Rocks that contain gold are a natural resource that you can find in many different parts of the world. These minerals can be found in many different rocks, such as Calavarite and quartz, as well as alluvial deposits, and Greenstone belts.
Calavarite
Calaverite is a unique mineral that is rare, and has been misidentified in the past. It is not found in most of the world, but there are some places where it is common. You can find it in some elixirs, and it is also used in spiritual reflection.
Calaverite is a gold telluride that is commonly found in veins and sulfides. It has a metallic luster, and may be brassy yellow. In certain locations, calaverite is also a source of silver. The mineral is a member of the krennerite group of sulfides.
Typically, Calaverite has a hardness of 2 1/2 to 3 on the Mohs scale. This varies depending on the formation, and the amount of gold. Normally, the ore treatment process is followed by crushing and gravimetry. However, in some cases, the process may be preceded by cyanidation, in which case the recovery can be as high as 90%.
When Calaverite is crystallized, it can be very brittle. Some collectors have referred to it as fool’s gold. These crystals are often striations, but they are not usually parallel. They can have smooth protrusions.
In some areas, the mineral can be found in placer stream gravel. In other parts of the world, however, it is mined, and can be worth hundreds of dollars at auction.
Although it is one of the most precious minerals, it has no biological use. Usually, it is found as an alloy with other metals.
Auriferous granite
Granite rocks are commonly associated with gold mineralization. Gold-bearing veins occur in metasedimentary rocks, diorite dikes, or in porphyritic granite. Although granite-hosted gold deposits are known, no one knows where or when they formed.
The gold-bearing veins in granite are usually free-formed, but may be buried by compact granite. They also can be influenced by walls or country-rock change. In addition, the nature of the ore is variable, and some veins are euhedral. Some have a very high content of gold and others contain less.
Minerals found in auriferous quartz vein ores are native gold, chalcopyrite, and electrum. Pyrite and arsenopyrite are present in disseminated ores. Fine-grained sulfides are found in the margins of stockwork veins.
Granite hosted gold deposits have been investigated by geochemical studies. Auriferous quartz vein ores are generally coarse-grained and have minor sulfides. These ores are hosted by a thrust fault structure. Occasionally, the ores are fractured and contain pyrite and native gold.
The fine-grained sulfide in disseminated ores is usually euhedral and contains pyrite and arsenopyrite. Minor minerals, such as galena and boulangerite, are often present as anhedral grains.
Granite-hosted gold deposits are believed to be derived from a magmatic fluid. However, it is unclear how the rock was cooled. Several hypotheses have been proposed. Some of these include mixed meteoric/magmatic fluids and metamorphic fluids. Nonetheless, these are all highly debated.
It is interesting to note that auriferous quartz vein ores and disseminated ores have similar mineral assemblages. Both types of ores are host to tetrahedrite, chalcopyrite, and native gold. Moreover, the d34S range of pyrites is narrow, suggesting that magmatic fluids were responsible.
Auriferous quartz
The Witwatersrand system in South Africa is one of the largest auriferous concentrations on Earth. It consists of quartzites and conglomerates with abundant pyrite.
Gold bearing veins can be found in sedimentary rocks and igneous rocks. These deposits are rich in gold and pyrite. The most productive conglomerates are located in the upper part of the Witwatersrand system.
Quartz, the most common silica mineral in the Earth’s crust, has numerous geochemical properties. Small metallic particles of gold are commonly found in quartz. They are also present in sulfide minerals. Minerals containing sulfides, such as chalcopyrite, siderite, and pyrite, are usually associated with gold.
Refractory gold deposits are those that occur when gold and pyrite are in solid solution. They are formed when the rock is altered in a heated way. This results in a high concentration of silica. If the dissolved mineral products are removed, the remaining residue is enriched with gold.
Some quartz veins are associated with sulfides, such as pyrite and siderite. These are often accompanied by tellurides. Tellurides occur as native gold, as tellurides of gold with various metals, or as a telluride of gold with antimony.
Auriferous quartz veins are generally found in granite and mafic dykes. Quartz gains are usually dark gray.
The Witwatersrand system is faulted and cut by diabase dikes. A syncline is located on the north side of the system. In this region, auriferous quartz is associated with a variety of lithified conglomerates, which are composed of rounded pebbles of quartz.
Auriferous basalt
Gold is a rare metal found in small quantities in some rocks. It is typically found in granitic and plutonic rocks, but can also be present in basalt and slate. Granite is a coarse-grained, quartz-rich intrusive igneous rock. Granite is often floated in a dilute cyanide solution with a zinc catalyst, and is sometimes subjected to cyanide extraction.
The presence of gold in basalt is believed to result from a combination of processes that occur at the lithospheric scale. Some of these processes are thought to interact with one another, and may overlap in space and time.
One of the processes may have led to the formation of an auriferous region in Patagonian Argentina. This auriferous region, a portion of the Chon Aike silicic large igneous province, contains several Au-Ag epithermal deposits. These deposits are associated with calc-alkaline rhyolites and basaltic andesites.
Other factors are believed to have contributed to the development of the auriferous province. They include the influence of a mantle plume, which acted as a source of heat. During this event, magmas migrated from the mantle to the continental crust. As they traveled, the magmas accumulated Au, which was eventually transported downstream.
Another factor is that the auriferous region is located in a subduction zone, which enhanced the possibility of magmas to transport Au. However, this process cannot be directly related to the formation of auriferous basalt.
Greenstone belts
Greenstone belts are geologically important because they host numerous gold deposits. They are comprised of volcanic rocks, which are classified into a variety of types. The rocks are primarily composed of basalts and lava. Mineralized rocks are also found in these regions.
These greenstone belts are formed in inter-arc basins, back-arc basins and the oceanic crust. Their formation is mainly due to volcanic activity. In addition, the structure of a greenstone belt varies with time. As a result, the amount of sediment within it has changed over time.
There are two main kinds of greenstone belts. One type of greenstone belt is an Archean greenstone belt. This belt is a combination of ancient volcanic rocks that have been metamorphosed over millions of years.
Another kind of greenstone belt is a Proterozoic greenstone belt. This belt is characterized by rocks that are placed on the basement of granite-gneiss cratons. A large part of the gold occurrences found in these belts occur in shear zones oblique to the deformation of the craton.
Greenstone belts are generally associated with orogenic gold systems. They are named for the green cast of their constituent minerals. Gold is not found in all greenstone belts, though.
Some greenstone belts are located in Africa. Examples include the Lake Victoria, Kaapvaal and Giyani cratons. Other examples are found in Western Australia, in the US, and in parts of Canada.
Alluvial deposits
Alluvial deposits that contain gold are located in many countries. The first recorded use of alluvial deposits for gold was during the ancient Roman Empire. Ancient Rome used sluices to extract gold from mountain sides. Today, mining is done using surface excavating equipment or open-pit mining.
These deposits have been found in most of the world’s countries. In Australia, the Kalgoorlie gold rush was brought on by a minor alluvial deposit. Other recent discoveries have been made on the Amazon region of Brazil.
These alluvial deposits are composed of coarse gold. They are relatively thick in diameter and usually only contain a small amount of precious metals. It’s a good idea to use your fingers to pick up these coarse gold grains.
Some of the different types of alluvial deposits are: conglomerate, bleed-off deposit, bench placer, delta deposit, and lode. A conglomerate is a large, crack-like rock that has been water worn. Depending on the size of the conglomerate, it may be narrow, long, or thin.
Another type of alluvial deposit is the beach. This type of deposit is found in some areas of New Zealand. Beach deposits are also found in other parts of the world.
Unconsolidated sediments are important for construction purposes. They can be thick or thin, and can cover only a few hundred square feet.
Usually, these deposits have a higher concentration of gold than the loose gold-bearing sediment. However, these are only a fraction of the total deposit.