HYDROGEN ISOTOPIC COMPOSITION OF ROCKS IN MAGMATIC CENTERS WITH MO-PORPHYRY MINERALIZATION IN EASTERN TRANSBAIKALIA AND STANOVOI RANGE

Abstract

Hydrogen isotopic composition was studied for amphiboles and biotites from ore-bearing porphyries and host granitoids in the Mesozoic magmatic centers with Mo-porphyry mineralization of Shakhtama and Zhireken (eastern Transbaikalia) and Chubachi (Stanovoi Range). The minerals have generally low δD values ranging within wide intervals from -105 to -141‰ for amphiboles and from -105 to -204‰ for biotites. The δ values of the Shakhtama and Zhireken minerals decrease from the host granitoid complex to the porphyry complex. They also decrease for both complexes at Shakhtama from the earlier (more primitive) to the later (more evolved) rocks. In contrast, the δD values of the Chubachi biotites increase from host granitoids to porphyries. Considering the geological data, Sr isotopic composition, and chemical features of biotites, we suggest that the D/H ratios in the rocks of the specified centers were generally controlled by involvement of mantle and crustal materials in the magmatic processes, crystal fractionation, and fluid separation from magma. The contribution of the Earth's crust to the hydrogen isotopic composition of magmatic rocks increases from Zhireken to Shakhtama and Chubachi. General variations in the D/H ratio were determined by the participation of Precambrian rocks in the formation of the Chubachi magmatic rocks and magma degassing, particularly during the emplacement of the ore-bearing porphyry complexes in the genesis of the Shakhtama and Zhireken rocks.