Most gold deposits discovered in Canada in recent years are associated with metallic sulfide mineralization. These relatively small deposits require careful detailing of the weakest of detectable induced polarization (IP) response. This requirement puts constraints on the design and conduct of gold exploration programs using the IP/resistivity method. A study of a suite of known gold bearing deposits using IP/resistivity techniques is presented. These case histories and examples of computer models reflecting these deposits indicate the need to consider carefully the survey parameters when exploring for relatively small low-grade sulfide targets.

Abstract The Cadia district of New South Wales contains four alkalic porphyry Au-Cu deposits (Cadia East, Ridgeway, Cadia Hill, and Cadia Quarry) and two Cu-Au-Fe skarn prospects (Big Cadia and Little Cadia), with a total of ~50 Moz Au and ~9.5 Mt Cu (reserves, resources, and past production). The ore deposits are hosted by volcaniclastic rocks of the Weemalla Formation and Forest Reefs Volcanics, which were deposited in a submarine basin on the flanks of the Macquarie Arc during the Middle to Late Ordovician. Alkalic magmatism occurred during the Benambran orogeny in the Late Ordovician to early Silurian, resulting in the emplacement of monzonite intrusive complexes and the formation of porphyry Au-Cu mineralization. Ridgeway formed synchronous with the first compressive peak of deformation and is characterized by an intrusion-centered quartz-magnetite-bornite-chalcopyrite-Au vein stockwork associated with calc-potassic alteration localized around the apex of the pencil-like Ridgeway intrusive complex. The volcanic-hosted giant Cadia East deposit and the intrusion-hosted Cadia Hill and Cadia Quarry deposits formed during a period of relaxation after the first compressive peak of the Benambran orogeny and are characterized by sheeted quartz-sulfide-carbonate vein arrays associated with subtle potassic, calc-potassic, and propylitic alteration halos.

Abstract The Wheeler River property, host to the Phoenix deposit, is located in the Athabasca basin, northern Saskatchewan, 35 km southwest of the McArthur River uranium mine complex. Depths to the unconformity between the overlying Paleoproterozoic to Mesoproterozoic undeformed Athabasca Group sandstones and the underlying Paleoproterozoic and Archean crystalline basement range from 170 to 600 m, which is shallow by Athabasca basin standards. The Wheeler and McArthur River properties were explored simultaneously, with fairly similar budgets, continuously from 1975 to 1988, until the McArthur River discovery in 1988. Subsequent to that, exploration on the Wheeler River property continued at minimal budget levels until Denison became the operator in 2004. Fifty-eight holes, each about 450 m, were drilled during the next four years prior to the Phoenix discovery hole, WR-249, which intersected 1.06 percent U 3 O 8 over 2.35 m in the summer of 2008. The Phoenix uranium deposit is a blind deposit (i.e., there is no indication of uranium at surface) located at a depth of 400 m. However, there were favorable regional features including a quartzite unit within the crystalline basement and extensive dravite-altered sandstones overlying the quartzite. Discovery drill hole WR-249 tested a direct current (DC)-resistivity anomaly adjacent to the quartzite unit, targeting an interpreted alteration chimney in the sandstone. Alteration chimneys represent clay alteration and structural disruption above unconformity or basement-hosted mineralization. Drill hole WR-251 tested the same resistivity low 600 m along strike to the southwest and also intersected favorable alteration, structures, and mineralization. Sandstone alteration is similar to that described from other unconformity-associated Athabasca basin uranium deposits and consists of silicification, desilicification, rotated bedding, drusy quartz, hydrothermal hematite, and a gray, pyritic zone. Alteration of the sandstone visually reaches a maximum height of 200 m above the unconformity. Basement alteration consists of irregular drusy quartz, often with clay gouge in the pelitic gneiss. The basement in the northeast part of the Phoenix deposit is much more bleached and clay altered than that to the southwest. To date (April 2010), the Phoenix deposit has been drill tested for >1 km of strike at generally 50-m spacings and remains open along strike to the northeast and southwest. The mineralization is primarily sandstone-hosted monomineralic uraninite, as pitchblende. Most mineralization occurs at or above the unconformity and is associated with a steeply easterly dipping, graphitic pelite basement unit, which has a maximum thickness of 75 m. Mineralization is generally located along the eastern margin of the quartzite ridge, within 25 m of the lithologic contacts of this unit. The mineralization is also directly associated with a thin, generally <1-m-wide, graphitic structure termed the WS shear. This is the only structural control recognized to date. The most enriched intersection is from drill hole WR-273, which returned 62.6 percent U 3 O 8 over 6.0 m. This represents the highest grade thickness reported worldwide from any uranium exploration property in the past decade. The mineralization drilled to date is estimated to contain from 45 to 95 million pounds (Mlb) U 3 O 8 , making Phoenix, even at the lower figure, the sixth largest known individual deposit in the Athabasca basin.