Major and Trace Elements of Magnetite from the Qimantag Metallogenic Belt: Insights into Evolution of Ore–forming Fluids  

作　　者：YI Liwen GU Xiangping LU Anhuai LIU Jianping LEI Hao WANG Zhiling CUI Yu ZUO Hongyan SHEN Can 

机构地区：[1]Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitor,Ministry of Education [2]School of Geosciences and Info–Physics,Central South University

出　　处：《Acta Geologica Sinica(English Edition)》2015年第4期1226-1243,共18页地质学报（英文版）

基　　金：supported by the Geological Survey Program of China Geological Survey (1212011121220)

摘　　要：Magnetite, as a genetic indicator of ores, has been studied in various deposits in the world. In this paper, we present textural and compositional data of magnetite from the Qimantag metallogenic belt of the Kunlun Orogenic Belt in China, to provide a better understanding of the formation mechanism and genesis of the metallogenic belt and to shed light on analytical protocols for the in situ chemical analysis of magnetite. Magnetite samples from various occurrences, including the ore-related granitoid pluton, mineralised endoskarn and vein-type iron ores hosted in marine carbonate intruded by the pluton, were examined using scanning electron microscopy and analysed for major and trace elements using electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The field and microscope observation reveals that early-stage magnetite from the Hutouya and Kendekeke deposits occurs as massive or banded assemblages, whereas late- stage magnetite is disseminated or scattered in the ores. Early-stage magnetite contains high contents of Ti, V, Ga, AI and low in Mg and Mn. In contrast, late-stage magnetite is high in Mg, Mn and low in Ti, V, Ga, AI. Most magnetite grains from the Qimantag metallogenic belt deposits except the Kendekeke deposit plot in the ＂ Skarn ＂ field in the Ca＋AI＋Mn vs Ti＋V diagram, far from typical magmatic Fe deposits such as the Damiao and Panzhihua deposits. According to the （MgO＋MnO）- TiO^-AI203 diagram, magnetite grains from the Kaerqueka and Galingge deposits and the No.7 ore body of the Hutouya deposit show typical characteristics of skarn magnetite, whereas magnetite grains from the Kendekeke deposit and the No.2 ore body of the Hutouya deposit show continuous elemental variation from magmatic type to skarn type. This compositional contrast indicates that chemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids. Moreover, a combination of petrography and magMagnetite, as a genetic indicator of ores, has been studied in various deposits in the world. In this paper, we present textural and compositional data of magnetite from the Qimantag metallogenic belt of the Kunlun Orogenic Belt in China, to provide a better understanding of the formation mechanism and genesis of the metallogenic belt and to shed light on analytical protocols for the in situ chemical analysis of magnetite. Magnetite samples from various occurrences, including the ore-related granitoid pluton, mineralised endoskarn and vein-type iron ores hosted in marine carbonate intruded by the pluton, were examined using scanning electron microscopy and analysed for major and trace elements using electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The field and microscope observation reveals that early-stage magnetite from the Hutouya and Kendekeke deposits occurs as massive or banded assemblages, whereas late- stage magnetite is disseminated or scattered in the ores. Early-stage magnetite contains high contents of Ti, V, Ga, AI and low in Mg and Mn. In contrast, late-stage magnetite is high in Mg, Mn and low in Ti, V, Ga, AI. Most magnetite grains from the Qimantag metallogenic belt deposits except the Kendekeke deposit plot in the ＂ Skarn ＂ field in the Ca＋AI＋Mn vs Ti＋V diagram, far from typical magmatic Fe deposits such as the Damiao and Panzhihua deposits. According to the （MgO＋MnO）- TiO^-AI203 diagram, magnetite grains from the Kaerqueka and Galingge deposits and the No.7 ore body of the Hutouya deposit show typical characteristics of skarn magnetite, whereas magnetite grains from the Kendekeke deposit and the No.2 ore body of the Hutouya deposit show continuous elemental variation from magmatic type to skarn type. This compositional contrast indicates that chemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids. Moreover, a combination of petrography and mag

关 键 词：MAGNETITE trace element LA-ICP-MS ore genesis Qimantag metallogenic belt 

分 类 号：P618.31[天文地球—矿床学]