Genesis of the Longmendian Ag–Pb–Zn Deposit in Henan (Central China): Constraints from Fluid Inclusions and H–C–O–S–Pb Isotopes

The Longmendian Ag–Pb–Zn deposit is located in the southern margin of the North China Craton, and the mineralization occurs mainly in quartz veins, altered gneissic wallrocks, and minor fault breccias in the Taihua Group. Based on vein crosscutting relations, mineral assemblages, and paragenesis, the mineralization can be divided into three stages: (1) quartz–pyrite, (2) quartz–polymetallic sulfides, and (3) quartz–carbonate–polymetallic sulfides. Wallrock alteration can be divided into three zones, i.e., chlorite–sericite, quartz–carbonate–sericite, and silicate. Fluid inclusions in all Stage 1 to 3 quartz are dominated by vapor-liquid two-phase aqueous type (W-type). Petrographic and microthermometric analyses of the fluid inclusions indicate that the homogenization temperatures of Stages 1, 2, and 3 are 198–332°C, 132–260°C, and 97–166°C, with salinities of 4.0–13.3, 1.1–13.1, and 1.9–7.6 wt% NaCleqv, respectively. The vapor comprises primarily H2O, with some CO2, H2, CO, N2, and CH4. The liquid phase contains Ca2+, Na+, K+, SO42−, Cl−, and F−. The sulfides have δ34S=–1.42 to +2.35‰ and 208Pb/204Pb=37.771 to 38.795, 207Pb/204Pb=15.388 to 15.686, and 206Pb/204Pb=17.660 to 18.101. The H–C–O–S–Pb isotope compositions indicate that the ore-forming materials may have been derived from the Taihua Group and the granitic magma. The fluid boiling and cooling and mixing with meteoric water may have been critical for the Ag–Pb–Zn ore precipitation. Geological and geochemical characteristics of the Longmendian deposit indicate that the deposit is best classified as medium- to low-temperature intermediate-sulfidation (LS/IS) epithermal-type, related to Cretaceous crustal-extension-related granitic magmatism.

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Ore Genesis of the Kuergasheng Pb–Zn Deposit, Xinjiang Province, Northwest China: Constraints from Geology, Fluid Inclusions, and H–O–C–S–Pb Isotopes

Minerals ◽

10.3390/min10070592 ◽

2020 ◽

Vol 10 (7) ◽

pp. 592

Author(s):

Shunda Li ◽

Chuan Chen ◽

Lingling Gao ◽

Fang Xia ◽

Xuebing Zhang ◽

...

Keyword(s):

Fluid Inclusions ◽

Northwest China ◽

Hybrid Origin ◽

Isotopic Data ◽

Quartz Veins ◽

Carbon Isotopic ◽

Ore Bodies ◽

Western Tianshan ◽

Homogenization Temperatures ◽

Stage 1

The Kuergasheng Pb–Zn deposit is located in the Western Tianshan Orogen, Xinjiang Province, China. The ore bodies are mainly hosted in sandstone of the Tuosikuertawu Formation and are controlled by NW-trending faults. Three paragenetic stages were identified: early pyrite–chalcopyrite–quartz veins (stage 1), middle galena–sphalerite–quartz veins (stage 2), and late sulfide-poor calcite–quartz veins (stage 3). Fluid inclusions (FIs) include liquid-rich aqueous (LV-type), vapor-rich aqueous (VL-type), halite-bearing (S-type), and monophase liquid aqueous (L-type). Homogenization temperatures for FIs from stages 1–3 are 221–251, 173–220, and 145–172 °C, respectively. Stage 1 fluids in LV-, VL-, and S-type FIs yield salinities of 6.2–9.6, 1.7–3.1, and 32.7–34.9 wt % NaCl equiv., respectively. Stage 2 fluids in LV- and S-type FIs have salinities of 5.1–7.9 and 31.9–32.1 wt % NaCl equiv., respectively. Stage 3 fluids in LV- and L-type FIs have salinities of 3.4–5.9 wt % NaCl equiv. Oxygen, hydrogen, and carbon isotopic data (δ18OH2O = −7.7 to 1.7‰, δDH2O = −99.2 to −83.1‰, δ13CH2O = −16.6 to 9.1‰) indicate that the ore-forming fluids have a hybrid origin —an initial magmatic source with input of meteoric water becoming dominant in the later stage. Sulfur and lead isotopic data for galena (δ34S = 5.6 to 6.9‰, 206Pb/204Pb = 18.002–18.273, 207Pb/204Pb = 15.598–15.643, 208Pb/204Pb = 38.097–38.209) reveal that the ore-forming materials were mainly derived from the Beidabate intrusive body and the Tuosikuertawu Formation.

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Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil

Geologia USP Série Científica ◽

10.11606/issn.2316-9095.v21-160595 ◽

2021 ◽

Vol 21 (4) ◽

pp. 13-30

Author(s):

Laécio Cunha de Souza ◽

Regina Celia de Oliveira Brasil Delgado ◽

Heitor Neves Maia

Keyword(s):

Fluid Inclusions ◽

Aqueous Fluid ◽

Fluid Circulation ◽

Two Phase ◽

Quartz Veins ◽

Melting Temperatures ◽

Three Phase ◽

Higher Temperature ◽

Homogenization Temperatures ◽

Liquid Vapor

Micaschists that host the Acari batholith (Ediacaran age, 572 to 577 My) are characterized by a large number of quartz veins. The veins are more abundant in higher-temperature metamorphic zones and, together with lower metamorphic zones, form an aureole centered in the batholith. Most of the fluid inclusions are two-phase (H2O-CO2 and liquid/vapor), but three-phase varieties (liquid/vapor/salt cubes; liquid/liquid/vapor) occur locally. The analyzed veins come from the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite metamorphic zones. CO2 melting temperatures (TmCO2) vary from -62.6 to -56.7°C, suggesting CH4 and/or N2. Eutectic temperatures (Te) in quartz veins show average values of -30.8°C in the biotite + chlorite + muscovite and biotite + garnet zones, and -38.6°C in the cordierite + andalusite and cordierite + sillimanite zones. Ice-melting temperatures (Tmice) are lower in the higher-temperature metamorphic zones. The mode values are -3.8, -5.5, -5.6, and -7.3°C, corresponding respectively to the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite zones. A fluid characterized by the H2O-Na-Cl (KCl)-MgCl2-FeCl2-CaCl2 system is defined by: Tmice from near -1.9 to -32°C, the presence of salt cubes mainly in the cordierite + andalusite and cordierite + sillimanite zones, and recorded eutectic temperatures (Te) from -16.5 to -59.1°C. In addition, total homogenization temperatures (Tht) ranging from 117 to 388°C were obtained for primary aqueous fluid inclusions. This indicates a long period of fluid circulation under conditions of falling temperatures. Our results are consistent with an increase in the salinity of the aqueous fluid across the thermal aureole toward the granitic batholith.

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Petrogenesis, Ore Mineralogy, and Fluid Inclusion Studies of the Tagu Sn–W Deposit, Myeik, Southern Myanmar

Minerals ◽

10.3390/min9110654 ◽

2019 ◽

Vol 9 (11) ◽

pp. 654

Author(s):

Kyaw Thu Htun ◽

Kotaro Yonezu ◽

Aung Zaw Myint ◽

Thomas Tindell ◽

Koichiro Watanabe

Keyword(s):

Fluid Inclusions ◽

Type A ◽

Type B ◽

Two Phase ◽

Metasedimentary Rocks ◽

Quartz Veins ◽

Liquid Co2 ◽

Type C ◽

Homogenization Temperatures ◽

Two Phases

Most of the granite-related Sn–W deposits in Myanmar are located in the Western Granitoid Province (WGP) of Southeast Asia. The Tagu deposit in the southern part of the WGP is a granite related Sn–W deposit. The biotite granite is composed of quartz, feldspars (plagioclase, orthoclase, and microcline), and micas (muscovite and biotite) and belongs to S-type peraluminous granite. Abundances of large-ion lithophile elements (LILEs), such as Rb, K, and Pb, coupled with the deficiency of high-field-strength elements (HFSEs), such as Nb, P, and Ti, indicate that the parental magma for the Tagu granite was derived from the lower continental crust at syn-collisional setting. Mineralized veins consist of early-formed oxide ore minerals, such as cassiterite and wolframite, which were followed by the formation of sulfide minerals. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by granite and metasedimentary rocks: Type-A—two phases, liquid (L) + vapor (V) aqueous inclusions; Type-B—two phases, vapor (V) + liquid (L) vapor-rich inclusions; And type-C—three phases, liquid + CO2-liquid + CO2-vapor inclusions. Quartz in the veins hosted in granite corresponding with earlier deposition contains type-A, type-B, and type-C fluid inclusions, whereas that in the veins hosted in metasedimentary rocks corresponding with later deposition contains only type-A fluid inclusions. The homogenization temperatures of type-A inclusions range from 140 °C to 330 °C (mode at 230 °C), with corresponding salinities from 1.1 wt.% to 8.9 wt.% NaCl equivalent for quartz veins hosted in metasedimentary rocks, and from 230 °C to 370 °C (mode at 280 °C), with corresponding salinities from 2.9 wt.% to 10.6 wt.% NaCl equivalents for quartz veins hosted in granite. The homogenization temperatures of type-B vapor-rich inclusions in quartz veins in granite range from 310 °C to 390 °C (mode at 350 °C), with corresponding salinities from 6.7 wt.% to 12.2 wt.% NaCl equivalent. The homogenization temperatures of type-C H2O–CO2–NaCl inclusions vary from 270 °C to 405 °C (mode at 330 °C), with corresponding salinities from 1.8 wt.% to 5.6 wt.% NaCl equivalent. The original ascending ore fluid was probably CO2-bearing fluid which evolved into two phase fluid by immiscibility due to pressure drop in the mineralization channels. Furthermore, the temperature and salinities of two-phase aqueous fluids were later most likely decreased by the mixing with meteoric water. The salinities of the type-B vapor-rich inclusions are higher than those of the type-C CO2-rich inclusions, which may have resulted from CO2 separation from the fluids. The escape of gases can lead to an increase in the salinity of the residual fluids. Therefore, the main ore-forming mechanisms of the Tagu Sn–W deposit are characterized by fluid immiscibility during an early stage, and fluid mixing with meteoric water in the late stage at a lower temperature.

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Ore Genesis at the Jinchang Gold–Copper Deposit in Heilongjiang Province, Northeastern China: Evidence from Geology, Fluid Inclusions, and H–O–S Isotopes

Minerals ◽

10.3390/min9020099 ◽

2019 ◽

Vol 9 (2) ◽

pp. 99 ◽

Cited By ~ 2

Author(s):

Shunda Li ◽

Xuebing Zhang ◽

Lingling Gao

Keyword(s):

Fluid Inclusions ◽

Copper Deposit ◽

Northeastern China ◽

Heilongjiang Province ◽

Quartz Veins ◽

Daughter Mineral ◽

Rich Liquid ◽

Three Stages ◽

Stage 1 ◽

Late Stages

The Jinchang gold–copper deposit is located in Eastern Heilongjiang Province,Northeastern China. The orebody comprises primarily hydrothermal breccias, quartz veins, anddisseminated ores within granite, diorite, and granodiorite. Three paragenetic stages are identified:early quartz–pyrite–arsenopyrite (Stage 1), quartz–pyrite–chalcopyrite (Stage 2), and latequartz–pyrite–galena–sphalerite (Stage 3). Gold was deposited during all three stages and Stage 1was the major gold-producing stage. Copper is associated with the mineralization but has loweconomic value. Fluid inclusions (FIs) within the deposit are liquid-rich aqueous, vapor-rich aqueous,and daughter-mineral-bearing types. Microthermometric data for the FIs reveal decreasinghomogenization temperatures (Th) and salinities of the ore-forming fluids over time. The Th forStages 1–3 of the mineralization are 421–479, 363–408, and 296–347 °C, respectively. Stage 1 fluidsin vapor-rich and daughter-mineral-bearing inclusions have salinities of 5.7–8.7 and 49.8–54.4 wt%NaCl equivalent, respectively. Stage 2 fluids in vapor-rich, liquid-rich, and daughter-mineral-bearinginclusions have salinities of 1.2–5.4, 9.5–16.0, and 43.3–48.3 wt% NaCl, respectively. Stage 3 fluids inliquid-rich and daughter-mineral-bearing inclusions have salinities of 7.9–12.6 and 38.3–42.0 wt% NaClequivalent, respectively. The estimated trapping pressures are 160–220 bar, corresponding toan entrapment depth of 1.6–1.2 km in the paleo-water table. Oxygen and hydrogen isotope data(δ18OV-SMOW = 8.6‰ to 11.4‰; δDV-SMOW = −92.2‰ to −72.1‰) suggest that the ore-forming fluidswere derived from magmatic fluids during the early stages of mineralization and subsequentlyincorporated meteoric water during the late stages. The sulfide minerals have δ34SVCDT values of0.2‰–3.5‰, suggesting that the sulfur has a magmatic origin. The Jinchang deposit is a typicalgold-rich gold–copper porphyry deposit.

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Au-Ag-Te–RICH MELT INCLUSIONS IN HYDROTHERMAL GOLD-QUARTZ VEINS, XIAOQINLING LODE GOLD DISTRICT, CENTRAL CHINA

Economic Geology ◽

10.5382/econgeo.4811 ◽

2021 ◽

Author(s):

Wei Jian ◽

Jingwen Mao ◽

Bernd Lehmann ◽

Nigel J. Cook ◽

Guiqing Xie ◽

...

Keyword(s):

Melt Inclusions ◽

Experimental Studies ◽

Gold Deposits ◽

Central China ◽

Lode Gold ◽

Quartz Veins ◽

The North ◽

Reduction Mechanisms ◽

Adsorption Reduction ◽

Lode Gold Deposits

Abstract We present petrographic and microthermometric evidence for precipitation of Au-Ag-Te–rich melt directly from hydrothermal fluids and subsequent entrapment as primary melt inclusions within pyrite from quartz veins of the Xiaoqinling lode gold district, southern margin of the North China craton. We propose the formation of Au-Ag-Te–rich melt through adsorption-reduction mechanisms on pyrite and subsequent growth of the melt nuclei via direct scavenging of metals from fluids. Because neither initial formation nor later growth of the melt require saturation of the ore fluid with respect to the constituent metals, this mechanism offers a new understanding of the enrichment of low-abundance ore components, such as gold. Our model may thus partly explain the discrepancy between the high gold solubilities reported from experimental studies and the much lower gold concentrations usually measured in natural fluids. This study also implies that Au-Ag-Te–rich melt has probably gone unrecognized in other lode gold deposits in which Au-Ag tellurides are present.

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Zircon U–Pb ages, major and trace elements, and Hf isotope characteristics of the Tiantangzhai granites in the North Dabie orogen, Central China: tectonic implications

Geological Magazine ◽

10.1017/s0016756813000976 ◽

2013 ◽

Vol 151 (5) ◽

pp. 916-937 ◽

Cited By ~ 3

Author(s):

XIN DENG ◽

KUNGUANG YANG ◽

ALI POLAT ◽

TIMOTHY M. KUSKY ◽

KAIBIN WU

Keyword(s):

Partial Melting ◽

Eastern China ◽

Major And Trace Elements ◽

Central China ◽

Dabie Orogen ◽

Crustal Rocks ◽

The North ◽

Granitic Magmatism ◽

Two Peaks ◽

Lower Crustal

AbstractCretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.

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Fluid Inclusions and H–O–C–S–Pb Isotopic Systematics of the Jinba Gold Deposit, NW China: Implications for Ore Genesis

Frontiers in Earth Science ◽

10.3389/feart.2021.638375 ◽

2021 ◽

Vol 9 ◽

Author(s):

Shun-Da Li ◽

Chuan Chen ◽

Ling-Ling Gao ◽

Fang Xia ◽

Xue-Bing Zhang ◽

...

Keyword(s):

Gold Deposit ◽

Fluid Inclusions ◽

Lead Isotope ◽

Early Devonian ◽

Nw China ◽

Carbon Isotopic ◽

Altay Orogenic Belt ◽

Isotope Studies ◽

Homogenization Temperatures ◽

Stage 1

The Jinba gold deposit is located in the Maerkakuli Shear Zone of the south Altay Orogenic Belt, NW China. Mineralization types are classified as altered rock–and quartz vein–type. Orebodies occur as veins or lenses controlled by NW–trending faults, and are hosted in phyllite (Early–Middle Devonian Ashele Formation) and plagiogranite (Early Devonian Habahe Pluton). Three paragenetic stages were identified: early quartz–pyrite–gold (Stage 1), middle quartz–chalcopyrite (Stage 2), and late calcite–quartz–galena–sphalerite (Stage 3). Fluid inclusions within the deposit are liquid–rich aqueous (LV–type), vapor–rich aqueous (VL–type), carbonic–aqueous (LC–type), and purely carbonic (C–type) FIs. Homogenization temperatures for stages 1–3 FIs were 373–406 °C, 315–345 °C, and 237–265 °C, respectively. Fluid salinities for stages 1–3 were 2.1–13.6 wt%, 3.2–6.1 wt% and 3.9–6.0 wt% NaCl equivalent, respectively. The ore–forming fluids evolved from a CO2–NaCl–H2O ± CH4 to a NaCl–H2O system from stage 1–3. Oxygen, hydrogen, and carbon isotopic data (δ18Ofluid = 1.7‰–8.1‰, δDfluid = –104.1‰ to –91.7‰, δ13Cfluid = –0.4‰–6.3‰) indicate that ore–forming fluids were metamorphic hydrothermal origin with the addition of a late meteoric fluid. Sulfur and lead isotope data for pyrite (δ34Spy = 3.3‰–5.3‰, 206Pb/204Pb = 17.912.3–18.495, 207Pb/204Pb = 15.564–15.590, 208Pb/204Pb = 37.813–38.422) show that the ore–forming materials were mainly derived from diorite and the Ashele Formation. Mineralization, FIs, and isotope studies demonstrate that the Jinba deposit is an orogenic gold deposit.

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The role of sulfate-rich fluids in heavy rare earth enrichment at the Dashigou carbonatite deposit, Huanglongpu, China

Mineralogical Magazine ◽

10.1180/mgm.2019.78 ◽

2019 ◽

Vol 84 (1) ◽

pp. 65-80 ◽

Cited By ~ 5

Author(s):

Delia Cangelosi ◽

Martin Smith ◽

David Banks ◽

Bruce Yardley

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Fluid Inclusions ◽

Central China ◽

Open Pit ◽

Secondary Phases ◽

Heavy Rare Earth ◽

The North ◽

Heavy Rare Earth Elements ◽

Total Sulfate

AbstractThe Huanglongpu carbonatites are located in the north-western part of the Qinling orogenic belt in central China. Calcite carbonatite dykes at the Dashigou open pit are unusual due to their enrichment in heavy rare earth elements (HREE) relative to light rare earth elements (LREE), leading to a flat REE pattern, and in that the majority of dykes have a quartz core. They also host economic concentrations of molybdenite. The calcite carbonatite dykes show two styles of mineralogy according to the degree of hydrothermal reworking, and these are reflected in REE distribution and concentration. The REE in the little-altered calcite carbonatite occur mostly in magmatic REE minerals, mainly monazite-(Ce), and typically have ΣLREE/(HREE+Y) ratios from 9.9 to 17. In hydrothermally altered calcite carbonatites, magmatic monazite-(Ce) is partially replaced to fully replaced by HREE-enriched secondary phases and the rocks have ΣLREE/(HREE+Y) ratios from 1.1 to 3.8. The fluid responsible for hydrothermal REE redistribution is preserved in fluid inclusions in the quartz lenses. The bulk of the quartz lacks fluid inclusions but is cut by two later hydrothermal quartz generations, both containing sulfate-rich fluid inclusions with sulfate typically present as multiple trapped solids, as well as in solution. The estimated total sulfate content of fluid inclusions ranges from 6 to >33 wt.% K2SO4 equivalent. We interpret these heterogeneous fluid inclusions to be the result of reaction of sulfate-rich fluids with the calcite carbonatite dykes. The final HREE enrichment is due to a combination of factors: (1) the progressive HREE enrichment of later magmatic calcite created a HREE-enriched source; (2) REE–SO42– complexing allowed the REE to be redistributed without fractionation; and (3) secondary REE mineralisation was dominated by minerals such as HREE-enriched fluorocarbonates, xenotime-(Y) and churchite-(Y) whose crystal structures tends to favour HREE.

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Carbonic fluids in the Hamadi gold deposit, Sudan: origin and contribution to gold mineralization

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2016-0058 ◽

2017 ◽

Vol 54 (5) ◽

pp. 494-511 ◽

Cited By ~ 2

Author(s):

Xi-hui Cheng ◽

Jiu-hua Xu ◽

Jian-xiong Wang ◽

Qing-po Xue ◽

Hui Zhang

Keyword(s):

Gold Deposit ◽

Melting Temperature ◽

Fluid Inclusions ◽

Gold Mineralization ◽

Narrow Range ◽

Shear Zones ◽

Quartz Veins ◽

Wide Range ◽

Homogenization Temperatures ◽

Gold Bearing

The Hamadi gold deposit is located in North Sudan, and occurs in the Neoproterozoic metamorphic strata of the Arabian–Nubian Shield. Two types of gold mineralization can be discerned: gold-bearing quartz veins and altered rock ores near ductile shear zones. The gold-bearing quartz veins are composed of white to gray quartz associated with small amounts of pyrite and other polymetallic sulfide minerals. Wall-rock alterations include mainly beresitization, epidotization, chloritization, and carbonatization. CO2-rich inclusions are commonly seen in gold-bearing quartz veins and quartz veinlets from gold-bearing altered rocks; these include mainly one-phase carbonic (CO2 ± CH4 ± N2) inclusions and CO2–H2O inclusions with CO2/H2O volumetric ratios of 30% to ∼80%. Laser Raman analysis does not show the H2O peak in carbonic inclusions. In quartz veins, the melting temperature of solid CO2 (Tm,CO2) of carbonic inclusions has a narrow range of −59.6 to −56.8 °C. Carbonic inclusions also have CO2 partial homogenization temperatures (Th,CO2) of −28.3 to +23.7 °C, with most of the values clustering between +4.0 and +20 °C; all of these inclusions are homogenized into the liquid CO2 state. The densities range from 0.73 to 1.03 g/cm3. XCH4 of carbonic fluid inclusions ranges from 0.004 to 0.14, with most XCH4 around 0.05. In CO2–H2O fluid inclusions, Tm,CO2 values are recorded mostly at around −57.5 °C. The melting temperature of clathrate is 3.8–8.9 °C. It is suggested that the lowest trapping pressures of CO2 fluids would be 100 to ∼400 MPa, on the basis of the Th,CO2 of CO2-bearing one-phase (LCO2) inclusions and the total homogenization temperatures (Th,tot) of paragenetic CO2-bearing two-phase (LCO2–LH2O) inclusions. For altered rocks, the Tm,CO2 of the carbonic inclusions has a narrow range of −58.4 to ∼−57.0 °C, whereas the Th,CO2 varies widely (−19 to ∼+29 °C). Most carbonic inclusions and the carbonic phases in the CO2–H2O inclusions are homogenized to liquid CO2 phases, which correspond to densities of 0.70 to ∼1.00 g/cm3. Fluid inclusions in a single fluid inclusion assemblage (FIA) have narrow Tm,CO2 and Th,CO2 values, but they vary widely in different FIAs and non-FIAs, which indicates that there was a wide range of trapping pressure and temperature (P–T) conditions during the ore-forming process in late retrograde metamorphism after the metamorphism peak period. The carbonic inclusions in the Hamadi gold deposit are interpreted to have resulted from unmixing of an originally homogeneous aqueous–carbonic mixture during retrogress metamorphism caused by decreasing P–T conditions. CO2 contributed to gold mineralization by buffering the pH range and increasing the gold concentration in the fluids.

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Fluid Inclusions and H-O-C-S Isotopes of the Wushan Copper Polymetallic Deposit in the Suizao Area, Hubei Province: Implications for Ore Genesis

Geofluids ◽

10.1155/2019/3431909 ◽

2019 ◽

Vol 2019 ◽

pp. 1-29

Author(s):

Pan-Pan Niu ◽

Shao-Yong Jiang ◽

Suo-Fei Xiong ◽

Qi-Sheng Hu ◽

Tian-liang Xu

Keyword(s):

Fluid Inclusions ◽

Late Stage ◽

Early Stage ◽

Central China ◽

Vein Deposit ◽

Hydrothermal Vein ◽

Polymetallic Deposit ◽

Dabie Orogenic Belt ◽

Homogenization Temperatures ◽

Multiphase Fluid

The Wushan copper polymetallic deposit is located in the Tongbai-Dabie orogenic belt in central China. Two small granitoid stocks (Donggushan and Xigushan) occur in the deposit, which is next to the largest Qijianfeng Granite Complex in the Suizao area. The mineralization of Wushan copper polymetallic deposit is mainly composed of ore-bearing quartz veins and quartz stockworks. Two hydrothermal stages are identified as the quartz-sulfide stage (early stage) and the barren quartz stage (late stage). A detailed petrographic study shows four types of fluid inclusions in quartz, including the aqueous fluid inclusions (L+V/V+L), the aqueous-carbonic fluid inclusions (L+V+CO2), the pure carbon dioxide fluid inclusions (pure CO2), and the daughter mineral-bearing multiphase fluid inclusions (S). The daughter mineral-bearing multiphase fluid inclusions (S) are further divided into three subclasses according to their different solid mineral assemblages, including (1) S1: L+V+Hal, (2) S2: L+V+CO2+S (chalcopyrite), and (3) S3: L+V+S (calcite, chalcopyrite, and hematite)±Hal. A laser Raman spectroscopic analysis shows that the main components of fluid inclusions are water and carbon dioxide. The solid minerals of the S-type fluid inclusions include halite, calcite, chalcopyrite, and hematite. The homogenization temperatures of fluid inclusions are 377 to 468°C for the early stage, with a salinity of 11.1 to 34.1 wt.% NaCl equivalent (11.1 to 17.4 wt.% NaCl equivalent and 28.4 to 34.1 wt.% NaCl equivalent, respectively) and an estimated pressure of 89 to 137 MPa. The homogenization temperatures of fluid inclusions in the late stage are 267 to 380°C with salinity of 7.0 to 12.1 wt.% NaCl equivalent and an estimated pressure of 46 to 115 MPa. Therefore, the temperature, salinity, and pressure of the fluid show a decreasing trend from the early to the late stage. In the early stage, the fluid is immiscible, which leads to the precipitation of sulfides. Pyrite shows a δ34S of approximately 0 (-1.8 to +3.4‰), and chalcopyrite also shows a similar δ34S of approximately 0 (+1.5 to +2.4‰), which indicates that the sulfur in the ore-forming fluid is mainly derived from deep-seated magma. Combined with C-H-O isotopic compositions, the initial ore-forming fluid is likely magmatic water, but with the addition of meteoric water in the late stage. By comparing with the typical characteristics of magmatic hydrothermal vein deposit and orogenic deposit related to shear zones, we suggest that the Wushan copper polymetallic deposit is most likely a magmatic hydrothermal vein deposit, which is of great significance for the further exploration work in the Wushan and surrounding areas. This new finding also fills the gap that no magmatic hydrothermal vein type Cu deposits have been found in the Suizao area or even in the Qinling-Dabie orogenic belt in central China.

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