Petrographic Analyses of the Button Schist (2023)

The Ambler mining district’s Arctic deposit, in the Brooks Range of northwestern Alaska, is a replacement type volcanic massive sulfide (VMS) prospect. The Arctic deposit is believed to be the consequence of hydrothermal alteration during episodes of Late Devonian and or Early Mississippian basalt-rhyolite volcanism, mainly on extensional tectonic margins. This research examines “button schist”, a metamorphosed rhyolite composed of porphyroblasts seemingly imprinted over a finer grained quartz and feldspar matrix. Feldspars come in two distinct populations: one that is mainly intact and one that has been nearly dissolved into, or by the matrix. Meta-rhyolite porphyries (MRP) are frequently found in and around the Arctic deposit. Using petrographic and scanning electron microscopes, along with whole rock data and hand samples (courtesy of Ambler Metals LLC), various analyses were performed to develop a history of the alteration episodes that produced the present-day Arctic deposit.