International Dredging Review

International Dredging Review

Equipment fabricator Pacifica has delivered a custom dredge for mining gold on a lease off the coast of Nome Alaska. The catamaran-style vessel is designed to work within a mile offshore in a maximum of 20 feet of water. Dredging is done by a diver operating a suction hose.

Pacifica is headquartered in Seattle Washington. Naval architect Art Anderson Associates (AAA) of Bremerton Washington designed the dredge.

AAA’s naval architects and marine engineers began by preparing a computer-generated model of the vessel based on concept drawings which formed the basis for initial hydrostatic and weight calculations. In Phase II of the project the designers developed construction drawings for the hull and superstructure and finalized the weight and stability calculations. In the project’s final phase the team provided fuel water and controls design assistance along with support for deployment.

The vessel was designed specifically to meet the unique requirements of dredging in the remote coastal waters of the Bering Sea. It features a custom-designed bow for cutting through the rough seas and all pump sluice and crane systems to conduct its gold dredging mission.

“This was a fun project in that we were able to learn quite a bit about the gold dredging business the unique equipment involved with it all while applying the engineering skills we enjoy” said Ben Anderson naval architect and project manager for AAA.

The gold in Norton Sound has been arranged by the current and geography over the millennia into low-lying areas or by the current in lines Rod Gleysteen of Pacifica said. The diver can see it and see where it is leading An experienced diver is a great asset he said.

The deposits may be covered by one inch to three feet of overburden so the diver must be able to locate the gold remove the overburden with the suction and then dredge the gold where it rests on or is embedded in the clay bottom. The gold is fine – two millimeters or a sixteenth of an inch at most – a size known as flour gold.

A crew of two operates the dredge – a diver who operates the suction underwater and a tender on the surface who monitors the pump suction and sluice box. The diver is equipped with a communication system for safety.

The material is delivered to a sluice box on deck containing a proprietary set of riffles that trap the gold. Gravel and other oversized material flows back over the side. The sluice box is 18 feet long and 40 inches wide with an open top.

The dredge is a catamaran design 50 feet long by 16 feet wide and built on 36-inch diameter round pontoons. A short 15-foot center pontoon provides stability and supports the wheelhouse. A raised forward platform gives the operators space to deploy into the water. All construction is with marine grade aluminum. The wheelhouse includes an enclosed marine head two bunks and a galley and a secure location for storing the gold.

Propulsion is by two 300-horsepower Yamaha outboards. The dredge has a full electronic package with Garmin chart plotter Garmin GPS radar and sidescan sonar all integrated by the customer.

The dredging unit is a Venturi pump system using a 40-foot long 10-inch diameter suction line driven by a four-cycle turbocharged Perkins diesel attached directly to a Berkeley centrifugal pump. The suction line is reinforced Kanaflex vinyl.

Two 100 to 150-pound fluke anchors hold the vessel in position during dredging and are raised and lowered by winches.

Besides the 50-foot dredge it built for a customer Pacifica has built two dredges for its own gold mining operations. The company holds eight near-shore leases in Norton Sound and operates two catamaran dredges of the same design as the new 50-foot dredge. One is 40 feet long and 14 feet wide and used for mining while a smaller 20-foot dredge is used for locating the deposits ahead of the larger dredge.

Pacifica and its customer are participants in a project that is allowing dozens of companies and individuals to continue Alaska’s gold dredging tradition.

Alaska DNR Holds Auction
On September 28 2011 the Alaska Department of Natural Resources (DNR) held a competitive auction of 84 offshore lease tracts comprising 23793 acres in Norton Sound near Nome. All the tracts were sold for a combined total of $9.3 million. Fifty-three near-shore tracts were sold in an outcry auction with 70 registered bidders participating bidding from $10000 to $90000 for parcels of from 40 to 60 acres. Thirty-one tracts in deeper water (up to 60 feet deep and extending to the edge of the three-mile offshore limit of Alaska land) were auctioned by sealed bid. These tracts are more than 160 acres each. After the outcry portion of the auction 111 sealed bids were opened and represented a total of $7.7 million in bids. The largest single tract Number 74 with an area of 2794 acres sold to AngloGold Ashanti for $1.6 million.

The leases are for 10 years with a renewable option.
AuruMar (Pty.) Ltd. is a technical services company that was established by AngloGold Ashanti and De Beers in October 2009. In the 2011 auction the joint venture acquired 26 of the 31 offshore tracts on offer ending up with leases that total 16800 acres.

Asked what type of dredging equipment his company would be using on the deposits Gary van Eck general manager of AuruMar told IDR on January 18 “We are currently finalizing and reviewing our concept study with our shareholders and so cannot yet provide you with a description of the type of mining equipment that we intend deploying in the placer marine mining leases offshore Nome.

We have however looked at a wide range of options and sizes suitable for operating in these waters. We will not be mining this summer but will continue exploration and sampling activities. Apologies for the brevity of response but once a mining concept has been selected we will be able to provide more meaningful information.”

AuruMar is headquartered in Cape Town South Africa and manages the technical and operational aspects of the joint venture’s projects which focus on exploring for gold and other heavy minerals on the continental shelves of the world. For its Nome project AuruMar maintains offices in Anchorage and works with local companies for permitting and environmental studies. Permits must be received from the Alaska Department of Fish and Game the DNR and the Corps of Engineers.

The Bima Story
AuruMar’s deliberate and thoughtful approach is understandable when remembering the experience of the only other sizeable gold dredge to work in that area.

Many in the dredging industry recall a dredge named Bima operated by Inspiration Gold in the 1980s that illustrated the risks presented by the treacherous wind wave and ice conditions in Norton Sound.

The Bima was an Indonesian tin mining dredge built in the 1970s to work in the Riau Archipelago. It was a 12000-ton bucket ladder dredge that was 565 feet long worked with a chain of 137 30-cubic-foot steel buckets had a superstructure that was 14 stories high and was stabilized by 81 tons of anchors. Inspiration Resources purchased the Bima in 1985 for an estimated $4 million and towed it to the U.S. They tested it successfully off the coast of Nome in the summer of 1986 towed it to Seattle for a $15 million modification for gold dredging and returned it to Nome in June 1987.

That year Inspiration Resources Corp. of New York and Luxembourg-based Minorco formed a limited partnership named Western Gold Exploration & Mining Co. LP (WestGold) who continued as owners of the Bima until it closed the operation down after the 1990 season.

Dennis Josephson a well-known West Coast dredgeman was manager of the operation. The dredge produced 36700 ounces of gold in 1987 10000 ounces short of the company’s expectations. At $450 an ounce the take was more than $15 million. Josephson told a reporter that “weather has been our big problem.” The waters off Nome didn’t thaw enough to permit work until mid-June and the Bering Sea is a notorious storm cradle forcing the dredge to close down for several full days when wind and waves made dredging impossible.

In 1988 the dredge produced only 35500 ounces and the price of gold dropped $30 an ounce causing the company to lay off 30 of the 124 workers on the dredge. The dredge shut down in 1990 after producing 126924 ounces of gold in five seasons only two of which were profitable.

Today people who worked on the project aren’t sure exactly what went wrong with the dredge but speculation ranges from hull damage by ice and rough seas to a broken drive shaft.

DNR Designates Public Mining Tracts
Because of the widespread interest in gold dredging in the area Alaska DNR set aside two areas for public use.

Members of the public can operate recreational gold dredges in these areas after obtaining a permit and must conform to strict rules such as staying out of the private leases and maintaining a certain distance from other dredges.

After the lease sale the Discovery Channel launched a reality series called Bering Sea Gold which gave the mistaken impression that anyone could obtain a gold claim in the Bering Sea. The DNR announced that it had received inquiries from viewers of the series asking about obtaining a claim.

“Regardless of what the Discovery Channel Series may convey” the DNR stated “gold claims in the Bering Sea are not available for the public to acquire. The only areas for the public to mine are two recreational mining areas. These areas have limitations however and can only accommodate recreational dredges.”

Sources for this story included the Alaska DNR Public Information Office Anchorage Daily News Art Anderson Associates Mining News The Nome Nugget North of 60 Mining News Pacifica and The Wall Street Journal.