The geology of the upper Clear Creek area is characterized by metasedimentary rocks assigned to the Cretaceous Settler Schist which have been intruded, from the east, by granitic rocks of the Early to Middle Cretaceous Spuzzum pluton.
In the immediate area of the occurrence, a 1200 by 550 metre Miocene-Oligocene aged quartz monzonite stock (Gem stock) intrudes foliated quartz diorite hosting bands of coarse-grained biotite schist and gneiss. An approximately circular breccia pipe (Gem breccia), 400 metres in diameter, occurs along the northeastern contact of this stock. The pipe's matrix consists of finely comminuted rock with conspicuous quartz phenocrysts supporting subangular to subrounded clasts of quartz latite, quartz monzonite, schist and aplite. Mixed breccia, comprising large clasts of coarse-grained schist and foliated quartz diorite, was also noted adjacent to the stock's contact. Narrow rhyolite porphyry, feldspar-quartz porphyry, black andesite and lamprophyre dykes emplaced within and around the stock represent the youngest igneous stage.
Mineralization consists predominantly of molybdenite occurring in all of the units except the feldspar-quartz and andesite dykes. The highest concentrations of molybdenite appear to have been emplaced adjacent to the quartz monzonite/schist-gneiss contact, occurring in a 490 by 60-metre crescent-shaped zone straddling the eastern edge of the breccia pipe. Molybdenite occurs as follows: 1) medium-grained crystals scattered along the edges and within a few centimetres of coarse quartz(-calcite) veins; 2) 0.5 to 1.5- centimetre isolated rosettes and blebs in 2 to 50-centimetre wide quartz veins; 3) 1 to 2-millimetre wide; blue coloured, fine-grained quartz-molybdenite veins; and 4) 'paint' along fractures. Two stages of molybdenite veining have been cut by barren quartz veining. Local minor pyrite and pyrrhotite have been observed in association with the quartz-molybdenite veins, which themselves occur as random, coarse stockworks. Minor disseminated chalcopyrite, sphalerite, scheelite and bismuthinite have also been observed locally (Canadian Mining and Metallurgical Bulletin, Volume 62, Number 681).
Alteration outside areas of intense quartz veining is generally absent. Silicification of stockwork host rocks is, however, moderate and saussuritization and chloritization of the quartz monzonite away from the breccia pipe has been observed. Sericitization is also reported adjacent to the quartz-molybdenite veins where they are hosted by rhyolite porphyry dykes and Gem breccia. White feldspar phenocrysts, present in many of the quartz veins, are probably a result of deuteric alteration.
Rough estimates by Utah Construction and Mining Co. in 1968, incorporating information from 20 diamond-drill holes totalling 4402 metres, put the deposit's reserves at 15,874,250 tonnes grading 0.125 per cent MoS2, using a 0.10 per cent MoS2 cutoff grade (Assessment Report 18358, page 4). Early estimates had been as high as 30,000,000 tonnes grading 0.205 per cent MoS2 (National Mineral Inventory 092H12 Mo1).
Pyrite, pyrrhotite and chalcopyrite occurrences hosted by schist have been reported south of Power Lake (Rugg, 1968 - Property File).