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

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At least 73 records · Page 4Linked to original sources
USGS1981

Geochemical evidence for a Brooks Range mineral belt, Alaska

Geochemical studies in the central Brooks Range, Alaska, delineate a regional, structurally controlled mineral belt in east—west-trending metamorphic rocks and adjacent metasedimentary rocks. The mineral belt extends eastward from the Ambler River quadrangle to the Chandalar and Philip Smith quadrangles, Alaska, from 147° to 156°W. longitude, a distance of more than 375 km, and spans a width from 67° to 69°N. latitude, a distance of more than 222 km. Within this belt are several occurrences of copper and molybdenum mineralization associated with meta-igneous, metasedimentary, and metavolcanic rocks; the geochemical study delineates target areas for additional occurrences. A total of 4677 stream-sediment and 2286 panned-concentrate samples were collected in the central Brooks Range, Alaska, from 1975 to 1979. The −80 mesh (< 177 μm) stream sediment and the heavy (specific gravity > 2.86) nonmagnetic fraction of the panned concentrates from stream sediment were analyzed by semiquantitative spectrographic methods. Two geochemical suites were recognized in this investigation; a base-metal suite of copper-lead-zinc and a molybdenum suite of molybdenum-tin-tungsten. These suites suggest several types of mineralization within the metamorphic belt. Anomalies in molybdenum with associated Cu and W suggest a potential porphyry molybdenum system associated with meta-igneous rocks. This regional study indicates that areas of metaigneous rocks in the central metamorphic belt are target areas for potential mineralized porphyry systems and that areas of metavolcanic rocks are target areas for potential massive sulfide mineralization.

Alaska↗
USGS1981

Heavy metals and manganese oxides in the genesee watershed, New York state: Effects of geology and land use

Manganese oxide coatings on gravels from 255 sites on tributary streams in the Genesee River Watershed were analyzed for Mn, Fe, Zn, Cd, Co, Ni, Pb, and Cu. The results were compared with data on bedrock geology, surficial geology and land use, using factor analysis and stepwise multiple regression. All metals except Pb show strong positive correlation with Mn. This association results from the well-known tendency of Mn oxide precipitates to adsorb and incorporate dissolved trace metals. Pb may be present in a separate phase on the gravel surfaces; alternatively Pb abundance may be so strongly influenced by environmental factors that the effect of varying abundance of the carrier phase becomes relatively unimportant. When the effects of varying Mn abundance are allowed for, Pb and to a lesser extent Zn and Cu abundances are seen to be related to commercial, industrial and residential land use. In addition to this pollution effect, all the trace metals, Cd and Ni most strongly, tend to be more abundant in oxide coatings from streams in the forested uplands in the southern part of the area. This probably reflects increased geochemical mobility of the metals in the more acid soils and groundwater of the southern region. A strong Zn anomaly is present in streams draining areas underlain by the Lockport Formation. Oxide coatings in these streams contain up to 5% Zn, originating from disseminated sphalerite in the Lockport and secondary Zn concentrations in the overlying muck soils. The same group of metals, plus calcium and loss on ignition, were determined in the silt and clay (minus 230 mesh) fraction of stream sediments from 129 of the same sites, using a hot nitric acid leach. The amounts of manganese in the sediments are low (average 1020 ppm) and manganese oxides are, at most, of relatively minor significance in the trace-metal geochemistry of these sediments. The bulk of the trace metals in sediment appears to be associated with iron oxides, clays and organic matter.

New York↗
USGS1981

Regional geochemical studies in the Patagonia Mountains, Santa Cruz County, Arizona

The Patagonia Mountains in southern Arizona contain the deeply buried porphyry copper system at Red Mountain as well as a number of other base- and precious-metal mines and prospects. The range contains complex Basin and Range geology with units ranging in age from Precambrian to Holocene. Rock types present include igneous intrusive and extrusive units as well as sedimentary and metamorphic units, most of which have been tectonically disturbed. A total of 264 stream-sediment samples were collected and analyzed for 32 elements. Geochemical maps for Sb, Ag, Pb, Te, B, Mn, Au, Zn, Cu (total), Cu (cold-extractable), and Mo, as well as for Cu (cold-extractable)/Cu (total) and Fe/Mn, are presented. Anomaly patterns for these elements generally occur over the Red Mountain deposit and (or) along a north-northwest trend parallel to the major Harshaw Creek Fault. Much of the entire area sampled contains widespread anomalies for Pb, Te, and Cu; the other elements are only locally anomalous. Various plots of ratios of Cu (cold-extractable) to Cu (total) did not produce any new information not readily apparent on either one of the two copper maps. A plot of ratios of Fe to Mn delineated many areas of pyrite mineralization. Several of these areas may represent the pyritic halos around deeply buried porphyry copper systems. The best ore guide for the Red Mountain porphyry system is the coincidence of positive anomalies of Mo, Pb, and Te and a negative anomaly of Mn. Other areas with anomalies of the same suite of elements are present within the Patagonia Mountains. It is concluded that geochemical sampling, even in a highly contaminated area, can be useful in delineating major geologic features, such as porphyry copper belts and major faults. Multielement geochemical surveys on a regional scale can effectively locate large, deeply buried, zoned mineral systems such as that at Red Mountain. Plots of element ratios, where adequately understood, can provide geochemical information not readily discernible from plots of single elements alone.

Arizona↗
USGS1981

Sequential extraction techniques applied to a porphyry copper deposit in the basin and range province

Samples of minus-80-mesh (<180 μm) stream sediment, rock containing exposed fracture coatings, and jarosite and chrysocolla were collected from an area surrounding the North Silver Bell porphyry Cu deposit near Tucson, Arizona. The samples were subjected to a series of extractions in a scheme originally designed for use on samples from humid or sub-humid environments, in which the following fractions can effectively be separated: (1) carbonates and exchangeable metals; (2) Mn oxides; (3) organic compounds and sulfides; (4) hydrous Fe oxides; and (5) residual crystalline minerals. Jarosite and chrysocolla, two major minerals of the North Silver Bell area, were found to dissolve over two or more steps of the extraction scheme. The results represent only a limited number of samples from one copper deposit. Nevertheless, they do suggest that in a semiarid to arid environment, where mechanical dispersion of such minerals predominates, uncritical assignment of unique phases, such as Mn oxides or organics to a given extraction would lead to false interpretations of weathering processes. However, the relative proportions of elements dissolved in each step of the jarosite and chrysocolla extractions could be used as a “fingerprint” for recognition of the presence of these two minerals in the stream-sediment and rock samples. The relative abundance of hydrous Fe oxide and jarosite and the alteration zoning could be mapped using data from jarosite and chrysocolla extractions. Manganese oxides were also found to have a greater influence on Zn than on Cu or Pb during supergene alteration. The rapid change in relative importance of the first (1 M -acetic acid) extraction for Cu, Zn, and Pb near the mineralized zone suggested the occurrence of minor hydromorphic processes within the stream sediments. Thus, the acetic acid extraction proved the most effective for pinpointing mineralization in sediments. In contrast, the residual fraction had the longest dispersion train, suggesting that total metal concentrations are most effective in arid environments for reconnaissance surveys.

Journal of Geochemical Exploration↗
USGS1981

Geochemical prospecting for hydrocarbons in the outer continental shelf, Southern Bering Sea, Alaska

This geochemical survey is based on 20 stations located on the outer continental shelf of the southern Bering Sea in an area of 30,000 km 2 that includes St. George basin. Hydrocarbon gases from sediment samples recovered by gravity coring at each of the stations were analyzed by gas chromatography. Data are summarized for a subbottom depth of 0.5 m, because core penetration, although variable, reached at least this depth at all of these stations. Two parameters were used to distinguish the possible presence of thermogenic hydrocarbons: (1) ratios less than 50 of methane to ethane plus propane; and (2) ratios greater than 1 of ethane to ethene. No major hydrocarbon anomalies were discovered; however, at two stations at the northern end of St. George basin, our data indicate that thermogenic hydrocarbons may be present at depth. Major faulting in the vicinity of these stations could provide the pathways for the gas.

Journal of Geochemical Exploration↗
USGS1981

Estimation of the geochemical threshold and its statistical significance

A statistic is proposed for estimating the geochemical threshold and its statistical significance, or it may be used to identify a group of extreme values that can be tested for significance by other means. The statistic is the maximum gap between adjacent values in an ordered array after each gap has been adjusted for the expected frequency. The values in the ordered array are geochemical values transformed by either ln( χ - α ) or ln( α - χ ) and then standardized so that the mean is zero and the variance is unity. The expected frequency is taken from a fitted normal curve with unit area. The midpoint of an adjusted gap that exceeds the corresponding critical value may be taken as an estimate of the geochemical threshold, and the associated probability indicates the likelihood that the threshold separates two geochemical populations. The adjusted gap test may fail to identify threshold values if the variation tends to be continuous from background values to the higher values that reflect mineralized ground. However, the test will serve to identify other anomalies that may be too subtle to have been noted by other means.

Journal of Geochemical Exploration↗
USGS1982

Uranium in spring water and bryophytes at basin creek in central idaho

Arkosic sandstones and conglomerates of Tertiary age beneath the Challis Volcanics of Eocene age at Basin Creek, 10 km northeast of Stanley, Idaho, contain uranium-bearing vitrainized carbon fragments. The economic potential of these sandstones and conglomerates is currently being assessed. Springs abound at the contacts of rock units, and water from these springs supports abundant growths of bryophytes (mosses and liverworts). Water from 22 springs and associated bryophytes were sampled; two springs were found to contain apparently anomalous concentrations (normalized) of uranium — as much as 6.5 μg/L (ppb) in water and 1800 μg/g (ppm) in ash of mosses. Moss samples from both springs also contained anomalous concentrations of arsenic, and one contained highly anomalous amounts of beryllium. Water from a third spring contained slightly anomalous amounts of uranium, and two species of mosses at the spring contained anomalous uranium (400 and 700 μg/g) and high levels of both cadmium and lead. Water from a fourth spring was normal for uranium (0.18 μg/L), but the moss from the water contained a moderate uranium level and highly anomalous concentrations of lead, germanium, and thallium. These results suggest that, in the Basin Creek area, moss sampling at springs may give a more reliable indication of uranium occurrence than would water sampling. The reason for this may be the ability of mosses to concentrate uranium and its associated pathfinder elements and to integrate uranium fluctuations that occur in the spring water over any period of time.

Idaho↗
USGS1982

Guidelines for finding concretionary Mn-Fe oxides in streams

Concretionary Mn-Fe oxides in streams form at interfaces between oxidizing and reducing environments. A reducing environment produces waters high in dissolved Mn and Fe, and an oxidizing environment causes precipitation. Mineralogical, microprobe, and optical studies of concretionary Mn-Fe oxides may further our understanding of the role of Mn-Fe oxides in determining the trace-element geochemistry of stream sediments.

Journal of Geochemical Exploration↗
USGS1983

Scoresum - A technique for displaying and evaluating multi-element geochemical information, with examples of its use in regional mineral assessment programs

A technique called SCORESUM was developed to display a maximum of multi-element geochemical information on a minimum number of maps for mineral assessment purposes. The technique can be done manually for a small analytical data set or can be done with a computer for a large data set. SCORESUM can be used with highly censored data and can also weight samples so as to minimize the chemical differences of diverse lithologies in different parts of a given study area. The full range of reported analyses for each element of interest in a data set is divided into four categories. Anomaly scores — values of O (background), 1 (weakly anomalous), 2 (moderately anomalous), and 3 (strongly anomalous) — are substituted for all of the analyses falling into each of the four categories. A group of elements based on known or suspected association in altered or mineralized areas is selected for study and the anomaly scores for these elements are summed for each sample site and then plotted on a map. Some of the results of geochemical studies conducted for mineral assessments in two areas are briefly described. The first area, the Mokelumne Wilderness and vicinity, is a relatively small and geologically simple one. The second, the Walker Lake 1° × 2° quadrangle, is a large area that has extremely complex geology and that contains a number of different mineral deposit environments. These two studies provide examples of how the SCORESUM technique has been used (1) to enhance relatively small but anomalous areas and (2) to delineate and rank areas containing geochemical signatures for specific suites of elements related to certain types of alteration or mineralization.

Journal of Geochemical Exploration↗
USGS1983

The use of sagebrush (Artemisia) as a biogeochemical indicator of base-metal deposits in Precambrian rocks of west-central Colorado

The efficacy of sagebrush ( Artemisia ) as a biogeochemical indicator of base-metal mineralization in stratabound Precambrian ore deposits in west-central Colorado was investigated by collecting new (mostly flowering) growth from several sagebrush shrubs over and near five such deposits in three different areas. These are the Sedalia mine and two mines in the Turret district near Salida, and two mines in the Cochetopa district southeast of Gunnison. Two species were used, A. tridentata and A. frigida , depending on the area. Sagebrush clippings were separated into two subsamples consisting of (1) stems, and (2) leaves and blossoms stripped from the stems. These subsamples were ashed separately and the ash analyzed with an emission spectrograph for 30 elements. There appear to be no appreciable differences in the analyses of the two subsamples, indicating that composite samples would provide adequate information for further investigations. Eight of these elements, Ag, Bi, Cu, Pb, Sn, Y, Zn, and Zr, are present in notably higher concentrations in the ash of samples growing over mineralized ground than in that of control samples growing over barren ground. Although the distribution pattern, and the number of these anomalous elements, differs at each of the five localities, three of them, silver, copper, and lead, show good contrast and close association with subjacent mineralization in all five study areas.

Journal of Geochemical Exploration↗
USGS1985

The copper-nickel concentration log: A tool for stratigraphic interpretation within the ultramafic and basal zones of the stillwater complex, Montana

An analogue to the electric well log was devised for copper-nickel concentration drill-hole data from the Basal and lower part of the Ultramafic zones of the Stillwater Complex using automated data processing. The copper-nickel concentration logs graphically represent intensity (concentration) values that reflect the distribution of the elements in sulfide and silicate minerals. Four major patterns are recognized by their characteristic variations in copper and nickel intensity: (1) relatively flat, low-level copper-intensity signatures associated with arcuate nickel-intensity patterns that correlate with rocks in the Peridotite member of the Ultramafic zone; (2) arcuate or bulb-like patterns of copper and nickel intensity that correlate closely with the Basal bronzite cumulate member of the Basal zone; (3) complex patterns consisting of intervals of low-intensity copper and moderate-intensity nickel, spikes of high nickel and copper intensity, and high copper intensity associated with low nickel intensity that correlate respectively with cordierite-pyroxene hornfels, massive sulfide, norites and mineralized diabase dikes in the Basal norite member; and (4) large intervals of extremely low copper and nickel intensity that correlate with quartz-orthopyroxene hornfels. The recognition and interpretation of these patterns allow two- and three-dimensional stratigraphic and lithologic reconstructions to be done by means of concentration-log correlations instead of variable quality lithologic logging.

Journal of Geochemical Exploration↗
USGS1985

Correlations among hydrocarbon microseepage, soil chemistry, and uptake of micronutrients by plants, Bell Creek oil field, Montana

Chelate-extractable iron and manganese concentrations in soils over and around the Bell Creek oil field suggest that compared to low average background values, there are moderate amounts of these elements directly over the production area and higher concentrations distributed in an aureole pattern around the periphery of the field. Adsorbed and organically bound iron and manganese appear to be readily taken up by plants resulting in anomalously high levels of these elements in leaves and needles over the oil field and suggesting correlation with corresponding low concentrations in soils. Iron and manganese appear to have bypassed the soil formation process where, under normal oxidizing conditions, they would have ultimately precipitated as insoluble oxides and hydroxides.

Journal of Geochemical Exploration↗
USGS1986

Geochemical and fluid zonation in the skarn environment at the tomboy-minnie gold deposits, Lander County, Nevada

The Tomboy—Minnie gold deposits are related to the middle Tertiary porphyry copper system centered at Copper Canyon. Gold-silver ores in the deposits occur mostly in a pyrrhotite- and pyrite-rich basal 30-m-thick sequence of altered calcareous conglomerate belonging to the Middle Pennsylvanian Battle Formation. The entire mineralized system contained at least 3.3 million troy oz gold before large-scale mining operations began. Alteration in the Tomboy—Minnie deposits includes actinolite- and chlorite-dominant assemblages, in marked contrast to the skarn, potassic, and phyllic assemblages characterizing the copper-gold-silver deposits of the system. Introduction of gold occurred penecontemporaneously with replacement of early diopside-alteration assemblages by actinolite and chlorite. Metals are zoned strongly in the Copper Canyon system: the West and East ore bodies occur in a copper-gold-silver zone that is followed outward by a gold-silver zone which includes the Tomboy deposit and in turn, is succeeded by a lead-zinc-silver zone. Locations of drill holes that have Au/Ag assay ratios of ⩾ 1 clearly outline the Tomboy—Minnie deposits within an area of rocks with Au/Ag ratios of ≈ 0.5. Fluid-inclusion studies suggest wide variations in temperature and chemistry prevailed in the fluids associated with mineralization at the Tomboy. Early fluids associated with diopsidequartz assemblages probably were dominantly CaCl 2 -rich brines and were boiling at temperatures higher than 500°C. These fluids were progressively enriched in sodium and potassium over time, and during the hydrosilicate stages, temperatures probably ranged from 320 to 500°C at the time actinolite formed, and from 220 to 320°C at the time chlorite was dominant. Sulfur isotopic data suggest that sulfur, mostly from a magmatic or deep-seated crustal source, was transported by hydrothermal fluids as aqueous H 2 S with a δ 34 S of about . 4 &#xB1; 1&#x2030; ">

Journal of Geochemical Exploration↗
USGS1986

A tubular-coring device for use in biogeochemical sampling of succulent and pulpy plants

A hand-operated, tubular-coring device developed for use in biogeochemical sampling of succulent and pulpy plants is described. The sampler weighs about 500 g (1.1 lb); and if 25 × 175 mm (1 × 7 in) screw-top test tubes are used as sample containers, the complete sampling equipment kit is easily portable, having both moderate bulk and weight.

Journal of Geochemical Exploration↗
USGS1987

Response of douglas fir (Pseudotsuga menziesii) to uraniferous groundwater in a small glaciated drainage, Northeastern Washington State

Douglas fir trees and associated soils were sampled from the slopes of a small (∼4 km 2 ) drainage basin in northeastern Washington to investigate the biogeochemical response to locally uraniferous groundwater. Uranium is preferentially incorporated in needles and twigs compared to larger branches or the trunk. The U concentration in needle ash ranges from 0.2 to 5.8μg g −1 (ppm) and shows no correlation with the U concentration in associated soils. Rather, the distribution of anomalously uraniferous douglas fir (> 1.0 μ g g −1 U in needle ash) appears to be controlled by observed or readily inferred pathways of near-surface groundwater movement in the drainage. These pathways include: (1) general downslope movement of subsurface runoff; (2) increased flux of near-surface groundwater near the toe of an alluvial fan; and (3) emergence of uraniferous (100–150 ng ml −1 [ppb] groundwater in the vicinity of a slope spring. The data also indicate the presence of near-surface uraniferous groundwater along a structurally controlled zone that parallels the north-south strike of the valley, and that includes the slope spring. The results suggest that biogeochemical sampling may be used to supplement more direct, but more limited, measurements of groundwater quality and flow regime in areas of near-surface contaminated groundwater.

Journal of Geochemical Exploration↗
USGS1988

Concentration of gold in natural waters

The purpose of this paper is to investigate the amount of gold present in natural waters. One hundred and thirty-two natural water samples were collected from various sources and analyzed for gold by the latest techniques. Background values for gold in natural waters range from <0.001 to 0.005 ppb, and anomalous values range from 0.010 to 2.8 ppb. Waters collected from mineralized areas have a mean gold value of 0.101 ppb, whereas waters collected from unmineralized areas have a mean of 0.002 ppb. Some of the high gold values reported in the earlier literature were probably due to interferences by high salt content in the sample and/or lack of proper filter procedures.

Journal of Geochemical Exploration↗
USGS1989

Geochemistry of placer gold, Koyukuk-Chandalar mining district, Alaska

The Koyukuk-Chandalar mining district of the Brooks Range mineral belt in north-central Alaska contains numerous placer gold deposits but few known lode gold sources. Gold grains, collected from 46 placer localities and 6 lode gold sites in the district, were analyzed for Ag and 37 trace elements utilizing direct current-arc optical emission spectroscopy. When possible, several measurements were made on each sample and averaged. Gold content was calculated by the summation of the 38 elements determined and subtracting from 100. The objectives of our study were to characterize the deposits by defining the type and number of distinct geochemical characteristics for the Au, to determine relationships of Au in placer deposits to possible lode sources (placer and lode), to identify possible primary sources of placer gold, and to study processes of placer formation. Interpretation of results emphasize that the Au grains are almost invariably ternary (Au-Ag-Cu) alloys. The average Cu content is 0.040% and the average Ag content and fineness [(Au/Au+Ag)×1,000] are 10.5% and 893 parts per thousand, respectively, for the 46 placer localities.

Journal of Geochemical Exploration↗