科研之友
微信
新浪微博
Facebook
分享链接
摘要
A close Zn-Ag association has been noted recently in several polymetallic sulfide ore deposits from the Indian Ocean. However, the role of nanotextural controls on "invisible" silver distribution within sphalerite (a significant Ag-carrier) is still not well understood. In this study, typical Zn-sulfide samples from the Edmond vent field (Central Indian Ridge) can be roughly classified into three different groups based on their chemical compositions and mineral textures. Among them, sulfosalt-bearing, Fe-poor zinc sulfides in sulfate-dominant outer chimney walls usually contain higher contents of Ag, Cu and Pb (up to wt% levels) than Fe-rich, massive to disseminated sphalerite in Zn-(Fe)-rich chimney fragments coated by silicified crusts. Such sphalerite is represented by colloform/botryoidal aggregates of optically anisotropic ZnS with a strongly disordered structure or hexagonal habit, which are actually formed by coalescence and agglomeration of colloidal nanocrystalline particles. Using high-resolution transmission electron microscopy (HRTEM) and in-situ micro-XRD techniques, we have investigated the ultrastructure and crystal-chemistry of the {1 1 1} twin boundaries and wurtzite-type stacking faults that occur in Ag-rich, colloform or porous dendritic sphalerite. Submicroscopic electrum and Ag nanoparticles appear to nucleate on the micro-/nano-pore walls as cavity-fillings, or occur along grain boundaries between chalcopyrite-tennantite inclusions and the host sphalerite. Interestingly, the inhomogeneous distribution of precious metals and other chalcophile elements is generally concordant with the extent of re crystallization, intragranular porosity as well as various degrees of structural disordering/imperfectness (i.e., bulk defect density) in ZnS domains. Lattice defects and interfaces may play a limited role in promoting the simultaneous introduction of exotic impurities into colloform sphalerite during rapid growth. Even though certain morphological traits and aggregation state at the nanoscale seem to support a biogenic origin of these ZnS particles characterized by admixed polytypic intergrowth structures, the mineralogical and geochemical features of highly-defective sphalerite crystals, in addition to their microscale S-isotope signatures with relatively high delta S-34 values, exhibit signs of abiologically-mediated, rapid precipitation caused by extensive mixing and cooling at Edmond. The physicochemical conditions and seafloor disequilibrium processes indicated by ZnS formation mechanism might facilitate the incorporation and enrichment of Ag or other trace elements in hydrothermal sphalerite.
- 出版日期2018-1
- 单位中山大学
