地学前缘 ›› 2016, Vol. 23 ›› Issue (5): 235-251.DOI: 10.13745/j.esf.2016.05.024

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弓长岭铁矿蚀变岩及富矿成因

 朱凯, 刘正宏, 徐仲元, 王兴安   

  1. 1. 吉林大学 地球科学学院, 吉林 长春 130061
    2. 东北师范大学 地理科学学院, 吉林 长春 130024
  • 收稿日期:2015-11-03 修回日期:2016-03-05 出版日期:2016-09-15 发布日期:2016-09-15
  • 通讯作者: 刘正宏(1960—)，男，教授，博士生导师，主要从事构造地质学研究。E-mail：zhliu@jlu.edu.cn
  • 作者简介:朱凯(1988—)，男，博士研究生，主要从事构造地质学和前寒武地质研究。
  • 基金资助:

    国家自然科学基金项目(41272223)；中国地质调查局项目(1212011220247)

Genesis of altered rocks and highgrade iron ore in Gongchangling iron deposit.

 SHU  Kai, LIU  Zheng-Hong, XU  Zhong-Yuan, WANG  Xin-An   

  1. 1. College of Earth Sciences, Jilin University, Changchun 130061, China
    2. College of Geographical Sciences, Northeast Normal University, Changchun 130024, China
  • Received:2015-11-03 Revised:2016-03-05 Online:2016-09-15 Published:2016-09-15

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摘要：

弓长岭铁矿床是鞍山本溪地区最典型的BIF型铁矿床之一，而且是该地区最大的富铁矿产区。从野外产出关系来看，弓长岭矿区的富铁矿与蚀变岩密切相关，蚀变岩与富铁矿基本上是形影相随。蚀变岩具有分带性，由富铁矿向外依次为镁铁闪石岩石榴石岩绿泥石岩弱蚀变斜长角闪岩斜长角闪岩。弱蚀变岩保留了蚀变原岩的岩貌特征，矿物的蚀变并不完全，可见残余的原生矿物。强蚀变岩的蚀变较彻底，基本无原生矿物残留。将蚀变岩与斜长角闪岩、磁铁石英岩的地球化学特征进行对比可以发现弱蚀变岩、石榴石岩、绿泥石岩与斜长角闪岩的痕量元素特征基本一致，而镁铁闪石岩的痕量元素特征更接近磁铁石英岩。再结合镜下特征、野外接触关系、主量元素特征等证据，认为除了镁铁闪石岩是由磁铁石英岩蚀变形成，其余蚀变岩都是由斜长角闪岩蚀变形成。根据各类蚀变岩中主要矿物的(Fe+Mg)/Si值以及蚀变岩的SiO2和Fe2OT3含量变化规律可以发现，在蚀变岩和富矿形成过程中发生了Mg、Fe以及Si的迁移。对本次取样的样品进行原岩恢复和构造环境判别投图，投图结果表明，绿泥石岩和弱蚀变岩的最初原岩都是形成于弧后盆地的玄武岩。

关键词: 弓长岭, 蚀变岩, 富铁矿, 地球化学, 元素迁移, 弧后盆地

Abstract:

Gongchangling iron deposit is one of the most typical BIFtype iron deposits in AnshanBenxi area, and it is the biggest producer of highgrade iron ore. Judging from the field relationship the ore is inseparately related to altered rocks.The altered rocks are characteristic of zonal distribution. In the order from highgrade iron ore outsides there are: cummingtonite rock→garnet rock→chlorite rock→weakly altered amphibolite and→amphibolite. In the weakly altered rocks, the original appearance of the primary rock is still preserved, the alteration of minerals are incomplete, the relicts of primary minerals can still be found. However， in the intensively altered rocks, the primary minerals are rarely found. The comparison on geochemistry of the altered rocks, amphibolite and magnetite quartzite indicates that the trace element characteristics of weakly altered rock, garnet rock and chlorite rock are similar to those of the amphibolites, and the trace element characteristics of cummingtonite rock are much similar with those of the lowgrade iron ores. Combined with the evidences from the microscopic characteristics, contact relationship and characteristics of major elements, we hold that the altered rocks were formed by hydrothermal interaction with amphibolites expect for cummingtonite rock. Cummingtonite rock is more likely to be formed by the hydrothermal interaction with lowgrade iron ores. According to the varying regulation of (Fe+Mg)/Si, SiO2 and Fe2OT3 showed by various altered rocks and amphibolites, there is migration of Mg, Fe and Si occurred during the hydrothermal metasomatism. The results of plottings on tectonic discrimination diagrams indicate that the protolith of these rocks are backarc basin basalts.

Key words: Gongchangling, altered rocks, high grade iron ore, geochemistry, migration, back arc basin

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