Search USGS⌕ Search

SEARCH · Search USGS

Results for “Rocks & Minerals”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources
USGS1990

Geology and mineralization at the Ishmas Kabir gold prospect, Ishmas gold district, Kingdom of Saudi Arabia

Ishmas Kabir ancient gold mine is located approximately 60 km southeast of the city of Ranyah and 9 km northwest of Jabal Ishmas in the southwestern part of the Ishmas gold district. The mine workings are located near the eastern edge of a flat plain covered by eolian sand and drained by Wadi Bishah. Two elongate dumps, 75 m wide and 530 m long (combined length), comprise the workings. Rising 4 m above the plain, they are prominent features in this area of low relief. Core drilling (1,023 m total depth drilled) was conducted to define the extent of potential gold occurrences at the prospect. The two northeasternmost of the four holes drilled unequivocally intersected the gold-bearing main vein zone. Drill hole 1, the northeasternmost hole drilled, passed through significant lengths of altered wall rocks + quartz veins containing > 100 ppb Au (threshold value). The average gold concentration of all intercepts in drill holes 1 through 4 is 278 ppb; the total length of drill core that assayed above the gold threshold value is 13.46 m. The highest gold concentration (1,620 ppb) reported in geochemical assay results was obtained from a 0.33 m length of core in drill hole 1. Gold-intercept occurrences are not economic in the rocks drilled; no further deep drilling is recommended at this time. Gold concentrations in samples obtained from mine dumps are much higher than in drill-core samples. Samples collected by earlier workers assayed 3-7 g/t, and tonnage estimates of mine spoil have been estimated to be as high as 120,000 tons. A possible sampling bias in earlier studies may favor larger gold-enriched, samples relative to samples from quartz tailings. Further work at Ishmas Kabir should be limited to defining gold resource potential in the dumps and in the oxidized, near-surface quartz-vein system. Primary gold at the Ishmas Kabir gold prospect occurs with quartz veins and associated sericite + pyrite alteration hosted by quartz diorite and mafic dikes. The highest gold concentrations both in dumps (earlier studies) and drill core (this investigation) are found with limonite + hematite in breccia zones, in stringer veins, and in sericitic alteration envelopes surrounding quartz veins. Secondary gold is significant in this system and attests to the importance of oxidizing, acidic solutions. Quartz veins intersected by drill holes are surrounded by mylonite schist. Quartz and carbonate veins less than 5 mm thick are boudined, whereas thick quartz veins (£ 1.2 m) have disrupted and brecciated margins; mylonitized country rock envelops quartz-vein fragments. Sulfide mineralization associated with vein formation predates this rock-deformation event. Contemporaneous brittle and ductile deformation of quartz veins and country rocks occurred during the Nabitah orogeny. Supergene gold enrichment took place much later.

Open-File Report↗
USGS1991

Regional study of mineral resources in Nevada: Insights from three-dimensional analysis of gravity and magnetic anomalies

A three-dimensional interpretation of the basins of Nevada was developed based on statewide data bases of digital-gravity, magnetic, geologic, well, and topographic information. An iterative technique was applied to isostatic residual gravity anomalies in Nevada in order to define the location and shape of pre-Tertiary basement and to produce a gravity map that reflects variations of density within the pre-Tertiary basement. The dominant feature of the basement gravity of Nevada is an enormous area of low gravity that spans the entire state between latitudes 37°N and 40.5°N. This regional low strongly correlates with the distribution of middle and late Tertiary volcanic rocks and may reflect silicic intrusions within the mid-crust and upper crust that are the counterparts of volcanic rocks at the surface. Although 80% of Nevada is covered by Cenozoic deposits, these deposits are thicker than 1 km over only about 20% of the state. The remaining 60% of Nevada may have pre-Tertiary basement rocks within reach of current mineral-exploration techniques. Aeromagnetic profiles from the National Uranium Resource Evaluation (NURE) were analyzed in order to produce a map showing the location of shallow magnetic sources in Nevada. This analysis shows that 46% of the state has magnetic sources, generally Mesozoic and Cenozoic igneous rocks, within 1 km of the surface. A linear magnetic anomaly in north-central Nevada has been interpreted by others as a rift zone active during middle Miocene time. The rift also is evident in NURE magnetic profiles, but our interpretation suggests that the magnetic expression of the rift continues south-southeast with similar strike to at least 38°N and perhaps to the amagmatic zone (lat. 37°N). The survival since the middle Miocene of this narrow crustal feature, essentially linear over a distance of 500 km, is difficult to interpret in light of later Basin and Range deformation. Our analysis of gravity anomalies shows that many deep Cenozoic basins are located near the rift, yet only two basins cut across it, and at least five others change strike near the rift, as if to avoid it. The rift may have remained linear because it is associated with crustal structures that acted to resist subsequent deformation.

Nevada↗
USGS1955

Ore deposits on northwestern Chichagof Island, Alaska

The area mapped includes most of northwestern Chichagof Island. The work, started in 1946, is a continuation of the geologic mapping done in the adjoining Chichagof mining district by Reed and Coats. The gold-bearing zone recognized by these writers continues through the area mapped by the writer to the northern shore of Chichagof Island. Stratified rocks ranging in age from Paleozoic through Early Cretaceous were intruded by gabbro, quartz diorite, norite-gabbro, and by younger quartz diorite. The igneous rocks from oldest to youngest are: gabbro, diorite, quartz diorite, the rocks associated with the nickel deposits, which include gabbro-norite and quartz diorite, and basalt. The diorite is believed to have been formed during Early Cretaceous time, and the gabbro is older by an unknown amount. The gabbro and diorite are believed to be, over large areas, recrystallized older rock. The oldest group of quartz diorite intrusives in places cuts the diorite and is therefore younger. The quartz diorite is minerally somewhat foliated and slightly metamorphosed. The igneous rocks associated with the nickel deposits are the youngest of the major igneous rock groups. They intruded the Cretaceous graywacke after it had been folded to essentially its present position. Gold is the most economically important mineral commodity mined to date. The Apex and El Nido are the two largest mines in the area, but some gold has been recovered from the Goldwin and Cobol properties and small amounts from some other small prospects. In addition to gold the area includes nickel-bearing deposits at Mirror Harbor on Chichagof Island and at Bohemia Basin on Yakobi Island. Copper mineralization occurs in the area north of Goulding Harbor. An attempt has been made to outline areas favorable for prospecting based on the regional geology and, on the number and kind of quartz veins found. In general the best area for prospecting appears to be on a northwest-trending zone which extends from the head Pinta Bay to the northern end of Althorp Peninsula.

Alaska↗
USGS1981

Geochemical survey of Shining Rock Wilderness, Heywood County, North Carolina

The U.S. Geological Survey (USGS) made a reconnaissance geochemical survey of the Shining Rock Wilderness (fig. 1) to test for unidentified or unexposed mineral deposits that might be recognized by their geochemical halos. Similar geochemical survey based on trace-element analyses have been credited with the discovery of many types of mineral deposits (Hawkes and Webb, 1962). Although no metallic mineral deposits are known in the study area, the same sequence of rocks that is exposed there contains small deposits of copper-bearing sulfides 10-18 mi (16-28 km) west and southwest of the wilderness (Gair and Slack, 1979). Keith (1907, p. 8) reports minor amounts of copper sulfides and iron sulfides in schist and in quartz veins cutting schist near Retreat, 4 mi (6.5 km) northwest of the wilderness. An old gold mine, the Boylston mine, on Forge Mountain 10 mi (16 km) east of the wilderness (Nitze and Hanna, 1896, p. 181-191) is in metasedimentary rocks of the Great Smoky Group (Hadley and Nelson, 1971) which are probably younger than the rocks exposed in the wilderness.

North Carolina↗
USGS2003

Isotopes and ages in the northern Peninsular Ranges batholith, southern California

Strontium, oxygen and lead isotopic and rubidium-strontium geochronologic studies have been completed on Cretaceous and Jurassic (?) granitic rock samples from the northern Peninsular Ranges batholith in southern California. Many of these samples were collected systematically and studied chemically by A. K. Baird and colleagues (Baird and others, 1979). The distribution of these granitic rocks is shown in the Santa Ana, Perris, and San Jacinto Blocks, bounded by the Malibu Coast-Cucamonga, Banning, and San Andreas fault zones, and the Pacific Ocean on the map of the Peninsular Ranges batholith and surrounding area, southern California. The granitic rock names are by Baird and Miesch (1984) who used a modal mineral classification that Bateman and others (1963) used for granitic rocks in the Sierra Nevada batholith. In this classification, granitic rocks have at least 10% quartz. Boundaries between rock types are in terms of the ratio of alkali-feldspar to total feldspar: quartz diorite, 0-10%; granodiorite, 10-35%; quartz monzonite 35-65%; granite >65%. Gabbros have 0-10% quartz. Data for samples investigated are giv in three tables: samples, longitude, latitude, specific gravity and rock type (Table 1); rubidium and strontium data for granitic rocks of the northern Peninsular Ranges batholith, southern California (Table 2); U, Th, Pb concentrations, Pb and Sr initial isotopic compositions, and δ 18 O permil values for granitic rocks of the northern Peninsular Ranges batholith (table 3).

California↗
USGS1980

Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the Talkeetna Quadrangle, Alaska

These summaries of data on metallic and selected nonmetallic mineral occurrences and lists of selected references to them in Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys (and predecessor State and Territorial agencies) reports and maps are designed to aid in library research on the mineral resources of the Talkeetna quadrangle, Alaska. The references listed are selected in the sense that mainly statistical reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and many annual and biennial reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on claims about which little more than their locations is known (for example, localities 40 and 41 in Reed and others, 1978 (MF-870-D)). These omissions should not be interpreted as a judgement that the claims are not on valid mineral occurrences, but only that there are insufficient data to describe any mineral deposit that might be present. Geochemical anomalies determined by analyses of rock and stream-sediment samples in which no metallic mineral was identified are also omitted.

Alaska↗
USGS1980

Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the McCarthy Quadrangle, Alaska

These summaries of data on metallic and selected nonmetallic mineral occurrences and lists of selected references to .them in Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys (and predecessor State and Territorial agencies) reports and maps and a very.few journal articles are designed to aid in library research on the mineral resources of the McCarthy quadrangle, Alaska. The references listed are selected in the sense that mainly statistical reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and many annual and biennial reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on claims about which little more than their locations is known (for example, localities 126- 130 in MacKevett and Holloway, 1977 (OF 77-169A). These omissions should not be interpreted as a judgement that the claims are not on valid mineral occurrences, but only chat there are insufficient data to describe any mineral deposits that might be present. Geochemical anomalies determined by analyses of rock and stream-sediment samples in which no metallic mineral was indentified are also omitted.

Alaska↗
USGS2009

Mapping the mineral resource base for mineral carbon-dioxide sequestration in the conterminous United States

This database provides information on the occurrence of ultramafic rocks in the conterminous United States that are suitable for sequestering captured carbon dioxide in mineral form, also known as mineral carbon-dioxide sequestration. Mineral carbon-dioxide sequestration is a proposed greenhouse gas mitigation technology whereby carbon dioxide (CO 2 ) is disposed of by reacting it with calcium or magnesium silicate minerals to form a solid magnesium or calcium carbonate product. The technology offers a large capacity to permanently store CO 2 in an environmentally benign form via a process that takes little effort to verify or monitor after disposal. These characteristics are unique among its peers in greenhouse gas disposal technologies. The 2005 Intergovernmental Panel on Climate Change report on Carbon Dioxide Capture and Storage suggested that a major gap in mineral CO 2 sequestration is locating the magnesium-silicate bedrock available to sequester the carbon dioxide. It is generally known that silicate minerals with high concentrations of magnesium are suitable for mineral carbonation. However, no assessment has been made in the United States that details their geographical distribution and extent, nor has anyone evaluated their potential for use in mineral carbonation. Researchers at Columbia University and the U.S. Geological Survey have developed a digital geologic database of ultramafic rocks in the conterminous United States. Data were compiled from varied-scale geologic maps of magnesium-silicate ultramafic rocks. The focus of our national-scale map is entirely on ultramafic rock types, which typically consist primarily of olivine- and serpentine-rich rocks. These rock types are potentially suitable as source material for mineral CO 2 sequestration.

Conterminous United States↗
USGS1982

Mineral resource potential map of the Savannah Roadless Area, Liberty County, Florida

The Savannah Roadless Area is underlain by sedimentary rocks having low potential for oil and gas and minerals. The low potential for oil or gas notwithstanding, the possibilities for discovery cannot be ruled out because the area and nearby lands have not been thoroughly explored. No minerals have been mined within the Savannah Roadless Area, and the only production nearby has been the digging of clayey sand used in stabilizing U.S. Forest Service roads. Fuller's earth, quartz sand and gravel, clayey sand, and common clay presently are produced elsewhere in the region, and limestone and peat have been produced in the past. No clay suitable for structural clay products or fuller's earth is present in the roadless area; however, a bed of quartz sand and gravel of excellent quality was penetrated at a depth interval of 37-50 ft by one drill hole. Although this bed is coarser grained-and therefore is more suitable for many uses-than the sand deposits worked elsewhere in the Big Bend region, its mineral resource potential is reduced by the thickness of overburden above it and by its distance from markets in population centers. The Apalachicola National Forest has been explored for phosphate and reconnoitered for heavy minerals, but no valuable deposits of either have been found.

Florida↗
USGS1997

Water quality in the Appalachian Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces, eastern United States

Chemical quality of ground water, spring water, and surface water differs substantially among the three physiographic provinces. Maps showing regional variations for 18 water properties and constituents are included in this Regional Aquifer System Analysis study report. Systematic variations in water quality are due to differences in geologic and hydrologic factors that include the dominant lithology, the availability of soluble minerals, and the degree of exposure of water to rock. Most ground water in the study area is low in concentrations of dissolved minerals, is moderately hard, and is slightly acidic. Spring water is generally harder than ground water and is slightly alkaline; whereas, surface water is softer than the ground water and is also slightly alkaline.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗
USGS2017

Re-Os systematics and geochemistry of cobaltite (CoAsS) in the Idaho cobalt belt, Belt-Purcell Basin, USA: Evidence for middle Mesoproterozoic sediment-hosted Co-Cu sulfide mineralization with Grenvillian and Cretaceous remobilization

We report the first study of the Re-Os systematics of cobaltite (CoAsS) using disseminated grains and massive sulfides from samples of two breccia-type and two stratabound deposits in the Co-Cu-Au Idaho cobalt belt (ICB), Lemhi subbasin to the Belt-Purcell Basin, Idaho, USA. Using a 185 Re + 190 Os spike solution, magnetic and non-magnetic fractions of cobaltite mineral separates give reproducible Re-Os analytical data for aliquot sizes of 150 to 200 mg. Cobaltite from the ICB has highly radiogenic 187 Os/ 188 Os ratios (17–45) and high 187 Re/ 188 Os ratios (600–1800) but low Re and total Os contents (ca. 0.4–4 ppb and 14–64 ppt, respectively). Containing 30 to 74% radiogenic 187 Os, cobaltite from the ICB is amenable to Re-Os age determination using the isochron regression approach. Re-Os data for disseminated cobaltite mineralization in a quartz-tourmaline breccia from the Haynes-Stellite deposit yield a Model 1 isochron age of 1349 ± 76 Ma (2σ, n = 4, mean squared weighted deviation MSWD = 2.1, initial 187 Os/ 188 Os ratio = 4.7 ± 2.2). This middle Mesoproterozoic age is preserved despite a possible metamorphic overprint or a pulse of metamorphic-hydrothermal remobilization of pre-existing cobaltite that formed along fold cleavages during the ca. 1190–1006 Ma Grenvillian orogeny. This phase of remobilization is tentatively identified by a Model 3 isochron age of 1132 ± 240 Ma (2σ, n = 7, MSWD = 9.3, initial 187 Os/ 188 Os ratio of 9.0 ± 2.9) for cobaltite in the quartz-tourmaline breccia from the Idaho zone in the Blackbird mine. All Mesoproterozoic cobaltite mineralization in the district was affected by greenschist- to lower amphibolite-facies (garnet zone) metamorphism during the Late Jurassic to Late Cretaceous Cordilleran orogeny. However, the fine- to coarse-grained massive cobaltite mineralization from the shear zone-hosted Chicago zone, Blackbird mine, is the only studied deposit that has severely disturbed Re-Os systematics with evidence for a linear trend of mixing with (metamorphic?) fluids. The new Re-Os ages and extremely high initial 187 Os/ 188 Os ratios of cobaltite reported here favor a magmatic-hydrothermal genetic model for a multi-stage REE-Y-Co-Cu-Au mineralization occurring at ca. 1370 to 1349 Ma, and related to the emplacement of the Big Deer Creek granite pluton at ca. 1377 Ma. In our model, deposition of paragenetically early xenotime and gadolinite was followed by an influx of Mesoproterozoic evaporitic brines and magmatic-hydrothermal fluids containing metals and reduced sulfur derived from mafic and oceanic island-arc Archean to Paleoproterozoic rocks in the Laurentian basement. Cobaltite mineralization occurred upon cooling of these fluids at an inferred temperature of 300 °C or below.

Idaho↗
USGS1995

Geologic map and structure sections of the Clear Lake Volcanics, Northern California

The Clear Lake Volcanics are located in the California Coast Ranges about 150 km north of San Francisco. This Quaternary volcanic field has erupted intermittently since 2.1 million years ago. This volcanic field is considered a high-threat volcanic system (Ewert and others, 2005) The adjacent Geysers geothermal field, largest power-producing geothermal field in the world, is powered by the magmatic heat source for the volcanic field. This report consists of three sheets that include the geologic map, one table, two figures, three cross sections, description of map units, charts of standard and diagrammatic correlation of map units, and references. This map supersedes U.S. Geological Survey Open-File Report 76-751. Descriptions of map units are grouped by geographic area. Summaries of the evolution, chemistry, structure, and tectonic setting of the Clear Lake Volcanics are given in Hearn and others (1981) and Donnelly-Nolan and others (1981). The geology of parts of the area underlain by the Cache Formation is based on mapping by Rymer (1981); the geology of parts of the areas underlain by the Sonoma Volcanics, Franciscan assemblage, and Great Valley sequence is based on mapping by McLaughlin (1978). Volcanic compositional map units are basalt, basaltic andesite, andesite, dacite, rhyodacite, and rhyolite, based on SiO2 content. Included in this report are maps showing the distribution of volcanic rocks through time and a chart showing erupted volumes of different lava types through time. A table gives petrographic data for each map unit by mineral type, abundance, and size. Most ages are potassium-argon (K/Ar) ages determined for whole-rock samples and mineral separates by Donnelly-Nolan and others (1981), unless otherwise noted. A few ages are carbon-14 ages or were estimated from geologic relationships. Magnetic polarities are from Mankinen and others (1978; 1981) or were determined in the field by B.C. Hearn, Jr., using a portable fluxgate magnetometer. Thickness for most units is estimated from topographic relief except where drill-hole data were available.

California↗
USGS1992

Ages, rare-earth element enrichment, and petrogenesis of tholeiitic and alkalic basalts from Kahoolawe Island, Hawaii

Kahoolawe Island, Hawaii (18×11 km), is a basaltic shield volcano with caldera-filling lavas, seven identified postshield vents, and at least two occurrences of apparent rejuvenated-stage eruptive. We examined 42 samples that represent all stages of Kahoolawe volcano stratigraphy for their petrography, whole-rock major-and trace-element contents, mineral compositions, and K−Ar ages. The two oldest shield samples have an average age of 1.34±0.08 Ma, and four postshield samples (3 are alkalic) average 1.15±0.03 Ma; ages of 1.08 and 0.99 Ma for two additional tholeiitic samples probably are minimum ages. Whole-rock major- and trace-element and mineral compositions of Kahoolawe shield and caldera-fill laves are generally similar to the lavas forming Kilauea and Mauna Loa tholeiitic shields, but in detail, Kahoolawe shield lavas have distinctive compositions. An unusual aspect of many postshield Ka-hoolawe lavas is anomalously high REE and Y abundances (up to 200 ppm La and 175 ppm Y) and negative Ce anomalies. These enrichments reflect surficial processes, where weathering and soil development promoted REE-Y transport at the weathering front. Major element abundances (MgO, 10–6 wt.%) for shield and caldera-fill basalts are consistent with fractionation of ol+px+pl in frequently replenished magma reservoirs. In general, tholeiitic basalts erupted from late vents are higher in SiO 2 than the shield lavas, and temporal differences in parental magma compositions are the likely explanation. Alkalic basalts that erupted from vents are comparable in composition to those at other Hawaiian volcanoes. Trace-element abundance ratios indicate that alkalic basalts represent either relatively lower degrees of melting of the shield source or a distinct source. Apparent rejuvenated-stage basalts (i.e., emplaced after substantial Kahoolawe erosion) are tholeiitic, unlike the rejuvenated-stages at other Hawaiian volcanoes (alkalic). Kahoolawe, like several other Hawaiian volcanoes, has intercalated tholeiitic and alkalic basalts in the postshield stage, but it is the only volcano that appears to have produced tholeiitic rejuvenated-stage lavas.

Hawaii↗
USGS1985

Paragenesis and tectonic significance of base and precious metal occurrences along the San Andreas fault at Point Delgada, California

Studies of sulfide vein mineralization at Point Delgada, California, suggest that the mineralizing process was intimately associated with the San Andreas fault system and/or plate-margin tectonism. The deposits occur along north-south to northeast-southwest-trending tension faults that intersect and cross a major northwest-trending fault previously considered to be a major trace of the San Andreas fault. Galena and sphalerite are concentrated near the intersection of the principal mineralized vein with the fault, suggesting that brecciated rocks at this intersection acted as a major conduit for hydrothermal circulation. Fluid inclusion data show that the sulfide mineralization occurred at a depth of at least 400 m, probably at a temperature of about 250 degrees C. Mineralization fluids were in the salinity range of 10.5 to 5.2 equivalent weight percent NaCl. Sodium and potassium were depleted from the mineralizing fluids in the early stages of mineralization, and traces of argentian tetrahedrite and cassiterite in the fluid inclusions probably account for some of the anomalous values of silver and tin in galena and sphalerite. The age of mineralization, based on K-Ar dating of adularia, is 13.8 + or - 0.4 m.y. This age suggests that the purported trace of the San Andreas fault crossed by the sulfide veins has been largely inactive since middle Miocene time. Lead isotope and geochemical data suggest that base and precious metals in the sulfide veins were derived largely from arc-related sedimentary rocks. The heat source for hydrothermal circulation may have been associated with intrusion of asthenosphere into a triangular slab window opened southeast of the northward-propagating Mendocino triple junction shortly before 13.8 m.y. ago.

Economic Geology↗
USGS1979

Preliminary geologic and geophysical data of the UE25a-3 exploratory drill hole, Nevada Test Site, Nevada

The UE25a-3 drill hole, located in the Calico Hills area, southwestern part of the Nevada Test Site, was drilled as part of an effort to evaluate the Calico Hills area as a possible nuclear waste repository site. The purpose of the drill hole was to verify the existence of an intrusive crystalline body in the subsurface and to determine the stratigraphy, structure, and nature of fractures of the cored rocks. Cored samples were obtained for mineral, chemical, and material property analyses. Continuous cores were taken from 30.5 m (100ft) to total depth of 771.2 m (2,530.1 ft) of units J and I{?) (Late Mississippian age) of the Eleana Formation. The drill hole penetrated 416.1 m (1 ,365ft) of argillite, and 304.5 m (999ft) of thermally altered argillite of unit J, and 50.6 m (166ft) of marble of unit I(?). No crystalline rocks were intersected by the drill hole. Numerous high-angle faults and brecciated zones were intersected by the drill hole. The units cored were intensely fractured with fracture analysis of the core consisting of frequency of fractures, dips of fractures, open and closed (sealed) fractures and types of fracture sealing or coating material. Twenty-four hundred and thirty fractures, representing approximately 30 percent of the fractures present, indicate an average fracture frequency of 13.2 fractures per meter, predominantly high-angle dips with 66 percent of the fractures closed. Fractures in the argillite interval are sealed or coated predominantly with kaolinite, nacrite, and dickite. Calcite, chlorite, and magnetite are present in fractures in the altered argillite interval. Fractures in the marble interval are sealed or coated with calcite, dolomite, and ferruginous clay. The core index indicates that the lower half of the drilled interval is more competent than the upper half. Borehole geophysical logs were run by the Birdwell Division of Seismograph Service Corporation for geologic correlations and lithologic characterizations. The logs include: caliper, density, resistivity, spontaneous potential, Vibroseis, 3-D velocity, neutron, and gamma-ray logs. Lithologic boundaries and structures correlate to responses in the logs.

Nevada↗
USGS1980

A lead isotope study of mineralization in the Saudi Arabian Shield

New lead isotope data are presented for some late Precambrian and early Paleozoic vein and massive sulfide deposits in the Arabian Shield. Using the Stacey Kramers (1975) model for lead isotope evolution, isochron model ages range between 720 m.y. and 420 m.y. Most of the massive sulfide deposits in the region formed before 680 m.y. ago, during evolution of the shield. Vein type mineralization of higher lead content occurred during the Pan African event about 550 m.y. ago and continued through the Najd period of extensive faulting in the shield that ended about 530 m.y. ago. Late post-tectonic metamorphism may have been responsible for vein deposits that have model ages less than 500 m.y. Alternatively some of these younger model ages may be too low due to the mineralizing fluids acquiring radiogenic lead from appreciably older local crustal rocks at the time of ore formation. The low207Pb/204Pb ratios found for the deposits in the main part of the shield and for those in north-eastern Egypt, indicate that the Arabian craton was formed in an oceanic crustal environment during the late Precambrian. Involvement of older, upper-crustal material in the formation of the ore deposits in this part of the shield is precluded by their low207Pb/204Pb and208Pb/204Pb characteristics. In the eastern part of the shield, east of longitude 44??20???E towards the Al Amar-Idsas fault region, lead data are quite different. They exhibit a linear207Pb/204Pb-206Pb/204Pb relationship together with distinctly higher208Pb/204Pb characteristics. These data imply the existence of lower crustal rocks of early Proterozoic age that apparently have underthrust the shield rocks from the east. If most of the samples we have analyzed from this easterly region were mineralized 530 m.y. ago, then the age of the older continental rocks is 2,100??300 m.y. (2??). The presence of upper crustal rocks, possibly also of early Proterozoic age, is indicated by galena data from Hailan in South Yemen and also from near Muscat in Oman. These data are the first to indicate such old continental material in these regions. ?? 1980 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1979

Preliminary report on Tertiary volcanism and uranium mineralization in the Thomas Range and northern Drum Mountains, Juab County, Utah

The Thomas Range and northern Drum Mountains have a history of volcanism, faulting, and mineralization that began about 42 m.y. ago. Volcanic activity and mineralization in the area can be divided into three stages according to the time-related occurrence of rock types, trace element associations, and chemical nature of mineralization. Volcanic activity switched abruptly from rhyodacite-quartz latite (42-39 m.y. ago) to rhyolite (38-32 m.y. ago) to alkali rhyolite stages (21 and 6-7 m.y. ago); these stages correspond to periods of chalcophile and siderophile metal mineralization, no mineralization, and lithophile metal mineralization, respectively. Angular unconformities record episodes of cauldron collapse and block faulting between the stages of volcanic activity and mineralization. The youngest angular unconformity formed between 21 and 7 m.y. ago during basin-and-range faulting. Early rhyodacite-quartz latite volcanism from composite volcanoes and fissures produced flows, breccias, and ash-flow tuff of the Drum Mountains Rhyodacite and Mt. Laird Tuff. Eruption of the Mt. Laird Tuff about 39 m.y. ago from an area north of Joy townsite was accompanied by collapse of the Thomas caldera. Part of the roof of the magma chamber did not collapse, or the magma was resurgent, as is indicated by porphyry dikes and plugs in the Drum Mountains. Chalcophile and siderophile metal mineralization, including copper, gold, and manganese, accompanied early volcanism. The middle stage of volcanic activity was characterized by explosive eruption of rhyolitic ash-flow tuffs and collapse of the Dugway Valley cauldron. Eruption of the Joy Tuff 38 m.y. ago was accompanied by subsidence of this cauldron and followed by collapse and sliding of Paleozoic rocks from the west wall of the cauldron. Landslides in The Dell were covered by the Dell Tuff, erupted 32 m.y. ago from an unknown source to the east. An ash-flow of the Needles Range Formation was erupted 30-31 m.y. ago, probably from a distant source outside the volcanic field. The rhyolitic stage of volcanism was barren of mineralization. The last stage of volcanism was contemporaneous with basin-and-range faulting and was characterized by explosive eruption of ash and pumice, forming stratified tuff, and by quiet eruption of alkali rhyolite as viscous flows and domes. The first episode of alkali rhyolite volcanism deposited the beryllium tuff and porphyritic rhyolite members of the Spor Mountain Formation 21 m.y. ago. After a period of block faulting, the stratified tuff and alkali rhyolite of the Topaz Mountain Rhyolite were erupted 6-7 m.y. ago along faults and fault intersections. Erosion of Spor Mountain may have provided abundant dolomite detritus to the beryllium tuff member. The alkali rhyolite of both formations is fluorine-rich, as is evident from abundant topaz, and contains anomalous amounts of lithophile metals. Alkali rhyolite volcanism was accompanied by lithophile metal mineralization which deposited fluorite, beryllium, and uranium. The structure of the area is dominated by the Thomas caldera, and the younger Dugway Valley cauldron, which is nested within the Thomas caldera; the Thomas caldera is surrounded by a rim of Paleozoic rocks at Spor Mountain and Paleozoic to Precambrian rocks in the Drum Mountains. The Joy fault and Dell fault system mark the ring fracture zone of the Thomas caldera. These structural features began to form about 39 m.y. ago during eruption of the Mt. Laird Tuff and cauldon subsidence. The Dugway Valley cauldron sank along a series of step-like normal faults southeast of Topaz Mountain in response to collapse of the magma chamber of the Joy Tuff. The caldera structure was modified by block faulting between 21 and 7 m.y. ago, the time of widespread extensional faulting in the basin-and-range province. Vents erupted alkali rhyolite 6-7 m.y. ago along basin-and-range faults. Uranium mineralization was associated with the stage of alkali rhyolite volcanism, extensional basin-and-range faulting, and lithophile metal mineralization; it occurred at least 11 m.y. after the end of the caldera cycle. Uranium, derived from alkali rhyolite magma, was concentrated in trace amounts by magmatic fluids and in potentially economic amounts by hydrothermal fluids and ground water. Hydrothermal fluids deposited uraniferous fluorite as pipes in carbonate rocks of Paleozoic age on Spor Mountain and uranium-bearing disseminated deposits of fluorite and beryllium in the beryllium tuff member of the Spor Mountain Formation. Uranium of hydrothermal origin is dispersed in fluorite and opal. Uranium in fluorite may be tetravalent(?) but that in opal is probably hexavalent; no primary minerals of tetravalent uranium are known to occur. Ground waters have concentrated significant ores of hexavalent uranium minerals in the beryllium tuff member of the Spor Mountain Formation at the Yellow Chief Mine, and are probably also responsible for widespread low concentrations (0.0X percent) of uranium that occur separately from beryllium ore in the beryllium tuff member. More deposits of the Yellow Chief type may occur in down-faulted sections of beryllium tuff beneath the Thomas Range. The ground water ores show no evidence of a reducing environment; instead, precipitation of hexavalent uranium minerals occurred by evaporation, decline in concentration of complexing ions such as carbonate, or some other mechanism. Reducing environments for hydrothermal deposits must be sought around rhyolite vents and in a hypothesized pluton of alkali rhyolite composition beneath Spor Mountain; for ground-water deposits, reducing environments may occur in basin fill such as that of the Dugway Valley cauldron.

Utah↗
USGS1973

Soda Creek springs - metamorphic waters in the eastern Alaska Range

The Soda Creek springs are a group of small, cold mineral springs on the southern flank of the eastern Alaska Range. The spring waters contain anomalous concentrations of carbon dioxide, sodium, chlorine, sulfate, boron, and ammonia and are actively precipitating deposits of calcite and aragonite. Sparingly present in these deposits are mixed-layer illite-montmorillonite clays and zeolite minerals. Low-temperature metamorphic reactions in subjacent marine sedimentary rocks of Jurassic and Cretaceous age may have produced the fluids and silicate minerals. With only a few exceptions, cool bicarbonate-rich springs in Alaska are concentrated south of the Denali fault system in south-central Alaska, southeastern Alaska, and along the Kaltag-Tintina fault system. These areas are characterized by active or recently active tectonism, major faults and folds, and an abundance of marine sedimentary rocks.

Alaska↗