The geology of Zimbabwe in southern Africa is centered on the Zimbabwe Craton, a core of Archean

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

composed in the main of granitoids, schist and gneisses. It also incorporates

greenstone belt Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies. The name comes from the green ...

s comprising mafic, ultramafic and

felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...

volcanics Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...

which are associated with epiclastic sediments and iron formations. The craton is overlain in the north, northwest and east by

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

and

Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...

sedimentary basins whilst to the northwest are the rocks of the Magondi Supergroup. Northwards is the Zambezi Belt and to the east the Mozambique Belt. South of the Zimbabwe Craton is the Kaapvaal Craton separated from it by the Limpopo Mobile Belt, a zone of deformation and metamorphism reflecting geological events from Archean to Mesoproterozoic times. The Zimbabwe Craton is intruded by an elongate ultramafic/ mafic igneous complex known as the Great Dyke which runs for more than 500 km along a SSW/NNE oriented

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

. It consists of

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...

s, pyroxenites, norites and bands of chromitite.

Stratigraphy

Precambrian

The oldest

supracrustal rocks Supracrustal rocks (''supra'' (Latin for "above")) are rocks that were deposited on the existing basement rocks of the crust, hence the name. They may be further metamorphosed from both sedimentary and volcanic rocks. The oldest minerals on Eart ...

are the Sebakwian Group (3.5 Ga) exposed around Shurugwi and Mashava, and northwest of Gweru, within the central craton. This group consist of metavolcanic rocks, including

komatiite Komatiite () is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite wa ...

and basalt, banded iron formation, and

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

metasedimentary rocks. The Sebakwian Group is succeeded by the Bulawayan Group, further differentiated by the Lower Greenstones (2.9 Ga) and Upper Greenstones (2.7 Ga). The Lower Greenstones include

volcanic and volcaniclastic rocks, komatiites, and komatiitic basalts with interbedded iron-formations and polymict clastic sediments. Overlying the Bulawayan Group is the Shamvaian Group (2.7 Ga), and it is these two groups which constitute the main

s. The tonalitic Sesombi Suite and granitic Chilimanzi Suite granitoids intruded the Upper Greenstones and Shamvaian Group between 2.7 Ga to 2.6 Ga. The last major

Archaen The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Archean ...

event was the intrusion of the Great Dyke (2.5 Ga). By 1982, 123 mines had produced 155 tonnes of gold from the stratabound iron-formations of the Sebakwian, and Lower and Upper Greenstones. Of these mines, 31 had produced more than 311 kg, with the Wanderer Mine near Shurugwi producing the most at 36 tonnes. Non-stratabound gold production included 128 tonnes from the Que Que Ultramafic Complex within the Mashaba Ultramafic Suite of the Upper Greenstones, while the Upper Greenstone Basaltic and Bimodal Units had produced 400 and 161 tonnes respectively. Granitoid host rocks had produced a total of 132 tonnes of gold, and include the Rhodesdale

Batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...

at 53 tonnes, the Sesombi Suite at 36 tonnes, and the Penhalonga quartz diorite at 10 tonnes.

Economic geology

Zimbabwe's mineral resources include, amongst others, coal, chromium ore, nickel, copper,

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...

vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer ( pas ...

, tin, platinum group metals (such as palladium) and diamonds. Globally it is a significant producer of lithium,

chrysotile asbestos Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in the United StatesOccupational Safety and Health Administration, United States Department of Labor, U.S. Departmen ...

and vermiculite. Gold, platinum group metals and chromium are Zimbabwe's key mineral resources. The Great Dyke provides most of Zimbabwe's chromium reserves. Zimbabwe experienced a decline in the mining of many minerals in the period to 2008 including the closure of several gold mines. However, diamond production increased making the country Africa's seventh largest producer by 2008. The country has considerable coal reserves which are used in power generation. Its coal-bed methane field, the largest in southern Africa has not yet been exploited to the full.Zimbabwe, oil and gas Extractive Industries Source Book
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References

External links

Geologic map of Zimbabwe
{{Africa topic, Geology of

Stratigraphy

Precambrian

Economic geology

See also

References

External links