Boulder Creek

Prospect, Undetermined

Alternative names

Purkeypile Boulder Creek
Boulder Creek Tin Lode
Purkey Tin

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Sn
Other commodities As; Sb
Ore minerals cassiterite; chalcopyrite; galena; tetrahedrite
Gangue minerals calcite; diopside; epidote; manganosiderite

Geographic location

Quadrangle map, 1:250,000-scale TL
Quadrangle map, 1:63,360-scale D-5
Latitude 62.903
Longitude -152.15
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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 (TL004) below Boulder Creek Glacier on the east bank of Boulder Creek in the southeast quarter of Section 32, T. 33 N. R. 15 W., of the Seward Meridian.

Geologic setting

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 greisen 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.
Geologic map unit (-152.152233709393, 62.9024465617411)
Mineral deposit model Sn Skarn Deposits (Cox and Singer, 1986; model 14b).
Mineral deposit model number 14b
Age of mineralization 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).
Alteration of deposit 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).

Production and reserves

Workings or 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)).
Indication of production None
Reserve estimates Warner (1985) estimates 136,000 kg Sn. Grab samples contain up to 18% Sn and 7,900 g/t Ag.

Additional 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.


MRDS Number A011559


Reporters Madelyn A. Millholland (Millholland & Associates)
Last report date 8/10/1998