The north-northwest 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 and is exposed on the north side of the Sumallo River.

The Star No.1 occurrence area lies west of the fault and is underlain by rocks of the Hozameen Complex comprised mainly of massive 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 the greenstone and forms isolated, commonly lenticular beds up to 30 metres in thickness.

Mineralization occurs within massive greenstone and consists of disseminated pyrite, pyrrhotite, marcasite, chalcopyrite and rare native copper. Pyrrhotite is associated with large, irregular grains of tourmaline and the native copper was noted in minute joint planes within the greenstone.

A quartz vein, striking 260 degrees and dipping 80 degrees south, hosts abundant arsenopyrite with minor galena. In 1923, a sample from the vein assayed 8.23 grams per tonne gold, 123.43 grams per tonne silver and 6.4 per cent arsenic (Minister of Mines Annual Report 1923, page 164).

In an upper working, mineralization occurs along a contact between limestone and greenstone. The replacement mineralization consists mainly of galena, minor chalcopyrite, pyrrhotite and sphalerite. In 1920, samples from the workings yielded high values in gold, silver and copper.