Age constraints on the Devonian shale-hosted Zn-Pb-Ba deposits, Gataga District, northeastern British Columbia, Canada

Abstract

Sedimentary exhalative barite and barite sulfide deposits occur in Upper Devonian basinal clastic sedimentary rocks of the Earn Group of the Gataga district, northern Canadian Cordillera. The deposits formed in a stratigraphic sequence from which conodont species and assemblages range in age from the Upper triangularis Zone to the Lower praesulcata Zone of the early to late Famennian, a time span of no more than 7 m.y. At the Driftpile deposit, which is the best constrained example, conodonts bracket at least two distinct mineralization events during the middle Famennian: the older event is the Lower-Upper marginifera Zone or Trench zone and East zone, and the younger event is the Uppermost marginifera-trachytera Zone or Main zone. The other Gataga deposits, although somewhat less well defined, are roughly of these ages or somewhat younger: one barite-pyrite unit at Cirque is late Famennian (postera and expansa Zones), the youngest unit so far recognized in the Gataga district. Exhalation of metalliferous brines into the Gataga basin was of relatively short duration and episodic, and the sites of active venting probably migrated along extensional faults through time. This data allow temporal correlation of these sedimentary exhalative deposits with other Devonian-Mississippian mineralization events on the North American margin, such as other sedimentary exhalative sulfide deposits and volcanogenic sulfide deposits located on the outermost western margin of the miogeocline. The sedimentary exhalative deposits of the Kechika trough formed during a brief geologic episode within a much longer lived time span of are and back-arc rifting and sea-floor hydrothermal mineralization.