Mining News: News Nuggets: DGGS finds undocumented gold, copper occurrences south of Tok
Alaska Division of Geological & Geophysical Surveys March 10 published a preliminary report on mineral occurrences observed during a 10-day preliminary geologic reconnaissance of the Tok River area in preparation for a proposed 2016 mapping project. This work included sampling of Hona, a gold-copper target about 17 miles southwest of the community of Tok; a previously undocumented lode gold occurrence about five miles southwest of Hona; and a placer deposit about 3.5 miles to the east. Hona, also known as Noah, was drilled by Kennecott Exploration in 1998. These holes intercepted quartz schist and porphyritic intrusive rocks, and well-developed breccias contain rounded clasts of schist and altered intrusive rocks. While results from this drilling have not been published, representative samples from the core can be found at the Geologic Materials Center in Anchorage. DGGS geologists identified a roughly 1.5-mile-wide complex of variably altered porphyritic granodiorite dikes and sills that intrudes quartz schist in the area of Hona. Portions of this intrusion carry up to several percent disseminated pyrrhotite and pyrite replacing mafic minerals. A grab sample collected from a 2.5-meter band of such mineralization returned 0.129 parts per million gold and 1,430 ppm arsenic. While the associated intrusion appears to be shallowly emplaced and has porphyritic to porphyry textures, DGGS sampling shows little copper and indicates levels of arsenic, bismuth, tellurium and cobalt that are significantly more enriched than typically would be found in a normal porphyry copper deposit. The deposit model for Hona is intrusion-related gold or porphyry copper-gold. A lode gold occurrence that has yet to be assigned an Alaska Resource Data File number also was identified during the 2015 DGGS program. About three miles east of the confluence of the Tok River with Natohona Creek, geologists observed a zone of gossanous-weathering altered and sheared igneous rocks crossing a ridgeline. A sample of brecciated and silicified rock collected from this 33-foot-wide zone assayed 1.3 ppm gold, 2.19 percent arsenic, and 352 ppm antimony. DGGS believes the mineralization may be Late Cretaceous in age, based on trace-element similarities to Hona and the Peak skarn gold-copper deposit, located slightly more than 20 miles to the east. At the placer deposit, situated on a creek draining east from Hona, a DGGS geologist panned seven ragged, 0.1 millimeter gold grains and 15 smaller ones in two pans collected from the edge of a cut from previous mining. Mining has only been carried out on a small portion of this creek. DGGS has identified the Tok River area as an underexplored area with potential to host deposits of gold, silver, zinc, and copper. “It’s an interesting area and it has only limited geological data- just the kind of place where DGGS can make a difference,” Evan Twelker, mineral resources geologist, DGGS, said in an email. Work on the area began with airborne geophysical surveying in 2014 (published in 2015) and continues this summer with a four-week geologic mapping project. The preliminary report is available in printed format at the Fairbanks DGGS office (3354 College Road), and can be downloaded at http://dx.doi.org/10.14509/29605.
- Shane Lasley
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