In processing our local ore with the �ǿ���Ƶ jaw crusher, hammer mill and shaker table, we get a p80 of ~30-50 mesh (80% passing 30 or 50 mesh sieve screen), depending upon the slot size in the hammer mill screen. Results show nearly 50% of the gold recovered was at <100 mesh, and a surprising amount of gold was at <325 mesh. So, contrary to some beliefs, gold ore does not need to be ground to 200 mesh to liberate 200 mesh gold. Here’s the video:

Overgrinding past the desired liberation size slows production and increases wear. Worse yet, overgrinding can result in values so fine that they will be lost in a gravity recovery circuit. For instance, the best gravity shaker tables begin to lose effectiveness at recovering gold smaller than about 50-35 microns (300-400 mesh). Smaller gold and finely-ground gold-bearing sulfides are lost to gravity tailings and commonly recovered only with flotation or leaching circuits.

Here is a simple procedure to determine the practical liberation size for the small scale miner with a high performance shaker table. It is a modified sizing-sorting-assay test. The strategy is to process the ore thru the system and test the various cuts off the shaker table to see where additional values might be found. The �ǿ���Ƶ shaker table has 4 discharge ports. The ore samples-of-interest are from port 3 (middlings, mostly sulfides) and port 4 (quartz tailings).

Simplified testing for liberation size with gravity recovery systems:

• Weigh an amount of head ore
• Run the ore through the system
• Methodically sample the discharge from ports 3 and 4. Typically, catch the discharge in a container for 5-10 seconds every minute or two to get a cross-section of the ore makeup from each port.
• When all the head ore is processed, drain and weight the total amounts from ports 1, 2 and 3 (not just the samples). Compensate for the water by multiplying by 0.85 to approximate the dry weights. Or dry them and then weigh them. There’s no need to weight the tailings, since the total ore weight was found before processing.

Processing the sample from port 3, middlings

• Port 3 will capture a high percentage of sulfides (if any) and some quartz gangue. Carefully pan the port 3 sample to detect any free-milling gold. We usually find less that 3% of the pannable, free milling gold reports to port 3. The port 3 middlings can be re-run on the table to extract detectable gold, if desired.
• Now, the sample should be barren of any pannable, free-milling gold (less than about 400 mesh).
• Screen the sample into these fractions: +200 and -200 mesh. Send these 2 fractions off for assay to a professional assayer. The results are too important for owner-testing.
• If gold is found, it is likely from gold-bearing sulfides. It’s not too important to know if the gold is in coarse or fine sulfide particles, as the circuit will not be tuned based on the size of the sulfides. Most small scale miners will save gold-bearing sulfides and send them to a refiner for processing.

Processing the sample from port 4, tailings

• Screen the sample into these fractions: +30 mesh, 30-100, 100-200, 200-325, <325. Send these off for assay to a professional assayer.
• If gold is found in the +30, 30-100, or 100-200 fractions, additional grinding may release it for capture via a gravity shaker table.
• Retest with smaller classification ranges to zero-in on the liberation size. Tune the grinding circuit to only grind fine enough to attain the commercially-viable liberation size.
• If gold is found in the 200-300 or <325 mesh fractions, it is likely gold-bearing sulfides or free milling gold <~400 mesh. This gold is not practical to recover via gravity concentration, so flotation or leaching could be used.

Additional notes

-Total gold-per-ton is computed using the 1) port 1 and 2 gold recovery, 2) assayer’s results and discharge weights from ports 3 and 4 to compute gold weight at these ports, divided by 3) weight of all material discharged from all ports.

–Percentage recovery of total gold is computing by taking total gold recovered in ports 1 and 2 (free milling, >~400 mesh), divided by total gold in ports 1, 2, 3, and 4 (includes very fine free gold and gold-bearing sulfides from assayer).

A hammer mill or impactor produces a fairly coarse grind. Usually, about 30-50 mesh is the practical limit. They are also high-wear machines that need frequent wear-part replacement and maintenance. But, they are comparatively inexpensive and are very useful for proof-of-concept testing for new prospects, or for limited production runs of smaller volumes. If testing shows that a finer grind liberates additional gold, the tailings from the hammer mill circuit can be stockpiled and rerun when a ball mill is installed in a more permanent installation.

Ball mills routinely produce P80 of 200 mesh, in preparation for flotation or leaching, but can be tuned to produce sizes from 50 mesh and smaller.�� Often, the discharge from the ball mill is processed on a shaker table to remove coarser gold. Then a classifier (hydrocyclone or spiral) is used to isolate the oversized table tailings material and send it back to the ball mill for re-grinding. The undersized slurry from the classifier is sent for further processing or to the settling pond.

Sincerely,

Steve Gaber (Co-Owner)

The post Finding the Ore Liberation Size For Gravity Circuits: Sizing-Sorting-Assay Test for Commercial Recovery appeared first on Mt Baker Mining and Metals.

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Most methods of concentration rely on gravity. The density of gold is 19 times greater than that of water, which means it’s exceptionally heavy. For comparison, Mercury is 13 times as dense, and lead is 10 times as dense as water. Due to this fact, even a very small flake of gold will sink to the bottom of a body of water, making gravity an excellent method for concentrating liberated gold.

Current ASGM Practices

Sluicing is one of the most common methods of concentration. Water and crushed ore are combined and washed down a sluice lined with a fibrous material. The heavy gold sinks and is caught in the lining which is rinsed into a pan to be further concentrated, usually by panning.

Gold Panning is something nearly all of us have seen before. Gold-rich ore is combined with water in a shallow pan and gently swirled around.

The motion of the water lifts the lighter particulate matter which is allowed to escape over the rim of the shallow pan, leaving the heavier gold at the bottom of the pan.

Effective concentration of gold is challenging and requires the right materials and techniques. The majority of small-scale artisanal miners do not have the resources to attain or build an ideal set-up. Because of this, miners can lose 25% to 75% of their gold during concentration due to inefficient practices. This is evidenced by testing the tailings, which show a substantial quantity of leftover gold.

Improved Practices

Improved sluicing: Education on modern techniques for increased gold capture is needed, as is the dissemination of improved sluice design. �ǿ���Ƶ has designed an improved gravity concentration sluice that has proven able to capture gold up to 300 mesh in size. We’ve offered the building schematics and consultation for the use of our sluices since 2007, and they’re still free to all. If you are interested in fabricating them or have questions, you can find out more at our website on the page.

Shaker tables: This very effective gravity method uses vibration and water flow to separate particles by their weight. The undesired, lightweight materials, called gangue, are washed along the surface of the table, while heavier particulates��remain to form a band of gold-rich concentrate. �ǿ���Ƶ’s shaker tables��feature custom-cut grooves and a subtle incline that guards against fine-gold loss and will retain 95% of free gold at >325 mesh, with customer reports of recoveries down to 425 mesh. To combat the elements and various environments in which gold is mined, our tabletops are fabricated from RPDM rubber which is exceptionally��resistant to heat exposure. They are capable of running between *1 and 2.25 tons of ore/hour and can operate using *6-14 gallons of water per minute. Water can be recycled, so they can be operated in locales where water isn’t available by implementing a closed circuit system.

When gold is concentrated efficiently, yield increases, waste decreases, and the need for mercury amalgamation is rendered obsolete. This means a boost to the livelihoods of mining communities, which in turn supports personal, social, economic and environmental health.

*Numbers quoted reflect the capability range of our 4′ x 8′ and 5′ x 12′ shaker table models. Please see our website for more information.

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Part one of our improved practices series covers the liberation of gold from hard rock. We’ll take a look at current practices used by artisanal small-scale gold miners (ASGM) and examine improved methods that mitigate the use of harmful chemicals while boosting productivity and yield.

The state of naturally existing gold varies, and so does the way humans retrieve it. The two primary types of gold deposits are known as lode and placer deposits.

Lode deposits are characterized by veins of gold trapped in hard rock.

In placer deposits, gold exists in tiny flakes sometimes fully liberated and other times attached to bits of rock.

Oftentimes, the gold found in various types of placers is already fully liberated and only requires concentration.

When the gold is attached to other minerals, it’s known as ore and must be milled in order to separate out the gold and concentrate it. Here, we’ll focus on lode deposits and how gold is liberated through the process of crushing and milling.

Current ASGM Practices

Primary Crushing: Ore needs to be reduced to the ideal size required for milling. After gold-bearing ore is extracted from mines, it is carried to the surface to be broken down. This is often done by hand with a hammer or mallet.

The miner will sit for hours, processing the rock manually until it is reduced to gravel. A more advanced but less used method is the stamp mill, which uses heavy weighted objects to pound ore into smaller sizes for further processing.

Milling: The goal with milling ore is to crush it into as fine a particle as possible, thus liberating the gold from anything it might be attached to. Ore is milled in two ways; with and without water.

In the case of dry milling, the additional step of laying the gravel-sized ore out on tarps in the sun is added. Hammer mills and ball mills are then utilized to pulverize the ore, though often inefficiently.

Conducive milling should yield a product with an even grain size, preferably 30 mesh (0.6 mm) or smaller. In a vast majority of small-scale milling operations, the ore is only milled to 10 mesh, which results in gold that is unliberated and unrecoverable. Miners endure unsafe working conditions, back-breaking manual labor and exposure to harmful dust and chemicals only to recover thirty percent of the gold in their ore due to inefficient processes and equipment.

Improved Practices

Primary Crushing: Jaw crushers are highly efficient at primary crushing. �ǿ���Ƶ offers a full range of jaw crushers that are optimally sized for small-scale processing needs.

Our crushers feature cast manganese jaw plates and can be powered via electric, gas or diesel motor. The processing capabilities range between one and sixty tons of ore an hour, and the discharge size of gravel is uniform and can be adjusted from 4” to ¾” in size. They are an excellent example of how improved technology can elevate the potential of a grassroots industry and eliminate inefficient processes.

Milling: Some upgraded technology has been widely adopted by the ASGM already. Tanzanian ball mills are widely used, for example, but samples of tailings show a wealth of unliberated gold. The difference lies in the quality and design of machinery, and all that missed gold goes to show that present tools and techniques are in need of change.

Our improved technology hammer and ball mills deliver a product that is uniform in particulate size and small enough to liberate the gold from its surrounding ore.

The hammer mills produced at �ǿ���Ƶ can run wet or dry material and discharge between 1-5 tons an hour with 70% of processed ore passing 30 mesh.

Our ball mills represent the ultimate in processing capability and can run continuously, 24 hours a day, 7 days a week, 365 days of the year.

The size of discharge can be customized to specification, ranging between 65 and 300 mesh, and the throughput varies from 0.3 and 11.0 tons/hour depending on mill and target discharge size.

If you’d like to see our equipment in action, have a look at the demo videos below or visit our website.

The post Improved Practices Series: The Process of Liberating Gold appeared first on Mt Baker Mining and Metals.

There are several ways that mercury is utilized by artisanal small-scale miners (ASGM). It may be ��mixed with concentrated ore through panning or added to sluices, ball mills or trommels in a process known as whole-ore amalgamation. The resulting amalgam of mercury/gold is called a prill, and it is roasted with a torch or over an open fire.

When the prill is heated, the mercury vaporizes and leaves behind a nugget of porous gold, often referred to as sponge gold. Whether the process takes place indoors or out, the effect is the same; the vapors are highly toxic when inhaled and lead to devastating health problems. The majority of the vapor enters the atmosphere where it contributes to widespread global pollution, turning up in lakes and rivers thousands of miles from ASGM sites.

Oftentimes, the leftover water used in ore concentration with mercury is released into streams and rivers, where it enters the soil and is consumed by microorganisms. This is where the process of biomagnification begins. Small contaminated animals are eaten by larger ones until you reach the most toxic suspects of all – top chain predators, such as tuna and marlin.

In 2013, the ASGM was identified by the United Nations Environmental Protection Agency (UNEP) as the largest contributor of mercury to the environment, accounting for 37% of total anthropogenic (manmade) mercury emissions to the atmosphere. Numbers like these directly contribute to the formulation of Minamata convention mandates and the fuel the imperative to scale down the human need for mercury.

A comprehensive overview of mercury use and its hazards was created by Jack Caravanos, Professor of Environmental Health and Research Director of . It can be viewed .

The post The Mercury-Gold Relationship: Mercury Use in Small-Scale Gold Mining appeared first on Mt Baker Mining and Metals.

The Minamata Convention derives its name from a catastrophic case of mercury poisoning that began in 1956 in the Japanese town of Minamata. The tragic incident has been a modern baseline for what can and will happen without safeguards against human-caused marcury pollution. To better understand the urgency of the convention’s imperative, I’ll give a brief overview of the cycling of mercury as it stands today.

Mercury is a well-documented neurotoxin that is especially harmful to children and pregnant women. What is less known is how easily it travels and how long it can stay. Mercury pollution can make its way across the miles to accumulate in your local waterways or lurk��unseen in the fish you eat.

There are three significant ways mercury moves around the world. First, it is a global commodity that passes hands through trade. Artisanal and small-scale gold mining (ASGM) represents the largest consumer of traded mercury and the single greatest contributor to mercury vapor into the atmosphere. Second, vaporized mercury from industrial��use can travel great distances before being deposited through the rain into soil and waterways. To illustrate, mercury released in Mongolia can circle the planet and make its way into Western lakes and rivers. Third, once mercury enters a waterway, existing bacteria absorb it and convert it into something far more toxic: methyl mercury. Methyl mercury travels through fish, its level increasing as it moves up the food chain in a process called biomagnification.

As apex predators, humans consume top food chain��species like tuna, swordfish or marlin, which contain the highest levels of methyl mercury.

This is the reasoning behind the FDA’s recommendation that pregnant women limit or avoid consumption of top predator fish. The mercury content of these fish has��reached levels that threaten the development of a growing fetus.

To recap: mercury spreads via human channels through trade, atmospheric deposition, and the food chain. Stopping mercury pollution in any given sector or country isn’t enough to protect ourselves and future generations. Mercury pollution is an active threat to global health, and it requires the proactive response of every nation.

If you’d like to know more, has produced an excellent short video about the ways mercury travels and the health impacts it has on people. You can view it .

How the Convention Works

International treaties can be complex. I’ve taken the liberty of breaking some of the language and governances for ease of understanding. Below is a snapshot of the Minamata Convention stipulations and what it means going into the future.

The Minamata Convention on Mercury is a global treaty to protect human health and the environment from the adverse effects of mercury. It entered into force on 16 August 2017, and 128 Countries have signed on with 105 ratified into law.

The Convention focuses on mercury, a naturally occurring metal that has broad uses in everyday objects and is released to the atmosphere, soil, and water from a variety of sources. Controlling the anthropogenic (man-made) releases of mercury throughout its lifecycle is the cornerstone that formed the basis of obligations under the Convention.

Minamata Convention key principles include the following:

• A ban on new mercury mines and the phase of of existing ones
• The phase-out and phase down of mercury use in a number of products and processes
• Control measures on emissions to air and on releases to land and water
• The regulation of the informal sector of the ASGM (artisanal and small-scale gold mining)

The Convention also addresses interim storage of mercury and its disposal once it becomes waste, sites contaminated by mercury, as well as health issues.

The post The Minamata Convention: What It Is and Why It Matters To You appeared first on Mt Baker Mining and Metals.

One of the greatest benefits of our improved sluicing technology is that it is familiar. Sluicing has been the standard method of gravity concentration in gold mining for hundreds of years, and the vast majority of the ASGM still employs it today.

Making an improvement on age-old technology��may not be as effective at recovery as some of the more recent high-tech solutions, but there are notable benefits attached. It is affordable, accessible, and there is no learning curve and very few outside resource necessities.

This makes improved sluicing a convenient method to implement, and the rate of recovery means a boost in yield for hard work. We’ve found��that��the yield of our fine-gold Popandson sluice shows recoveries of +95%��of gold from 100 to 200 mesh, and +85% of gold from 200-325 mesh at��small-scale production rates.

�ǿ���Ƶ has made our Popandson Sluice technology available to all for over a decade. They are free for all, and it is our wish to see them being made and used where they belong–out in the field making a difference for people.

��The schematics for building a Popandson sluice can be found on our website.

Further information can be found on our Improved Sluicing Technology page.

Please let us know if you begin a project that uses our improved gravity concentration techniques. We’d love to know about where and how technology is making a difference in the lives of the ASGM community.

The post PACT Fabricates Popandson Sluices in Nigeria appeared first on Mt Baker Mining and Metals.

As luck would have it, our paths crossed while in Kenya, and Matt invited us to join him and see first-hand the work he’s involved in.

We spent several days with him in Lolgorian, where we toured FOG’s office and met with the local mining community. It was an added bonus that we were able to demonstrate the use of the sluice and retort to some of the lead miners in the community. Nothing beats immersion when trying to understand an issue, and being there with the miners as they worked was both enlightening and motivating.

About The Farmers of Gold Project

Date Founded: The Farmers of Gold Project was founded in January 2018 ��by Matthew Hales and Don Moriarty as a subsidiary project of The Cora Blue Fund charity which was established on 05/20/2016

Founder(s): Abigail Preston, Matthew Hales, Janyne Preston, Don Moriarty

Sponsor(s): Private donations

Mission: The Farmers of Gold Project mission is to improve the safety of impoverished artisanal gold miners in Kenya & around the world by providing access to safety gear & training.

Achievements:

• Created a working partnership between our private NGO Farmers of Gold, the UNDP and the Kenyan Ministry of Mining.
• Opened a main office for the gold miners chairman, on-site in ��Lolgorien, Kenya which includes a safety equipment store for purchases and rental ��of safety gear
• Acquired a legal operating license for miners of Lolgorien organized under the Farmers of Gold Project
• Supplied almost all 500+ local Artisan Gold miners with at least some of the basic equipment required including dust masks, helmets, ear plugs, gloves, and gumboots, since January.

Future Goals:

• Create a safety training video course with several videos including safety gear, safety techniques, safety hazards in artisanal gold mining practices, the use of mercury, silica from dust, hearing protection, and safe mine construction.
• Create a short and comprehensive safety quiz pertaining to the training videos. Issue a certificate of completion upon passing the safety quiz. This certificate would also allow subsidized purchases of safety gear that will be made available thru the Farmers of Gold project.
• Organize these small independent gold miners to become more self-aware and stringent in the use of safety gear and use of toxic materials.
• Help provide the safety program and gear mandated in order to maintain mining legally.
• Help remove mercury all together from the process, by investing in mercury-free extraction equipment manufactured by �ǿ���Ƶ Corporation.
• Implement cleanup of the environmental programs.

Note from Matt Hales:��We are very grateful to be working with you all! �ǿ���Ƶ is helping pave the road to safer mining practices to the most impoverished miners in the most needed areas. To think of a manufacturing company caring about the most negatively affected and poorest miners is truly remarkable!

Partnerships are an incredible way to magnify the positive impact of any effort. If you have an interest in partnering with Matt’s cause, please contact him or find out more on the

The latest updates with FOG are also available on their Facebook page:

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