North Sudan Gold - Galat Sufar South, Wadi Doum, Gabgaba/Qbgbih
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Northern Sudan gold deposits include Galat Sufar South, Wadi Doum and Gabgaba/Qbgbih. Galat Sufar South is located ~700 km north of Khartoum and ~180 km due north of Abu Hamad. Wadi Doum is ~55 km due east of Galat Sufar South. Gabgaba/Qbgbih is ~100 km north of Abu Hamad (#Location: Galat Sufar South - 21° 13' 14"N, 33° 9' 35"E).
Gold mining in the Red Sea Hills and Nubian Desert of Sudan has taken place since ~3000 BC, with numerous documented sites of historic mining
infrastructure throughout the terrane. Colonial gold mining occurred across the Red Sea Hills in the early 19th century, whilst there has been a rapid rise in artisanal gold mining activity since ~2008. Prior to 2008, production was solely come from the Hassai/Ariab operation (~6 tonnes of gold in 2005), but by 2018, an estimated ~85% of Sudan's production was from artisanal mining.
A regional exploration program was initiated in 1996 by the Bureau de Recherches Géologiques et Minières (BRGM) in joint venture with the Geological Research Authority of Sudan. This program involved a low density stream sediment survey using the Bulk Leach Extractable Gold (BLEG) technique over 9000 km2 at a density of one sample per 9 km2, and detected all of the known gold occurrences in the region. From 1999 to 2001, BRGM/La Source undertook followup on a number of prospects in the region, with more detail in the Gabgaba deposit area, including drill testing, before withdrawing. In 2008, the Moroccan company Managem began more detailed work centred on Gabgaba (also known as Qbgbih) and by 2012 commenced pilot scale mining, before announcing an 'internal resource' of ~125 t of contained gold in 2013 and then in 2014 an NI 43-101 compliant resource of 66 t of gold (Duckworth et al. et al., 2018; Abanyin et al., 2015).
In 2010, a Sudanese company, Meyas Nub Multi Activities Company Ltd, began exploration in a prospecting licence that surrounded the area in which the Galat Sufar South deposit was subsequently discovered. In 2011, the Canadian company Shark Metals (to become Orca Gold Inc. in 2013), commenced exploration in neighbouring blocks, and in 2012 entered into a joint venture with Meyas Nub. Later that same year, Galat Sufar South was identified and by 2014 a maiden resource of 69 t of gold was released. Orca Gold continued exploration in the area and in 2014 discovered the Wadi Doum deposit. A feasibility study of the Galat Sufar South and Wadi Doum project was completed in late 2018 (Duckworth et al., 2018; Abanyin et al., 2015).
Gold mineralisation, that has been classified as orogenic (although some may be epithermal) in northern Sudan occurs in the Gabgaba and Halfa terranes and intervening Keraf Suture Zone. The Neoproterozoic juvenile, intra-oceanic arc sequences of the Gabgaba Terrane, to the east, are part of the western, or Nubian, section of the Arabian Nubian Shield in northeastern Africa. The similarly aged Halfa Terrane successions were apparently deposited on continental crust represented by the Sahara Metacraton to the west.
For an overview of the regional setting of the Shield and its geology and distribtion of mineralisation, see the separate Arabian Nubian Shield Overview record.
The southward tapering, wedge shaped Gabgaba Terrane is interpreted to be a structurally detached segment of the neighbouring Gebeit Terrane (see the Jebel Ohier record for a summary of the geology of that terrane). The two are separated by the major NNE-SSW Hamisana Shear Zone. To the NE it is separated from the younger Eastern Desert Terrane by the NW-SE trending Allaqi-Heiani Suture Zone. To the west the Gabgaba Terrane is bounded by the up to 50 km wide, Keraf Suture Zone which is dominated by sinistral transpressive shear zones, and separates the former from the Halfa and Bayuda terranes, and the Sahara Metacraton. The eastern margin of the Keraf Suture Zone is marked by the Eastern Gabgaba Fault System (Duckworth et al., 2018).
The geological and structural character of the Gabgaba Terrane is relatively simple, dominated by thick sequences of andesitic and subordinate felsic volcanic rocks with some metasedimentary rocks. The mafic dominated bi-modal volcanic arc is classified, according by Galley et al. (2007), as an immature oceanic tectonic setting. The arc sequence is intruded by multiple phases of collisional syn-tectonic diorites and post-collisional sub-alkalic intrusive rocks. The latter cross the Keraf Suture Zone and occur into both the Gabgaba and Halfa terranes, and are probably <500 Ma in age. The andesite dominated sequences of the Gabgaba Terrane are unfoliated and only poorly folded, with their original mineralogy and textures preserved. The observable primary layering of volcano‐sedimentary rocks is east‐west.
In contrast, the succession within the Keraf Suture Zone comprises a thick sequence of folded and thrusted marine sedimentary rocks, dominated by pelites, marls and limestone units, with localised coarser grained siliciclastic sediments (Duckworth et al., 2018). The Keraf Suture Zone also includes remnants of intra-oceanic island arc and/or back arc ophiolite assemblages (Abanyin et al., 2015). Prior to assembly of eastern and western Gondwana across this structural zone, at least two phases of isoclinal folding are recognised, whilst a continuum of regional steep folding and segmentation is evidenced by the juxtaposition of coaxial and non-coaxial interference fold patterns across shear zones (Abanyin et al., 2015). The core of the suture zone is masked by Cenozoic clastic infill sedimentary rocks within the the NNW-SSE aligned Wadi Gabgaba extensional rift valley.
The Halfa Terrane sequence to the west of the Keraf Suture Zone is characterised by a package of shallow, calcareous, marine sedimentary rocks containing iron formations and numerous discrete volcanic centres, and has been classified as an immature continental tectonic setting (Galley et al., 2007).
Galat Sufar South
The Galat Sufar South deposit is located close to the eastern margin of the Halfa Terrane, at the junction between the north-south Keraf Suture Zone and the east-west Atmur-Delgo structure. The structural geology of the area is dominated by complex interference folding within the sedimentary rocks of the Keraf Suture-Halfa Terrane, which is unique to this structural intersection. At Galat Sufar South, an annular interference structure some 15 km in diameter comprises peripheral mafic volcanic rocks surrounding a package of intermediate-subalkalic volcanic and calcareous meta-sedimentary rocks that host the deposit on the southern flanks, but near the core, of the structure. This structure, also known as the 'Galat Sufar Andesite Domain', is a culmination/anticlinorium and has an axial trace at surface trending ENE. A silicified dolomite marker unit surrounds the core of the dome and is part of an interleaved package of lower greenschist facies metamorphosed carbonate, marl and volcanic rocks (Abanyin et al., 2015). The Galat Sufar South deposit is situated just south of the contact between marine sediments to the north, marked by the silicified dolomite marker unit that dominates a ridge line, and an andesitic volcanic sequence to the south. The andesitic sequence is heterogeneous comprising lava flows, pyroclastic deposits and primary volcanic breccias (Duckworth et al., 2018). The northeastern apices of this doubly plunging antiform hosts the Galat Sufar North prospect, whilst other prospects are located on its northern flanks.
The Galat Sufar South deposit is hosted by a discrete, 80 to 200 m wide package of proximal calc-alkaline to sub-alkalic intermediate volcanic rocks deposited together with shallow marine calcareous sedimentary rocks, and intruded by sills/dykes of diorite and syenite. Mineralisation and alteration are concentrated in this unit that is bounded to the north and south by increasingly unaltered andesitic flows and further volcaniclastic rocks with distinct and different geochemical signatures (Duckworth et al., 2018). These rocks have undergone lower greenschist facies metamorphism and at least two phases of upright regional folding to produce a pronounced schistosity in all but the cores of intrusive bodies. This penetrative S1 schistosity which is sub‐vertical and trends NW-SE (150 to 160°), but varies to near 110°, both controls and is cut by well-developed shearing, alteration and mineralisation. Shearing within the deposit area dominantly follows two directions, the first at ~110°, which is sub-parallel to the S1 cleavage, while the second is at 10°. These trends control both alteration and veining, and are steep, with well developed C-S fabrics. The second set is better developed in the main deposit area where it is mylonitic. The lineation formed by the intersection of these two shear sets is defined by pipe-like ore shoots that plunge steeply to the NW. The main deposit is separated into eastern and western sections, the separation of which, known as The Gap (see below), is not well understood.
According to Abanyin et al., 2015), alteration associated with mineralisation is, overall, pervasive, and at a deposit-scale is defined by assemblages that are variably zoned outward from the gold mineralisation, but is also influenced by the protolith composition and rheology. Within the core of the deposit, alteration is pervasive and strong resulting in the almost complete destruction of primary mineralogy and textures. The the main deposit is associated with a core of dominantly sericite alteration, with the strongest mineralisation accompanied by a quartz-sericite-pyrite schistose alteration zone, passing out into more weakly mineralised quartz-sericite domain. On the eastern margin of the deposit, K feldspar alteration overprints a foliated and a porphyritic diorite forming a rigid body that is sheared on its contacts and overprinted by the quartz-sericite schist and quartz-sericite-pyrite schist. Where the K feldspar alteration is intense, a texture destructive black-red diorite with incipient hornfelsing is preserved with overprinting highly sheared quartz-sericite-pyrite schist altered high-grade mineralisation. Elsewhere, the foliated diorite and K feldspar alteration contains only weak, variable mineralisation (Abanyin et al., 2015).
K feldspar alteration, syenite intrusives, felsic stocks and early quartz blows all form rigid bodies that act as buttresses deflecting shearing, and thereby creating brecciated pipes and laminated shear zones. Such tectonic breccias are common in the Main and East zones (see below) where they are often pervasively overprinted by K feldspar and/or quartz-sericite alteration and subsequent shear foliation. All of these zones are surrounded by a chlorite-epidote bearing sequence of monotonous andesitic volcanic rocks. Directly south of the deposit, the development of chlorite-epidote is controlled by through-going faults, which on approaching mineralisation contain quartz-epidote (epidosite; Abanyin et al., 2015).
Duckworth et al. (2018) describes a series of lithologies that grade from distal, less altered country rocks, the protoliths of which are recognisable, to strongly altered host rocks in which the primary mineralogy and textures have been virtually obliterated. Consequently, the latter are defined by their
alteration assemblages only, as follows:
• Andesitic volcanics comprising chlorite altered lavas, volcanic sediments and breccias.
• Volcano-sedimentary rocks with a clastic matrix of varied grain size, occurring as a fine grained muscovite schist interpreted to represent a volcaniclastic protolith.
• Massive basaltic andesite that has commonly been subjected to early hematite-albite alteration, giving the rock a characteristic black red colouration.
• Sericite altered varieties of a range of rocks, where the sericite formation was not texturally destructive and the protolith can be identified.
• Weak to intensely altered, fine grained, foliated, schist, in which the protolith is not recognisable, composed of green and mustard yellow sericite with Fe carbonate streaks/laminae. This alteration overprints the first three lithological units listed above. This lithology occurs outbound of the silicified core of the deposits, represented by the gold-bearing alteration/rock types described below, and forms a broad, laterally extensive low grade alteration halo. Volcano-sedimentary rocks occur throughout as scattered and discontinuous pockets suggesting it is the principal protolith that has been hydrothermally altered.
• Very fine grained, massive, pale green altered rock with occasional relict phenocrysts. These rocks, the protoliths of which are unrecognisable, underwent early massive albite flooding, overprinted in places by sericite and Fe carbonate. Brittle deformation is common with multiple stages of fracturing and brecciation which is veined/cemented with silica and moderate to high grade gold mineralisation.
• Albite and/or K feldspar and sericite altered massive basaltic andesite, that is weakly foliated and locally massive, often containing fine sulphide disseminations.
• Fine grained, strongly foliated, intensely altered schist that is a major gold bearing lithology. Alteration comprises early albite, sericite-silica and late Fe carbonate, typically carrying 5 to 10% pyrite as fine disseminations and clusters.
• Massive, smokey grey silicification that is also a major gold bearing lithology which carry 5 to 10% disseminated sulphide. It occasionally exhibits porphyritic texture and occurs as distinct bodies in the East Zone, where it is interpreted to represent original dioritic sills that have undergone brittle fracturing and intense pervasive silicification.
• A lithology characterised by advanced brecciation and silica alteration of the very fine grained, massive, pale green albite-sericite-Fe carbonate lithology detailed above. It carries 5 to 10% disseminated pyrite and is a host to gold mineralisation.
• Silicified massive basaltic andesite, composed of >50% quartz with visible remnants of albite and K feldspar, but no foliation.
• A rock containing K feldspar/albite altered clasts within a dull siliceous matrix carrying significant pyrite. It contains anomalous to low grade gold, and occurs as an irregular plug within a fold closure to the west of the East Zone.
Prior to deformation and mineralisation this sequence is interpreted to have comprised an ENE striking volcaniclastic suite containing porphyritic intrusions sandwiched between two units of andesitic volcanic rocks.
Gold is primarily associated with intense sericite-carbonate alteration, the presence of pyrite, zones of moderate silicification and quartz veining from a mm scale to a maximum of 1.5 m. The best mineralisation occurs in areas of increased deformation, with the widest, best developed shear zones containing the largest resources. Gold mineralisation is predominantly restricted to foliated quartz-sericite-pyrite schist or to silicified host host rock. Both host significant intersections over broad intervals with true widths of 15 to >80 m @ grades of 1.25 to 5 g/t Au and 0.5 to 6 g/t Ag. Gold is present either as free grains disseminated within the host rock or in association with pyrite, with a further ~5% as petzite (Ag3AuTe3). Free gold is very rarely visible, predominantly occurring as very fine 1 to 10 µm grains which contain ±20% silver. A minor amount of the gold occurs in quartz-carbonate veins. Some 16 to 18% and 2 to 4% of gold is locked in sulphide and in host rocks respectively. The sulphide content in mineralised zones rarely exceeds 5%. Pyrite is by far the dominant sulphide with occasional chalcopyrite, sphalerite, galena and tennantite/tetrahedrite.
The first phase of silicification occurred as milky white, fused quartz blows that are randomly oriented and are cross-cut by shear zones and associated subsequent veining. Vein quartz is present within all of the mineralised zones, and at surface has been the focus of exploitation by artisanal miners. There are multiple generations of quartz veining which have subsequently also been mylonitised and brecciated in the main ore zones. Quartz blows are found throughout the region, although outside of the deposit areas often carry no gold. At Galat Sufar South, quartz blows have sheared contacts, are brecciated and can contain significant gold.
Six fault separated domains of mineralisation have been differentiated at Galat Sufar South by Abanyin et al. (2015), defining a 1500 m long ENE trend. These are, from west to east, the:
• 320 Zone, which occurs as discontinuous ribbons and plunging shoots within a 140° oriented shear zone that is parallel with the local schistosity. This zone contains high-grade, >10 g/t Au, shoots plunging steeply NW, paralleling the intersection lineation of the 10 and 110° shear trends.
• Main Zone, an up to 90 m wide, laminar, 150 m strike length zone that is oriented at 20°. It represents a set of 10° trending shears that link two through-going 110° trending shears that cross a rigid body of syenite/K feldspar altered diorite in the footwall. Shear fabrics in the zone are extreme and locally mylonitised. It converges with, and in the south, is fault juxtaposed with the 320 Zone. Grades are highest within the Main Zone, closest to the intersection of the two.
• 050 Zone, a narrow domain linking the East Zone (to the east) and a north-south trending set of mineralised veins under cover in area known as The Gap (in the west). It is considered to be a compressional duplex that translates movement from the East Zone into a large through-going 10° trending shear within The Gap. It also links into a 110° tending shear containing the J Zone veins that connect the Main and 050 zones in the south.
• East Zone, hosted by an ~100° oriented corridor which contains several small, often brecciated and dismembered intrusive stocks. Shear fabrics wrap around the intrusive bodies, although the kinematics are complex. The true width of the zone is >90 m in its central sections, whilst subsidiary, parallel mineralised structures occur to the north and south with a similar, although less well defined, trend. Shear fabrics dominantly have a 110° orientation and dip steeply to the west. Sub-ordinate shearing striking at ~10° is also evident, although associated mineralisation is often obliterated by silicification. A third subordinate fabric oriented at 30° is related to steep, irregular, coarse grained, gold bearing cataclasite, interpreted to be the product of a late stage deformation. A barren plug of alteration occurs adjacent to high-grade tectonic breccias and may be associated with a quartz blow seen at surface.
• Far East Zone, which has a similar trend to the East Zone. Discontinuous mineralisation is hosted by a sheared sericitised microdiorite, within steep-to-vertical mineralised trends which pass under cover.
• Shareg Zone, a steep, north-south striking trend, hosted by a sericite-carbonate altered diorite to microdiorite. It separates the Far East Zone of the Galat Sufar South deposit from an extension, the NE Zone, which is a braided, >1 km long shear containing components of the main shear trends.
Duckworth et al. (2018) suggest that the alteration and mineralisation is synchronous with the development of the S1 foliation, as alteration products, including silicification, sericite alteration and quartz veins are all parallel to subparallel the S1 fabric, although the overall trend of alteration and gold mineralisation is at a high angle to that fabric. Discernible folding in the East Zone of the Galat Sufar South deposit deforms the andesitic volcanics-volcanosedimentary sequence contact. These folds do not deform the S1 foliation which is parallel to the axial plane of these structures. The S1 foliation is interpreted to have resulted from ENE-WSW shortening of the ENE striking volcaniclastic/sedimentary and enclosing volcanic succession. It is suggested that early syn‐tectonic emplacement of intense quartz veining/silicification with associated sericite and pyrite alteration was focussed within the weak volcaniclastic/sedimentary suite containing the porphyritic subvolcanic intrusions. Duckworth et al. (2018) suggest that as deformation progressed, veins were transposed into parallelism with the S1 foliation, resulting in an ore body whose overall geometry is broadly perpendicular to the NW strike of the foliation. The vein bearing unit began to fold and late stage shearing developed and locally disjointed the deposit.
Ore Reserves and Mineral Resources after Duckworth et al. (2018)
Mineral Resources as of January 2018 at a 0.6 g/t Au cutoff were:
Oxide - 9.6 Mt @ 1.32 g/t Au, 1.41 g/t Ag;
Transition - 13.2 Mt @ 1.22 g/t Au, 1.31 g/t Ag;
Hypogene - 52.7 Mt @ 1.27 g/t Au, 1.54 g/t Ag;
TOTAL - 75.6 Mt @ 1.27 g/t Au, 1.48 g/t Ag;
Oxide - 1.0 Mt @ 1.0 g/t Au, 1.1 g/t Ag;
Transition - 1.5 Mt @ 1.0 g/t Au, 1.1 g/t Ag;
Hypogene - 14.4 Mt @ 1.2 g/t Au, 1.4 g/t Ag;
TOTAL - 16.9 Mt @ 1.2 g/t Au, 1.4 g/t Ag;
TOTAL Resources - 92.5 Mt @ 1.26 g/t Au, 1.47 g/t Ag for 116 t of contained gold. These Mineral Resources include a
TOTAL Ore Reserve of - 77.356 Mt @ 1.07 g/t Au.
The high grade core of the Wadi Doum deposit, which outcrops at the base of a hill, is hosted by a strongly sulphidic volcaniclastic unit that dips at 20°SW, and is in contact with a rhyolite unit to the immediate east. This rhyolite is, in turn, bounded to the east by a dacitic unit that has been intruded by syn‐tectonic syenite and a potassic altered diorite body which forms the summit of the hill. These rocks are cut by thin, barren, late, post-mineral felsic and mafic dykes. The rhyolite and dacite dip at 75°E. In addition to the volcaniclastic unit, mineralisation also occurs as stringer zones within the syenite and locally in smaller shears.
Mineralisation within the volcaniclastic unit is divided into a:
• Western Unit, which has a characteristic dark colour due to very fine grained, >10 to 15% sulphides, and contains some of the best intersections;
• Central Unit of paler, sulphide rich felsic volcaniclastics that contain deformed sulphide veinlets; and
• Footwall Unit that is of lower grade, and is largely composed of un‐deformed felsic volcaniclastics.
The dominant sulphide is ~85% pyrite with the remainder comprising a mix of sphalerite, galena, chalcopyrite and freibergite. In contrast to Galat Sufar South, gold is also observed in close association with arsenopyrite, spahlerite and galena as well as pyrite. The gold contains ~35% Au.
A strong and pervasive, north‐south trending schistosity dominates, and is largely followed by the late dykes. The high grade mineralisation is apparently often un‐affected by structure, with the exception of that hosted by the syenite on and around the summit of the hill. Ore occurs as four distinct high-grade shoots.
Alteration is predominantly sericite within the felsic volcanics, within a wider halo of carbonate development. Silicification is absent or weak within the high grade section of the deposit.
Ore Reserves and Mineral Resources after Duckworth et al. (2018)
Mineral Resources as of January 2018 at a 0.6 g/t Au cutoff were:
Oxide - 0.6 Mt @ 1.90 g/t Au, 2.82 g/t Ag;
Transition - 0.2 Mt @ 2.02 g/t Au, 3.69 g/t Ag;
Hypogene - 3.6 Mt @ 1.89 g/t Au, 5.93 g/t Ag;
TOTAL - 4.3 Mt @ 1.90 g/t Au, 5.45 g/t Ag;
Oxide - 0.1 Mt @ 1.0 g/t Au, 1.6 g/t Ag;
Transition - 0.04 Mt @ 0.9 g/t Au, 1.6 g/t Ag;
Hypogene - 1.5 Mt @ 1.2 g/t Au, 3.8 g/t Ag;
TOTAL - 1.6 Mt @ 1.2 g/t Au, 3.6 g/t Ag;
TOTAL Resources - 5.9 Mt @ 1.71 g/t Au, 4.95 g/t Ag for 10 t of contained gold. These Mineral Resources include a
TOTAL Ore Reserve of - 2.588 Mt @ 2.36 g/t Au.
Gold mineralisation has been known in the Wadi Gabgaba region since ancient time, having been mined by the Nubians, the ancient Egyptians, the Ottomans and the British. Operations at Gabgaba were commenced by the Moroccan company Managem in 2012 and were upgraded to a capacity of 1.2 My pa in 2018.
The Gabgaba deposit, also known as Qbgbih, is located within the broad Keraf Suture zone and is reported to have an initial resource of ~66 t of contained gold at an unspecified grade (Johnson et al., 2017).
The Galat Sufar South and Wadi Doum summaries are mainly drawn from Abanyin et al., 2015 (see below) and Duckworth et al., G., 2018 - Feasibility Study, Block 14 Gold Project, Rewpublic of Sudan; an NI 43-101 Technical Report prepared by Lycopodium Minerals Pty Ltd for Orca Gold Inc., 313p.
The most recent source geological information used to prepare this summary was dated: 2018.
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.
Abanyin, E., Abdel Salam, B., Ackah, E., Appiah, M., Mohamedy, M., Mills, S. and Stuart, H., 2015 - The discovery and geology of the Galat Sufar south deposit, Republic of the Sudan: in NewGenGold 2017, Conference, Case Histories of Discovery, 17-18 November 2017, Perth Western Australia, Paydirt Media, Perth, Conference Proceedings, pp. 115-130.|
Johnson, P.R., Zoheir, B.A., Ghebreab, W., Stern, R.J., Barrie, C.T. and Hamer, R.D., 2017 - Gold-bearing volcanogenic massive sulfides and orogenic-gold deposits in the Nubian Shield: in S. Afr. J. Geol. v.120, pp. 63-76.|
Perret, J, Feneyrol, J., Bosc, R., Eglinger, A., Andre-Mayer, A.-S., Hartshorne, C. and Abanyin, E., 2019 - The structural control on the gold mineralization at the Galat Sufar South deposit (Block 14, NE Sudan): in Proceedings of the 15th Biennial SGA Meeting, Glasgow, Scotland, 27-30 August, 2019, Conference Proceedings, pp. 631-634.|
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