A primary mineral is any mineral formed during the original crystallization of the host
igneous
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
primary rock Primary rock is an early term in geology that refers to crystalline rock formed first in geologic time, containing no organic remains, such as granite, gneiss and schist as well as igneous and magmatic formations from all ages. Webster's Revise ...
and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In
ore
Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...
deposit
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
,
hypogene In ore deposit geology, hypogene processes occur deep below the earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.
At great dept ...
processes occur deep below the Earth's surface, and tend to form deposits of primary minerals, as opposed to
supergene processes that occur at or near the surface, and tend to form secondary minerals.
![Gunthorpe_formation_-_diagonal_beds_-_geograph](https://upload.wikimedia.org/wikipedia/commons/8/88/Gunthorpe_formation_-_diagonal_beds_-_geograph.org.uk_-_653299.jpg)
The elemental and mineralogical composition of primary rocks is determined by the chemical composition of the
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
or
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
tic flow from which it is formed.
Extrusive rocks (such as
basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
,
rhyolite,
andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...
and
obsidian) and
intrusive rocks (such as
granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...
,
granodiorite
Granodiorite () is a coarse-grained ( phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar.
The term banatite is sometimes used informally for various rocks ranging from gr ...
,
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...
and
peridotite) contain primary minerals including
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
,
feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
,
plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...
,
muscovite
Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...
,
biotite,
amphibole,
pyroxene and
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
in varying concentrations. Additionally, primary sulfate minerals occur in igneous rocks. Primary sulfate minerals may occur in veins, these minerals include;
hauynite,
noselite,
barite,
anhydrite
Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...
,
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...
(primary and secondary mineral),
celestite,
alunite (primary and secondary mineral),
creedite
Creedite is a calcium aluminium sulfate fluoro hydroxide mineral with formula: Ca3Al2SO4(F,OH)10·2(H2O). Creedite forms colorless to white to purple monoclinic prismatic crystals. It often occurs as acicular radiating sprays of fine prisms. It is ...
, and
thaumasite
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedron, octahedral configuration, with chemical formula calcium, Ca3silicon, Si(Ohydrogen, H)6(carbon, Coxygen, O3)(sulfur, SO4)·12water, H2O, also sometimes more simply ...
.
Primary minerals can be used to analyze geochemical dispersion halos, and indicator minerals. Furthermore, the most dominant primary minerals in soils are
silicate minerals
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually con ...
.
A variety of silica groups have been discovered, and are controlled by their bonding arrangement, and silica tetrahedron.
Geochemistry
Geochemical dispersion halos
Primary ore deposits contain primary ores that may develop a geochemical dispersion halo known as primary dispersion expressions.
"These primary expressions are syndepositional in nature, and thus can occur at or close to the time of ore formation".
Primary ore expressions may show alteration of the host rocks. These alterations include;
silicification
In geology, silicification is a petrification process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and ...
,
pyritization
Permineralization is a process of fossilization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, perminera ...
,
sericitization,
chloritization,
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
alteration, tourmalinization, and
greisens.
Indicator minerals
Heavy indicator minerals can lead to a good approximation of primary geology and presence of mineral deposits. Primary indicator minerals can be used to identify
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
deposits,
kimberlites, and massive sulfide deposits.
The indicator minerals are further used to track dispersal trains in streams, which may determine the location of primary ores/minerals, and their source.
Characteristics
Minerals in soils are found in two types; primary and secondary.
"A primary mineral has not been altered chemically since its crystallization from a cooling magma."
Additionally, a primary mineral is defined as a mineral that is found in soil but not formed in soil, whereas secondary minerals are formed during weathering of
![Elbaite](https://upload.wikimedia.org/wikipedia/commons/4/4f/Elbaite.jpg)
primary minerals.
The latter is further defined by Dr. Broome of North Carolina State: the particle size of primary minerals is primarily larger than 2μm, which includes; silt, sand, and gravel.
The most dominant primary minerals in soil are the
silicate mineral
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually consid ...
s. Silicate minerals consist of more than 90% of the minerals in the Earth's crust.
There are six silica mineral groups, based on bonding arrangement, and silica tetrahedron.
The silica groups include: nesosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, and tectosilicates.
Tectosilicates such as
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
, and
cristobalite
Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the ...
are common in soils.
Phyllosilicates are known as the sheet silicates, and include
muscovite
Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...
,
biotite, and clay minerals.
Cyclosilicates are known as ring silicates, and include
tourmaline
Tourmaline ( ) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is a gemstone and can be found in a wide variety of colors.
The te ...
.
Inosilicates are known as single/double chain silicates, and include amphiboles, and pyroxenes.
Sorosilicates contain double silica tetrahedra, such as
vesuvianite
Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism. It was first discovered within ...
.
Nesosilicates have one silica tetrahedra, such as
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
.
The earth's crust and soils are dominated by
silicic acid
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
in combination with Na, Al, K, Ca, Fe and O ions. The following elements are components of primary minerals, whereas primary minerals are components of parent rocks. Primary rocks are the source of primary minerals and
primary water. For the classical discussions of the origin of primary ores, see the two publications "Ore Deposits" (1903 and 1913). According to W.A. Tarr (1938) the primary mineral deposits are the result of direct magmatic action; he states that the splitting of magmas results in the basic igneous rocks and their accompanying group of accessory minerals formed by the first crystallization in the magma, on the one hand, and in the acidic igneous rocks and a second group of accessory minerals which were formed by deposition from the residual
mother liquors.
[Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc., p. 31.]
Beneficiation of primary ores
Leaching of primary sulfate minerals occurs through the process of
bioleaching
Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cyanide. Bioleaching is one of several applications within biohydrometallurgy and several ...
for the separation of primary sulfide ores.
Primary ores are also extracted through dense media separation (DMS), which is a technique that involves the removal of
gangue
In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...
through the variation of specific gravity within particles.
The dense minerals (high specific gravity) containing primary ores sink, and the lighter gangue minerals float to the surface.
DMS plants have been widely used for different mining applications, such as the beneficiation of lithium bearing ores from pegmatites, like the main lithium-bearing mineral known as
spodumene
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, Li Al( Si O3)2, and is a source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite (see below), yellowish-green or emerald-green hiddenite, pr ...
.
Another method of beneficiation is through magnetic separation. Magnetic separation involves the separation of iron-bearing gangue, such as
hematite.
Hematite cannot be used in the iron and steel industry without beneficiation.
Roasting of primary low grade ores, such as
siderite
Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...
and hematite occurs further forming
magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With th ...
.
Once the conversion of iron-oxides occurs, magnetic separation may proceed to extract magnetic ores.
Additionally, another beneficiation technique used for primary ores is froth flotation.
Froth flotation is used after roasting of primary ores, where the magnetite (or other primary ore) is further separated forming a concentrate.
References
{{reflist
Bibliography
* Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc.
Minerals