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Abstract:

The Thayer Lindsley mine, located in the geographic South Range of the 1.85 Ga Sudbury Igneous Complex (SIC), hosts both contact-style Ni-Cu-PGE sulfide mineralization and footwall-style Cu-Ni-PGE mineralization. In this study, we examine contact-style ore zones at the mine that are overprinted by lower-amphibolite-grade shear zones that offset the contact between the SIC and the underlying footwall rocks of the Paleoproterozoic Southern Province. Strongly sheared sulfide ore is characterized by depleted Ni content and enriched Pt and Pd concentrations relative to undeformed sulfide ore, and by extensive replacement of pentlandite by pyrrhotite and of pyrrhotite by pyrite and marcasite. Although variations in the metal content of magmatic sulfide deposits are commonly attributed to primary processes such as R-factor, fractional crystallization of monosulfide solid-solution, or variable oxygen fugacity, f(O (sub 2) ), none wholly explain the variable Ni content of undeformed and sheared sulfide ore at the Thayer Lindsley mine. The observed Ni depletion in sheared sulfide ore is best explained by the replacement of pentlandite by pyrrhotite, with subsequent remobilization of the liberated Ni. Increased replacement of pentlandite occurs in the most strongly deformed sulfide ore and is associated with abundant syntectonic quartz veins. Increased permeability during shearing likely facilitated the alteration of pentlandite and the mobilization or loss of Ni via metamorphic fluids circulating in the amphibolite-grade assemblage.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2007-038818<br/>South Range<br/>Thayer Lindsley Mine