The Minto Mine uses conventional open pit mining techniques and equipment for all of its ore and waste extraction and uses crushing, grinding and flotation to produce copper concentrates with gold and silver credits. The gold and silver at Minto has been sold in a streaming transaction to Silver Wheaton for the life of the mine. Explosives are loaded into blast holes and the rock is blasted to manageable rock sizes. Shovels are used to load haul trucks that transport the rock to the crusher feeding the mill or to temporary stockpiles according to the grade characteristics of the ore. Waste rock is transported to waste rock storage piles.
The ore is fed into the primary crusher and the Semi-Autogenous Grinding (SAG) mill where it is crushed and ground to reduce particle size. The ore enters a number of flotation circuits where copper, gold and silver minerals are separated out from other minerals. The concentrated ore is thickened and de-watered using thickeners and filters. The concentrate is moved to the concentrated storage shed where it is loaded onto trucks and exported via the Port of Skagway, Alaska, to overseas smelters for treatment and sale.
The Minto Mine commenced commercial production in October 2007 at 1,800 tonnes per day with a four year mine life. The mine is accessible via the Klondike Highway to the Minto Landing on the east side of the Yukon River, where the mine operates a barge across the river in the summer months and constructs an ice bridge for accessibility during the winter months. For approximately six weeks in each of Spring and Fall there is no access to the mine via ground transportation so concentrate is produced and stored on site until the river becomes accessible.
The Minto deposit is spread over a series of high grade areas interspersed with large deposits of low grade material. The mine plan was designed for the highest grade deposits to be mined sequentially in a series of small pits supplemented with additional ore from underground.
Open pit mining of the Minto North pit was completed at the end of September 2016 and the operation will continue to benefit from stockpiled high grade ore in the first quarter of 2017. An additional open pit phase, Area 2 Stage 3, was approved for mining in 2017 with activities commencing early in January and completion expected in the third quarter of 2017. The decision to mine the third stage of the Area 2 pit was based partially on the offset benefit gained by placing the Stage 3 overburden as topsoil cover during progressive reclamation. Underground mining will continue until early Q4, after which the mill will process stockpiled material, with milling currently scheduled to run at full capacity until the end of 2017. Head grade is expected to average just over 2% in the first quarter, falling gradually to 1% in the fourth quarter as all of the remaining stockpiles are processed. The operation is currently slated to be temporarily placed on care and maintenance at the end of 2017. However with an approximate 3 year mine life beyond 2017 in reserves, we are continuing to review the economics of additional mining which could extend operations into 2018 and beyond. Future decisions will depend on a number of factors, most notably a continuing improvement in the copper market outlook, which may allow Capstone to consider further options.