Summary:
The Porcupine mines are situated in the Porcupine Camp in Archean rocks of the western Abitibi Greenstone belt in the Canadian Shield. These consist of ultramafic and mafic volcanic rocks of the Keewatin subgroup overlain by sedimentary rocks of the Timiskaming group. The lands lie adjacent and to the north of the regionally significant Porcupine Destor Fault. Gold mineralization is found in a number of different structural settings and consists of continuous quartz carbonate veins, quartz tourmaline veins, quartz stockworks and gold associated with disseminated sulphides.
Mineralization at Hollinger and Hoyle, in Timmins, comprises multiple generations of quartz-carbonate-tourmaline albite veins, associated pyrite alteration envelopes, and disseminated pyrite mineralization. Mineralization at Borden consists of a shear zone containing quartz-vein hosted sulfides within a high-grade metamorphic greenstone package.
Hoyle Pond.
The Hoyle Pond Main Zone and 1060 Zone deposits occur on opposite limbs of an open, northeast-plunging antiformal structure, hosted within carbonatized north-dipping tholeiitic basalts. The 7 Vein System occurs as a series of stacked, flat to gently northeast-dipping veins in the nose of the antiformal structure.
The Hoyle Pond Main Zone includes a series of generally northeast-striking, linked, quartz vein zones folded on a small scale with moderate west- and northeast-plunging axes.
The 1060 Zone consists of at least five main vein structures (1060 B1, B2 and B3 zones, A zone and Porphyry zone) with orientations ranging from north to northeast and a generally subvertical dip. The veins are strongly boudinaged, with the long axis of the boudin oriented from subhorizontal to shallow west–southwest plunging.
The mineralization at Hoyle Pond occurs as coarse free gold in white to grey–white quartz veins with a variable ankerite, tourmaline, pyrite, and locally arsenopyrite, content. Alteration halos are generally narrow, consisting of mainly grey zones (carbon, carbonate, sericite, cubic pyrite) in the Hoyle Pond system and carbonate–sericite, plus fuchsite with pyrite, arsenopyrite and trace amounts of chalcopyrite and sphalerite within the 1060 structure.
Gold at the Hoyle Pond Mine predominantly occurs as coarse free gold in white to greyishwhite quartz veins with variable ankerite, tourmaline, pyrite, pyrrhotite and local arsenopyrite. Trace amounts of chalcopyrite and sphalerite have also been noted.
The Hoyle Pond Main Zone includes a series of generally northeast-striking, linked quartz vein zones. There are at least 11 veins of economic significance. These veins are folded on a small scale with moderate west and northeast plunging axes. The 1060 zone consists of at least five main vein structures with orientations ranging from north to northeast, are strongly boudinaged, and generally have a subvertical dip.
A series of auriferous zones occurs along what is termed the “South Trend”, stretching from the Bell Creek deposit (to the west of Hoyle Pond) for 6.4 km to the 1060 zone (includes Blackhawk–Vogel deposit, Owl Creek West, Owl Creek, Owl Creek East and the 950 zone). Mineralization in these zones consists of quartz–ankerite veining with varying amounts of pyrite, pyrrhotite and free gold.
Hollinger
The Hollinger-McIntyre deposit is hosted by mafic volcanic rocks of the central and upper Tisdale assemblages that are intruded by porphyritic intrusions. Mafic volcanic rocks in the deposit have generally been divided into three units: the Northern, Central and Vipond Formations.
The Hollinger Mine historically was developed on gold bearing veins which are structurally controlled by lithologic contacts and deformation zones associated with altered Central and Vipond Formation volcanics. These units strike N55E and 70 SE, and are folded into an anticline. The Northern formation occurs in the core of Central Tisdale Anticline. The Central Formation hosts most of the major veins systems in the Hollinger and McIntyre mines. It is comprised of a heterogeneous sequence and the basal units in the Central Formation are the most important ore hosts in the deposit. The Vipond Formation is the youngest volcanic package in the deposit area (J. Floyd, email, Goldcorp Canada Ltd., September 24, 2007).
The lavas have been intruded by a group of porphyry stocks, the largest of which is the Pearl Lake Porphyry. The porphyries are generally conformable to the folds within enclosed rocks and plunge at 45 to 50 degrees E. The porphyry deposits occur in areas of bedrock depressions beneath the lakes, suggesting that they are softer and more prone to erosion than the mafic volcanic rock units that they intrude into.
The core of the Hollinger-McIntyre deposits is an elliptical area of high strain developed along the south limb of the Central Tisdale anticline which surrounds the Pearl Lake porphyry and is approximately 450 to 600 m wide by more than 3 km in length. The elliptical fold of Central Tisdale anticline contains a series of subsidiary folds including the Northern anticline, Hollinger syncline and the Hollinger anticline. The elliptical nature of this structure in plan is due to the non- cylindrical, doubly plunging properties that closes the structure to both the east and west.
Borden
Owing to its metamorphic grade, the Borden Gold deposit is markedly different from most known Archean-aged mesothermal gold occurrences. On the basis of visual evidence, which is yet to be supported by detailed petrographic studies, it is believed that the Borden Gold deposit is most closely associated with the disseminated gold sub-class.
The gold mineralization at the Borden Gold deposit occurs as a broad zone of disseminated and fracture-controlled sulphides within a volcano- metasedimentary package of variable composition. The main sulphides are pyrite and pyrrhotite, with the former typically dominating. The mineralization generally consists of low- to moderate-grade gold, with minor silver, and is characterized by a persistent higher-grade core surrounded by a lower-grade envelope. Results to date indicate that the higher-grade core improves in grade towards the southeast where it develops into a High-Grade Zone (HGZ) with average grades typically above 2.5 g/t Au.
The northwest portions of the deposit are characterized by local silicification but lack lithological control and quartz veining; while to the southeast a well-developed hydrothermal system consisting of local quartz flooding and potassic alteration predominates and defines the HGZ. The broad mineralized zone encompasses multiple/variable host rocks, dominated by metasedimentary horizons and subordinate intrusives of acidic to intermediate composition, all of which display feldspathic, chloritic and biotitic alteration. Outcropping in the northwest parts of the deposit, the lower-grade mineralization rarely exhibits visible gold grains, while in the southeast HGZ it is much more common, particularly in the quartz-rich core. A higher-grade core is also consistently present within the lower-grade zone, locally attaining very high grades reminiscent of the HGZ.
The deposit displays continuity and is consistently intersected along strike, reaching a current length of 3.7 kilometres, while remaining open in both the northwest and southeast directions. Structurally, the deposit is described by a consistent northeast dip and, locally, a shallow southeast plunge, which is mostly evident in the HGZ. Mineralization appears to be controlled by a ductile shear zone, which appears much better developed in the HGZ. The mineralized zone is up to 120 m wide, and has been confirmed to a vertical depth of approximately 650 m.