Gold mineralization in the Timmins, Thunder Creek, and 144 Gap Deposits occurs in steep northnorthwest plunging mineralized zones which plunge parallel to the local orientations of the L4 lineation features which also plunge parallel to the lineation, including folds and elongate lithologies. Mineralization occurs within, or along favourable lithostructural settings within 100 metres of the Holmer and Rusk Shear Zones. Mineralization comprises multiple generations of quartz-carbonatetourmaline ±albite veins, associated pyrite alteration envelopes, and disseminated pyrite mineralization. Textural evidence suggests that veining formed progressively through D3 and D4 deformation. All phases of gold-bearing veins cut and postdate the AIC and syenitic to monzonitic intrusions, although mineralization is often spatially associated with ore preferentially developed within these intrusive suites (Rhys, 2010).

At the Timmins Deposit, the character and sequence of veining in the Main, V1 and V2 veins is similar in all exposures. Rhys (2003) defined three phases of veining in the Timmins Deposit surface showings, all of which were also apparent in his recent observations (Rhys, 2010 and 2011), although an additional phase of shallow dipping quartz extension veins was also recognized during this field work (Rhys, 2010). The sequence of veining observed is as follows, with most veins in the upper Timmins Deposit mineralization forming composite veins which have this paragenetic sequence.

In the Thunder Creek area, there are two main styles of mineralization: 1) the Rusk Shear Zone adjacent to and in the footwall of the pyroxenite unit, and; 2) the Porphyry Zone which is hosted by the quartz monzonite intrusion which lies to the southeast in the immediate footwall to the Rusk Shear Zone below an elevation of approximately 500 metres below surface.

Mineralization in the Rusk Shear Zone comprises areas of either higher quartz-carbonate-pyrite vein density, and/or areas of elevated medium- to coarse-grained disseminated pyrite and associated pyritequartz veinlets. Both of these styles were observed to occur in the intensely foliated, often compositionally laminated carbonate-albite-quartz-magnetite portions of the shear zone. Mineralization also locally preferentially overprints pink, K-feldspar-rich syenite dykes and local plagioclase-dominant probable diorite dykes in the shear zone, with clots and aggregates of coarsepyrite, often associated with quartz-albite-carbonate veinlets.

“Porphyry Zone” mineralization is developed in the quartz monzonite intrusion that occurs at depth in the footwall to the Rusk Shear Zone immediately adjacent to areas of mineralization in the shear zone. Mineralization is associated with sheeted sets of quartz extension veins which occur in abundance of up to several veins per metre within the intrusion. Most veins are less than 3 centimetres thick and comprise white quartz with pyrite. Disseminated pyrite locally occurs in the wall rock adjacent to the veins and free visible gold was locally observed in association with pyrite both in veins and disseminated in the host rock.

Gold mineralization in the 144 Gap Deposit occurs generally between 600 and 1,000 metres below surface in the footwall of the high strain zone within and adjacent to syenite bodies in the footwall mafic volcanic lobe. The main mineralized areas occur between approximately 20 to 120 metres into the footwall of the high strain zone; however, mineralization also occurs locally within the shear zone itself. There are two main styles of mineralization identified in the 144 Gap Deposit area: 1) syenite-hosted quartz-pyrite extension vein sets and associated mineralization, and; 2) disseminated and vein-controlled pyrite in carbonate-sericite altered areas of higher strain in the shear zone and in altered mafic units along and within dyke margins.

Gold mineralization in the Bell Creek area as occurring along selvages of quartz veins and wall rocks, in stylolitic fractures in quartz veins, in fine grained pyrite, and in association with amorphous carbon. High grade gold mineralization occurs within quartz veins contained in alteration zones. The alteration zones are characterized by carbonate, graphitic and amorphous carbon, fine grained pyrite, sericite, and/or paragonite and are enriched in Au, As, Bi, and W. This style of alteration is referred to by mine geologists as “grey zones” and is an exploration target in Hoyle Township.

The Bell Creek mineralization differs in style from many deposits in the Porcupine Mining camp in being composed largely of disseminated pyrite-pyrrhotite-related mineralization; slightly younger gold-bearing quartz veins may be present but are not predominant.  This style of mineralization occurs in the deeper parts of the Dome Mine and in the Rusk Zone at the Timmins West mine, but is more common to the east, in the Holloway-Holt McDermott area and at the Larder Lake, where pyritic mineralization is often termed “flow ore” (Rhys 2012).

The Thunder Creek, Timmins, and 144 Gap deposits at the Timmins West Mine are accessed by a 5.5 metre diameter production shaft and 5 metre by 5 metre ramp from surface; the three deposits are connected by internal ramps and drifts.

Production from the Timmins, Thunder Creek and 144 Gap deposits comes from a combination of ore development and transverse and longitudinal longhole stoping. Sublevel spacing at the Timmins deposit is at 20 metre vertical intervals; sublevel spacing at the Thunder Creek and 144 Gap deposits is on 35 metre vertical intervals. Stopes are backfilled with either paste fill or cemented rock fill.

At the Bell Creek Mine the primary access to the underground workings is via an existing portal and main ramp from surface. Longitudinal longhole stoping is the primary mining method. Broken ore is removed from the stope using remote controlled LHDs, and trucked to surface. The main ramp is 5.0 metre wide by 5.0 metre high and currently extends to the 895L. There is an existing 6.3 metre by 2.6 metre rectangular, three- compartment timbered shaft. The shaft is 290 metres deep. A main shaft station exists at the 240L. The headframe and hoisting facilities remain in place, but are currently not being used. Material at Bell Creek Mine is drawn out by scoop trams and trucked to surface up the ramp.

Ore from the Bell Creek Mine and the Timmins West Mine is processed at the Bell Creek Mill. Throughput at the Bell Creek process plant averaged just above 3,400 tpd in 2016.

Ore from the Bell Creek Mine is milled exclusively at the Bell Creek Mill located approximately 6.7 kilometres north of Highway 101 in South Porcupine, Ontario.   

The current processing plant consists of a one stage crushing circuit, ore storage dome, one-stage grinding circuit with gravity recovery, followed by pre-oxidation and cyanidation of the slurry with CIL and CIP recovery.

Ore from the Bell Creek Mine and the Timmins West Mine is dumped directly onto a 16” by 16” grizzly at the truck dump and a remote controlled rockbreaker is used to break up the oversized material. The ore is fed with an apron feeder to a series of conveyors reporting to a scalping grizzly feeder in the crushing building. The openings between the fingers on the grizzly feeder are 3.5”, with the oversize reporting to a 44” x 34” C110HD Metso jaw crusher. The jaw crusher is set to a closed side setting of 4”. The discharge from the crusher is combined with the -3.5” material from the grizzly feeder and conveyed to the ore storage dome. The dome has a 20,000MT storage capacity, 6,000MT of which is live. Three apron feeders pull ore from the dome and convey it to the SAG mill building.

The grinding circuit consists of one 22’ diameter by 36.5’ length low aspect ratio Metso SAG mill and is powered by twin 6,250 hp (4,600 kW) motors. The SAG mill is a repurposed ball mill converted to a SAG by installing 0.5” grates and a trommel with 0.75” openings. Oversize from the trommel reports to a collection bin which is fed back into the SAG mill feed chute. Undersize from the trommel reports to a pumpbox which feeds a cyclopac equipped with 6 outlets. Four of the outlets are fitted with 20” Krebs gMAX cyclones, and the other two outlets are capped and available for possible future expansion. The SAG cyclone overflow reports to the thickener feed box and the underflow reports back to the SAG mill. A portion of the cyclone underflow is fed to a 30” Knelson. Knelson concentrate is collected in a hopper and is pumped daily to the refinery for further treatment, while the Knelson tails flow by gravity back to the SAG mill. Target grind is 80% passing 200 mesh.

Flocculent is added to the cyclone overflow and is pumped to a 20 meter diameter thickener. The slurry from the cyclones is 25-35% solids by weight with the thickener underflow at 55% solids by weight. The thickener overflow water is pumped to the process water tank and reused in the grinding process. The thickener underflow slurry is pumped to the leach circuit. The leach circuit consists of five agitated tanks in series with a total volume of 1,940 cubic meters. Pure oxygen is sparged into the first three leach tanks to passivate the contained pyrrhotite in the ore, as well to maintain a target dissolved oxygen level, which is required for efficient gold dissolution in cyanide. Cyanide is then added to leach tank #4, or #5.

There are three carbon-in-leach (CIL) tanks equipped with Kemix screens having a total volume of 7,500 cubic meters. The first tank (CIL #5) operates without carbon, so it is essentially a leach tank. The second (CIL #2) and third (CIL #1) tanks contain roughly 8 grams of carbon per liter of slurry. The circuit will reach equilibrium for loading of the carbon with the grade of the loaded carbon in the range of 2,500 to 4,500 grams per tonne. Loaded carbon is pumped from CIL #2, screened, washed, and then transferred to the loaded carbon tank. Carbon in the CIP and CIL tanks is advanced counter-current to the flow of slurry in the circuits.

The slurry from CIL #1 tank reports to the carbon-in-pulp (CIP) circuit, and is split into two trains of three CIP tanks in parallel with
approximately 45 grams of carbon per liter of slurry. Recovery of the gold from the carbon is a batch process with carbon being stripped at a rate of 3.5 tonnes per batch. The turnaround time between batches is 24 hours. Carbon can be cleaned with acid, reactivated with the kiln and reused in the circuit.

The loaded solution from the strip circuit is passed through two electro-winning cells in the refinery. The gold collects on the cathodes in a sludge form. The cells are washed weekly and the sludge is collected in filter bags and dried. The dried sludge is then mixed with reagents and melted in the induction furnace. Gold bullion bars are poured when the melt is completed.

The gravity gold material collected from the Knelson concentrator is transferred to the refinery and a gravity table is used to increase the gold content. The concentrate is then dried, reagentsare added and the material is melted in the induction furnace. The gravity concentrate and the CIP gold sludge are melted separately due to the differing amounts of reagents used in each, and to more accurately determine recoveries in each circuit.

The final clean out of the electro-winning cell is completed by the refiner or his designate, under security control. All sludge is collected and dried. The washed cathodes from the cells are weighed and the weights are recorded to determine whether any plating buildup is occurring. The dried cell sludge and the gravity concentrate collected over the same period are smelted and bullion bars are poured. The bars are stamped and their weights are recorded and verified. Bullion samples are taken and are assayed at the Bell Creek Lab. These sample results are used in the metallurgical balance.