Pogo

Overview

Pogo gold mine is a conventional underground mine located 145 km southeast of Fairbanks, Alaska, USA.

In 1981, WGM Inc. had conducted stream sediment sampling in the Goodpastor River area and had identified Au, As and W anomalies in Pogo and Liese Creeks, creeks with no history of serious placer mining.  Follow up exploration identified the gold deposit. In July 2009, Teck Cominco sold its 40% interest in the mine to the Sumitomo Group.

The mine is presently expected to produce 350,000 and 500,000 ounces of gold per annum over a 10-year mine life. The underground mine and surface mill commenced production during the first quarter of 2006. Commercial production was reached in April 2007.

In 2012, successful exploration programs identified new gold resources within the mine lease area which could extend the mine life to 2020. 

Location

Pogo mine is located 145 southeast of of Fairbanks, Alaska, USA.

Located on state land in the upper Goodpaster River valley 85 miles east-southeast of Fairbanks and 40 air miles (64 kilometres) from Delta Junction at the terminus of the Alaska Highway, the Pogo property is approximately 16,700 hectares in size. The mine area is the subject of a mining lease, which requires annual rental payments. The balance of the property is comprised of 1,281 State mining claims, each requiring a specified nominal amount of annual assessment work.

The mine complex is situated on the Goodpaster River and includes includes a mill, camp, dry stack tailings pile, waste rock dumps, recycle water tailings pond, an airstrip, gravel pits, laydown and fuel storage areas, and a local network of roads.

Current access to the region is by the Goodpaster Winter Trail in winter, and by boat in summer. Human habitation is limited to recreational and remote homesteads located on the lower Goodpaster.

Very little historical placer mining occurred in the Goodpaster region, and prior to the Pogo discovery, there had been little hardrock mineral exploration.

The Goodpaster region is also within the range of the Forty-Mile Caribou herd, and has good moose, bear and wolf habitat.

Geology & Mineralization

The Pogo claims are underlain by high-grade gneisses of the Yukon-Tanana terrane which have been locally intruded by granitic rocks. Common rock types include biotite gneiss, augen gneiss, mafic schist and gneiss, pelitic schist, quartzite and quartzo-feldspathic schist.

The gold deposit occurs as two "stacked" shallow-dipping quartz vein systems, generally 4 to 12 meters in thickness, named the "L1" and "L2" lenses. A third vein system has been encountered at depth, but requires additional drilling to determine its significance. The "L1" and "L2" veins are dominantly quartz with approximately 3% sulfide minerals. Approximately 96% of the gold occurs as free gold. 

The quartz, which appears to be both vein-fill and replacement in origin, contains approximately 3% ore minerals, including pyrite, pyrrhotite, loellingite, arsenopyrite, chalcopyrite, various bismuth minerals and gold.  The mineralized intervals contain elevated Ag, Te, Bi, As, Sb, Cu, Pb, Mo and/or Co and exhibit a strong correlation between Au and Bi.

The deposit is interpreted to be a deep-seated manifestation of an intrusion-related gold deposit.

In March 2012, the company announced the discovery of a new gold deposit located some 1,000 feet northeast of the main Liese gold deposit which is estimated to hold 1.2 million ounces gold.

Total reserves and resources as of March 2012, were estimated at 12.3 million tonnes at 12.45 g/t gold for 4.9 million ounces gold (new East Deep deposit resources included).

Mining & Operation

The ore is extracted using conventional underground mining techniques. The mine is accessed by three declines: two are used for worker/material access and ventilation, the third for conveying the ore to surface. The ore is mined by a method called "drift and fill" in which a horizontal drift (ranging from 9' x 9' up to 12' x 12') is driven though the ore and then backfilled with cemented fill before the next cut is taken. The ore is then hauled to a central underground bin, from where it is conveyed to the surface mill.

As the main mine workings are underneath the Liese Creek water infiltrates the mine and has to be pumped out not before being treated in an underground facility.

A new access drive is to be built in 2012 to access the newly identified East Deep deposit.

Processing

Pogo run-of-mine ore is brought to the surface via conveyor, then ground in a SAG-ball mill circuit. The circulating load is fed to a gravity circuit where approximately 60% of the gold is recovered. The cyclone overflow feeds a sulphide flotation circuit, with the concentrate reground before cyanidation. The slurry is then passed though a carbon-in-pulp circuit. The gold recovered in the gravity circuit as well as the gold stripped from the carbon is smelted into bars. The gold dore is then shipped to an off-site for further refining. 

The mill treats 2,500 tpd to produce 1,000 ounces of gold per day.

The flotation tailings that have not come into contact with cyanide are pressure-filtered and placed into a dry stack storage area or used as part of the backfill. Tailings that have run through the CIP circuit are detoxified using a multi-step process, which involves decanting and recycling the majority of the cyanide solution, and chemically breaking down the cyanide in the remainder. The detoxified tailings are mixed with cement and placed underground as cemented pastefill. Approximately 50% of tailings are being returned to underground as fill for the mine workings.

All precipitation and mine drainage from the mill, camp, shop, site roads and tailings is collected and treated in an on-site water treatment plant, before being discharged into large mixing ponds constructed adjacent to the Goodpaster River. All water is tested to ensure compliance before being released to the river.

Environment & Community

In an effort to bolster the local economy the mine has entered into a Payment in Lieu of Taxes Agreement with the community of Delta Junction located 64 kilometers southwest. Under the agreement, payments of US$1.25 million will be paid to the town anually for a period of 3 years. 

The United States is the world's leader in the introduction of environmental assessments, and Alaska has many national parks and wildlife refuges with very stringent environmental protection standards requiring 83 separate permits. Sumitomo recognized that coexistence with the environment and relating to local residents were essential in the mine's development, which led Sumitomo to conduct a full environmental review from the design stage. This is the only gold mine employing unique processes others cannot realize. Sumitomo also held open forums with local residents to gain their understanding of the critical efforts we were making for the environment.

At the end of the mine life the mine would be closed, sealed and the mine site reclaimed.