The Lost Atlantis occurrence is situated on the New Denver-Three Forks highway, about 2 kilometres west of Three Forks at 884 metres elevation above sea level, in the Slocan Mining Division.

Regionally, the area lies on the western margin of the Kootenay Arc, in allochthonous rocks of the Quesnel Terrane. In the vicinity of the occurrence, the Quesnel Terrane is dominated by the Upper Triassic Slocan Group, a thick sequence of deformed and metamorphosed shale, argillite, siltstone, quartzite and minor limestone. Rocks of the Slocan Group are tightly and disharmonically folded. Early minor folds are tight to isoclinal with moderate east plunging, southeast inclined axial planes and younger folds are open, southwest plunging with subhorizontal axial planes. The sedimentary sequence has been regionally metamorphosed to lower greenschist facies.

South of the occurrence, the Slocan Group has been intruded by the Middle Jurassic Nelson intrusions which comprise at least six texturally and compositionally distinct phases ranging from diorite to lamprophyre. The most dominant phase is a medium to coarse grained potassium feldspar porphyritic granite. Several feldspar porphyritic granodiorite dikes, apparently related to the Nelson intrusions, also cut the sedimentary sequence near the occurrence (Paper 1989-5).

The property is underlain by massive argillite and carbonaceous argillite of the Slocan Group and by a granite porphyry plug probably related to the Nelson intrusions. Small lenses of galena and sphalerite occur along bedding planes within the argillite near the granite porphyry. Two adits, ten metres apart vertically, were driven to explore the downdip potential of the mineralization.

In 1957, three tonnes of ore were mined from the occurrence to produce 5163 grams of silver, 537 kilograms of lead and 232 kilograms of zinc.