AGE CONSTRAINTS ON THE DEVONIAN SHALE-HOSTED ZN-PB-BA DEPOSITS, GATAGA DISTRICT, NORTHEASTERN BRITISH-COLUMBIA, CANADA

Sedimentary exhalative barite and barite sulfide deposits occur in Upp er Devonian basinal elastic sedimentary rocks of tile Earn Group of th e Gataga district, northern Canadian Cordillera. The deposits formed i n a stratigraphic sequence from which conodont species and assemblages range in ape from the Upper triangularis Zone to the Lower praesulcat a Zone of the early to late Famennian, a time span of no more than 7 m .y. At tile Driftpile deposit, which is the best constrained example, conodonts bracket at least two distinct mineralization events during t he middle Famennian: tile older event is tile Lower-Upper marginifera Zone or ''North Trench zone'' and ''East zone,'' and the younger event is the Uppermost marginifera-trachytera Zone or ''Main zone.'' The ot her 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), tile 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 fa ults through time. This data allow temporal correlation of these sedim entary exhalative deposits with other Devonian-Mississippian mineraliz ation events on the North American margin, such as other sedimentary e xhalative sulfide deposits and volcanogenic sulfide deposits located o n the outermost western margin of the miogeocline. The sedimentary exh alative deposits of the Kechika trough formed during a brief geologic episode within a much longer lived time span of arc and back-arc rifti ng and sea-floor hydrothermal mineralization.