Yukon innovation increases gold recovery for placer miners

Yukon is home to a new innovation that has the potential to benefit placer miners around the world. Randy Clarkson, of Klondike Placer Miners’ Association has developed a simple method of removing fine gold particles from difficult concentrates in an economical, lucrative and environmentally-friendly way.

After two years of research, prototype development and field testing, Clarkson is able to upgrade difficult gold concentrates by taking advantage of the malleability of gold. This technique uses a small rod mill to grind the brittle waste minerals to powder in a few minutes while only flattening gold particles. The ground slurry is then washed through a fine screen capturing the flattened and polished gold particles.

“This method allows us to recover fine gold particles from labor intensive concentrates that are normally considered a waste to time, and apparently a waste of gold”, said Randy Clarkson, P.Eng., Klondike Placer Miner Association. “This technique recovered between 5 and 10 ounces of gold per day of testing this summer at a profit of over $5,000 per day – from concentrates that would normally be left behind”, said Clarkson.

Many Yukon placer miners have been storing these difficult concentrates on site in coffee cans, peanut butter jars and other containers for years waiting for an efficient method of upgrading to be developed. Previously the concentrates would have to be sorted by hand, one by one, a tedious and very time consuming process.

“This simple but effective method of separating gold particles from galena particles using a small rod mill and screens has allowed me to process concentrates that I have had in storage for some time. I didn’t want to throw them out because they still have gold in them and I don’t have the time to hand sort each particle”, said Claus Barchen, a placer miner from Mayo.

The procedure has been tested on many types of gold concentrates including those with high density minerals such as galena (mineral containing lead), cassiterite (tin), hematite (iron), illmenite (iron) and pyrite (fool’s gold) as well as more durable minerals such as garnet (used in sandpaper). The cleaned concentrates are generally 97% or purer native gold and are suitable for direct sale to a gold buyer.

The small rod mill can also be used to grind up gold furnace slag to recover any lost gold from smelting and to regrind concentrates which have become cemented together due to oxidation of the contained minerals. A small rod mill can be fabricated locally using a piece of steel pipe, rolled rods and an adapted portable cement mixer for a total cost of less than $2000.

A small shaking table with a magnetic separator (~$3500) was also demonstrated to pre-concentrate the difficult gold concentrates prior to grinding (if desired) and to separate out magnetic material such as magnetite and bits of iron more quickly than with hand magnets.
The concentration process does not use any chemicals or substances harmful to the environment and would have applications in any placer or hard rock gold mine using gravity recovery techniques such as sluiceboxes or centrifugal concentrators. It could also be used in the developing world at artisanal mines to help eliminate any harmful chemicals used to upgrade gold concentrates.
Clarkson will be making this technique available to all placer miners through a final report which will be available at the KPMA office and on the Yukon Geological Survey Website. This summer, a number of placer miners used this technique with great success. Clarkson will not be commercializing this innovation as he intends to share his work with those who will benefit. He will also be demonstrating the technique and equipment at the Placer Geoscience Forum on Sunday, November 16th at the Gold Rush Inn and later in the week at the Geoscience Trade Show.

The research was funded by contributions from CanNor's Strategic Investments in Northern Economic Development Program, Economic Development’s Strategic Industries Development Fund, the Cold Climate Innovation of the Yukon Research Centre at Yukon College, and the Klondike Placer Miners’ Association. The KPMA would like to thank the funding agencies and all the miners that participated in the research program.

Background -Yukon Placer Mines
Placer mining has been a cornerstone of the Yukon’s economy and culture since the great Klondike Gold Rush of 1898. Placer mining is responsible for the accelerated early development of northwestern Canada. The industry has been the Yukon’s most reliable generator of economic wealth and has continued unabated through the great depression of the 1930’s and recent economic recessions. In recent years placer mines were the only operating mines in the Yukon.

Currently there are over 100 family based placer mines with a combined gross income in excess of $60 million annually. Spin off benefits to the local economy are in the order of 2.5 times that amount with local labor, purchases of fuel, equipment, parts, groceries and other supplies. Placer mining is especially vital in the Yukon’s rural areas including Dawson, Mayo and Haines Junction. Most of the recent “gold rush” (2010-2012 with total annual exploration at $150 to $300 million) to explore for lode gold mines is based on the presence of placer mining in those areas.

Typical placer mines range from small Mom and Dad operations to those employing a dozen workers and several of the largest available sizes of heavy equipment. Placer mines are heavy equipment intensive resource industries. The next greatest concentration of large scale heavy equipment (D11 bulldozers) would be found several hundreds of kilometers southeast in the Alberta oil sands mega projects.
Background - Placer Gold
Placer gold ranges in size from finer than 74 microns (200 mesh) to coarse nuggets depending on the source of the gold, size and gradient of the stream and many other factors. Sluiceboxes are the primary means of concentrating the low grade alluvial gravels and can provide relatively efficient concentration (in excess of 95% recovery efficiencies) at high ratios of concentration (20,000:1).

These primary sluicebox concentrates must be upgraded to a purer saleable product. Secondary concentration methods generally include long toms (small sluices), hydraulic jigs, hand panning, hand-held magnets and hand sorting. Many of the secondary concentration methods are very labor intensive, arduous and result in some gold losses. Often the tailings from secondary concentrates are stored in buckets for years awaiting time-consuming hand sorting methods. Extended periods of hand sorting of gold concentrates also pose a security risk to placer miners.

In recent years due to the depletion of higher grade reserves and due to higher gold prices, the industry has focused on mining and processing lower grade deposits (side pay), deposits with fine gold and other accessory minerals, and on reprocessing tailings from previous operations.

As mining has progressed in the Klondike, the placer industry in Yukon is faced with lower grade ground and areas with fine gold and with reprocessing tailings to recover gold that was lost in previous mining eras. Many of the sluicebox concentrates contain very fine -74 micron, -200 mesh) flattened particles in a mixture of high density minerals such as galena, hematite, illmenite, magnetite, scheelite, wolframite, cassiterite, pyrites and phyrhotites.

Separation of both the coarser >1 mm and fine <150 micron particles can be tedious and problematic. Generally the coarser gold sizes are hand-picked. Magnetic minerals such as magnetite and tramp iron are removed with hand held magnets. In the Yukon and Alaska, the finer gold particles are processed in small sluices, concentrating tables and gold wheels, often with gold losses.