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At least 217 records · Page 12Linked to original sources
USGS1971

A heavy mineral study of Pleistocene and Holocene sediments near Nome, Alaska

A heavy mineral study was carried out for sand-size fractions of onshore Holocene sediments (modern beach and river sediments), nearshore Holocene and Pleistocene relict sediments, and Pleistocene and Pliocene sediments from several nearshore drill-holes. Heavy mineral assemblages of these sediments are dominated by garnet, chlorite, epidote, chloritoid, sphene, and staurolite. The nearshore region of Nome is mainly underlain by various types of Pleistocene sediments such as relict gravel that Mantles glacial drift, relict gravel over Nome River outwash fan, relict gravelly sand of submerged beaches, and relict gravel that mantles bedrock. In places these relict sediments are covered by Holocene sandy and muddy sediments. The high concentration of heavy minerals is expected for various relict sediments, because the latter were winnowed by several transgressions and regressions of the sea during Pleistocene time. Concentration of heavy minerals, however, is greater for Holocene sand than relict gravel, which mantles glacial drift and relict gravelly sand of submerged beaches. The high concentration of heavy minerals in Holocene sand suggests the winnowing of sand by strong bottom currents. The low concentration of heavy minerals in the relict gravel on glacial drift and relict gravelly sand of submerged beaches is probably due to the heterogenous nature of relict sediments. Sand fractions of the relict sediments probably have been introduced during the Holocene time. Also, contamination of samples of relict gravel from underlying glacial drift is suspected. A greater concentration of coarse gold particles (1 iiuii. or larger) is found in nearshore relict gravel that mantles glacial drift than in any other sediment type. Relict gravel on glacial drift, which carries high gold values, does not show a high concentration of heavy minerals or a high concentration of garnet. Two factors account for the lack of correlation between concentration of gold and the other heavy minerals: (1) contrast between hydraulic properties of the gold particles and other heavy minerals, and (2) the heterogeneous nature of relict sediments. Because of their extremely high specific gravity, coarse gold particles are not moved by longshore currents or bottom currents from relict gravel which mantles glacial drift, whereas the heavy minerals which are mostly medium to fine sand in size, are transported by longshore currents and strong bottom currents. The Holocene sand winnowed by strong bottom currents shows a high concentration of heavy minerals. Heavy mineral assemblages are more or less similar for the various sediments. Minor compositional variations mainly reflect the effect of sorting of mineral grains according to size and specific gravity. The frequencies of garnet and staurolite are slightly higher than average for modern beach and river sediments. In nearshore sediments, garnet is most abundant in Holocene sand winnowed by strong bottom currents. Holocene silty sediment which occurs in small patches is characterized by high concentration of micaceous minerals and low concentration of garnet, because the weak currents which deposit fine sediments usually carry light micaceous minerals in great abundance and minerals of high specific gravity like garnet in small amounts. Samples of Pleistocene glacial till and Pliocene marine silt from several nearshore drill-hole locations show high concentrations of micaceous minerals and low concentration of garnet. Holocene, Pleistocene, and Pliocene sediments of Nome are mostly derived from the same general metamorphic source rocks of the inland region. The majority of the minerals found in heavy mineral assemblages, such as garnet, chlorite, epidote, chloritoid, sphene, staurolite, hornblende, and tremolite-actinolite, are reported to occur in the metamorphic rocks of Nome and the adjacent region.

Alaska↗
USGS1976

Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Fairbanks Quadrangle, Alaska

For each mineral occurrence there is a page that gives the name of the occurrence; the mineral commodities present (listed alphabetically for metallic commodities and then for nonmetallic commodities); the mining district (Ransome and Kerns, 1954) in which the occurrence is located; the name of the 1:250,000-scale topographic quadrangle (Fairbanks); coordinates (as described by Cobb and Kachadoorian, 1961, p. 3-4); the metallic mineral resources map number (KF-410) and the occurrence number on that map if the occurrence is shown; and the latitude and longitude of the occurrence. These data, presented at the top of the page, are followed by a short, general summary of the published information on the occurrence. This is followed (continued on additional pages, if necessary) by more detailed summaries, arranged chronologically, of all references to the occurrence. Material in brackets is interpretive or explanatory and is not in the summarized reference.

Alaska↗
USGS2016

GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska

Alaska has considerable potential for undiscovered mineral resources. This report evaluates potential for undiscovered critical minerals in Alaska. Critical minerals are those for which the United States imports more than half of its total supply and which are largely derived from nations that cannot be considered reliable trading partners. In this report, estimated resource potential and certainty for the state of Alaska are analyzed and mapped for the following six selected mineral deposit groups that may contain one or more critical minerals: (1) rare earth elements-thorium-yttrium-niobium(-uranium-zirconium) [REE-Th-Y-Nb(-U-Zr)] deposits associated with peralkaline to carbonatitic igneous intrusive rocks; (2) placer and paleoplacer gold (Au) deposits that in some places might also produce platinum group elements (PGE), chromium (Cr), tin (Sn), tungsten (W), silver (Ag), or titanium (Ti); (3) platinum group elements(-cobalt-chromium-nickel-titanium-vanadium) [PGE(-Co-Cr-Ni-Ti-V)] deposits associated with mafic to ultramafic intrusive rocks; (4) carbonate-hosted copper(-cobalt-silver-germanium-gallium) [Cu(-Co-Ag-Ge-Ga)] deposits; (5) sandstone-hosted uranium(-vanadium-copper) [U(-V-Cu)] deposits; and (6) tin-tungsten-molybdenum(-tantalum-indium-fluorspar) [Sn-W-Mo(-Ta-In-fluorspar)] deposits associated with specialized granites. This study used a data-driven, geographic information system (GIS)-implemented method to identify areas that have mineral resource potential in Alaska. This method systematically and simultaneously analyzes geoscience data from multiple geospatially referenced datasets and uses individual subwatersheds (12-digit hydrologic units) as the spatial unit of classification. The final map output uses a red, yellow, green, and gray color scheme to portray estimated relative potential (High, Medium, Low, Unknown) for each of the six groups of mineral deposit types, and it indicates the relative certainty (High, Medium, Low) of that estimate for each 12-digit hydrologic unit through color shading. Accompanying tables describe the data layers employed to score favorability for the presence of each mineral deposit group, the values assigned for specific analysis parameters, and the relative weighting of each data layer that contributes to estimated measures of potential and certainty . Core datasets used include the Alaska Geochemical Database, Version 2.0 (AGDB2); the Alaska Division of Geological & Geophysical Surveys (ADGGS) web-based geochemical database; the digital “Geologic Map of Alaska;” the Alaska Resource Data File (ARDF); and aerial gamma-ray surveys flown as part of the National Uranium Resource Evaluation (NURE) Program by the U.S. Department of Energy. Maps accompanying this report illustrate the scores for estimated mineral resource potential for the six deposit groups for the state of Alaska. Areas that have known potential, as well as new areas that were not previously known to have potential, for the targeted minerals and deposit groups are identified and described. Numerous areas in Alaska, some of them large, have high potential for one or more of the selected groups of deposit types within Alaska. Contributors Matthew Granitto, Timothy S. Hayes, James V. Jones, III, Susan M. Karl, Keith A. Labay, Jeffrey L. Mauk, Jeanine M. Schmidt, Nora B. Shew, Erin Todd, Bronwen Wang, Melanie B. Werdon, and Douglas B. Yager

Alaska↗
USGS1993

Maps showing metallic mineral resources of the Bendeleben and Solomon quadrangles, western Alaska

This report summarizes the potential for metallic mineral resources in the Bendeleben and Solomon quadrangles, central Seward Peninsul, Alaska (fig. 1), and was prepared as part of the AMRAP (Alaska Mineral Resources Appraisal Program) studies for these quadrangles, which were begun in 1981. Geologic mapping during this study (TILL and others, 1986) included the southern part of the Kotzebue quadrangle. However, stream-sediment and panned-concentrate samples were not collected in that area, and the mineral resources of the southern part of the Kotzebue quadrangle are not assessed in this report.

Alaska↗
USGS2017

Geospatial analysis identifies critical mineral-resource potential in Alaska

Alaska consists of more than 663,000 square miles (1,717,000 square kilometers) of land—more than a sixth of the total area of the United States—and large tracts of it have not been system atically studied or sampled for mineral- resource potential. Many regions of the State are known to have significant mineral-resource potential, and there are currently six operating mines in the State along with numerous active mineral exploration projects. The U.S. Geologi cal Survey and the Alaska Division of Geological & Geophysical Surveys have developed a new geospatial tool that integrates and analyzes publicly available databases of geologic information and estimates the mineral-resource potential for criti cal minerals, which was recently used to evaluate Alaska. The results of the analyses highlight areas that have known mineral deposits and also reveal areas that were not previously considered to be prospective for these deposit types. These results will inform land manage ment decisions by Federal, State, and private landholders, and will also help guide future exploration activities and scientific investigations in Alaska.

Alaska↗
USGS2007

Landscape geochemistry near mineralized areas of eastern Alaska

The Pogo lode gold deposit was discovered in eastern Alaska in the early 1990s and provided the opportunity to study elemental distribution and mobility in the natural environment prior to mine development. Studying mineralized systems prior to mining allows us to compare the natural biogeochemical signature in mineralized versus nonmineralized areas. The resultant data and interpretation also provide a baseline for evaluating what, if any, changes in elemental distribution result from development. This report investigates the chemistry of stream water, streambed sediment, and soil in the context of regional bedrock geology. The major-ion chemistry of the waters reflects a rock-dominated aqueous system, and the waters are classified as Ca 2+ and Mg 2+ - HCO 3 - to Ca 2+ and Mg 2+ - SO 4 -2 waters. Creeks draining the gneissic lithologies tend to be more sulfate dominated than those draining the intrusive units. Sulfate also dominated creeks draining mineralized areas; however, the underlying paragneiss unit could be contributing substantially to the sulfate concentration, and the sulfate concentration in these creeks may reflect a complex baltholith-paragneiss boundary rather than mineralization. Arsenic concentrations in bed sediments were elevated in mineralized areas relative to nonmineralized areas. Elevated concentrations of nickel, chromium, iron, manganese, and cobalt appear to reflect the presence of ultramafic rocks in the drainage. In general, aqueous metal concentrations were below the State of Alaska’s Aquatic Life Criteria and Drinking Water Standards, with the exception of arsenic in stream water, which ranged in concentration from less than 1 to 14 micrograms per liter (μg/L) and exceeded the drinking water standard at one site. The arsenic and antimony concentration in the A, B, and C soil horizons ranged from 3 to 410 milligrams per kilogram (mg/kg), 6.1 to 440 mg/kg, and 2 to 300 mg/kg, respectively, for arsenic and 0.4 to 24 mg/kg, 0.6 to 25 mg/kg, and 0.2 to 16 mg/kg, respectively, for antimony. The arsenic and antimony concentrations in stream waters correlate well with the concentrations in soils. However, significantly less arsenic and antimony was extracted from C horizon soils in water leaching experiments, indicating that the arsenic and antimony in the C horizon is present in a less available form than in the A or B horizons. Arsenic and antimony uptake by grayleaf willow (Salix glauca L.) appears minimal, with arsenic concentrations ranging from less than 0.01 to 0.14 mg/kg and antimony concentrations ranging from less than 0.003 to 0.23 mg/kg in willow leaves. In general, the highest concentrations of both arsenic and antimony in water and soils were found near mineralized areas. Elevated arsenic concentrations were also found in bed sediments from mineralized areas. In these sample matrices, the presence of arsenic and (or) antimony was a good indicator of contact with mineralized rock units.

Alaska, Yukon↗
USGS1988

Brief descriptions of mines, prospects, and mineral occurrences in the Port Moller and Stepovak Bay quadrangles, Alaska peninsula

This report contains brief descriptions of known mines, prospects, and mineral occurrences in the Port Moller and Stepovak Bay quadrangles on the Alaska Peninsula. These quadrangles, and the adjoining Simeonof Island quadrangle to the south were the subject of an Alaska Mineral Resource Assessment Program (AMRAP) mapping and mineral resource assessment project. This compilation of descriptions was made from the published literature (Wilson and others, 1986) and unpublished reports and data of The Aleut Corporation, the U.S. Bureau of Mines, and the U.S. Geological Survey. The initial compilation was primarily based on data from Cobb (1972) and MacKevett and Holloway (1977), however information provided by The Aleut Corporation and data gathered during the Port Moller AMRAP project added most of the information in the descriptions and the database. Compilation of this database is an ongoing process and this is a progress report of work completed to date. The authors would appreciate any corrections or additional information that users may be able to contribute. To facilitate active use of the descriptions, where information is not available for a particular field in the database, it is left blank so that the use can write in data as they obtain it.

Alaska↗
USGS2015

Geospatial compilation of results from field sample collection in support of mineral resource investigations, Western Alaska Range, Alaska, July 2013

This Data Series summarizes results from July 2013 sampling in the western Alaska Range near Mount Estelle, Alaska. The fieldwork combined in situ and camp-based spectral measurements of talus/soil and rock samples. Five rock and 48 soil samples were submitted for quantitative geochemi­cal analysis (for 55 major and trace elements), and the 48 soils samples were also analyzed by x-ray diffraction to establish mineralogy and geochemistry. The results and sample photo­graphs are presented in a geodatabase that accompanies this report. The spectral, mineralogical, and geochemical charac­terization of these samples and the sites that they represent can be used to validate existing remote-sensing datasets (for example, ASTER) and future hyperspectral studies. Empiri­cal evidence of jarosite (as identified by x-ray diffraction and spectral analysis) corresponding with gold concentrations in excess of 50 parts per billion in soil samples suggests that surficial mapping of jarosite in regional surveys may be use­ful for targeting areas of prospective gold occurrences in this sampling area.

Alaska↗