The M-21 occurrence area is centred near a teardrop-shaped diorite plug which intrudes Upper Triassic Quatsino Formation (Vancouver Group) limestone.

The M-21 zone is identified by an area of white recrystallized limestone cut by numerous, variably altered dykes mineralized with pyrrhotite and pyrite. Weak skarn development is evident in limestone and is expressed as a garnet-magnetite-pyrrhotite zone. A rock sample from this zone assayed 4.26 grams per tonne gold over 0.7 metres (Assessment Report 18672). Shallow diamond drilling encountered an altered andesite dyke mineralized with pyrite and chalcopyrite which assayed 11.92 grams per tonne gold over 0.5 metres. Another drill hole intersected a zone of quartz veins cutting an altered andesite dyke mineralized with pyrite and pyrrhotite; a sample from here assayed 7.19 grams per tonne gold over 0.5 metres (Assessment Report 18672).