Copper-Nickel Grade Maps for the Spruce Road Deposit, South Kawishiwi Intrusion, Duluth Complex

Abstract

This report describes the Cu-Ni mineralization of the Spruce Road area in the northern portion of the South Kawishiwi intrusion. The mineralization in the area is defined by > 9,500 assays from approximately 140,000 feet of core from 232 exploration holes drilled by INCO (220 holes), Bear Creek (6 holes), U.S. Bureau of Mines (3 holes), Hanna Mining (2 holes), and Wallbridge Mining (1 hole). Drilling in the Spruce Road area largely occurred during two time periods: the middle 1950s, following the original discovery of Cu-Ni mineralization, and from 1966 to 1973. Assay data from all of the drill holes within the South Kawishiwi intrusion have been compiled by the author into a comprehensive geological and geochemical database. Drill hole assays for the Spruce Road area have been exported out of this database and form the geochemical basis for this report. Preliminary analysis of the drill hole assay data for all of the deposits of the South Kawishiwi intrusion has led to the identification of two main styles of mineralization associated with the base of the intrusion. These mineralization types include: 1) “Open” – vertically extensive (> 450 meters) mineralization with moderate Cu-Ni grade and low Au+PGE grades. Examples of this open style include the Spruce Road, Serpentine, and Dunka Pit deposits. 2) “Confined” – vertically restricted (< 150 meters) mineralization with high Cu-Ni grades and moderate to very high (locally) Au+PGE grades. Examples of the confined style include the Maturi, Maturi Extension, and the Birch Lake deposits. Regional crosscutting relationships indicate that the “Open” style mineralization preceded the “Confined” style. Moreover, the curvilinear nature of the contact between the styles of mineralization is similar to the regional contacts of most of the intrusions of the Duluth Complex and adds further support to this theory.