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Sinai Peninsula Copper - Bir Nasib District, Serabit El-Khadem, Wadi Magharah, Wadi Kharag, Abu-Zinima |
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Super Porphyry Cu and Au
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The widespread Lower to Mid Palaeozoic and Mesozoic sediment hosted copper mineralisation of the Levant, as described in detail in the Wadi Araba (Jordon) and Timna Valley (Israel) records, extends westward below younger Mesozoic and Cenozoic cover to re-emerge at surface in southwestern Sinai Peninsula. In this region, mines of antiquity have exploited 'oxide' copper mineralisation and turquoise. The more notable of these are the copper deposits at and around the Bir Nasib District and the turquoise mines at Serabit El-Khadem, distributed over an area of several hundred square kilometres. While this ancient mining was of considerable archaeological significance and a major copper and ornamental turquoise source of the day, resources currently known are of no economic importance. However, the manganese mineralisation that is closely associated with, and hosts some of the copper of the district, is economically exploited to feed a silicomanganese plant at Abu-Zinima (Abu Zenima) on the Gulf of Suez coast.
The earliest settlers in the Sinai Peninsula are believed to be miners who arrived ~8000 years ago, drawn to the region's abundant copper and
turquoise showings. These settlers slowly progressed southward from occurrence to occurrence, until by ~3500 BCE the great turquoise veins of Serabit El-Khadem had been discovered. At about the same time, the kingdoms of Egypt were united under its first dynasty pharaohs, who then became masters of the Sinai and its mines. This included setting up 'large scale' and systematic operations at Serabit El-Khadem. Over the next thousand years, large quantities of turquoise were extracted from this operation and shipped to Egypt from the port at El-Markha on the northeastern coast of the Gulf of Suez, just south of Abu Zenima (Megahed, 2018).
In addition to the turquoise workings, debris of ancient copper smelters, which date back to the 'Old Kingdom' between 2780 and 2230 BCE, and the Middle
Kingdom from 2134 to 1778 BCE, has been recognised, as have large copper slag dumps, and remains of pots and casting moulds from the same period. Large slag dumps and ruins of several smelting furnaces have been recognised at Bir Nasib, in particular, in the vicinity of small adits into the sandstone cliffs where malachite, paratacamite and quartz mineralisation are exposed. One of the most significant and oldest mines in the area is at Wadi Kharag, NW of Wadi Nasib, where an irregular adit, ~100 m long, 10 m wide and 2 m high has been excavated. This mine operated during the old and middle kingdom copper mining and is the earliest Pharaonic copper mining camp so far discovered in Sinai (Megahed, 2018). Carbon dating and isotope studies of charcoal fuel used at smelting sites in the area suggest an age of ~3500 BCE, and furnace temperatures of 1180 to 1350°C, sufficient to melt malachite ore with the assistance of a forced draft and the indicated use of nearby iron oxide flux. Copper smelter slag, fragments of copper casting crucibles and furnace fragments accompanied by Egyptian sherds (pottery fragments), are found along Wadi Kharag, taken to be evidence of in situ copper smelting (Megahed, 2018). Another important site, Wadi Maghara, appears to have yielded both copper and turquoise ores.
Geological Setting
The Neoproterozoic and Phanerozoic sequences of the southwestern Sinai Peninsula are broadly a stratigraphic extension of those described for the similar Timna Valley deposits in Israel and the Wadi Araba mineralisation in Jordan, both 150 to 170 km to the east. All three are interpreted to represent a sequence developed on a similar basement on the northern margin of the Arabian Nubian Shield. However, a series of erosive events have meant that large slices of the succession present at any one of these localities may be absent from one or both of the others and have a different stratigraphic name and/or reflect different depositional facies/environments. Never-the-less, all three represent poorly to un-deformed, mainly flat-lying sequences that for most of the period from the Late Neoproterozoic to the present have alternated from emergent, to fluviatile coastal plain to lagoonal to shallow marine settings. This has produced a strongly permeable and porous succession of extensive aquifers, partially separated by finer grained and carbonatic aquitards that have permitted widespread fluid circulation over that same long period to the present.
The geology of southwestern Sinai Peninsula and surrounds can be summarised, as follows, from the basement upwards:
The Neoproterozoic basement of the Sinai Peninsula is the northernmost exposure of the Arabian-Nubian Shield and is composed of juvenile crustal rocks. These rocks are a collage of island arc complexes accreted during the closure of the Mozambique Ocean that separated East and West Gondwana (e.g., Samuel et al., 2014 and references cited therein). Within the Sinai Peninsula, the juvenile crust is composed of:
i). ~820 to 740 Ma pre-collisional stage island arc complexes, made up of extensive remnant blocks of metamorphosed volcano-sedimentary rocks, and para- and orthogneisses with associated migmatites and amphibolites. These metamorphic complexes occurs as enclaves within the later batholithic intrusions and cover around one-third of the basement exposure in the Sinai Peninsula. They comprise strongly deformed and metamorphosed sedimentary, arc volcanic and calc-alkaline granitoid protoliths that have been subjected to a single, low-pressure, greenschist to amphibolite-facies metamorphic event (e.g., Abu El-Enen et al., 2007).
ii). A collisional stage suite characterised by ~670 to 630 Ma, variably deformed, calc-alkaline granodiorites, diorites and gabbros (Adel et al., 2010; Azer et al., 2021).
iii). A post-collisional succession that comprises two major Ediacaran episodes, specifically a). an early pulse of undeformed calc-alkaline granitoids, quartz diorites and minor gabbros that range in age from ~630 to 610 Ma and may involve either the continuation of, or remelting of, the preceding cal-alkaline suite, and by b). a younger ~610 to 580 Ma suite of alkaline to peralkaline A-type granites (Adel et al., 2010; Azer et al., 2021). Each of these two magmatic episodes includes both plutonic rocks and their volcanic equivalents. The early calc-alkaline volcanism was emplaced in two cycles of eruption that produced medium- to high-K calc-alkaline volcanic rocks. Each was accompanied by the deposition of immature clastic sedimentary rocks that remain un-deformed and un-metamorphosed. Some of the more evolved early episode calc-alkaline volcanic sequences are transitional to alkaline A-type. The late alkaline/peralkaline volcanic units were emplaced after the termination of Pan-African orogenic activity reflected by the regional ~605 Ma unconformity. They are represented by alkali rhyolite, comendite and pantellerite flows, with abundant ignimbrites and pyroclastic deposits, and were emplaced during an extensional regime, accompanied by block faulting and differential uplift. During the closing stages of this volcanic phase, large-scale caldera subsidence occurred and ring dykes were injected into the bordering fractures (Azer et al., 2021). Volcanic rocks of this post-collisional phase are variously known as the Dokhan or Aheimir Suite volcanics that include basalt, andesite, dacite, rhyodacite to rhyolite, and are widespread in Jordan, the Sinai Peninsula and eastern desert of Egypt, and elsewhere within the Arabian-Nubian Shield.
In southwest Sinai Peninsula, the Neoproterozoic basement is unconformably overlain by Palaeozoic successions as follows:
Lower Palaeozoic Sequence, which comprises (after Afify et al., 2022) the:
• Cambro-Ordovician Araba Formation, which is up to 195 m thick, and is made up of,
- Sarabeet El Khadim Member, up of 50 m of conglomerate, conglomeratic sandstone, cross-bedded pebbly sandstone and a few silty sandstone intercalations. It was deposited in a low sinuosity braided fluvial channel and shallow marine to tidal flat environment (Kora, 1984; El-Araby and Abdel-Motelib, 1999; Khalifa et al., 2006; Wanas, 2011), and is overlain across a sharp contact by the,
- Abu Hamata Member, which comprises 25 m of fine- to medium-grained sandstone and silty clays, with subordinate sandy dolostone interbeds. This member has been further subdivided into lower, middle and upper intervals. The lower and upper of these are cross-bedded red sandstone-siltstone with flaser, hummocky, trough, recumbent and folded, and planar structures. The middle interval comprises green to greyish-green copper-bearing cross-bedded sandstone-siltstone and mud rocks containing biogenic structures. This member contains worm burrow tubes and biogenic structures, thin sandy dolostone interbeds and fine- to coarse-grained sandstones with bi-directional cross-bedding, taken to suggest an intertidal-subtidal marine environment (Allam, 1989; El-Araby and Abdel-Motelib., 1999; Khalifa et al., 2006; Wanas, 2011).
- Adediya Member, comprises up to 120 m of thick-bedded and cross-bedded sandstone with a few claystone interbeds. It is interpreted to have been deposited either in a fluviatile environment (Kora, 1984) or a transgressive shallow marine tidal flat regime (Khalifa et al., 2006).
Carboniferous Sequence, which comprises the:
• Middle Visean Um Bogma Formation, that unconformably overlies the Araba Formation and has a maximum thickness of 41 m. It is characterised by the occurrence of large manganese and iron oxide lenses and concretions in all three of it's constituent members. This mineralisation is found on the downthrown side of the main faults cutting the area. It is also characterised by an abundance of marine fossils implying an open marine, subtidal to warm environment of deposition, whilst the presence of dolostone, sandy dolomitic limestone and marl facies suggest an intertidal-subtidal depositional environment. The three members are:
- Ras Samra Member, composed of up to 17 m of mainly hard to very hard pinkish brown, thick-bedded dolostones that are strongly brecciated and have undergone karstic dissolution to form cavities, some of which were filled by manganese and iron oxide pockets and concretions. The main manganese-iron horizon occurs at different stratigraphic positions within the Ras Samra Member and usually has sharp contacts with the host rocks. The Mn-Fe oxide bands are usually bounded above and below by thin layers of calcareous shales, kaolinitic clays, siltstones or sandstones. These clastics layers are brown, purple-yellow
and black, soft to fissile, and are also rich in manganese and iron oxides.
- El Qor Member, a 12 to 25 m thickness of alternating yellow, moderately hard, thinly bedded, marly dolostones and dolomitic limestones with soft siltstones and shaly interbeds. It includes thin beds of variegated shales and siltstones, rich in iron and manganese oxides. This is the only member of the Um Bogma Formation where un-dolomitised limestones remain. Some thin, black, organic-rich shales have also been recorded.
- Um Shebba Member, 18 m of brown to grey thick-bedded, very hard brown and grey, coarsely-crystalline dolostone and sandy dolostone containing variable amounts of coarse sand grains and quartz pebbles. There is an abrupt change from dolostones to coarse grained sandstones at the top of the member.
• Upper Visean Abu Thora Formation, that is ~120 m thick, and, according to Taha and Edress (2022), has been informally divided into three rock units that comprise a lower and upper sandstone, sandwiching a middle coal and shale sequence. The middle coal and shale strata are not homogenous, and have been further subdivided into four units from the base to the top. The lower shale unit is 4 m thick and composed of kaolinite-rich shale. The second is the 5.1 m thick middle shale, composed of Fe-shale containing 2.04 to 16.45 wt.% hematite). The third is the 0.55 m coal seam, and the fourth is the 6 m thick upper shale unit, composed of wacke.
• Upper Carboniferous (Westphalian) Abu Durba Formation, which conformably overlies the Abu Thora Formation, is also divided into three, i). lower dark grey to black shales with lesser interbeds of laminated siltstone and thin-bedded grey sandstone beds; ii). a middle white or multi-coloured, medium to coarse grained sandstones; and iii). an upper dark grey to green, fossiliferous shale horizon with two sandy dolostone/dolomitic sandstone interbeds. The formation is ~90 m thick.
• Permian to Triassic basaltic sills and feeder dykesthat intrude the upper Abu Thora and Abu Durba formations, locally intruded along the contact between the two formations.
• Permo-Triassic Qiseib (Qusyeb) Formation red bed sequence that is 30 to 100 m thick, bounded above and below by unconformities. It is mainly Triassic in age, with Late Permian basal units, and comprises red, brown and violet sandstones, which are conglomeratic at the base, within an overall fining upward trend, and local yellow-orange fossiliferous dolostone lenses in the middle. This unit is better developed on the western side of the Cenozoic Gulf of Suez, but in southwestern Sinai, is represented entirely by continental facies sedimentary rocks.
• Early Cretaceous Malha Formation of Barremian, to Aptian to Albian age, that varies from ~50 to 340 m in thickness. This formation outcrops semi-continuously eastward across the central Sinai Peninsula to where it becomes the generally equivalent Kurnub Group in Israel, as described in more detail in the Timna Valley record (Knox et al., 2011). Similarly to that group in Israel, it has been subdivided, from the base, into the:
- Amir (or Raqaba) Member, which comprises 20 to 70 m of mainly white, fine to medium-grained, moderate to moderately-well sorted, cross-stratified sandstone, alternating with thin layers of grey and red siltstone. The sandstones are cemented by ~20 wt.% well ordered authigenic kaolinite. Syntaxial quartz overgrowths are common, whilst quartz also sporadically occurs as cement (Weissbrod and Snee, 1997).
- Avrona (or Temmariya and overlying Drab) Member, composed of 40 to 60 m of pebbly sandstone, made up of grey-white, medium- to
coarse-grained, cross-stratified sandstones and grits with stringers and lenses of pebbles and lenticular layers of grey sandy siltstone. Planar and trough-cross-bedding is common. Lenses of basal, clast-supported, imbricated sandy conglomerate with intraclasts of rounded quartz pebbles and a coarse sand matrix occurs locally. The sandstone is interpreted to have been deposited in braided alluvial channels with no clearly defined overbank terrain (Weissbrod and Snee, 1997). The Temmariya Member subdivision are distinguished by being mostly coarser. Red and variegated sandstones, siltstones and shales are found in the upper part of the same member, as are concretions rich in iron and manganese oxides, as well as iron and manganese crusts. The Drab Member subdivision, as its name suggests, has no bright colours, unlike the underlying Temmariya and Variegated members and has two kaolinite beds at its base representing a period of non-deposition and erosion.
- Samar (or Variegated) Member, which is ubiquitously distributed, and varies from 50 to >150 m in thickness. It is composed of variegated grey, white, purple, and yellowish, friable, fine- to medium-grained quartz arenites, alternating with red, purple, and ocher layers of siltstone
and paleosols, locally mottled, and iron crusts. Quartz pebbles, granules and mudclasts are randomly distributed throughout. Predominantly small- to medium-scale planar/tabular cross-bedding, and several upward-fining sequences are evident, some of which are bounded by palaeosols. The unit was deposited in a fluvial, braided river setting, with lacustrine and marine influence toward the top.
• The Upper Cretaceous, sequence varies considerably across the Sinai Peninsula, from south to north. The principal structural feature influencing facies variatons is the WSW-ENE trending, dextral, transtensional Sinai Hinge Belt, a major crustal boundary that passes through the head of the Gulf of Suez and is cut by the Wadi Araba-Dead Sea Transform Fault in the east, well to the north of the Feinan and Timna districts. The broad sequence is as follows, (after Abdel-Gawad et al., 2004; Zalat, et al., 2012; Moustafa et al., 2013; Obaidalla et al., 2018) from the base:
- Early to Late Cenomanian Raha Formation, that occurs in the southwestern Sinai Peninsula, where it comprises ~140 m of intercalated shale, marl and sandstone with minor limestone interbeds, which laterally grades to the north into the
- Late Albian to Late Cenomanian Galala Formation, a northward thickening stratigraphic equivalent that ranges from ~60 to >400m in thickness and is composed of dolomitic limestone and argillaceous shale, with minor marl and shale-siltstone interbeds. To the north, above the Sinai Hinge Belt it becomes the
- Cenomanian Halal Formation, which is 300 to 550 m thick, and grades upward from basal quartz arenite, into bioclastic-oolitic grainstone, overlain by bioclastic packstone and wackestone, with highstand dolostone beds.
- Late Cenomanian to Early Turonian Abu Qada Formation, which varies from 40 to 60 m in thickness, and is only found to the south of the Sinai Hinge Belt. It is mainly composed of intercalated marl and shale, with some limestone interbeds. Towards the north, it is overlain by the up to 37 m thick Buttum Formation shale and gypsum with intercalated claystone and siltstone.
- Turonian Wata Formation that is variably found from the southwestern Sinai Peninsula to the Sinai Hinge Belt. It varies from <50 to >120 m in thickness in the south to 130 to 200 m over the hinge belt, and is composed of chalky and dolomitic, argillaceous to sandy limestone, with marl shale and sandstone interbeds towards the middle of the sequence.
- Coniacian to Santonian Matala (or Matulla) Formation, an extensive, 93 to 170 m thick, Coniacian to Santonian Upper Cretaceous succession of sandstone and a thick suite of organic-rich shales with limestone and marl intercalations. This formation which predominates in southwestern Sinai, has been divided into a (after Zalat, et al., 2012):
i). Lower Member, that ranges from 21 to 61 m in thickness, and consists of alternating beds of shale, claystone and calcareous, ferruginous, glauconitic and carbonaceous sandstone with thin interbeds of fossiliferous limestone, dolostone and ironstone, capped by a by a thick dolostone bed. The carbonaceous sandstone is grey to black, fine to medium-grained, banded and mottled in parts.
ii). Middle Member, which ranges from 32 to 58 m thick, is composed of mixed intercalations of glauconitic, calcareous, cross-bedded greyish white ripple marked sandstones with thin ironstone bands and thin beds of greenish to grey shale, limestone and claystone. It is conformably overlain by the
iii). Upper Member, which varies from 29 to 70 m in thickness, and is predominantly composed of thick shale and claystone with thin interbeds of phosphatic sandstone, microcrystalline limestone and dolostone. These beds are glauconitic, ferruginous, gypsiferous, sometimes in the form of ferruginous concretions and highly fossiliferous.
To the north, the Matala/Matulla Formation grades into the:
- Coniacian to Santonian Themed Formation that varies from 15 to 40 m in thickness, expanding to 85 to 105 m to the north over the Sinai Hinge Belt. In north-central Sinai, this formation is composed of marl, intercalated with shale limestone and sandstone, whilst over the hinge line the sequence is predominantly chalky limestone and marl. The Matala/Matulla and Themed formations are overlain by the:
- Campanian to Maastrichtian Sudr Chalk, which is the uppermost member of the Upper Cretaceous sequence, and varies from 160 to 200 m in thickness over the Sinai Hinge Belt in the north. It is widely distributed, and is composed of snow-white, massive chalk with minor marl, shale and limestone beds. It represents a major transgression directly following the regressive cycle that had led to the deposition of Matulla Formation siliciclastic facies.
• The Cenozoic Cover. The widespread, 60 to 80 m thick, clay rich, Paleocene Esna Shale and the overlying ~165 m of carbonates and dolostones of the Lower and Middle Eocene Egma and Mokattam Limestones Formations are found in the structurally low areas to the north, east, and south of the Sinai hinge belt. Whilst these rocks are flat lying to the east and south of the hinge zone, they have been folded to the north.
Mineralisation
The bulk of the known sediment hosted copper mineralisation within the Sinia Peninsula is hosted within the Cambro-Ordovician Araba Formation and the Middle Visean Carboniferous Um Bogma Formation. Sections of these occurrences have been variously exploited for turquoise [CuAl6(PO4)4(OH)8 • 4H2O] and for copper metal. Other copper mineralisation has been exploited to a much lesser degree within the Neoproterozoic igneous complexes within the basement to the sediment hosted accumulations.
• Neoproterozoic Nubian-Arabian Shield Basement, where copper mineralisation has been exploited in historic mines, such as that at El Regita. Ancient vertical shafts exploiting copper have reached depths of 10 m. The host magmatic complex and country rocks at El Regeita are arc related juvenile rocks, and include Neoproterozoic meta-volcanosedimentary rocks, intermediate and felsic metavolcanics and related pyroclastics, meta-gabbro-diorite, olivine bearing gabbro, monzogranite, monzonite, alkaline granite, syenite to quartz syenite, dyke-like granophyre intrusion, and later phase of andesitic dykes. Mineralisation at El Regeita is characterised by structurally controlled 'mesothermal' epi-genetic copper sulphides deposited in the NW-SE trending El Regeita shear zone. The mineralised shear zone dips at 72°SW and extends over a 600 m strike length and is 3 m thick (Abdel Gawad, et al., 2021). Representative samples of the mineralised alteration halo returned values of up to 1.7 wt.% Cu,1.6 g/t Au, and 4 g/t Ag (Salem et al., 2011). Bluish to greenish oxidised copper mineralisation occurs as fissure filling and staining of the monzogranite shear walls and diorite/andesite dykes. Copper mineralisation occurs as chalcocite, covellite, bornite and chalcopyrite, accompanied by barite and titanite, within the highly altered shear zone. Mineralisation has associated argillic, phyllic and propylitic alteration zones. The argillic and phyllic zones are developed within the monzogranite host rock, while propylitic alteration is characteristic of the mineralised NW-SE trending diorite/andesite dykes and the peripheral monzogranite. This sequence is unconformably overlain, just to the north of the El Regita Mine, by sedimentary rocks of the Cambro-Ordovician Araba Formation (Salem et al., 2011). The El-Regeita shear zone also hosts elongated to subrounded pegmatite bodies with an anomalous radioactive signature due to the presence of U-bearing minerals (Bishr et al. 2008).
• Cambro-Ordovician Araba Formation, where copper mineralisation is hosted by interbedded grey sandstone-siltstone between two red-bed intervals of vanadiferous sandstones, hosted within the middle Abu Hamata Member of the Araba Formation. Vanadium-bearing minerals are abundant in the red sandstone beds, where copper mineralisation is absent. The contacts between the grey copper-bearing layers and the vanadium-rich red sandstones is gradational (Afify et al., 2022).
The hosts to the Cu-V deposits are intercalated calcareous sandstone, siltstone and dolostone beds. Both copper- and vanadium-bearing sandstones are mainly composed of fine- to medium-grained, poorly-sorted, red and green to grey arkose to sub-arkosic arenites, generally containing flaser, trough and bi-directional cross-bedding (Afify et al., 2022).
The copper- and vanadate-bearing rocks exhibit a range of fabrics, including layered; concretionary; dispersed crystals interstitial to detrital grains in the sandstones, siltstones and carbonates; pore-filling cement and laminated stratabound and sheet-like bodies; lenticular fabrics; pockets; and concretionary fabrics, but only rarely as fracture-filling veinlets. Relics of carbonate concretions, lenses and thin laminae were observed in association with the copper mineralisation (Afify et al., 2022).
The host siliciclastic rocks of the Abu Hamata Member are mainly arkosic and subarkosic arenites (to siltstones) predominantly composed of quartz, microcline, orthoclase, albite, muscovite and biotite, with an interstitial assemblage that is predominantly hematite, goethite, dolomite, ankerite, siderite, calcite and pyrite. Detrital minerals include zircon, rutile, olivine and other heavy minerals. Clay minerals are kaolinite and illite (Afify et al., 2022).
The mineralised sandstone-siltstone beds are dominated by copper carbonates and phosphates, particularly
malachite [Cu2(CO3)(OH)2],
azurite [Cu3(CO3)(OH)2] and
pseudomalachite [Cu5(PO4)2(OH)4],
copper oxides such as cuprite [Cu2O] and
auriacusite [Fe3+Cu2+(AsO4)O],
copper silicates, mainly chrysocolla [(Cu2-xAlx)H2-xSi2O5(OH)4⋅nH2O],
copper chlorides, mainly atacamite [Cu2Cl(OH)3],
with subordinate Pb-Fe-As-V minerals that include, mottramite [PbCu(VO2)(OH)],
mimetite [Pb5(AsO4)3Cl],
cerussite [PbCO3],
carnotite [K2(UO2)2(VO4)2•3H2O],
descloizite [Pb,Zn(VO4)(OH)],
vanadinite [Pb5(VO4)3Cl],
beudantite (PbFe33+>(AsO4)(SO4)(OH)6)
and duftite [PbCu(AsO4)(OH)]
(Afify et al., 2022)
Under the microcope, copper mineralisation is seen in siltstone, shale and rarely in dolostone. In each of these facies, the copper minerals commonly occur as green and blue streaks, seams, veinlets, laminae and disseminated crystals. Some fill stylolites, forming irregular streaks and seams. Goethite pseudomorphs after pyrite micro-concretions are evident and are associated with copper- and vanadium-bearing minerals. The Cu minerals are also found as thin laminae parallel to bedding planes in the siltstones and mudrocks/shales, whilst green- and turquoise coloured malachite occurs as pore-filling crystals in sandy dolostone. Fine grained euhedral Mn-dolomite rhombohedra are observed to cement the clasts of the cupriferous sandstones. These dolomite crystals are, in turn, seen to be partially dissolved and replaced by copper silicates and carbonates (mostly chrysocolla and/or malachite), copper chloride (mostly atacamite) and copper carbonates (mostly malachite and/or cuprite) to form pseudomorphs after the dolomite and/or associated siderite crystals. These same copper minerals also occur as small aggregates filling pores, whilst some are enveloped by and/or are associated, with kaolinitic clays to form flakes. Micro-chemical and semi-quantitative analyses indicate these Cu-bearing minerals have a wide variation in copper content between 6.07 and 51.18 wt.%. Chlorine ranges up to 15.07 wt.% (Afify et al., 2022).
The strongly ferruginous and vanadiferous sandstones that sandwich the more reduced cupriferous sandstones, commonly contain high vanadium content minerals as pore-filling euhedral crystals rich in Pb, Fe and As as well as V. These crystals are micron sized, always <70 µm across, and are mainly associated with altered and variably dissolved feldspar grains of the sandstone, and enveloped with flakey and booklet-like kaolinitic and illitic clays. Microchemical analysis of these minerals shows the V content is variable, ranging from 7.67 to 34.69 wt.%, with high Pb of up to 66.5 wt%, whilst As is very low, never exceeding 1 wt.%. Al and Si within the lattice of V-bearing minerals may come from the associated kaolinitic clays. The Fe content, which can reach 31.18%, increases inversely to the Pb content decreases, and reaches as much as 31.18 wt%. The vanadium content of these racks varies from 25.8 to 362.3 ppm V (Afify et al., 2022).
These observations might be interpreted to suggest hypogene copper mineralisation, most likely only of low grade, was deposited from a percolating, strongly oxidised fluid within the thick, regional aquifer that is the Araba Formation. Deposition of copper and vanadium would have been triggered by intersection with the reduced, less permeable siltstone-mudstone section of the formation, most likely as copper sulphides, extracted from solution by both the reduced oxidation state and reaction with clay minerals. Continued, or subsequent percolating, strongly oxidised fluids would have both oxidised, dissolved and removed copper sulphide, leaving vanadium. This would have been more pronounced in the more porous flanking sandstone, whilst within the reduced mudstone-siltstone, the sulphides were oxidised, copper dissolved, but re-precipitated as Fe-oxides and Cu silicates/chlorides/phosphates, etc. in the flat-lying, reduced mudstone-siltstone hosts most likely controlled by a low angle, intersecting palaeo-water table. The presence of vanadium may suggest the percolating fluids could have leached a mafic source.
• Carboniferous Um Bogma Formation - Copper occurs as i). green and blue minerals within the black manganese ore deposits hosted by the three members of the Um Bogma Formation; and ii). within the black shale of the middle unit of the Um Bogma Formation, the El Qor Member.
The manganese mineralisation of the Um Bogma Formation occurs within all three members of the formation, although economically exploited deposits are confined to the Ras Samra Member, the lower of the three. Manganese mineralisation is hosted by carbonate beds that have undergone strong karst dissolution. As such, the manganese occurs in a number of forms that include lenses, cavern-fill, stratabound bands, disseminations, irregularly bedded and as large concretions up to 10 m in diameter. Economic mineralisation is largely concentrated along the main faults where they cut the carbonate hosts. The associated copper mineralisation is found as thin laminations to irregular streaks, as disseminations, and as acicular, fibrous and pore-filling crystals. Barite is associated with the copper, occurring as veins, cavity fill and disseminated crystals (Afify et al., 2022).
The host carbonate units are predominantly dolostones composed of dolomite with lesser calcite and subordinate quartz.
The Fe-Mn mineralisation is composed of:
pyrolusite [MnO2],
jacobsite [Mn2+Fe3+2O2],
hollandite [Ba(Mn4+6Mn3+2)O16],
todorokite [(Na,Ca,K,Ba,Sr)1-x(Mn,Mg,Al)6O12.3•4H2O],
cryptomelane [K(Mn4+7Mn3+)O16],
birnessite [(Na,Ca,K)0.6(4+,Mn3+)2O4.1•5H2O],
romanechite [(Ba,H2O)2(Mn4+,Mn3+)5O10],
manganite [Mn3+O(OH)],
manjiroite [Na(Mn3+7Mn3+)O16],
hematite [Fe2O3],
goethite [FeO(OH)].
Remnant sulphides include:
pyrite [FeS2],
covellite [CuS] and
chalcocite [Cu2S].
Other copper minerals are:
chrysocolla [Cu2-xAlx)H2-xSi2O5(OH)4•nH2O)],
chalcanthite [CuSO4•5H2O],
antlerite [Cu3+2(SO4)(OH)4] and
cuprite [Cu2O] (Afify et al., 2022).
Under the microscope, Fe-Mn minerals can be seen to have formed either between saddle dolomite crystals (that are the product of dolomitisation), or as pore-filling cement, and were mostly formed after the dissolution of carbonates. In transmitted polarised light, they occur as black, undifferentiated oxides and oxyhydroxides with striated fabrics. The associated copper-bearing minerals are found as green and blue acicular and fibrous crystals set in a colourless (black) Fe-Mn groundmass. High-resolution textural and chemical analyses of the copper mineralisation within the manganese ore deposits, show they occur as pore-filling oxides, carbonates and sulphates. The copper minerals cut and overprint the Fe-Mn mineralisation with amorphous, acicular and fibrous textures as well as network and cross-cut structures. They are also accompanied by zinc-bearing Fe-Mn oxides (e.g., chalcophanite). Representative samples collected by Afify et al. (2022) assayed as follows: MnO - 9 to 84% MnO with a small number with <1%; Fe2O3 - 15 to 72% with a few <10%; Cu - 90 to 550 ppm. Within these same samples, BaO varies from 0.03 to 2.86 wt.%, S <0.01 to 0.452 wt.%; and Ni from 0.012 to 0.041 wt.%.
A similar copper assemblage is found associated with thin black organic-rich shales within the middle El Qor Member of the Um Bogma Formation, accompanied by strongly disseminated pyrite which occur as euhedral disseminated crystals and/or as framboidal concretions. The copper minerals have variable Cu and S contents, and include native copper, copper sulphides such as covellite and chalcocite and copper sulphates, including chalcanthite, with sparse silicates such as chrysocolla along with the dominant Fe-Mn bearing minerals.
The main manganese ores of the Ras Samra Member are mainly found as stratabound lenticular bodies that occur as a series of disconnected ~2 to 3 m thick lenses. The main ore horizon occurrence is exploited at a number of localities in a strip ex-tending from the SW to the NE. Manganese lenses pass upward into more iron-rich layers and/or are surrounded by iron ores. In many occurrences, manganese lenses are completely separated from the iron mineralisation. A few vein-like occurrences are also recorded, apparently associated with fissures and faults. At one locality, a fissure ~0.3 m thick cuts across the hard dolostones of the Ras Samra Member, extending from the underlying ore lense for 4 m vertically. Disseminated mineralisation sometimes occur in association within a network of fractures in the pink dolostones of the Ras Samra Member. Within the exploited ores of the Um Bogma Formation, the dominant manganese minerals are pyrolusite and hausmannite. In most samples, helvite and hematite are noted in association with pyrolusite (El-Shafei et al., 2022).
As described in this record, copper mineralisation occurs in both the predominantly siliciclastic middle member of the Cambro-Ordovician Araba Formation and the unconformably overlying Carboniferous Um Bogma Formation, separated by the up to 120 m thick sandstones of the upper member of the Araba Formation. The copper mineralisation of the Araba Formation is associated with vanadium, whilst relatively weaker copper is associated with Fe-Mn oxide mineralisation within karst weathered carbonates of the Um Bogma Formation. No mineralisation has been recorded from higher in the sequence in this part of Sinai Peninsula, in contrast to Timna, ~170 km to the ENE, where mineralisation is found in both the Araba Formation equivalent and the unconformably overlying Lower Cretaceous Kurnub Group. While the latter is present on the SW Sinai Peninsula, it is not apparently mineralised.
Reserves and Resources
Whilst the Bir Nasib district of southwestern Sinai Peninsula was a significant producer of copper and ornamental turquoise over several thousand years in antiquity, no modern or resource has been established. A 'large' slag heap at Bir Nasib, was surveyed by Petrie (1906) who calculated it contained ~100 000 tonnes of slag. This was confirmed more recently by Bachmann (1978), who calculated the quantity of metallic copper produced at Bir Nasib was ~5000 tonnes, a huge quantity of metal in ancient times (Petrie, 1906).
However, in modern times, manganese has been mined from the cupriferous Fe-Mn bodies of the Carboniferous Um Bogma Formation. A silicomanganese plant was initially established at Abu Zenima on the Gulf of Suez coast to treat these resources in 1966 by the State owned Sinai Manganese Company. However, the onset of the Arab Israel war in 1967 and the Israeli occupation of Sinai prevented any further activity. After the withdrawal of the Israel forces from Sinai in 1993, a rehabilitation program was initiated under the supervision of the Norwegian Ferro-alloy producer, Elkem, and production commenced. The Sinai Manganese Company currently (2023) operates a 36 000 tonnes per annum electrical furnace at Abu-Zinima Sinai, to treat the resources mined. The total reserve of manganese ores in Um Bogma Formation has been estimated at about 1.7 Mt of contained metal (El-Shafei et al., 2022).
The most recent source geological information used to prepare this decription was dated: 2022.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Afify, A.M., Osman, R.A., Wanas H.A. and Khater, T.M., 2022 - Mineralogical and geochemical studies of copper mineralization in the Paleozoic sedimentary section in southwestern Sinai, Egypt: in Ore Geology Reviews v.47, 22p. doi.org/10.1016/j.oregeorev.2022.104994.
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El-Shafei, S., Ramadan, F., Essawy, M., Henaish, A. and Nabawy, B., 2022 - Geology, mineralogy and geochemistry of manganese ore deposits of the Um Bogma Formation, south-western Sinai, Egypt: Genesis implications: in Mining of Mineral Deposits, v.16, issue 3, pp. 86-95.
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Megahed, M.M., 2018 - Archaeo-mineralogical characterization of ancient copper and turquoise mining in south Sinai, Egypt,: in Archaeomatica No.4, pp. 24-33.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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