云南墨江金厂矿床金镍赋存状态及成因关系探讨

墨江金厂金镍矿床位于哀牢山造山带中段,九甲—安定大断裂上盘,是西南三江成矿带内一个独特的金镍矿床。本文在详细野外地质调查基础上,通过显微镜下观察、扫描电镜和能谱分析,结合矿石微量元素分析,对矿石中金、镍赋存状态及成因关系进行了研究。结果显示,金赋存形式主要有可见金和不可见金。可见金又可分为粒间金和包体金;不可见金是以Au~+赋存于硫锑铜银矿、黄铁矿中。镍赋存状态有两种:一是以独立矿物,如辉砷镍矿、锑硫镍矿等存在;二是以离子态赋存于黄铁矿、硫锑铜银矿中。矿石结构构造、矿物共生组合及微量元素含量等显示,金和镍为同期热液成矿,金来自岩浆热液系统远端的低温热液,镍是含金低温热液流经超基性岩体时萃取而来。成矿过程可分为早期富硅质热液和晚期富钙质热液两个阶段,成矿是在幕式构造活动下多期流体运移和沉淀的结果。

On the occurrence and genesis of gold and nickel in Jinchang deposit, Mojiang County, Yunnan Province

The Jinchang gold-nickel deposit in Mojiang County is located in the middle of the Ailaoshan orogenic belt and the hanging wall of Jiujia-Anding fault within southwestern Yunnan Province, It is an unique gold-nickel paragenetic deposit. The gold and nickel minerals in ores were studied by field geological observations, microscope, scanning electron microscope and energy spectrum analysis. The result shows that the forms of gold are mainly visible gold and invisible gold. Visible gold can be divided into intergranular gold (natural gold particles existing in quartz veins) and inclusion gold (mainly coated by polybasite), while invisible gold occurs in polybasite and pyrite as Au⁺. There are two kinds of modes of occurrences of nickel:independent minerals, such as gersdorffite and ullmannite; and minerals hosted in lattice of pyrite and polybasite as ionic form. The ore structure, mineral association and trace element content show that the gold and nickel share the same hydrothermal fluids. Gold came from the low temperature hydrothermal solution at the far end of the magmatic hydrothermal solution, whereas nickel was extracted when the hydrothermal solution migrated through the ultrabasic rock. The mineralization processes can be divided into two stages:early silica-rich hydrothermal solution and later calcium-rich hydrothermal fluids. The mineralization resulted from multiphase fluid migration and precipitation under the condition of episodic structural movement.