Petrofabric investigation of the sulfide-rich basal zone of the Duluth Complex

The South Kawishiwi Intrusion (SKI) of the 1.1 Ga Duluth Complex hosts significant Cu–Ni–PGE sulfide deposits concentrated within its basal contact zone. Although the geochemical signatures of these ores are well documented, the physical mechanisms responsible for focusing sulfur-rich melts remain unclear. This study investigates whether dynamic magma flow, characterized by shearing that produces mineral alignments or fabrics—influenced sulfide mineralization by transporting immiscible sulfide droplets within a flowing, crystal-rich mush prior to deposition.We analyzed oriented drill core samples from eleven closely spaced sites spanning mineralized and unmineralized zones in the SKI, including the unmineralized Duluth Layered Series (DLS) using a combination of techniques. Anisotropy of magnetic susceptibility (AMS) analysis identifies a well-developed, magnetite/titanomagnetite-dominated, pseudo-single-domain (grain size ~0.1–10 µm), oblate magnetic fabric in the mineralized zone, which is weaker in unmineralized rocks. Fabric orientations vary within the ore zone, reflecting highly dynamic and likely turbulent conduit flow capable of suspending and mixing immiscible sulfide droplets during ore formation. Bulk magnetic susceptibility (Kₘ) is variable in the SKI basal zone, reflecting lithological heterogeneity as confirmed by petrography, but uniformly high in distal zones such as the DLS. Electron backscatter diffraction (EBSD) analyses show that crystallographic preferred orientations of silicate minerals are generally subparallel to magnetic lineations, confirming the magmatic origin of the magnetic fabric. X-ray computed tomography (XCT) reveals that, where silicate minerals are well-aligned, sulfides form interconnected, net-textured networks along grain boundaries, whereas in rocks with disordered textures, sulfides remain diffuse and disseminated. These integrated results support the hypothesis that magma-flow-induced fabrics within conduit-like segments of the SKI have a link to sulfide transport, segregation, and localization. The combined AMS, EBSD, and XCT methodologies thus provide a powerful and transferable toolkit for studying magmatic sulfide deposits and decoding magma-flow processes in layered mafic–ultramafic intrusions globally.

Author dc:creator

• Cobbinah, Ishmael

• Anisotropy of Magnetic Susceptibility
• Duluth Complex
• Fabrics
• Layered Intrusions
• Magma flow
• Sulfide Mineralization

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/11299/277951

OAI identifier oai:identifier

oai:conservancy.umn.edu:11299/277951