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Sudbury District

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Ames, D.E., and Farrow, C.E.G., 2007, Metallogeny of the Sudbury mining camp, Ontario, in Goodfellow, W.D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, p. 329-350. METALLOGENY OF THE SUDBURY MINING CAMP ,ONTARIO DOREEN E. AMES 1 AND CATHARINE E. G. F ARROW 2 1. 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 author’s email: [email protected] Abstract The 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 Canada’s 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 <10% in “footwall-hosted” deposits. Trace element sig- natures of the ores tend to be related to host rock (As, Sb) or deposit type (Zn, Cd, Pb). The key to effective exploration in the Sudbury camp is a solid understanding of the 3-D geology followed by appropriate EM/RIM geophysical meth- ods that increase the sampling radius of drillholes. The recognition of the evolution of the Sudbury area from a Ni-based camp to a polymetallic Ni-Cu-PGE producer is illustrated by the fact that over 50% of the exploration expenditures for 2005 focused on the footwall-hosted Cu-Ni- PGE systems due to the high Cu and PGE grades of the sulphide ore. The result was the discovery of new deposits (Levack Footwall Deposit) in a mature mining camp. New exploration models for low-sulphide, high-PGE (PM Deposit) styles of mineralization are being refined for both the North and South ranges. Base metal deposits are regu- larly discovered in the Sudbury camp with evolving deposit models, exploration techniques, and genetic models. Résumé La structure de Sudbury est le vestige d’un bassin d’impact multi-anneaux déformé datant du Paléoprotérozoïque (1 850 Ma), qui recèle d’énormes quantités de minéralisations sulfurées à Ni-Cu-ÉGP. La région de Sudbury constitue le principal district minier pour les métaux communs au Canada. On y compte 77 gisements de Ni-Cu-ÉGP exploités par le passé ou encore aujourd’hui ainsi que 11 gîtes de Ni-Cu-ÉGP rendus à un stade d’exploration avancé; le volume de la production passée, des réserves et des ressources s’élève à 1,655 milliard de tonnes. La région de Sudbury ren- ferme en outre des ressources minérales formées antérieurement à 1,850 Ma, dont des gîtes d’uranium et de Ni-Cu-ÉGP, de Au-Cu et de Au, ainsi que des gîtes hydrothermaux de Zn-Pb-Cu de formation contemporaine de l’impact météori- tique à 1,850 Ma. Les minéralisations contemporaines de l’impact météoritique à 1,850 Ma, formées des gisements de Ni-Cu-ÉGP de classe mondiale et des gîtes mineurs de Zn-Pb-Cu d’origine hydrothermale à l’intérieur du bassin, sont apparentées au Complexe igné de Sudbury. Plus de la moitié des minéralisations de Ni-Cu-ÉGP appartiennent à des gîtes de la zone de contact du complexe, 25 % à des gîtes associées à des apophyses du complexe, environ 15 % à des gîtes de la zone bréchique de Frood-Stobie et moins de 10 % à des gîtes encaissés dans le mur du complexe. Les signatures en éléments traces des minerais ont tendance à refléter la nature de la roche hôte (As, Sb) ou le type de gîte (Zn, Cd, Pb). Dans le camp minier de Sudbury, le succès de l’exploration repose sur une excellente compréhension de la géologie en 3-D et l’application de méthodes géophysiques EM/RIM appropriées, qui permettent d’étendre le rayon d’investigation des sondages. La reconnaissance du fait que la région de Sudbury soit passée d’un camp fondé sur la mise en valeur du Ni à une région productrice de Ni-Cu-ÉGP est reflétée par les dépenses d’exploration en 2005, dont plus de 50 % ont été con- sacrées aux systèmes de Cu-Ni-ÉGP dans les roches du mur du complexe, en raison des teneurs élevées du minerai sul- furé en Cu et en ÉGP. Il en résulte que de nouveaux gisements (gisement de Levack Footwall) ont pu être découverts dans un camp minier parvenu à maturité. De nouveaux modèles d’exploration visant les styles de minéralisations à faible concentration de sulfures et à teneur élevée en ÉGP (gisement de PM) font l’objet de raffinements aussi bien sur le flanc nord que sur le flanc sud. L’amélioration des modèles gîtologiques, des méthodes d’exploration et des modèles génétiques rend possible, à intervalles réguliers, la découverte de gîtes de métaux communs dans le camp minier de Sudbury. Introduction and History The Sudbury Structure is the remnant of a deformed 1.85 Ga multi-ring impact crater. This geological feature is of extraordinary economic and scientific significance, but remains enigmatic in many important respects. Sudbury, Canada and Noril’sk-Talnakh, Russia are the greatest Ni- producing districts in the world. The Sudbury ore deposits have produced an estimated US$ 280 billion or CDN$ 330 billion (with a US$/CDN$ exchange rate of 0.85) worth of metal in the past century (using 2005 average metal values) from more than 77 Ni-Cu-PGE deposits and two minor, past- producing hydrothermal Zn-Pb-Cu deposits. The continued prosperity of the Sudbury region depends on mining in the Sudbury structure at increasing depths and on the use of new geoscience knowledge created to find valuable hydrother- mal, magmatic Cu-PGE vein deposits at shallow levels. The Sudbury mining camp was discovered in 1856 when Alexander Murray reported sulphides in a Geological
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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: [email protected] 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


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