Exploration activity and setting of uranium in New Brunswick
Malcolm McLeod and Susan Johnson (NBDNR)

This year, the total number of mineral claims held in New Brunswick is comparable to record levels attained during the 1950’s following the discovery of the world-class base metal sulphide deposits in the Bathurst Mining Camp. The current staking rush is largely due to the rejuvenation of uranium exploration by numerous companies, particularly in the southern part of the province.

The main geological environments favourable for the formation of uranium deposits in New Brunswick were created in Late Paleozoic time during the waning stages of the Acadian Orogeny. In the wake of continental collisional events associated with the orogeny, late to post orogenic, uraniferous, felsic intrusive and extrusive activity related to evolved I-type and/or A-type granitoid magmatism was generated periodically from latest Silurian to Late Mississippian time. Extensive successor basins were filled with thick successions of alluvial, marine evaporite, and organic-rich and locally pyritiferous fluvial and lacustrine strata of Late Devonian and Carboniferous age. Throughout this period, these extensional basins were subjected to compressive and/or transpressive events resulting in periodic episodes of basin inversion and dismemberment, and a proliferation of faults throughout the section.

Prevailing views for the formation of uranium deposits in the region contend that Devonian-aged magmatic systems provided the main source of uranium. Models invoked include:

1. mineralization directly associated with these granitoid intrusions and related volcanic rocks;
2. uranium being transported by migrating groundwaters that derived uranium and thermal gradients from the older basement highs, especially those containing the Devonian uraniferous igneous rocks, and being deposited at unconformities, at reducing horizons within the sedimentary successions, or along faults containing reductants.

Here, it is proposed that other possible sources for uranium may originate from within the sedimentary successions where uranium could have been initially concentrated in situ in phosphate- hydrocarbon- and/or carbonate-rich lacustrine deposits, in proximal coarse-grained facies that contain abundant erosional products of the surrounding basement highs, and in finer grained deposits containing silicic ash. Also, heat sources other than the basement and Devonian igneous suites likely provided thermal gradients to promote fluid migration within the basins, at least locally. These include at least two periods of Mississippian magmatism, one Early Pennsylvanian high-temperature hydrothermal event, and magmatism during Early Jurassic time. Further investigation of these factors may provide new models and targets for exploration.