Geology of the Negaunee quadrangle, Marquette County, Michigan

Abstract

The Negaunee quadrangle covers about 52 square miles of the east-central part of Marquette County, Mich. Most of the area is of low relief, drainage is not integrated, and glacial deposits cover more than half the area.Rocks of Precambrian age underlie the entire quadrangle. Lower Precambrian granitic and mafic metavolcanic rocks border two areas of downfolded• middle Precambrian metasedimentary rocks of the Marquette Range Supergroup. The downfolded rocks form the Eagle Mills syncline on the north limb of the Marquette synclinorium in the southern part of the quadrangle and the eastern part of the Dead River basin in the west-central part of the quadrangle. The middle Precambrian rocks are unconformable against the older rocks, but faulting has juxtaposed rocks of different ages. Keweenawan diabase dikes cut most of the older Precambrian rocks.Lower and middle Precambrian rocks are metamorphosed. Early metamorphism converted the volcanic rocks to amphibolite near the Compeau Creek Gneiss; later, lower grade metamorphism converted most of the other rocks to the chlorite grade. The Keweenawan diabase dikes are not metamorphosed.Lower Precambrian rocks are ma:fic to intermediate metavolcanic rocks and felsic intrusive rocks. The metavolcanic rocks include the Kitchi Schist and the Mona Schist. The felsic rocks include the Compeau Creek Gneiss and Dead River pluton, which have intruded the Mona Schist.The Kitchi Schist, the oldest formation in the quadrangle, is gray-green pyroclastic rock ranging from lapilli tuff to agglomerate with clasts as large as 5 inches. Chemically, the rocks ra:nge from dacite to rhyodacite but are dominantly dacitic. The formation is nearly equivalent in age to subaqueous pillow lavas in the lower member of the Mona Schist. Maximum thickness in the quadrangle is about 4,500 feet.The Mona Schist consists mainly of metabasalt and layered amphibolite and is here divided into four members: lower member, Nealy Creek Member, sheared rhyolite tuff member, and Lighthouse Point Member. Undifferentiated greenstone is mapped in two areas. Total thickness of the formation is about 23,000 feet.The lower member of the Mona Schist, about 10,000 feet thick, is dark-green fine-grained massive metabasalt characterized in many outcrops by large pillow structures. Layers of pillows dip steeply, and the top direction is to the north. Small, widely separated quartz and quartz-carbonate veins contain sparse copper minerals. Axinite occurs as large crystals in a quartz-calcite vein.The Nealy Creek Member of the Mona Schist, 2,000-3,000 feet thick, is greenish gray quartz-sericite-chlorite schist, near rhyodacite in composition, and originally was an air-fall tuff. Cataclastic deformation is common.

The Sudbury impact layer in the Paleoproterozoic iron ranges of northern Michigan, USA

“…On the positive side, the iron ranges of the region have been mined and explored for more than 150 years, and extensive collections of mineral exploration drill core are available in public repositories or have been made available to us by mining companies, which has helped greatly in overcoming the lack of natural exposures. In two cases (McClure and Iron River-Crystal Falls), the Sudbury impact layer is thick and extensive enough to constitute a mappable unit and, although not recognized as impactrelated rocks at the time of mapping, appears as breccia beds on U.S. Geological Survey (USGS) 1:24,000 scale geologic maps (Puffett, 1974;Clark et al, 1975;James et al, 1968).…”

“…Its base is ~300 m stratigraphically above the basal unconformity with Archean volcanic rocks. The area has been mapped in detail (Puffett, 1974;Clark et al, 1975), and the Sudbury layer is thick and continuous enough to be mapped as a unit for ~10 km along strike (mapped as chert conglomerate and breccia). We have divided the Sudbury layer here into two lithologic types, a lower chert breccia unit and an upper sandstone unit.…”

Boundary between Archean greenstone and gneiss terranes in northern Wisconsin and Michigan

“…2); they are covered locally-in the Dead River, Clark Creek, and Baraga basins-by strata of the middle Precambrian Schist is composed of pillowed and massive basalt and layered amphibolite; the amphibolite is interpreted as metamorphosed mafic tuff (Gair and Thaden, 1968, p. 12). The Kitchi Schist is mainly a pyroclastic rock of latitic to dacitic composition that is approximately the same age as the lower part of the Mona Schist (Puffett, 1974). The available data indicate that the regional metamorphic grade is greenschist facies but that amphibolitefacies metamorphic assemblages were formed adjacent to the intrusive granitic rocks.…”

“…4). The diabase dikes are described (Gair and Thaden, 1968;Puffett, 1974;Schmidt, 1976) as containing dominant plagioclase (An«-7o) and clinopyroxene, mainly augite but partly pigeonite. Small amounts of olivine or its alteration products and magnetite are present.…”

Water supply potential of the Lake Sally System, Marquette County, Michigan

“…4). The Negaunee Iron-formation, characterized by parallel laminae of chert and iron minerals (Puffet, 1974), is the principal source of iron ore throughout the Marquette Iron Range. Mineral composition and fracturing make the Negaunee Iron-formation less resistant to erosion than the greenstone bodies.…”