Bonnell (Neversweat)

Mine, Inactive

Commodities and mineralogy

Main commodities Ag; Pb; Zn
Other commodities Au; Cu; Sb; Zn
Ore minerals anglesite; arsenopyrite; boulangerite; chalcopyrite; galena; jamesonite; scheelite; sphalerite; stibnite; tetrahedrite
Gangue minerals calcite; potassium feldspar; quartz

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale C-3
Latitude 63.5026
Longitude -151.0158
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Bonnell or Neversweat mine (Cobb, 1980 [OFR 80-363] ) is on the east side of Eldorado Creek opposite the mouth of Reinhart Creek. The mine is at an elevation of about 2200 feet, on a west-trending ridge below hilltop elevation 2725. The location is accurate.
The mine is location 4 of Bundtzen, Smith, and Tosdal (1976), B of Hawley and Associates (1978), 4 of Bundtzen (1981), 7 of Thornsberry, McKee, and Salisbury (1984), and 2 of Cobb (1972 [MF 366]) and MacKevett and Holloway (1977). The site includes several nearby similar mineral occurrences, including numbers 6-9 of Thornsberry, McKee, and Salisbury (1984). The Bonnell mine and nearby prospects occupy a large part of the N1/2 section 27, T. 16 S., R. 18 W., Fairbanks Meridian.

Geologic setting

Geologic description

The Bonnell mine is at or near the intrusive contact between a quartz porphyry pluton and graphitic, quartz-mica schist (Bundtzen, 1981). The east-west, elongate outcrop area of the pluton is about a mile long and a maximum of about 1300 feet wide. It is bisected by Eldorado Creek. An east-west component to the mainly ENE-aligned topography suggests that the pluton may extend beneath Busia Mountain and perhaps part of Brooker Mountain. The pluton has been dated at 48.3 +/- 1.4 Ma (Bundtzen and Turner, 1979); it intrudes Birch Creek Schist of probable Precambrian age (Bundtzen, 1981, p. 37).
The main deposits are polymetallic quartz-calcite-potassium feldspar veins at the Neversweat or Bonnell workings east of Eldorado Creek. The veins are in the quartz porphyry and in the contact zone between the porphyry and the quartz-mica schist. They pinch and swell and are as much as 4 feet thick . The veins contain chiefly arsenopyrite and galena, along with some chalcopyrite, stibnite, tetrahedrite, boulangerite, jamesonite, and, locally, scheelite. Anglesite occurs in oxidized ore. Soil samples collected along the outcrop of the pluton are generally anomalous in antimony and some are strongly anomalous in silver, lead, and zinc; the entire quartz porphyry body appears to be at least weakly mineralized.
Samples of the richest ore assay of as much as 74 ounces of silver per ton and 0.48 ounce of gold per ton, but most samples assay 10 to 35 ounces of silver per ton and less than 0.05 ounce of gold per ton. Antimony content is generally in the 1-5 percent range, and combined lead and zinc values approach 30 percent in some of the veins (Thornsberry, McKee, and Salisbury, 1984, v. 2, occurrence 7 and occurrences 6, 8, and 9).
Geologic map unit (-151.018083510034, 63.5020916536809)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization The deposit is probably Eocene, based on the approximate 48 Ma age of the quartz porphyry hostrock (Bundtzen and Turner, 1979) (also see record MM091).
Alteration of deposit Silicification and introduction of potassium feldspar. Oxidation of lead minerals.

Production and reserves

Workings or exploration The Bonnell or Neversweat deposit was discovered and first explored by John Busia, who reported galena-rich float that contained about 74 ounces of silver per ton and almost one-half ounce of gold per ton. An adit driven about 40 feet above creek level in search of the high-grade ore encountered only weakly mineralized schist (Wells, 1933, p. 376). More extensive underground work was done in about 1955 and some lead-silver ore may have been shipped (Bundtzen, 1981, p. 198). At least two additional adits were driven by Bonnell, a subsequent owner of the prospect. One adit was about 60 feet above the original prospect; and a third adit was about 30 feet higher. The upper adit was being extended in 1963 by Bonnell (Morrison, 1964, p. 97). Bundtzen (1981, pl. 3) shows that four main adits were driven on the property. The original, and longest, adit by Busia, a second adit called the Blacksmith level, a third-level adit, and an upper adit. The workings were mapped by Hawley and Associates (1978) and by T. K. Hinderman and McKee (Thornsberry, McKee, and Salisbury (1984, v. 2, occurrence 7). The mine apparently has been inactive since the work done by Bonnell in the 1960s.
Indication of production Undetermined
Production notes Some lead- and silver-rich ore may have been shipped in 1955.

Additional comments

The mine is in Denali National Park and Preserve.

References

MRDS Number A011204

References

Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p.
Morrison, D. A., 1964, Geology and ore deposits of Kantishna and vicinity, Kantishna district, Alaska: College, AK, University of Alaska, M. S. Thesis, 109 p.
Reporters C.C. Hawley
Last report date 4/14/2001