四川天宝山铅锌矿床硫化物微量元素组成：LA-ICPMS研究

Trace elements in sulfide from the Tianbaoshan Pb-Zn deposit,Sichuan Province,China:A LA-ICPMS study

"川滇黔接壤铅锌矿集区"是我国西南大面积低温成矿域的重要组成部分,对于其中铅锌矿床是否属于MVT型矿床存在较大争议。本文以该矿集区中代表性矿床——四川天宝山矿床为例,通过LA-ICPMS原位元素分析,结合元素Mapping,以认识该矿床中闪锌矿和方铅矿微量元素组成特征及其赋存状态。研究表明,矿床中闪锌矿以富集Cd、Ge贫Fe、Mn、In、Sn、Co为特征,这些元素均以类质同象形式赋存于闪锌矿中,但含量变化范围较大,这可能与其成矿流体属于低温混合流体有关,这类盆地卤水流体在长期和长距离运移过程中,流经不同基底地层,活化出其中不同微量元素,因此成分变化较大,但以低温元素为主。此外,矿床中闪锌矿Ge和Cu呈现较好正相关关系,暗示其与Zn置换方式为:nC u^(2+)+Ge^(2+)(n+1)Zn^(2+),这可能是该矿床富集Ge的重要原因之一;矿床中方铅矿以富集Ag、Sb贫Bi为特征,含微量Cd和Tl,类质同象是这些元素主要赋存形式,其置换方式为(Ag)^(1+)+(Sb)^(3+)2Pb^(2+);矿床中Ge主要赋存于闪锌矿中,而方铅矿中不含Ge。总体上,本矿床硫化物微量元素组成与MVT型矿床基本一致,明显有别于喷流沉积型矿床、岩浆热液型矿床和远源夕卡岩型矿床,其成矿温度属于低温范围,成矿流体运移方向可能为深部→浅部。结合其矿床地质地球化学特征,本文认为天宝山铅锌矿床属于MVT型矿床,但其中闪锌矿中富集Cu,而方铅矿中富集Ag,可能暗示其形成具有一定特殊性。

The Siehuan-Yunnan-Guizhou Pb-Zn mineralization province is an important part of the large-scale low-temperature metallogenic domainin southwestern China, and there are different opinions about the genetic type of Pb-Zn ore deposit in the area. Analyzed by LA-ICPMS with mapping for the Tianbaoshan Pb-Zn ore deposit, Huidong, Sichuan Province, China, it is researched on the trace elements in sphalerite and galena and its existing state from the deposit in the paper. The results show that the sphalerite is characterized by enrichment of Cd, Ge and depleted in Fe, Mn, In, Sn, Co, and those trace elements occur as isomorphous substitution in the sphalerite with a wide content range, related possibly to the low temperature ore-forming fluid which come from the basin brine. In the process of long distance migration of the fluid with a long time, the different trace elements were leached out from different basement strata by the fluid, resulted in the formed sulfide minerals were rich in low temperature elements with a wide content range. There is a good positive correlation between Ge and Cu in the sphalerite, implying the replacement mechanism is nCu2 ＋ ＋ Ge2＋ （ n ＋ 1 ） Zn2＋ , which is an important possible factor of the enrichment of Ge in the deposit. The galena is characterized by enrichment of Ag, Sb and depleted in Bi with trace Cd and TI, which occur as isomorphous substitution in the galena, and the replacement mechanism is （Ag）1＋ ＋ （Sb）3 ＋ ←→2Pb2＋. Apart from this, our research shows that the occurrence of Ge is dominated by the sphalerite rather than the galena. In brief, the trace elements in sulfide from Tianbaoshan Pb-Zn ore deposit are similar to that of MVT Pb-Zn deposit, and different with that of exhalative sedimentary type deposit, magmatic hydrothermal type deposit and skarn deposit. The Pb-Zn mineralization formed at low temperature （ 〈 200℃ ）, and the ore forming fluid migrated from the bottom to the top. It is suggested that the ore genesis of Tianbaoshan Pb-Zn deposit belong to the MVT deposit, while the sphalerite is rich in Cu and the galena is rich in Ag, implying a special ore forming process.