本文選題：豆莢狀鉻鐵礦 + 蛇綠巖　； 參考：《中國(guó)地質(zhì)》2017年02期

【摘要】：中國(guó)鉻鐵礦資源的瓶頸狀態(tài)已持續(xù)多年。最近,在西藏羅布莎蛇綠巖地幔橄欖巖的深部勘探發(fā)現(xiàn)200萬t致密塊狀鉻鐵礦床,這是中國(guó)近50年來鉻鐵礦找礦的重大突破,對(duì)今后繼續(xù)尋找同類型的鉻鐵礦床具有重要指導(dǎo)意義。蛇綠巖地幔橄欖巖中產(chǎn)出的豆莢狀鉻鐵礦床是工業(yè)需求鉻的重要來源。研究豆莢狀鉻鐵礦的成礦作用和礦體圍巖地幔橄欖巖地質(zhì)特征,建立鉻鐵礦的成礦模型和找礦標(biāo)志,是開展尋找同類型礦床的重要保證。隨著近些年在豆莢狀鉻鐵礦及圍巖地幔橄欖巖中金剛石等深部礦物的不斷發(fā)現(xiàn)和深入研究,人們對(duì)蛇綠巖型鉻鐵礦的物質(zhì)來源和形成過程,有了新的認(rèn)識(shí),提出了鉻鐵礦的深部成因模式。研究認(rèn)為深部成因鉻鐵礦床主要經(jīng)歷了4個(gè)階段:(1)早期俯沖到地幔過渡帶(410~660 km)的陸殼和洋殼物質(zhì)被脫水和肢解,過渡帶產(chǎn)生的熱和流體促成了地幔的熔融和Cr的釋放和匯聚;(2)鉻鐵礦漿在地幔柱驅(qū)動(dòng)下,運(yùn)移到過渡帶頂部冷凝固結(jié),并有強(qiáng)還原的流體進(jìn)入,后者攜帶了深部形成的金剛石、斯石英等高壓礦物,進(jìn)入"塑性—半塑性地幔橄欖巖"中;(3)隨著物質(zhì)向上移動(dòng),深度降低,早期超高壓相礦物發(fā)生相變,如斯石英轉(zhuǎn)變成柯石英,高壓相的鉻鐵礦中出溶成柯石英和單斜輝石;(4)在侵位過程和俯沖帶環(huán)境下,含水熔體與方輝橄欖巖反應(yīng)形成了不含超高壓礦物的規(guī)模相對(duì)較小的浸染狀鉻鐵礦及純橄巖巖殼。進(jìn)一步研究表明,同處雅魯藏布江縫合帶西段的幾個(gè)大型地幔橄欖巖巖體與羅布莎巖體可以對(duì)比,經(jīng)歷了相同的構(gòu)造背景和豆莢狀鉻鐵礦的成礦作用,存在較大的找礦空間。
[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.
【作者單位】： 西藏自治區(qū)地質(zhì)礦產(chǎn)勘查開發(fā)局第六地質(zhì)大隊(duì);CARMA大陸構(gòu)造與動(dòng)力學(xué)重點(diǎn)實(shí)驗(yàn)室中國(guó)地質(zhì)科學(xué)院地質(zhì)研究所;西藏礦業(yè)發(fā)展股份有限公司;
【基金】：中國(guó)地質(zhì)調(diào)查局項(xiàng)目(DD20160023) 國(guó)家自然科學(xué)基金(41502062、41672046、41541017、41641015) IGCP-649項(xiàng)目聯(lián)合資助~~
【分類號(hào)】：P618.3

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