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甘肃毕家山铅锌矿床中镉的赋存状态及其矿床成因研究：来自硫化物LA

花匠小妙招
2024-09-19 05:48

陈雪锋, 白荣龙2, , 郭东宝1, 3, 4, 刘光贤5 1.

自然资源部黄河上游战略性矿产资源重点实验室

天水师范学院资源与环境工程学院

甘肃省有色金属地质勘查局兰州矿产勘查院

兰州大学资源环境学院

东华理工大学

基金项目: 天水师范学院 2021年产业支撑引导项目;甘肃省自然资源厅科技创新项目;甘肃省高等学校青年博士基金项目

计量文章访问数: 100 HTML全文浏览量: 0 PDF下载量: 4 出版历程收稿日期: 2023-02-19 修回日期: 2023-06-01 录用日期: 2023-06-05 网络出版日期: 2024-09-18

摘要

摘要: 毕家山铅锌矿床是西成矿田发现的首个铅锌矿床，累计探明铅锌资源120万吨，Pb和Zn的品位分别为1.86%和5.42%。矿床中发育两类矿体，第一类矿体赋存于灰岩中，矿石类型为灰岩型；第二类矿体赋存于千枚岩中，矿石类型为千枚岩型。两类矿体的矿石矿物组合均为闪锌矿＋方铅矿±黄铁矿±黄铜矿。前人对毕家山铅锌矿床地质特征、岩相学、同位素地球化学和流体包裹体开展了深入研究，但关于Cd的赋存状态研究尚不明确。本文通过激光剥蚀电感耦合等离子质谱仪（LA-ICP-MS）分别对灰岩型和千枚岩型矿石中的硫化物（闪锌矿、方铅矿、黄铁矿和黄铜矿）进行了微量元素分析，研究结果显示灰岩型和千枚岩型矿石中闪锌矿的Cd平均含量分别为2076×10-6和1695×10-6，高于矿产工业一般标准，而灰岩型和千枚岩型矿石中方铅矿、黄铁矿和黄铜矿中的Cd、Ga、Ge、Se、In、Tl含量均低于矿产工业一般标准。本文结合岩相学和LA-ICP-MS分析发现毕家山铅锌矿床无Cd的独立矿物和以吸附形式存在的Cd，Cd主要以Cd2+↔Zn2+类质同象替换d 形式赋存于闪锌矿中，其次为Cd2+ +Fe2+ ↔ 2Zn2+。通过闪锌矿微量元素温度计获得灰岩型和千枚岩型矿石中闪锌矿的形成温度分别为189~254℃（平均值为218℃）和193~245℃（平均值为229℃），与前人通过流体包裹体和矿物对温度计研究的结果一致，指示成矿温度为中温。综合闪锌矿微量元素数据、岩相古地理、矿床地质特征、同位素地球化学和成矿温度证据进行对比分析，本文认为毕家山铅锌矿床的成因类型属于SEDEX型。

Abstract: The Bijiashan Lead-Zinc deposit (BJS Pb-Zn deposit) is the first been discovered Lead-Zinc deposit in the Xicheng ore field, with reserves of 1.2 million tons of lead and zinc, and the grades are 1.86% and 5.42%, respectively. There are two ore bodies developed in the BJS Pb-Zn deposit: the first kind of ore body occurs in limestone, the ore type is limestone type. The second type of ore body occurs in phyllite, the ore type is phyllite type. The mineral combinations are all sphalerite + galena + pyrite + chalcopyrite. Previous research works are focus on the geological characteristics, petrography, isotope geochemistry and fluid inclusions of the Bijiashan Pb-Zn deposit, but the Cd occurrence status is still uncertain. In this study, the LA-ICP-MS were used to analysis different sulfides (sphalerite, galena, pyrite, and chalcopyrite) in two types of ore bodies (limestone type and phyllite type). The analysis results show that the average Cd content of sphalerite in limestone type and phyllite type ores is 2075.72 ppm and 1694.70 ppm in the Bijiashan Pb-Zn deposit, respectively. However, the contents of Cd, Ga, Ge, Se, In and Tl in galena, pyrite and chalcopyrite of limestone type and phyllite type ores are lower than the general standards of the mineral industry. Based on petrography and LA-ICP-MS analysis, this study finds there is no independent Cd minerals and adsorption form Cd exists in sphalerite in the BJS Pb-Zn deposit. Cd is mainly incorporated into sphalerite by the substitution of Cd2+ ↔ Zn2+, with minor substitution of Cd2+ + Fe2+ ↔ 2Zn2+. The estimated formation temperature of sphalerite in limestone type and phyllite type ores in the Bijiashan Pb-Zn deposit yield 189~254°C (mean of 218°C) and 193~245°C (mean of 229°C) respectively, which is consistent with the previous fluid inclusions thermometers studies, indicating that the ore-forming mineralization temperature is moderate. Based on the comparative analysis of the trace element data of sphalerite, lithofacies palaeo geography, deposit geological characteristics, isotope geochemistry, and metallogenic temperature evidence, it is believed that the Bijiashan Pb-Zn deposit should belong to SEDEX type deposit.

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