对岩浆岩中的巴德磊石-锆石对进行 SIMS U-Pb 测定,以确定一个镍-铜(PGE)矿床中岩浆成矿和热液再移动的年龄

IF 3.2 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
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引用次数: 0

摘要

与岩浆岩-超岩浆岩有关的镍-铜-(铂族元素)硫化物矿床是世界上最重要的镍和铂族元素(PGE)来源。这些矿床还含有大量的铜。这类矿床一般被认为是由原生岩浆富集和次生热液再移动等多个阶段形成的。但事实证明,确定镍-铜(PGE)硫化物矿床的年龄具有挑战性,尤其是那些经历了岩浆后热液叠加和再移动的矿床。缺乏可靠的地质年代数据阻碍了人们对这一重要矿化类型的地质控制的了解。位于华北克拉通的赤柏松镍-铜(PGE)硫化物矿床的特征是岩浆过程形成的散发状和净纹理矿石,并被热液富铜脉网覆盖。富铜脉网状结构受断裂控制,含有镍铜硫化物(黄铜矿、黄铁矿、辉铜矿)、闪石和石英等矿物组合。与散布的岩浆黄铜矿相比,热液网状结构中的黄铜矿镍含量相对较低,但银和镉含量较高,这是其他地方记载的热液叠加矿石的典型特征。我们在千柏松矿床的热液叠加矿石中发现了与镍铜硫化物相关的巴德来石-锆石对,其中巴德来石明确来源于原生火成岩,而锆石则是巴德来石在热液蚀变过程中的置换产物。对巴德来石和锆石的原位 SIMS U-Pb 测定得出的 207Pb/206Pb 加权平均年龄分别为 2181 ± 21 Ma 和 1892 ± 33 Ma,可解释为岩浆成矿和随后热液再移动镍-铜(PGE)矿床的时间。我们的研究结果解释了之前从该矿床获得的硫化物 Re-Os 年龄的巨大差异。这项研究表明,在详细的 BSE 成像的基础上,对巴德莱特-锆石对进行原位 SIMS U-Pb 测定,可以为岩浆成矿和热液再活化岩浆岩-超岩浆岩侵入体中蕴藏的镍-铜-(PGE)硫化物矿床提供可靠的年龄约束,尽管还需要进一步的研究来检验这类矿床的形成是否通常包含多个热液再活化阶段。由于baddeleyite或baddeleyite-锆石对是含镍-铜(PGE)岩浆岩-超基性岩中常见的附属矿物,本研究采用的测年方法可能适用于其他地方的类似矿床。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
SIMS U-Pb dating of baddeleyite-zircon pairs in mafic rocks to determine the ages of magmatic mineralization and hydrothermal remobilization in a Ni-Cu-(PGE) deposit

Ni-Cu-(PGE) sulfide deposits associated with mafic–ultramafic rocks are the most important sources of Ni and platinum-group elements (PGE) in the world. These deposits also contain significant amounts of Cu. Such deposits are generally considered to have formed by multiple stages of primary magmatic concentration and secondary hydrothermal remobilization. However, constraining the ages of Ni-Cu-(PGE) sulfide deposits has proven challenging, particularly those that have experienced post-magmatic hydrothermal overprinting and remobilization. The lack of robust geochronology data has hindered understanding of the geological controls on this important type of mineralization. The Chibaisong Ni-Cu-(PGE) sulfide deposit in the North China Craton is characterized by disseminated and net-textured ores formed by magmatic processes and overprinted by hydrothermal Cu-rich vein stockwork. The Cu-rich vein stockwork is fracture-controlled, and contains a mineral assemblage of Ni-Cu sulfides (chalcopyrite, pyrrhotite, pentlandite), amphibole and quartz. Chalcopyrite in the hydrothermal stockwork is relatively depleted in Ni but enriched in Ag and Cd compared with disseminated magmatic chalcopyrite, typical of hydrothermal superimposed ores as documented elsewhere. We identified baddeleyite-zircon pairs associated with Ni-Cu sulfides in hydrothermal superimposed ores of the Chibaisong deposit, in which the baddeleyite is unequivocally of primary igneous origin whereas the zircon represents the replacement product of baddeleyite during hydrothermal alteration. In situ SIMS U-Pb dating of baddeleyite and zircon yielded weighted mean 207Pb/206Pb ages of 2181 ± 21 Ma and 1892 ± 33 Ma, respectively, interpreted as the timing of magmatic mineralization and subsequent hydrothermal remobilization of the Ni-Cu-(PGE) deposit. Our results explain the large discrepancies in sulfide Re-Os ages previously obtained from this deposit. This study demonstrates that on the basis of detailed BSE imaging, in situ SIMS U-Pb dating of baddeleyite-zircon pairs can provide robust age constraints for both magmatic mineralization and hydrothermal remobilization of Ni-Cu-(PGE) sulfide deposits hosted in mafic–ultramafic intrusions, although further studies are needed to test whether the formation of such deposits commonly entails multiple stages of hydrothermal remobilization. Since baddeleyite or baddeleyite-zircon pairs are common accessory minerals in Ni-Cu-(PGE)-bearing mafic–ultramafic rocks, the dating approach employed in this study may be applicable to similar deposits elsewhere.

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来源期刊
Precambrian Research
Precambrian Research 地学-地球科学综合
CiteScore
7.20
自引率
28.90%
发文量
325
审稿时长
12 months
期刊介绍: Precambrian Research publishes studies on all aspects of the early stages of the composition, structure and evolution of the Earth and its planetary neighbours. With a focus on process-oriented and comparative studies, it covers, but is not restricted to, subjects such as: (1) Chemical, biological, biochemical and cosmochemical evolution; the origin of life; the evolution of the oceans and atmosphere; the early fossil record; palaeobiology; (2) Geochronology and isotope and elemental geochemistry; (3) Precambrian mineral deposits; (4) Geophysical aspects of the early Earth and Precambrian terrains; (5) Nature, formation and evolution of the Precambrian lithosphere and mantle including magmatic, depositional, metamorphic and tectonic processes. In addition, the editors particularly welcome integrated process-oriented studies that involve a combination of the above fields and comparative studies that demonstrate the effect of Precambrian evolution on Phanerozoic earth system processes. Regional and localised studies of Precambrian phenomena are considered appropriate only when the detail and quality allow illustration of a wider process, or when significant gaps in basic knowledge of a particular area can be filled.
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