The Arabian-Nubian Shield (ANS) is an exposure of

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

crystalline rocks on the flanks of the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

. The crystalline rocks are mostly

Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...

in age. Geographically – and from north to south – the ANS includes parts of

Israel Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

Saudi Arabia Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in West Asia. Located in the centre of the Middle East, it covers the bulk of the Arabian Peninsula and has a land area of about , making it the List of Asian countries ...

Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...

Eritrea Eritrea, officially the State of Eritrea, is a country in the Horn of Africa region of East Africa, with its capital and largest city being Asmara. It is bordered by Ethiopia in the Eritrea–Ethiopia border, south, Sudan in the west, and Dj ...

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

Yemen Yemen, officially the Republic of Yemen, is a country in West Asia. Located in South Arabia, southern Arabia, it borders Saudi Arabia to Saudi Arabia–Yemen border, the north, Oman to Oman–Yemen border, the northeast, the south-eastern part ...

, and

Somalia Somalia, officially the Federal Republic of Somalia, is the easternmost country in continental Africa. The country is located in the Horn of Africa and is bordered by Ethiopia to the west, Djibouti to the northwest, Kenya to the southwest, th ...

. The ANS in the north is exposed as part of the

Sahara Desert The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in the world and the list of deserts by area, third-largest desert overall, smaller only than the deserts of Antarctica and the northern Ar ...

and

Arabian Desert The Arabian Desert () is a vast desert wilderness in West Asia that occupies almost the entire Arabian Peninsula with an area of . It stretches from Yemen to the Persian Gulf and Oman to Jordan and Iraq. It is the fourth largest desert in the ...

, and in the south in the

Ethiopian Highlands The Ethiopian Highlands (also called the Abyssinian Highlands) is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , whil ...

Asir Asir, officially the Aseer Province, is a province of Saudi Arabia in southern Arabia. It has an area of , and an estimated population of 2,024,285 (in 2022). Asir is bounded by the Mecca Province to the north and west, al-Bahah Province to the ...

province of Arabia and Yemen Highlands. The ANS was the site of some of man's earliest geologic efforts, principally by the

ancient Egyptians Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower ...

to extract

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

from the rocks of Egypt and NE Sudan. This was the most easily worked of all metals and does not tarnish. All of the gold deposits in Egypt and northern Sudan were found and exploited by Egyptians. The earliest preserved

geological map A geological map or geologic map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...

was made in 1150 BCE to show the location of gold deposits in Eastern Egypt; it is known as the Turin papyrus. New gold discoveries have been found in Sudan, Eritrea, and Saudi Arabia. Pharonic Egyptians also quarried

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

near

Aswan Aswan (, also ; ) is a city in Southern Egypt, and is the capital of the Aswan Governorate. Aswan is a busy market and tourist centre located just north of the Aswan Dam on the east bank of the Nile at the first cataract. The modern city ha ...

and floated this down the Nile to be used as facing for the

pyramids A pyramid () is a Nonbuilding structure, structure whose visible surfaces are triangular in broad outline and converge toward the top, making the appearance roughly a Pyramid (geometry), pyramid in the geometric sense. The base of a pyramid ca ...

. The Greek name for Aswan, ''Syene''; is the type locality for the

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). It is considered a porphyry and

were mined and shaped for shipment. Precious and industrial metals, including gold, silver, copper, zinc, tin, and lead, have been mined in Saudi Arabia for at least 5,000 years. The most productive mine in Saudi Arabia, Mahd adh Dhahab ("Cradle of Gold"), has been periodically exploited for its mineral wealth for hundreds or even thousands of years and is reputed to be the original source of King Solomon's legendary gold. Today, mining at Mahd adh Dhahab is conducted by the Saudi Arabian Mining Company, Ma'aden. Deposits of iron, tungsten, mineral sands, copper and phosphates have been found in many locations. Mining in the Eastern Desert of Egypt and Sudan is limited due to a shortage of water and infrastructure.

Development of the Arabian-Nubian Shield

The Arabian-Nubian Shield (ANS) is the northern half of a great collision zone called the

East African Orogeny The East African Orogeny (EAO) is the main stage in the Neoproterozoic assembly of East and West Gondwana (Australia–India–Antarctica and Africa–South America) along the Mozambique Belt. Gondwana assembly The notion that Gondwana was assem ...

. This collision zone formed near the end of

time when East and West Gondwana collided to form the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. The East African orogeny extends southward to the

Mozambique Belt The Mozambique Belt is a band in the Earth's crust that extends from East Antarctica through East Africa up to the Arabian-Nubian Shield. It formed as a suture between plates during the Pan-African orogeny, when Gondwana was formed. The Mozambi ...

, and is a subset of the overall

Pan-African orogeny The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Oro ...

. The assembly of Gondwana coincided with the breakup of

Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago (Ga) and broke up 750–633 million years ago (Ma). wer ...

, closure of the Mozambique Ocean, and growth of the shield at 870 million years ago ( Ma). This shield growth extended for the next 300 million years, and included

island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...

convergence and

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...

suturing A surgical suture, also known as a stitch or stitches, is a medical device used to hold Tissue (biology), body tissues together and approximate wound edges after an injury or surgery. Application generally involves using a Sewing needle, needle w ...

at 780 Ma, with final assembly by 550 Ma. At this time, the East African Orogen became a passive margin and the southern shore of the

Paleo-Tethys Ocean The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; ex ...

. The shield is divided into crustal blocks or

tectonostratigraphic terrane In geology, a terrane (; in full, a tectonostratigraphy, tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a plate tectonics, tectonic plate (or broken off from it) and accretion (geology), accreted or "suture (geology ...

s delineated by

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...

s or sutures. These terranes are paired across the

, starting from the south, these include Nakfa (870–840 Ma) with Asir (785–720 Ma, 850–790 Ma), Haya (870–790 Ma) with Jiddah (870–760 Ma), Gabgaba (735–700 Ma) and Gebeit (832–810 Ma) with Hijaz (870–807 Ma), and Eastern Desert (810–720 Ma) with Midyan (780–710 Ma). In addition the Halfa (2600–1200 Ma, 750–718 Ma) and Bayuda (806 Ma) terranes are in the western portion of the shield, and the Hulayfah (720 Ma), Ha'il (740 Ma), Afif (750–695 Ma, 840–820 Ma, 1860–1660 Ma), Ad-Dawadimi (695–680 Ma), and Ar-Rayn (667 Ma) terranes in the eastern portion. Key amalgamation events, starting 780–760 Ma, with the formation of the Tabalah–Tarj Shear Zone, the

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

Afaf Belt, and the long and wide Bi'r Umq and Nakasib Suture (780–760 Ma), an ophiolite-decorated fold-shear zone, between the Jiddah–Haya and Hijaz–Gebeit Terranes. Then between 750 and 660 Ma, the Atmur–Delgo Suture formed as Halfa Terrane ophiolite

nappe In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the ...

s were

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

onto the Bayuda Terrane. Simultaneously, the Allaqi–Heiani–Sol and Hamed–Onib–Yanbu Suture formed, consisting of nappes and portions of ophiolite along an east-trending shear zone between the Gebeit–Hijaz and Eastern Desert Terrane and Midyan Terranes. Between 680 and 640 Ma, the long and wide Hulayfah–Ad-Dafinah–Ruwah Suture formed between the Afif Terrance and terranes to the southwest. Simultaneously, the Halaban Suture formed between the Afif and Ad-Dawadimi Terranes as a nappe of Halaban ophiolite thrust westward. In addition, the Al-Amar Suture, consisting of the Al-Amar Fault zone with ophiolite lenses, between the Ad-Dawadimi and Ar-Rayan Terranes, while the Nabitah Fault Zone formed in Asir Terrane. The final amalgamation event occurred 650–600 Ma, when the Keraf Suture, consisting of ophiolite folded and sheared rocks, formed between the Bayuda–Halfa and GebeitGabgaba Terranes. Post-amalgamation events include the formation of the Huqf Supergroup (732–540 Ma) in Oman and western Saudi Arabia, which accumulated in basement basins, the first of which include glaciomarine deposits with

diamictite Diamictite (; from Ancient Greek (): 'through' and (): 'mixed') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that range in size from clay to boulders, suspended ...

s and

dropstone Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks or pyroclasts, pyroclastic beds. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is eviden ...

s from the Sturtian and Marinoan glaciations. Gneiss belts and domes forming in the Late Neoproterozoic include the Kirsh gneiss in the Arabian shield and the Meatiq gneiss dome in the Eastern Desert. Late Neoproterozoic shear zones include the Hamisana Shear Zone (665–610 Ma), the Ar-Rika–Qazaz Shear Zone (640–610 Ma) within the Najd Fault System, and the Oko Shear Zone (700–560 Ma). A number of features have been ascribed to late stage

extensional tectonics Extensional tectonics is concerned with the structures formed by, and the Tectonics, tectonic processes associated with, the stretching of a planetary body's Crust (geology), crust or lithosphere. Deformation styles The types of structure and the ...

including a widespread northeast trending dyke swarm, northeast–southwest trending normal faults and northwest–southeast trending

sedimentary basins Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

filled with post-orogenic

molasse __NOTOC__ In geology, "molasse" () are sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a foreland basin, especially on top of flys ...

deposits Crustal weaknesses before 500 Ma influenced

continental rifting In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

, as the Arabian peninsula moved away from Africa, and the formation of the Red Sea Basin at the start of the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

. By then, some of the

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

and

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

rocks had been eroded, if ever deposited. In fact, the wide ANS orogenic belt, has a present-day layered crustal structure, with a uniform Moho depth of . Post-rift deposition of

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

s occurred until the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58overthrust A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

"superstructure". The infrastructure consists of

migmatite Migmatite is a composite rock (geology), rock found in medium and high-grade metamorphic environments, commonly within Precambrian craton, cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an old ...

and gneiss domes such as Gebel Hafafit and Gebel Meatiq. The metamorphism is associated with overthrust tectonics, but bear no relationship to the ancient gold mines. The superstructure consists of an

-like sequences with

volcanics Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and met ...

, Hammamat sediments, and post orogenic

s. The ophiolite sequences range in age from 746 to 832 million years ( Ma) and are mainly serpentite with elevated gold values of 25

parts per billion In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measur ...

. The Hammamat sediments, common in Wadi Hammamat and referred to as "bekhen" stone, consist of

greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...

s and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s, which are slightly enriched in gold. The Hammamat sediments include dike

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s and the

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

Dokhan volcanics, which formed in the early stages of

orogeny Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...

at 625–600 Ma. These volcanics include the Roman imperial porphyry quarries. The granite intrusions include two sequences, an older one 709–614 Ma, and a younger sequence at 596–544 Ma, which includes the Aswan granite at 565 Ma. The margin of the includes

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 gra ...

and

diorite Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is Intermediate composition, inter ...

, and most importantly, auriferous quartz veins. These veins mineralized from hydrothermal flow inside tectonic extensional gaps, or within cavities from shearing. These characteristics were exploited by

New Kingdom of Egypt The New Kingdom, also called the Egyptian Empire, refers to ancient Egypt between the 16th century BC and the 11th century BC. This period of History of ancient Egypt, ancient Egyptian history covers the Eighteenth Dynasty of Egypt, Eighteenth, ...

prospectors. This is especially true for ancient gold exploitations oriented in north-northwest–south-southeast shear zones, such as the sites at Hammama, Abu Had North, Wad Atalla el-Mur, Atalla, Umm el Esh Sarga, Fawakhir, El-Sid, Umm Soleimat and Hamuda. Wadi el-Sid was the chief mining area for the

, with high gold grades of 30 grams per tonne in the mineralized quartz veins within sheared ophiolite sequences of serpentinite and

metabasalt Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (fla ...

, imbricated with Hammamat sediments, in direct contact with the

tonalite Tonalite is an igneous rock, igneous, plutonic (Intrusive rock, intrusive) rock (geology), rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali fe ...

margins of the Fawakhir granite

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

. The ophiolite

dates from 850 to 770 Ma, while the Fawakhir pluton dates from 574 Ma. These gold-rich veins are oriented according to post-tectonic extension, something the Egyptian prospectors understood. The well of Umm el-Fawakhir area includes a Large Ptolemaic settlement and round stone mills dating from the Roman or Early Arab Period to the oval stone mills of the New Kingdom. Even fist hammers from the Old/Middle Kingdom are present.

Tailings In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material ...

were reworked by the Louison Company from the 1930s until 1956.

Volcanogenic massive sulfide ore deposit external links

Hamama VMS deposit in EgyptBisha VMS deposit in EritreaHassai VMS deposit in Northern SudanJabal Sayid VMS deposit in Saudi Arabia

References

External links

The Eastern Desert of Egypt in Ancient Times

* ttps://web.archive.org/web/20061023213115/http://www.dmmr.gov.sa/geology-ksa.php Geology of Saudi Arabiabr>USGS pamphlet on gold, including early mining in Egypt and ArabiaWebsite for the Saudi Geological Survey, which does a lot of work on the Arabian-Nubian Shield.UNESCO World Heritage site for St. Catherine monastery area. This is built upon ANS exposures in Sinai.
{{Authority control Shields (geology) Geology of Egypt Geology of Ethiopia Geology of Saudi Arabia Geology of Sudan Plate tectonics

Development of the Arabian-Nubian Shield

Volcanogenic massive sulfide ore deposit external links

See also

References

Further reading

External links