万古金矿中碳质物的成因及其与金成矿的关系

万古金矿位于江南造山带中部，是该成矿带最具代表性的金矿床之一。万古金矿的赋矿围岩和矿石中可见大量碳质物（CM），然而碳质物的类型、成因及其与金成矿的关系仍不明确。通过进行系统的岩相学和激光拉曼光谱分析，发现万古金矿有3种类型的碳质物（CM1、CM2和CM3）。其中，CM1（T=507~613 ℃）呈粒状，分布在石英和云母中；CM2（T=390~470 ℃）呈层状，分布在黄铁矿和毒砂等矿物中；CM3（T=240~355 ℃）与石英和黄铁矿等热液矿物共生，且其形成温度与成矿温度相近。由此推断，CM1和CM2可能是变质成因，而CM3可能是热液成因。通过硫化物LA-ICP-MS分析，认为与CM2相关的黄铁矿更富Au和As。结合前人研究，认为万古金矿成矿前形成的层状CM2可作为还原剂，与含矿热液中金的络合物发生反应，致使金沉淀；CM3与黄铁矿共同沉淀，也有利于金成矿作用。

Genesis of Carbonaceous Material in the Wangu Gold Deposit and Its Relationship with Gold Mineralization

The Wangu gold deposit，located in the central Jiangnan orogenic belt，is one of the most repre-sentative gold deposits.The orebodies are mainly hosted in the Neoproterozoic Lengjiaxi Group.Large amounts of carbonaceous material（CM） occurs in the host rocks and ores.However，the types and genesis of CM in the deposit and its relationship with gold mineralization are still unclear，which restricts the understanding of the precipitation mechanism of mineralization elements and the deep prospecting and exploration work. Systematic petrographic and laser Raman spectroscopic analyses of CM in surrounding rocks and ores show that there are three types of CM in the deposit，namely CM1，CM2 and CM3.Among them，CM1（T=507~613 ℃） is granular with small particles，which are distributed in quartz and micamineral particles or pores，in disseminated distribution，smooth edges and corners and good roundness，which may be the source of debris.CM2（T=390~470 ℃） is layered and distributed around minerals such aspyrite and arsenopyrite or in pyrite.CM3（T=240~355 ℃） coexists with hydrothermal minerals such as siderite，quartz and pyrite，and the formation temperature is close to the metallogenic temperature，surrounded by a large amount of pyrite，which is mainly produced in vein form.Consequently，CM1 and CM2 may have been formed by pre-ore metamorphism，which is of metamorphic origin，while CM3 may be the product of hydrothermal process，which is of hydrothermal origin.Sulfide LA-ICP-MS Mapping and trace element analyses show that the Au-As coupling phenomenon of sulfide in CM2 is wonderful.The pyrite rim is more enriched in Au，As，Co and Ni than the core，and poor in Bi，Pb，and Sb.In the vicinity of pores in the core of pyrite，most of them have abnormally high Au.The location of abnormally high Au，As，Co，and Ni is very similar，forming a growth ring of pyrite.The pyrite grains associated with both CM2 and CM3 contain gold，but those related to CM2 are richer in Au and As，and poor in trace elements such as Cu，Co，Ni，Bi，Pb.The sulfide of CM2 have no Te，however，the content of CM3 are less.Combining with previous studies，pre-ore layer CM2 can react with Au-bearing fluid as efficient reductant to prompt Au precipitation.However，hydrothermal CM3 together with pyrite precipitating from ore-bearing fluid，was also favorable to gold mineralization.