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Highland Valley - JA |
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British Columbia, Canada |
| Main commodities:
Cu Mo
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The JA deposit straddles the north striking contact between granodiorites of the Guichon Variety of the Highland Valley Phase to the east, and the younger Bethlehem Phase, both of which belong to the Guichon Creek Batholith, near Kamloops in British Columbia, Canada.
For details of the geological setting see the Highland Valley overview record.
A small elliptical stock, with a long axis parallel to that of the ore, lies along its southern contact. It has a carapace of quartz-plagioclase aplite which grades inwards to porphyritic biotite-quartz monzonite. This carapace is mineralised, and weakly disseminated sulphides occur throughout the stock. Regional geology and bedrock geometry suggest that a series of steeply dipping northward and north-westward striking faults comprise the framework of the deposit. The ore zone is present as an elliptical body, disposed parallel to the stock and occurs along its northern contact. The 0.3% Cu cutoff defines a zone some 900 x 250 m (McMillan W J, 1976a).
Mineralisation occurs primarily in fractures, veins and their alteration envelopes. The predominant economic mineral is chalcopyrite, with lesser bornite. Sulphide zoning comprises a core zone in which bornite grades are greater than or equal to chalcopyrite, grading outward through a zone of where chalcopyrite exceeds bornite, to a zone where chalcopyrite is in excess of pyrite, and finally to a pyrite rich interval. Pyrite in the halo averages <2% by volume. The orebody is predominantly within the chalcopyrite and chalcopyrite+pyrite zone, with the zones in which pyrite and bornite respectively predominate being sub-economic. Although sulphide bearing quartz and quartz-epidote veins, and quartz-sericite zones markedly influence grades locally, the density of sulphide bearing mineralised fractures is the most important overall grade control. Most veins and fractures have moderately steep to steep dips. Molybdenum is common in small amounts throughout the bornite, chalcopyrite and chalcopyrite-pyrite zones, with the best values in general appearing to coincide with the best Cu values (McMillan W J, 1976a).
The main stage of mineralisation apparently occurred in two major episodes. The earlier involved sulphides associated with quartz or quartz and flaky sericite, while in the latter they are associated with epidote and quartz. Hydrothermal chlorite was formed throughout the main ore stage. Minor amounts of magnetite, specularite, calcite, zeolite (laumontite) and anhydrite (now gypsum) are also associated with the sulphides. K-feldspar and biotite alteration is, however, concentrated both in and adjacent to the carapace of the porphyry stock. Although this alteration is largely geologically controlled, it also geometrically forms a core to the orebody. The orebody is centred in an elliptical zone of weak to moderate pervasive alteration of feldspar, which occurs throughout the deposit and for up to 200 m outside of its limits. In this zone sericite predominates, but in the typical alteration assemblage, is accompanied by kaolinite and montmorillonite, with or without carbonate. Mafic minerals in the deposit may be either fresh, chloritised, sericitised or epidotised. The epidote zone overlaps the orebody, but is largely geologically controlled, favouring the mafic rich Guichon Granodiorite. Zeolite, gypsum and calcite are largely post-ore and are found outside of the ore zone (McMillan W J, 1976a).
Published reserve and production figures include:
286 Mt @ 0.43% Cu, 0.017% Mo (Res. 1984, No Prod. 1984, Dawson, etal. 1991).
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription 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.
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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
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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