The Arabian-Nubian Shield (ANS) is an exposure of Precambrian crystalline rocks on the flanks of the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

. The crystalline rocks are mostly

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

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

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

Jordan Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ' is a country in Western Asia. It is situated at the crossroads of Asia, Africa, and Europe, within the Levant region, on the East Bank of the Jordan Rive ...

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...

Saudi Arabia Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the A ...

, Sudan, Eritrea,

Ethiopia Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...

Yemen Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...

, and

Somalia Somalia, , Osmanya script: 𐒈𐒝𐒑𐒛𐒐𐒘𐒕𐒖; ar, الصومال, aṣ-Ṣūmāl officially the Federal Republic of SomaliaThe ''Federal Republic of Somalia'' is the country's name per Article 1 of thProvisional Constituti ...

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

Sahara Desert , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

and Arabian Desert, and in the south in the

Ethiopian Highlands The Ethiopian 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 , while the summits reach heights of up to . ...

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

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 ...

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 geologic map 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 ( 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 ...

near

Aswan Aswan (, also ; ar, أسوان, ʾAswān ; cop, Ⲥⲟⲩⲁⲛ ) 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 ...

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

pyramids A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...

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

igneous rock 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 o ...

syenite. The Romans followed this tradition and had many quarries especially in the northern part of the Eastern Desert of Egypt where 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 The Mahd Al Thahab ( ar, مَـهـد الـذّهـب, "Cradle of (the) Gold"), is a small gold area in the Arabian Peninsula. It is located in the Province of Al-Madinah, in the Hejazi region of Saudi Arabia. Gold was first mined in Arabia c. ...

("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 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 asse ...

. 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 continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

Gondwana. 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 Mozambiq ...

, 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, closure of the

Mozambique Ocean 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 Moz ...

, and growth of the shield at 870 Ma This shield growth extended for the next 300 Ma., and included

island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

convergence and

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a tectonic plate (or broken off from it) and Accretion (geology), accreted or "Suture (geology), sutured" to crust lying on another pla ...

suturing 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; exi ...

. The shield is divided into crustal blocks or tectonostratigraphic terranes delineated by

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

shear zones 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 (2.6-1.2 Ga, 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, 1.86-1.66 Ga), 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 ( ) 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. Gneiss forms at higher temperatures a ...

Afaf Belt, and the 600 km long and 565 km 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 o ...

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 sys ...

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 600 km long and 5–30 km 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 Ar 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 Gebeit-Gabgaba Terranes. Post-amalgamation events include the formation of the Huqf Supergroup (732-540 Ma) in Oman and W. Saudi Arabia, which accumulated in basement basins, the first 1100 m of which include glaciomarine deposits with diamictites and

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

s from the

Sturtian The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, ...

and

Marinoan The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma (million years ago) during the Cryogenian period. This glaciation possibly cove ...

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 including a widespread NE-SW trending dyke swarm, NE-SW trending normal faults and NW-SE 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 subsiden ...

filled with post-orogenic

molasse __NOTOC__ The term "molasse" () refers to 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 flysc ...

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-grabe ...

, as the Arabian peninsula moved away from Africa, and the formation of the

Red Sea Basin The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

at the start of the Oligocene. By then, some of the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

and

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

rocks had been eroded, if ever deposited. In fact, the 1200 km wide ANS orogenic belt, has a present-day layered crustal structure, with a uniform Moho depth of 35–45 km. 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 ocean ...

s occurred until the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million 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 found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock th ...

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 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 ...

, Hammamat sediments, and post orogenic

s. The ophiolite sequences range in age from 746 to 832 Ma and are mainly serpentite with elevated gold values of 25 ppb. The Hammamat sediments, common in

Wadi Hammamat Wadi Hammamat ( en, Valley of Many Baths, ''India way; gateway to India'') is a dry river bed in Egypt's Eastern Desert, about halfway between Al-Qusayr and Qena. It was a major mining region and trade route east from the Nile Valley in ancie ...

and referred to as "bekhen" stone, consist of

greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

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

dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

intrusions 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 ...

to rhyolite Dokhan volcanics, which formed in the early stages of orogeny at 600-625 Ma. These volcanics include the Roman imperial porphyry quarries. The granite intrusions include two sequences, an older one 614-709 Ma, and a younger sequence at 544-596 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 gr ...

and

diorite Diorite ( ) is an 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 in composition between low-sili ...

, and most importantly,

auriferous The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

quartz vein In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved ...

s. 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 referred to as the Egyptian Empire, is the period in ancient Egyptian history between the sixteenth century BC and the eleventh century BC, covering the Eighteenth, Nineteenth, and Twentieth dynasties of Egypt. Radioca ...

prospectors. This is especially true for ancient gold exploitations oriented in NNW-SSE 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 ton (g/t) 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 (flak ...

, imbricated with Hammamat sediments, in direct contact with the

tonalite Tonalite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total ...

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

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 Cratons 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