甘肃北山花牛山金银铅锌矿床成因探讨

Metallogenic Study of Huaniushan Au-Ag-Pb-Zn Deposit,Beishan area,Gansu Province

花牛山金银铅锌矿床位于塔里木板块塔敦煌地块北缘花牛山-黑山-双鹰山早古生代陆缘裂谷带中。矿体赋存于蓟县纪碳酸盐岩与碎屑岩的接触带和奥陶纪花牛山群中基性火山岩-沉积碎屑岩夹碳酸盐岩建造中。矿体多呈似层状,次为扁豆状、透镜体状,少量为囊状、柱状等。围岩蚀变以铁白云石化为主,普遍见角岩化、矽卡岩化。稳定同位素研究表明,铅具有多源特点,来源于地幔及地壳,并与岩浆岩具有内在联系;硫来源主要为同化了海水硫酸盐的岩浆硫,并有少量生物还原硫参与。氢、氧、碳同位素指示成矿流体早期可能有岩浆热液,主成矿期主要是地层中的建造水参与成矿。结合成矿地质背景,认为花牛山金银铅锌矿床是火山喷发沉积-变质变形改造-后期岩浆热液叠加的多成因金银铅锌矿床。

Huaniushan Au-Ag-Pb-Zn deposit is situated at Huaniushan-Baishantang Early Paleozoic continental margin rift zone belongs to north margin of Dunhuang block.The ore-bodies are found in the contact zone of carbonate and clastic rocks of Jixianian Period,or basic volcanic rock and holoclastic rock with carbonate interlay assemblage of Ordovician Huaniushan Group.The textures of the ore-body are dominantly stratiform-like,with some flatschig and lenticle-like shape,and little saccate and stylolite shape.Wallrock alteration is composing of iron dolomitization,with universal brecciation and skarnization.Stable isotopic analysis of ore minerals indicated that the source of lead is complex,mainly comes from the mantle and the crust,and closely related to magma intrusion,while the sulfur originated mainly from magma which is contaminated by sulfate from seawater and biological deoxidized sulfur.The hydrogen,oxygen,and carbon isotope analyzing indicated that ore-forming fluid is mainly coming from magma,and a little formation water from the strata.This research comes into the conclusion that Huaniushan Au-Ag-Pb-Zn deposit is an multiple genesis one including early volcanic eruption and sediment,and then metamorphic alteration,finally magmatic hydrothermal overlay processing.