EXPLORATION ROUNDUP — Japanese explorer Sumitomo outlines large gold deposit in central Alaska

With assistance from Watts, Griffis & McOuat (WGM) and the Metal Mining Agency of Japan (MMAJ), Sumitomo has been exploring for the yellow metal in little-known parts of east-central Alaska. The fruit of their labors is the Pogo gold project, a significant discovery 20 miles east of the Delta Junction.

Jason Bressler, a senior geologist for WGM, describes the project as a grassroots geochemical discovery.

In the early 1980s, WGM conducted a regional reconnaissance program, collecting more than 6,000 soil samples. A decade later, in 1991, the company formed the Stone Boy venture, consisting of 12 properties, of which Pogo was one.

Early participants included Noranda and Hemlo Gold, though today the property is mostly held by Sumitomo. WGM operates the venture, with funding provided by the MMAJ.

Pogo comprises 750 state mining claims and is accessible only by air, though several winter trails wind through the area.

Based on 3,000 additional soil samples, WGM has defined a large gold-in-soil anomaly measuring 6,000 by 4,000 ft.

The property consists of sillimanite-bearing quartz feldspar gneiss, which has been intruded by the biotite granodiorite Pogo pluton. Gold mineralization is associated outside the main intrusive in a zone of numerous plugs and dykes.

The mineralization exhibits many similarities to the nearby Fort Knox gold deposit, most notably an association between gold and bismuth. And like Fort Knox, Pogo contains little in the way of base metals and is low in sulphides.

Indeed, the total sulphide content is a mere 3-5%, with arsenopyrite and pyrite being the dominant minerals. The age of the plutonic rocks, in both deposits, is about 90-95 million years.

Where Pogo differs from Fort Knox is in the way its mineralization is hosted.

Fort Knox, a low-grade, large-tonnage operation, is hosted in intrusive rocks, whereas Pogo’s mineralization exists as high-grade, flat-lying mesothermal quartz veins in gneissic rocks.

Fluid inclusion studies of the two deposits reveal another difference: Fort Knox formed about 1.4 km below the surface), whereas Pogo formed at a much deeper level — somewhere between 1.7 and 2 km below the surface. In this sense, Pogo can be said to be a more deeply eroded analog of Fort Knox.

Lisa quartz vein

The main body of mineralization at Pogo is called the Lisa quartz vein, though WGM is uncertain if the 35-ft.-thick structure is a true vein or, rather, a quartzite unit in the gneiss.

The structure contains significant gold values: One previous drill hole intercepted 22 ft. grading 1.83 oz. per ton, while another cut 79 ft. of 0.19 oz.

To date, WGM has drilled 38 holes at Pogo, totalling 37,000 ft.; 17 of these (20,000 ft.) were drilled this year.

The project area has virtually no outcrops; nevertheless, drill results have enabled WGM to assess the geometry of the deposit with considerable accuracy.

The company has located similar high-grade mesothermal structures in amphibolite grade gneisses, but, so far, none has been found to be as laterally extensive as Pogo.

Bressler says he believes WGM, Sumitomo and the MMAJ have found something totally new in an area where little else of significance has been reported.