METALLOGENY OF THE SUDBURY MINING CAMP, ONTARIODOREEN E. AMES1 AND CATHARINE E. G. FARROW21. Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8 2. FNX Mining Company Inc., 1300 Kelly Lake Road, Sudbury, Ontario PE3 5P4 Corresponding authors email: dames@nrcan.gc.ca AbstractThe Paleoproterozoic (1850 Ma) Sudbury Structure, the remnant of a deformed multi-ring impact basin, is host to an enormous amount of Ni-Cu-PGE sulphide mineralization. Sudbury is Canadas principal base metal mining district with 77 producing and past-producing Ni-Cu-PGE deposits and 11 Cu-Ni-PGE advanced exploration projects with a 1.655 billion tonne past production, reserve, and resource. The Sudbury region is also host to significant pre-1850 Ma mineral resources comprising uranium, Ni-Cu-PGE, Au-Cu, and Au deposits and syn-1850 Ma hydrothermal Zn-Pb-Cu deposits. The1850 Ma world-class Ni-Cu-PGE deposits and minor hydrothermal Zn-Pb-Cu deposits within the basin are related to the Sudbury Igneous Complex, with over half of the Ni-Cu-PGE in Contact deposits, 25% in Offset deposits, approximately 15% in Frood-Stobie breccia belt deposits, and 5% + inclusions >50% metres Outcrop 0 20 Shear zone

FIGURE 13. Geological map of the Totten deposit, Worthington offset, illustrating the mineralized inclusion quartz diorite in the core of the dyke (Stewart, 2002).

vein stockwork, and disseminated Cu, PGE, Au, Ag, and Ni orebodies (Naldrett and Kullerud, 1967; Li and Naldrett, 1993; Morrison et al., 1994). Textural variations in the widely distributed Sudbury breccia have resulted in the interpretation that thermally metamorphosed Sudbury breccia zones are prospective hosts for Cu-Ni-PGE systems (Morrison et al., 1994; Fedorowich et al., 1999; Hanley and Mungall, 2003). Progressive textural changes in the matrix of the Sudbury breccia from a black, aphanitic matrix and discrete felsic fragments (cold) to a recrystallized, finegrained leucocratic, equigranular matrix with diffuse felsic fragments and irregular felsic patches (hot) reflect the thermal metamorphism prospective for footwall-hosted Cu-NiPGE mineralization. Poikiloblastic biotite and/or amphibole growth, quartz recrystallization, and anatexis with the formation of granophyric patches are characteristic of intense thermal metamorphism of Sudbury breccia that may contain anomalous levels of Cu, Ni, PGE, Au, and Ag in positions up to several hundreds of metres from ore-grade mineralization. Sharp-walled Cu-Ni-PGE deposits are characterized by chalcopyrite-rich veins with sharp, planar surfaces across which the modal proportion of sulphide drops from greater than 80% to less than 5%. As a result, production grades are directly linked to vein thickness as much as to Ni or PGE tenor of the sulphides. Veins with greater than 30 m strike length are observed to be up to 7 m wide but are typically in the range of centimetres to decimetres. The largest veins are typically oriented subparallel to the SIC contact (e.g. McCreedy East 153 zone), however, some are conjugate systems or are randomly oriented (e.g. McCreedy West Footwall Cu; Fraser-Strathcona Powderhouse zone) (Fig. 14C). The massive chalcopyritecubanite vein-style footwall deposits (e.g. McCreedy East 153 zone, McCreedy West Footwall Cu; Fraser-Strathcona Cu zones, Ni Rim Footwall, Victor Deep, and the Levack Footwall deposits) contain minor pyrrhotite, pentlandite, millerite, bornite, and magnetite. Mineral abundances and base and precious metal ratios can vary along the length of individual veins. Metal zonation patterns have been demonstrated to change gradu338

ally with increasing Cu/Ni ratios with distance from the SIC contact (i.e. McCreedy West Footwall Cu:Cu/Ni 3.5 to 6.75, Morrison et al., 1994; Fraser-Strathcona Deep Copper zones, Li et al., 1992; Money, 1993; Kormos, 1999). The Cu/NiA NCraig Shaft

Levack #2 Shaft

S

Main Orebody Keel Zone1600 L

#7 Orebody

2650 L

30 - 1 Drift

Robs Footwall Zone3600 L

40 - 1 Drift

250 m

Lower Levack Footwall Zone

Sudbury Igneous Complex Footwall breccia Granite gneiss Sudbury breccia Mineralized zones Mine drift Property boundary

Exploration Corridor: Exploration Corridor:

Levack footwall deposit =Massive Cu-Ni-PGE-rich veins with possible bornite-enriched margin and low-S hanging wall

Robs Footwall = Transitionalzone with Cu:Ni ~ 1:1

Lower footwall = High-tenorPGE in sulphide veins and disseminations

Levack Footwall DepositsSchematic section looking east

Keel zone = 2004/2005 discoveryof massive Cu-Ni-PGE-rich veins

FIGURE 14. Cross-sections of footwall-type mineralization showing the relationship with contact-type mineralization at the base of the Sudbury Igneous Complex. (A) Levack footwall deposits.

F a lc on b rid g e

F N X M in in g

Levack Footwall Deposit

Metallogeny of the Sudbury Mining Camp, Ontario ratio of the sulphides is typically SIC Contact zone B Contact-type greater than 6.5 with correspondMassive sulphide Norite mineralization Footwall breccia ingly high PGE tenor (Pt+Pd+Au > Footwall zone Inclusion-bearing 7.7 g/t; Farrow and Lightfoot, Felsic gneiss sublayer norite Transitional Disseminated 2002). Data compiled as part of this sulphide mineralization study and from Naldrett et al. Sudbury breccia (1999) show that massive sulphide, Granodiorite sharp-walled vein deposits in production and advanced exploration projects from both the North and East ranges typically grade more than 20% Cu, and vary from 0.70% Fringe to more than 4% Ni, and from 10 mineralization g/t to more than 30 g/t Pt+Pd+Au. These Cu-Pt-Pd-rich deposits are characteristically Ir-Rh-Os poor Footwall zone (Naldrett et al., 1999). Cu-Ni-PGE system Low-sulphide PGE footwall Nickel Rim South Mine Approximate Scale mineralization (e.g. McCreedy Schematic section 50 m looking northwest West PM deposit) occurs as blebs, stringers, and disseminated sulphides and may or may not be ecoC nomically connected to vein-style West East footwall mineralization. The lowsurface sulphide McCreedy West PM deposit is the first stand-alone East Main 700 low-sulphide system to be put Complex into production in the Sudbury Upper Main camp. It is hosted in Sudbury breccia and is approximately 350 x 400 Inter Main x 40 m with an indicated resource 900 L of 2.25 million tons at 1.11 wt.% Cu, 0.26 wt.% Ni, and 5.58 g/t Pt+Pd+Au and an inferred resource of 1.06 million tonne at 1.11 wt.% 1600 L Cu, 0.28 wt.%, Ni, and 6.40 g/t Pt+Pd+Au (Farrow et al., 2005). Middle Upper PM The low sulphide PGE mineralizaMain Deposit tion of the PM deposit is dominated by chalcopyrite and minor milPM Deposit 500 m lerite, with a total sulphide content of less than 5 modal percent. The mineralization is defined by a Contact deposits series of stacked sulphide veins McCreedy West Mine (typically