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1.
In this paper the authors present the REE concentrations and Sr and Nd isotopic compositions of fluorites from the Bailashui tin deposit of the Furong ore field, southern Hunan Province. The results showed that the total amount of REE in fluorites is usually low, ranging from 0.705 to 8.785 μg/g with the chondrite-normalized REE distribution patterns similar to those of the Qitianling granites in the study area, characterized by LREE-enrichment patterns with pronounced negative Eu anomalies. The fluorites vary in Sr isotopic composition within the range of 0.7083-0.7091, the values are lower than those of the granites and higher than those of the host carbonate rocks in this area. The εNd（t） values of fluorites vary between -9.4 and ＋10.3, revealing that both the crust- and mantle-source materials were involved in the ore-forming hydrothermal fluids. Combined with previous studies on this ore deposit, the Bailashui tin deposit is temporally and spatially closely related with granitic magmatism in this area. The hydrothermal fluorites are the product of fluid/rock interactions between granitic magmatic hydrothermal fluid and marine carbonate rocks. The REE and F in the ore-forming fluid were derived from the granites, whereas Sr in the ore-forming fluid came mainly from the granitic magmatic hydrothermal fluid and marine carbonate rocks, although variations in Sr isotopic composition cannot be explained by a simple mixture of these two end-members. Evidence demonstrated that the ore-forming fluids are of crustal-mantle mixing origin, but that the fluids were probably incompletely homogenized and this may be caused by inhomogeneous mixing of the fluids of different sources.  相似文献   

2.
The Dahutang tungsten polymetallic ore field is located north of the Nanling W-Sn polymetallic metallogenic belt and south of the Middle—Lower Yangtze River Valley Cu-Mo-Au-Fe porphyry-skarn belt.It is a newly discovered ore field,and probably represents the largest tungsten mineralization district in the world.The Shimensi deposit is one of the mineral deposits in the Dahutang ore field,and is associated with Yanshanian granites intruding into a Neoproterozoic granodiorite batholith.On the basis of geologic studies,this paper presents new petrographic,microthermometric,laser Raman spectroscopic and hydrogen and oxygen isotopic studies of fluid inclusions from the Shimensi deposit.The results show that there are three types of fluid inclusions in quartz from various mineralization stages:liquid-rich two-phase fluid inclusions,vapor-rich two-phase fluid inclusions,and three-phase fluid inclusions containing a solid crystal,with the vast majority being liquid-rich two-phase fluid inclusions.In addition,melt and melt-fluid inclusions were also found in quartz from pegmatoid bodies in the margin of the Yanshanian intrusion.The homogenization temperatures of liquid-rich two-phase fluid inclusions in quartz range from 162 to 363℃ and salinities are 0.5wt%-9.5wt%NaCI equivalent.From the early to late mineralization stages,with the decreasing of the homogenization temperature,the salinity also shows a decreasing trend.The ore-forming fluids can be approximated by a NaCl-H_2O fluid system,with small amounts of volatile components including CO_2,CH_4 and N_2,as suggested by Laser Raman spectroscopic analyses.The hydrogen and oxygen isotope data show that δ5D_(V-smow) values of bulk fluid inclusions in quartz from various mineralization stages vary from-63.8‰ to-108.4‰,and the δ~(18)O_(H2O) values calculated from the δ~(18)O_(V-)smow values of quartz vary from-2.28‰ to 7.21‰.These H-O isotopic data are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water in the early stage,and meteoric water was added and participated in mineralization in the late stage.Integrating the geological characteristics and analytical data,we propose that the ore-forming fluids of the Shimensi deposit were mainly derived from Yanshanian granitic magma,the evolution of which resulted in highly differentiated melt,as recorded by melt and melt-fluid inclusions in pegmatoid quartz,and high concentrations of metals in the fluids.Cooling of the ore-forming fluids and mixing with meteoric water may be the key factors that led to mineralization in the Dahutang tungsten polymetallic ore field.  相似文献   

3.
The Anqing Cu-Fe deposit is one of the representative large Cu-Fe deposits along the Yangtze River in Anhui province, with controversial metallogenic mechanism. Based on the ore-forming geological characteristics, this paper focus on the sulfur, carbon and oxygen isotopic compositions of the ores and surrounding rocks, and discuss the sources and evolution processes of the ore-forming materials. The Cu-Fe deposit occurs in the contact zone between the early Yanshanian Yueshan diorite and Triassic marble, with clear horizontal zonings in the skarns and ore bodies. The garnet skarn and thick massive magnetite ore body commonly occur within the external contact zone, which have clear boundaries with the surrounding rocks; whereas the diopside skarns with disseminated copper sulfide commonly occur within the internal contact zone and show gradual and transitional relations with the diorite. The δ34S values of the ores range from -6.5‰ to 10.6‰, and show a V-shaped trend from the diorite to the outer marble. This compositional variation indicates that most of the sulfur may come from magma, with involvement of some pre-Triassic clastic strata sulfur and Triassic marine sulfates in the later stage. The δ13C values of the gangue minerals range from -5.5‰ to 2.0‰, which decrease from the external contact zone to internal contact zone, indicating that the carbons of the ore-forming fluids may be mainly derived from magma, with some Triassic carbonate stratigraphic carbon involved. The marbles nearby the orebody show δ18O values lower than those of the Triassic strata, indicating that they have been remolded by the low δ18O magmatic hydrothermal fluids. The magnetite have some magma filling geological features and extremely low δ18O value, may be the result from the filling of the high temperature iron-rich fluids along the contact zone and fault. This study shows that the ore-magma filling type and hydrothermal-metasomatic type ore bodies coexist in the Anqing Fe-Cu deposit. The immiscibility between iron oxide and silicate melt occurred in magma chamber, which resulted in the formation of iron-rich fluid. The fluid migrated upward and eventually precipitated in a favorable tectonic area or contact zone, and the magnetite ore bodies were formed in the outer contact zone. By the later fluid mixing, filling metasomasis, and water-rock reaction between the differentiated hydrothermal solutions and diorite, the copper ore bodies and the copper-bearing altered diorite were formed in the internal contact zone. © 2018, Science Press. All right reserved.  相似文献   

4.
Located in Alxa Zuoqi (Left Banner) of Inner Mongolia, China, the Zhulazhaga gold deposit is the first largescale gold deposit that was found in the middle-upper Proterozoic strata along the north margin of the North China craton in recent years. It was discovered by the No. l Geophysical and Geochemical Exploration Party of Inner Mongolia as a result of prospecting a geochemical anomaly. By now, over 50 tonnes of gold has been defined, with an average Au grade of 4 g/t. The ore bodies occur in the first lithological unit of the Mesoproterozoic Zhulazhagamaodao Formation (MZF), which is composed mainly of epimetamorphic sandstone and siltstone and partly of volcanic rocks. With high concentration of gold,the first lithological unit of the MZF became the source bed for the late-stage ore formation. Controlled by the interstratal fracture zones, the ore bodies mostly appear along the bedding with occurrence similar to that of the strata. The primitiveore types are predominantly the altered rock type with minor ore belonging to the quartz veins type. There are also some oxidized ore near the surface. The metallic minerals are composed mainly of pyrite, pyrrhotite and arsenopyrite with minor chalcopyrite, galena and limonite. Most gold minerals appear as native gold and electrum. Hydrothermal alterations associated with the ore formation are actinolitization, silicatization, sulfidation and carbonation. A total of 100 two-phase H2O-rich and 7 three-phase daughter crystal-beating inclusions were measured in seven goldbearing quartz samples from the Zhulazhaga gold deposit. The homogenization temperatures of the two-phase H2O-rich inclusions range from 155 to 401℃, with an average temperature of 284℃ and bimodal distributions from 240 to 260℃ and 300 to 320℃ respectively. The salinities of the two-phase H2O-rich inclusions vary from 9.22wt% to 24.30wt% NaCl eqniv, with a mode between 23 wt% and 24wt% NaC1 equiv. Comparatively, the homogenization temperatures of the threephase daughter crystal-beating inclusions vary from 210 to 435℃ and the salinities from 29.13wt% to 32.62wt% NaCl equiv. It indicates that the ore-forming fluid is meso-hypothermal and characterized by high salinity, which is apparently different from the metamorphic origin with low salinity. It suggests a magmatic origin of the gold-bearing fluid. The δ^18O values of quartz from auriferous veins range from 11.9 to 16.3 per mil, and the calculated δ^18OH2O values in equilibrium with quartz vary from 1.06 to 9.60 per mil, which fall between the values of meteoric water and magmatic water. It reflects that the ore-forming fluid may be the product of mixing of meteoric water and magmatic water.Based on geological and geochemical studies of the Zhulazhaga gold deposit, it is supposed that the volcanism in the Mesoproterozoic might make gold pre-concentrate in the strata. The extensive and intensive Hercynian tectono-magmatic activity not only brought along a large number of ore-forming materials, but also made the gold from the strata rework. It can be concluded that the ore bodies were mainly formed in late hydrothermal reworking stage. Compared with typical gold deposits associated with epimetamorphic clastic rocks, the Zhulazhaga deposit has similar features in occurrence of ore bodies, ore-controlling structure, wall-rock alterations and mineral assemblages. Therefore, the Zhulazhaga gold deposit belongs to the epimetamorphic clastic rock type.  相似文献   

5.
The Sin Quyen-Lung Po district is an important Cu metallogenic province in Vietnam, but there are few temporal and genetic constraints on deposits from this belt. Suoi Thau is one of the representative Cu deposits associated with granitic intrusion. The deposit consists of ore bodies in altered granite or along the contact zone between granite and Proterozoic meta-sedimentary rocks. The Cu-bearing intrusion is sub-alkaline I-type granite. It has a zircon U-Pb age of ~776 Ma, and has subduction-related geochemical signatures. Geochemical analysis reveals that the intrusion may be formed by melting of mafic lower crust in a subduction regime. Three stages of alteration and mineralization are identified in the Suoi Thau deposit, i.e., potassic alteration; silicification and Cu mineralization; and phyllic alteration. Two-phase aqueous fluid inclusions in quartz from silicification stage show wide ranges of homogenization temperatures(140–383℃) and salinities(4.18wt%–19.13wt%). The high temperature and high salinity natures of some inclusions are consistent with a magmatic derivation of the fluids, which is also supported by the H-O-S isotopes. Fluids in quartz have δD values of –41.9‰ to –68.8‰. The fluids in isotopic equilibrium with quartz have δ~(18)O values ranging from 7.9‰ to 9.2‰. These values are just plotted in the compositional field of magmatichydrothermal fluids in the δD_(water) versus δ~(18)O_(water) diagram. Sulfide minerals have relatively uniform δ~(34)S values from 1.84‰ to 3.57‰, which is supportive of a magmatic derivation of sulfur. The fluid inclusions with relatively low temperatures and salinities most probably represent variably cooled magmatic-hydrothermal fluids. The magmatic derivation of fluids and the close spatial relationship between Cu ore bodies and intrusion suggest that the Cu mineralization most likely had a genetic association with granite. The Suoi Thau deposit, together with other deposits in the region, may define a Neoproterozoic subduction-related ore-forming belt.  相似文献   

6.
The sediments atop the sequence of ophiolite usually contain Fe(-Mn-Si)exhalites,chemical sediments that aremainlycomposedofamorphousFe-Mn oxy-hydroxides and chert/jasper.They were precipitated from hydrothermal fluids produced by deep leaching of basalt particularly during volcano activity or seafloor spreading.These hydrothermal Fe exhalites provide a good record for the depositional environment and the ocean environment as well.A well-preserved Phanerozoic Fe deposit,Motuosala Fe-Mn deposit,resulted from hydrothermal exhalation,was investigated for its trace element and Fe isotope geochemistry.The deposit is located in Xinjiang province,China and is hosted in a suit of Carboniferous volcano-sedimentary clastic rocks.The Fe deposit is mainly composed of massive hematite Fe oreand banded hematite-jasper ore.The hematite ore/band and jasper band were subjected to be analyzed.They are both composed mainly of Fe2O3 and Si O2,with very low contents of Al2O3 and Ti O2(1%),indicating they werechemical precipitates with little detrital contamination.They both show slightly LREE depleted or near flat PAAS-normalised REE patterns,with positive Eu anomalies and Y anomolies,indicating that they were sourced from a mixture of high-temperature fluids and seawater.Compared to the hematite Fe ore/band,the jasper band shows higher EuSN/EuSN*but lower Y/Ho values.δ56Fe values for the hematite Fe ores are clustered around-0.3‰,similar to those for high-temperature fluids.The jasper samples show heavier Fe isotope compositions varying from-0.1‰to0.5‰,indicating that they were resulted from partial Fe precipitation.For all samples,δ56Fe values are related to Y/Ho and EuSN/EuSN*values.The results indicate that the hematite Fe ore and jasper were deposited in different environments.The jasper was deposited in a more anoxic condition with higher hydrothermal fluids/seawater ratio,probably when the hydrothermal activity was more intense;while the hematite Fe ore was deposited in a more oxic condition with lower hydrothermal fluids/seawater ratio,probably when the hydrothermal activity was weaker.  相似文献   

7.
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.  相似文献   

8.
The Sanshenjiang gold deposit in southeastern Guizhou Province, China, is hosted by the Neoproterozoic metasedimentary rocks which experienced low-grade greenschist facies metamorphism. Gold mineralization occurs mainly in the ribbon chiltern slate of the first member of the Longli Formation and is controlled by both strata and faults. Ore bodies are characterized by abundant quartz-arsenopyrite-gold-pyrite-bedding veins, veinlets and small lenses within the shear zone. In this study, trace element and REE geochemistry was analyzed to constrain the origin and genesis of this deposit. The trace element signatures of wall rocks and veins display a basically similar tendency in the spider diagram, showing the genetic relationship. The values of Co/Ni, Y/Ho, Hf/Sm, Nb/La and Th/La reflect that the hydrothermal fluids of this deposit were derived from the mixture of multiple sources with marked enrichment of Cl and moderate to high temperature. There is a broad similarity in the chondrite-normalized patterns and REE fractionation between wall rocks and ore bodies, possibly reflecting their similar origin. Based on the difference in δCe and δEu, quartz veins and lenses can be subdivided into weakly negative Ce-anomalies (δCe=0.81 to 1.06) with slight Eu anomalies (δEu=0.81 to 1.06) type and the significant positive Ce-anomalies (δCe=1.13 to 1.97) with moderate negative Eu-anomalies type, probably suggesting physical-chemical changes in the evolution process of ore-forming fluids from the early to late stage. It can be concluded that the ore-forming process may have experienced three stages: formation of the original ore source bed, regional metamorphism and gold mineralization, on the basis of trace element and REE analysis and field observation.  相似文献   

9.
It has long been a controversy about the source of ore-forming materials of Au-Ag polymetallic deposits both in metallogenic theory and in ore-searching practice. In terms of a large wealth of the isotopic statistics data from Indosinian-Yanshanian endogenic ore deposits in northern Hebei (generally referring to the areas along the northern part of Taihang Mountains and northern Hebei, the same below) , it is considered that the ore-forming materials came from the deep interior of the Earth, which had migrated through plumes to the Earth surface while ex-perienced multi-stage evolution and then emplaced progressively in favorable structural loci to form ores. Their isotope data show that 559 sulfur isotopic data from 40 ore deposits are, for the most part, within the range of -5‰ -5‰, with a high degree of homogenization, indicating that the sulfur is derived mainly from magma; 200 lead isotope data from 37 ore deposits indi-cate that the ore-forming materials are principally of mantle source though some crust-source ma-terial was involved; 96 oxygen, hydrogen and carbon isotope data from 34 ore deposits illustrate that the ore-forming fluids are dominated by magmatic water while other sources of water would be involved. It may therefore be seen that the formation of endogenic deposits has nothing to do with the strata .  相似文献   

10.
The Yinchanggou-Qiluogou Pb-Zn deposit,located in the western Yangtze Block,southwest China,is hosted by the Upper Sinian Dengying Formation dolostone.Ore bodies occur in the Qiluogou anticline and the NS-and NNW-trending faults.Sulfide ores mainly consist of sphalerite,pyrite,galena and calcite,with subordinate dolomite and quartz.Seventeen ore bodies have been discovered to date and they have a combined 1.0 million tons of sulfide ores with average grades of 2.27wt%Zn and 6.89wt%Pb.The δD_(H2O-SMOW) and δ~(18)O_(H2O-SMOW) values of fluid inclusions in quartz and calcite samples range from-68.9‰ to-48.7‰ and 7.3‰ to 15.9‰,respectively,suggesting that H_2O in the hydrothermal fluids sourced from metamorphic water.Calcite samples have δ~(13)C_(PDB) values ranging from-6.2‰ to-4.1‰ and δ~(18)O_(SMOW) values ranging from 15.1‰ to 17.4‰,indicating C and O in the hydrothermal fluids likely derived from a mixed source of metamorphic fluids and the host carbonates.The δ~(34)S_(CDT) values of sulfide minerals range from 5.5‰ to 20.3‰,suggesting that thermal chemical reduction of sulfate minerals in evaporates were the most probable source of S in the hydrothermal fluids.The ~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios of sulfide minerals fall in the range of 18.11 to 18.40,15.66 to 15.76 and 38.25 to 38.88,respectively.The Pb isotopic data of the studied deposit plot near the upper crust Pb evolution curve and overlap with the age-corrected Proterozoic basement rocks and the Upper Sinian Dengying Formation hosting dolostone.This indicates that the Pb originated from a mixed source of the basement metamorphic rocks and the ore-hosting carbonate rocks.The ore geology and C-H-O-S-Pb isotopic data suggest that the YinchanggouQiluogou deposit is an unusual carbonate-hosted,strata-bound and epigenetic deposit that derived ore-forming materials from a mixed source of the underlying Porterozoic basements and the Sinian hosting carbonates.  相似文献   

11.
More than 140 middle-small sized deposits or minerals are present in the Weishan-Yongping ore concentration area which is located in the southern part of a typical Lanping strike-slip and pull-apart basin. It has plenty of mineral resources derived from the collision between the Indian and Asian plates. The ore-forming fluid system in the Weishan-Yongping ore concentration area can be divided into two subsystems, namely, the Zijinshan subsystem and Gonglang arc subsystem. The ore-forming fluids of Cu, Co deposits in the Gonglang arc fluid subsystem have δD values between −83.8‰ and −69‰, δ18O values between 4.17‰ and 10.45‰, and δ13C values between −13.6‰ and 3.7‰, suggesting that the ore-forming fluids of Cu, Co deposits were derived mainly from magmatic water and partly from formation water. The ore-forming fluids of Au, Pb, Zn, Fe deposits in the Zijinshan subsystem have δD values between −117.4‰ and −76‰, δ18O values between 5.32‰ and 9.56‰, and Δ13C values between −10.07‰ and −1.5‰. The ore-forming fluids of Sb deposits have δD values between −95‰ and −78‰, δ18O values between 4.5‰ and 32.3‰, and Δ13C values between −26.4‰ and −1.9‰. Hence, the ore-forming fluids of the Zijinshan subsystem must have been derived mainly from formation water and partly from magmatic water. Affected by the collision between the Indian and Asian plates, ore-forming fluids in Weishan-Yongping basin migrated considerably from southwest to northeast. At first, the Gonglang arc subsystem with high temperature and high salinity was formed. With the development of the ore-forming fluids, the Zijinshan subsystem with lower temperature and lower salinity was subsequently formed. Translated from Mineral Deposits, 2006, 25(1): 60–70 [译自: 矿床地质]  相似文献   

12.
This paper systematically deals with the geochemical features of major gold deposits in the Shaoxing-Longquan Uplift Zone, Zhejiang Province, including the content and association of ore-forming elements and trace elements, stable isotopic characteristics, the existing forms of gold, and the composition of ore fluids. The authors consider that the ore-bearing formations in this zone are a good supply of necessary elements and ore fluids for the gold deposits in this area. It is also considered that some Au+-Cl− and Au+-HS− or Au+-CO2 coordinated ions are the main transport forms of gold in ore fluids and the metallogenesis of gold involves two stages: formation of pyrite and mineralization of Cu, Pb and Zn. In this paper is also presented a comprehensive geochemical model for the formation of gold deposits in this uplift zone.  相似文献   

13.
Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases were sericitized and theAn values declined rapidly, finally all of them were transformed to albites; dark minerals were gradually replaced by chlorites (mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied from calcite to dolomite and ankerite with the development of deformation. The δ13C values of the carbonates are −3.0‰ – −5.6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume one (f v≈1). With the enhancement of shear deformation, SiO2 in the two mylonite series rocks was depleted, while volatile components suchs as CO2 and H2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of Au in both the mylonite series rocks did not reach the paygrade of gold. The released SiO2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along microfractures, and preciptated auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure of the ore-forming fluids are 245–292°C and 95.4–131.7 MPa respectively; the salinity is 12.88–16.33wt% NaCl; the fluid-phase is rich in Ca2+, K+, Na+, Mg2+, F− and Cl−, while the gaseous phases are rich in CO2 and CH4. The δD and δ18O, values of the ore-forming fluid are −84.48‰ – −91.73‰ and −0.247‰ – +2.715‰ respectively, suggesting that the fluid is composed predominantly of meteoric water. This project is financially supported by the National Natural Science Foundation of China (No. 9488010).  相似文献   

14.
The experimental study of an F-bearing silicic melt—U, Nb, Ta minerals—chloride-fluoride fluid system is focused on ascertaining the origin of uranium deposits spatially related to intraplate silicic volcanism. The first series of experiments on uranium solubility in silicic melts close in composition to ore-bearing rhyolite of the unique Strel’tsovka Mo-U ore field has been performed in order to determine more precisely the ore genesis. As starting solid phases, model homogeneous glass of the chemical composition (wt %) 72.18 SiO2, 12.19 Al2O3, 1.02 FeO, 0.20 MgO, 0.33 CaO, 4.78 Na2O, 3.82 K2O, 1.44 Li2O, and 2.4 F (LiF, NaF, KF, CaF2, MgF2); synthetic UO2 and UO3·0.33H2O; and natural columbite were used. The starting solutions contained 1.0 m Cl and 10−2 m F. The runs were conducted in a gas vessel at a pressure of 1000 bar and in a high-pressure hydrothermal vessel at 2000 bar. The O2 (H2) fugacity was set by Ni-NiO, Co-CoO, Fe3O4-Fe2O3, and Cu-Cu2O buffers. The equilibrium between melt and solution for major elements is reached during the first day, whereas 5–7 days are required for ore elements (U, Nb, Ta) to come into equilibrium. The solubility of Nb and especially Ta in Cl-F solutions equilibrated with F-bearing melt is extremely low. The solubility of U is much higher (10−4−10−5 mol/kg H2O). The energy dispersive spectroscopy of run products allowed us to establish that columbite dissolved incongruently with formation of U- and F-bearing pyrochlores. The performed experiments have shown that a silicic melt close to the rhyolitic magma of the Strel’tsovka caldera in composition is not able to generate postmagmatic ore-forming solutions containing more than 10−6−10−5 mol U/kg H2O under the relatively low pressure necessary for the existence of the first type of fluid. The amount of uranium that could have precipitated from this fluid in the zone of ore deposition is estimated at 216–9000 t. This estimate is two orders of magnitude lower than the total uranium resources of the deposits localized in the Strel’tsovka caldera. Thus, the upper crustal silicic magma chamber hardly was a source of uranium for Mo-U deposits of the Strel’tsovka ore field.  相似文献   

15.
THEJINLONGSHANGOLDOREBELTINZHEN’ANCOUN TY,SOUTHERNSHAANXIPROVINCE,ISLOCATEDINTHEWEST ERNQINLINGGOLDPROVINCE(NO.16INFIG.1;CHEN YANJINGETAL.,2004).ITWASDISCOVEREDINTHEDEVO NIANSTRATAINTHELATE1980S).ITSGEOLOGICALSETTING ANDMETALLOGENICEVOLUTIONARESIMILARTOT…  相似文献   

16.
Gold ore-forming fluids of the Tanami region, Northern Australia   总被引：1，自引：0，他引：1  
Fluid inclusion studies have been carried out on major gold deposits and prospects in the Tanami region to determine the compositions of the associated fluids and the processes responsible for gold mineralization. Pre-ore, milky quartz veins contain only two-phase aqueous inclusions with salinities ≤19 wt% NaCl eq. and homogenization temperatures that range from 110 to 410°C. In contrast, the ore-bearing veins typically contain low to moderate salinity (<14 wt% NaCl eq.), H2O + CO2 ± CH4 ± N2-bearing fluids. The CO2-bearing inclusions coexist with two-phase aqueous inclusions that exhibit a wider range of salinities (≤21 wt% NaCl eq.). Post-ore quartz and carbonate veins contain mainly two-phase aqueous inclusions, with a last generation of aqueous inclusions being very CaCl2-rich. Salinities range from 7 to 33 wt% NaCl eq. and homogenization temperatures vary from 62 to 312°C. Gold deposits in the Tanami region are hosted by carbonaceous or iron-rich sedimentary rocks and/or mafic rocks. They formed over a range of depths at temperatures from 200 to 430°C. The Groundrush deposit formed at the greatest temperatures and depths (260–430°C and ≤11 km), whereas deposits in the Tanami goldfield formed at the lowest temperatures (≥200°C) and at the shallowest depths (1.5–5.6 km). There is also evidence in the Tanami goldfield for late-stage isothermal mixing with higher salinity (≤21 wt% NaCl eq.) fluids at temperatures between 100 and 200°C. Other deposits (e.g., The Granites, Callie, and Coyote) formed at intermediate depths and at temperatures ranging from 240 to 360°C. All ore fluids contained CO2 ± N2 ± CH4, with the more deeply formed deposits being enriched in CH4 and higher level deposits being enriched in CO2. Fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of N2. The one exception is the Tanami goldfield, where the quartz veins were dominated by aqueous inclusions with rare CO2-bearing inclusions. Calculated δ 18O values for the ore fluids range from 3.8 to 8.5‰ and the corresponding δD values range from −89 to −37‰. Measured δ 13C values from CO2 extracted from fluid inclusions ranged from −5.1 to −8.4‰. These data indicate a magmatic or mixed magmatic/metamorphic source for the ore fluids in the Tanami region. Interpretation of the fluid inclusion, alteration, and structural data suggests that mineralization may have occurred via a number of processes. Gold occurs in veins associated with brittle fracturing and other dilational structures, but in the larger deposits, there is also an association with iron-rich rocks or carbonaceous sediments, suggesting that both structural and chemical controls are important. The major mineralization process appears to be boiling/effervescence of a gas-rich fluid, which leads to partitioning of H2S into the vapor phase resulting in gold precipitation. However, some deposits also show evidence of desulfidation by fluid–rock interaction and/or reduction of the ore-fluid by fluid mixing. These latter processes are generally more prevalent in the higher crustal-level deposits.  相似文献   

17.
The Rushan gold deposit, explored in recent years in the Jiaodong area, Shandong Province, is a quartz vein-type gold deposit hosted in granite. The temperature of its major mineralization episode is between 220°C and 280°C. The salinity of the ore-forming fluid is 5 % to 9% NaCl equivalent, with H2O and CO2 as the dominant gas constituents. The fluid is rich in Na+, Ca2+ and Cl−, but relatively impoverished in K+ and F−, characterized by either Ca2+ > Na+ > K+ (in three samples) or Na+ > Ca2+ > K+ (in six samples). Hydrogen and oxygen isotopes in the ore-forming fluid are highly variable with δ18 ranging between − 7.70‰ and 5. 97‰ and between − 128‰ and − 71‰. The possibility of lamprophyre serving as the source of gold can be excluded in view of its low gold content on the order of 2.5 × 10−9. Rb-Sr isochron ages of the deposit and the host Kunyushan granite are ( 104.8 ± 1.5) Ma and 134.6 Ma respectively with the respective initial Sr ratios of 0. 71307 and 0.7096. It is considered that the emplacement of the lamprophyre under a tensile environment had provided sufficient heat energy to facilitate deep circulation of meteoric water by which ore metals were extracted from the Kunyushan granite through long-term water-rock reaction. This project was financially supported by the National Natural Science Foundation of China.  相似文献   

18.
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+, SO42‐, 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.  相似文献   

19.
Summary Telluride-bearing gold deposits of the Pingyi area, western Shandong, China, are located on the southeastern margin of the North China Craton. There are two main types of deposits: (i) mineralized cryptoexplosive breccia, e.g., Guilaizhuang; and (ii) stratified, finely-disseminated mineralization hosted in carbonate rocks, e.g., Lifanggou and Mofanggou deposits. In Guilaizhuang, the cryptoexplosive breccia is formed within rocks of the Tongshi complex and Ordovician dolomite. The mineralization is controlled by an E–W-trending listric fault. Stratified orebodies of the Lifanggou and Mofanggou deposits are placed along a NE-trending, secondary detachment zone. They are hosted within dolomitic limestone, micrite and dolomite of the Early-Middle Cambrian Changqing Group. The mineralization in the ore districts is considered to be related to the Early Jurassic Tongshi magmatic complex that formed in a continental arc setting on the margin of the North China Craton. The host rocks are porphyritic and consist predominantly of medium- to fine-grained diorite and pyroxene (hornblende)-bearing monzonite. SHRIMP U–Pb zircon dating of diorites give a 206Pb/238U weighted mean age of 175.7 ± 3.8 Ma. This is interpreted as representing the crystallization age of the Tongshi magmatic complex. Considering the contact relationships between the magmatic and host sedimentary rocks, as well as the genetic link with the deposits, we conclude that this age is relevant also for the formation of mineralization in the Pingyi area. We hence consider that the deposits formed in the Jurassic. The principal gold minerals are native gold, electrum and calaverite. Wall-rock alteration comprises pyritization, fluoritization, silicification, carbonatization and chloritization. Fluid inclusion studies indicate that all the analyzed inclusions are of two-phase vapor–liquid NaCl–H2O type. Homogenization temperatures of the fluid inclusions vary from 103 °C to 250 °C, and the ice melting temperatures range from −2.5 °C to −13.5 °C, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl equiv. The δ34S values of pyrite associated with gold mineralization exhibit a narrow range of −0.71 to + 2.99‰, implying that the sulfur was probably derived from the mantle and/or dioritic magma. The δ13CPDB values of the fluid inclusions in calcite range from −7.3 to 0.0‰. The δ18OSMOW values of vein quartz and calcite range from 11.5 to 21.5‰, corresponding to δ18Ofluid values of −1.1 to 10.9‰; δD values of the fluid inclusions vary between −70 and −48‰. The isotope data for all three deposits suggest mixing of ore-forming fluids derived from the mantle and/or magma with different types of fluids at shallow levels. Pressure release and boiling of the fluids, as well as fluid-rock interaction (Lifanggou and Mofanggou) and mixing of magmatically-derived fluids with meteoritic waters (Guilaizhuang) played an important role in the ore-forming processes.  相似文献   

20.
Most altered clay minerals in uranium ore deposits in granites in the selected provinces of South China haveδ 18O m values ranging from 6.22 to 7.24,δDm from −60 to −70,δ 18O from +3.05 to −3.07, and from −20.2 to −37.5‰. Relative enrichment of32S in the uranium ore deposits and greater variations in Pb isotopic composition of galenas from them show that uranium ores in the granites were formed in such a way that uranium in shallow-source granites had been mobilized by heated meteoric waters and then migrated to local favourable locations along great faults to form uranium ore deposits. Zhang Shaoli, Yang Wenjin, Tang Chunjing and Xu Wenxin did part of this work.  相似文献   

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