Petrologic tools to understand ore-formation in felsic igneous systems

了解长英质火成岩系统中成矿作用的岩石学工具

• 批准号: RGPIN-2022-04097
• 负责人: Brenan, James
• 金额: $ 3.72万
• 依托单位: Dalhousie University
• 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=750941
• 关键词: Petrologic; tools; understand; ore; formation

Mineral deposits of some of the critical metals essential to society are associated with the end stages of crystallization of the felsic magmas produced by melting of Earth's sedimentary crust. A unique attribute of these felsic magmatic systems is their extreme level of chemical fractionation, and it has been postulated that a magmatic vapour phase plays a significant role in this behaviour. Key to determining how these deposits form, and where to find new ones, lies in understanding how crystal-liquid separation, magma redox state and the development of a magmatic vapour phase (MVP) affect element behaviour. Biotite and apatite are common minerals in such magmas, and incorporate a variety of elements that can yield such information. However, meaningful interpretation of element abundances in these minerals requires calibration of crystal/melt partitioning at known conditions of pressure, temperature and oxygen fugacity. Information on the relative melt-vapour partitioning of key fractionated elements, including the geochemical twins Nb and Ta, is scarce, but essential to evaluating the roles of melt and vapour in ore formation. The proposed Discovery Grant projects will generate new data on biotite-melt and biotite-apatite partitioning of a large number of elements, including the critical metals and halogens, which can be used to develop quantitative models of crystallization, assess the timing of MVP formation and provide the basis for new methods of magma oxygen barometry. Additional research will evaluate the role of the MVP on fractionating Nb from Ta, and therefore better understand the origin of the extreme level of chemical fractionation exhibited by these unique magmatic systems. From this, it can be established the ways by which relatively "normal" crustal abundances of critical elements can be concentrated to economic levels and unravel the processes that result in chemical fractionation within Earth's crust.

一些对社会至关重要的关键金属的矿藏与地球沉积地壳融化产生的长英质岩浆的结晶末期有关。这些长英质岩浆系统的一个独特属性是其极端水平的化学分馏，并且推测岩浆气相在这种行为中发挥着重要作用。确定这些沉积物如何形成以及在哪里找到新沉积物的关键在于了解晶液分离、岩浆氧化还原状态和岩浆气相 (MVP) 的发展如何影响元素行为。黑云母和磷灰石是此类岩浆中常见的矿物质，并含有多种可以产生此类信息的元素。然而，对这些矿物中元素丰度的有意义的解释需要在已知的压力、温度和氧逸度条件下校准晶体/熔体分配。有关关键分馏元素（包括地球化学孪生铌和钽）的相对熔体-蒸气分配的信息很少，但对于评估熔体和蒸气在成矿中的作用至关重要。拟议的发现补助金项目将生成有关大量元素（包括关键金属和卤素）的黑云母-熔体和黑云母-磷灰石分配的新数据，这些数据可用于开发结晶的定量模型、评估 MVP 形成的时间和为岩浆氧气压测定新方法提供基础。其他研究将评估 MVP 在从 Ta 中分馏 Nb 方面的作用，从而更好地了解这些独特的岩浆系统所表现出的极端化学分馏水平的起源。由此，可以确定如何将相对“正常”的地壳丰度集中到经济水平，并揭示导致地壳内化学分馏的过程。