喀喇昆仑多宝山矿床非硫化铅锌矿物形成机制研究

Recently years many Pb-Zn deposits have been discovered in Tianshuihai area of Karakorum Mountains, Xinjiang Province. The secondary oxidation is widespread in many deposits. And various types of nonsulfide Pb-Zn minerals developed in these deposits. However, mechanisms of the secondary oxidation are not very clear at present. Hence, relative researches are done at Duobaoshan deposit, which developed both Pb-Zn sulfide and nonsulfide Pb-Zn minerals. The oxidation ratio of lead ore and zinc ore were from 16% to 90% and 33% to 100%, respectively. Many nonsulfide Pb-Zn minerals, including anglesite, cerussite, miniumite, massicot, cotunnite, smithsonite, hydrozincite, hemimorphite, etc, were found in this deposit. Through detailed petrographic, mineralogical observations, the fabric characteristics, paragenetic association, formation orders, the migration and enrichment of ore forming elements in the secondary enrichment zone will be discussed. Basing on the isotope geochemistry analysis of different minerals, ore-forming material sources will be identified. And also, the change of isotope composition will be trace the different ore-forming material sources in the secondary oxidation process. The possible mechanisms of the secondary oxidation will be explored here. This study will enrich the theoretical understanding of nonsulfide Pb-Zn deposit and also important significance for discovery of similar deposits in this area.

近年新疆喀喇昆仑甜水海地区发现多处铅锌矿床，其中铅锌矿物氧化作用强烈，形成类型多样的非硫化铅锌矿物，目前对其形成机制研究薄弱，制约着本区成矿规律的认识。其中多宝山矿床内铅锌硫化物、非硫化矿物均发育，铅氧化率16-90%，锌氧化率33-100%。形成极为丰富的非硫化铅锌矿物，包括：铅矾、白铅矿、铅丹、铅黄、氯铅矿、菱锌矿、水锌矿、异极矿等，是开展本次研究的理想对象。在野外调研基础上，通过岩相学、矿相学观测，对其铅锌硫化物、非硫化矿物的组构特征、共生组合、生成顺序、成分变化进行对比分析，探讨其氧化过程中元素迁移富集过程。其次，对比不同成矿阶段矿物中Pb、S、C、O同位素组成，结合Zn、Cd非传统同位素分析，揭示其成矿流体来源及其变化特征，阐明非硫化铅锌矿物富集的控制因素，探讨其形成机制。本研究将深化区带内铅锌矿床氧化作用的理论认识，对寻找类似铅锌矿床具有重要指示意义。

新疆喀喇昆仑多宝山铅锌矿床兼有硫化物型和碳酸盐型铅锌矿物，是研究非硫化物铅锌形成机制的良好对象。其成因主要存在MVT型和构造热液型不同认识，制约了该区铅锌矿成矿规律深化和找矿工作推进。通过对多宝山铅锌矿床矿物组构及其形成演化研究，将其划分为铅锌硫化物、氧化交代和次生氧化等3个成矿阶段。厘清了矿物生产序列，识别出两期不同成因的菱锌矿。方铅矿、白铅矿、菱锌矿Pb同位素显示其Pb同位素比值变化范围小，铅源较为单一，指示来源于上地壳碳酸盐岩沉积盖层。原位微区S同位素显示，方铅矿δ34SCDT值-25.75‰~4.08‰，铅矾-15.8‰~2.44‰，浸染状黄铁矿为-21.55‰~ -15.89‰。铁龙滩组灰岩中黄铁矿为13.5‰~32.49‰，球粒集合体状、似草莓状方铅矿为-30.11‰~ -29.78‰，其具有极低δ34SCDT值，认为其是生物细菌还原作用的产物，揭示出在成矿前Pb的预富集，为晚期热液矿体的形成提供物源。方铅矿、铅矾具有相近的SCDT值，介于地层中原生硫化物和海相硫酸盐二者之间，反映出成矿流体据原生硫化物、海相硫酸盐矿物混合来源。系统的S同位素示踪和成矿流体组分分析显示在铅锌硫化物期浸染状黄铁矿δ34SCDT组成与地层中原生硫化物关系密切。氧化交代阶段碳酸盐铅锌单矿物C，O同位素显示，菱锌矿δ13C PDB值为2.9‰~9.1‰，δ18O SMOW值为16.9‰~ 29.1‰。白铅矿δ13C PDB值为2.7‰~4.4‰，δ18O SMOW值为15.8‰~20.3‰。方解石δ13CPDB值为-5.8‰~5.7‰，主体变化在3.44‰~5.7‰，δ18O SMOW值为16.0‰~ 27.1‰。该阶段与海相碳酸盐去碳酸作用关系密切，并受表生碳酸盐溶解作用影响，有大气水和二氧化碳参与，属直接交代型表生非硫化物矿床。晚期次生氧化期发育铅黄、铅丹、角铅矿等，同时发育第二期菱锌矿，该阶段形成富锌成矿流体的运移，与青藏高原隆升剥蚀有关。区内流体包裹体测量显示其成矿流体为低温度和中低盐度热卤水。上述揭示在硫化物期成矿物质来源具有碳酸盐岩地层还原硫和盆地卤水共同参与，具MVT型铅锌矿成矿特征，后期氧化成矿阶段，与表生非硫化物铅锌矿床一致。综上，多宝山铅锌矿床是MVT+氧化交代的产物。