At various times since its discovery the Minto deposit has been described as an example of Porphyry Copper, Volcanogenic Massive Sulphide (VMS), Redbed Copper, Magnetite Skarn (see discussion by Pearson and Clark, 1979) and Iron Oxide Copper Gold “IOCG”(Minto Explorations Ltd., 2003). Based on the preceding paragraph it is reasonable to say that the origin of the Minto deposit is enigmatic. Various workers (including the current authors) appear to have ascribed different interpretations for the most part based on their empirical observations, the background of the observer and the popular models of the day. The abundance of the high Cu/S mineraln bornite in a moderately oxidized magmatic system along with the obvious magnetite association suggests that Minto belongs to one of two recognized deposit types: Magnetite Skarn or Iron Oxide Copper Gold (“IOGC”). The lack of a typical calc-silicate skarn mineral assemblage seems to preclude the skarn deposit type, this appears to leave the IOCG model or alternatively it belongs to a previously unrecognized deposit type.

The host rocks to the Minto deposit were emplaced in a deep batholitic setting (exceeding 9 km deep to perhaps as much as 18-20 km deep), which is not considered to be the typical porphyry environment. The host is a moderately oxidized magma (Tafti and Mortensen, 2004) with widespread iron oxide (magnetite and hematite) mineralization. At least some of the hematite is supergene in origin but it is unclear if some hematite is also primary. There are very strong structural controls on ore mineral emplacement and there is no apparent genetic link to a specific phase of intrusion. Typical porphyry-type alteration zoning such as widespread propylitization, argillization, barren silicic core, or large barren pyritic halo is not recognized. Stockwork style, fracture or vein mineralization is also not present.

MintoEx geologists have been advised that some examples of IOCG mineralization (in personal communications) exhibit some similar characteristics and setting to Minto including Copperstone in Arizona, Candelaria in Chile, and Ernest Henry in Australia (Williams et al., 2005). From a genetic and structural prospective, albeit not size wise, the Sossego Deposit in Brazil may be a reasonable analog. While an IOCG origin for the Minto Deposit cannot be unequivocally demonstrated, MintoEx geologists are of the opinion that this style of deposit provides the most consistent model for their current level of understanding. However, the unique nature of this mineralization style and apparent lack of close analogs elsewhere suggests the Minto Copper-Gold deposits may represent an unrecognized mineral deposit type.

The Minto Mine is an open pit and underground mining operation that commenced in 2007. Open pit mining uses conventional drill and blast, and truck and shovel contractor fleet. Pit designs vary on the site but are typically 12 m benches with a double bench configuration. Underground operations primarily use long-hole open stoping, with some smaller areas of room and pillar. Access to the underground workings is via a single service and haulage ramp.

In 2016, open pit mining activities were focused on the continued mining and completion of Minto North pit. Underground mining activities were focused on the completion of Area 118 production, and the development and start of production in Area 2.

Underground mining at Minto will continue until early Q4 2017 and surface mining of the Area 2 Stage 3 pit commenced in Q1 with completion expected in Q3 2017. The mill will continue to process stockpiledmaterial and is scheduled to run at full capacity until the end of 2017. The current plan is to place the operation on temporary care and maintenance at the end of 2017. However, as Minto has an approximate 3-year mine life beyond 2017 in reserves, Capstone management is continuing to review the economics of additional mining which could extend operations. Depending on the outlook for copper prices in the second half of 2017, the option may exist to extend production from Minto into 2018 and beyond.

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.