The 1st Yukon Pilot Processing Plant
In 2016, Golden Predator completed its first bulk sampling program and built the 1st Yukon-based pilot processing plant. Golden Predator’s decision to begin bulk sampling at 3 Aces in the early stages of exploration was greatly influenced by the high-grade, nuggety nature of the gold mineralization found on the property. Known as “the nugget effect,” gold occurring in this manner is not distributed evenly throughout the deposit but is accumulated in clumps within the vein corridors. Initial independent metallurgical testing indicated gold recovery of over 80% with simple gravity and mechanical methods without the use of chemicals.
Golden Predator's Processing Plant, Pouring Gold
Golden Predator’s 2016 bulk sampling program at 3 Aces confirmed that the gold was “free-milling,” which only requires crushing rock into the size of silt grains followed by running it through a gravity circuit with water to separate the gold from the rock. With no existing processing plant in the Yukon and faced with the challenges of shipping bulk sample materials out of the Yukon, Golden Predator decided to build their own plant. The plant consists of a closed system, without any water discharge, and a gravity circuit using water and no chemicals. The plant is located off-site and has been connected to the electric grid. It is managed by a team skilled in engineering, metallurgy and operations. A Company-owned, Yukon-based pilot processing plant provides the ability to test recovery methods, cost controls, better manage actual recovery while benefiting local communities and retaining knowledge and technical skills.
The company’s 2016 bulk sampling program at 3 Aces recovered 953.4 troy ounces with an average gold grade of 46.18 g/t from 774 metric tonnes of rock. The gold recovery rate was greater than 85 percent using the chemical-free conventional gravity processing circuit.
In addition to being able to closely control and observe the test processing of the gold bearing rock by running its own plant, the Company is able to address the security issues of gold recovery with much greater control and confidence than by a third party. Furthermore, a closed circuit water-only test process may have ecologically friendly impacts on future permitting and potential commercial scale milling while retaining knowledge and creating community-based spinoff benefits.
Golden Predator's Bulk Sample Processing Plant
Pilot Processing Plant
After the initial bulk sample, the Company upgraded its processing equipment to optimize sample throughput and gold recovery. The new plant design and equipment provides better recovery, cleaner concentrates and an increased throughput of approximately 50 tonnes per day.
In 2017 Golden Predator conducted close-spaced Grade Control drilling in three areas in the central Spades Zone at the 3 Aces Project. Significant gold mineralization was encountered in 39 of the 43 holes. The three areas were drilled on grids with a 5 m spacing to compare results with observed gold grade from previous drilling, and as a more definitive estimate of grade for comparison against future bulk sampling. This process of reconciliation of bulk sampling against drill results is intended to accurately predict the returns that could be expected from a mining operation.
Programs of close-spaced drilling followed-up by bulk sampling are an integral part of the Company’s commitment to continuously evaluate the quality of drill hole assays, optimal drill spacing for resource delineation and optimal metallurgical recovery.
Bulk sampling at 3 Aces commenced in the Fall of 2018, with blasting completed and initial processing underway. The material will be processed at the pilot processing plant and results publicly released once necessary information on bench sampling and assaying is complete.
Bulk sampling as an exploration tool
Bulk sampling is an underutilized tool that provides critical technical information that establishes the amenability of any given type of mineralization to various recovery methods and also provides unique three dimensional insight into the structure, mineralization, and geometry of a mineral deposit that is not available through any other technique.
- A bulk sample gives you information about the actual and true grade of the ore on any project where drilling alone often does not. This is particularly true of higher grade deposits.
- You can choose one area or mix ore from several areas, depending on what kind of information you want to have from the explored area.
- A variety of technical information including geology, extractive metallurgy and mining engineering can be gained via bulk sampling; all necessary in reducing the risks of moving a project into commercial production.
Yukon Processing Plant
Frequently Asked Questions
- What is bulk sampling? Why did Golden Predator decide to use bulk sampling as an exploration tool?
Bulk sampling typically extracts tonnages ranging from hundreds of tonnes to as much as 100,000 tonnes and is a standard evaluation practice utilized throughout the world. In British Columbia some companies such as Pretium and Barkerville have conducted extensive bulk sampling. Bulk sampling provides necessary technical information to assess and reconcile drill-predicted amounts of mineralization as well as whether or not the mineral of interest (gold, silver, copper etc.) can be efficiently recovered. Further information critical to predicting future potential mining methods will be gained by observing the way in which various rock types break and shatter with the use of explosives as well as the quantity and density of blast holes and blasting agents.
In Golden Predator’s case we bulk sampled our 3 Aces Project in the Yukon in 2016 on a very small scale to determine if the gold present in the veins was recoverable from the enclosing quartz veins economically. This testing proved that the gold was “free-milling” requiring only gravity recovery methods and water. This process required no chemicals in order to achieve up to 90% recovery of the gold. Although free milling gold was not uncommon in the 1800s, most of it has already been mined making the 3 Aces project notable. The bulk sampling continued in 2018 with the extraction of an expected 6,000 to 7,000 tonnes from an adjacent area that had previously been drilled on close spacing (up to 5m x5m) and had been modeled to predict the distribution, grade and total gold content of the area sampled. During the next few months, we will be reconciling the actual gold recovered from the plant, on a bench by bench basis (the 2018 sample involved surface cuts each 2m high), and again as a total on all materials extracted, these results will permit us to verify or make necessary adjustments to our drill density and our modelling parameters.
The only true grade
Complex gold deposits are generally characterized by strong structural controls on grade distribution and often they have a pronounced nugget effect. The use of larger diameter diamond drilling, reverse circulation and fire assays in this environment help but are still subject to uncertainty of grade. Bulk samples are likely to be the closest estimators of true grade and may be required to evaluate true grade.
When doing a bulk sample, you take ore from certain places depending on what kind of information you want from the area you are exploring. You can choose to bulk sample only from one place to get the true grade in one area or you could choose to mix ore from different areas to get a broader estimate of true grade. Bulk sampling also gives more confidence to predict grade from drill holes.
In the final analysis nothing is more important than the actual recoverable ounces of gold available at a profit. The milled or recoverable grade is critical to this analysis.
Size of the bulk sample
The size of the bulk sample can vary but depending on the factors being analyzed will generally increase with the variability of the ore present, the presence of multiple veins or structures containing the valuable mineral and the number and types of rocks present that will ultimately be included in any potential mine plan.
- Why did Golden Predator build its own plant? Cost? Benefit?
Mother was the necessity of invention in our case. We needed to try to find a way to process the gold from the bulk sample to achieve results scientifically, efficiently and accurately. This led to the conclusion that it would be most cost effective and allow the best internal control if the plant was located in the Yukon. With no such facility available in the Yukon, we built the Yukon’s first plant dedicated to bulk sample processing. As we began processing we started improving the plant. What started as a plant that processed a ton a day manually operated and built largely of scrap material has turned into a closed system plant with a skilled team that runs consistently at 50 tpd. With visible gold, many times sitting loosely in open spaces (vugs) and along fractures, we suspected that the gold might well be free milling which gave us the opportunity to look at alternative processing methods and kept exploring and expanding the chemical free option.
The key to the success of the plant is the team you put in place. Geologists are perfect for the field work that gets the sample to the test plant. They oversee the grade control drilling, the extraction and sample area calculations. But without those people skilled in extraction and processing, the system would not operate effectively. Golden Predator has built the infrastructure and put together an amazing team. Best of all the knowledge is now local which can benefit the Yukon mining and exploration industry. It’s now a competitive advantage for the Yukon due to innovation.
- Explain the chemical-free process Golden Predator uses for bulk sampling?
Its basically crushing rock into small particles smaller than sand grains, then using gravity and water to separate the gold from the rock. Gold is much heavier than quartz so it settles. Our first goal in the plant was to determine if we could get the gold out and we quickly demonstrated from lab results that gravity and water, done right, could get over 80%.
By having the right people and the right equipment we have built that up to over 87% without the use of chemicals. Our goal now is to try to get consistent 90% recovery at our plant and see how far we can push the testing without chemicals as this would be a huge benefit for future mining and to the First Nation and the Yukon. It is a big factor in looking at potential mining as we need to test different areas of the property to see if the chemical free processing continues to work or what modifications can be made; at all times the goal is to minimize the use of any chemicals where possible. If the project can be successfully operated with water alone, it will provide cost savings as well as streamline permitting and significantly reducing any environmental concerns.
- Why do so few companies conduct bulk sampling?
Bulk sampling is used by companies to test metallurgy but it is not fully eligible as an exploration expense under flow through financing so not generally used in Canadian companies until much later in the project, if at all. It is generally employed to determine how mineable a project is once a resource is known. It is not a meaningful process to build resource ounces as part of the 43-101 process. Yet bulk sampling helps answer several critically important questions right up front; all of which lead to whether or not the project can be mined economically. All the drilling in the world will not answer that question. You need both methods on a project like 3 Aces and we believe how mineable a project is should be a question that is answered earlier rather than later.