Trace element composition of magnetite from the Xinqiao Fe–S(–Cu–Au) deposit, Tongling, Eastern China: constraints on fluid evolution and ore genesis  

作　　者：Yichang Wang Jianfeng Gao Xiaowen Huang Liang Qi Chuan Lyu 

机构地区：[1]State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences,Guiyang 550081, China [2]University of Chinese Academy of Sciences, Beijing 100049,China

出　　处：《Acta Geochimica》2018年第5期639-654,共16页地球化学学报（英文）

基　　金：supported by grants from the National Key R&D Program of China(2016YFC0600207);the Chinese 973 project(2012CB416804);the National Natural Science Foundation of China(41503039);the ‘‘CAS Hundred Talents’’Project to J.F.Gao(Y5CJ038000)

摘　　要：The Xinqiao deposit is one of several polymetallic deposits in the Tongling ore district. There are two types of mineralization in the Xinqiao： skarn-type and stratiform-type. The skarn-type mineralization is characterized by iron oxides such as magnetite and hematite, whereas stratiform-type mineralization is characterized by massive sulfides with small amounts of magnetite and hematite. We defined three types of ores within the strati- form-type mineralization by the mineral assemblages and ore structures. Type Ⅰ ore is represented by magnetite crosscut by minor calcite veins. Type Ⅱ is a network ore composed of magnetite and crosscutting pyrite. Type Ⅲ is a massive ore containing calcite and hematite. Type Ⅰ magnetite is characterized by highly variable trace element content, whereas Type Ⅱ magnetite has consistently higher Si, Ti, V, and Nb. Type Ⅲ magnetite contains more In, Sn, and As than the other two types. Fluid-rock interaction, oxygen fugacity （fO2）, and temperature （T） are the main factors controlling element variation between the different magnetite types. Type I magnetite was formed by more extensive fluid-rock interaction than the other two types at moderate fO2 and T conditions. Type Ⅱ magnetite is thought to have formed in relatively low fO2 and high-Tenvironments, and Type Ⅲ in relatively high fOe and moderate-T environments. Ca ＋ Al ＋ Mn and Ti ＋ V discrimination diagrams show that magnetite in the Xin qiao deposit is hydrothermal in origin and is possibly linked with skarn.The Xinqiao deposit is one of several polymetallic deposits in the Tongling ore district.There are two types of mineralization in the Xinqiao:skarn-type and stratiform-type.The skarn-type mineralization is characterized by iron oxides such as magnetite and hematite,whereas stratiform-type mineralization is characterized by massive sulfides with small amounts of magnetite and hematite.We defined three types of ores within the stratiform-type mineralization by the mineral assemblages and ore structures.Type I ore is represented by magnetite crosscut by minor calcite veins.Type II is a network ore composed of magnetite and crosscutting pyrite.Type III is a massive ore containing calcite and hematite.Type I magnetite is characterized by highly variable trace element content,whereas Type II magnetite has consistently higher Si,Ti,V,and Nb.Type III magnetite contains more In,Sn,and As than the other two types.Fluid–rock interaction,oxygen fugacity(fO_2),and temperature(T)are the main factors controlling element variation between the different magnetite types.Type I magnetite was formed by more extensive fluid–rock interaction than the other two types at moderate fO_2 and T conditions.Type II magnetite is thought to have formed in relatively low fO_2 and high-T environments,and Type III in relatively high f O_2 and moderate-T environments.Ca+Al+Mn and Ti+V discrimination diagrams show that magnetite in the Xinqiao deposit is hydrothermal in origin and is possibly linked with skarn.

关 键 词：Xinqiao SKARN MAGNETITE In-situ analysis TONGLING 

分 类 号：P618.2[天文地球—矿床学]