Boulder Creek

Site Name

Primary: Boulder Creek
Secondary: Purkeypile Boulder Creek
Secondary: Boulder Creek Tin Lode
Secondary: Purkey Tin
Secondary: Wonder
Secondary: Scenic
Secondary: Basin
Secondary: Lead

---

Commodity

Primary: Silver
Primary: Tin
Primary: Lead
Primary: Copper
Secondary: Arsenic
Secondary: Antimony

---

Location

State: Alaska
District: McGrath

---

Land Status

Not available

---

Holdings

Not available

---

Workings

Not available

---

Ownership

Not available

---

Production

Not available

---

Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

---

Physiography

Not available

---

Mineral Deposit Model

Model Name: Sn skarn

---

Orebody

Not available

---

Structure

Not available

---

Alterations

Alteration Type: L
Alteration Text: Development of tactite mineral assemblage in host rocks because of thermal effects of nearby biotite granite. Locally intense silicification (C.C. Hawley and Associates, Inc., 1978).

---

Rocks

Not available

---

Analytical Data

Not available

---

Materials

Ore: Cassiterite
Ore: Chalcopyrite
Ore: Galena
Ore: Tetrahedrite
Gangue: Calcite
Gangue: Diopside
Gangue: Epidote

---

Comments

Comment (Reference): Primary Reference = Conwell, 1977; C.C. Hawley and Associates, Inc., 1978

Comment (Reserve-Resource): Reserves = Warner (1985) estimates 136,000 kg Sn. Grab samples contain up to 18% Sn and 7,900 g/t Ag.

Comment (Workings): Workings / Exploration = F. B. Jules and Ed Knutson of Poorman, Alaska concentrated their effort on the Jiles-Knudson prospect between 1910(?) and 1923. Mr. I.W. Purkeypile and son David Purkeypile 'rediscovered' and prospected the Boulder Creek area since the late 1940s (C.C. Hawley and Associates, Inc., 1978). The area was evaluated by numerous private mining companies in the 1970s and 1980s. ? Shallow shafts, dozer cuts and diamond drill holes have been used to explore the prospect. Mapping and ground geophysical surveys, including magnetics and Chrone VLF (C.C. Hawley and Associates, Inc., 1978, Fig. 4.2-C and Fig. 4.2C(3)-A(1)).

Comment (Geology): Age = Tertiary; mineralization in the Boulder Creek area is interpreted to be linked to the Tonzona granite (Tmt), part of the McKinley Sequence, that has been determined to range from 52.3 to 56.2 m.y. in age (Reed and Lanphere, 1972; Reed and Nelson, 1980).

Comment (Geology): Age = Chron age is for McKinley Sequence.

Comment (Geology): Geologic Description = C.C. Hawley and Associates, Inc. (1978, Fig. 4.2 - C(3) - A(1)) locate the Boulder Creek occurrence about 300 feet north-northeast of the J+K discovery adit. Shallow shafts, dozer cuts and diamond drill holes have been used to explore the prospect. Host rocks are thermally metamorphosed calc-silicate rock, felsic schist, dolomite, and argillite approximately 300 to 600 feet north of Tonzona pluton. In plan the main exposure is circular with about a 40-foot diameter. Disseminated cassiterite, arsenopyrite, chalcopyrite, galena and pyrrhotite occur in clusters of narrow, open-space fracture fillings, suggestive of a stockwork-type deposit, and in veins up to five or six feet long and a foot wide. A six-foot-wide zone of manganosiderite is noted along the southern contact of one 18-inch-wide vein. Silicification and fracturing are intense. C.C. Hawley and Associates, Inc.(1978) report up to 4 percent tin, 0.3 percent copper, 2.8 percent zinc, 1 oz/ton silver and a trace of gold in rock chip samples. A nine-foot channel sample across a mineralized sheeted vein set averaging 1.57percent tin and 10.0 oz/ton silver is described by Conwell (1977). Selected samples from adjacent clusters contained as much as 18 percent tin and 230 oz/ton silver. Drill hole data suggest the deposit overlies a marginal cusp of the granite. Twelve of twenty-three drill holes intersected zones containing more than 0.53 percent tin. Intercepts were between 1.9 and 7.8 feet wide, with an average grade of about 2 percent tin. One interval contained 5 percent tin over an 11.5-foot intercept (Conwell, 1977; Warner, 1985). C.C. Hawley and Associates, Inc.(1978) suggest that the drill holes may have been drilled down dip and thus did not adequately test the configuration of the mineralization. Warner (1985) estimated this occurrence contains at least 136,000 kg Sn. ? In the entire Boulder Creek area there are widely separated, mineralized outcrops. Mapping and ground geophysical surveys, including magnetics and Chrone VLF, suggest extensive skarn development and skarn mineralization across Boulder Creek from the J+K adit. Little sub-surface exploration has been completed (C.C. Hawley and Associates, Inc.). Reed and others (1978) report that high tin values in pan concentrate samples collected along the northern granite-sedimentary contact suggest that tine mineralization occurs for at least 5 kilometers west of the Boulder Creek prospect and the possibility that addtional tin-silver deposits occur along this northern contact zone is considered excellent. The Boulder Creek region, probably due to its remote location and the low tin prices, is relatively under-explored.? the geologic setting of the Boulder Creek area is provided, as follows, from work done by C.C. Hawley and Associates, Inc. (1978) and Reed and Nelson (1980). Blocky slate, argillite, thin-bedded siliceous limestone and chert define a belt of lower Paleozoic sedimentary and metavolcanic rocks (possibly Keevy Peak, other Totalanika series, or equivalents) bordered by the Tonzona granitic pluton (Tmt), part of the McKinley sequence of Late Cretaceous and early Tertiary age intrusive rocks mapped by Reed and Nelson (1980). The granite has three phases; a coarse-grained, locally porphyritic biotite granite; a medium-grained biotite granite; and a late fine-grained, leucocratic, locally aplitic, muscovite-tourmaline granite in which ovoid clusters of small black tourmaline crystals give the rock a 'dalmatian' appearance. Muscovite may exceed biotite and accessory minerals include tourmaline with lesser amounts of topaz, fluorite, garnet, zircon, and apatite. Late-stage greissen veinlets contain muscovite, topaz, tourmaline, locally abundant beryl, and occasionally, cassiterite. Lead, silver and tin mineralization occurs in Paleozoic metasediments and metavolcanic rocks along the north and northeast contact of the pluton.

Comment (Commodity): Gangue = manganosiderite

Comment (Deposit): Other Comments = In much of the literature the Purkeypile group of lode claims includes the Jiles-Knudson (TL004), Mespelt (TL005) and Hogback (TL006) prospects. The Jiles-Knudson prospect is probably on related mineralization and very likely part of the same mineralization and alteration event.

Comment (Deposit): Model Name = Sn Skarn Deposits (Cox and Singer, 1986; model 14b).

---

References

Reference (Deposit): MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.

Reference (Deposit): Clark, A.L., and Cobb, E.H., 1972, Metallic mineral resources map of the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-369, 1 sheet, scale 1:250,000.

Reference (Deposit): Capps, S.R., 1927, The Toklat-Tonzona River region: U.S. Geological Survey Bulletin 792-C, p. 73-110.

Reference (Deposit): Berg, H.C., and Cobb, E.H., 1967, Metalliferous Lode Deposits of Alaska. U.S. Geological Survey Bulletin 1246, 254 p.

Reference (Deposit): Reed, B.L., and Lanphere, M.A., 1972, Generalized geologic map of the Alaska-Aleutian range batholith showing potassium-argon ages of the plutonic rocks: U.S. Geological Survey Miscellaneous Field Studies Map MF-372, 2 sheets, scale 1:1,000,000.

Reference (Deposit): Maloney, R.P., and Thomas, B.I., 1966, Investigation of the Purkeypile prospects, Kuskokwim River basin, Alaska: U.S. Bureau of Mines Open-File Report 5-66, 12 p.

Reference (Deposit): Brooks, A.H., 1911, The Mount McKinley region, Alaska, with descriptions of the igneous rocks and of the Bonnifield and Kantishna districts by L.M. Prindle: U.S. Geological Survey Professional Paper 70, 234 p.

Reference (Deposit): Capps, S.R., 1925, An early Tertiary placer deposit in the Yentna district: U.S. Geological Survey Bulletin 773, p. 53-61.

Reference (Deposit): Conwell, C.N., 1977, Boulder Creek tin lode deposits: Alaska Division of Geological and Geophysical Surveys Geologic Report 55, p. 35 -38.

Reference (Deposit): C.C. Hawley and Associates, Inc., 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U.S. Bureau of Mines Open-File Report 24-78, 275 p., 7 plates.

Reference (Deposit): Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, scale 1:250,000.

Reference (Deposit): Warner, J.D., 1985, Critical and strategic minerals in Alaska: tin, tantalum, and columbium: U.S. Bureau of Mines Information Circular 9037, 42 p.

Reference (Deposit): Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p.

Reference (Deposit): Cobb, E.H., and Reed, B.L., 1980, Summaries of data and lists of reference to metallic and selected nonmetallic mineral deposits in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-884, 106 p.

Reference (Deposit): Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1978, Mineral resources map of the Talkeetna Quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, 1 sheet, scale 1:250,000.

---

The Top Ten Gold Producing States

These ten states contributed the most to the gold production that built the West from 1848 through the 1930s. The Top Ten Gold Producing States.