Nicolas Gomez, PhD

Two epithermal-style Au mineralization belts are hosted in the Late Neoproterozoic volcanic and sedimentary sequences of the Avalon terrane in Newfoundland. The pervasive epidote and titanite early replacement of mafic minerals from volcanic and plutonic rocks reflects the protracted latest Edicaran hydrothermal alteration. Oxygen isotope data and hydrothermal zircon U-Pb ages link this event to the Avalonian volcanic arc-back arc magmatism before ca. 550 Ma. However, widespread epidote-allanite cement replacement in clastic sedimentary successions cast doubt on the duration and extension of hydrothermal activity and the effects of the Acadian orogeny. This study presents data on heavy minerals, U-Pb calcite, and epidote-allanite from Ediacaran sedimentary units in the Bonavista Peninsula of Newfoundland. The heavy mineral assemblage is dominated by epidote-allanite-clinozoisite, titanite, biotite-muscovite, and garnet, which corroborate the enrichment in hydrothermal/metamorphic minerals at the expense of primary magmatic mafic phases. Early calcite cement yield 415 – 390 Ma U-Pb ages associated with a low-grade metamorphic thermal resetting. Allanite results disclose different ca. 698 Ma, 587 Ma, and 430 Ma populations. The first two are interpreted as magmatic/hydrothermal, whereas the latter suggests a metamorphic overprint of sedimentary cover. Similarly, epidotes are divided into three groups based on texture and rare earth elements (REE), from which patchy REE-rich epidote yields a metamorphic age ca. 390 Ma. These new findings agree with previous detrital titanite and apatite geochronological and geochemical data from the same units, indicating hydrothermal and magmatic crystallization during Cryogenian-Edicaran, later affected by a regional metamorphic event between 430 – 370 Ma along the Avalon zone margin related to the Acadian Orogeny.