Geology, geochemistry and metallogeny of the Burnt Lake area, central mineral belt, Labrador, Canada

Mackenzie, Leonard M. (1991) Geology, geochemistry and metallogeny of the Burnt Lake area, central mineral belt, Labrador, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Burnt Lake area, located within the central region of the Central Mineral Belt of Labrador, is underlain by the Early Proterozoic (1855 Ma) supracrustal sequence of the Upper Aillik Group felsic volcanic and associated sedimentary rocks. Intruded into this volcanic pile is the 1650 Ma Burnt Lake Granite, a high level, leucocratic, post-tectonic granite. -- The area was the focus of uranium exploration in the late 1970's and hosts open pit reserves of 140,000 tonnes grading 0.082% U₃O₈. -- Uranium was originally deposited (1855 Ma) by subvolcanic leaching of volcanic glasses and concentration during K- metasomatic alteration of the felsic volcanic rocks (Burnt Lake Potassic Showing) and later upgraded during a period of magmatic and metamorphic activity between 1800 Ma - 1740 Ma (Burnt Lake Sodic, Emben amd Aurora River Showings). This produced uranium enrichments associated with intense Na- metasomatism and is characterized as epigenetic-hydrothermal. -- Base metal (and possibly some uranium) mineralization was later superimposed on the Burnt Lake uraniferous occurrences which originated as magmatic fluids from the Burnt Lake Granite (1650 Ma). The mineraliza-tion is characterized as epigenetic magmatic-hydrothermal (granophile) with potassium, lead, zinc, copper, fluorite and molybdenite enrichments. -- Model ages from a galena separate from Burnt Lake, hosted in felsic volcanic rocks of the Upper Aillik Group (1355 Ma) are 1651 Ma for the lower crust-type reservoir. This indicates an age of 1651 Ma for at least some of the lead mineralization derived from a magmatic source. -- An Rb/Sr isocron for the Burnt Lake Granite has produced an age of 1651 ± 140 Ma, however, the isotopic signature has been disturbed by fluid effects and a partial re-setting of the isotopic clock during the Grenville Orogeny. -- Significant concentrations of molybdenite occur near the contact of the Burnt Lake Granite and the meta-felsic volcanic rocks. Differentiation trends in geochemical data for this granite indicate vapour phase concentration towards the top of the pluton.

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