Bedrock is the result of long-term geological processes. By the type of their origin, they are divided into igneous (igneous), sedimentary, metamorphic (altered).
Igneous rocks
Their formation occurred due to the fact that in the process of tectonic activity, natural substance, molten in the depths of the earth, rose to the surface. At the same time, magma cooled and hardened. If it was subjected to cooling and solidification at great depths, namely, slowly under the influence of high pressure, and could not get rid of gaseous inclusions, then these rocks are usually called intrusive (deep). They possess, as a rule, a large-crystalline structure.
If magma cools near the surface of the earth, then these rocks are called effusive. Magma, rising, was cooled in a shorter time. The pressure on her was negligible. Gaseous products exited freely. The structure of such rocks differs from intrusive, despite the fact that initially they had the same composition. Effusive rocks are characterized by a fine crystalline structure or are generally amorphous.
Magmatic primary rocks - granite, syenite, diabase, basalt, gabro, andesite and others. Typically, these rocks contain valuable minerals, namely platinum, chromium, titanium, nickel, cobalt, iron, etc.
Sedimentary rocks
These rocks are formed due to the deposition of organic substances and suspended minerals at the bottom of reservoirs (lake, river, sea). Their origin is the result of weathering and destruction of igneous or more ancient sedimentary rocks.
In geology, it is customary to separate them by their origin into chemical (mineral salt, gypsum), organic (coal, oil shale, limestone). Sedimentary rocks are also the so-called clastic rocks, which include sand, gravel, crushed stone, clay, etc. The main characteristic of sedimentary rocks is their lamination.
Metamorphic rocks
They owe their education to specific chemical and physical processes. If igneous or sedimentary rocks were exposed to high temperature, gas pressure due to recrystallization of associated rocks during magma movement. In this case, new minerals and rocks were formed. In such processes, crystalline schists were created from clay, which contained granite, mica, skarns, hornfelses, etc. Metamorphic rocks have a crystalline structure, have a banded or slate structure.
Sediment
These rocks were formed due to the destruction of the bedrock. They are quite loose deposits, the so-called secondary rocks. Sediments are located at the very surface of the earth, under vegetation. This is a combination of sand, clay, loam, as well as other cracked rocks. The thickness of the overburden (thickness) is relatively small, usually from a meter to 50 m.
The earth’s crust, to which humanity has access, reaches a depth of about 20 km. It consists of 95% of igneous rocks, 4% of metamorphic rocks and 1% of sedimentary rocks. Indigenous rocks in geology, related to a variety of rocks that can be used by mankind and for their own purposes, are called minerals.
Natural accumulations of these minerals in the earth's crust are mineral deposits, they can be loose and indigenous.
Gold process
The bedrock of gold appeared in the Earth's crust due to magmatic processes. As a result of centuries-old manifestations of the activity of volcanoes, rivers of red-hot magma flowed onto the earth's surface. It was a mixture of molten compounds. Their melting point is different, therefore when solidifying magma, initially refractory elements crystallize. However, fusible elements continued to circulate in the frozen magma. Their molten consistency broke through the tears and cracks of solidifying magma. In this case, veins were formed. They continued the process of circulation of hot solutions of gold-containing salts. After the cooling process was over, the destruction of salts began, gold in the veins remained and crystallized.
Indigenous rocks of gold were formed in different ways, but for the most part they are always located in the mountains, in those places where the rocks were formed according to the results of magmatic activity.
Differences in gold deposits
Gold deposits are distinguished by the conditions of their occurrence
Indigenous deposits (endogenous). They arose as a result of deep processes. Their other name is ore or primary. Now the bulk of gold in the world, approximately 95-97 percent, is mined from ore deposits.
Alluvial deposits (exogenous). They appear on the earth's surface due to the destruction of the indigenous gold rock. Sometimes they are designated as secondary deposits.
Deposits are metamorphosed exogenous. These are conglomerates and sandstones with a gold content. They appeared due to the fact that the ancient gold placers were naturally transformed. In Russia, no such deposits have been established.
Gold Locations
The period of geological transformations of the Earth totals millions of years. In place of the destroyed and weathered rocks, new ones rise from the depths to its surface. The processes associated with the destruction and lifting of sections of the earth's crust are ongoing. There is a continuous update of the earth's surface. As a result of this, it is a collection of native elements, including gold. So, when rocks are destroyed, gold is released and does not disappear without a trace, like other unstable elements of bedrock. Accumulates in placers. However, the activity of mankind has led to the fact that gold placer deposits have already been developed. Gold is now mainly mined from deep bed ore. The largest reserves of this noble metal are owned by several countries: Australia, South Africa, USA, China, Russia. About 2,500 tons of gold are mined annually in the world. Russia accounts for almost 200 tons of this metal.