| 西昆仑塔什库尔干叶里克铁矿成因:矿床地质与磁铁矿LA-ICP-MS原位分析约束 |
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| 引用本文： | 丁明朋,汤好书,陈衍景,董连慧,李基宏,屈迅,李秋根,孙晓辉,周振菊,石光辉.西昆仑塔什库尔干叶里克铁矿成因:矿床地质与磁铁矿LA-ICP-MS原位分析约束[J].地球科学,2018,43(9):3169-3185. |
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| 作者姓名： | 丁明朋 汤好书 陈衍景 董连慧 李基宏 屈迅 李秋根 孙晓辉 周振菊 石光辉 |
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| 作者单位： | 1.中国科学院地球化学研究所矿床地球化学国家重点实验室, 贵州贵阳 550081 |
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| 基金项目： | 国家自然科学基金项目41402061中国地质调查局项目1212011140056国家自然科学基金项目41672086国家自然科学基金项目41503035 |
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| 摘 要： | 新疆塔什库尔干铁矿带是我国西部地区新近发现的重要富铁矿带.叶里克铁矿是该成矿带大型铁矿床之一，对该矿床成因方面的研究尚在起步阶段.通过对叶里克铁矿开展矿床地质研究与磁铁矿LA-ICP-MS原位分析，结果表明矿体产于布伦阔勒变质火山-沉积岩中，矿体与围岩产状基本一致，具有明显的层控特征.稠密浸染状或块状富矿体中磁铁矿主要有两种产出形式:与硬石膏或与方解石共生.这两类磁铁矿中多数微量元素含量较均一，如Mg（119×10-6~313×10-6）、Al（692×10-6~1 034×10-6）、Ti（540×10-6~840×10-6）、V（3 340×10-6~3 971×10-6）、Mn（950×10-6~1 160×10-6）、Co（4×10-6~5×10-6）、Ni（52×10-6~64×10-6）、Zn（84×10-6~143×10-6）、以及Ga（26×10-6~31×10-6），并与高温热液中磁铁矿类似；磁铁矿Al、Ti、V含量高，Ni/Cr比高以及Ti/V比低揭示出其形成于相对还原、富Al、Ti的海底高温热液体系且沉积环境稳定.（Al+Mn）-（Ti+V）特征指示其形成温度在300~500 ℃之间.与硬石膏共生的磁铁矿比与方解石共生的磁铁矿具有相对高的Ti（前者平均690×10-6，后者平均574×10-6）、P（从27×10-6骤降到7×10-6）含量，低的Ca含量（从36×10-6骤升到203×10-6）并亏损Zr、Hf、Sc、Ta等高场强元素，指示前者形成于更剧烈的热液活动中，并且硬石膏磁铁矿在热液作用过程中多数Ca离子进入硬石膏晶格中，造成磁铁矿Ca含量降低.综合区域地质、矿床地质及磁铁矿组成等多种证据，表明叶里克铁矿形成于早寒武世的海底高温热液系统.铁矿形成与原特提斯洋南向俯冲引发的火山弧岩浆作用有关，属于海相火山岩型铁矿.
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| 关 键 词： | 西昆仑 叶里克铁矿 布伦阔勒岩群 矿体特征 矿床成因 地球化学 |
| 收稿时间： | 2018-02-05 |
Genesis of the Erik Iron Ore Deposit in the Taxkorgan Area of the West Kunlun,Xinjiang: Constraints from Ore Deposit Geology and In Situ LA-ICP-MS Analysis of Magnetite |
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| Abstract: | The Erik iron deposit is one of the biggest deposits in the Taxkorgan iron deposit belt in Xinjiang, an important high-grade one recently discovered in West China, which has been rarely studied. To identify the genesis of the Erik iron deposit, ore deposit geology survey and in situ LA-ICP-MS analysis of magnetite have been conducted in this study. It is found that mineralization occurs at the Bulunkuole meta-volcano-sedimentary sucession. Ore occurrences are basically coordinated with those of host rocks, and exhibit obviously stratabound characteristics. Two main mineral associations of magnetite+anhydrite and magnetite+calcite in variable proportions commonly occurred in the high-grade iron bodies and formed dense disseminations and massive ores. Both magnetite grains from these two associations show constant contents of many elements including Mg (119×10-6-313×10-6), Al (692×10-6-1 034×10-6), Ti (540×10-6-840×10-6), V (3 340×10-6-3 971×10-6), Mn (950×10-6-1 160×10-6), Co (4×10-6-5×10-6), Ni (52×10-6-64×10-6), Zn (84×10-6-143×10-6), and Ga (26×10-6-31×10-6) and similar to those of in high-temperature hydrothermal environment. It is interpreted that the high Al, Ti, V contents, with high Ni/Cr and low Ti/V ratios in magnetites result from relatively reduced, Al-Ti-rich seafloor hydrothermal activities under a stable sedimentary environment. The (Al+Mn)-(Ti+V) feature of the Erik magnetites implies a high-temperature crystallization (300-500℃). The magnetites coexisting with anhydrite have higher Ti (690×10-6), P (27×10-6) concentrations in average, and lower Ca (36×10-6) than those coexisting with calcites (Ti=574×10-6, P=7×10-6, Ca=203×10-6). Moreover, the former are more depleted in high field strength elements of Zr, Hf, Sc, Ta, suggestting them have suffered more severely hydrothermal activities and Ca contents in magnetites are reduced with Ca2+ entering into crystal lattice of anhydrites. Integrating obtained evidences, including regional geology, ore deposit geology, magnetite composition, and we conclude that the Erik iron deposit was formed from an Early Cambrian seafloor high-temprature hydrothermal system. The development of the Erik iron deposit is related with a volcanic arc caused by southward subduction of Proto-Tethyan Plate. The Erik iron deposit is classified into a marine volcanic-sedimentary hosted Fe oxide deposit formed at or near the seafloor in submarine volcanic settings. |
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