The Whirlpool showing of the Zen claims occurs in the coarse-grained biotite quartz monzonite outer zone of the Horsethief Batholith. Surrounding the batholith are coarse clastic sediments of the Upper Proterozoic Horsethief Creek Group.

Molybdenite occurs as flakes and rosettes in quartz veins (as selvages) and fractures in quartz monzonite. It also occurs less commonly as flakes, disseminations or in fractures in aplite dikes and as lenses or pods in pegmatites. Mineralization is most intense near the contact but mineralized veins are found up to 240 metres away. The mineralized fractures are highly altered with secondary potassium feldspar, sericite and quartz. Minor chloritization of the mafic minerals are also observed. Molybdenite, pyrite and some chalcopyrite are associated with the altered fractures.

The most impressive surface showing is reported to be 107 metres long by 30 metres wide, having a minimum of 24 exposed mineralized quartz veins varying in width from 2.5 to 20 centimetres. The strike of the veins are 110 degrees dipping 35 to 45 degrees south. Surface chip sampling of this zone indicates 0.17 per cent molybdenum (0.25 per cent MoS2) over the full 107-metre length of outcrop (Assessment Report 4559).

Mineralization was first discovered in 1971 by Canadian Johns-Manville Company Limited. The company conducted a mapping program and a geochemical survey, collecting 152 samples for analysis. Canadian Johns-Manville followed up in 1973 with more detailed mapping and a 16-metre diamond-drill hole. Canadian Johns-Manville was noted as the owner in 1980 but Denison Mines was the operator. They drilled two diamond-drill holes totalling 445 metres.