Copper Mountain, Ingerbelle, Similkameen
British Columbia, Canada
Super Porphyry Cu and Au|
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The Copper Mountain and Ingerbelle alkalic porphyry copper deposits are located 15 km south of Princeton and 180 km east of Vancouver, in southern British Columbia, Canada.
Published reserve and production figures include:
31 Mt @ 0.9% Cu, 0.19 g/t Au (Prod.+Res. 1984, incl. Prod. 31 Mt,1917-62, Dawson, et al., 1991).
Similkameen /Ingerbelle :
141 Mt @ 0.47% Cu, 0.13 g/t Au (Prod.+Res. 1984, incl. Prod. 77 Mt, 1972-84, Dawson, et al., 1991).
Copper Mt and Ingerbelle:
123 Mt @ 0.43% Cu, 0.12 g/t Au, 1 g/t Ag (Production 1972-92, Dawson, et al., 1991),
23 Mt @ 0.45% Cu, 0.1 g/t Au (Econ. Res. 1992), and,
122 Mt @ 0.39% Cu, 0.1 g/t Au (Sub-econ. Res., 1992).
Copper Mt and Ingerbelle: as at 1 January 2019 (Copper Mountain Mining Reserve and Resource Report, 2019)
Proved+Probable Ore Reserves at a 0.1% Cu cut-off (included within Mineral Resources)
Copper Mountain Pit - 175.069 Mt @ 0.27% Cu, 0.08 g/t Au, 1.24 g.t Ag;
New Ingerbelle - 192.81 Mt @ 0.24% Cu, 0.15 g/t Au, 0.48 g/t Ag;
COMBINED - 367.879 Mt @ 0.25% Cu, 0.12 g/t Au, 0.84 g/t Ag.
Measured+Indicated Mineral Resources at a 0.1% Cu cut-off
Copper Mountain Pit - 327.704 Mt @ 0.23% Cu, 0.08 g/t Au, 0.93 g.t Ag;
New Ingerbelle - 220.016 Mt @ 0.24% Cu, 0.15 g/t Au, 0.47 g/t Ag
COMBINED - 548.72 Mt @ 0.24% Cu, 0.11 g/t Au, 0.75 g/t Ag.
Inferred Mineral Resources at a 0.1% Cu cut-off
Copper Mountain Pit - 131.254 Mt @ 0.19% Cu, 0.08 g/t Au, 0.57 g.t Ag;
New Ingerbelle - 106.0 Mt @ 0.22% Cu, 0.13 g/t Au, 0.41 g/t Ag
COMBINED - 237.254 Mt @ 0.21% Cu, 0.10 g/t Au, 0.50 g/t Ag
The Copper Mountain and Ingerbelle deposits lie within a 1100 x 4300 m septum of upper Triassic Nicola Group volcanics and are hosted almost entirely by fragmental andesitic volcanics between the concentrically differentiated Copper Mountain and Lost Horse stocks.
The Nicola Group rocks consist of andesitic to basaltic coarse agglomerate, tuff-breccia, tuff and massive flow units with some volcanics siltstone layers. Epidote, chlorite, tremolite-actinolite, sericite, carbonate, biotite and prehnite which are widespread within the volcanics overlap with the alteration in the mine areas. The volcanics are generally hornfelsed and are hard and brittle. The Copper Mountain Stock is concentrically zoned from diorite at its margins to syenite/perthosite pegmatite at its core. It intruded the volcanics prior to the mineralising event and apparently formed a solid buttress to mineralisation and alteration. The Lost Horse Complex consists of dykes, sills and irregular bodies of porphyritic diorite to syenite and breccias which were intruded in a sub-volcanic environment. A particular phase, the 'LH2 Unit' of the Lost Horse Complex contains large phenocrysts of feldspar and is though to be the causative intrusion of copper mineralisation. Both volcanic and intrusive rocks are cut by a swarm of north trending felsite dykes during the late Cretaceous to early Tertiary, which are significant dilutants to ore in some pits.
The orebodies are associated with zones of extensive, and locally intense alteration. Alteration involves widespread development of biotite, followed by albite, epidote and chlorite, with subsequent local potash feldspar and/or scapolite metasomatism, affecting both the intrusives and volcanics. Scapolite was dominant in the Ingerbelle orebody, with lesser diopside, garnet and
sphene. Fracture fill calcite-chalcopyrite-pyrite with chlorite envelopes are common. Mineralised fractures are near vertical and have a random orientation away from major faults. The alteration displays zonal relationship with both stocks. The orebodies are essentially disseminated sulphide deposits, although fracture fillings are important in many areas where silica deficient stockworks of chalcopyrite-pyrite, with lesser bornite and hematite, are developed. The proximity to rocks of the LH2 Unit apparently has a control on grade. The orebodies grade outward into pyritic haloes, but pyrite seldom exceeds 3% by volume (Fahrni, et al., 1976).
Mineralisation & Alteration
While the economic deposits are localised within the 1100 x 4300 m corridor, numerous other occurrences of Cu mineralisation related to the Copper Mountain intrusion are found over an area of up to 10 x 11 km, sub-divided as follows, i). disseminations and stockworks mostly of chalcopyrite-pyrite and locally important bornite within the Nicola Volcanics and Lost Horse intrusive, accounting for all of the economic producers; ii). hematite-chalcopyrite with minor magnetite and pyrite replacements in the nearby Voigt Stock, which although frequently high grade are rendered un-economic by narrow-ness; iii). bornite-chalcopyrite concentrations associated with pegmatite veins of the Copper Mountain Stock, producing small high grade lenses; iv). magnetite breccias and replacement in Lost Horse intrusive rocks with copper sulphides generally scarce to absent (Fahrni, et al., 1976).
The Ingerbelle orebody which straddles an east-west striking fault, was crudely 'L' shaped, with arms oriented NE and NW, and maximum dimensions of 520 x 760 m. Ore is preferentially developed in altered tuffs and fragmental andesites in this deposit, although around 15% is within small irregular masses of Lost Horse monzonite and diorite. Subtle stratigraphic control is shown by the preference for fragmental andesite. Faulting, numerous discontinuous shears and intense mineralised fractures indicate that thorough shattering occurred prior to alteration and mineralisation. An important feature at Ingerbelle is the irregular distribution of Cu mineralisation. Total sulphide amounts to 2 to 5%, predominantly chalcopyrite and pyrite, although their ratios change abruptly from place to place, and pyrite gets up to 10% locally to the south of the ore. Pyrrhotite is found to the south-east. Sulphide mineralisation occurs as fine disseminations and thin discontinuous fracture fillings, and less commonly as coarser blebs or veinlets of appreciable thickness. Sphalerite and molybdenite are found in minor quantities. Recoverable precious metals have averaged 0.18 g/t Au and 0.81 g/t Ag (Fahrni, et al., 1976).
The alteration at Ingerbelle does not appear to be centred on the mineralisation, but the adjacent Lost Horse Stock, and diminishes in intensity with increasing distance from the complex. The zone of volcanic rocks some 270 m wide between the orebody and the Copper Mountain Stock has some of the least altered and most barren rocks in the area. The sequence of alteration at Ingerbelle involved pervasive 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 in the albite-epidote stage. The two latter stages, and particularly the formation of scapolite, contributed to the healing of a large number of fractures and in a many places produced a pale grey to pinkish-grey hard rock which is nearly devoid of sulphides. This rock is resistant to weathering and forms cliffs. Sulphides favour 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 found extensively along fault zones. The main difference between Ingerbelle and Copper Mountain is the extensive veining and flooding by pink feldspar and scapolite at Ingerbelle. Most of the pink feldspar is apparently albite, with K-feldspar limited to a later phase at the centre of some of the veins (Fahrni, et al., 1976).
At Copper Mountain the mineralised zone extends for 1160 m along the contact of the Copper Mountain Stock, and reaches a maximum thickness of 330 m. It had been mined over a total vertical interval of 850 m in 1976. Within this zone the orebodies were concentrated at intersections of either the north-westward trending diorite contact or the Main Fault and its branches, or a series of steeply dipping E-W Lost Horse porphyry dykes with NE trending breaks or pegmatite sheeted zones. The orebody segments were pipe-like, with the old underground mining following segments of 15 to 60 m diameter. The contact body which formed half the ore was 9 to 38 m wide and 900 m long, which was mined over a vertical interval of 400 m. The surface pits were of the order of 700 x 270 m and 170 m deep (Pit 1), and 900 x 90 to 360 m and 170 m deep (Pit 2) (Fahrni, Macauley, etal., 1976; Dawson, et al., 1991).
As at Ingerbelle there is a preference for ore to be developed in the fine grained bedded tuffs which are more brittle than the adjacent flows, tuffs and agglomerates and shattered more readily to form more ore fractures. Similarly the Lost Horse Stock where it occurred in the less favourable volcanics was more fractured and contained more ore. Ore minerals were chalcopyrite and bornite in roughly equal amounts, with the majority of the high grade bornite being within 60 m of the stock contact. Minor chalcocite accompanied bornite, while pyrite was found with chalcopyrite, but was absent where bornite was present. In Pit 1 the bulk of the ore was along the 'Main Fault' in massive and fragmental rocks above the lower tuff horizon, while recognisable pre-ore intrusive rocks are scarce. Sulphides occur as fine disseminations of chalcopyrite and pyrite, and only rarely as blebs and stringers. Mineralisation in the west end of the orebody between the fault and the stock consisted typically of thin fracture coatings of bornite and chalcopyrite in a fine grained tuff bed. In Pit 2, the limits of the ore is apparently largely controlled by faults. Within the orebody, the ore grade material is distributed irregularly, but several local trends and centres of Cu mineralisation occur. The sulphides are predominantly chalcopyrite and pyrite, with bornite being rare. The largest known breccia pipe in the area which is 90 m in diameter and at least 150 m deep is found in the north-central part of the orebody. Although fine disseminations and fracture coatings are common, the Pit 2 orebody has a larger proportion of coarse blebs and veinlets than at Ingerbelle or Pit 1 (Fahrni, et al., 1976).
Concentric patterns of alteration in and around the Copper Mountain orebodies are not evident, and alteration appears to be related mainly to the intrusive bodies, and is also controlled by the faults and fractures. Biotite is well developed along the stock contact in the old underground mine, and appears to be associated with the orebodies and forms selvages on bigger veins. Pale green bleaching of both volcanics and intrusives is best developed in Pit 2, and involves the formation of albitic plagioclase and epidote and the destruction of biotite and magnetite. Pink K-feldspar developed along fractures in the latest stage of alteration and is often accompanied by pegmatite veins (Fahrni, et al., 1976).
The high grade bornite dominant ore (>1% Cu) in the original Copper Mountain underground mine was fracture controlled, with the intense faulting and interpreted ponding of fluids against the overhanging sides of the Copper Mountain Stock diorite producing higher grade zones mined in stopes up to 18 m wide. The lower grade halo to these zones in Pit 3 has a chalcopyrite-bornite-(pyrite) assemblage in less fractured rock with an average of 0.45% Cu. The old underground mine and Pit 3 also contained replacive pegmatite veins of K-feldspar, biotite, calcite, fluorite, apatite, bornite and chalcopyrite.
The most recent source geological information used to prepare this summary was dated: 1996.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Fahrni K C, Macauley T N and Preto V A G, 1976 - Copper Mountain and Ingerbelle: in Sutherland Brown A (Ed.) 1976 Porphyry Deposits of the Canadian Cordillera Canadian Institute of Mining and Metallurgy, Special Volume 15, pp 368-375|
Logan, J.M. and Mihalynuk, M.G., 2014 - Tectonic Controls on Early Mesozoic Paired Alkaline Porphyry Deposit Belts (Cu-Au ± Ag-Pt-Pd-Mo) Within the Canadian Cordillera : in Econ. Geol. v.109, pp. 827-858.|
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