The Thornhill Creek limestone occurrence is located approximately 2.4 kilometres up Thornhill Creek on the southeast side of Salmon Inlet, a northeast- trending extension of Sechelt Inlet.

Locally, a mass of white, crystalline limestone is reported to occur. The deposit is situated near the north end of a 6-kilometre long pendant of andesitic to rhyodacitic flows and pyroclastics, greenstone, argillite and schist of the Lower Cretaceous Gambier Group lying in quartz diorite of the Tertiary-Cretaceous Coast Plutonic Complex.

In 1982, and 1983, Columbia Geophysicist Services and Stackpool Resources completed programs of rock, silt and soil sampling and an airborne magnetic and electromagnetic survey on the area as the Tetra 1 to 4 claims. The geophysical surveys indicated an area immediately northwest of Tetrahedron Peak to be of interest. The programs were directed towards base and precious metal exploration.