The GBRM (the Gallowai Bull River Mine) deposit is hosted within poorly exposed graded turbidite beds of the middle Aldridge Formation of the Middle Proterozoic Purcell Supergroup. Interbedded quartzites, siltstones, and argillites make up a turbidite sequence whose bedding plane strikes approximately east-west and dips 20° to 30° to the north. The host rocks of the deposit are a northward pinching series of anticlines and synclines.

The Aldridge Formation is intruded by a series of dykes varying in composition from diorite to gabbro known as the Moyie intrusive suite. The mid-Proterozoic Moyie dykes trend approximately east-west and dip at 30° to 80° to the south and are composed predominantly of hornblende and plagioclase phenocrysts in a fine grained groundmass of plagioclase, quartz, hornblende, chlorite and epidote. These dykes have been traced from the Bull River eastward to the flank of Iron Mountain where they form the target of two adits.

Mineralization.
The GBRM mineralized zones comprise a vertical to subvertical network of sulphide-bearing quartz carbonate veins striking approximately east-west hosted in sheared and brecciated Aldridge Formation sediments. The veins pinch and swell forming stockworks or thick tabular bodies that are often cut by smaller veins and stringers of quartz and quartz-siderite. The main vein structure and associated stringer zones can range from a few centimetres to 30 m wide.

Mineralization consists of pyrite, pyrrhotite, and chalcopyrite with minor local galena, sphalerite, arsenopyrite, and cobaltite and traces of tetrahedrite and native gold. Sulphides range from massive, irregular bodies within the vein system to thin discontinuous veins, veinlets, and disseminations in the host rock. Gangue mineralogy of the veins is variable, with the eastern parts of the deposit consisting of quartz and siderite. The western part of the vein system is dominated by siderite.

The extent of the currently known mineralization is approximately 1200m along strike, varies in width from 2.5m to 30m and has a down-dip extent of 200m based on currently drilling, which remains open at depth.

The Bull River deposit has been described as a Churchill-type vein copper-silver deposit. The deposit type displays characteristics of relatively low tonnage (typically range from 10Kt to 1Mt) but high-grade (typically range from 1% to 4% Cu).

A main access ramps and seven levels of development, including vent raises and an escape route, are in place and in operational condition. There are also numerous mill feed access cross-cuts and sill drifts in areas where future mining is planned. The main access ramp is 2555 meters long and there is an additional 14,050 meters of level development.

Subsequent to the open pit mining, the operations have been shut down, but significant underground development was carried out to provide sites for underground exploration drilling. This development also established a decline and six sublevels at approximately 40m vertical intervals. It is presumed that the extensive in-place underground development was built for more than just exploration, but also to define vein continuity for defining reserves. The existing development has sufficient dimensions to be functional for production equipment on the declines and levels.

Selection of Mining Method.
Analysis of the resulting grade-shells shows that the expected mining areas follow the strike of the veins, are narrow across the width of the veins, and are steeply dipping. This arrangement is conceptually best mined using Longitudinal Longhole Open Stoping (LLHOS).

Stope Design.
Stopes are designed to meet various operational design criteria such as minimum mineable width and connectivity to other mining areas. Isolated or discontinuous pods that are too small or difficult to access and areas that are too thin to be mined are not included in the stope designs.

The veins of interest are near vertical and between 3 and 8 meters true thickness. They have a welldefined strike but irregular edges. The stopes are designed to follow the veins, but the drives on the development levels are smoothed to a more regular shape which is achievable with the mining equipment and therefore does not follow the veins exactly. The stopes are designed with a minimum width of 3.5 meters. Access considerations require that the stopes are continuous from end to end of each production level.

There are five stopes in the mine plan. Each stope block is defined by the sill drive which is 4m high and the same width as the stope. Where the vein is thicker, the sill drive is driven to the full width of the vein. The sill drive is the mucking level with flat floors for the mechanized equipment to work on and near- vertical edges to allow for easy mucking.

Geotechnical Assumptions.
The existing underground excavations are currently pumped dry and have remained intact and open for safe access for over thirty years. The rock conditions are strong and it has been assumed for this scoping level study that there will not be any adverse ground conditions with the prescribed LLHOS mining method. However, until a Geotechnical evaluation verifies this, stopes are designed with sill and rib pillars. It is also planned to dispose of the mill tailings underground as cemented backfill into the mined out stopes. Geotechnical evaluation in future studies may reduce need for pillars and it may be possible to minimize the use of cement in the backfill depending on the mining sequence and the geotechnical needs to fill the open stopes. The sill pillars also provide a rock surface for equipment to operate on, as the open stopes are advanced from the bottom of the mine upwards to the upper levels. The sills also isolate the mining areas so that they can be filled with tailings. The sill pillars are 6 meters tall and spaced every 50 meters vertically. The location of the sill and rib pillars has not been optimized to take advantage of any lower grade areas in the stopes.

Process Description.
Crushing.
ROM mill feed is dumped onto a fixed grizzly with 22” openings. Grizzly undersize reports to a 65t coarse mill feed bin. Coarse mill feed is fed to the primary crusher by a 48” wide and 10’ long hydrastroke feeder.

The primary crusher is a 25 x 40D Telsmith jaw crusher operated at a setting of 4 inches. Crushed mill feed, with a work index of 15, passes through a 5’x 10’ Nordberg screen with a 3/8” aperture before reporting to the fine mill feed bin with a capacity of 3100ST. The screen oversize is fed to a 5 1/2 ‘Symons Cone Crusher operated at 5/16” setting. Cone crusher discharge is fed back to the screen.

Dust control in the crusher building is accomplished with American air filter type “R” Roto-Clone exhausting at 17,000cfm.

The current crushing circuit design is able to process mill feed at a significantly higher rate than the mill. This allowed the crushing plant to operate on weekday dayshifts during previous operations. There may be an opportunity to reduce the crusher product feed size reporting to the mill and thereby increase the mill throughput.

Grinding.
Fine mill feed is milled in closed circuit with a 10’x14’ Ball Mill and cyclone. The Ball Mill is driven by a 700HP (522kW) motor connected to the pinion gear with an air clutch control system.

Mill discharge at 78% solids is pumped to cyclones at 6psi. Cyclone overflow containing 40% solids at 65% minus 200 Mesh (75 micron) is fed to the floatation conditioning tank. Cyclone underflow reports back to mill feed.

Dust is collected in the mill building by a Medusa scrubber MR-30 exhausting 300 CFM of air.

Flotation.
Feed to the flotation plant is conditioned for ten minutes in a Denver 8’ x 8’ super agitator at 40% solids.

The flotation circuit included rougher, scavenger, and cleaner flotation. Scavenger concentrate and Cleaner tails are pumped to a 5’x 8’ regrind ball mill.

Rougher and scavenger flotation is carried out in No. 60 Agitair flotation machines at 27% solids. Air is supplied to the flotation machines by a Canadian Forge blower. There are four Rougher and six Scavenger cells. Concentrate from the first two scavenger cells is routed to the rougher concentrate.

The cleaner circuit consisted of ten No. 21 Denver Sub A flotation machines. Launders and piping is arranged for three-stage cleaning.

Cleaner concentrate is pumped to a 30’ thickener at 17% solids. Thickener underflow is pumped to a Door disc filter at 55% solids. Concentrate from the filter is stored in a 1500t storage bin with moisture levels ranging from 8.8 to 12.6%. Tailings from the scavenger cells is pumped to tailings management facilities.