Lode gold deposits (gold from bedrock sources: occur dominantly in terranes with an abundance of volcanic and clastic sedimentary rocks of a low to medium metamorphic grade. Greenstone-hosted quartz-carbonate vein deposits are a subtype of lode-gold deposits (Poulsen et al., 2000). They correspond to structurally controlled, complex epigenetic deposits hosted in deformed metamorphosed terranes.

Greenstone-hosted quartz-carbonate vein deposits consist of simple to complex networks of gold-bearing, laminated quartz-carbonate fault-fill veins in moderately to steeply dipping, compressional brittle-ductile shear zones and faults with locally associated shallow-dipping extensional veins and hydrothermal breccias. They are hosted by greenschist to locally amphibolite facies metamorphic rocks of dominantly mafic composition and formed at intermediate depth in the crust (5-10 km). They are distributed along major compressional to transtensional crustal scale faults zones in deformed greenstone terranes of all ages, but are more abundant and significant, in terms of total gold content, in Archean terranes. Greenstone-hosted quartz-carbonate veins are thought to represent a major component of the greenstone deposit clan. They can coexist regionally with iron formation-hosted vein and disseminated deposits, as well as with turbidite-hosted quartz-carbonate vein deposits.

The main gangue minerals are quartz and carbonate with variable amounts of white micas, chlorite, scheelite and tourmaline. The sulphide minerals typically constitute less than 10% of the ore. The main ore minerals are native gold with pyrite, pyrrhotite and chalcopyrite without significant vertical zoning.

The mineralized lenses at Croinor range from 60 to 120 metres long (Chénard and Turcotte, 2003). The lenses can generally be followed from one section to another (10-m sections) over lateral distances varying from several tens of metres up to 600 metres. To date, about forty (40) gold rich lenses have been identified. Gold-hosting structures within the dioritic Croinor Sill consist of a series of narrow breaks and reverse shears with dips of 25° to 60° to the north. These structures display enechelon patterns and are variably oriented between N290°-N330°. They can cause displacements of a few centimetres to tens of metres. Tectonic breccias of pyritic quartz-tourmaline-ankerite material occupy the central portion of these shears. Two (2) types of veins are observed: 1- shear-parallel veins (shear veins); and 2-subhorizontal tension veins. The veins consist of quartz, tourmaline and carbonates with minor amounts of pyrite, chalcopyrite and native gold.

The tension veins are generally several centimetres thick and dip gently towards the east. Gold is restricted to rocks affected by pyritic metasomatism; that is, it mainly occurs in pyritic vein selvedges, breccia fragments in tectonic breccias, and fragments in brecciated veins. Pyrite is locally associated with minor amounts of chalcopyrite and pyrrhotite. Gold is found as inclusions within pyrite grains or along its boundaries, or within fractures cutting pyrite. Although pyrite is a good indicator of the presence of gold, not all pyritic zones are mineralized with gold, and not all gold occurs with pyrite. Isolated flecks of native gold were also observed in veins and veinlets of smoky quartz associated with shearing, and in the highly altered selvedges of such veins.

Pyrite occurs as two distinct forms that may correspond to distinct crystallization phases. The earliest phase is present as amorphous clusters and threads that frequently show evidence of deformation and a preferential orientation subparallel to the main foliation. The last phase appears as disseminated cubes with individual grains reaching 0.5 centimetre, locally to 1 centimetre.

Other than pyrite content, the intensity of deformation and the type of alteration constitute the essential criteria for the presence of economic gold grades. Sericiteankerite alteration combined with tourmaline and silicification appears to be directly associated with the highest grades within brecciated zones containing pyritic quartztourmaline-ankerite material.

Quartzo-feldspathic rocks that intrude the Croinor deposit area may have played an important role in gold mineralization. The relatively late emplacement of these intrusives may have accentuated the intensity of deformation and thus increased host rock porosity, in addition to prolonging the mineralization event while contributing to the remobilization of local hydrothermal fluids.

Two mining methods are proposed to accommodate the geometry of the mineralization: sublevel long-hole retreat and conventional room and pillar.

The long-hole stopes will be mined from 3-m-high sublevels at 13-m vertical intervals. For stope heights exceeding 13 m, the maximum stope panel was defined as 15 m long. It is assumed that stopes will not be backfilled and 5-m pillars are left between panels and mining horizons. For stope heights of 13 m and less, longer stope panels were considered on a case by case basis. The method consists of drilling and blasting 54 mm-diameter holes in a pattern parallel to the walls. Holes are drilled upward or downward depending on the context.

The room and pillar mining method entails the excavation of a series of “rooms” following the vein, leaving “pillars” or columns of rock in place to help support the mine roof. In conventional room and pillar mining, drilling is achieved using handheld drill equipment and holes are loaded with explosives. Bolts are then installed in the mine roof to ensure the roof is properly supported. The broken rock is scraped to either a raise or a drawpoint where it is taken with a scooptram to be hauled to surface.

The planned production rate at the Croinor deposit ranges from 425 to 675 tpd over a 5-year period. Only four gold concentrators within a 120 km radius have the capacity to process the Croinor ore: Beacon Gold Mill, Aurbel Gold Mill, SigmaLamaque Complex and Camflo Mill.

At the moment, based on the metallurgical results the Camflo mill seems to be the best option. In addition to having successfully processed the Croinor ore in the past, thereby mitigating any technical risk, the plant is likely to have availability for new custom feed, and has been in the custom milling business for years. Therefore, this plan assumes that the ore will be processed at Camflo for the purpose of estimating milling and transportation costs although a final evaluation and decision will have to be made at the outset of the project.

The Camflo Mill, with a rated capacity of 1,200 tonnes per day, is a Merrill-Crow conventional type mill with circuits for crushing, grinding, gold cyanidation and precipitation using zinc powder.