内蒙古二道河子矿床闪锌矿LA-ICP-MS微量元素地球化学特征及成因意义

Genesis of the Erdaohezi deposit,Inner Mongolia,China:constraints from LA-ICP-MS trace element geochemistry of sphalerite

额尔古纳地块是我国东部重要的铅锌银矿集区之一,本文以该地块中的代表性矿床——二道河子铅锌多金属矿床为例,用激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)和电子探针测试了该矿床三个世代闪锌矿(sph1、sph2、sph3)的主、微量元素组成,以期揭示闪锌矿中元素的赋存状态和富集规律,制约成矿物理化学条件,并为判定矿床成因提供更多依据。结果表明,闪锌矿相对富集Fe、Mn、Cd和In,亏损Ga、Ni、Ge、Tl和Se等元素;随着成矿作用从早到晚的演化,Fe、Mn含量逐渐降低,Hg含量逐渐升高;与其他两个世代闪锌矿相比,sph2中的Cu、Pb、Bi、Sn和Ag等元素含量相对高,In含量相对低。通过时间分辨率剖面曲线及相关性分析,表明Mn、Cd、In、Hg和Sn等元素主要以类质同象形式进入到闪锌矿中,Pb和Cu多以微小矿物包裹体的形式存在,而Fe和Ag则两种形式均有。闪锌矿的微量元素组成和Zn/Cd、Ga/In值表明早中期闪锌矿形成于中高温、还原环境,至成矿晚期,温度下降,还原性减弱。根据闪锌矿微量元素的特征,并结合前人研究,本文认为二道河子矿床属于与晚期次火山岩(或隐伏侵入岩)有关的浅成热液型铅锌银多金属矿床。

The Erguna block is one of the most important Pb-Zn-Ag metallogenic provinces in East China.In this study,the laser ablation-inductively coupled plasma mass spectrometry(LA-ICP-MS)and electronic probe have been used to determine the major and trace element concentrations of three generations sphalerites(sph1,sph2 and sph3)from the Erdaohezi Pb-Zn polymetallic deposit,a representative deposit in the Erguna block,in order to reveal the enrichment regulation and occurrence state of elements in sphalerites of the deposit,to explore physico-chemical conditions controlling the mineralization of the deposit,and to provide much more insights for discriminating genesis of the deposit.Our results show that the sphalerite is enriched in Fe,Mn,Cd,and In,but is depleted in Ga,Ni,Ge,Tl,and Se.From the earliest sphalerite generation(sph1)to the youngest sphalerite generation(sph3),the Fe and Mn contents of sphalerites are gradually decreased,whereas the Hg contents of sphalerites are gradually increased.Comparing to other two generations of sphalerite,the sph2 sphalerite contains relatively high concentrations of Cu,Pb,Bi,Sn,and Ag but relatively low contents of In.The time-resolved depth profiles and elemental correlation analyses of sphalerite reveal that elements including Mn,Hg,Cd,In,and Sn are mainly incorporated into the sphalerite lattice in the form of homomorphic substitution,Pb and Cu occurred mostly as mineral micro-inclusions in the sphalerite,but Fe and Ag occurred both as solid solution and mineral micro-inclusions in the sphalerite.The trace element contents and ratios of Zn/Cd and Ga/In of sphalerites indicate that sphalerites of the first two generations were formed under a condition of medium-high temperature and reduced environment,whereas the sphalerite of latest generation was formed under a condition of relatively low reduced environment at relatively low temperature.On the basis of field observations,previous studies,and characteristics of trace element of sphalerites using the in situ microanalysis,we have concluded that the Erdaohezi Pb-Zn polymetallic deposit belongs to an epithermal Pb-Zn-Ag polymetallic deposit related to late-stage subvolcanic rocks or concealed intrusions.