The Gold Field occurrence lies in the Zeballos gold camp which is underlain by the Lower Jurassic Bonanza Group. The Bonanza Group is an island arc sequence consisting of basaltic to rhyolitic volcanic rocks. Conformably underlying the Bonanza Group rocks are limestones and limy clastics of the Quatsino and Parson Bay formations, and Karmutsen Formation tholeiitic basalts, all belonging to the Upper Triassic Vancouver Group. Dioritic to granodioritic plutons of the Zeballos intrusion phase of the Early-Middle Jurassic Island Plutonic Suite have intruded all older rocks. The Eocene Zeballos stock, a quartz diorite phase of the Tertiary Catface Intrusions, is spatially related to the areas gold-quartz veins. Bedded rocks are predominantly northwest striking, southwest dipping, and anticlinally folded about a northwest axis.
Recorded production for the Zeballos gold camp totals 9465 kilograms of gold and 4119 kilograms of silver from 652,000 tonnes of ore mined (Fieldwork 1982, page 291). Most of the production came from the Spud Valley deposits (092L 013 and 092L 211) and Privateer mine (092L 008).
The Gold Field mine and associated vein occurrences are hosted in quartz diorite of the Zeballos stock, near its western contact with Bonanza Group andesites and tuffs. Seven veins are recognized, among them the Goldfield and its branching Spur vein, which together produced all of the ore in the past. The AT, Linton and Linton North veins are located over a distance of 250 metres northwest from the Goldfield vein, and the GF2 and GF5 veins are located short distances southeast of the Goldfield vein. The Roper vein (092L 013) is 200 metres southeast of the Goldfield vein.
The veins are associated with steeply dipping northeast trending structures. Narrow zones of chloritic and argillic alteration envelope the structures, ranging from a few centimetres to a metre or more in width. Mafic components of the quartz diorite are altered to chlorite and feldspar minerals are clay-altered. Only the Goldfield and Spur veins are detailed here. Other veins are indicated on various maps and reports (see Property File) and have undergone some exploration activity.
The Goldfield vein strikes 050 to 062 degrees, dips 75 to 85 degrees north, and ranges in width from less than 1 centimetre to 40 centimetres. It follows a generally well-defined shear zone up to 60 centimetres wide. The vein, locally sheeted, is generally competent with thin bands of fine-grained pyrite, arsenopyrite, sphalerite, galena and chalcopyrite in a quartz (plus or minus calcite) gangue. Weakly mineralized, short, diagonal veins striking east, are also present.
The Spur vein strikes 070 degrees, dips vertically to 85 degrees north, and branches off the Goldfield vein, with which it shows a strong similarity. Its average width is 15 centimetres and mineralization is usually less than that of the Goldfield vein, but some high-grade sections, with assays up to 6.86 grams per tonne gold, were mined (Bulletin 27, page 92). The northeast end of the Spur vein ends in 0.6 centimetre of quartz in 1.2 centimetres of gouge.
Bulletin 27 (pages 92,94) reports production from the Spur vein totalling 24,130 tonnes averaging 9.6 grams per tonne gold. The Goldfield vein produced 63,500 tonnes grading 11.7 grams per tonne gold. Recent work on the AT, Linton and Linton North veins returned values up to 109.3 grams per tonne gold over 0.24 metres (Sample G20), 24.8 grams per tonne gold over 0.31 metres (Sample G12) and 223.5 grams per tonne gold over 0.64 metres (Sample G18), respectively. Drifting on the Linton North vein followed it for 61 metres. The average gold content over 59.0 metres was 12.07 grams per tonne over an average width of 1.2 metres (Property File - Prospectus, McAdam Resources, Spud Valley Project, 1988).
Production figures are combined production for the Roper (092L 013) and Gold Field occurrences. The combined occurrences are known as Spud Valley.
Proven/probable/possible reserves in 4 veins (combined with the Roper deposit, 092L 013) are 220,429 tonnes grading 10.7 grams per tonne gold. In view of an unsuccessful 1989 mill test, the reserve figure of 49,890 tonnes in old workings grading 4.6 grams per tonne gold reported in 1942 near the end of the mine life, may be more credible (McAdam Resources Inc. Annual Report 1988).