Overview
The Mt. Milligan gold-copper mining project is located in North Central British Columbia, Canada approximately 155 km northwest of Prince George.
Mount Milligan is the highest and the northernmost peak of a chain of mountains aligned north-south that is surrounding the mineral property.
Mineral claims have been staked over the deposit since 1930s but sustained mineral exploration had not been carried out until 1990 when Placer Dome acquired the property.
In 2006 Barrick Gold purchased Placer Dome and sold Mt. Milligan to Goldcorp which in turn sold some assets to a company later renamed Terrane Metals Corp. On October 20, 2010 Thompson Creek Metals Company - one of the largest publicly traded, pure molybdenum producers in the world - acquired Terrane Metals.
As of 2010, the porphyry type mineral deposit contains 6 million oz gold and 2.1 Billion pounds copper in reserves, which make it one of the largest undeveloped gold reserves in Canada.
Large scale open pit mining will provide mill feed at a nominal rate of 60,000 tonnes per day (21.9 Mt/a). Annual mine production of ore and waste will peak at 44 Mt/a, with a life-of-mine stripping ratio of 0.82/1. The estimated mine life is 22 years.
Over its 22 year projected life-of-mine gold production will average 194,500 oz per year and account for 51% of the revenue. Net of a copper credit, LOM gold production cash cost is US$ 51 per oz.
The copper, gold, and silver concentrate will be trucked 82 km to a storage and loadout facility then and transferred onto railcars for transport to port of North Vancouver and delivered to Pacific Rim Asian smelters.
Location
Canada, "the True North strong and free", is the world's second largest country and is spanning a territory that stretches west to east from the Pacific to the Atlantic Ocean and up north to the frozen shores of the Arctic Ocean. It is a federation of ten provinces and three territories governed as a parliamentary democracy and constitutional monarchy. It is a bilingual country - English and French are both official languages.
British Columbia is the westernmost Canadian province and a real Canadian jewel which is renowned for its natural beauty that is also reflected in its motto: 'splendor without diminishment'.
Gold was discovered in the Omineca region of British Columbia in 1861 by Edward Carry and William Cust. A fully fledged gold rush began in 1870 and continued for decades to come.
Gold-bearing floats were discovered on Mt. Milligan in 1937 by a George Snell, a local prospector. In 1984, prospector Richard Haslinger staked a few claims over the deposit that entitle him to a 2% NSR for any future production recorded on these claims.
Mt. Milligan is located within the Omineca Mining Division in North Central British Columbia approximately 155 km northwest of Prince George, 86 km north of Fort St. James, 95 km west of Mackenzie. Mt. Milligan's primary access will be from Fort St. James, although access can also be gained from the east via Mackenzie.
The project site is situated on the Nechako Plateau, a region of flat to gently rolling terrain. Local relief is provided by a northwest trending ridge which rises approximately 300 to 500 m above the local plateau elevation of 1000 m. The area was extensively glaciated during the last glacial period. The Mt. Milligan deposits are to the south of 1,508 m Mt. Milligan at an elevation of 1,100 m in an area of gentle relief.
The property is well-drained except for depressions where natural vegetation succession has filled in ponds to form boglike fens. Drainage from the area is to the northeast via Nation River into Williston Lake, which forms part of the Peace-MacKenzie River basin.
The area has short cool summers and cold winters.
Important towns in the region are the former fur trade posts of Fort St. James (population 5,000) and, Prince George (population 71,000).
Geology
The Project is within Quesnel Terrane, part of the Intermontane Belt, a composite of low metamorphic grade magmatic arc segments of mixed oceanic and continental affinities, and oceanic plates, which amalgamated with North America in the Early Jurassic Period.
Mt. Milligan is a tabular, near-surface, alkalic copper-gold porphyry deposit that measures some 2500 m north-south, 1500 m east-west and is 400 m thick. It consists of two principal zones, the Main Zone and Southern Star (SS) Zone. The Main Zone includes four contiguous sub-zones: MBX, WBX, DWBX and 66, all of which are spatially associated with the MBX monzonite stock and Rainbow Dyke. The SS Zone is centred on a monzonite stock of the same name and is some 500 m south of the Main Zone.
Main Zone mineralization and associated alteration are primarily hosted in volcanic rocks, whereas in the SS Zone, mineralization is hosted equally in monzonite stock and volcanic rocks. Mineralization in both zones consists of pyrite, chalcopyrite and magnetite with bornite localized along intrusive-volcanic contacts. The pyritic 66 sub-zone is notable in that it is comparatively gold-rich and copper-poor. Gold occurs as micro-fracture fillings and inclusions in sulphides and magnetite.
Copper-gold mineralization is primarily associated with potassic alteration with both copper grade and alteration intensity decreasing outwards from the monzonite stocks. Pyrite content increases dramatically outward from the stocks where it occurs in association with propylitic alteration, which forms a halo around the potassic-altered rocks.
As of October 2009, Mt. Milligan's measured and indicated (mineral resources which are inclusive of mineral reserves) were estimated at 706.7 Mt grading 0.182% copper, 0.33 g/t gold.
Mining & Operation
Mt. Milligan is designed as a typical open pit truck and shovel operation.
Large scale open pit mining for the Project will provide mill feed at a nominal rate of 60,000 t/d (21.9 Mt/a). Annual mine production will peak at 44 Mt/a, with a life-of-mine stripping ratio of 0.82/1. The mine life was estimated at 22 years.
A 15 m bench height has been selected for mining both ore and waste. The overall mining sequence was developed through a series of mining pushbacks specific to the MBX, 66 Zone, and SS phases.
Major equipment would include: Two P&H 300XPC Blasthole Drill; two P&H 2800XPC Cable Shovel; one Cat 994F Wheel Loader; twelve Cat 793D Haul Truck; four Cat D10T Track Dozer; two Cat 834H Wheel Dozer; three Cat 16M Motor Grader; three Cat 785C Water Truck; two Cat 988H Wheel Loader; three Cat 773F Haul Truck; one ROC Drill D7; one Cat 325D Excavator (W/Hammer).
Support equipment would include: one Cable Reeler; one Fuel & Lube Truck (18,000 L); one Flatbed Truck (7.3 t); one Snow Plow/Sanding Truck; one Crane Truck (25 t); one Rough Terrain Crane (50 t); one Shop Forklift (Hyster H100XM); one RT Forklift (Sellick SD-100); one Tire Truck W/Tire Handler; one Mechanics Truck; one Welding Truck; one Cat 430E Backhoe Loader (1 cum); one Tractor & Lowboy (160 t); one Cat 988H W/Tire Handler - In Pit; two Crew Cab Pickup Truck (4x4); twelve Pickup Truck; four Light Plant/Towers; one Mine Pumps and Piping.
A sustaining capital expenditure of C$55.3 million during Years 2013 to 2027 for additions, replacements and re-builds of mining equipment has been estimated to match the annual production schedule tonnages and unit operating hours of the mining fleet.
Overburden and 30.6 Mt of waste rock materials from the open pit will be used to construct the Tailings Storage Facility (TSF) which will impound tailing and potentially reactive waste materials.
Electric power can be accessed from the BC Hydro Kennedy Substation south of Mackenzie.
Process
The Mt. Milligan concentrator is designed to process 60,000 t/d of ore to produce a marketable concentrate containing copper, gold, and silver. The process will use a conventional bulk rougher/scavenger flotation followed by regrinding and three stages of cleaner flotation.
The concentrator will consist of the following: a primary crushing plant, including a 1,525 x 2,870 mm gyratory crusher; a coarse ore stockpile; a SAG/ball mill/crusher (SABC) grinding circuit, including one 20 MW SAG mill, 12,200 diameter x 6,710 mm, two 13 MW ball mills, 7,620 diameter x 12,200 mm, two 750 kW pebble crushers. Flotation circuits include: rougher flotation (fourteen 200 m3 tank cells in two trains; 1st cleaner flotation) seven 100 m3 tank cells; 2nd and 3rd cleaner flotation (six 30 m3 tank cells). Regrinding circuits and a gravity concentration circuit, including: five 1.1 MW tower mills; one centrifugal concentrator. A concentrate dewatering circuit would also be in place.
The reagents which will be used include potassium amyl xanthate (PAX) and A3477 as collectors, methyl isobutyl carbinol (MIBC) as a frother and pebble lime as a pH regulator.
Run-of-mine (ROM) ore will be crushed to 80% passing 150 mm and then ground to 80% passing 220 microns (?m) prior to flotation. The rougher/scavenger flotation circuit will produce a high-grade rougher concentrate and a lower-grade rougher/scavengerconcentrate. These concentrates will be separately re-ground in a tower mill circuit and then upgraded by three cleaner flotation stages to produce a final flotation concentrate grading on average 27% Cu.
Low sulphide final rougher/scavenger tailing will account for 88.6% of material delivered to and stored in the TSF. High sulphide cleaner tailing will account for 11.4% of the material and will be stored underwater in a separate isolated cell inside the main TSF.
To recover coarse metallic gold, a gravity circuit consisting of a centrifugal concentrator and shaking table gravity circuit will treat a portion of the cyclone underflow from the rougher concentrate regrinding circuit. The gravity concentrate will be combined with the thickened final flotation concentrate, pressure-filtered to 8% moisture and stockpiled and trucked for 82 km to the railhead load-out facility at Fort St. James.
The TSF has been designed to contain 312.8 million m3 of material and will require 47.0 million m3 of construction material, about 96% of which will be waste rock and overburden from the open pit. The TSF embankment will be an engineered, zoned earthfill/rockfill structure with a compacted till core and filter zones constructed using the centreline method. The project is situated in a region where the level of seismic activity has been historically low.
A 2.6 million m3 capacity water supply pond will be constructed to begin collecting water for process plant operations.
