The Thelma occurrence is located near the southeastern shore of Hesquiat Lake, approximately 2.2 kilometres north of Rae Basin.

Exploration work in the area has been closely linked to that of Brown Jug (092E 016) and Agnes (092E 013). Much of the assessment work is common to all occurrences, with some early references to the Brown Jug (MINFILE 092E 016) magnetite occurrence appear to describe this location.

The Hesquiat Lake area is underlain by limestone and volcanics of the Pennsylvanian to Permian Sicker Group (Geological Survey of Canada Map 1537A). These rocks are intruded by the Muchalat Batholith granodiorite of the Jurassic Island Plutonic Suite.

Magnetite is reported to occur in a skarn zone within a sequence of tuff and limestone. The skarn zone strikes southwest and has been traced over 300 metres. Magnetite occurs as disseminations, small patches and masses up to 0.5 metres thick, apparently dipping at a low angle to the southeast. The zone of disseminated magnetite encompasses an area of 70.0 metres long and up to 8.0 metres thick, possibly containing 20.0 per cent magnetite (Assessment Report 464, page 9).

Lenses of massive magnetite distributed over a strike length of 152 metres may constitute a volume of no more than 0.5 million tonnes of "medium grade" (Assessment Report 464). The estimated potential tonnage ranges from 500,000 tonnes of 40.0 per cent iron to 1.5 million tonnes of 30.0 per cent iron (Assessment Report 462, page 9).

In 1962, Paco Resources completed a program of geological mapping and a ground magnetometer survey on the area. In 1982, Cominco completed a program of prospecting and geochemical sampling on the area as the Basin and Lake claims. In 1982, Cominco completed a program of prospecting and geochemical sampling on the area as the Basin and Lake claims. In 1984, Flow Resources completed a program of geological mapping, soil sampling, trenching, a ground electromagnetic survey and 13 diamond drill holes, totalling 643.2 metres. The drill program explored a strike length of 84 metres and a total down dip extension of 28.5 metres on the Brown Jug structure, approximately 300 metres south of Thelma.