闽中梅仙丁家山铅锌矿床硫化物微量元素地球化学特征及其成矿意义

Trace element characteristics of sulfides from Dingjiashan Pb-Zn deposit in Meixian of central Fujian Province and their metallogenic significance

梅仙丁家山铅锌矿床是闽中新元古代马面山群中多个大中型铅锌多金属矿床的典型代表。本文以丁家山铅锌矿床两类矿石(含磁黄铁矿矿石和含磁铁矿矿石)内的闪锌矿和黄铁矿为研究对象,通过电子探针及LA-ICP-MS微量元素分析技术,揭示二者的微量元素组成和赋存状态,探讨成矿温度及矿床成因方面的重要信息。分析结果显示:闪锌矿内Fe、Mn、Cd、Cu、In、Pb、Bi元素较为富集,两类矿石内的闪锌矿除Fe元素含量相差较大以外(平均值分别为9.3%和1.7%),其他元素含量并无明显差异;电子探针面扫描和LA-ICP-MS剥蚀图像显示元素Mn、Cd、In以类质同象形式存在,而Fe、Cu、Pb、Bi则有类质同象和显微包体2种存在形式。黄铁矿微量元素含量整体较低,元素Co、Ni、Pb、Bi相对富集,Ni、Mn主要以类质同象形式存在,Cu、Co有类质同象替换和显微包体2种形式,Pb、Bi主要以方铅矿包体形式存在。两类矿石中的闪锌矿Zn/Cd比值分别在120~150之间和93~210之间,均指示中温成矿条件。两类闪锌矿内Fe、Cd、Mn元素含量特征与典型矽卡岩型矿床内的闪锌矿相吻合;矿床内硫化物硫同位素组成揭示成矿物质来自于岩浆岩。上述证据共同支持梅仙丁家山铅锌矿矿床属矽卡岩型矿床。

The Dingjiashan Pb-Zn deposit in Meixian is a typical representative of many large and medium-sized leadzinc polymetallic deposits in the Neoproterozoic Mamianshan Group in central Fujian Province.There are two types of ores in the Dingjiashan Pb-Zn deposit,i.e.,pyrrhotite-bearing and magnetite-bearing ores.EPMA and LA-ICP-MS were used to reveal the trace element composition and modes of occurrence of sphalerite and pyrite,and then important information concerning the mineralization temperature and the genesis of the deposit was investigated.The analytical results show that sphalerite is relatively enriched in Fe,Mn,Cd,Cu,In,Pb,Bi,and there is no significant difference in the content of other trace elements in sphalerite from two types of ore except Fe,whose average values are 9.3%and 1.7%respectively.EPMA elemental mapping and time-resolved laser ablation depth-profiles reveal that Mn,Cd,and In exist in the form of isomorphism in sphalerite,while Fe,Cu,Pb and Bi exist in the form of isomorphism and microscopic inclusion.The content of trace elements in pyrite is generally low,but Co,Ni,Pb,and Bi are relatively concentrated in pyrite.Ni and Mn mainly exist in the form of isomorphism.Cu and Co exist in two forms of isomorphism replacement and microscopic inclusions.Pb and Bi are present in galena inclusions.The Zn/Cd ratios of sphalerite from two types of ores respectively are 120~150 and 93~210 respectively,indicating that the two types of ores were formed at medium temperature.The Fe,Cd,and Mn content characteristics in the two types of sphalerite are consistent with those in typical skarn deposits;the sulfur isotope composition of the sulfide reveals that sulfur in ore-forming material came from the magmatic rock body.The above evidence jointly supports the argument that the Dingjiashan Pb-Zn deposit in Meixian is a skarn deposit.