Summary:
At the McCreedy West Mine, mineralization occurs as Contact and Footwall Deposits. Historic and current operations exploit both Contact Ni-Cu mineralization along the base of SIC within Sublayer Norite and granite breccia-filled embayments, and Footwall Cu-Ni- PGM mineralization in the footwall Sudbury Breccia environment.
The Contact Deposits on the property (Inter Main, Upper Main, and East Main), are related to a suite of sulphide and inclusion-rich sublayer norites and leucocratic granitic breccias. The orebodies occupy embayment structures and traps that often penetrate into the footwall of the SIC. These embayment structures are characterized by significant thickening of the mafic norite and sublayer units accompanied by thicker zones of granite breccia. Hanging-wall rocks composed of basal mafic norite and felsic norite of the main SIC overlie the contact mineralized zones. Brecciated rocks of the Levack Complex consisting of granodiorite, granodiorite gneiss and migmatites form the footwall to the deposits.
The Footwall Type Cu-Ni-PGM vein deposits are represented by the 700 Vein Complex; 950 Vein Complex; and the PM Deposit. These are now regarded as one deposit with a progression from sharpwalled massive chalcopyrite veins in the 700 Deposit passing down through the 950 (now referred to as the Upper PM) to the PM Deposit where mineralization occurs both within veins and as matrix fill within the Sudbury.
Contact-Type Ni-Cu Deposits.
Upper Main Deposit.
The Upper Main Deposit comprises two mineralized lenses; each consisting of disseminated to massive pyrrohotite-pentlandite-chalcopyrite-pyrite predominately hosted within granite breccia.
Inter Main Ni-Cu Deposit.
The Inter Main Deposit consists of nickel-rich, Sudbury Basin contact-type and hanging-wall mineralization. The main body of mineralization is controlled by footwall irregularities, and gneissic blocks and fragments in the hanging-wall at or near the contact of the Sudbury Igneous Complex (SIC) with the underlying footwall. The reserve model of the Inter Main suggests that mineralization occurs over a strike direction of at least 1100 ft and down dip for 800 ft. Recent drilling has shown the potential for significant additions to the reserve tonnage. Though the dominant mineralization is associated with physical traps at the base of the SIC however, mineable hanging-wall lenses occur throughout the ore body. The dominant host rock for both contact and hanging-wall environments is granite breccia.
East Main Deposit.
The East Main Deposit occurs to the east of the main ramp between surface and 920 Level, and consists of semi-massive to massive pyrrhotite-pentlandite- chalcopyrite-pyrite contact-style mineralization. The central portion of the deposit occupies a south easterly trending embayment that extends from surface, down dip to a depth of at least 600 ft below surface. The mineralized zone is typically between 8 and 25 ft thick and predominantly occurs near the base of the granite breccia horizon adjacent to the gneissic footwall rocks. In the southern, down dip extension of the East Main, the mineralization splays into two narrow zones, each between eight and 15 ft wide, and separated by 12 – 30 ft of weakly mineralized granite breccia and sublayer.
Footwall-Type Cu-PGM Deposit Targets.
Footwall deposits of the Sudbury Basin are emplaced within zones of Sudbury Breccia adjacent to, or in the general vicinity of, contact ore environments. The Sudbury Breccia zones are usually much larger than the footwall ore deposits themselves. Exploration to date has shown the presence of significant mineralization proximal to the contact- type deposits at McCreedy West. This mineralization is part of an eastwardplunging and south-dipping structural zone contained within an area of footwall Sudbury Breccia that extends from surface to a depth of at least 3000 ft. The Footwall Type Cu- (+Ni) -PGM deposits are represented at McCreedy West by the 700 Deposit and the PM Deposit (the upper part of which was formerly known as the 950 Deposit). As our geological knowledge grows through mapping and an increasingly higher density of drilling in this environment it is now apparent that rather than being three distinct deposits, the deposits represent a continuum from the sharp walled massive chalcopyrite veins of the 700 Deposit through an increasing amount of sulphides in the breccia matrix (950) to a dominance of breccia hosted mineralization in the PM Deposit.
700 Deposit.
Mineralization within the 700 Deposit is restricted to sharp walled veins which cross cut both the Sudbury Breccia matrix and clasts. Individual veins, ranging in thickness from several inches up to 13 ft, are composed of massive chalcopyrite with accessory pentlandite, millerite and pyrrhotite, and have strike and dip lengths ranging from 25 to 350 ft.
Upper PM Deposit (formerly 950 Deposit).
The Upper PM Deposit is located to the east and down plunge from the 700 Deposit described above. This deposit comprises two distinct styles of mineralization: (i) massive chalcopyrite, pentlandite and millerite veins ranging in thickness from 3 inches to 3.0 ft, and (ii) a broader zone of irregular stringers and disseminated chalcopyrite blebs.
PM Deposit (Main).
The PM Deposit is located down dip from the Upper PM below the 1450 Level at McCreedy West Mine and within a broad package of footwall Sudbury Breccia. Mineralization typically consists of chalcopyrite ± millerite ± pendlandite + PGM (Pt+Pd Bismuth Tellurides) + gold within a mineralized envelope which generally dips 38° to the southeast.
In the area of the PM Deposit, the host Sudbury Breccia is typically 300 to 400 ft wide and dips to the south east. At the known western extent of the deposit, the Sudbury Breccia is intersected at approximately 200 ft below the SIC contact, whereas at the eastern extent it occurs 600 ft from the contact. One-hundred foot thick ‘necks’ of Sudbury Breccia extend obliquely from the broader package to the SIC, and blocks and clasts ranging from microscopic to 100 ft scale are common. The PM Deposit mineral envelope occurs at the mid- to lower part of the Sudbury Breccia package. The current known dimensions of the PM Deposit are approximately 1000 ft in an east-west direction, 1800 ft down plunge, and a true thickness up to 120 ft. It remains open locally down dip and up dip to the north east.
The character of the PM Deposit is defined by a series of stacked veins (the largest rarely greater than 2 ft thick) and vein sets which occur at steeper angles (40° to 50°) than the overall dip of the deposit (35°). The orientation of these veins is locally disrupted by large clasts (typically >20 ft in diameter). Veins will tend to wrap large clasts on one side, or bifurcate and surround them. In areas where the vein sets are proximal to one another, stockworks have developed between the veins, forming ‘lode’ zones which are well mineralized for tens to hundreds of feet along strike and dip.
Mineralization within the PM Deposit typically consists of chalcopyrite +/- millerite + PGM (Pt+Pd bismuth tellurides) veins, veinlets, stockworks and disseminations within a mineralized envelope which generally dips -35 degrees to the southeast.