The Promestora occurrence is located on a ridge, west of Mineral Creek and approximately 4.7 kilometres north of its junction with Caribou Creek.

The area is underlain by east-trending argillite, siltstone, slate, limestone and mafic volcanic rocks of the Triassic Slocan Group. Quartz diorite of the Jurassic Ruby Range stock outcrops north of the area.

The Promestora vein system is composed of single or multiple quartz veins that reach maximum thicknesses of 50 centimetres but average 20 centimetres. They occur discontinuously within a "shear zone", dipping 70 to 75 degrees north, in Slocan Group argillites. The veins strike east-west and dip approximately 80 degrees north. Mineralization consists of massive and disseminated pyrrhotite with minor disseminated sphalerite and pyrite occurring over a strike length of 40 metres in the adit and exposed at surface by trenching, discontinuously, for approximately 270 metres. Fine- grained native gold has reportedly been panned from high-grade ore.

In 1949, sampling of the Promestora tunnel yielded up to 55.4 grams per tonne gold and 26.0 grams per tonne silver over 75 centimetres (Property File - Promistora Gold Mines Ltd. [1950-01-01]: Summary Report on Work Accomplished in 1949 on the Promistora Group of Mineral Claims).

In 1958, a 15 centimetre sample of a heavily mineralized quartz vein from above the portal of the tunnel assayed 302 grams per tonne gold and 311 grams per tonne silver, whereas a 75 centimetre sample from a trench, located just west of the tunnel, assayed 116 grams per tonne gold and 113 grams per tonne silver (Property File - F.C. Buckland [1958-06-01]: Report on the Promistora Group of Mineral Claims).

In 1984, sampling of underground workings yielded up to 46.79 grams per tonne gold and 34.3 grams per tonne silver across 34 centimetres (Assessment Report 13797).

Other workings are reported approximately 180 metres to the east on the Oro Granda (L.4659) Crown grant, on strike of the Promestora vein, and expose a 90- centimetre wide vein. In 1949, a sample assayed 13.0 grams per tonne gold (Property File - Promistora Gold Mines Ltd. [1950-01-01]: Summary Report on Work Accomplished in 1949 on the Promistora Group of Mineral Claims).

In 1896, 23 metres of drifting were completed and 8 tonnes of were ore produced and shipped to the Trail smelter, yielding 762 grams of gold. Between 1896 and 1920, the adit was extended to a total length of 83 metres. In 1956, an additional 8 tonnes were shipped to the Trail smelter, yielding 840 grams of silver, 715 grams of gold, 84 kilograms of lead and 116 kilograms of zinc.

In 1983, Falconbridge completed 60 kilometres of airborne magnetic and electromagnetic surveying and took nine underground samples the following year, which were assayed for gold and silver. In 1987, Golden Pyramid Resources examined the area.