滇西大坪金矿床地质特征及成因初探

摘要

大坪金矿床被视为哀牢山造山带南段最典型的造山型金矿,但其诸多地质特征明显不同于国外典型造山型金矿床,而呈现出与浅成低温热液型金矿床的一致性.区域上,脉型金铜铅银矿床的产出与中酸性侵入岩及中基性火山岩密切相关.大坪金矿床形成于主要赋矿的桃家寨闪长岩侵位之后约800Ma的新生代构造-岩浆热事件中,金矿床是区域尺度伸展和转换拉伸应力体制的产物；成矿作用过程中,研究区构造动力体制发生了转换,主成矿期容矿断裂带显示为张剪性正断层性质.矿脉多(55条)、薄(0.2～0.8m)、长(200 ～ 1500m)、陡(56°～ 85°)、延深大(约700m),且近平行成带产出；矿体中Au品位高(超过10×10-6),Au/Ag低(o.1 ～o.5),且伴生Pb、Cu、Ag.矿石的充填型结构构造和矿物共生组合指示矿脉形成温度低、深度浅；矿化-蚀变样式以及蛋白石和氧化矿的出现表明成矿体系处于开放的氧化环境,成矿后保存良好.大坪金矿床这种特殊的地质特征可能与其复杂的区域构造背景及成矿演化过程密切相关,金矿床虽然具有造山型金矿的基本特征,但在成矿作用晚期,矿床浅部叠加了浅成低温热液型金铜铅银成矿作用.即大坪金矿床属于深部造山型+浅部低温热液型矿床套叠组合,成矿体系保存完整,现发现的均为浅部矿体,深部找矿潜力巨大.%Daping gold deposit, situated in the south section of the Ailaoshan orogenic belt, once considered to be an orogenic gold deposit, displays many distinct geological characteristics which are inconsistent with the classical orogenic gold deposits around the world, but accord with the epithermal gold deposits. The vein type gold, copper, lead, silver deposits commonly develop in close association with intermediate-acidic intrusive and intermediate-basic volcanic rocks regionally. Daping gold deposit was formed in the Neozoic tectonic-magmatic activity, which is 800Ma later than the emplacement of Taojiazhai diorite which is the main host rocks, besides the gold metallogenesis is closely related to the regional structural framework and the transition of tectonic regime. The host faults of main ore-forming period are generally believed as a transtensional normal faults, and ore veins within are abundant (55), thin (0. 2 -0. 8m) , long (200 ~ 1500 m) , steep (56° -85°) , deeply extensive (700m) and developed in parallel, besides ore bodies in association with Pb, Cu and Ag display high-grade Au (above 10 x 10 ~6), low Au/Ag ratio (0. 1 -0.5). Textures and structures of filling type as well as mineral assemblages indicate that ore veins formed at a low-temperature and shallow-depth environment, what' more, mineralization-alteration types and the growth of opal and oxidized ores restrict an open and oxidizing environment The distinguished geological characteristics of Daping gold deposit may be closely related to the complicated tectonic regime and metallogenic evolution, though the deposit is distinguished by its feature of orogenic gold deposits, epithermal gold, copper, lead, silver mineralization is overlapped in the shallow during the late stage of mineralization. The metallogenic characteristics, combined with documented geological information, indicate Daping gold deposit is distinguished by its orogenic in the deep and epithermal in the shallow, besides the metallogenic system is well preserved. Considering all the ores proven now are in the shallow, Daping gold deposit is of great prospecting potentiality in the deep.