New geological mapping around the Fyre Lake Cu-Co-Au deposit in Yukon-Tanana Terrane, southeastern Yukon, has established the continuity of stratigraphic units from nearby Grass Lakes map area and affirmed the stratigraphic context of the deposit. The deposit is located near the top of a regionally persistent chlorite schist and phyllite unit that is spatially associated with voluminous mafic and ultramafic intrusive rocks. As in Grass Lakes map area, chloritic schist and associated mafic and ultramafic meta-intrusive rocks in the Fire Lake area overlie a regionally persistent quartz-rich metaclastic and carbonate unit and underlie a thick carbonaceous phyllite unit with lesser marble and felsic meta-volcanic rocks.
Yukon-Tanana Terrane rocks are truncated to the east by a shear zone of mylonitic Mississippian granite that lies at the base of the Money Klippe. The klippe is composed of undeformed (except in the shear zone) Mississippian granite and granodiorite of the Simpson Range Plutonic Suite and their wall rocks and roof pendants. Wall rocks and pendants include meta-sedimentary, meta-volcanic and meta-intrusive rocks. Layered wall rocks include a lower quartz-rich metaclastic and carbonate unit and a chlorite-actinolite-epidote phyllite unit with mafic breccia, ?augite porphyry, bands of green chert, and variably thick and laterally persistent accumulations of white marble. Rocks of intrusive protolith include ca. 361 Ma quartz porphyry, gabbro and ultramafic rock. Most contacts are observed or inferred to be intrusive or stratigraphic and are not everywhere faulted as previously mapped. With the exception of the chert and marble in the mafic phyllite, the wall rocks bear a strong resemblance to Yukon-Tanana Terrane rocks beneath the shear zone and are tentatively correlated with them. Indeed, as the wall rock sequence is intruded by granite and granodiorite of the Simpson Range Plutonic Suite, a fundamental component of Yukon-Tanana Terrane, such a correlation seems required. Such a correlation would suggest that the basal shear zone of the klippe is a minor intra-terrane structure and not a major structure or terrane boundary as previously inferred.
