The Zhaotong Native Copper Deposit Associated with the Permian Emeishan Flood Basalts, Yunnan, Southwest China

Abstract

The Zhaotong native copper deposit in Yunnan, Southwest China, is associated with the upper Middle Permian Emeishan flood basalts and is mainly hosted in the upper part of the Emeishan volcanic succession. Native copper mainly appears as disseminations in basaltic tuffs, and vesicular and brecciated tops of subaerial lava flows. Sheets of native copper up to 30 x 10 x 0.2 cm have also been found along fractures within the volcanic breccias. The native copper is associated with bitumen, zeolite, quartz, and calcite, typical of a low-temperature (100-150°C) hydrothermal alteration assemblage. The ore grades vary from ~0.1 to 20 wt% Cu. Copper was likely a result of organicinorganic interactions under conditions of the paucity of reduced S.