江西金山金矿田朱林西—竹叶岭矿区岩石地球化学特征及矿床成因探讨

Litho-geochemical characteristics of Zhulinxi-Zhuyeling District in Jinshan Gold Field of Jiangxi Province and its genesis

江西金山金矿田朱林西—竹叶岭矿区主要的岩石类型为糜棱岩、超糜棱岩、千糜岩、变质安山玄武岩。糜棱岩类岩石SiO_2质量分数为60.95%~67.81%,w(K_2O)/w(Na_2O)介于0.37~0.83,表现出富Na贫K的特征;富集Th、U、K、Rb等大离子亲石元素及La、Ce、Nd、Hf等元素,亏损Ba、Ta、Sr、P、Ti、Nb等强不相容元素;稀土元素总量偏低,富集轻稀土元素,显示中等强度的Eu负异常,配分曲线呈右倾型。根据主微量、稀土元素特征并结合前人对金山金矿区的研究成果表明,朱林西—竹叶岭矿区具有和金山金矿区相一致的糜棱岩类岩石学和地球化学特征。糜棱岩类岩石原岩为一套以火山物质为主的火山碎屑沉积岩,富集深部地幔物质,是成矿的主要物质来源,成矿流体主要为岩浆水+大气降水。晋宁期为成矿聚集期,初步成矿,加里东、海西、燕山期的岩浆活动可能进一步成矿或对早期矿体叠加改造。

The main rock types in Zhulinxi-Zhuyeling District of Jinshan Gold Field are mylonite,ultramylonite,phyllonite and metamorphic andesitic basalt. The SiO_2 mass fraction of mylonite rocks is 60. 95 %-67. 81 % and w（ K_2O）/w（ Na_2O） ranges from 0. 37 to 0. 83,showing the feature of enrichment in Na but depletion in K; large ion lithophile elements such as Th,U,K and Rb as well as La,Ce,Nd and Hf are enriched,while the strong incompatible elements of Ba,Ta,Sr,P,Ti and Nb are depleted. The total REEs are relatively low and the LREE is relatively rich,showing medium negative Eu negative anomalies with the right-leaning REE patterns. In combination with precedent studies on Jinshan Gold District,the characteristics of major,trace and REE elements show that the petrological and geochemical characteristics of the mylonite in Zhulinxi-Zhuyeling District are consistent with those in Jinshan Gold District. The mylonite protoliths are a set of pyroclastic sedimentary rocks mainly composed of volcanic materials,which is the main source of the deposit enriched in the deep mantle materials. The ore-forming fluids dominantly derives from magmatic water ＋ atmospheric precipitation. Jinningian was the ore-forming stage for preliminary mineralization. The Caledonian,Hercynian and Yanshanian magmatic activities might further mineralize or superimpose and reform the early-stage ore bodies.