lead-zinc-gold-polymetallic mineralization which was controlled by later hydrothermal process. The characteristics of the ore-forming fluids and mineralization were discussed by using the fluid inclusion petrography, Laser Raman Spectrum and micro-thermometry methods. Three stages, namely, S1-stage(copper-iron-sulfide stage), S2-stage(lead-zinc-sulfide stage) and C-stage(carbonate stage) were included in the hydrothermal process as indicated by the results of this study. The fluid inclusions are in three types: aqueous inclusion(type I), CO2-aqueous inclusion(type II) and pure CO2 inclusion(type III). Type I inclusions were observed in the S1-stage, having homogenization temperature at 240–320oC, and salinities ranging from 19.8% to 25.0%(wt % NaCl equiv.). All three types of inclusions, existing as immiscible inclusion assemblages, were presented in the S2-stage, with the lowest homogenization temperature ranging from 175 oC to 295oC, which represents the metallogenic temperature of the S2-stage. The salinities of these inclusions are in the range of 1.5% to 16%. The fluid inclusions in the C-stage belong to types I, II and III, having homogenization temperatures at 120–210oC, and salinities ranging from 0.9% to 14.5%. These observations indicate that the ore-forming fluids evolved from high-temperature to lowtemperature, from high-salinity to low-salinity, from homogenization to immiscible separation. Results of Laser Raman Spectroscopy show that high density of CO2 and CH4 were found as gas compositions in the inclusions. CO2, worked as the pH buffer of ore-forming fluids, together with reduction of organic gases(i.e. CH4, etc), affected the transport and sediment of the minerals. The fluid system alternated between open and close systems, namely, between lithostatic pressure and hydrostatic pressure systems. The calculated metallogenic pressures are in the range of 30 to 87 Mpa corresponding to 3 km mineralization depth. Under the influence of tectonic movements, immiscible separation occurred in the original ore-forming fluids, which were derived from the previous highsalinity, high-temperature magmatic fluids. The separation of CO2 changed the physicochemical properties and composition of the original fluids, and then diluted by mixing with extraneous fluids such as meteoric water and groundwater, and metallogenic materials in the fluids such as lead, zinc and gold were precipitated.     

Genesis of tin and tantalum mineralization in pegmatites from the Bynoe area,Pine Creek Geosyncline,Northern Territory

The tin‐ and tantalum‐bearing pegmatites of the Bynoe area are located in the western Pine Creek Geosyncline. They are emplaced within psammopelitic rocks in the contact aureole of the Two Sisters Granite. The latter is a Palaeoproterozoic, fractionated, granite with S‐type characteristics and comprises a syn‐ to late‐orogenic, variably foliated, medium‐grained biotite granite and a post‐orogenic, coarse‐grained biotite‐muscovite granite. The pegmatites comprise a border zone of fine grained muscovite + quartz followed inward by a wall zone of coarse grained muscovite + quartz which is in turn followed by an intermediate zone of quartz + feldspar + muscovite. A core zone of massive quartz is present in some occurrences. Feldspars in the intermediate zone are almost completely altered to kaolinite. This zone contains the bulk of cassiterite, tantalite and columbite mineralization. Fluid inclusions in pegmatitic quartz indicate that early Type A (CO₂ + H₂O ± CH₄) inclusions were trapped at the H₂O‐CO₂ solvus at P～100 MPa, T～300°C (range 240–328°C) and salinity ～6 wt% eq NaCl. Pressure‐salinity corrected temperatures on Type B (H₂O + ～20% vapour), C (H₂O + < 15% vapour) and D (H₂O + halite + vapour) inclusions also fall within the range of Type A inclusions. Oxygen and hydrogen isotope data show that kaolin was either formed in isotopic equilibrium with meteoric waters or subsequent to its formation, from hydrothermal fluid, underwent isotopic exchange with meteoric waters. Fluid inclusion waters from core zone quartz show enrichment in deuterium suggesting metamorphic influence. Isotope values on muscovite are consistent with a magmatic origin. It is suggested that the pegmatites were derived from the post‐orogenic phase of the Two Sisters Granite. Precipitation of cassiterite took place at about 300°C from an aqueous fluid largely as a result of increase in pH due to feldspar alteration.     

Fluid Inclusion and Stable Isotope Studies at Don Sixto,a Precious Metal Low Sulfidation Deposit in Mendoza Province,Argentina

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (～4 km²), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (T_h) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaCl_equiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaCl_equiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ¹⁸O_H2O = ?6.92 up to ?3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ³⁴S_H2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.     

The world-class Natalka gold deposit, northeast Russia: REE patterns, fluid inclusions, stable oxygen isotopes, and formation conditions of ore

REE patterns of hydrothermally altered rocks, fluid inclusions, and stable oxygen isotopes of quartz were studied at the Natalka gold deposit. Metasomatic rocks formed under decompression reveal gradual depletion in LREE and HREE relative to siltstone of the protolith. The HREE patterns of metasomatic rocks formed under decompression are uniform; an insignificant removal of LREE can be noted. The progressive extraction of REE with increasing alteration of rocks could have been due to the effect of magmatogenic or meteoric fluid. Because a Ce anomaly is absent, the participation of oxidized meteoric water was limited. The inverse correlation between the total REE content and the Eu anomaly value in altered rocks indicates a substantial role of magmatogenic fluid. The REE patterns of altered rocks formed under compression show that the role of metamorphic fluid was not great. All metasomatic rocks are enriched in LREE, so that the enrichment of fluid in LREE as well may be suggested. Three fluid compositions were captured as fluid inclusions: (1) H₂O-CO₂-NaCl-MgCl₂ with a salinity of 1.0–4.9 wt % NaCl equiv, (2) CO₂-CH₄, and (3) H₂O-NaCl-MgCl₂ with a salinity of 7.0–5.6 wt % NaCl equiv. Compositions (1) and (2) coexisted in the mineral-forming system at 250–350°C and 1.1–2.4 kbar as products of phase separation under conditions of decreasing P and T. The interaction of this fluid with host rocks resulted in the formation of extensive halos of beresitized rocks with sulfide disseminations. The precipitation of arsenopyrite and pyrite led to the substantial depletion of mineral-forming fluid in H₂S and destabilization of the Au(HS)^2? complex. The fluid with the third composition arose due to the boiling of the H₂O-CO₂-CH₄-NaCl-MgCl₂ liquid and was responsible for metasomatic alteration of host rocks. The late mineral assemblages were deposited from this fluid at the initial stage of ore formation. The high methane concentrations in the ore-forming fluid were likely caused by interaction of hydrothermal ore-bearing solutions with carbonaceous host rocks. The δ¹⁸O values of quartz from quartz-scheelite-pyrite-arsenopyrite and sulfide-sulfosalt mineral assemblages vary from +11.6 to +14.1‰ and +11.2 to +13.5‰, respectively. The parental fluids of the early and late mineral assemblages probably were derived from a magmatic source and were characterized by $ \delta ^{18} O_{H_2 O} REE patterns of hydrothermally altered rocks, fluid inclusions, and stable oxygen isotopes of quartz were studied at the Natalka gold deposit. Metasomatic rocks formed under decompression reveal gradual depletion in LREE and HREE relative to siltstone of the protolith. The HREE patterns of metasomatic rocks formed under decompression are uniform; an insignificant removal of LREE can be noted. The progressive extraction of REE with increasing alteration of rocks could have been due to the effect of magmatogenic or meteoric fluid. Because a Ce anomaly is absent, the participation of oxidized meteoric water was limited. The inverse correlation between the total REE content and the Eu anomaly value in altered rocks indicates a substantial role of magmatogenic fluid. The REE patterns of altered rocks formed under compression show that the role of metamorphic fluid was not great. All metasomatic rocks are enriched in LREE, so that the enrichment of fluid in LREE as well may be suggested. Three fluid compositions were captured as fluid inclusions: (1) H₂O-CO₂-NaCl-MgCl₂ with a salinity of 1.0–4.9 wt % NaCl equiv, (2) CO₂-CH₄, and (3) H₂O-NaCl-MgCl₂ with a salinity of 7.0–5.6 wt % NaCl equiv. Compositions (1) and (2) coexisted in the mineral-forming system at 250–350°C and 1.1–2.4 kbar as products of phase separation under conditions of decreasing P and T. The interaction of this fluid with host rocks resulted in the formation of extensive halos of beresitized rocks with sulfide disseminations. The precipitation of arsenopyrite and pyrite led to the substantial depletion of mineral-forming fluid in H₂S and destabilization of the Au(HS)²⁻ complex. The fluid with the third composition arose due to the boiling of the H₂O-CO₂-CH₄-NaCl-MgCl₂ liquid and was responsible for metasomatic alteration of host rocks. The late mineral assemblages were deposited from this fluid at the initial stage of ore formation. The high methane concentrations in the ore-forming fluid were likely caused by interaction of hydrothermal ore-bearing solutions with carbonaceous host rocks. The δ¹⁸O values of quartz from quartz-scheelite-pyrite-arsenopyrite and sulfide-sulfosalt mineral assemblages vary from +11.6 to +14.1‰ and +11.2 to +13.5‰, respectively. The parental fluids of the early and late mineral assemblages probably were derived from a magmatic source and were characterized by = +6.3 to +8.8‰ at 350°C and +3.6 to +5.9‰ at 280°C, respectively. The narrow interval of oxygen isotopic compositions shows that this source was homogeneous. The data obtained allow us to suggest that the deposit formation was related to magmatic activity, including the direct supply of ore components from a magma chamber and mobilization of these components in the processes of dehydration and decarbonation during contact and regional metamorphism. Original Russian Text ? N.A. Goryachev, O.V. Vikent’eva, N.S. Bortnikov, V.Yu. Prokof’ev, V.A. Alpatov, V.V. Golub, 2008, published in Geologiya Rudnykh Mestorozhdenii, 2008, Vol. 50, No. 5, pp. 414–444.     

Rare earth element and strontium isotope geochemistry in Dujiali Lake,central Qinghai-Tibet Plateau,China: Implications for the origin of hydromagnesite deposits

Rare earth element (REE) and strontium isotope data (⁸⁷Sr/⁸⁶Sr) are presented for hydromagnesite and surface waters that were collected from Dujiali Lake in central Qinghai-Tibet Plateau (QTP), China. The goal of this study is to constrain the solute sources of hydromagnesite deposits in Dujiali Lake. All lake waters from the area exhibit a slight LREE enrichment (average [La/Sm]_PAAS = 1.36), clear Eu anomalies (average [Eu/Eu*]_PAAS = 1.31), and nearly no Ce anomalies. The recharge waters show a flat pattern (average [La/Sm]_PAAS = 1.007), clear Eu anomalies (average [Eu/Eu*] _PAAS = 1.83), and nearly no Ce anomalies (average [Ce/Ce*]_PAAS = 1.016). The REE+Y data of the surface waters indicate the dissolution of ultramafic rock at depth and change in the hydrogeochemical characteristics through fluid-rock interaction. These data also indicate a significant contribution of paleo-groundwater to the formation of hydromagnesite, which most likely acquired REE and Sr signatures from the interaction with ultramafic rocks. The ⁸⁷Sr/⁸⁶Sr data provide additional insight into the geochemical evolution of waters of the Dujiali Lake indicating that the source of Sr in the hydromagnesite does not directly derive from surface water and may have been influenced by both Mg-rich hydrothermal fluids and meteoric water. Additionally, speciation modeling predicts that carbonate complexes are the most abundant dissolved REE species in surface water. This study provides new insights into the origins of hydromagnesite deposits in Dujiali Lake, and contributes to the understanding of hydromagnesite formation in similar modern and ancient environments on Earth.     

Origin of Ore-forming Fluids Responsible for Gold Mineralization of the Pongkor Au-Ag Deposit, West Java, Indonesia: Evidence from Mineralogic, Fluid Inclusion Microthermometry and Stable Isotope Study of the Ciurug–Cikoret Veins

The Pongkor gold–silver mine is situated at the northeastern flank of the Bayah dome, which is a product of volcanism in the Sunda–Banda Arc. The hydrothermal alteration minerals in the Ciurug–Cikoret area are typical of those formed from acid to near‐neutral pH thermal waters. On the surface, illite/smectite mixed layer mineral (I/Sm), smectite and kaolinite, and spotting illite, I/Sm and K‐feldspar alteration occur at the top of the mineralized zone. Silicification, K‐feldspar and I/Sm zones are commonly formed in the wall rock, and gradually grade outwards into a propylitic zone. The mineralization of precious metal ore zone is constrained by fluid temperatures between 180 and 220°C, and with low salinity (<0.2 wt% NaCl equivalent) and boiling condition. The minimum depth of vein formation below the paleo‐water table is approximately 90–130 m for the hydrostatic column. Hydrogen and oxygen isotope data for quartz and calcite show relatively homogeneous fluid composition (?53 to ?68‰δD and ?5.7 to +0.3‰δ¹⁸O H₂O). There is no specific trend in the data with respect to the mineralization stages and elevation, which suggests that the ore‐forming fluids did not significantly change spatially during the vein formation. The stable isotope data indicate mixing between the hydrothermal fluids and meteoric water and interaction between the hydrothermal fluids and the host rock.