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At least 1,099 records · Page 61Linked to original sources
USGS1983

Geologic interpretation of geophysical data for the Wadi al Jarir and Al Jurdhawiyah quadrangles, sheets 25/42 C and D, Kingdom of Saudi Arabia

Interpretations of aeromagnetic and gravity data made in support of geologic mapping clearly outline the near-surface shape of Proterozoic granitic units in the Wadi al Jarir (25/42 C) and Al Jurdhawiyah (25/42 D) 1:100,000-scale quadrangles of the northern part of the Arabian Shield. The aeromagnetic data show marked correlation with the surface geology, and the resulting interpretation defines nine magnetic provinces inferred to reflect bodies of granitic rock possessing homogeneous magnetic properties. Several magnetic lineations of possible structural significance are identified and probably relate to Najd faulting. Older structures of the Hijaz tectonic cycle cannot unequivocally be defined. Four of the younger granitic bodies are interpreted to be tabular in cross-section and of finite thickness on the basis of magnetic anomalies defined by high-amplitude, short-wavelength, positive anomalies along the southern margin of the body and counterpart negative anomalies along the northern margin. One of these bodies, a granodiorite porphyry in the northwestern part of the Al Jurdhawiyah quadrangle, is estimated to be from 4 to 7 km thick on the basis of calculations of gravity data. Older granites possess no edge anomalies and therefore are interpreted to extend to greater depth. Peralkaline granites are distinctively nonmagnetic and are identifiable in the aeromagnetic data as areas of little magnetic relief. Correlation of aeromagnetic data and mineral deposit information provide justification for some prospecting guides. Small granodiorite-porphyry plutons with distinct edge anomalies in Murdama metasediments commonly are associated with copper-gold-bearing quartz veins. Vein orientations in these and most other known deposits in the northeastern Shield cannot be sensibly related to the stress field of the Najd fault system, and are believed to predate the Najd or to have been governed by local factors. Small, weakly magnetic targets such as the Bald al Jimalah West tungsten deposit are not indicated by the regional magnetic data.

Open-File Report↗
USGS1983

Geologic and geophysical investigations of Climax Stock intrusive, Nevada

The Climax stock is a composite granitic intrusive of Cretaceous age, composed of quartz monzonite and granodiorite, which intrudes rocks of Paleozoic and Precambrian age. Tertiary volcanic rocks, consisting of ashflow and ash-fall tuffs, and tuffaceous sedimentary rocks overlie the sedimentary rocks and the stock. Erosion has removed much of the Tertiary volcanic rocks. Hydrothermal alteration of quartz monzonite and granodiorite is found mainly along joints and faults and varies from location to location. The Paleozoic carbonate rocks have been thermally and metasomatically altered to marble and tactite as much as 457 m (1,500 ft) from the contact with the stock, although minor discontinuous metasomatic effects are noted in all rocks out to 914 m (3,000 ft). Three major faults which define the Climax area structurally are the Tippinip, Boundary and Yucca faults. North of the junction of the Boundary and Yucca faults, the faults are collectively referred to as the Butte fault. The dominant joint sets and their average attitudes are N. 32? W., 22? NE; N. 60? W., vertical and N. 35? E., vertical. Joints in outcrop are weathered and generally open, but in subsurface, the joints are commonly filled and healed with secondary mineral s. The location of the water table and the degree of saturation of the granitic rocks are presently unknown. Measurement from drill holes indicated that depth to perched water levels ranges from 30 to 244 m (100-800 ft). Recent field investigations have shown the contact between the Pogonip marble and the granodiorite is a contact rather than a fault as previously mapped. The thickness of the weathered granodiorite is estimated to be 8 to 46 m (25 to 150 ft).

Open-File Report↗
USGS1983

Sourcebook of locations of geophysical surveys in tunnels and horizontal holes including results of seismic-refraction surveys, Rainier Mesa, Aqueduct Mesa, and Area 16, Nevada Test Site

Seismic refraction surveys have been obtained sporadically in tunnels in zeolitized tuff at the Nevada Test Site since the late 1950's. Commencing in 1967 and continuing to date (1982), extensive measurements of shear- and compressional-wave velocities have been made in five tunnel complexes in Rainier and Aqueduct Mesas and in one tunnel complex in Shoshone Mountain. The results of these surveys to 1980 are compiled in this report. In addition, extensive horizontal drilling was initiated in 1967 in connection with geologic exploration in these tunnel complexes for sites for nuclear weapons tests. Seismic and electrical surveys were conducted in the majority of these holes. The type and location of these tunnel and borehole surveys are indexed in this report. Synthesis of the seismic refraction data indicates a mean compressional-wave velocity near the nuclear device point (WP) of 23 tunnel events of 2,430 m/s (7,970 f/s) with a range of 1,846-2,753 m/s (6,060-9,030 f/s). The mean shear-wave velocity of 17 tunnel events is 1,276 m/s (4,190 f/s) with a range of 1,140-1,392 m/s (3,740-4,570 f/s). Experience indicates that these velocity variations are due chiefly to the extent of fracturing and (or) the presence of partially saturated rock in the region of the survey.

Nevada↗
USGS1983

Selected physical properties of rocks from the Baid al Jimalah West tungsten deposit, Kingdom of Saudi Arabia, and recommendations for geophysical surveys

Bulk density and magnetic susceptibility of 11 outcrop samples representing the Proterozoic lithologic units at the Baid al Jimalah West tungsten deposit, Kingdom of Saudi Arabia were measured. Induced polarization response, apparent resistivity, and electromagnetic conductivity were determined for four specimens of the sample suite. Measurements show that there is a negative density contrast of about -0.17 g-cm^-3 between metasedimentary rocks of the Murdama group and the Bald al Jimalah graaite and that this contrast decreases with increasing mineralization of the granite. Similarly, the bulk magnetic susceptibility of the granite is about one-third that of the Murdama rocks for this sample suite; however, magnetic susceptibility increases with increasing mineralization in the granite specimens. Electromagnetic conductivities are uniformly low, in part because the specimens are weathered, but probably also because intense silicification accompanies the mineralization. Induced polarization chargeability increases in the granitic specimens with increasing mineralization and reflects higher percentages of sulfide minerals. Chargeability for the mineralized rocks is about four times higher than for the Murdama host rocks, and apparent resistivity values are about one-fifth the values of host rocks. Based on these results, it is recommended that during reconnaissance exploration of the area 15 detailed high-precision gravity profiles at 10 m to 50 m station spacing and eight induced polarization dipole-dipole profiles at 25 m dipole spacing and maximum 'n' of 6 be measured. To help define subsurface structure, a high-precision, ground-magnetic survey (map at 2-gamma contour interval) and a four-channel gamma ray spectrometric survey on a 25x50 m grid covering the area of the profiles are recommended.

Open-File Report↗
USGS1983

Geologic, geotechnical, and geophysical properties of core from the Acme Fire-Pit-1 drill hole, Sheridan County, Wyoming

A preliminary core study from the Acme Fire-Pit-1 drill hole, Sheridan County, Wyoming, revealed that the upper portion of the core had been baked by a fire confined to the underlying Monarch coal bed. The baked (clinkered) sediment above the Monarch coal bed was determined to have higher point-load strength values (greater than 2 MPa) than the sediment under the burned coal

Open-File Report↗
USGS1983

Geophysical investigations in the Dhahar-Al Hajrah region, Wadi Malahah Quadrangle, southwestern Saudi Arabia

Crone electromagnetic, self-potential, and induced polarization surveys were conducted in the Dhahar-Al Hajrah region, southwestern Saudi Arabia, in support of geological and geochemical exploration for volcanogenic sulfide deposits. Although a previous, airborne electromagnetic survey found no anomalies in the vicinity of the ancient mines in the region, surface indications of anomalous copper and zinc at both Dhahar and Al Hajrah are abundant. Reconnaissance Crone electromagnetic traverses across the Dhahar prospect area delineated numerous conductive zones, but none had a dip-angle anomaly of more than 10?. Similar results were obtained at Al Hajrah. With one or two encouraging exceptions, self-potential surveys at Al Hajrah showed only broad gradients and anomalies having amplitudes of less than 40 mV. Dipole-dipole induced polarization surveys at Al Hajrah delineated two nearly continuous polarizable zones having an aggregate strike length of almost 7 km. The two zones are symmetrically disposed on either side of a median aplitic dike and may lie on opposing limbs of a south-plunging antiform. Chargeabilities in the anomalous zones are weak to moderate but in most places are clearly associated with anomalous copper and (or) zinc concentrations found by surface sampling. Ground electromagnetic traverses are recommended to determine the most conductive intervals of anomalous induced polarization effect in the anomalous zones; these conductive intervals should then be tested by drilling, where appropriate. Reconnaissance self-potential traverses are also recommended at Dhahar, and additional ground electromagnetic surveys are recommended across two airborne electromagnetic anomalies located immediately southeast of the Al Hajrah target.

Open-File Report↗