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At least 883 records · Page 49Linked to original sources
USGS2014

Pb isotope geochemistry of stratabound Zn-Pb(-Ag-Au-Ba-F) deposits and occurrences in the Nome Complex, Seward Peninsula, Alaska: Metal sources and regional comparisons

A detailed study of the Pb isotope geochemistry of Zn-Pb(-Ag-Au-Ba-F) stratabound sulfide deposits within metasedimentary rocks of the Neoproterozoic to Mississippian(?) Nome Complex provides key information for understanding deposit genesis and crustal evolution. A total of 106 new analyses of galena (and other sulfi des) and metasedimentary rocks hosting the deposits shows that (1) Pb isotope signatures of the deposits are heterogeneous when considered as a group; (2) the stratabound Nelson deposit, and deformed veins at Quarry and Galena, are isotopically similar; (3) stratabound and locally stratiform lenses such as Wheeler North and Aurora Creek had different isotopic evolutions; and (4) the occurrence at Bluff and the postmetamorphic, undeformed Pb-Zn-Ag veins and replacements at Hannum, Independence, Foster, and Omilak show the highest values of 206 Pb/ 204 Pb in the region. Pb isotope data for the stratabound Zn-Pb deposits and occurrences do not lie along similar secondary or anomalous lead evolution lines, and there is no shared, two-stage lead line that would provide intersections with a primary or single-stage lead isotope growth curve. Lead isotopic characteristics of the Nelson stratabound deposit and the deformed veins at Quarry and Galena indicate that they largely shared metal and fluid sources. Quarry and Galena also display sufficient Pb isotopic contrast compared to Aurora Creek and Wheeler North to eliminate such veins as subsurface “feeders” for these stratabound deposits, if the deformed veins and deposits formed as closed isotopic systems (without a contribution from externally derived lead). The Pb isotope composition of galena from Aurora Creek formed by a multistage process. It is thus possible that the Aurora Creek deposit originally contained Pb isotope compositions that resembled those from Quarry and Galena. That early-formed Pb was probably remobilized and mixed with radiogenic lead contributed by Mesozoic hydrothermal fluids similar to those associated with the gold-quartz veins in the region. Values of 207 Pb/ 204 Pb and 206 Pb/ 204 Pb from each of the deposits and occurrences plot within the Pb isotope fields of the host metasedimentary rocks and Mesoproterozoic basement rocks of Seward Peninsula; Pb isotope compositions in the deposits thus reflect a local source control. The processes that generated the premetamorphic Zn-Pb(-Ag-Au-Ba-F) sulfide deposits in the Nome Complex differed from those that generated Zn-Pb-Ag deposits in the western Brooks Range, such as the giant Red Dog ore body. Taken as a group, the stratabound lenses and deformed veins in the Nome Complex did not form in a single, widespread, homogeneous hydrothermal system. The Brooks Range deposits, which consist of a range of host rock types and styles of mineralization distributed over a large area, have a high degree of regional Pb isotope homogeneity. The Wheeler North deposit is isotopically similar to Red Dog and related deposits and may have formed in a related hydrothermal system. A preliminary comparison of the Pb isotope compositions of sedimentary-exhalative (SEDEX)–type deposits within the Arctic Alaska–Chukotka terrane and deposits in crustal blocks of Laurussia shows: (1) noteworthy Pb isotopic overlap exists between some of Zn-Pb-Ag deposits in Ireland and the deposits in Arctic Alaska ; but (2) no exact isotopic match exists between any of the deposits in Arctic Alaska and any deposit in crustal blocks involved in the Paleozoic evolution of Laurussia.

Alaska↗
USGS2017

Geochemistry and mineralogy of the Dotson Zone HREE deposit in the Bokan Mountain peralkaline igneous complex, southeastern Alaska, USA

The Bokan Mountain igneous complex (BMIC) is a typical example of a peralkaline intrusive system that has evolved to the point of developing late stage HFSE- and REE-rich silicic pegmatites and dikes. The Dotson Zone comprises a series of felsic dikes that extend from the southeast margin of the composite pluton and may represent an important resource of critical HREEs. Petrographically, the primary igneous mineral assemblage is altered by late-igneous and hydrothermal fluids resulting in redistribution and enrichment of REEs. An area of flexure in the southeastern end of the Dotson Zone was the primary locus of enrichment as shown by the pervasive alteration and consistently high REE+Y values. We favor a model in which the dikes were emplaced concurrently with the marginal intrusions, and then altered during emplacement of the inner, main intrusion in a relatively rapid series of overlapping intrusive and late magmatic fluid-high temperature hydrothermal events as the complex cooled. A much later sodic intrusive event focused on the BMIC may have resulted in additional silica-Na-Zr-rich alteration in proximity to the pluton.

Conference Paper↗
USGS2004

The Anarraaq Zn-Pb-Ag and barite deposit, northern Alaska: Evidence for replacement of carbonate by barite and sulfides

The Anarraaq deposit in northern Alaska consists of a barite body, estimated to be as much as 1 billion metric tons, and a Zn-Pb-Ag massive sulfide zone with an estimated resource of about 18 Mt at 18 percent Zn, 5.4 percent Pb, and 85 g/t Ag. The barite and sulfide minerals are hosted by the uppermost part of the Mississippian Kuna Formation (Ikalukrok unit) that consists of carbonaceous and siliceous mudstone or shale interbedded with carbonate. The amount of interbedded carbonate in the Anarraaq deposit is atypical of the district as a whole, comprising as much as one third of the section. The total thickness of the Ikalukrok unit is considerably greater in the area of the deposit (210 to almost 350 m) than to the north and south (maximum of 164 m). The mineralized zone at Anarraaq is lens shaped and has a relatively flat top and a convex base. It also ranges greatly in thickness, from a few meters to more than 100 m. Textures of some of the carbonate layers are distinctive, consisting of nodules within siliceous mudstone or layers interbedded with shale. Many of the layers contain calcitized sponge spicules or radiolarians in a carbonate matrix. Textures of barite and sulfide minerals mimic those of carbonate and provide unequivocal evidence that replacement of precursor carbonate was an important process. Barite and sulfide textures include either nodular, bladed grains of various sizes that resemble spicules (observed only with iron sulfides) or well-rounded forms that are replaced radiolarians. Mineralization at Anarraaq probably occurred in a fault-bounded Carboniferous basin during early diagenesis in the shallow subsurface. The shape and size of the mineralized body suggest that barite and sulfides replaced calcareous mass flow deposits in a submarine channel. The distribution of biogenic and/or early diagenetic silica may have served as impermeable barriers to the fluids, thereby focusing and controlling fluid flow through unreplaced carbonate layers. ?? 2004 by Economic Geology.

Economic Geology↗
USGS1947

Stratigraphy and structure of the area of the Kurupa, Oolamnagavik, Killik, and Colville Rivers

The area between 68° 3C' and 69° 08 N. latitude and between 154° and 155° 20 W. longitude was covered by U. S. Geological Survey party 4 during the period May 18 to September 2. Traverses were confined mainly to the valleys of the Kurupa, Oolamnagavik, and Colville Rivers inasmuch as very little rock is exposed in the interstream areas. This report is a compilation of the field data and of the results of office and laboratory work on rock specimens, fossils, and aerial photographs of the area. An interpretation of the structure and stratigraphy of this area is presented, and possible correlations with the Killik River area to the east are suggested. Some revisions of the conclusions in this report may become necessary in the light of further field work in adjacent areas and heavy mineral studies, but it is believed that any changes will not materially alter the geologic picture of the area.

Alaska↗
USGS1964

Placer gold occurrences in Alaska

The following references give data on localities of placer gold by quadrangle and are keyed by number within each quadrangle to locations shown on map. The quadrangle boundaries and names used on the map are those selected by the U. S. Geological Survey for topographic mapping in Alaska on a scale of 1:250,000. The references cited for each group of localities are the most complete or most recent descriptions as of December 31, 1960.

Alaska↗
USGS2012

Map showing extent of glaciation in the Eagle quadrangle, east-central Alaska

This map covers the Eagle 1:250,000-scale quadrangle in the northeastern part of the Yukon-Tanana Upland in Alaska. It shows the extent of five major glacial advances, former glacial lakes, and present fragmented terrace deposits related to the advances. The Yukon-Tanana Upland is an area of about 116,550 km 2 between the Yukon and Tanana Rivers in east-central Alaska that extends into the western part of the Yukon Territory of Canada. Traditionally, the Yukon-Tanana Upland was thought to be a part of unglaciated central Alaska, however, a rather long history of localized alpine glaciation during Pleistocene and possibly Tertiary time can be shown. Deposits of five of the glacial episodes can be found in the Eagle quadrangle. This report is an outcome of studies conducted in conjunction with bedrock mapping intended for mineral resource assessment.

Alaska↗
USGS1951

Antimony ore in the Fairbanks district, Alaska

Antimony-bearing ores in the Fairbanks district, Alaska, are found principally in two areas, the extremities of which are at points 10 miles west and 23 miles northeast of Fairbanks; and one of two minor areas lies along this same trend 30 miles farther to the northeast. These areas are probably only local manifestations of mineralization that affected a much broader area and formed antimony-bearing deposits in neighboring districts, the closest of which is 50 miles away. The ores were exposed largely as a result of lode gold mining, but at two periods in the past, high prices for antimony ore warranted an independent production and about 2500 tons of stibnite ore was shipped. The sulfide deposits occupy the same fractures along which a gold-quartz mineralization of greater economic importance occurred; and both are probably genetically related to igneous rocks which intrude the schistose country rock. The sulfide is in part contemporaneous with some late-stage quartz in which it occurs as disseminated crystals; and in part the latest filling in the mineralized zones where it forms kidney-shaped masses of essentially solid sulfide. One extremely long mass must have contained nearly 100 tons of ore, but the average of the larger kidneys is closer to several tons. Much of the ore is stibnite, with quartz as a minor impurity, and assays show the tenor to vary from 40 to 65 percent antimony. Sulphantimonites are less abundant but likewise occur as disseminated crystals and as kidney-shaped bodies. Antimony oxides appear on the weathered surface and along fractures within the sulfide ore. Deposits containing either stibnite or sulphantimonite are known at more than 50 localities, but only eighteen have produced ore and the bulk of this came from the mines. The geology of the deposit, and the nature, extent, and period of the workings are covered in the detailed descriptions of individual occurrences. Several geologic and economic factors, which greatly affect prospecting and mining for stibnite ore in the area, are outlined. The principal available ore and reserves are considered to be ores earlier mined but never shipped, ore minable from near-surface deposits, and ores recoverable as a by-product of future gold mining. The outlook for stibnite production in the district is very uncertain. Apparently the greater portion of stibnite ore has already been recovered and present operations will strip the two principal areas of the district. This conclusion is based on the scanty discoveries since the last war and the fact that the areas are so pock-marked with prospects that there is little likelihood that any other large near-surface bodies remain to be discovered. Future prospecting would essentially be limited to attempts to seek the continuation of lodes previously having high yields of stibnite.

Open-File Report↗
USGS2015

Studies by the U.S. Geological Survey in Alaska, Volume 15

Summary Professional Paper 1814— Studies by the U.S. Geological Survey in Alaska, Volume 15 —continues a long-running series of collected volumes of U.S. Geological Survey (USGS) scientific reports on Alaska. This series presents new and sometimes preliminary findings that are of interest to Earth and biological scientists in academia, government, and industry; to land and resource managers; and to the general public. The series covers a broad spectrum of scientific topics, from various parts of Alaska, serving to emphasize the diversity of USGS efforts to meet the Nation’s needs for Earth-science information in the State. The USGS provides reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.

Professional Paper↗
USGS2010

Reconnaissance study of the Taylor Mountains pluton, southwestern Alaska

The Taylor Mountains pluton is a Late Cretaceous to early Tertiary (median age 65 + or ? 2 Ma) epizonal, composite biotite granite stock located about 235 km (145 mi) northeast of Dillingham in southwestern Alaska. This 30 km2 (12 mi2) pluton has sharp and discordant contacts with hornfels that developed in Upper Cretaceous clastic sedimentary rocks of the Kuskokwim Group. The three intrusive phases in the Taylor Mountains pluton, in order of emplacement, are (1) porphyritic granite containing large K-feldspar phenocrysts in a coarse-grained groundmass, (2) porphyritic granite containing large K-feldspar and smaller, but still coarse, plagioclase, quartz, and biotite phenocrysts in a fine-grained groundmass, and (3) fine-grained, leucocratic, equigranular granite. The porphyritic granites have different emplacement histories, but similar compositions; averages are 69.43 percent SiO2, 1.62 percent CaO, 5.23 percent FeO+MgO, 3.11 percent Na2O, and 4.50 percent K2O. The fine-grained, equigranular granite is distinctly felsic compared to porphyritic granite; it averages 75.3 percent SiO2, 0.49 percent CaO, 1.52 percent FeO+MgO, 3.31 percent Na2O, and 4.87 percent K2O. Many trace elements including Ni, Cr, Sc, V, Ba, Sr, Zr, Y, Nb, La, Ce, Th, and Nd are strongly depleted in fine-grained equigranular granite. Trace elements are not highly enriched in any of the granites. Known hydrothermal alteration is limited to one tourmaline-quartz replacement zone in porphyritic granite. Mineral deposits in the Taylor Mountains area are primarily placer gold (plus wolframite, cassiterite, and cinnabar); sources for these likely include scattered veins in hornfels peripheral to the Taylor Mountain pluton. The granite magmas that formed the Taylor Mountains pluton are thought to represent melted continental crust that possibly formed in response to high heat flow in the waning stage of Late Cretaceous subduction beneath interior Alaska.

Professional Paper↗
USGS2008

Temporal variation and the effect of rainfall on metals flux from the historic Beatson mine, Prince William Sound, Alaska, USA

Several abandoned Cu mines are located along the shore of Prince William Sound, AK, where the effect of mining-related discharge upon shoreline ecosystems is unknown. To determine the magnitude of this effect at the former Beatson mine, the largest Cu mine in the region and a Besshi-type massive sulfide ore deposit, trace metal concentration and flux were measured in surface run-off from remnant, mineralized workings and waste. Samples were collected from seepage waters; a remnant glory hole which is now a pit lake; a braided stream draining an area of mineralized rock, underground mine workings, and waste piles; and a background location upstream of the mine workings and mineralized rock. In the background stream pH averaged ???7.3, specific conductivity (SC) was ???40 ??S/cm, and the aqueous components indicative of sulfide mineral weathering, SO4 and trace metals, were at detection limits or lower. In the braided stream below the mine workings and waste piles, pH usually varied from 6.7 to 7.1, SC varied from 40 to 120 ??S/cm, SO4 had maximum concentrations of 32 mg/L, and the trace metals Cu, Ni, Pb, and Zn showed maximum total acid extractable concentrations of 186, 5.9, 6.2 and 343 ??g/L, respectively. With an annual rainfall of ???340 cm (estimated from the 2006 water year) it was expected that rain water would have a large effect on the chemistry of the braided stream draining the mine site. A linear mixing model with two end members, seepage water from mineralized rock and background water, estimated that the braided stream contained 10-35% mine drainage. After rain events the braided stream showed a decrease in pH, SC, Ca + Mg, SO4, and alkalinity, due to dilution. The trace metals Ni and Zn followed this same pattern. Sodium + K and Cl did not vary between the background and braided stream, nor did they vary with rainfall. At approximately 2 and 3 mg/L, respectively, these concentrations are similar to concentrations found in rainfall on the coasts of North America. High concentrations of total acid extractable Al and Fe were found at near-neutral pH in most of the waters collected at the site. Equilibrium solubility simulations, performed with PHREEQC, show that the stream waters are saturated with respect to Al, Fe and SiO2 solid phases. Because the "dissolved" sample fractions (acid preserved and filtered to 0.45 ??m) show significant concentrations of Al and Fe it is presumed that these are present as colloids. The relationship between concentrations of Al and Fe, and rainfall was the opposite of that observed for the major ions Ca + Mg, SO4, and alkalinity, in that Al and Fe concentrations increased with increasing rainfall. Concentrations of Cu and Pb followed the same pattern. Adsorption calculations were performed with Visual MINTEQ, using the diffuse double layer electrostatic model and surface complexation constants for the ferrihydrite surface. These results suggest that 30-93% of Cu and 58-97% of Pb was adsorbed to ferrihydrite precipitates in the stream waters. Ni and Zn showed little adsorption in this pH range. Flux calculations show that the total mass of trace metals transported from the mine site, during the 60 day study period, was ranked as Zn (196 kg) > Cu (87 kg) > Pb(1.9 kg) ??? Ni(1.9 kg). Nickel and Zn were transported mostly as dissolved species while Cu and Pb were transported mostly as adsorbed species. pH control on adsorption was evident when Cu and Pb isotherms were normalized by ferrihydrite flux. Decreased stream water pH due to periods of frequent and high volume rain events would cause desorption of Cu and Pb from the ferrihydrite surface, thus changing not only their speciation in solution but also their mechanism of transport. ?? 2007 Elsevier Ltd. All rights reserved.

Applied Geochemistry↗
USGS1988

Models of grades and tonnages of some lode tin deposits

Descriptive and grade/tonnage models have recently been built for many types of deposits. Such models consist of descriptions of mineralogy, host rocks, ore textures, controls, alteration, geochemical signatures, age, and tectonic settings, together with statistical models of grades, tonnages, and contained metal of deposits of each type. The models are used to identify areas that may contain undiscovered deposits of given types, to convey to non-geologists an idea of the importance of such deposits, and to test and refine classifications of mineral deposits. Descriptive and grade/tonnage models have recently been built for five types of primary tin deposits: rhyolite-hosted such as in Mexico; hydrothermal lodes such as in Cornwall, England, and the Herberton district, Queensland; replacement (or exhalative?) such as Renison Bell, Tasmania; skarn such as at Lost River, Alaska; and greisen such as in the Erzgebirge. Analyses of frequency distributions of tonnage, contained metal, tin grades and the relationships between these variables show that the deposits fall into four well-defined domains that have definite geological characteristics. Rhyolite-hosted, or Mexican, deposits contain a median of 4 t of tin and have a median grade of 0.4% Sn. Hydrothermal lode deposits have the highest grades. Half of such deposits have grades over 1.0% Sn, and the majority contain more than 1,000 t Sn. Large hydrothermal vein deposits contain more than 50,000 t Sn. Replacement (or exhalative?) deposits contain the largest amount of tin (median = 40,000 t). They are only of slightly lower grade (median = 0.80% Sn) than the hydrothermal lodes. Greisen or stockwork deposits have larger tonnages than replacement deposits, but contain less tin (median = 25,000 t).They are also of much lower grade (median = 0.3% Sn). Though grades and tonnages are available for only four skarn deposits, they appear to be more like greisen deposits than replacement deposits when compared using grades, tonnage and contained tin. Although these individual models of primary tin deposits must be regarded as preliminary because of the relatively small number of deposits upon which they are built, they clearly demonstrate differences among types and provide basic information that can be useful in making decisions about exploration strategy, land classification, and tin supply.

Book chapter↗
USGS2008

Geochemical controls of elevated arsenic concentrations in groundwater, Ester Dome, Fairbanks district, Alaska

Ester Dome, an upland area near Fairbanks, Alaska, was chosen for a detailed hydrogeochemical study because of the previously reported elevated arsenic in groundwater, and the presence of a large set of wells amenable to detailed sampling. Ester Dome lies within the Fairbanks mining district, where gold-bearing quartz veins, typically containing 2–3 vol.% sulfide minerals (arsenopyrite, stibnite, and pyrite), have been mined both underground and in open cuts. Gold-bearing veins on Ester Dome occur in shear zones and the sulfide minerals in these veins have been crushed to fine-grained material by syn- or post-mineralization movement. Groundwater at Ester Dome is circumneutral, Ca–HCO 3 to Ca–SO 4 type, and ranges from dilute (specific conductance of 48 µS/cm) to more concentrated (specific conductance as high as 2070 µS/cm). In general, solute concentrations increase down hydrologic gradient. Redox species indicate that the groundwaters range from oxic to sub-oxic (low dissolved oxygen, Fe(III) reduction, no SO 4 reduction). Waters with the highest Fe concentrations, as high as 10.7 mg/L, are the most anoxic. Dissolved As concentrations range from < 1 to 1160 µg/L, with a median value of 146 µg/L. Arsenic concentrations are not correlated with specific conductance or Fe concentrations, suggesting that neither groundwater residence time, nor reductive dissolution of iron oxyhydroxides, control the arsenic chemistry. Furthermore, As concentrations do not covary with other constituents that form anions and oxyanions in solution (e.g., HCO 3 , Mo, F, or U) such that desorption of arsenic from clays or oxides also does not control arsenic mobility. Oxidation of arsenopyrite and dissolution of scorodite, in the near-surface environment appears to be the primary control of dissolved As in this upland area. More specifically, the elevated As concentrations are spatially associated with sulfidized shear zones and localities of gold-bearing quartz veins. Consistent with this interpretation, elevated dissolved Sb concentrations (as high as 59 µg/L), also correlated with occurrences of hypogene sulfide minerals, were measured in samples with high dissolved As concentrations.

Chemical Geology↗
USGS1971

Origin and emplacement of the ultramafic rocks of the Emigrant Gap area, California

The ultramafic bodies of the Emigrant Gap area are part of a mafic complex within a large composite pluton of the northern Sierra Nevada. The pluton was magmatically emplaced and is surrounded by an aureole of hornblende-hornfels facies rocks. Inclusions of country rock in ultramafic rock are of pyroxene-hornfels facies and appear to have been partly melted. Gravity studies indicate that the ultramafic bodies have near-vertical contacts extending to depths of at least 1½ to 2½ km. The mafic complex shows rough concentric zoning of rock types: ultramafic bodies occur at the core; gabbro forms a discontinuous intermediate unit; and diorite, tonalite, and granodiorite occur at the margins. Within the ultramafic bodies, unserpentinized wehrlitic peridotite is dominant; dunite and olivine clinopyroxenite are present but greatly subordinate. The ultramafic rocks consist almost entirely of olivine (FO 80 ) and diopside (Ca 46 Mg 46 Fe 8 ); orthopyroxene, hornbolende, and plagioclase occur locally. The gabbro, diorite, tonalite, and granodiorite contain both ortho- and clinopyroxene. Both ultramafic and two-pyroxene-bearing rocks were emplaced nearly simultaneously, as partly crystallized magmas and magmatic crystal mushes that had similar temperature. In all the rocks the structures are dominantly magmatic and were produced by sorting and orientation of crystals by magmatic flow. Structures produced by post-consolidation deformation and replacement are minor and local. The structural and chemical relations within the mafic complex suggest that all the rocks are derived from a single gabbroic magma by crystal fractionation, with the ultramafic rocks formed by mechanical accumulation of early crystallized mafic minerals, and the two pyroxene-bearing granodiorite crystallized from a felsic differentiate. It is likely that flowage differentiation was the dominant process of crystal segregation. The Emigrant Gap mafic complex is similar in structure, rock texture, and mineralogy to zoned ultramafic complexes, such as those of south-eastern Alaska, and is very different from either stratiform or alpine-type bodies. Though unlike the Alaskan bodies in detail, it appears that this complex should be classed with the zoned complexes in any broad grouping of ultramafic occurrences.

California↗
USGS2022

Searching for refuge: A framework for identifying site factors conferring resistance to climate-driven vegetation change

Climate change is occurring at accelerated rates in high latitude regions such as Alaska, causing alterations in woody plant growth and associated ecosystem patterns and processes. Our aim is to assess the magnitude and speed that climate-induced changes in woody plant distribution and volume may be reduced and/or slowed by relatively static landscape features like physical characteristics (e.g. depth to gravel, mineral cover percent and slope degree) and/or edaphic properties (e.g. soil organic matter, soil pH and site wetness rating) that resist climate-vegetation responses

Alaska↗
USGS1905

Geology of the central Copper River region, Alaska

It is an interesting evidence of the prompt responsiveness of our governmental organization to popular needs that the year 1898, which saw the first rush of argonauts to Alaska as a result of the discovery of the Klondike in 1986, saw also several well-equipped Federal parties at work in the Territory, mapping its great waterways and mountain ranges, investigating the feasible means of transportation within it, laying out routes for future lines of communication, and studying the mineral resources and the plant and animal life. It is true that before that year, in which the general attention of the world was fixed upon our heretofore lightly regarded northern province, fur traders, adventurous travelers, and hardy prospectors had made little-heralded journeys through the interior, and that one or another of the governmental departments had had representatives on special errands within its borders, but the amount of private and public energy expended there in 1898 probably exceeded that of any ten previous years.

Alaska↗
USGS1968

Gold gradients and anomalies in the Pedro Dome-Cleary Summit area, Fairbanks district, Alaska

Anomalous gold values have been discovered in hydrothermally altered quartz diorite, quartz monzonite, and quartz mica schist at the head of Fox Creek; and in similarly altered quartz diorite in the Granite Creek area. Channel samples across some of these altered zones have produced anomalous gold values over widths which merit further investigation as potential large tonnage low-grade gold deposits. Trace gold gradients have also been detected in the wall rocks adjacent to mineralized veins and in hydrothermal alteration zones in the Pedro Dome-Cleary Summit area. Although most of the gradients may not materially increase the mineable width of the deposit under current economic conditions, such gradients can be used to locate auriferous quartz veins and altered zones by geochemical methods. Gold enrichment is accompanied by anomalous concentrations of arsenic and antimony, and gold bearing quartz veins and altered zones are frequently signaled by peripheral haloes of these metals before trace gold is detectable. Hydrothermally altered and/or sheared zones in both granitic and metamorphic rocks should be carefully prospected, along the trend of the Cleary Antiform.

Open-File Report↗
USGS1970

Molybdenum in the United States, exclusive of Alaska and Hawaii

The accompanying map shows the principal deposits and many minor occurrences of molybdenum in the conterminous United States. Six types are distinguished by shapes of the symbols used, and three size categories indicate the relative importance of the deposits.

Mineral Investigations Resource Map↗
USGS1953

Reconnaissance for radioactive deposits in the Darby Mountains, Seward Peninsula, Alaska, 1948

Radioactivity in the southern and eastern parts of the Darby Mountains, Seward Peninsula, Alaska, appears to be directly related to the occurrence of granite. Concentrates from placers derived from areas containing granite are more radioactive than concentrates from placers not derived from the granite and, generally, contain from 0.01 to 0.05 percent equivalent uranium. The radioactivity of these concentrates is largely due to radioactive elements in common accessory minerals in granite, such as sphene, allanite, zircon, and, locally, monazite. Locally, in the Clear Creek-Vulcan Creek rea, the headwaters of the Kwiniuk River, and on Golovnin Bay near McKinley Creek, concentrates from placers derived from granitic terrain contain as much as 0.1 percent equivalent uranium. The higher radioactivity of the concentrates from the Clear Creek area and on Golovnin Bay is due chiefly to an unidentified uranium-titanium niobate, whereas the higher radioactivity at the headwaters of the Kwiniuk River is due to thorianite.

Circular↗