Geology of The Crescent Alkalic Porphyry Copper-Gold Deposit, Afton Mining Camp, British Columbia (921/9)
James R. Lang, 1994. "Geology of The Crescent Alkalic Porphyry Copper-Gold Deposit, Afton Mining Camp, British Columbia (921/9)", 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 Crescent deposit is one of several porphyry-style deposits located within the Iron Mask batholith. Other mined deposits in the district include the Afton, Ajax East and West, and Pothook deposits; the Big Onion, DM, and Python zones have published reserves but have had no production (Figure 1; Kwong, 1977). The Iron Mask is a composite intrusion of alkalic affinity which was emplaced at about 207±3 Ma (Ghosh, 1993) into coeval volcanic rocks of the Nicola Group which is part of the Quesnellia oceanic island-arc terrane (Souther, 1992). The copper-gold deposits within the batholiths have been classified within the silica-saturated group of alkalic porphyry deposits (Lang et al., 1992). The Crescent deposit is located 3 kilometres due east of the Afton deposit, the largest orebody in the district (Figure 1), and yielded 1.36 million tonnes of ore with an average grade of 0.46% copper and 0.2 gram per tonne gold during production in 1989 and 1990.
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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