豆荚状铬铁矿床的研究现状及进展  被引量:11

Present situation and advances in the study of podiform chromite deposits

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作  者:周二斌[1] 

机构地区:[1]东华理工大学,江西抚州344000

出  处:《岩石矿物学杂志》2011年第3期530-542,共13页Acta Petrologica et Mineralogica

基  金:国家科技支撑计划重点资助项目(2006BAB01A08);国家危机矿山办公室资助项目(200809951)

摘  要:豆荚状铬铁矿床是工业上冶金级铬铁矿石的最主要来源,对于其成因研究依然是各国地质学家最为关注的热点之一。文章着重概述了近年来国内外地质学者对豆荚状铬铁矿床成因研究的现状和最新进展。最新研究表明,显生宙以来的豆荚状铬铁矿床具有一定的成矿专属性,主要赋存于蛇绿岩套底部(壳-幔边界,即岩石莫霍面)地幔橄榄岩中的一定层位中。世界上含矿的地幔橄榄岩普遍具有垂直熔融分带特征,即上部偏基性,下部偏酸性。豆荚状铬铁矿床与纯橄岩-方辉橄榄岩相密接相关,却很少见有豆荚状铬铁矿床产于二辉橄榄岩中。豆荚状铬铁矿的成矿作用经历了由洋中脊(MOR)扩张环境向岛弧体系俯冲环境的转变过程,而岛弧环境(岛弧、弧后盆地、弧前盆地等)是形成冶金级豆荚状铬铁矿的最为有利的构造环境。富铬铬铁矿与纯橄岩、玻安岩(Boninite)均为亏损地幔橄榄岩再次高度熔融的最终产物,而玻安岩普遍产于岛弧环境。虽然玻安岩不是铬的有效载体,但玻安岩的熔离促使铬铁矿达到进一步的富集。铬铁矿中的铬来自原始地幔,主要来自于地幔橄榄岩中两种辉石的不一致熔融及其对副矿物铬尖晶石的改造。随着部分熔融程度的增高,地幔橄榄岩逐渐向富镁方向演变,而对应的造矿铬尖晶石也逐渐向富镁、富铬方向演变。The podiform chromite deposit constitutes the main source of metallurgical-grade chromite in industry,but its genesis remains one of the problems for which geologists all over the world show great concern.This paper outlined the status and latest progress in the study of podiform chromite deposits.The latest studies show that podiform deposits mainly occur in a certain layer of the mantle peridotite,which has been the lowest part of ophiolite(CMB,crust-mantle boundary) since Phanerozoic.The podiform chromite deposit-bearing mantle peridotites in the world usually exhibit vertical zoning of melting,with more basic material in the upper part and more acid material in the lower part.With the increasing of partial melting from the bottom upward,there appears lherzolite,harzburgite and dunite in turn.Alpine-type podiform chromite deposits generally have a fairly thick dunitic "envelop".After the mineralization of the podiform chromite deposit,the gravity of itself caused the sinking and dragging of some of the dunite around the ore body downward into the harzburegite facies side under the contact interface with the upside dunite facies,thus forming the typical dunitic "envelop" of the Alpinetype chromite deposit.The authors have thus reached the conclusion that the harzburgite facies under the contact interface is the best target area in search for large chromite deposits.Podiform deposits have a very close genetic relationship with harzburgite and dunite;however,it is really rare to find chromite deposits in lherzolite.The abundance of chromium in primitive mantle is much higher than that in the crust,the chromium element of chromitite was derived from primitive mantle itself,mainly coming from the alteration of associated spinel and the incongruent melting of the two pyroxene(chromium diopside and enstatite).With the increase of partial melting,the mantle peridotite gradually evolved in the magnesium-rich direction,and the mineralization of spinel evolved in the magnesium-rich and chromium-rich direc

关 键 词:豆荚状铬铁矿 地幔橄榄岩 蛇绿岩 玻安岩 

分 类 号:P618.33[天文地球—矿床学]

 

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