PRELIMINARY IDENTIFICATION AND CLASSIFICATION OF THE ROCK TYPES OF WILLOW LAKE, EASTERN WASHINGTON

This poster presents the initial mapping and unit classification of the Willow Lake aureole. The site contains unique outcrops of metamorphic and intrusive rocks, intermingling with sedimentary wall rock of an unknown age. Preliminary mapping and XRF data analysis find that contact metamorphism of quartzite to shale wall rocks is extensive, however amphibolite with varying grain size dominates the site. Several metamorphic outcrops show foliation of varying thickness, most with a similar strike. Possible partial melting of amphibolite may have produced a granodioritic rock containing many enclaves. Mafic dikes crosscut the many rock types and show evidence that they may have been metamorphosed as well, suggesting a Cretaceous age. The site has been previously mapped as tertiary intrusives, however further analysis will test this hypothesis. The wall rock has been suggested to be the Wallace formation of the Peigan Group of the belt Supergroup , however geochemical results of samples from the wall rock show signs of having a mafic source. Further work will be conducted on these rocks to produce a detailed map and geochemical identification of the units.