Rocks of the Lower Jurassic Betty Creek Formation (Hazelton Group) underlie much of the Jeff grid area. They are altered, moderately to strongly, to quartz-ankerite-pyrite, and contain local concentrations of base metals, to the south mainly sphalerite and galena, and to the north mainly pyrrhotite and chalcopyrite. Anomalous values of gold and silver associated with arsenic and antimony in soils and rocks were tested by diamond drilling.
Jeff grid gold and silver mineralization is shear-vein type hosted in lower andesite and upper mafic volcanic sequence lithologies. A detailed work program by Granges in 1991 led to drilling of 30 diamond drill holes on coincident geophysical and geochemical anomalies. Drilling was concentrated predominantly in two areas of interest: the 750 and 900 zones located on southern Jeff grid.
The best results obtained were in DDH-J91-7 with 41.49 grams per tonne gold and 458.75 grams per tonne silver over 4.0 metres (Assessment Report 22113). Mineralization occurred as anastomosing veins, masses and disseminations of pyrite, pyrrhotite with lesser volcanics containing quartz carbonate, veins and sericite sphalerite, galena and chalcopyrite in Vesicular mafic volcanics containing quartz carbonate, veins and sericite alteration.
Drill results show electrum and minor native gold associated with sphalerite, galena, and pyrite, and minor tetrahedrite and cinnabar in replacement patches and veins with a gangue dominated by quartz and ankerite. The highest gold values are associated with cinnabar and quartz.
The focus of the 1994 Granges Inc exploration program was to extend coverage of the Jeff grid to the north and south limits of Coul 3 claim and laterally from the Jeff fault to the Unuk flood plain.
In 2020, Eskay Mining Corp. completed a program of prospecting, rock sampling, ground and airborne geophysical surveys and 4335 metres of diamond drilling in 20 holes on the area as part of the Sib-Corey-North Mitchell property. The geophysical surveys consisted of a 911.7 line-kilometre airborne electromagnetic survey, a 55.85 line-kilometre induced polarization survey and a 43.19 line-kilometre magnetotelluric survey. Drilling was performed on the TV (MINFILE 104B 385) and Jeff occurrences. Drillhole J20-33, on the Jeff occurrence, yielded 9.5 grams per tonne gold and 70.0 grams per tonne silver over 35.5 metres, including 80.18 grams per tonne gold and 169.7 grams per tonne silver over 3.00 metres (Lindsay, D., Prowse, N.D. [2021-06-08]: NI 43-101 Technical Report on the Sib-Corey-North Mitchell Property).
See AP (104B 083) for details of a common property work history.