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首页> 外文期刊>Australian Journal of Earth Sciences >Hydrothermal alteration events controlling magnetite-rich iron ore at the Matthew Ridge prospect, Jack Hills greenstone belt, Yilgarn Craton
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Hydrothermal alteration events controlling magnetite-rich iron ore at the Matthew Ridge prospect, Jack Hills greenstone belt, Yilgarn Craton

机译：在马修里奇勘探区，杰克希尔斯绿岩带，伊尔加恩·克雷顿控制富磁铁矿铁矿的热液蚀变事件

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摘要

Archean Banded Iron Formation (BIF) hosts high-grade (>55% Fe) iron ore at the Matthew Ridge prospect, in the Jack Hills greenstone belt, of the Narryer terrane, Yilgarn Craton. The ca 3000 Ma (SHRIMP U–Pb on zircons) Algoma-type BIF contains magnetite–hematite ore zones that are a product of successive overprinting hydrothermal alteration events. Rock types in the prospect area include Archean gneiss, metasedimentary rocks and BIF that are interlayered with dolerite. All rocks record peak amphibolite metamorphic mineral assemblages that are variably replaced by greenschist facies metamorphic minerals. Hypogene iron ore formed owing to: (1) the replacement of primary silica-rich bands in the quartz–magnetite BIF by Stage 1 hypogene magnesite and magnetite alteration; and (2) subsequent removal of Stage 1 magnesite to concentrate residual Stage 1 magnetite. These magnetite-rich ore bodies define <50 m-long by 20 m-wide lenses that trend NE and coincide with the hinge zones of Zshaped, tight F_1 folds, which are most likely parasitic folds to the regional NE-trending, steeply NEplunging anticline in the Jack Hills greenstone belt. Magnetite-rich ore zones are enriched in Fe and depleted in SiO_2, with only minor changes in other major oxides and trace elements, compared with least-altered BIF. Magnetite-rich ore zones are locally cut by shear zone-hosted, talc–magnetite hydrothermal alteration overprinted by talc–microplaty hematite alteration. The shear zones and both talc mineral assemblages formed during a second deformation event that was characterised by NNE–SSE shortening. The third deformation event resulted in at least two generations of NE- to NW-trending extensional veins and strike-slip faults that locally cut the talc-rich shear zones. Supergene goethite– hematite replaces magnetite-rich ore bodies within 80 m of the present surface. The strong structural control and distinct hydrothermal alteration assemblages of the Matthew Ridge prospect are the best exploration indices for high-grade magnetite-rich ore in the region.
机译：太古代带状铁矿（BIF）在纳里耶（Yarryn Craton）纳里（Narryer）地带的杰克山（Jack Hills）绿岩带中的马修岭（Matthew Ridge）矿床蕴藏高品位（> 55％铁）铁矿石。大约3000 Ma（锆石上的SHRIMP U–Pb）Algoma型BIF包含磁铁矿-赤铁矿矿带，这是连续叠印的热液蚀变事件的产物。勘探区的岩石类型包括太白质片麻岩，准沉积岩和与白云石夹层的BIF。所有岩石均记录了峰闪石变质矿物组合，并被绿片岩相变质矿物替代。表观铁矿石的形成是由于：（1）第1阶段表观菱镁矿和磁铁矿蚀变取代了石英-磁铁矿BIF中富含二氧化硅的主要谱带; （2）随后去除阶段1菱镁矿以浓缩残留的阶段1磁铁矿。这些富含磁铁矿的矿体定义了小于50 m长，20 m宽的晶状体，这些晶状体趋向NE并与Z形紧密F_1折叠的铰链区重合，这很可能是区域NE趋势的陡峭NE倾斜背斜的寄生褶皱。在杰克山绿岩带。与最少改变的BIF相比，富含磁铁矿的矿带富含Fe，而SiO_2却贫乏，而其他主要氧化物和微量元素只有很小的变化。富含磁铁矿的矿带被剪切带状的滑石-磁铁矿热液蚀变局部覆盖，滑石-微板赤铁矿蚀变叠印。在第二次变形事件中，以NNE–SSE缩短为特征，形成了剪切带和滑石矿物组合。第三次变形事件导致了至少两代从NE到NW趋势的延伸脉和走滑断层，这些断层局部切割了富含滑石的剪切带。超基因针铁矿–赤铁矿替代了当前表面80 m内富含磁铁矿的矿体。 Matthew Ridge矿床的强大结构控制和独特的热液蚀变组合是该地区高品位富磁铁矿矿石的最佳勘探指标。

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