ZHANG Liang-ju，QIN Min-feng，ZENG Wei-lai，LI Dong-sheng，ZENG Nan-shi，RUAN Qing-feng，SONG Chu-xin，HU Hui-yi
( College of Earth Science, Guilin University of Technology, Guilin 541004, China)

Abstracts: Bitumen and a variety of Cu-bearing minerals occur widely in amygdaloid basalt from Puge County in southern Sichuan Province. Bitumen is mainly distributed in pores, geodes and factures within the basalt, as well as in the terminations of quartz crystals. Thenprincipal Cu-bearing minerals are native copper, cuprite, tenorite, chrysocolla and malachite. Native copper occurs as euhedral crystals at the terminations of quartz crystals and as granular or tabular assemblages in veins within amygdaloid factures of bitumen or in the core of Cu-bearing spherulites. Cuprite is closely associated with tabular native copper found in the factures of quartz or chalcedony veins. Tenorite is closely associated with native copper and is generally distributed in the factures of amygdaloids and Cu-bearing spherulites. Chrysocolla occurs as veins within factures of bitumen, and as hull shape in the surfaces of native copper, quartz crystals and Cu-bearing spherulites. Malachite forms the outermost layers of Cu-bearing spherulites. A commonly recognized mineral sequence of bitumen and the Cu-bearing minerals is bitumen → native copper → cuprite → tenorite → chrysocolla → malachite. The results suggest that the bitumen formed in the late stages of the quartz crystallization and that native copper crystallized after bitumen. The carbon isotope (δ13C) present in the bitumen suggests its biogenesis, likely originating from the carbonate rocks in the Permian strata (P13). The infra-red spectrum, spiral growth patterns and vesicular structures also demonstrate that the bitumen was transformed from crude oil in the mineralized hydrothermal fluids. In addition, the higher grade of maturity of the organic matter in the mineralized hydrothermal fluids, the more native copper is deposited from the mineralized hydrothermal fluids. The evolution of Cu-bearing minerals (Cu→Cu2+) is closely related with the variations of the oxidizing reduction environment and the components in the organic matter-bearing mineralized hydrothermal fluids.

Keywords: bitumen; native copper; quartz; Cu-bearing mineral; infra-red spectrum; carbon isotope; organic matter; genesis; Sichuan Province

Email: zljpgig@glut.edu.cn

ACTA MINERALOGICA SINICA Vol. 35, No. 2, 2015, Page 127-135