Analysis of Mineralogical Characteristics of Leucosphenite from the Fengcheng Formation in the Junggar Basin by Electron Probe Microanalyzer and X-ray Diffractometer

Leucosphenite, a borosilicate mineral with a biaxial monoclines crystal structure, is a typical hydrothermal mineral. The mineralogy of leucosphenite in the shale of the Fengcheng Formation in the Junggar Basin in China has not been studied, and its genesis is not clear.

To understand the mineralogical characteristics of leucosphenite in the Fengcheng Formation and its genesis.

Electron probe microanalysis (EPMA), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to analyze the mineral composition and crystal structure.

The crystal size of the leucosphenite in the Fengcheng Formation is at micron scale, and the morphology is plate-like or short columnar. Leucosphenite is associated with reedmergnerite. Leucosphenite is composed of 12.64% BaO, 13.47%TiO₂, 10.69% Na₂O, 53.46% SiO₂, and 10.11% B₂O₃. Crystal planes corresponding to d=4.22(-220), d=8.45(-110), d=3.37(-112) are the three most developed planes.

The element composition and crystal diffraction characteristics of leucosphenite in the Fengcheng Formation are consistent with that found abroad, but the former is richer in B. Due to the obvious positive correlation between B content and salinity in the hydrothermal fluid, the leucosphenite of the Fengcheng Formation was formed in the hydrothermal fluid with higher salinity. Deep hydrothermal fluids intruded into the shale of the Fengcheng Formation, forming reedmergnerite and leucosphenite in turn.