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At least 415 records · Page 23Linked to original sources
USGS1998

Map showing areas with potential for garnet resources in bedrock and placer in the Blacktail Mountains and the Gravelly, Greenhorn, Ruby, and Snowcrest ranges of southwestern Montana

Garnet crystals, some of gem quality, have been sought by rock hounds for many years in the alluvial deposits of the Alder Gulch-Ruby River area. Since 1995, garnet have been extracted from these gravels for industrial products at two separately own placer mines in the region: (1) at Cominco American's "Ruby Garnet" operation at Alder , Montana and (2) at the "Sweetwater Garnet" operation in the Sweetwater Basin of the Ruby Range. The two placer mines excavate different types of garnetiferous deposits, but both produce sized concentrates of almandine garnet derived from similar source rocks.

Montana↗
USGS1988

KAr ages, chemical composition and geothermal significance of cenozoic basalt near the Jordan rift

Late Cenozoic mafic lavas crop out locally along the Jordan rift. Some of these lavas are spatially associated with thermal springs, and this association has prompted some workers to hypothesize that the hot water derives its thermal energy from the shallow, still hot intrusive roots of the volcanic rocks. However, all of the volcanic rocks appear to represent mantle-derived mafic magma that rose rather quickly to the Earth's surface, without filling crustal reservoirs within which differentiation would have produced evolved, derivative products. Moreover, the lavas are too old and of too small a volume to represent the surface expression of an active reservoir of magma within the crust. These interpretations of the volcanic geology are consistent with conclusions drawn from the chemistry of the thermal water; the water has equilibrated with host rocks at no more than 110°C, probably at depths of 2–3 km. Thus, thermal springs along the Jordan rift appear to reflect heating during circulation through a regional regime of average crustal heat flow (Galanis et at. , 1986). The magmatic activity may only be a second or third order contributor to this heat flow.

Geothermics↗
USGS1976

Geology and ore deposits of the Mahd Adh Dhahab District, Kingdom of Saudi Arabia

Mahd adh Dhahab is the principal gold-silver mine in Saudi Arabia; it was productive during three principal periods, two during ancient times (about 950 B.C. and 750-1258 A.D.) and one in modern times (1939-54). The early production is not known, but the recorded production in 1939-54 is 765,768 fine ounces gold and 1,002,029 ounces silver. The district is underlain by a sequence of pyroclastic and clastic rocks which probably belong to the Murdama Group. From oldest to youngest the units are andesite, lower agglomerate, lower tuff, upper agglomerate, and upper tuff. These units have been tilted northerly, forming a homocline, and they are complexly broken by six sets of faults; three of these sets, which strike N.25°-30°W., N.10°W. to N.20°E., and N.30°-60'E., contain productive quartz veins. The principal ore minerals are pyrite, chalcopyrite, sphalerite, galena, and minor tetrahedrite, argentite, and native gold and silver. The gold and silver occurs finely disseminated in the veins and in the altered selvages of the veins. Widespread potassic and propylitic alteration accompanied the ore-forming processes. Potassium feldspar was introduced during an early stage of vein formation. Isotopic analyses of lead in vein potassium feldspar and galena yield a model age of about 900-1050 million years with the possibility of the original lead source having been remobilized about 600 million years ago. Chlorite and carbonate are also prominent vein minerals.

Open-File Report↗
USGS1978

Gases and water isotopes in a geochemical section across the Larderello, Italy, geothermal field

Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by (1) Total gas contents increasing south to north from 0.003 to 0.05 mole fraction; (2) Constant CO2 (95??2 percent); near constant H2S (1.6??0.8), N2 (1.2??0.8), H2 (2??1), CH4 (1.2??1), and no O2 in the dry gas; (3) Presence of numerous, straight chain and branched C2 to C6 hydrocarbons plus benzene in amounts independent of CH4 contents with highest concentrations in the deeper wells; (4) Oxygen-18 contents of steam increasing south to north from -5.0??? to -0.4??? with little change in deuterium (-42??2???). These observations are interpreted as showing: (1) Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production; (2) Synthesis of CH4 from H2 and CO2 with CO2 and H2 produced by thermal metamorphism and rock-water reactions; (3) Extraction of C2 to C6 hydrocarbons from rock organic matter; (4) Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ???220??C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south. ?? 1978 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗
USGS2005

Inorganic, isotopic, and organic composition of high-chloride water from wells in a coastal southern California aquifer

Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Los Angeles. Wells with the higher Cl − concentrations were near faults that bound the valley. Depending on well construction, high-Cl − water from different sources may enter a well at different depths. For example, Cl − concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg/L, and Cl − concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg/L. These high-Cl − waters mix within the well during pumping and produce the water sampled at the surface discharge. Changes in the major ion, minor ion, trace element, and δ 34 S and δ 13 C isotopic composition of water in wells with depth were consistent with changes resulting from SO 4 reduction, precipitation of calcite, and cation exchange. The chemical and isotopic composition of high-Cl − water from deep wells trends towards the composition of oil-field production water from the study area. Chloride concentrations in oil-field production water present at depths 150 m beneath freshwater aquifers were 2200 mg/L, and Cl − concentrations in underlying marine rock were as high as 4400 mg/L. High-Cl − concentrations in water from deeper parts of wells were associated with dissolved organic C composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits. These compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination.

Applied Geochemistry↗
USGS2022

A quantitative soil-geomorphic framework for developing and mapping ecological site groups

Land management decisions need context about how landscapes will respond to different circumstances or actions. As ecologists’ understanding of nonlinear ecological dynamics has evolved into state-and-transition models (STMs), they have put more emphasis on defining and mapping the soil, geomorphological, and climate parameters that mediate these dynamics. The US Department of Agriculture Natural Resources Conservation Service ecological site descriptions (ESDs) have become the foremost system in classifying lands into ecological units based on STMs. However, an exhaustive inventory of ESDs has proved challenging to complete in the United States, and there have been questions about the consistency of detail in areas completed and the ability to objectively support some assertions made in existing ESDs. To address these issues, this study examines ESDs in the diverse Upper Colorado River region, where ESDs are only partially complete, to look at quantitative approaches to generalizing ecological site concepts based on unifying underlying soil, geomorphology, and climate patterns. Using existing ESDs and vegetation monitoring plot data, results show that a simple hierarchical soil geomorphic unit (SGU) framework based on topographic mediation of moisture, soil salinity, soil depth, slope, rock content, and soil texture can represent much of the ecological dynamics cataloged in ESDs. Analyses of reference plant production data, ecological state attribution, and regional monitoring data show that the new SGUs represent more variation than common climate parameters. This study also included predictively mapping SGUs at 30-m resolution (Kappa of 0.53, 74% agreement with top two predictions in validation). An optimized combination of SGUs with climate zones derived from an aridity index and maximum temperature of the hottest month resulted in an ecological site group framework that condensed over 826 unique ecological site records at various stages of completeness in the regional soil survey down to 35 intuitive and mappable ecological site groups.

Rangeland Ecology and Management↗
USGS1981

Summary report on the regional geology, environmental considerations for development, petroleum potential, and estimates of undiscovered recoverable oil and gas resources of the United States southeastern Atlantic continental margin in the area of proposed oil and gas lease sale No. 78

This report summarizes our general knowledge of the geology and petroleum potential, as well as potential problems and hazards associated with development of petroleum resources, of the area proposed for nominations for lease sale number 78. This area includes the U.S. eastern continental margin from the mouth of Chesapeake Bay to approximately Cape Canaveral, Florida, including the upper Continental Slope and inner Blake Plateau. The area for possible sales and the previous areas leased are shown in figure 1; physiographic features of the region are shown in figure 2. Six exploration wells have been drilled within the proposed lease area (figs. 3 and 4) but no commercial discoveries have been made. All six wells were drilled on the Continental Shelf in the Southeast Georgia Embayment. No commercial production has been obtained onshore in the region. The areas already drilled have thin sedimentary sections, and the deeper rocks are dominantly continental facies. Petroleum formation may have been hindered by a lack of organic material and sufficient burial for thermal maturation. Analysis of drill and seismic profiling data presented here, however, indicates that a much thicker sedimentary rock section containing a much higher proportion of marine deposits exists seaward of the exploratory wells on the Continental Shelf. These geologic conditions imply that the offshore basins may be more favorable environments for generating petroleum.

Open-File Report↗
USGS2009

Low-btu gas in the US Midcontinent: A challenge for geologists and engineers

Several low-btu gas plays can be defined by mapping gas quality by geological horizon in the Midcontinent. Some of the more inviting plays include Permian strata west of the Central Kansas uplift and on the eastern flank of Hugoton field and Mississippi chat and other pays that subcrop beneath (and directly overlie) the basal Pennsylvanian angular unconformity at the southern end of the Central Kansas uplift. Successful development of these plays will require the cooperation of reservoir geologists and process engineers so that the gas can be economically upgraded and sold at a nominal pipeline quality of 950 btu/scf or greater. Nitrogen is the major noncombustible contaminant in these gas fields, and various processes can be utilized to separate it from the hydrocarbon gases. Helium, which is usually found in percentages corresponding to nitrogen, is a possible ancillary sales product in this region. Its separation from the nitrogen, of course, requires additional processing. The engineering solution for low-btu gas depends on the rates, volumes, and chemistry of the gas needing upgrading. Cryogenic methods of nitrogen removal are classically used for larger feed volumes, but smaller feed volumes characteristic of isolated, low-pressure gas fields can now be handled by available small-scale PSA technologies. Operations of these PSA plants are now downscaled for upgrading stripper well gas production. Any nitrogen separation process should be sized, within reason, to match the anticipated flow rate. If the reservoir rock surprises to the upside, the modularity of the upgrading units is critical, for they can be stacked to meet higher volumes. If a reservoir disappoints (and some will), modularity allows the asset to be moved to another site without breaking the bank.

Oil & Gas Journal↗
USGS2024

Updated three-dimensional temperature maps for the Great Basin, USA

As part of the periodic update of the geothermal energy assessments for the USA (e.g., last update by Williams and others, 2008), a new three-dimensional temperature map has been constructed for the Great Basin, USA. Williams and DeAngelo (2011) identified uncertainty in estimates of conductive heat flow near land surface as the largest contributor to uncertainty in previously published temperature maps. The new temperature maps incorporate new conductive heat flow estimates developed by DeAngelo and others (2023). Predicted temperatures at depth are compared with representative measurements (for conductively dominated conditions), showing good agreement under relatively simple uniform conditions. Inputs included radiogenic heat production for all layers of 1.89 μW/m 3 , effective bulk thermal conductivity of 2.7 W/m/°C for all rocks underlying sedimentary basins, and a previously published (Williams and DeAngelo, 2011) empirically driven estimate of increasing thermal conductivity with depth in sedimentary sequences. The resulting three-dimensional temperature model is published in a USGS data release associated with this manuscript (Burns and others, 2023).

Arizona, California, Idaho, Nevada, Oregon, Utah↗
USGS1983

Petroleum geology and resources of southeastern Mexico, northern Guatemala, and Belize

Petroleum deposits in southeastern Mexico and Guatemala occur in two main basinal provinces, the Gulf Coast Tertiary basin area, which includes the Reforma and offshore Campeche Mesozoic fields, and the Peten basin of eastern Chiapas State (Mexico) and Guatemala. Gas production is mainly from Tertiary sandstone reservoirs of Miocene age. Major oil production, in order of importance, is from Cretaceous, Paleocene, and Jurassic carbonate reservoirs in the Reforma and offshore Campeche areas. Several small oil fields have been discovered in Cretaceous carbonate reservoirs in west-central Guatemala, and one major discovery has been reported in northwestern Guatemala. Small- to medium-sized oil accumulations also occur in Miocene sandstone reservoirs on salt structures in the Isthmus Saline basin of western Tabasco State, Mexico. Almost all important production is in salt structure traps or on domes and anticlines that may be related to deep-seated salt structures. Some minor oil production has occurred in Cretaceous carbonate reservoirs in a buried overthrust belt along the west flank of the Veracruz basin. The sedimentary cover of Paleozoic through Tertiary rocks ranges in thickness from about 6,000 m (20,000 ft) to as much as 12,000 m (40,000 ft) or more in most of the region. Paleozoic marine carbonate and clastic rocks 1,000 to 2,000 m (3,300 to 6,500 ft) thick overlie the metamorphic and igneous basement in part of the region; Triassic through Middle Jurassic red beds and evaporite deposits, including halite, apparently are present throughout the region, deposited in part in a Triassic graben system. Upper Jurassic (Oxfordian) through Cretaceous rocks make up the bulk of the Mesozoic regional carbonate bank complex, which dominates most of the area. Tertiary marine and continental clastic rocks, some of deep water origin, 3,000 to 10,000 m (10,000 to 35,000 ft) thick, are present in the coastal plain Tertiary basins. These beds grade eastward into a carbonate sequence that overlies the Mesozoic carbonate complex on the Yucatan platform. During the past 10 years, about 50 large oil fields were discovered in the Reforma and offshore Campeche areas. Oil is produced from intensely microfractured Cretaceous, Paleocene, and Upper Jurassic dolomite reservoirs on blockfaulted salt swells or domes. Most fields are located in the Mesozoic carbonate-bank margin and forebank talus (Tamabra) facies, which passes through the offshore Campeche and onshore Reforma areas. Oil source rocks are believed to be organic-rich shales and shaly carbonate rocks of latest Jurassic and possibly Early Cretaceous age. At least six of the Mesozoic discoveries are giant or supergiant fields. The largest is the Cantarell complex (about 8 billion to 10 billion barrels (BB)) in the offshore Campeche area and the Bermudez complex (about 8 BB) in the Reforma onshore area. Oil columns are unusually large (from 50 m to as much as 1,000 m, or 160 ft to 3,300 ft). Production rates are extremely high, averaging at least 3,000 to 5,000 barrels of oil per day (bo/d); some wells produce more than 20,000 bo/d, particularly in the offshore Campeche area, where 30,000- to 60,000-bo/d wells are reported. Tertiary basin fields produce primarily from Miocene sandstone reservoirs. About 50 of these are oil fields ranging from 1 million barrels (MMB) to 200 MMB in size, located on faulted salt structures in the Isthmus Saline basin. Another 30 are gas or gas-condensate fields of a few billion cubic feet to 3 trillion to 4 trillion cubic feet (Tcf) located on salt structures or probable salt structures in the Macuspana, Comalcalco, Isthmus Saline, and Veracruz basins. Source rocks for the gas are believed to be carbonaceous shales interbedded with the sandstone reservoir bodies. Identified reserves in the southeastern Mexico-Guatemala area, almost all in the Mesozoic fields, are about 53 BB of oil, 3 BB of natural gas liquids, and 65 Tcf of gas. The estimat

Circular↗
USGS2013

Report A: Fish distribution and population dynamics in Rock Creek, Klickitat County, Washington

The U.S. Geological Survey collaborated with the Yakama Nation starting in fall of 2009 to study the fish populations in Rock Creek, a Washington State tributary of the Columbia River 21 kilometers upstream of John Day Dam. Prior to this study, very little was known about the ESA-listed (threatened) Mid-Columbia River steelhead (Oncorhynchus mykiss) population in this arid watershed with intermittent stream flow. The objectives of the study were to quantify fish habitat, document fish distribution, abundance, and movement, and identify areas of high salmonid productivity. To accomplish these objectives, we electrofished in the spring and fall, documenting the distribution and relative abundance of all fish species to evaluate the influence of biotic factors on salmonid productivity and survival. We surveyed the distribution of perennial pools and established a network of automated temperature recording devices from river kilometer (rkm) 2 to 23 in Rock Creek and rkm 0 to 8 in Squaw Creek, a major tributary entering Rock Creek at rkm 13, to better understand the abiotic factors influencing the salmonid populations. Salmonid abundance estimates were conducted using a mark-recapture method in a systematic subsample of the perennial pools. The proportion and timing of salmonids migrating from these pools were assessed by building, installing, and operating two passive integrated transponder (PIT) tag interrogation systems at rkm 5 and at the confluence with Squaw Creek (rkm 13). From fall 2009 to fall 2012, we PIT-tagged 3,088 O. mykiss and 151 coho salmon (O. kisutch) during electrofishing efforts. In the lowest flow periods of 2010 to 2012, we found that an average of 36% of the surveyed streambed length was dry, and 17% remained as perennial pools. The maximum temperature recorded in those pools was 24.4°C, but most pools had a maximum temperature that was less than 21°C. O. mykiss were present in most pools, and non-native fish species, such as smallmouth bass (Micropterus dolomieu), were typically found downstream of rkm 5. Coho salmon were present in nearly every pool that was sampled in 2011, but were rare in 2009, 2010, and 2012. About 27% of the PIT-tagged O. mykiss and 38% of the PIT-tagged coho were detected outmigrating to the Columbia River. Of those fish, 92% (n=695) were detected leaving Rock Creek as smolts in April and May. As of November 2013, 9 O. mykiss and 4 coho that we tagged in Rock Creek as juveniles have returned as adults to Bonneville Dam. Also, an additional 34 PIT-tagged adult steelhead, and 6 PIT-tagged coho that were tagged by other groups have been detected in Rock Creek, of which, 22 were of known origin (tagged as juveniles). Of these, 85% were tagged or released in the Snake River. The PIT-tag interrogation systems will be operated for several more years to allow time for the fish tagged as juveniles to return as adults and complete their life cycles. The Yakama Nation will use the information collected from this study to prioritize and gauge the effectiveness of ongoing and future restoration actions.

Washington↗
USGS2008

Methane hydrates

Gas hydrate is a solid, naturally occurring substance consisting predominantly of methane gas and water. Recent scientific drilling programs in Japan, Canada, the United States, Korea and India have demonstrated that gas hydrate occurs broadly and in a variety of forms in shallow sediments of the outer continental shelves and in Arctic regions. Field, laboratory and numerical modelling studies conducted to date indicate that gas can be extracted from gas hydrates with existing production technologies, particularly for those deposits in which the gas hydrate exists as pore-filling grains at high saturation in sand-rich reservoirs. A series of regional resource assessments indicate that substantial volumes of gas hydrate likely exist in sand-rich deposits. Recent field programs in Japan, Canada and in the United States have demonstrated the technical viability of methane extraction from gas-hydrate-bearing sand reservoirs and have investigated a range of potential production scenarios. At present, basic reservoir depressurisation shows the greatest promise and can be conducted using primarily standard industry equipment and procedures. Depressurisation is expected to be the foundation of future production systems; additional processes, such as thermal stimulation, mechanical stimulation and chemical injection, will likely also be integrated as dictated by local geological and other conditions. An innovative carbon dioxide and methane swapping technology is also being studied as a method to produce gas from select gas hydrate deposits. In addition, substantial additional volumes of gas hydrate have been found in dense arrays of grain-displacing veins and nodules in fine-grained, clay-dominated sediments; however, to date, no field tests, and very limited numerical modelling, have been conducted with regard to the production potential of such accumulations. Work remains to further refine: (1) the marine resource volumes within potential accumulations that can be produced through exploratory drilling programs; (2) the tools for gas hydrate detection and characterisation from remote sensing data; (3) the details of gas hydrate reservoir production behaviour through additional, well-monitored and longer duration field tests and (4) the understanding of the potential environmental impacts of gas hydrate resource development. The results of future production tests, in the context of varying market and energy supply conditions around the globe, will be the key to determine the ultimate timing and scale of the commercial production of natural gas from gas hydrates.

Book chapter↗
USGS2020

Natural gas hydrates: Status of potential as an energy resource

Gas hydrate is a widespread naturally-occurring combination of water and natural gases. Gas hydrate is found in shallow sediments of deepwater regions of the continental margins and in areas of continuous permafrost. Where gas supply is sufficient and migration pathways connect gas sources to favorable reservoirs, gas hydrate can accumulate to resource densities that may be attractive for gas production. Global research on the potential commercial viability of gas extraction from gas hydrates continues, predominantly in Asia and in the United States, where current efforts focus on the controlled destabilization of high-saturation deposits housed in sand and/or silt-rich reservoirs. This chapter reviews the current state of gas hydrate resource exploration and appraisal, the most promising production approaches identified to date, and the likely technical challenges to commercial production.

Book chapter↗
USGS1979

Effects of karst and geologic structure on the circulation of water and permeability in carbonate aquifers

The results of the natural processes caused by solution and leaching of limestone, dolomite, gypsum, salt and other soluble rocks, is known as karst. Development of karst is commonly known as karstification, which may have a pronounced effect on the topography, hydrology and environment, especially where such karst features as sinkholes and vertical solution shafts extend below the land surface and intersect lateral solution passages, cavities, caverns and other karst features in carbonate rocks. Karst features may be divided into two groups: (1) surficial features that do not extend far below the surface; and (2) karst features such as sinkholes that extend below the surface and affect the circulation of water below. The permeability of the most productive carbonate aquifers is due chiefly to enlargement of fractures and other openings by circulation of water. Important controlling factors responsible for the development of karst and permeability in carbonate aquifers include: (1) climate, topography, and presence of soluble rocks; (2) geologic structure; (3) nature of underground circulation; and (4) base level. Another important factor is the condition of the surface of the carbonate rocks at the time they are exposed to meteoric water. A carbonate rock surface, with soil or relatively permeable, less soluble cover, is more favorable for initiation of karstification and solution than bare rocks. Water percolates downward through the cover to the underlying carbonate rocks instead of running off on the surface. Also, the water becomes more corrosive as it percolates through the permeable cover to the underlying carbonate rocks. Where there is no cover or the cover has been removed, the carbonate rocks become case hardened and resistant to erosion. However, in regions underlain not only by carbonate rocks but also by beds of anhydrite, gypsum and salt, such as the Hueco Plateau in southeastern New Mexico, subsurface solution may occur where water without natural acids moves down from bare rock surfaces through cracks to the beds that are more soluble than carbonate rocks. For example, in the area of Carlsbad Caverns in southeastern New Mexico, much of the water responsible for solution that formed the caverns apparently entered the groundwater system through large open fractures and did not form sinkhole topography. East of the Carlsbad Caverns, however, in the Pecos River Valley where the carbonate rocks are overlain by the less soluble Ogallala Formation of Late Tertiary age, solution began along escarpments as the Pecos River and its tributaries cut through the less soluble cover. As these escarpments retreated, sinkholes and other karst features developed. Joints or fractures are essential for initiation of downward percolation of water in compact carbonate rocks such as some Paleozoic limestone in which there is no intergranular permeability. Also joints or fractures and bedding planes may be essential in the initiation of lateral movement of water in the zone of saturation. Where conditions of recharge and discharge are favorable, groundwater may move parallel to the dip. However, the direction of movement of water in most carbonate rocks is not necessarily down dip or parallel to the dip. The general direction of movement of both surface and groundwater may be parallel to the strike in a breached anticline. Faults may restrict the lateral movement of water, especially if water-bearing beds are faulted against relatively impervious beds. Conversely, some fault may serve as avenues through which water may move as, for example, in the Cretaceous Edwards aquifer in the San Antonio area, Texas. Karst aquifers, chiefly carbonate rocks, may be placed in three groups according to water-bearing capacity. Water in aquifers of group 1 occurs chiefly in joints, fractures, and other openings that have not been enlarged by solution. The yield of wells is small. Aquifers in group 2 , with low to intermediate yields, are those in which water occurs in joints and fractures with some cavities and channels enlarged by solution. Aquifers in group 3 are those in which the yield of wells and springs range from intermediate to very large. This group includes five of the most productive aquifers in the U.S.A. The water-bearing beds of all of these productive aquifers, except the Biscayne aquifer in southeastern Florida, contain buried paleokarst in which the permeability has been reactivated and enlarged by the present circulation system.

Journal of Hydrology↗
USGS1963

Epigenetic, diplogenetic, syngenetic, and lithogene deposits

Much of the disagreement over " epigenetic " And " Syngenetic " Deposits Is Semantic; Some Ores And altered rocks are in part syngenetic and in part epigenetic and for them the term " diplogenetic " is proposed. All these terms are primarily time terms related to the contemporaneity of the deposit and the enclosing rock, but in a secondary sense they are space terms; they do not, however, imply process of formation or source of the chemical constituents. Process or source terms such as "magmatic," "hydro-thermal," "sedimentary" are generally satisfactory, but the process term "lateral secretion" is now vague in meaning. A more precise term is needed for the process of mobilization of elements from a solid rock and their transportation and redeposition elsewhere; for this process I propose the term " lithogene " ("stone-born"), to stress the source and process as do "magmatic" and "sedimentary." Such deposits could be derived from syngenetic , diplogenetic , or epigenetic deposits through the action of metamorphic, hydrothermal, supergene or other solutions. If one wishes, however, to emphasize the distance the mobilized elements have moved from the source rock, the resulting deposit can be described best as a locally derived lithogene deposit ("lateral secretion"), or as a regionally derived lithogene deposit ("product of regional metamorphism"). The classification of many deposits such as epigenetic replacement bodies of magnetite in limestone, and syngenetic gold in recent placers is not controversial; however, where large parts of the mineral deposit are made up both of syngenetic elements and introduced elements, the term " diplogenetic " is appropriate. Examples include mineral deposits in which syngenetic cations are united with epigenetic anions, as in fluorite replacements in limestones, or where the reverse relationship holds and epigenetic cations are united to syngenetic sulfur or other anions-as may be true of certain black cupriferous shales of the Mansfeld type. Guides for distinguishing the various types of mineral deposits are discussed at length and include: mineralogy; texture; isotopic composition of hydrogen, carbon, oxygen, sulfur, and perhaps other elements; form; age relations; alteration; zoning; position and quantitative adequacy of supposed source rocks; lithology; structural geology; paleogeography; and regional geologic relations. The criteria developed are used in a critical review of several examples of controversial deposits -including the African Copper-belt deposits and those of the graphitic schists of Fenno-Scandia.

Economic Geology↗
USGS1985

K-Ar ages and Pb, Sr isotopic characteristics of Cenozoic volcanic rocks in Shandong Province, China

28 samples of Cenozoic volcanic rocks collected from Shandong Province have been dated by K-Ar method. They are mainly Neogene with an age range of 4-19 m. y. The basalts from Linqu and Yishui in west Shandong Province are Miocene and those from Penglai and Qixia in east Shandong Province are Miocene and Pliocene in age. The basalts from Wudi in north Shandong Province are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2-3 m. y. Pb and Sr isotopic compositions and U, Th, Pb, Rb, Sr, and major elements in most of the samples were determined. The isotopic compositions are:206Pb/204Pb-16.92-18.48,207Pb/204Pb-15.30-15.59,208Pb/204Pb-37.83-38.54, and (87Sr/86Sr)i-0.70327-0.70632. There are some positive or negative linear correlations between206Pb/204Pb and207Pb/204Pb, Pb isotopes and Pb content, Pb isotopes and Sr isotopes, and Sr isotopes and other elements. The basaltic rocks from east and west Shandong Province have somewhat differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source, although they were influenced, to some extent, by the contamination of crustal materials. ?? 1985 Institute of Geochemistry, Chinese Academy of Sciences.

Chinese Journal of Geochemistry↗
USGS2013

Pre-flight calibration and initial data processing for the ChemCam laser-induced breakdown spectroscopy instrument on the Mars Science Laboratory rover

The ChemCam instrument package on the Mars Science Laboratory rover, Curiosity, is the first planetary science instrument to employ laser-induced breakdown spectroscopy (LIBS) to determine the compositions of geological samples on another planet. Pre-processing of the spectra involves subtracting the ambient light background, removing noise, removing the electron continuum, calibrating for the wavelength, correcting for the variable distance to the target, and applying a wavelength-dependent correction for the instrument response. Further processing of the data uses multivariate and univariate comparisons with a LIBS spectral library developed prior to launch as well as comparisons with several on-board standards post-landing. The level-2 data products include semi-quantitative abundances derived from partial least squares regression. A LIBS spectral library was developed using 69 rock standards in the form of pressed powder disks, glasses, and ceramics to minimize heterogeneity on the scale of the observation (350–550 μm dia.). The standards covered typical compositional ranges of igneous materials and also included sulfates, carbonates, and phyllosilicates. The provenance and elemental and mineralogical compositions of these standards are described. Spectral characteristics of this data set are presented, including the size distribution and integrated irradiances of the plasmas, and a proxy for plasma temperature as a function of distance from the instrument. Two laboratory-based clones of ChemCam reside in Los Alamos and Toulouse for the purpose of adding new spectra to the database as the need arises. Sensitivity to differences in wavelength correlation to spectral channels and spectral resolution has been investigated, indicating that spectral registration needs to be within half a pixel and resolution needs to match within 1.5 to 2.6 pixels. Absolute errors are tabulated for derived compositions of each major element in each standard using PLS regression. Sources of errors are investigated and discussed, and methods for improving the analytical accuracy of compositions derived from ChemCam spectra are discussed.

Spectrochimica Acta Part B: Atomic Spectroscopy↗
USGS2014

Notes on the elasticity of the Lloyd sand on Long Island, New York

The Lloyd sand is a productive artesian aquifer underlying all of Long Island except the westernmost part. It rests unconformably upon a floor of crystalline rock that slopes toward the southeast at about 100 feet to the mile. Locally the bed‐rock surface has a relief of more than 100 feet. The Lloyd sand consists of white quartz‐sand and gravel, with some layers of clay. It is considered to be part of the Raritan—the basal formation of the Upper Cretaceous series. At Rockaway Park, on the south shore of the Island, the Lloyd is about 200 feet thick and is overlain by 300 feet of clays of Raritan age. The Raritan clays are in turn overlain by about 150 feet of sands, believed to be of Magothy age, and about 315 feet of Pleistocene sediments.

New York↗