how gold-mining operations benefit from heap leaching extraction
Building and permitting a mill to process mined resources can take at least a decade, not to mention a large outlay of capital. Heap leaching is a hydrometallurgical technique with lower operational costs than more conventional processing technologies. The technique offers gold producers a user-friendly extractive solution with the ability to significantly improve recovery rates and fast-track a property into production. This well-proven and cost-effective approach to precious metals extraction has been used by majors including Barrick Gold (TSX:ABX,NYSE:GOLD) and Newmont (TSX:NGT,NYSE:NEM), and is increasingly being considered both in the design of new mines and the expansion of existing operations.
The heap leaching process for precious metals typically begins with low-grade surface ore that has been separated through crushing. To maximize recoveries, this crushed ore is then agglomerated prior to leaching. This involves mixing the ore with lime or portland cement to produce larger masses of material that are more uniform and easier to leach than fine particulate matter which can clog and slow down the flow of solution as it percolates through the heap. Once the agglomeration stage is complete, the material is then spread over high-density polyethylene membrane-lined leaching pads specially designed to prevent contaminants from entering the soil and groundwater. Next, a leaching solvent such as sulfuric acid or cyanide is sprayed over the ore, dissolving the gold and silver as it passes through the heap. This creates a solution pregnant with valuable minerals that can be recovered via carbon absorption or the Merrill-Crowe process.
Gold projects that host near-surface mineralization associated with low-grade oxides that are also capable of supporting a large-scale mining project are more amenable to the heap leach process. The process can also be used to recover economical amounts of valuable metals from tailings and waste stockpiles. High grade, sulphide gold often requires more sophisticated processing techniques with more expensive equipment. In deposits that contain both oxides and sulfides , heap leaching the oxide resources can move a project to cash flow at a quicker pace and generate the capital required to finance the more expensive processing facilities required to tackle a sulphide orebody.
Exploration companies like CANEX Metals (TSXV:CANX) have the potential to leverage on heap leaching extraction systems as a low cost mining technology. CANEX is currently developing a new gold discovery at its flagship Gold Range project in Arizona. Were right on the edge of the discovery curve. We have sampled widespread gold mineralization over a 5 by 3 kilometre area. We have mapped key controlling structures with geophysics and identified several targets across our Gold Range property. Our current focus is on the Eldorado oxide gold target which has a potential size of 200m x up to 3km. While it is early days, RC drilling to date is giving us some good bulk tonnage grades with good continuity. The preliminary metallurgical (cyanide soluble gold results from Eldorado) confirm the potential as a bulk tonnage heap leach target and further de-risk the exploration concept. The average cyanide soluble gold value of 79.5% compares very well to current heap leach producers and development projects in western North America. Were really excited to see this opportunity develop as the market is in need of high value, heap leach, low-cost mining targets, said CANEX Metal CEO Dr. Shane Ebert.
The World Gold Council has reported that new gold discoveries have declined over the past three decades and the average grade of new discoveries is also in decline. In a world where new gold discoveries are harder to find and gold grades are declining, heap leaching technology offers miners the ability to recover more gold from lower grade material at a lower cost. Heaping leaching can improve the economic viability of new projects, breathe new life into old mines and extend the life of existing mines.
Northern Vertex Mining (TSXV:NEE) owns and operates the nearby Moss gold mine, currently the largest precious metals mine in Arizona with open pit mine and heap leach processing. Argonaut Gold (TSX:AR) has successfully developed and operated several open pit heap leach mines. The companys latest project is the Nevada-based oxide gold heap leach project Florida Canyon.
Heap leaching has proven successful for large-scale use in gold projects for decades. Heap leaching technology was a major breakthrough because it significantly reduced gold recovery costs for low-grade but high-tonnage Carlin deposits such as those found in Nevada, according to Kitco contributor Jack Graham. The heap leaching technique was first used for precious metals recovery in 1969 at the Cortez gold mine where it proved highly-efficient at improving recoveries from near-surface oxidized ore, notes Graham. Today, Barrick Golds Cortez property includes the Pipeline complex open-pit operation and the recently discovered Cortez Hills deposit, which is Nevadas longest-running gold mine.
This INNSpired article is sponsored by CANEX Metals (TSXV:CANX). This INNSpired article provides information which was sourced by the Investing News Network (INN) and approved by CANEX Metals in order to help investors learn more about the company. CANEX Metalsis a client of INN. The companys campaign fees pay for INN to create and update this INNSpired article.
INN does not provide investment advice and the information on this profile should not be considered a recommendation to buy or sell any security. INN does not endorse or recommend the business, products, services or securities of any company profiled.
The information contained here is for information purposes only and is not to be construed as an offer or solicitation for the sale or purchase of securities. Readers should conduct their own research for all information publicly available concerning the company. Prior to making any investment decision, it is recommended that readers consult directly with CANEX Metalsand seek advice from a qualified investment advisor.
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goldmining inc: home
GoldMining Inc. is a junior resource company trading under the symbol GOLD on the TSX Venture Exchange and GLDLF on OTC Markets. The Company is focused on the acquisition, exploration and development of resource stage gold projects in the Americas.
mercury usage in gold mining and why it is a problem
Most large-scale and regulated gold mining companies do not use mercury in their mining operations. However, Small-scale and illegal gold mining operations will sometimes use mercury to separate the gold from other materials.
Large mining companies include Barrick Gold, Newmont Mining, and AngloGold Ashanti. Many investors will invest in these companies either directly through owning company shares or through investing in gold exchange-traded funds (ETFs).
First, mercury is mixed with the materials containing gold. A mercury-gold amalgam then is formed because gold will dissolve in the mercury while other impurities will not. The mixture of gold and mercury is then heated to a temperature that will vaporize the mercury, leaving behind the gold. This process does not result in gold that is 100% pure, but it does eliminate the bulk of the impurities.
The problem with this method is the release of the mercury vapor into the environment. Even if the equipment is used to catch the vapor, some still can get into the atmosphere. Mercury also can get into the soil and water if it still is contaminating other waste materials from the mining process that may be discarded.
Mercury first was used to extracting gold as many as 3,000 years ago. The process was prominent in the U.S. up until the 1960s, and the environmental impact on northern California is still felt today, according to sciencing.com.
Mercury vapor negatively impacts the nervous, digestive, and immune systems, and the lungs and kidneys, and it can be fatal, according to the World Health Organization. These health effects can be felt from inhaling, ingesting, or even just physical contact with mercury. Common symptoms include tremors, trouble sleeping, memory loss, headaches, and loss of motor skills.
The Guyana Shield region (Surinam, Guiana and French Guiana), Indonesia, The Philippines and part of Western Africas coast (e.g., Ghana) are particularly impacted by the phenomenon. Under the socio-economic and political conditions found in the small-scale gold mining operation, the use of mercury is often considered as the easiest and most cost-effective solution for gold separation.
Gold is heavier than most other particles, so alternative methods typically use motion or water to separate the gold from lighter particles. Panning involves moving sediment that potentially contains gold in a curved pan with water and moving in such a way that any gold will settle at the bottom while the water and other particles will leave the pan. Sluicing involves sending sediment down a platform with water. The platform has a carpet-like material at the bottom that will catch the heavier gold particles while the water and other particles wash away. Other more complex methods involve magnets, chemical leaching, and smelting.
tips on reducing the impact of gold mining and processing
Gold has been one of the most valuable commodities since the beginning of time. It has been treasured since the days the Pharoahs of Egypt built their pyramids and the Aztecs paid homage to their god Montezuma. Although gold is a metal full of luster and the universal symbol of wealth, it has a dark side to it. The biggest problem with gold is that its a commodity that leaves a harsh footprint on the environment.
There are a lot of environmental problems associated with gold. It damages the environment when it is mined, smelted and processed. The good news is that these problems can be mitigated with the right steps.
Todays gold rates are on an upward trajectory, with the latest reported prices touching $1,280, testing resistance at $1,300. There are a number of reasons that demand for gold has risen. One is that it is a good hedge against economic instability. Its true that gold has contributed to the global economy, but it has taken a toll on the environment.
The gold rush bolstered the world economy and put wealth into the hands of many opportunistic investors, but rapid industrial gold mining comes at a steep cost to the environment. As it stands, traditional methods of mining gold releases huge swathes of toxic waste and ravages the landscape. In many poorer parts of the world, miners easily get away with using illegal means of obtaining gold.
The worst of such practices is the use of cyanide in mining operations. This toxic chemical is used to process gold because it provides a cheap and effective alternative to remove the lustrous metal from low grade ore. Cyanide has devastating environmental and health effects, affecting not just humans but other animals, with more than 30 major accidents occurring worldwide in the past 25 years.
The gold mining boom has caused destruction on the Amazon rainforest as artisanal and unlicensed gold miners tear down the environment to access hard to reach gold deposits underneath. These illegal gold miners use mercury to extract gold, leaching the toxic chemical into the air and water. About 1,000 tons of mercury is released into the environment every year by the 15 million artisanal gold miners around the world.
Innovative technology only gains mainstream acceptance if it can be implemented economically while not deviating too far from traditional practices. To this end scientists and researchers around the world have found ways to mitigate the environmental impact of the mining industry. Lets go through a few examples:
Zero liquid discharge is when wastewater is processed to be reused for mining activities. The idea is to bring the ratio of disposed wastewater to recovered wastewater down to zero. This allows miners to forego costly disposal processes while making more efficient use of the mining projects water supply. The two most prominent methods that help achieve zero liquid discharge are crystallization and vacuum evaporation.
Many mining operations can be optimized to use less energy for the same output. Some Canadian miners are already striving to make their mining operations less wasteful when it comes to resources. Vehicles are using clean diesel fuels, and in rare cases, green sources of energy. More machines will be powered by alternative sources of energy such as hydrogen fuel cell batteries and solar energy to produce less pollution.
Old mines that have reached maturity are reseeded to cultivate the growth of natural vegetation. The National Mining Association in the US has reported that mining companies have reclaimed around 2.8 million acres of mined land, converting them into wildlife reserves and recreational areas. If nothing else, these older mines are being put to good use and generate income for the local economy.
Gold has not been good for the environment. The good news is that contemporary mining and processing methods can reduce this harmful impact. This is important, since demand for gold is higher than ever.
gold: history of use, mining, prospecting, assay & production
Egyptian gold: Artisans of ancient civilizations used gold lavishly in decorating tombs and temples, and gold objects made more than 5,000
years ago have been found in Egypt. Image copyright iStockphoto / Akhilesh Sharma.
Gold was among the first metals to be mined because it commonly occurs in its native form, that is, not combined with
other elements, because it is beautiful and imperishable, and because exquisite objects can be made from it. Artisans
of ancient civilizations used gold lavishly in decorating tombs and temples, and gold objects made more than 5,000 years ago have been found in Egypt. Particularly noteworthy are the gold items discovered by Howard Carter and Lord
Carnarvon in 1922 in the tomb of Tutankhamun. This young pharaoh ruled Egypt in the 14th century B.C. An exhibit of
some of these items, called "Treasures of Tutankhamun," attracted more than 6 million visitors in six cities during a
tour of the United States in 1977-79.
The graves of nobles at the ancient Citadel of Mycenae near Nauplion, Greece, discovered by Heinrich Schliemann in 1876,
yielded a great variety of gold figurines, masks, cups, diadems, and jewelry, plus hundreds of decorated beads and buttons.
These elegant works of art were created by skilled craftsmen more than 3,500 years ago.
The ancient civilizations appear to have obtained their supplies of gold from various deposits in the Middle East. Mines in
the region of the Upper Nile near the Red Sea and in the Nubian Desert area supplied much of the gold used by the Egyptian
pharaohs. When these mines could no longer meet their demands, deposits elsewhere, possibly in Yemen and southern Africa, were exploited.
Artisans in Mesopotamia and Palestine probably obtained their supplies from Egypt and Arabia. Recent studies of the Mahd adh
Dhahab (meaning "Cradle of Gold") mine in the present Kingdom of Saudi Arabia reveal that gold, silver, and copper were
recovered from this region during the reign of King Solomon (961-922 B.C.).
The gold in the Aztec and Inca treasuries of Mexico and Peru believed to have come from Colombia, although some undoubtedly was
obtained from other sources. The Conquistadores plundered the treasuries of these civilizations during their explorations of the
New World, and many gold and silver objects were melted and cast into coins and bars, destroying the priceless artifacts of the Indian culture.
Gold coin: As a highly valued metal, gold was used as a financial standard and has been used in coinage for thousands of years. United States ten dollar gold coin from 1850. Image copyright iStockphoto / Brandon Laufenberg.
Nations of the world today use gold as a medium of exchange in monetary transactions. A large part of the gold stocks of the
United States is stored in the vault of the Fort Knox Bullion Depository. The Depository, located about 30 miles southwest of
Louisville, Kentucky, is under the supervision of the Director of the Mint.
Gold in the Depository consists of bars about the size of ordinary building bricks (7 x 3 5/8 x 1 3/4 inches) that weigh
about 27.5 pounds each (about 400 troy ounces; 1 troy ounce equals about 1.1 avoirdupois ounces.) They are stored without
wrappings in the vault compartments.
Aside from monetary uses, gold, like silver, is used in jewelry and allied wares, electrical-electronic applications, dentistry, the
aircraft-aerospace industry, the arts, and medical and chemical fields.
The changes in demand for gold and supply from domestic mines in the past two decades reflect price changes. After the United
States deregulated gold in 1971, the price increased markedly, briefly reaching more than $800 per troy ounce in 1980. Since
1980, the price has remained in the range of $320 to $460 per troy ounce. The rapidly rising prices of the 1970's encouraged
both experienced explorationists and amateur prospectors to renew their search for gold. As a result of their efforts, many new
mines opened in the 1980's, accounting for much of the expansion of gold output. The sharp declines in consumption in 1974 and
1980 resulted from reduced demands for jewelry (the major use of fabricated gold) and investment products, which in turn reflected
rapid price increases in those years.
Gold is called a "noble" metal (an alchemistic term) because it does not oxidize under ordinary conditions. Its chemical symbol Au is
derived from the Latin word "aurum." In pure form gold has a metallic luster and is sun yellow, but mixtures of other metals, such as
silver, copper, nickel, platinum, palladium, tellurium, and iron, with gold create various color hues ranging from silver-white to green and orange-red.
Pure gold is relatively soft--it has about the hardness of a penny. It is the most malleable and ductile of metals. The specific gravity or density of pure gold is 19.3 compared to 14.0 for mercury and 11.4 for lead.
Impure gold, as it commonly occurs in deposits, has a density of 16 to 18, whereas the associated waste rock (gangue) has a
density of about 2.5. The difference in density enables gold to be concentrated by gravity and permits the separation of gold
from clay, silt, sand, and gravel by various agitating and collecting devices such as the gold pan, rocker, and sluicebox.
Mercury (quicksilver) has a chemical affinity for gold. When mercury is added to gold-bearing material, the two metals form an
amalgam. Mercury is later separated from amalgam by retorting. Extraction of gold and other precious metals from their ores by
treatment with mercury is called amalgamation. Gold dissolves in aqua regia, a mixture of hydrochloric and nitric acids, and in
sodium or potassium cyanide. The latter solvent is the basis for the cyanide process that is used to recover gold from low-grade ore.
Hydraulic placer mining at Lost Chicken Hill Mine, near Chicken, Alaska. The firehose blasts the sediment outcrop, washing away sand, clay, gravel and gold particles. The material is then processed to remove the gold. USGS image.
The degree of purity of native gold, bullion (bars or ingots of unrefined gold), and refined gold is stated in terms of gold content. "Fineness" defines gold content in parts per thousand. For example, a gold nugget containing 885 parts of pure gold and 115 parts of other metals, such as silver and copper, would be considered 885-fine. "Karat" indicates the proportion of solid gold in an alloy based on a total of 24 parts. Thus, 14-karat (14K) gold indicates a composition of 14 parts of gold and 10 parts of other metals. Incidentally, 14K gold is commonly used in jewelry manufacture. "Karat" should not be confused with "carat," a unit of weight used for precious stones.
The basic unit of weight used in dealing with gold is the troy ounce. One troy ounce is equivalent to 20 troy pennyweights. In
the jewelry industry, the common unit of measure is the pennyweight (dwt.) which is equivalent to 1.555 grams.
The term "gold-filled" is used to describe articles of jewelry made of base metal which are covered on one or more surfaces with a
layer of gold alloy. A quality mark may be used to show the quantity and fineness of the gold alloy. In the United States no article
having a gold alloy coating of less than 10-karat fineness may have any quality mark affixed. Lower limits are permitted in some countries.
No article having a gold alloy portion of less than one-twentieth by weight may be marked "gold-filled," but articles may be marked
"rolled gold plate" provided the proportional fraction and fineness designations are also shown. Electroplated jewelry items carrying
at least 7 millionths of an inch (0.18 micrometers) of gold on significant surfaces may be labeled "electroplate." Plated thicknesses
less than this may be marked "gold flashed" or "gold washed."
Gold sluice: Portable gold sluice. Miners place the sluice in the stream and dump sediments in the upstream side. The current transports the sediments through the sluice and the heavy gold particles become lodged in the sluice. One miner can process a lot more sediment through a sluice than through a gold pan. Image copyright iStockphoto / LeeAnn Townsend.
Gold is relatively scarce in the earth, but it occurs in many different kinds of rocks and in many different geological environments. Though scarce, gold is concentrated by geologic processes to form commercial deposits of two principal types: lode (primary) deposits and placer (secondary) deposits.
Lode deposits are the targets for the "hardrock" prospector seeking gold at the site of its deposition from mineralizing solutions.
Geologists have proposed various hypotheses to explain the source of solutions from which mineral constituents are precipitated in lode deposits.
One widely accepted hypothesis proposes that many gold deposits, especially those found in igneous and sedimentary rocks, formed from circulating groundwaters driven by heat from bodies of magma (molten rock) intruded into the Earth's crust within about 2 to 5 miles of the surface. Active geothermal systems, which are exploited in parts of the United States for natural hot water and steam, provide a modern analog for these gold-depositing systems. Most of the water in geothermal systems originates as rainfall,
which moves downward through fractures and permeable beds in cooler parts of the crust and is drawn laterally into areas heated by
magma, where it is driven upward through fractures. As the water is heated, it dissolves metals from the surrounding rocks. When the
heated waters reach cooler rocks at shallower depths, metallic minerals precipitate to form veins or blanket-like ore bodies.
Another hypothesis suggests that gold-bearing solutions may be expelled from magma as it cools, precipitating ore materials as they
move into cooler surrounding rocks. This hypothesis is applied particularly to gold deposits located in or near masses of granitic rock,
which represent solidified magma.
A third hypothesis is applied mainly to gold-bearing veins in metamorphic rocks that occur in mountain belts at continental margins.
In the mountain-building process, sedimentary and volcanic rocks may be deeply buried or thrust under the edge of the continent, where
they are subjected to high temperatures and pressures resulting in chemical reactions that change the rocks to new mineral assemblages (metamorphism). This hypothesis suggests that water is expelled from the rocks and migrates upwards, precipitating ore materials as
pressures and temperatures decrease. The ore metals are thought to originate from the rocks undergoing active metamorphism.
The primary concerns of the prospector or miner interested in a lode deposit of gold are to determine the average gold content (tenor) per ton of mineralized rock and the size of the deposit. From these data, estimates can be made of the deposit's value.
One of the most commonly used methods for determining the gold and silver content of mineralized rocks is the fire assay. The results
are reported as troy ounces of gold or silver or both per short avoirdupois ton of ore or as grams per metric ton of ore.
Gold dredge: A scuba diver vacuums sediment to be processed by a portable gold dredge. Scuba gear allows the prospector to carefully get access to cracks and crevices on the stream bed where gold nuggets might be lodged. Image copyright iStockphoto / Gary Ferguson.
Gold is extremely resistant to weathering and, when freed from enclosing rocks, is carried downstream as metallic particles
consisting of "dust," flakes, grains, or nuggets. Gold particles in stream deposits are often concentrated on or near bedrock,
because they move downward during high-water periods when the entire bed load of sand, gravel, and boulders is agitated and is
moving downstream. Fine gold particles collect in depressions or in pockets in sand and gravel bars where the stream current
slackens. Concentrations of gold in gravel are called "pay streaks."
Gold drywasher: A portable dry washer used to sift gold nuggets from soil where water is not available. Soil is dumped into the top pan and is shaken through the bottom pan. Heavy gold nuggets are mechanically separated from lighter materials. Image copyright iStockphoto / Arturo M. Enriquez.
In gold-bearing country, prospectors look for gold where coarse sands and gravel have accumulated and where "black sands" have concentrated and settled with the gold. Magnetite is the most common mineral in black sands, but other heavy minerals such as cassiterite, monazite, ilmenite, chromite, platinum-group metals, and some gemstones may be present.
Placer deposits have formed in the same manner throughout the Earth's history. The processes of weathering and erosion create
surface placer deposits that may be buried under rock debris. Although these "fossil" placers are subsequently cemented into hard
rocks, the shape and characteristics of old river channels are still recognizable.
The content of recoverable free gold in placer deposits is determined by the free gold assay method, which involves amalgamation
of gold-bearing concentrate collected by dredging, hydraulic mining, or other placer mining operations. In the period when the
price of gold was fixed, the common practice was to report assay results as the value of gold (in cents or dollars) contained in
a cubic yard of material. Now results are reported as grams per cubic yard or grams per cubic meter.
Through laboratory research, the U.S. Geological Survey has developed new methods for determining the gold content of rocks and
soils of the Earth's crust. These methods, which detect and measure the amounts of other elements as well as gold, include
atomic absorption spectrometry, neutron activation, and inductively coupled plasma-atomic emissionon spectrometry. These methods
enable rapid and extremely sensitive analyses to be made of large numbers of samples.
Gold was produced in the southern Appalachian region as early as 1792 and perhaps as early as 1775 in southern California. The
discovery of gold at Sutter's Mill in California sparked the gold rush of 1849-50, and hundreds of mining camps sprang to life
as new deposits were discovered. Gold production increased rapidly. Deposits in the Mother Lode and Grass Valley districts in
California and the Comstock Lode in Nevada were discovered during the 1860's, and the Cripple Creek deposits in Colorado began
to produce gold in 1892. By 1905 the Tonopah and Goldfield deposits in Nevada and the Alaskan placer deposits had been discovered,
and United States gold production for the first time exceeded 4 million troy ounces a year--a level maintained until 1917.
During World War I and for some years thereafter, the annual production declined to about 2 million ounces. When the price of
gold was raised from $20.67 to $35 an ounce in 1934, production increased rapidly and again exceeded the 4-million-ounce level
in 1937. Shortly after the start of World War II, gold mines were closed by the War Production Board and not permitted to reopen until 1945.
From the end of World War II through 1983, domestic mine production of gold did not exceed 2 million ounces annually. Since 1985,
annual production has risen by 1 million to 1.5 million ounces every year. By the end of 1989, the cumulative output from deposits
in the United States since 1792 reached 363 million ounces.
Consumption of gold in the United States ranged from about 6 million to more than 7 million troy ounces per year from 1969 to 1973,
and from about 4 million to 5 million troy ounces per year from 1974 to 1979, whereas during the 1970's annual gold production from
domestic mines ranged from about 1 million to 1.75 million troy ounces. Since 1980 consumption of gold has been nearly constant at
between 3 and 3.5 million troy ounces per year. Mine production has increased at a quickening pace since 1980, reaching about 9
million troy ounces per year in 1990, and exceeding consumption since 1986. Prior to 1986, the balance of supply was obtained from
secondary (scrap) sources and imports. Total world production of gold is estimated to be about 3.4 billion troy ounces, of which more
than two-thirds was mined in the past 50 years. About 45 percent of the world's total gold production has been from the Witwatersrand
district in South Africa.
The largest gold mine in the United States is the Homestake mine at Lead, South Dakota. This mine, which is 8,000 feet deep, has
accounted for almost 10 percent of total United States gold production since it opened in 1876. It has combined production and
reserves of about 40 million troy ounces.
In the past two decades, low-grade disseminated gold deposits have become increasingly important. More than 75 such deposits have
been found in the Western States, mostly in Nevada. The first major producer of this type was the Carlin deposit, which was
discovered in 1962 and started production in 1965. Since then many more deposits have been discovered in the vicinity of Carlin,
and the Carlin area now comprises a major mining district with seven operating open pits producing more than 1,500,000 troy ounces
of gold per year.
About 15 percent of the gold produced in the United States has come from mining other metallic ores. Where base metals- -such as
copper, lead, and zinc--are deposited, either in veins or as scattered mineral grains, minor amounts of gold are commonly deposited
with them. Deposits of this type are mined for the predominant metals, but the gold is also recovered as a byproduct during processing
of the ore. Most byproduct gold has come from porphyry deposits, which are so large that even though they contain only a small amount
of gold per ton of ore, so much rock is mined that a substantial amount of gold is recovered. The largest single source of byproduct
gold in the United States is the porphyry deposit at Bingham Canyon, Utah, which has produced about 18 million troy ounces of gold since 1906.
Geologists examine all factors controlling the origin and emplacement of mineral deposits, including those containing gold. Igneous
and metamorphic rocks are studied in the field and in the laboratory to gain an understanding of how they came to their present
location, how they crystallized to solid rock, and how mineral-bearing solutions formed within them. Studies of rock structures,
such as folds, faults, fractures, and joints, and of the effects of heat and pressure on rocks suggest why and where fractures
occurred and where veins might be found. Studies of weathering processes and transportation of rock debris by water enable geologists
to predict the most likely places for placer deposits to form. The occurrence of gold is not capricious; its presence in various rocks
and its occurrence under differing environmental conditions follow natural laws. As geologists increase their knowledge of the mineralizing
processes, they improve their ability to find gold.
gold mining & mining shares | guide from bullionvault
Buying gold mining shares is widely seen as a way of gaining exposure to movements in the gold price. If that is your aim you should also check out buying gold bullion which is increasingly popular, having become very much easier over recent years.
Gold's average concentration in the Earth's crust is 0.005 parts per million. The technology of extraction is expensive primarily because the process always requires gold mining companies to manipulate large physical quantities of ore for small results. The energy required to heave, grind and process ore is itself valuable, as are the chemicals used in the process, and this places a lower limit on the quality of ore which can be profitably worked in the gold mining process.
At different points concentration of minerals within the earth's crust varies from their average, and it is those variations which produce workable ores for gold mining. Iron, for example, accounts for an average 5.8% of the content of the Earth's crust. It needs to be concentrated by natural variations to about 30% to be considered an ore, indicating a required geological concentration of about 5 times. A lower grade gold ore would contain something like 5 grams per tonne (5 parts per million). So gold ore needs to be concentrated by about 1,000 times above its average dispersion to become viable for gold mining.
The process of gold concentration happens both above and below the surface of the Earth. On the surface there is alluvial gold which has been concentrated by the effects of running water, usually rivers. Because of its extreme density metallic gold will readily fall out of suspension as water slows down. So where a river cuts through gold bearing rock, and then slows down as it hits a flatter/wider river bed, gold will concentrate in a 'placer' deposit, allowing extraction of gold particles by panning and the modern day industrial gold mining equivalents.
Underground gold veins or 'lodes' are produced in association with various metallic deposits, often including sulphides and pyrites. Gold concentration may occur as other minerals are leached away over a long period. Ore of sufficient yield to support gold mining is very rare.
Amalgamation is a mercury based process which works because of gold's willingness to be dissolved by mercury. The mercury is applied on an ore, picks up the gold, and the resulting amalgam is distilled, with the mercury being boiled off to remove it. Mercury is highly toxic and therefore environmentally sensitive, making the industrial plant to perform this type of extraction expensive.
The most important purification process in gold mining is cyanidation. Sodium cyanide solution in the presence of air causes gold to enter into solution. Good quality ores give up their gold under cyanidation in what is called vat leaching. Lesser quality ores require heap leaching, which involves huge piles of ore being repeatedly re-sprayed with the cyanide solution over a prolonged period.
Relatively raw gold is purified in two main ways. The cheaper first stage of purification is the Miller process which uses chlorine gas and reaches purification of 99.5%, and then there is the more expensive Wohlwill process which electrolyses gold to purities of 99.99%.
These disadvantages of gold mining shares have got worse in recent years. Exploration businesses which have found gold in smaller countries have been forced to build roads, hospitals, schools and other social infrastructure, as well as repair the damage they do. The host government is quite quickly able to assess the value of a newly discovered resource, and to load the permission to mine accordingly. The social costs have increased far faster than the value of the gold found.
Gold mining shares are a potentially risky but simultaneously exciting investment. They tend to be reasonably correlated to gold prices but typically much more volatile, and subject to many variations which are independent of bullion market forces. Buying gold bullion is less expensive on dealing costs.
Choosing the right gold mining stocks - or even just the right gold mining index to follow - is crucial. But while individual gold mining companies can offer the potential of high-risk returns, the gold mining industry as a whole is facing growing problems of cost, politics and finance.
First, the "easy gold" available in relatively safe and secure parts of the world has already gone. Annual gold mining output in increasingly unpredictable South Africa - until recently the world's No.1 gold mining producer - has halved since 1998. China - now the world's top producer - remains dangerous both to its miners themselves, and in financial terms remains dubious. In the world's safest mines in North America gold mining output is now just 78% of 2002 levels.
The quality of gold ore mined is falling fast too, meaning more digging is needed to produce each ounce, and less stable regions have yet to pick up the pace. Zimbabwe's gold output, for instance, has fallen to "pathetic levels" according to press reports from Harare.
Gold mining stock investors also face the classic problem thrown up by a commodities boom - populist governments stealing their assets. In the winter of 2006/07 alone, the military government in Fiji seized the Vatukoula mine belonging to DRDGold, while the Russian environmental agency Rospriradnadzor revoked two mining licenses owned by Peter Hambro, the London-listed gold producer.
Gabriel Resources' project at Rosia Montana in Romania, for instance, may hold the largest undeveloped gold mining reserves in Europe. But upturning five mountains to get at 450 tonnes of gold just doesn't fit with today's green politics. There are no "carbon offset" contracts for spilling mercury, cyanide and heavy metals into local rivers.
China's gold mining output has surged recently, but this growth could reverse sharply according to a leading industry figure. "It's urgent for Chinese companies to develop gold mines overseas," says Ren Guangzhi, investment manager at Zijin Mining Group, owner of China's biggest gold mine. Unless new deposits are found and developed soon, he believes China's reserves - including gold-only mines now producing 200 tonnes per year - could run out within six years.
Westhouse Securities estimates that between 1985 and 2003, new gold ounce discoveries slipped by 30% from the previous 15 years. Each new troy ounce discovered also cost 2.6 times as much to locate, too. And large deposits - judged at 2.5 million ounces or more - have simply been too few and far between to replace the major gold mining companies' current rate of production.
With new gold deposits proving costly and difficult to locate, gold mining companies are trying to mine more gold from their existing properties. Again, this adds to the growing costs of gold mining, and it also increases risks for gold mining workers.
Gold Fields, the world's fourth largest gold mining company, is now starting work on the world's deepest-ever mining projects - more than 4 kilometers below ground. According to Mining Weekly magazine, Gold Fields will spend 4.7 billion Rand (almost $0.7 billion) to deepen both its Kloof and Driefontein mines near Carletonville, South Africa, giving it access to 10.8 million ounces of gold from 2011 onwards.
"Mining deeper and deeper does not come cheaply," says Mining Weekly. "At Driefontein, apart from the capital costs to get there, mining at depth will cost ZAR66,000 per kilo ($296 per ounce) over the life of the mine."
South Africa already has higher gold-mining costs per ounce than even North America, where Newmont Mining, the second largest gold miner in the world, saw its average gold mining costs rise by two-thirds per ounce between 2002 and 2007.
Thanks to soaring costs and shrinking reserves, Prudential Equity forecasts that Newmont's combined output with Barrick Gold, the largest gold mining stock in the world, would be 40 or 50 tonnes less than expected in 2007.
How can the world's major gold mining companies defend their share price? "It is still easier and cheaper to find gold on the stock market than to find it through exploration," noted Michael Martin, a 28-year veteran of gold stock investing at R.F.Lafferty in New York, recently.
But while gold-mining M&A (mergers & acquisitions) can help boost an individual gold mining company's shrinking reserves, digging for gold on the stock market does nothing to increase total global supplies. The net effect, in fact, is to cut exploration spending.
Over the last ten years, post-merger exploration budgets have shrunk by 20% compared with the money spent 12 months' previous by the individual gold miners involved. And at the very same time, falling reserves replacement over the last 10 years "may result in gold supply shortages in the long term," warn analysts at the Metals Economics Group.
Some investment advisors have compared investing in gold mining stocks to playing the "lottery". Sound analysis and detailed research should certainly give you a better edge than that, but the risks to any gold mining investment can be severe - and they are now mounting.
Unlike buying gold bullion itself, investing in gold mining stocks invites political & management risk, plus the danger of rising costs eating into new profits. If you're looking to buy gold for security - rather than the chance of high-risk, turbo-charged returns - then you should beware chasing the idea of "leverage" to the gold price.
Gold is a separate asset class from gold mining stocks altogether. And with the gold mining industry struggling to raise output, growing demand for the security of gold bullion is now crashing into slowing supply.
Please Note: This analysis is published to inform your thinking, not lead it. Previous price trends are no guarantee of future performance. Before investing in any asset, you should seek financial advice if unsure about its suitability to your personal circumstances.
environmental impacts of gold mining | brilliant earth
Dirty gold mining has ravaged landscapes, contaminated water supplies, and contributed to the destruction of vital ecosystems. Cyanide, mercury, and other toxic substances are regularly released into the environment due to dirty gold mining.
Modern industrial gold mining destroys landscapes and creates huge amountsof toxic waste. Due to the use of dirty practices such as open pit mining and cyanide heap leaching, mining companies generate about 20 tons of toxic waste for every 0.333-ounce gold ring. The waste, usually a gray liquid sludge, is laden with deadly cyanide and toxic heavy metals.
Many gold mines dump their toxic waste directly into natural water bodies. The Lihir gold mine in Papua New Guinea dumps over 5 million tons of toxic waste into the Pacific Ocean each year, destroying corals and other ocean life. Companies mining for gold and other metals in total dump at least 180 million tons of toxic waste into rivers, lakes, and oceans each yearmore than 1.5 times the waste that U.S. cities send to landfills on a yearly basis.
To limit the environmental damage, mines often construct dams and place the toxic waste inside. But these dams do not necessarily prevent contamination of the surrounding environment. Toxic waste can easily seep into soil and groundwater, or be released in catastrophic spills. At the worlds estimated 3,500 dams built to hold mine waste, one or two major spills occur every year.
Toxic waste spills have had devastating consequences in Romania, China, Ghana, Russia, Peru, South Africa, and other countries. In 2014, a dam collapsed at the Mount Polley gold and copper mine in British Columbia, sending about 25 million cubic meters of cyanide-laden waste into nearby rivers and lakesenough to fill about 9,800 Olympic-sized swimming pools. The spill poisoned water supplies, killed fish, and harmed local tourism.
Dirty gold mining often leads to a persistent problem known as acid mine drainage. The problem results when underground rock disturbed by mining is newly exposed to air and water. Iron sulfides (often called fools gold) in the rock can react with oxygen to form sulfuric acid. Acidic water draining from mine sites can be 20 to 300 times more concentrated than acid rain, and it is toxic to living organisms.
The dangers increase when this acidic water runs over rocks and strips out other embedded heavy metals. Rivers and streams can become contaminated with metals such as cadmium, arsenic, lead, and iron. Cadmium has been linked to liver disease, while arsenic can cause skin cancer and tumors. Lead poisoning can cause learning disabilities and impaired development in children. Iron is less dangerous, although it gives rivers and streams a slimy orange coating and the smell of rotten eggs.
Once acid mine drainage starts, it is difficult to stop. Acidic waters flowing from abandoned mines can raise acidity levels and destroy aquatic life for generations. Roman mining sites in England are still causing acid mine drainage more than 2000 years later.
The use of mercury in gold mining is causing a global health and environmental crisis. Mercury, a liquid metal, is used in artisanal and small-scale gold mining to extract gold from rock and sediment. Unfortunately, mercury is a toxic substance that wreaks havoc on miners health, not to mention the health of the planet.
For every gram of gold produced, artisanal gold miners release about two grams of mercury into the environment. Together, the worlds 10 to 15 million artisanal gold miners release about 1000 tons of mercury into the environment each year, or 35 percent of man-made mercury pollution. Artisanal gold mining is actually among the leading causes of global mercury pollution, ahead of coal-fired power plants.
When mercury enters the atmosphere or reaches rivers, lakes, and oceans, it can travel across great distances. About 70 percent of the mercury deposited in the United States is from international sources. Still more mercury reaches the United States through imported fish. Once it reaches a resting place, mercury is not easily removed. Sediments on the floor of San Francisco Bay remain contaminatedwith mercury left by the California gold rush of the 19th century.
Mercury is extremely harmful to human health. The amount of vapor released by mining activities has been proven to damage the kidneys, liver, brain, heart, lungs, colon, and immune system. Chronic exposure to mercury may result in fatigue, weight loss, tremors, and shifts in behavior. In children and developing fetuses, mercury can impair neurological development.
A gold mining boom is accelerating the destruction of the Amazon rainforest, a biologically diverse ecosystem that acts as a check on global warming. Artisanal, or small-scale, gold miners are tearing down the forest to access the rich gold deposits beneath. One study found that deforestation rates in the Madre de Dios region of the Peruvian Amazon have increased six-fold due to gold mining.
Gold mining is also responsible for releasing large amounts of mercury into the Amazons air and water. The mercury is poisoning plants, animals, fish, and people. In one city in the Peruvian Amazon, unsafe mercury levels were recorded in 80 percent of local residents. The gold mining boom does not bode well for the Amazon or the people, both locally and globally, who depend on it.