HUANG Yong-sheng1,2, ZHANG Hui1*, LYU Zheng-hang1, TANG Yong1, TANG Hong1,2
(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)
Abstract: The invasion depth, commonly, has close relation to temperature and pressure of diagenesis and mineralization of pegmatite, which indirectly influences the thermal history of magmatic evolution and influences the processes of migration, enrichment and precipitation of metallogenetic materials. In this work, 4 Permian pegmatites and 5 Triassic pegmatites were selected for conducting the microthermometry of type-B fluid inclusions which were captured by quartz in the early and late textural zones of pegmatites and were aqueous carbon dioxide fluid inclusions. The type-B fluid inclusions in Kaluan ore district (805, 806, and 807) which were captured by quartz/spodumeneare generally syngenetic with melt-fluid inclusions(type-A2), indicating that they formed from magma-hydrotherm system. Whereas, the type-B fluid inclusions in the early textural zones of other pegmatites are negative crystal shape, isolated, generally syngenetic with melt inclusions(type-A1), indicating magmatic genesis. The salinity value of type-B fluid inclusion ranges from 2.20% to 3.89%NaCleqv; the total homogenization temperature ranges from 400 to 581℃ in the early textural zones of Triassic pegmatites, and the calculated pressure ranges from 235 to 308 MPa, corresponding to emplacement depth within the limits of 8.4 to 11.0 km. Whereas, type-B fluid inclusions in the early textural zones of Permian pegmatites manifested that their salinity values are within the range of 4.62% to 6.54%NaCleqv; total homogenization temperature ranges between 430 and 580℃, and the calculated pressure ranges from 319 to 406 MPa, which corresponds to emplacement depth within the limits of 11.4 to 14.5 km. The results suggest that there is an obvious discrepancy of emplacement depth between the two periods. Triassic pegmatites have a shallower depth and are more fertile and more complex than that of the Permian, such as Li-mineralization in Kaluan ore district (805, 806, and 807), Li-Be-Nb-Ta-mineralization in Kelumute112, and Li-Be-Nb-Ta-C-Rb-Hf-mineralization in Keketuohai No.3 pegmatite, demonstrating that the relatively shallow emplacement depth is conductive to evolution and mineralization of pegmatite-forming melt.
Keywords: Altay orogeny; pegmatite; fluid inclusion; pressure; depth of invasion
ACTA MINERALOGICA SINICA Vol. 36, No. 4, 2016, Page 571-584
