LIU Xi-qiang1,2, ZHANG Hui1*, TANG Yong1, LIU Yun-long3
(1. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. University of the Chinese Academy of Sciences, Beijing 100049, China;
3. School of Management Science, Guizhou University of Finance and Economics, Guiyang 550025, China)
Abstract: The study of petrography of phosphorites and microthermometry of fluid inclusions in quartz and dolomite of phosphorites from the Motianchong orebody of the Guohua Oreblock and Linfeichang orebody of the Gezhongwu Oreblock in the Zhijin phosphorite-type REE deposit have been carried out in this paper. The results show that the collophanite of siliceous phosphorites in the Linfeichang orebody is distributed mainly in form of clastic apatite particles with their sizes varying from 50 to 200 ？m. The apatite particles are mainly cemented by siliceous and dolomitic matrixes. The fluid inclusion hosted in quartz and dolomite have homogenization temperatures in a range of 87.5-127.8℃, salinities varying from 0.88 to 3.9 wt% NaCl, and calculated pressures of 5.54～8.02 MPa. The collophanite of dolomitic phosphorites in the Motianchong orebody is also mainly distributed in form of clastic apatite particles with their sizes changing from 50 to 300 ？m. The phosphorite is dominantly cemented by dolomite. The fluid inclusions in dolomite have homogenization temperatures varing from 99.8 to 184.3℃, salinities varing from 12.31 to 20.61 wt% NaCl, and the calculated pressures varing from 13.7 to 22.6 MPa. The significant differences between the homogenization temperatures and salinities of fluid inclusions and the cement components of the clastic apatites of phosphorites in the Motianchong orebody of the Guohua Oreblock and those of phosphorites in the Linfeichang orebody of the Gezhongwu Oreblock indicate that the hydrothermal system unravelled by the Motianchong dolomitic phosphorite could be resulted from the mixing of hot brine with normal seawater. However, the dolomitic phosphorite, which was formed in the early stage, in the Linfeichang orebody of the Gezhongwu Oreblock was significantly influenced by theNaCl-depleted but SiO2-enriched low temperature hydrothermal fluid in the late stage.
Keywords: homogenization temperature, salinity, fluid inclusions, ore genesis, the Zhijin phosphorite
ACTA MINERALOGICA SINICA Vol. 39, No.4, 2019, page 403-411
