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1.
Abstract: The Wenyu mesothermal gold deposit is located in the Xiaoqinling district about 1000 km southwest of Beijing in central China. It occurs in the Late Archean to Early Proterozoic metamorphosed volcanic and sedimentary rocks. Three distinct stages of veins have been identified: (I) gold‐poor quartz–pyrite veins, (II) gold‐rich sulfide–quartz veins, and (III) gold‐poor carbonate–quartz veins. Stage II can be subdivided into IIa and IIb. Gold typically occurs as fracture‐fillings associated with chalcopyrite and galena. Fluid inclusions were examined in quartz samples from veins of both stage I and II. Three types of fluid inclusions are identified: CO2–H2O, CO2–rich, and aqueous inclusions. The first two types are of primary in origin. The last type occurs in two ways: coexisting with CO2–H2O and CO2–rich inclusions and thus primary in origin; and occurring along late healed fractures and hence secondary in origin. CO2–H2O inclusions display progressively decreasing Th and increasing Thco2, from the highest Th (311–408C) and lowest Thco2 (average 18C) in stage I quartz through middle Th (284–358C) and ThCO2(average 25C) in stage IIa quartz to the lowest Th (275–314C) and highest ThCO2 (average 28C) in stage IIb quartz, indicating an evolving H2O–CO2–NaCl fluid system. CO2–rich and primary aqueous inclusions show consistent ThCO2 or Th with their coexistent CO2–H2O inclusions. Whereas the secondary aqueous inclusions in stage I and IIa quartz have almost the same Th and salinity as the primary aqueous inclusions in stage IIb quartz. Comparing with CO2–H2O inclusions, these non–CO2, low salinity aqueous inclusions may come from different origin, most probably meteoric water. Unlike in both stage I and IIa quartz, fluid inclusions in stage IIb do not show evidence of fluid immiscibility. The fact that most of gold is associated with stage IIa and IIb veins and not with veins of stage I which is the main stage of vein formation suggests that gold deposition occurs at the later stage of fluid immiscibility. The continuing phase separation led to the deposition of large amounts of gold at the Wenyu mine.  相似文献   

2.
The Datuanshan deposit is one of the largest and most representative stratabound copper deposits in the Tongling area,the largest ore district in the Middle-Lower Yangtze River metallogenic belt.The location of the orebodies is controlled by the interlayer-slipping faults between the Triassic and Permian strata,and all the orebodies are distributed in stratiform shape around the Mesozoic quartz monzodiorite dikes.Based on field evidence and petrographic observations,four mineralization stages in the Datuanshan deposit have been identified:the skarn,early quartz-sulfide,late quartzsulfide and carbonate stages.Chalcopytite is the main copper mineral and mainly formed at the late quartz-sulfide stage.Fluid inclusions at different stages were studied for petrography,microthermometry,laser Raman spectrometry and stable isotopes.Four types of fluid inclusions,including three-phase fluid inclusions(type 1),liquid-rich fluid inclusions(type 2),vapour-rich fluid inclusions(type 3) and pure vapour fluid inclusions(type 4),were observed.The minerals from the skarn,early and late quartz-sulfide stages contain all fluid inclusion types,but only type 2 fluid inclusions were observed at the carbonate stage.Petrographic observations suggest that most of the inclusions studied in this paper are likely primary.The coexistence of different types of fluid inclusions with contrasting homogenization characteristics(to the liquid and vapour phase,respectively) and similar homogenization temperatures(the modes are 440-480℃,380-400℃ and 280-320℃ for the skarn,early and late quartz-sulfide stages,respectively) in the first three stages,strongly suggests that three episodes of fluid boiling occurred during these stages,which is supported by the hydrogen isotope data.Laser Raman spectra identified CH_4 at the skarn and early quartz-sulfide stages.Combined with other geological features,the early ore-forming fluids were inferred to be under a relatively reduced environment.The CO_2 component has been identified at the late quartz-sulfide and carbonate stages,indicating that the late ore-forming fluids were under a relatively oxidized environment,probably as a result of inflow of and mixing with meteoric water.In addition,microthermometric results of fluid inclusions and H-O isotope data mdicate that the ore forming fluids were dominated by magmatic water in the early stages(skarn and early quartz-sulfide stages) and mixed with meteoric water in the late stages(late quartz-sulfide and carbonate stages).The evidence listed above suggests that the chalcopyrite deposition in the Datuanshan deposit probably resulted from the combination of multiepisode fluid boiling and mixing of magmatic and meteoric water.  相似文献   

3.
The Nuri Cu‐W‐Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu‐Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz‐polymetallic sulfide stage and quartz‐carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two‐phase aqueous inclusions, daughter mineral‐bearing multiphase inclusions, CO2‐rich inclusions and single‐phase inclusions. The homogenization temperature of the fluid inclusions are 280°C–386°C (skarn stage), 200°C–340°C (oxide stage), 140°C–375°C (quartz‐polymetallic sulfide stage) and 160°C–280°C (quartz‐carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz‐carbonate stage. The salinity of the corresponding stages are 2.9%–49.7 wt% (NaCl) equiv., 2.1%–7.2 wt% (NaCl) equiv., 2.6%–55.8 wt% (NaCl) equiv. and 1.2%–15.3 wt% (NaCl) equiv., respectively. The analyses of CO2‐rich inclusions suggest that the ore‐forming pressures are 22.1 M Pa–50.4 M Pa, corresponding to the depth of 0.9 km–2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H2O, with some CO2 and very little CH4, N2, etc. δD values of garnet are between ?114.4‰ and ?108.7‰ and δ18OH2O between 5.9‰ and 6.7‰; δD of scheelite range from ?103.2‰ to ?101.29‰ and δ18OH2O values between 2.17‰ and 4.09‰; δD of quartz between ?110.2‰ and ?92.5‰ and δ18OH2O between ?3.5‰ and 4.3‰. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The δ34S values of sulfides, concentrated in a rage between ?0.32‰ to 2.5‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen‐oxygen and sulfur isotopes data, show that the ore‐forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO2 or other gases. During the reaction, the ore‐forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore‐forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO2 from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.  相似文献   

4.
The succession of mineral assemblages, chemistry of gangue and ore minerals, fluid inclusions, and stable isotopes (C, O, S) in minerals have been studied in the Mangazeya silver–base-metal deposit hosted in terrigenous rocks of the Verkhoyansk Fold–Thrust Belt. The deposit is localized in the junction zone of the Kuranakh Anticlinorium and the Sartanga Synclinorium at the steep eastern limb of the Endybal Anticline. The deposit is situated at the intersection of the regional Nyuektame and North Tirekhtyakh faults. Igneous rocks are represented by the Endybal massif of granodiorite porphyry 97.8 ± 0.9 Ma in age and dikes varying in composition. One preore and three types of ore mineralization separated in space are distinguished: quartz–pyrite–arsenopyrite (I), quartz–carbonate–sulfide (II), and silver–base-metal (III). Quartz and carbonate (siderite) are predominant in ore veins. Ore minerals are represented by arsenopyrite, pyrite, sphalerite, galena, fahlore, and less frequent sulfosalts. Three types of fluid inclusions in quartz differ in phase compositions: two- or three-phase aqueous–carbon dioxide (FI I), carbon dioxide gas (FI II), and two-phase (FI III) containing liquid and a gas bubble. The homogenization temperature and salinity fall within the ranges of 367–217°C and 13.8–2.6 wt % NaCl equiv in FI I; 336–126°C and 15.4–0.8 wt % NaCl equiv in FI III. Carbon dioxide in FI II was homogenized in gas at +30.2 to +15.3°C and at +27.2 to 29.0°C in liquid. The δ34S values for minerals of type I range from–1.8 to +4.7‰ (V-CDT); of type II, from–7.4 to +6.6‰; and of type III, from–5.6 to +7.1‰. δ13C and δ18O vary from–7.0 to–6.7‰ (V-PDB) and from +16.6 to +17.1 (V-SMOW) in siderite-I; from–9.1 to–6.9‰ (V-PDB) and from +14.6 to +18.9 (V-SMOW) in siderite-II; from–5.4 to–3.1‰ (V-PDB) and from +14.6 to +19.5 (V-SMOW) in ankerite; and from–4.2 to–2.9‰ (V-PDB) and from +13.5 to +16.8 (V-SMOW) in calcite. The data on mineral assemblages, fluid inclusions, and ratios of stable isotopes allow us to speak about the formation of the Mangazeya deposit in relation to the activity of the hydrothermal–magmatic system. The latter combines emplacement of subvolcanic granitic stocks and involvement of fluids variable in salinity and temperature in ore deposition zone. The fluids released from crystallizing felsic magma and were formed in a convective cell by heating of meteoric and marine waters. The mechanism of ore deposition is related to phase separation (boiling) and mixing of fluids.  相似文献   

5.
Gold mineralization of the Seolhwa mine occurs in a single stage of massive quartz veins which filled the north‐east‐trending fault shear zones in the Jurassic granitoid of 161 Ma within the Gyeonggi Massif. The vein quartz contains three main types of fluid inclusions at 25°C: (i) aqueous type I inclusions (0–15 wt.% NaCl) containing small amounts of CO2; (ii) gas‐rich (more than 70 vol. %), vapor‐homogenizing, aqueous type II inclusions; and (iii) low‐salinity (less than 5 wt.% NaCl), liquid CO2‐bearing, type III inclusions. The H2O‐CO2‐CH4‐N2‐NaCl inclusions represent immiscible fluids trapped earlier along the solvus curve in the temperature range 250–430°C at pressures of ～1 kb. Detailed fluid inclusion chronologies suggest a progressive decrease in pressure during the mineralization. Aqueous inclusion fluids represent either later fluids evolved through extensive fluid unmixing from a homogeneous H2O‐CO2‐CH4‐N2‐NaCl fluid due to decreases in temperature and pressure, or the influence of deep circulated meteoric waters. Initial fluids were homogeneous H2O‐CO2‐CH4‐N2‐NaCl fluids as follows: 250° to 430°C, 16–62 mol% CO2, 5–14 mol% CH4, 0.06–0.31 mol% N2 and salinities of 0.4–4.9 wt.% NaCl. The T‐X data for the Seolhwa mine suggest that the hydrothermal system has been probably located nearer to the granitic melt, which facilitated the CH4 formation and resulted in a reduced fluid state indicated by the predominance of pyrrhotite. Measured and calculated isotopic compositions of the hydrothermal fluids [δ18O = 5.3–6.5‰; δD =?69 to ?84‰] provide evidence of the CH4‐H2O equilibria and further indicate that the auriferous fluids were magmatically derived. Both the dominance of δ34S values of sulfides close to the meteoric reference (?0.6–1.4‰; δ34SΣS values of 0.3–1.1‰) and the available δ13C data (?4‰) are consistent with their deep igneous source. The Seolhwa mine was probably formed by extensive fracturing and veining due to the thermal expansion of water derived from the Jurassic granitoid melt.  相似文献   

6.
The Bairendaba vein-type Ag–Pb–Zn deposit, hosted in a Carboniferous quartz diorite, is one of the largest polymetallic deposits in the southern Great Xing'an Range. Reserves exceeding 8000 tonnes of Ag and 3 million tonnes of Pb?+?Zn with grades of 30 g/t and 4.5% have been estimated. We identify three distinct mineralization stages in this deposit: a barren pre-ore stage (stage 1), a main-ore stage with economic Ag–Pb–Zn mineralization (stage 2), and a post-ore stage with barren mineralization (stage 3). Stage 1 is characterized by abundant arsenopyrite?+?quartz and minor pyrite. Stage 2 is represented by abundant Fe–Zn–Pb–Ag sulphides and is further subdivided into three substages comprising the calcite–polymetallic sulphide stage (substage 1), the fluorite–polymetallic sulphide stage (substage 2), and the quartz–polymetallic sulphide stage (substage 3). Stage 3 involves an assemblage dominated by calcite with variable pyrite, galena, quartz, fluorite, illite, and chlorite. Fluid inclusion analysis and mineral thermometry indicate that the three stages of mineralization were formed at temperatures of 320–350°C, 200–340°C, and 180–240°C, respectively. Stage 1 early mineralization is characterized by low-salinity fluids (5.86–8.81 wt.% NaCl equiv.) with an isotopic signature of magmatic origin (δ18Ofluid = 10.45–10.65‰). The main ore minerals of stage 2 precipitated from aqueous–carbonic fluids (4.34–8.81 wt.% NaCl equiv.). The calculated and measured oxygen and hydrogen isotopic compositions of the ore-forming aqueous fluids (δ18Ofluid = 3.31–8.59‰, δDfluid?=??132.00‰ to??104.00‰) indicate that they were derived from a magmatic source and mixed with meteoric water. Measured and calculated sulphur isotope compositions of hydrothermal fluids (δ34S∑S?=??1.2–3.8‰) indicate that the ore sulphur was derived mainly from a magmatic source. The calculated carbon isotope compositions of hydrothermal fluids (δ13Cfluid?=??26.52‰ to??25.82‰) suggest a possible contribution of carbon sourced from the basement gneisses. The stage 3 late mineralization is dominated (1.40–8.81 wt.% NaCl equiv.) by aqueous fluids. The fluids show lower δ18Ofluid (?16.06‰ to??0.70‰) and higher δDfluid (?90.10‰ to??74.50‰) values, indicating a heated meteoric water signature. The calculated carbon isotope compositions (δ13Cfluid?=??12.82‰ to??6.62‰) of the hydrothermal fluids in stage 3 also suggest a possible contribution of gneiss-sourced carbon. The isotopic compositions and fluid chemistry indicate that the ore mineralization in the Bairendaba deposit was related to Early Cretaceous magmatism.  相似文献   

7.
The Paleoproterozoic terranes (Birimian) of West Africa are well known to host numerous economic gold mineralizations. The Angovia gold mineralization is located in a brecciated and mylonitic zone within the Birimian greenstones. The sulfide–gold mineralization is mainly represented by gold associated with pyrite and chalcopyrite. A fluid inclusion study undertaken on mineralized quartz veins revealed the presence of aqueous-carbonic (CO2–H2O) fluids, the association of carbonic (CO2) and early aqueous fluids, followed by later aqueous (H2O-salt) and finally nitrogen-rich fluids. Entrapment of the initial homogeneous aqueous-carbonic fluids prior to fluid immiscibility depicts the evolution of the P–T conditions during the exhumation of the terranes after the peak of green-schist metamorphism. The CO2 rich-fluid occurs especially in gold-bearing quartz, and are considered as the main evidence of the ore-forming process in the gold-bearing quartz veins. It is considered as a product of immiscibility of the CO2–H2O parent. The volatile fraction of carbonic and aqueous-carbonic fluid inclusions is dominated by CO2, containing minor amounts of N2, even smaller amounts of CH4 and sporadically, H2S. The aqueous-carbonic fluids have moderate salinity (3–10 wt.% eq. NaCl). Late aqueous and N2 – (CH4–CO2) fluids are considered as later, unrelated to the main ore stage, and were trapped during the cooling of the hydrothermal system from 300 to 200 °C.The immiscibility has been favored by a strong pressure drop, the main trapping P–T conditions being 320–370 °C and 105–135 MPa. The mineralizing process is likely related to the immiscibility event, which was probably favored by the release of the fluid pressure after fracturing along the main shear zones. The ore process is likely to have occurred along the main shear zones or related secondary structures affected by cycling of the fluid pressure and quartz sealing–fracturing processes. The superimposed process can also explain the relative complexity of the quartz textures and fluid inclusion microfractures, and the rather wide range in the density of both parent fluid and CO2-dominated fluid.  相似文献   

8.
The differentiated Mesozoic alkali dolerite Prospect Intrusion contains a wide range of secondary minerals, including carbonates (primarily calcite), laumontite, prehnite and heulandite, whose stability relationships imply a formation temperature of <200°C. The δ18O data for carbonates define a higher temperature (160 – 195°C) suite, and a lower temperature (51 – 73°C) suite. The δ13C, δ18O and 87Sr/86Sr isotope systematics for these carbonates suggest derivation of the higher temperature group from magmatic fluids, whereas the other group had a major meteoric component that probably originated from porewater in the country rock. Source fluids for prehnite were meteoric rather than magmatic in origin based on their δD and δ18O ratios. Early in the intrusion's emplacement, CO2-rich hydrothermal fluids formed a carbonate rind sealing the upper part of the hydrothermal system and produced the higher temperature carbonates (calcite) and laumontite. Later, cooler fluids with a meteoric component infiltrated vesicles and fractures, depositing the lower temperature carbonates (calcite, aragonite), heulandite and prehnite.  相似文献   

9.
Fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the Naxos Metamorphic Core Complex (Attic‐Cycladic‐Massif, Greece) were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile/brittle transition. Three sets of quartz veins (V‐M2, V‐BD & V‐B) are distinguished. The V‐M2 and V‐BD are totally or, respectively, partially transposed into the foliation of the leucogneiss. They formed by hydrofracturing alternating with ductile deformation accommodated by crystal‐plastic deformation. The V‐B is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition. Fluids trapped during crystal–plastic deformation comprise two very distinct fluid types, namely a CO2‐rich fluid and a high‐salinity brine, that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively. They were initially trapped at ～625 °C and 400 MPa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end‐members with later trapping conditions of ～350 °C and 140 MPa. In contrast, brittle microcracks contain aqueous fluids trapped at 250 °C and 80 MPa. All veins display a similar δ13C pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history. In contrast, the δD signature is marked by a drastic difference between (i) V‐M2 and V‐BD veins that are dominated by carbonic, aqueous‐carbonic and high‐salinity fluids of metamorphic and magmatic origin characterized by δD between ?56‰ and ?66‰, and (ii) V‐B veins that are dominated by aqueous fluids of meteoric origin characterized by δD between ?40‰ and ?46‰. The retrograde P–T pathway implies that the brittle/ductile transition separates two structurally, chemically and thermally distinct fluid reservoirs, namely (i) the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 °C km?1 at lithostatic pressure, and (ii) the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 °C km?1 at hydrostatic pressure.  相似文献   

10.
Footwall rocks of the northern Snake Range detachment fault (Hampton and Hendry's Creeks) offer exposures of quartzite mylonites (sub-horizontal foliation) that were permeated by surface fluids. An S–C–C′ mylonitic fabric is defined by dynamically recrystallized quartz and mica. Electron backscatter diffraction analyses indicate a strong preferred orientation of quartz that is overprinted by two sets of sub-vertical, ESE and NNE striking fractures. Analyses of sets of three perpendicular thin sections indicate that fluid inclusions (FIs) are arranged according to macroscopic fracture patterns. FIs associated with NNE and ESE-striking fractures coevally trapped unmixed CO2 and H2O-rich fluids at conditions near the critical CO2–H2O solvus, giving minimum trapping conditions of T = 175–200 °C and ∼100 MPa H2O-rich FIs trapped along ESE-trending microcracks in single crystals of quartz may have been trapped at conditions as low as 150 °C and 50 MPa indicating the latest microfracturing and annealing of quartz in an overall extensional system. Results suggest that the upper crust was thin (4–8 km) during FI trapping and had an elevated geotherm (>50 °C/km). Footwall rocks that have been exhumed through the brittle-ductile transition in such extensional systems experience both brittle and crystal-plastic deformation that may allow for circulation of meteoric fluids and grain-scale fluid–rock interactions.  相似文献   

11.
《Resource Geology》2018,68(1):37-50
The large, newly discovered Lijiagou pegmatite spodumene deposit, is located southeast of the Ke'eryin pegmatite ore field, in the central Songpan–Garze Fold Belt (SGFB), Eastern Tibet. The Lijiagou albite spodumene pegmatites are unzoned, granite‐pegmatites of the subtype LCT (Lithium, Cesium, and Tantalum) and consist of medium‐ to coarse‐grained spodumene, lepidolite, microcline, albite, quartz, muscovite, and accessory amounts of beryl, cassiterite, columbite–tantalite and zircon. Secondary fluid inclusions in quartz and spodumene include two‐phase aqueous inclusions (V + L), mono‐phase vapor inclusions (V); three‐phase CO2‐rich CO2–H2O inclusions (CO2 + V + L) and less abundant liquid inclusions (L). The homogenization temperature of the fluid inclusions are low (257.3 to 204.3°C in early stage, 250.3 to 199.6°C in middle stage, 218.7 to 200.6°C in late stage). Fluid inclusions were formed during the long cooling period from the temperature of the pegmatite emplacement. Liquid–vapor–gas boiling was extensive during the middle and late stages. The salinity of the corresponding stages are 15.4 to 13.0 wt.% NaCl equiv., 12.5 to 9.1 wt.% NaCl equiv. and 9.8 to 7.8 wt.% NaCl equiv., respectively. δ18O values of fluid are 7.2 to 5.2‰, 5.6 to 3.9‰ and 2.7 to −0.2‰ from early to late stages; and δD range from −75.1 to −76.8‰, −59.0 to −73.5‰ and −61.6 to −85.5‰ respectively. The δ13C of CO2 values are −5.6 to −6.6‰, −8.5 to −19.9‰, −11.8 to −18.7‰ from early to late stages, suggesting that CO2 in the fluids were probably sourced from a magmatic system, possibly with some mixing of CO2 dissolved in groundwater. δD and δ18O values of fluid indicate that the fluids were originally magmatic water and mixed with some meteoric water in late stage. The magma evolution sequence in the Ke'eryin orefield, from the central two‐mica granite through the Lijiagou deposit out to the distal pegmatites, with the ages gradually decreasing, indicates that the Ke'eryin complex rocks are the product of multistage magmatic activity. The large Lijiagou spodumene deposit is a typical magmatic, fractional crystallization related pegmatite deposit.  相似文献   

12.
Post-Variscan hydrothermal base-metal mineralization of the Taunus ore district, SE Rhenish Massif (Germany), has been studied through combination of stable (S, C, O) and radiogenic (Pb) isotope geochemistry. Based on field and textural observations, five hydrothermal mineralization types can be distinguished. These are (1) tetrahedrite–tennantite bearing quartz–ankerite veins, (2) quartz veins with Pb–Zn–Cu ores, (3) giant quartz veins, (4) metasomatic dolomite in Devonian reef complexes, and (5) calcite–(quartz) mineralization in Devonian reefs. The δ18OV-SMOW quartz values of base-metal veins are in the range of 18.0–21.5‰, whereas those of giant quartz veins have lower values of 15.9–18.6‰. This difference reflects the higher fluid fluxes and smaller extent of rock-buffering for the giant quartz veins. Hydrothermal carbonates from the tetrahedrite and Pb–Zn–Cu veins have variable but distinctly negative δ13CV-PDB values. They can be explained by contributions from fluids that had picked up low δ13CV-PDB carbon via oxidation of organic matter and from fluids that interacted with Devonian reef carbonate having positive δ13CV-PDB. Metasomatic dolomite has positive δ13CV-PDB values that closely reflect those of the precursor limestone. By contrast, carbonates of calcite–(quartz) mineralization have negative δ13CV-PDB values which are negatively correlated with the δ18O values. This pattern is explained by fluid mixing processes where contributions from descending cooler fluids with rather low salinity were dominant. The isotope data suggest that tetrahedrite veins, Pb–Zn–Cu veins, and giant quartz veins formed from fluid mixing involving two end-members with contrasting chemical features. This is supported by fluid inclusion data (Adeyemi, 1982) that show repeated alternation between two different types of fluid inclusions, which are hotter intermediate- to high-salinity NaCl–CaCl2 fluids and cooler low-salinity NaCl-dominated fluids. The metal-rich saline fluids were likely generated at the boundary between the pre-Devonian basement and the overlying Devonian–Carboniferous nappe pile. Fault activation resulted in strong fluid focusing and upward migration of large volumes of hot Na–Ca brines, which mixed with cooler and more dilute fluids at shallower crustal levels. Variable contributions from both fluid types, local fluid fluxes, temperature variations, and variations in pH and oxidation state have then controlled the vein mineralogy and metal inventory.  相似文献   

13.
The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized, temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81), muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite, and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types of C–O–H fluids: CO2-rich, CO2–H2O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H2O–NaCl–CO2 fluids (1,500–5,000 bar, average 3,200) with T htotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H2O–NaCl fluids (140–1,300 bar, average 700) with T htotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility of H2O–NaCl–CO2 fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ34SH2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic source. The calculated and measured oxygen and hydrogen isotope compositions (δ18OH2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous Daebo orogeny.  相似文献   

14.
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.  相似文献   

15.
Homogenization temperatures and salinity data are presented for fluid inclusions from hydrothermal gangue minerals (quartz and fluorite) associated with porphyry wolframite-molybdenite-arsenopyrite-sphaleritebismuth-chalcopyrite-cassiterite mineralization within the Fire Tower ore zone, Mt Pleasant, New Brunswick. The data indicate that ore mineral precipitation occurred within a temperature range of 260° to 490°C from moderate to high salinity (10–42 wt% NaCl equivalent) aqueous fluids. Two stages of hydrothermal activity characterized by high (>30 wt% NaCl equivalent) salinity fluids are recognized; one which occurred at relatively high temperature (350°–490°C); and one which took place at lower temperature (180°–250°C). The high salinity, high temperature stage is interpreted to be the result of resurgent boiling. Dilution of these early fluids by convecting meteoric water resulted in low to moderate salinity fluids, which dominate the inclusion population. The low temperature, high salinity fluid inclusions are interpreted to represent late residual fluids derived from boiling which occurred as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions.  相似文献   

16.
The Wenyu giant gold deposit is hosted in the Precambrian Taihua Supergroup metamorphic rocks within the Xiaoqinling terrane (Qinling Orogen), on the southern margin of the North China Craton. The mineralization can be divided into three stages: quartz–pyrite veins early, quartz–sulfide veins middle (main), and carbonate–quartz veinlets late, with gold being mainly introduced in main stage. Quartz formed in two earlier stages contains three compositional types of fluid inclusions, i.e. pure CO2, CO2–H2O and NaCl–H2O, but the late-stage minerals only contain the NaCl–H2O inclusions. The inclusions in quartz formed in the early, main and late stages yield total homogenization temperatures of 262–417 °C, 236–407 °C and 114–239 °C, respectively, with salinities no higher than 13 wt.% NaCl equiv. Trapping pressures estimated from CO2–H2O inclusions are 139–399 MPa and 111–316 MPa in the early and main stages, corresponding to mineralization depths of 14 km and 11 km, respectively. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ18Owater values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Wenyu gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic–Early Cretaceous continental collision between the North China and Yangtze Cratons.  相似文献   

17.
The Zhaxikang Pb-Zn-Sb deposit is one of the most important deposits in the Southern Tibet metallogenic belt. Based on field geology, petrography, melt- and fluid inclusions and C-H-O isotopes, we describe and discuss the mineralization, alteration, and their possible link with magmatic fluids. Our results show that the Zhaxikang deposit shares many geological and geochemical similarities with typical intermediate-sulfidation (IS) epithermal deposits. The Pb-Zn-Sb mineralization is closely related to Fe-Mn carbonate- and silicic alterations, which formed the outer rim around the greisen in the Cuonadong Dome. Orebodies occur mainly as structurally-controlled veins and breccia dikes, with major minerals include sphalerite, galena, pyrite, arsenopyrite, and Fe-Mn carbonates. Main stage ore-forming fluids were of medium temperature (214–292 °C), low salinity (2.6–5.3 wt.% NaCl eqv.) and CO2-bearing.Melt/fluid inclusions in beryl and quartz from the pegmatite indicate that the primary magmatic fluids were derived from the melt-fluid immiscibility. The magmatic fluids were of low salinity (0.2–7.9 wt.% NaCl eqv.), high temperature (298–457 °C) and CO2-rich, and contained minor CH4, N2, C2H6, C3H8 and C6H6. The presence of Mn-Fe carbonates and daughter gahnite minerals in the beryl-hosted inclusions indicates high Mn, Fe and Zn contents in the parental magma and related magmatic fluids. This implies a genetic link between magmatic fluids and the Pb-Zn-Sb mineralization, as also supported by Ar-Ar dating and H-O-C isotopic evidence. We suggest that the Zhaxikang is best classified as an IS epithermal deposit, and the ore-forming fluids are likely to be magma-derived. Boiling of the magmatic fluids led to high-salinity fluids and metal enrichment. High regional geothermal gradient caused by the thermal doming event may have facilitated long distance transportation of magmatic fluids, and led to the formation of a wide alteration zone and distal Pb-Zn-Sb mineralization. The temperature drop and meteoric water involvement may have precipitated the Pb-Zn-Sn minerals in the distal fault systems.  相似文献   

18.
The Okrouhlá Radouň shear zone hosted uranium deposit is developed along the contact of Variscan granites and high-grade metasedimentary rocks of the Moldanubian Zone of the Bohemian Massif. The pre-ore pervasive alteration of wall rocks is characterized by chloritization of mafic minerals, followed by albitization of feldspars and dissolution of quartz giving rise to episyenites. The subsequent fluid circulation led to precipitation of disseminated uraninite and coffinite, and later on, post-ore quartz and carbonate mineralization containing base metal sulfides. The fluid inclusion and stable isotope data suggest low homogenization temperatures (～50–140 °C during pre-ore albitization and post-ore carbonatization, up to 230 °C during pre-ore chloritization), variable fluid salinities (0–25 wt.% NaCl eq.), low fluid δ18O values (?10 to +2 ‰ V-SMOW), low fluid δ13C values (?9 to ?15 ‰ V-PDB), and highly variable ionic composition of the aqueous fluids (especially Na/Ca, Br/Cl, I/Cl, SO4/Cl, NO3/Cl ratios). The available data suggest participation of three fluid endmembers of primarily surficial origin during alteration and mineralization at the deposit: (1) local meteoric water, (2) Na–Ca–Cl basinal brines or shield brines, (3) SO4–NO3–Cl–(H)CO3 playa-like fluids. Pre-ore albitization was caused by circulation of alkaline, oxidized, and Na-rich playa fluids, whereas basinal/shield brines and meteoric water were more important during the post-ore stage of alteration.  相似文献   

19.
A granite‐related scheelite deposit has been recently discovered in the Wuyi metallogenic belt of southeast China. The veinlet–disseminated scheelite occurs mainly in the inner and outer contact zones of the porphyritic biotite granite, spatially associated with potassic feldspathization and silicification. Re–Os dating of molybdenite intergrowths with scheelite yield a well‐constrained isochron age of 170.4 ± 1.2 Ma, coeval with the LA–MC–ICP–MS concordant zircon age of porphyritic biotite granite (167.6 ± 2.2 Ma), indicating that the Lunwei W deposit was formed in the Middle Jurassic (~170 Ma). We identify three stages of ore formation (from early to late): (I) the quartz–K‐feldspar–scheelite stage; (II) the quartz–polymetallic sulfide stage; and (III) the quartz–carbonate stage. Based on petrographic observations and microthermometric criteria, the fluid inclusions in the scheelite and quartz are determined to be mainly aqueous two‐phase (liquid‐rich and gas‐rich) fluid inclusions, with minor gas‐pure and CO2‐bearing fluid inclusions. Ore‐forming fluids in the Lunwei W deposit show a successive decrease in temperature and salinity from Stage I to Stage III. The homogenization temperature decreases from an average of 299 °C in Stage I, through 251 °C in Stage II, to 212 °C in Stage III, with a corresponding change in salinity from an average of 5.8 wt.%, through 5.2 wt.%, to 3.4 wt.%. The ore‐forming fluids have intermediate to low temperatures and low salinities, belonging to the H2O–NaCl ± CO2 system. The δ18OH2O values vary from 1.8‰ to 3.3‰, and the δDV‐SMOW values vary from –66‰ to –76‰, suggesting that the ore‐forming fluid was primarily of magmatic water mixed with various amounts of meteoric water. Sulfur isotope compositions of sulfides (δ34S ranging from –1.1‰ to +2.4‰) and Re contents in molybdenite (1.45–19.25 µg/g, mean of 8.97 µg/g) indicate that the ore‐forming materials originated mainly in the crust. The primary mechanism for mineral deposition in the Lunwei W deposit was a decrease in temperature and the mixing of magmatic and meteoric water. The Lunwei deposit can be classified as a porphyry‐type scheelite deposit and is a product of widespread tungsten mineralization in South China. We summarize the geological characteristics of typical W deposits (the Xingluokeng, Shangfang, and Lunwei deposits) in the Wuyi metallogenic belt and suggest that porphyry and skarn scheelite deposits should be considered the principal exploration targets in this area.  相似文献   

20.
The Badi copper deposit is located in Shangjiang town, Shangri-La County, Yunnan Province. Tectonically, it belongs to the Sanjiang Block. Vapor–liquid two-phase fluid inclusions, CO2-bearing fluid inclusions, and daughter-bearing inclusions were identified in sulfide-rich quartz veins. Microthermometric and Raman spectroscopy studies revealed their types of ore-forming fluids: (1) low-temperature, low-salinity fluid; (2) medium-temperature, low salinity CO2-bearing; and (3) high-temperature, Fe-rich, high sulfur fugacity. The δ18O values of chalcopyrite-bearing quartz ranged from 4.96‰ to 5.86‰, with an average of 5.40‰. The δD values of ore-forming fluid in equilibrium with the sulfide-bearing quartz were from ? 87‰ to ? 107‰, with an average of ? 97.86‰. These isotopic features indicate that the ore-forming fluid is a mixing fluid between magmatic fluid and meteoric water. The δ34S values of chalcopyrite ranged from 13.3‰ to 15.5‰, with an average of 14.3‰. Sulfur isotope values suggest that the sulfur in the deposit most likely derived from seawater. Various fluid inclusions coexisted in the samples; similar homogenization temperature to different phases suggests that the Badi fluid inclusions might have been captured under a boiling system. Fluid boiling caused by fault activity could be the main reason for the mineral precipitation in the Badi deposit.  相似文献   

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