云南金沙厂铅锌矿床地球化学特征及其指示意义

Geochemical Characteristics and Indication Significance of Jinshachang Lead-zinc Deposit,Yunnan Province

位于扬子地块西南缘的“川滇黔铅锌矿集区”是我国西南大面积低温成矿域的重要组成部分,金沙厂铅锌矿床是其中典型矿床之一,前人针对金沙厂矿床的成矿物质来源和成矿流体特征开展了大量研究,但围岩对成矿的贡献和矿床成因仍不明确。针对这一问题,本文系统分析了金沙厂闪锌矿及围岩的微量元素组成,结合围岩和萤石的稀土元素特征,探讨了围岩对成矿的贡献,厘定了矿床成因。研究表明,闪锌矿以富集Cd、Ge、Cu、Ga,贫Fe、Mn、In、Co、Ni为特征,这些元素多以类质同象的形式赋存在闪锌矿中,个别元素如Cu、Ge等含量变化范围较大,可能与低温流体有关。矿床中闪锌矿存在多种颜色的原因可能是Cu、Ge等多种元素共同作用的结果。近矿端的围岩明显富集Zn、Pb、As、Cd等元素,而闪锌矿中同样富集这些元素,说明围岩为成矿提供了部分金属元素。萤石继承了围岩的Eu、Ce负异常,并受到了具有较高Ce负异常的成矿流体影响。萤石较围岩具有较高的Y/Ho比值,说明萤石中的部分Y来源于围岩,从而导致萤石具有较高的Y/Ho值。总体上,该矿床中闪锌矿微量元素组成与MVT矿床基本一致,明显有别于喷流沉积型、岩浆热液型和远端夕卡岩型矿床,其成矿温度属于低温范围,结合其矿床地质地球化学特征,本文认为金沙厂铅锌矿床属于MVT铅锌矿床。

The Sichuan–Yunnan–Guizhou lead-zinc ore cluster at the southwest margin of the Yangtze Plate is an important part of the large area of low-temperature metallogenic field in southwest China.The Jinshachang lead-zinc deposit is one of the typical deposits in the Sichuan–Yunnan–Guizhou lead-zinc ore cluster.Some studies have been carried out on the sources of metals and the characteristics of ore-forming fluids in the Jinshachang lead-zinc deposit.However,the contribution of surrounding rocks to mineralization and the genesis of the deposits are still unclear.In view of this problem,trace element compositions of sphalerite and surrounding rocks in the deposit were systematically analyzed.According to the REE characteristics of surrounding rocks and fluorite,the contribution of the surrounding rocks to mineralization was discussed and the genesis of the deposit was determined.The study shows that sphalerite is characterized by high Cd,Ge,Cu and Ga contents and low Fe,Mn,In,Co and Ni content,which are mainly formed and enriched in sphalerite due to isomorphous substitution.The contents of elements such as Cu and Ge vary greatly,which may be related to the low-temperature fluid.The multicolor sphalerite from the deposit may be attributed to the synergistic effect of Cu,Ge,As,Ag and other elements.The surrounding rocks near the ore-forming end are enriched in Zn,Pb,Ba,Cd and other elements,which are also enriched in the sphalerite,indicating that the surrounding rocks provide some metallic elements for mineralization.Fluorite inherits the negative Eu and Ce anomalies of the surrounding rocks and is affected by the ore-forming fluids with highly negative Ce anomalies.The fluorite has a higher Y/Ho ratio than the surrounding rock,indicating that part of the Y in fluorite originates from the surrounding rock,resulting in the fluorite having a higher Y/Ho ratio.Overall,the sulfur trace element composition of sphalerite in this deposit is consistent with that of MVT type deposits,which is obviously different from exhalative sedimentary deposits,magmatic hydrothermal deposits and distant source skarn-type deposits.The metallogenic temperature belongs to the low-temperature range.Combined with the geological and geochemical characteristics of the deposit,this study inferred that the Jinshachang lead-zinc deposit belongs to the MVT Pb-Zn deposit.