Metamorphic remobilization of Archean Au: Insights from the world-class Hemlo deposit, Canada

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Precambrian Research Pub Date : 2025-02-10 DOI:10.1016/j.precamres.2025.107710

O Nadeau , M.I. Leybourne , A Voinot , A Poirier

{"title":"Metamorphic remobilization of Archean Au: Insights from the world-class Hemlo deposit, Canada","authors":"O Nadeau , M.I. Leybourne , A Voinot , A Poirier","doi":"10.1016/j.precamres.2025.107710","DOIUrl":null,"url":null,"abstract":"<div><div>Although most Archean orogenic Au deposits formed after the related metamorphic events, numerous deposits have formed prior to peak metamorphic conditions, and abundant research has focused on the remobilization of Au by metamorphic-hydrothermal fluids. At the Archean Hemlo Au deposit, Canada, most recent research agrees that Au mineralization first occurred prior to metamorphism and that Au was subsequently remobilized. Given that Li is mobile, relatively compatible in micas and clay minerals, and experiences isotopic fractionation primarily as a result of fluid-rock reactions, here, Li isotopic composition is analyzed using multiple collector ICP-MS and used to investigate Au remobilization during metamorphic-hydrothermal alteration. It is shown that bulk rock Li concentrations and isotopic compositions changed simultaneously with Au remobilization, as a result of the metamorphic recrystallization of biotite, chlorite, muscovite, and white mica. The concentration of Li increased from 2.6-58 ppm in hydrothermally-altered rocks, and δ<sup>7</sup>Li values decreased simultaneously, from + 10.5 to + 1.4 ‰. Interestingly, the δ<sup>7</sup>Li values correlate positively with Au and Li concentrations, indicating that the metamorphic-hydrothermal fluid remobilized Au as the rocks were fluxed with Li, and the biotite-chlorite-muscovite-white mica assemblages were recrystallized. In addition to bulk rock analyses, the concentration of Li-Au was measured in minerals using laser ablation ICP-MS, in order to investigate why bulk rock δ<sup>7</sup>Li values and Li concentrations are systematically correlated with Au concentrations. The presence of Au in K-feldspar is ascribed to primary mineralization and related K-feldspar alteration, whereas that in prograde and retrograde biotite, as well as in retrograde chlorite, muscovite, and white mica, must have resulted from the metamorphic-hydrothermal alteration and related Au remobilization. The decrease in Au counts and concentrations in minerals representing the sequence of recrystallization support bulk rock results suggesting that some Au was remobilized during metamorphism. Overall, these results highlight the strong potential of Li isotopes for Au exploration and metallogenic studies.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":"419 ","pages":"Article 107710"},"PeriodicalIF":3.2000,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Precambrian Research","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0301926825000361","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}

引用次数: 0

Abstract

Although most Archean orogenic Au deposits formed after the related metamorphic events, numerous deposits have formed prior to peak metamorphic conditions, and abundant research has focused on the remobilization of Au by metamorphic-hydrothermal fluids. At the Archean Hemlo Au deposit, Canada, most recent research agrees that Au mineralization first occurred prior to metamorphism and that Au was subsequently remobilized. Given that Li is mobile, relatively compatible in micas and clay minerals, and experiences isotopic fractionation primarily as a result of fluid-rock reactions, here, Li isotopic composition is analyzed using multiple collector ICP-MS and used to investigate Au remobilization during metamorphic-hydrothermal alteration. It is shown that bulk rock Li concentrations and isotopic compositions changed simultaneously with Au remobilization, as a result of the metamorphic recrystallization of biotite, chlorite, muscovite, and white mica. The concentration of Li increased from 2.6-58 ppm in hydrothermally-altered rocks, and δ⁷Li values decreased simultaneously, from + 10.5 to + 1.4 ‰. Interestingly, the δ⁷Li values correlate positively with Au and Li concentrations, indicating that the metamorphic-hydrothermal fluid remobilized Au as the rocks were fluxed with Li, and the biotite-chlorite-muscovite-white mica assemblages were recrystallized. In addition to bulk rock analyses, the concentration of Li-Au was measured in minerals using laser ablation ICP-MS, in order to investigate why bulk rock δ⁷Li values and Li concentrations are systematically correlated with Au concentrations. The presence of Au in K-feldspar is ascribed to primary mineralization and related K-feldspar alteration, whereas that in prograde and retrograde biotite, as well as in retrograde chlorite, muscovite, and white mica, must have resulted from the metamorphic-hydrothermal alteration and related Au remobilization. The decrease in Au counts and concentrations in minerals representing the sequence of recrystallization support bulk rock results suggesting that some Au was remobilized during metamorphism. Overall, these results highlight the strong potential of Li isotopes for Au exploration and metallogenic studies.

Abstract Image

查看原文本刊更多论文

太古宙金的变质再活化作用：来自世界级加拿大Hemlo矿床的启示

虽然太古宙造山带的金矿大多是在相关变质事件之后形成的，但也有不少金矿是在变质高峰条件之前形成的，变质热液对金的再活化作用已引起了大量的研究。在加拿大太古宙Hemlo金矿床，最近的研究一致认为，金矿化首先发生在变质作用之前，随后又被重新活化。考虑到Li是可移动的，在云母和粘土矿物中相对兼容，并且主要由于流体-岩石反应而经历同位素分馏，本文利用多捕收剂ICP-MS分析了Li的同位素组成，并用于研究变质-热液蚀变过程中Au的再活化。结果表明，由于黑云母、绿泥石、白云母和白云母的变质重结晶作用，大块岩石Li浓度和同位素组成与Au再活化同时发生变化。热液蚀变岩中Li浓度从2.6 ~ 58 ppm上升，δ7Li值从+ 10.5‰下降到+ 1.4‰。有趣的是，δ7Li值与Au和Li浓度呈正相关，表明变质-热液流体对Au进行了再活化，岩石被Li注入，黑云母-绿泥石-白云母组合被重结晶。除了块状岩石分析外，还使用激光烧蚀ICP-MS测量了矿物中的Li-Au浓度，以研究块状岩石δ7Li值和Li浓度与Au浓度系统相关的原因。钾长石中金的存在是原生矿化和钾长石蚀变的结果，而在顺行和逆行黑云母中，以及在逆行绿泥石、白云母和白云母中，金的存在则是变质-热液蚀变和相关的金再活化的结果。代表重结晶顺序的矿物中Au计数和浓度的下降支持大块岩石的结果，表明在变质作用过程中有一部分Au被重新活化。总之，这些结果突出了Li同位素在金矿找矿和成矿研究中的巨大潜力。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

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.