Facies sequence reestablishment and metallogenic analysis of Middle Triassic Anisian meta-volcanic rocks in the Kafang ore district, Gejiu, Yunnan

Abstract：The Middle Triassic Anisian meta-volcanic rocks in Kafang Member of Gejiu Formation could be restored into a set of alkaline basic-ultrabasic rock assemblages. The restored volcanic and sedimentary lithofacies includes explosive facies, effusive facies, volcanic sedimentary facies, tidal flat facies, late-basin-fluid superimposed facies and skarn facies. It is considered that the vertical facies sequence might be in order of explosive facies→effusive facies→volcanic sedimentary facies→tidal flat facies, belonging to the facies sequence structure and facies assemblage formed in a back-arc rift basin background. Kafang Member is divided into 3 volcanic stages in the study area, which composed a volcanic cycle. The characteristics of the vertical phase sequence indicate multi-stages of volcanic activities and variation of volcanic activities from strong to weak. Late-basin-fluid superimposed facies and skarn facies can be regarded as ore-bearing lithofacies and an ore-prospecting index in future.