REFINING THE CHARACTERISTICS, AGE, AND EXTENT OF THE PERMIAN KLONDIKE ASSEMBLAGE IN EASTERN ALASKA

The Klondike assemblage, comprising Middle to Late Permian felsic to mafic metavolcanic rocks and co-magmatic plutons (now schist and orthogneiss), is a well characterized litho-tectonic unit in western Yukon, Canada. It is interpreted to represent an arc formed on the allochthonous Yukon-Tanana terrane (YTT) as the Slide Mountain ocean closed and the YTT collided with and was accreted along the ancestral North American continental margin. The Klondike assemblage is economically important as the primary lode source for abundant placer gold in the Klondike district. Despite its regional significance, where the Klondike assemblage might extend into eastern Alaska is not well constrained. New geological mapping in the eastern Tanacross quadrangle, Alaska, is focused on possible Klondike exposures tentatively identified by previous workers. In Alaska, the Klondike appears to be dominantly quartz-muscovite and chloritic schist. Zircon geochronology of the schistose rocks is in progress. The schistose rocks are primarily in contact with coarse-grained to K-feldspar-megacrystic augen gneiss. Multiple augen gneiss samples have yielded preliminary Late Devonian U-Pb zircon ages, suggesting that they correlate with parautochthonous North America litho-tectonic assemblages. The contacts between the Klondike schist and underlying Late Devonian orthogneiss are generally low-angle and marked by pervasive mylonite and abundant vein quartz up to a half meter thick. The schistose rocks are structurally high relative to the gneiss and preserve evidence for at least four deformational events including multiple crenulation cleavages. The structural styles observed in outcrop and our interpreted deformation history are compatible with published interpretations from other Klondike exposures to the northeast in Yukon. Resolving the extent of the Klondike assemblage in the eastern Tanacross quadrangle will help to address one of the key uncertainties in many of the geologic compilations that cross the international border. Our findings will also provide new insights into the tectonic evolution of the YTT and ancestral North American continental margin, with implications for geological controls on mineral deposit formation and distribution in the region.