Huang F.,Northeastern University China |
Gao S.,Northeastern University China |
Liu J.,Northeastern University China |
Gao W.,Northeastern University China |
And 4 more authors.
Earth Science Frontiers | Year: 2013
The giant barite crystals with FeS2 whiskers girdle were found in the geode in the concealed explosion breccia in Gengzhuang gold deposit, Shanxi Province, China. The mineral characteristics of the barite and the FeS2 whiskers contained were systematically analyzed by SEM, EPMA and XRD systematically. The results showed that the barite chemical composition is single, its crystal structure is standard and its crystal growth is perfect. The whiskers belong to the FeS2-Fe(Ni, Co)S2 isomorphism series. According to the geological background and the inclusion research results, combined with the crystal growth and the geochemical theory, the genesis of the barite and the whiskers contained has been discussed. The barite was the product of the reaction between the barium in the surrounding rock and the SO4 2- when the hydrothermal evolution came to the last period after the Yanshanian granitic magmatic activity. The FeS2 whiskers contained were the products of the H2S and SO2 which were formed by continued concealed volcano explosion and the Fe2+, Ni2+ and Co2+ which came from the decomposition of the hydrothermal fluids. The rich alkali, the increasing H2S solubility and the increasing S2- content were conducive to the whisker growth. The geological environments of the growths of barite and whisker had consistency in macro and differences in specific conditions. While the pH ranged from 1 to 8.5, and the lgfO2 ranged from -31 to -38, the superior field for the FeS2 growth was attained and the FeS2 whiskers formed. While the pH ranged from 5.5 to 10 and the lgfO2 ranged from -25 to -36, the barite formed. The symbiosis of the FeS2 whiskers girdle and the barite was the result of the interactive growth. The barite intussusceptive growth and the presence of FeS2 whiskers girdle are the signs of the pulsated and cyclical concealed explosions in the Gengzhuang area. The giant barite crystal with FeS2 whiskers girdle clearly marked the geological conditions and processes of their formation, which provided a mineralogical evidence for further research of concealed explosion and understanding the mineralization in that area.