U-Pb geochronology of intrusive rocks associated with copper-gold porphyry deposits in the Canadian Cordillera

Special Volume, Vol. SV 46, No. 1995, 1995

Copper-gold porphyry deposits are associated with both alkaline and calc-alkaline, Early Mesozoic plutonic rocks in the Canadian Cordillera. These intrusions were emplaced into mainly volcanic and sedimentary strata of the Upper Triassic Nicola, Triassic to Lower Jurassic Takla and Triassic Stuhini groups of Quesnellia and Stikinia. In several instances the volcanic country rocks are strongly alkaline in character. Intrusive rocks that either host, or are closely spatially and probably genetically associated with, six main coppergold porphyry camps in British Columbia have been dated using U-Pb methods on zircon and titanite. With the exception of intrusions in the Mt. Milligan area, all of the crystallization ages obtained are in the range of 210 Ma to 200 Ma, for porphyry-related intrusions in both Quesnellia and Stikinia, and of both alkaline and calc-alkaline composition. The age data indicate that intrusions related to the copper-gold porphyry deposits represent either a very late phase of the Late Triassic Nicola/ Takla/ Stuhini magmatic event in Quesnellia and Stikinia, or a completely separate event between the end of the Late Triassic magmatic pulse and the subsequent Late and Middle Jurassic magmatism. Intrusions in the Mt. Milligan area compositionally resemble plutons associated with other copper-gold porphyry systems, but give crystallization ages that are 14 m.y. to 20 m.y. younger.

Mots Clés: Copper-gold porphyry deposits, Canadian Cordillera,