福建永安丰门坑多金属矿地质特征及找矿前景

永安丰门坑多金属矿呈似层状、层状、透镜状,贮存在寒武系林田组下段钙质碎屑岩中,矿床具明显的层控和热液叠加改造特征,为沉积-热液改造型多金属矿床。该多金属矿床的发现,为我省在寒武系林田组中寻找该类矿床提供新的目标。     

国外超大型浅变质细碎屑岩型金矿床的地质特征

国外浅变质碎屑岩型金矿床的含矿岩系以含碳和黄铁矿,夹火山物质和热水沉积物,金含量高为特征.在含矿岩系的沉积、成岩过程中,局部可以形成贫金的含矿层,少数情况下以至于形成金矿体.含矿岩系的变质作用可能形成金矿化,或为后来的成矿作用造成有利的物理和化学环境.岩浆作用为成矿作用提供了部分成矿物质,或为改造成矿作用提供热源和动力.金矿床受构造控制,位于地热正异常区,金矿床的形成与热水沉积成矿作用、变质成矿作用、岩浆期后热液成矿作用和大气降水改造成矿作用等有关.超大型浅变质碎屑岩金矿床的形成过程持续时间长,具有多期多阶段的特点.改造成矿作用在超大型浅变质细碎屑岩型金矿床形成中起重要作用,中生代形成的超大型金矿床中,构造岩浆活化作用叠加十分重要.     

塔里木盆地阿克苏-柯坪地区寒武系-奥陶系的沉积环境

本文讨论了塔里木西北缘厚一千余米的寒武系-奥陶系暗色碳酸盐岩夹细碎屑岩系的沉积环境。寒武系以粉-细晶白云岩、微晶叠层石白云岩夹细碎屑岩为主;奥陶系以含硅粉-细晶白云岩、内碎屑岩、细碎屑岩与灰岩的混合岩互层为主。根据矿物成分、生物化石、结构构造、岩石的元素、稳定同位素、矿物组合等判断,其沉积环境为半封闭的潮坪环境至开阔的陆棚沉积环境。     

老厂海洋山铅锌成矿作用模式

老厂海洋山产于寒琥－奥陶系与泥盆系不整合面之下的铅锌矿床,形成条件复杂,矿床成因独特。研究表明：该区铅锌矿床产于砂页岩古风化壳中由“生物－热卤水”成矿作用形成,成矿作用始于地下水,生物作用矿化预富集期,主要成矿作用发生在热卤水作用矿化叠加富集期。     

内蒙古地区锑矿床特征及成矿规律

通过对内蒙古地区锑矿床地质特征的总结及典型锑矿床地质特征的详细研究，对比中国典型锑矿床控矿因素，从成矿大地构造背景、含矿岩系、控矿构造等方面对该地区锑矿的成矿规律进行初步探讨，认为内蒙古地区锑矿的成因类型可以划分为碎屑岩地层中热液型、火山热液型两种类型；各矿床中含矿岩系多为晚古生代泥盆系至二叠系之间，具有近东西向线性分布的特征；矿（化）体主要受控于近东西向断裂构造带，成矿作用可能与板块碰撞过程中的俯冲增生造山作用有关；滨海相、浅海相、半深海相或海陆交互相沉积环境下的还原条件中形成的暗色细碎屑岩系是赋矿的有利层位；锑矿热液的形成可能与深部偏幔源-幔源的构造岩浆活动有关.     

广西凤凰山银矿床成因探讨

广西隆安县凤凰山银矿床位于寒武系黄洞口组，赋岩矿岩为一套具复理式建造特征的浊流沉积暗色细碎屑岩。矿体受近东西向的断裂破碎带控制。通过地质特征和氢氧、硫、铅同位素地球化学特征及包裹体特征、成矿温度的研究，认为银矿的成矿物质主要来自寒武系地层；成矿温度为低－中浊国。     

青海东昆仑驼路沟钴(金)矿床地质特征--一种新型的与富钠火山岩有关的钴(金)矿床

钴多以伴生金属产出,独立的或以钴为主的工业矿床甚为罕见。我国除吉林南部大横路地区早元古代变质含炭细碎屑岩夹碳酸盐岩地层中的钴矿床和赣西五宝山钴矿床等外,主要也为伴生矿床。     

贵州丹寨县排庭金矿成矿地质条件分析

排庭金矿为贵州三都-丹寨Hg-Au-Sb成矿带内近期新发现,产于中、下寒武统细碎屑岩建造中的微细浸染型金矿床,矿体主要赋存于断裂破碎带及其旁侧构造裂隙中,矿体的产状、形态、规模严格受次级断裂构造控制。矿床在时空上受断裂构造控制明显,该区构造作用贯穿于整个金矿床的形成过程中。     

苏南锶矿成矿作用讨论

近年来在长江中下游的溧水和宁芜火山岩盆地不断发现一些与火山碎屑岩有关的锶矿床和含锶重晶石,本文通过阐述这些矿床的地质特征,分析其成矿作用,为今后火山热液型锶矿的找矿工作提供理论依据。     

青海祁连县红土沟金矿矿床成因

金矿体赋存于碎屑岩系与岩体接触部位构造破碎蚀变带中,成矿作用与超基性岩蚀变作用密切相关,矿床属于受构造破碎蚀变带控制的蛇绿岩中-低温变质热液型金矿床。     

The Talgan massive sulfide deposit, the southern Urals, Russia, as an example of subseafloor ore deposition from magmatic fluid

The sequence of orebody formation at the Talgan massive sulfide deposit; morphology of sulfide orebodies; mineralogy, texture, and structure of ore; chemical composition of minerals; and fluid inclusions and relationships between stable isotopes (S, C, O) in sulfides from ores and carbonate rocks are discussed. The deposit is localized in the Uzel’ga ore field of the northern Magnitogorsk Megazone. The sulfide ore is hosted in the upper felsic sequence of the Middle Devonian Karamalytash Formation, composed of basalt, basaltic andesite, and rhyodacite. Orebodies are irregular lenses lying conformably with host rocks. Pyrite, chalcopyrite, sphalerite, and fahlore are the major ore minerals; galena, bornite, and hematite are of subordinate abundance. Sulfide mineralization bears attributes of deposition under subseafloor conditions. The carbonate and rhyolite interlayers at the roofs of orebodies and the supraore limestone sequence served as screens. Zoning typical of massive sulfide deposits was not established. The study of fluid inclusions has shown that the temperature of the hydrothermal solution varied from 375 to 110°C. δ³⁴S‰ ranges from ?2.4 to +3.2‰ in pyrite, from ?1.2 to +2.8‰ in chalcopyrite, and from ?3.5 to +3.0‰ in sphalerite (CDT). These parameters correspond to an isotopic composition of magmatic sulfur without a notable percentage of sulfate sulfur. δ¹³C and δ¹⁸O of carbonates vary from ?18.1 to +5.9‰ (PDB) and from +13.7 to +27.8‰ (SMOW), respectively. The carbon and oxygen isotopic compositions of carbonates from ores and host rocks markedly deviate from the field of marine carbonates; a deep source of carbon is suggested. The results obtained show that the main mass of polysulfide ore at the Talgan deposit was formed beneath the floor of a paleoocean. The ore-forming system was short-lived and its functioning did not give rise to the formation of zonal orebodies. Magmatic fluid played the leading role in mineral formation.     

S,Pb, and Sr isotope geochemistry and genesis of Pb–Zn mineralization in the Huangshaping polymetallic ore deposit of southern Hunan Province,China

The Huangshaping Pb–Zn–W–Mo polymetallic deposit, located in southern Hunan Province, China, is one of the largest deposits in the region and is unique for its metals combination of Pb–Zn–W–Mo and the occurrence of significant reserves of all these metals. The deposit contains disseminated scheelite and molybdenite within a skarn zone located between Jurassic granitoids and Carboniferous sedimentary carbonate, and sulfide ores located within distal carbonate-hosted stratiform orebodies. The metals and fluids that formed the W–Mo mineralization were derived from granitoids, as indicated by their close spatial and temporal relationships. However, the source of the Pb–Zn mineralization in this deposit remains controversial.Here, we present new sulfur, lead, and strontium isotope data of sulfide minerals (pyrrhotite, sphalerite, galena, and pyrite) from the Pb–Zn mineralization within the deposit, and these data are compared with those of granitoids and sedimentary carbonate in the Huangshaping deposit, thereby providing insights into the genesis of the Pb–Zn mineralization. These data indicate that the sulfide ores from deep levels in the Huangshaping deposit have lower and more consistent δ³⁴S values (− 96 m level: + 4.4‰ to + 6.6‰, n = 13) than sulfides within the shallow part of the deposit (20 m level: + 8.3‰ to + 16.3‰, n = 19). The δ³⁴S values of deep sulfides are compositionally similar to those of magmatic sulfur within southern Hunan Province, whereas the shallower sulfides most likely contain reduced sulfur derived from evaporite sediments. The sulfide ores in the Huangshaping deposit have initial ⁸⁷Sr/⁸⁶Sr ratios (0.707662–0.709846) that lie between the values of granitoids (0.709654–0.718271) and sedimentary carbonate (0.707484–0.708034) in the Huangshaping deposit, but the ratios decreased with time, indicating that the ore-forming fluids were a combination of magmatic and formation-derived fluids, with the influence of the latter increasing over time. The lead isotopic compositions of sulfide ores do not correlate with sulfide type and define a linear trend in a ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram that is distinct from the composition of the disseminated pyrite within sedimentary carbonates and granitoids in the Huangshaping deposit, but is similar to the lead isotopic composition of sulfides within coeval skarn Pb–Zn deposits in southern Hunan Province. In addition, the sulfide ores have old signatures with relative high ²⁰⁷Pb/²⁰⁶Pb ratios, suggesting that the underlying Paleoproterozoic basement within southern Hunan Province may be the source of metals within the Huangshaping deposit.The isotope geochemistry of sulfide ores in the Huangshaping deposit shows a remarkable mixed source of sulfur and ore-forming fluids, and the metals were derived from the basement. These features are not found in representative skarn-type Pb–Zn mineralization located elsewhere. The ore-forming elements (S, Pb, and Zn) from the granitoids made an insignificant contribution to sulfide precipitation in this deposit. However, the emplacement of granitoids did provide large amounts of heat and fluids to the hydrothermal system in this area and extracted metals from the basement rocks, indicating that the Jurassic magmatism associated with the Huangshaping deposit was crucial to the Pb–Zn mineralization.     

云南白牛厂矿区古生代沉积盆地的成矿流体系统

白牛厂矿区发育在多旋回演化的裂谷盆地之中 ,超大型银多金属矿床由中寒武世海底喷溢沉积作用形成。海底热液来源于裂谷盆地沉积物中超高压流体 ,热液属于富含 K+、SO2 -4的卤水 ,w ( Zn) /w ( Zn+Pb) <0 .7,与世界超大型 SEDEX矿床特征相似。滇东南下寒武统可能为重要的矿源层 ,该区具有良好的找矿前景     

The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion- and wall rock-hosted Cu–Fe–Au, Mo, Zn, Pb, Ag deposits

The lower valley of Changjiang, from Wuhan of the Hubei Province in the west to Zhenjiang of the Jiangsu Province in the east, contains more than 200 polymetallic (Cu–Fe–Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts in China. This metallogenic belt, situated at the northern margin of the Yangzi craton and bordered by the Dabieshan ultrahigh pressure metamorphic belt to the north, consists mainly of Cambrian–Triassic marine clastic sedimentary rocks and carbonate and evaporite rocks, which overlay a Precambrian basement and are intruded by Yanshanian (205 to 64 Ma) granitoid intrusions and subvolcanic complexes. Repeated tectonism from Late Proterozoic to Triassic resulted in extensively developed networks of faults and folds involving the Cambrian–Triassic sedimentary strata and the Precambrian basement. The Yanshanian granitoid intrusions and subvolcanic complexes in the Lower Changjiang metallogenic belt are characterized by whole-rock δ¹⁸O of +8‰ to +10‰, initial ⁸⁷Sr/⁸⁶Sr of 0.704 to 0.708, and εNd^t from −10 to −17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials. Also, the Yanshanian granitoids exhibit eastward younging and increase in alkalinity (i.e., from older calc–alkaline in the west to younger subalkaline–alkaline in the east), which are related to oblique collision between the Yangzi and Sino-Korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes. Most polymetallic deposits in the Lower Changjiang metallogenic belt are clustered in seven districts where the Yanshanian magmatism is particularly extensive: from west to east, Edong, Jiurui, Anqing–Guichi, Luzhong, Tongling, Ningwu and Ningzhen. Mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits: orebodies in Yanshanian granitoid intrusions, skarn orebodies at the contact zones between the Yanshanian intrusions and Late Paleozoic–Early Mesozoic sedimentary rocks, and stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata. The most important host sedimentary strata are the Middle Carboniferous Huanglong Formation, Lower Permian and Lower–Middle Triassic carbonate and evaporite rocks. The intrusion-hosted and skarn orebodies exhibit well-developed zonation in alteration assemblages, metal contents, and isotopic compositions within individual deposits, and apparently formed from hydrothermal activities related to the Yanshanian magmatism. The stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano-sedimentary exhalative processes in shallow marine environments. However, extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization. On the basis of geological relationships and isotope geochemical characteristics, we propose a carbonate-hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies. This model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the Yanshanian intrusions with carbonate and evaporite wall rocks. Mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion-hosted orebodies. The stratabound massive sulfide deposits of the Lower Changjiang metallogenic belt share many features with the well-studied, high-temperature, carbonate-hosted replacement deposits of northern Mexico and western United States, particularly with respect to association with small, shallow granitoid complexes, structural and stratigraphic controls on mineralization, alteration assemblages, geometry of orebodies, metal association, metal zonation and isotopic systematics.     

Sulphur and Lead Isotope Compositions of the Dajiangp—ing Deposit in Western Guangdong Province1

Abstract The Dajiangping pyrite deposit located in the middle sector of the Yunkai uplift in western Guangdong is a stratiform sulphide deposit occurring in Sinian marine clastic and fine clastic rocks. The formation of the deposit was related to submarine exhalation and hot brine deposition. A part of it was reformed by late-stage hydro thermal solution. The δ³⁴S values of pyrite vary from — 25.55‰ to + 21.07‰, which are inversely proportional to the content of organic carbon in ore and pyrite. Passing from striped fine-grained pyrite ore to massive coarse-grained pyrite ore, i.e. from south to north, the sulphur isotopic composition changes from the light sulphur-enriched one to the heavy sulphur-enriched one. The lead isotopic composition of striped ore is consistent with that of the country locks of orebodies and the lead is radiogenic lead derived from the upper crust. The lead isotopic composition of massive ore is relatively homogeneous and its ²⁰⁶/Pb²⁰⁴Pb, ²⁰⁷/Pb²⁰⁴Pb and ²⁰⁸/Pb²⁰⁴Pb ratios are a bit lower than those of striped ore; the lead result from mixing of synsedimentary ore lead with that derived from basement migmatite brought by late-stage hydrothermal solutions.     

Porphyry-Style Petropavlovskoe Gold Deposit,the Polar Urals: Geological Position,Mineralogy, and Formation Conditions

Geological and structural conditions of localization, hydrothermal metasomatic alteration, and mineralization of the Petropavlovskoe gold deposit (Novogodnenskoe ore field) situated in the northern part of the Lesser Ural volcanic–plutonic belt, which is a constituent of the Middle Paleozoic island-arc system of the Polar Urals, are discussed. The porphyritic diorite bodies pertaining to the late phase of the intrusive Sob Complex play an ore-controlling role. The large-volume orebodies are related to the upper parts of these intrusions. Two types of stringer–disseminated ores have been revealed: (1) predominant gold-sulfide and (2) superimposed low-sulfide–gold–quartz ore markedly enriched in Au. Taken together, they make up complicated flattened isometric orebodies transitory to linear stockworks. The gold potential of the deposit is controlled by pyrite–(chlorite)–albite metasomatic rock of the main productive stage, which mainly develops in a volcanic–sedimentary sequence especially close to the contacts with porphyritic diorite. The relationships between intrusive and subvolcanic bodies and dating of individual zircon crystals corroborate a multistage evolution of the ore field, which predetermines its complex hydrothermal history. Magmatic activity of mature island-arc plagiogranite of the Sob Complex and monzonite of the Kongor Complex initiated development of skarn and beresite alterations accompanied by crystallization of hydrothermal sulfides. In the Early Devonian, due to emplacement of the Sob Complex at a depth of approximately 2 km, skarn magnetite ore with subordinate sulfides was formed. At the onset of the Middle Devonian, the large-volume gold porphyry Au–Ag–Te–W ± Mo,Cu stockworks related to quartz diorite porphyry—the final phase of the Sob Complex— were formed. In the Late Devonian, a part of sulfide mineralization was redistributed with the formation of linear low-sulfide quartz vein zones. Isotopic geochemical study has shown that the ore is deposited from reduced, substantially magmatic fluid, which is characterized by close to mantle values δ³⁴S = 0 ± 1‰, δ¹³C =–6 to–7‰, and δ¹⁸O = +5‰ as the temperature decreases from 420–300°C (gold–sulfide ore) to 250–130°C (gold–(sulfide)–quartz ore) and pressure decreases from 0.8 to 0.3 kbar. According to the data of microanalysis (EPMA and LA-ICP-MS), the main trace elements in pyrite of gold orebodies are represented by Co (up to 2.52 wt %), As (up to 0.70 wt %), and Ni (up to 0.38 wt %); Te, Se, Ag, Au, Bi, Sb, and Sn also occur. Pyrite of the early assemblages is characterized by high Co, Te, Au, and Bi contents, whereas the late pyrite is distinguished by elevated concentrations of As (up to 0.7 wt %), Ni (up to 0.38 wt %), Se (223 ppm), Ag (up to 111 ppm), and Sn (4.4 ppm). The minimal Au content in pyrite of the late quartz–carbonate assemblage is up to 1.7 ppm and geometric average is 0.3 ppm. The significant correlation between Au and As (furthermore, negative–0.6) in pyrite from ore of the Petropavlovskoe deposit is recorded only for the gold–sulfide assemblage, whereas it is not established for other assemblages. Pyrite with higher As concentration (up to 0.7 wt %) is distinguished only for the Au–Te mineral assemblage. Taking into account structural–morphological and mineralogical–geochemical features, the ore–magmatic system of the Petropavlovskoe deposit is referred to as gold porphyry style. Among the main criteria of such typification are the spatial association of orebodies with bodies of subvolcanic porphyry-like intrusive phases at the roof of large multiphase pluton; the stockwork-like morphology of gold orebodies; 3D character of ore–alteration zoning and distribution of ore components; geochemical association of gold with Ag, W, Mo, Cu, As, Te, and Bi; and predominant finely dispersed submicroscopic gold in ore.     

Unique Origin of Skarn at the Ohori Base Metal Deposit,Yamagata Prefecture,NE Japan: C,O and S Isotopic Study

The Ohori ore deposit is one of the Cu–Pb–Zn deposits in the Green Tuff region, NE Japan, and consists of skarn‐type (Kaninomata) and vein‐type (Nakanomata) orebodies. The former has a unique origin because its original calcareous rocks were made by hydrothermal precipitation during Miocene submarine volcanism. Carbon and oxygen isotope ratios of skarn calcite and sulfur isotope ratios of sulfides were measured in and around the deposit. Carbon and oxygen isotope ratios of the skarn calcite are δ¹³C = ?15.51 to ?5.1‰, δ¹⁸O = +3.6 to +22.5‰. δ¹³C values are slightly lower than those of the Cretaceous skarn deposits in Japan. These isotope ratios of the Kaninomata skarn show that the original calcareous rocks resemble the present submarine hydrothermal carbonates at the CLAM Site, Okinawa Trough, than Cenozoic limestones, even though some isotopic shifts had occurred during later skarnization. δ³⁴S ratios of the sulfide minerals from the Kaninomata and Nakanomata orebodies are mostly in a narrow range of +4.0 to +7.0‰ and they resemble each other, suggesting the same sulfur origin for the both deposits. The magnetite‐series Tertiary Kaninomatasawa granite is distributed just beneath the skarn layer and has δ³⁴S ratios of +7.5 to 8.1‰. The heavy sulfur isotope ratio of the skarn sulfides may have been affected by the Kaninomatasawa granite.     

Genesis of the Weiquan Ag–Polymetallic Deposit in East Tianshan, China: Evidence from Zircon U–Pb Geochronology and C–H–O–S–Pb Isotope Systematics

The Weiquan Ag-polymetallic deposit is located on the southern margin of the Central Asian Orogenic Belt and in the western segment of the Aqishan-Yamansu arc belt in East Tianshan,northwestern China. Its orebodies, controlled by faults, occur in the lower Carboniferous volcanosedimentary rocks of the Yamansu Formation as irregular veins and lenses. Four stages of mineralization have been recognized on the basis of mineral assemblages, ore fabrics, and crosscutting relationships among the ore veins. Stage I is the skarn stage(garnet + pyroxene), Stage Ⅱ is the retrograde alteration stage(epidote + chlorite + magnetite ± hematite 士 actinolite ± quartz),Stage Ⅲ is the sulfide stage(Ag and Bi minerals + pyrite + chalcopyrite + galena + sphalerite + quartz ± calcite ± tetrahedrite),and Stage IV is the carbonate stage(quartz + calcite ± pyrite). Skarnization,silicification, carbonatization,epidotization,chloritization, sericitization, and actinolitization are the principal types of hydrothermal alteration. LAICP-MS U-Pb dating yielded ages of 326.5±4.5 and 298.5±1.5 Ma for zircons from the tuff and diorite porphyry, respectively. Given that the tuff is wall rock and that the orebodies are cut by a late diorite porphyry dike, the ages of the tuff and the diorite porphyry provide lower and upper time limits on the age of ore formation. The δ~(13)C values of the calcite samples range from-2.5‰ to 2.3‰, the δ~(18)O_(H2 O) and δD_(VSMOW) values of the sulfide stage(Stage Ⅲ) vary from 1.1‰ to 5.2‰ and-111.7‰ to-66.1‰, respectively,and the δ~(13)C, δ~(18)O_(H2 O) and δD_(V-SMOW) values of calcite in one Stage IV sample are 1.5‰,-0.3‰, and-115.6‰, respectively. Carbon, hydrogen, and oxygen isotopic compositions indicate that the ore-forming fluids evolved gradually from magmatic to meteoric sources. The δ~(34)S_(V-CDT) values of the sulfides have a large range from-6.9‰ to 1.4‰, with an average of-2.2‰, indicating a magmatic source, possibly with sedimentary contributions. The ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of the sulfides are 17.9848-18.2785,15.5188-15.6536, and 37.8125-38.4650, respectively, and one whole-rock sample at Weiquan yields~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of 18.2060, 15.5674, and 38.0511,respectively. Lead isotopic systems suggest that the ore-forming materials of the Weiquan deposit were derived from a mixed source involving mantle and crustal components. Based on geological features, zircon U-Pb dating, and C-H-OS-Pb isotopic data, it can be concluded that the Weiquan polymetallic deposit is a skarn type that formed in a tectonic setting spanning a period from subduction to post-collision. The ore materials were sourced from magmatic ore-forming fluids that mixed with components derived from host rocks during their ascent, and a gradual mixing with meteoric water took place in the later stages.     

新疆火烧云超大型非硫化物铅锌矿床:发生表生氧化的密西西比河谷型矿床

火烧云矿床是我国新发现具有超大型规模的非硫化物铅锌矿床,成因倍受关注.矿床主要由菱锌矿和白铅矿组成,形成块状及少量纹层状和角砾状矿石,构成了层状矿体.赋矿围岩为中侏罗统含沉积石膏的台地相碳酸盐岩,为密西西比河谷型矿床的典型赋矿围岩,而非喷流沉积型矿床的赋矿围岩.矿石中普遍出现被白铅矿交代的方铅矿残留,表明原生矿化为硫化物.方铅矿δ34SV-CDT值为-34‰^-18‰,显示还原硫的来源与细菌还原作用作用有关,这在MVT矿床中较为常见,而在与岩浆作用有关的铅锌矿床中少见.同时,矿床也不具有与岩浆有关的热液矿化和蚀变特征,故矿床的原生硫化物矿化应为MVT型.通过菱锌矿和白铅矿的O同位素组成,计算出形成这两种矿物的流体具有低温、低δ18O值的大气降水的特征,结合白铅矿交代方铅矿的这一现象,表明目前观察到的由菱锌矿和白铅矿构成铅锌矿体系是在表生作用下直接交代原生硫化物矿体形成.     

Sulfide saturation mechanism of the Poyi magmatic Cu-Ni sulfide deposit in Beishan,Xinjiang, Northwest China

The Poyi Cu-Ni deposit is hosted by the Early Permian Pobei mafic-ultramafic complex along the northern margin of the Tarim Plate. This series of multiple intrusions in the Poyi deposit can be divided into four lithologies: gabbro, dunite, hornblende peridotite, and wehrlite. The ore body consists mainly of disseminated sulfides hosted by hornblende peridotite. All the Poyi deposit sulfides show positive Δ³³S values from 0.004 to 0.221‰ and negative δ³⁴S values from −0.8 to −3.5‰. High Ni contents occur in the hornblende peridotites, which exhibit the highest Δ³³S value of 0.221‰ and the lowest δ³⁴S value of −3.5‰, indicating contamination by sulfides from Archean sedimentary rocks. This contamination was important during sulfide saturation in the Poyi intrusions and likely occurred at depth before the emplacement of the Poyi intrusions. The intrusions incorporated country rocks during their emplacement and consolidation, and the degree of assimilation increases from the central lithofacies (i.e., the hornblende peridotite) to the marginal lithofacies (i.e., the wehrlite, dunite, olivine gabbro, and gabbro). Higher Ni contents are correlated with lower degrees of contamination; thus, we infer that the contamination by the country Paleoproterozoic rocks, which contain significant amounts of gneiss and marble, hindered sulfide saturation.The whole-rock Ni content is negatively correlated with the MgO and Fo contents in the olivine and positively correlated with the FeO and MnO contents in the olivine. During crystallization, olivine becomes gradually richer in FeO but poorer in MgO, and Mn tends to be enriched in the late stages of the melt. We infer that the fractional crystallization of olivine was an important factor during sulfide saturation.