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Highland Valley - Bethlehem, East Jersey, Jersey, Huestis, Iona

British Columbia, Canada

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The Bethlehem group of porphyry copper deposits, the East Jersey, Jersey, Huestis and Iona orebodies, are located near the centre of the 198 Ma Guichon Creek Batholith, near Kamloops in British Columbia, Canada.

For details of the geological setting see the Highland Valley overview record.

Geology

All four deposits are located predominantly within the younger Bethlehem phase, immediately adjacent to the Guichon Granodiorite variety of the Highland Valley Phase of the Guichon Creek Batholith. Rocks of the Bethlehem phase form a digitated north-ward elongated apophysis that is intrusive into the rocks of the Guichon Granodiorite. This apophysis apparently follows the north trending zone of structural weakness that subsequently localised the intra-batholith porphyry dyke swarm. Mining operations removed thin cappings of Guichon Granodiorite from parts of the Huestis, Jersey and East Jersey orebodies, indicating that the current level of exposure is near the roof of the apophysis. Intrusive breccias, dacite and rhyodacite porphyry dykes, small masses of granite, granodiorite and porphyritic quartz latite, faults, fractures, mineralisation and hydrothermal alteration have all been localised along this irregular contact, principally within individual digitations of the Bethlehem phase. Mineralisation is believed to be related to the late stage dacite porphyries which apparently post-date all other intrusive rocks and breccias of the batholith. Important post breccia faults strike north, north-east and north-west and dip steeply with no significant offset (Briskey & Bellamy, 1976).

The occurrence of breccias is widespread at Bethlehem, as well as in the nearby Highmont deposit. They occur locally within a the north-trending zone, characterised by swarms of porphyry dykes, in the central part of the Guichon Creek Batholith. At Bethlehem they occur in all of the orebodies except the Huestis orebody. All of the breccias are near the contact between the Guichon and Bethlehem granodiorites, but only locally are they separated by breccias. The breccias are preferentially localised within the Bethlehem Granodiorite, and none have been found entirely within the Guichon Granodiorite. They tend to be anastomosing, steeply dipping masses with a northerly elongation. With increasing depth they tend to decrease in size and pinch out. Breccia fragments include Guichon and Bethlehem granodiorites, dacite, porphyry, porphyritic quartz latite and silicic aplite. Clasts are generally between 1 and 20 cm in diameter and range from rounded to angular, but are predominantly sub-rounded to sub-angular. Comminution of entrained fragments has resulted in a cataclastic matrix, reflecting the mineralogical composition of the hosts and grade into a fine rock flour. Vugs up to 30 cm across are not unknown. The boundaries of the breccia pipes are generally steep and range from sharp to gradational over as much as several metres (Briskey & Bellamy, 1976).

The orebodies within the Bethlehem area are contained 35% within the Guichon Granodiorite, 45% within the Bethlehem Granodiorite and 20% within the breccias and dacite porphyry dykes (Muggeridge & Price, 1993).

Mineralisation & Alteration

Mineralisation in the Bethlehem deposits includes variable amounts of chalcopyrite, bornite, pyrite, specularite and molybdenite, with white mica, chlorite, epidote, calcite, quartz, zeolites, secondary biotite and tourmaline. These minerals occur in veins, veinlets, fracture coatings, irregular blebs and disseminations. Veinlets and fracture coatings predominate in the ore zone, while disseminated finely crystalline sulphides replacing primary and secondary mafic minerals adjacent to mineralised fractures are common but volumetrically subordinate to fracture controlled mineralisation. Veins (defined as thicker than 2.5cm) occur in a zone peripheral to the central parts of the Jersey and Huestis orebodies, but in contrast are centrally located at East Jersey and Iona. Mineralisation is commonly higher in grade and more uniformly distributed in the breccias. The combined abundance's of chalcopyrite and bornite within the ore zones rarely exceeds 2% by volume. Concentrations of pyrite in the halo zones are normally less than 1%, although locally they reach 5%. Molybdenite is sporadically distributed, and commonly peripheral to the central part of the ore zone, occurring either alone or associated with chalcopyrite, quartz and bornite in veinlets, or less commonly in quartz stockworks. Specularite is peripheral to pyrite, which in turn concentrically surrounds a bornite rich core. The outer low grade copper mineralisation approximately coincides with the pyrite halo, and the high grade ore is largely within the bornite core at Jersey, (Briskey & Bellamy, 1976).

The following association of minerals are characteristic at Bethlehem, chalcopyrite with chlorite, bornite, pyrite, quartz, secondary biotite, epidote and calcite; bornite with chalcopyrite, chlorite, secondary biotite, quartz and calcite (in veins); and pyrite with chlorite, chalcopyrite, epidote, calcite and quartz (Briskey & Bellamy, 1976).

The Jersey and Huestis orebodies are roughly oval in plan. The 0.1% Cu cut-off at Jersey defining an ellipse some 500 x 400 m with a high grade +0.5% Cu core which at depth splits into a series of downward extending roots. In contrast the East Jersey and Iona orebodies are elongate northwards, reflecting control by breccias and major shear zones. The East Jersey orebody is composed of multiple narrow, northerly trending ore shoots that dip steeply westward. Most occur within breccias, and commonly coincide with shear zones. At Iona, copper mineralisation is chiefly confined to breccias, but these are unevenly mineralised (Briskey & Bellamy, 1976).

Mineralogical zoning is exhibited by these deposits, particularly Jersey. At Jersey a central Cu rich core, defined by relatively large amounts of bornite and secondary biotite, is surrounded by an intermediate zone of pyrite and white mica, which is in turn enveloped by a peripheral fringe of specularite and epidote (Briskey & Bellamy, 1976).

Common hypogene non-metallic minerals include white mica, chlorite, epidote, calcite, zeolites, secondary bioite and tourmaline. Smaller amounts of kaolinite, albite, actinolite, montmorillonite, secondary K-feldspar, rutile and prehnite are also present, while scheelite and alunite have also been reported. Epidote is most abundant at the outer margins of the Jersey and Heustis orebodies, forming a roughly concentric zone outside of the central biotite rich core. White mica (mainly sericite) is widespread in all but the most un-altered rocks at Heustis and Jersey. Significant quantities of white mica roughly coincide with areas of >0.1% Cu, even though zonal distributions are not obvious (Briskey & Bellamy, 1976). This then would appear to overlap the K-silicate zone and the inner fringes of the epidote rich outer ring. In the Iona deposit white mica is largely confined to the breccia zones and pervades host rocks only near area of quartz flooding. Reconnaissance at East Jersy indicates that white mica accompanies significant Cu mineralisation (Briskey & Bellamy, 1976).

Secondary biotite of the K-silicate zone at Jersey is largely restricted to the lower part of the bornite rich core zone. It is widespread in near surface localities of the Iona breccias, but is only a minor constituent in the Heustis and East Jersy ore zones. Although some secondary biotite occurs in veinlets and fracture coatings, most replaces primary biotite and hornblende, secondary chlorite and actinolite, and breccia matrix. Breccias may contain up to 50% secondary biotite, while other rock types seldom have more than 15%, with 3 to *% being more representative. Chlorite is the outermost alteration product on the margins of the ore zones, while epidote and white mica become common closer to the orebodies. Chlorite occurs as replacements of primary biotite and hornblende, breccia matrix and secondary actinolite, biotite and epidote, and as veinlets. The local occurrence of chlorite is generally controlled by rock type, although it is present throughout the ore zone. Within mineralised zones and rock types other than breccias, chlorite typically composes 5 to 15%. Breccias with a chloritic matrix may contain up to 25% (Briskey & Bellamy, 1976).

Quartz is the predominant constituent of veinlets that are locally abundant in the central parts of the Heustis and East Jersy orebodies, and the bornite rich core at Jersy. It is also a common component of the peripheral vein assemblage. Calcite is common in the peripheral vein assemblage also, some of which are post-ore where it is associated with zeolites. Black schlorlitic tourmaline has a widespread but erratic distribution, being present both within and marginal to ore (Briskey & Bellamy, 1976).

Published reserve and production figures comprised:

144 Mt @ 0.48% Cu (Prod.+Res. 1984, incl. Prod. 106 mt, Dawson, etal. 1991).
    - including,
    East Jersey -     3.4 Mt (Total Prod. Briskey & Bellamy, 1976).
    Jersey -     60 Mt @ 0.46% Cu (Prod.+Res., Briskey & Bellamy, 1976).
    Huestis -     25 Mt @ 0.45% Cu (Prod.+Res., Briskey & Bellamy, 1976).
    Iona -     12 Mt @ 0.47% Cu (Total Res., Briskey & Bellamy, 1976).

For detail consult the reference(s) listed below.

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.


  References & Additional Information
   Selected References:
Alva-Jimenez, T., Tosdal, R.M., Dilles, J.H., Dipple, G., Kent, A.J.R. and Halley, S.,  2020 - Chemical Variations in Hydrothermal White Mica Across the Highland Valley Porphyry Cu-Mo District, British Columbia, Canada: in    Econ. Geol.   v.115, pp. 903-926.
Byrne, K., Lesage, G., Gleeson S.A., Piercey, S.J., Lypaczewski, P. and Kyser, K.,  2020 - Linking Mineralogy to Lithogeochemistry in the Highland Valley Copper District: Implications for Porphyry Copper Footprints: in    Econ. Geol.   v.115, pp. 871-901.
Byrne, K., Trumbull, R.B., Lesage, G., Gleeson, S.A., Ryan, J., Kyser, K. and Lee, R.G.,  2020 - Mineralogical and Isotopic Characteristics of Sodic-Calcic Alteration in the Highland Valley Copper District, British Columbia, Canada: Implications for Fluid Sources in Porphyry Cu Systems: in    Econ. Geol.   v.115, pp. 841-870.
DAngelo, M., Alfaro, M., Hollings, P., Byrne, K., Piercey, S. and Creaser, R.A.,  2017 - Petrogenesis and Magmatic Evolution of the Guichon Creek Batholith: Highland Valley Porphyry Cu ±(Mo) District, South-Central British Columbia: in    Econ. Geol.   v.112, pp. 1857-1888.
McMillan W J,  2005 - Porphyry Cu-Mo Deposits of the Highland Valley District, Guichon Creek Batholith, British Columbia, Canada: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide,   v.1 pp. 259-274

   References in PGC Publishing Books: Want any of our books ? Pricelist
McMillan W J, 2005 - Porphyry Cu-Mo Deposits of the Highland Valley District, Guichon Creek Batholith, British Columbia, Canada,   in  Porter T M, (Ed),  Super Porphyry Copper and Gold Deposits: A Global Perspective,  v1  pp 259-274
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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