The Paleo‐Proterozoic High Heat Production Richardson Granite, Great Bear Magmatic Zone, Northwest Territories, Canada: Source of U for Port Radium?

Abstract

Airborne radiometric survey and field studies outlined a large, elongate, high-level plutonic suite within the Richardson pluton south of the Contact Lake Belt in the Great Bear Magmatic Zone, Northwest Territories, Canada. In terms of content of radioactive elements, the Richardson pluton is composed of two distinct granite types, low heat production (LHP) and high heat production (HHP). Uranium content in the LHP and HHP granites ranges from 3.0 to 4.9 ppm and 6.5 to 24.6 ppm, respectively, showing similarity of the LHP granite to average granites. Geochemical studies indicate that there is a genetic relationship between these two types of granite; the LHP granite was the early product of magma crystallization, whereas the HHP granite is the result of extensive crystal fractionation of biotite, plagioclase and apatite. The presence of magmatic fluorite in granite suggests that high fluorine content lowered the liquidus temperature of magma causing lower temperature fractionation during ascent to high crustal levels, which increased U and Th concentrations in the resultant HHP granite. Weak U mineralization occurs locally as discontinuous quartz Ϯ hematite Ϯ pitchblende veins and veinlets within the HHP granite. Stronger U mineralization (U Ϯ Ag Ϯ Ni Ϯ Co Ϯ Cu) occurred in the past-producing Contact Lake and Port Radium deposits. It appears that such mineralization may have had a spatial and temporal genetic-paragenetic relationship with the HHP granite.

Hydrothermal Mineralization and Mineral Chemistry of Arsenides and Sulfarsenides in the Fe-Co-Ni-As-S System and Introduction of Three Unique Minerals, Port Radium Deposit, Canada

“…This magmatism created a perfect geological environment for the formation of a variety of ore deposits and introduced a substantial number of metals such as Fe, Cu, Pb, Zn, Ni, Co, U, Bi, and Ag [20,22,33]. The Richardson high heat production pluton located 9 km south of Port Radium (Figure 1) belongs to the 1.85 Ga suite of plutons and is enriched in some of these metals (particularly U and Th) and may have partially been the source of some of these metals [50]. Such plutons forming the later-stage batholiths of the GBMZ may have induced renewed fluid circulation and mineralization.…”

Fault reconstructions using aeromagnetic data in the Great Bear magmatic zone, Northwest Territories, Canada

“…North of ϳ64.5°N, the low magnetic biotite granite suite intrusions are concentrated along the western edge of the exposed Great Bear magmatic zone. Local albitisation, sericitisation, and replacement of magnetite may have contributed to their low magnetic signatures (Somarin and Mumin 2012). However, some plutons of this suite to the east (Hildebrand 2011) have higher magnetic signatures.…”