The Tan occurrence is located in the Cassiar Mountains in northwestern British Columbia approximately 24 kilometres south of Kilometre 1144 of the Alaska Highway, and 3.2 kilometres south of Plate Lake.
A folded and faulted assemblage of Upper Paleozoic (early Mississippian and older) Dorsey assemblage quartzite, phyllite, siltstone and limestone is intruded by stocks, dikes and sills of quartz monzonite, granodiorite and diorite related to the Middle Jurassic Nome Lake batholith.
At the Tan showing, a 20 centimetre-wide quartz vein contains stibnite and pyrite. Limonite and goethite replaces pyrite. It is located within an area of normal faulting. Some of the faults in the vicinity display zones of alteration, brecciation and iron staining. Iron oxide boulders occur in talus over the trace of one of the faults. The boulders, probably of fault breccia, consist of small, angular chert fragments in a rusty limonitic matrix. The fragments are much more angular and more regular in size than the surface talus, evidence that these are not parts of a dismembered ferrocrete deposit.
Two grab samples (00JN-2-4; 00JN-2-7) from nearby gossanous zones are anomalous in barium (847 and 2379 parts per million, respectively). The area is characterized by anomalous stream sediment results as well: the sample in the drainage containing the Tan showing is statistically rated as third highest in total base metal content, and eighth highest in total precious metals plus indicators (gold, silver, antimony, arsenic) for the whole sample suite in the Jennings River map area. The regional geochemical survey shows it as part of a northwesterly trend of high base metal as well as gold, arsenic and antimony values in stream sediments, that parallels Plate Creek for a distance of over 10 kilometres. The highest gold analysis in this trend is 206 parts per billion and is from a creek that drains northeast into Plate Creek, 10 kilometres northwest of the Tan showing (Fieldwork 2000, page 63).
In 1979, the Plate 1-2 claims were staked to cover a stream sediment anomaly identified from Geological Survey of Canada data released in Open File 561, and a known antimony occurrence, the Tan showing. In 1980, the Plate 3-4 claims were staked to cover a stream sediment silver anomaly resulting from a Canadian Occidental Petroleum Ltd. survey conducted in June. In the same year, a total of 74 rock, 9 heavy mineral, 75 stream sediment and 519 soil samples were collected and analyzed. In addition, 33 stream water samples were collected and analyzed in the field for pH and specific conductivity.
