The Coffee gold deposits are controlled by east and north-striking structures that initiated in the Jurassic and were re-activated in the Cretaceous. Cretaceous igneous rocks and Jurassic-altered Paleozoic rocks were overprinted by Late Cretaceous (or younger) gold mineralization and the paragenetic sequence for the main prospects has been established. Jurassic alteration is characterized by zones of pervasive quartz sericite alteration of metamorphic minerals and disseminated brassy pyrite. Jurassic pyrite is locally anomalous in gold, but is generally barren. Cretaceous gold mineralization overprints Jurassic sericite alteration and is characterized by veins and breccia infilled with gold-bearing, dark grey, ‘sooty’ arsenian pyrite. In biotite-rich host gneiss, disseminated arsenian pyrite extends outwards from fracture zones along biotite-rich metamorphic foliation and pre-existing Jurassic shears. In altered Late Cretaceous igneous rocks, gold-bearing arsenian pyrite replaces primary biotite. Compared to other nearby prospects, the Coffee gold project is most similar to the Boulevard trend but textures suggest it formed at shallower levels.
