The Iron Mask batholith lies in the southern part of the Quesnel trough, also known as the Nicola belt. The most important pre- Tertiary rocks in this belt are Upper Triassic volcanic and sedimentary rocks of the Nicola Group. The batholith is a subvolcanic, multiple intrusion which is comagmatic and coeval with the Nicola rocks. It is situated along the southwest side of a regional northwest trending fracture zone and is itself cut by numerous northwesterly faults. The batholith comprises two major northwest trending plutons separated by 6 kilometres of Eocene Kamloops Group volcanic and sedimentary rocks. The Tertiary rocks occupy what appears to be a graben structure resulting from renewed fault movement around the margins of the plutons during Paleocene or Early Eocene time (Bulletin 77). The larger pluton, the 18-kilometre long southern part of the batholith, is called the Iron Mask pluton. The smaller Cherry Creek pluton farther northwest, outcrops on either side of Kamloops Lake. The combined exposure of the batholith, including the intervening younger rocks, is about 33 kilometres long and 5 kilometres wide. Sedimentary and volcanic rocks of the Kamloops Group unconformably overlie the Nicola rocks and the Iron Mask batholith. These include tuffaceous sandstone, siltstone and shale with minor conglomerate, as well as basaltic to andesitic flows and agglomerates with minor dacite, latite and trachyte.
In the vicinity of the batholith, the Nicola Group is dominated by volcanic and volcaniclastic sedimentary rocks. They are generally recognized by albitization of feldspars, occurrence of patchy epidote, and/or rare hematite alteration. On the southwestern flank of the Iron Mask pluton, well-indurated, massive and bedded tuff, breccia and interbedded flows and flow breccia are prominent and are weakly metamorphosed. On the northeast flank, less well-indurated and less altered tuff and tuff breccia predominate. However, adjacent to the intrusive contact, these rocks are also well indurated and epidotized and are locally mineralized with sulphides. At the southeastern tip of the Iron Mask pluton and locally along the southwestern flank, the Nicola rocks comprise distinctive porphyritic augite-hornblende basalt.
The Cherry Creek unit is the most widely distributed phase of the batholith. It constitutes the entire Cherry Creek pluton. The unit consists of rocks with composition ranges from diorite, monzonite, syenite to their porphyritic and fine grained equivalents as well as local intrusive breccias. Copper and minor iron mineralization is prominent in the Cherry Creek unit, particularly in zones of intense brecciation associated with alkali metasomatism.
On the Copper King property, diorite and monzonite of the Cherry Creek unit of the Late Triassic-Early Jurassic Iron Mask Batholith cut Nicola Group andesitic volcanics and are covered by tuffs of the Eocene Kamloops Group. A northwest trending shear zone measuring 155 by 62 by 25 metres occurs in the intrusive rocks and contains chalcopyrite, bornite, pyrite and magnetite as disseminations and veins. Epidote alteration is predominant and related to mineralization when associated with potassic alteration and magnetite veining. Tetrahedrite is sparsely disseminated in fractures.
In 1935, a 2.1-metre sample assayed 13 grams per tonne gold, 20.6 grams per tonne silver and 2 per cent copper (Minister of Mines Annual Report 1935). A 1972 drillhole intersected 10 metres of 3.2 grams per tonne gold, 9.3 grams per tonne silver and 0.90 per cent copper (Assessment Report 3800).
Minor amounts of pitchblende occur in patches and veinlets with the copper sulphides and magnetite at the gloryhole of the old workings. A 15-centimetre sample taken in the area assayed 0.1 per cent uranium (McCammon, 1958).
The Copper King claims were staked in 1897 by J.H. Hill and a 7.6-metre shaft was sunk. During the next three years a lower adit level was driven and an intermediate level was driven from the shaft. Little work was done until 1906 when the property was acquired by A.N. Gray, who shipped between 816 and 907 tonnes. The claims were acquired by Mr. Beckman in 1908. In 1929, H.R. Graham of Kamloops made a small shipment of ore from the stope and dump. In 1937, McKelvie Brothers of Grand Forks optioned the property and during the next year carried the old stopes to the surface, drove a second raise and stoped above a small sub-level. About 645 tonnes of ore was shipped to the Tacoma smelter in 1938. A 32-tonne mill from the Jenny Long property near Stump Lake was purchased and put in operation late in 1938 and 13 tonnes of concentrate shipped to the smelter. During 1939, 222 tonnes of concentrates were shipped; 32 tonnes of ore were also shipped. The mill was destroyed by fire in 1940. Total development includes 228 metres of adits and shafts along two levels. In 1972, the Copper King property was held by Rolling Hills Copper Mines Ltd. and optioned to Torwest Resources Ltd. Extensive geological, geochemical (1060 soil samples), magnetometer, VLF-EM and induced polarization (32 kilometres) surveys, diamond drilling (7 holes totalling 1129 metres) and percussion drilling (5 holes totalling 426 metres) were undertaken. Results showed a northwest striking shear zone containing copper, silver and gold that was 155 metres long, 25 metres wide and 62 metres deep.