Afton: A Supergene Copper Deposit
J. M. Carr, A. J. Reed, 1994. "Afton: A Supergene Copper Deposit", Selected Mineral Deposits of British Columbia, Canada: I. Porphyry Ore Deposits Of Southern British Columbia II. Mineral Deposits Of Northern Vancouver Island, C.R. Stanley, W.J. McMillan, Andre Panteleyev
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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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Selected Mineral Deposits of British Columbia, Canada: I. Porphyry Ore Deposits Of Southern British Columbia II. Mineral Deposits Of Northern Vancouver Island
km 0 Depart from the Delta Town and Country Inn. Zero your odometer at the Inn. Turn right onto River Road (Highway # 17). Cross the overpass and take the freeway on-ramp onto Highway # 99 south toward Seattle.
km 8 Take Exit # 20 (Highway # 10) east toward Langley and Hope. The road climbs a hill from the Fraser River delta late Holocene (< 8000 years before present) Salish Sediments (shoreline sand and clayey silt; river gravel, sand, silt and clay; peat bogs and swamps) through Pleistocene Vashon Drift (Fraser Glaciation) and pre-Vashon deposits from the Olympia and Highbury non-glacial intervals and the Semiahmoo and Westlynn Glaciations (tills, glaciofluvial, glaciolacustrine, glaciomarine and deltaic sediments), onto early Holocene (10,000 to 8000 years before present) glacial retreat and melt-out deposits of the Sumas Drift, Ft. Langley Formation and Capilano Sediments (Armstrong, 1990).
Lacustrine (principally oxbow lake) environments of these units near Maple Ridge, British Columbia are the only good local source of fire clay. These are valuable deposits because of their low Ca concentrations, relative to Na and K, and true clay mineralogy. Other clay deposits within British Columbia are predominantly glacial, and thus generally contain only un-weathered clay-sized particles instead of clay minerals. Furthermore, the overall quartz diorite composition of the country rocks that underlie the Fraser River drainage basin generally results in Ca-rich bricks which form a generally undesirable white precipitate over time.
km 32 Highway# 10 turns left toward Fort Langley.
km 36 Highway # 10 turns right.
km39 Turn right onto Highway # 1 (the Trans-Canada Freeway) toward Hope. This freeway crosses the ‘Lower Mainland’, the agriculturally important Fraser River delta (here consisting predominantly of Ft. Langley Formation glacial and deltaic sediments; Armstrong, 1990), which narrows to a significant defile at the town of Hope.
Km 51 In clear weather, Mt. Baker (3285 m), a Cascade andesite stratovolcano is in view directly ahead. This most-northerly United States Cascade volcano last erupted in 1843 during the waning stages of its third cycle of volcanism (approximately 50, 31–34 and 17 million years ago). It is now considered to be dormant, although minor fumarolic activity has occurred within and immediately adjacent to its 90 m wide summit crater since 1975 (Armstrong, 1990). Mt. Baker is considered to be a ‘coherent’ Cascade volcano (McBimey, 1968), meaning that it is dominated by relatively quiescent andesitic lava and phreatic ash eruptions, without