云南西邑MVT型铅锌矿床地质特征与硫化物电子探针分析

Geological Characteristics of Sulfides of the Xiyi MVT-Type Pb-Zn Ore Deposit in Yunnan and EPMA Analysis of the Sulfides

云南保山西邑铅锌矿位于保山地块中北部,是实现隐伏铅锌矿找矿重大突破的典型矿床。矿体赋存于下石炭统香山组灰岩地层中,受NE向断裂及次级断裂构造控制,矿体与围岩界线清晰且受到一定地层层位控制;矿体形态变化较大,主要呈脉状、网脉状、透镜状、层状;金属矿物组合为闪锌矿、方铅矿±黄铁矿±毒砂。矿体主要为产于似层状含炭质褪色灰岩中的似层状铅锌矿体,以V3号矿体为代表,其Zn/Pb值平均为1.6,含较多的方铅矿,成矿温度相对较低;次为穿切岩层的破碎带型铅锌矿体,其Zn/Pb值平均为24.9,以铁闪锌矿为主,方铅矿少见,成矿温度相对较高。电子探针分析(EMPA)测定结果显示,西邑铅锌矿区闪锌矿中的Zn平均值为60.0%,S平均为32.9%,含Fe平均达6.2%(大于6%),为铁闪锌矿,是中-低温下析出的产物;方铅矿的Pb/S平均为1.01,接近理论值;黄铁矿的Fe平均为46.0%,S平均值为52.8%,S/Fe值为2.0,Co/Ni值平均为1.1,表现出热液成因黄铁矿的特点。这些数据表明,云南保山西邑铅锌矿具有MVT型矿床的特征。

The Xiyi lead- zinc ore deposit is located in the central- northern Baoshan block in Yunnan. It is typical in Pb- Zn prospecting breakthrough of concealed orebodies. Its orebodies are hosted in the limestone sequences of Lower Carboniferous Xiangshan Formation（ C1x）,controlled by NE- striking faults and secondary fracture structures. Mineralization is closely related to carbonates. On the basis of field observations,combined with microscopic identification and electron probe（ EPMA） analysis of thin sections,this work has revealed the geological characteristics of the ore deposit,ore structures,and mineral composition of this deposit. The results suggest that the ores are hosted mainly in limestone,and the most important ore- controlling factors are the faults and fractures. Orebodies are distinct from the wall rocks with clear boundaries and controlled by specific stratigraphic horizons.The shape of orebodies is highly variable,including veins,stockwork,lenticular,and layered structure. Ore mineral association includes sphalerite ＋ galena ± pyrite ± arsenopyrite. Orebodies can be subdivided into two kinds. One is the＂strata- like＂lead- zinc orebody that occurs within the carbonaceous decolorized limestones of stratiform- like. Its Zn / Pb ratio is 1. 6 on average,containing relative more galena,and the metallogenic temperature is relatively low. It is represented by the orebody V3 as the main orebody type in the Xiyi district. The other is the Pb- Zn orebody cutting through the strata as fracture zones,with an average Zn / Pb ratio of 24. 86,dominated by christophites. Its metallogenic temperature is relatively high. It is the secondary type in the Xiyi district with small and sparse veins. Electron microprobe（ EMPA） analysis shows that lead- zinc ore deposit in Xiyi district has averages of Zn 59. 99%,S 32. 92%,and Fe 6. 17%（ 6%）,indicative of christophites which formed under a relatively high temperature condition. The galena has Pb / S ratio of 1. 01 on average,nearly close to the theoretical value. The pyrite has averages of Fe 45. 96% and S 52. 79%,thus the S / Fe ratio is 1.999. Its Co / Ni ratio is 1. 05 on average,implying hydrothermal genesis of pyrite. These data suggest that the Xiyi lead- zinc ore deposit in Baoshan,Yunnan could be attributed to the MVT Pb- Zn type.