Bonanza Ridge Prospect, Aniak Mining District, Bethel Census Area, Alaska, USAi

Regional Level Types
Bonanza Ridge Prospect	Prospect
Aniak Mining District	Mining District
Bethel Census Area	Census Area
Alaska	State
USA	Country

Location: 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. The location is accurate.
Geology: 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.
Workings: 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.
Age: 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: 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.

Commodities (Major) - Au
Development Status: No
Deposit Model: Low-sulfide Au-Bi-Te-quartz veins.

Other Databases

Link to USGS - Alaska:	RM037

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References