云南富乐铅锌矿床黄铁矿微量(稀散)元素组成及成因信息:LA-ICPMS研究

The trace( dispersed) elements in pyrite from the Fule Pb-Zn deposit,Yunnan Province,China,and its genetic information: A LA-ICPMS study

川滇黔铅锌矿集区是华南大面积低温成矿域的重要组成部分,区内铅锌矿床是否属于MVT型矿床长期存在争议。该区铅锌矿床以富集Ge等稀散元素为特征,闪锌矿是其主要载体矿物,但稀散元素在黄铁矿中是否富集、赋存状态及微量元素组成特征等研究基本属于空白。本文通过LA-ICPMS研究富乐黄铁矿中微量元素(尤其是稀散元素)的富集特征,发现黄铁矿中也相对富集Ge。本研究样品选自富乐矿床的富乐和富盛两个矿段,包括1350、1410和1536三个中段(由深到浅),LAICPMS分析结果表明,该矿床黄铁矿以富集Cu、As、Co、Ni为特征,局部富集Pb(Sb)和Zn(以方铅矿和闪锌矿显微包裹体形式赋存于黄铁矿中),该类黄铁矿富集的稀散元素主要为Se、Ge及少量Tl、Te,而Cd和In以类质同象形式赋存于含Zn的显微包裹体(闪锌矿)中,类质同象是其余稀散元素主要赋存形式,且黄铁矿中Ge与Cu存在较好相关关系,可能存在Cu2++Ge2+?2Fe2+耦合置换方式。此外,黄铁矿中稀散元素的富集与成矿元素(特别是Cu)的富集密切相关,随着成矿作用的进行,从矿体深部到浅部,成矿温度逐渐降低,Se/Te比值逐渐升高,且稀散元素与成矿元素呈逐渐增加趋势。研究表明,该矿床黄铁矿的Co/Ni比值基本都小于1. 00,暗示其属于沉积改造型黄铁矿,在Co-Ni和稀散元素Se-Tl含量投影图上,富乐矿床黄铁矿的投影点与MVT型矿床投影区基本一致,而明显有别于SEDEX、VMS和矽卡岩型矿床中黄铁矿的投影区,结合富乐矿床类似于MVT型的地质特征,我们认为富乐矿床属于MVT型铅锌矿床。

The Sichuan-Yunnan-Guizhou Pb-Zn mineralization province( SYGMP) is an important part of the large-scale lowtemperature metallogenic domain in Southwest China. There is always controversy on whether the Pb-Zn deposits in the SYGMP belong to a MVT-type. Additionally,these deposits are mainly characterized by enrichment in dispersed elements( especially Ge) which is chiefly hosted in sphalerite. Owing to the lack of study on trace elements in pyrite,in this paper,we analyzed the characteristics of trace( including dispersed) elements in pyrite from the Fule Pb-Zn deposit by LA-ICPMS,showing that the pyrite is one of carrier minerals of Ge except the sphalerite. Three samples were collected from Fule and Fusheng ore blocks,which represent ore bodies in level 1350,1410 and 1536 meters,respectively,i. e. from deep to shallow. The results show that the pyrites are characterized by enrichment of Cu,As,Co and Ni,and local high contents of Pb( Sb) and Zn are identified as micro-inclusions like galena and sphalerite. The dispersed elements in pyrite are typically recognized by enrichment of Se and Ge,together with minor Tl and Te. Most of the dispersed elements occur as isomorphous substitution in the pyrite,except Cd and In which principally hosted in Zn-bearing micro-inclusions( sphalerite) as isomorphous substitution too. The strongly positive correlations between Ge and Cu in the pyrite indicate the replacement mechanism is Cu2 ++ Ge2 +?2 Fe2 +. The enrichment of dispersed elements in pyrite is closely related to the enrichment of ore-forming elements,especially Cu. With the development of the mineralization( ore-bodies from deep to shallow),the Se/Te ratios,dispersed and ore-forming elements are concentrated gradually. Most of the Co/Ni ratios are less than 1. 00,suggesting pyrites have experienced a sedimentary-reworked process. In the scattergrams of the Co-Ni and dispersed elements Se-Tl,pyrites from the Fule deposit were plotted within the field of typical MVT deposit,and are different from that of pyrites in the SEDEX,VMS and skarn deposits. Combining the evidence of the geological features,the Fule deposit is similar to MVT deposit,it is suggested the Fule Pb-Zn deposit belong to a MVT-type deposit.