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Using Geochemistry as a Tool in Solving Problems Related to Ni-sulfide Mineralization: Crustal Contamination Signature of the Midcontinent Rift System-associated Tamarack Intrusion (1105.6 ± 1.2 Ma), Minnesota

V. Taranovic, E. Ripley, and C. Li
Department of Geological Sciences, Indiana University, Bloomington, IN 47405

Conduit type magmatic Ni-sulfide deposits reflect a complex formational history sometimes involving multiple batches of magma emplaced through different paths. The addition of crustal sulfur plays an important role in controlling sulfide saturation in the magmas during emplacement. The Tamarack intrusion (MN) occurs within the Paleoproterozoic Animikie Basin hosting potentially economic Ni-Cu-(PGE) mineralization. The two main intrusive units, the ores and country rocks have distinctly different δ34S values. Os isotope mixing calculations involving the country rocks and primitive mantle are suggestive of the addition of 1-2% of a crustal contaminant to the mantle-derived magma. Anomalous Δ33S values suggest that along the variable pathways through the system, magmas that produced the semi-massive ores incorporated an Archean sulfur source. The lesser degrees of crustal contamination indicated by the Re-Os system may be related to isotopic exchange between contaminated and pristine magmas in the conduit system. The addition of crustal sulfur was the principal cause of sulfide saturation in the magmas at Tamarack; isotopic data indicate that both Archean and Proterozoic sulfur were involved in the contamination of distinct magma batches.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013