The Alaskan Mineral Resource Assessment Program: Guide to information contained in the folio of geologic and mineral-res

By W. W. Patton, Jr., E. J. Moll, and H. D. King

WILLIAM P. CLARK, Secretary

Dallas L. Peck, Director

Free on application to Distribution Branch, Text Products Section, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 Abstract Introduction •.••••••••••••••••••••••••.•••••••••••••••

Ge o 1o g i c s t u d i e s •••••••••••••••••••••••••••••..•••••••

Description of component maps and reports of the Me d f r a qua d r an g 1e f o 1 i o • . • • • • • • • • • • • • • • • • • • • • • • • • • • •

Results and statistical summary of analyses of

Mineral-resource assessment ••••••••••••••••••.••• Maps and histograms showing the distribution and

Multielement maps showing the distribution and

Purpose and scope ••••.••••..•••.••••••••••••.•••• Geography and access ••••••••••.•••••••••.•••••••• Mineral production and exploration •.•.••••••••••• Acknowledgments ••••••••••••••••••••••.•••••••••••

Previous investigations .•••••.••••••••••••••••••• Recent investigations •.••••••.••••••••••••.•••.••

Ge o 1ogy ••••••••••••••••••••••••••.••••••••••••••• Pre-Late Cretaceous rocks ••.••••••.•••••••••

Middle and Late Cretaceous rocks ••••••••••••

Late Cretaceous and early Tertiary rocks •••• Structure ••••••••.•••••••••.••••••••••••••••

Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks ••••••.••••..••••••••••••• Interpretation of Landsat imagery •••••••••••••••• Aeromagnetic interpretation ••••••.•••••.••••••.••

g e o c h em i c a 1 s amp 1e s • • • • • • • • . • • • • • • • • • • • • • • • • • • •

abundance of 12 different elements in various s amp 1 i n g me d i a ••••••••••.••••••••••••••.••••••

relative amounts of selected elements in four g eo c hem i c a 1 s amp 1 i n g me d i a • • • . • • • • • • • • • • . . • • • • •

in west-central Alaska....................

2. Map showing distribution of pre-middle Cretaceous geologic terranes in the Medfra quadrangle................................

quadrangle mineral-resource assessment..... Nixon Fork terrane •••.•.••••••••••••••• Innoko terrane •••••••..•••••••••••••••• Minchumina terrane •••••••••••••••••••••

TABLE

IV The Alaska Mineral Resource Assessment Program: Guide to Information Contained in the Folio of Geologic and Mineral-Resource Maps of the Medfra Quadrangle, Alaska

Mineral Production and Exploration

Geography and Access Previous Investigations

Figure 1.--Location of the Medfra quadrangle (shaded) in west-central Alaska.

Recent Investigations Figure 2.--Distribution of pre-middle Cretaceous geologic terranes in the Medfra quadrangle.

Figure 2.--Distribution of pre-middle Cretaceous geologic terranes in the Medfra quadrangle. Terrane boundaries are faults, dashed in areas of poor control.

supratidal, characterized by laminated silty limestone in Lower Ordovician beds, to shallow marine, distinguished by a complex array of shallow-water carbonate facies that include reefoid bodies in the Upper Ordovician and Middle Devonian beds. Dark platy limestone and shale containing mid-Silurian graptolites paleoenvironments prevailed between Late Ordovician and Late Silurian time.

The metamorphic complex, composed of greenschist-facies pelitic schist, calc schist, and metavolcanic rocks, unconformably underlies and locally is faulted against the platform carbonate rocks in the north-central and northeastern parts of the quadrangle. suggest that these metamorphic rocks are Precambrian and possibly earliest Paleozoic in age (Patton and Dutro, 1979; Silberman and others, 1979b).

About 500 m of Permian, Triassic, and Early Cretaceous (Valanginian to Aptian) quartz-carbonate terrigenous sedimentary rocks and spiculite beds are exposed beneath the middle and Late Cretaceous deposits of the Kuskokwim basin and locally rest unconformably on the metamorphic complex. relation of these terrigenous rocks to the platform carbonate rocks is obscured by faulting. However, the debris which composes them clearly was derived, in large part, from erosion of the platform carbonate rocks.

Terrane boundaries are faults, dashed in areas of poor control.

indicate that deeper water

Stratigraphic relations and K-Ar data

The Innoko terrane, which occupies the northwest corner of the quadrangle (fig. 2), appears to be faulted against the Nixon Fork terrane along a conspicuous topographic lineament that parallels the Susulatna River valley. The oldest stratigraphic unit is composed of radiolarian chert and subordinate limestone turbidites of Mississippian and Pennsylvanian age. This unit is succeeded by a unit of cherty tuff, crystal and lithic tuff, and volcanic breccia of Triassic and Early Jurassic(?) age which, in turn, is overlain by an earliest Cretaceous (Neocomian) unit of volcanic graywacke and conglomerate. These three units are thought to compose a tectonic package of island-arc and oceanic rocks which has been thrust-faulted across a metamorphic complex from the northwest (Patton and Moll, 1982). The metamorphic complex is exposed only at two isolated localities in creekbeds along the west margin of the Medfra quadrangle but is widely exposed in the adjoining Ophir quadrangle (Chapman and others, 1982). It is uncertain whether these metamorphic rocks are part of the same metamorphic complex that underlies the Nixon Fork terrane.

The Minchumina terrane is sparsely exposed in a few isolated groups of hills in the Tanana-Kuskokwim lowlands in the southeastern part of the quadrangle (fig. 2). It appears to be faulted against the Nixon Fork terrane in the hills bordering the lowlands on the northwest side of the North Fork of the Kuskokwim River. The East Fork Hills and the hills that border the lowlands on the northwest are composed chiefly of Ordovician to Devonian slightly schistose shaly limestone and chert, which are interpreted to be a deep-water facies of the early Paleozoic platform carbonate rocks of the Nixon Fork terrane. At the top of this sequence, the deep-water beds grade upward into shallow-water limestone and dolomite, an association suggesting a seaward progradation of the carbonate platform during Devonian time. The Telida Mountains are composed of an assemblage of quartzite, quartz grit, quartz-feldspar grit, _and argillite which tentatively is assigned a Precambrian and early Paleozoic age on the basis of correlation with similar assemblages to the northeast in the Kantishna River and Livengood quadrangles (Chapman and others, 1971; Chapman and others, 1975). The source area and depositional environment of these coarse clastic rocks are uncertain. The Slow Fork Hills, in the southeast corner of the quadrangle, consist of sheared grit, quartzite, quartz-mica schist, and phyllite which are interpreted to be a metamorphic equivalent of the quartzite and grit beds of the Telida Mountains.

Middle and Late Cretaceous Rocks

The middle and Late Cretaceous rocks of the Kuskokwim basin form a broad southwest-plunging syncline which unconformably overlies the Innoko and Nixon Fork terranes in the southwestern and west-central parts of the quadrangle (fig. 2). Contacts with the underlying rocks are complicated in many places by high-angle faults. The stratigraphic section comprising the basin, which has an aggregate thickness of 3,000 to 4,000 m, is composed of shallow-marine and fluvial sandstone, shale, and conglomerate. The largely marine lower part of the section locally contains early Late Cretaceous (Cenomanian) fossils, but the base may be as old as late Early Cretaceous (Albian). The largely nonmarine upper part of the section cannot be dated more closely than Late Cretaceous.

Late Cretaceous and Early Tertiary Rocks

Calc-alkalic volcanic, hypabyssal, and plutonic rocks of Late Cretaceous and early Tertiary (71-59 m.y.) age overlie and intrude the pre-middle Cretaceous rocks of the Nixon Fork, Innoko, and Minchumina terranes and the middle and Late Cretaceous sedimentary rocks of the Kuskokwim basin. These igneous rocks consist of: (1) A large volcanic field composed of more than 500 m of felsic flows, domes, and tuffs in the Sischu Mountains in the northeastern part of the quadrangle; (2) a large volcanic field, more than 1,000 m thick, of chiefly intermediate flows in the Nowitna River area in the northwestern part of the quadrangle; (3) felsic and intermediate sills, dikes, flows, and plugs in the upper Nixon Fork-Sulukna River area in the central part of the quadrangle; (4) granite and monzonite stocks scattered in a broad east-west-trending belt across the center of the quadrangle; and (5) several circular volcanic-plutonic complexes of intermediate flows and stocks in the southwestern part of the quadrangle.

The bedrock in the Medfra quadrangle has a general northeast-trending regional grain except in the vicinity of the Mystery Mountains in the central part of the quadrangle, where it is locally deflected to the northwest. All the pre-latest Cretaceous (that is, older than 71 m.y.) bedrock units are strongly deformed and locally display isoclinal folding and overturned beds. The latest Cretaceous and early Tertiary volcanic units are much less deformed and are characterized by gentle dips and broad open folds.

The Iditarod-Nixon Fork fault can be traced from the Medfra quadrangle southwesterly across west-central and southwestern Alaska for more than 400 km (Beikman, 1980). It is regarded as a probable strike-slip fault with possibly as much as 110 km of right-lateral displacement (Grantz, 1966). In the southwestern part of the Medfra quadrangle, the fault marks the boundary between the Kuskokwim basin and the platform carbonate rocks of the Nixon Fork terrane. The fault appears to die out along the valley of the upper Nixon Fork, and at this point major strike-slip movement may have been taken up by parallel faults that continue to the northeast along the valley of the North Fork of the Kuskokwim River.

The report by Schwab and others (1981) consists of a 1:250,000-scale map and tables providing information on the known mineral occurrences of the Medfra quadrangle. The term "mineral occurrence" is used here in the broad sense to include lode and placer mines and prospects as well as unclaimed occurrences, regardless of economic significance. Their map shows the locations of mines, prospects, mineralized-bedrock samples, and geochemical anomalies in bedrock samples; the accompanying tables describe the mines and prospects, as well as selected geochemical data for the bedrock samples.

Table 1 of Schwab and others (1981) lists 35 previously reported mines and prospects, all but four of which are gold placer or lode deposits. Among these mines and prospects, significant gold production has been recorded only from the Nixon Fork district in the south-central part of the quadrangle. A gold placer on Colorado Creek along the west margin of the quadrangle is being mined at present, but production figures are not available.

Tables 2 and 3 of Schwab and others (1981) present descriptive and geochemical data for 92 separate occurrences of sulfides and other indicators of mineralization which were observed during geologic mapping and geochemical sampling of the bedrock units in the quadrangle between 1975 and 1979. The most abundant minerals found were tourmaline, pyrite, and iron-oxide minerals. Tourmaline is abundant in the Mystery and Telida Mountains, where it is associated with felsic subvolcanic and intrusive rocks. A small deposit of magnetite was discovered in a skarn zone near White Mountain Creek (map nos. 60-62), and galena-bearing quartz veins were found at the head of the Susulatna River (map no. 50). carbonate rocks on upper Soda Creek yielded a strong zinc geochemical anomaly (map no. 111). Table 4 of Schwab and others (1981) lists and describes 49 samples of bedrock which contain anomalous geochemical values but have no visible mineralization. established partly on the basis of statistical analysis of background geochemical data obtained for each bedrock map unit and partly from the data of Parker (1967, p. D13-D14) on the abundances of elements in the Earth's crust. above-background amounts of Be, Sn, Y, Pb, Hg, U, Zn, and Mo (map Nos. 168-173) in strongly radioactive uranium- and thorium-rich rhyolitic rocks in the Sischu Creek area in the northeast corner of the quadrangle (Miller and others, 1980).

The report by Moll and others (1981) discusses the results of chemical analyses and K-Ar age determinations for igneous and metamorphic rocks of the Medfra quadrangle. plutonic rocks in the quadrangle are latest Cretaceous and earliest Tertiary in age. Small bodies of gabbro and diabase in the eastern and northwestern parts of the quadrangle are of uncertain but probable older age. The metamorphic rocks, which are widely exposed in the Nixon Fork terrane in the north-central part of the quadrangle and in the Slow Fork Hills in the Minchumina terrane, are of Precambrian and early Paleozoic age.

The latest Cretaceous and earliest Tertiary igneous-rock suite consists of volcanic, hypabyssal, and plutonic rocks ranging in composition from mafic to felsic. They are divided into six map units: (l) Chiefly andesite lava flows of the Nowitna River area; (2) intermediate southwestern part of the quadrangle; (3) granite stocks; (4) intermediate sills, dikes, flows, and plugs of the Nixon Fork-upper Sulukna River area; and (6) felsic flows and domes of the Sischu Mountains. The chemical data show that the entire igneous-rock suite is calc-alkalic and characterized by high K__20 contents. K is 2 to 4 weight percent at S8 weight percenl: Si0 about 4 to 6 weight percent at 72 to 75 weight percent Si0

• Analyzed samples contain from 53 to 75 weight

percent Si0 trachyandesite rhyolite. A total of 30 K-Ar ages for these rocks give ages ranging from 59 to 71 m.y. Concordant mineralpair ages from several samples indicate that this volcanoplutonic

and are classified as basaltic andesite, Anomalous values were arbitrarily

Of particular interest are the

monzonite stocks; (5) felsic and

(high-K Most of the volcanic and

andesite), A gossan in

dacite, igneous episode is well documented by the K-Ar data. The overlapping ages and calc-alkaline chemistry of the plutonic, hypabyssal, and volcanic rocks suggest that the hypabyssal and plutonic rocks represent subsurface magmas related to the same magmatic episode that produced the volcanic rocks.

bodies that occur in the eastern and northwestern parts of the quadrangle. indicates a possible age range of from Devonian to Cretaceous, and four K-Ar determinations give ages ranging from 85 to 267 m.y. Ages of 267 and 176 m.y. were obtained on a low-Ti0 on an olivine tholeiitic gabtiro, and 85 m.y. on a calc-alkalic gabbro. This range in ages may be due to partial resetting by postcrystallization thermal events or may represent several ages of mafic intrusive activity.

including pelitic schist, calc schist, and felsic metavolcanic rocks, crop out in a broad area of the Nixon Fork terrane in the north-central part of the quadrangle. Stratigraphic evidence suggests that they are pre-Ordovician in age (Patton and Dutro, 1979). Four K-Ar ages on micas in these rocks in the Medfra quadrangle range from 274 to 514 m.y. To the north, in adjoining parts of the Ruby quadrangle, nine additional K-Ar ages on micas and amphiboles yielded ages ranging from 254 to 921 m.y. (Silberman and others, 1979b). The fact that several of these ages are older than 500 m.y. seems to support the pre-Ordovician age suggested by stratigraphic evidence.

metamorphic assemblage of sheared grit, quartzite, and quartz-mica schist composes the Slow Fork Hills in the southeastern part of the quadrangle. assemblage is interpreted to be the metamorphic equivalent of a quartzite, grit, and argillite unit in the Telida Mountains and on the basis of this correlation has been assigned a Precambrian or early Paleozoic age. However, three K-Ar ages obtained from this assemblage yielded ambiguous results. Muscovite from two samples of metagrit gave ages of 108 and 176 m.y., and amphibole from metagabbro intruding metagrit and quartzite gave an age of 421 m.y.

the 1:250,000-scale generalized geologic maps of the Medfra quadrangle on which are superimposed linear, circular, and arcuate features interpreted from Landsat imagery. Interpretations of the Landsat data were made on: (1) A black-and-white Landsat mosaic of Alaska, (2) false-color images, and (3) computerenhanced simulated natural-color images. All these and images were analyzed for linear, circular, and arcuate features as a possible aid in the mineral assessment of the quadrangle. observed from the imagery, no marked spatial and relations between the features and known mineral deposits are apparent. circular, and arcuate features do show good spatial correlation with known geologic features. For exam-Few data are available for the small gabbro

In the Minchumina terrane, a greenschist-facies

The report by Le Compte (1981) consists of two

Although many features were

However, numerous linear, Stratigraphic evidence

tholeiitic gabbro, 98 m.y.

This ple, a conspicuous lineament in the south-central part of the quadrangle corresponds closely to a segment of the Nixon Fork fault. Other lineaments in the central and northeastern parts of the quadrangle also mark important faults. encircle the volcanoplutonic complexes at Page Mountain, Cloudy Mountain, and near bench mark Alone, and they rim the granite cores and bordering hornfels zones in the Sunshine, Cripple Creek, and Telida Mountains and at Von Frank Mountain. These concentric features may reflect circular fracture patterns resulting from doming during magma emplacement or from cauldron subsidence during magma withdrawal during Late Cretaceous and early Tertiary time. Similar circular and arcuate features were observed in the Mystery Mountains and in a small mountainous area at the head of the Nowitna River. Although no plutonic rocks are exposed in either of these two areas, the occurrence of these features and of widespread sedimentary hornfels suggests that granitic plutons may be present at shallow depths.

rangle was flown in 1978 and subsequently compiled (U.S. Geological Survey, 1979) at a scale of 1:250,000. The survey was flown at an altitude of 300 m above the ground along northwest-southeast flightlines spaced approximately 1.6 km apart. In 1979, 10 separate ground magnetic traverses were carried out, using a hand-held magnetometer and susceptibility meter. selected to provide additional details on specific aeromagnetic anomalies and to determine the magnetic characteristics of the various geologic-map units.

is divided into three broad terranes, each with distinctive first-order magnetic characteristics: Terrane I (eastern and central parts of the quadrangle)

is characterized by broad anomalies of less than 50y relief which are interpreted to reflect a magnetic metamorphic basement complex of probable Precambrian age beneath a cover of weakly or nonmagnetic late Precambrian(?) and early Paleozoic sedimentary rocks. Superimposed on this pattern of broad deep-seated anomalies are several clusters of smaller steep-gradient anomalies which have their source in surface and near-surface volcanic and intrusive bodies, chiefly of Late Cretaceous and early Tertiary age but also including some older gabbro and metavolcanic bodies. Terrane II (southwestern and west-central parts of the quadrangle) is characterized by a background of shallow-gradient low-intensity anomalies on which are superimposed scattered isolated steep-gradient anomalies. This area approximately corresponds to the outline of the Kuskokwim basin. The field intensity is 50 to 150y lower than in terrane I and decreases to the southwest; this decrease may reflect the increasing thickness of the nonmagnetic Cretaceous sedimentary rock sequence in that direction. All the steep-gradient anomalies appear Arcuate and circular features

An aeromagnetic survey of the Medfra quad-

The ground traverses were

For descriptive purposes, the aeromagnetic map to be caused by surface and near-surface Late Cretaceous intermediate intrusive and volcanic rocks, or by hornfels zones in the Cretaceous sedimentary rock units. Terrane III (northwestern and north-central parts of the quadrangle) is characterized by rugged steep-gradient anomalies with a strong northeast-trending grain in the northwestern part of the quadrangle and a northwest-trending grain in the north-central part of the quadrangle. reflects a mixed geologic assemblage of gently deformed Late Cretaceous and early Tertiary volcanic rocks, highly deformed Mississippian to Cretaceous volcaniclastic rocks, chert, and mafic igneous rocks, and Precambrian or early Paleozoic metamorphic rocks.

Stream sediment, heavy-mineral concentrates, and reconnaissance in the Medfra quadrangle were sampled to provide interpretation of the mineral-resource potential of the quadrangle. results for 513 minus-80-mesh (smaller than 0.177 mm) stream-sediment samples, 370 nonmagnetic-heavy-mineral concentrates (C3 fraction), 422 moderately magnetic heavy-mineral concentrates (C2 fraction), and 355 ash-of-aquatic-bryophytes (moss) samples. In all, 517 sites were sampled in 1978 and 1979.

Most samples were taken from channels of active streams with averaging about 9 km • Samples were taken from first- and second-order streams wherever possible. Larger, or third-order, streams were sampled when landing sites along first- or second-order tributary streams were inaccessible. quadrangle, particularly along valley bottoms, is densely covered by vegetation, and so accessibility of helicopter landing sites commonly determined the points along the streams at which samples wer;p taken. mainly in the southern and southeastern parts of the quadrangle, were not sampled because of the thick cover of Quaternary unconsolidated deposits.

Stream-sediment and concentrate samples were analyzed spectrographic method (Grimes and Marranzino, 1968) for 31 elements, including Fe, Mg, Ca, Ti, Mn, Ag, As, Au, B, Ba, Be, Bi, Cd, Co, Cr, Cu, La, Mo, Nb, Ni, Pb, Sb, Sc, Sn, Sr, V, W, Y, Zn, Zr, and Th. Moss samples were analyzed for these same elements, except Ca, Sc, and Th, and were analyzed for Na, Ga, Ge, In, and Tl by a semiquantitative emission-spectrographic method for plant materials (Mosier, 1972; modified by Curry and others, 1975). Stream-sediment samples were also analyzed for Au, Hg, and Zn, using the atomic-absorption methods of Ward and others (1969). The report by King and others (1980) consists of a text describing sampling, sample preparation, and analytical methods; tables of statistical summaries; tables of analytical data; and a map showing sample-Results and Statistical Summary of Analyses of Geochemical Samples

Lowland areas, approximately 4,000 km ,

Geochemical data include analytical early

This pattern of anomalies

upstream catchment areas Tertiary mafic

A large part of the

emissionsite locations. Further information on the distribution and abundance of key elements in the various sample media is given in the reports by King and Tripp (19S3) and King and others (19S3a, b, c, d, e).

known mineral deposits, outlines areas designated as favorable for the occurrence of undiscovered mineral deposits, and discusses the mineral-fuels potential of the quadrangle. occurrence map and tables found in the report by Schwab and others (19S1), a table summarizing criteria used in the selection of areas favorable for the occurrence of undiscovered mineral deposits, and a table listing the threshold geochemical values above which an element is considered anomalous in each of the sampling media.

quadrangle are gold-copper skarn deposits and gold placers within the Nixon Fork district in the central part of the quadrangle, and gold placer deposits in the Innoko district along the west edge of the quadrangle. At the time of the investigation, active mining in the quadrangle was limited to a single gold placer deposit on Colorado Creek in the Innoko district.

occurrence of undiscovered mineral deposits are delineated on the map. Criteria used in their selection include: alteration; (2) known mineral occurrences; (3) geochemical anomalies in bedrock, stream-sediment, heavy-mineral-concentrate, and moss samples; (4) occurrence of ore concentrates; and (5) aeromagnetic data suggesting possible mineralization in the subsurface or in unexposed areas.

generally to conform to the distribution of favorable host-rock units or hornfels zones. Specific mineraldeposit types are identified or suggested for each area. These deposit types include: (1) Berylliumfluorite-uranium vein deposits and precious-metal deposits in Late Cretaceous and early Tertiary felsic volcanic fields of the Sischu Mountains; (2) skarn deposits and carbonate-hosted sulfide deposits in early Paleozoic carbonate rocks of the Nixon Fork terrane; (3) porphyry tin deposits in felsic volcanic rocks and sedimentary hornfels in the Mystery Mountains; (4) precious-metal and skarn deposits in the granite-cored Sunshine Mountains; (5) lead-silver, tin-silver, or leadzinc-silver vein deposits in sedimentary hornfels in a small group of unnamed hills at the head of the Susulatna River; (6) precious-metal deposits in rhyolite domes and andesite flows within a large Late Cretaceous and early Tertiary volcanic field in the northwestern part of the quadrangle; (7) precious- or base-metal deposits in a belt of sedimentary hornfels and Late Cretaceous and early Tertiary volcanic and plutonic rocks that extends from Cloudy Mountain to the Sunshine Mountains in the southwestern part of the The report by Patton and Moll (19S3) describes

The report includes the mineral-

The only mines and prospects in the Medfra

A total of 10 areas considered favorable for the

(1) Favorable rock types, structures, and

Boundaries of the favorable areas are drawn

s

quadrangle; and (S) tin lode deposits within granitic rocks and associated sedimentary hornfels in the Telida Mountains.

are considered to be low because of the thermal history of the pre-Tertiary rocks. Although the lower Paleozoic platform carbonate rocks appear to have favorable source-bed characteristics, their thermal history, as revealed by the color-alteration index of conodonts (Epstein and others, 1977), suggests that hydrocarbons, if present, would be limited to dry gas. The hydrocarbon potential of the Cretaceous rocks of the Kuskokwim basin also appears to be unfavorable, owing to the widespread presence of Late Cretaceous and early Tertiary volcanic and plutonic rocks.

d, e) summarize the results of a geochemical survey carried out in 197S and 1979. distribution and abundance of Au, Ag, Cu, Pb, Zn, Mo, Sn, W, As, Bi, Sb, and Hg in nonmagnetic and moderately magnetic heavy-mineral concentrates, minus-SO-mesh stream sediment, and ash-of-aquaticbryophytes samples.

The report by King and Tripp (19S3) consists of four maps and histograms showing the distribution and relative amounts of Ag, As, Au, Bi, Cd, Cu, Hg, Mo, Pb, Sb, Sn, W, and Zn in four sampling media: (1) Nonmagnetic-heavy-mineral concentrates, (2) moderately magnetic heavy-mineral concentrates, (3) minus-SO-mesh stream sediment, and (4) ash-of-aquaticbryophytes samples. Several geochemically anomalous areas are indicated by the results of the survey and displayed on the maps, and 16 of the more conspicuous areas are described in the text. Eight of these areas, including anomalies related to the Nixon Fork area and the Stone mine, are in the belt of early Paleozoic rocks quadrangle. Other anomalous areas are in the Telida, Sischu, Mystery, and Sunshine Mountains, an area south of the Sunshine Mountains, the Ivy Creek and Cloudy Mountain area, unnamed mountains north of Page Mountain and southeast of the Cripple Creek Mountains, and an area about 16 to 32 km northeast of the Cripple Creek Mountains.

Table 1 of King and Tripp (19S3) lists threshold anomalous values of Ag, As, Au, Bi, Cd, Cu, Hg, Mo, Pb, Sb, Sn, W, and Zn in four separate sample media: The minus-SO-mesh fraction of stream sediment, moss, the moderately magnetic heavy-mineral fraction of The petroleum possibilities of the quadrangle

The five reports by King and others (19S3a, b, c,

that extends northeasterly across the pan-concentrated stream sediment, and the nonmagnetic-heavy-mineral fraction of pan-concentrated stream sediment. Table 2 of King and Tripp lists anomalous concentrations of these elements in bedrock, stream-sediment, moss, and pan-concentrate samples from areas designated as permissive for certain types of deposits.

Alaska Division of Geological and Geophysical Surveys, 1982, Mining claim location maps, Medfra quadrangle, scale 1:250,000, 2 sheets. Anderson, L. A., Reed, B. L., and Johnson, G. R., 1970, Geologic interpretation of aeromagnetic map of the Nixon Fork District, Alaska, in Geological Survey research, 1970: U.S. Geological Survey Professional Paper 700- D, p. D129-D133. Beikman, H. M., 1980, Geologic map of Alaska: U.S.

Geological Survey special 1:2,500,000, 2 sheets. Brown, J. S., 1926, The Nixon Fork country, in Mineral resources of Alaska: Report on progress of investigations in 1924: U.S. Geological Survey Bulletin 783, p. 97-144. Bundtzen, T. K., Eakins, G. R., and Conwell, C. N., 1982, Review of Alaska's mineral resources: Alaska Department of Commerce and Economic Development, 52 p. Chapman, R. M., Patton, W. w., Jr., and Moll, E. J., 1982, Preliminary summary of the geology in eastern part of Ophir quadrangle, in Coonrad, W. L., ed., The United States Geological Survey in Alaska: Accomplishments during 1980: U.S. Geological Survey Circular 844, p. 70-73. Chapman, R. M., Weber, F. R., and Taber, Bond, 1971, Preliminary geologic map of the Livengood quadrangle, Alaska: open-file report, scale 1:250,000, 2 sheets. Chapman, R. M., Yeend, W. E., and Patton, W. w., Jr., 1975, Preliminary reconnaissance map of the western half of the Kantishna River quadrangle, Alaska: U.S. Geological Survey Open-File Map 75-351, scale 1:250,000. Curry, K. J., Cooley, E. F., and Dietrich, J. A., 1975, An automatic filter positioner device for emission spectroscopy: Applied Spectroscopy, v. 29, no. 3, p. 274-275. Dutro, J. T., Jr., and Patton, W. W., Jr., 1981, Lower Paleozoic platform-carbonate sequence in the Medfra quadrangle, west-central Alaska, in Albert, N. R. D., and Hudson, Travis, eds., The United States Geological Survey in Alaska: Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B42-B44. Eakin, H. M., 1916, Exploration in the Cosna-Nowitna region, in Mineral resources of Alaska: Report on progress of investigations in 1915: U.S. Geological Survey Bulletin 642, p. 211-221. --1918, The Cosna-Nowitna region, Alaska: U.S.

Geological Survey Bulletin 66 7, 54 p. Eberlein, G. D., Chapman, R. M., Foster, H. L., and Gassaway, J. S., 1977, Map and tables describing known metalliferous and selected nonmetalliferous mineral deposits in central a residual

map, scale Alaska: Report 77-168-D, scale 1:1,000,000. Epstein, A. G., Epstein, J. B., and Harris, L. D., 1977, Conodont color alteration-an index to organic metamorphism: Professional Paper 995, 27 p. Fernald, A. T., 1960, Geomorphology of the upper Kuskokwim region, Alaska: Survey Bulletin 1071-G, p. 191-279. Grantz, Arthur, 1966, Strike-slip faults in Alaska: u.s.

Geological Survey open-file report, 82 p. Grimes, D. J., and Marranzino, A. P., 1968, Directcurrent arc and alternating-current spark emission spectrographic field methods for the semiquantitative materials: U.S. Geological Survey Circular 591,

Herreid, G., 1966, Geology and geochemistry of the Nixon Fork area, Medfra quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 22, 34 p. Jasper, M. W., 1961, Report on the Mespelt Mine of Strandberg Mines, Inc., Nixon Fork District, Medfra Department of Natural Resources Division of Mines and Minerals Report PE 65-1, 9 p. King, H. D., Cooley, E. F., Gruzensky, A. L., and Spiesman, D. L., Jr., 1983a, Distribution and abundance of gold and silver in nonmagnetic and moderately concentrate sediment samples and silver in ash of aquatic-bryophyte Alaska: Report 80-811-H, 3 sheets. King, H. D., Cooley, E. F., and Spiesman, D. L., Jr., 1983b, Distribution and abundance of arsenic and bismuth in nonmagnetic and moderately magnetic heavy-mineral-concentrate samples and arsenic in minus-80-mesh stream-sediment and ash of aquatic-bryophyte samples, Medfra quadrangle, Alaska: Open-File Report 80-8ll-K, 3 sheets. King, H. D., O'Leary, R. M., Risoli, D. A., and Galland, D. w., 1983c, Distribution and abundance of antimony and mercury in minus-80-mesh stream-sediment and antimony in nonmagnetic and moderately concentrate Alaska: Report 80-811-L, 2 sheets. King, H. D., Risoli, D. A., Cooley, E. F., O'Leary, R.

M., Speckman, W. A., Spiesman, D. L., Jr. and Galland, D. W., 1980, Final results and statistical summary of analyses of geochemical samples from the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80- 811-F, 134 p. King, H. D., Risoli, D. A., and Tripp, R. B., 1983d, Distribution and abundance of molybdenum, tin, and tungsten in nonmagnetic and moderately magnetic heavy-mineral-concentrate samples and tin in minus-80-mesh stream-sediment and ash of aquatic-bryophyte samples, Medfra quadrangle, Alaska: Open-File Report 80-811-J, 4 sheets. U.S. Geological Survey Open-File

samples, U.S. Geological Survey Open-File

U.S. Geological Survey Open-File analysis

U.S. Geologic~ Survey Alaska:

Medfra quadrangle, U.S. Geological

stream-King, H. D., and Tripp, R. B., 1983, Multi-element

King, H. D., Tripp, R. B., O'Leary, R. M., and Cooley,

Le Compte, J. R., 1981, Maps showing interpretation

Martin, G. c., 1922, Gold lodes in the upper

Mertie, J. B., Jr., 1936, Mineral deposits of the Ruby-

Mertie, J. B., Jr., and Harrington, G. L., 1916, Mineral

-- 1924, The Ruby-Kuskokwim region, Alaska: U.S.

Miller, T. P., Moll, E. J., and Patton, W. W., Jr., 1980,

Moll, E. J., Silberman, M. L., and Patton, W. W., Jr.,

Mosier, E. L., 1972, A method for semiquantitative

biogeochemical and environmental studies:

Parker, R. L., 1967, Composition of the Earth's crust,

Patton, w. W., Jr., 1976, Newly discovered Upper

1977, Pre-Ordovician unconformity in central

-- 1978, Juxtaposed continental and oceanic-island maps showing the distribution and relative amounts geochemical quadrangle, Alaska: Open-File Report 80-811-M, 4 sheets.

E. F., 1983e, Distribution and abundance of copper, lead, and zinc in nonmagnetic and moderately concentrate, minus-80-mesh stream-sediment, and ash of aquatic-bryophyte samples, Medfra quadrangle, Alaska: Open-File Report 80-8ll-I, 6 sheets.

of Landsat imagery of the Medfra quadrangle, Alaska: Report 80-811-D, 2 sheets.

Kuskokwim region, in Mineral resources of Alaska: Report on progress of investigations in 1920: U.S. Geological Survey Bulletin 722, p. 149-161.

Kuskokwim region, Alaska: Survey Bulletin 864-C, p. 115-245.

resources of the Ruby-Kuskokwim region, in Mineral resources of Alaska: Report on progress of investigations in 1915: Survey Bulletin 642, p. 223-266.

Geological Survey Bulletin 754, 129 p.

Uranium- and thorium-rich volcanic rocks of the Sischu Creek area, Medfra quadrangle, Alaska: Report 80-803, 9 p.

1981, Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks of the Medfra quadrangle, Alaska: Open-File Report 80-811-C, 2 sheets.

spectrographic analysis of plant ash for use in

Applied Spectroscopy, v. 26, no. 6, p. 636-641.

chap. D of Fleischer, Michael, ed., Data of geochemistry (6th ed.): U.S. Geological Survey Professional Paper 440-D, p. D1-D19.

Triassic and Lower Cretaceous strata in the northern Kuskokwim Mountains, in Cobb, E. H., ed., The United States Geological Survey in Alaska: Accomplishments during 1975: U.S. Geological Survey Circular 733, p. 42-43.

Alaska, in Blean, K. M., ed., The United States Geological Survey in Alaska: Accomplishments during 1976: U.S. Geological Survey Circular 751-B, p. B39.

arc terranes in the Medfra quadrangle, west-central Alaska, in Johnson, K. M., ed., The United States Geological Survey in Alaska: of selected elements in four sampling media,

U.S. Geological Survey Open File

U.S. Geological Survey Open-File Medfra

U.S. Geological Patton, w. W., Jr., Cady, J. W., and Moll, E. J., 1982,

Patton, w. w., Jr., and Dutro, J. T., Jr., 1979, Age of

Patton, W. W., Jr., Dutro, J. T., Jr., and Chapman, R.

Patton, W. W., Jr., and Moll, E. J., 1982, Structural

Patton, W. W., Jr., and Moll, E. J., 1983, Mineral-

Patton, W. w., Jr., Moll, E. J., Dutro, J. T., Jr.,

Plumley, P. W., Coe, R. S., Patton, W. W., Jr., and

Reed, B. L., and Miller, R. L., 1971, Orientation geochemical soil survey at the Nixon Fork

Geological Survey Bulletin 1312-K, p. K1-K21. Schwab, C. E., Patton, W. W., Jr., and Moll, E. J., 1981, Mineral occurrence map of the Medfra quadrangle, Alaska: Open-File Report 80-811-B, 2 sheets. Silberman, M. L., Moll, E. J., Chapman, R. M., Patton,

rocks from the Ruby, Medfra, and adjacent quadrangles, west-central Alaska, in Johnson,

Survey Circular 804-B, p. B63-B66. Silberman, M. L., Moll, E. J., Patton, W. W., Jr., Chapman, R. M., and Connor, C. L., 1979b, Precambrian age of metamorphic rocks from the quadrangles-preliminary radiometric age data, in Johnson, K. M., and Williams, J. R., eds:;- The United States Geological Survey in Alaska: Accomplishments Accomplishments during 1977: U.S. Geological Survey Circular 772-B, p. B38-B39.

Aeromagnetic interpretation of the Medfra quadrangle, Alaska: Open-File Report 80-811-E, 14 p.

the metamorphic complex in the northern Kuskokwim Mountains, west-central Alaska, in Johnson, K. M., and Williams, J. R., eds., The United States Geological Survey in Alaska: Accomplishments during 1978: U.S. Geological Survey Circular 804-B, p. B61-B63.

M., 1977, Late Paleozoic and Mesozoic stratigraphy of the Nixon Fork area, Medfra quadrangle, Alaska, in Blean, K. M., ed., The United States Geological Survey in Alaska: Accomplishments during 1976: U.S. Geological Survey Circular 751-B, p. B38-B40.

and stratigraphic section along a transect between the Alaska Range and Norton Sound, in Coonrad, W. L., ed., The United States Geological Survey in Alaska: Accomplishments during 1980: U.S. Geological Survey Circular 844, p. 76-78.

resource assessment of the Medfra quadrangle, Alaska: Report 80-811-G, 3 sheets.

Silberman, M. L., and Chapman, R. M., 1980, Preliminary geologic map of Medfra quadrangle, Alaska: Report 80-811-A, scale 1:250,000.

Moll, E. J., 1981, Paleomagnetic study of the Nixon Fork terrane, west-central Alaska abs. : Geological Society of America Abstracts with Programs, v. 13, no. 7, p. 530.

Mines, Medfra quadrangle, Alaska:

W. W., Jr., and Connor, C. L., 1979a, Potassium-argon age of granitic and volcanic

K. M., and Williams, J. R., eds., The United

Accomplishments during 1978: U.S. Geological

Ruby U.S. Geological Survey Open-File

U.S. Geological Survey Open-File

province, Survey in Alaska:

Medfra and evidence U.S.

Ruby from during 1978: U.S. Geological Survey Circular 804-B, p. B66-B67. Throckmorton, M. L., and Patton, W. W., Jr., 1978, Contact-metasomatic magnetite deposit, Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-26, 13 p. U.S. Geological Survey, 1979:~ Aeromagnetic map of the Medfra 1 degree by 3 degree quadrangle, Alaska: Open-File Report 79-380, scale 1:250,000. Wahrhaftig, Clyde, 1965, Physiographic divisions of Alaska: U.S. Geological Survey Professional Paper 482, 52 p. Ward, F. N., Nakagawa, H. M., Harms, T. F., and VanSickle, G. H., 1969, Atomic-absorption methods of analysis useful in geochemical exploration: U.S. Geological Survey Bulletin 1289, 45 p. White, M. G., and Stevens, J. M., 1953, Reconnaissance for radioactive deposits in the Ruby-Poorman and Nixon Fork districts, west-central Alaska, 1949: U.S. Geological Survey Circular 279, 19 p.

Where this page came from

This page was imported from U.S. Geological Survey. Published by the U.S. Geological Survey and, as a work of the United States government, in the public domain.

Nobody has written it yet — it is the source material at a new address, which is why search engines are asked to skip it and why no one earns from it. It is up for grabs: take it on, and it is yours to rewrite and to earn from.