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金属的矿藏与地球沉积地壳熔化产生的长英质岩浆结晶的末期有关。这些长英质岩浆系统的一个独特属性是其极高的化学分馏水平，人们推测岩浆蒸气相在这种行为中起着重要作用。要确定这些矿床是如何形成的，以及在哪里找到新的矿床，关键在于了解晶液分离、岩浆氧化还原状态和岩浆蒸气相(MVP)的发展如何影响元素的行为。黑云母和磷灰石是这种岩浆中常见的矿物，它们包含了各种元素，可以产生这样的信息。然而，要有意义地解释这些矿物中的元素丰度，需要在已知的压力、温度和氧逸度条件下对晶体/熔体分配进行校准。关于关键分馏元素，包括地球化学孪生元素Nb和Ta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。拟议的发现赠款项目将产生关于黑云母熔体和黑云母磷灰石对包括关键金属和卤素在内的大量元素的分配的新数据，这些数据可用于开发结晶的定量模型，评估MVP的形成时间，并为岩浆氧气气压测量的新方法提供基础。更多的研究将评估MVP在从Ta中分馏Nb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的起源。由此，可以确定将相对“正常”的地壳关键元素丰度集中到经济水平的方法，并揭示导致地壳内化学分馏的过程。