Finding gold is a dream for many people, but it can be difficult to find. Gold often occurs in veins that run through specific types of rocks, and it is important to know where these rock formations occur to increase your chances of finding the precious metal.
Sedimentary rocks contain more gold than any other type of rock. This is because igneous and metamorphic rocks sometimes part their gold with other stones, resulting in sedimentary deposits.
Quartz
Quartz is a common mineral and is known for its hardness and durability. Besides being found in jewelry, it is also used to make glass and scientific instruments. Quartz can have many hues due to the impurities that exist within it. It can be icy clear or have inclusions, veils and bubbles in it. The ancients referred to this stone as a crystal ball or talisman and believed it held the secrets of life.
Interestingly, quartz can contain gold. This is because it has a tendency to trap minerals and metals in its crevices. This happens as it forms and solidifies in nature. As the rock ages, these minerals and metals tend to rush out. They leave behind voids and tiny cracks that the gold can become trapped in. The resulting rock is called a quartz vein and can contain varying amounts of gold.
These quartz veins are formed when magma or rock that originates deep in the Earth travels to the surface through volcanic activity. As the magma cools, it leaves behind quartz and other minerals and metals. They can be found in igneous rocks such as basalt or gabbro and also in metamorphic stones like slate. Gold-bearing quartz can be found in these rocks as well as in schists such as greenschist.
When quartz contains gold, it usually concentrates in one of three locations within the vein. These locations are the hanging wall, foot wall or right down the centerline of the vein. When prospecting, look for auriferous quartz in these areas with a metal detector.
Over time, gold can be eroded and carried by streams and rivers downstream. When this happens, it can become deposited in sand and gravel deposits. This is usually comprised of white quartz and is often found in places where the stream flows slows down, such as eddies or behind large rocks.
This is why it is important to know the geology of a particular location before starting a gold hunt. You may be able to find an auriferous quartz deposit miles away from the actual lode that is producing the gold.
Igneous Rocks
While gold may be found in many different types of rock formations, some are more prone to holding the precious metal than others. If you’re a prospector or simply curious, knowing what rocks can hold gold can help you determine the best places to look for this fascinating metal.
Gold is primarily associated with igneous rock, which is formed when magma or lava cools down. There are two main types of igneous rock: intrusive and extrusive. Intrusive rocks are those that form underneath the earth, while extrusive rocks are those that erupt from the surface of the ground.
Igneous rock can be classified based on its mineral composition, texture or color. The most common classification method is based on the relative abundance of felsic (feldspar and silica-quartz) versus mafic (magnesium and ferrum or iron) minerals. Felsic minerals tend to be light colored, while mafic minerals are dark.
In addition to being classified based on their mineral composition, igneous rock can also be grouped based on how quickly the magma or lava cooled. For example, a rock that cools very rapidly will typically have a glassy or vitreous texture with few crystals, while a rock that cooled slowly will have a crystalline texture.
You can find igneous rock throughout the world, but some of the most common examples are granite and diorite. These rocks are commonly used as construction material and for decorative items, such as statues and vases. Diorite, for example, is a strong, dense rock that can withstand extreme heat and pressure, making it ideal for carving. Other igneous rocks include basalt, syenite, tuff and obsidian.
While not all igneous rocks contain gold, some do, such as greenschist, which contains up to 20 parts per million of the element. However, it is still rare to find gold in igneous rocks. Most of the time, it ends up in metamorphic rock that has been derived from igneous stones like gabbro or basalt.
Slate
Gold is found in many types of rocks. It occurs as invisible disseminated grains and, more rarely, as flakes and masses large enough to see. It can also occur in sand and gravel deposits that have been eroded from other rocks and carried downstream by water, such as rivers and streams. Gold typically settles in areas where the flow of water slows down, such as eddies or behind boulders.
One rock type that contains gold is slate, a fine-grained metamorphic rock that splits easily into thin sheets and has high tensile strength. Slate is gray, black, bluish or greenish in color and can contain mica, chlorite, quartz, calcite, pyrite, hematite and other minerals. It is formed under low-grade metamorphic conditions, meaning it was heated and compressed in a relatively cool environment.
Slate can be derived from mudstone, shale or basalt, and may transition into other types of metamorphic rock, such as phyllite or schist over time. It can be any color, but dark slates owe their color to carbonaceous material and dark blue or purple slates owe their color to iron sulfides. Green varieties of slate owe their color to chlorite, a green micaceous clay mineral.
The presence of gold in slate is rare, but it can sometimes be found associated with quartz reefs in schist. The gold is usually hidden beneath layers of micas that glitter in the sunlight. The micas may include silvery muscovite, metallic gray graphite, white grey or green talc and black brown biotite.
A person who is looking for gold can check whether a rock contains the precious metal by scratching it on a piece of unglazed ceramic, such as a kitchen tile. Genuine gold leaves a golden streak, while fool’s gold leaves a greenish-black streak.
A gold prospector can also test for the existence of gold by poking a rock with a pin and seeing how hard it is to dent or break. The hardness of a gold-colored mineral, such as chalcopyrite, is often an indication that the rock in which it is embedded contains a small amount of gold.
Sand and Gravel
Gold can be found in sand and gravel as well, but these aren’t usually the primary targets of gold prospectors. Instead, these rocks are generally found in areas where gold-bearing veins or deposits are known to exist and can be useful indicators of their presence. The gold in these rocks is often found as tiny particles or flakes, which require extensive crushing and chemical treatment to extract.
Gold and other heavy elements can also be found in sedimentary rocks like sandstone and shale. This is because these types of rock were once part of larger, more massive meteorites that collided with the Earth or other planets. Over time, these meteorites eroded and the sediment was pushed by gravity into creek and river beds and other depressions. Because of gold’s greater density than other sedimentary materials, it is more likely to settle at the bottom of these deposits rather than being carried away by water and other forces.
Sand and gravel are loose, granular mineral materials produced by the natural disintegration of rock caused by weathering. The terms sand, gravel, clay and silt refer to grain size rather than composition. Sand is material that passes through a number 4 (4.76 mm) sieve, while gravel is granular material that remains on the number 200 (74 um [micron]) sieve or larger. Material finer than 200 mesh is considered silt or clay.
These materials are among the most important geological resources we use in our daily lives, providing the coarse aggregate for concrete and asphalt used in roads and buildings. They are added to garden soil, roof shingles and bricks, as an ingredient in glass, fiberglass, insulation and for abrasive purposes, and are used in water filtration. They are also used in erosion control, as a traction aid on sidewalks and roads and in the production of petroleum and gas.
Because of their high concentrations of gold, these sand and gravel deposits are considered a source of the precious metal. As such, they are important to any mining operation. In fact, it is a major factor in determining the viability of any potential gold deposit, along with factors such as groundwater levels and tectonic activity. In addition, these deposits are often associated with gemstones, including rubies and sapphires (variety of corundum), emeralds and malachite.