Petrogenesis, emplacement setting, and magmatic-hydrothermal mineralization of the peralkaline Flowers River Igneous Suite, Hopedale Block, Labrador

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University of New Brunswick


The peralkaline Flowers River Igneous Suite intrudes the southernmost region of the Mesoproterozoic Nain Plutonic Suite composite batholith in north-central Labrador. The Flowers River complex comprises a voluminous series of peralkaline granite ring intrusions and their coeval volcanic assemblage, the latter of which has been identified as a target for rare metal exploration. Peralkaline igneous complexes throughout Labrador show a ubiquitous spatial association with earlier anorthosite-mangerite-charnockite-granite (AMCG)-affinity plutonism, suggesting the geodynamic conditions responsible for generating the latter may have systematically conditioned those sites to subsequently produce highly evolved, incompatible element-enriched magmas. Laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS) U-Pb zircon geochronology is used to define a high-resolution magmatic and hydrothermal timeline for the Flowers River complex and its host suites. The Flowers River Granite intruded the local Nain Plutonic Suite rocks after ca. 8 Myr of quiescence, though trace element compositions indicate these rocks share a common, incompatible element-enriched source. Protracted fractionation of the liquids derived from this source gave rise to two contrasting styles of magmatic-hydrothermal (Zr-Nb-Y-)REE mineralization, both hosted by the cogenetic volcanic rocks overlying the plutonic complex.