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USGS2012

Local-area-enhanced, high-resolution natural-color and color-infrared satellite-image mosaics of mineral districts in Afghanistan

The U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Defense Task Force for Business and Stability Operations, prepared databases for mineral-resource target areas in Afghanistan. The purpose of the databases is to (1) provide useful data to ground-survey crews for use in performing detailed assessments of the areas and (2) provide useful information to private investors who are considering investment in a particular area for development of its natural resources. The set of satellite-image mosaics provided in this Data Series (DS) is one such database. Although airborne digital color-infrared imagery was acquired for parts of Afghanistan in 2006, the image data have radiometric variations that preclude their use in creating a consistent image mosaic for geologic analysis. Consequently, image mosaics were created using ALOS (Advanced Land Observation Satellite; renamed Daichi) satellite images, whose radiometry has been well determined (Saunier, 2007a,b). This DS consists of the locally enhanced ALOS image mosaics for each of the 24 mineral project areas (referred to herein as areas of interest), whose locality names, locations, and main mineral occurrences are shown on the index map of Afghanistan (fig. 1). ALOS was launched on January 24, 2006, and provides multispectral images from the AVNIR (Advanced Visible and Near-Infrared Radiometer) sensor in blue (420-500 nanometer, nm), green (520-600 nm), red (610-690 nm), and near-infrared (760-890 nm) wavelength bands with an 8-bit dynamic range and a 10-meter (m) ground resolution. The satellite also provides a panchromatic band image from the PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) sensor (520-770 nm) with the same dynamic range but a 2.5-m ground resolution. The image products in this DS incorporate copyrighted data provided by the Japan Aerospace Exploration Agency, but the image processing has altered the original pixel structure and all image values of the JAXA ALOS data, such that original image values cannot be recreated from this DS. As such, the DS products match JAXA criteria for value added products, which are not copyrighted, according to the ALOS end-user license agreement. The selection criteria for the satellite imagery used in our mosaics were images having (1) the highest solar-elevation angles (near summer solstice) and (2) the least cloud, cloud-shadow, and snow cover. The multispectral and panchromatic data were orthorectified with ALOS satellite ephemeris data, a process which is not as accurate as orthorectification using digital elevation models (DEMs); however, the ALOS processing center did not have a precise DEM. As a result, the multispectral and panchromatic image pairs were generally not well registered to the surface and not coregistered well enough to perform resolution enhancement on the multispectral data. Therefore, it was necessary to (1) register the 10-m AVNIR multispectral imagery to a well-controlled Landsat image base, (2) mosaic the individual multispectral images into a single image of the entire area of interest, (3) register each panchromatic image to the registered multispectral image base, and (4) mosaic the individual panchromatic images into a single image of the entire area of interest. The two image-registration steps were facilitated using an automated control-point algorithm developed by the USGS that allows image coregistration to within one picture element. PRISM image orthorectification for one-half of the target areas was performed by the Alaska Satellite Facility, applying its photogrammetric software to PRISM stereo images with vertical control points obtained from the digital elevation database produced by the Shuttle Radar Topography Mission (Farr and others, 2007) and horizontal adjustments based on a controlled Landsat image base (Davis, 2006). Before rectification, the multispectral and panchromatic images were converted to radiance values and then to relative-reflectance values using the methods described in Davis (2006). Mosaicking the multispectral or panchromatic images started with the image with the highest sun-elevation angle and the least atmospheric scattering, which was treated as the standard image. The band-reflectance values of all other multispectral or panchromatic images within the area were sequentially adjusted to that of the standard image by determining band-reflectance correspondence between overlapping images using linear least-squares analysis. The resolution of the multispectral image mosaic was then increased to that of the panchromatic image mosaic using SPARKLE logic, which is described in Davis (2006). Each of the four-band images within each resolution-enhanced image mosaic was individually subjected to a local-area histogram stretch algorithm (described in Davis, 2007), which stretches each band's picture element based on the digital values of all picture elements within a specified radius that was usually 500 m. The final databases, which are provided in this DS, are three-band, color-composite images of the local-area-enhanced, natural-color data (the blue, green, and red wavelength bands) and color-infrared data (the green, red, and near-infrared wavelength bands). All image data were initially projected and maintained in Universal Transverse Mercator (UTM) map projection using the target area's local zone (either 41 or 42) and the WGS84 datum. Most final image mosaics were subdivided into overlapping tiles or quadrants because of the large size of the target areas. The image tiles (or quadrants) for each area of interest are provided as embedded geotiff images, which can be read and used by most geographic information system (GIS) and image-processing software. The tiff world files (tfw) are provided, even though they are generally not needed for most software to read an embedded geotiff image. Approximately one-half of the study areas have at least one subarea designated for detailed field investigations; the subareas were extracted from the area's image mosaic and are provided as separate embedded geotiff images.

Data Series↗

USGS2004

Paleozoic sedimentary rocks in the Red Dog Zn-Pb-Ag district and vicinity, western Brooks Range, Alaska: provenance, deposition, and metallogenic significance

Geochemical analyses of Paleozoic sedimentary rocks in the western Brooks Range reveal a complex evolutionary history for strata surrounding the large Zn-Pb-Ag deposits of the Red Dog district. Data for major elements, trace elements, and rare earth elements (REE) were obtained on 220 samples of unaltered and unmineralized siliciclastic rocks from the Upper Devonian-Lower Mississippian Endicott Group (Hunt Fork Shale, Noatak Sandstone, Kanayut Conglomerate, Kayak Shale), the overlying Carboniferous Lisburne Group (Kuna Formation, unnamed drowned shelf facies), and the Pennsylvanian-Permian Siksikpuk Formation. Major base metal sulfide deposits of the region are present only in the Kuna Formation, which in the Red Dog district comprises siliceous black shale and black chert, minor limestone (calcareous radiolarite), and sparse lithic turbidite and bedded siliceous rock. Gray and rare black shales of the Kayak Shale and common black shales of the Kuna Formation are anomalously low in iron (avg Fe/Ti = 6.25 and 6.34, respectively) relative to other Paleozoic shales in the region (9.58-10.6) and to average shales worldwide (10.1-10.5). In contrast, the bedded siliceous rocks contain appreciable hematite (avg Fe/Ti = 35.0) and high U/Ti and REE/Ti ratios that are interpreted to reflect low amounts of detrital material and a major Fe-rich eolian component. Geochemical data (e.g., MnO <0.01 wt %; avg Cr = 317 ppm), sizes of framboidal pyrite grains, and limited bioturbation suggest anoxic and denitrifying depositional conditions for most black shales of the Kuna Formation; low Mo/Ti ratios argue against euxinic (sulfate-reducing) conditions. Organic-rich black shales of the Kuna Formation with up to 8.4 wt percent C organic and gray to black shales of the Kayak Shale with up to 4.1 wt percent C organic typically have only sparse pyrite (<1 wt % S) and very low iron-limited S/C ratios (mostly <0.2). Immobile element plots (e.g., Th-Zr/10-Sc) suggest that source terranes for all of the formations were dominated by one or more felsic-rich continental arcs; a small proportion of recycled sediments is present locally. A minor mafic igneous component also occurs in several shales of the Kuna and Siksikpuk Formations. High average values for the chemical index of alteration [Al 2 O 3 /(Al 2 O 3 + CaO + Na 2 O + K 2 O)] ∞ 100 for shales of the Endicott Group (76.4-81.5) imply moderate to intense chemical weathering in source areas of these sediments. A lower average for black shales of the Kuna Formation (73.7) does not require such weathering. Textural and geochemical data record the effects of diagenetic and/or hydrothermal fluid flow in some of the Paleozoic rocks. Mobility of P, F, U, and light REE is documented in black shales of the Kuna Formation by phosphate replacements of carbonate clasts and of matrix material surrounding the clasts. A relatively low average Ce/Ce* value of 0.73 for P-poor black shales of the Kuna Formation ( < 0.05 wt % P 2 O 5 ) and a similar Ce/Ce* value of 0.78 for a siderite concretion in Kayak Shale suggest that these diagenetic fluids were oxidizing. Many shales of the Kuna Formation have high (K 2 O ∞ 100)/(K 2 O + Al 2 O 3 ) ratios of 21.0 to 23.0, which contrast with low ratios of generally <18.0 for shales of the underlying Endicott Group. The high ratios in shales of the Kuna Formation reflect preferential reaction of smectite to illite during the Jurassic-Cretaceous Brookian orogeny, owing to high silica activities in pore fluids that were generated by the dissolution of abundant biogenic silica. The distribution and composition of Paleozoic strata in the western Brooks Range may have played a fundamental role in Zn-Pb mineralization of the Red Dog district. In our model, deposition and early lithification of biogenic chert and bedded siliceous rocks in the upper part of the Kuna Formation served as a regional hydrologic seal, acting as a cap rock to heat and hydrothermal fluids during Late Mississippian base-metal mineralization. Equally important was the iron-poor composition of black shales of the Kuna Formation (i.e., low Fe/Ti ratios), which limited synsedimentary pyrite formation in precursor sediments, resulting in significant H 2 S production in pore waters through the interaction of aqueous sulfate with abundant organic matter. This H 2 S may have been critical to the subsurface deposition of the huge quantities of Zn and Pb in the district. On the basis of this model, we propose that low Fe/Ti and S/C ratios in black shale sequences are potential basin-scale exploration guides for giant sediment-hosted, stratiform Zn-Pb-Ag deposits.

Alaska↗

USGS1962

Copper in the United States, exclusive of Alaska and Hawaii

The copper districts in the United States (exclusive of Alaska and Hawaii) are shown on the accompanying map. In compiling the map, the estimated total quantity of copper present before mining was used to assign districts to size categories, and both production and reserves are included without distinction as to the status of exploitation. Four categories have been distinguished: deposits that contain 50+ to 1,000 tons; 1,000 to 50,000 tons; 50,000 to 1 million tons; and over 1 million tons of copper respectively. In many of the smaller deposits copper occurs with other metals, as gold, silver; lead, or zinc, that may be quantitatively and economically more important than the contained copper. Thus, for example, a deposit that contains large values in gold or zinc may contain only a small amount of copper and is shown on this map as a small copper deposit. Five principal morphologic types of deposits have been distinguished on the map by letter symbols. These are disseminated, replacement, vein, massive sulfide, and native copper deposits (see Explanation). They are not strictly genetic types, however, for the disseminated deposits, the massive sulfide deposits, and many of the vein deposits were formed largely or entirely by replacement processes. The symbols show either individual mines or the approximate centers of districts. Some of the more prominent districts are identified by name on the map, and all with over 1,000 tons of copper are numbered to correspond to the Locality Index. As mining district names do not always correspond to locality names, and a name established through common usage may not be the legal name of the mining district, several names are given in the index for some localities. The index is arranged alphabetically by States. Both published and unpublished data were used, and at least one reference is given for each locality if reports on it have been published.

Mineral Investigations Resource Map↗

USGS1962

Asbestos in the United States, exclusive of Alaska and Hawaii

The asbestos deposits in the United States (exclusive of Alaska and Hawaii) are shown on the accompanying map. The principal mineralogic types of asbestos (chrysotile and amphibole) are indicated by the shape of symbols, and the relative importance of the deposit is indicated by the size of symbols. The text lists localities by State by numbers that are keyed to the map. Localities are distinguished by name of mine, prospect, or geographic area; their coordinates are given to the nearest minute of latitude and longitude. Geologic relations of each occurrence, if known, are characterized briefly. The text and map were compiled from published and unpublished information, and at least one reference is given for each locality if reports on it have been published. Chrysotile asbestos, a variety of serpentine, occurs chiefly in serpentinized peridotite and is distributed in the United States in two principal belts, the eastern extending from Maine to Alabama, and the western extending from Washington to California, where numerous masses of ultramafic rocks were intruded in Paleozoic and Mesozoic time, respectively. Domestic production from deposits of this type has not been large compared with that of Canada from the extensively developed deposits in Quebec, Ontario, and British Columbia. The principal mine in the United States is located at Belvidere Mountain, Vt. Minor amounts of asbestos have been produced from other deposits in these belts and from scattered occurrences of chrysotile elsewhe,re in a number of States between them. Increased exploration and development activity for short-fiber chrysotile has recently been reported in California. Chrysotile also occurs in bedded limestone, metamorphosed close to intrusions of diabase. The principal occurrences of this type are in Arizona, where small quantities of long-fiber, low-iron chrysotile have been mined from numerous small deposits. Several species of amphibole occur in fibrous forms; in the United States only anthophyllite and tremolite are known to have commercial importance. As both the anthophyllite and tremolite occur in ultramafic rocks, associated greenstone, and amphibolite, the overall distribution of amphibole asbestos in the United States is like that of chrysotile. The deposits are generally small and erratic in distribution.

Mineral Investigations Resource Map↗

USGS2014

Geophysical investigations of the geologic and hydrothermal framework of the Pilgrim Springs Geothermal Area, Alaska

Pilgrim Hot Springs, located on the Seward Peninsula in west-central Alaska, is characterized by hot springs, surrounding thawed regions, and elevated lake temperatures. The area is of interest because of its potential for providing renewable energy for Nome and nearby rural communities. We performed ground and airborne geophysical investigations of the Pilgrim Springs geothermal area to identify areas indicative of high heat flow and saline geothermal fluids, and to map key structures controlling hydrothermal fluid flow. Studies included ground gravity and magnetic measurements, as well as an airborne magnetic and frequency-domain electromagnetic (EM) survey. The structural and conceptual framework developed from this study provides critical information for future development of this resource and is relevant more generally to our understanding of geothermal systems in active extensional basins. Potential field data reveal the Pilgrim area displays a complex geophysical fabric reflecting a network of intersecting fault and fracture sets ranging from inherited basement structures to Tertiary faults. Resistivity models derived from the airborne EM data reveal resistivity anomalies in the upper 100 m of the subsurface that suggest elevated temperatures and the presence of saline fluids. A northwest trending fabric across the northeastern portion of the survey area parallels structures to the east that may be related to accommodation between the two major mountain ranges south (Kigluaik) and east (Bendeleben) of Pilgrim Springs. The area from the springs southward to the range front, however, is characterized by east-west trending, range-front-parallel anomalies likely caused by late Cenozoic structures associated with north-south extension that formed the basin. The area around the springs (~10 km2 ) is coincident with a circular magnetic high punctuated by several east-west trending magnetic lows, the most prominent occurring directly over the springs. These features possibly result from hydrothermal alteration imposed by fluids migrating along intra-basin faults related to recent north-south extension. The Pilgrim River valley is characterized by a NE-elongate gravity low that reveals a basin extending to depths of ~300 m beneath Pilgrim Springs and deepening to ~800 m to the southwest. The margins of the gravity low are sharply defined by northeasttrending gradients that probably reflect the edges of fault-bounded structural blocks. The southeastern edge of the low, which lies very close to the springs, also corresponds with prominent NE-striking anomalies seen in magnetic and resistivity models. Together, these features define a structure we refer to as the Northeast Fault. The location of the hot springs appears to be related to the intersection of the Northeast Fault with a N-oriented structure marked by the abrupt western edge of a resistivity low surrounding the hot springs. While the hot springs represent the primary outflow of geothermal fluids, additional outflow extends from the springs northeast along the Northeast fault to another thaw zone that we interpret to be a secondary region of concentrated upflow of geothermal fluids. The Northeast Fault apparently controls shallow geothermal fluid flow, and may also provide an important pathway conveying deep fluids to the shallow subsurface. We suggest that geothermal fluids may derive from a reservoir residing beneath the sediment basin southwest of the springs. If so, the shape of the basin, which narrows and shallows towards the springs, may funnel fluids beneath the springs where they intersect the Northeast Fault allowing them to reach the surface. An alternative pathway for reservoir fluids to reach intermediate to shallow depths may be afforded by the main Kigluaik range front fault that coincides with a resistivity anomaly possibly resulting from fluid flow and associated hydrothermal mineralization occurring within the fault zone.

Conference Paper↗

USGS2022

The ~400 yr B.P. eruption of Half Cone, a post-caldera composite cone within Aniakchak caldera, Alaska Peninsula

Aniakchak volcano is a historically active caldera located on the central Alaska Peninsula. The largest eruption from Aniakchak since the ~3,400 yr B.P. caldera-forming eruption occurred ~400 yr B.P. from Half Cone volcano, an intracaldera composite cone on the northwest floor of the Aniakchak caldera that was largely destroyed by the eruption. The ~400 yr B.P. eruption produced a widely dispersed pumice fall deposit known as the Pink and Brown Pumice. Following small phreatomagmatic explosions, a buoyant Plinian eruption column combined with southwesterly winds dispersed ~1.3 km3 of crystal-poor dacite (66.1–67.1% SiO2) Pink Pumice at least 70 km to the northeast from Half Cone (~0.05 km3 dense rock equivalent; DRE). Fluctuations in the diameters of pyroclasts and accidental lithics in the Pink Pumice indicate at least two cycles of waxing and waning mass flux at the Half Cone vent. This vent produced an eruption column that twice expanded and gained altitudes of ~15–20 km before weakening to lower altitudes. Brown Pumice scoria (58.2– 66.9% SiO2) as well as compositionally banded pyroclasts at the top of the Pink Pumice indicate that both dacite magma and an increasing amount of low-SiO2 (58.2–60.5% SiO2) andesite magma were erupted simultaneously during the transition to the Brown Pumice phase of the eruption. The reversely graded Brown Pumice fall deposit records an escalating Plinian column dominated by low-SiO2 Brown Pumice scoria that reached altitudes of ~20–24 km and led to the emplacement of least ~3.5 km3 of fall deposits up to at least 230 km to the northeast (~1 km3 DRE). Over time, the Brown Pumice eruption column repeatedly experienced partial collapse that ultimately produced thick pyroclastic density current deposits, most of which were confined to within the caldera. Lithic-rich agglutinate and spatter exposed in 60-m-thick deposits atop the severed flanks of Half Cone and within ~2 km of Half Cone were emplaced at the end of the Brown Pumice phase. Agglutinate deposits range from 58.6 to.64.8% SiO2, which generally falls in the compositional range between Brown and Pink Pumice compositional endmembers. Most of the Half Cone edifice was destroyed by the end of the Brown Pumice phase. The ~0.1 km3 crystal-rich dacitic Cobweb lava flow (64.8–65.8% SiO2) filled a basin left behind by the destruction of Half Cone as a series of radiating lobes. Subsequently, a small andesitic tuff cone (62.2–62.8% SiO2) formed over the Cobweb lava flow vent. In all, we estimate that at least ~5.4 km3 of tephra and ~0.1 km3 of lava erupted during the ~400 yr B.P. eruption, yielding a total magmatic volume (DRE) of ~1.3 km3. Titanomagnetite-ilmenite pairs in Pink and Brown Pumice samples record similar equilibrium temperature ranges (944–997 °C and 959–985 °C, respectively) but different fO2 conditions—Pink Pumice pairs plot between NNO and NNO +0.5, Brown Pumice pairs plot below the NNO buffer. Titanomagnetite-ilmenite pairs in Brown Pumice agglutinate record a wider range of temperatures than either Pink or Brown Pumice samples (899–1018 °C) but also show two populations of fO2—one that overlaps the Pink Pumice array at higher fO2 and one that overlaps the Brown Pumice array at lower fO2. Titanomagnetite-ilmenite pairs from the Cobweb lava flow have the largest fO2 range (NNO -0.5 to NNO +0.5), although most pairs overlap Brown Pumice samples at lower fO2 conditions near NNO -0.5. Pairs in Cobweb lava samples record temperatures from 837 to 1054 °C, which is the largest temperature range recorded in deposits emplaced during any phase of the ~400 yr B.P. eruption. Geothermometry results of titanomagnetite-ilmenite pairs in ≤3,400 yr B.P. samples erupted from Aniakchak volcano record a similar temperature range and the presence of two fO2 arrays as the ~400 yr B.P. samples, which implies the existence of two magma regions of the mush column; each the product of slightly different evolution. In addition, results from in situ compositional analyses of plagioclase suggest that the ~400 yr B.P. eruption may have been initiated, at least in part, by intrusion of basaltic magma, which ascended from the lower crust into the shallow subvolcanic magma mush column prior to and during eruption. The bimodal distribution of whole-rock compositions and the two plagioclase populations in the low-SiO2 Brown Pumice—one defined by An40–An60 cores and one defined by An79–An95 cores—is consistent with an abbreviated period of mixing between intruding basalt and resident dacite mush prior to eruption. Progressive mixing between mafic and felsic magmas during and after the eruption likely produced the subsequently erupted Cobweb lava flow, which has an intermediate composition with abundant mineral disequilibria. Aniakchak volcano continues to show episodic signs of unrest, suggesting that eruptions will occur in the future.

Alaska↗