The north-nothwest trending Hozameen fault separates the low greenschist facies rocks of the Permian-Jurassic Hozameen Complex on the west, from the Lower-Middle Jurassic sediments of the Ladner Group to the east. A Late Cretaceous quartz diorite stock intrudes the sediments along the east side of the Hozameen fault on the north side of the Sumallo River.

The Defiance showing lies west of the fault and is underlain by rocks of the Hozameen Complex comprised of greenstone, volcanic chert, argillaceous chert and limestone. The regionally metamorphosed rocks generally contain fine-grained actinolite, epidote, chlorite and locally prehnite. The limestone is interbedded with greenstone and forms isolated, commonly lenticular beds up to 30 metres in thickness.

Mineralization occurs along a highly altered contact between limestone and greenstone. Replacement mineralization consists of nearly massive nickeliferous pyrrhotite. The mineralized zone ranges from 3.6 to 9.1 metres in width, and is traceable for 45 metres to the south.

The limestone unit hosts acicular, green actinolite crystals and in 1920, strontianite was reported.