Geology of the Upper Precambrian Flambeau Quartzite, Chippewa County, North-Central Wisconsin
1981-12
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Geology of the Upper Precambrian Flambeau Quartzite, Chippewa County, North-Central Wisconsin
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1981-12
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The Upper Precambrian Flambeau Quartzite of north-central Wisconsin is exposed only on Flambeau Ridge, near the confluence of the Chippewa and Flambeau Rivers. Contacts with adjacent rock uits are covered by glacial drift. Available geophysical data and information from nearby outcrops, diamond drill holes and water-wells indicate that the Flambeau is probably underlain by felsic volcanics and/or granite. The formation is an outlier in the Middle (?) Precambrian Flambeau Volcani-Sedimentary Province. Flambeau Ridge is a 120 meter high linear monadnock which trends east-west. Outcrops indicate that the quartzite is at least 800 meters thick. The structure of the formation is a steep syncline which plunges sharply to the northwest. The most abundant lithology of the Flambeau Quartzite is quartz arenite. Variations in pebble and matrix content create a wide range in texture and composition. Many lithologies are conglomeratic. Framework grains are mostly rounded common and polycrystalline quartz. Sand- and pebble-sized grains of vein quartz, chert, argillite, iron-formation, quartzite and felsic volcanics are also present. Heavy minerals include rounded to well-rounded magnetite, hematite, zircon and tourmaline. These components suggest a dominant quartz-rich sedimentary source, with contributions from felsic igneous and high-grade metamorphic terranes. Paleocurrent data show that the source terrane was probably located to the west and southwest of the outcrop area. The Flambeau Quartzite has been correlated with the Upper Precambrian Barron Quartzite by some investigators. The southeast edge of the Barron Quartzite is exposed approximately 20 miles (30 Km.) northwest of Flambeau Ridge. The Barron is thin (200 meters) but areally extensive and mostly flat-lying. The basal contact is exposed in outcrop; rocks which unconformably underlie the Barron are Lower and Middle Precambrian granites, slates and metavolcanics. Based on limited petrographic and heavy mineral data, the Barron is very similar to the Flambeau, although it is finer-grained and better sorted. In addition, the Barron contains layers of argillite which are interbedded with quartzite. Source materials were predominantly quartz-rich sedimentary rocks including iron-formation and quartzite. Paleocurrent data are sparse and scattered, and suggest southerly and northerly sources for the Barron. This crude bimodal pattern may be the result of marine (tidal) or lacustrine deposition. The Flambeau and the Barron are lithologically similar, and probably shared a common source terrane. Various lines of evidence indicate that the two quartzites occupy the same stratigraphic position. It is probable that they are correlative and are lateral equivalents. The apparent differences between the two formations in thickness, structure and texture may be due to differences in their respective depositional environments. The Flambeau Quartzite is probably a braided stream deposit; the poorly sorted, pebbly texture, local abundance of c1ayey fragments and matrix, and unimodal paleocurrent pattern with low variance (2500) strongly support this interpretation. The Barron Quartzite exhibits features of both marine-shelf-and braided stream deposits. The high variance (7000) of cross-bed azimuths in the Barron is characteristic of marine deposition. Features which imply fluvial deposition of the Barron include mud-chip conglomerates and high-angle (>20°) tabular cross-bedding. Important controls on the sedimentation of both quartzites were the lack of land vegetation, aeolian transport and intense weathering. The tectonic environment was stable during deposition and was probably cratonic. The Flambeau and Barron Quartzites probably are correlative with other Upper Precambrian quartzites in the region, including the Baraooo, Waterloo, Sioux, and McCaslin Quartzites. Radiometric ages and other data indicate deposition of some of these formations after a 1760 m.y. igneous event, and prior to a 1630 m. y. metamorphic-deformational event. Radioactivity of the Flambeau conglomerate is due to placer-like deposition of zircon grains. The possibility of placer gold in the Flambeau should not be overlooked, but it is not supported by heavy mineral data.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Frederick Kedney Campbell in partial fulfillment of the requirements for the degree of Master of Science, December 1981. Plate 1 referenced in the thesis is also attached to this record.
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Campbell, Frederick Kedney. (1981). Geology of the Upper Precambrian Flambeau Quartzite, Chippewa County, North-Central Wisconsin. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/220195.
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