The Keystone-Delaware is a fault controlled, quartz vein deposit within argillites and argillitic quartzites of the Lower Jurassic Hall Formation of the Rossland Group. Granodiorite of the Middle to Late Jurassic Nelson Intrusions intrudes to the northeast of the occurrence. Typical of such vein deposits in the area there are also lamprophyre dykes and possible localized silicification. It is presumed that the Keystone-Delaware is the up-dip extension of the Arlington ore zone (082FSW205).

The vein has an average strike of about 035 degrees and dips about 20 degrees northwest while the host stratigraphy strikes about 015 degrees and dips about 65 degrees west. The vein varies from about 5 centimetres to about 1.5 metres in width but averages about 0.6 metres, it is partly filled with quartz plus pyrite and some galena, sphalerite, tetrahedrite and rare pyrrhotite. Locally some mineralized cross fracturing is developed.

Gold values vary from 2 to 100 grams and intermittent production from 1901 to 1942 of 1669 tonnes indicates an average grade of about 50 grams per tonne gold and 100 grams per tonne silver. Additional production took place from 1979-1981.