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Ogden Tweto

Publications and source records attributed to Ogden Tweto.

At least 19 recordsLinked to original sources
USGS1978

Ore deposits of the Gilman District, Eagle County, Colorado

The Gilman mining district, known also in the past as the Red Cliff district, is in the mountains of southeastern Eagle County, west-central Colorado. The district is the leading source of zinc in Colorado and one of the major base-metal mining districts in the State. As valued at the time of production, total output of zinc, silver, copper, lead, and gold through 1972 was about $328 million. About 90 percent of this total was produced after 1930. The productive part of the district is an area of about 3 square miles (7.8 square kilometers) on the northeast side of the deep canyon of the Eagle River between the small towns of Gilman and Red Cliff. The ore deposits are principally replacement deposits in dolomites of Mississippian and Devonian age and in quartzite of Cambrian age. A few productive veins occur in Precambrian rocks. The replacement deposits crop out in the cliffs of the canyon wall and extend northeastward downdip beneath Battle Mountain, which is composed of a thick sequence of Pennsylvanian clastic rocks. The deposits were originally worked through several separate mines along the canyon wall, but since 1918, all deposits in dolomite rocks, except some small ones near Red Cliff, have been worked through the Eagle mine of the New Jersey Zinc Company at Gilman. The Gilman district lies on the eastern flank of the huge anticline of the Sawatch Range, near the steeply plunging north end of the anticline. Sedimentary rocks on the flank of this part of the anticline dip homoclinally northeastward to a synclinal axis about 8 mi (miles) (13 km (kilometers> northeast of Gilman and then rise more steeply to the Gore fault at the edge of the Gore Range. The homocline is broken by only a few faults most of which have displacements of less than 100 ft (feet) (30 m (meters>. In contrast, the underlying Precambrian rocks are broken by numerous faults and shear zones related to the Homestake shear zone, a northeast-trending master shear zone several miles wide. Fractures and shear zones along the northwest side of the master zone extend beneath the Gilman district. The Gilman district is at the northwestern edge of the northeast-trending Colorado mineral belt as defined by mineralized areas and bodies of intrusive porphyries. Neighboring mining districts in the mineral belt to the southeast of Gilman are the Kokomo lead-zinc district, 13 mi (21 km) distant; the Climax molybdenum district, 16 mi (26 km) distant; and the Leadville district, 20 mi (32 km) distant. These districts, as well as others farther away, are characterized by abundant intrusive rocks of Laramide and middle Tertiary ages and by complex faults systems. The Gilman district, in contrast, contains only a single sill of porphyry and has very simple geologic structure. This probably reflects a position either at the side of or high above a batholith that is inferred from geologic and geophysical data to underlie the mineral belt at shallow depth. The rock column preserved in the district consists, in succession downward, of (1) grit, conglomerate, sandstone, and shale of the Pennsylvanian Minturn Formation, as much as 6,300 ft (1,920 m) thick; (2) shale, limestone, and. sandstone of the Pennsylvanian Belden Formation, 200 ft (61 m) thick; (3) a sill of quartz latite porphyry of the Cretaceous Pando Porphyry about 80 ft (24 m) thick intruded in the basal shale of the Belden Formation; (4) dolomitized limestone of the Mississippian Leadville Dolomite, 110-140 ft (34-43 m) thick; (5) sandstone and sandy and cherty dolomite of the Mississippian or Devonian Gilman Sandstone, 15-50 ft (4.5-15 m) thick; (6) thin-bedded primary or diagenetic dolomite of the Mississippian(?) and Devonian Dyer Dolomite, 50-80 ft (15-24 m) thick; (7) quartzite, conglomerate, and green shale of the Devonian Parting Formation, 35-50 ft (11-15 m) thick; (8) sandstone and shale of the Ordovician Harding Sandstone, 14-80 ft (4.2-24 m) thick; (9) shaly and sandy dolomite and dolom

Professional Paper↗
USGS1974

Geologic map and sections of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado

This map was first published as a printed edition in 1974. The geologic data have now been captured digitally and are presented here along with images of the printed map sheets. The map encompasses the area of four 7.5-minute quadrangles between 39º15' and 39º 30'N and 106º15' and 106º30'W in the Sawatch and Gore mountain ranges, and upper part of the Arkansas River drainage in central Colorado. The Holy Cross geologic map depicts in detail the complex geology at the north end of the Sawatch Range on the west at its junction with south end of the Gore Range on the east. The ranges are separated in the southern part of the map area by the upper reaches of the Arkansas River, and in the northeast part by the narrow valley of the upper Eagle River. Sixty map units and numerous individual beds and thin units within the principal map units are shown. Paleoproterozoic and Mesoproterozoic metamorphic rocks are the principal rocks of the Sawatch Range. In the Gore Range, lower and upper Paleozoic sedimentary rocks rest unconformably on the Precambrian metamorphic rocks. Paleozoic rocks that range in age from Upper Cambrian though Middle Pennsylvanian support the Gore Range along the eastern quarter of the map. The sequence includes a basal quartzite overlain by interbedded, shale, dolomite, quartzite, and sandstone. The Leadville Dolomite, below the dark shale, is the host rock for the ore deposits at Leadville and the neighboring lead-zinc-silver districts. A wide range of Miocene to Cretaceous intrusive rocks dip east off the Sawatch Range. The Dry Union Formation of Pliocene and Miocene age fills the valley of the Arkansas River and is covered by Quaternary alluvium and glacial sediment. Glacial deposits of Bull Lake, Pinedale, and neoglacial age are present in many of the mountain valleys. The geologic structure of the quadrangle is complex in geometry and time with a distinct structural and geographic break along the west front of the Gore Range in the eastern quarter of the quadrangle. In general, Paleozoic strata intruded by Tertiary and Cretaceous irregular linear plutons and sills of the Gore Range are tilted east from the Sawatch Range. These rocks are broken by major normal faults in a complex pattern commonly associated with Paleocene? and Cretaceous intrusive porphyries. In the Sawatch Range, two large Precambrian igneous complexes are separated by a broad shear zone of Precambrian age that extends northwest across the quadrangle and beneath Paleozoic rocks of the Gore Range. Down-to-valley normal faults define the margins of the Arkansas and upper Eagle River valleys. The Leadville, Sugarloaf, and St. Kevin districts have produced significant amounts of silver. The Homestake mine at the head of West Tennessee Creek produced silver and lead from veins bearing siderite and barite. Scattered veins in shear zones along Homestake Creek are mainly argentiferous galena veins; some are quartz and copper. Veins at Holy Cross City produced gold. Other veins in the area have produced gold, silver, and minor amounts of copper.

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