The country rocks in the area of the Ibex prospect are Triassic Texas Creek Granodiorite, which underlies and locally intrudes pelitic metasedimentary and subordinate andesitic metavolcanic strata of the Jurassic or older Mesozoic Hazelton Group; and the Eocene Hyder Quartz Monzonite, which intrudes the Hazelton and Texas Creek rocks (Smith, 1977; Koch, 1996).
The deposit consists of quartz fissure veins in granodiorite and overlying argillite and quartzite within 200 feet of the contact between the Texas Creek and its Hazelton roof. Buddington (1925, p. 88-89) describes a pinch-and-swell vein 15 inches to 2 feet thick of quartz and sulfides in argillite and quartzite cut by granite porphyry and granodiorite. The sulfides are mainly interbanded sphalerite and galena; pyrite, chalcopyrite, and tetrahedrite are also present. Assays of picked specimens reportedly showed high values of Ag, Cu, and Pb.
Buddington (1926, p. 53-54) also describes a second lode, discovered in 1924. It is 5 inches to 3 feet thick and was traced in outcrop for several hundred feet. This lode consists of galena- and pyrite-bearing quartz stringers in a fissure zone in granodiorite.Lead-isotope studies of galena from the Ibex prospect (Maas and others, 1995, p. 229-248) indicate that the deposit is Eocene in age, contemporaneous with emplacement of the Hyder Quartz Monzonite.