研究生知识库

处于扬子地块西南缘右江盆地中的诸多卡林型金矿床主要集中分布在云南、贵州和广西三省交界处，为我国重要的金矿产地、世界第二大卡林型金矿矿集区。右江盆地卡林金矿又可分为以不纯碳酸盐岩为主要容矿岩石的台地相金矿 （Platform-type CTGDs，简称P-CTGDs）和以陆源碎屑岩为主要容矿岩石的盆地相金矿（Basin-type CTGDs，简称B-CTGDs）。前者主要包括水银洞、紫木凼、太平洞、戈塘、泥堡等超大（中-大）型金矿，后者则主要包括金牙、烂泥沟、高龙等金矿。近些年研究表明，在盆地相区即右江盆地南缘发现了产于二叠纪辉绿岩体内或辉绿岩-沉积岩接触带的金矿类型（如广西龙川金矿和云南安那金矿等），也有一些矿床同时产在沉积岩和辉绿岩体中（广西八渡金矿和云南者桑金矿等）。整体而言，两沉积相区金矿矿体明显受断裂和地层双重控制，As、Sb、Hg、Tl、Cu、S等元素密切共生，均具有去碳酸盐化、硅化、粘土化、硫化和碳酸盐化等围岩蚀变特征，但又有很多细节上的差别。本文以近年来快速发展的激光剥蚀等离子体质谱（LA-ICP-MS）、纳米二次离子探针（NanoSIMS）、离子探针（SIMS）、高分辨率透射电镜（HRTEM）等技术为主要研究手段，并以传统成熟的测试技术（EPMA-SEM）为辅助。拟选取台地相三个典型金矿（水银洞金矿、紫木凼金矿、泥堡金矿），盆地相三个金矿（金牙金矿、八渡金矿、者桑金矿）进行系统野外地质调查和矿相学对比研究。并对黄铁矿为主的硫化物进行微区原位S-Fe同位素-微量元素点分析或线/面扫描工作，以查明成矿元素组合的分布特征、含量组成以及内在联系；结合单矿物Pb-Hg同位素组成分析结果，探究两沉积相区金矿成矿物质来源有何异同，探讨包含金在内的成矿元素的赋存状态和富集机制。并结合前人流体包裹体岩相学、C-H-O传统同位素成果，讨论代表矿床成矿流体的来源和演化，进一步刻画反演成矿过程。以期丰富和完善两沉积相区矿床成因模式及成矿规律，为区域找矿提供有力支撑。取得的主要认识如下：（1）查明了两沉积相区各金矿的围岩蚀变和矿物组成特征。台地相金矿（P-CTGDs）赋矿岩性以碳酸盐岩、凝灰岩夹层和粘土岩组合为主，而盆地相金矿（B-CTGDs）主要以辉绿岩和砂泥岩等碎屑岩为主。围岩蚀变类型包括：脱碳酸盐化、硅化（±萤石化）、粘土化、硫化（以黄铁矿和毒砂为主）、碳酸盐化等。主要的矿物组合有黄铁矿、毒砂、雄黄（±雌黄）、辉锑矿、黄铜矿、闪锌矿、方铅矿、金红石、磷灰石、石英、方解石（白云石）、伊利石（±高岭石）、绢云母等。部分矿床发育次显微金、硫砷汞铜矿、硫汞锌矿、辉砷镍矿及（锑）黝铜矿等矿物，多以矿物包裹体或在黄铁矿/毒砂裂隙中的形式产出，代表了变质变形作用。（2）元素地球化学研究表明，6个矿床中矿石样品的 Au、Cu、Hg、As、S、Sb、Ag、Tl和少量Fe、K等元素都是由热液带入的，MnO、SiO2、TiO2和Al2O3的含量变化不大，Na2O、CaO等则相对亏损或略微富集，是热液交代围岩的结果，而Pb、Zn基本没有变化或略微亏损。Fe多由含铁碳酸盐矿物、钛铁矿、含Fe辉石-角闪石等矿物释放提供。Cu在八渡金矿辉绿岩矿体中含量变化不大，可能跟辉绿岩中含有较多黄铜矿有关。Al2O3和K2O的高含量通常与矿石样品粘土蚀变过程中出现的含Al、K的粘土矿物（如伊利石、高岭石或绢云母等）有紧密联系。较高含量的CaO和MgO也多与卡林型金矿碳酸盐化过程中大量出现的方解石等碳酸盐矿物有关。其他微量元素如W、Sn等在局部矿体中的略微富集及亏损，可能与成矿流体改造或扰动有关。（3）矿相学工作显示，两沉积相区黄铁矿均具有环带结构，即显示成岩和热液两种成因。相比较成岩期黄铁矿而言，热液期黄铁矿多富集As-Au-Cu元素组合，并亏损Fe和S。台地相金矿和右江断裂以北的金矿黄铁矿Au含量较高；而右江断裂以南的盆地相金矿黄铁矿Au含量较低，可能暗示有部分Au赋存在毒砂中。（4）各金矿各期次黄铁矿原位微量元素组成特征显示，热液期黄铁矿均富集As-Au-Cu-Sb(-Hg)-Tl等成矿元素组合。整体而言，台地相金矿比盆地相金矿Au含量高，而前者As含量则略低于后者。台地相金矿和盆地相金矿中的沉积岩矿体Au、As等元素富集特征比较相似，而盆地相辉绿岩矿体Au含量较低，但都略小于美国卡林型金矿Au含量；盆地相辉绿岩矿体As含量略高于沉积岩矿体。台地相金矿成矿期黄铁矿Au/As比值在1:100-1:100000之间，而盆地相金矿成矿期黄铁矿则在1:1000-1:10000000之间。（5）LA-ICP-MS及HRTEM结果显示，Au在含砷黄铁矿中以固溶体金（Au1+）和纳米金（Au0）两种形式存在；纳米金和次显微金的存在可能是脆性变形或晚期热液改造影响下的出溶结果。这一认识更新和完善了我们对右江盆地卡林型金矿Au赋存形态的认知。（6）NanoSIMS原位S同位素结果表明两沉积相区金矿的S可能主要来自元古代变质基底岩石。相对右江断裂以南的盆地相金矿而言，台地相和右江断裂以北金矿的S更有可能来源于岩浆，但与大厂层构造蚀变体的水岩反应和流体氧化对成矿期黄铁矿低硫同位素组成的影响不可忽视。泥堡金矿中重结晶草莓状黄铁矿的超重硫同位素组成，可能与深海沉积物的缺乏或者相对封闭系统下的瑞利分馏有关。单颗粒黄铁矿NanoSIMS面扫描和线扫描结果显示，As-Au-Cu元素间的耦合或失耦关系，可能与成矿流体在物理化学条件剧烈变化下的选择性分异和卸载沉淀有关。（7）各金矿硫化物Pb同位素结果显示，两沉积相区金矿中的Pb大部分来自于元古代基底。对台地相金矿和右江断裂以北的盆地相金矿而言，Pb更可能来自于深部岩浆；硫化物Hg同位素组成和微弱的同位素非质量分馏（MIF）可能暗示了Hg的基底来源，但不能排除岩浆来源的可能性。（8）SIMS原位Fe同位素结果显示，成岩期黄铁矿和成矿期黄铁矿的Fe同位素组成差异较大，可能暗示了不同的Fe质来源；也暗示成矿期黄铁矿中的Fe可能不全部来自于赋矿地层，还可能有其他来源。（9）C-H-O同位素结果显示，均有以变质流体为主的深源流体的参与，且同位素组成受赋矿地层岩性影响较大。变质流体可能与二叠纪右江盆地南侧越北逆冲推覆褶皱带的构造变质变形有关，这一认识也和镜下可见的次显微金、硫砷汞铜矿、硫汞锌矿、辉砷镍矿及（锑）黝铜矿等变质作用下的标型矿物吻合。右江盆地成矿流体可能主要是来自于深部基底变质流体（±大气降水），相比较右江断裂以南的盆地相矿床而言，台地相金矿和右江断裂以北的盆地相矿床更有可能有岩浆流体的参与；而盆地相金矿则可能有盆地卤水的混入。（10）台地相金矿和右江断裂以北的金矿成矿时代可能主要以燕山期（130~150Ma）为主，而右江断裂以南的卡林型金矿则以印支期（200~230Ma）为主，并有燕山期的叠加。

Carlin-type gold deposits (CTGDs) in the Youjiang Basin on the southwest margin of the Yangtze block are mainly distributed at the junction of Yunnan, Guizhou and Guangxi provinces. CTGD is an important gold deposit type in China, which is the second largest mining area of Carlin-type gold deposit clusters in the world. CTGDs in the Youjiang Basin can be divided into Platform-type CTGDs (P-CTGDs for short) hosted in the impure carbonate rocks, and Basin-type CTGDs (B-CTGDs for short) within the terrigenous clastic rocks. The former mainly includes the Shuiyindong, Zimudang, Taipingdong, Getang, Nibao deposit, etc. In recent years, detailed studies have shown that in the basin facies area, namely the southern margin of the Youjiang Basin, many gold deposits occur in the Permian diabase or the contact zone of the diabase and sedimentary rock (such as the Longchuan gold deposit of Guangxi and the Anna gold deposit of Yunnan, etc.). There are also some deposits located in both the sedimentary rocks and diabase at the same deposit (such as the Badu gold deposit in Guangxi and the Zhesang gold deposit in Yunnan, etc.). On the whole, the gold deposits of the two sedimentary facies area are obviously controlled by both faults and strata, and closely associated with As, Sb, Hg, Tl, Cu, S and other elements. They share the alteration types such as decarbonatization, silicification, argillization, sulfidation and carbonation, but there are many differences in detail.In order to break the limitations of traditional methods, this study mainly chose LA-ICP-MS, NanoSIMS, SIMS, HRTEM, and other techniques rapidly developed in recent years, with the auxiliary supplement of the traditional testing methods (EPMA and SEM, etc.). This study selected three representative P-CTGDs (the Shuiyindong, Zimudang and Nibao deposits), three B-CTGDs (the Jinya, Badu and Zhesang deposits). Systematic field geological survey and mineralogy work, the analysis of in situ S-Fe isotopes, trace elements and line/plane scans of the pyrite and arsenopyrite were completed to find out the inner distribution, composition, combination characteristics of ore-forming elements. Combined with the analytical results of Pb-Hg isotope composition of individual grains, this study explored the similarities and differences of the metal sources of the two CTGD types, discussed the mechanism of occurrence of trace elements including gold. Based on the previous results of the petrography of fluid inclusions, the C-H-O isotopic compositions, the origin and evolution of ore-forming fluids were discussed, and the evolution process was further characterized. To enrich and refine the genetic model and the metallogenic theory of the deposits in the two-sedimentary facies area, in order to provide support for regionally prospecting model, the main achievements are summarized as follows:(1) The wall rock alteration and the mineral composition characteristics of the gold deposits in the two sedimentary facies areas were identified. P-CTGDs are mainly hosted in carbonate rocks, tuff and argillite assemblages, while B-CTGDs mainly occur in diabase and clastic rocks such as sandstone, mudstone. The alteration types include the decarbonization, silicification (±fluoritization), argillization, sulfidation (mainly pyritization, arsenopyritization), carbonation, etc. The main mineral assemblages are pyrite, arsenopyrite, realgar (±orpiment), stibnite, chalcopyrite, sphalerite, galena, rutile, apatite, quartz, calcite (dolomite), illite (±kaolinite), sericite, etc. Some deposits develop minerals of submicroscopic gold, aktashite, polhemusite, gersdorffite and (Sb) tetrahedrite and they occur in the form of mineral inclusions or growing along the fractures of pyrite/arsenopyrite, representing the metamorphic deformation processes.(2) The geochemistry of ores and host rocks of six gold deposits shows that Au, Cu, Hg, As, S, Sb, Ag, Tl, K and minor Fe were added by ore fluids, while MnO, SiO2, Al2O3 and TiO2 changed little, Na2O and CaO were relatively at loss or slightly enriched, and the contents of Pb, Zn did not change or were slightly at loss. Fe was mainly provided by the dissolution of ferroan carbonate minerals, ilmenite, Fe-bearing pyroxene and amphibole. Cu content in the diabase-hosted orebody of the Badu gold deposit changed little, which might be related to the high content of chalcopyrite in the fresh diabase. The high contents of Al2O3 and K2O are closely related to clay minerals containing Al and K (such as illite, kaolinite or sericite) during the argillization process. The higher contents of CaO and MgO are also related to calcite and other carbonate minerals during the carbonation process. The slight enrichment and loss of other trace elements such as W and Sn in some orebodies may be caused by the alteration or disturbance of ore-forming fluids.(3) According to the mineralogical work, pyrites in two sedimentary facies areas obviously show zoned textures, indicating the diagenesis and hydrothermal genesis. Compared with the diagenetic pyrite, the hydrothermal pyrite is enriched in As-Au-Cu elements and deficient in Fe, S. The Au content of ore-related pyrites of gold deposits in platform facies area and the north of the Youjiang fault is higher. However, the Au content of ore-related pyrites of gold deposits in platform facies area and the south of the Youjiang fault is lower, which may indicate that Au partially occurs in arsenopyrite.(4) In situ trace element compositions of all pyrite types of six deposits showed that the hydrothermal pyrite was enriched in As-Au-Cu-Sb(-Hg)-Tl. The Au content of P-CTGDs is higher than that of B-CTGDs, while the As content of the former is slightly lower than that of the latter. The Au, As of P-CTGDs and the sediment-hosted orebodies of B-CTGDs are similar, while the Au content of the diabase-hosted orebodies of B-CTGDs is low, all of which are slightly less than those of CTGDs in the Nevada. The content of As in the diabase-hosted orebody is slightly higher than that in the sediment-hosted orebody. The Au/As ratio of hydrothermal pyrite of P-CTGDs is between 1:100 and 1:100,000, while that of B-CTGDs is between 1:1,000 and 1:10,000,000.(5) LA-ICP-MS and HRTEM results showed that Au existed in two forms of solid solution (Au1+) and nanoparticles (Au0) in pyrite. The presence of gold nanoparticles and submicroscopic gold may be the result of exsolution owing to the influence of brittle deformation or late hydrothermal reformation. This has probably renewed our cognition of the occurrence and distribution of Au in CTGDs of the Youjiang Basin.(6) The result of in situ S isotope obtained by NanoSIMS indicates that the S of CTGDs in the two sedimentary facies area probably originated from the Proterozoic metamorphic basement rocks. Compared with the B-CTGDs in the southern of the Youjiang fault, sulfur of the P-CTGDs and the CTGDs in the northern of the Youjiang fault was more likely to originate from a magmatic source. But the isotopic fractionation ascribed to the fluid-rock reaction in the structural alteration zone (SBT) and fluid oxidation might not be precluded. The superheavy sulfur isotopic composition of recrystallized framboid pyrite in the Nibao gold deposit might be due to the potential influence of closed-system Rayleigh fractionation or the lack of preservation of deep-sea sediments. NanoSIMS plane and line scans of individual pyrite show that the coupling or decoupling relationship among As, Au and Cu elements may be related to the selective partitioning, unloading and metal precipitation of the ore-forming fluid ascribed to the drastic changes of physico-chemical conditions.(7) Pb isotope results of various sulfides of CTGDs show that most of Pb came from the Proterozoic basement rocks. Similarly, Pb of the P-CTGDs and the CTGDs in the north of the Youjiang fault was more likely to originate from a deep magmatic source. The Hg isotopic compositions and weak MIF of sulfide may indicate the potential source of basement rocks, but the possibility of a magmatic origin cannot be ruled out.(8) In situ Fe isotope data acquired by SIMS indicated that the Fe isotopic composition of diagenetic pyrite was significantly different from that of ore-related pyrite, which may reflect different sources of Fe. It is also suggested that Fe in pyrite during mineralization may not entirely from the host strata, but partially from other potential sources.(9) C-H-O isotope results implied a deep source dominated by metamorphic fluids, with the isotopic composition greatly affected by the lithology of the host strata. The metamorphic fluid involved may be related to the tectonic metamorphism and deformation of the fold belt in North Vietnam block, the south of the Youjiang Basin during the Permian. And this is also matched with the occurrence of typomorphic minerals such as submicroscopic gold, aktashite, polhemusite, gersdorffite and (Sb) tetrahedrite during the metamorphism processes. The ore fluids in the Youjiang Basin may mainly come from metamorphic fluid (±meteoric water) from the deep basement. Compared with the B-CTGDs in the south of the Youjiang fault, the magmatic fluid was more likely involved in the P-CTGDs and the CTGDs in the north of the Youjiang fault. The B-CTGDs may be mixed of basin brine.(10) The dating age of the P-CTGDs and the CTGDs in the north of the Youjiang fault dominantly formed at the Yanshanian (130-150 Ma), while the B-CTGDs in the south of the Youjiang fault dominated formed at the Indosinian (200-230 Ma) and superimposed by the Yanshanian