南京平山头铁锰帽型银(金)矿床地质特征

平山头铁锰帽型银(金)矿床位于南京栖霞山铅锌多金属矿的氧化带内，矿床特征可与长江中下游“五通组之上层状硫化物矿床的氧化铁帽”相对比。银、金矿体赋存于纵向断裂F2破碎带内，削面上可分为氧化带、混合带和原生带。银主要以硫酸盐矿物及类质同象形式存在，少量呈独立矿物辉银矿和自然银；金以显微一超显微吸附状微粒自然金存在。银与Mn、Ba、S相关．金除与As、Si有一定相关性外，一般与其它元素的相关性差。银、金表生成矿作用过程即是原生硫化物中的银、金经氧化、迁移、重新沉淀聚集的过程，银的沉淀是在SO4^2-、Fe^3 等氧化剂和H2S、Cl^-、Fe^2 、Mn^2 等还原剂作用下完成的；金主要以AuCl^2-、Au(SO4)2^3-等络合物形式迁移，并在Fe^2 、H2S等还原剂作用下沉淀。

Geological characteristics of Pingshantou iron-manganese hat-type Ag (Au) ore deposit in Nanjing

Pingshantou as an iron-manganese hat-type Ag(Au) ore deposit, is located within the oxidation belt of Qixiashan Pb-Zn polymetallic deposit and can be compared with the other gossan-type ore deposits of stratified sulphate deposits in uppermost Devonian Wutong formation of Yangzi middle-lower valley. The Ag (Au) ore bodies are controlled by F_2 longitudinal fault, and can be divided into three zones, i.e., oxidized zone, mixed zone and primary zone. Ag exists mostly as sulphide minerals or isomorphs, but a small quantity as argentite and natural silver, while Au exists as micro or super micro-grain adsorbed natural gold. Ag is correlated to Mn, Ba and S, however Au is less correlated to other elements except As and Si. The supergene minerogenic process can be summarized as fallows: Oxidation made Ag, Au dissolve and migrate in primary sulphide. Ag precipitated when oxidizers such as SO_4~2- , Fe~3+ , met reducers such as H_2S, Cl-, Fe~2+ and Mn~2+ .Au migrated in the form of complexes of AuCl_2-, Au(SO_4)_2~3- and precipitated when the complexes met reducers of Fe~2+ and H_2S.