WANG Li1,2, ZHOU Li3,1*, ZHANG Shuai1,2, WANG Chun-yao1,2, ZHOU Wen-ge1
(1. Key Laboratory of High-temperature and High-pressure Study of the Earth's Interior，Institute of Geochemistry，Chinese Academy of Sciences，Guiyang 550081，China;
2. University of Chinese Academy of Sciences，Beijing 100049，China;
3. School of Geography and Environmental Science, Guizhou Normal University, Guiyang 550025, China)
Abstract: Barite (BaSO4) is a common sulfate mineral in nature. It can be as an ore mineral for exploitation and utilization. It is also a common gangue mineral in hydrothermal deposits. Hydrothermal synthesis of barite is of great significance to reveal its forming conditions. At present, the hydrothermal synthesis of barite mainly adopts the experimental method of the first nucleation of barite in mixed barium salt and sulfate solution at room temperature and the subsequent growth of barite by heating (the method of nucleation at room temperature and ripening growth at high temperature). In order to make better simulation for the growth condition of barite at hydrothermal system, a novel barite synthesis method (the in-situ mixing at high temperature method) has been introduced in this paper to undertake exploratory experiment of the barite synthesis by using the in-situ mixed barium salt and sulfate solution at high temperature and to compare with experimental results of the barite synthesis by using the mixed barium salt and sulfate solution at room temperature. The experimental results show that the size and morphologies of barite crystals synthesized by using the two different methods were completely different. The barite synthesized by using the method of nucleation at room temperature and ripening growth at high temperature is mainly near-equiaxed granular crystal. In contrast, the barite synthesized by using the method of in-situ growth at high temperature is dendritic crystal with large axial ratio. The barite synthesized by using the nucleation at room temperature and ripening growth at high temperature method, due to the low nucleation temperature, has a few lattice defects or vacancies. It is conducive to the crystal growing along the crystal configuration. In the subsequent ripening growth stage at high temperature, due to the existence of a large number of formed crystal nuclei, , the barite crystal is grown slowly and mainly along the original crystal growth direction rather than the preferred growth direction in the relatively less supersaturated solution to have formed the near-equiaxed granular crystal with well-developed faces. However, the barite formed by using the method of in-situ mixing of barium salt and sulfate solution at high temperature, due to its almost simultaneous nucleation and growth in a very short time at high temperature, has no produced perfect crystal nuclei . In addition, due to the crystal nuclei were surrounded by relatively high degree of supersaturated solution, the barite crystals had grown preferentially to have formed dendritic crystals with large axial ratios. These dendritic crystals are morphologically similar to the dendritic barite formed in the submarine hydrothermal vents due to the mixing of hydrothermal fluid and seawater. The experimental results show that the dendritic shape of barite crystal may be the important morphological typomorphic characteristics of barite grown under the high-temperature fluid-mixing condition.
Keywords: Barite; in-situ mixing at high temperature; hydrothermal synthesis; typomorphic characteristics
ACTA MINERALOGICA SINICA Vol. 41, No.2, 2021, page 139-149
