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.

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More than 70 breccia pipes lie along northwesterly trends near Spanish valley in Grand and San Juan Counties, a few kilometers southeast of Moab, Utah. The structures generally are roughly oval in plan and only several tens of meters in diameter, but are inferred to extend downward about 1,000 m. The pipes contain a breccia that has been dropped as much as several hundreds of meters by solution collapse. Much sandstone in the breccia has been decemented and in places has flowed, as shown by foliation and sandstone dikes. Contacts of the breccia and country rock are sharp. The country rock is unaltered. The structures apparently formed in the Tertiary and may be contemporary with igneous intrusions of the nearby La Sal Mountains. The breccia pipes probably result from solution of deeply buried salts and carbonate rocks by migrating waters heated by the igneous intrusions, followed by upward stoping of younger strata. The breccia pipes of Spanish valley and environs are not known to be mineralized, but they resemble uranium-and copper-bearing breccia pipes elsewhere on the Colorado Plateau.

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