A genetic reinterpretation of the Falun and Åmmeberg ore types,Bergslagen, Sweden

The stratiform sulphide and oxide ores of Bergslagen, south-central Sweden, constitute the largest concentration of base metal and iron ores in northern Europe. They are hosted by Early Proterozoic metamorphosed volcanic and sedimentary successions, which (together with later granitoids) belong to the Svecofennian Domain. An earlier genetic model suggested that two principal types of sulphide ores existed in Bergslagen (Falun and Åmmeberg), which had been formed through two contrasting granitoid-related processes, whereas the iron oxide ores were considered exhalative-volcanogenic. The prevailing view for the Bergslagen ores is that all stratiform sulphide (and oxide) ores were formed by exhalative-volcanogenic processes from one homogenous metal source. In this paper are presented new high-precision determinations of the ore lead isotopic composition of twentytwo stratiform sulphide and oxide ores in Bergslagen (among them Falun, Zinkgruvan-Åmmeberg and Dannemora), in order to provide an improved base for their genesis. The results show that significant variations in metal sources existed in Bergslagen for the volcanogenic ores. Most ores (including the Falun Cu-Zn-Pb deposit) were formed from a major isotopic reservoir that occurs in the interior parts of Bergslagen. This source is defined as the Falun reservoir and is dominated by calcalkaline felsic volcanic rocks. A variable input from a more evolved source component (recycled pre-Svecofennian crustal components) is locally important in sedimentdominated areas, particularly the Stockholm archipelago. A third source, representing relatively primitive metabasalts, influenced the lead isotopic pattern of ores in westernmost Bergslagen. The composition of the Zinkgruvan (Åmmeberg) ore lead is distinctly different from that of the Falun reservoir, but forms, together with other sulphide deposits along the southern margin of Bergslagen, a pronounced linear trend in standard isotope diagrams. The linear trend is interpreted as a mixing line and shows that the lead in these ores were derived partly from evolved and partly from primitive sources. The evolved end member has an isotopic composition, which is comparable with the sediment-dominated sources in the interior parts of Bergslagen and in the Stockholm archipelago. The primitive end member is represented by tholeiitic volcanics, which are more abundant in the southern margin of Bergslagen than elsewhere in Bergslagen. A significant variation with respect to metal sources and depositional environments can thus be recognized for the Bergslagen ores and a renaissance for the genetic concepts Falun and Åmmeberg types is suggested.     

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.     

Some new lead isotope determinations from the proterozoic sulfide ores of central Sweden

Lead isotope determinations were made on galenas from three strata-bound sulfide ores in the early Proterozoic (Svecokarelian) Bergslagen district of central Sweden and four epigenetic deposits in the Älvdalen and Vansbro districts in the early to middle Proterozoic post-Svecokarelian belt. The leads from the strata-bound Bergslagen deposits show exceptional isotopic homogeneity over large areas. Their isotopic composition suggests the existence of a pre-Svecokarelian crust in the district and is consistent with exhalative-sedimentary ore formation in an active continental margin environment. The Vansbro and Älvdalen leads display constant compositions within each district, but marked divergence between the districts. Their compositions preclude derivation exclusively from recycled Svecokarelian lead and suggest a substantial lead contribution from a mantle-like source. The difference between model ages and geologic ages for many of the deposits, with a small but significant excess of radiogenic lead, suggests a significant deviation of the Fennoscandian Shield from conventional global lead evolution models.     

Lead isotope systematics of the giant massive sulphide deposits in the Iberian Pyrite Belt

Lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the Iberian Pyrite Belt, as well as on overlying gossans and associated volcanic rocks. All the massive sulphide deposits (except for Neves-Corvo), and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18.183 (²⁰⁶Pb/²⁰⁴Pb), 15.622 (²⁰⁷Pb/²⁰⁴Pb) and 38.191 (²⁰⁸Pb/²⁰⁴Pb), indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks. The isotopic compositions are representative of the average south Iberian crust during the Devonian to Early Carboniferous (Dinantian), and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems. This isotopic constancy is incompatible with multiple, small, independent hydrothermal cells of the East Pacific Rise type, and fits much better with a model of hydrothermal convections driven by “magmatic floor heating”. Neves-Corvo is the only south Iberian massive sulphide deposit to have a heterogeneous isotopic composition with, in particular, a highly radiogenic stanniferous ore (²⁰⁶Pb/²⁰⁴Pb of the cassiterite is >18.40). A model of lead mixing with three components is proposed to explain these variations: (1) one derived from the Devonian to Early Carboniferous (Dinantian) continental crust that generated all the other massive ores; (2) an Eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides, but independent of them; and (3) a Precambrian continental crust component. The juxtaposition of three different sources places Neves-Corvo in a specific paleogeographic situation that could also explain its mineralogical specificity. The geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism. The fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the Iberian Pyrite Belt.     

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）.     

东天山康古尔金矿床成矿物源的同位素地球化学特征

康古尔金矿床属晚古生代火山岩区剪切带蚀变岩型金矿。同位素地球化学研究表明,矿石中铅为正常铅,热液系统硫同位素组成为陨石硫型,矿石中碳、钕同位素组成具深源特征,同时矿石与火山岩围岩中的Ｓｉ、Ｓｒ、Ｓ、Ｐｂ等同位素组成相近,说明成矿物质主要来自矿体围岩———火山岩,晚期有少量来自矿区附近的侵入岩。铅、锶同位素组成反映成矿过程中也有少量壳源物质的加入。     

Implications of Pb isotope signatures of rocks and iron oxide Cu-Au ores in the Candelaria-Punta del Cobre district,Chile

Lead isotope ratios of ores of the Candelaria-Punta del Cobre iron oxide Cu-Au deposits and associated Early Cretaceous volcanic and batholithic rocks have been determined. For the igneous rocks, a whole-rock acid attack technique based on the separate analyses of a leachate and the residual fraction of a sample was used. The lead isotope systematics of leachate–residue pairs are significantly different for unaltered and altered igneous rocks of the Candelaria-Punta del Cobre district. Residues of unaltered igneous rocks likely represent the common lead. In contrast, residues of all the altered igneous rocks except two samples have higher Pb isotope ratios than those of unaltered magmatic rocks and cannot represent common lead. We suggest that this is a result of the hydrothermal alteration suffered by these rocks and that the common lead composition of the altered igneous (volcanic and plutonic) rocks must have been similar to that of the unaltered batholith rocks. The conclusion that the altered volcanic rocks originally had a similar common lead isotope composition as the batholith is consistent with geological and geochemical arguments (e.g., setting, regional geologic evolution, ages and relative distribution of volcanic and intrusive rocks, magmatic affinities), which indicate that these rocks were derived from similar Early Cretaceous parent magmas. The modification of the leachate–residue pair lead isotope systematics of most altered igneous rocks is consistent with a selective removal of lead and uranium from these rocks by an oxidized hydrothermal fluid. The result of the hydrothermal leaching has been to alter magmatic rocks in a way that (1) their leachable fraction is presently a mix of common lead similar to that of the ore event and of radiogenic lead evolved from a source with a consistently high Th/U, and that (2) their residual fraction has less common lead than unaltered rocks. The outcrop area with altered volcanic rocks displaying anomalously high lead isotope ratios extends over 25 km along the eastern margin of the batholith. Since lead of the ores in the Candelaria-Punta del Cobre district has the same isotopic composition as the common lead of unaltered magmatic rocks of the area, the lead isotope data are consistent with a derivation of the ore lead (and by inference of other metals like Cu) both directly from a magmatic fluid exsolved during crystallization of the batholith and/or from hydrothermal leaching of the volcanic rocks originally having similar isotopic compositions as the batholith.Editorial handling: B. Lehmann     

Brine pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. I. Comparisons with the Iberian pyrite belt

The Ordovician Zn–Pb–Cu massive sulphide ore deposits of the Bathurst mining camp share many features with those of the Devonian/Carboniferous Iberian pyrite belt, particularly the tendency to large size (tonnage and metal content); shape, as far as can be determined after allowing for deformation; metal content, particularly Fe/Cu, Pb/Zn and Sn; mineral assemblages (pyrite + arsenopyrite ± pyrrhotite and lack or rarity of sulphates); sulphide textures (particularly framboidal pyrite); lack of chimney structures and rubble mounds; irregular metal or mineral zoning; and the low degree of zone refining compared to Hokuroku ores. The major differences between the provinces are the lack of vent complexes and the presence of Sn–Cu ores in the Iberian pyrite belt. There are also similarities in the geological setting of the two camps: both lie within continental terranes undergoing arc-continent and continent–continent collision, and in each case massive sulphide mineralisation followed ophiolite obduction; the ore deposits are associated with bimodal volcanic rocks derived from MORB and continental crust and marine shales; and mineralisation was locally accompanied or followed by deposition of iron formations.Fluid inclusion data from veins in stockworks from at least six of the Iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline, ore-forming fluids (brine pools), and it is suggested that most of the major features of the Bathurst deposits can be explained by similar processes. The proposed model is largely independent of ocean sulphate and O₂ content, whereas low values of each are requisites for the current, spreading-plume model of sulphide deposition in the Bathurst camp.     

新疆西天山晚古生代主要磁铁矿床(点)成因类型与成矿过程探讨

新疆西天山晚古生代磁铁矿带是中国重要的铁矿带,其成矿地质背景与成因类型一直以来存在很大的争论.本文在已有研究成果的基础上,结合大量野外调查资料和室内研究工作,对西天山主要磁铁矿床的成因类型、成矿背景、成矿规律进行了详细研究.研究表明,主要磁铁矿床矿石矿物Sr、Nd、Pb同位素基本落入洋陆俯冲碰撞下的岛弧环境;矿石形成年龄介于火山岩与中酸性侵入岩之间,接近于火山岩年龄,矿石与火山岩具有密切的成因联系.矿床总体归为海相火山岩型铁矿,可划分出3个亚类:火山喷溢型、火山-次火山热液型、火山喷溢-热液叠加型,不同亚类矿床具有不同的矿体、矿石特征.铁矿石的形成与俯冲带流体的交代作用有着密切的关系,早期为富铁岩浆交代后分异结晶作用的产物,后期则为火山热液沿断裂、裂隙交代、卸载的产物.     

Lead isotopic systematics for native copperchalcocite 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 sili-ceous-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 iso-topic 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.     

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-Znpolymetallic metailogenetic belt. In order to find out the material genesis and mineralization period ofMeixian-type Pb-Zn-Ag deposits, S and Pb isotope analysis and isotope geochronology of ores and wallrocks for five major deposits are discussed. It is concluded that the composition of sulfur isotope fromsulfide ore vary slightly in different deposits and the mean value is close to zero with the δ34S rangingfrom -3.5‰ to 5.6‰ averaging at 2.0‰, which indicates that the sulfur might originate from magmaor possibly erupted directly from volcano or was leached from ore-hosted volcanic rock. The lead fromores in most deposits displays radioactive genesis character (206Pb/204Pb>18.140, 207Tb/204Pb>15.584,208Pb/204Pb>38.569) and lead isotope values of ores are higher than those of wall rocks, which indicatesthat the lead was likely leached from the ore-hosted volcanic rocks. Based on isotope data, twosignificant Pb-Zn metallogenesis are delineated, which are Mid- and Late-Proterozoic sedimentaryexhalative metallogenesis (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 hydrothermalsuperimposed and alternated metallogenesis (intrusive SHRIMP zircon U-Pb and Rb-Sr isochronalages between 127-154 Ma).     

黔西罐子窑铅锌矿床Pb同位素研究及地质意义

罐子窑铅锌矿床位于川、滇、黔铅锌成矿区东缘,矿体赋存于上泥盆统-下石炭统的白云质灰岩和白云岩中,呈似层状或陡倾斜脉状产出。在分析该矿床成矿地质条件的基础上,系统研究了矿石和围岩的Pb同位素组成特征,探讨了成矿时代与成矿物质来源。研究结果表明,该矿床矿石Pb同位素组成稳定,属于正常普通铅,利用H-H法计算获得了矿脉铅的主模式年龄150~169 Ma。研究表明该矿石Pb模式年龄应该代表矿床成矿年龄,反映Pb主成矿期在燕山期,燕山期NE向断裂(带)控制着本区铅锌矿体(点)的分布。同位素示踪结果显示本区矿石Pb同位素具有多来源特征,不同时代的碳酸盐岩围岩和基底岩石均为罐子窑铅锌矿床提供了成矿物质。综合研究认为,川、滇、黔铅锌成矿区内铅锌成矿具有多阶段、多旋回性,构造与同位素年代学均揭示,该成矿区存在较大规模的燕山期铅锌成矿作用,在今后的找矿研究工作中应当充分重视。     

Origin of a carbonate-hosted Fe-Mn-(Ba-As-Pb-Sb-W) deposit of Långban-type in central Sweden

The Sjögruvan deposit is one of the Långban-type Fe-Mn oxide deposits hosted by marble interbeds within Svecofennian metavolcanic rocks in the Bergslagen region, central Sweden. Mineralogical and geochemical studies have been carried out to clarify the premetamorphic origin of this type of deposit, which is set apart from most other Mn mineralizations by a significant enrichment in Ba, As, Sb, Pb, W and Be contained by various oxyminerals. The principal ore types at Sjögruvan are (1) hematite+quartz-magnetite, (2) hausmannite+calcite+tephroite and (3) braunite+celsian+phlogopite. The Mn ores are compositionally akin to modern Mn deposits formed by submarine hydrothermal processes (with a high Mn/Fe ratio and low contents of Co, Ni, Th, U and REE) and likely owe their existence to similar mechanisms of formation. Pb isotope data indicate that the metal source and timing of deposition is similar to the major stratabound base-metal and iron deposits in Bergslagen. All the key elements have been leached from the local felsic volcanic units and were deposited on the sea floor; the excellent Mn-Fe separation occurred in an Eh-pH gradient that essentially corresponded to the mixing zone of hydrothermal solutions and seawater. The braunite ore is chemically distinct from the hausmannite ore, with a high concentration of refractory elements (Al, Ti, Zr) and a positive Ce anomaly, which indicate a detrital/hydrogenetic contribution to its protolith. Carbon isotope ('¹³C) values around 0‰ (relative PDB) suggest that carbonates in the deposit formed directly from seawater.     

Sulfur, lead and helium isotopic compositions of sulfide minerals from the Dachang Sn-polymetallic ore district in South China: implication for ore genesis

Summary The Dachang Sn-polymetallic ore district is one of the largest tin producing districts in China. Its origin has long been in dispute between magmatic-hydrothermal replacement and submarine exhalative-hydrothermal origin. The Dachang ore district comprises several types of ore deposits, including the Lamo magmatogenic skarn deposit near a granite intrusion, the Changpo-Tongkeng bedded and vein-type sulfide deposit, and the Gaofeng massive sulfide deposit. Sulfide minerals from the Lamo skarn ores show δ³⁴S values in the range between −3 and +4‰ with a mean close to zero, suggesting a major magmatic sulfur source that likely was the intrusive Longxianggai granite. Sulfide minerals from the Gaofeng massive ores show higher δ³⁴S values between +5 and +12‰, whereas sulfide minerals from the Changpo-Tongkeng bedded ores display lighter δ³⁴S values between −7 and −0.2‰. The difference in the sulfur isotope ranges in the two deposits can be interpreted by different degrees of inorganic thermochemcial reduction of marine sulfate using a one-step batch separation fractionation model. Sulfur isotopic compositions from the vein-type ores at Changpo-Tongkeng vary widely from −8 to +4‰, but most of the data cluster around −2.9‰, which is close to that of bedded ores (−3.6‰). The sulfur in vein-type ores might be derived from bedded ores or it represents a mixture of magmatic- and sedimentary-derived sulfur. Pb isotopic compositions of sulfide minerals in the Dachang ore district reveal a difference between massive and bedded ores, with the massive ores displaying more radiogenic Pb isotope ratios. Correlations of ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb or ²⁰⁸Pb/²⁰⁴Pb for the massive and bedded ores are interpreted as two-component mixing of Pb leached from sedimentary host rocks and from deep-seated Precambrian basement rocks composed of metamorphosed volcano-sedimentary rocks. Pb isotopic compositions of sulfide minerals from vein-type ores overlap with those of bedded sulfides. Similar to the sulfur, the lead in vein-type ores might be derived from bedded ores. Skarn ores at Lamo show very limited variations in Pb isotopic compositions, which may reflect a major magmatic-hydrothermal lead source. Helium isotope data of fluid inclusions trapped in sulfides indicate that He in the massive and bedded ores has a different origin than He in fluorite of granite-related veins. The ³He/⁴He ratios of 1.2–2.9 Ra of fluid inclusions from sulfides at Gaofeng and Changpo-Tongkeng imply a contribution of mantle-derived fluids. Overall our data support a submarine exhalative-hydrothermal origin for the massive and bedded ore types at Dachang. Supplementary material to this paper is available in electronic form at Appendix available as electronic supplementary material     

Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China： A Case Study of the Langshan-Zha＇ertaishan Belt, Inner Mongolia, China

Most ore-forming characteristics of the Langshan-Zha‘ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha‘ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical zonation of sulfides; (5) The Cu/(Pb Zn Cu) ratio of the large and thick Pb Zn Cu orebodies gradually decreases from bottom to top; and (6) barite is interbedded with pyrites and sometimes with sphalerite. However, some characteristics such as the Co/Ni radio of the pyrites, the volcanism, for example, of the Langshan-Zha‘ertalshan metallogenic belt, are different from those of the typical SEDEX deposits of the world. The meta-basic volcanic rock in Huogeqi, the sodic bimodal volcanic rocks in the Dongshengmiao and potassic bimodal-volcanic rocks with blastoporphyfitic and blasto-glomeroporphyritic texture as well as blasto-amygdaloidal structure in the Tanyaokou deposits have been discovered in the only ore-bearing second formation of the Langshan Group in the past 10 years. The metallogeny of some deposits hosted in the Langshan Group is closely related to syn-sedimentary volcanism based on the following facts: most of the lead isotopes in sphalerite, galena, pyrite, pyrrhotite and chalcopyrite plot on both sides of the line for the mantle or between the lines for the mantle and lower crust in the lead isotope composition diagram; cobalt content of some pyrites samples is much higher than the nickel content (Co/Ni= 11.91-12.19). Some volcanic blocks and debris have been picked out from some pyritic and pyrrhotitic ores. All Zn-Pb-Cu-Fe sulfide orebodies in these deposits occur in the strata overlying metamorphic volcanic rocks in the only ore-bearing second formation. In the Jiashengpan deposit that lacks syn-sedimentary volcanic rocks in the host succession only Pb and Zn ores occur without Cu ore, but in the Dongshengmiao, Tanyaokou and Huogeqi deposits with syn-sedimentary volcanic rocks in the host succession Cu ores occur. This indicates a relatively higher ore-forming temperature. The process of synsedimentary volcanic eruption directly supplied some ore-forming elements, and resulted in secular geothermal anomaly favorable for the circulation of a submarine convective hydrothermal system, which accounts for the precipitation of deep mineralizing fluids exhaling into anoxidic basins along the syn-sedimentary fault system in the Langshan-Zha‘ertai rift. The Dongshengmiao, Tanyaokou, and Huogeqi deposits hosted in the Langshan Group appear to be a transitional type of mineral deposit between SEDEX and VMS-types but with a bias towards SEDEX, while the Jiashengpan deposit hosted in the Zha‘ertai Group is of a characteristic SEDEX type. This evidence, together with other new discoveries of Mesoproterozoic volcanic rocks and the features of lithogeny and metallogeny of the Bayun Obo deposit in the neighborhood emphasize the diversity, complexity and uniqueness of the Mesoproterozoic Langshan-Zha‘ertal-Bayun Obo ore belt.     

内蒙古狼山—渣尔泰山中元古代被动陆缘热水喷流成矿特征

狼山—渣尔泰山中元古代被动陆缘产有东升庙、炭窑口、霍各乞和甲生盘等热水喷流沉积矿床 ,与世界中元古代的SEDEX型矿集区有许多相似之处 :①矿床的产出受华北古陆北缘裂陷槽内三级断陷盆地控制 ;②各大矿床都具有鲜明的层控特征 ,所有矿体总体呈层产在中元古界的白云石大理岩、碳质千枚岩 (或片岩 )中 ;③矿石具有细纹层状、条带状构造 ,喷流沉积成矿特征十分明显 ;④成矿过程中伴有明显的同生断裂活动 ,它在一定程度上控制了矿体的空间分布及其组合 ;但不同矿床同生断裂活动的强度、时限、规模都不同 ,从而导致不同矿床在相同含矿岩组中矿体产出的先后顺序不同和大量层间砾岩与同生角砾状矿石的形成 ;⑤厚大Zn ,Pb ,Cu复合矿体具有明显的分带性 ,自下至上 ,Cu/ (Zn +Pb +Cu)比值由高→低 ;⑥重晶石层发育 ,多与黄铁矿层互层状产出 ,也有与闪锌矿层互层 ,但与世界典型SEDEX型矿床又有重要差别。成矿期间火山活动明显 ,在霍各乞、东升庙、炭窑口矿床惟一容矿的狼山群第二岩组中先后发现了具有变余斑状或聚斑状结构、变余杏仁构造的基性火山岩、钠质“双峰式”火山岩和钾质“双峰式”海相火山岩及凝灰岩夹层。结合①各种硫化物的铅同位素主要分布在地幔和下地壳铅演化曲线附近 ;②部分黄铁矿的Co/Ni值远     

Lead sources in Mesozoic and Cenozoic Andean ore deposits,north-central Chile (30–34°S)

Mesozoic and Cenozoic ore deposits in the Chilean Andes between La Serena (~30°S) and Santiago (~34°S) include polymetallic vein, low- and high-sulfidation epithermal vein, skarn, porphyry copper-molybdenum and porphyry copper-gold. These deposits are associated with volcanic and plutonic complexes emplaced in eastward-migrating longitudinal arcs which formed during subduction along the continental margin of South America since the Middle Jurassic. Stratabound, but epigenetic, volcanic rock- and sedimentary rock-hosted manto deposits contain additional copper resources. Lead isotopic compositions in ore minerals from 29 deposits vary with age and geographic location, and hence with basement and host rocks. Lead in most ore deposits is derived from temporally related igneous rocks, except for the manto deposits whose lead is derived from host volcanic and sedimentary rock sequences. Lead in the ore deposits is dominated by two crustal sources. Low ²⁰⁷Pb/²⁰⁴Pb characterizes one source whereas high ²⁰⁷Pb/²⁰⁴Pb characterizes the second source. Lead isotopic compositions of Jurassic and Miocene ore minerals (²⁰⁶Pb/²⁰⁴Pb>18.50; ²⁰⁷Pb/²⁰⁴Pb>15.61) lie along the average crustal growth curve. By contrast, most Cretaceous deposits have ore minerals with lower ²⁰⁶Pb/²⁰⁴Pb (<18.39) and ²⁰⁷Pb/²⁰⁴Pb (<15.58) than Jurassic ore minerals. The shift in lead isotopic composition to lower lead isotopic values precludes derivation of lead from a source of similar composition to those in the Jurassic or Tertiary deposits. For Cretaceous deposits, polymetallic and low-sulfidation epithermal veins and a skarn have lower ²⁰⁶Pb/²⁰⁴Pb than a porphyry copper-gold system and peripheral gold veins at Andacollo (18.43-18.50). Late Cretaceous veins from the Bellavista deposit have the lowest ²⁰⁶Pb/²⁰⁴Pb (18.33) of all deposits. Ore minerals in Miocene and Pliocene porphyry copper-molybdenum deposits have higher ²⁰⁶Pb/²⁰⁴Pb (18.58-18.67) than Cretaceous deposits, consistent with their age being younger. The Miocene and Pliocene ore minerals also have higher ²⁰⁷Pb/²⁰⁴Pb (15.58-15.66) than Cretaceous ore minerals, thereby requiring an additional input from the high-²⁰⁷Pb/²⁰⁴Pb source into the younger deposits. Miocene auriferous deposits in the north have similar ²⁰⁶Pb/²⁰⁴Pb values as the Miocene and Pliocene porphyry copper-molybdenum deposits in the south, but they are distinguished by higher and variable ²⁰⁷Pb/²⁰⁴Pb (15.61-15.66) and ²⁰⁸Pb/²⁰⁴Pb (38.54-39.01), which are arrayed along steep mixing trends. These ore minerals have the largest input of high-²⁰⁷Pb/²⁰⁴Pb material in the deposits studied. By contrast, lead in the epigenetic manto deposits appears to be derived from the host volcanic or sedimentary rock-dominated sequences, and locally exhibits large-scale isotopic heterogeneity within a deposit. Overall, the lead isotopic compositions of ore minerals mimic the values and variations established in age-equivalent rock sequences. The low-²⁰⁷Pb/²⁰⁴Pb material in the deposits is derived from Cretaceous igneous rocks or their sources as they evolved with time; low ²⁰⁷Pb/²⁰⁴Pb characterizes these rocks. By contrast, high-²⁰⁷Pb/²⁰⁴Pb material is likely derived from Carboniferous to Triassic igneous rocks or their sources, as this lead isotopic characteristic dominates these rocks.     

深穿透地球化学异常源同位素识别研究:以新疆金窝子金矿床、内蒙古拜仁达坝—维拉斯托多金属矿床为例

通过研究两个已知隐伏矿床(新疆金窝子金矿床、内蒙古拜仁达坝—维拉斯托多金属矿床)不同介质(地气、细粒级土壤、围岩、矿石)中的铅、硫同位素特征,探讨铅、硫同位素对地气、土壤中异常物质来源的示踪,得到以下结论:(1)两矿床的介质从地气、矿石、围岩到土壤,铅同位素比值(208Pb/204Pb、207Pb/204Pb、206Pb/204Pb)一般依次增加;土壤异常区相对土壤背景区,δ34S偏高。但对两个矿床背景区、异常区地气中的铅同位素组成、土壤中的铅、硫同位素组成进行方差分析后发现,数据均没有明显的差异,从统计学的角度初步证明研究区不适宜用铅、硫同位素示踪地气、土壤中异常物质的来源。(2)两个矿床的矿石、围岩中铅同位素组成均有明显差异,即围岩中明显有放射成因铅的积累。但这种差异没有显著地反映到背景区、异常区的地气中,原因有待进一步查证。仅从捕获剂的角度初步探讨了其原因。用土壤全量中铅、硫同位素组成特征来示踪土壤异常源,并没有成功,建议采用偏提取的方法测量其中活动态中的铅、硫同位素组成,在深穿透地球化学研究中更合理。     

Distinctive features of Late Palaeozoic massive sulphide deposits in South China

More than 20 sediment-hosted massive sulphide deposits occur in Late Palaeozoic basins in South China. These deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their Cu, Pb, Zn, Au and Ag reserves. The deposits and their host strata were commonly intruded by Mesozoic granitoids. Remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein-, skarn- and porphyry-type orebodies in the same region or within a single deposit. The ore-containing basins occur in different tectonic settings. The Lower Yangtze basin occurs on a passive continental margin, where the deposits are high in Cu and Au with minor Pb and Zn and recoverable Ag, Co and Mo. The ores have a lower concentration of radiogenic lead, and δ³⁴S values close to zero. Fluid inclusions are highly saline and Na-rich. Fluids and metals of the Lower Yangtze Region are interpreted to have been derived essentially from deep sources including the Precambrian basement. By contrast, basins of the Nanling Region formed in an intracontinental setting developed on a folded Caledonian basement. These deposits are higher in Pb, Zn, Sn and W, as well as Cu, with recoverable Ag, Sb, Hg, U, Bi, Tl and Mo. The ores are characterised by a higher concentration of radiogenic lead and a wide variation of δ³⁴S composition. Fluid inclusions have lower salinities and higher K⁺/Na⁺ ratios. Fluids are considered to have been sourced substantially from seawater by convection. Metals for the Nanling deposits were essentially derived from the Caledonian basement by leaching. The contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore-forming basins.     

黔西北福来厂铅锌矿床Pb同位素研究及地质意义

单阶段演化正常铅用H-H法可获得高准确性的模式年龄,在黔西北福来厂铅锌矿床中采集16件矿脉和围岩样品,测定它们的Pb同位素组成,206 pb/204 Pb为18.5346 ～ 18.7294(均值18.5935),207pb/204 Pb为15.7408～15.7603(均值15.7519),208 pb/204 Pb...