Metamorphosed volcanic rocks of the Middle Jurassic Hazelton Group are intruded by a granodiorite stock which forms the core of Iron Mountain. The intrusive and associated dykes are part of the Cretaceous to Tertiary Coast Plutonic Complex. Within the volcanic rocks, which are largely andesite, are irregular epidote-garnet- magnetite-silica skarns and related lenses of magnetite with minor pyrite and chalcopyrite. The mineralized area strikes about 010 degrees and dips 75 degrees west, is exposed over a 1.4 kilometre length, from 75 to 530 metres elevation, and varies in width from 100 to 150 metres. Total reserves include 5.36 megatonnes averaging 22.09 per cent soluble iron (Lazenby, 1962).
The magnetite occurs in three zones known as the "A" zone, "B" zone, and Summit zone. The "A" zone, lowest in elevation, is about 180 by 120 metres, with drill indicated reserves of 2,194,563 tonnes of 22.62 per cent acid soluble iron. The Summit zone, 1100 metres to the north-northeast, measures 300 by 90 metres and contains 3,160,465 tonnes of 21.73 per cent acid soluble iron (Property File - Lazenby, H.S., 1962). The "B" zone, between the above two zones contains irregular mineralization. Drilling has been shallow and it is estimated that more magnetite can be found downdip. The northern extension also remains open. A maximum of 9 megatonnes of 20 per cent soluble iron is postulated (Lazenby, 1962).
The rocks are cut by post-ore felsic to mafic dykes and north- trending faults.