The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
Freegold begins first full season of bulk sampling at Interior property; gravity-plant upgrades may produce higher recoveries
Freegold Ventures Ltd. has started its first full season of bulk sampling at the Golden Summit property outside of Fairbanks with an upgraded version of the gravity-based gold recovery plant first used last fall.
The recovery plant was delivered to Golden Summit late summer 2007 and was put into operation in September, giving the company about four weeks to test-drive the plant before temperatures were too cold to continue operations.
Over the winter the Vancouver B.C.-based junior analyzed what it learned from the month of processing ore and conducted metallurgical tests in order to optimize recovery rates and improve the quality control of the bulk samples taken from the property.
A close-spaced shallow drill program also continued throughout the winter and a 15,000-foot core drilling program began in March to evaluate the potential for deeper gold mineralization in areas where high-grade vein mineralization has been identified with shallow, close-spaced drilling and surface bulk sampling.
Smaller size key to larger recoveries
Freegold learned through last fall's operations and metallurgical tests that significantly higher gold recoveries could be expected if the recovery plant was fed with smaller-sized material. In response to this information, the company purchased several components to increase the crushing capabilities of the plant.
A total of 17 samples with head grades ranging from 2.9 grams of gold per metric ton to 44.6 g/t gold were tested over the winter. The samples were crushed to various sizes using a laboratory scale ball mill crusher and were then run through a 4-inch concentrator, a laboratory scale version of the one being used for the bulk sampling. The tests concluded that an 85 percent to 90 percent recovery could be achieved with a relatively coarse grind - 65- to 80-mesh.
The tests also indicate that by regrinding the rougher concentrates and feeding them through a primary concentrator a direct smelter concentrate could be produced from the plant.
New crushers added
A portion of the additional equipment needed to optimize recoveries was found at a mill site about 15 miles away from Golden Summit. Freegold purchased several pieces of equipment from the 500-metric- ton-per- day mill - including a 4 by 4-foot and 4 by 8-foot ball mill, a 2 by 3-foot regrind mill, plus miscellaneous hydro-cyclones, slurry pumps, motors, conveyors and tanks - which have already been dismantled and moved from the plant site and incorporated into the bulk-sample plant.
The company also purchased a new closed-circuit cone crushing plant to be used in a secondary crusher. The plant has a 6 by20-foot triple-deck screen and conveying system. The material passing through a 65-mesh screen will be fed directly into the recovery circuit and the oversized material will be fed into the 4 by 8-foot ball mill, which is expected to reduce more than 80 percent of the remaining material to a size smaller than 65-mesh. The material then will be fed into the recovery plant via a primary concentrator.
All of the components of the bulk sampling mill are modular and can be reconfigured in a matter of a few hours to optimize recovery rates to accommodate the various mineralized rock types. Ongoing tests are underway to determine the optimum configuration for each rock type that will be included in the bulk sampling program.
Upgraded plant ready for 68,500-metric-ton program
Freegold plans to process 68,500 metric tons of material during the 2008 summer season. Currently, there is 23,500 metric tons of material in five stockpiles. The additional 45,000 metric tons will be collected and processed from two cuts in the Beistline area, additional sampling from Fence 1, and a new bulk sampling area that will be opened up to test extensive shearing and stockwork veining discovered in the Tolovana area during 2007 drilling.
About 6,100 metric tons of material collected from the Beistline area in 2006 will be among the first samples processed in 2008. 2,850 metric tons of the material was collected from the vein system, an additional 3,250 metric tons of mineralized material was collected from the hanging walls of the vein.
In 2007 about 5,500 metric tons of bulk sample material was stockpiled from the Beistline area and about 7,000 metric tons was collected from the Fence 1 area. These larger samples are more indicative of the bulk metric tonnage mineralization present. These areas were close-spaced drilled prior to excavation; therefore, the samples can be compared against the grades predicted by the drill results.
About 3,500 metric tons of coarse tailings from the one month of bulk sampling in 2007 will be used to test the upgraded bulk sampling plant. The operation last year crushed the material to about quarter-inch size; the crushing capabilities of the implemented upgrades will allow additional gold to be recovered. The oversize tailings will make ideal feedstock to test the new circuits added to the plant.
Freegold President and CEO Steve Manz told Mining News the final upgrade components to the gravity plant were set in place during his June 11 visit to the project and the first material was fed into the plant June 17.
The bulk-sampling program at Golden Summit will determine the continuity and average grades of gold mineralization within numerous gold-bearing shear zones discovered along about a mile of strike length over the past two years and the gold recovered will generate cash flow to help fund ongoing exploration.
Over his more than 16 years of covering mining and mineral exploration, Shane has become renowned for his ability to report on the sector in a way that is technically sound enough to inform industry insiders while being easy to understand by a wider audience.
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