金属硫化物出溶结构特征与成因机制研究

Exsolution microstructures are widely distributed in metal sulfides from hydrothermal deposits. These microstructures are closely related to the conditions for deposit formation, and show indicative significance for their genesis. However, many exsolution microstructures are difficult to distinguish from intergrowth microstructures with other genesis(such as hydrothermal replacement) and the formation mechanism of the exsolution microstructures in metal sulfide remain controversial. In this project，we present an electron backscatter diffraction (EBSD) analysis, combined with Transmission Kikuchi Diffraction(TKD), transmission electron microscope (TEM) and electron probe micro-analyzer (EPMA) and optics microscope observations, for the exsolution microstructures in sphalerite, chalcopyrite, bornite and pyrrhotine. Morphology, crystallographic orientation, chemistry, phases, volume fractions of exsolutions from the host crystals will be characterized. On this basis, the crystallographic discriminant characteristics of exsolution microstructures in metal sulfides wil be established. Relationships between exsolution microstructures in metal sulfides and degree of internal structure matching, as well as that between exsolution microstructures and external metallogenic conditions will be discussed. In this study, we plan to establish the crystallographic thermobarometer for the exsolution microstructures in metal sulfides. It can provide theoretical basisand practical examples for using exsolution microstructures in metal sulfides to indicate metallogenic temperature and pressure.

金属硫化物出溶结构在热液矿床中广泛发育，并与成矿条件密切相关，具有重要的成因指示意义。然而，金属硫化物出溶结构与其它成因（如热液交代）的交生结构较难区分，出溶体与主晶的结晶学取向关系、出溶体的形貌、地球化学特征等与形成条件的关系尚不明确。本研究拟采用电子背散射衍射、透射菊池衍射、透射电镜和电子探针等多种测试手段，对闪锌矿、黄铜矿、斑铜矿、磁黄铁矿这四种常见的金属硫化物的出溶结构进行研究。分析出溶体和主晶之间的结晶学取向关系，出溶体在主晶中的形貌与分布特征、出溶体的成分及物相。在此基础上，建立金属硫化物出溶结构的结晶学识别特征，探讨金属硫化物出溶结构与晶体内部结构匹配度和外部成矿地质条件的关系等科学问题，尝试建立金属硫化物出溶结构的结晶学温压计，为利用金属硫化物出溶结构指示成矿温压条件提供理论依据和实际范例。

金属硫化物出溶结构在热液矿床中广泛发育，并与成矿条时的物理化学条件密切相关，具有重要的成因指示意义。本研究采用扫描电镜、电子探针、电子背散射衍射和透射电镜等分析手段，对闪锌矿(Sph)、黄铜矿(Ccp)、斑铜矿(Bn)中的出溶和交生结构进行了测试。查明了出溶体的形貌及在主晶中分布特征、出溶体的成分及物相，统计了出溶体和主晶之间的结晶学取向关系，探讨了金属硫化物出溶结构与晶体内部结构匹配度和外部成矿地质条件的关系，获得了如下主要认识：. 1. 闪锌矿中不同形态（病毒状、乳滴状、叶片状）的黄铜矿大部分均与主晶具有Sph{100}//Ccp{001}, Sph{100}//Ccp{100}, Sph{110}//Ccp{110}, Sph{111}//Ccp{112}的取向关系。闪锌矿中病毒状黄铜矿为交代成因，而乳滴状和叶片状黄铜矿为出溶成因。. 2. 斑铜矿与其中的叶片状、格状黄铜矿之间存在3种不同的结晶学取向的关系。第一组黄铜矿叶片和斑铜矿主晶具有 Bn{100}//Ccp{001}, Bn{010}//Ccp(100), Bn{001}//Ccp(100)的取向关系。第二组斑铜矿黄铜矿叶片和斑铜矿主晶具Bn{100}//Ccp(100), Bn{010}//Ccp(100), Bn{001}//Ccp{001}。第三组黄铜矿叶片和斑铜矿主晶具有Bn{100}//Ccp(100), Bn{010}//Ccp(001), Bn{001}//Ccp(100), Bn{111}//Ccp(111)。结合矿相学和扫描电镜观察，初步认为其为降温过程中快速冷区时固溶体出溶形成。.3. 黄铜矿中，多数星状、雪花状闪锌矿和黄铜矿主晶具有Ccp{001}//Sph{100}, Ccp{100}//Sph{100}, Ccp{110}//Sph{110}, Ccp{112}//Sph{111}的结晶学取向关系。星状闪锌矿多和沿黄铜矿的开放裂隙相关，表明其很能是后期闪锌矿交代黄铜矿的产物。. 本研究表明，硫化物出溶或交生结构中，包裹体的结晶学取向关系主要受晶体内部结构匹配程度的控制，其形貌则和形成过程及外部物理化学条件有关，深化了对金属硫化物矿石结构的成因和成矿过程的认识。