Application of Lead Isotopes to Geochemical Exploration of Gold Deposits in Baoban,Hainan Province, China

Lead isotopes have been widely applied in geochemical explora tion and evaluation of ore deposits, as well as in ascertaining the age of miner alization and the source of ore fluids. Long-term practice showed that the meth od of lead isotope targeting is somewhat efficient for macroscopic evaluation of forecasting areas, but not powerful enough for forecasting concealed orebodies. As the contents of U and the variation of U/Pb ratio sharply decrease with dept h in the lithosphere, U-Th-Pb isotopic differentiation must have occurred duri ng the crust-mantle evolution. Lead isotopic ratios show a wide variation range , varying in the front of mineralization and shallow-derived ores, but maintain ing very stable in the major orebody and being usually close to the average isot opic composition of the crust and mantle of the continent block from which the o res were derived. Therefore, the lead isotopic composition can serve as a measur e for identifying the position of mineralization. The lead isotope geochemistry was applied to the exploration and evaluation of the Baoban gold deposits of Hai nan Province, China. The analytical results of ore veins and adjacent rocks show ed that there is a correlation between the lead isotope data and the position of orebody. Based on the experience from the Baoban gold deposits and other ore de posits in Yunnan Province, an exploration principle has been established, that i s, positive anomalies of lead isotope eigenvectors for prospecting deep-seated orebodies and negative anomalies of eigenvectors for enlarging lateral explorati on surrounding the known deposit. The ore beds in the Erjia and Beiniu mining di stricts should be assigned to the deep part of the orebody and those in the Tuwa ishan mining district should be the shallow part, so ore beds corresponding to t hose in the Erjia and Beiniu mining districts may be found in the Tuwaishan mini ng district.

Identification and quantification of lead source in sediment in the northern East China Sea using stable lead isotopes

Stable Pb isotopes in surface and core sediments were determined to identify the sources of Pb contaminants in the northern East China Sea(ECS).The Bayesian stable isotope mixing model was used to quantify the contributions of Pb sources.The results show that since the late 1980 s,ratios of^(207)Pb/^(206)Pb and^(208)Pb/^(206)Pb increased in the top 34-cm sediment shown in the coastal core samples,reflecting elevated anthropogenic Pb input in coastal sea.Seaward increase of^(207)Pb/^(206)Pb and^(208)Pb/^(206)Pb ratios in surface sediments reveals that anthropogenic Pb came mainly via atmospheric transmission into the ECS.Anthropogenic sources accounted for 12.0%-21.1%of the total Pb in sediments after the 1990 s.Coal combustion was the largest anthropogenic contributor(47.5%±18.8%),and Pb mining and smelting,cement production,and vehicle exhaust/gasoline contributed 23.2%±7.1%,19.0%±13.0%,and 10.3%±6.9%,respectively.The proportions of the anthropogenic sources gradually increased while geogenic source(riverine sediment)decreased from the coast to the outer shelf.This study demonstrated that the significant influence of atmospheric input of Pb contaminants into the ECS,and also the urgent need to control coal combustion and Pb discharge from industrial dust and fume emission in China.It also highlights the promising application of the Simmr model to quantify the proportions of multiple sources of trace elements in an environment.

Ore-forming material of Dachang tin deposit in Guangxi, China:Lead isotope evidence

For revealing the ore sources of the Dachang tin?polymetallic ore deposit, the lead isotopes were analyzed systematically by using the single minerals of sulphides, including pyrite, pyrrhotite, sphalerite, and galena. Then, the mineral sources and their characteristics were discussed based on the classical lead isotope discriminating model. The results show that the lead isotope ratios of206Pb/204Pb,207Pb/204Pb, and208Pb/204Pb range from 17.478 to 18.638, 15.440 to 15.858, and 37.556 to 39.501, respectively. According to Zartman lead model, the ore lead contains the upper crust composition; however, the granite does not provide all ore leads, and other material sources exist. Obviously, the ore deposit belongs to the result of the combined effect of crust?mantle. The source rocks are characterized by a certain degree of similarity with the island arc material. Moreover, its distant origin in the upper and lower crusts may be related to the subduction island arc material or oceanic crust. The mantle-derived material may have a certain status in the source region. Meanwhile, based on the lead isotope three-dimensional topology projection vectors, the ore leads are concentrated in zoneA, which indicates the characteristics of Yangtze lead isotope province and a possible genetic relationship with Yangtze block.

Lead Isotopic Composition and Lead Source in the Bainiuchang Ag-polymetallic Deposit, Yunnan Province, China

The Bainiuchang deposit in Yunnan Province, China, is located geographically between the Gejiu ore field and the Dulong ore field. In addition to the 〉7000 t Ag reserves, the deposit also boasts of large-scale Pb, Zn and Sn reserves with a lot of dispersed elements （In, Cd, Ge, Ga, etc.）. We have determined systematically the Pb isotope composition of the deposit. The Pb isotope ratios of the ores that are of sea-floor exhalative sedimentary origin in the northwest of the mining district, are 206pb/204pb = 17.758-18.537, 207pb/204pb = 15.175-15.862 and 206pb/204pb = 37.289-39.424, while those of ores that are of magmatic hydrothermal superimposition origin in the southeast of the mining district, are 206pb/204pb = 17.264-18.359, 207pb/204pb = 14.843-15.683 and 208pb/204pb = 36.481-38.838, respectively. In terms of the Pb isotope composition of feldspar in magmatic rocks or magmatic whole- rock samples from the mining district, we have determined the Pb isotope composition and acquired the Pb isotope ratios as： 206pb/204pb -- 18.224-18.700, 207pb/204pb -- 15.595-15.797 and 208pb/204pb -- 38.193-39.608. Then, in the light of the Pb isotope composition of metamorphic rock samples from the Proterozoic basement exposed in the Dulong ore field, we have determined the Pb isotope composition and obtained the isotope ratios as： 206pb/204pb -- 18.434-19.119, 207pb/204pb -- 15.644-15.693, and 208pb/204pb = 38.514-38.832. And the Pb isotope ratios of Cambrian sedimentary rocks, which are exposed in the Bainiuchang mining district, are 206pb/204pb = 18.307-19.206, 207pb/204pb = 15.622-15.809, and 208pb/204pb = 38.436-39.932. By comparing the two types of ores with respect to their Pb isotope compositions, it is indicated that lead in the Bainiuchang deposit was derived largely from the lower-crust granulite which is earlier than Neoproterozoic in age, but the Yanshanian magmatic hydrothermal fluids probably provided a part of ore-forming elements such as Sn for the ore blocks in the south of the mining district.

Lead Isotopic Steep-Dipping Zone and Mineralization—An Example from Mineral Deposits Concentrated Area in East Qinling,China

Lead isotopic geochemical steep-dipping zone usually exists on inhomogeneous boundaries of earth blocks. Its crossing with the geophysical gradient zone often convergently occurs at giant deposits. Deep structures or concealed structural planes obviously have the coupling relationship with the convergent area of mineral deposits. The geochemical steep-dipping zone is usually distributed along the boundary of ancient continental blocks. Its crossing effect with geophysical gradient zone is usually presented as depression or swell of Moho discontinuity on the crossing direction with the ancient continental margin, which would lead to form deep fractures of earth crust at block margins or lead to adjustment of earth crust texture. The deep hydrothermal liquid would rise up along the structural planes to form the convergent areas of mineral deposits. For example, Luonan- Luanchuan area in east Qinling is a typical crossed area of the geochemical steepdipping zone and geophysical gradient zone. The mineral deposit belt extends along EW direction. It was controlled by the geochemical steepdipping zone equidistantly distributed along NE direction like a string of beads controlled by a gravity gradient zone in NE direction and a mantle depression slope. Along a plunging mantle syncline on EW plunging direction, from the east to the west, checkform was distributed which controls synergic crustmantle granoporphyry rocks. Therefore, a convergent mineralization area of Mo, W, Zn and Au giant deposits occurred.

Lead Isotopic Composition and Lead Source of the Huogeqi Cu-Pb-Zn Deposit,Inner Mongolia,China

The Huogeqi orefield located on the northern side of Mt. Langshan, Inner Mongolia occurs in the Middle Proterozoic Langshan Group metamorphic rocks, and the orebodies arc stratiform. In the past twenty years, many Chinese geologists have conducted researches on the Huogeqi Cu-Pb-Zn deposit, but there has been still a controversy on its origin. Some advocate that the deposit is of sedimentary-metamorphic rcworking origin, some hold that it is of sea-floor SEDEX origin, and others have a preference for magmatic superimposition origin. The crux of the controversy is that there is no common understanding about the source of ore-forming materials. In this paper, the Pb isotopic compositions of regional Achaean-Early Proterozoic basement rocks, various types of sedimentary- metamorphic rocks and volcanic rocks in the mining district, Late Proterozoic and Hercynian magmatic rocks arc introduced and compared with the orc-lead composition, so as to constrain the source of the ore lead. The result indicates that （1） sulfides in the ores have homogeneous Pb isotopic compositions, showing a narrow variation range. Their ^206pb/^204pb ratios arc within a range of 17.027- 17.317; ^207Pb/^204pb ratios, 15.451-15.786 and ^208Pb/^204pb ratios, 36.747-37.669; （2） the Pb isotopic compositions of the regional Achaean-Early Proterozoic basement rocks arc characteristic of the old Pb isotopic composition at the early-stage evolution of the Earth, which varies over a wider range, reflecting significant differences in Pb isotopic compositions of the ores. All this indicates that the source of ore lead has no bearing on the basement rocks; （3） the sedimentary-metamorphic rocks in the mining district arc characterized by highly variable and more radiogenic Pb isotopic compositions and their Pb isotopic ratios arc obviously higher than those of ores, demonstrating that ore lead did not result from metamorphic rcworking of these rocks; （4） Pb isotopic compositions of Late Proterozoic diorite-gabbro and Hercynian granite are higher than those of ores. Meanwhile, the Pb isotopic compositions of sulfides in the small-sized strata-penetrating mineralized veinlets formed at later stages arc completely consistent with that of sulfides in stratiform-banded ores, suggesting that these veiniets arc the product of autochthonous rcworking of the stratiform-banded ores during the period of metamorphism and the late magmatic superimposition-mineralization can be excluded; （5） amphibolite, whose protolith is basic volcanic rocks, has the same Pb isotopic compositions as ores, implying that ore lead was derived probably from basic volcanism. So, the source of ore-forming materials for the Huogeqi deposit is like that of the volcanic massive sulfide （VMS） deposits. However, the orebodies do not occur directly within the volcanic rocks, and instead they overlie the volcanic rocks, showing some differences from those typical VMS-type deposits.

Assessment of heavy metal pollution in sediments from Xiangjiang River(China) using sequential extraction and lead isotope analysis

The heavy metal(such as Cr,Ni,Cu,Cd,Pb,and Zn)concentration,speciation,and pollution source in 43 sediment samples from the Xiangjiang River were investigated using sequential extraction combined with Pb isotope analysis.Cu,Cd,Pb,and Zn concentrations are higher than their background values,while Cr and Ni concentrations are close to those.Sequential extraction demonstrates that heavy metals have different fractions,showing different bioavailabilities.The w(206Pb)/w(207Pb)ratio increases with decreasing bioavailability in the order of exchangeable<carbonate≈Fe-Mn oxides≈organic<residual(p<0.05).Wastewater,dust,and slag from mining and smelting areas,and the residual Pb are assumed to be the primary anthropogenic and natural sources of Pb,respectively.The percentages of anthropogenic Pb in the exchangeable,carbonate,Fe-Mn oxides,and organic fractions are(91.5±16.7)%,(61.1±13.9)%,(57.4±11.1)%,and(55.5±11.2)%,respectively,suggesting a significant input of anthropogenic Pb in these four fractions.

Isotopes and Geochronology of the Meixian-type Pb-Zn-(Ag)Deposits,Central Fujian Rift,South China:Implications for Geological Events

Central Fujian Rift is another new and important volcanogenic massive sulfide Pb-Zn polymetallic metallogenetic belt. In order to find out the material genesis and mineralization period of Meixian-type Pb-Zn-Ag deposits, S and Pb isotope analysis and isotope geochronology of ores and wall rocks for five major deposits are discussed. It is concluded that the composition of sulfur isotope from sulfide ore vary slightly in different deposits and the mean value is close to zero with the 834S ranging from -3.5‰ to ＋5.6‰ averaging at ＋2.0‰, which indicates that the sulfur might originate from magma or possibly erupted directly from volcano or was leached from ore-hosted volcanic rock. The lead from ores in most deposits displays radioactive genesis character （206pb/204pb〉18.140, 207Pb/204pb〉15.584, 208pb/204pb〉38.569） and lead isotope values of ores are higher than those of wall rocks, which indicates that the lead was likely leached from the ore-hosted volcanic rocks. Based on isotope data, two significant Pb-Zn metallogenesis are delineated, which are Mid- and Late-Proterozoic sedimentary exhalative metailogenesis （The single zircon U-Pb, Sm-Nd isochronal and Ar-Ar dating ages of ore- hosted wall rocks are calculated to be among 933-1788 Ma.） and Yanshanian magmatic hydrothermal superimposed and alternated metallogenesis （intrusive SHRIMP zircon U-Pb and Rb-Sr isochronal ages between 127-154 Ma）.

Accurate and precise determination of lead isotope composition in selected geochemical reference materials

Lead(Pb)isotopes have been extensively employed in tracing sources of Pb and its transport pathways through the environment.However,Pb isotopic ratios in related geochemical reference materials are scarce.Here,we report high-precision Pb isotopic ratios measured by Nu Plasma II MC-ICP-MS using calibrated ^(205)Tl/^(203)Tl=2.38865(NIST SRM 997)for mass discrimination correction.The long-term external precision(2SD)for NISTSRM 981 of Pb,BCR-2,and BHVO-2 are 0.31‰(n=105),0.42‰(n=11),and 0.25‰(n=5)for ^(208)Pb/ ^(206)Pb and 0.16‰,0.53‰,and 0.07‰for ^(206)Pb/ ^(207)Pb,both respectively,and their Pb isotopic ratios are in excellent agreement with the recommended values.Using this method,we report for the first time Pb isotopic compositions in shale SGR-1b(USGS);coal CLB-1(USGS);stream sediments GSD-17,-21,and-23(IGGE);soils GSS-12,-13,-14,-15,and-16(IGGE);plants GSV-1,-2,and-3(IGGE);and human hair GSH-1(IGGE).

Characterization of Galena and Vein Paragenesis in the Penjom Gold Mine,Malaysia:Trace Elements,Lead Isotope Study and Relationship to Gold Mineralization Episodes

The Penjom Gold Mine is located 30 km from the Bentong-Raub Suture at the western boundary of the Central Belt in Peninsular Malaysia. Gold mineralization hosted within the vein system is associated with pyrite, arsenopyrite, and minor base metals including galena. Trace element and lead isotope analysis was undertaken on nine samples that represent two stages of galena formed during two tectonic events. Both the Pb isotopes and the trace elements show that the first stage galena within the mineralized areas at the footwall has different geochemical characteristics compared with galena in non mineralized areas in the hanging wall, suggesting that galena crystallized from two different ore fluids and probably at two different times. Higher Te, Se and Bi in the galena from the mineralized area may indicate hydrothermal fluids that migrate through the structural conduit and leached out the metal along the pathway that consist of dominant carbonaceous unit. The Pb isotopic ratio composition are transitional between the bulk crustal growth and an upper crustal growth curve, indicating that derivation was from arc rocks associated with continental crust or a crustal source that includes arc volcanic and old continental sedimentary rocks.

Lead isotope signatures of Pb-Zn sulfide mineralization in the Reshian-Lamnian area of Azad Jammu and Kashmir,Pakistan

The Reshian-Lamnian area within the Hazara-Kashmir syntaxis in Pakistan is composed mainly of the rocks of the Salkhala,Panjal and Murree formations.Base metal sulfide mineralization in the form of sphalerite and galena with lesser amounts of chalcopyrite and pyrite is present within the Salkhala Formation of the study area.Chemically all these ore phases are homogeneous in composition.The Pb isotopic composition of galena from the area suggests that there is very little or negligible variation in the ratios of 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb.Modal ages ranging from 509 to 562 Ma and the μ values of 10.71 to 10.93 have been calculated for the studied Pb-Zn mineralization.On the basis of field features,mineralogy and Pb-isotope signatures,it is concluded that the Pb-Zn sulfide mineralization in the Reshian-Lamnia area is pre-Himalayan in age and can be correlated with the Cambro-Ordovician(Pan-African) orogenic event.

Re–Os dating of molybdenite and in-situ Pb isotopes of sulfides from the Lamo Zn–Cu deposit in the Dachang tin-polymetallic ore field, Guangxi, China

The Dachang tin-polymetallic district, Guangxi,China, is one of the largest tin ore fields in the world. Both cassiterite-sulfide and Zn–Cu skarn mineralization are hosted in the Mid-Upper Devonian carbonate-rich sediments adjacent to the underlying Cretaceous Longxianggai granite(91–97 Ma). The Lamo Zn–Cu deposit is a typical skarn deposit in the district and occurs at the contact zone between the Upper Devonian limestone and the granite.The ore minerals mainly consist of sphalerite, arsenopyrite,pyrrhotite, galena, chalcopyrite, and minor molybdenite.However, the age of mineralization and source of the metals are not well constrained. In this study, we use the molybdenite Re–Os dating method and in-situ Pb isotopes of sulfides from the Lamo deposit for the first time in order to directly determine the age of mineralization and the tracing source of metals. Six molybdenite samples yielded a more accurate Re–Os isochron age of 90.0 ± 1.1 Ma(MSWD = 0.72), which is much younger than the reported garnet Sm–Nd isochron age of 95 ± 11 Ma and quartz fluid inclusions Rb–Sr isochron age of 99 ± 6 Ma. This age is also interpreted as the age of Zn–Cu skarn mineralization in the Dachang district. Further, in this study we found that in-situ Pb isotopes of sulfides from the Lamo deposit and feldspars in the district's biotite granite and granitic porphyry dikes have a narrow range and an overlap of Pb isotopic compositions(^(206) Pb/^(204) Pb =18.417–18.594,^(207) Pb/^(204) Pb = 15.641–15.746, and^(208) Pb/^(204) Pb = 38.791–39.073), suggesting that the metals were mainly sourced from Cretaceous granitic magma.

The Background of Regional Lead Isotopic Compositions and Its Application in the Lower and Middle Reaches of the Yangtze River and Neighbouring Areas

The paper systematically deals with the background of regional isotopic compo-sitions in the lower and middle reaches of the Yangtze River and neighbouring areas. It isshown that the lead isotopic compositions of different geological formations and units are con-trolled by the primary mantle heterogeneity, dynamic process of crust-mantle interchange,abundances of uraninm, thorium and lead of various layers of the earth and timing. Studies onthe background of regional isotopic compositions may offer significant information forgeochemical regionalization, tracing of sources of ore-forming materials, and regionalprognosis of ore deposits.

Equilibrium mercury and lead isotope fractionation caused by nuclear volume effects in crystals

To investigate equilibrium mercury(Hg)and lead(Pb)isotope fractionation caused by the nuclear volume effect(NVE)in crystals,the electron densities at nuclei(i.e.,|Ψ(0)|2)for Hg-or Pb-bearing crystalline compounds were investigated by using the relativistic spin orbit zeroth-order regular approximation(ZORA)method with a three-dimensional periodic boundary condition based on the density functional theory(DFT).Many isotope fractionation factors of crystalline compounds are provided for the first time.Our results show,even at1000℃,NVE-driven Hg and Pb isotope fractionation are meaningfully large,i.e.,range from 0.12‰to 0.49‰(202Hg/^(198)Hg),from-0.20‰to 0.17‰(208Pb/^(206)Pb)and from-0.08‰to 0.06‰(207Pb/^(206) Pb)relative to Hg0 vapor and Pb0 vapor,respectively.Specifically,the fractionations range from-0.06‰to-0.20‰(208Pb/^(206)Pb)and from-0.02‰to-0.08‰(207Pb/^(206)Pb)for Pb2+-bearing species,from 0.10‰to 0.17‰(208Pb/^(206)Pb)and from 0.04‰to 0.06‰(207Pb/^(206)Pb)for Pb4+-bearing species in crystals.All calculated Hg-bearing species in crystals will enrich heavier isotope(202Hg)relative to Hg0 vapor.Meanwhile,Pb4+-bearing species enrich heavier Pb isotopes(208Pb and 207Pb)than Pb^(2+)-bearing species in crystals,which the enrichment can be up to 0.37‰(208-Pb/^(206)Pb)and 0.14‰(207Pb/^(206)Pb)at 1000℃,due to their NVEs are in opposite directions.The NVE-driven MIFs of Hg isotopes,which are compared to the Hg202-Hg198baseline,are up to-0.158‰(ΔNV199Hg),-0.024‰(ΔNV200Hg)and-0.094‰(ΔNV201Hg)relative to Hg0 vapor at5000 C.For all studied Hg-bearing species in crystals,the MIFs of two odd-mass isotopes(i.e.,ΔNV199Hg andΔNV201Hg)will be changed proportionally and their ratio(i.e.,ΔNV199Hg/ΔNV201Hg)will be a constant 1.67.The NVE can also cause mass-independent fractionations for 207Pb and 204 Pb compared to the baseline of 208Pb and 206Pb.The largest NVEdriven MIFs are 0.043‰(ΔNV207Pb)and-0.040‰(ΔNV204Pb)among all the studied species relative to Pb0 vapor at 5000 C.The magnitudes of odd-mass isotope MIF(ΔNV207Pb)and even-mass isotope MIF(ΔNV204Pb)are almost the same but with opposite signs,leading to the MIF ratio of them(i.e.,ΔNV207Pb/ΔNV204Pb)is-1.08.

Lead isotope geochemical characteristics of Pb-Zn-Cu deposits on the southwestern margin of Tarim,and their significance

The polymetallic(Pb,Zn,Cu,etc) ore belt on the southwestern margin of Tarim is one of the major regions with the greatest prospecting potential in Xinjiang.Reported in this paper are the lead isotope data for 66 sulfide samples(including 50 galena samples,15 chalcopyrite samples and 1 pyrite sample) collected from such representative deposits as Tamu,Tiekelike,Kalangu,Abalieke,etc.in this ore belt.The Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb in the galena samples range from 17.931 to 18.176,15.609 to 15.818 and 38.197 to 38.944,with the average values of 18.017,15.684 and 38.462,respectively.Those in the chalcopyrite samples range from 17.926 to 18.144,15.598 to 15.628 and 38.171 to 38.583,with the average values of 18.020,15.606 and 38.262,respectively.The pyrite sample has the Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb to be 17.980,15.604 and 38.145,respectively.In combination with the previous Pb isotope data for sulfides,it is found that there is only a slight variation in the Pb isotopic composition of galena,chalcopyrite,sphalerite and pyrite in the ore belt.However,there is some difference in Pb isotopic characteristics between galena and chalcopyrite,especially the Pb isotopic composition of galena shows an obvious linear correlation with some other relevant parameters(e.g.β and γ).The comprehensive analysis suggested that lead in galena(maybe including sphalerite and pyrite) was derived principally from wall rocks and underlying basement,and that in chalcopyrite only originated from the basement.The single-stage model ages of these sulfides couldn't indicate the time limit of metallogenesis(Pb,Zn,Cu,etc.),and the positive linear correlations for the Pb isotopic composition of galena are of no single-stage and two-stage Pb-Pb isochron significance.Furthermore,there are significant differences in Pb isotopic composition characteristics between the genetic type of deposits in this polymetallic ore belt and the Mississippi Valley type(MVT).In addition,the authors also pointed out that there is a phenomenon of differentiation(not paragenesis) for lead and copper elements during the process of metallogenesis in this ore belt.

Lead Isotope Studies of Massive Surphur-Iron-Gold Deposits in the Tongling Area, Anhui Province

Pb isotope ratios and their variation have been measured and explained on ores of massive S-Fe-Au depos-its hosted in the Middle-Upper Carboniferous, on feldspars from diorite bodies closely related tomineralization and on whole rocks from ore-hosting strata (carbonate rocks) in the Tongling area, Anhui Prov-ince. Through a comparison of Pb isotope features of these geological bodies, it has been suggested that oresubstances of the deposits were derived from ore-hosting strata. In the meanwhile, the measurement of ore Pbisotopes of different mineralization types of the same deposit indicates that different mineralization types havedistinct Pb isotope characteristics, showing the potentiality of the Pb isotopic method used in mineral explora-tion.

Isotopic Compositions of Sulfur in the Jinshachang Lead–Zinc Deposit, Yunnan, China, and its Implication on the Formation of Sulfur-Bearing Minerals

The Jinshachang lead-zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan-Yunnan-Guizhou （SYG） Pb-Zn-Ag multi- metal mineralization area in China. Sulfides minerals including sphalerite, galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite, quartz, and barite, making this deposit distinct from most lead-zinc deposits in the SYG. This deposit is controlled by tectonic structures, and most mineralization is located along or near faults zones. Emeishan basalts near the ore district might have contributed to the formation of orebodies. The j34S values of sphalerite, galena, pyrite and barite were estimated to be 3.6‰-13.4‰, 3.7‰-9.0‰, -6.4‰ to 29.2‰ and 32.1‰34.7‰, respectively. In view of the similar δ34S values of barite and sulfates being from the Cambrian strata, the sulfur of barite was likely derived from the Cambrian strata. The homogenization temperatures （T ≈ 134--383℃） of fluid inclusions were not suitable for reducing bacteria, therefore, the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district. Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur, it was not the main mechanism. Considering other aspects, it can be suggested that sulfur of sulfides should have been derived from magmatic activities. The δ34S values of sphalerite were found to be higher than those of coexisting galena. The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions, suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium.

Lead Isotope and Rock Geochemistry of Zaibian Mafic-Ultramafic Rock,Southeast Guizhou Province,China

The Zaibian mafic-ultramafic rock is located in the transitional zone of the Yangtze craton and south China fold system,where is the southwest of Jiangnan orogenic belt(Zeng et al.,2003;Wang et al.,in press).

Lead isotopic systematics for native copper-chalcocite mineralization in basaltic lavas of the Emeishan large igneous province, SW China: Implications for the source of copper

The Emeishan continental flood basalt, which is widespread in Yunnan, Guizhou and Sichuan provinces of Southwest China, is the volcanic product of a Permian mantle plume, and native copper-chalcocite mineralization associated with the basalt is very common in the border area of Yunnan and Guizhou provinces. The mineralization occurred in the tuff intercalation and terrestrial sedimentary rock intercalation which were formed during the main period of basalt eruption. The orebodies are controlled by the stratigraphic position and faults. Metal ore minerals in the ores are mainly native copper, chalcocite and tenorite, with small amounts of chalcopyrite, bomite, pyrite and malachite, and sometimes with large amounts of bitumen, carbon and plant debris. Several decades of ore deposits are distributed in the neighboring areas of the two provinces, while most of them are small-scale deposits or only ore occurrences. By comparing the lead isotopic composition of the ores with that of the wall-rocks, cover and basement rocks of various periods, the source of copper in this type of ore deposits was studied in this paper. The results showed that: (1) The Pb isotopic composition of the ores from ten deposits is absolutely different from that of siliceous-argillaceus rocks of the Upper Permian Xuanwei Formation, limestones of the Lower Permian Series and Carboniferous, Cambrian sandstone-shale and recta-sedimentary rock and dolomite from the upper part of the Meso-Proterozoic Kunyang Group. This indicates that ore lead was derived neither from the cover rock nor from the basement rocks; (2) Although the Neo-Proterozoic Siman dolomite and silicalite, and dolomite in the lower part of the Kunyang Group are similar in Pb isotopic composition to the ores, lead and copper contents in these rocks are very low and they have not made great contributions to copper mineralization; (3) The ores have the same Pb isotopic composition as the basalt, the latter being enriched in copper. These facts indicate that lead and copper were derived from the basalt. According to the regional geological data and the geological-geochemical characteristics of the ore deposits, it is suggested that ore-forming materials were leached out from the basalt. The thickness and buried depth of the basalt and regional tectonic dynamics can affect the formation of large-scale copper deposits. Therefore, exploration for this type of ore deposits should be conducted in the areas from western Yunnan to western Sichuan, where there are developed basalts of great thickness, with extensive tectonic movement and magmatic activity.