新疆库尔尕生铅锌矿床成矿作用:来自石英和闪锌矿原位微区成分的约束

Pb-Zn Mineralization in Kuergasheng Pb-Zn Deposit,Xinjiang:Constraints from In-situ Micro Composition of Quartz and Sphalerite

库尔尕生铅锌矿床位于新疆西天山赛里木地区,是一个形成于板内伸展环境中的热液脉型铅锌矿床。矿体呈脉状、网脉状以及透镜状赋存于上泥盆统托斯库尔他乌组上亚组中,并受控于3条近平行展布的NW向断裂带。成矿过程可分为无矿石英阶段(Ⅰ)、石英–多金属硫化物阶段(Ⅱ)(主成矿阶段)和方解石阶段(Ⅲ)3个阶段。笔者利用LA-ICP-MS方法对不同成矿阶段石英和闪锌矿进行了原位微区分析。结果表明:①库尔尕生铅锌矿床Ⅰ阶段和Ⅱ阶段石英中含有多种微量元素,主要富集Al、K、Na和Li。Al、K、Na、Li的质量分数分别为547.56×10^(-6)~4355.49×10^(-6)、9.41×10^(-6)~626.66×10^(-6)、23.78×10^(-6)~994.40×10^(-6)以及43.37×10^(-6)~265.52×10^(-6),Al与Li+Na+K之间呈显著的线性正相关关系;Ti、Ge含量较低,分别为3.17×10^(-6)~14.05×10^(-6)、1.77×10^(-6)~6.50×10^(-6),反映成矿温度较低。从Ⅰ阶段到Ⅱ阶段,石英中Ti含量在逐渐降低,指示成矿流体温度在逐渐降低;Al含量也在降低,反映成矿流体的pH值在逐渐升高。与世界典型的斑岩型和浅成低温热液型铅锌矿床相比,库尔尕生铅锌矿床的石英微量元素特征更类似于浅成低温热液型矿床。②闪锌矿中Mn、In、Fe、Ga、Ge等微量元素的含量和比值表明矿石形成于中低温环境,进一步利用闪锌矿GGIMFis温度计限定成矿温度为122~178℃。Ga/In值与lnw(Ga)-lnw(In)特征反映闪锌矿的形成与沉积作用有关。综合围岩地层的微量元素特征及前人Pb同位素研究,推测库尔尕生铅锌矿床部分成矿物质来源于围岩地层。

The Kuergasheng Pb-Zn deposit,located in the Serimu area of the western Tianshan of Xinjiang,is a hydrothermal vein-type Pb-Zn deposit formed in the extensional environment of the plate.The ore body is veined,reticulated and lenticular in the upper subgroup of the Upper Devonian Toskurtau Formation,and is con-trolled by three north-west fault zones that are spread in parallel with each other.The mineralization process can be divided into three stages:the pre-ore quartz stage(I),the quartz-polymetallic sulphides stage(II)(main min-eralization stage)and the calcite stage(III).In this study,the LA-ICP-MS method was used to analyze quartz and sphalerite at different stages of mineralization.The results showed that:(1)The Quartz in the I and II stages of the Kuergasheng Pb-Zn ore area contained more trace elements.Among them,Al,K,Na and Li are mainly enriched.The mass fractions of Al,K,Na and Li varied from 547.56×10^(-6)~4355.49×10^(-6),9.41×10^(-6)~626.66×10^(-6),23.78×10^(-6)~994.40×10^(-6),and 43.37×10^(-6)~265.52×10^(-6),respectively,showing a significant lin-ear positive correlation between Al and Li+Na+K.The contents of Ti and Ge were low,and the contents of Ti and Ge varied from 3.17×10^(-6)~14.05×10^(-6),and 1.77×10^(-6)~6.50×10^(-6),respectively,reflecting the low mineral-ization temperature.Compared with the world's typical porphyry-type and epithermal Pb-Zn deposits,the quartz trace elements characteristics of the Kuergasheng Pb-Zn deposit are more similar to the epithermal Pb-Zn de-posits.(2)The content and ratio of trace elements such as Mn,In,Fe,Ga,Ge in sphalerite indicate that the de-posit was formed in a medium to low temperature environment,and the mineralization temperature was further limited to be 122~178℃by using sphalerite GGIMFis thermometer.The Ga/In ratio and lnw(Ga)-lnw(In)characteristics indicate that the formation of sphalerite is related to sedimentation.Combining the trace element characteristics of host rock with the previous Pb isotopic data,it is speculated that the ore-forming materials of the Kuergasheng Pb-Zn deposit were mainly derived from the host rock.