Refining the sedimentary pyrite proxy: Applications for understanding past ocean chemistry

精炼沉积黄铁矿代理：了解过去海洋化学的应用

• 批准号: RGPIN-2019-04843
• 负责人: Gregory, Daniel
• 金额: $ 1.82万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751226
• 关键词: Refining; sedimentary; pyrite; proxy; Applications

This proposal funds the development of the pyrite proxy tool for ocean chemistry studies. Our oceans hold the key to the beginning and evolution of life on Earth. Paleo-ocean studies can provide not only clues on how life evolved on Earth, but also how to identify exoplanets that may also support life. The research outcomes will also feed into economic geology, with applications in mineral exploration and mining practices. The use of LA-ICPMS analysis of pyrite for ocean chemistry offers several benefits over traditional bulk sample proxies: 1) the in-situ analysis allow only one mineral to be examined, thus excluding the mixed geochemical signatures from coexisting minerals; 2) the technique allows sample selection by mineral texture, which means only the early stage pyrite grains are considered; and 3) since pyrite TE content may be preserved up greenschist facies, more basins can be included in our investigations, especially during the Precambrian. While this pyrite proxy tool is an enticing breakthrough, there are still several aspects that must be assessed before it can be widely implemented in both paleo-ocean. First, the degree to which TEs vary within a sedimentary basin and under different local redox conditions is an important aspect that is poorly understood. We will systematically investigate the TE content of pyrite along transects across well studied sedimentary basins to see how TE content of pyrite varies from near shore to deep water settings. We will also conduct Fe speciation, S-isotope, and whole rock trace and major element analyses on the same samples as the pyrite analyses to unravel how depositional redox conditions affect the pyrite TE content. The ability of pyrite to preserve its TE content through metamorphism means the pyrite TE proxy has the potential to allow additional (metamorphosed) sedimentary basins to be considered for ocean chemistry studies, especially important in the Precambrian. However, it has not been thoroughly tested whether the TE content of pyrite in the unaltered, innermost core of a metamorphosed sample is indeed the same as unmetamorphosed sedimentary pyrite. Using pyrite from sedimentary basins that have experienced contact metamorphism, we will compare the TE content of sedimentary pyrite and cores of metamorphosed pyrite to determine whether the TEs are preserved through metamorphism. The project will then be expanded to examine regional metamorphism. We will use a series of nano- and micro-analytical techniques (LA-ICPMS, TEM, APT, nanoSIMS, and XANES) to detail how TEs are hosted in pyrite. The use of APT to characterise how TEs are held in pyrite in 3D space at the atomic scale will provide invaluable data for other pyrite-related studies, such as metallurgy and mine site reclamation. The data generated through this study with further support mineral exploration studies in developing geochemical targeting tools by establishing a TE range for background, unmineralized pyrite.

该提案为开发用于海洋化学研究的黄铁矿代用工具提供资金。我们的海洋是地球生命起源和进化的关键。古海洋研究不仅可以提供地球上生命如何进化的线索，还可以提供如何识别可能支持生命的系外行星的线索。研究成果还将用于经济地质学，并应用于矿产勘探和采矿实践。LA-ICPMS分析黄铁矿在海洋化学中的应用与传统的大批量样品替代物相比具有以下优点：1）原位分析仅允许检测一种矿物，从而排除了共存矿物的混合地球化学特征：2）该技术允许根据矿物结构进行样品选择，这意味着仅考虑早期黄铁矿颗粒; 3）由于黄铁矿TE含量可能保存在绿片岩相之上，因此我们的研究可以包括更多的盆地，特别是在前寒武纪。虽然这种黄铁矿代用工具是一个诱人的突破，但在它在古海洋和古海洋中广泛应用之前，仍有几个方面必须进行评估。首先，在沉积盆地内和不同的局部氧化还原条件下，TE变化的程度是一个重要的方面，这是知之甚少。我们将系统地调查沿沿着剖面的黄铁矿TE含量，研究沉积盆地，了解黄铁矿TE含量如何从近海岸到深水环境变化。我们还将进行Fe形态，S-同位素，全岩微量元素和主要元素分析的黄铁矿分析相同的样品，以解开沉积氧化还原条件如何影响黄铁矿TE含量。黄铁矿通过变质作用保持其TE含量的能力意味着黄铁矿TE代用品有可能允许额外的（变质）沉积盆地被考虑用于海洋化学研究，特别是在前寒武纪。然而，还没有彻底的测试是否TE含量的黄铁矿在未变质的，最里面的核心变质样品确实是相同的未变质沉积黄铁矿。利用来自经历过接触变质作用的沉积盆地的黄铁矿，我们将比较沉积黄铁矿的TE含量和变质黄铁矿的岩心，以确定TE是否通过变质作用保存下来。该项目随后将扩大到研究区域变质作用。我们将使用一系列的纳米和微观分析技术（LA-ICPMS，TEM，APT，nanoSIMS和XANES）来详细说明TE如何在黄铁矿中托管。利用APT在原子尺度上在3D空间中模拟黄铁矿中的TE，将为其他黄铁矿相关研究提供宝贵的数据，如冶金和矿山复垦。通过本研究生成的数据进一步支持矿产勘探研究，通过建立背景未矿化黄铁矿的TE范围来开发地球化学靶向工具。