An integrated genefical model and exploration/evaluation system for chromittite and platinum-group element ores

铬铁矿、铂族元素矿综合成因模型及勘查评价体系

基本信息

批准号：
13554017
负责人：
ARAI Shoji
金额：
$ 3.52万
依托单位：
KANAZAWA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

An integrated model for chromitite genesis has been established through the petrological research of upper crustal podifarm chromitite that we found from the Oman ophiolite. Ihis chromitite is lenficular and was formed at the boundary between the late-intrusive peridotite and felsic partial meltfrom gabbroic blocks captured by the late intrusion. Despite the podiform character, its spinel is perfectly euhedral and fine and has a matrix of plagioclase. Spinel is rich in Cr and total Fe. These features are similar to those of the stratiform chromitite. In short, this chromitite has an intermediate character between the podiform and stratiform chromitites. It was formed by mixing of two kinds of magma, a basaltic one from the late intrusive body and a felsic one from the partial melt of gabbro. The chemical similarity between the upper crustal chromitite from Oman and the stratifrom chromitite may mean that the latter is also formed by mixing of magmas, a basaltic magma and a silicic one formed by partial melting of wall of the magma reservoir as first suggested by Irvine(1975). Combined with an interpretation of Arai and Yurimoto(1994) on the origin of podiform chromitite in peridotite, the mixing of two kinds of magma, basaltic and silicic ones, is indispensable to genesis of chromitite irrespective of type. This mechanism favors the precipitation of primary PGM by supplies of PGE from basalt and of S from a silicic melt.

通过对阿曼蛇绿岩中发现的上地壳podifarm铬铁矿的岩石学研究，建立了铬铁矿成因的综合模型。铬铁矿是透镜状的，形成于晚期侵入橄榄岩和由晚期侵入捕获的辉长岩块体的长英质部分熔体之间的边界处。尽管具有豆荚状特征，但其尖晶石却是完美的自形且细腻，并具有斜长石基质。尖晶石富含Cr和总Fe。这些特征与层状铬铁矿相似。简而言之，这种铬铁矿具有介于豆荚状和层状铬铁矿之间的中间特征。它是由两种岩浆混合形成的，一种是来自晚期侵入体的玄武质岩浆，另一种是来自辉长岩部分熔融的长英质岩浆。阿曼的上地壳铬铁矿和地层铬铁矿之间的化学相似性可能意味着后者也是由岩浆、玄武质岩浆和硅质岩浆混合形成的，而硅质岩浆是由岩浆库壁部分熔融形成的，正如 Irvine 首先提出的那样（ 1975）。结合Arai和Yurimoto(1994)对橄榄岩中豆状铬铁矿成因的解释，无论何种类型的铬铁矿成因，玄武岩和硅质两种岩浆的混合是必不可少的。该机制有利于通过玄武岩中的 PGE 和硅熔体中的 S 的供应来沉淀初级 PGM。