Spinning Gold: From Ore to Bullion
Since the California Gold Rush over 150 years ago, the prospect of finding gold has driven men to great lengths. For the hardscrabble 49ers, the search for gold meant wading in riverbeds to sift gold from the rushing water. Today, gold is mined from the earth, since most of the surface gold ? known as alluvial gold ? has been found. The gold-mining process is intricate and multi-faceted, tying cutting-edge technologies with old-fashioned determination.
Finding Gold: Eureka!
While gold exploration used to be a matter mostly of “boot and hammer” prospecting, gold mining today is largely a matter of technology. First, geologists use geology maps to look for favorable areas to explore. Ore deposits are not easy to find and many of the ones exposed on surface have already been found. Geologists use the physical and chemical characteristics of the rocks they are looking for to zero in on prospective areas. Once favorable geology is established, remote sensing, airborne and ground geophysics and geochemistry are used to outline targets for drill testing.
Drilling and Engineering: Taking stock
Drilling at these sites brings up rock samples from various locations. These samples are analyzed to determine if any gold exists there, the size of the deposit, and the quality of the gold. Using this information, mining engineers determine if enough gold is under the surface to make the mining worthwhile; the type of mine needed; the physical obstacles to getting to the gold; and what impact a mine would have on the area’s wildlife and environment. If the gold is close to the surface, the engineers will design an open-pit mine; if the gold is buried deeply, they will plan an underground mine.
Building a Mine: Be prepared
Before the gold can be mined, an infrastructure must be created. Even if the gold is close to the surface, the simplest open-pit mine can take up to a year to build. In fact, the time between discovering gold and actually bringing it out of the earth can be up to five years. Since mines are often in remote locations, an entire infrastructure ? roads, administrative offices, equipment storage areas, even towns, schools and medical facilities ? must be built. The plans for the mines must be given the green light by a number of authorities at each level of government. Also, the mining company must put aside money for reclaiming the land once the gold is mined. In all, the preparation process can end up costing hundreds of millions of dollars ? before a single ounce of gold is mined.
Mining and Processing: Taking the good from the bad
Ore samples are taken and examined for the metallurgical quality of the gold in order to determine the appropriate processing technique required to remove the gold. The mine site infrastructure includes a processing area where the ore is crushed and undergoes various processes depending on the nature of the associated minerals and then the loose rock is sent to the appropriate processing location. The process for low-grade ore is relatively simple: a cyanide solution is applied to the heap, dissolving the gold, which is then collected. High-grade ore, on the other hand, heads to the grinding mill for a more extensive process. There are several different ore types which require different processes for optimal recovery of the gold. For example:
- Oxide ore goes directly to the leaching circuit, where cyanide dissolves the gold.
- Refractory ore, which contains carbon, is roasted at 1000 degrees Fahrenheit, burning off the sulphide and carbon, then heads to the leaching circuit.
- Sulphide refractory ore, which does not contain carbon, is oxidized in an autoclave in order to separate the sulphide safely, and in an environmentally friendly manner, from the ore, which then enters the leaching circuit.
In the leaching circuit, the gold is extracted from the solution and deposited onto activated carbon, from which the gold is then chemically stripped. The impure gold is then melted into doré bars, which are about 90 percent pure gold. These bars are usually shipped to a refinery where they undergo further processing.
Refining: From 90 percent to 99.99 percent pure
The refining process strips out the remaining impurities from the gold, which is either recycled scrap being upgraded or gold destined to become bullion bars. In the first step, crude gold is melted and treated with chloride, converting remaining metals to chlorides that will drift off the gold. The resulting 99.5 percent pure gold is cast into electrodes known as anodes, which are put into an electrolytic cell. After a current is passed through the cell, the end product is 99.99 percent pure gold.
Reclamation: Giving back the land
After a number of years, the gold reserves in a mine will be exhausted. In the old days, a spent mine would be boarded up and abandoned, but nowadays a reclamation project returns the land, as much as possible, to its previous natural state. The project follows the plan submitted to government authorities before the mine was built, which details the strict guidelines the company will follow, during the life of the mine and its closure, to protect wildlife and the surrounding environment. The reclamation project will include such things as planting trees and grass, and returning wildlife to the area.
How Gold is Used
Five thousand years ago, our ancestors cherished gold for its mystical qualities, believing it warded off evil spirits and healed the sick. Now in the 21st Century, non-toxic and biologically benign gold is used by modern medicine to help us lead longer, healthier lives.
Focused lasers: With gold-plated interiors, lasers give off a more focused beam, helping save the lives of heart patients suffering from once-inoperable heart conditions and tumors.
Accurate thermometers: Gold-plated thermometers give accurate body temperatures of newborns and unconscious patients.
Life-saving medicines: Biochemists use gold to bond with complex and compound materials, such as proteins, to create needed drugs.
Genetic research: Researchers place gold on DNA strands to study the hybrid genetic material of cells.
An Everyday Lifesaver
Outside the world of medicine, gold is at work, usually unseen, helping make people’s lives safer.
In cars, airbags depend on gold-coated contacts and electronic sensors for reliability, saving hundreds of thousands of lives in the past 15 years.
In the air, commercial airplanes rely on gold-bonded compressor vanes to cool their turbines from exhaust that can reach up to 1150 degrees Fahrenheit.
At work, gold-coated infrared equipment is used to detect a dangerous build-up of carbon monoxide and other air pollutants.
Below ground, miners rely on gold-activated sensors to warn of low levels of oxygen and trigger an automatic replenishment in seconds.
Exploring the Heavens
Since Neil Armstrong first set foot on the moon in 1969, gold has played a key role in our conquest of space. Thanks to its unmatched reflective qualities, gold is used to protect spacecrafts and astronauts from the searing heat of the sun and infrared radiation. From spacewalks to weather satellites, gold coating is making space accessible from the earth.
In spacewalks, an astronaut relies on gold coating to protect the vital lifeline tethering him to the ship, while the astronaut’s eyes are shielded from the sun’s rays by a gold-coated visor.
In the space shuttles, rocket engines have four miles of gold-brazed tubing, which safely carries liquid hydrogen without melting the ship’s nozzle at operating temperatures of up to
6000 degrees Fahrenheit.
In geo-stationary weather satellites, sheets of gold-coated Mylar deflect heat that would otherwise degrade their performance.
In the Hubble telescope, all parts of its electronic camera are coated with gold to insulate against heat damaging its celestial snapshots.
Opening a New Era of Global Communications
Since the first rudimentary computer, gold has been at the vanguard of the march of digital technologies. Today’s Information Age is dependent on gold, making possible the free exchange of ideas from every corner of the world.
- Computers, the heart of the digital revolution, depend on gold circuitry.
- Electronics and telecommunications equipment count on gold for reliable performance, since gold does not corrode in normal atmospheric conditions.
- Trading in securities and other financial instruments depends on gold for static-free transmissions worth billions of dollars.
- National security is aided through the major role gold plays guaranteeing the reliability of sophisticated electronic monitoring and communications.