In 1981, WGM Inc., financed by Phillips Petroleum, conducted a stream sediment and pan concentrate sampling program in the Goodpaster River area, identifying Pogo Creek and to a lesser extent Liese Creek as anomalous for Au, As and W. Follow-up work confirmed this anomaly and identified mineralized quartz float, but no further work was conducted for nearly ten years. In 1997, Sumitomo Metal Mining Co., Ltd and Teck Resources Inc. signed a letter of intent whereby Teck could earn a 40% interest in the property. In mid-2009, Sumitomo Metal Mining Co., Ltd agreed to buy Teck’s 40% stake for US$245 million therefore becoming the operator of Pogo Mine.
In mid-2018, Northern Star agreed to purchase the Pogo Mine from Sumitomo Metal Mining Co., Ltd (85% interest and mine operator) and Sumitomo Corporation (15% interest) for US$260 million, becoming the sole owner and operator of the Pogo Mine on September 28, 2018.
The Pogo gold deposit consists of numerous massive auriferous quartz +/- sulphide veins hosted in a sequence of amphibolite-grade, paragneiss and orthogneiss of Proterozoic to mid-Paleozoic age. Mid-Cretaceous age granitic plutons and dikes intrude the gneisses, which in turn, are cut by the veins. The Proterozoic gneiss and Cretaceous granitoid sequence are part of the Yukon-Tanana terrain, a gold belt extending from Fairbanks into the historic gold mining areas of the Yukon Territory.
The age of the gold mineralisation is approximately 104 million years (Cretaceous) and is controlled by a low angle regional shear and high angle fault structures, which are interpreted as the fluid conduits for hydrothermal fluids. The field has undergone regional metamorphism, peaking at 110 million years, resulting in moderate folding and foliation of the metamorphic host rocks. Retrograde metamorphism resulted incooling, which transformed the ductile deformation of the metamorphic fabric to brittle (semi-ductile to brittle) deformation resulting in a low-angle shear across the region. Gold in the quartz veins is characterized as “Pogo Type” mineralization and occurs as inclusions in arsenopyrite, inclusions in quartz, composite intergrowths with Bi-Te+/-S minerals in quartz and invisible Au (<1um) inclusions to solid-solution atomically bounded in loellingite, coupled with “low arsenic” arsenopyrite.
The ultimate source of the hydrothermal fluids responsible for the Pogo deposit remains unknown. Both the “Intrusion Related Gold” and “Orogenic Gold” models have characteristics that support the evolution of the Pogo deposit. However, currently, the IRG model best fits current observations and measurements.
Ore is currently mined at rate of ~3,300 short tons per day. Four portals are in use which provide access to the various underground mining block areas. Mining block areas are named Liese, East Deep, North Zone, X Vein, South Pogo and Fun Zone. Portals are named by their approximate elevation on the topography. Mining methods at the Pogo Mine vary due to variability in vein thickness, dip, grade and continuity, and the selection of method is driven by the geometry of the structure during the initial planning stage of the mine design.
The Pogo processing circuit involves gravity concentration, gold and sulphide flotation, and leaching and adsorption of gold with a leach/carbon-in-pulp (CIP) unit operation. The process plant has an original design, hard rock processing capacity of in excess of 0.8M tonnes per annum, current stable operation has been established at 1.0M tonnes per annum and work is currently being done to look at increasing the current throughput rate.