Petrological characteristics, geochemical feature and metallogenetic relation of alkaline-rich rocks in northwest of Yunan Province, China

Abstract

The alkali-rich rocks, spreading along the suture zone of Jingsha River, refer to the alkali-rich porphyry rocks, which emplace during the Himalaya epoch in northwest of Yunnan Province, and consist of syenit, syenit porphyry, monzonite porphyry and granite porphyry. Petrological chemical analysis results suggest that silica is poor and aluminum is rich, and high potassium large ion lithophile elements (LILE), light rare earth element (LREE) and Sr are obviously detracted in these rocks. High field strength elements (HFSE) and heavy rare earth element (HREE) are depleted, especially Nb, Ta, P and Ti. δ Eu : 0.09−1.64 shows that plagioclase does not appear fractional crystallization during the formation of alkali-rich rocks. δ 34 S, H and O isotopes and Pb isotopes suggest that ore-forming fluid is derived from the mantle, and Pb is possibly mixed by mantle, wall rock and crust. The age of Pb in alkali-rich rocks is about 250−220 Ma. The age of alkali porphyry rock (dykes) varies from 30 Ma to 50 Ma. Alkali rocks have strong metallogenetic relation. Au mineralization is associated to the alkali magmatic activities with a relatively high temperature, low pressure and high oxygen fugacity. However, copper mineralization is mainly associated with alkali-sub-alkali magmatic activities in a process of relatively low temperature, high pressure and lower oxygen fugacity.

Hydrothermal alteration and element migration in the Egongtang uranium deposit, central Nanling Range, South China

“…Based on the characteristics of trace elements and REEs, the uranium content of the Qingzhangshan granite (mean 13.11 ppm) is much higher than that of the South China uranium-producing granite (mean 3.0 ppm; Yu, 1979; Yu et al 2005), and significantly higher than the average uranium content in the crust of eastern China (1.5 ppm; Gao et al 1998, 1999) and global mean uranium content of granites (3.0 ppm; Zhang et al 1988), indicating that the Qingzhangshan granite has the potential to provide a sufficient uranium source for uranium mineralization in the area. The distribution curves of trace and rare earth elements of various samples in the Egongtang uranium deposit are similar, and there is a gradual relationship to some extent between different zones (Figs 8, 9), which also implies that the uranium source of the deposit is mainly from the Qingzhangshan granite.…”