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

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.