云南东川播卡金矿床黄铁矿成因矿物学特征研究

播卡金矿床是20世纪90年代在云南东川地区古—中元古界地层中首次发现的金矿床,但到目前为止,其矿床成因仍存在争议。为查明矿床成因,通过光学显微镜、粉末及原位X射线衍射和电子探针等手段对播卡金矿床中不同世代黄铁矿进行成因矿物学特征研究。结果表明,研究区黄铁矿可划分为3个世代:第一世代黄铁矿未发育环带结构、晶胞参数最小,富S亏Fe,低Co、Ni、As,为岩浆热液成因;第二世代黄铁矿广泛发育修复生长和环带结构,晶胞参数最大,富S亏Fe,富S程度有所降低,高Co、Ni、As,为岩浆热液和地下热卤水混合成因;第三世代黄铁矿多呈碎裂、碎粒状或经动力变质重结晶形成的自形晶,富S亏Fe,富S程度降低更为明显,晶胞参数和Co、Ni、As含量介于第一、二世代黄铁矿之间,为第一、二世代黄铁矿的变形变质产物。这些成因标型特征表明,播卡金矿床经历了印支—燕山早期的岩浆热液、岩浆热液和地下热卤水混合以及喜马拉雅期的变形变质阶段,其中,含矿热液流体由岩浆热液阶段的单一岩浆热液流体演化为岩浆热液和地下热卤水混合阶段的岩浆热液和地下热卤水双源流体。由此可见,播卡金矿床为岩浆热液型金矿床,但后期遭受动力剪切变形变质的叠加和改造,矿体进一步富集。

Genetic Mineralogical Characteristics of Pyrite in Boka Gold Deposit from Dongchuan Area,Yunnan Province

In the 1990s,the Boka gold deposit was first found in paleo-mesoproterozoic strata in Dongchuan district,Yunnan Province.The genesis of the deposit is still controversial.In order to determine the characteristics of its ore genesis,this study examine the genetic mineralogical characteristics of pyrites of different generations from the Boka gold deposit using optical microscope(OM),powder and in-situ X-ray diffraction(XRD),electron microprobe analyses(EPMA).The results show that pyrites from the deposit can be divided into three generations. Py1 has undeveloped zoning structure and the smallest lattice constant of the three.It has enrichment in S and depletion in Fe,low As,Co,Ni.It formed in a magmatic hydrothermal environment.In Py2 repair growth and zoning structure are developed very well and the lattice constant is the largest.The enrichment in S is lower than in Py1,it has depletion of Fe,high As,Co,Ni.Its deposition was related to mixed magmatic and underground thermal brines. Py3 is crushed and granulated,with minor euhedral crystals formed by dynamic metamorphic recrystallization.It has enrichment of S and depletion in Fe.The degree of S enrichment is significantly lower than Py1 or Py2.The lattice constant and As,Co,Ni contents are between Py1 and Py2.These results indicate the deposit originally formed in an environments similar to Py2 in the Indosinian-early Yanshanian and subsequently underwent a deformation-metamorphic stage in Himalayanian.Among them,the single magmatic hydrothermal ore-forming fluid in magmatic hydrothermal stage has been evolved the double-sources of those fluids in the mixture stage.This study shows that the Boka deposit is a magmatic hydrothermal type gold deposit which was transformed by dynamic shear deformation and metamorphism that resulted in further enrichment of the orebodies.