A Special Issue Devoted to Proterozoic Iron Oxide-Apatite (±REE) and Iron Oxide Copper-Gold and Affiliated Deposits of Southeast Missouri, USA, and the Great Bear Magmatic Zone, Northwest Territories, Canada: Preface

Abstract

This special issue is focused on the geology and mineral deposits in the Mesoproterozoic St. Francois Mountains terrane of southeast Missouri, United States, and in the Paleoproterozoic Great Bear magmatic zone of Northwest Territories, Canada. Contributions in this special issue emphasize iron oxide-apatite (IOA) ± rare earth element (REE) and iron oxide-copper-gold (IOCG) and affiliated deposits (e.g., Hitzman, 2000; Barton, 2014). The volume includes results of studies by the U.S. Geological Survey (USGS) and Geological Survey of Canada (GSC), derived from research done for the USGS Mineral Resources Program, and from GSC research completed under auspices of the Geomapping for Energy and Minerals and Targeted Geoscience Initiative programs. These studies took advantage of extensive historic drilling at and near IOA and IOCG deposits in Missouri, and of exceptional field exposures in the Great Bear magmatic zone. Collectively, results of this cumulative body of work provide new insights into the geological, geochemical, geophysical, and temporal characteristics of IOA ± REE, IOCG, and affiliated deposits, leading to enhanced understanding of diverse magmatic-hydrothermal systems, and refining of genetic models and exploration strategies for such deposits, within these terranes and elsewhere in the world. Both North American terranes contain iron oxide-alkali alteration zones that formed during predominantly I-type, calc-alkaline (including S-type and shoshonitic in the Great Bear zone) volcano-plutonic magmatism. Later magmatism in both terranes was mainly of A-type affinity. Locally, the IOA deposits are spatially associated with high REE concentrations. The IOCG and affiliated deposits include Co- and Birich variants. Skarns, polymetallic veins, and albitite-hosted U deposits are also present within the footprints of the regional iron oxide-alkali alteration systems. Mineralization occurred contemporaneously with mafic to felsic volcanism and local volcanogenic sedimentation, including within or marginal to large ash-flow calderas. Proterozoic rocks in both the St. Francois Mountains terrane and the Great …