阿尔金喀腊达坂铅锌矿床金属硫化物元素地球化学特征及其对成矿作用的制约

Geochemical characteristics of metallic sulfides from the Kaladaban deposit in Xinjiang and its implications for Pb-Zn ore-forming mechanism

喀腊达坂铅锌矿床是近年来在阿尔金北缘红柳沟-拉配泉金铜铁多金属成矿带内发现的一处大型铅锌矿床(铅锌铜金属资源量82.88万吨,平均品位:Zn 4.14%、Pb2.52%和Cu 1.10%)。相比找矿勘查取得的重大突破,对其成矿作用的研究则显得相对薄弱,目前有关该矿床成因的认识还存在分歧。本文试图通过硫化物电子探针和LA-ICPMS微量元素分析,结合元素Mapping面分析,查明闪锌矿和方铅矿中微量元素的分布特征和赋存状态,以期为理解该矿床成因提供有益信息。分析结果显示:闪锌矿相对富Fe、Mn和Cd等元素,贫In、Sn、Ga、Cr、Ge和Co等元素,Cu和Pb的含量变化大,Fe、Mn、Cd、In、Ga和Cr在闪锌矿中以类质同象形式存在,而Cu和Pb则可能既以类质同象形式又以显微包体形式存在;方铅矿相对富Bi、Sb、Ag和Tl,贫Cd、Cu、Sn和Te为特征,其中前者以类质同象形式赋存于方铅矿中。达坂闪锌矿的颜色以红褐色、灰白色和米黄色为主,其Zn、Fe、Cd、Ga和In含量及Zn/Cd、Zn/Fe和Ga/In比值显示闪锌矿的形成温度为中温。基于闪锌矿-方铅矿共生矿物对Cd地质温度计获得的温度范围为277～321℃,平均值为290℃,亦说明达坂矿床硫化物的形成温度不高。与全球不同成因铅锌矿床的微量元素及相关比值相比,达坂铅锌矿床硫化物的微量元素组成特征与VMS型矿床(如Marketorp、Eskay Creek、澜沧老厂等)更为类似,但达坂矿床的闪锌矿中黄铜矿"病毒"结构十分发育,加之矿体变质变形特征明显。因此,本文认为达坂铅锌矿床以VMS型成因为主,但不排除后期热液对其形成有一定程度的影响。

The newly-discovered Kaladaban deposit is a large-scale Pb-Zn deposit,and it has a total Zn ＋ Pb ＋ Cu metal reserve of0. 83 Mt with mean grades of Zn 4. 14%,Pb 2. 52% and Cu 1. 10%,respectively. It is located in the Hongliugou-Lapeiquan Au-CuFe polymetallic metallogenic belt,northern Altun Mountains. Although great achievements and breakthroughs have been made in its ore exploration,studies upon its mineralization are relatively lacking,and its ore genetic mechanism is still controversial. In this paper,trace elements of the sphalerite and galena in the Kaladaban Pb-Zn deposit were studied by electron probe microanalysis（ EPMA）,LAICPMS together with elemental mapping analysis. The results show that sphaleriteis are relatively rich in Fe,Mn and Cd,and depleted in In,Sn,Ga,Cr,Ge and Co,while the contents of Cu and Pb vary greatly. Among them,Fe,Mn,Cd,In,Ga and Cr are in the lattice of sphalerite in the form of isomorphism,whereas Cu and Pb may exist in the forms of isomorphism and micro-inclusions. The galena is relatively rich in Bi,Sb,Ag and Tl,depleted in Cd,Cu,Sn and Te,among which the enriched elements occur as isomorphism in galena forms. The Dazan sphalerite is dominated by reddish brown,grayish white and beige,showing that its formation temperature is medium,which is also surpported by the calculated temperatures according to the Zn,Fe,Cd,Ga and In contents and Zn/Cd,Zn/Fe and Ga/In ratios of the sphaleritein this deposit. Based on the sphalerite-galena symbiotic mineral pairs,the formation temperature range obtained was 277 ~ 321℃ with an average value of 290℃,which also shows that the Daban sulfide formation temperature is not high. Compared with the trace elements and related ratios of different genesis Pb-Zn deposits in the world,the trace element compositions of the sulfides in the Daban Pb-Zn deposit are more similar to that of the VMS deposits（ such as Marketorp,Eskay Creek,Lancang Laochang,etc.）. However,a large number of chalcopyrite＂disease＂structures exist in the sphalerite,and the characteristics of metamorphism and deformation of the ore body are obvious. Therefore,we think that the Daban Pb-Zn deposit is dominated by the VMS type,but does not exclude the late hydrothermal effect on it to a certain extent.