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Highland Valley - Valley Copper |
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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 Valley Copper deposit is located within the Guichon Creek Batholith, near Kamloops in British Columbia, Canada.
For details of the geological setting see the Highland Valley overview record.
Geology
The rocks which host this deposit are mainly porphyritic Bethsaida phase granodiorites, the most central and youngest of the Guichon Creek Batholith. Minor dyke phases are the only other lithologies in the mine area, and include pre-mineralisation granodiorite and quartz-diorite porphyries, and aplite; syn-mineralisation tan felsite porphyry; and post-mineralisation lamprophyres. Localisation of the deposit is apparently related to the formation of a zone of intense fracturing near the intersection of the northerly trending Lornex Fault and the easterly trending Highland Valley Fault. Predominant orientations of faults, fractures and quartz veinlets in the deposit are parallel to these two regional faults (Osatenko & Jones, 1976).
The hosts to ore are mainly porphyritic granodiorite of the Bethsaida Phase. The main Bethsaida granodiorites in the mine area are medium to coarse grained with coarse phenocrysts of quartz and biotite. A typical composition is 56% plagioclase, 10% K-feldspar, 29% quartz and 4% biotite, with accessory hornblende, magnetite, hematite, sphene, apatite and zircon. Granodiorite and quartz-diorite porphyries dykes, which have medium to coarse plagioclase phenocrysts and minor quartz in a fine matrix, are pre-mineralisation in age, occur in the western, central and southern parts of the deposit and vary from 0.6 to 35 m in thickness. These dykes dip steeply eastward in the in the western and central areas of the pit and to the north in the southern section of the mine. Pre-mineralisation aplite dykes up to 30 cm in width occur throughout the deposit. Tan felsite porphyry. A swarm of tan felsite porphyry dykes intrude the Bethsaida granodiorite in the north-western part of the deposit. These dykes were intruded in the waning stages of mineralisation. They are up to 4.5 m in thickness and are characterised by a higher proportion of matrix (over 80%) in comparison with the granodiorite and quartz-diorite porphyry dykes. The tan matrix is mainly K-feldspar and quartz, with up to 20% phenocrysts of quartz, plagioclase, K-feldspar and biotite. Post-mineral lamprophyre dykes dated at 132 Ma cut the ore (Osatenko & Jones, 1976).
Mineralisation & Alteration
The alteration types recognised are propylitic, pervasive sericitic and kaolinitic, vein sericitic, K-feldspathic, biotitic, silicic; and post mineralisation veining, mainly gypsum. The K-feldspar alteration is dominant in the central deeper parts of the deposit, where it is intimately associated with, and enveloped by an extensive zone of moderate to strong vein sericitic and pervasive sericitic and kaolinitic alteration, which grades outwards into a zone dominated by weak to moderate pervasive sericitic and kaolinitic alteration. This in turn grades outwards into areas of weak to moderate propylitic alteration and zones of no alteration at all. A well developed silicic zone, in the form of barren quartz veins, is found in the south-eastern part of the deposit. Elsewhere quartz veins, generally mineralised, are only moderately developed. The age of hydrothermal alteration has been dated at 191 Ma at Valley Copper. Fracture controlled vein sericitic alteration is apparently younger than the pervasive sericitic and kaolinitic alteration, but is consistently cut by quartz veinlets with vein sericitic alteration. Pervasive sericitic and kaolinitic alteration and vein sericitic alteration are typically cut by quartz veinlets with associated secondary K-feldspar, while gypsum veinlets cut all alteration types (Osatenko & Jones, 1976).
The dominant structural directions for faulting and fractures are north-west, parallel to the Highland Valley Fault, and north-south parallel to the Lornex Fault. Fractures are generally spaced at 1 to 5 cm and are the dominant control of Cu mineralisation (Muggeridge & Price, 1993).
The individual alteration styles are present as follows (after Osatenko & Jones, 1976, and Muggeridge & Price, 1993):
K-feldspar alteration is common at Valley Copper, especially at deeper levels. It occurs in association with vein sericite in some replacement zones, as veinlet envelopes, along fractures and disseminated in quartz veinlets. Where it is associated with vein sericitic alteration it typically forms thin discontinuous selvages at the outer margins of sericite replacement zones where it apparently replaces sericitised plagioclase or vein sericite. It also occurs as thin fracture controlled replacement zones, but is more common in quartz veinlets occurring as disseminations within, or as fine well developed envelopes on the veins. Copper mineralisation is typically sparse in this type of alteration and consists of chalcopyrite with traces of bornite and molybdenite. The composition of the K-feldspar is very close to that of the original hosts. Secondary biotite replaces primary biotite in places, and less commonly plagioclase as well as forming thin veinlets and replacement patches, but does not occur as a distinct alteration zone.
Vein sericite alteration is manifested by replacement zones and envelopes around quartz veinlets and is the main alteration type associated with quartz stockwork and fracture copper mineralisation at Valley Copper. Sericite replacement zones follow fractures and range in width from about 0.5 to 30 mm. They typically show diffuse irregular contacts with adjacent rocks and are often vuggy. Sericite envelopes to quartz veins range in width from 0.5 to 25 mm, and do not correlate well to the thickness of enclosed quartz veins. These sericite replacement zones and veinlet envelopes consist predominantly of fine grained quartz and medium grained sericite, with minor calcite, hematite, highly sericitised and kaolinised feldspar, sericitised biotite, bornite, chalcopyrite and trace amounts of pyrite and molybdenite. It is interpreted that the quartz veinlets represent a later re-opening of the fracture controlling the sericite vein and introduction of quartz.
Pervasive sericitic and kaolinitic alteration grades outwards into the propylitic zone. It includes rocks in which plagioclase has been altered to a soft white or green, very fine grained variable mixture of sericite and kaolinite, and biotite which has been chloritised or partly to completely sericitised. Kaolinite is the dominant clay, although some montmorillonite is found on the west side. Pervasive alteration tends to be strongest where fractures are most closely spaced (in contrast to propylitisation which is in zones of little or no fracturing). Where pervasive sericitisation and kaolinisation is strongest plagioclase has been completely altered to a mixture of sericite, quartz, kaolin and calcite. In the same areas biotite has gone to sericite, siderite, kaolinite and quartz. K-feldspar has been weakly altered to sericite and kaolinite and magnetite has been pervasively hematised. Chalcopyrite, pyrite and sphalerite are present in trace amounts. In plan the strongest alteration, with more than 40% plagioclase alteration coincides with the distribution of areas with 0.5% Cu, while zones of moderate sericitisation and kaolinisation and plagioclase alteration ranging from 15 to 40% extend and average of 100 m beyond the 0.3% Cu contour. Beyond this point propylitic alteration dominates. In vertical section the area of moderate to strong pervasive alteration corresponds to >0.3% Cu. A large low grade core corresponds to the zone of strong K-feldspar alteration.
Propylitic alteration occurs in relatively small areas within the deposit and in zones peripheral to it. It is characterised by weak to moderate alteration of plagioclase to clay, by some sericite, epidote, clinozoisite and calcite and by the alteration of biotite to chlorite and epidote. The extent of the peripheral propylitic zone is hard to define as the propylitic minerals are found in the regional metamorphic assemblage.
Quartz veinlet stockworks and silicic alteration are a common feature and typically are 1 to 2 cm in width, although some are up to 25 cm. Silicic alteration is restricted to secondary quartz produced by the sericitisation and kaolinisation of plagioclase. The quartz stockwork is present in two classes. The first is quartz veinlets with envelopes of medium grained sericite, intergrown sericite and K-feldspar, which are closely associated with mineralisation. The vary in grain size from 0.4 to 2.5 mm (averaging 1.5 mm) and carry minor amounts of sericite, sericitised plagioclase, secondary K-feldspar, calcite, hematite, bornite, chalcopyrite, pyrite, molybdenite, digenite and covellite. The second class of veinlets have no alteration envelopes and carry essentially no sulphides.
The sulphides present in order of decreasing abundance are predominantly bornite and chalcopyrite, with minor amounts of digenite, covellite, pyrite, pyrrhotite, molybdenite, sphalerite, galena and gudmundite (FeSbS). The sulphides at Valley Copper are present as disseminations in quartz veinlets and in vein sericitic and K-feldspar alteration zones. The greater part of the Cu mineralisation is in areas with abundant vein sericite alteration and associated quartz veinlets. Bornite is the dominant sulphide in this sericitic association, whereas chalcopyrite is the dominant sulphide accompanying the K-feldspathic alteration. Pyrite abundance in the central part of the orebody is less than 5% of the total sulphides. There is however a pronounced halo from 200 to 300 m wide around the periphery of the deposits where pyrite ranges up to 62% of the total sulphides. Even in this halo however pyrite seldom exceeds 1% of the of the rock (Osatenko & Jones, 1976).
Bornite:chalcopyrite ratios show highest values in the central part of the deposit, where they exceed 3:1, and decrease away from the core to the fringes of the deposit, where chalcopyrite predominates, and bornite is rare outside of the 0.3% Cu contour. Chalcopyrite forms a low grade halo around the deposit with +0.1% Cu values persisting up to 600 m outside of the ore zone. Molybdenite occurs chiefly with chalcopyrite, with or without pyrite, in quartz veinlets which cut zones of vein sericite alteration. It also occurs within the pyritic halo where values of from 50 to 530 ppm are recorded. A outer zone of 50 to 1700 ppm Zn extends over 500 m west and south-west from the orebody (Osatenko & Jones, 1976; Muggeridge & Price, 1993).
The 0.3% Cu cut-off line defines an irregular shaped body some 1400 x 1000 m, which have been tested to a depth of 442 m, to give 790 mt @ 0.48% Cu (Osatenko & Jones, 1976). Drilling to the west and north-west of Valley Copper has intersected the Bethsaida Vein, a 3 m thick quartz-chalcopyrite vein grading 5 to 10% Cu, and at least 200 long (Muggeridge & Price, 1993).
Published reserve and production figures include:
565 Mt @ 0.48% Cu (Prod.+Res. 1984, incl. Prod. 17 mt, Dawson, etal. 1991).
790 Mt @ 0.48% Cu (Res. 1976, Osatenko & Jones, 1976).
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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