大兴安岭北部砂宝斯蚀变砂岩型金矿地质特征

GEOLOGICAL CHARACTERISTICS OF THE SHABAOSI ALTERED SANDSTONE TYPE GOLD DEPOSIT IN NORTH DA HINGGAN MOUNTAINS

砂宝斯金矿为我国最近在黑龙江省漠河县发现的一大型蚀变砂岩型金矿床 (平均品位 4 .0 2× 10 -6)。矿体仅赋存于侏罗系二十二站组砂岩中 ,其下伏地层并不含矿。矿体分缓倾顺层矿体和陡倾穿层矿体 ,分别受 NS向缓倾断裂和陡倾断裂构造控制。矿石类型有蚀变砂岩型和构造破碎蚀变砂岩型 ,为少硫化物型矿石 ,其中金主要为微细粒金。稳定同位素及流体包裹体资料表明成矿流体是以天水为主的中低温热液。

The Shabaosi gold deposit in Mohe County, Heilongjiang Province, is a large altered sandstone type gold deposit with an average grade of 4 02×10 -6 . Three ore belts discovered in the deposit all occur in Jurassic sandstone rather than in the underlying Devonian limestone and Proterozoic marble. Two kinds of orebodies, one steeply and the other gently dipping, are respectively controlled by steeply dipping and gently dipping NS\|trending faults. Gold ores that contain minor sulfides can be classified into altered sandstone type (major type) and structurally fractured and altered sandstone type. Native gold from the ores is mainly micrograined. Besides silicification and pyritization, argillation is an important type of wall rock alteration distributed extensively in the gold ore field. Fluid inclusion studies show that the temperature of the ore fluids ranges from 130℃ to 250℃, fluid salinity is 5% NaCl and ore\|forming pressure is 40 9 MPa.H, O isotopic analysis indicates that the ore fluids are mainly composed of meteoric water. Divergent δ 34 S values of pyrite probably suggest that the deposit is a shallow\|seated one. The Pb isotope composition of pyrite, similar to that of volcanic rocks in eastern China, shows that the formation of the deposit is probably related to the magmatic (volcanic) activity in middle Jurassuc or later.