Integrated O, Fe, and Ti isotopic analysis elucidates multiple metal and fluid sources for magnetite from the Ernest Henry Iron oxide copper gold (IOCG) Deposit, Queensland, Australia
Integrated O, Fe, and Ti isotopic analysis elucidates multiple metal and fluid sources for magnetite from the Ernest Henry Iron oxide copper gold (IOCG) Deposit, Queensland, Australia
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DOI：
10.1016/j.oregeorev.2022.105170
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发表时间：
2022-11
影响因子：
3.3
通讯作者：
Christopher R. Emproto;R. Mathur;A. Simon;I. Bindeman;L. Godfrey;C. Dhnaram;V. Lisitsin
中科院分区：
文献类型：
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作者：
Christopher R. Emproto;R. Mathur;A. Simon;I. Bindeman;L. Godfrey;C. Dhnaram;V. Lisitsin
氧化铁铜金矿床(IOCG)是全球重要的铜来源；然而，关于其形成所涉及的金属和流体来源，人们对其来源仍知之甚少。在这项工作中，我们利用磁铁矿的综合Fe、Ti和O同位素数据来追踪元古界Ernest Henry IOCG矿床的主要金属和流体输入，该矿床是澳大利亚昆士兰州Cloncurry区已知的最大IOCG矿床。分析了欧内斯特-亨利矿期磁铁矿和矿前黑云母-磁铁矿(bt-mGt)和磁铁矿-阳起岩(mgt-act)蚀变组合中的磁铁矿的氧、铁和钛同位素丰度，分别为δ18O(VSMOW)、δ56Fe(IRMM-14)和δ49Ti(OL-Ti)。精选的磁铁矿样本也被分析了17O(报告为Δ‘17O0.5305)，范围从−0.118到−0.056-‰-建议蒸散输入。矿物期(+1.57~+7.36‰)、bt-Mgt(+0.34~+5.68‰)和MGT-ACT(+1.68~+2.10‰)样品的MGT 18O值与欧内斯特-亨利的岩浆-热液成因相一致；非岩浆‰18O值可通过局部碳酸盐围岩同化作用来解释。尽管如此，矿物期的δ56Fe值(−0.50~+0.33‰)、bt-mgt(−0.65~+0.38‰)和mgt-act(−0.26~+0.30‰)磁铁矿的同位素轻于火成岩和岩浆热液磁铁矿的可接受范围(c.+0.06~+0.49‰)，并显示出较大的c1~‰范围，表明矿床内存在铁源混合。矿石阶段磁铁矿δ49Ti(−1.64至+1.79‰；AVG：+1.49‰；2σ‰=2.63‰)的组成一般高于bt-mgt(-0.44至+1.49‰；avg：+0.62σ‰；2 mgt-‰)或mgt-ACT(+0.27至+1.89‰；Avg：+1.05σ；2‰=1.56‰)，表明钛同位素分馏是由于流体中的不同活动性造成的。引用岩浆和非岩浆金属和流体输入的模型可以很好地解释这些数据。下盘和上盘剪切带之间的流体流动引入了可能被岩浆-热液从当地镁铁质单元淋溶的非岩浆铁，导致新形成的磁铁矿被岩浆δ18O重新置换，但在矿前蚀变过程中非岩浆δ56Fe值。在磁铁矿形成之前，这些流体可能与贫铁的蒸发流体混合。成矿阶段后期岩浆贡献的Fe和O导致磁铁矿具有可变的δ56Fe和不可分辨的δ18O叠加。欧内斯特·亨利是已知的第一个IOCG矿床的例子，其主要淋溶金属成分通过金属稳定同位素地球化学法确定。
Iron oxide copper gold (IOCG) deposits are globally important sources of Cu; however, their origins remain poorly understood with respect to the metal and fluid sources involved in their formation. In this work, we utilize integrated Fe, Ti, and O isotopic data for magnetite to trace major metal and fluid inputs for the Proterozoic-aged Ernest Henry IOCG deposit—the largest known IOCG deposit in the Cloncurry District, Queensland, Australia. Magnetite separates from ore stage and pre-ore biotite-magnetite (bt-mgt) and magnetite-actinolite (mgt-act) alteration assemblages from Ernest Henry were analyzed for their O, Fe, and Ti isotope abundances, reported as δ18O (VSMOW), δ56Fe (IRMM-14), and δ49Ti (OL-Ti). Select magnetite samples were also analyzed for17O (reported as Δ’17O0.5305) and range from −0.118 to −0.056 ‰—suggesting evaporitic input. The δ18O values from ore stage (+1.57 to +7.36 ‰), bt-mgt (+0.34 to +5.68 ‰), and mgt-act (+1.68 to +2.10 ‰) samples are consistent with a magmatic-hydrothermal origin for ore and pre-ore mineralizing fluids at Ernest Henry; non-magmatic δ18O values > c. 5 ‰ may be explained through localized carbonate wall rock assimilation. Despite this, δ56Fe values for ore stage (−0.50 to +0.33 ‰), bt-mgt (−0.65 to +0.38 ‰), and mgt-act (−0.26 to +0.30 ‰) magnetite are generally isotopically lighter than the accepted range (c. +0.06 to +0.49 ‰) for igneous and magmatic-hydrothermal magnetite and exhibit a relatively large range of c. 1 ‰, suggesting Fe source mixing within the deposit. Ore stage magnetite δ49Ti (−1.64 to + 3.79 ‰; avg: +1.49 ‰; 2σ = 2.63 ‰) compositions are generally higher and more variable than either the bt-mgt (-0.44 to + 1.49 ‰; avg: +0.62 ‰; 2σ = 1.13 ‰) or mgt-act (+0.27 to + 1.89 ‰; avg: +1.05 ‰; 2σ = 1.56 ‰) and suggest that Ti isotope fractionation occurred due to differential mobility in the fluid. The data are best explained by models invokingbothmagmatic and non-magmatic metal and fluid input. Fluid flow channeled between the footwall and hanging wall shear zones introduced non-magmatic Fe that may have been leached from local mafic units by magmatic-hydrothermal fluids, resulting in neoformed and regeneratively replaced magnetite with magmatic δ18O, but non-magmatic δ56Fe values during pre-ore alteration. These fluids may have mixed with Fe-poor evaporitic fluids prior to magnetite formation. Later magmatic Fe and O contributions during ore stage mineralization resulted in magnetite with variable δ56Fe and irresolvable δ18O overprinting. Ernest Henry is the first known example of an IOCG deposit with a major leached metal component identified through metal stable isotope geochemistry.