贵州普克金矿区黄铁矿和方解石地球化学特征及地质意义

Geochemical Characteristics and Geological Significance of Pyriteand Calcitein the Puke Gold Prospect Area,Guizhou Provinc

贵州普克金矿区位于我国著名的滇-黔-桂“金三角”地区泥堡大型金矿西南方向的外围区域,与泥堡金矿处于相同的大地构造环境,地层特征、构造样式基本相同,成矿地质条件良好,对其开展成矿流体性质和物质来源研究,有助于理解普克矿区金的成矿作用,并为下一步找矿勘探提供新的参考。本文在对普克金矿区地表发育的(褐铁矿化)黄铁矿-方解石脉进行野外地质调查的基础上,开展矿物学、方解石稀土元素以及黄铁矿电子探针与微区原位LA-ICP-MS分析,结果显示普克金矿区内大部分方解石脉显示出与泥堡金矿床不含矿方解石脉相似的稀土元素配分特征,少数方解石样品显示出与黔西南卡林型金矿成矿期方解石稀土元素一样的中稀土元素富集和Eu正异常特征。该类方解石脉中的黄铁矿Au元素含量高出平均地壳丰度及沉积成因黄铁矿中Au的含量几个数量级,且Au在黄铁矿中以Au+离子形式存在,表明这些黄铁矿形成于金成矿期的热液环境。含金方解石出现中稀土元素富集模式和Eu正异常特征,表明金成矿流体系还原性质。由于地壳抬升剥蚀的影响,普克金矿区内中稀土元素富集、Eu正异常的方解石脉在地表的露头较少,也可能与普克金矿有利成矿地层层位(二叠系峨眉山玄武岩组)埋深较大、能运移到现今地表层位(三叠系永宁镇组)的成矿热液相对较少有关,指示深部有较好的金成矿潜力。

The Puke gold prospecting area is located 3 km southwest of the famous Nibao gold deposit,sharing the same regional geological background,similar stratigraphic characteristics,tectonic style,and ideal geolo-gical conditions for gold mineralization.Based on field observations of the calcite veins(limonitization)deve-loped on the surface and in drill holes,we conducted mineralogical analysis of calcite and pyrite,rare earth ele-ment(REE)analysis of calcite,electron probe micro-analysis(EPMA),and LA-ICP-MS analysis of pyrite to constrain the origin of the ore-forming fluids and materials in the Puke gold prospecting area.The results show that most of the calcite veins in the Puke gold prospect area have similar characteristics to those in the Nibao gold deposit;however,the latter does not contain ore-bearing calcite veins.Most calcite veins in the Puke gold prospect area exhibit REE patterns similar to those of the Nibao gold deposit,and a few calcite samples show positive Eu anomalies,similar to the calcite from the mineralization period of Carlin-type gold deposits in South-eastern Guizhou.However,the Au content of pyrite in these calcite veins is several orders of magnitude higher than that of the average crustal abundance and sedimentary pyrite,with Au existing in pyrite in the form of Au+.This suggests that these pyrite veins are of hydrothermal origin.The gold-bearing calcite exhibits an en-richment pattern of medium REE and positive Eu anomalies.This suggests that the gold-forming fluids are reducing,possibly controlled by acidic ore-forming fluids as in the case of the Nibao gold deposit.There are fewer calcite veins exposed on the surface in the Puke gold prospect area,possibly because the favorable ore-forming strata of the Puke gold are deeper.There is less ore-forming hydrothermal fluid transported to the pre-sent-day surface strata,implying that ideal gold mineralization developed at deeper levels.