Timing and nature of mafic magmatism and iron-alkali-calcic metasomatism at Clarke Head, Nova Scotia

Abstract

1 online resource (90 pages) : illustrations (some colour), maps (some colour), charts (some colour), graphs (some colour)Includes abstract and appendices.Includes bibliographical references (pages 76-84).The objective of this project is to constrain the timing of mafic magmatism and metasomatism at Clarke Head, Nova Scotia, and to discern their relationships to metasomatic occurrences along the Cobequid-Chedabucto Fault Zone (CCFZ). Clarke Head is located within the CCFZ, a 300 km E-W striking, terrane-bounding fault system that hosts numerous metasomatic iron ± copper, gold, and cobalt deposits suggested to be part of a Metasomatic Iron Alkali Calcic system. The source of metasomatic fluids may be from the melting or dissolution of Viséan-aged Windsor Group carbonates and evaporites by mafic magmatism. Field evidence of mafic rocks north of and east along the CCFZ indicate syn- to post-Viséan magmatism occurred. Clarke Head exposes a megabreccia, bounded to the north by the Clarke Head fault, a NE-SW striking fault splay of the CCFZ, that incorporates igneous and sedimentary blocks of varying size, age, and deformation history. Metasomatism related to the undated igneous blocks at Clarke Head may be related to this hydrothermal event. Field work and petrography aided by scanning electron microscopy and micro-X-ray fluorescence spectroscopy show that primary minerals in monzodiorite and gabbro blocks, consisting of andesine-labradorite, are overprinted by metamorphism followed by metasomatism. The metamorphic assemblage consists of Cl-rich hornblende-pargasite-actinolite + Cl-F-rich apatite + LREE-rich epidote + magnetite + hematite + Co-rich pyrite ± Cl-rich biotite, consistent with greenschist/amphibolite facies metamorphism. Three hydrothermal alteration events are shown through assemblages consisting of: i) apatite + chlorite + scapolite ± oligoclase ± albite ± pumpellyite ± quartz ± K-feldspar, ii) analcime, and iii) calcite. In-situ U-Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry of hydrothermal and altered primary apatite yielded no successful ages due to low U contents (<0.1 ppm). Results show alteration may be related to alteration at the Bass River Fe-Co prospect and the West Moose River pluton