四川会东小街金矿床成矿机理分析

Ore forming mechanism analysis on Xiaojie gold deposit in Huidong, Sichuan

四川会东小街金矿床为川西产于元古宙绿片岩地层中的菱铁矿型金矿床的典型代表。金矿体呈脉状产于中元古界会理群青龙山组碳质板岩、流纹质凝灰岩、变粗面岩和花岗斑岩的内外接触带中 ,受 EW向基底断裂的次级断裂和层间破碎带的严格控制。矿石矿物组合为黄铁矿、毒砂、黄铜矿、黝铜矿族、 Au- Ag系列矿物、石英和菱铁矿。其成矿元素组合为 Au- Cu- Ag- Pb- Sb- As- Fe。围岩蚀变以硅化、粘土化和碳酸盐化 (菱铁矿化、方解石化 )为主。由稀土元素、同位素和流体包裹体特征可以推定 ,矿石中矿质主要来自青龙山组板岩、千枚岩等 ,流体可能主要属岩浆热液。含金硫化物石英脉体可能主要形成于澄江期。矿床是在浅成条件下由低密度、中等盐度的弱碱性 -碱性流体在还原环境中生成的火山喷流沉积 -区域变质预富集 -岩浆热液改造型矿床。

Xiaojie gold deposit in Huidong, Sichuan is a typical Proterozoic greenschist hosted Au siderite one. Gold ore bodies occur as vein in inner and outer contact zones among granite porphyrite and carbonaceous slate, rhyolitic tuff, and meta trychyte in Qinglongshan Formation of Middle Proterozoic Huili Group, which are strictly controlled by subsidiary faults and interstratified fractured belts of EW trending regional basement fault. Gold ores have a mineral association of pyrite, arsenopyrite, chalcopyrite, tetrahedrite, Au Ag series minerals, quartz and siderite, and element association of Au, Cu, Ag, Pb, Sb, As and Fe. Wallrock alterations are mainly silicification, argillization, and carbonatization (sideritization, calcitization). It can be inferred from the REE, isotope, and fluid inclusion studies that ore forming materials are mainly derived from the slate and phyllite in Qinglongshan Formation, the mineralized fluid may be chiefly magmatic water. The gold bearing quartz veins were probably formed during Chengjiang period. The deposit was formed by the low density, intermediate salinity, alkalescent or less alkalescent fluid in reductive epithermal environment. It belongs to magmatic hydrothermal reworked gold deposit, which experienced volcanic exhalation sedimentary and regional matamorphic preenrichment.