Chemostratigraphic constraints on the nature and origin of felsic schist units hosting stratabound and orogenic vein gold on Lone Star Ridge, Klondike Gold District, Yukon

Abstract

Felsic schist units in the Lone Star Ridge area of the northern Klondike Gold District, Yukon, Canada, host both locally gold-bearing orogenic quartz veins and much more extensive zones of disseminated gold mineralization that is stratabound within specific schist units and is interpreted to be syngenetic in origin. Scarcity of outcrop and the difficulty in distinguishing between subtly different schist units has hampered correlation between surface exposures and drill core, and production of a detailed geological map of the area. Lithogeochemistry offers an alternative, unbiased way to map and interpret the various subunits of the felsic schist package that host disseminated gold mineralization and gold-bearing veins in parts of the Klondike, and that can potentially form the basis for correlations between various drill holes, and between drill holes and surface exposures. A detailed investigation of 4590 multi-element geochemical analyses (by 4-acid digestion) from a set of 27 diamond drill holes in the vicinity of the Boulder Lode open cut (Lone Star gold occurrence) on Lone Star Ridge has revealed several lithogeochemical signatures that correlate closely with gold content and to some extent with lithological units distinguished during initial logging of the drill core. Research quality geochemical analyses for a suite of representative rock units selected from the 2005 drill holes have been used to verify the multi-element geochemical analyses, and to determine the petrochemical character of some of the individual rock units. Results of this study demonstrate that it is possible to construct a chemostratigraphic framework for the felsic schist units in the vicinity of the Boulder Lode. Distinctive rock units can be broken out that have very consistent geochemical signatures, and elevated gold values related to the presence of disseminated gold appear to be consistently associated with specific rock units. These chemostratigraphic marker units have been utilized to constrain the geology and structure of the immediate study area, and in particular to define the geometry of the schist units that contain disseminated gold. The same approach has also been applied to a very extensive set of geochemical data (comprising nearly 34,000 individual samples) from chip samples, diamond drill core, reverse circulation drill samples, and conventional soil samples obtained during other historical and more recent exploration programs, to better resolve the geological interpretation of entire Lone Star Ridge area.