The Mary Jane showing is hosted in granodiorite of the Miocene Mount Barr batholith. Quartz veins or lenses carrying molybdenite occur in a shear zone which is highly fractured and altered. Molybdenite occurs as disseminated flakes or as lumps of considerable size within the quartz.

On the old Mary Jane claim, an adit was driven for 6 metres along the strike of the vein. The width of the vein varied from about 1 millimetre up to 38 centimetres. On the Annie Lou claim, a vein ranging from 30 to 90 centimetres in width was exposed in an opencut for a length of about 9 metres. In this opencut, molybdenite also occurs as disseminations in the granitic footwall near cleavage planes of the shearing.

Samples graded from 0.2 to 2.5 per cent molybdenite with traces of gold, silver and copper (Minister of Mines Annual Report 1918, page 286).