贵州贵定半边街锌矿床地球化学特征与找矿进展

Geochemical characteristics and ore prospecting progress of the Banbianjie Zn deposit in Guiding City, Guizhou Province, China

贵定半边街锌矿床位于湘西—黔东铅锌成矿带西南部黄丝背斜西翼,赋存于泥盆系碳酸盐岩中。该矿床矿物组成简单,主要由闪锌矿和碳酸盐矿物(方解石、白云石)组成,黄铁矿和方铅矿次之。矿物结构以半自形-他形粒状、交代、港湾状等为主,矿石构造多为块状、纹层状和脉状。硫化物(闪锌矿、黄铁矿和方铅矿)单矿物颗粒法和LA-MC-ICPMS原位法获得的δ^(34)S值介于-20.35‰~-4.65‰,具有明显的亏重硫同位素特征,暗示该矿床成矿流体中的硫很可能来自赋矿围岩中的海相硫酸盐矿物,且经历了海相硫酸盐矿物的细菌还原作用(BSR)。方铅矿LA-MC-ICPMS原位Pb同位素组成变化范围较窄,且其^(206)Pb/^(204)Pb比值介于18.362~18.365,^(207)Pb/^(204)Pb比值介于15.714~15.723,^(208)Pb/^(204)Pb比值介于38.275~38.286,壳源特征明显,暗示成矿流体中的金属地壳来源且来源单一或多来源但均一化程度很高。通过与潜在源区及邻区矿床对比,本文认为半边街锌矿床成矿流体中的金属很可能来自赋矿地层及其下伏地层(包括基底),并经历了成矿流体均一化过程,是流体-构造-岩性耦合成矿的产物。在新的流体-构造-岩性耦合成矿模式指导下,半边街锌矿床实现锌金属增储39万吨,并发现锗的显著超常富集,取得了找矿重要新进展。

The Banbianjie Zn deposit in Guiding City,Guizhou Province is located in the west limb of the Huangsi anticline within the southwestern part of the Western Hunan-Eastern Guizhou Pb-Zn metallogenic belt.Its orebodies are hosted in the Devonian carbonate.It has relatively simple mineral components,including major minerals of sphalerite and carbonate minerals(calcite,dolomite),and minor minerals of pyrite and galena.The ores have dominant semi-euhedral to anhedral granular,metasomatic or harbour-like textures and dominant massive,lamellar,and vein-type structures.The δ^(34)S values of sulfides(sphalerite,pyrite,and galena)obtained by analyzing separates of mineral particles and analyzing in-situ particles using the LA-MC-ICPMS in-situ method range from-20.35‰to-4.65‰,with obvious characteristics of depleted heavy sulfur isotopes.This suggests that the sulfur in the ore-forming fluid of the deposit could be sourced from the bacterial reduction(BSR)of marine sulfate minerals within the ore-hosted wall rocks.The in-situ LA-MC-ICPMS Pb isotopic compositions of galena grains vary in relatively narrow ranges,with the ^(206)Pb/^(204)Pb ratios varying from 18.362 to 18.365,^(207)Pb/^(204)Pb ratios varying from 15.714 to 15.723,and ^(208)Pb/^(204)Pb ratios ranging from 38.275 to 38.286.These Pb isotopic compositions are obviously characterized with those of the crust source,suggesting that the metals in the ore-forming fluid could be derived from a single source or the highly homogenized one originally from multiple sources.By comparing with the potential source rocks and the similar deposits in the neighboring areas,it is believed that the metal in the ore-forming fluid of the Banbianjieb Zn deposit could be derived from the ore-hosted strata and the underlying strata(including the basement),and then had undergone the homogenization process in the ore-forming fluid.Orebodies of the Banbianjieb Zn deposit were productes of the fluid-structure-lithology coupling metallogenesis.In addition,under the guidance of the newly established fluid-structure-lithology coupling metallogenic model,an important new progress of the mineral exploration,including an increase of 390,000 tons of zinc metal reserve and the discovery of significant and extraordinary enrichment of germanium in the Banbianjie Zn deposit has been achieved.