Microplaty hematite—its varied nature and genesis
Microplaty hematite—its varied nature and genesis
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微片状赤铁矿——其不同的性质和成因
DOI：
10.1080/08120099.2011.626453
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发表时间：
2012
影响因子：
1.2
通讯作者：
R. C. Morris
中科院分区：
文献类型：
--
作者：
R. C. Morris
次生微板状赤铁矿(MplH)赋存于许多不同的环境中，但重要的是，在没有变质作用的情况下，它是世界上以马铁矿(M，磁铁矿之后的赤铁矿假象)为主的高品位BIF赋存铁矿石的定义次要成分。这一术语是在CSIRO-Amira 1976-1994哈默斯利省铁矿石项目的早期引入的，目的是从新开发的、多产的表生马铁矿-针铁矿(M-G)矿石(约白垩纪-古新世)中，方便地区分当时主要出口的马铁矿-微板状赤铁矿(M-mplH)类型的惠莱巴克山(Mt Whaleback)、汤姆普赖斯山(Mt Tom Price)和帕拉布杜(Paraburdoo)(约2000 Ma)。后者与海峡铁矿石一起，现在是哈默斯利省的主要铁矿石出口。CSIRO-AMIRA模型认为，它们是在表生针铁矿中生长的元古界M-G矿在低温(∼80~100℃)区域变质过程中形成的。将针铁矿转化为赤铁矿的过程中，∼的体积减少了27%，所产生的微孔洞中的mplH增长是通过过程本身产生的水中的铁转移来实现的，本质上是一个内部的水热过程，不需要引入低成因流体。替代模型提出，引入的菱铁矿通过加热的陨石流体与保存在汤姆普莱斯山两个地点的热液交代的BIF‘原岩’反应，氧化生成mplH+铁闪石。早些时候在CSIRO-Amira计划期间，这种假定的“原生”被描述为局部矿石后BIF交代残留物。这些新概念导致了不同的热液模型，这些模型目前主导着国际铁矿石文献。对所提出的两种mplH形成机制进行了关键的比较，包括来自一系列环境的mplH相关物质的例子，包括BIF、GIF、铁矿石和含铁沉积物。针铁矿转化为mplH似乎是更可能的过程。
Secondary microplaty hematite (mplH) occurs in many different environments but importantly, where unmodified by metamorphism, it is the defining minor component of the high-grade BIF-hosted iron ores of the world that are dominated by martite (M, hematite pseudomorphs after magnetite). The term was introduced early during the CSIRO–AMIRA 1976–1994 program on the Hamersley Province iron ores to conveniently distinguish the then main export martite–microplaty hematite (M–mplH) ore type of Mt Whaleback, Mt Tom Price and Paraburdoo (ca2000 Ma) from the newly exploited, prolific supergene martite–goethite (M–G) ores (ca Cretaceous–Paleocene). The latter, with the channel iron ores, are now the major iron-ore exports of the Hamersley Province. The CSIRO-AMIRA model proposed that theM–mplH ores formed during regional metamorphism of Proterozoic M–G ores at low temperatures (∼80–100°C) by mplH growth in the supergene goethite. The conversion of goethite to hematite involves a ∼27% reduction in volume, with suggested mplH growth in the resulting microvoids by iron transfer through water resulting from the process itself, essentially an internal hydrothermal process requiring no introduced hypogene fluids. Alternative models have proposed oxidation of introduced siderite resulted in mplH + ankerite by reaction of heated meteoric fluids with hydrothermally metasomatised BIF ‘protore’ preserved in two locations in the Mt Tom Price deposits. This postulated ‘protore’ had earlier been described during the CSIRO–AMIRA program as local post-ore BIF metasomatic residuals. These new concepts have resulted in varying hydrothermal models that currently dominate the international literature of iron ore. A critical comparison of the two suggested mechanisms of mplH formation includes examples of mplH-related material from a range of milieus including BIF, GIF, iron ores and ferruginous sediments. Conversion of goethite to mplH appears the more likely process.