VABM Bonanza

Prospect, Active

Alternative names

Bonanza Ridge

Commodities and mineralogy

Main commodities Au
Ore minerals bismuthinite; chalcopyrite; gold; magnetite; molybdenite; pyrite
Gangue minerals carbonate; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale RM
Quadrangle map, 1:63,360-scale A-3
Latitude 61.0729
Longitude -159.8453
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect about a half mile east of the head of Rocky Creek in the Nyac district. It is at an elevation of about 2650 feet, about 0.3 mile southwest of triangulation station Bonanza near the center of section 1, T. 11 N., R. 60 W., of the Seward Meridian. This location is accurate to within 1000 feet of the center of the prospect.

Geologic setting

Geologic description

At this prospect, gold-bearing quartz veins cut granitic rocks of the Bonanza pluton (Wenz, 2004, 2005). The Bonanza pluton is a composite intrusion; it has a margin of diorite, quartz diorite, tonalite, and monzodiorite around a core of granodiorite and granite. Mafic minerals make up 10 to 25 percent of the intrusive; they include biotite, hornblende, and minor pyroxene. The more mafic parts of the pluton can have up to one percent apatite. Argon-argon radiometric ages reported by Wenz (2004, 2005) for this pluton are 109 +/- 1 Ma, 113 +/- 0.4 Ma, and 113 +/- 1 Ma.
As described by Wenz, quartz veining makes up to one to two percent of the more strongly mineralized rocks. Potassic alteration includes narrow K-feldspar-bearing selvages along barren quartz veins. Gold-bearing veins with sericite-chlorite-carbonate alteration overprint the potassic alteration. Ore minerals in the gold-bearing veins include pyrite, chalcopyrite, magnetite, bismuthinite, molybdenite, and native gold; pyrite and chalcopyrite are the most abundant. The highest gold value reported by Wenz (2004, 2005) is 20.8 parts per million (ppm). Both bismuth and tellurium correlate closely with gold. Primary fluid inclusions indicate a wide range of homogenization temperatures of from 221 to 486 degrees centigrade and the salinities vary from 21.3 to 54.7 weight percent NaCl.
Tonogold Resources, Inc. has a mining lease agreement with Calista Corporation covering the Nyac area (Tonogold Resources, Inc., 2006). They completed detailed soil geochemical surveys in several areas including this prospect in the summer of 2005. Tonogold reported that 58 of 518 surface samples contained 0.105 to 2.86 ppm gold. Seven rock chip samples contained 0.121 to 15.1 ppm gold. There is a strong correlation of bismuth and gold values in these samples. Arsenic values are low.
Tonogold (2007) drilled 4 holes at the Bonanza prospect in the summer of 2006. The drilling encountered a series of quartz-calcite-pyrite-chalcopyrite veinlets associated with an aplite dike in sericitically-altered granodiorite. The alteration increases downward in each of the holes. Numerous veinlets and mineralized fractures were cut; there were several 2-meter intercepts with up to 1.0 gram of gold per ton and the best intercept was 0.6 meter with 8.6 gram of gold per ton.
Since at least as early as 2009, Nyac Gold LLC has been operating summer exploration programs on behalf of Calista Corporation (Flanders and others, 2009).
In 2009, Nyac Gold LLC completed prospecting and drilling at VABM Bonanza. This work resulted in identifying various mineralized breccias that were tentatively interpreted to result from breccia-hosted or porphyry-style gold mineralization (Flanders and others, 2009). In 2010, Nyac performed reconnaissance prospecting and drilling at VABM Bonanza. The prospecting generated additional understanding of the plutonic rocks and their contacts in the areas, while the drilling resulted in identification of gold mineralization subsurface (Flanders and others, 2010).
Geologic map unit (-159.8476038915, 61.072168389033)
Mineral deposit model Low-sulfide Au-Bi-Te-quartz veins.
Age of mineralization The Bonanza pluton that hosts the deposit is 109 to 113 Ma (Wenz, 2004, 2005). Wenz also reports a Ar-Ar age of 111 +/- 1 Ma for muscovite from a gold-bearing quartz vein in the Bonanza pluton.
Alteration of deposit The gold-bearing quartz veins are accompanied by envelopes of sericite-chlorite-carbonate alteration. These veins and alteration overprint earlier quartz veins with some narrow K-feldspar-bearing alteration selvages (Wenz, 2005).

Production and reserves

Workings or exploration
Tonogold Resources, Inc. has a mining lease agreement with Calista Corporation covering the Nyac area. They completed detailed soil geochemical surveys in several areas including this prospect in the summer of 2005. Tonogold drilled 4 holes on this prospect in 2006.
Since at least as early as 2009, Nyac Gold LLC has been operating summer exploration programs on behalf of Calista Corporation (Flanders and others, 2009).
In 2009, Nyac Gold LLC completed prospecting and drilling at VABM Bonanza(Flanders and others, 2009). In 2010, Nyac performed reconnaissance prospecting and drilling at VABM Bonanza (Flanders and others, 2010).
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Flanders, R., Hall, W., Wilkinson, S., 2009, 2009 Drilling and Exploration for Lode Gold Deposits in the Nyac District, Southwest Alaska, Private Report.
Flanders, R., Hernandez, D., Seals, J., Proffett, J., Van der Poel, W.I., Minehane, D., 2010, 2010 Drilling and Exploration for Lode Gold Deposits in the Nyac District, Southwest Alaska, 123 p. (Report held by Calista Corporation, Anchorage, Alaska).
Strachan, D. G., 2005, A summary and interim status report on Tonogold's 2005 geochemical exploration of the Nyac gold district, southwest Alaska: Private report for Tonogold Resources, 20 p. (Available online at: http://www.tonogold.com/i/pdf/2005_Final_Report_5m[1].pdf).
Tonogold Resources, Inc., 2006: http://www.tonogold.com/s/Nyac.asp (as of April, 2007).
Tonogold Resources, Inc., 2007: http://www.tonogold.com/s/Nyac.asp (as of April, 2007).
Wenz, Z. J., 2004, Geology and gold mineralization of the Nyac district, southwest Alaska: MS thesis, University of Alaska, Fairbanks, 133 p.
Reporters Travis L. Hudson (Applied Geology, Inc.); D.J. Grybeck (Port Ludlow, WA); V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 12/20/2014