Natural Resources

Open File LAB/1684 - Uranium Mineralization within the Central Mineral Belt of Labrador: A Summary of the Diverse Styles, Settings and Timing of Mineralization

G.W. Sparkes

St. John's, Newfoundland, January, 2017

Abstract

The Central Mineral Belt (CMB) of Labrador is a diverse geological environment and is host to widespread uranium mineralization. It contains a variety of different styles of uranium mineralization that are developed within a number of different rock units. This study classifies the main uranium occurrences within the CMB, which have been subdivided on the basis of host rock, alteration and textural characteristics, displayed by the uranium mineralization. Based on these attributes, the uranium mineralization, within the CMB, has been interpreted to have formed in three different mineralizing environments; namely magmatic, metamorphic–metasomatic and sedimentary environments.

Magmatic-related mineralization includes syngenetic mineralization occurring as pegmatite- and aplite-hosted occurrences, and volcanic-hosted mineralization occurring in relatively unaltered and undeformed volcanic rocks, as well as magmatic–hydrothermal mineralization of an epigenetic affinity. The latter is associated with alkali (Ca, Na) metasomatism in association with the development of iron-rich breccias displaying V, Cu and Ag enrichment (e.g., Moran Lake Upper C Zone deposit) and may represent so-called iron-oxide-copper-gold (IOCG) mineralization within the region.

Metamorphic–metasomatic styles of mineralization are primarily hosted within felsic metavolcanic and pelitic metasedimentary rocks and commonly display a fundamental structural control. Within the CMB, this style of mineralization is currently the most economically significant with respect to the associated uranium resource and includes the high-grade Kitts deposit, as well as the lower grade, larger tonnage, Michelin and Jacques Lake deposits. The largest deposit in the region, the Michelin deposit, is associated with the development of strong sodium metasomatism and may be related to the so-called ‘metasomatite’ or ‘albite’ style of uranium mineralization.

Sedimentary-hosted mineralization primarily occurs within terrestrial sedimentary rocks; here uranium mineralization is associated with localized reduced zones within an otherwise oxidized sedimentary sequence. This style of mineralization has several affinities to sandstone-hosted mineralization, known mostly from Phanerozoic sequences, or to some mineralization associated with Proterozoic unconformity-style deposits.

U–Pb geochronological data from the region is used to bracket the timing of the various styles of uranium mineralization into four main mineralizing events. Uranium mineralization within the eastern CMB is primarily bracketed between 2030‒1880 and 1860‒1800 Ma. In more western parts of the region, uranium mineralization is bracketed between 1860‒1660, and later than 1650 Ma. There is some overlap in the timing of mineralization between the eastern and western CMB, and the possibility exists for a common mineralizing event between these two regions; however, further study is required to investigate such a relationship. U–Pb geochronological results from titanite and monazite also provide additional data for several deformational events that are syn- to post-development of uranium mineralization. Data obtained as part of this study highlight the Makkovikian (1900‒1710 Ma), Labradorian (1710‒1620 Ma) and Grenvillian (ca. 1000 Ma) orogenies, as locally playing a role in the formation and/or local remobilization of uranium mineralization in the region.

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