A sequence of Mississippian felsic volcanic rocks up to 600 m thick occurs in the St. Cyr Range of the Pelly Mountains. The volcanic rocks occur in a belt 80 km long and up to 25 km wide. This belt lies within the Pelly-Cassiar Platform which is bounded to the southwest by the Yukon Crystalline Terrane and to the northeast by the Selwyn Basin. Chemical analyses indicate that most of the volcanic rocks of the Seagull Creek volcanic belt are alkali rich and potassic.
Silver, lead and zinc in the form of argentiferous galena and sphalerite and barium in barite constitute most of the mineralization associated with the volcanic rocks. Two main styles of mineralization occur:: stratabound-tpe and vein-type.
A model of origin for the deposit is speculative, but at this preliminary stage, two classes of stratiform mineralization are proposed for this area, both related to exhalative centres. The first type is local (proximal) and consists of more massive and thicker layered sulphide units interbedded with the regional clastic and exhalite horizons. The second type of mineralization is regional (distal) in extent and consists of barite and chert horizons with minor to negligible amounts of disseminated and/or thinly layered sulphide.