The Endako deposit (093K 006) is located on a hillcrest approximately 160 kilometres west of Prince George in central British Columbia. The mine area encompasses several showings (093K 007, 10, 13, 14) and includes the 1.7-kilometre long Endako pit, the mined out Denak East pit and the partially developed Denak West pit. The Denak deposit is a westerly extension of the Endako orebody.
In 1988, Placer Dome completed 18 diamond-drill holes in the mine area. In 1989, Placer Dome completed 14 diamond-drill holes in the mine area in an attempt to extend known ore reserves and to gather geotechnical information. In 1991, 31 diamond-drill holes were completed on the western part of Endako mine property. Production began in 1965 and by 1993 a total of 231 million tonnes had been mined yielding more than 157.5 million tonnes of molybdenum.
The Endako orebody is centrally situated within the Late Jurassic Francois Lake batholith. At least ten phases based on distinct textural and compositional changes have been recognized in the composite batholith. The orebody consists of an elongate stockwork of quartz-molybdenite veins developed within the Endako quartz monzonite phase and three types of felsic pre-ore dikes. The Endako quartz monzonite is bounded on the south by Francois granite and on the north by Casey alaskite and Glenannan granite. Post-ore basalt and andesite dikes crosscut the quartz monzonite, pre-ore dikes and mineralized stockwork.
In general terms, the orebody is a series of major east-striking veins oriented en echelon to form a zone elongated in a northwesterly direction. Length and width dimensions of the zone are approximately 3360 by 370 metres, of which the western 1830 metres is offset to the north by the West Basalt fault with a 1150 metre relative right-hand movement. Divided by this fault into two distinct domains, the east half dips moderately south and plunges west, while the west half dips east. Molybdenite, pyrite and magnetite are the most abundant primary metallic minerals. Minor chalcopyrite and traces of sphalerite, bornite, specularite and scheelite are also present. Single occurrences of beryl and bismuthinite have been reported. Molybdenite occurs in two types of veins. Large veins (up to 1.2 metres wide) contain laminae and fine disseminations of molybdenite. Fine fracture-fillings and veinlets of quartz-molybdenite occur as stockworks adjacent to the major veins. Alteration types include pervasive kaolinization, envelopes with potassium feldspar and envelopes with sericite.
A pyrite zone bounds the orebody to the south across a major fault. In this zone, mineralization consists of quartz, pyrite, minor magnetite and rare molybdenite. The mineralization occurs as fracture-filling in a poorly developed stockwork. The orebody is localized at or near the intersection of regional northwest and east structures.
Three distinct hydrothermal alteration phases are seen in the Endako ore zone. Introduced K-feldspar is noted as envelopes adjacent to veins and fractures. A second type of envelope seen is a fine-grained band of quartz-sericite and finely disseminated pyrite. Both of these envelopes can vary in width from 0.3 to 5 centimetres. Also pervasive kaolinization of the Endako quartz monzonite is present.
The orebody has been mined in three different open pits: the Endako, Denak East and Denak West. The Denak East open pit is mined out and is currently being backfilled with waste (ca. 1994). The ore contains progressively less stockwork and dips shallower as one traverses from the Endako pit in the southeast to the Denak West pit in the northwest.
The claims were originally staked in 1927 when two local men staked four mineral claims to cover an area of quartz-molybdenite float. Two short shafts were sunk in 1934, one on the 0.6 metre “Stellar” vein. During the period of 1934 to 1961, the property was examined by many geologists and several mining companies, but physical work was confined primarily to trenching and some sampling.
In May of 1962, trenching and a diamond drilling programs were commenced by Endako Mines Limited. Canex Aerial Exploration Ltd. entered the exploration of the property in October of the same year, and completed 190 diamond-drill holes for a total of 24,000 metres and 810 metres of underground work for bulk sampling. The decision to develop the property for production was announced in March of 1964. Construction of the 9,000 tonne-per-day mine plant and development of the open pit began in June 1964, and the mine was officially opened on June 8, 1965.
In 1965, pit development by Endako Mines Ltd. consisted of the removal of 1.01 million cubic metres of overburden to permit the extension of mining from the west pit into the east pit. At the beginning of the year, a 9,000 tonne-per-day concentrator commenced operation; later improvements to the concentrator increased this rate to 13,500 tonnes per day. A total of 3,569,000 tonnes of ore at an average grade of 0.174 per cent Mo were milled for the year of 1965. Mill recovery was reported at 81.3 per cent with a total of 4.67 million kilograms of molybdenum being produced. Mineable reserves as of April 30, 1966 were 79,079,000 tonnes at 0.132 per cent Mo or 142,839,000 tonnes at 0.102 per cent Mo (Property File Cyprus Anvil Endako Mines Ltd., 1966).
Proven and probable ore reserves estimated by the company were 117,600,000 tonnes grading 0.077 per cent molybdenum on January 1, 1995; in addition measured and indicated mineral resources were estimated at 147,850,000 tonnes grading 0.061 per cent molybdenum (Information Circular 1996-1, page 8).
Reserves as of January 1, 1996 were 104.8 million tonnes grading 0.077 per cent molybdenum (Schroeter, T. and Lane, R., personal communication, 1996).
Production and reserves are included with the Endako mine figures.
Drilling in 1995 in the Watkin's Creek area northwest of the Denak West pit was intended to test molybdenum mineralization along strike from the Denak West orebody. Drilling intersected molybdenite mineralization in sheared quartz veins and gouge with pyrite, chalcopyrite, magnetite and hypogene hematite as common accessories but without the significant potassic alteration that characterizes the highest grade molybdenite mineralization in the main zone of the Endako pit. Significant mineralization appears to occur in a northwest trending zone 60 to 91 metres wide (Assessment Report 24627).
According to Thompson Creek Metals Company Inc.'s 2007 Annual Report the focus of mining activities in 2008 will primarily be the Denak West pit. The company also plans to mine the walls between Endako, Denak West, and Denak East in order to create one large single pit.