The area is primarily underlain by argillite which is cut by intrusions. At the mouth of Mostique Creek coarse placer gold occurs in a buried channel deposit, and fine gold orginated mainly from post-glacial gravels overlying the deposit.

"Data from the Cariboo mining district indicate that supergene leaching of gold dispersed within massive sulphides by Tertiary deep weathering followed by Cenozoic erosion is the most likely explanation for the occurrence of coarse gold nuggets in Quaternary sediments" (Exploration in British Columbia 1989, page 147).