西藏扎西康铅锌矿集区的物探方法组合试验

Comparative research on the combinational test of geophysical methods in the Zhaxikang lead-zinc ore concentration area,Tibet

西藏扎西康铅锌多金属矿床在大地构造上位于特提斯—喜马拉雅构造域中段的北喜马拉雅大陆边缘褶冲带内,是中国西藏为数不多的以富含硫盐矿物为重要特征的大型铅锌锑银共生矿床之一。矿床主要赋存于下侏罗统日当组,容矿岩石为含炭钙质板岩、钙质板岩、绢云母板岩、页岩和石英砂岩。矿体严格受近南北向和北东—南西向两组断裂控制,呈脉状、透镜状产出。对于构造控矿这一特点,在典型矿床及其外围开展了激发极化法、高密度电法、瞬变电磁法、音频大地电磁法勘探,并针对某些方法进行了效果和反演对比。结合以往地质、物探资料和工程验证情况,认为大地电磁法、激发极化法是较为可信且经济的物探方法,此外,还需结合不同反演方法针对典型矿床进行剖析和判断,达到矿体初步预测的目的。

Located geotectonically within the North Himalayan epicontinental warped fault belt in the middle segment of the TethyanHimalayan tectonic domain,the Zhaxikang lead-zinc polymetallic deposit in Tibet is one of the rarely-seen large-size lead-zinc-silver association deposits with rich sulfosalt minerals in Tibet. The ore deposit is mainly hosted in Lower Jurassic Ridang Formation,with the ore-hosting rocks being carbon-bearing calcareous slate,calcareous slate,sericite slate,shale and quartz sandstone. The orebodies are strictly controlled by two sets of NE-SW trending faults and exhibit veinlike and lenticular forms. In view of characteristics of the orecontrolling structures,the authors employed the high density resistivity method,induced polarization method,transient electromagnetic method and audio frequency magnetotelluric method to conduct investigation in the typical ore deposit and its periphery,and made inverse comparison of the effects of some methods. In combination with the previous geological and geophysical data as well as engineering verification,the authors hold that the magnetotelluric method and the induced polarization method are fairly credible and economical. In addition,different inversion methods should be jointly arranged to analyze and judge the typical deposits; only in this way can the aim of preliminary prognosis of the orebody be achieved.