Summary:
The Magino Property is located in the Michipicoten Greenstone Belt (MGB), which is part of the Wawa Subprovince within the Archaean Superior Province. The MGB is approximately 140 km long and up to 45 km wide. The metamorphic grade of the subprovince is greenschist but amphibolite facies can be seen locally or proximal to intrusions. A major regional deformation zone called the Goudreau Lake Deformation Zone (“GLDZ”) is situated throughout the area. It is a north-easterly trending structure that has been traced along strike for 30 km with a width of 4.5 km and is believed to be the main control of gold mineralization for the Project area. It is a high-angle oblique-slip fault zone with an overall dextral movement cutting stratigraphy at a shallow angle. There are three main splays to the GLDZ in the area, the southernmost of which hosts the Island Gold Mine structure, and the Webb Lake Intrusion, host of the Magino Gold Deposit.
The Michipicoten Greenstone Belt area is part of the Wawa Sub-Province and hosts mainly precious metal deposits. Major breaks such as the Goudreau-Lochalsh Deformation Zone (GLDZ) host a number of gold deposits in the Wawa Sub-province.
There are two distinct styles of gold mineralization:
• Orogenic lode-gold greenstone hosted mesothermal gold;
• Intrusive-related ‘porphyry’ disseminated style.
Gold mineralization at Magino Project fits both the sub-volcanic ‘porphyry’ and orogenic style model. Gold associated with the ‘porphyry-style’ at Magino is characteristic of 1) Webb Lake/Lovell Lake Stock granodiorite-tonalite-trondhjemite (GTT) host, 2) widespread phyllic alteration with Nadepletion and K-enrichment, 3) weakly disseminated pyrite ± molybdenite mineralization, 4) weakly veined quartz stockwork network. The orogenic model at Magino involves steeply plunging intersecting lineation in high strain ductile/brittle structures and receptive chemical host traps.
Mineralization
Gold mineralization at the Magino gold mine occurs primarily within the Webb Lake granodiorite. The WLS underwent variable metasomatic alteration during deformation and gold mineralization (Heather and Arias, 1992). Distinct haloes of quartz-sericite with minor pyrite, iron-carbonate and hematite alteration are typically located adjacent to the quartz vein systems. In addition, narrow zones of mineralization have also been identified in metavolcanic rocks in both the footwall and hanging wall of the WLS.
Gold mineralization at the Magino mine is primarily hosted by the Webb Lake Stock, which intrudes mafic volcanic rocks. The Webb Lake Stock is a felsic intrusion that has been interpreted as being a trondhjemite but is referred to as a granodiorite in mine terminology and therein. The Webb Lake Stock is east northeast-striking and has a steep northerly dip. The granodiorite contains 5 to 10% veins of quartz. The veins generally parallel the orientation of the Webb Lake Stock.
Gold mineralization occurs in several sub-parallel high-strain zones striking 070º to 080º within the Webb Lake Stock and within mafic metavolcanic rocks immediately along the northern and southern margins of the stock (Heather and Arias, 1992). These zones are often closely related to mafic and felsic dykes within both units. Deevy (1992, 1994) distinguished and described two types of mineralized material shoots, namely “zones” and “veins”. The “zones” are usually 2 to 4.5 m wide and have a strike length of 25 to 70 m. They consist of foliated, bleached, and silicaflooded granodiorite. The zones are folded in places, which, during underground mining, produced mineable widths of up to 10.5 m. The zones dip at about the same angle as the foliation and have a vertical plunge. The vertical continuity of the zones is at a vertical to horizontal ratio of 2.5:1 (Deevy, 1994). Weak to moderate bleaching and silica flooding are the distinguishing features of the zones (Deevy, 1994). Silica flooding consists of incipient pale gray quartz occurring within the foliated granodiorite. Gold content is directly related to the amount of silica flooding and quartz veining (Deevy, 1994).
The veins consist of discrete pale grey to pale green to almost white quartz veins varying in width from a few to 45 cm. They have a strike length of several to 35 m. Gold values are distributed erratically within the veins, but overall grades can be quite high. The veins are folded in places, with gold sometimes concentrated in fold noses (Deevy, 1992, 1994). Vertical continuity of the veins is similar to that of the zones, and the plunge is also vertical. Native gold occurs in zones of pervasive silicification and in narrow (i.e., less than 1 to 20 cm wide) quartz veins that form complex systems 1 to 3 m wide. Gold occurs within both quartz veins and foliated and altered wall rocks, but the better gold grades are in the veins (T. Deevy, Magino mine geologist 2001, personal communication, as cited in Heather and Arias, 1992). Finely disseminated leaf-like visible gold can be observed in quartz veins exposed in diamond drill cores (Koskitalo, 1983). The gold tends to form plates or leaves along fractures in quartz rather than coarse nuggets. The quartz hosting the gold tends to be fine-grained and dull milky grey (Koskitalo, 1983). Up to 10% disseminated pyrite is locally present, commonly found in alteration haloes around the gold-bearing quartz veins (Heather and Arias, 1992).