What Types Of Rocks And Minerals Are Associated With Gold
There are a number of different rocks and minerals that are found near gold or are part of gold deposits. By starting your search for these rocks and minerals, you are essentially looking for a broader footprint of where the gold might be.
Properties Occurrences And Uses
Gold is one of the densest of all metals. It is a good conductor of heat and electricity. It is also soft and the most malleable and ductile of the elements an ounce can be beaten out to 187 square feet in extremely thin sheets called gold leaf.
Because gold is visually pleasing and workable and does not tarnish or corrode, it was one of the first metals to attract human attention. Examples of elaborate gold workmanship, many in nearly perfect condition, survive from ancient Egyptian, Minoan, Assyrian, and Etruscan artisans, and gold continues to be a highly favoured material out of which to craft jewelry and other decorative objects.
Gold is widespread in low concentrations in all igneous rocks. Its abundance in Earths crust is estimated at about 0.005 part per million. It occurs mostly in the native state, remaining chemically uncombined except with tellurium, selenium, and bismuth. The elements only naturally occurring isotope is gold-197. Gold often occurs in association with copper and lead deposits, and, though the quantity present is often extremely small, it is readily recovered as a by-product in the refining of those base metals. Large masses of gold-bearing rock rich enough to be called ores are unusual. Two types of deposits containing significant amounts of gold are known: hydrothermal veins, where it is associated with quartz and pyrite and placer deposits, both consolidated and unconsolidated, that are derived from the weathering of gold-bearing rocks.
Gold Deposits At The Zortman
This page was written by Erin Klauk as part of the DLESE Community Services Project: Integrating Research in Education.
Gold is one of the most economically important metals produced. As of 1991, more than 83% of gold consumption went into jewelry, 6% was used for medals and official coins, 6% was used in electronic equipment, 2.2% was used for dental materials, and 2.8% was consumed in a variety of industrial applications. These markets support an annual gold production of about 2,200 tons worth almost $25 billion .
There are many types of gold deposits including vein deposits, contact deposits, replacement deposits, disseminated ore and placers. A few miles south of the Fort Belknap Indian Reservation lies the Zortman-Landusky mine where gold is found in intrusion related breccia-hosted deposits in the Little Rocky Mountains. In this type of deposit, gold mineralization is found in magmatic-hydrothermal or phreatomagmatic pipe-like breccias associated with the intrusion of stocks, plugs, sills or dikes into a wide variety of host rocks ranging in age from Precambrian to Tertiary ).
To further investigate gold deposits at the Zortman-Landusky mine, follow the links below.
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Public Information For Gold Prospectors
Locations of important gold-producing districts of the United States are shown in some of the reports of the United States Geological Survey listed at the bottom of this page. Geological surveys of the principal gold-producing States where additional information may be obtained also are listed. Information may be obtained, too, from U.S. Bureau of Mines State Liaison offices located in the capital cities of most States. There are also a large number of layman’s books about gold that describe gold deposits and gold prospecting.
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 Geology Of Placer Deposits
A placer deposit is a concentration of a natural material that has accumulated in unconsolidated sediments of a stream bed, beach, or residual deposit. Gold derived by weathering or other process from lode deposits is likely to accumulate in placer deposits because of its weight and resistance to corrosion. In addition, its characteristically sun-yellow color makes it easily and quickly recognizable even in very small quantities. The gold pan or miner’s pan is a shallow sheet-iron vessel with sloping sides and flat bottom used to wash gold-bearing gravel or other material containing heavy minerals. The process of washing material in a pan, referred to as “panning,” is the simplest and most commonly used and least expensive method for a prospector to separate gold from the silt, sand, and gravel of the stream deposits. It is a tedious, back-breaking job and only with practice does one become proficient in the operation.
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Eight Natural Geologic Signs Pointing Toward Gold
Sometimes I get asked, What should I look for when metal detecting that will tell me there is gold present in the ground? I always respond that I wish there was a simple, easy answer. The problem is that gold occurs in many types of deposits, and what indicators work great for one type of deposit dont always work well for another. As an example, in some places the presence of vein quartz on the ground is a valuable indicator, yet I have been in places where there is so much vein quartz everywhere that is worthless as an indicator, and other places that have good gold but are essentially devoid of any vein quartz at all.
Here is a listing of some common geologic indicators that you can look for which will be helpful in many cases, but not in all.
Many Placer Deposits Have Been Worked
Many believe that it is possible to make wages or better by panning gold in the streams of the West, particularly in regions where placer mining formerly flourished. However, most placer deposits have been thoroughly reworked at least twice–first by Chinese laborers, who arrived soon after the initial boom periods and recovered gold from the lower grade deposits and tailings left by the first miners, and later by itinerant miners during the 1930’s.
Geologists and engineers who systematically investigate remote parts of the country find small placer diggings and old prospect pits whose number and wide distribution imply few, if any, recognizable surface indications of metal-bearing deposits were overlooked by the earlier miners and prospectors.
Convergent plate boundaries are the plate tectonic setting of many gold deposits. There, magma produced by the melting of descending lithosphere rises as magma chambers and crystallizes close to the surface. Gold in these hot environments is often dissolved in superheated water and carried away from the magma chamber along faults and fractures. The water temperature is very high near the magma chamber but drops with distance. As the water travels farther from the magma chamber, gold starts to crystallize out within the fracture to produce a vein gold deposit. USGS image.
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Where Does Gold Come From
Gold is heavenly, in every sense of the word. Most people dont know this but, while we mine for gold here on earth, all of the gold thats deposited in our planet was formed during the explosions of stars and collisions of asteroids, and eventually found its way to earth over time.On earth, gold is one of the most valuable precious metals and rarest natural minerals. It is also one of the 118 elements so far discovered and classified by humans.Pure gold is a bright warm yellow, malleable and soft substance. Its so soft that, in its purest form, it cant really be used for everyday wear. To harden it, it is alloyed with a mixture of metals like silver, copper, platinum, palladium and zinc.Its primary use is in jewellery, but its also used in finance, electronics, computers, dentistry, medicine, aerospace, glassmaking, and as awards and status symbols.Its clearly present in the formation and upkeep of many of our innovations, but how is gold made?
Similar Appearances To Nearby Gold Districts
One of the best ways to find new, undiscovered gold deposits is to study the geology of known gold districts and then explore the fringes of that known district. Identify areas that have a similar geological appearance.
We are not discussing any specific indicator here. This could be one or several natural indicators that are similar to a gold district with a known history of gold production. This is one of the best ways to find an area that nobody has ever prospected before, but it can take a lot of time and patience, and you will likely spend a lot of time searching before you stumble upon any gold.
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The Many Rewards Of Finding Gold
Anyone who pans for gold hopes to be rewarded by the glitter of colors in the fine material collected in the bottom of the pan. Although the exercise and outdoor activity experienced in prospecting are rewarding, there are few thrills comparable to finding gold. Even an assay report showing an appreciable content of gold in a sample obtained from a lode deposit is exciting. The would-be prospector hoping for financial gain, however, should carefully consider all the pertinent facts before deciding on a prospecting venture.
Undiscovered Gold Is Finely Disseminated
Gold, if present, may not be visible in the rock, and detection will depend on the results of laboratory analyses. Usually, samples of 3 to 5 pounds of representative mineralized rock will be sent to a commercial analytical laboratory or assay office for assay. Obviously, knowledge about the geological nature of gold deposits and particularly of the rocks and deposits in the area of interest will aid the prospector.
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Study Persistence And Financial Backing
Some degree of success in finding gold still remains for those choosing favorable areas after a careful study of mining records and the geology of the mining districts. Serious prospecting should not be attempted by anyone without sufficient capital to support a long and possibly discouraging campaign of preliminary work. The prospective gold seeker must have ample funds to travel to and from the region he selects to prospect and to support the venture. He must be prepared to undergo physical hardships, possess a car capable of traveling the roughest and steepest roads, and not be discouraged by repeated disappointments. Even if a discovery of value is not found, the venture will have been interesting and challenging.
Fortitude Mine in Nevada produced about 2 million ounces of gold between 1984 and 1993. USGS image.
Where Did Gold Come From
So you know the different places where gold can be found, but how did this precious metal end up beneath our earths crust? This element arrived on our planet around 200 million years after its creation, when meteorites full of gold and other metals hurtled into the surface from space. Later, as the planets formation shifted, a vast quantity of molten iron sank to the earths core, and with it took almost all the precious metals on earth. The amount is estimated to include enough gold, platinum, and other precious metals in a 4-meter thick layer.
In the many millennia, since this occurred, varying amounts of gold and other minerals have been transported up to the earths crust, where it is accessible to our mining operations. Superheated fluid from the core of the earth flows upwards towards the crust, depositing gold in rock crevices. This process forms primary gold, and in turn creates secondary gold, providing this incredibly useful precious metal to us.
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Presence Of Various Minerals
Its worth knowing that gold presence is often associated with well-known minerals. If it helps, be sure to be well-acquainted with various types of minerals in a certain location. That said, conduct research and do your homework before heading off to the site for gold prospecting because it will increase your chances of finding gold deposits in the area!
Identifying Rocks That Contain Gold
Most rocks cannot be identified as containing gold, even though many of them do. Quartz rocks containing gold can easily be identified because you can actually see the gold. Large quartz rocks containing visible gold are often desired by rock and mineral collectors.
For rocks where you cannot see the gold there is a process of extraction. This usually requires breaking up the rocks, doing measurements, and using heat. Once you have some gold, you can calculate how much of it you have, compared to how much rock you extracted it from.
If there is enough gold extracted, it may be worth continuing to extract it from that gold ore.
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Soils Associated With Gold Deposits
By far, the best-known type of soil which may indicate the presence of gold is known as black sand. Black sands are certainly not proof of the existence of nearby gold, only that the soil has a lot of minerals and heavy metals, one of which is gold. Gold is one of the heaviest substances about 19 times the weight of water so any gold being carried by water in a stream is the first to fall. Black sand is not as heavy as gold, which is more than 3 times as heavy as the iron which makes up much of the black sand, it still weighs more than most other substances. So, while black sand does not guarantee gold, it is definitely worth a look for that elusive treasure.
Changes in the color of soil can be another indicator of nearby gold. Iron staining is another excellent indicator that gold may be present. The iron stains are in yellow or reddish soil. Soil which contains iron may also be black, provided it has not oxidized. Where iron or other heavy metals are located, gold may also be found. Soil and rocks are sometimes bleached to a lighter color than other nearby rocks due to acid from lode deposits underground. Sometimes, gold is near that lighter rock and soil.
I find more specimens like this one than I do with just gold and white quartz.
Few Prospectors Find Valuable Gold Deposits
Only a few prospectors among the many thousands who searched the western part of the United States ever found a valuable deposit. Most of the gold mining districts in the West were located by pioneers, many of whom were experienced gold miners from the southern Appalachian region, but even in colonial times only a small proportion of the gold seekers were successful.
Hydrogeochemical prospecting for gold: Groundwater collected from wells, springs, and drill holes may provide clues to the presence of subsurface gold deposits. As groundwater flows through the deposit, minute amounts of gold are leached from the rocks. These can sometimes be detected in groundwater samples collected from wells located down gradient from the deposit. USGS image.
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Not Just Rocks But Minerals Can Contain Gold
Calaverite and sylvanite are minerals that contain gold. There chemical formula makeup includes the element Au. Sylvanite will contain around 34% gold, calaverite will contain around 43%.
These two minerals are almost the same in chemical composition. What separates them as two different minerals is the content of silver. If there is less than a little over 13% of silver, replaced by gold, then it is considered calaverite.
Many other minerals can contain amounts of gold in them. Though they may not be part of the chemical makeup of the mineral, they may present in the mineral as an impurity.
Pyrite is a good example of this. Though pyrite is often called fools gold, it can actually contain gold. At times, if the contents of gold is high enough in pyrite, it will be extracted. Keep in mind the ratio of gold to current price of gold, as your cost to extract may exceed your profit!
Pyrite is a wonderful mineral that many people especially kids love to collect. I have written a great article on pyrite All About Pyrite including information and pictures.