The area is underlain by rhythmically layered amygdaloidal, feldspar porphyritic and spherulitic basalt flows of the Karmutsen Formation conformably overlain by limestone of the Quatsino Formation, both of the Upper Triassic Vancouver Group. The limestone is in fault contact (Ideal fault) with the basalts near the Manto occurrence.

The Manto occurrence was discovered during quarrying of limestone at the Ideal Cement deposit (see 092F 395). A sulphide mineralized area is exposed for 54 metres on an east trending limestone bench in the quarry. The mineralized zone is bounded on the west by a narrow northwest trending vertical dyke. Most of the mineralization is within an apparent fault zone approximately 30 metres wide. Predominant pyrite, sphalerite and minor chalcopyrite occurs as fracture-fillings. In places the host limestone is brecciated with fragments surrounded by sulphides.

Recent channel sampling assayed up to 9.59 grams per tonne gold, 21.59 grams per tonne silver, 8.47 per cent zinc and 0.29 per cent copper across 79 centimetres (George Cross Newsletter #13, 1988).