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Abstract

The Afton copper deposit is 13 km west of Kamloops and contains 30.8b. × 106 tonnes of open-pit ore grading 1.0 per cent copper, at 0.25 per cent copper cutoff, together with recoverable gold and silver. At 6300 tonnes per day, this orebody will support a planned mine, mill and smelter complex. The deposit is 520 m long and tabular, with a strike of about N 70°W and a dip of 55 degrees S. It widens and deepens westward, with an average width of 90 m and an explored depth of 600 m. To a depth of Xoo m, the deposit is largely supergene and contains metallic copper and chalcocite. The underlying hypogene material contains bornite and chalcopyrite and its average grade is fractionally higher than the average supergene grade.

Geologically, the deposit is at the northwestern extremity of the Iron Mask pluton, a subyolcanic multiple intrusion of dioritic to syenitic composition. The pluton lies lengthwise in a major cross structure of the Quesnel Trough and is emplaced in contemporaneous volcanic rocks of the Upper Triassic Nicola Group. Control of the cross structure by long-active, deep-seated faults is evidenced by the manner of emplacement of plutons and by the development of adjacent sedimentary and volcanic basins of Eocene or possibly much earlier age. The deposit occurs in late-phase plutonic rocks which include latite porphyry and related breccias. Hypogene alteration has no recognized pattern and it includes potassic, saussuritic and phyllic varieties. Supergene alteration is characterized by rock disintegration and abundant earthy hematite with limonites. Adjoining Eocene strata postdate the supergene event. Faults, although numerous, mostly defy correlation and cause only minor apparent disruption of the deposit. However, the western end of the deposit is terminated by a fault. Geochemical and geophysical surveys fail to distinguish the orebody clearly from widespread sub-economic mineralization.

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