Determination of Fe^(2+)/Fe^(3+)Ratios of Magnetite using Different Methods:A Case Study from the Qimantag Metallogenic Belt  

作　　者：YI Liwen LI Qiuping LU Anhuai GU Xiangping CHI Guoxiang 

机构地区：[1]School of Geographical Sciences,Hunan Normal University,Changsha 410081,China [2]School of Geosciences and Info-Physics,Central South University,Changsha 410083,China [3]School of Earth and Space Sciences,Peking University,Beijing 100871,China [4]Department of Geology,University of Regina,Regina,Saskatchewan S4S 0A2,Canada

出　　处：《Acta Geologica Sinica(English Edition)》2022年第6期2135-2147,共13页地质学报（英文版）

基　　金：obtained grants from the National Key Research and Development Program Project"Enhanced Bioremediation Technology and Equipment for Chromium Residuation Site",the Scientific Research Project of Hunan Provincial Department of Education(Grant No.19C1178);the Construction Program for the First-Class Disciplines(Geography)of Hunan Province,China.The anonymous reviewers and editors are thanked for constructive suggestions on improving the quality of the manuscript.

摘　　要：Determination of Fe^(2+)/Fe^(3+) ratios from metallogenic belts to explore controlling physical and chemical conditions of rock formation is of great significance.In order to explore magnetite Fe^(2+)/Fe^(3+) ratios of the Qimantag metallogenic belt,part of the Eastern Kunlun orogenic belt in the northeastern margin of the Qinghai–Tibetan plateau,western Central Orogenic Belt of China,and overcome the limitation of the traditional electronic probe,five different measurement methods are proposed and their respective advantages and disadvantages evaluated,with the composition data of the magnetite obtained using electron probe microanalysis(EPMA).The direct oxygen measurement method has a significant impact on the determination results of FeO and Fe2O3,but the accuracy and uniformity of the results are low.The valence method(Flank method)based on the spectral intensity ratio of Lαto Lβfor iron is also unreliable for FeO and Fe_(2)O^(3) measurements because it is difficult to establish a relationship between Lβ/Lα,the spectral intensity ratio,and the Fe^(2+)/Fe^(3+) content ratio.In comparison,the charge difference method,the surplus-oxygen method and the Mössbauer spectrum method are still the most favorable.Mössbauer spectroscopy,with its isomer movement particularly sensitive to the oxidation state of iron,yields results closer to 0.5,which is relatively reliable.Earlier magnetite deposits are located in intrusions or contact zones and formed by magmatic fluids with high Fe2+/Fe3+ratios,whereas later magnetite deposits are farther away from intrusions and have low Fe^(2+)/Fe^(3+) ratios.The transformation mechanism of hematite and magnetite in the Qimantage metallogenic belt is also studied.No large volume changes,such as pore filling and shrinkage fracture,were detected in the metallogenic belt,and the transformation mechanism is more similar to a reoxidation and reduction mechanism.

关 键 词：iron MAGNETITE direct oxygen measurement flank-charge difference-surplus-oxygen methods Mössbauer spectra Qimantage 

分 类 号：P618.31[天文地球—矿床学]