Mineralogical,geochemical characteristics and formation mechanism of skarns in Banlun magnetite ore cluster area,southeastern Yunnan
The Banlun magnetite ore cluster area in southeastern Yunnan,located at the junction of Cathaysian,Yangtze and Indosinian plates,is an important part of the Gejiu-Wenshan-Debao skarn type Sn-W polymetallic metallogenic belt.The predecessors have carried out a small amount of research work on the geological characteristics and genesis of the skarn type magnetite deposit in this area,but there is still no systematic study on the genesis of the skarn,which seriously restricts the further understanding of the genesis of skarns and the accurate evaluation of magnetite prospecting potential in this magnetite ore cluster area.This paper focus on the skarns and related rocks from the most typical Kunhong and Dongha magnetite deposits in Banlun magnetite ore cluster area.Based on the detailed study of the field geological characteristics and petrography of the skarns and related rocks,their geochemical and mineralogical characteristics are systematically studied by LA-ICP-MS and EPMA.The results show that the diagenetic and metallogenic evolution of skarns can be divided into three stages:early progressive metamorphic skarn stage,late degenerative metamorphic skarn stage and sulfide-carbonate stage;There are significant differences between siliceous rock bands of(magmatic-)hydrothermal origin and Late Permian OIB type basic complexs(namely"Banwa type"pluton)in primitive mantle-normalized spider diagrams and chondrite-normalized REE pattern diagrams;However,they are relatively similar to the model curves between siliceous rock bands of(magmatic-)hydrothermal origin and Middle Triassic island arc type intermediate-basic complexs(namely"Anding type"pluton),showing the characteristics of obvious depletion of Nb,Ta,P and Ti elements;The model curves of skarns are also similar to that of siliceous rock bands,and ore-bearing skarns are very close to siliceous rock bands than ore free skarns in terms of trace element contents and model curves.The research results of mineral chemistry show that the first generation garnets belongs to the series of Andradite-Almandite-Grossularite(And80-83 Alm9-11 Gro5-7),and containing more Grossularite(Gro);The second generation garnets belongs to the series of Andradite-Almandite(And86-93 Alm6-12),and basically contains no or only a small amount of Grossularite(Gro);From early pyroxene to late pyroxene,the proportion of hedenbergite is relatively reduced,while the content of diopside is significantly increased in the end member component of pyroxene.Comprehensive analysis shows that the hydrothermal fluid forming skarns mainly come from Middle Triassic island arc type intermediate-basic complexs;The diagenetic and metallogenic environment of skarn type magnetite deposits has at least experienced a transformation process from the relative reduction environment in the early stage of progressive metamorphic skarn stage to the relative oxidation environment in the late stage of progressive metamorphic skarn stage and degenerative metamorphic skarn stage to the relative reduction environment in the late sulfide-carbonate stage.
万方数据
维普
