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At least 73 records · Page 4Linked to original sources
USGS2026

Top-down targeted network analysis of critical mineral commodities applied to international geochemistry database

The global demand for critical mineral commodities is rapidly increasing, making domestic production an important factor in supporting the economy and national security. Large scale, publicly available geochemical databases allow for the application of data informatics methods to interrogate critical mineral commodities data for correlations in deposit formation and distribution, particularly for identifying enrichment of multiple critical mineral commodities at the same deposit. In this study, we applied network analysis to the Critical Minerals Mapping Initiative (CMMI) ore geochemistry (Critical Minerals in Ores, CMiO) database to identify the high concentration (defined as 10× bulk crustal abundance) co-occurrence of different critical mineral commodities across a mineral system hierarchy from deposit environments to individual deposits. Identifying patterns or unique outliers in enrichment in network communities will allow for the location of secondary critical mineral commodity resources from under-utilized deposits. We find trends in the enrichment of critical mineral commodities in network-communities between the elements praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy) across multiple CMiO database deposit environments and groups down to specific deposit types and sites. A separate trend in network community deposition is observed as well between iridium (Ir) and platinum (Pt) in deposit environments, groups, types, and sites. Network analysis focused on critical minerals in magmatic-hydrothermal deposits identified multiple deposit sites from different deposit types within the CMiO database with concentrations of Dy, Nd, Tb, Pr, Ir, and Pt that are at least ten times greater than the crustal average. This approach can be applied to any target element(s) or deposit(s) of interest, allowing broad investigation of co-enriched critical mineral commodities.

Journal of Geochemical Exploration↗
USGS1991

Fluid inclusion gas chemistry as a potential minerals exploration tool: Case studies from Creede, CO, Jerritt Canyon, NV, Coeur d'Alene district, ID and MT, southern Alaska mesothermal veins, and mid-continent MVT's

Recent advances in instrumentation now permit quantitative analysis of gas species from individual fluid inclusions. Fluid inclusion gas data can be applied to minerals exploration empirically to establish chemical (gas composition) signatures of the ore fluids, and conceptually through the development of genetic models of ore formation from a framework of integrated geologic, geochemical, and isotopic investigations. Case studies of fluid inclusion gas chemistry from ore deposits representing a spectrum of ore-forming processes and environments are presented to illustrate both the empirical and conceptual approaches. We consider epithermal silver-gold deposits of Creede, Colorado, Carlin-type sediment-hosted disseminated gold deposits of Jerritt Canyon, Nevada, metamorphic silver-base-metal veins of the Coeur d'Alene district, Idaho and Montana, gold-quartz veins in accreted terranes of southern Alaska, and the mid-continent base-metal sulfide deposits of Mississippi Valley-Type (MVT's). Variations in gas chemistry determine the redox state of the ore fluids, provide compositional input for gas geothermometers, characterize ore fluid chemistry (e.g., CH 4 CO 2 , H 2 SSO 2 , CO 2 /H 2 S, organic-rich fluids, gas-rich and gas-poor fluids), identify magmatic, meteoric, metamorphic, shallow and deep basin fluids in ore systems, locate upwelling plumes of magmatic-derived volatiles, zones of boiling and volatile separation, interfaces between contrasting fluids, and important zones of fluid mixing. Present techniques are immediately applicable to exploration programsas empirical studies that monitor fluid inclusion gas threshold concentration levels, presence or absence of certain gases, or changes in gas ratios. We suggest that the greater contribution of fluid inclusion gas analysis is in the integrated and comprehensive chemical dimension that gas data impart to genetic models, and in the exploration concepts based on processes and environments of ore formation derived from these genetic models.

Journal of Geochemical Exploration↗
USGS1995

A summary of the effects of mining and related activities on the sediment-trace element geochemistry of Lake Coeur d'Alene, Idaho, USA

During 1989 and 1990 a series of 12 gravity cores, and 150 surface grab samples were collected in Lake Coeur d'Alene, Idaho to determine trace element concentrations, partitioning and surface and subsurface distribution patterns in the bed sediments of the lake. In addition, selected subsamples from one core were analyzed for 117 Cs activity to begin to establish a trace element geochemical history for the lake. The intent was to try and relate the trace element concentrations and distributions in the sediment column to past and present mining and mining related activities in the area. Substantial portions of the surface and near-surface sediments in Lake Coeur d'Alene are markedly enriched in Ag, As, Cd, Hg, Pb, Sb and Zn, and somewhat enriched in Cu, Fe and Mn. Surface distribution patterns, as well as variations in the thickness of the trace element-rich subsurface sediments, indicate that the source of much of this enriched material is the Coeur d'Alene River. The similarity between the trace element-rich surface and subsurface sediments with respect to: their location, their bulk chemistry, and their trace element partitioning indicate that the sources and/or concentrating mechanisms causing the trace element enrichment in the lake sediments probably have been the same throughout their depositional history. An estimated 75 million metric tons of trace element-rich sediments have been deposited on or in the lakebed. Based on a Mt. St. Helens' ash layer from the 1980 eruption, ages estimated from 137 Cs activity, and the presence of 80 discernible and presumably annual layers in a core collected near the Coeur d'Alene River delta, indicate that the deposition of trace element-rich sediments began, at least in the Coeur d'Alene River delta, some time between 1895 and 1910, dates consistent with the onset of mining and ore-processing activities that began in the area in the 1880's.

Journal of Geochemical Exploration↗
USGS2022

Tungsten skarn potential of the Yukon-Tanana Upland, eastern Alaska, USA—A mineral resource assessment

Tungsten (W) is used in a variety of industrial and technological applications and has been identified as a critical mineral for the United States, India, the European Union, and other countries. These countries rely on W imports mostly from China, which leaves them vulnerable to supply disruption. Consequently, the U.S. government has a current initiative to understand domestic resource potential. The eastern Alaska portion of the Yukon-Tanana Upland (YTU), is prospective for W skarn deposits, the major source of global W supply. The regional geology consists of juxtaposed Paleozoic lithotectonic packages that were reaccreted to North America in the Mesozoic . Multiple subsequent episodes of arc-related magmatism intruded the lithotectonic packages, accompanied by W skarn formation mostly associated with 100–90 Ma intrusions; major W skarn deposits in Canada are part of the same metallogenic event (e.g., Mactung, Cantung). In this paper, we present an assessment for undiscovered W skarn resources for parts of the lesser-explored western (Alaskan) portion of the YTU. We used GIS proximity analysis to map the intersection of pluton and carbonate-bearing rocks to define three permissive tracts for W skarn deposits. The permissive tracts were qualitatively assessed by mineral potential mapping using region-wide sediment geochemistry and mineral concentrate datasets. This analysis showed that much of the western YTU has high potential for undiscovered W skarn deposits, whereas the eastern and southern YTU had only isolated areas of medium to high potential. Historical production and the quality of the geochemistry data of the western YTU tract (ca. 9200 km 2 ) permitted a quantitative assessment of undiscovered W resources. Probabilistic estimates by a panel of 20 experts predicted a 70% chance of one to three undiscovered W skarn deposits in the western YTU tract. The rationale for favorability employed by the expert panel included favorable lithology, previous production, clustering of previously mined deposits, W placers in the area, lack of recent exploration, pan concentrates containing W minerals, and W geochemical anomalies. Estimates were combined with a global grade and tonnage model for W skarns in a Monte Carlo simulation and provided a median estimate of undiscovered resources of 94 kt WO 3 . If the undiscovered W skarn deposits are located close to infrastructure (e.g., near Fairbanks, or close to roads and/or power grid), application of an economic filter indicates that the median total economically recoverable WO 3 is 63 kt with a net present value (NPV) of $330 million USD (2008 dollars). Whereas if deposits are far from infrastructure, median recoverable WO 3 is only 30 kt and the NPV is $44 million. Our models for contained WO 3 resources and NPV estimates for the western YTU tract are considerably lower than the known resources in skarns in adjacent areas in Canada. Estimates for the western YTU are also lower than preliminary estimates for undiscovered W skarn deposits in areas of the western conterminous United States. We speculate that lower permeability and continuity of favorable carbonate rock horizons in the relatively higher-grade metamorphic country rocks in the Alaska portion of the YTU may explain some of the differences in prospectivity. More detailed geologic mapping, modern geochemistry, and geophysical surveys are needed to refine the resource potential of the whole YTU. Regardless, quantitative mineral resource assessment provides a useful tool for making first-order regional estimates of undiscovered resources, identifying target areas for new data acquisition, and guiding research on the fundamental controls of district-scale metallogenic endowments.

Alaska↗
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 ± 1‰ ">

Journal of Geochemical Exploration↗
USGS2014

Geochemistry of hydrothermal alteration at the Qolqoleh gold deposit, northern Sanandaj–Sirjan metamorphic belt, northwestern Iran: Vectors to high-grade ore bodies

The Qolqoleh orogenic gold deposit in the northern part of the Sanandaj–Sirjan metamorphic belt in northwestern Iran is hosted by a steeply dipping sequence of greenschist facies Cretaceous volcano–sedimentary rocks, including mafic to intermediate metavolcanic rocks, sericite and chlorite schist, and marble. Geochemical and petrochemical data including the ∑ REE, (La/Yb) N and Eu/Eu* ratios were obtained from country rocks, ore-enveloping alteration zones, and mineralized zones to assess the nature of the trace element and rare earth element (REE) interaction between the wall rock and the mineralizing fluid. Quartz–sulfide veins at the deposit are characterized by a pyrite–pyrrhotite–chalcopyrite–sphalerite–arsenopyrite–native gold assemblage. Alteration halos border the mineralized zones and broadly comprise: (1) an outer carbonate–chlorite alteration zone in all rock types, particularly in chlorite schist; (2) a middle sericite–carbonate alteration zone in the sericite schist; and (3) an inner quartz–sulfide alteration zone in sericite schist and mafic to intermediate metavolcanic rocks. The geochemical data indicate that the concentrations of Al 2 O 3 , P 2 O 5 , TiO 2 , Y, and Zr are relatively constant, suggesting that these elements were the least mobile during hydrothermal activity. Using Al 2 O 3 as the immobile component, there is evidence for mobility of trace elements, particularly light REE, TiO 2 , and Zr in the altered wall rocks. The altered rocks show a relatively light REE depletion ((La/Yb) N ≅ 9.41), which clearly correlates with the grades of gold mineralization and intensity of the alteration (3 ppm Au). The depletion of light REE is best indicated by a decrease in (La/Yb) N as shown by ratios of 10.5 to 11.8. Wall rock decarbonation reactions during infiltration of the mineralizing fluid resulted in differential mobilization of REE, from a fluid with initially low REE content. The overall trace element geochemistry of the altered wall rock is controlled by the initial composition of the wall rocks and the ore-fluid composition. Hydrothermal ore-forming fluids are recognized as CO 2 -rich near-neutral reduced fluids with high values of H 2 S, K, and S content. Observed variability in alteration halos at the Qolqoleh deposit points to major differences in REE and trace element content in original host rocks that have interacted with a relatively similar ore fluid. Therefore, depending on the composition of each host rock lithology, the geochemistry of hydrothermal alteration (e.g., ∑ REE content and (La/Yb) N ratios) and alteration mineralogy including the carbonate–sericite–quartz–sulfide assemblages may be used as a primary tool for lithogeochemical exploration for gold deposits in northwestern Iran.

Journal of Geochemical Exploration↗
USGS1990

A comparison of geochemical exploration techniques and sample media within accretionary continental margins: an example from the Pacific Border Ranges, Southern Alaska, U.S.A.

The Pacific Border Ranges of the southern Alaskan Cordillera are composed of a number of allochthonous tectonostratigraphic terranes. Within these terranes are widespread volcanogenic, massive sulfide deposits in and adjacent to portions of accreted ophiolite complexes, bands and disseminations of chromite in accreted island-arc ultramafic rocks, and epigenetic, gold-bearing quartz veins in metamorphosed turbidite sequences. A geochemical pilot study was undertaken to determine the most efficient exploration strategy for locating these types of mineral deposits within the Pacific Border Ranges and other typical convergent continental margin environments. High-density sediment sampling was carried out in first- and second-order stream channels surrounding typical gold, chromite and massive sulfide occurrences. At each site, a stream-sediment and a panned-concentrate sample were collected. In the laboratory, the stream sediments were sieved into coarse-sand, fine- to medium-sand, and silt- to clay-size fractions prior to analysis. One split of the panned concentrates was retained for analysis; a second split was further concentrated by gravity separation in heavy liquids and then divided into magnetic, weakly magnetic and nonmagnetic fractions for analysis. A number of different techniques including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and semi-quantitative emission spectrography were used to analyze the various sample media. Comparison of the various types of sample media shows that in this tectonic environment it is most efficient to include a silt- to clay-size sediment fraction and a panned-concentrate sample. Even with the relatively low detection limits for many elements by plasma spectrometry and atomic absorption spectrometry, anomalies reflecting the presence of gold veins could not be identified in any of the stream-sediment fractions. Unseparated panned-concentrate samples should be analyzed by emission spectroscopy and atomic absorption spectrometry for Ag and Au. If, however, magnetic and nonmagnetic concentrate fractions are used in a reconnaissance program, semiquantitative emission spectrography is adequate for all analytical work.

Journal of Geochemical Exploration↗
USGS2016

Pb-Sr isotopic and geochemical constraints on sources and processes of lead contamination in well waters and soil from former fruit orchards, Pennsylvania, USA: A legacy of anthropogenic activities

Isotopic discrimination can be an effective tool in establishing a direct link between sources of Pb contamination and the presence of anomalously high concentrations of Pb in waters, soils, and organisms. Residential wells supplying water containing up to 1600 ppb Pb to houses built on the former Mohr orchards commercial site, near Allentown, PA, were evaluated to discern anthropogenic from geogenic sources. Pb (n = 144) and Sr (n = 40) isotopic data and REE (n = 29) data were determined for waters from residential wells, test wells (drilled for this study), and surface waters from pond and creeks. Local soils, sediments, bedrock, Zn-Pb mineralization and coal were also analyzed (n = 94), together with locally used Pb-As pesticide (n = 5). Waters from residential and test wells show overlapping values of 206 Pb/ 207 Pb, 208 Pb/ 207 Pb and 87 Sr/ 86 Sr. Larger negative Ce anomalies (Ce/Ce*) distinguish residential wells from test wells. Results show that residential and test well waters, sediments from residential water filters in water tanks, and surface waters display broad linear trends in Pb isotope plots. Pb isotope data for soils, bedrock, and pesticides have contrasting ranges and overlapping trends. Contributions of Pb from soils to residential well waters are limited and implicated primarily in wells having shallow water-bearing zones and carrying high sediment contents. Pb isotope data for residential wells, test wells, and surface waters show substantial overlap with Pb data reflecting anthropogenic actions (e.g., burning fossil fuels, industrial and urban processing activities). Limited contributions of Pb from bedrock, soils, and pesticides are evident. High Pb concentrations in the residential waters are likely related to sediment build up in residential water tanks. Redox reactions, triggered by influx of groundwater via wells into the residential water systems and leading to subtle changes in pH, are implicated in precipitation of Fe oxyhydroxides, oxidative scavenging of Ce(IV), and desorption and release of Pb into the residential water systems. The Pb isotope features in the residences and the region are best interpreted as reflecting a legacy of industrial Pb present in underlying aquifers that currently supply the drinking water wells.

Pennsylvania↗
USGS2018

Geochemical and Pb isotopic characterization of soil, groundwater, human hair, and corn samples from the Domizio Flegreo and Agro Aversano area (Campania region, Italy)

A geochemical survey was carried out to investigate metal contamination in the Domizio Littoral and Agro Aversano area (Southern Italy) by means of soil, groundwater, human hair and corn samples. Pb isotope ratios were also determined to identify the sources of metals. Specifically, the investigation focused on topsoils ( n = 1064), groundwater ( n = 26), 25 human hair ( n = 24) and corn samples ( n = 13). Topsoils have been sampled and analysed in a previous study for 53 elements (including potentially harmful ones), and determined by ICP-MS after dissolving with aqua regia. Groundwater was analysed for 72 elements by ICP-MS and by ICP-ES. Samples of human hair were prepared and analysed for 16 elements by ICP-MS. Dried corn collected at several farms were also analysed for 53 elements by ICP-MS. The isotopic ratios of 206 Pb/ 207 Pb and 208 Pb/ 207 Pb in selected topsoil ( n = 24), groundwater ( n = 9), human hair ( n = 9) and corn ( n = 4) samples were analysed from both eluates and residues to investigate possible anthropogenic contamination and geogenic contributions. All data were processed and mapped by ArcGis software to produce interpolated maps and contamination factor maps of potentially harmful elements, in accordance with Italian Environmental Law (Legislative Decree 152/06). Results show that soil sampling sites are characterized by As, Cd, Co, Cr, Cu, Hg, Pb, Se, and Zn contents exceeding the action limits established for residential land use (RAL) and, in some cases, also the action limits for industrial land use (IAL) as established by Legislative Decree 152/06. A map of contamination factors and a map showing the degrees of contamination indicate that the areas in the municipalities of Acerra, Casoria and Giugliano have been affected by considerable anthropogenic-related pollution. To interpret the isotopic data and roughly estimate proportion of Pb from an anthropogenic source we broadly defined possible natural and anthropogenic Pb end-member fields based on literature data. For example, we summarized data for Vesuvius and Campi Flegrei volcanic rocks, gasoline, and aerosol deposits. Lead isotope data show mixing between geogenic and anthropogenic sources. Topsoil, groundwater, human hair and corn samples show a greater contribution from geogenic sources like the Yellow Tuff (from Campi Flegrei) and volcanic rocks from Mt. Vesuvius. Aerosols, fly ash and gasoline (anthropogenic sources) have also been contributors. In detail, 46% of the topsoil residues, 96% of topsoil leachates, 88% of groundwater, 90% of human hair, and 25% of corn samples indicate that > 50% percent of the lead in this area can be ascribed to anthropogenic activity.

Campania region↗
USGS1998

Electrogeochemical sampling with NEOCHIM - results of tests over buried gold deposits

Electrogeochemical extraction methods are based on the migration of ions in an electric field. Ions present in soil moisture are transported by an applied current into fluids contained in special electrodes placed on the soil. The fluids are then collected and analyzed. Extractions are governed by Faraday's and Ohm's laws and are modeled by the operation of a simple Hittord transference apparatus. Calculations show that the volume of soil sampled in an ideal electrogeochemical extraction can be orders of magnitude greater than the volumes used in more popular geochemical extraction methods, although this has not been verified experimentally. CHIM is a method of in-situ electrogeochemical extraction that was developed in the former Soviet Union and has been tested and applied internationally to exploration for buried mineral deposits. Tests carried out at the US Geological Survey (USGS) indicated that there were problems inherent in the use of CHIM technology. The cause of the problems was determined to be the diffusion of acid from the conventional electrode into the soil. The NEOCHIM electrode incorporates two compartments and a salt bridge in a design that inhibits diffusion of acid and enables the collection of anions or cations. Tests over a gold-enriched vein in Colorado and over buried, Carlin-type, disseminated gold deposits in northern Nevada show that there are similarities and differences between NEOCHIM results and those by partial extractions of soils which include simple extractions with water, dilute acids and solutions of salts used as collector fluids in the electrodes. Results of both differ from the results obtained by total chemical digestion. The results indicate that NEOCHIM responds to mineralized faults associated with disseminated gold deposits whereas partial and total chemical extraction methods do not. This suggests that faults are favored channels for the upward migration of metals and that NEOCHIM may be more effective in exploration for the deposits. It defines anomalies that are often narrow and intense, an observation previously made by CHIM researchers. The field tests show that NEOCHIM is less affected by surface contamination. A test over the Mike disseminated gold deposit indicates that the method may not be effective for locating deposits with impermeable cover. Faradaic extraction efficiencies of 20-30%, or more, are frequently achieved with NEOCHIM and the method generally shows good reproducibility, especially in extraction of major cations. However, ions of other metals that are useful in exploration, including Au and As, may be collected in low and temporally variable concentrations. The reason for this variability is unclear and requires further investigation.CHIM is a method of in-situ electrogeochemical extraction developed for the exploration of buried mineral deposits. However, electrode problems like diffusion of acid into the soil were encountered during the use of CHIM. The NEOCHIM electrode was developed to inhibit the diffusion of acid and enable collection of anions or cations. Tests over buried gold deposits showed that NEOCHIM responds to mineralized faults associated with disseminated gold deposits whereas partial and total chemical extraction methods do not. This suggests that faults are favored channels for the upward migration of metals and NEOCHIM may be effective in exploration for the deposits. But ions of metals may be collected in low and variable concentration.

Journal of Geochemical Exploration↗
USGS1975

Uranium determination in natural water by the fissiontrack technique

The fission track technique, utilizing the neutron-induced fission of uranium-235, provides a versatile analytical method for the routine analysis of uranium in liquid samples of natural water. A detector is immersed in the sample and both are irradiated. The fission track density observed in the detector is directly proportional to the uranium concentration. The specific advantages of this technique are: (1) only a small quantity of sample, typically 0.1–1 ml, is needed; (2) no sample concentration is necessary; (3) it is capable of providing analyses with a lower reporting limit of 1 μg per liter; and (4) the actual time spent on an analysis can be only a few minutes. This paper discusses and describes the method.

Journal of Geochemical Exploration↗
USGS1977

Application of gold compositional analyses to mineral exploration in the United States

Native gold is a mineral composed of Au, Ag and Cu in solid solution and it usually contains one or more trace metals as lattice impurities, as mineral inclusions, in grain boundaries or in surface coatings. Alloy proportions of Au, Ag and Cu, together with certain other elements, can be thought of as constituting a gold “signature”. Gold is associated with a great variety of ore deposits and has characteristic signatures for each of several types of ore deposits. Signatures for gold derived from igneous-metamorphic, hypothermal, mesothermal and epithermal deposits reflect conditions of ore formation by their content of Ag, Cu and characteristic associated elements. At higher temperatures of ore formation, gold has low Ag and high Cu content, and Bi and Pb are the most abundant trace elements. But at lower temperatures of ore formation, Ag is high, Cu is low, and Pb is the most abundant trace element. The same trend in gold signatures is observable in gold mining districts, such as Central City, Colorado, where zoning as shown by mineral assemblages indicates ore deposition at progressively lower temperatures as the distance from a central high-temperature zone increases. The signatures of gold may be useful in searching for porphyry Cu deposits. Signatures from Butte (Montana), Mineral Park (Arizona) and Cala Abajo (Puerto Rico), on the basis of limited sampling, are similar and distinctive. They are characterized by a similar assemblage of trace elements and are relatively high in both Ag and Cu. Another application of gold compositional data is in tracing placer gold to its bedrock source. For example, the Ag content of placer gold in the Tarryall district of Colorado differed from that of nearly all of the bedrock sources of gold found by early prospectors. However, one lightly prospected area peripheral to the Tertiary quartz monzonite stock at Montgomery Gulch contains gold with a Ag content similar to that of the placer gold. This area is the most likely source of the gold in the productive placers and may be a potential exploration target. Gold signatures may be useful in prospecting for metals other than gold. Several metals of low crustal abundance — notably Sn, W, Mo and the Pt group metals — are detected in analyses of some gold samples and may indicate economic deposits of these metals.

Journal of Geochemical Exploration↗
USGS1977

Tellurium, a guide to mineral deposits

Te dispersion patterns are useful in exploring for different types of mineral deposits and in providing additional information about known ore deposits. The Te content of rocks is given for five mining districts in the western United States: Coeur d'Alene, Idaho; Robinson, near Ely, Nevada; Montezuma, Colorado; Crater Creek area, Colorado; Cripple Creek, Colorado. Many of the analyses were obtained by use of a new analytical method sensitive to 0.001 ppm Te. The principal ore deposits in the Coeur d'Alene district, Idaho, are Pb-Zn-Ag replacement veins in Precambrian rocks of the Belt Supergroup. Te dispersion patterns show the outlines of the original mineral belts, the effects of intrusive events, the location of ore deposits, the displacements caused by post-ore faulting, and the borders of the 780-km 2 district. The disseminated porphyry Cu deposits of the Robinson mining district, Nevada, are associated with Cretaceous quartz monzonite stocks that have intruded Palaeozoic carbonate rocks. Te is present in rock samples in concentrations as high as 10,000 ppm and forms a halo around the areas containing the Cu deposits. The alteration zones in the porphyry Mo district near Montezuma, Colorado, are developed around several small Tertiary intrusions occurring along a regional shear zone. Te haloes reflect the locations of porphyry intrusives, individual deposits and their ore shoots, and the pattern and intensity of adjacent alteration. The Te content of soils over the Montezuma stock is higher than, and varies independently from, the Te content of adjacent outcrops. Soils generally contain more Te than adjacent outcropping rocks. Soil may collect gaseous Te compounds from mineral deposits. The Crater Creek area is a northwestern extension of the Summitville mining district, Colorado. Te dispersion patterns radiate out from exposed Cu-Pb-Zn veins, from an outcrop of molybdenite stockwork veins and from associated iron-stained altered rock. Te haloes intensify exponentially with proximity to known ore and suggest the presence of Summitville-type chimney deposits. Most of the gold- and silver-telluride ore in the Cripple Creek district, Colorado, is found in fracture fillings within a volcanic subsidence basin. Haloes of Au, Ag and Te all define the mineralized portions of the fissure veins.

Journal of Geochemical Exploration↗
USGS1977

Uranium and coexisting element behaviour in surface waters and associated sediments with varied sampling techniques used for uranium exploration

Optimum sampling methods in surface water and associated sediments for use in uranium exploration are being studied at thirty sites in Colorado, New Mexico, Arizona and Utah. For water samples, filtering is recommended to increase sample homogeneity and reproducibility because for most elements studied water samples which were allowed to remain unfiltered until time of analysis contained higher concentrations than field-filtered samples of the same waters. Acidification of unfiltered samples resulted in still higher concentrations. This is predominantly because of leaching of the elements from the suspended fraction. U in water correlates directly with Ca, Mg, Na, K, Ba, B, Li and As. In stream sediments, U and other trace elements are concentrated in the finer size fractions. Accordingly, in prospecting, grain size fractions less than 90 μm (170 mesh) should be analyzed for U. A greater number of elements (21) show a significant positive correlation with U in stream sediments than in water. Results have revealed that anomalous concentrations of U found in water may not be detected in associated sediments and vice versa. Hence, sampling of both surface water and coexisting sediment is strongly recommended.

Journal of Geochemical Exploration↗
USGS1979

Disequilibrium in the 238uranium series in samples from Yeelirrie, Western Australia

Uranium-series disequilibrium studies carried out on samples from the Yeelirrie uranium deposit, Western Australia, indicate that uranium and radium have been migrating within the deposit during recent times, and are actually being removed from the deposit. Samples collected for 230 Th/ 234 U age dating were found to be substantially out of equilibrium, with 230 Th/ 234 U activity ratios ranging from 0.750 to 1.345. This can be explained by a dynamic hydrologic system in which there has been, and continues to be, uranium migration caused by leaching in this arid, oxidizing environment, and a fluctuating water table. Recent, extensive 226 Ra migration ( 226 Ra/ 230 Th activity ratios range from 0.53 to 1.30), and a very low emanation factor ( E ) of 222 Rn limit the quantitative application of radon exploration techniques in this environment.

Journal of Geochemical Exploration↗
USGS1981

Uranium in big sagebrush from western U.S. and evidence of possible mineralization in the Owyhee mountains of Idaho

Two regional studies of big sagebrush ( Artemisia tridentata ), a widely distributed and dominant shrub in the western United States, have shown its responsiveness to known uranium mineralization in the Monument Hill and Pumpkin Buttes districts of the southern Powder River Basin, Wyoming, and the Uravan mineral belt area in southeastern Utah and southwestern Colorado. Uranium concentrations in the ash of 154 stem-and-leaf samples of sagebrush are plotted on two maps, one representing the sampling design for the Powder River Basin study, and the other representing the sampling design for the Colorado Plateaus, the Basin and Range, and the Columbia Plateaus physiographic provinces of the West. Sites having high concentrations in sagebrush correspond not only to the above uranium districts, but also reveal an area along the northeast flanks of the Owyhee Mountains in Idaho that should be further explored for its possible uranium potential.

Journal of Geochemical Exploration↗