金坝金矿床地质特征

GEOLOGICAL CHARACTERISTICS OF JINBA GOLD DEPOSIT IN SOUTHEAST YUNNAN

金坝超微粒型金矿床有３０多个矿体，划分６个矿带．矿带ＮＥ向展布，带长３５０～２０００ ｍ．矿体呈透镜状、似层状、串珠状产出．者桑复背斜控制矿化带的分布，断裂构造为含矿热液提供运移通道，次级构造控制矿体具体储存部位及矿体的形态产状．赋矿层位以上二叠统为主（含５个矿带），还有下中三叠统．容矿岩石有泥质粉砂岩、粉砂岩、粉砂质凝灰岩、凝灰岩、泥质白云岩、细碧岩、辉绿岩脉等．矿化类型：地层岩石破碎带蚀变岩型、脉岩破碎蚀变岩型以及石英脉型．围岩蚀变有黄铁矿化、毒砂化、硅化、碳酸盐化等．矿石类型按自然分类为氧化矿石和原生矿石；按岩石类型划分为凝灰岩类矿石，粉砂岩、粉砂质泥岩类矿石，泥质白云岩矿石，辉绿岩矿石以及细碧岩矿石．矿石含金品位 ０．５×１０－６～１５．９×１０－６．原生矿石金属矿物有黄铁矿、毒砂、黄铜矿；氧化矿石金属矿物有褐铁矿、臭葱石等；而脉石矿物主要取决于各自的容矿岩石．矿石的化学组成：ＳｉＯ２比原岩低，（Ｆｅ２Ｏ３＋ＦｅＯ）高于原岩，富Ｋ贫Ｎａ．微量元素Ａｕ、Ａｇ、Ａｓ、Ｓｂ、Ｃｕ高于原岩 矿石为泥质结构、细碎屑结构、凝灰结构、辉绿结构、粒状结晶结构、环边环带结构；碎裂构造、角砾构造、浸染状构造。

Jinba gold deposit of ultramicro-grained type, located in the southeast of Yunnan Province, includes more than 30 ore bodies, which are grouped into 6 ore belts trending NE and 350 ~ 2000 m in length. The ore bodies are in lens, sub-stratiform or moniliform. The Zhesang anticlinorium controls the distribution of ore belts. The faults provide migratary channels for ore solution. The secondary sturctures control the location and occurrence of ore bodies. The host strata are mainly Upper Permain (containing 5 ore belts), with also Middle and Lower Triassic. The wall rocks are pelitic siltstone, siltstone, silty tuff, tuff, argillaceous dolomite, spilite, diabase dyke, ets. The mineralization types cover altered rock of fractured formation, altered rock of fractured dyke, and quartz vein. The wallrock alteration involves pyritization, arsenopyritization, silicification and carbonation. The oxidized and primary ores may be lithologically classified into tuffaceous ore, silty/silty-argillic ore, argillaceous dolomite ore, diabase ore and spilite ore. The Au grades of ore range from 0.5 × 10-6 to 15.9×10-6. The metallic minerals in primary ore are pyrite, arsenopyrite and chalcopyrite; while in oxidized ore, are limonite and scorodite. The gangue minerals depend on the types of wall rocks. Chemically, the content of SiO2 in the ore is lower than that in primary rocks; while Fe2O3 + FeO is higher. The ore is rich in K and poor in Na. The trace elements such as Au, Ag, As, Sb and Cu are more in the ore than in the primary rock. The ores are in pelitic, fine-clastic, tuffaceous, diabasic, granular crystalline and rim-zonal textures, and cataclastic, breccia, disseminated, nodular and honeycomb structures. The gold is hosted in limonite, arsenopyrite and chalcopyrite as micro-inclusions.