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Wadi Araba Copper District - Feinan, Faynan, Phaino, Khirbet el Nahas, Abu-Khusheiba |
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The Wadi Araba (Araba Valley) straddles the Jordan (or Dead Sea) Rift Valley that lies along the boundary between the African and Arabian plates, and includes the Gulf of Aqaba, the Dead Sea and Sea of Galilee. It is flanked to the east, and on its west, by sediment hosted copper deposits. These include, from north to south, over an interval of ~140 km and width of ~20 km, the Feinan (or Faynan, or the Roman centre of Phaino as mentioned by the historian Eusebius) and Khirbet el Nahas deposits on the central eastern flank of the Wadi Araba, the Abu-Khusheiba area along the eastern southern margin of the Wadi and ~100 km north of Aqaba at the head of the Gulf of the same name. The similar Timna district is located in southern Israel, within the western half of the wadi in the south, 20 km north of Aquaba. Other related mineralisation, well to the west of the Wadi, include the Bir Nasib District copper and turquoise cluster, 170 km SW to WSW of Timna, on the southwestern margin of the Sinai Peninsula in Egypt.
(#Location: Feinan - 30° 37' 37"N, 35° 29' 37"E); (#Location: Khirbet el Nahas - 30° 40' 51"N, 35° 26' 10"E); (#Location: Wadi Abu Khushaybah - 30° 15' 41"N, 35° 19' 4"E).
It should be noted that the generally NNE-SSW elongation of the Wadi Araba and exposures of the Lower Palaeozoic host sequence, as well as the alignment of copper deposits, is largely an artifact of late Mesozoic to Cenozoic tectonics related to the Africa-Arabia plate boundary and Dead Sea Rift Valley, rather than the Lower Palaeozoic architecture. However, this trend is subparallel to the elongation of the Late Neoproterozoic graben network that unconformably underlies the northward thickening, Lower Palaeozoic, fluvial to passive margin host succession.
Ancient copper mining on an industrial scale is evident within this belt, particularly early copper workings spread over an area of ~20 x 25 km at Feinan, which is the largest by far in the region, and includes smelting sites with dumps containing a total of 150 to 200 000 tonnes of slag (Hauptmann et al., 1992). Less significant, but more studied activity is evident at Timna and Bir Nasib in Israel and Egypt respectively. Feinan is regarded as having played an important role in the early copper supply to the southern Levant. The extensive disturbed outcrops of copper mineralisation and associated dated artefacts from villages in the immediate area indicate the Feinan district deposits have been exploited for more than eight millennia (Hauptmann 1991), whilst their occurrence eventually stimulated the development of smelting technology. Mining began very early in the Pre-Pottery Neolithic period (10 000 to 6500 BCE) for ornamental beads and green powder for cosmetic purposes, with such products identified as originating from Feinan being found as far to the north as the Balkan Peninsula. Smelting is not evident until the Chalcolithic (or Copper) Period (the transitional period between the Neolithic and the Bronze Age, between ~4400 and ~3000 BCE). Exploitation continued sporadically, but peaked in the third and first millennia BCE, and then again during the second to fourth centuries CE (AD). During the Chalcolithic period, there appears to have been little metal produced at Feinan, with ore indicated to have been mined and transported to other centres in Palestine for smelting. Subsequent extensive mining and smelting at Feinan has been dated as during the Early Bronze Ages II (1650 to 1550 BCE) and III (1550 to1200). At least 100 tonnes of metal are estimated to have been produced during the Early Bronze Age. Between the Early Bronze Age and the Late Iron Age (1200 to 500 BCE) the dominant ore mined and smelted were those containing both copper and manganese, which were self-fluxing in the smelting process, and represented a technological breakthrough. These ores resulted in the easy formation of liquid slag, and increased yield of metallic copper from a smelt. A second period of copper production took place during the Iron Age lIB and IIC (between 900 and 500 BCE), when copper production boomed before iron became the main metal of daily life. Production was active at both Feinan and Khirbet en-Nahas during this period, with a total of >100 000 tonnes of slag being accumulated, placing them among the most important historic sites of copper mining and smelting known in southwestern Asia. Ore was mined from shafts to a depth of 50 to 60 m from >100 mines in the wadis/valleys of the area and transported to a restricted number of central smelting sites. Iron Age copper production ceased at ~400 BCE, following the fall of the Edomite empire which had been responsible for the mining (Hauptmann et al., 1992). To this time, exploitation of the mines of the Wadi Araba had spanned the heights of the Egyptian and Assyrian civilisations. Major mining and smelting was resumed during Roman times, mainly between the second and fifth centuries CE. However, by then, much of the high grade carbonate-shale hosted copper-manganese ores had been exhausted, and the Romans resorted to exploiting the remaining low-grade Cambrian sandstone copper ores that had been mined since the Chalcolithic Period. More than 120 Roman mines surrounding Feinan were exploited, with ore being transported to a central smelter near Feinan, where 50 to 70 000 tonnes of slag suggest production of several thousand tonnes of copper (Hauptmann et al., 1992). A final phase of activity is recorded from the Mamluk period (1250 to 1516 CE), although it has been suggested that this involved reprocessing some of the ancient slags.
Whilst these deposits were of great significance to the regional economies and mining technology of antiquity, in modern terms they would be regarded as only modest to inconsequential resources. Modern testing has outlined much larger, but still modest, non-JORC compliant resources as detailed below in the Reserves and Resources section. Never-the-less more significant resources may remain to be discovered.
Modern exploration included a program undertaken by a German company, Otto Gold Engineering, between 1961 and 1964 in the Wadi Abu-Khusheiba area, concentrating on copper in sandstone. Investigations were subsequently also carried out by the Mining Division of the Jordanian Natural Resources Authority, the results of which were reviewed by the French Government BRGM in 1975, as part of a feasibility study that proved negative due to low prevailing copper prices. In 1984, Seltrust Engineering Limited conducted extensive ore processing and metallurgical studies on the deposits of the Feinan district and recommended a solvent extraction-electro winning (SXEW) process, although no mining proceeded. Between 1988 and 1993, the Jordanian Natural Resources Authority carried out further exploration at Khirbet el Nahas and the adjacent Wadi Jaryia prospect, and at Abu-Khusheiba. This work was reviewed in 1993 by the French BRGM as part of a further feasibility Study and resources calculated (as outlined below).
Regional Setting
The NNE-SSW trending Wadi Araba cuts across the shallowly dipping Phanerozoic successions that overlie the generally east-west trending, northern passive margin of the Arabian-Nubian Shield, deposited within and on the shorelines of the Tethyan Ocean which lay to the north. The mineralised Palaeozoic sedimentary rocks of the district are deposited on a basement of Neoproterozoic juvenile crystalline and sedimentary rocks of the shield.
The Wadi Araba also straddles and parallels the NNE-SSW trending Cretaceous to Cenozoic Jordan (or Dead Sea) Rift Valley which lies along the boundary between the African and Arabian Plates. This rift also corresponds to the major, ~360 km long, Wadi Araba-Dead Sea Transform Fault on its western margin which resulted in sinistral displacement of ~100 km during the late Mesozoic and Cenozoic, predominantly since initiation of seafloor spreading in the Red Sea in the early Miocene (Quennell, 1958; Freund et al., 1970; Garfunkel, 1981; Hatcher et al., 1981; ten Brink et al., 2007). Subsidence in the rift has also persisted since Cretaceous time. The exposed segment of this transform fault represents the southern to mid section of a giant, 800 km tectonic element that extends from the Red Sea spreading centre in the south, to merge with the Cyprian-Taurus-Zagros Suture/collisional belt in the eastern Mediterranean to southern Turkey. The latter marks the collision zone between the African and Arabian plates to the south and the Eurasian plate to the north.
The Arabian-Nubian Shield largely comprises tracts of juvenile Neoproterozoic crust, dominated by intra-oceanic arc volcanism, widespread batholithic granitoid intrusions and late molassic volcano-sedimentary sequences. The deposition of these sequences followed the rifted opening of the north-south Mozambique Ocean during the 870 to 800 Ma breakup of the Rodinian Supercontinent, separating what were to become East and West Gondwana. The subsequent inversion of this rift led to a period of oblique transpressional convergence and tectonic reorganisation, and the development of a series of intra-oceanic arcs. This contraction was terminated by the NW-SE directed approach and collision of East and West Gondwana between 650 and 600 Ma (e.g., Johnson et al., 2011, and references therein). This was succeeded from ~600 to 550 Ma by a period of post-collisional crustal and lithospheric reworking that involved continued shortening and thickening, gravitational collapse and deposition, as well as both extrusive and intrusive magmatism and late tectonic relaxation. Shortening during this period resulted in NW-SE directed thrusting and folding to 605 Ma, followed by the development of a broad, up to 200 km wide zone of NW-SE sinistral strike-slip faulting to 590 Ma, known as the Najd Fault System. This fault system occupied the northeastern quarter of the shield in Saudia Arabia, Jordan, Israel and the Sinai Peninsula of northern Egypt. In Jordan and Israel, this fault system produced a series of half grabens, as seen in east-west seismic profiles. These grabens were filled with at least a kilometre thick sequence of red beds and bimodal volcanic rocks and was intruded by granitoids, all of which belong to the Araba Complex described below. A subsequent period of tectonic relaxation and rebound from 587 to 579 Ma with NW-SE to north-south directed extension, was accompanied by deposition of a wide Palaeozoic passive margin sequence on the northern margin of the shield.
See the Tectonic and Structural Setting section and images of the Arabian Nubian Shield Overview record for more detail.
The geology of southwestern Jordan can be summarised, within this framework, as follows, from the basement upwards:
▸ Neoproterozoic crystalline basement, which has been divided into the Aqaba and Araba Complexes, and is predominantly restricted to far southwestern Jordan, with sporadic exposures forming a linear string along the eastern margin of the Wadi Araba-Dead Sea Transform Fault to as far north as the Dead Sea. These older rocks in the main development immediately to the north of Aqaba, were exposed by Cenozoic rift margin uplift.
• Aqaba Complex - According to Abudayeh (2018), after Powell et al. (2015) the Aqaba Complex is the older of the two, and is divided into ten units, representing oceanic crust, intra-oceanic arcs and intrusive complexes developed within the Mozambique Ocean. These units include remnants and mega-xenoliths of high grade metamorphic rocks, including a heterogeneous migmatite complex of paragneisses and sillimanite-cordierite-bearing schists in the south intruded by calc-alkaline igneous rocks (McCourt and Ibrahim, 1990; Ibrahim, 1993). The ten units include four metamorphic suites which range in age between 860 and 617 Ma, one calc-alkaline gabbro, five post-orogenic calc-alkaline granitoid suites (including diorite, granodiorite, monzogranite and granite) and one foliated granitic suite that were emplaced between 620 and 605 Ma (Powell, et al., 2015).
• Araba Complex, which follows a 605 Ma unconformity and comprises a major cycle of rocks ranging in age between 605 and 550 Ma that followed the intrusion and amalgamation of the Aqaba Complex (Powell, et al., 2015). These Ediacaran rocks were predominantly volcanic and coarse clastic units deposited in the series of half grabens formed during the extensional collapse phase associated with the transform faulting of the Najd strike-slip fault system, as described above.
The Araba Complex sequence in southern Jordan is divided into two sub-cycles. The first of these begins with the sedimentary Safi Group, the basal unit of which is the Saramuj Conglomerate, a coarse-grained to granule-size reddish-brown to dark green-grey arkosic matrix, deposited as a proximal alluvial fan sequence. This conglomerate can be up to 630 m thick (Powell et al., 2015) and is clast-supported, containing well-rounded pebbles and cobbles, up to boulder-size, of Aqaba Complex granitoids, including granite, diorite, metamorphic rocks, and doleritic and rhyolitic dyke rocks. The early extensional basin hosting this unit appears to have been orientated ~north-south with the depocentre to the west, and can be traced from north Sinai to Lebanon, approximately parallel to the present-day Dead Sea Transform. The rapid isostatic uplift and weathering of the granitoid basement to feed this basin resulted in a high sediment flux that kept pace with rapid basin subsidence, which, in turn, led to erosion and partial peneplanation of the hinterland. Subsequent to this early, rapid, basin-fill, continued crustal extension resulted in tapping of rhyolitic and basaltic effusive volcanic and volcaniclastic magmas to deposit the Haiyala Volcaniclastic and Museimir Effusive formations between ~598 and 595 Ma. These included flow-banded rhyolitic lavas and air-fall tuffs, the latter deposited in a lacustrine or shallow-water environment (Powell et al., 2015). The Haiyala Volcaniclastics, which are generally 200 to 220 m thick (Powell, et al., 2015), are grey-green to reddish-brown, and range from dominantly coarse grained sedimentary tuffs, to fissile, finely laminated claystones and siltstones with angular grains of quartz, feldspar and muscovite that form thinly bedded sedimentary rhythm cycles that are each up to 0.60 m thick. These tuffaceous sedimentary rocks, which are generally upward-fining with wave ripples and desiccation cracks, are locally interbedded with rhyolitic lavas. The Museimir Effusives, dated at 598.2 ±3.8 Ma, are fragmental effusives, dominated by lithic tuffs and ignimbrites/welded tuffs, with local agglomerates intercalated tuffaceous sandstones-siltstones and fragmental, relatively massive flows of porphyritic felsite-rhyolite. They are variously placed within the Safi Group, or linked to the younger Aheimir Volcanic Formation.
The Safi Group was followed by a second Araba sub-cycle between 595 and 586 Ma, characterised by renewed extension and basin subsidence, and emplacement of alkaline and per-alkaline magmatism, beginning with the Araba Mafic Suite. The latter suite included shallow, stock-like intrusion of the 595 ±2 Ma (U-Pb) Qunaia Monzogabbro, and the 598 ±5 and 585 ±13 Ma (U-Pb) Mureihil or Umm Rachel Diorite. These intrusions resulted in thermal contact metamorphism of the Saramuj Conglomerate, and were accompanied by extrusion of the predominantly basalts to basaltic andesites of the 572 ±48 Ma (Rb-Sr) Ghuweir Volcanics (Jarrar et al., 2008).
These were broadly coeval with the intrusion of granitic plutons e.g. the 603.6 ±2.6 Ma (U-Pb) Fidan Syenogranite, 600 ±5 to 586.2 ±5 Ma (U/Pb) Feinan-Humrat-Mubarak Suite and younger dolerite dykes. This magmatism also progressed to the deposition of further volcanic rocks, the Aheimir Volcanics, and the thick monomict conglomerates of the Umm Ghaddah Formation that were locally sourced from volcanic rocks on the rift margins. The Aheimir Volcanic Formation, is locally 300 to 500 m thick, and has been dated at ~553 Ma (Powell et al., 2015). It has been subdivided into a number of units that include basaltic trachyandesite, trachyandesite, trachyte/trachydacite, and massive fine-grained porphyritic and non-porphyritic rhyolitic lavas to sub-volcanic intrusives, with the locally intercalated oligomictic Mufaraqad Conglomerate (Jarrar et al., 2012). It has been mapped at surface, extending from Gharandal in the south, to Feinan in the north, distributed in a narrow belt with a strike length of 65 to 75 km and width varying from 2 to 10 km. To the SE, distal to the Wadi Araba, the up to 125 m thick Ma'an Volcanic Formation, which is probably a temporal equivalent of the Aheimir Volcanics, directly overlies granite basement. It is a purple-brown to brown, very finely crystalline volcanic unit with frequent phenocrysts and masses of hematite. Where present, it is overlain by the Jafr Formation, a 268 m thick siliciclastic succession separating it from the Cambrian sedimentary sequence. The Jafr Formation, which is correlated with the Umm Ghaddah Formation described below, contains sandstones with brecciated anhydrite
and carbonate cements, taken to infer deposition in a restricted marginal-marine/sabkha environment.
Within the Wadi Araba, the Aheimir Volcanic Formation and intrusives are overlain by the late Ediacaran to early Cambrian terrestrial Umm Ghaddah Formation, which is up to 60 m thick, and was deposited in a series of NNE–SSW elongated intracontinental rift system basins and sub-basins, bounded by active listric half-graben faults. Basin fill is composed of a conglomerate facies deposited in a transverse alluvial fan system that drained to the NW, grading laterally into a sandstone facies deposited by braided river systems flowing to the NNE, axial to the rift basins. It is dominated by a large-scale fining-upward sequence of these terrestrial conglomerates and sandstones, interpreted to reflect the gradual termination of the Pan African Orogeny. Within this large-scale trend, there are lesser fining and coarsening upward cycles, attributed to repeated minor tectonic pulses.
The distribution of the Umm Ghaddah Formation, the underlying Ediacaran Sarmuj Conglomerates, Hiyala Volcaniclastics and Aheimir Volcanics in Jordan and adjacent countries are localised in isolated or interconnected extensional half-grabens and grabens formed during the extensional collapse phase of Arabia associated with the Najd Fault System. In addition, these grabens seem to be unrelated to the present day Wadi Araba-Dead Sea Transform Fault System (Amireh et al., 2008). Distal to these localised depositories, similar aged sequences, where present, are frequently composed of carbonates and evaporites e.g., in southern Iraq, western Iran, Oman, Yemen and southern Saudia Arabia (Amireh et al., 2008).
The Araba Complex volcano-sedimentary sequence is largely steeply dipping up to and including the Haiyala Volcanoclastics, although the youngest of these, the Umm Ghaddah Formation, is generally only moderately dipping (Powell et al., 2015).
▸ Early to Mid Palaeozoic Succession, which only dips shallowly, and overlies the Neoproterozoic crystalline basement across a 530 Ma unconformity:
• Cambro-Ordovician Ram Group, lapping onto the irregular basement topography, with units as young as Late Cambrian resting directly on that surface. The sequence comprises:
- Early Cambrian Salib Arkosic Sandstone which varies from 0 to >200 m in thickness along the margins of the Wadi Araba, but expands to >750 m in petroleum wells some 200 km to the east. It predominantly comprises yellow-brown, red, pink-white and purple, medium- to very coarse-grained, hematite-bearing pebbly, cross-bedded, arkosic and sub-arkosic, continental sandstone, deposited in a braided alluvial setting, with micaceous, sandy claystone laminae, overlain by red-brown micaceous sandstone. Locally, the lowermost beds include laminae rich in mica and detrital heavy minerals. Restricted marine sandstone and minor carbonates are also locally evident. The unit is taken to be 530 to 511 Ma in age and sourced from uplifted basement granitoids, with a high sediment flux and northward progradation of alluvial braided river lithofacies, and brief marine incursions onto a coastal plain (Powell et al., 2014).
- Early Middle Cambrian Burj Formation (after Powell et al., 2014) composed of dolostone, dolomitic sandstones and shales, which wedges out to the south of the Feinan area where it passes into the broadly coeval mixed intertidal to fluvial Abu Khushayaba Sandstone. This corresponds to the southward diminution of the marine influence that progresses until both the Burj and Abu Khusheiba units are absent in the Southern Desert if Jordan. The main Burj Formation is interpreted to have been deposited between 511 and 509 Ma, and underlies most of Jordan, thickening to the NNE, from ~60 m just to the south of Feinan, to ~110 m at the central Dead Sea to ~130 m in the north of Jordan and southern Syria. It generally has four members, as follows, from the base:
i). Tayan Member, which ranges from 18 to 20 m in thickness, and comprises finely laminated, tidal-dominated, green, mauve and red or buff, micaceous, fine-grained sandstone and siltstone. Thin dolomite lenses are present near the middle of the member, whilst the upper margin is defined as the base of the first thick bed of limestone or dolomitic limestone.
ii). Numayri Member, representing the maximum marine flooding event of the formation, and comprises a carbonate ramp sequence of shelly wackestone, packstone and grainstone with ooids and oncolites, and a diverse shelly fauna including trilobites, brachiopods and hyolithids. It generally ranges from 38 to 60 m in thickness, before wedging out to the south of Feinan, as described previously. The basal, ~5 m thick carbonate unit contains abundant fine-grained quartz sand with ripple cross-lamination, low-angle scours, and sandstone intra-clasts. This unit passes up into a massive, 20 to 30 m thick, brown-weathering grey dolostone and dolomitic limestone with glauconite peloids, and cross- and parallel-laminated oolites. Irregular lenses of orange-brown dolostone are intercalated with the clast-rich carbonates. In the upper sections of the member, the quartz sand content increases, with alternating sand-rich and sand-poor lenses. The sand-rich lenses are cross laminated, with shallow scours, whilst local beds of oolitic, oncolitic or brachiopod shell-rich dolomicrite limestone occur at the top of the member in the south. The contact with the overlying Hanneh Member siltstone/fine-grained sandstone is sharp.
iii). Hanneh Member, composed of lithologies very similar to those of the Tayan Member, but with a higher proportion of silt grade
siliciclastics over sand. To the south it merges with the Tayan Member where the intervening Numayri Member wedges out. It represents a return to a regressive, tidal influenced regime of sandstone and siltstone prompted by renewed uplift of the Arabian-Nubian Shield. It is generally between 30 and 40, and locally up to 51 m thick adjacent to the Dead Sea. It comprises red-mauve, buff-brown and green, micaceous, ripple cross-laminated siltstone, with thicker, ~0.5 m beds of buff, medium-grained, bimodal, trough cross-bedded, fine-grained, micaceous sandstone beds. Mudstone and dolostone clasts are common at some horizons.
iv). Abu Khusheiba Formation, which partially overlies and laterally interfingers with the Hanneh Member. It ranges from ~110 m thick at Abu Khusheiba in the south, but thins gradually northwards to 50 m at Feinan. It is composed of white to pale-grey and pinkish, fine- to medium-grained, micaceous, well sorted sandstone that is clayey in part. Unlike the Salib and Umm Ishrin formations, quartz pebbles and granules are rare. Where the unit rests unconformably on the palaeohigh formed by the Aheimir Volcanic Suite of the Araba Complex, it contains scattered fragments of quartz porphyry or rhyolite. Small-scale, up to 2 m thick, tabular trough cross-bedding sets are common. These sets are generally separated by thin, 0.7 to 1.3 m thick, planar bedded, laminated, micaceous, fine-grained sandstone or siltstone beds.
- Middle to Early-Late Cambrian Umm Ishrin Formation, a thick, 230 to 320 m (Abu-Jaber and El-Naser, 2016) of variably white, pink, orange, yellow-buff, red-brown, purple, pale green, well-bedded, medium-grained sandstone with thin stringers and interclasts of red-brown and pale-green claystone representing thin tidal intercalations. It is commonly trough cross-bedded, and represents a prograde, high velocity-high discharge fluvial braided river siliciclastic system with a high sediment flux in a rapidly subsiding foreland basin (Powell et al., 2014).
- Late Cambrian to Lower Ordovician Disi Formation, which, in the type area, is ~250 m thick, and conformably overlies the Umm Ishrin Formation. Three lithofacies are recognised, namely:
i). Clast supported conglomerate, occurring as channel hosted layers throughout the sequence, commonly truncating underlying siltstone-mudstone beds. The dominant clasts are up to 13 cm across and are white to colourless or light pink, rounded quartz, with subordinate mudstone, siltstone or sandstone lithoclasts, and individual lithofacies bands that vary from a few to 30 cm in thickness;
ii). Cross-bedded, medium to coarse grained sandstone, the dominant lithofacies, which is predominantly white, due to it compositional maturity, the absence of iron oxides, and the presence of authigenic kaolinite. Individual beds of this facies vary from 1 to 8 m in thickness;
iii). Thin bedded to laminated silt- to claystone which occur as 10 to 50 cm beds or lenses (Amireh, 1993).
- Middle Ordovician Umm Sahm Formation, which grades conformably upward over an interval of a few metres from the Disi Formation, to similar massive fine- to coarse-grained white sandstone, with rounded pebbles. It is ~200, to a maximum of 300 m thick in southern Jordan, and comprises a succession of fluvial quartz-arenites, with subordinate claystone and siltstone lithologies, deposited under shallow marine conditions. Over much of its thickness however, the sandstone is characterised by a dark brown colour, abundant jointing and steep scarps in exposure. The formation is composed of two main lithofacies, i). a lesser tidal suite which occupies three intervals in the middle of the succession, and is composed of laminated and thin-bedded sandstone, siltstone and claystone, and ii). the more prevalent fluvial regime, accounting for ~90% of it's total thickness. Light brown quartz-arenites similar to those of the Cambrian Umm Ishrin Formation are common in the upper part of the succession. The vertical distribution of these lithofacies imply three successive short-lived transgressions and regressions, and progressive shoreline advances from the Tethyan Ocean, that was situated to the north, inundating the southern braid plain (Makhlouf, Hamad and Moh'd, 2017).
• Ordovician to Silurian Khrayim (Khreim) Group, which is separated by an unconformably from the upper Ram Group, marking the onset of a distinct transgressive phase. It is predominantly a marine sequence, containing alternating sandstone and lenses of quartz-pebble conglomerates, siltstone and clay. The group is characterised by glacial diamictites at the end of the Ordovician, before sedimentation of further sandstones and cessation of deposition during the Silurian. The sequence has been subdivided as follows:
- Late Ordovician Hiswah Formation, which, in southern Jordan generally comprises a 50 to 70 m succession of clastic rocks that can be divided into a
i). lower, mainly fine-grained sequence of red, mauve and greenish, laminated, distal mudstones with only occasional thin beds of rippled siltstone; and
ii). upper, coarser-grained suite that is more proximal and contains sandstone-siltstone alternations with some hummocky cross-stratification and trough cross-bedding, ripple cross-lamination and planar cross-lamination, indicating shallower-water conditions.
The formation thickens to ~150 m to the NE, but is absent in the central and southwestern section oc the country. Graptolites suggest deposition during the middle to late Darriwilian stage of the late Middle Ordovician.
- Late Ordovician Dubaydib Formation, which is generally ~165 m thick in south-western Jordan, but expands to as much as 1300 m in the NE, while wedging out in central and SW Jordan. The lower boundary is marked by the onset of thin bedded, intensely bioturbated, sandstone representing a lower intertidal marine to shallow subtidal environment. The upper sections of the unit include sandstones and siltstones with some shales, deposited on the lower foreshore to upper shoreface and mid-shelf. The fossil record suggests a latest Middle to early Late Ordovician age.
- Late Ordovician Tubayliyat (previously Mudawwara) Formation, with a total thickness of ~200 m in southern Jordan, increasing to as much as 1300 m in the NE. It begins with an up to 15 m thick distinctive bed of varicoloured siltstone to fine-grained sandstone bed, overlain by sheet like beds of thin-bedded silty sandstones and siltstones with extensive ripple cross-lamination and hummocky cross-stratification, representing shallow marine
upper and lower shoreface facies. The fossil record indicates a Late Ordovician age.
- Late Ordovician Ammar (or Rishi) Formation (previously upper Tubayliyat Member), which includes all of the uppermost Ordovician glacio-fluvial facies and post-glacial shoreface, shales. It includes up to 150 m thick glacial valley fill deposits, with narrower lateral equivalents. The lower parts of the sequence are shoreline sandstone, glacial channel fill and palaeo-valley facies fine- to coarse-grained sandstone, sometimes with a diamictitic texture and large subangular exotic clasts. The overlying upper section comprises alternating thin beds of shale and sandy siltstone.
- Early Silurian Batra Formation (also known as the Mudawwara Shale Formation), which is 230 to 340 m thick in southwestern Jordan, thickening to 875 to 1550 m in the NE of the country. It overlies the glacial sequence of the Late Ordovician Ammar Formation, across a sharply defined unconformity. It is characterised by a succession of fine grained offshore clastics, mainly preserved as pale green, grey, and blue-grey shales with thin red siltstone laminae at surface. These are sub-divided into three units, the
i). 9 to 18 m thick Lower Hot Shale, which is a black, fissile, micaceous and very graptolite and organic rich (up to 7% TOC) shale;
ii). Middle Hot Shale, dominated by micaceous claystone with stringers of very fine grained sandstone and a low (0.4 to 1.5% TOC) organic content, deposited in a low energy open marine shelf;
iii). Upper Hot Shale, which is ~50 m thick, composed of micaceous shale with a moderate total organic carbon (TOC) content of 0.8 to 2.0%. Like the lower unit, the Upper Hot Shale was deposited in a pelagic to hemi-pelagic regime, under anoxic conditions and high organic productivity (Alsharhan, 2003).
The sequence is interpreted to represent a major marine transgression and contains typical early Silurian graptolites. It was deposited during a period of rapid deglaciation at high palaeo-latitudes. Post-depositional oxidation has changed much of the original black shale and partially or completely destroyed it's organic content, although carbonaceous intervals remain. These rocks have been a major regional source that produced hydrocarbons in greater Arabia, the Levant, The Gulf and North Africa (Rahmani, Naderi and Hosseiny, 2021).
- Middle Silurian Alna (or Khishsha) Formation, which gradationally overlies the shale sequence of the Batra Formation and comprises siltstones and sandstones, but dominantly arenaceous rocks of a slowly prograding deltaic complex, deposited in a shallow marine, outer to inner sub-littoral environment. Overall it comprises a very fine-, medium- and coarse-grained, argillaceous sandstone with interbedded claystone. It also contains lesser glauconitic sands, limonitic ooids and dolostone, and is intruded by a 74 to 92 m thick dolerite at the base of the sequence. The maximum thickness of the succession is from 710 to 920 m, although the total thickness is largely an artifact of Devono-Carboniferous erosion. Silurian strata of both formations are restricted to a belt in eastern Jordan, as they have been removed during the same erosive period in the western and central parts of the sequence, although indications are that Silurian strata extended much farther west than the current eastern Jordanian subcrop termination (Lüning, et al., 2005).
The lower Palaeozoic rocks occupy the southernmost 50 to 60 km of Jordan, with the east-west contact with the overlying Mesozoic succession swinging northward, such that to the NW, Palaeozoic rocks only occur as a narrow, generally <10 km wide string of exposures on the eastern margin of the Wadi Araba to as far north as the Dead Sea (Alsharhan, 2003).
▸ Late Silurian to Lower Permian hiatus during which major erosion occurred removing large sections of the preceding succession, from Proterozoic to Silurian in age in large parts of the country.
▸ Late Palaeozoic to Mesozoic - following the Silurian to Lower Permian hiatus, deposition resumed in the Permian with the ~60 m thick Umm Irna Sandstone, the lowest unit of the Permo-Triassic Ramtha Group, which is predominantly composed of sandstones, with an intercalated limestone unit. Triassic rocks in Jordan are represented by the Zarqa-Ma'in Group which is exposed to the east of the Dead Sea. Marginal marine sandstone and siltstone dominates the lower part of the group, overlain by open marine carbonate sediments, whilst evaporites are characteristic of the upper sections, including up to 60 m of gypsum/anhydrite. The Zarqa-Ma'in Group is regarded by some authors as part of the Ramtha Group. The latter grades upward into the Jurassic Azab Group, which is limited to northern Jordan, and is also composed of shale, sandstone and shallow marine limestones (Andrews 1992).
These are unconformably overlain by coarse grained clastic sediments of the Lower Cretaceous Kurnub Group, including coarse-grained, poorly sorted and pebbly sandstones, fluvial quartz-arenites and intercalated subordinate thin alluvial mudstone beds. This sequence varies from 50 m thick in the east of Jordan, to 350 m in the west, reaching a maximum of 600 m to the west of the Dead Sea. The succeeding Upper Cretaceous Ajlun Group is composed of shallow marine platform carbonate (limestone) rocks, intercalated with marine and fluvial siliciclastic rocks in the south and east of Jordan (Powell and Moh'd 2011), with a thickness ranging from zero in the SE to ~800 m in the north (Andrews 1992).
▸ Late Cretaceous to Cenozoic - the Late Cretaceous to Eocene Belqa Group, which disconformably overlies the Ajlun Group sedimentary rocks, and occupies the greater part of the Jordan plateau, is dominated by chalk, chert and phosphorite. The regional scale disconformity at the base of the Belqa Group indicates a rapid change to a pelagic or hemi-pelagic ramp setting depositional environment (Burchette and Wright 1992; Powell and Moh'd 2011).
During the Late Cretaceous to Eocene an open, 'S'-shaped structural corridor, known as the Syrian Arc Fold and Fault System, was developed, stretching across Syria, NW Jordan, Israel and the northern Sinai Peninsula in Egypt. This corridor was ~100 km wide and trended WSW-ENE in the Sinai Peninsula, rotating to SW-NE and SSW-NNE where displaced by the intersecting and temporally overlapping younger Dead Sea Rift in Israel and NW Jordan, to become the ENE-WSW Palmyrides Syria to the NE. It comprises a series of asymmetric anticlines (monoclines) and synclines attributed to Late Mesozoic motion along pre-existing early Mesozoic normal faults, and late reverse faulting. Its development was contemporaneous with the thrusting of the SE vergent major Cyprian-Tauros-Zagros subduction zone (described above) that was ~300 km to the NW. The Palmyrides are bounded to the SE by a major south-vergent reverse fault zone. The Syrian Arc is similarly bounded to the south by a shear zone and a series of WSW-ENE to east-west faults over a broad zone that cross the Sinai Peninsula to be cut/displaced to the east by the Dead Sea Rift. Similar faults are redeveloped to the east of the rift (Al-Zoubi and Salameh, 2003; Eyal, 2011).
▸ Neogene to Quaternary Basaltic Magmatism - the platform sequence is terminated by basalts and horizons of travertine that cover large areas of the north-eastern part of Jordan and neighbouring southern Syria. Smaller basalt fields also occur along the Dead Sea and in central Jordan, where they only occur as small sub-volcanic intrusions and vents related to the Red Sea-Dead Sea rifting episode, occurring in three episodes between 23.8 and 1.5 Ma.
For more detail of the Permian and younger stratigraphic sections of the sequence see the Central Jordan Uranium Project description.
Aquifers - This succession incorporates a number of major areally extensive and temporally/long-lived aquifers, including the reservoirs for the major Arabian oil and gas fields. The first of these, the Saq-Ram Aquifer System extends from the eastern margins of the Arabian Shield in Saudia Arabia, into the Ram Aquifer of Jordan to the Dead Sea and the Southern Desert, and underlies most of Jordan. It comprises the 500 to >4000 m thick sandstones of the Cambro-Ordovician Ram Group. Another of the major aquifers is the Nubian Sandstone Aquifer, particularly the Lower Cretaceous Kurnub Group which overlies a regional angular disconformity in Jordan and Saudia Arabia, and is capped by a thick Upper Cretaceous carbonate aquitad, the Ajlun Group. Both of these aquifers are potential conduits for the passage of oxidised metal bearing fluids from the Lower Palaeozoic to the present day.
Deposit Geology and Copper Mineralisation
Along the southeastern margin of the Wadi Araba, there are limited exposures of crystalline basement, including the felsic Aheimir Volcanic Suite of the Araba Complex which contains primary copper sulphides (Burgath, Hagen and Siewers, 1984), although no information is readily available as to the levels of Cu they contain or the volume of mineralisation they represent. In the main Feinan-Khirbet el Nahas-Abu Khusheiba deposits area in Jordan, four local units have been distinguished within the overlying Lower Palaeozoic host succession (after Hauptmann et al., 1992), which are from the base:
• Arkosic Sandstones, representing the Lower Cambrian Salib Arkosic Sandstone described above. It is ~60 m thick and is a fluviatile sequence of medium- to coarse-grained sandstones, locally containing abundant gravel and rock fragments.
• Dolostone-Limestone-Shale Unit, that is up to 30 m thick and represents the Burj Formation. It is interpreted to have been deposited in a marine lagoonal environment. The main mineralisation hosted by this unit is one of two ore styles recognised in the Feinan district, and was exploited by ancient miners. It is hosted by manganese-rich, sandy shales with dolostone, phosphorite, and minor baryte, and occurs as a 1 to 2 m thick stratabound layer of copper-manganese mineralised shales and claystones that occur within the upper part of the Dolostone-Limestone-Shale Unit. It persists upwards into the succeeding Variegated Sandstone Unit for a few tens of centimetres. It is composed of 'secondary' copper minerals, and is associated with manganese oxides. Locally, the manganese mineralisation has been replaced by hematite. The mineralised horizon exhibits pronounced irregularities in lateral distribution. Strongly mineralised exposures are evident in the vicinity of both the main Feinan, and the Khirbet el Nahas deposit ~12 km to the WNW, whilst copper decreases to the NE as Mn increases, until pure manganese mineralisation prevails with little or no copper (as at Wadi Dana described below).
Limited variations in the copper mineralogy are evident, with those present showing distinct intergrowths. The principal Cu minerals in this mineralisation style are chrysocolla [CuSi03•2(H20)] and malachite [Cu2CO3(OH)2]. A typical characteristic of the main orebody of this style is the replacement of quartz by copper silicates, leading to macroscopically coloured blue quartz grains in sandstones and conglomerates. Chrysocolla is the principal of these copper silicates, having formed as a composite intergrowth with multiple pulses of cryptocrystalline bisbeeite [(Cu,Mg)SiO3•nH2O] and other amorphous copper silicate phases. The chrysocolla has also undergone intergrowth with varying amounts of clay minerals. It forms emerald green, 1 to 10 cm nodules and pockets within the host rock, often closely intergrown with black manganese oxides or speckled with bluish plancheite [Cu8Si8O22(OH)4•2(H20)]. Dioptase [CuSiO3•H20], another crystalline modification of chrysocolla is also present. The other prominent copper mineral, malachite, is closely intergrown with chrysocolla and manganese minerals. Additional minerals like paratacamite [Cu2(OH)3Cl2], an omnipresent copper chloride, and copper-iron-sulphides are subordinate. These relationships are illustrated by petrography of samples from Wadi Khalid, near Feinan, which show a paragenesis of microcrystalline chrysocolla (after quartz), intergrown with fibrous bisbeeite, both of which are partly replaced by a fine-grained mixture of malachite and paratacamite, with inclusions of quartz grains and black manganese oxides. NOTE: Might some of the 'manganese minerals' mentioned associated with the chrysocolla actually be Cu-bearing Neoticite [MnO(OH)CuSiO2•nH2O] ?.
• Variegated Sandstone Unit, marking a return to terrigenous sedimentation, presumably representing the basal Umm Ishrin Formation. Coarse grained sandstone at it's base, above the 'mineralised shales', is locally 'richly copper mineralised' presumably as a style similar to that described in the immediatley underlying Dolostone-Limestone-Shale Unit.
• Massive Brown Sandstone Unit, that comprises up to 250 m of fluviatile sandstones, most likely the upper Umm Ishrin Formation. The sandstone within this unit locally carries copper that has been exploited by ancient miners, occurring as disseminations or as veins that follow joint planes. This second mineralisation style is associated with efflorescences of chlorite, interpreted to reflect an anomalous salt content within the sandstone host. Mineralisation is not limited to any preferred structural trend, but forms an irregular network of very thin veinlets. The principal Cu mineral is malachite, with relicts of chalcocite and 'tile ore', a brick-red earthy iron hydroxide rich variety of cuprite [Cu2O]. This mineralisation is characterised by brecciation composed of chalcocite and/or 'tile ore' set within a matrix of malachite that produces a distinct network pattern. This latter variation may locally contain up to 55% Cu at Feinan, but was absent from the ancient workings in the Timna District further to the west.
Hauptmann et al. (1992) have suggested, on the basis of the remaining grades in mined units and historic mineralisation stockpiled, that the ore worked by the ancients in the Feinan District averaged >10% Cu and >20% Mn. The same authors collected and assayed a suite of samples from this high grade range, but also leaner samples containing 0.5 to 5% Cu. Samples taken from the Dolostone-Limestone-Shale Unit, as expected, and discussed previously, showed a variation in Cu, Mn and Fe, from high Cu with Mn and Fe, to Mn dominant. These samples are also virtually sulphur free and have little to no Ag. In contrast, those from the fissure/disseminated mineralisation in the Massive Brown Sandstone are anomalously low in Mn, generally with <0.02% Mn, although the Fe content occasionally reaches 15%. These latter samples may have up to 3.5% S, reflecting the presence of sulphides, and from a few to >25 g/t Ag. Minor and trace element levels are low, with the exception of Pb and Zn in mineralisation from the Dolostone-Limestone-Shale Unit, which reach as much as 6 and 0.2% respectively, but are of a much lower tenor in the Massive Brown Sandstone hosted mineralisation. There is a high correlation coefficients between Mn, Pb, Zn and Co, taken to indicate that Pb and Co are mainly associated with Mn rather than with Cu mineralisation. Further, the Dolostone-Limestone-Shale Unit mineralisation tends to be higher in Ni and As and lower in Ag than those of the Massive Brown Sandstone. Silver has been shown to be carried in copper minerals, as suggested by the Cu:Ag correlation coefficient of 0.75.
Wadi Dana Manganese Mineralisation
Whilst the main mineralisation at Feinan, Khirbet el Nahas and Abu-Khusheibais is of copper and associated manganese, at Wadi Dana, ~12 km to the NE of Feinan, manganese predominates, with only traces of chrysocolla. Mineralisation at Wadi Dana comprises a massive 2 to 3 m thick band with grades of up to 27 vol.% of Mn. EI-Hasan et al. (2001) described this mineralisation as follows:
Manganese at Wadi Dana is mainly hosted within the Middle Cambrian dolomite, limestone and shale of the Burj Formation, separated from the crystalline basement by the Early Cambrian Salib Arkosic Sandstone which locally commences with 3 to 4 m of basal conglomerate. The sandstone is composed of brown to pinkish, cross-bedded and ripple marked, medium to coarse grained bedded arkosic sandstone with randomly scattered gravel sized quartz pebbles, and intercalated red shale. It varies from 20 to 35 m in thickness, and has minor manganese mineralisation preserved as encrustation and dissemination within the sandstone.
The underlying Neoproterozoic crystalline basement consists of three igneous suites: i). the 620 ±14 Ma Hunayk Suite porphyritic granite; ii). the 538 ±30 Ma Fidan syenogranite unit, alkali feldspar granite and quartz monzogranite (Brook and Ibrahim, 1987); and iii). the >485 Ma basaltic to andesitic Ghuweir (Ghuwayr) Volcanics, with dolomitic sandstone, and dolostone layers, intercalated with thin deep-brown and violet clay and siltstone bands. The dolostone contains lesser manganese, which generally mainly occurs as secondary veinlets or as joint fillings. The principal manganese oxide mineralisation is associated with the sandstone and claystone beds, occurring as disseminations, thin bands, irregular lenses, concretions, veins, and as massive bands.
The host Burj Formation is overlain by the Upper Cambrian to Ordovician Um-Ishrin Sandstone, and then the Lower Cretaceous vari-coloured Kurnub Sandstone, the Upper - Cretaceous carbonates, and the Tertiary marl-silicified limestone formations. Pleistocene to Holocene flood basalts overlay all of these units.
The area has been strongly deformed by the Najd Fault System, the north-south Wadi Araba-Gulf of Aqaba strike-slip fault regime and the east-west Dana shear-Fault that belongs to the same tectonic regime.
There is a marked variation in the mode of occurrence of mineralisation, grade, and degree of crystallinity from west to east across the mineralised zone, from mainly disseminated in the west, with Mn-cementing the host sandstone, gradually grading eastward to 0.5 to 2 cm thick lenses as the Mn content increases. These lenses are mainly composed of cryptomelane and psilomelane, with poor crystallinity. A few 20 to 30 cm long lenses that are 5 to 10 cm thick were found embedded in sandstone and clay layers. These lenses are highly fractured, and usually contain some gangue minerals such as kaolinite and quartz. These are followed by thin, 1 to 5 cm thick alternating beds and layers of concretions, intercalated with sandstone and clay layers, generally with a high Fe content, resembling a banded iron formation, and although it has a very poor crystallinity, is shown to contain cryptomelane and hollandite. The mineralisation discussed thus far is generally only low grade. On the furthest eastern site, at Wadi Dabbah, it becomes a massive 2 to 3 m thick band. This gradation corresponds to a progressive increase in grade and degree of crystallinity in the same direction. The mineral assemblages of the eastern higher-grade mineralisation is also more clear and euhedral, with lesser amorphous phases. Across this gradation the mineralisation changes from low 3.44 to 7.21 vol.% Mn in the west, to high-grade 25.6 and 26.1 vol.% Mn ores in the east.
High grade manganese mineralisation occurs in a number of forms, which include:
i). Concretions, that are embedded within sandstone between red clay layers, usually occurring singly with a diameter of 5 to 10 cm, but sometimes as binodular pairs or aggregates. They are spherical or elliptical in shape, and usually contain nucleus-like quartz particles concentrated in the centre, surrounded by mainly
cryptomelane [K(Mn4+7Mn3+)O16],
psilomelane [(Ba,H2O)2Mn5O10] and
pyrolusite [Mn4+O2],
sometimes with an alternating rhythmic texture involving the latter two minerals.
ii). Massive bands, the best example of which is found at Wadi Dabbah in the NE of the field, where it comprises a massive 2 to 3 m thick band, with limited lateral extent, representing a large lense. It has a complicated composition, being an intimate intergrowth of cryptomelane, hollandite [Ba(Mn4+6Mn3+2)O16], psilomelane, pyrolusite and hematite.
iii). Stockwork Veins are found in the uppermost parts of the Burj Formation to the NE at Wadi Mahjoob and Wadi Dabbah, occurring as discontinuous intersecting veins within medium to coarse grained sandstone. They mainly contain psilomelane, coronadite [Pb2+(Mn4+6Mn3+2)O16],
hematite and goethite. The presence of coronadite, which is restricted to these veins, is taken to indicate a late stage of mineralisation during laterite development, or extensive weathering. In contrast, vein mineralisation within the Lower Cambrian Salib Arkosic Sandstone at Wadi Jamal (between Wadi Dabbah and Wadi Dana) is composed of psilomelane and pyrolusite.
iv). Oolites, predominantly composed of strongly altered todorokite [(Ca,K,Na,Mg,Ba,Mn)(Mn,Mg,Al)6O12•3H2O] and birnessite [(Na,Ca)0.5(Mn4+Mn3+)2O4•1.5H2O], which have been replaced by psilomelane and cryptomelane. These oolites are microscopic, mostly spherical to elliptical to kidney shaped, embedded in a calcareous matrix, and have been found within the stockwork veins cutting the Salib Arkosic Sandstone. They are taken to represent a remnant of the earliest mineralised phase.
Hematite is the principal gangue mineral in the mineralised assemblage, whilst quartz is also a major gangue. Apatite is associated with Mn in the low-grade mineralisation to the west, occurring as apatite-carbonate within dolostone and siltstone. Calcite is also associated with Mn oxides, mainly as secondary vein and joint fillings. Dolomite is both a host rock and gangue to Mn mineralisation, occurring as host to manganiferous veins and forming secondary veinlets within the mineralised zone. Ankerite and kutnahorite are also evident, but rarely. Clay minerals, mainly kaolinite, often accompany the Mn-oxides assemblages, with lesser smectite and illite.
EI-Hasan et al. (2001) interprets the following paragenesis for the Wadi Dana manganese mineralisation. The earliest mineralisation is characterised by micro-crystalline oolitic and interstitial todorokite and bimessite, as locally preserved cementing the Lower Cambrian Salib Arkosic Sandstone. This assemblage is seen as authigenic, the result of the circulation of mineralised fluids during early diagenesis. Mineralisation is accompanied by quartz, dolomite, kaolinite and apatite, as well as the late formation of kutnahorite and ankerite.
This phase is interpreted to have been followed by an episode of 'supergene enrichment', the result of changes in the Eh-pH conditions in an oxic shallow sedimentary regime. This caused the dissolution of the primary phases and conversion to a new assemblage of cryptomelane, psilomelane, pyrolusite and hollandite in two diagenetic episodes. The first of these episodes spanned the transition to 'supergene enrichment', involving leaching and vertical transport, accompanied by the development of hematite and goethite. It is taken to be represented by the colloform and interstitial style mineralisation, and the production of the amorphous Mn phase observed to the west. The second phase of supergene diagenesis produced a new generation of the same assemblage by the addition of further Mn modification of the former suite, and led to the development of massive, well-developed, crystals as seen to the east. The supergene assemblage dominates all sites and ore types.
A late stage overprinted the two diagenetic 'supergene' episodes, producing coronadite and hollandite-coronadite solid solutions, with further associated hematite and goethite. This phase is interpreted to likely be related to chemical weathering and lateritisation in humid-wet climatic conditions, accompanied by extensive chemical weathering, as suggested by the presence of further hematite, goethite and secondary psilomelane. Descending meteoric water leached Cu, Pb and Zn as well as Mn and Ba from overlaying layers to form coronadite in the upper zone, secondary psilomelane and barite veinlets. Chrysocollar is associated with coronadite in the upper part of the system.
Evolution and Discussion
As outlined in this record and those describing the equivalent copper mineralisation in the Timna Valley of southern Israel and the Sinai Peninsula in Egypt, sediment hosted copper mineralisation on the northern margin of the Arabian-Nubian Shield is developed at a number of stratigraphic positions that range from Lower Cambrian to the Cenozoic. The host succession mainly comprises flat-lying to very shallow-dipping 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 brief intervals in shallow marine settings. The overall succession has been punctuated by a series of erosive events/unconformities related to emergence that have meant that large slices of the succession present at any one localities may be absent from others. The resultant sedimentary pile represents a strongly permeable and porous succession of extensive, thick sandstone aquifers, partially separated by finer grained and carbonatic aquitards. This succession has permitted widespread fluid circulation over that same long period, to the present.
Sediment hosted copper mineralisation within this sequence is found as follows, from oldest to youngest:
• 1 to 2 m thick layers containing chrysocolla and malachite in the upper part of the 60 to 110 m thick, Lower Cambrian Burj Formation, manganese-rich, sandy shales with dolostone and phosphorite beds that overlies unmineralised arkosic sandstones and then Neoproterozoic magmatic basement in southwestern Jordon;
• disseminated and vein malachite, with relicts of chalcocite and cuprite in the Variegated and Brown Sandstone units overlying the Lower Cambrian Burj Formation, in the same area of Jordan;
• relict Cu-sulphides encapsulated by malachite and paratacamite, within dolostones and decalcified sandy facies (after dolostones) of the Early to Middle Cambrian Timna Formation (equivalent of the Burj Formation) at Timna in southern Israel;
• predominantly as chrysocolla, with no sulphides, within the sandy facies of the Early to Middle Cambrian Shehoret Formation that immediately overlies the Timna Formation in the same area of southern Israel;
• within an interbedded grey sandstone-siltstone band between two red-bed intervals of vanadiferous sandstones, hosted within the middle member of the Cambro-Ordovician Araba Formation in south-western Sinai Peninsula of Egypt;
• remnant sulphides and accompanying chrysocolla, chalcanthite, antlerite and cuprite closely associated with lenses of high grade Mn-Fe oxides within the Carboniferous Um Bogma Formation that unconformably overlies the Cambro-Ordovician Araba Formation in south-western Sinai Peninsula of Egypt;
• as Cu-sulphides that both replace plant debris, and occur as the core of malachite encrusted nodules and malachite cemented sandstone within the Lower Cretaceous Kurnub Group which unconformably overlies the ~35 m thick Early to Middle Cambrian Shehoret Formation in the Timna Valley of southern Israel as detailed above;
• as structurally controlled veins and veinlets of Cu carbonates, chlorides, silicates and sulphides or Cu-enriched iron oxide veins hosted by Early Cretaceous to Miocene carbonates, sandstones and conglomerates. These veins follow structures related to the longitudinal faults of the Dead Sea Rift Valley, or the transverse shear zones. These occurrences appear related to young rift-related basaltic magmatism or recent hot spring activity (Ilani, Flexer and Kronfeld, 1987).
These observations raise the question of whether mineralisation was the result of i). a number of hypogene and supergene events distributed over this temporal interval; or ii). one or perhaps two events whereby a large scale fluid cell circulated through the mega-aquifer, perhaps driven by an igneous event, to deposit leached metal at favoured sites. Such sites would include the base of a reduced cap in the presence of a sulphur source such as anhydrite, sour gas or diagenetic sulphides.
Zientek et al. (2015) suggest thick, late Neoproterozoic evaporite beds common in the region, but as far afield as western Iran, hundreds of kilometres to the NE, were partially dissolved in the subsurface to produce highly saline groundwater that could leach and transport copper at high concentrations. They further suggest these oxidised brines likely percolated through regional aquifers and mixed with fluids from the dewatering Lower Palaeozoic depocenters to the north, and then moved up-section to the south, where the Ram Group tapers onto basement. These brines might also have been complemented by fluids from the underlying Neoproterozoic Aquaba Complex, red beds of the Araba Complex and weakly mineralised Aheimir Volcanic Formation that were released into the overlying Ram Group aquifer (Burgath and others, 1984). They also propose the mineralisation possibly formed in the Early Devonian from a gravity-driven fluid circulation system that developed when the northern basin margin was tectonically elevated. This was followed by a Late Devonian 380 to 365 Ma thermal event, possibly promoting a second mineralising pulse, which was reflected by annealed zircons in the sandstone (Vermeesch et al., 2009) and by illite in dolostone (Segev et al., 1985). Another alternative is during the Cretaceous rift related magmatism following deposition of the Lower Cretaceous Kurnub Group that is mineralised in Timna.
No detail of a reductant or similar chemical agent that promoted deposition of copper is apparent in the English language literature studied in this review. Zientek et al. (2015) suggest the Burj Formation represents a laterally continuous, more reduced, confining bed overlying the oxidised continental clastic Salib Formation. This configuration would imply that the upper Salib sandtones and lower Burj Formation would be the favourable host to sediment hosted copper mineralisation. However, the actual deposit is hosted within the basal sections of the Umm Ishrin Formation sandstones and the upper margin of the underlying Burj Formation. No well defined cap is described within the Umm Ishrin Formation, although it apparently contains narrow claystone layers representing thin tidal intercalations and clay from palaeoweathering of the arkosic sandstone which could possibly have occluded porosity and formed an internal aquitard.
The distribution, mineralogy, and the chemistry of the copper-bearing minerals within the Massive Brown Sandstone of the Umm Ishrin Formation are consistent with sediment hosted copper mineralisation, deposited within semi-lithified to lithified, porous sandstone. This mineralisation appears to have originally been deposited as disseminated and open space/fracture filling sulphides that have undergone substantial subsequent oxidation in the weathering profile. In contrast, the silicate-carbonate (chrysocolla-malachite) mineralisation of the upper section of the underlying Burj Formation Dolostone-Limestone-Shale unit lacks evidence of primary sulphides, is devoid of remaining sulphur, and is characterised by chrysocolla replacing silica, silicates and clays.
The pattern of distribution of copper mineralisation by facies listed above, with the exception of the youngest Cenozoic hosted, is not consistent with the major sediment hosted copper deposits of the world, i.e., immediately below or in the lower sections of a reduced 'cap' to a thick oxidised arenite where pregnant, overpressured brines are trapped. Instead, the final mineralisation is deposited in the upper section of a finer grained 'floor', below a thick oxidised arenite, with few remnant sulphides, and commonly indication of direct replacement of silicates and carbonates to form 'secondary' copper minerals.
This is more consistent with an 'exotic supergene origin', and suggests oxidation and leaching of the overlying sandstone hosted sulphides within the Umm Ishrin Formation, transported down through the sandtone aquifer, and deposited at the interface with the less permeable 'floor' that was the upper surface of the underlying shales, clays and carbonates where they intersect the palaeo-water table. Analogues to this mechanism include i)> the Exotica deposit at Chuquicamata, Chile, where supergene fluids that leached oxidised sulphides from the porphyry copper deposit are transported laterally down a coarse clastic channel to be deposited in altered silicates in the floor of the channel, directly forming Cu-silicates, or ii)> the Maroochydore copper deposit in Western Australia where weak hypogene sediment hosted Cu sulphides in reduced siltstones are oxidised and leached, and pregnant solutions transported laterally along broad depressions/channels in the undulose base of an unconformably overlying porous sandstone. These 'channels' cut the leached source and allow transport of those fluids to where the unconformity intersects the base of oxidation and the underlying reduced hypogene mineralisation, to deposit a supergene 'blanket' in the floor below the unconformity. Subsequent lowering of the base of oxidation and water table then leached the supergene sulphides to form oxides and a second supergene enrichment.
Such a mechanism would also be consistent with the observations relating to the accompanying manganese mineralisation as described above, although deposition of the manganese appears to have predated the copper as also appears to be the case further west on the Sinai Peninsula. Such 'supergene' activity could have occurred at a number of periods including during a high-stand in the Cambrian which was deposited in a braided stream setting on a coastal plain, or the break marked by the mid-Ordovician unconformity at the top of the Ram Group or the major Late Silurian to Lower Permian hiatus. The Ram Group, has, from its Lower Cambrian deposition to the present remained a major, high volume, regional aquifer amenable to fluid circulation permitting brines to have circulated in a variety of pulses throughout the Phanerozoic. Similarly, other units higher in the sequence, partially or wholly hydraulically connected to the Ram Group have acted as long-lived aquifers.
Resources and Reserves
The following non-JORC compliant Mineral Resources have been published (Zientek, et al., USGS, 2015; Metalbank Limited ASX Announcement July, 2023):
Khirbet et Nahas - 25 Mt @ 2.33% Cu; for 0.58 Mt of contained copper;
Feinan - 36 Mt @ 1.36% Cu; for 0.49 Mt of contained copper (of which 15.9 Mt of ore is an Inferred Resource);
Wadi Abu Khushaybah - 8 Mt @ 0.6% Cu.
Both the Feinan and Khirbet en Nuhas deposits lie within the Dana Biosphere Reserve within which permission to mine is unlikely.
Whilst the copper deposits of the Wadi Araba have made the district one of the great mining centres of antiquity and have influenced classical history and the development of metallurgical processes, the remaining resource is only modest. The largest of the ancient dumps, those at Feinan, contain up to 200 000 tonnes of slag. Assuming an average ore grade of 10% Cu, this would suggest a production of only ~20 000 tonnes of copper to the end of Roman mining. Such a tonnage of copper, which was extracted over a period of >5000 years would be mined in 10 days from the world's current largest copper mine.
Geological Setting References
Al Zoubi, A.S. and Salameh, E., 2003 - A new evidence for lateral displacement along Wadi Araba Fault/Dead Sea Transform, Jordan; Pakistan Journal of Applied Sciences, v.3, pp. 216-224.
Amireh, B.S., Amaireh, M.N. and Abed, A.M.,, 2008 - Tectono sedimentary evolution of the Umm Ghaddah Formation (late Ediacaran-early Cambrian) in Jordan; Journal of Asian Earth Sciences, v.33, pp. 194-218.
Elicki, O., Meischner, T., Gürsu, S., Ghienne, J.-F., Masri, A., Moumani, K.A. and Demircan, H., 2022 - The Ordovician System in the Levant region (Middle East) and southern Turkey: review of depositional facies, fauna and stratigraphy; The Geological Society, London, Special Publication 533, 34p.
Eyal, Y., 2011 - The Syrian Arc Fold system: Age and rate of folding; Geophysical Research Abstracts, Vol. 13, EGU2011-7401, EGU General Assembly 2011, 1p.
Jarrar, G., Stern, R.J., Saffarini, G. and Al-Zubi, H., 2003 - Late- and post-orogenic Neoproterozoic intrusions of Jordan: implications for crustal growth in the northernmost segment of the East African Orogen; Precambrian Research, v.123, pp. 295-319.
Makhlouf, I., Hamad, A.A. and Moh'd, B.,, 2017 - Sedimentology and depositional environments of the Ordovician Umm Sahm Sandstone Formation in southern Jordan; Arabian Journal of Geosciences, v.10:178, 12p.
Powell, J.H., Abed, A.M. and Le Nindre, Y.-M., 2014 - Cambrian stratigraphy of Jordan; GeoArabia, v.19, no.3, pp. 81-134.
Powell, J.H., Abed, A.M. and Jarrar, G.H., 2015 - Ediacaran Araba Complex of Jordan; GeoArabia, v.20, no.1, pp. 99-156.
Rahmani, A., Naderi, M. and Hosseiny, E., 2022 - Shale gas potential of the lower Silurian hot shales in southern Iran and the
Arabian Plate: Characterization of organic geochemistry: Petroleum, 10p. doi.org/10.1016/j.petlm.2022.03.004.
The most recent source geological information used to prepare this decription was dated: 2015.
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.
Feinan Khirbet el Nahas Wadi Abu Khushaybah
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Selected References:
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Alnawafleh, H., Tarawneh, K. and Alrawashdeh, R., 2013 - Geologic and economic potentials of minerals and industrial rocks in Jordan: in Natural Science, v.5, pp. 756-769.
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Hauptmann, A., Begemann, F., Heitkemper, E., Pernicka, E. and Schmitt-Strecker, S. 1992 - Early Copper Produced at Feinan, Wadi Araba, Jordan: The Composition of Ores and Copper: in Archeomaterials, v.6, pp. 1-33.
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Ilani, S, Flexer, A. and Kronfeld, J., 1987 - Copper mineralization in sedimentary cover associated with tectonic elements and volcanism in Israel: in Mineralium Deposita v.22, pp. 269-277.
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Zientek, M.L., Wintzer, N.E., Hayes, T.S., Parks, H.L., Briggs, D.A., Causey, J.D., Hatch, S.A., Jenkins, M.C., and Williams, D.J., 2015 - Egypt-Israel-Jordan Rift, Egypt, Israel, and Jordan-Assessment Tract 002rfCu2001: in Qualitative assessment of selected areas of the world for undiscovered sediment-hosted stratabound copper deposits U.S. Geological Survey Scientific Investigations Report 2010-5090-Y pp. 41-52, http://dx.doi.org/10.3133/sir20105090Y.
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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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