扬子地块西南缘金、锑矿床中方解石形成与成矿过程联系及找矿意义

The southwestern Yangtze massif is one of the most important accumulation areas of Carlin-type gold deposits and antimony deposits in China. These two types of ore deposits have close tempo-spatial and genetic relations. Calcite, as one of the most important gangue minerals, is widely developed in them. Previous studies have shown that the ore-related calcites have special MREE- and HREE-enriched characteristics and other typomorphic characteristics. This makes calcite with significant potential to be an indicator of ore-forming process and an important prospecting criterion. However, what kinds of typomorphic characteristics of calcites are closely related to mineralization? What are the mechanisms? How to use these typomorphic characteristics of calcites to guide ore-prospecting? These questions are still weakly studied. Consequently, in this project, the Banqi gold deposit and Muli antimony deposit from southwestern Yangtze massif have been selected as the main research objects. Through systematically research on the various kinds of physical and chemical typomorphics, it is aimed to explore the fluid mobilization and evolution processes, symbiosis and differentiation of ore-forming elements; illuminate the inner links between formation of ore-related calcites and ore-forming processes; systematically identify the differences of typomorphic characteristics and their causes between ore-related and barren calcites; construct a mineral-prospecting geological model for Au and Sb deposits based on multi parameter characteristics of calcites. It will help us to better understand such special geological phenomenon based on all above studies, and it is of significance to study of metallogenic mechanism, mineral exploration for Au and Sb deposits.

扬子地块西南缘是我国最重要的卡林型金矿及锑矿聚集区，两者时空相伴，成因密切联系。方解石作为重要的脉石矿物在这两类矿床中广泛发育，以往研究发现：与金、锑成矿密切相关的方解石具有特殊的中重稀土元素富集及其它标型特征，这使得方解石具有指示成矿过程并作为重要找矿标志的潜力。但方解石的哪些标型特征与成矿最为密切？其机制是什么？如何利用方解石的标型特征来指导找矿？仍是目前研究的薄弱环节。因此，本项目拟以扬子地块西南缘中的板其金矿床及木利锑矿床作为主要研究对象，通过对方解石各种物性标型和化学标型特征的系统研究，探索金、锑成矿过程中元素的迁移转化、共生分异等问题；阐明与成矿有关方解石的形成与金、锑成矿的内在联系；系统查清成矿与非成矿方解石的标型特征差异及原因；基于方解石多参数标型特征构建金、锑矿床找矿矿物学地质模型。通过以上研究，将对深入认识这一特殊地质现象并对金、锑成矿机制研究和找矿勘查具有重要意义。

扬子地块西南缘是我国最重要的卡林型金矿及锑矿聚集区，方解石是其中最常见的脉石矿物，蕴藏着重要的成因信息和找矿信息。本项目选取滇东南者桑卡林型金矿床和木利锑矿床作为典型矿床，在详细的矿物学填图基础上，采集大量不同期次、不同阶段的方解石样品。利用电子探针、透射电镜、FIB超薄切片、阴极发光、流体包裹体分析等手段对方解石的物性标型特征进行研究，通过微量元素、C-H-O-Sr-Nd同位素等分析对其化学标型特征进行研究，分析方解石与锑、金成矿过程的关系，深入探讨金、锑矿床成矿物质、流体来源和演化问题，并利用方解石标型特征构建金、锑矿床矿物学找矿模型。. 结果表明者桑金矿床成矿流体是由大气降水淋虑围岩形成，并含少量基性岩浆流体参与，具有中低温、中等盐度、低密度的特征。成矿期后的流体来源于大气降水对海相碳酸盐岩的溶解，其具有低温、低盐度、低密度特征。方解石在卡林型金矿形成过程中起着重要作用，当者桑金矿床方解石MREE/LREE比值大于0.92，MREE/HREE比值大于5.69，Fe元素含量大于3827μg/g和δ18OV-SMOW值小于14.40‰，Sr元素含量小于704μg/g、Ba小于3.7μg/g、包裹体盐度大于10.6%、以及均一温度大于193.6°C被视为成矿期方解石，可作为者桑金矿床的重要找矿线索。. 木利锑矿床成矿期方解石富集中、重稀土元素，其晶体内部包裹有Fe、Mn白云石微晶。成矿流体具有中低温、低盐度的特征，早期成矿流体具有岩浆来源信息，晚期成矿流体则有大气降水的加入。方解石的形成与锑成矿过程密切相关，方解石不同的地球化学特征代表不同的预测因子，当选取其中两个预测因子作为判别标准时，将R（Mn，δ18OV-SMOW）、R（Sr，δ18OV-SMOW）、R（Li，δ18OV-SMOW）的值分别与-3.31、-10.2和-23.4作对比，若大于上述值则说明该方解石为成矿期方解石；若选取三个预测因子作为判别标准则将R（Mn，δ18OV-SMOW，Li）、R（Sr，δ18OV-SMOW，Li）的值分别与-24.1和-29.6对比，若大于上述值则为成矿期方解石，识别出成矿期的方解石便可作为木利锑矿床重要的找矿指标。