| 新疆智博铁矿火山岩中富铁岩屑地球化学特征及其地质意义 |
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| 引用本文： | 骆文娟,张作衡,段士刚,蒋宗胜,王大川,康永建.新疆智博铁矿火山岩中富铁岩屑地球化学特征及其地质意义[J].矿床地质,2019,38(1):61-79. |
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| 作者姓名： | 骆文娟 张作衡 段士刚 蒋宗胜 王大川 康永建 |
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| 作者单位： | 中国地质科学院矿产资源研究所自然资源部成矿作用与资源评价重点实验室;中国地质大学地质过程与矿产资源国家重点实验室 |
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| 基金项目： | 国家自然科学基金项目（编号：41503041）、中央级公益性科研院所基本科研业务专项资金（编号：K1412）和中国地质调查局地质调查项目（编号：DD20160124）资助 |
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| 摘 要： | 研究表明,西天山阿吾拉勒铁铜成矿带中智博铁矿区火山碎屑岩中的富铁岩屑主要由自形针状/板条状钠长石和富铁基质组成,呈辉绿/斑状结构。电子探针分析显示,富铁岩屑中钠长石端员组分变化范围为An=0.38～2.89,Ab=95.2～99.32,Or=0.17～2.79,端员组分平均值为An_(0.94)Ab_(98.01)Or_(1.06),类似于火山岩中钠长石端员组分变化范围(An=0.74～6.75,Ab=92.85～98.91,Or=0.32～1.76,端员组分平均值为An_(2.63)Ab_(96.65)Or_(0.72)),两者均为岩浆成因钠长石,而非热液交代成因钠长石。富铁基质成分变化范围较大且连续(w(SiO_2)为0.08%～50.04%,w(FeO)为24.89%～87.13%,w(Al_2O_3)为0.04%～14.83%,w(TiO_2)为0.01%～2.83%,w(Na_2O)为0～9.76%,w(MgO)为0.03%～4.88%,w(MnO)为0～0.61%),富铁基质中高Ti磁铁矿和低Ti磁铁矿同时发育,总体上成分不均一,且钠长石呈细针状,为浅成-超浅成低压下快速结晶的产物或为火山喷发作用下快速冷凝结晶所致。通过对磁铁矿-磷灰石矿物组合与安山岩中副矿物磷灰石、矿区磁铁矿的对比研究,认为智博铁矿发生磁铁矿-磷灰石岩浆不混溶作用的可能性很小。通过安山岩基质成分与安山岩成分的对比研究,得出安山岩基质比原岩w(SiO_2)、w(Al_2O_3)、w(CaO)有所降低,w(FeO)、w(Na_2O)、w(MgO)有一定升高,但是程度有限,表明岩浆结晶分异不足以使残留岩浆形成富铁矿。钠长石-磁铁矿富铁岩屑的发育是一种碱铁效应的表现,而碱铁效应对于海相火山岩型铁矿的形成具有重要意义。
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| 关 键 词： | 地球化学 富铁岩屑 碱铁效应 铁矿成因 智博铁矿 海相火山岩型铁矿 |
| 收稿时间： | 2018/5/9 0:00:00 |
| 修稿时间： | 2018/10/19 0:00:00 |
Geochemistry of iron-rich debris from Zhibo submarine volcanic rocks in Xinjiang and its geological implications |
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| LUO WenJuan,ZHANG ZuoHeng,DUAN ShiGang,JIANG ZongSheng,WANG DaChuan and KANG YongJian.Geochemistry of iron-rich debris from Zhibo submarine volcanic rocks in Xinjiang and its geological implications[J].Mineral Deposits,2019,38(1):61-79. |
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| Authors: | LUO WenJuan ZHANG ZuoHeng DUAN ShiGang JIANG ZongSheng WANG DaChuan and KANG YongJian |
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| Institution: | MNR Key Laboratory of Metallogeny and MineralAssessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China,MNR Key Laboratory of Metallogeny and MineralAssessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China,MNR Key Laboratory of Metallogeny and MineralAssessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China,MNR Key Laboratory of Metallogeny and MineralAssessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China,State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China and MNR Key Laboratory of Metallogeny and MineralAssessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | Iron-rich debris in the Zhibo submarine volcanoclastic rocks from the Awulale Fe-Cu metallogenic belt, Western Tianshan Mountains, is composed of acicular or lath-shaped euhedral albite and iron-rich matrix and exhibits diabasic or porphyritic texture. Electron microprobe analyses of albites from iron-rich debris show the compositional spectrum ofAn from 0.38 to 2.89,Ab from 95.2 to 99.32 and Or from 0.17 to 2.79, with the average endmember being An0.94Ab98.01Or1.06, which are similar to the compositional variation of the albites from volcanic rocks (An=0.74~6.75, Ab=92.85~98.91,Or=0.32~1.76,with the average endmember beingAn2.63Ab96.65Or0.72). Both of them are magmatic albites rather than hydrothermal metasomatic albites. The chemical composition of iron-rich matrix is variable and continuous e. g., w(SiO2) range from 0.08% to 50.04%,w(FeO) range from 24.89% to 87.13%, w(Al2O3) range from 0.04% to 14.83%, w(TiO2) range from 0.01% to 2.83%, w(Na2O) range from 0 to 9.76%, w(MgO) range from 0.03% to 4.88%, and w(MnO) range from 0 to 0.61%. The modes of occurrence of high Ti magnetite, low Ti magnetite and the acicular albite in the iron-rich matrix suggest the debris formed under hypabyssal-ultrahypabyssal conditions or through rapid condensation crystallization during a volcanic eruption. The comparisons of the magnetite-apatite paragenesis with accessory mineral apatite from andesite and magnetite from iron ores in terms of the element features show that the Zhibo iron ore deposit did not originate from the immiscibility of magnetite-apatite magma. Furthermore, the matrix of andesite has lower SiO2, Al2O3, CaO and higher FeO, NaO, MgO than those of the whole rock. However, the Fe-enrichment in the matrix of andesite is not too obvious on the whole, and thus the authors hold that single magma crystallization differentiation would not cause the residual magma to form iron-rich ores. In summary, it is considered that the iron-rich debris was produced by "alkali-iron effect", which was likely the key factor inducing the mineralization of submarine volcanic-hosted iron deposit. |
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| Keywords: | geochemistry iron-rich debris alkali-iron effect genesis of iron deposit Zhibo iron deposit submarine volcanic-hosted iron deposit |
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