云南金平铜厂Cu-Mo矿床矽卡岩地球化学特征及成因

Geochemical Characteristics and Genesis of Skarns in the Tongchang Cu-Mo Deposit of Jinping County,Yunnan Province

云南金平铜厂Cu-Mo矿床位于滨太平洋与特提斯构造域结合部位哀牢山构造成矿带南端,该矿床主要由矽卡岩Cu-Mo矿体组成,其中Cu储量0.862×10^4t(品位1.24%),Mo储量1.706×10^4t(品位0.21%)。为查明矿区内与成矿关系密切的矽卡岩成因及其与围岩的关系,分析其不同元素的性质及分布规律,揭示矽卡岩矿床成岩、成矿地质过程,本文通过采集铜厂Cu-Mo矿区矽卡岩及矽卡岩化正长斑岩和大理岩样品进行主微量、稀土元素地球化学分析,研究其特征。研究表明:Si、Fe、Ca、Ti、Al、Mg、Mn等主量元素在矽卡岩、正长斑岩之间曾发生明显置换交代地质作用;三种岩性都具有富集LREE元素,亏损HREE元素,发育较弱Eu负异常,Ce异常不明显,REE配分模式相似的稀土元素特征,说明矽卡岩、正长斑岩和大理岩有一定的成因联系。结合三者REE配分模式、Eu弱负异常及Ce异常不明显等地球化学特征,推测矿区矽卡岩形成于低温弱氧化环境,由来自深部热液流体与围岩接触交代形成,成岩流体主要来源于深部岩浆。

The Tongchang Cu-Mo deposit hosts silicite Cu-Mo orebodies,with reserves of Cu 0.862×10^4 t(1.24%)and Mo 1.706×10^4 t(0.21%).It lies in the southern end of the Ailaoshan mineralization zone,conjunction of coastal Pacific and Tethys tectonic domains.The purpose of this work was to clarify the relationship between wall rock and silicalite which is closely related to the mineralization in the mining area,analyze the properties and distribution of different elements,and infer the geological processes of diagenesis and mineralization.We collected samples of skarn,skarnization syenite porphyry and marble in the Cu-Mo mining area of Tongchang,and analyzed the geochemistry characteristics of major,trace and rare earth elements.The study shows that obvious exchanges occurred among Si,Fe,Ca,Ti,Al,Mg and Mn in skarn and biotite granite for the major elements.The three kinds of lithology are rich in LREE and depleted in HREE,with weak Eu negative anomalies,and little Ce anomalies.Their REE distribution modes are similar,implying that skarns,biotite granite and marble have some genesis association.Combining characteristics of their REE distribution modes,weak Eu negative anomalies and less Ce negative anomalies,it is inferred that the skarn was formed by deep hydrothermal fluid and surrounding rock contact metasomatism in a low-temperature weak oxidizing environment,where diagenetic fluid was mainly originated from magma at depth.