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E. A. Du Bray

Publications and source records attributed to E. A. Du Bray.

52 records · Page 3Linked to original sources
USGS1984

Reconnaissance geology of the Al Mukhul Quadrangle, sheet 26/42 B, Kingdom of Saudi Arabia

The Al Makhul quadrangle (26/42 B) lies in the northern part of the Arabian Shield between lat 26°30' and 27°00' N. and long 42°30' and 43°00' E. Amphibolite, the oldest metamorphic rock exposed in the quadrangle, crops out in a restricted area in the south-central part of the quadrangle. Younger, weakly metamorphosed rhyolite, basalt, and graywacke sandstone on the west edge of the quadrangle are correlated with lithologically similar rocks exposed to the southwest that comprise the Hibshi formation. The Turmus formation, located in the north-central part of the quadrangle, is composed of weakly metamorphosed andesite flow rocks, andesitic agglomerate, and related volcanic graywacke and is similar in metamorphic grade, age relations with intrusive rocks, and structural character to the rocks on the west edge of the quadrangle; it is thought to be approximately coeval with them. Seven plutonic units, ranging in composition from gabbro and diorite to alkali-feldspar granite, intrude the weakly metamorphosed rocks. Some of these plutons are offset along a northwest-trending fault of the Najd fault system but their emplacement postdates all other major tectonic episodes in the area. The weakly metamorphosed rocks were deposited on an erosional surface underlain by a pluton composed of quartz diorite. Quaternary alkali basalt crops out in the northwest part of the quadrangle. These rocks are at the southeast edge of Harrat al Hutaymah, a basalt field composed of flow rocks, tuff rings, and cinder cones. Mineral potential in the quadrangle is low. At a very small prospect pit in the north-central part of the quadrangle, massive, milky quartz veins cutting weakly metamorphosed volcanogenic sedimentary rocks are stained blue and green by copper minerals. A previously reported mine site in the southern part of the quadrangle was not relocated.

Open-File Report↗
USGS1983

Geochemical evaluation of felsic plutonic rocks in the eastern and southeastern Arabian Shield, Kingdom of Saudi Arabia

In a geochemical evaluation of the eastern and southeastern Arabian Shield, which included collection of 696 rock samples and 694 pan concentrate samples, a province of tin-anomalous granitoid plutons was defined. Pan concentrates collected in and around these plutons were enriched in tin and tungsten relative to the concentrate population. Rock samples of these leucocratic, muscovite-bearing, peraluminous granites contained anomalously high concentrations of lithium, fluorine, beryllium, lead, rubidium, niobium, yttrium, tin, bismuth, silver, and tungsten. Ten tin-anomalous plutons were located in the study area. The plutons are typically small, less than 10 km2 in areal extent, and circular to elliptical in plan view. The resource potential of these latest Proterozoic plutons has not been established; economically exploitable concentrations of tin, tungsten, molybdenum, or zinc may be present, and followup studies are warranted. Further, two of the plutons are characterized by higher than normal total-count radioactivity and have potential for uranium, thorium, or rare-earth element deposits.

Open-File Report↗
USGS1983

Reconnaissance geology of the Jabal Saq Quadrangle, sheet 26/43 C, Kingdom of Saudi Arabia

The Jabal Saq quadrangle is located in the northeastern part of the Arabian Shield at the northern end of the Najd region between lat 26?00' and 26?30' N. and long 43?00' and 43?30' E. The northeastern two-thirds of the quadrangle is underlain by Paleozoic sedimentary rocks, the southwestern one-third by Proterozoic metamorphic and igneous rocks. The oldest rocks in the quadrangle are weakly metamorphosed immature sandstones that may correlate with the Murdama group. They have been intruded by several large plutons ranging in composition from mafic granodiorite to syenogranite. A densely developed fracture cleavage cuts the metamorphic rocks; otherwise, no structural features were recorded. The quadrangle has low mineral potential; no ancient mines were identified. The Dharaymeeah syenogranite forms a large pluton and bears some petrologic resemblance to alkali granites identified elsewhere in the Arabian Shield that have documented potential for containing deposits of lithophile rare metals. Analyses of wadi sediment samples collected in the quadrangle suggest that the syenogranite may also be enriched in some of these elements. The anomalously radioactive Usba monzogranite resembles highly evolved peraluminous granite plutons that elsewhere in the world are associated with deposits of tin and tungsten.

Open-File Report↗
USGS1983

Map showing distribution and classification of felsic plutonic rocks in the eastern Arabian Shield, Kingdom of Saudi Arabia

This 1:500,000-scale compilation shows the distribution of felsic plutonic rocks, lithologic types, and associated mineralization in an area between lat 21° and 24°30’ N., long 43°30’ and 46° E. It is part of a shieldwide compilation being done within the framework of Saudi Arabian Deputy Ministry for Mineral Resources projects 2.04 and 3.12.

Open-File Report↗
USGS1982

Maps and interpretation of geochemical anomalies in the John Muir Wilderness, Fresno, Inyo, Madera and Mono counties, California

A geochemical survey of the John Muir Wilderness was conducted by the U.S. Geological Survey between 1969 and 1978. The 755-mi 2 (1,956-km 2 ) wilderness is located in the central Sierra Nevada, Calif. (fig. 1). Stream-sediment samples were collected at 1,434 sites in the wilderness and immediately adjacent areas. Analytical data for these samples and a map of smapling sites are presented by du Bray and Dellinger (1980) and Diggles and others (1981). A geologic map of the area was compiled by du Bray (1981). These maps and tables present the results of the analysis of geochemical data for lead, zinc, gold, silver, arsenic, chromium, molybdenum, manganese, tungsten, tin, copper, and nickel. These are elements of economic interest which have historically been found in mineral deposits of the Sierra Nevada or other geologically similar areas.

California↗
USGS1982

Mineral resource potential map of the John Muir Wilderness, Fresno, Inyo, Madera, and Mono counties, California

Under the provisions of the Wilderness Act (Public Law 88-577, September 3, 1964) and the Joint Conference Report on Senate Bill 4, 88th Congress, the U.S. Geological Survey and the U.S. Bureau of Mines have been conducting mineral surveys of wilderness and primitive areas. Areas officially designated as "wilderness," "wild," or "canoe" when the act was passed were incorporated into the National Wilderness Preservation System, and some of them are presently being studied. The act provided that areas under consideration for wilderness designation should be studied for suitability for incorporation into the Wilderness System. The mineral surveys constitute one aspect of the suitability studies. The act directs that the results of such surveys are to be made available to the public and be submitted to the President and the Congress. This report discusses the results of a mineral survey of the John Muir Wilderness, Inyo and Sierra National Forests, Fresno, lnyo, Madera, and Mono Counties, California. The area was established as a wilderness by Public Law 88-577, September 3, 1964.

California↗
USGS1982

Reconnaissance geochemical survey of the At Taif-Al Bahah region, southern Hijaz, Kingdom of Saudi Arabia

Pan concentrates were prepared from 265 wadi sediment samples collected during a geochemical reconnaissance conducted between At Taif and Al Bahah to further assess previously identified tungsten anomalies and to locate additional mineralized rock. The samples were analyzed by semiquantitative spectrographic methods for 30 elements, and tungsten was determined by colorimetry. All determinations in excess of two standard deviations greater than the population mean are considered anomalous, although any detectable amount of tin or tungsten (detection limits 10 and 50 parts per million, respectively) is defined as anomalous. An area south of At Taif containing significant tungsten was confirmed and found to be larger than initially determined. A possible porphyry copper pluton was discovered 50 km south-southeast of At Taif. Thirty kilometers south of At Taif, a low-grade tin anomaly associated with an S-type granite was identified. In addition, the sampling identified seven anomalous areas attributable to rock geochemically atypical of the study region. Finally, although samples from the A1 Lith-Hajrah area collected for an earlier study were found to contain anomalous concentrations of tungsten, samples collected there during this study do not support those findings.

Open-File Report↗