U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Geochemical data for stream-sediment, heavy-mineral-concentrate, and rock samples

collected from the Fortyseven Creek gold-arsenic-antimony-tungsten prospect,

southwestern Alaska

By

John E. Gray, Gregory K. Lee, Richard M. O'Leary, and Peter M. Theodorakos

Open-File Report 99-584

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial

standards. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S.

Government.

U.S. Geological Survey, P.O. Box 25046, MS 973, Federal Center, Denver, CO 80225-0046

1999
2

U.S. DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

________________________________________________________________________

For additional information Copies of this report can

 write to: be purchased from:

Chief Scientist, Central Region Books and Open-File Reports

Mineral Resources Program U.S. Geological Survey

U.S. Geological Survey Federal Center

Box 25046, Federal Center Box 25046

Denver, CO 80225-0046 Denver, CO 80225-0046
3

TABLE OF CONTENTS

Introduction......................................................................................................... 4

Site Description and History....................................................................................... 4

Geology............................................................................................................... 4

Methods of Study................................................................................................... 5

Sample Media.................................................................................................. 5

Sample Preparation........................................................................................... 5

Analytical Methods................................................................................................ 5

Semiquantitative Spectrography............................................................................ 5

Inductively Coupled Plasma-Atomic Emission Spectrometry.......................................... 6

Atomic Absorption Spectrophotometry.................................................................... 6

Visible Spectrophotomety.................................................................................... 6

Selective Ion Analysis.................................................. 6

X-ray Fluorescence........................................................................................... 7

Coulometric Titration........................................................................................ 7

Digital Data......................................................................................................... 7

Description of the Data Tables................................................................................... 7

Acknowledgments.................................................................................................. 7

References............................................................................................................ 7

FIGURES

Figure 1. Location of the Fortyseven Creek prospect........................................................ 10

Figure 2. Location of samples collected in the Fortyseven Creek area ................................... 11

TABLES

Table 1. Limits of determination for the spectrographic analysis of stream-sediment samples...... 12

Table 2. Limits of determination for the analysis of stream-sediment and rock samples

by several analytical techniques........................................................................... 13

Table 3. Geochemical data for stream-sediment samples in the Fortyseven Creek study......47tab3.xls

Table 4. Geochemical data for heavy-mineral-concentrate samples in the

Fortyseven Creek study......................................................................47tab4.xls

Table 5. Geochemical data for rock samples in the Fortyseven Creek study.....................47tab5.xls
4

INTRODUCTION

In the summer of 1991, we conducted a reconnaissance geochemical survey around the Fortyseven Creek

Au-As-Sb-W prospect that is located in the southwestern part of the Sleetmute quadrangle. At that time, this

project was a small part of a more comprehensive Alaska Mineral Resource Assessment Program (AMRAP) study

of the Sleemute quadrangle. AMRAP studies were conducted by the U.S. Geological Survey (USGS) to fulfill

requirements of the Alaska National Interests Lands Conservation Act (Public Law 96-487, 1980) to survey certain

federal lands to determine their mineral potential. Although AMRAP is no longer in operation, this study

represents a small topical study that was conducted during the Sleetmute quadrangle AMRAP study. The objective

of the Fortyseven Creek work was to characterize the geochemistry of samples collected downstream from the

Fortyseven Creek prospect, as well as mineralized and altered rock samples collected from the prospect. In this

report, we describe the samples collected in 1991, the methods used for the analysis of the samples, and the

geochemical data for these samples. The data in this report are also available in digital form on computer diskette

in Gray and others (1999). An interpretation of these data appears in Gray and others (1998).

SITE DESCRIPTION AND HISTORY

The Fortyseven Creek Au-As-Sb-W prospect is located about 95 km southeast of Aniak, on the ridge crest

at the headwaters of Fortyseven Creek, a tributary of the Holitna River (fig. 1). This lode and an associated gold

placer mine on Fortyseven Creek about 3 km downstream from the prospect were discovered in 1947 by Russell

Schaeffer. The lode was first described by Cady and others (1955) as a quartz-scheelite-gold-bearing shear zone

cutting highly silicified graywacke and shale of the Kuskokwim Group. Additional exploration and geologic

mapping of the Fortyseven Creek area was conducted by Hawley (1989), who described quartz veins cutting

silicified sedimentary rock hornfels of the Kuskokwim Group; granite porphyry intrusions also cut the sedimentary

rocks in this area. Hawley (1989) also found minor amounts of arsenopyrite, scheelite, stibnite, gold, pyrite,

wolframite, jamesonite, and argentite in the veins, with locally abundant sericite (hydrothermal muscovite); these

veins were traceable laterally for greater than 1,000 m. Some mineralized samples contain greater than 34 ppm

Au (1 oz/t) (Hawley, 1989). The vein has not been mined. However, between 1948-1954, about 28 kg of gold (891

oz) and about 1,900 kg (5000 lbs) of scheelite, containing 67-77 percent WO3, were recovered by Schaeffer from

the placer mine on Fortyseven Creek downstream from the lode (Hawley, 1989).

Several companies conducted exploration of the Fortyseven Creek area in the 1970’s and 1980’s including

Homestake, Amax, American Copper and Nickel, and Anaconda (Hawley, 1989). More recently, from 1991-1994,

Nevada Star Resources conducted exploration of the area that included minor prospect trenching, an extensive soil

geochemical survey, and exploration drilling (Maynard, 1995). Nevada Star collected over 200 soil samples along

the ridges at the headwaters of Fortyseven Creek and found highly elevated concentrations of Au (as much as 1.3

ppm), As (as much as 8,230 ppm), Bi (as much as 100 ppm), Cu (as much as 322 ppm), Sb (as much as 106 ppm),

and W (as much as 510 ppm) in these soils. Nevada Star used soil anomalies of Au, As, and Bi to delineate several

target areas for three exploration drill holes. Drilling was difficult due to circulation loss and hole caving

problems. Consequently, only one drill hole penetrated significant mineralized rock about 44-105 m (145-345 ft)

below the surface that contained as much as 1.2 ppm Au (Maynard, 1995).

The Fortyseven Creek prospect has geologic and geochemical characteristics similar to other gold deposits

in southwestern Alaska such as the Au-As-W Golden Horn mine near Flat, and the Au-As-Sb Donlin Creek

deposit (fig. 1). There is presently considerable exploration for such gold deposits in southwestern Alaska, but

these deposits have not been well studied.

GEOLOGY

Rocks in the Fortyseven Creek area consist mostly of interbedded graywacke and siltstone of the

Cretaceous Kuskokwim Group that are cut by small granite porphyry intrusions of probable Late Cretaceous or

early Tertiary age (Cady and others, 1955; Hawley, 1989). The Kuskokwim Group is a sequence of flysch

representing turbidite fan, foreslope, shallow-marine, and shelf facies deposited into an elongate, northeast

trending, fault-controlled Cretaceous basin (Decker and Hoare, 1982; Bundtzen and Gilbert, 1983). Fossil ages for

the Kuskokwim Group range from Albian to Campanian (Cady and others, 1955; Hoare and Coonrad, 1959; Box

and Murphy, 1987; Box and Elder, 1992; Miller and Bundtzen, 1994). Granite porphyry intrusions in the

Fortyseven Creek area are similar to those found elsewhere in southwestern Alaska. These intrusions are generally
5

peraluminous in composition, with Al2O3 exceeding Na2O + K2O + CaO, and locally contain igneous garnet

(Bundtzen and Swanson, 1984; Moll-Stalcup, 1994). The granite porphyry near Fortyseven Creek has not been

dated, but similar rocks in southwestern Alaska are Late Cretaceous and early Tertiary (about 72 to 61 Ma), based

on K-Ar determinations (Reifenstuhl and others, 1984; Robinson and Decker, 1986; Decker and others, 1986;

1995; Miller and Bundtzen, 1994; Bundtzen and Miller, 1997). Gray and others (1998) obtained a 40Ar/

39Ar

plateau age of 67.1 ± 0.1 Ma for hydrothermal sericite separated from a sample of mineralized quartz vein from the

Fortyseven Creek prospect. This age represents the best estimate of the timing of mineralization at Fortyseven

Creek and is coeval with Late Cretaceous-early Tertiary granite porphyry intrusions found throughout southwestern

Alaska. Late Cretaceous and early Tertiary magmatism is interpreted to be related to a broad subduction arc

(Moll-Stalcup, 1994; Szumigala, 1993). Granite porphyry intrusions are important in southwestern Alaska

because they show a close spatial and temporal association with Au-As-Sb-W and Hg-Sb veins (Cady and others,

1955; Bundtzen and Miller, 1997; Gray and others, 1997).

METHODS OF STUDY

Sample Media

In this study, stream-sediment and heavy-mineral-concentrate samples were collected to provide information

about the rocks eroded from the drainage basin upstream from each sample site (fig. 2). Analyses of streamsediment samples are representative of the geochemistry of rocks contained within the drainage basins. Heavymineral-concentrate samples provide information about higher density minerals that are eroded from rocks in the

drainage basins. The heavy-mineral-concentrate collection procedure selectively concentrates the minerals with

high specific gravity, many of which may be related to mineral deposits. Collection of heavy-mineral-concentrate

samples facilitates concentration of some elements that are not easily detected in stream-sediment samples.

Altered and mineralized rock samples were collected from the Fortyseven Creek prospect to characterize the

geochemistry of this type of mineral deposit.

The stream-sediment material collected consisted of alluvium (bed sediment) in the active stream channel.

Where possible, samples were composited by collecting sediment from several localities in the active channel. The

stream sediment was screened to minus-10 mesh (2 mm) and collected in a stainless steel gold pan. About 2 kg of

sediment was taken from the pan and saved as the stream-sediment sample.

Heavy-mineral-concentrate samples were collected from the same active alluvium (bed sediment) as the

stream-sediment samples. At each sample site, the gold pan was filled with stream sediment screened to minus-10

mesh and panned until most of the less dense minerals, organic materials, and clays were removed. This resulting

panned-concentrate sample was later processed in the laboratory as described below to obtain a heavy-mineralconcentrate sample.

Sample Preparation

In the laboratory, the stream-sediment samples were air dried, sieved to minus-80 mesh (0.18 mm), pulverized

to less than 100 mesh (0.15 mm), and chemically analyzed by the methods described in the following section. The

heavy-mineral-concentrate samples were sieved to minus-35 mesh (0.50 mm), and then separated using bromoform

(specific gravity 2.85) to remove any remaining lighter minerals, primarily quartz and feldspar. The resultant

heavy-mineral-concentrate samples were then separated into magnetic, paramagnetic, and nonmagnetic fractions

using a modified Frantz Isodynamic Separator. The most magnetic material was removed at a setting of 0.25

ampere and contained mostly magnetite. The paramagnetic fraction was removed at 1.75 ampere and consisted

largely of ferromagnesian silicates and iron oxides. The nonmagnetic fraction of the heavy-mineral-concentrate

samples contained sulfide minerals, gold, and some nonmagnetic oxides and silicates; this was the only fraction

chemically analyzed. Rock samples were crushed, ground, pulverized to less than 100 mesh, and analyzed by the

analytical methods described below.

ANALYTICAL METHODS

Semiquantitative Spectrography (SQS)

The rock, minus-80-mesh stream-sediment, and minus-35-mesh nonmagnetic-heavy-mineral-concentrate

samples were analyzed by semiquantitative, direct-current arc emission spectrography (SQS) using a technique
6

adapted from Grimes and Marranzino (1968). Spectrographic results were determined by visually comparing

spectra derived from the sample against spectra obtained from laboratory reference standards made from pure

oxides and carbonates. Standard concentrations are geometrically spaced over any given order of magnitude as

follows: 100, 50, 20, 10, etc. Samples whose concentrations were estimated to fall between those values were

assigned values of 70, 30, 15, etc. The precision of this analytical technique is approximately ± one reporting

interval at the 83 percent confidence level and ± two reporting intervals at the 96 percent confidence level

(Motooka and Grimes, 1976). Values determined for the major elements Fe, Mg, Ca, Na, Ti, and P are given in

weight percent; all other values are in parts per million (micrograms/gram). In addition, Pd and Pt were

determined in the heavy-mineral-concentrate samples by emission spectrography. The elements determined by

emission spectrography and their limits of determination are listed in table 1. Data for stream-sediment samples

determined by this technique are listed in table 3; the heavy-mineral-concentrate data are listed in table 4, and the

rock data are listed in table 5.

Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES)

Concentrations of Ag, As, Au, Bi, Cd, Cu, Mo, Pb, Sb, and Zn were determined in the rock and streamsediment samples by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) using the procedure

developed by Motooka (1996). The sediments were decomposed with concentrated hydrochloric acid and hydrogen

peroxide in a hot-water bath. The metals were extracted in diisobutyl ketone (DIBK) in the presence of ascorbic

acid and potassium iodide. The DIBK phase was then aspirated directly into the plasma and element

concentrations were determined simultaneously with a multichannel ICP instrument.

Atomic Absorption Spectrophotometry (AAS)

Concentrations of Au, Te, and Tl in the rock and stream-sediment samples were determined by an atomic

absorption spectrophotometry (AAS) technique adapted from Hubert and Chao (1985). The samples were digested

using a series of hydrogen peroxide, hydrofluoric acid, aqua-regia, and hydrobromic acid-bromine solutions. Gold,

Te, and Tl were separated and concentrated by extraction into methyl isobutyl ketone and determined by flame

atomic absorption spectrophotometry. Concentrations for Au in the range of 0.002 to 0.050 ppm were determined

by graphite furnace atomic absorption spectrophotometry on samples that were shown to be less than 0.050 ppm by

the flame atomic absorption spectrophotometry technique. The graphite furnace atomic absorption

spectrophotometry technique for Au was adapted from Meier (1980).

Mercury was measured in the rock and stream-sediment samples using a modified version of the coldvapor atomic AAS technique (Kennedy and Crock, 1987). The samples were decomposed with nitric acid and

sodium dichromate. Mercury (II) was reduced to elemental mercury with hydroxylamine hydrochloride/sodium

chloride and stannous chloride in a continuous flow system releasing the vapor into a quartz cell of an atomic

absorption spectrophotometer where the concentration of mercury was determined.

The rock and stream-sediment samples were analyzed for Se using continuous-flow hydride generation

AAS (Sanzolone and Chao, 1987). In this method, the stream-sediment samples were digested using nitric,

perchloric, and hydrofluoric acids; hydrochloric acid was added to reduce Se (VI) to Se (IV), which is necessary

for the accurate determination of Se using hydride generation AAS. A mixture of hydrochloric acid, sodium

borohydride, and sodium hydroxide was added to produce selenium hydride, which is then stripped and transported

with inert gas to the atomizer of the atomic absorption spectrophotometer where Se concentration was determined.

Visible Spectrophotometry (VS)

Tungsten was determined in the rocks and stream-sediment samples by a visible spectrophotometric (VS)

method by decomposing the samples with nitric, hydrofluoric, and hydrochloric acids (Welsch, 1983). Stannous

chloride and dithiol solution was added to reduce the W, forming the blue tungsten-dithiol complex, which was

then extracted into heptane. The color intensity of the tungsten-dithiol complex is proportional to the

concentration of W in the sample. Tungsten concentrations were determined using a visible absorption

spectrophotometer.

Selective Ion Electrode Analysis (SIE)

Fluoride concentrations were determined in the rock and stream-sediment samples by selective ion

electrode (SIE) analysis using a method modified from Bodkin (1977). Samples were fused with lithium
7

metaborate, and then dissolved in nitric acid. A complexing buffer was added, and concentrations were

determined using a fluoride-selective ion electrode.

X-Ray Fluorescence (XRF)

The rock samples were also analyzed for major element oxides by a wavelength dispersive X-ray

fluorescence spectroscopy (XRF) method (Taggart and others, 1990). In this procedure the samples were fused

with lithium tetraborate and formed into a glass disk. The disks were irradiated with X-rays, and X-ray photons

emitted by the elements present in the sample were counted and concentrations determined using calibrated

standards. The weight of the sample loss on ignition (LOI) at 925oC was determined gravimetrically. The

elements determined by this technique and the concentration range limitations are shown in table 2.

Coulometric Titration (CT)

Concentrations of CO2 and H2O were measured in the rock samples. The amount of CO2 was determined

by a coulometric titration (CT) technique following sample digestion with perchloric acid (Jackson and others,

1987). Total water was determined by coulometry using a titration method after fusion with a PbO-PbCrO4-CaCO3

flux at 900oC (Norton and Papp, 1990). The amount of moisture (H2O

-

) was determined by weight loss after

heating the samples at 110oC. The amount of H2O

+

 was determined by the calculation: [H2OTotal - H2O

-

 = H2O

+

].

Lower limits of determination for CO2 and H2O are shown in table 2.

DIGITAL DATA

The geochemical data in this report are also part of the USGS National Geochemical Database in Denver that

contains both descriptive geological information and analytical data. This report may also be obtained on the

USGS webb site at: greenwood.cr.usgs.gov/pub/open-file-reports/ofr-99-0584/.

DESCRIPTION OF DATA TABLES

Table 3 contains the geochemical data for the stream-sediment samples collected during this study; table 4

contain the data for the heavy-mineral-concentrate samples, and table 5 contain the data for the rock samples.

Sample site locations are given in latitude and longitude and decimal degrees in the tables, and these sample sites

are shown on figure 2. The analytical method for each element shown in tables is abbreviated as a suffix in the

column headings. The designation "SQS" indicates semiquantitative emission spectrography, "ICP" indicates

inductively coupled plasma-atomic emission spectroscopy, "AAS" indicates atomic absorption spectrophotometry,

“VS” indicates visible spectrophotomety, “SIE” indicates selective ion electrode analysis, “XRF” indicates X-ray

fluorescence spectroscopy, and “CT” indicates coulometric titration. Discrepancies in analyses for certain elements

duplicated by different analytical methods, such as values determined for Au in stream-sediment samples, may be

attributable to the particulate nature of minerals that contain Au (i.e., nugget effect), different sample aliquots

used, and different extraction procedures. Due to the larger sample aliquot analyzed, the atomic absorption

spectrophotometry analysis of Au generally provides more representative results than emission spectrography. For

example, a 10-gram sample aliquot is used for the atomic absorption spectrophotometry analysis, whereas a 10-

milligram sample aliquot is used in the emission spectrography technique. There is no data for heavy-mineralconcentrate sample 91FS02C because there was insufficient material for geochemical analysis following

preparation in the laboratory.

Acknowledgments--John Bullock, Phil Hageman, Jerry Motooka, Clara Papp, Dave Siems, and Eric Welsch

(USGS) provided chemical analyses of samples. Carter Borden assisted with field work and sample collection.

REFERENCES

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lithium metaborate: The Analyst, v. 102, no. 1215, p. 409-413.

Box, S.E., and Elder, W.P., 1992, Depositional and biostratigraphic framework of the Upper Cretaceous

Kuskokwim Group, southwest Alaska, in Bradley, D.C., and Ford, A.B., eds., Geologic studies in Alaska
8

by the U.S. Geological Survey, 1990: U.S. Geological Survey Bulletin 1999, p. 8-16.

Box, S.E., and Murphy, J.M., 1987, Late Mesozoic structural and stratigraphic framework, eastern Bethel

quadrangle, southwest Alaska, in Hamilton, T.D., and Galloway, J.P., eds., Geologic studies in Alaska by

the U.S. Geological Survey during 1986: U.S. Geological Survey Circular 998, p. 78-82.

Bundtzen, T.K., and Gilbert, W.G., 1983, Outline of geology and mineral resources of upper Kuskokwim region,

Alaska: Journal of the Alaska Geological Society, v. 3, p. 101-119.

Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous

rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska:

Economic Geology Monograph 9, 242-286.

Bundtzen, T.K., and Swanson, S.E., 1984, Geology and petrology of igneous rocks in the Innoko River area,

western Alaska: Geological Society of America Abstracts with Programs, v. 16, no. 5, p. 273.

Cady, W.M., Wallace, R.E., Hoare, J.M., and Webber, E.J., 1955, The central Kuskokwim region, Alaska: U.S.

Geological Survey Professional Paper 268, 132 p.

Decker, John, Bergman, S.C., Blodgett, R.B., Box, S.E., Bundtzen, T.K., Clough, J.G., Coonrad, W.L., Gilbert,

W.G., Miller, M.L., Murphy, J.M., Robinson, M.S., and Wallace, W.K., 1994, Geology of southwestern

Alaska, in Plafker, George, and Berg, H.C., eds., The Geology of Alaska: Geological Society of America,

Boulder, Colorado, The Geology of North America, v. G-1, p. 285-310.

Decker, John, and Hoare, J.M., 1982, Sedimentology of the Cretaceous Kuskokwim Group, southwest Alaska, in

Coonrad, W.L., ed., U.S. Geological Survey in Alaska, Accomplishments during 1980: U.S. Geological

Survey Circular 844, p. 81-83.

Decker, John, Reifenstuhl, R.R., Robinson, M.S., and Waythomas, C.F., 1986, Geologic map of the Sleetmute A-5,

A-6, B-5, and B-6 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys

Professional Report 93, 22 p., 1 sheet, scale 1:250,000.

Decker, John, Reifenstuhl, R.R., Robinson, M.S., Waythomas, C.F., and Clough, J.G., 1995, Geology of the

Sleetmute A-5, A-6, B-5, and B-6 quadrangles, southwestern Alaska: Alaska Division of Geological and

Geophysical Surveys Professional Report 99, 16 p.

Decker, John, Robinson, M.S., Murphy, J.M., Reifenstuhl, R.R., and Albanese, M.D., 1984, Geologic map of the

Sleetmute A-6 quadrangle: Alaska Division of Geological and Geophysical Surveys Report of

Investigations 84-8, scale 1:40,000.

Gray, J.E., Lee, G.K., O’Leary, R.M., and Theodorakos, P.M., 1999, Digital geochemical data for stream sediment,

heavy-mineral-concentrate, and rock samples collected from the Fortyseven Creek gold-arsenic-antimonytungsten prospect, southwestern Alaska: U.S. Geological Survey Open-File Report 99-584, 1.2 MB

Diskette.

Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold-bearing vein

deposits of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska:

Economic Geology Monograph 9, p. 287-305.

Gray, J.E., Gent, C.A., Snee, L.W., and Theodorakos, P.M., 1998, Age, isotopic, and geochemical studies of the

Fortyseven Creek Au-As-Sb-W prospect and vicinity, southwestern Alaska, in Gray, J.E., and Riehle, J.R.,

eds., Geologic Studies by the U.S. Geological Survey, 1996: U.S. Geological Survey Professional Paper

1595, p. 17-29.

Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc and alternating-current spark emission

spectrographic field methods for the semiquantitative analysis of geological materials: U.S. Geological

Survey Circular 591, 6 p.

Hawley, C.C., 1989, The Forty Seven Creek prospect, southwest Alaska, summary of data and recommendations:

unpublished report prepared for Holitna Basin Mining and Exploration, Inc., 7 p.

Hoare, J.M., and Coonrad, W.L., 1959, Geology of the Bethel quadrangle, Alaska: U.S. Geological Survey

Miscellaneous Geologic Investigations Map I-285, scale 1:250,000.

Hubert, A.E., and Chao, T.T., 1985, Determination of gold, indium, tellurium and thallium in the same sample

digestion of geological materials by atomic-absorption spectroscopy and two-step solvent extraction:

Talanta, v. 32, p. 383-387.

Jackson, L.L., Brown, F.W., and Neil, S.T., 1987, Major and minor elements requiring individual determination,

classical whole rock analysis, and rapid rock analysis, in Baedecker, P.A., ed., Geochemical Methods of

Analysis: U.S. Geological Survey Bulletin 1770.

Kennedy, K.R., and Crock, J.G., 1987, Determination of mercury in geological materials by continuous flow,
9

cold-vapor, atomic-absorption spectrophotometry: Analytical Letters, v. 20, p. 899-908.

Maynard, G.B., 1995, 47 Creek Property Southwestern Alaska, Results of the Phase Three Exploration Program:

unpublished report prepared for Nevada Star Resource Corp., Seattle, Washington.

Meier, A.L., 1980, Flameless atomic-absorption determination of gold in geological materials: Journal of

Geochemical Exploration, v. 13, p. 77-85.

Miller, M.L., and Bundtzen, T.K., 1994, Generalized geologic map of the Iditarod quadrangle, Alaska, showing

potassium-argon, major-oxide, trace-element, fossil, paleocurrent, and archaelogical sample localities:

U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-A, 1 plate, scale 1:250,000.

Moll-Stalcup, E.J., 1994, Latest Cretaceous and Cenozoic magmatism in mainland Alaska, in Plafker, George, and

Berg, H.C., eds., The Geology of Alaska: Geological Society of America, Boulder, Colorado, The Geology

of North America, v. G-1, p. 589-619.

Motooka, J.M., 1996, Organometallic halide extraction for 10 elements by inductively coupled plasma-atomic

emission spectrophotometry, in Arbogast, B.F., ed., Analytical methods manual for the Mineral Resources

Surveys Program, U.S. Geological Survey: U.S. Geological Survey Open-File Report 96-525, p. 102-108.

Motooka, J. M., and Grimes, D. J., 1976, Analytical precision of one-sixth order semiquantitative spectrographic

analyses: U.S. Geological Survey Circular 738, 25 p.

Norton, D.R., and Papp, C.S.E., 1990, Determination of moisture and total water in silicate rocks, in Arbogast,

B.F., ed., Quality Assurance Manual for the Branch of Geochemistry, U.S. Geological Survey: U.S.

Geological Survey Open-file Report 90-668, 184 p.

Reifenstuhl, R.R., Robinson, M.S., Smith, T.E., Albanese, M.D., and Allegro, G.A., 1984, Geologic map of the

Sleetmute B-6 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of

Investigations 84-12, scale 1:40,000.

Robinson, M.S., and Decker, John, 1986, Preliminary age dates and analytical data for selected igneous rocks from

the Sleetmute, Russian Mission, Taylor Mountains, and Bethel quadrangles, southwestern Alaska: Alaska

Division of Geological and Geophysical Surveys Public-Data File 86-99, 9 p.

Sanzolone, R.F., and Chao, T.T., 1987, Determination of selenium in thirty-two geochemical reference materials

by continuous-flow hydride generation atomic absorption spectrophotometry: Geostandards Newsletter, v.

11, p. 81-85.

Szumigala, D.J., 1993, Gold mineralization related to Cretaceous-Tertiary magmatism in the Kuskokwim

Mountains of west-central and southwestern Alaska: Ph.D. dissertation, University of California, Los

Angeles, 301 p.

Taggart, J.E., Jr., Bartel, Ardith, and Siems, D.F., 1990, High precision major element analysis of rocks and

minerals by wavelength dispersive X-ray fluorescence spectroscopy, in Arbogast, B.F., ed., Quality

Assurance Manual for the Branch of Geochemistry: U.S. Geological Survey: U.S. Geological Survey

Open-file Report 90-668, 184 p.

Welsch, E.P., 1983, A rapid geochemical spectrophotometric determination of tungsten with dithiol: Talanta, v.

30, p. 876-878.
10

Figure 1. Map showing the location of the Fortyseven Creek prospect in southwestern Alaska. Geology

generalized from Cady and others (1955), Hoare and Coonrad (1959), Decker and others (1984; 1994; 1995),

Miller and Bundtzen (1994), and Bundtzen and Miller (1997).
11

0

0 1 Kilometer

1 Mile

158 15' 158 10' 158 5' o o o

61 0' o

61 5' o

Figure 2. Location of samples collected in the Fortyseven Creek study. Circles indicate streamsediment and heavy-mineral-concentrate sites and triangles indicate rock sample sites.

91FS00

91FS01

91FS02

91FS03

91FS04

91FS05

91FS06

91FS08

91FS07

47X

47B - 47G
12

Table 1. Limits of determination for the spectrographic analysis of stream-sediment

samples, based on a 10-mg sample.

[The spectrographic limits of determination for heavy-mineral-concentrate samples are based on a 5-mg sample weight, and are therefore two reporting

intervals higher than the limits given for stream sediments]

Elements Lower determination limit Upper determination limit

Percent

Iron (Fe) 0.05 20

Magnesium (Mg) 0.02 10

Calcium (Ca) 0.05 20

Sodium (Na) 0.2 5

Titanium (Ti) 0.002 1

Phosphorous (P) 0.2 10

Parts per million

Silver (Ag) 0.5 5,000

Arsenic (As) 200 10,000

Gold (Au) 10 500

Boron (B) 10 2,000

Barium (Ba) 20 5,000

Beryllium (Be) 1 1,000

Bismuth (Bi) 10 1,000

Cadmium (Cd) 20 500

Cobalt (Co) 10 2,000

Chromium (Cr) 10 5,000

Copper (Cu) 5 20,000

Gallium (Ga) 5 100

Germanium (Ge) 10 100

Lanthanum (La) 50 1,000

Manganese (Mn) 10 5,000

Molybdenum (Mo) 5 2,000

Niobium (Nb) 20 2,000

Nickel (Ni) 5 5,000

Lead (Pb) 10 20,000

Antimony (Sb) 100 10,000

Scandium (Sc) 5 100

Tin (Sn) 10 1,000

Strontium (Sr) 100 5,000

Thorium (Th) 100 2,000

Vanadium (V) 10 10,000

Tungsten (W) 20 10,000

Yttrium (Y) 10 2,000

Zinc (Zn) 200 10,000

Zirconium (Zr) 10 1,000

Palladium (Pd)*5 1,000

Platinum (Pt)*20 1,000

*Determined in heavy-mineral-concentrate samples only.
13

Table 2. Limits of determination for the analysis of stream-sediment and rock samples by several analytical

techniques.

[ICP-AES, inductively coupled plasma-atomic emission spectroscopy; AA, atomic absorption spectrophotometry; VS, visible spectrophotomety; SIE,

selective ion electrode analysis; CT, coulometric titration, and XRF, X-Ray fluorescence spectroscopy;].

Analytical Lower limit Upper limit

Element Method

Silver (Ag) ICP-AES 0.045 ppm 1,500 ppm

Arsenic (As) ICP-AES 0.6 ppm 3,000 ppm

Gold (Au) ICP-AES 0.15 ppm 2,400 ppm

Bismuth (Bi) ICP-AES 0.6 ppm 1,500 ppm

Cadmium (Cd) ICP-AES 0.03 ppm 500 ppm

Copper (Cu) ICP-AES 0.03 ppm 1,200 ppm

Molybdenum (Mo) ICP-AES 0.09 ppm 1,500 ppm

Lead (Pb) ICP-AES 0.6 ppm 12,000 ppm

Antimony (Sb) ICP-AES 0.6 ppm 800 ppm

Zinc (Zn) ICP-AES 0.03 ppm 500 ppm

Tellurium (Te) AAS 0.050 ppm

Thallium (Tl) AAS 0.050 ppm

Gold (Au) AAS 0.002 ppm

Mercury (Hg) AAS 0.02 ppm

Selenium (Se) AAS 0.1 ppm

Tungsten (W) VS 1.0 ppm

Fluoride (F) SIE 200 ppm

Tungsten (W) ICP-MS 1.0 ppm

Carbon dioxide (CO2) CT 0.01 %

Water (H2O) CT 0.1 %

Calcium (CaO) XRF 0.02 %

Iron (Fe(T)O3) XRF 0.04 %

Magnesium (MgO) XRF 0.1 %

Sodium (Na2O) XRF 0.15 %

Phosphorous (P2O5) XRF 0.05 %

Titanium (TiO2) XRF 0.02 %

Manganese (MnO) XRF 0.01 %

Silica (SiO2) XRF 0.1 %

Alumina (Al2 O3) XRF 0.1 %

Potassium (K2O) XRF 0.02 %