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A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. 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.

The elemental and mineralogical composition of primary rocks is determined by the chemical composition of the volcanic or magmatic flow from which it is formed. Extrusive rocks (such as basalt, rhyolite, andesite and obsidian) and intrusive rocks (such as granite, granodiorite, gabbro and peridotite) contain primary minerals including quartz, feldspar, plagioclase, muscovite, biotite, amphibole, pyroxene and olivine 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, Gypsum (primary and secondary mineral), Celestite, Alunite (primary and secondary mineral), Creedite, and Thaumasite.

Primary minerals can be used to analyze geochemical dispersion halos, and indicator minerals. Furthermore, the most dominant primary minerals in soils are silicate minerals. A variety of silica groups have been discovered, and are controlled by their bonding arrangement, and silica tetrahedron.

Geochemistry Associated with Primary Minerals

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, pyritization, sericitization, chloritization, 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 deposits, kimberlites, and massive sulfide deposits. The indicator minerals are further used to track dispersal trains in streams, which may determine location of primary ores/minerals, and their source.

Primary Mineral Characteristics

Minerals in soils are found as 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 primary minerals. 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 minerals. Silicate minerals consist of more than 90% of the minerals in the Earth's crust.

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.

Modern soil science offers the following definition: "Primary Minerals: The thickness of the earth's crust varies from 10 km under the ocean to 30 km under the continents. Of the 88 naturally occurring elements on earth, only 8 make most of the crust. The earth's crust and soils are dominated by the silicic acid in combination with Na, Al, K, Ca, Fe and O ions. ...Those elements are components of primary minerals, whereas primary minerals are components of parent rocks. There are almost 3000 known minerals, but only 20 are common and just 10 minerals make up 90 % of the earth's crust. Primary minerals are defined as minerals found in soil but not formed in soil. This definition is different from that of secondary minerals, which are defined as minerals formed in soils." This is further defined by Dr. Broome of North Carolina State:

Primary rocks are the source of primary minerals and primary water.

References

1. Ailsa Allaby and Michael Allaby. "primary mineral." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 1 Oct. 2016.
2. Rakovan, John (2003). "A Word to the Wise: Hypogene & Supergene". Rocks & Minerals. 78 (6): 419. doi:10.1080/00357529.2003.9926759.
3. "Primary and Secondary Minerals". Lawr.ucdavis.edu. Retrieved 2020-01-30.
4. Butler, Bert (December 1, 1919). "Primary (Hypogene) Sulphate Minerals in Ore Deposits". Economic Geology. 14: 581–609 – via GeoscienceWorld.
5. ^ Nanzyo, Kanno, Masami, Hitoshi (2018). Inorganic Constituents in Soil. Singapore: Springer Nature Singapore Pte Ltd. pp. 11–14. ISBN 978-981-13-1214-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
6. ^ Mcqueen, Kenneth (2005). ORE DEPOSIT TYPES AND THEIR PRIMARY EXPRESSIONS. Bentley, WA: CRC LEME. p. 3. ISBN 9781921039287.
7. ^ Bowell, Cohen, R.J., D.R. (2014). Treatise on Geochemistry (Second Edition) Chapter 13.24 Exploration Geochemistry. Amsterdam ; San Diego, CA, USA.: Elsevier Ltd. p. 635. ISBN 9780080983004.{{cite book}}: CS1 maint: multiple names: authors list (link)
8. ^ "Sabine Grunwald - Soil and Water Sciences Department - University of Florida, Institute of Food and Agricultural Sciences - UF/IFAS". Soils.ifas.ufl.edu. 2019-07-31. Retrieved 2020-01-30.
9. Nanzyo, Kanno, Masami, Hitoshi (2018). Inorganic Constituents in Soil. Singapore: Springer Nature Singapore Pte Ltd. pp. 11–14. ISBN 978-981-13-1214-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
10. Rickard, T.F.; Ore Deposits: Engineering and Mining Journal, 1903; and Emmons, S.F.; Ore Deposits: A. I. M. E., 1913: pp. 837-846.
11. Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc., p. 31.

Bibliography

• Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc.

• Minerals