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Geology topics

David M. Miller

Publications and source records attributed to David M. Miller.

100 records · Page 6Linked to original sources
USGS1990

Chapter 7: Jurassic granitoids and related rocks of the southern Bristol Mountains, southern Providence Mountains, and Colton Hills, Mojave Desert, California

Jurassic plutons in the east-central Mojave Desert region are markedly different from older and younger Mesozoic plutons in the region. They form a chemically and texturally heterogeneous group that ranges in composition from diorite to syenogranite; some phases are alkalic. Igneous rocks in the southern Bristol Mountains, southern Providence Mountains, and Colton Hills are subdivided into five broadly defined groups on the basis of field relations and geochemistry: mafic intrusive rocks; mixed intrusive rocks, consisting of subequigranular and porphyritic subgroups; felsic intrusive rocks; metavolcanic and hypabyssal rocks; and dikes. There is a general trend from older, more mafic and heterogeneous rocks to younger, more felsic and homogeneous plutonic phases. Extreme spatial variations in composition and texture and other field relations indicate that the plutons were intruded during a relatively short time span. Field relations also indicate that the plutons were intruded at upper crustal levels. The plutons were affected by extensive late- or early post-magmatic sodium metasomatism (albitization), which resulted from the introduction and circulation of predominantly meteoric fluids. We propose that the plutons in this region were derived from compositionally heterogeneous but genetically related magmas generated from an upper mantle/lower crustal amphibolitic source. Similar Jurassic rocks are found elsewhere in the southern Cordillera, indicating that the genesis of these unusual rocks is a regional phenomenon.

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USGS1987

COGEOMAP; a new era in cooperative geologic mapping

A program of cooperative geologic mapping was established between the U.S. Geological Survey and the State geological surveys in fiscal year 1985. The main purpose of the program is to increase general-purpose geologic mapping throughout the Nation. By combining State and Federal resources for geologic mapping through this cooperative program, new mapping has been started, and both geologic and geophysical maps that resulted from the program have already been published. The program grew from mapping projects in 18 States in fiscal year 1985 to a program involving 29 States in 1986, as the combined State and Federal resources in the program grew from about $2 million to nearly $3 million. As the program enlarges its scope, it faces the challenge of producing high-quality maps with uniform standards while promoting the use of new technologies to increase the speed of geologic and geophysical mapping and map production.

Circular↗
USGS1986

Mineral resources of the Castle Peaks Wilderness Study Area, San Bernardino County, California

The Castle Peaks Wilderness Study Area (CDCA266) comprises approximately 45,000 acres in the northern New York Mountains, San Bernardino County, California. At the request of the Bureau of Land Management, 39,303 acres of the wilderness study area were studied. The area was investigated during 1982-1985 using combined geologic, geochemical, and geophysical methods. are considered preliminarily suitable for wilderness deignation. There are no mineral reserves or identified resources in the study area. Fluorspar, occurring in sparse veins, has moderate resource potential, as do silver and lead in fault zones, and gold and silver in sparse, high-grade veins and fault breccia. Each area of moderate resource potential encompasses less than one square mile. These same commodities have low resource potential in similar occurrences throughout much of the study area. In addition, there is low resource potential for gold in placer deposits, uranium in altered breccia and gouge, and rare-earth elements in pegmatite dikes. There is no resource potential for oil and gas resources over most of the study area, but the potential is unknown along its western margin. In this report, the area studied is referred to"the wilderness study area", or simply "the study area."

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