The region in which the Tan showing occurs is within the Intermontane Belt, underlain dominantly by Lower to Middle Jurassic volcanic and sedimentary rocks of the Hazelton Group. These assemblages are overlain by the Upper Cretaceous to Lower Tertiary Ootsa Lake Group and Miocene plateau basalt. Intruding Lower Jurassic rocks of the Hazelton Group in the northeastern part of the map sheet is a belt of granodiorite, diorite and quartz diorite plutons of the Lower Jurassic Topley intrusive suite. Felsic plutons of probable Cretaceous age intrude both Lower and Middle Jurassic Hazelton strata.

The Topley intrusive suite ranges in composition from diorite to alaskite but consists mainly of quartz monzonite and diorite. In the area of the showings, two main intrusive phases have been recognized, the Nithi quartz monzonite and the Casey quartz monzonite to alaskite.

The showing is within well-jointed Nithi quartz monzonite, which is partially surrounded by Casey quartz monzonite to alaskite. Molybdenite mineralization occurs in quartz veinlets and veins that commonly trend 065 to 070 degrees. Argillic alteration of the hostrock is moderate to intense while minor potassic alteration occurs adjacent to some of the veins.

In 1969, the northeast and southern slopes of Nithi Mountain were being prospected staked by Nithex Exploration and Development Limited. A geochemical survey was completed in 1970 and outlined and an anomalous area, 1200 by 1600 metres. Grab samples from this area returned values ranging from 0.09 to 0.98 per cent MoS2 (Property File Cyprus Anvil Nithex Exploration and Development Corp., 1971).