Major deposit types and genesis of Yimen-type copper deposits, Yunnan, China.

Abstract：The Yimen copper deposit is a large-scale copper deposit with exploration indicated the basic reserves and pre-mining reserves of economy of about 0.6 million tonnes with Cu averaging 1.0%. There are two major deposit types in the Yimen copper orefield: one is the volcano-hydrothermal sedimentation—reworking type (the Shishan-type), while the other is the volcano-hydrothermal sedimentation-strong reworking—magmatic superimposition type (the Fengshan-type). On the basis of the geological setting of metallogenesis of the Yimen copper orefield and the geological characteristics of the Yimen-type copper deposits, the relations between volcano-hydrothermal sedimentation, tectonic transformation, magmatic superimposition, underground hot water reworking and metallogenesis is discussed in this paper. It is considered that the ore-forming materials are of diverse sources, and are complex in origin. The homogenization temperatures and salinities of mineral fluid inclusions fall mainly within the two ranges: 110~200℃ and 220~320℃; 20.5wt％ and 4～10 wt％ and 12～18 wt％. The δ34S values of minerals (Chalcopyrite, Pyrite, bornite and bismuthinite) vary within the range of –7.2～-20.0‰. The metallogenic model of Yimen-type deposits is the “rift metallogenic setting→volcano-hydrothermal sedimentation→tectonic transformation-enrichment→deep-source magmatic superimposition→underground hot water reworking ”. The ore-forming model has been established for the dynamics of tectonic ore-forming processes and the exploration of Yimen-type copper ore deposits.