While gold sourcing is often referred to simply as “mining,” mining is, in fact, just one piece of the production puzzle. The process of obtaining gold is actually multi-faceted and can be more or less summed up in four steps: prospecting, mining, extractingand refining. In this blog post, we'll explore the initial phases of prospecting and mining.
While images of eager 19th-century frontiersmen panning for gold in riverbeds of the American West are undoubtedly ingrained in most of our minds, the truth is that gold sourcing came about well before the famed mid-1800s gold rushes.
It's difficult to know precisely when the practice began but giving us some indication is the fact that the oldest known gold pieces were discovered in the prehistoric Bulgarian burial site, Varna Necropolis. This cemetery was operational for over 200 years in the 5th millennium BC, suggesting that perhaps gold sourcing dates back nearly 6,500 years.
Since then, evidence of gold in human history can be found in cultures around the world – from Bronze Age artifacts to Roman money to Indian mining to the enterprise-scale operations we see today.
As of 2017, China was the world’s largest producer of gold, sourcing more than 400 metric tons. Next was Australia, then Russia, and finally, the United States.
Today, gold production is big business, with operations located on every continent, except Antarctica. Profitable sourcing requires extensive research that relies on experts like geologists, geographers, engineers, and even chemists. From there, each subsequent stage – from mine set-up to post-op site rehabilitation – may take several years to complete, resulting in a lifecycle that can span 60+ years and require substantial amounts of capital at each turn.
Step 1: Prospecting
Gold prospecting is when a company, person or other entity inspects an area of land for viable gold deposits.
Methods of prospecting differ by deposit type. For placer deposits – which are loose accumulations of sand, silt or dirt mixed with valuable materials like gold – panning or similar methods are used. Placer deposits are typically found around the banks of water bodies.
In panning, the wet earth is scooped up and sifted through a specially designed hand-held pan. Since gold is denser than rock, it will sink to the bottom of the pan, letting the prospector know the area may be viable for more extensive mining.
Trenching or drilling are used for placer deposits buried deeper in the ground. More sophisticated geophysical techniques such as seismic activity, gravity or magnetics can be employed to detect underground water beds that may contain gold.
On the opposite end of the spectrum, you have lode, or hard rock, deposits.
Several prospecting methods are available for this type of deposit, too. At the most basic level, a visual examination of the earth’s surface can be done to detect signs of desired deposits. Such signs include exposed mineral veins or hydrothermal changes to the ground’s appearance.
For more deeply embedded deposits, where surface-level indicators may not be present, prospectors often drill down into the lode to extract samples, which are then sent to a lab or assay office for gold content assessment.
Step 2: Mining
If a prospector finds an acceptable amount of gold in an area, mining begins.
As with prospecting, approaches to mining will vary depending on the type of deposits at hand and amount of funding available.
Since placer deposits are composed of loosely assembled materials, tunneling and other underground methods are not feasible. Instead, placer mining typically uses water-based techniques.
The most straightforward approach is, again, panning. However, since panning is primarily a manual process, it’s often not commercially viable. To process more significant amounts of placer deposits, sluicing or dredging operations can be deployed.
Sluicing employs a man-made water channel called a sluice box. Scoops of the wet earth are dumped into the top of the box, which sits in a downward angle, and cascade through the channel. Riffles carved into the bottom of the box create “dead spaces” within the cascading current that allow the gold to “drop” out of the liquid and collect on the box’s bottom for easy removal.
Dredging, which has mostly been replaced by other methods, is essentially sluice boxing done in the water. In this case, sluice boxes are affixed to the top of pontoons – allowing them to float – and a submerged suction hose feeds material from under the water up into the overhead boxes. The same sluicing process carries on from there.
While placer mining is still done around the world, most of today’s gold supply is sourced from hard rock deposits. Like placer deposits, hard rock deposits can be located near ground level or be embedded deeper within the earth.
For surface-level sources, open-pit mining is often used. The Fort Knox Mine in central Alaska or Barrick Gold’s Goldstrike property in northeastern Nevada are examples of open-pit mines. Tiered “steps” or “benches” are carved into the walls of the earth, making pathways of sorts allowing machines and workers to move about, extracting shallowly situated ore.
For embedded deposits, a producer will dig underground tunnels or shafts for ore excavation.
Underground mining requires in-depth planning and often dangerous phases of execution. The first phase – development mining – creates access to the underground ore that will be mined. This is when “waste rock” is excavated (often involving explosives to dislodge the rock) and support infrastructure is installed. Next, paths of ingress and egress – known as declines, shafts or adits – are established for workers and mining equipment to enter and exit the newly carved out space.
Production mining follows and is when the gold-bearing ore is actually mined and excavated for further processing. Plans for power, dewatering and ventilation must also be considered in underground mining, all of which are hefty investments in their own rights.
Prospecting and mining – particularly for underground deposits – are multi-faceted, in-depth and often taxing endeavors. While legends of individuals and families striking it rich in the fertile lands of California and the Yukon are certainly inspiring, today's landscape calls for something entirely different. The "little guy" miner has been overridden by global enterprises with enough time and money to compete within the industry successfully.