Determination of Solid-Liquid Phase Composition of Fluid Inclusions in Minerals by SEM-EDS Coupled with Cryotransfer

Daughter mineral species, chemical compositions and distribution of daughter minerals in fluid inclusions can provide important constraints on the composition of hydrothermal fluids, physicochemical conditions of mineralization, the regularity of fluid evolution and ore-forming mechanisms. The traditional methods however, have many limitations such as finding target minerals and identifying opaque minerals. Described in this paper, fluid inclusions in minerals are frozen and then opened by Frozen Transmission Equipment (Cryotransfer). The compositions of daughter minerals and liquid phases are determined by Scanning Electron Microscope (SEM) and Energy Disperse Spectroscope. This method solved the difficulty in finding target minerals by SEM. Daughter minerals cannot be lost after opening liquid inclusions, and cannot be mixed with debris. This method can effectively determine the compositions of small-sized (1-2 μm) opaque daughter minerals and the solid-liquid phases of fluid inclusions in opaque minerals. Mass fractions of Na⁺, K⁺, Cl^- in liquid inclusions of Wangjiazhuang copper deposit in Zouping of Shandong province are 5.85%, 3.60% and 16.18%, respectively, and the calculated salinity is 35.35%. The opaque daughter minerals are identified to be chalcopyrite, which proves that chalcopyrite has crystallized from hydrothermal fluids with high salinity. This study provides a new determination method for fluid inclusion, and has great significance in analyzing the compositions of solid and liquid phases in fluid inclusions.