PRELIMINARY LITHOLOGICAL AND LITHOGEOCHEMICAL ANALYSIS OF THE PICKETT MOUNTAIN VMS DEPOSIT, MAINE

The Pickett Mountain base-metal deposit (PMD), formerly known as “Mt Chase deposit”, is a volcanogenic massive sulfide (VMS) deposit, within the southeast limb of the Weeksborough-Lunksoos Lake Belt (WLLB), in northern Maine. The WLLB is a part of the Ordovician Northern Maine Volcanic Belt (NMVB) situated within the Gander terrane. The Gander terrane also includes the Bathurst Mining Camp (BMC), a world-class system of VMS deposits. As part of the Gander terrane, the NMVB has potential to host other VMS deposits. Paired with lithogeochemical analyses, via portable X-ray fluorescence (pXRF), this study utilizes geological mapping and petrographic analysis to differentiate lithological units, tie altered and/or strained units back to protolith equivalents, and observe important micro-structures. Field mapping and drill core logging confirm that the PMD is a bimodal VMS system dynamically metamorphosed to greenschist grade with footwall felsic crystal tuff (dominant), tuffaceous lapillistone, tuff, minor rhyolite, hanging-wall mafic and felsic tuff, basaltic flows and hyalotuffaceous units interlayered with graphitic slate. This Ordovician volcanic system is underlain by pelitic slates and siltstone of the Cambro-Ordovician Grand Pitch Formation. The system has gone through complex hydrothermal alteration, shown by the presence of alteration products (chlorite, sericite, and quartz veins), as well the differential development of foliation and shearing. Systematic analysis of cores from two boreholes was performed by pXRF. Results show depletion of Mg, Ca, and Ti at the boundary of the heavily altered mafic flow unit overlying hanging-wall, felsic pyroclastic tuff units. The pXRF analyzer detected compositional changes of Al, Si, P, Ca, K, Fe, Ti, Zr, etc. in the felsic pyroclastic units both in the hanging-wall and footwall. Spikes in base metals (Zn, Pb, and Cu) indicate proximity to sulfide horizon(s), while elevated levels of Si and K show silica and sericite alteration associated with the footwall stockwork zone. The lithologic and lithogeochemical study of the PMD sequence helps understand geological associations and alteration related to this important VMS deposit and refine the overall geology of the WLLB.