Symposium proceedings; a national program for the assessment and development of the mineral resources of the United States Exclusive Economic Zone; November 15, 16, 17, 1983
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ECONOMICS AND THE SEARCH FOR OFFSHORE HEAVY MINERAL DEPOSITS.
This paper examines the relative importance, in terms of a deposit's commercial status, of physical characteristics of onshore titanium-bearing heavy-mineral placer deposits, and applies these findings to the search for and evaluation of offshore deposits. Results obtained by applying statistical discriminant analysis show that the characteristics most useful for predicting a deposit's commercial status are the grades of the constituent titanium minerals and the size of the deposit. Heavy-mineral grade or even the combined grades of all titanium-bearing minerals (without information and constituent mineral grades) are inferior predictors of a deposit's commercial status. When data from homogeneous regions are analyzed separately, the ability to accurately predict the deposit's commerical status improves.
Marine Mining↗
The geochemical and textural transition between the Reef Package and its hanging wall, Stillwater Complex, Montana, USA
The highest grade Pd-Pt deposit on Earth, the J-M Reef, is hosted in coarse-grained to pegmatoidal cumulates called the Reef Package. Decades of mine development of the J-M Reef have revealed that a distinct discontinuity in rock fabric marks the top of the rock unit that hosts economic-grade sulfide mineralization. Mine geologists refer to this discontinuity as the hanging wall contact. This contact is the top of the Reef Package and is always locatable—either by the change in rock fabric or by distinctive hanging wall textures of silicate minerals—even when the reef sulfide mineralization is absent. This rather subtle textural feature is used reliably by mine geologists to follow the Reef during exploration and mine development. Although some high tenor sulfides (>1000 ppm Pd in 100% sulfide) are found sporadically in the hanging wall cumulates, these accumulations are too small to be economically viable. We present quantitative rock fabric data for four Reef Package and hanging wall intersections collected by electron back-scattered diffraction (EBSD). Plagioclase fabrics in the hanging wall are characterized by low variance in grain sizes and a strong point maximum concentration of (010) and a perpendicular girdle distribution of [100] consistent with an axial B-type fabric. These fabrics are indicative of either compaction of the crystal mush or crystal settling of nucleated crystals, the bulk magma in a chamber. Conversely, the fabrics of the Reef Package show higher variance grain in size distributions and weak to undeveloped preferred orientation of plagioclase crystals that did not undergo significant alignment or textural equilibration of plagioclase grains. The absence of foliation in the Reef Package stands in contrast both to hanging wall fabrics and to other reported EBSD datasets of plagioclase crystals orientations from the Bushveld Complex, the Skaergaard Intrusion, and the Rum Intrusion. Furthermore, plagioclase crystal size distributions for the Reef Package show flatter slopes and convex profiles with fewer crystals at small size fractions indicating the dissolution of small crystals during partial melting and textural coarsening (i.e . Ostwald ripening) and crystal growth. Crystal growth was favored over the nucleation of new crystals during prolonged interaction with a hot infiltrating melt into the resident mush resulting in the coarse-grained textures of the Reef Package cumulates. The hanging wall contact represents a boundary between partially remelted crystal mush of the Reef Package, where sulfide mineralization formed and accumulated, and an overlying essentially barren cumulate pile. The hanging wall cumulates formed following the cessation of footwall erosion and the resumption of crystal accumulation by normal magma chamber processes.
Montana↗
Mineral resources of the Citico Creek Wilderness Study Area, Monroe County, Tennessee
The proposed Citico Creek Wilderness comprises about 5,670 hectares (56.7 km2) in the Cherokee National Forest south of the Little Tennessee River in easternmost Monroe County, Tennessee. Principal drainages are Citico Creek and Doublecamp Creek. Rocks of the study area include greenschist-facies arkosic metasandstone, metagraywacke, slate, and metaconglomerate of the Great Smoky Group of late Precambrian age. Minor deposits of unconsolidated Quaternary alluvium locally mantle the bedrock. Deformation is shown by asymmetric and overturned folds and by several major faults. More than 500 sample s of soil, rock, and stream sediment were collected and analyzed for 31 major, minor, and trace elements by semiquantitative spectrographic, atomic absorption, and fire assay methods No significant metal anomalies were detected. Concentrations of Cu, Co, As, Pb, and Zn slightly higher than background are found within sulfidic parts of a distinctive stratigraphic unit composed of graphitic slate and metagraywacke. Pyrite and pyrrhotite are the chief sulfide minerals, with traces o f accessory sphalerite, chalcopyrite, galena, and arsenopyrite occurring as microscopic intergrowths. A reconnaissance ground radiometric survey and subsequent neutron activation analyses of selected radioactive rock samples show that the sulfidic parts of the graphitic slate unit have a relatively high content of Th and U, but are not potentially economic. No metallic mineral resources appear to exist within the Citico Creek Wilderness Study Area. Resources of slate, silica, and stone are present, but they display no special qualities to differentiate them from other such material throughout the region. Ceramic evaluation tests on selected samples of slate indicate that the slate would have only marginal use for structural clay products such as brick and tile. Minor sand and gravel deposits occur along a few streams but are present in larger quantities and are more easily recovered in other areas.
Tennessee↗
Passive seismic survey of sediment thickness, Dasht-e-Nawar basin, eastern Afghanistan
Exploration of water resources is needed for public supply, extraction of mineral resources, and economic development in Afghanistan. Remotely-sensed data are useful for identifying the general nature of surface sediments, however, “boots on the ground” geophysical surveys or drilling programs are needed to quantify the thickness of sediments or aquifers. The nature of such investigations presents a risk to field crews that may prohibit exploration of potentially valuable aquifers or mineral resources. The Dasht-e-Nawar basin, in east-central Afghanistan, contains a 400 km2 playa that includes evaporative mineral deposits, particularly lithium, which has been of interest since the 1970s. However, exploration of the basin, as with many areas of Afghanistan, has been hampered by decades of conflict. In 2014, an investigation of the basin was conducted by the U.S. Department of Defense Task Force for Business and Stability Operations (TFBSO), and their contractor, in cooperation with the U.S. Geological Survey (USGS). For this investigation the USGS compared the results of a rapid passive seismic survey of basin sediment thickness to the results of an independently conducted gravity survey of the same area. Each point measurement for the passive seismic method requires less than 30 minutes in the field by one person. The technique utilizes ambient seismic noise without an external sound source such as required by traditional seismic surveys. Additionally, the technique does not require external sensor arrays, which can be kilometers long for some geophysical techniques. The passive seismic equipment used in this study weighs approximately 1 kilogram and is about 10 cm3 in size. Although relatively new for assessment of sediment thickness, several investigations have found this method to be capable of estimating sediment thicknesses, in the 10’s to 1000 meter range, in settings with unconsolidated sediment over bedrock and a contrast in acoustic impedance. In this investigation, the gravity survey was conducted during a period of 3 weeks by an experienced field crew; required a detailed, centimeter-scale land elevation survey; and required laboratory analyses of sediment and rock densities to interpret the gravity data. In contrast, the passive seismic survey was collected by two inexperienced operators over a period of 8 days and required no additional data to interpret. Due to security restrictions, USGS personnel could not visit the site and the seismic operator was trained immediately prior to the field work. Although the quality of the seismic survey was affected by strong afternoon winds, and by the inexperience of the field operator, the results were fairly comparable to the gravity survey. Similar basin sediment thicknesses and patterns in sediment thickness were identified by both surveys in the basin with an estimated maximum thickness of approximately 170 m. The passive seismic technique required substantially less field resources and time than would be required by other geophysical surveys. Although this method will not be effective in all geologic settings, it may be a valuable assessment tool for use before conducting other, more intensive, geophysical efforts or drilling programs, especially in regions with elevated security risks such as Afghanistan.
Dasht-e-Nawar basin↗
Design of exploration and minerals-data-collection programs in developing areas
This paper considers the practical problem of applying economic analysis to designing minerals exploration and data collection strategies for developing countries. Formal decision rules for the design of government exploration and minerals-data-collection programs are derived by using a minerals-industry planning model that has been extended to include an exploration function. Rules derived are applicable to centrally planned minerals industries as well as market-oriented minerals sectors. They pertain to the spatial allocation of exploration effort and to the allocation of activities between government and private concerns for market-oriented economies. Programs characterized by uniform expenditures, uniform information coverage across regions, or uniform-density grid drilling progrmas are shown to be inferior to the strategy derived. Moreover, for market-oriented economies, the economically optimal mix in exploration activities between private and government data collection would require that only private firms assess local sites and that government agencies carry out regional surveys.
Socio-Economic Planning Sciences↗
Factors that Influence the Price of Al, Cd, Co, Cu, Fe, Ni, Pb, Rare Earth Elements, and Zn
This report is based on a presentation delivered at The 12th International Battery Materials Recycling Seminar, March 17-20, 2008, Fort Lauderdale, Fla., about the factors that influence prices for aluminum, cadmium, cobalt, copper, iron, lead, nickel, rare earth elements, and zinc. These are a diverse group of metals that are of interest to the battery recycling industry. Because the U.S. Geological Survey (USGS) closely monitors, yet neither buys nor sells, metal commodities, it is an unbiased source of metal price information and analysis. The authors used information about these and other metals collected and published by the USGS (U.S. production, trade, stocks, and prices and world production) and internationally (consumption and stocks by country) from industry organizations, because metal markets are influenced by activities and events over the entire globe. Long-term prices in this report, represented by unit values, were adjusted to 1998 constant dollars to remove the effects of inflation. A previous USGS study in this subject area was 'Economic Drivers of Mineral Supply' by Lorie A. Wagner, Daniel E. Sullivan, and John L. Sznopek (USGS Open File Report 02-335). By seeking a common cause for common behavior of prices among the various metal commodities, the authors found that major factors that influence prices of metal commodities were international events such as wars and recessions, and national events such as the dissolution of the Soviet Union in 1991 and economic growth in China, which started its open door policy in the 1970s but did not have significant market impact until the 1990s. Metal commodity prices also responded to commodity-specific events such as tariff or usage changes or mine strikes. It is shown that the prices of aluminum, cadmium, copper, iron, lead, nickel, and zinc are at historic highs, that world stocks are at (or near) historic lows, and that China's consumption of these metals had increased substantially, making it the world's leading consumer of these metals.
Open-File Report↗
Deposit model for heavy-mineral sands in coastal environments
This report provides a descriptive model of heavy-mineral sands, which are sedimentary deposits of dense minerals that accumulate with sand, silt, and clay in coastal environments, locally forming economic concentrations of the heavy minerals. This deposit type is the main source of titanium feedstock for the titanium dioxide (TiO 2 ) pigments industry, through recovery of the minerals ilmenite (Fe 2+ TiO 3 ), rutile (TiO 2 ), and leucoxene (an alteration product of ilmenite). Heavy-mineral sands are also the principal source of zircon (ZrSiO 4 ) and its zirconium oxide; zircon is often recovered as a coproduct. Other heavy minerals produced as coproducts from some deposits are sillimanite/kyanite, staurolite, monazite, and garnet. Monazite [(Ce,La,Nd,Th)PO 4 ] is a source of rare earth elements as well as thorium, which is used in thorium-based nuclear power under development in India and elsewhere. The processes that form coastal deposits of heavy-mineral sands begin inland. High-grade metamorphic and igneous rocks that contain heavy minerals weather and erode, contributing detritus composed of sand, silt, clay, and heavy minerals to fluvial systems. Streams and rivers carry the detritus to the coast, where they are deposited in a variety of coastal environments, such as deltas, the beach face (foreshore), the nearshore, barrier islands or dunes, and tidal lagoons, as well as the channels and floodplains of streams and rivers in the coastal plain. The sediments are reworked by waves, tides, longshore currents, and wind, which are effective mechanisms for sorting the mineral grains on the basis of differences in their size and density. The finest-grained, most dense heavy minerals are the most effectively sorted. The result is that heavy minerals accumulate together, forming laminated or lens-shaped, heavy-mineral-rich sedimentary packages that can be several meters and even as much as tens of meters thick. Most economic deposits of heavy-mineral sands are Paleogene, Neogene, and Quaternary in age; some are modern coastal deposits. Superimposed on these basic processes of ore formation are a multitude of contributing and modifying factors, such as the following: Strong, sustained wave action moves sand from offshore to the shore, where the sand and heavy minerals are sorted by size and density. Mineral sorting occurs mainly on the upper part of the hightide swash (wave) zone. Fine-grained sands and heavy minerals on the foreshore can be remobilized by winds, forming heavy mineral-rich sand dunes behind the beach. Longshore drift combined with the geomorphology of the coast exert strong influence on the location of the heavy-mineral sands deposits. Sea level changes are a function of climatic changes, such as ice ages. Rises in regional sea level (transgression) and lowering of sea level (regression) strongly influence the deposition and preservation of heavy-mineral sands. The majority of heavy-mineral sands accumulation appears related to seaward progradation of the shore during regression events. Local faulting may affect the geomorphology of the coast, which controls the distribution of heavy mineral deposition in a coastal basin. Heavy mineral grains appear to weather primarily after their deposition in the coastal plain; this weathering is caused by groundwaters, humic acids, and other intrabasinal fluids. This weathering can enhance the TiO 2 content of ilmenite. Iron is leached from ilmenite during weathering, which thereby upgrades the TiO 2 content of the ilmenite, forming leucoxene. The resulting deposits of heavy-mineral sands can be voluminous. Individual bodies of heavy mineral-rich sands are typically about 1 kilometer wide and more than 5 kilometers long. Many heavy-mineral sands districts extend for more than 10 kilometers and contain several individual deposits that are spread along an ancient or modern strandline. Reported thicknesses of economic deposits range from 3 to 45 meters. Individual ore deposits typically comprise at least 10 megatonnes of ore (the total size of the individual sand-silt body), whose overall heavy-mineral content is 2 to greater than 10 percent. Heavy-mineral sands deposits are relatively easy to mine because they are weakly to poorly consolidated, and they are relatively easy to process. From a geoenvironmental standpoint, mining of heavy mineral-sands generates little or no acid or solubilized metals. However, environmental and human health concerns related to such mining include potential effects on indigenous flora and fauna, effects on local hydrology, and issues related to processing and storing thorium-bearing monazite, owing to its radioactivity. Regional exploration for deposits of heavy-mineral sands can utilize the analyses of stream sediment samples for Ti, Hf, the rare earth elements, Th, and U, and geophysical surveys, particularly radiometric (gamma-ray spectrometry for K, U, and Th) and magnetic methods. Geophysical anomalies may be small, and surveys are generally more successful when conducted close to sources of interest.
Scientific Investigations Report↗
Mineral reconnaissance of the southern part of the Wadi Qaraqir quadrangle, Saudi Arabia
Introduction At the end of a field trip to the Wadi as Surr quadrangle (Johnson and Trent, 1967) a few days were spent in the southern part of the adjoinning Wadi Qaraqir quadrangle in order to extend our mineral reconnaissance as far east as the Arabian Plateau. The area examine is shown by the distribution of sample localities on the accompanying map. No mineral deposits of economic interest were seen. The terrain is one of broad plains and low hills that extend westward from the base of a prominent erosional scarp which forms the western edge of the Arabian Plateau. Streams cutting headward into the low-dipping massive sandstone of the Plateau have carved deep canyongs with vertical walls, and outliers of the sandstone are preserved as buttes and erosional forms of varied shapes. There are no permanent settlements in the mapped areas. The one road leads up a tributary of Wadi Qaraqir to some date gardens at the base of the sandstone cliffs. A well-travelled caravan route crosses the passes at Al Khuraytah to reach the Plateau H. St. John Philby strongly recommended that a road be constructed through these passes to provide direct access from Tabuk to the Red Sea coast. Burton (1878) was probably the first European to visit the area. He was searching for mineral deposits and he also located some Nabatcan ruins. Philby in company with R. G. Bogue, U. S. Geological Survey, explored the scarp in the Wadi Qaraqir valley and drove northwestward to Al Khuraytah pass. The geology of the Wadi Qaraqir quadrangle shown on the geologic map of the Northwestern Hijaz (Brown and others, 1963) was compiled from Bogue's work. Our work consisted of making traverses around the hilly area and up accessible wadis. We examined the rocks along the traverse routes and visited target areas that had been selected by examination of aerial photographs. Samples of wadi sediment were collected from fault zones, granite contacts, and areas that showed some evidence of hydrothermal alteration. The work was made possible by the cooperation fo the officials of the Directorate General of Mineral Resources, Ministry of Petroleum and Mineral Resources, who arranged for vehicles and accompanying personnel. We did not have a counterpart Saudi geologist for this portion of our trip.
Open-File Report↗
High REE and Y concentrations in Co-Cu-Au ores of the Blackbird district, Idaho
Analysis of 11 samples of strata-bound Co-Cu-Au ore from the Blackbird district in Idaho shows previously unknown high concentrations of rare earth elements (REE) and Y, averaging 0.53 wt percent ???REE + Y oxides. Scanning electron microscopy indicates REE and Y residence in monazite, xenotime, and allanite that form complex intergrowths with cobaltite, suggesting coeval Co and REE + Y mineralization during the Mesoproterozoic. Occurrence of high REE and Y concentrations in the Blackbird ores, together with previously documented saline-rich fluid inclusions and Cl-rich biotite, suggest that these are not volcanogenic massive sulfide or sedimentary exhalative deposits but instead are iron oxide-copper-gold (IOCG) deposits. Other strata-bound Co deposits of Proterozoic age in the North American Cordillera and elsewhere in the world may have potential for REE and Y resources. IOCG deposits with abundant light REE should also be evaluated for possible unrecognized heavy REE and Y mineralization. ?? 2006 by Economic Geology.
Economic Geology↗
Radioactive deposits of Nevada
Thirty-five occurrences of radioactive rocks had been reported from Nevada prior to 1952. Twenty-five of these had been investigated by personnel of the U. S. Geological Surveyor of the U. S. Atomic Energy Commission. Of those investigated, uranium minerals were identified at 13 sites; two sites contained a thorium mineral (monazite); the source of radioactivity on nine properties was not ascertained, and one showed no abnormal radioactivity. Of the other reported occurrences, one is said to contain uraniferous hydrocarbons and nine are placers containing thorian monazite. Pitchblende occurs at two localities, the East Walker River area, and the Stalin's Present prospect, where it is sparsely disseminated in tabular bodies cutting granitic rocks. Other uranium minerals found in the state include: carnotite, tyuyamunite, autunite, torbernite, gummite, uranophane, kasolite, and an unidentified mineral which may be dumontite. Monazite is the only thorium mineral of possible economic importance that has been reported. From an economic standpoint, only four of the properties examined showed reserves of uranium ore in 1952; these are: the Green Monster mine, which shipped 5 tons of ore to Marysvale, Utah, during 1951; the Majuba Hill mine; the Stalin's Present prospect; and the West Willys claim in the Washington district. No estimate has been made of thorium reserves and no commercial deposits of thorium are known.
Bulletin↗
Geology of the Anlauf and Drain quadrangles, Douglas and Lane counties, Oregon
The Anlauf and Drain quadrangles, Oregon, lie about 20 miles south of the City of Eugene, in Douglas and Lane Counties. They constitute an area of about 435 square miles that includes parts of both the Cascade Range and Coast Range physiographic provinces. A sequence of lower Tertiary sedimentary and volcanic rocks with a maximum thickness of about 20,000 feet is exposed in the area. The oldest part of this sequence is the Umpqua formation of early Eocene age consisting of a lower Member of vesicular and amygdaloidal olivine basalt flows, a middle member of water-laid vitric and lapilli crystal tuff, and an upper member of interbedded fissile siltstone and basaltic sandstone which contains a 300-foot tongue of massive to thick-bedded basaltic sandstone near its top. These rocks are predominantly of marine origin, although the general absence of pillow structures Which are common in basaltic lavas of equivalent age elsewhere in the Coast Ranges suggests that some of the flows were poured out subaerially. The overlying tuff member, however, contains Foraminifera and in places has a lime content slightly in excess of 10 percent. Mollusca and Foraminifera indicate that the Umpqua formation is of early Eocene age and is a correlative of the Capay formation of California. The Tyee formation of middle Eocene age overlies the Umpqua formation and consists of more than 5,000 feet of rhythmically deposited sandstone and siltstone in beds 2 to 30 feet thick. The basal part of each bed consists of medium- to coarse-grained sandstone that grades upward into line-grained sandstone and siltstone. The principal constituents of the sandstone are quartz, partly altered feldspar, mica, clay, and fragments of basalt, fine-grained argillaceous rocks, and mica schist. Other detrital minerals include epidote, garnet, blue-green hornblende, tourmaline, and zoisite. The depositional environment of the Tyee formation is poorly known, although the rhythmic-graded bedding suggests turbidity currents. About 500 feet of sandstone and siltstone assigned to the Spencer formation of late Eocene age unconformably overlies the Tyee formation. The Spencer formation, better exposed in the east-central part of the Coast Ranges, contains marine fossils but also has thin impure coal beds, indicative of strand-line accumulation. The sandstone in the Spencer formation is very similar to that in the Tyee formation, from which it was probably derived. The Fisher formation contains about 5,500 feet of nonmarine pyroclastic and Volcanic rocks that are related to the volcanic rock sequences of the western Cascade Range. The formation is characterized by a wide variety of rock types, including conglomerate, tuffaceous sandstone and siltstone, vitric and crystal tuff, waterlaid and mudflow breccia, and andesitic lava flows. These rocks generally occur in lenticular beds that have little stratigraphic significance. The rocks apparently accumulated on a plain slightly above sea level that was subjected alternately to flooding by running water and to desiccation. Fossil leaves from the lowermost part of the Fisher formation are of late Eocene age; the upper part of the formation is of early, and possibly middle, Oligocene age. A few exposures of olivine basalt were mapped in the extreme northern part of the Anlauf quadrangle. The flows, more extensively exposed to the north, overlie the Fisher formation, and, therefore, are tentatively considered to be post-Oligocene in age. All these stratigraphic units, but principally the Fisher formation, are cut by dikes, sills, and stocklike bodies of porphyritic basalt, diabase, and norite. Contemporaneously with the emplacement of most of these rocks, in late Miocene(?) time, hydrothermal solutions locally altered the sedimentary and extrusive igneous rocks and deposited cinnabar and other sulfide minerals, carbonates, and silica. Three parallel northeastward-trending anticlines in the older marine rocks are the most conspicuous structural features in the area. These folds plunge both to the northeast and southwest and expose in their central parts basalt flows of the Umpqua formation. The rocks along the west margin of the area dip westward into a structural basin in the adjacent Elkton quadrangle, whereas to the east the Fisher formation generally has an easterly dip typical of the nonmarine rocks in the western Cascade Range. Geologic studies in the Anlauf and Drain quadrangles were undertaken principally to evaluate the petroleum possibilities of the area. Available data indicate that source beds and reservoir rock suitable for the formation and accumulation of petroleum are absent in this part of the Coast Ranges, but because of the lack of subsurface information, this evaluation is only tentative. Mineral deposits of economic value in the area include quicksilver and alumina clay.
Oregon↗
Detection and mapping of hydrothermally altered rocks in the vicinity of the Comstock Lode, Virginia Range, Nevada, using enhanced Landsat images
The Virginia Range, immediately southeast of Reno, Nev., consists mainly of flows, breccias, and turfs of Miocene age. Most of these volcanic rocks are of intermediate composition; rhyodacite is the most common rock type. Basalt, rhyolite and rhyolite tuff, and tuffaceous sedimentary rocks of Miocene and Pliocene age also cover substantial areas in the range. Pre-Tertiary metasedimentary, metavolcanic, and granitic rocks are exposed in scattered inliers, mostly along the southern and eastern margins of the range. Several large areas and many small areas within the volcanic pile were subjected to hydrothermal alteration during and after the period of intermediate volcanic activity. Economic precious metal mineralization is spatially and temporally associated with the hydrothermal alteration in several areas. The most important deposit is the Comstock Lode, which produced 192 million troy ounces of silver and 8.3 million troy ounces of gold from epithermal veins (Bonham, 1969). The hydrothermally altered rocks include silicified, advanced argillic, montmorillonite-bearing argillic, and propylitic types. The first three types typically contain pyrite, and some propylitic rocks contain pyrite as well. Supergene oxidation of these pyritic rocks produces limonitic bleached rocks. The term 'limonite,' as used here, refers to any combination of the minerals hematite, goethite, and Jarosite. Where vegetation cover is sparse to moderate, these limonitic rocks are readily identified on Landsat images enhanced by the color-ratio composite technique developed by Rowan and others (1974), so the altered areas can be mapped. About 30 percent tree cover (here mainly pinyon pine) is sufficient to change the spectral signature of individual picture elements (pixels) enough so that limonitic materials can no longer be uniquely identified. As in all other areas where this technique has been applied, limonitic unaltered rocks with intermediate to high albedos have the same appearance on the color-ratio composite as limonitic altered rocks. This problem represents the most important limitation to the use of enhanced Landsat images for detection and mapping of hydrothermally altered rocks. Reflectance spectra of altered and unaltered rocks taken in the field in the Virginia Range show that most altered rocks have a conspicuous absorption band near 2.2 ?m produced by clay minerals or alunite, whereas unaltered rocks have no features in this spectral region. Thus spectral information for selected bands in the 1.1-2.5 ?m region may allow discrimination between limonitic altered and limonitic unaltered rocks (Rowan and others, 1977; Abrams and others, 1977; Rowan and Abrams, 1978). Another potential limitation is loss of spectral information on slopes with low effective sun angle. Although a minor problem in the Virginia Range, loss of information sufficient to preclude identification of limonitic altered rocks occurs with effective sun angle lower than 20-25 degrees. Thus, even at moderate latitudes substantial parts of areas with high topographic relief may be lost to observation.
Open-File Report↗
Reconnaissance geology of the Ishash Quadrangle, sheet 26/39C, Kingdom of Saudi Arabia
The Ishash quadrangle occupies an area of about 2,725 km2 on the northern border of the Precambrian shield in north-central Saudi Arabia between lat 26?00' and 26?30' N. and long 39?00' and 39?30' E. The northern quarter is covered by Cambrian Siq Sandstone and the southeastern corner is covered by Quaternary to Tertiary basalt. The remainder of the area is underlain by trachyandesite, andesite, and metasedimentary rocks of the lower part of the Hulayfah group and rhyolitic flows and ruffs of the upper part of the Hulayfah group. These rocks have been intruded by rocks that range in composition from gabbro to alkali-feldspar granite. Two small outcrops of Tertiary rhyolite are present in the quadrangle. The predominant structures are folds and faults initiated by the formation of the caldera in the southwestern part of the area. The northerly trending structures were reactivated during the late Precambrian Najd orogenic event and again in the Tertiary during the opening of the Red Sea. No mineral deposits of economic importance were found in the quadrangle.
Open-File Report↗
Radioactive deposits of Nevada
Thirty-five occurrences of radioactive rocks had been reported from Nevada prior to 1952. Twenty-five of these had been investigated by the U. S. Geological Survey and the U. S. Atomic Energy Commission. Of those investigated, uranium minerals were identified in 13; two contained a thorium mineral (monazite); the source of radioactivity on 7 properties was not ascertained; and one showed no abnormal radioactivity. Of the other reported occurrences, one is said to contain uraniferous hydrocarbons and 9 are placers containing thorian monazite. Pitchblende occurs at two localities; the East Walker River area, and the Stalin's Present prospect, where it is sparsely disseminated in tabular bodies cutting granitic rocks. Other uranium minerals found in the state include: carnotite, tyuyamunite, autunite, torbernite, gummite, uranophane, kasolite, and an unidentified mineral which may be dumontit. Monazite is the only thorium mineral of possible economic importance that has been reported. From an economic standpoint 9 only 4 of the properties examined showed reserves of uranium ore in 1952; these are: the Green Monster mine, which shipped 5 tons of ore to Marysvale, Utah, during 1951, the Majuba Hill mine, the Stalin's Present prospect, and the West Willys claim in the Washington district. Reserves of ore grade are small on all of these properties and probably cannot be developed commercially unless an ore-buying station is set up nearby. No estimate has been made of thorium reserves and no commercial deposits of thorium are known.
Nevada↗
Editorial: From cold seeps to hydrothermal vents: Geology, chemistry, microbiology, and ecology in marine and coastal environments
This Research Topic compiles contemporary studies on cold seeps, hydrothermal vents, mud volcanoes, and related seafloor features that are associated with focused fluid emissions and the transfer of carbon, other chemical species, and sometimes heat from the geosphere to the ocean. Because these features sometimes tap fluids and gas originating kilometers below the seafloor, they provide an important window into deep processes that are otherwise inaccessible to scientists. At the shallow portion of their journey, migrating fluids nearing the seafloor contribute to a range of unique biological, physical, and chemical processes within the sediments themselves and at the sediment-water interface. Seafloor fluid emissions play a critical role in global biogeochemical cycles, ocean chemistry, and possibly even climate change. Seafloor leakage points often emit hydrocarbon gases (especially methane and CO 2 ) and are sometimes the loci for deposition of seafloor minerals that have economic value. A burgeoning area of research focuses on natural products generated at these features, seeking compounds with potential pharmaceutical or other applications. Multidisciplinary studies have become routine for characterization of seafloor fluid emission sites, attesting to the inseparability of geologic, physical, chemical, and biological processes in these settings. It is increasingly common for researchers to combine in a single research cruise: subbottom imaging and seafloor mapping; porewater and water column geochemistry and gas sampling; sediment retrieval for lithologic, biostratigraphic, and solid phase analyses; and studies of benthic and subseafloor communities at the microbial to macrofaunal scales. This multidisciplinary approach has the advantage of ensuring the spatial and temporal coincidence of surveys and samples, an important factor at highly dynamic seafloor fluid emission sites. In addition, researchers often use remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), or human-occupied vehicles (HOVs) to record video of the seafloor, compile photomosaics, collect targeted samples, and survey with high-resolution geophysical near-seafloor systems, providing a degree of detail about seafloor fluid emission sites that is unprecedented compared to most areas of the deep ocean. While rarer, long-term cabled observatories or shorter-term deployments of portable observatories are also used at some loci for seafloor fluid flux and are particularly helpful for capturing temporal variations at these dynamic features. Here we summarize the Research Topic’s contribution to multidisciplinary seafloor emission studies in the categories of cold seeps, mud volcanoes, and hydrothermal vents. Figure 1 shows the geographic distribution of the studies in this Research Topic and key features referred to in this Introduction.
Frontiers in Earth Science↗
Statistical methods of estimating mining costs
Until it was defunded in 1995, the U.S. Bureau of Mines maintained a Cost Estimating System (CES) for prefeasibility-type economic evaluations of mineral deposits and estimating costs at producing and non-producing mines. This system had a significant role in mineral resource assessments to estimate costs of developing and operating known mineral deposits and predicted undiscovered deposits. For legal reasons, the U.S. Geological Survey cannot update and maintain CES. Instead, statistical tools are under development to estimate mining costs from basic properties of mineral deposits such as tonnage, grade, mineralogy, depth, strip ratio, distance from infrastructure, rock strength, and work index. The first step was to reestimate "Taylor's Rule" which relates operating rate to available ore tonnage. The second step was to estimate statistical models of capital and operating costs for open pit porphyry copper mines with flotation concentrators. For a sample of 27 proposed porphyry copper projects, capital costs can be estimated from three variables: mineral processing rate, strip ratio, and distance from nearest railroad before mine construction began. Of all the variables tested, operating costs were found to be significantly correlated only with strip ratio.
Conference Paper↗
Mineral resources of the U.S. Atlantic continental margin
Most geologic materials may be usable resources in some form and at some time, whether it be for general land fill and aggregate, beach replenishment, construction material, or as a source of metals and fuels. Thus, most natural materials occurring within the Atlantic continental margin are resources, defined as “materials, including those only surmised to exist, that have present or anticipated future value” (U.S.G.S., 1980). Whether a resource becomes a reserve or not (an economically recoverable commodity) depends upon the properties and economic values of that material, which are determined by the following factors: (a) availability, concentration, and occurrence of the material; (b) methods of recovering and processing the commodity; (c) transportation costs of ore and beneficiated products; and (d) environmental setting and costs of permitting and mitigation. Also, the economics of a given mineral resource change dramatically in response to new technological advances, discoveries of new deposits, or as industrial and social demands change through time. An increasingly critical component associated with the economics for development of any mineral commodity, is a good geologic knowledge of the resource base.
Atlantic Continental Margin↗