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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=714807
• 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.

这项提议为开发用于海洋化学研究的黄铁矿替代工具提供了资金。我们的海洋是地球上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也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，并在矿产勘探和采矿实践中应用。使用LA-ICPMS分析黄铁矿进行海洋化学分析与传统的整体样品分析相比有几个优点：1)现场分析只允许检测一种矿物，因此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选择样品，这意味着只考虑早期黄铁矿颗粒；以及3)由于黄铁矿含量可能保存在绿片岩相中，我们的研究可以包括更多的盆地，特别是在前寒武纪。 虽然这个黄铁矿代理工具是一个诱人的突破，但在它能够在两个古海洋中广泛实施之前，仍有几个方面必须进行评估。首先，沉积盆地内和不同局部氧化还原条件下TES的差异程度是一个重要的方面，人们对此知之甚少。我们将沿着研究充分的沉积盆地的横断面系统地研究黄铁矿的TE含量，以了解从近岸到深水环境黄铁矿的TE含量是如何变化的。我们还将对与黄铁矿分析相同的样品进行Fe形态分析、S同位素和全岩痕量及常量元素分析，以揭示沉积氧化还原条件对黄铁矿TE含量的影响。 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替代物有可能使额外的(变质)沉积盆地被考虑用于海洋化学研究，尤其是在前寒武纪。然而，未变质样品最内核黄铁矿的TE含量是否真的与未变质的沉积黄铁矿相同，还没有得到彻底的检验。利用接触变质作用后的沉积盆地中的黄铁矿，对比沉积黄铁矿和变质黄铁矿的岩心中的TE含量，以确定变质作用是否保存了TES。然后，该项目将扩大到研究区域变质作用。 我们将使用一系列纳米和微观分析技术(LA-ICPMS、TEM、APT、NanSIMS和XANES)来详细说明TES是如何赋存在黄铁矿中的。利用APT在原子尺度的3D空间中表征TES是如何存在于黄铁矿中的，将为其他与黄铁矿相关的研究提供宝贵的数据，如冶金和矿场复垦。通过这项研究产生的数据进一步支持矿产勘查研究，通过建立背景未矿化黄铁矿的TE范围来开发地球化学靶标工具。