The Virginia mine lies mostly on the north side of Lost Horse Gulch, 450 to 850 metres west of Wolfe Creek and 13 kilometres due south of Princeton.
The area in the vicinity of Wolfe Creek is underlain by Early Jurassic intrusive rocks of the Lost Horse Intrusions and the Voigt stock (Copper Mountain Intrusions), both of Early Jurassic age, and volcanics of the Upper Triassic Nicola Group. Wolfe Creek flows along the contact separating the Voigt stock to the east from the Lost Horse Intrusions and Nicola Group volcanics to the west. The Nicola Group volcanics were previously included with the Wolf Creek Formation (Geological Survey of Canada Memoir 171). All units are cut by north-striking post-Early Cretaceous quartz feldspar porphyritic felsite dykes ("Mine Dykes"), and unconformably overlain to the north by volcanics of the Eocene Princeton Group.
This porphyry copper-gold deposit is hosted in basaltic to andesitic flows and pyroclastics and diorite to monzonite and syenite of the Lost Horse Intrusions. The volcanics are comprised mostly of dark grey to black feldspar porphyritic andesite/basalt, frequently containing numerous euhedral plagioclase phenocrysts up to 2 millimetres long in an aphanitic matrix. Augite and/or hornblende phenocrysts are sometimes also present. Weak to moderate propylitic alteration gives the rock a medium to dark greenish grey colour. A thick section of fresh, homogeneous andesite/basalt underlies the western part of the deposit.
The pyroclastics consist of pale green to white to purplish grey, massive to thinly bedded to laminated "cherty" tuff, locally grading to "cherty" lapilli tuff. The cherty nature of the pyroclastics is largely due to pervasive albite flooding. Bedding is shallow to moderately dipping.
These volcanics are intruded by a network of dykes, sills and irregular bodies of medium to fine-grained, pale grey monzonite and monzodiorite and less commonly diorite of the Lost Horse Intrusions. Slender, prismatic hornblende phenocrysts up to 1 centimetre long are sparsely distributed throughout the monzonite. Occasional pervasive albite flooding gives the rock a pale greenish grey appearance. Extensive sections of monzonite occur in the east-central part of the deposit.
This initial phase of the Lost Horse Intrusions is cut by a second phase comprised of dykes and small irregular bodies of fine- grained pink syenite to syenodiorite (microsyenite), locally dark purplish to pinkish grey latite and "andesite". This intrusive is variably feldspar, augite, quartz and biotite porphyritic. One distinctive microsyenite porphyry contains numerous tabular orthoclase phenocrysts commonly up to 5 centimetres in length in a pink aphanitic matrix. The second phase intrusions frequently contain blebs of magnetite, calcite or an intergrowth of both, up to 5 millimetres in diameter.
All units are in turn intruded by two suites of postmineral dykes. The "Mine Dykes" are the more important of the two, and consist of creamy white, feldspar quartz porphyritic felsite, sometimes with gradational, greenish margins. These dykes commonly exhibit fine to coarse banding (flow banding?) along their margins. They pinch and swell, and split and coalesce, commonly enclosing lenticular bodies of country rock.
The Virginia deposit is cut by four major dykes and a number of smaller satellite dykes. The main dykes are commonly 10 to 30 metres wide, but sometimes swell up to 60 metres. They strike north-northeast or north-northwest and dip steeply east. The second suite of dykes are comprised of dark greenish grey to black aphanitic basalt. Diamond drilling indicates they are steeply dipping and sometimes cut the felsite dykes.
The hydrothermally altered host rocks have undergone propylitic, potassic and argillic alteration. Minor oxidation is also evident. Propylitic alteration is most common and usually occurs as pervasive albite in the Lost Horse Intrusions (first phase) and "cherty" tuff, and as albite stringers, blotches, and vein alteration envelopes in the volcanics. Albite blotches are occasionally cored by pyrite. Epidote forms stringers and veins, in both intrusives and volcanics; it also occurs as patches and blebs, mostly in the intrusives. Epidote is commonly associated with orthoclase along fractures. Chlorite occurs as blotches and along veins in intrusives and volcanics. The mafic postmineral dykes tend to be moderately to strongly chloritized. Chlorite stringers and blotches usually occur with calcite or orthoclase. Both epidote and chlorite tend to be associated with copper mineralization.
Moderate to strong pervasive potassic alteration is developed locally in the pyroclastics and intrusives, in the form of pink orthoclase. Secondary orthoclase occurs more commonly as veins and blotches in the volcanics and intrusives. The mineral also forms alteration envelopes along calcite, magnetite +/- calcite, epidote and chlorite veins and stringers, and is strongly associated with copper mineralization.
Argillic alteration is largely confined to the Lost Horse monzonites and monzodiorites, and occurs mostly along the east and west sides of the deposit. Argillic-altered intrusives along the west side are occasionally strongly mineralized. Blotches and patches of clay are sometimes developed in magnetite. The felsite dykes are commonly clay altered.
Oxidation is the least significant form of alteration and is usually associated with surface weathering. Minor malachite and azurite occur at surface and traces are found at up to 30 metres depth. Minor limonite alteration of sulphides has occurred near surface. Gypsum is sometimes associated with limonite at greater depths. Magnetite is occasionally replaced by hematite, sometimes together with clay.
Mineralization consists of pyrite and chalcopyrite as disseminations and blebs and in steeply dipping veins and fracture fillings in both the volcanics and intrusives. Most of the disseminated pyrite and chalcopyrite is contained in the first phase of the Lost Horse Intrusions. Similar sulphide mineralization is well developed in tuffaceous horizons which tend to be richer in chalcopyrite in the eastern part of the deposit. The second Lost Horse intrusive suite carries minor disseminated pyrite and only traces of chalcopyrite.
Fracture and vein controlled sulphide mineralization is best developed in the volcanics, but is also present in the Lost Horse Intrusions (first phase). Epidote-orthoclase +/- calcite and orthoclase-chlorite +/- calcite veins tend to be mineralized with pyrite and chalcopyrite. The sulphides are also disseminated through chlorite and orthoclase +/- chlorite blotches and patches associated with this veining. Disseminated to semimassive pyrite and chalcopyrite are present in calcite, magnetite-calcite and massive magnetite veins and stringers. In the larger magnetite and magnetite-calcite veins, pyrite blebs and cubes several centimetres in diameter are frequently rimmed with chalcopyrite. Sulphides and calcite occur interstitially to blades and fibres of magnetite in sulphide-magnetite +/- calcite veins. White calcite veins commonly up to 0.3 metre wide, sometimes up to 12 metres wide (core length), contain semimassive to massive pyrite, mostly along margins but also as bands in the interior of the veins. These calcite-pyrite veins occasionally contain irregular blebs of chalcopyrite up to 5 centimetres in diameter in pyrite-free sections of the veins. Massive pyrite-chalcopyrite veins are not as common as the other vein types.
Minor to trace amounts of molybdenite and native copper are also present. Traces of molybdenite occur in massive sulphide and calcite veins. Flakes of native copper are developed along chloritic fractures in the western part of the deposit.
Overall, copper grades are similar in both the volcanics and intrusives. However, grades frequently change abruptly at lithologic contacts. Copper values tends to also increase along the margins of barren felsite dykes. Precious metal values are elevated in magnetite and chalcopyrite-rich mineralization. One magnetite- calcite vein with semimassive pyrite and chalcopyrite averaged 2.21 per cent copper, 1.06 grams per tonne gold and 4.8 grams per tonne silver over 17.1 metres (Northern Miner July 30, 1990, hole VB-90-10).
Total indicated (probable) reserves are estimated at 13.6 million tonnes grading 0.40 per cent copper and 0.21 gram per tonne gold (George Cross News Letter No. 212 (Nov. 1), 1990). These reserves contain 6.26 million tonnes of mineable reserves grading 0.36 per cent copper and 0.17 gram per tonne gold at a cutoff grade of 0.2 per cent copper and a strip ratio of 1.12 to 1 (Property File - Princeton Mining Corporation, 1991, pages 11,12). Most of the reserves are contained in one zone trending west for 300 metres and averaging 100 metre wide. Copper mineralization extends to depths of in excess of 240 metres in this zone. Smaller areas of mineralization occur along the zone's northern flank up to 120 metres to the north. One narrow zone (Connection zone) extends to the northwest, and appears to link with the Alabama prospect (092HSE013).
This deposit was initially explored by Fort Reliance Minerals Ltd., which conducted geological mapping, sampling and trenching in 1964. Cumont Mines Ltd. drilled one hole and completed soil and geophysical surveys between 1966 and 1968. Magnetometer and induced polarization surveys, in addition to soil and rock sampling, were carried out by Newmont Exploration of Canada Ltd. in 1987. Similco Mines Ltd. drilled 21 holes in 1988 and 1989 while searching for barren ground suitable for the dumping of waste rock from the nearby Similco (Copper Mountain) mine (092HSE001) to the south. The resulting discovery prompted the drilling of 105 holes totalling 19,471 metres in 1990. Similco Mines began mining the deposit in December, 1991, with ore being treated at its adjacent mining and milling complex.
The geologic resource of the Virginia deposit as at December 31, 1996 is 1,305,317 tonnes grading 0.420 per cent copper at a copper cutoff grade of 0.21 per cent and a strip ratio of 1.37 (Princeton Mining Corporation 1996 Annual Report, page 9).