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At least 1,171 records · Page 65Linked to original sources
USGS2022

Systematic mapping of the ocean-continent transform plate boundary of the Queen Charlotte fault system, southeastern Alaska and western British Columbia—A preliminary bathymetric terrain model

In 2015, U.S. Geological Survey scientists in collaboration with scientists from other institutions began a study of the Queen Charlotte fault—the first systematic study of the fault in more than three decades. The primary goal of the study was to gain a better understanding of the earthquake, tsunami, and underwater-landslide hazards throughout southeastern Alaska, as well as gather data to develop geologic models that can be applied to similar plate boundaries around the globe, such as the San Andreas fault system in southern California, the Alpine fault in New Zealand, and the North Anatolian fault in Turkey. A bathymetric terrain model was compiled from six different multibeam surveys of the previously unmapped Queen Charlotte fault offshore of southeastern Alaska and Haida Gwaii archipelago.

Alaska, British Columbia↗
USGS2024

Using the horizontal-to-vertical spectral ratio method to estimate thickness of the Barry Arm landslide, Prince William Sound, Alaska

Conducting detailed investigations of large landslides is difficult, especially in the subsurface, largely due to environmental factors such as steep slopes, difficult access, and numerous objective hazards. These factors have made it challenging to accurately estimate the depth to the failure surface of the Barry Arm landslide, a large (roughly 10 8 cubic meters), deep-seated bedrock landslide in Prince William Sound, Alaska, recognized in 2019. The landslide has exhibited accelerated movement in recent years and poses a potential tsunamigenic hazard if rapid failure occurs. Failure surface depth, equivalent to landslide thickness, is a necessary metric for landslide-volume calculations and associated tsunami wave models. In this report, we used seismic noise recorded by a seismometer located on the Barry Arm landslide in Alaska to calculate the horizontal-to-vertical spectral ratio (HVSR) to investigate the site fundamental frequency ( f 0 ) and depth of the failure surface. To ensure that observed peak frequencies in the spectral ratio were related to the underlying stratigraphy (and not caused by other noise sources like nearby glaciers, topographic resonance, weather, or human activities), we also calculated HVSRs using earthquake signals, HVSRs at other seismic stations within a 2.5-kilometer radius, and a standard spectral ratio between the landslide station and other sites. We observed multiple peaks in the landslide HVSR curves at 1.5 hertz (Hz), 4–5 Hz, and 7–11 Hz. The frequencies of these peaks were consistent at the landslide site through time and across methods and were dissimilar to those identified at other seismic stations in the area, making it unlikely the peaks were caused by local noise. Directional HVSRs calculated at 15-degree intervals showed amplification of the higher frequency peaks in the direction parallel to slip, indicating two-dimensional site effects. We used the distinct frequency peaks in the seismic record to develop a 4-layer conceptual model of the landslide wherein the top of the deepest layer represents the primary failure surface, or the boundary between damaged (mobile) and undamaged material. We inverted Rayleigh wave ellipticity curves within this 4-layer configuration with constraints on S-wave velocity and layer thickness based on analogous material properties identified in the literature. This was necessary absent any site-specific subsurface S-wave velocity data. The best-fitting models indicate a mean slope-normal depth to the failure surface of 188 (±9) meters (m), with additional stratigraphic boundaries at 4 and 20 m below ground surface, potentially representing layered motion. These results agree with and improve upon ranges estimated by previous studies and can support future modeling and assessment efforts at Barry Arm.

Alaska↗
USGS1944

Chromite occurrences and a nickel prospect, Baranof Island, southeastern Alaska

This report presents the results of a brief geologic reconnaissance of some of the chromite-bearing sills between Red Bluff Bay and Silver Bay in central Baranof Island, southeastern Alaska (see figs. 1 and 2), and the results of a magnetic study of a chromite body in the ultrabasic rocks at Red Bluff Bay. Also included are the results of a brief examination of a nickel prospect near Sitka. The field work, upon which this report is largely based, was done by the authors in the early part of August 1943 as a part of a Geological Survey project to investigate some of the ultrabasic rocks of southeastern Alaska to determine the presence or absence in them of significant nickel-copper or chromium deposits. Previous studies of some of the chromite-bearing ultrabasic rocks of Baranof Island were made by Guild and Balsley during the summer of 1941.

Alaska↗
USGS1947

Preliminary report on the gypsum deposits near Iyoukeen Cove, Chicagof Island, southeastern Alaska

The only known gypsum deposits in Alaska are on northeastern Chichagof Island, southeastern Alaska, at Iyoukeen Cove (fig. 1). The area first developed and for a time worked by the Pacific Coast Gypsum Co. is approximately 1 mile upstream from the mouth of Gypsum Creek at an elevation of about 70 feet (fig. 2). The second deposit, known as the Gypsum-Camel property, is on tidewater 12 miles northeast of the mouth of Gypsum Creek (fig. 2). Iyoukeen Cove is about 35 air miles southwest of Juneau and is on both the mail-boat and the airline routes between Juneau and Sitka. The two deposits were examined by a Geological Survey party during the summer of 1946. Topographic and geologic maps were made of the vicinity of both deposits (figs. 2 and 3). Accessible underground workings at the Gypsum-Camel property also were mapped,

Alaska↗
USGS1948

Preliminary report on a lead-zinc occurrence at Berg Basin, Wrangell district, southeastern Alaska

A brief examinatin of lead-zinc occurrence at Berg Basin, Wrangell district, southeastern Alaska, was undertaken in 1947 as part of the U.S. Geological Survey's program of minerals investigations in Alaska. No lead-zinc ore body has yet been proved at Berg Basin, but because of recent interest in that area this preliminary report has been prepared for the purpose of making available immediately all data collected to date. A more complete report is in preparation.

Alaska↗
USGS1952

Pumice deposits in the Alaska Peninsula-Cook Inlet region

Three principal areas of pumice deposition have been found in the Alaska Peninsula-Cook Inlet region: Katmai National Monument, Augustine Island, and the Veniaminof-Aniakchak area. Vast quantities of pumice were deposited in Katmai National Monument resulting from the eruption of Mt. Katmai and related volcanic action in 1912. The principal deposits in the coastal areas of the Monument occur in the valley of the Katmai River and in the Amalik Bay-Kukak Bay area. Several areas of pumice deposition have been found on the south and west sides of Augustine Island, located 200 miles southwest of Anchorage. Mining was carried on by the Alaska Katmalite Corporation during the period 1946-1949, but no production has taken place since that time. Pumice deposits found in the Aniakchak-Veniaminof area have probably been derived from three principal sources: Aniakchak Crater, Mt. Veniaminof and Purple Crater. The limited data available indicate the deposits of chief interest occur in the valley of the Aniakchak River and in areas adjacent to Chignik Bay.

Alaska↗
USGS1952

Preliminary report on the Nelson and Radovan copper prospects, Nizina district, Alaska

Renewed copper exploration by Alaska Copper Mines, Incorporated, at the Nelson and Radovan prospects, Nizina district, Alaska, led the Geological Survey in 1951 to map in detail the Nelson fault block, and to re-examine the old workings. In addition, two new prospects were studied. The Nelson fault block is cut by many dominantly strike-slip faults of small displacement, and by bedding faults. Slickensided chalcocite shows post-mineral movement, and chalcocite veinlet in a filled solution cavity indicates that some of the chalcocite is secondary, perhaps very recent. Structural relations indicate two overthrust faults cut the block. The Radovan Greenstone prospect shows massive chalcocite, up to 3 feet wide, in a silicified, epidotized fault zone in the Nikolai greenstone. Ore indicated by surface exposures may amount to 450 tons of chalcocite. The Radovan Low-Contact prospect is on a continuation of the same fault approximately 3 miles southwest of the Greenstone prospect, and 150 feet above the contact of the Nikolai greenstone and the overlying Chitistone limestone. Limonite staining is widespread in bedding planes and small faults near the fault zone; mineralization in the fault zone consists of pyrite, chalcocite, bornite, malachite, realgar, orpiment and stibnite. The sulphides in the fault zone, plus the widespread silicification and epidotization indicate a strong zone of hydrothermal activity which merits extensive prospecting.

Open-File Report↗
USGS1952

Coal investigations in the Homer district, Kenai coal field, Alaska, in 1950 and 1951

This report presents the results of work done in the last three weeks of the 1950 field season and in all of the 1951 season, and supplements reports by Barnes (19149) and Cobb (1950, 1951). Barnes' report covers investigations of coal-bearing rocks of the Tertiary Kenai formation in a coastal belt between Bluff Point and the head of Kachemak Bay (pl. 2). Cobb's reports deal with similar rocks exposed along the coast between Bluff Point and the beach bluffs about 7 miles south of the village of Cohoe, and in the lower reaches of the Ninilchik River valley. The present report covers extensions of previous mapping in the valleys of Deep Creek and the Anchor River, and on high land between the area covered by Barnes' report and the Anchor River valley. The results of ground and aerial reconnaissance of most of the Homer district also are presented. The writer, assisted by F. J. Markewioz, carried on the field work which is the basis for this report, between August 13 mad September 6, 1950, and between May 10 and August 30, 1951. Field work included traverses along Deep Creek and the Anchor River, and between the southeast end of Tustumena Lake and the head of Kachemak Bay. It included also the detailed measurement and tracing of coal beds on the upland north and northwest of Homer, sampling of coal beds along the northwest shore of Kachemak Bay and the southeast shore of Cook Inlet, and both ground and aerial reconnaissance of the rest of the Homer district and adjoining areas. The writer is indebted to James W. Scott, Forester, U. S. Bureau of Land Management, Lomer, Alaska, who accompanied him on a traverse from Tustumena Lake to Kaohemak Bay and assisted at many other times during the 1950 and 1951 field seasons. Ralph Gaetano and Thomas Shelford of Homer were of great assistance in locating and reaching isolated outcrops of coal-bearing rooks. Daniel B. Krinsley, of the Alaska Terrain and Permafrost Section of the U. S. Geological Survey, has generously made available the results of many of his observations in remote parts of the Homer district which could not be visited by the writer.

Alaska↗
USGS1954

Geologic investigations of proposed power sites at Cooper, Grant, Ptarmigan and Crescent Lakes, Alaska

The Geological Survey, as part of its program of the classification of public lands with respect to mineral and water resources, is currently making a systematic study and evaluation of the potential water power sites in Alaska. This report describes the geologic conditions and their relation to possible plans for the development of water power at Cooper, Grant, Ptarmigan, and Crescent Lakes on the Kenai Peninsula near Seward, Alaska.

Alaska↗
USGS1955

Geochemical exploration for antimony in southeastern Alaska

Preliminary geochemical prospecting by the Geological Survey was carried out in 1952 in muskeg-covered ground at Caamano Point, Cleveland Peninsula, Alaska, in an effort to delimit areas of stibnite concentrations. It was conducted to aid, if possible, a prospecting project of the Defense Minerals Exploration. Samples were collected from soil and decomposed limestone-and-schist bedrock at depths ranging from 18 inches to 60 inches, by means of a pipe with an interior plunger. Initial sampling was followed by detailed sampling of the areas where the antimony content of the soils consistently averaged more than 300 ppm. These Areas of major soil concentrations were prospected by surface trenching and percussion drilling to depths of 20 feet which proved the existence of stibnite ore. Next a shaft and drifts made in the most favorable area proved disseminated stibnite ore to depths of 60 feet. This geochemical work of soil sampling to indicate hidden ore bodies in a typical Alaskan muskeg area is believed to be the first application in Alaska of such techniques in active ore exploration. The results show the economic feasibility of such exploration as a first step in extending the known boundaries of mineralized areas, and in directing initial exploration toward the most favorable areas of near-surface ore bodies. Data are presented to help establish values of soil content of antimony that may be considered as normal in this type of geologic terrain.

Alaska↗
USGS1963

Placer tin deposits in central Alaska

Placer tin, in the form of cassiterite (Sn02) and (or) tinstone (fragments including cassiterite and some vein or rock material), is known or reported in deposits that have been prospected or mined for placer gold in four areas adjacent to the Yukon River in central Alaska, 120 to 240 miles west of Fairbanks. These areas are: the Morelock Creek area, on the north side of the Yukon River about 30 miles upstream from Tanana; the Moran Dome area, about 16 miles north of the Yukon River and 25 miles northwest of Tanana; the Mason Creek area, on the north side of the Yukon River about 36 miles west of Tanana; and the Ruby-Long area, on the south side of the Yukon River near Ruby and about 40 miles east of Galena. The only extensive placer mining in these areas has been in the Ruby-Long area. Other placer deposits including some cassiterite are known in central Alaska but are not discussed in this report. Bedrock in these areas is predominantly schist of various types with some associated greenstone and other metamorphic rocks. Some granite is exposed in the Moran Dome and Ruby-Long areas and in areas close to Morelock and Mason Creeks. Barren, milky quartz veins and veinlets transecting the metamorphic rocks are common. No cassiterite was found in the bedrock, and no bedrock source of the tin has been reported. In the Moran Dome and Mason Creek areas, and in part of the Ruby-Long area, tourmaline is present in the rocks of the tin-bearing drainage basins, and apparently absent elsewhere in these areas. The placer deposits are in both valley floor and bench alluvium, which are predominantly relatively thin, rarely exceeding a thickness of 30 feet. Most of the alluvium deposits are not perennially frozen. In the Morelock Creek area tin-bearing deposits are 5 to 5? miles above the mouth of the creek, and meager evidence indicates that cassiterite and gold are present in Morelock Creek valley and some of the tributaries both upstream and downstream from these deposits. The concentrates recovered in samples average about 57 percent tin, and the gold averages about 922 fine. Prospecting indicates that the placer tin deposits are small and of relatively low grade, and that the greater part of the value of the deposits is the gold. In the Moran Dome area the known tin-bearing deposits are in the valley floor and bench gravels along upper Tozimoran Creek. Much of the alluvium is unfrozen, but the deeper portions of the bench gravels and the gravels some distance from the streams are in part frozen. Tin-bearing samples have been obtained from prospect pits and drill holes at a number of sites on Tozimoran Creek between its head and the confluence with Slate Creek. Gold recovered from some of these samples has a fineness of 835. The presence of cassiterite and gold on Ash Creek has been confirmed by sampling. Cassiterite and gold reportedly occur on upper Melozimoran Creek, and several other stream valleys in this area may be tin bearing. In the Mason Creek area cassiterite has been reported in the valley floor and bench alluvial deposits on Mason Creek, but its presence could not be confirmed in the brief field examinations of creek and dump-pile gravel that were made. The limited number of pits and cuts available precluded a valid sampling without additional drilling, pitting, or trenching. In the Ruby-Long area the valleys of Midnight, Birch, and Big Creeks are known to have appreciable concentrations of cassiterite in the gold-bearing placer deposits. The alluvial deposits in the valleys of Ruby, Glacier, Flint, Trail, Long, Fifth of July, Short, Flat, Greenstone, and Monument Creeks contain some cassiterite, but sufficient information could not be obtained to make an evaluation of these occurrences. Cassiterite concentrates, reportedly ranging from 52 to 70.24 percent tin, have been recovered in connection with gold mining operations on Midnight, Birch, and Big Creeks.

Open-File Report↗
USGS1964

Reconnaissance geochemistry of stream sediments from three areas near Juneau, Alaska

Results of a preliminary inquiry into background metal content of stream sediments near Juneau, Alaska, and whether this background is related to geologic terrane indicate that stream sediments derived chiefly from metamorphic rocks show significantly higher modal nickel, zinc, and arsenic than do sediments derived mainly from sedimentary or igneous rocks. Metal-content data that are closely related to areal geology will be required before systematic geochemical prospecting by stream-sediment sampling in southeast Alaska will be very effective.

Alaska↗
USGS1965

Geology of the Romanzof Mountains, Brooks Range, northeastern Alaska

This remote 700 square mile area in the Brooks Range is topographically rugged and geologically diverse; it contains a granitic pluton, low-grade metamorphic rocks, sedimentary rocks, and mafic igneous rocks, as well as glacial features. Rocks of sedimentary origin include from oldest to youngest: 1.Neruokpuk Formation Middle and Upper Devonian(?), more than 4000 feet thick, a variety of units which represent the greenschist facies, including quartzitic- and schistose-feldspathic graywacke; phyllite, argillite, and slate, as well as dark limestone, sandy limestone, and silicified carbonate rocks. The succession of units in parts of the area is uncertain. Correlations between these units and with others in the eastern Brooks Range are provisional. 2.Kekiktuk Conglomerate and Kayak(?) Shale (Upper Devonian(?) to Upper Mississippian), a single map unit, from absent(?) to 400+ feet thick, containing dark shale Kayak(?) in its uppermost part and quartzite, interbedded dark shale, and some pebble- to boulder-conglomerate in the locally absent lower part (Kekiktuk). The unit overlies the Neruokpuk with angular unconformity, which may reflect either a pre-Kayak(?) or pre-Kekiktuk hiatus or both. 3.Lisburne Group, almost entirely carbonate rocks, and relatively thin in this area, 600 to 800 feet thick. Alapah Limestone (Upper Mississippian), to 560 feet thick, includes gray sandy, crystalline, and cherty limestone; minor dark shale; and dark cherty carbonate rocks in the upper part. The lower contact is gradational with the Kayak(?). Wahoo(?) Limestone (Pennsylvanian(?) to Permian) conformably overlies the Alapah, is absent to 200+ feet thick, and is characterized by light-gray crinoidal limestones in its upper part. 4. Sadlerochit Formation, consisting of three intraconformable units: ferruginous sandstone member (Permian) of ironstained orthoquartzite and dark slate, 175 to 240 feet thick which unconformably overlies the Wahoo(?) and Alapah Limestones; shale member of dark shale, slate, and minor quartzite averaging 400 feet in thickness; and quartzite member (Lower(?) Triassic), 700 feet thick, mostly orthoquartzite with minor shale and conglomerate. The basal clastics were probably shed from the north. 5.Shublik Formation (Middle(?) and Upper Triassic), 600 to 700 feet thick, with the thin phosphatic sandstone member overlain by dark phosphatic limestones and limy shales of the limestone member. 6.Kingak Formation (Jurassic), more than 1000 feet thick. The siltstone member, resistant sandstone and siltstone 75 to 150 feet thick, is overlain by an undetermined thickness of black shale. The basal part contrasts sharply with the underlying Shublik, indicating possible disconformity. 7.Ignek(?) Formation (Cretaceous), represented in the foothills where lithic graywacke, shale, and coaly shale constitute the few exposures examined. 8.Glacial and glaciofluvial materials of five advances recognized on the basis of morphology and position, which are tentatively correlated with five glaciations 15 miles west of the area. 9. Recent alluvial and colluvial deposits including fans which appear to represent at least three stages of encroachment. The Ramanzof granite, exposed in the Okpilak batholith and Jago stock, is mostly light-gray quartz monzonite to granite, and contains essential quartz, perthitic microcline, albite-oligoclase, and partly chloritized biotite. Limited modal and chemical data are presented. Three textural facies are: 1) porphyritic (marginal), with abundant large microcline megacrysts; 2) variable (middle to marginal), which exhibits textural and mineralogical banding; and 3) coarse (inner to marginal), which is gneissoid to equigranular. Facies relationships appear to be mostly gradational but may be locally intrusive. Some schistose metasedimentary(?) rock occurs in the granite. Aplite dikes, inclusions, tourmaline veins and replacements, and chlorite and quartz veins are locally common, as well as quartz monzonite and mafic igneous dikes. Contacts with Neruokpuk Formation rocks are mostly abrupt, concordant to cross-cutting, and locally adjoin tactite and hornfels of the albite-epidote-hornfels and hornblende-hornfels facies. Contacts with Kekiktuk Conglomerate are apparently gradational through a schistoze zone. Both primary and secondary structural elements are present in the Romanzof in granite. Textural and mineralogical banding and, in general, feldspar foliation are considered to be primary in origin; biotite foliation, gneissic and schistose foliation, and schistose zones are considered secondary. Lead-alpha age of zircons appears to be Late Devonian, K-Ar age of biotite is Cretaceous, possibly indicating updating by later reheating. Field age relationships are inconclusive but suggest pre-Kayak(?) (Upper Devonian) granite emplacement. The pluton is interpreted to be essentially the product of melt crystallization, synorogenically emplaced by forceful injection with minor stoping, and may include marginally granitized rock. Mafic igneous rocks of altered basaltic composition (greenstones) include dikes in granitic and Neruokpuk Formation rocks, and volcanics(?). A late Paleozoic age is suggested for them. Structural grain strikes east-northeast; south-dipping elements are common. Structures include the major positive nature of the area (first order), relatively broad folds (second order) which contain small tight folds (third order). Related south-dipping cleavage, schistosity, and biotite foliation in granite in the northern part of the area are cut by prominent sets of transverse joints and faults. Other features are longitudinal normal and reverse faults, at least one large-scale overthrust fault, and sheared zones in granite with possible attendant retrograde metamorphism. Although Mesozoic and Tertiary deformational features are dominant in northern Alaska, the Romanzof area may have been part of a Late Devonian orogenic belt continuous with one in northern Canada. Three alternate trends of such a belt in northern Alaska are discussed, but evidence is inconclusive. The mineral potential of the area is largely unknown. Minor amounts of metallic sulfides and oxides are present in granite and Neruokpuk Formation rocks. Analyses of stream silt samples suggest the possibility of tin and beryllium potential. The Shublik Formation contains rock phosphate.

Alaska↗
USGS1970

Water-resources reconnaissance of the Kwiguk (Emmonak) area, Alaska

As part of an agreement between the Alaska Department of Natural Resources and the United States Geological Survey, Water Resources Division, a reconnaissance visit was made of the area in the vicinity of the village of Kwiguk (Emmonak), Alaska, during the period June 17-19, 1970, to evaluate the water resources and to suggest methods of developing additional sources of water.

Alaska↗
USGS1970

Petroleum possibilities of the Yukon-Koyukuk Province, Alaska

The recent discovery of major oil resources on Alaska's North Slope has rekindled interest in the petroleum possibilities of the Yukon-Koyukuk province, a vast tract of Cretaceous rocks stretching along the west coast of Alaska from the Brooks Range to the Yukon delta. Attention was first focused on this region in the early 1950's, after oil and gas were discovered in the Cretaceous of the North Slope by the U.S. Navy. The presence of similar Cretaceous strata in the Yukon-Koyukuk province and the possibility that some of the broad alluviated lowlands within the province might be underlain by Tertiary basins were pointed out by Gryc and others (1951) and Payne (1955). Between 1954 and 1961 large parts of the province were reconnoitered by oil company surface parties and a small amount of geophysical work was carried out in the Nulato-Kateel and Bethel areas. The explorational activity culminated in 1960-61 with the drilling of two deep tests, a 12,000-foot hole near Nulato on the Yukon River and a 15,000-foot hole at Napatuk Creek in the Yukon-Kuskokwim Coastal Lowland. Apparently neither test revealed oil shows or favorable reservoir rocks, as exploration and leasing activity in the province declined sharply thereafter. Since 1954 the U.S. Geological Survey has maintained a modest but continuing program of reconnaissance geologic mapping of the province and its borderlands. Nearly all parts of this vast area have been visited either by helicopter or river boat. Although information in many places is still sketchy, the broad outlines of the surface geology are now known. Subsurface data, however, are almost totally lacking. The mapping indicates that the petroleum possibilities over most of the province are limited because of complex structure and scarcity of promising reservoir rocks. Two areas where further exploration seems warranted are the Yukon-Kuskokwim Coastal Lowland and the western part of the Kobuk-Selawik Lowland.

Alaska↗
USGS1972

The status of mineral resource information on the major land withdrawals of the Alaska Native Claims Settlement Act of 1971

This report is an analysis of the adequacy of the present level of geologic knowledge for making mineral resource potential evaluations of 126 federal land withdrawals made under the Alaska Native Claims Settlement Act. The withdrawals considered are Native village and regional deficiency areas (Sec. 11.A.3, ANCSA), classification and national interest study areas for possible inclusion in the four national systems (Sec. 17.d.2) and classification and public interest areas (Sec. 17.d.1). Neither prior withdrawals, utility corridors, state selections, open lands, or Indian Reserves are included. Native village withdrawals are also not included because they were the subject of an earlier report (Cobb, E. H., and Trollman, W. T., 1971). The present report consists of two sections. The introduction explains the method of preparation and presents a summary table and some general remarks on the mineral potential of Alaska. The second part, the discussion of withdrawals, contains listings of the investigations that have been made and analyses of their adequacy in view of what needs to be known about the withdrawals.

Alaska↗