Kensington mine

Coordinates: 58°51′53″N 135°04′54″W / 58.86472°N 135.08167°W / 58.86472; -135.08167

Location of Kensington Mine Lease and the defunct Jualin Mine.

Aerial view of a portion of the mine in May 2015.

Berners Bay map with the location of the Kensington Mine, "8", and Jualin Mine, "1", relative to other mines in the area.

Kensington mine is a gold mine located 45 mi (72 km) north of Juneau, Alaska.^[1] The present mine is owned by Coeur Alaska Inc., a subsidiary company of Coeur Mining.^[2]

Disambiguation: The Kensington mine has dual operational timeframes and locations. The historic workings exist near the top of the ore body, about 2000 feet and more above sea level. These workings were mined in the early 1900s, while the modern Kensington mine accesses the ore body 1,100 feet deeper and is advancing up and down from that point, eventually reaching the historic workings sometime in the late teens of 2000.

The Current Kensington Mine consists of a land package that stretches from Slate Creek Cove in Berners Bay, over Lions Head Mountain, and west to Comet Beach on Lynn Canal. The property is divided into two primary parts, with the northern and western portions generally described as the Kensington side, and the southern and eastern portions belonging to the Jualin side, as referenced to the historic Jualin Mine.

The first recorded gold production from what would eventually become the Berners Bay district came from the Northern Lights claim on the Johnson vein in 1887. By the early 1900s, numerous other gold-bearing quartz veins had been discovered and mined. These included the Ophir, Bear, Kensington, Horrible, Ivanhoe, Northern Belle, Comet, Johnson, and the Jualin Mine. Intermittent production continued until the late 1920s when organized mining of the Jualin Mine ceased. Attempts were made to revive the Kensington and Jualin mines during the 1930s with little success, and the district became completely inactive by the beginning of World War II.

Historic recorded production from the district (prior to cessation of activity in 1928) is estimated at nearly 137,000 tons containing about 61,000 ounces of gold. Most of this came from the Comet and Jualin mines which produced 22,500 and 36,000 ounces gold, respectively. The Kensington mine (historic) produced approximately 2,600 ounces. Average grades ranged from 0.3 oz/t for Kensington to 0.6 oz/t for Comet and Jualin.

The Kensington mine was subsequently acquired by Alan Wright in the early 1960s and optioned to Homestake Mining Co. for the 1980 field season; it was then optioned to Placid Oil Company from late 1980 through 1985. Their efforts resulted in identification of significant gold mineralization in the upper levels of the Kensington deposit.

Coeur Alaska Inc. acquired the property from Placid in 1987 and formed the Kensington Joint Venture with Echo Bay Mines. The Kensington Joint Venture, with Echo Bay as operator, brought the project to a feasibility-study level by 1993. The project was then placed on care and maintenance due to declining gold prices. Coeur Alaska Inc. acquired total control of Kensington in July 1995 by purchasing Echo Bay’s 50% interest. By 1997, Coeur had redefined the project, completed another feasibility study, developed an endorsed reserve, revised engineering studies and cost estimates, and completed permitting. Gold prices continued to decline, however, making the project economically unattractive at the time.

Coeur undertook an extensive exploration program in 1998 to define additional mineral resources directly adjacent to the main deposits. The program added nearly 300,000 ounces of gold to the mineral resource base.

Nearby exploration interest in Jualin was renewed in 1978 when Hyak Mining Company located claims covering the core of the vein system. Bear Creek Mining Company explored the property during 1983 and 1984 under a lease agreement with Hyak. Bear Creek terminated their lease in 1984. The property remained idle until 1987 when Hyak optioned it to International Curator Resources. Curator staked additional claims and drilled additional core holes. Results were encouraging enough to warrant a decision to build an access road from Slate Creek cove to the historic Jualin mine portal. Curator joint ventured the project with Granges, and road construction commenced in June and was completed during August 1988.

Placer Dome U.S. Inc. joined the Curator-Granges joint venture in June 1989 to continue exploration of Jualin. Placer explored the property between 1989 and 1991, and returned the property to Curator-Granges at the end of 1991. During 1992, Curator continued exploration of Jualin and completed additional geochemical sampling and geophysical surveying.

Coeur Alaska, Inc. entered into a joint venture with Curator during June 1993 whereby Coeur could earn a two-thirds interest in the property. An exploration program was initiated in July, and by September additional in-fill geochemical sampling, re-logging of selected core-hole intervals, and district-scale aerial photography had been completed. Surveying and aerial photography which tied the Jualin and Kensington properties to common survey control and to the Alaska State grid was completed. A new topographic map of the area between Slate Creek Cove and Independence Lake (north of Kensington) was completed during early 1994. Coeur acquired 100% interest in the property from Curator during 1994.

Coeur Alaska^[2] undertook an extensive exploration program in 1998 to define additional resources adjacent to the main deposits, with subsequent exploration, feasibility and design work ongoing until 2005. Mine construction began in 2005, with nearly all surface facilities except the tailings disposal facility completed by 2007. There was also extensive underground lateral excavation taking place in 2007 (approximately 13,400 feet) which connected the east side of the mountain (Jualin side) with the west side of the mountain (Kensington side) driven from both sides of the mountain concurrently. One side was driven by Coeur personnel, and the other by contractors. Subsequent mining infrastructure was also put in place at this time with the intent to begin mining in 2008.

When construction work began after Coeur received its final construction permits in 2005, including the use of the Slate Lake drainage as a location to dispose of tailings created by the milling of ore from the mine in order to handle waste disposal. The work required a permit, which was acquired in 2005 from the United States Army Corps of Engineers to dispose of the tailings in Lower Slate Lake.^[1] Construction of the tailings facility was halted however, as following the issuance of the permit for tailings disposal, a lawsuit was filed by a group of environmental non-governmental organizations. The Alaskan court sided with the mining company, and the decision was appealed and overturned by the United States Court of Appeals for the Ninth Circuit. Following the successful appeal, the issue was brought before the Supreme Court, who found in favor of the company by a vote of 6-3.^[3]

Construction on the Tailings Treatment Facility resumed in 2009 after the US Army Corps of Engineers Section 404 Permit was reinstated following a decision by the US Supreme Court. In 2010 the camp facilities were upgraded with permanent sleeping quarters and dining facilities, and the mine and mill brought into production. Between 2010 and 2012 the camp facilities were further upgraded, the assay lab built, an additional dormitory constructed, a new administration building completed, the underground paste backfill plant and shop built and commissioned, the water treatment facilities upgraded, and numerous other smaller projects were completed in the mine and on the surface. Full production began in June 2010, with the mine processing approximately 1,500 short tons of ore per day, and with subsequent upgrades, and improvements processing capacity has increased up to approximately 1,750 short tons per day by 2015.^[4]

The camp has a capacity of just over 300 people, with full facilities for sleeping, eating, laundry, and recreation. There are spectacular views, and while the weather is not always the most complimentary, the scenery is always beautiful.

References