The regional geological setting is characterized by major north-striking high-angle faults which form an ancient, long-lived rift system that extends from the United States border to at least 160 kilometres north. This system was the locus of a long, narrow marine basin in which Nicola Group rocks were deposited during Triassic time, and it then accommodated basins of continental volcanism and sedimentation in Early Tertiary time. The central part of the Nicola basin is marked by an abundance of high-energy, proximal volcanic rocks and contains a large number of coeval, comagmatic, high-level plutons with several associated copper deposits. A group of such plutons, some of which are differentiated, are known as the Copper Mountain Intrusions.
The copper deposits of the Copper Mountain camp occur chiefly in a northwest-trending belt of Upper Triassic Nicola Group rocks, approximately 1100 metres wide and 4300 metres long, that is bounded on the south by the Copper Mountain stock, on the west by a major normal fault system known as the Boundary fault and on the north by a complex of dioritic to syenitic porphyries and breccias known as the Lost Horse Intrusions. Copper mineralization diminishes markedly to the east, where the Copper Mountain stock and Lost Horse complex diverge sharply.
The Nicola rocks in the vicinity of Copper Mountain are andesitic to basaltic and are composed predominantly of coarse agglomerate, tuff breccia and tuff, with lesser amounts of massive flow units and some lensy layers of volcanic siltstone. The coarse fragmental rocks, which locally contain clasts up to 35 centimetres in diameter, rapidly grade to the southeast and south into massive flows, abundant waterlain tuff and some pillow lava. This distribution of coarse fragmental volcanics, and their spatial association with the porphyry breccia complex and with the copper deposits indicate that one or more Nicola volcanic centres were localized close to the Lost Horse Intrusions. It also indicates the close relationship between copper mineralization and Nicola magmatism in this camp.
West of the Boundary fault, the Nicola Group consists of intercalated volcanic and sedimentary rocks that include massive and fragmental andesites, tuff and generally well-bedded calcareous shale, siltstone and sandstone.
The Copper Mountain Intrusions include the Copper Mountain stock and the Smelter Lake and the Voigt stocks. These plutons form a continuous alkalic-calcic rock series ranging in composition from pyroxenite to perthosite pegmatite and syenite. The Copper Mountain stock is a concentrically differentiated intrusion elliptical in plan and approximately 17 square kilometres in area. Its major axis is 10 kilometres long and trends 300 degrees. The stock is zoned, with diorite at its outer edge grading through monzonite to syenite and perthosite pegmatite at the core. The two smaller satellites, the Smelter Lake and Voigt stocks, show no differentiation, but are similar in composition to the outer phase of the Copper Mountain stock.
The Lost Horse complex is approximately 4300 metres long and 760 to 2400 metres wide, and consists of porphyries and porphyry breccias which range in composition from diorite to syenite, showing widespread but variable albitization, saussuritization and pink feldspar alteration. These porphyries are not a continuous mass, but are a complex of dykes, sills and irregular bodies. Some phases of the complex are mineralized, but others, such as some major dykes, are clearly post-mineral.
Radiometric age dates on the Lost Horse and Copper Mountain intrusions, and on sulphide-bearing pegmatite veins indicate that the apparent age of these intrusions and of the associated mineralization is Early Jurassic (Bulletin 59, page 43; Canadian Journal of Earth Sciences, Volume 24, page 2533).
Nicola Group rocks near Copper Mountain exhibit secondary mineral assemblages which are characteristic of greenschist facies, or of albite-epidote hornfels. The volcanic rocks have widespread epidote, chlorite, tremolite-actinolite, sericite, carbonate and locally biotite and prehnite. In the immediate vicinity of the Copper Mountain stock, a narrow aureole of contact metamorphism, generally less than 60 metres wide, overprints the above assemblages and is characterized by a widespread development of granoblastic diopsidic pyroxene, green hornblende, brown to reddish biotite, abundant epidote, intermediate plagioclase and some quartz.
In the narrow belt of Nicola rocks, between the Ingerbelle mine and Copper Mountain (Similco) mine (092HSE001), the alteration differs and, where best developed, involves widespread development of biotite, followed by albite-epidote, with subsequent local potash feldspar and/or scapolite metasomatism in both Nicola rocks and Lost Horse Intrusions. The feldspar and scapolite metasomatism is characterized by intense veining and is controlled by the presence and intensity of fractures and by the proximity of large bodies of Lost Horse intrusive rocks.
The area near Copper Mountain is characterized by brittle deformation which produced a large number of faults and locally, intense fracturing. Very broad, northerly striking folds have been recognized or postulated at widely-spaced localities, but these folds decrease quickly in amplitude and down section. The area is dominated regionally by well-developed, northerly striking, high-angle faults which are best described as forming a rift system. Copper Mountain is dominated by strong easterly and northwesterly faulting. The narrow belt of Nicola rocks between Ingerbelle and Copper Mountain, confined between the Copper Mountain stock and the Lost Horse complex, is highly faulted and fractured, but does not appear appreciably folded. The strata are mostly flat-lying or very gently dipping where marker beds exist, and the few areas of steep dips can best be explained as blocks tilted by faulting. Faults in this area have been grouped in order of decreasing relative age of their latest movement into: easterly faults (Gully, Pit), "Mine breaks", northwest faults (Main), northeast faults (Tremblay, Honeysuckle) and the Boundary fault. Of these, the Boundary fault is part of the regional rift system; the others appear to be local structures the genesis and history of which are closely related to the evolution of the Copper Mountain Intrusions (CIM Special Volume 15).
The known orebodies are confined to an 1100 by 4300-metre belt. Numerous other occurrences of copper mineralization related to the Copper Mountain Intrusions are found over an area with maximum dimensions of 10 by 11 kilometres.
The Ingerbelle orebody, a skarn deposit transitional to a porphyry, has been developed by both underground and open pit methods. It is crudely L-shaped, with arms oriented northeast and northwest and maximum dimensions of 520 by 760 metres. It straddles the east-striking Gully fault and can be divided into three zones. The southwest zone is a steeply northerly plunging pipe-like body on the south side of the fault. The southeast zone dips steeply to the south and also lies immediately south of the Gully fault. The north zone includes all ore north of the fault, and may be the down-faulted extension of the southeast zone. The hostrocks are mainly altered tuffs and fragmental andesite, previously mapped as the Wolf Creek Formation (Geological Survey of Canada Memoir 171). But, approximately 15 per cent of the ore is found in small, irregular masses of Lost Horse monzonite or diorite. Faults and numerous discontinuous shears and intense mineralized fractures indicate that thorough shattering occurred prior to alteration and mineralization. An important feature of Ingerbelle is the very irregular distribution of copper mineralization.
Chalcopyrite and pyrite are the dominant sulphide minerals, but their ratios change abruptly from place to place. Total sulphide content varies from 2 to 5 per cent, but some of the more pyritic material on the southern side of the ore zones carries up to 10 per cent sulphides. Pyrrhotite is found in the southeast zone. Sulphide mineralization occurs as fine disseminations and thin discontinuous fracture-fillings, and less commonly as coarser blebs or veinlets of appreciable thickness. Sphalerite is rare. Molybdenite is found most commonly in the north zone.
Alteration at Ingerbelle involved pervasive development of biotite, followed by albite, epidote and chlorite, which were in turn followed by the development, mostly along fractures, of pink feldspar and then scapolite. Secondary pyroxene, garnet and sphene are found in some places and appear to have formed during the albite-epidote stage. The two later stages of alteration, and especially the formation of scapolite, contributed to the healing of a large number of fractures and in many places produced a pale grey to pinkish grey, hard rock which is nearly devoid of sulphides. Sulphide mineralization favours the intervening, less altered, softer, greenish grey albite-epidote hornfels, which has only small amounts of pink feldspar and scapolite veining.
Clay minerals and minor calcite are developed extensively along the Gully fault. The major difference between rock alteration at Ingerbelle and that at the Copper Mountain mine is the extensive veining and flooding by pink feldspar and scapolite at Ingerbelle. Most of the pink feldspar is albite, with potash feldspar apparently limited to a later phase at the centre of some of the veins. The alteration does not form a concentric pattern about the Ingerbelle orebody, but rather appears to be centred on the Lost Horse Intrusions and diminishes in intensity with increasing distance away from the complex. The zone of volcanic rocks, 270 metres wide, that lies between the orebody and the Copper Mountain stock, has some of the least altered and most barren rocks in the area.
The well-differentiated Copper Mountain stock is thought to have been emplaced at the roots of an active volcanic centre. The various phases of the Lost Horse complex were intruded, with rapid uplift and erosion, as a series of separate injections from a differentiating magma. Their shallower, subvolcanic level of emplacement is indicated by their finer grained porphyritic texture, their highly variable contact relationships, including chilled margins, and the pipes and irregular bodies of breccia. The various characteristics of the orebodies suggest that they formed during the later stages of this magmatism. The Copper Mountain stock was probably not the immediate source of hydrothermal fluids at that time, but it most likely was still a hot mass and could easily have provided a temperature gradient as well as a physical and chemical barrier to the sulphide-bearing fluids which probably came from the same source as the Lost Horse rocks (CIM Special Volume 15).
Production from the Ingerbelle orebody commenced in 1972 and mining in the Ingerbelle pit was completed in August 1981. Production for the last 3 months of 1980 and the first 8 months of 1981 was in part from the Copper Mountain mine (see 092HSE001). The Copper Mountain mine is located across the Similkameen River, east of the Ingerbelle pit and mill.
In 1977-78, the Ingerbelle and Copper Mountain mines consolidated operations. With the installation of an ore conveyor across the Similkameen River canyon, the delivery of Copper Mountain ore from Pit 2 to the mill began on a limited scale in October 1980, but full production was not implemented until September 1981 after the Ingerbelle orebody was depleted. Currently, the Copper Mountain mine is mining from Pits 1 and 3 and is known as the Similco copper mine operations.
Previous drilling in the Ingerbelle area had indicated a geological resource of 20 million tonnes grading 0.35 per cent copper (Information Circular 1994-19, page 7). Mining began in the Ingerbelle pit using reserves developed from a 1994 drilling program (Ingerbelle East zone). The first ore was processed in April 1995 (T. Schroeter, personal communication, 1995). Production is included with Similco (092HSE001).
The geological resource of Ingerbelle, Phase 2 as at December 31, 1996 is 35,638,144 tonnes grading 0.329 per cent copper at a copper cutoff grade of 0.20 per cent and a strip ratio of 1.74 (Princeton Mining Corporation 1996 Annual Report, page 9).
In January 2019, an updated mineral resource for the combined Copper Mountain and New Ingerbelle mines was reported at 548.720 million tonnes measured and indicated grading 0.24 per cent copper, 0.11 gram per tonne gold and 0.75 gram per tonne silver with an additional 237.254 million tonnes inferred grading 0.21 per cent copper, 0.10 gram per tonne gold and 0.50 gram per tonne silver, using a 0.10 per cent copper cut-off grade (Collins, S.E. (2019-02-25): Intergrated Life-Of-Mine NI 43-101 Technical Report for the Copper Mountain Mine Including New Ingerbelle).
In September 2020, an updated mineral resource for the combined Copper Mountain and New Ingerbelle deposits, using 0.18 and 0.10 per cent copper cut-off grades, was reported at 319 091 000 and 654 395 000 tonnes measured and indicated grading 0.311 and 0.223 per cent copper, 0.136 and 0.096 gram per tonne gold and 1.007 and 0.684 grams per tonne silver, respectively, with an additional 140 765 000 and 323 502 000 tonnes inferred grading 0.282 and 0.199 per cent copper, 0.140 and 0.097 gram per tonne gold, 0.665 and 0.501 gram per tonne silver, respectively, whereas the proven and probable reserve was reported at 462 339 000 tonnes grading 0.23 per cent copper, 0.72 gram per tonne silver and 0.10 gram per tonne gold using a 0.10 per cent copper cut-off grade (Copper Mountain Mining Corporation [2020-11-30]: Copper Mountain Mine 65 kt/d Expansion Study and Life-of-Mine Plan NI 43-101 Technical Report, Princeton, British Columbia, Princeton, British Columbia).
