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Jebel Ohier - Quartz Knob, Malachite Mountain, Alfrasco |
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Sudan |
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Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Jebel Ohier porphyry copper deposit is located ~220 km west of Port Sudan in the Red Sea Hills of Sudan, between the Nile River which is ~180 km to the SW and the Red Sea to the east.
(#Location: 19° 47' 9"N, 35° 8' 16"E).
Regional Setting
Jebel Ohier is situated within the Neoproterozoic Gebeit Terrane, that is, in turn, located within the western half of the 1.9 million km2 Arabian-Nubian Shield.
For a description of the regional setting of the shield and its geology and distribtion of mineralisation, see the separate Arabian Nubian Shield Overview record.
Gebeit Terrane - The Jebel Ohier porphyry copper deposit is located within the Gebeit Terrane of the western Arabian-Nubian Shield, just east of the NNE trending Hamisana Shear Zone that separates the Gebeit Terrane from the younger wedge shaped Gabagaba Terrane to its west. The Gebeit Terrane margins are defined by suture zones that mostly include suites and/or tectonic slices of ophiolite separating it from other geologically distinct crustal segments/terranes. It is separated from the Eastern Desert Terrane to the north by the NE-SW trending Onib-Sol Hamed Suture (or ophiolite belt) and by the Cenozoic Red Sea Rift to the east. Across the Red Sea, in Saudi Arabia, the similar Hijaz Terrane is interpreted to be the pre-Cenozoic rift continuation of the Gebeit Terrane. To the south, the latter is juxtaposed with the Haya Terrane across the Nakasib Suture, a broad NE trending, north dipping ophiolite bearing fold and thrust belt that formed as a result of an arc-arc collision between the two terranes at ~750 Ma (Abdelsalam and Stern, 1993). This collision resulted in the accretion of a dislocated intra-oceanic island arc and back-arc basin complex to the Gebeit Terrane. The Nakasib Suture is, in turn, displaced by the ophiolite-free, NNE trending Hamisana Shear Zone mentioned above. Volcanic rocks within the accreted Nakasib Suture arc-back arc zone host significant volcanic hosted Au-Cu-Zn massive sulphide deposits, e.g., Hassai-Ariab. In contrast, the interior of the Gebeit Terrane is characterised by ancient and recent artisanal workings exploiting orogenic gold mineralisation (Elsamani et al., 2001).
While the terrane bounding suture/shear zones are strongly deformed and metamorphosed, up to amphibolite facies, the interior of the terrane has generally been less deformed and metamorphosed to greenschist facies, but has been variably dislocated by numerous reverse, normal and strike-slip faults (Bierlein et al., 2020).
The Gebeit Terrane comprises a geologically distinct block dominated by arc-related, low-grade metamorphosed volcano-sedimentary sequences and syn-tectonic igneous complexes (Klemenic, 1985; Vail, 1985; Kröner et al., 1987; Reischmann and Kröner, 1994). The following lithofacies units have been recognised within the terrane, from oldest to youngest (Yassin et al., 1984):
• Kashebib Series - an amphibolite-facies granite gneiss complex consisting of silicic gneiss, crystalline hornblende schists, quartzite, migmatite and some associated anatectic granite, representing pre-Rondonian breakup basement continental rocks. These may represent rift separated blocks from the pre-rift continent stranded within the orogen. The granite gneiss has been dated at 1.95 Ga (K/Ar; Vail, 1976). Some rocks within the terrane that have been equated with this series have not been found to be separated by an unconformable contact with the overlying less metamorphosed suite. For this reason Reischmann and Kröner (1994) regarded some of the rocks correlated with the Kashebib Series as being a more strongly metamorphosed section of the overlying Nafirdeib Series (Yassan et al., 1984);
• Nafirdeib and Odi Series, which are found in different parts of the terrane and are interpreted to be of Neoproterozoic age. The Nafirdeib Series is composed of greenschist facies mafic to intermediate volcanic rocks, mainly green andesitic tuff, agglomerate and meta-andesite and minor meta-dacite, with intercalated siliceous schists, marbles and greywackes. Sedimentary rocks are more common in the upper part of the series, with interbedded tuffs and mafic volcanic rocks. The Odi Series comprises schist, marble, and quartzite with rare intercalations of amphibolite and mafic volcanic rocks. Both series suites are cut by ultramafic, gabbro, diorite and batholithic granitic complexes. Both series are deformed by linear folds, although the Odi Series is more intensely deformed to form isoclinal and often overturned folds, and may correspond to the more heavily metamorphosed rocks of Reischmann and Kröner (1994) as mentioned above (Yassan et al., 1984).
• Homogar Series, which is >1000 m thick and overlies the Nafirdeib and Odi Series with angular unconformity. It is only weakly metamorphosed and is predominantly composed of mafic to felsic volcanic rocks, intruded by gabbro, granite and syenite. It is only weakly deformed, occurring in open folds with limbs that dip at 20 to 30° (Yassan et al., 1984).
• Awat Series, a weakly metamorphosed and deformed sequence of sedimentary and volcanic rocks, cut by mafic and alkali intrusions. It comprises conglomerate, mudstone, andesite, rhyolite, trachyrhyolite and tuffs with flat dips, deposited in restricted troughs, and separated from underlying Nafirdeib and Homogar series rocks by an angular unconformity (Yassan et al., 1984).
• Phanerozoic cover, composed of platformal rocks that include Jurassic to Cretaceous sandstones, occurring in narrow longitudinally trending grabens, lagoons and other Red Sea littoral deposits of Cenozoic age, as well as Mesozoic to Cenozoic volcanic rocks, mainly basalts (Yassan et al., 1984).
The older sequences, namely the Nafirdeib and Homogar series contain subalkaline, calc-alkaline and tholeiitic, mostly supra-subduction intrusive and extrusive rocks. However, some rocks with Ti/V ratios of >20 are interpreted to possibly reflect an incipient back-arc basin suite in an immature, intra-oceanic island-arc environment (Gaskell, 1985; Reischmann and Kröner, 1994; Johnson and Woldehaimanot, 2003). Volcanic and plutonic rocks from the terrane have been dated at ~720 Ma (whole rock Rb/Sr isochron ages; Fitches et al., 1983; Almond and Ahmed, 1987). Volcanic rocks elsewhere in the terrane have been dated at 830 Ma (Sm-Nd; Reischmann, 1986). Johnson and Woldehaimanot (2003) interpreted low initial 87Sr/86Sr ratios, and crystallisation ages that were similar to their Nd model ages, to present strong evidence of a juvenile oceanic setting. They also interpreted strongly positive εNd(t) values of between +6.1 and +8.4 as indicative of depleted mantle sources (e.g., Bierlein et al., 2016).
Geology
The area surrounding Jebel Ohier is dominated by gabbroic to granodioritic intrusions and associated volcano-sedimentary rocks of the Nafirdeib Series (Reischmann and Kröner, 1994). Igneous and epiclastic rocks have been variably deformed and metamorphosed/altered to greenschist facies assemblages that typically include actinolite, chlorite, epidote and clinozoisite. However, metamorphism increases to amphibolite facies locally, in the vicinity of batholithic intrusions and locally within prominent shear zones. Extensive areas of low topography are underlain by late-orogenic granites, particularly to the north and west, with a number of post-collisional alkaline syenite intrusions forming prominent peaks. Faulting is common, although the sequence has not generally suffered significant structural dismemberment (Bierlein et al., 2016).
Jebel Ohier comprises a cluster of mineralised intrusive porphyry centres, of which Quartz Knob and Malachite Mountain are best exposed and most extensively investigated. Other interpreted porphyry centres occur within a 2 km radius, but are less well tested, include the 'Old Mine Jebels', the site of ancient hard-rock gold workings which constitutes a high-level, advanced argillic-altered zone containing epithermal Au mineralisation, possibly overlying concealed porphyry mineralisation; Jebel Ohier North widespread development of D‐type veins occur within quartz-sericite-pyrite (phyllic) and clay alteration zones; Jebel Ohier Eastern Extension or Alfrasco reflected by an extensive zone of weak to moderate A-type quartz vein stockwork associated with pervasive pyrophyllite, muscovite, and kaolinite alteration of the dacitic host rock.
The principal lithologies in the deposit area, after Bierlein et al. (2020) include:
• Nafirdeib Series andesite - a voluminous, fine-grained, homogeneous, andesitic volcanic and volcaniclastic unit that is exposed within 2 to 3 km on all sides of Jebel Ohier, although extrusive units and their proximal clastics are almost absent from the immediate deposit area.
• Diorite porphyry ID1 - a >816 Ma, fine- to medium-grained, subalkaline hornblende-feldspar diorite that intrudes the andesitic country rocks and covers most of the ~5 × 3 km area immediately surrounding the deposit that has not been intruded by younger rocks. It comprises phenocrysts of ~20% euhedral to subhedral plagioclase crystals that are up to 3 mm across and ~15% euhedral, 3 to 5 mm hornblende, set in a fine‐grained plagioclase and hornblende groundmass. It is a pre-mineral phase and one of the principal hosts to stockwork mineralisation at Jebel Ohier.
• Dacite porphyry - a >816 Ma, pre-mineral intrusion characterised by anhedral feldspar phenocrysts, with up to 10% rounded, 1 to 2 mm quartz-eye phenocrysts in a very fine grained to aphanitic matrix of feldspar, hornblende and quartz. It is the principal host to A/B stockwork veining at Jebel Ohier Eastern Extension/Alfrasco.
• Diorite porphyry ID2 - an ~816 to 812 Ma, syn-mineral intrusion that is mineralogically and geochemically virtually identical to ID1, although less strongly altered. Similarly, mineralisation is more weakly developed as A/B-type veins, and where intruding ID1, it truncates veins in that earlier phase, whilst veins in ID2 also cut ID1.
• Granodiorite porphyry ID3 - a <812 Ma, post-mineral granodioritic intrusion that is mineralogically and texturally similar to ID1 and ID2, but is devoid of stockwork veining and mineralisation, with only moderate phyllic or propylitic alteration. It consistently cuts ID1 and ID2 and the Jebel Ohier mineralisation.
• Late granodioritic dykes - occurring as unmineralised late granodioritic dykes that are more or less mineralogically identical but markedly more porphyritic and substantially less altered than ID1–3.
• Quartz‐feldspar porphyry QFP - which is younger than 812 Ma and occurs as rare, relatively thin (0.5 to 10 m), post-mineral dykes cutting all of the ID intrusives and porphyry mineralisation. It has an uncrowded, quartz‐feldspar porphyritic texture with subrounded quartz phenocrysts ±rare feldspar phenocrysts, set in a groundmass of very fine grained to aphanitic quartz, feldspar and iron oxides with sporadic mafic phenocrysts. These dykes are unmineralised and only very weakly altered. Voluminous post mineral intrusive bodies, identical in composition to the QFP, but with rare mafic xenoliths, are mapped distal to Jebel Ohier, predominantly exposed to the northeast of the mineralised system.
• Feldspar‐quartz porphyry FQP - also younger than 812 Ma, and equally rare, thin (<2 m) and post-mineral. It has a crowded feldspar porphyritic texture and granodioritic composition, composed of subrounded plagioclase, K silicate and rounded quartz phenocrysts in an aphanitic matrix with mafic xenoliths.
• Dolerite-granitoid complex DGC - dated at 723.7±6.7 Ma (206Pb/238U; Bierlein et al., 2020), this is the most extensive post-mineral composite intrusions within the immediate deposit area, ranging in composition from diorite to granodiorite. The different phases of the intrusion exhibit magma‐mingling textures at their contacts, implying close to coeval emplacement.
DGC_bt - granodiorite, the most voluminous phase, occupies ~40% of the complex, and is medium-grained and equigranular, with a granodioritic composition containing ~60% plagioclase (3 to 5 mm); 20% hornblende (~2 mm) and ~20% biotite (3 mm), and rare rounded quartz phenocrysts (<3 mm). This phase, which is characterised by magmatic biotite, forms large irregular intrusive bodies and thick dykes that have irregular undulating contacts with other phases of the DGC intrusive suite.
DGC_hb granodiorite constitutes <1% of the composite DCG intrusion, occurring as irregular bodies and thick dykes with undulose contacts and localised magma‐mingling textures with the other phases. It contains large, unaltered, anhedral to locally euhedral hornblende phenocrysts (2 to 5 mm) or phenocryst clusters, set in an equigranular, fine to medium grained 1 to 2 mm groundmass of 60% plagioclase and 40% hornblende that otherwise closely resembles DGC_bt, less the magmatic biotite.
DGC_MD andesitic basalt - which occurs as variably medium to fine-grained, equigranular to porphyritic, mafic to intermediate intrusions of basaltic‐andesite composition. It is composed of 10 to 35% large, to locally exceptionally large (1 to 50 mm) phenocrysts of plagioclase and 5 to 20% smaller (1 to 5 mm) hornblende, set in a 50 to 85% groundmass of <1 mm plagioclase and hornblende in approximately equal proportions. It is predominantly found as narrow to moderately thick (0.5 to 20 m) dykes that trend NE to ENE and have variably planar to irregular/undulating margins. It also commonly has chilled margins, while the dyke grain size generally increasing with dyke thickness. Rare magma‐mingling textures are observed with other DGC magma phases, particularly DGC_bt.
• Andesitic basalt NWD - which occurs as a swarm of narrow (0.3 to 15 m thick) dykes that generally have planar margins striking NW to NNW and dip steeply to the ENE to NE and crosscut all mapped units including the DGC pluton. It is an aphanitic to fine‐grained (<<1 to 2 mm), equigranular basaltic‐andesitic that is mineralogically, texturally and geochemically indistinguishable from the DGC_MD but forms thinner and more planar dykes and dosed no exhibit magma-mingling textures. Never-the-less, they can only be reliably identified by crosscutting relationship with DGC intrusions.
Mineralisation
The two main mineralised porphyry centres at Jebel Ohier are Quartz Knob to the NW, which has a broadly ovoid 600 x 500 m shape, whilst Malachite Mountain, several hundred metres to its SE, is a NW-SE elongated zone with dimensions of ~1600 x 700 m. Together the two define a NW-SE trend. Both have a core of intense A-type stockwork veining and an outer zone of weak stockwork veining. In addition, less intense A-vein stockworking over a 1000 x 500 m zone to the east of Malachite Mountain defines the Alfrasco mineralised centre, and several other centres, as described above. Beyond these zones, weak A‐vein stockworks transition, across a relatively steep gradient, into phyllic alteration that is dominated by D‐type veins. B‐type quartz veins have orientations similar to those of the A-type veins but are less abundant. C veinlets are irregular, only sporadic and are not a volumetrically important mineralised vein set at Jebel Ohier. Anhydrite veins are irregularly developed throughout the proximal stockwork and breccia domains but tend to be most abundant toward the deeper parts of mineralised centres. Locally developed, mineralised magmatic-hydrothermal breccias form discrete subvertical breccia pipes or sheets and cut the Malachite Mountain stockwork. Each of these vein type may be further described as follows, after Bierlein et al. (2020):
• A-veining - where intensely developed, A-vein stockworks typically have two to three mutually crosscutting dominant primary quartz‐sulphide vein orientations at any locality and numerous subordinate vein orientations, with abundances that range from 5 to 20 vol.% of the rock. The more distal, weak stockworks of these veins have both a significantly smaller total volume of veins, typically <5 vol.%, but also fewer vein orientations with only one to three well-developed vein orientations discernible. These veins are composed of sugary textured grey-quartz with interstitial chalcopyrite ±pyrite and are typically 0.2 to 2 cm, but locally up to 5 cm thick, with slightly irregular to locally 'folded' vein margins. Most in the proximal mineralised zone occur as dominantly steeply dipping 78 to 88° arrays with subvertical vein set intersection lineations, suggesting little significant post-emplacement tilting. The dominant population strikes WNW-ESE, subparallel to the Malachite Mountain-Quartz Knob trend, which is, in turn, coincident with a deep linear, NW-trending magnetic high recognized in ground magnetic data. Distinct domains are evident where sheeted vein arrays of a single dominant vein orientation predominate over stockwork developments. However, within these domains, there are also rare, mutually crosscutting, undeformed veins at a high angle to the dominant vein orientation. In other areas, vein arrays have apparently been rotated into parallelism by intense ductile deformation within either NE‐striking sinistral shear zones or within a NW-striking flattening fabric and associated localised shear zones.
A group of veins informally known as VQZ quartz veins ±chalcopyrite ±pyrite are prominently developed in the Jebel Ohier porphyry centres and are closely similar in distribution and orientation to A‐type veins. They are between 5 and 300 cm in thickness, but mostly between 5 and 50 cm, with slightly irregular to undulose vein boundaries. The vein fill has a fractured massive quartz texture ±fine internal sulphide stringers (chalcopyrite and/or pyrite) predominantly following fractures within the vein fill. These veins are interpreted as synchronous with the A‐vein stockworks (or at least the latest A‐type veining) as many horse‐tail out into a sheeted array of thinner sugary textured mineralised A‐type veins, and like the A‐type veins, they are commonly crosscut by C- and D‐type veins.
• B-veining is less abundant than the A-veining at Jebel Ohier, but has similar orientations. These veins are characterised by their distinctive centre line comprising chalcopyrite ±pyrite, planar vein margins, and more massive internal quartz textures compared to the A-type veins. Most are between 0.5 and 2.5 cm in thickness and lack selvages, although some are sandwiched by an assemblage of shreddy chlorite, K-feldspar, and sericite.
• C-veining, which occurs as irregular, narrow sulphide‐only veinlets that are not volumetrically important at Jebel Ohier, and are only sporadically recognised in drill core. They predominantly, but not always, crosscut A‐ and B-type veins and are typically thin, generally <5 mm, with narrow phengite selvages. They form networks that commonly crosscut and displace A‐ and B‐type veins. The dominant vein fill is 80 to 100 vol.% chalcopyrite ±pyrite ±bornite, with little or no quartz or other minerals. Drilling suggest these veins are distributed throughout the proximal stockwork domains and are locally abundant in some of the hydrothermal breccia domains. They are spaced at from >2 m to 10 to 20 cm within the proximal stockwork domain where they are a significant contributor to grade wherever present above trace abundance.
• Anhydrite veins are irregularly developed throughout the core stockwork and breccia, but tend to increase in abundance to dominate toward the deeper parts of mineralised porphyry centres. They have several different morphologies, have slightly to highly irregular margins, and enclose rare angular wall‐rock clasts. The vein thickness varies from 0.5 to 20 cm and is highly variable. They are also spatially associated with irregular tensile vein and breccia A‐vein arrays, and with hydrothermal breccia zones. Whilst most anhydrite veins are dominantly composed of anhydrite-quartz ±chalcopyrite, they have additional spatial and temporal relationships with chlorite, actinolite, epidote, molybdenite and other sulphides (pyrite, bornite, etc.) as alteration halos, proximal alteration assemblages, or, rarely, vein fill.
• D-veining is recognised by its 0.2 to 2 cm wide, grey to white bleached, texturally destructive, quartz-sericite-pyrite phyllic halos sandwiching a central seam of pyrite-sericite-quartz in varying proportions. They may contain abundant quartz, but are mostly characterised by the absence of sharp vein walls and occur as stringers of pyrite-sericite-quartz. At Jebel Ohier, they are predominantly NNW striking with steep dips, similar to the orientation of A‐type veins.
• Mineralised magmatic-hydrothermal breccias are locally developed, forming discrete subvertical siliceous breccia pipes or sheets that cut the Malachite Mountain stockwork. These pipes are adjacent to intensely developed ductile shear zones and are typically monomictic, composed of subangular to subrounded fragments of sericite-altered ID1 and A-vein fragments within a matrix of quartz-sericite-anhydrite. Pyrite and chalcopyrite cluster in the matrix where they replace and are interstitial to anhydrite and quartz grains. Bornite can locally constitute up to 1 vol.% in some of the chalcopyrite-rich zones. Chlorite-epidote rich tectonic breccias are also known that appear to postdate most, if not all, stockwork mineralisation and commonly contain monomict to polymict breccia clasts that are variably angular to rounded and contain evidence of ductile flattening and shearing.
• Other veins include infrequent quartz-molybdenite, as well as rare epidote-chalcopyrite, actinolite-chlorite-chalcopyrite (-bornite), and magnetite-only.
Sulphide mineralisation occurs within A- and B-type quartz veins and as C-type veins, as well as disseminations in halos proximal to these veins, particularly in zones of high vein density. The highest Cu grades, locally having a close correlation with elevated Mo of up to 120 ppm, are spatially associated with the steep to irregular magmatic-hydrothermal breccia pipes.
Oxidation - The stockwork mineralised zones at Jebel Ohier have been weathered to depths of 40 to 80 m and locally deeper as at Malachite Mountain. The profile within the proximal stockworks includes zones of Cu depletion, particularly near surface, and secondary copper oxide enrichment. Such enrichment is generally concentrated either near the base of oxidation, or on the margins of the relatively alkaline of barren, late mafic dykes. On the latter it occurs as chrysocolla and pseudomalachite, as well as minor azurite, black copper, neotocite, tenorite and pitch limonite. Within the oxide zone, sulphides of the chalcopyrite rich A‐type veins are weathered to a rich-brown goethite. Glassy limonite, jarosite, hematite, and goethite are also variably developed in the oxidized portion of the deposits.
Alteration
Hydrothermal alteration is strongly zoned around the Malachite Mountain and Quartz Knob porphyry copper mineralised centres, as defined by the A-vein stockwork zones at each. This zonation comprises relict potassic biotite/K feldspar alteration proximal to the main centres of mineralisation, overprinted by sericite-chlorite, passing outward into a propylitic epidote-chlorite assemblage distal to mineralisation. These zones are mutually overprinted by an spatially intervening more intense quartz-sericite-pyrite phyllic domain. The main alteration styles may be summarised as follows, after Bierlein et al. (2020):
• Potassic alteration, although evident in the Jebel Ohier mineralised porphyry centres has been overprinted and obscured by subsequent moderate to strong sericite‐chlorite alteration. The intensity of mineralisation and corresponding distribution of relict K feldspar (±magnetite-biotite) alteration is spatially related to both the abundance of sugary quartz A-type veins containing bornite-chalcopyrite-pyrite and to sulphide‐only veins (chalcopyrite and/or pyrite). Within the proximal, relict K-silicate altered domain these veins have rare dark alteration halos containing copper sulphides. These selvages vary from 1 to 4 cm in width and are composed of a mixture of dark-green to brown and grey‐green flaky biotite ±chlorite and magnetite replacing both mafic and felsic magmatic minerals. Relict potassic altered rocks within the proximal stockwork zones also have textures suggesting primary magmatic amphiboles were replaced by shreddy hydrothermal biotite, but that this hydrothermal biotite was subsequently replaced by sericite and chlorite. Sericite also replaces feldspar minerals to varying degrees. This sericite overprint is most likely an incipient stage ahead of the main descending phyllic alteration front.
• Popylitic alteration is generally marked by a peripheral halo of strong epidote alteration in which igneous textures are usually well preserved. Chlorite is mostly finely disseminated in the groundmass and occurs as a replacement of mafic minerals, whilst epidote may replace feldspar and mafic minerals, form discrete veins, or completely flood the rock mass. However, chlorite-epidote alteration is also developed locally within some post-mineralisation intrusions, while late epidote veins are documented both regionally and within many parts of the deposit. This indicates propylitic alteration has been produced by both the porphyry mineralisation and other post-mineral alteration and metamorphic events.
• Phyllic quartz-sericite-pyrite alteration overprints the core potassic alteration zone and the inner propylitic halo of the Jebel Ohier mineralised porphyry centres, and is accompanied by D‐type veining. It forms a zone that spatially separates the other two alteration assemblages in the upper levels of each of the porphyry centres. A 1 to 2 m wide transition marks the change from i). relict precursor K‐silicate alteration with mineralised A‐type veins, overprinted by green sericite‐chlorite altered host rock with preserved igneous textures, to ii). bleached, intensely quartz-sericite-pyrite altered rock with D‐type veins, where lithological textures are destroyed, and A‐type veins are absent. The outer limit of the phyllic alteration overprint in the NE and SW of the deposit area coincides with the inner limit of propylitic alteration (chlorite-epidote ±albite). At surface, in the phyllic zone south of Malachite Mountain and Quartz Knob, quartz-sericite-pyrite alteration with characteristic cubic boxwork voids after disseminated pyrite, is widespread in the oxide zone. Weathered more intense phyllic outcrops have an appearance that is a combination of soft bleached rock with Fe staining after pyrite which produces a distinctive white and red colouration. Sericite is commonly very coarse and flaky within this domain.
The more weakly developed incipient chlorite-sericite alteration in the zone of relict potassic alteration and A‐vein stockworking is less intense, generally preserving textures, and is not apparently grade destructive. Within this zone, texturally destructive phyllic alteration is only evident as D‐type veins with sericitic alteration halos..
• Advanced argillic alteration - pod-like to linear developments of quartz-pyrite occur within a broad zone of pyrophyllite-kaolinite alteration to delineate a distal hydrothermal domain that is most prominent to the south of Malachite Mountain and Quartz Knob. At surface, they are evident as a very strongly quartz altered rock with fine‐grained disseminated ex-pyrite boxworks, locally with fresh pyrite preserved at surface. Kaolinite is also widespread throughout the altered zone, although its origin is unclear.
Resources
The Jebel Ohier porphyry copper-gold deposit has NI 43-101 compliant Indicated + Inferred Mineral Resources at a cut-off of 0.15% Cu (Bierlein et al., 2020) of:
593 Mt @ 0.33% Cu, 0.05 ppm Au, for 1.953 Mt of contained Cu and 29 t of contained gold.:
According to the QMSD Mining Company Limited website (viewed Jan 2020) the Maiden Inferred Mineral Resource as at 31 December, 2017 at a cutoff of 0.2% Cu, was:
246.3 Mt @ 0.44% Cu, 0.08 g/t Au, including;
oxide resources of 71.8 Mt @ 0.38% Cu, 0.11 g/t Au; sulphide resource of 174.5 Mt @ 0.47% Cu, 0.07 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2020.
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.
Jebel Ohier
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Selected References:
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Bierlein, F.P., McKeag, S., Reynolds, N., Bargmann, C.J., Bullen, W., Murphy, F.C., Al-Athbah, H., Brauhart, C., Potma, W., Meffre, S. and McKnight, S., 2016 - The Jebel Ohier deposit - a newly discovered porphyry copper-gold system in the Neoproterozoic Arabian-Nubian Shield, Red Sea Hills, NE Sudan: in Mineralium Deposita v.51, pp. 713-724
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Bierlein, F.P., Potma, W., Cernuschi, F., Brauhart, C., Robinson, J., Bargmann, C.J., Bullen, W., Henriquez, J.F., Davies, I. and Kennedy, A., 2020 - New Insights into the Evolution and Age of the Neoproterozoic Jebel Ohier Porphyry Copper Deposit, Red Sea Hills, Northeastern Sudan: in Econ. Geol. v.115, pp. 1-31.
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Bierlein, F.P., Reynolds, N., Arne, D., Bargmann, C.J., McKeag, S., Bullen, W., Al-Athbah, H., McKnight, S. and Maas, R., 2016 - Petrogenesis of a Neoproterozoic magmatic arc hosting porphyry Cu-Au mineralization at Jebel Ohier in the Gebeit Terrane, NE Sudan: in Ore Geology Reviews v.79, pp. 133-154.
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Fritz, H., Abdelsalam, M., Ali, K.A., Bingen, B., Collins, A.S., Fowler, A.R., Ghebreab W., Hauzenberger, C.A., Johnson, P.R., Kusky, T.M., Macey, P., Muhongo, S., Stern, R.J. and Viola, G., 2013 - Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution: in J. of African Earth Sciences v.86, pp. 65-106.
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Johnson, P.R., 2014 - An Expanding Arabian-Nubian Shield Geochronologic and Isotopic Dataset: Defining Limits and Confirming the Tectonic Setting of a Neoproterozoic Accretionary Orogen: in The Open Geology Journal, v.8, pp. 3-33.
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Johnson, P.R., Andresen, A., Collins, A.S., Fowler, A.R., Fritz, H., Ghebreab, W., Kusky, T. and Stern, R.J., 2011 - Late Cryogenian-Ediacaran history of the Arabian-Nubian Shield: A review of depositional, plutonic, structural, and tectonic events in the closing stages of the northern East African Orogen: in J. of African Earth Sciences, v.61, pp. 167-232.
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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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