A metallogenic study of polymetallic granophile mineralization within the early Proterozoic Upper Aillik Group, Round Pond Area, Central Mineral Belt, Labrador

Abstract

The Round Pond area, located within the coastal region of the Central Mineral Belt of Labrador, is underlain by Early Proterozoic, dominantly calc-alkaline felsic volcanic rocks of the Upper Aillik Group. The volcanic rocks were deposited during subduction-related volcanic activity, and have been subjected to at least two phases of deformation, metamorphism of upper greenschist - lower amphibolite facies, and a widespread synvolcanic soda metasomatic event. -- Numerous post-tectonic granitoids intrude the rocks of the Upper Aillik Group in the coastal region, and two satellite stocks of the Monkey Hill Granite occur in the study area. The granitic stocks are highly differentiated, epizonal, leucogranitic intrusions which exhibit geochemical trends towards metallogenic specialization. Trace element and rare earth element evidence suggest that a metal-bearing volatile phase escaped into the surrounding country rock from the leucogranitic stocks. -- The Round Pond area is characterized by widespread and varied Mo-(W)-base metal-U-F mineralization spatially associated with the contact margin of a satellite stock of Monkey Hill Granite. A crude metallogenic zonation is developed outwards from the granite ranging from proximal Mo-(W)-Cu-F mineralization, intermediate carbonate-hosted Zn-(Pb) mineralization, and distal U-Zn mineralization. Associated alteration mineral assemblages depict a typical calcic skarn mineral evolution. -- Field relations, ore, accessory, and alteration mineral assemblages, as well as geochemical evidence suggest that the widespread and varied mineral occurrences in the Round Pond area have a common magmatic-hydrothermal origin related to the high level igneous activity of the Monkey Hill Granite. Ar/Ar age dating of alteration minerals reveals the mineralization is contemporaneous with the emplacement of the Monkey Hill Granite. -- An epigenetic magmatic-hydrothermal model of origin is envisaged for the polymetallic, granophile mineralization hosted by the felsic volcanic rocks of the Upper Aillik Group, in the Round Pond area.