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Dungash |
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Egypt |
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Au
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Super Porphyry Cu and Au
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The Dungash gold mining district is located in the Eastern Desert of Egypt, ~120 km west of the Sukari gold deposit and 200 km NE of Aswan, between the River Nile and the Red Sea.
The Dunagsh gold deposit has likely been exploited since the Ptolemaic to early Roman eras in Egypt from 332 to 330 BC, based on the abundant mining ruins and millstones that are widespread in the mine area. The operation was synchronous with the nearby Samut mine where a Roman fort is still preserved. There is also evidence of sporadic activity in the early 20th century (Zoheir et al., 2019).
For a description of the regional setting of the Arabian Nubian Shield and its geology and distribtion of mineralisation, see the separate Arabian Nubian Shield Overview record.
The Dungash gold mineralisation is developed within a sequence of strongly folded and contorted back-arc basin volcano-sedimentary rocks which include large bodies of allochthonous ophiolitic serpentinite, cut by granitoid-gabbroid intrusions all of which are generally of Neoproterozoic age. These rocks are part of the 'Meulha-Dungash' mélange sequence (cf. El-Gaby et al., 1990), which is mainly composed of remnants of obducted oceanic crust tectonically intermixed with back arc sedimentary and volcanoclastic rocks and later metamorphosed to greenschist facies. The metasedimentary rocks are predominantly chlorite schist and mudstones with subordinate volcano-sedimentary tuffs which commonly form the matrix to the mélange blocks of serpentinite, metagabbro and pillowed metabasalt. They less commonly occur as free bands tectonically interleaved with the metavolcanic rocks. The main metavolcanic rocks in the mine area, range from andesite to basaltic-andesite. Pyroclastics rocks are intercalated with the metavolcanics sequences along the original ~east-west striking bedding planes and are mainly volcanogenic tuffs and agglomerates with incidental carbonate fragments. Discrete, mostly NW-SE trending basic and acid dykes cut the basement complex in the region (Zoheir et al., 2019).
The Dungash gold deposit is interpreted to be a mesothermal vein-type gold system developed in island arc metavolcanic/volcaniclastic rocks. The bulk of the oreshoots are structurally attenuated and sheared along flexural-slip planes outwards of a major antiform. Regional ductile deformation is manifested by NW-trending F1 antiforms on which ENE- to NE-trending upright F2 folds and associated large shear zones have been superimposed. The gold bearing structures and related alteration halos are centred on a kilometre-scale ENE-trending dilation zone between interbedded andesitic tuffs/agglomerates and turbiditic volcaniclastic sediments. Most rocks have been dislocated and brecciated by faults with different trends which intersect in the deposit area. In particular, early NW-trending sinistral faults are cut by late ENE- and ~E-W trending dextral fault/fracture zones. Analysis of structural elements, including foliation, shear cleavages, intersection lineation and slickensides indicate quartz veining was synchronous with dextral shear caused by flexural transpression between intensely foliated sediments and coherent, massive metavolcanic blocks. Gold is confined to an ~E- to ENE-trending quartz vein system dipping steeply to the south and cutting the host rock foliation which trends WNW-ESE and dips at 55 to 65°N (Zoheir et al., 2019).
Gold mineralisation occurs as a series of grey and milky quartz ±carbonate lodes within a brittle-ductile shear zone. Within this structure, abundant disseminated sulphides occur within highly strained, metavolcanic and volcanosedimentary wallrocks. The deposit is divided into eastern and western ore zones and covers an area of ~1 km2. The eastern zone occurs over an ~800 m, ENE-trending strike length, and is characterised by variably deformed milky quartz and quartz-carbonate veins cutting through intensely sericite, chlorite and sulphide altered andesitic agglomerate. This zone, including both quartz veins and the halo altered wallrocks, has a north-south width varying from 100 to 160 m. The main eastern ore body splits into three quartz veins (a southern 135 m; middle 170 m; and northern 230 m long) with a maximum vein thickness of up to 150 cm. The western ore zone comprises a single, mainly fragmented, grey quartz vein with an east-west strike length of ~500 m. The alteration zones in both the eastern and western ore zones grade ≤6 g/t Au, whilst the quartz veins carry up to 23 g/t Au. The maximum gold contents were encountered in the grey quartz veins in the western ore zone (Zoheir et al., 2019).
The ore mineralogy of the deposit comprises several generations of pyrite with arsenopyrite and subordinate chalcopyrite, pyrrhotite, gersdorffite, tetrahedrite, gold/electrum and galena. Late marcasite and covellite replace pyrite and chalcopyrite, respectively. A three-stage paragenetic sequence of the gold-sulphide mineralisation is suggested on the basis of ore textures and electron microprobe studies, comprising assemblages of:
• early pyrrhotite+pyrite+aresenopyrite +gersdorffite;
• transitional arsenopyrite+As-pyrite+chalcopyrite+Sb-gersdorffite+ electrum; and
• late gold+tetrahedrite+galena+ sphalerite+marcasite+covellite.
Electron microprobe studies suggest refractory Au is confined to Sb-bearing gersdorffite, Sb-Ni bearing arsenopyrite and arsenian pyrite. Au/Au+Ag (fineness) is higher, ~5, in gold grains accompanying the late sulphides in contrast to those intergrown with the transitional sulphides (≤4). Mobilisation and re-distribution of early refractory gold by low temperature Sb-rich hydrothermal fluids is likely responsible for abundant high fineness gold specks associated with the transitional and late sulphide assemblages, i.e. tetrahedrite and galena (Zoheir et al., 2019).
High gold grades are restricted to arsenopyrite-rich grey quartz lodes ( averaging ~23 ppm Au: 3479 ppm As; 492ppm Sb), whilst gold is more dispersed in the sulphidised wallrocks containing abundant Fe-Mg-carbonate (with up to 6 ppm Au; 354 ppm As; 72 ppm Sb; Zoheir et al., 2019).
While Dungash was an important gold source in ancient Egypt, no production or resource figures have been encountered when generating this summary. Botros (2004) quotes vein grades averaging 3.87 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2004.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Botros, N.S., 2015 - Gold in Egypt: Does the future get worse or better?: in Ore Geology Reviews v.67, pp. 189-207.
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Botros, N.S., 2015 - The role of the granite emplacement and structural setting on the genesis of gold mineralization in Egypt: in Ore Geology Reviews v.70, pp. 173-187.
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Botros, N.S., 2004 - A new classification of the gold deposits of Egypt: in Ore Geology Reviews v.25, pp. 1-37.
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Khalil K I, Helba H A, Mucke A 2003 - Genesis of the gold mineralization at the Dungash gold mine area, Eastern Desert, Egypt: a mineralogical-microchemical study: in J. of African Earth Sciences v37 pp 111-122
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Zoheir B A, El-Shazly A K, Helba H, Khalil K I and Bodnar R J, 2008 - Origin and Evolution of the Um Egat and Dungash Orogenic Gold Deposits, Egyptian Eastern Desert: Evidence from Fluid Inclusions in Quartz: in Econ. Geol. v.103 pp. 405-424
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Zoheir, B. and Weihed, P., 2014 - Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt: in J. of African Earth Sciences v.99, pp. 165-187.
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Zoheir, B.A., Johnson, P.R., Goldfarb, R.J. and Klemm, D.D. 2019 - Orogenic gold in the Egyptian Eastern Desert: Widespread gold mineralization in the late stages of Neoproterozoic orogeny: in Gondwana Research v.75, pp. 184-217.
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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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