湘中白马山-紫云山金矿带成矿年代学研究

Gold deposits in metamorphic terranes are the most important type of gold deposits throughout the world, among them, geologists have placed emphases on orogenic gold deposits, and usually ignored those intrusion-related gold deposits in recent several decades. Gold deposits are widespread in the Baimashan-Ziyunshan gold metallogenic belt, central Hunan, there gold mineralizations hosted in metamorphic rocks are closely associated with the emplacement of felsic intrusions, thus it is an ideal location to study the intrusion-related gold deposits in metamorphic rocks. Compared with those gold deposits hosted in the Precambrian low-grade metamorphic clastic rocks in the adjacent Xuefengshan Range, these gold deposits in the Baimashan-Ziyunshan gold metallogenic belt are very poorly constrained, the metallogenic timing, relationship between gold mineralization and magmatic activities, and those major geological events corresponding to gold mineralization in central Hunan are still unclear. Therefore, by means of different discipline methods including economic geology, petrology, mineralogy and geochemistry, integrated with different isotope dating methods including Re-Os,Ar-Ar,Sm-Nd and U-Pb isotope systematics, we attempt to determine the precise formation time of gold deposits and related flesic intrusions, ascertain the temporal and spatial relationships between gold mineralization and magmatic emplacement, and further reveal coupling relationship between gold mineralization in central Hunan and those major geological events happened in South China. Some importance of this program can be summarized as follows: (1) it will help to ascertain the ore genesis and formation mechanism of gold deposits in central Hunan; (2) it will help to promote the further understandings of the intrusion-related gold deposits; (3) it will develop the metallogenic theory for gold deposits in metamorphic terranes, and provide theoretical guidance for the prospecting of similar gold deposits.

变质地体中的金矿是世界上最重要的一类金矿，目前人们对变质地体中造山型金矿的研究较多，但对变质岩中与侵入岩有关的金矿，普遍关注较少。湘中白马山-紫云山一带浅变质岩中金矿床分布广泛，金矿与长英质侵入岩关系密切，是研究变质岩中与侵入岩有关金矿床的理想场所。目前该金矿带的研究程度较低，其成矿时代、岩浆活动与金成矿的关系、金成矿与华南主要地质事件的耦合关系，均不太清楚。本项目试图借助矿床学、岩石学、矿物学和地球化学的研究方法，并利用Re-Os、Ar-Ar、Sm-Nd、U-Pb等多种同位素定年手段，精确厘定该区金矿和相关岩体的形成时限，查明金矿与侵入岩的关系，并探讨金成矿与区域构造－热事件之间的耦合关系。本项目的开展，将有助于深化对湘中金矿的矿床成因和成矿机理的认识，促进与侵入岩有关的金矿床的研究，对丰富和完善变质地体中金矿的成矿理论，以及指导类似金矿床的寻找，均具有非常重要的意义。

变质地体中的金矿是世界上最重要的一类金矿，目前人们对变质地体中造山型金矿的研究较多，但对变质岩中与侵入岩有关的金矿关注较少。湘中白马山-紫云山一带浅变质岩中金矿床分布广泛，且与长英质侵入岩关系密切，是研究变质岩中与侵入岩有关金矿床的理想场所，但目前该金矿带的研究程度较低，其成矿时代、岩浆活动与金成矿的关系、金成矿与华南主要地质事件的耦合关系，均不太清楚。在野外地质调查和室内镜下研究的基础上，本项目借助矿床学、岩石学、矿物学和地球化学的研究方法，利用Re-Os、Ar-Ar、Sm-Nd、U-Pb等多种同位素定年手段，精确厘定了该区金矿和相关岩体的形成时限，查明湘中地区岩浆岩主要形成于晚三叠世，是印支构造运动的产物，该区金矿与长英质侵入岩关系密切，其成矿成岩时间基本一致，与还原性侵入岩有关的IRGS型金矿。湘中白马山-紫云山金矿带成矿时间的厘定，有助于认识该区金矿床的成矿过程和成矿机理，并指导类似金矿的寻找；本项目的开展也有助于深入认识湘中地区构造-岩浆演化历史，促进我国对与侵入岩有关的金矿床的研究。另外，在杏枫山金矿区发现高品位的钨矿体，资源潜力巨大，具有非常重要的经济价值和社会效益。