Mineral and Geochemical Characteristics of the Tieshanmiao-Type BIF-Iron Deposit in Wuyang Region of Henan Province and Its Implications for Ore-Forming Processes
详细信息
- 责任者：Lan Caiyun (University of Chinese Academy of Sciences ; Beijing 100049 ; China) ; Zhang Lianchang
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(7)
- 关键词：铁矿 ; iron ores ; 矿床地球化学 ; mineral deposit geochemistry ; 河南 ; Henan Province
- 页码：p.2567-2582
- 图表：13 illus., 5 tables, 64 refs.
- 分类号：1001
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Tieshanmiao-type iron deposit,part of the Wuyang iron deposit,is located at the southern margin of the North China Craton. The iron formation occurs in the supracrustal rocks of the Tieshanmiao Formation of the Neoarchaean Taihua Group. The chemical compositions of the magnetites and whole-rock samples from three types of ores ( banded quartz-pyroxene-magnetite ore, massive pyroxene-magnetite ore,and massive quartz-magnetite ore) from the Tieshanmiao-type iron deposit are presented to investigate the ore-forming processes. The bulk chemistry of magnetite from different iron ore is as follows: FeO T ( total iron oxide) contents of banded quartz-pyroxene-magnetite ore range from 90. 6% to 93. 1% and the average is 91. 8% . FeO T contents of massive pyroxene- magnetite ore range from 90. 7% to 91. 2% and the average is 91. 0% . FeO T contents of massive quartz-magnetite ore range from 92. 0% to 93. 0% and the average is 92. 4% . All these values are consistent with the theoretical FeO T value of magnetite. TiO 2 ,MgO, MnO,CaO,Al 2 O 3 ,Cr 2 O 3 and NiO contents of the magnetites from different iron ores are all very low ( < 0. 1% ) without obvious variations among different types,suggesting that they are nearly pure magnetite,and typical of the banded iron formations ( BIF) . Mineral assemblages of ores ( orthopyroxene + clinopyroxene) and host rock near orebody ( hypersthene + plagioclase + quartz) indicate that the Tieshanmiao-type iron deposit has suffered high grade metamorphism. Quartz and magnetite became coarse-grained after recrystallization but still kept the original geochemical compositions. The three types of ores have similar SiO 2 ,TiO 2 ,Al 2 O 3 and P 2 O 5 contents. But massive pyroxene-magnetite ore have higher MgO,MnO and CaO contents than the others,due to the presence of abundant ferroaugite and ferrosalite in the massive pyroxene-magnetite ore. All the ores have very low TiO 2 and Al 2 O 3 contents, suggesting clastic materials were not involved in the ore-forming process. They also have similar REE + Y patterns with LREE depletions ( ( La/Yb) PAAS = 0. 29 ～ 0. 995 < 1) and positive anomalies of La,Eu,and Y ( La/La *=1.10～1. 89; Eu/Eu * = 1. 30 ～ 2. 23; Y/Y * =1. 47～1. 84 ) ,characteristics of modern seawater and hydrothermal fluids from mid-oceanic ridges. Therefore,we conclude that the Tieshanmiao-type iron deposit can be classified as BIF despite of later-stage metamorphism.