Author : Suzanne Mickey Costaschuk
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (145 download)
Book Synopsis Uraniferous Pegmatites in the Grease River Area, Northern Saskatchewan by : Suzanne Mickey Costaschuk
Download or read book Uraniferous Pegmatites in the Grease River Area, Northern Saskatchewan written by Suzanne Mickey Costaschuk and published by . This book was released on 1979 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study involves a portion of the Western Craton subdivision of the Churchill structural province of northern Saskatchewan. It is a detailed study of radioactive pegmatites bordering the Grease River in the Fond-du-Lac map area. Results from field, microscopic, oxygen stable isotope, O-Th-Pb mineral age dating, heavy mineral and electron microprobe mineral studies are used to summarize the geology and uranium mineralization of the Grease River property. The Precambrian basement is comprised of Tazin Group biotite gneisses and pink felsic gneisses. The thinly banded plagioclase-quartz -biotite gneisses developed under middle amphibolite facies metamorphism. The coarser-grained, leucocratic, K-feldspar-plagioclase-quartz-biotite gneisses are evidence of upper amphibolite facies conditions. The pelitic and felsic gneisses formed contemporaneously during a regional metamorphic event involving high temperatures and pressures. Petrological evidence suggests the biotite gneisses formed from low Al, Ca and high Fe, Mg, Ti argillaceous sediments, while the granitic rocks were derived by partial melting of a source similar in compostion to the more mafic units. White, massive pegmatites intrude and migmatize the Tazin Group assemblages. They mainly vary in compositon from trondhjeaite to two-feldspar and alaskite granites depending on the extent of K-metasomatism. The initial plagioclase-guartz-biotite trondhjemitic melt likely formed at temperatures greater than 685°C. At the time of intrusion, high temperatures existed which thermally metamorphosed and melted the gneisses. A later intrusive phase involving qua rtz-m usco vite veining, transformed some white pegmatites into quartz-rich granitoids and quartzolites. The silrcifiction took place during hypothermal conditions (300 to 50U°CJ which, consequently caused extensive alteration of the affected rocks. Zircon separates from biotite and granitic gneisses yield mid-Aphebian d-Pb dates of 2250 Ma. These results are interpreted as Kenoran (2500 0a) survival ages, up-dated by the younger Hudsonian orogeny which essentially re-set their U-Pb radiometric clocks. The white pegmatites have originated from more intensely remobilized portions of the Archean crust. The main trondhjemite to granite pegmatite is dated at 1970 0a, while the late-stage quartz enrichment yields 1845 Ma ages. Condiderable tectonic activity occured during the Hudsonian reactivation. Shearing, plastic deformation and major faulting of the biotite and granitic gneisses are observed in the affected portions of the Grease Fiver linear belt. Also, structural control of the emplacement of the syntectonic pegmatites is inferred since they form in an elongated, discontinuous zone paralleling the NE regional strike. Uranium mineralization is localized in the white pegmatites. Two periods of uranium enrichment are inferred from radiometric, geochronological, petrological and probe studies. In the first, cubic, Th-rich uraninite crystallized with the plagioclase-quartz-biotite assemblage. Common accessories are zircon, molybdenite, apatite, sphene, thorite and iron opaques. A second mineralization period occured during the hydrothermal silicification of the initial pegmatites. Uranium enriched zircons,thorium-bearing minerals and yellow uranyl mineralization are believed to have formed during this time.
