FNX’S PM Deposit, McCreedy West Mine, Sudbury: The Evaluation of a ‘Low-Sulphide' Cu-Ni-PGE Resource

CIM Vancouver 2006
John Everest, Catherine Farrow,
Abstract FNX Mining Company Inc.’s McCreedy West Mine is located 34 km northwest of Sudbury along the North Range of the Sudbury Igneous Complex (SIC). Past production, until closure in 1998, totaled 15,758,000 tons at 1.7% Cu, 1.44% Ni and 0.43 oz/ton Pt+Pd+Au, from both Contact Ni-rich sulphide mineralization along the base of the SIC, and Cu(-Ni)-PGE footwall sulphide vein mineralization. FNX began renewed production at the mine in 2003 from previously known and newly discovered (Inter Main Deposit) ‘Contact’ Ni-sulphide deposits, and from extensions of Cu(-Ni)-PGE footwall ‘sharp-walled’ veins known as the 700 Complex. Prior to 2003, the previous operator had drilled 44 holes into the PM Deposit, a ‘low-sulphide’ style of Sudbury mineralization. At the time the PM Deposit defined the psychological challenges associated with geologically modeling a new, poorly understood, style of mineralization. Initially FNX began exploring the deposit from surface diamond drilling until the main underground access ramp was rehabilitated and an underground drill programme was initiated in February 2003. Since then, extensive diamond drilling, underground mapping, and bulk sampling have defined an ‘Indicated’ resource of 2.8 million tons with an average grade of 1.2% Cu, 0.3% Ni and 0.17 oz/ton Pt+Pd+Au. Current ‘Inferred’ resources total 1.1 million tons at 1.1% Cu, 0.3% Ni and 0.21 oz/ton Pt+Pd+Au. Commercial production from the zone was announced in May, 2005. The host environment for the PM Deposit is Sudbury Breccia, a fine-grained matrix and locally clast-rich breccia, which has been developed in the gneissic footwall to the SIC at McCreedy West Mine. The current known extents of the PM Deposit is approximately 1000 feet E-W, and 1200 feet down dip (-35º SE), with a true thickness up to 120 feet and is open in three directions. Sulphide mineralization within the PM Deposit typically consists of discontinuous chalcopyrite +/- millerite + platinum-group minerals (Pt+Pd bismuth tellurides) veins, veinlets, stockworks and disseminations. A limited volume of PM Deposit mineralization is represented by relatively continuous sulphide-rich veins >20 cm in thickness, unlike ‘sharp-walled’ vein environments. PM deposit resource modeling is based on the geological modeling of Sudbury Breccia, with three lithologic units: massive veins (defined as <15% Cu+Ni), breccia matrix and clasts. Idealized wireframes of known, large clasts are created. For block modeling the expected proportion of each lithology was estimated for each block with an independent Id2 estimate and grade interpolation for each lithology. This approach to resource modeling has resulted in robust reconciliation with measured production tonnages and grades from individual stope blocks on the west side of the deposit. This resource modeling technique has proven to be highly effective for ‘low-sulphide’ styles of Sudbury mineralization.
Keywords: Sudbury, McCreedy West, Nickel
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