西藏罗布莎豆荚状铬铁矿床深部找矿突破与成因模式讨论

发布时间：2018-07-09 19:15

本文选题：豆荚状铬铁矿 + 蛇绿岩　；参考：《中国地质》2017年02期

【摘要】：中国铬铁矿资源的瓶颈状态已持续多年。最近,在西藏罗布莎蛇绿岩地幔橄榄岩的深部勘探发现200万t致密块状铬铁矿床,这是中国近50年来铬铁矿找矿的重大突破,对今后继续寻找同类型的铬铁矿床具有重要指导意义。蛇绿岩地幔橄榄岩中产出的豆荚状铬铁矿床是工业需求铬的重要来源。研究豆荚状铬铁矿的成矿作用和矿体围岩地幔橄榄岩地质特征,建立铬铁矿的成矿模型和找矿标志,是开展寻找同类型矿床的重要保证。随着近些年在豆荚状铬铁矿及围岩地幔橄榄岩中金刚石等深部矿物的不断发现和深入研究,人们对蛇绿岩型铬铁矿的物质来源和形成过程,有了新的认识,提出了铬铁矿的深部成因模式。研究认为深部成因铬铁矿床主要经历了4个阶段:(1)早期俯冲到地幔过渡带(410~660 km)的陆壳和洋壳物质被脱水和肢解,过渡带产生的热和流体促成了地幔的熔融和Cr的释放和汇聚;(2)铬铁矿浆在地幔柱驱动下,运移到过渡带顶部冷凝固结,并有强还原的流体进入,后者携带了深部形成的金刚石、斯石英等高压矿物,进入"塑性—半塑性地幔橄榄岩"中;(3)随着物质向上移动,深度降低,早期超高压相矿物发生相变,如斯石英转变成柯石英,高压相的铬铁矿中出溶成柯石英和单斜辉石;(4)在侵位过程和俯冲带环境下,含水熔体与方辉橄榄岩反应形成了不含超高压矿物的规模相对较小的浸染状铬铁矿及纯橄岩岩壳。进一步研究表明,同处雅鲁藏布江缝合带西段的几个大型地幔橄榄岩岩体与罗布莎岩体可以对比,经历了相同的构造背景和豆荚状铬铁矿的成矿作用,存在较大的找矿空间。
[Abstract]:The bottleneck state of chromite resources in China has lasted for many years. Recently, 2 million tons of dense massive chromite deposits were discovered in deep exploration of mantle peridotite in Lobusa ophiolite, Tibet. This is a major breakthrough in chromite prospecting in China in the past 50 years. It is of great significance to continue to search for the same type of chromite deposit in the future. The pod chromite deposit produced in mantle peridotite of ophiolite is an important source of industrial chromium demand. To study the mineralization of pod-like chromite and the geological characteristics of mantle peridotite in the surrounding rock of the orebody, to establish the metallogenic model and prospecting mark of chromite is an important guarantee for the exploration of the same type of ore deposit. With the discovery and in-depth study of deep minerals such as diamond in pod-like chromite and mantle peridotite of surrounding rock in recent years, people have a new understanding of the material source and formation process of ophiolite chromite. The deep genetic model of chromite is proposed. It is considered that the deep chromite deposit has undergone four main stages: (1) the continental and oceanic crust materials from the early subduction to the mantle transition zone (410 ~ 660 km) were dehydrated and dismembered. The heat and fluid generated from the transitional zone contributed to the melting of the mantle and the release and aggregation of Cr. (2) the chromite slurry was driven by mantle plume and moved to the top of the transition zone to be condensed and consolidated, and strong reduced fluids entered, the latter carrying diamond formed in the deep part. High pressure minerals, such as quartz, enter the "plastoplastic and semi-plastic mantle peridotite". (3) with the material moving upward and the depth decreasing, the early ultrahigh pressure phase minerals undergo phase transformation, such as the transformation of the quartz to coesite, Coesite and clinopyroxene are dissolved in high-pressure chromite, (4) in the emplacement process and subduction zone, the water-bearing melt reacts with the oblate peridotite to form relatively small disseminated chromite and peridite crust without ultrahigh pressure minerals. Further study shows that several large mantle peridotite bodies in the western section of the Yalu Zangbo River suture belt can be compared with the Lobusa rock body, and have experienced the same tectonic setting and pod-like chromite mineralization, and there is a large prospecting space.
【作者单位】：西藏自治区地质矿产勘查开发局第六地质大队;CARMA大陆构造与动力学重点实验室中国地质科学院地质研究所;西藏矿业发展股份有限公司;
【基金】：中国地质调查局项目(DD20160023) 国家自然科学基金(41502062、41672046、41541017、41641015) IGCP-649项目联合资助~~
【分类号】：P618.3

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