The Mudstone area is underlain mainly by andesitic rocks of the Lower Jurassic Unuk River Formation, Hazelton Group. A granodioritic pluton of the Early Jurassic Texas Creek Plutonic Suite intrudes the strata to the immediate west.

Ascot Resources reports in 2009 that rust-stained mudstones exposed in outcrop along the Granduc road became of interest when a prospecting sample yielded 136.70 grams per tonne gold, 867.0 grams per tonne silver, 4.87 per cent lead, and 3.61 per cent zinc and was followed by chip sampling, which yielded 24.67 grams per tonne gold over a 3.0 metre interval (Assessment Report 31489). Sampling was done across mudstones adjacent to the footwall of a felsic dike. The best intersection of two drill holes (the last of the season) in P09-047 was 0.36 gram per tonne gold over 2.0 metres at 58.0 metres; other results were poor (Assessment Report 31489). P09-048 encountered 1.17 grams per tonne gold over 1.0 metre at 92.0 metres and several additional 1.0 metre results around 0.5 gram per tonne gold, however most results were poor (Assessment Report 31489).

Drill logs (2009) for hole P09-47 report quartz-carbonate crackle breccia and moderate to strong pyrite as blebs, fracture fillings and disseminations (Assessment Report 31489). From 79.42-93.90 in hole P09-48 is reported weak brecciation, minor blebs/fracture fill pyrite and a dark coloured, fine grained matrix (chlorite/biotite).

Refer to Big Missouri (MINFILE 104B 046) for details of a common work history on the Dilworth/Premier property operated by Ascot Resources in the 2000s.