Imaging the Whole‐Lithosphere Architecture of a Mineral System—Geophysical Signatures of the Sources and Pathways of Ore‐Forming Fluids. (8th August 2022)

• Record Type: Journal Article
• Authors: Comeau, Matthew J.; Becken, Michael; Kuvshinov, Alexey V.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 23:Number 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-08
• Subjects: magnetotellurics -- electrical resistivity -- shear‐wave velocity -- mineral exploration -- fertilization -- fluid pathways; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010379
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Mineral systems can be thought of as a combination of several critical elements, including the whole‐lithosphere architecture, favorable geodynamic/tectonic events, and fertility. Because they are driven by processes across various scales, exploration benefits from a scale‐integrated approach. There are open questions regarding the source of ore‐forming fluids, the depth of genesis, and their transportation through the upper crust to discrete emplacement locations. In this study, we investigate an Au–Cu metal belt located at the margin of an Archean‐Paleoproterozoic microcontinent. We explore the geophysical signatures by analyzing three‐dimensional models of the electrical resistivity and shear‐wave velocity throughout the lithosphere. Directly beneath the metal belt, narrow, vertical, finger‐like low‐resistivity features are imaged within the resistive upper‐middle crust and are connected to a large low‐resistivity zone in the lower crust. A broad low‐resistivity zone is imaged in the lithospheric mantle, which is well aligned with a zone of low shear‐wave velocity, examined with a correlation analysis. In the upper‐middle crust, the resistivity signatures give evidence for ancient pathways of fluids, constrained by a structure along a tectonic boundary. In the lower lithosphere, the resistivity and velocity signatures are interpreted to represent a fossil fluid source region. We propose that these signatures were caused by a combination of factors related to refertilization and metasomatism of the lithospheric mantle by long‐lived subduction at the craton margin, possibly including iron enrichment, F‐rich phlogopite, and metallic sulfides. The whole‐lithosphere architecture controls the genesis, evolution, and transport of ore‐forming fluids and thus the development of the mineral system. Plain Language Summary: The whole‐lithosphere structure of mineral systems, the link between deep and shallow regions, and the nature, origin, and depth of the source fluids that form mineral deposits are open questions. In this study, we investigate a gold and copper metal belt that is located at the margin of an ancient microcontinent and craton with a history of long‐lived subduction. We explore the region by examining three‐dimensional geophysical images of both the electrical resistivity structure and the shear‐wave velocity structure throughout the lithosphere. Narrow, vertical, fingers of low resistivity in the crust give evidence for ancient pathways of fluids beneath the metal belt. Low velocity and low resistivity signatures in the lower lithosphere are interpreted to represent a fossil fluid source region. We suggest that the geophysical signatures observed were caused by a combination of factors related to mantle metasomatism caused by long‐lived subduction and magmatism. The possible causes include iron enrichment in a more fertile mantle, the presence of F‐rich phlogopite in the lithospheric mantle, and metallic sulfides in the lower lithosphere, including at the base of the crust. The whole‐lithosphere structure and favorable geodynamic/tectonic events control the evolution of ore‐forming fluids that create metal/mineral deposits. Key Points: Vertical, finger‐like low‐resistivity zones in the upper crust beneath an Au‐Cu metal belt give evidence for ancient pathways of fluids Low velocity and low resistivity in the lower lithosphere are interpreted to represent a fossil source region for ore‐forming fluids Signatures may be due to a combination of factors: Metallic sulfides, phlogopite, and iron enrichment by refertilization and metasomatism