Petrogeochemical assessment of the various felsic volcanic and subvolcanic igneous rocks associated with Sn- Cu-Zn and W-Mo-Bi mineralization in the north zone, Mount Pleasant, New Brunswick
University of New Brunswick
Mount Pleasant is located in southern New Brunswick along the northern segment of the Appalachian Mountains and sits 370 m above sea level. It is a late Devonian sub- volcanic-eruptive complex and consists of a 13 by 35 km caldera containing sedimentary and volcanic rocks dating to the upper Devonian and is intruded by sub volcanic-plutonic rocks, while the Saint George Batholith, forms the southern boundary of the caldera. Granitic intrusions in the Mount Pleasant caldera are the McDougall Brook and Mount Pleasant Granitic suites. Mount Pleasant is divided into two main mineralized zones: the North Zone and the Fire Tower Zone. It has numerous Sn-Cu-Zn-In (North Zone) and several W-Mo-Bi (Fire Tower Zone & North Zone) deposits. This study was focused in the North Zone where 35 samples were collected and used for geochemical analyses to characterize the highly altered rocks associated in the area and to try to date the Mount Pleasant Granitic intrusions (GRI, GRII, GRIII). Work with the pXRF, XRD and SEM has been done to discriminate and characterize the rocks sampled from the North Zone. The Th/Ti ratio derived from the pXRF data was used as a discriminating factor to determine the protoliths of the rocks sampled. Based on geochemical attributes, three grouping were distinguished that represent the Little Mount Pleasant Formation, McDougall Brook tuff and Granite II. Further geochemical work was done with respect to alteration and mineralization, and this study found that sericitization, chloritization, sulfidation and fluorite alteration are major alteration assemblages in the area. With respect to mineralization, W, Sn, Bi and Mo correlate the strongest to this alteration index (Fe/K). The age of GRII was established to be 371 ± 2 Ma based on U-Pb dating of a hydrothermal monazite found in a quartz vein related to Sn+Zn-In mineralization.