兰坪白秧坪铜银多金属矿床流体地球化学特征及成矿机制探讨

GEOCHEMICAL CHARACTERISTICS OF FLUID AND MECHA NISM FOR ORE FORMATION IN THE BAIYANGPINGCOPPER-SILVER DEPOSIT,YUNNAN

白秧坪铜银多金属矿床主要产于白垩系下统景星组石英砂岩、粉砂岩中 ,矿体受一组北东向的压扭性断层控制而呈似层状、脉状产于断裂带中。包裹体分析表明成矿流体为低温 (平均124～141℃ )、低矿化度的盆地卤水 ,流体的H、O同位素组成位于大气降水线附近 ,反映了水 /岩作用程度较低、水 /岩反应时限短 ,流体流动与循环速度较快。计算机模拟结果表明在景星组沉积之后的13～16Ma期间断裂作用所产生的断裂渗透性达到最大 ,此期间流体演化的温度也达到125～140℃。断裂作用所产生的高断裂渗透性对周围地层中的流体产生泵吸作用并形成流体流动的断裂引水渠 ,从而导致大量流体在断裂带中快速流动。

The Baiyangping copper-silver deposit occurs in the lower Cretaceous Jingxing Formation quartz sandstone and siltstone.The deposit is controlled by a batch of northeast-trending fractures and occurs as bedded and veined orebodies.Geochemical studies of fluid inclusions indicate that the ore-forming fluid is a basin brine with a lower temperature(124～141℃ on an average) and lower mineralization degree.The composition of hydrogen-oxygen isotopes is nearthe SMOW line,suggesting that the degree of water/rock interaction is quite low,its time limit is short and the speed of fluid flowage and circulation is quitefast.The results of computer modeling indicate that during the period 13～16 Ma after the deposition of the Jingxing Formation,faulting made the fracture permeability up to the most,at the same time the temperature of fluid evolution reached 125～140℃.The high fracture permeability brought a pump-absorb action to the fluid in the around strata and formed a tunnel for fluid flowage.Thus,the high fracture permeability causes large-scale fluid flowing, circulating and mineralization in the fracture zone.