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Hamash - Um Hagalig, Ara West, Ara East, Um Tundub, Hamash North |
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Egypt |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Hamash cluster of copper-gold deposits are located ~65 and ~80 km WSW to SW of the Sukari gold mine and Red Sea port of Marsa Alam respectively, in the western Red Sea Hills, part of the southern-central Eastern Desert region of Egypt (#Location: 24° 40' 50"N, 34° 5' 40"E).
Copper and gold mineralisation is known at five localities within the Hamash district, distributed over an ENE-WSW elongated ~2 x 1 km area, namely at Um Hagalig, Ara West, Ara East, Um Tundub, Hamash North, Abou Tarda and the Hamash Gold Mine.
For details of the regional setting see the separate Arabian Nubian Shield Overview and Sukari records.
The Hamash deposits are situated close to the contact between Neoproterozoic basement igneous rocks and the widespread, flat lying, late Neoproterpozoic to Mesozoic Nubian Sandstone cover sequence. The dominant rocks of the host sequence in the deposit area are metasedimentary mudstones, phyllites, and chlorite-quartz-epidote and actinolite-epidote schists. A tectonically bound, east west trending, ~500 m long sheet like mass of serpentinite and talc-carbonate rocks is enclosed in the metasedimentary rocks at Um Hagalig (which is 1 km east of the Hamash gold mine). To the south of the Hamash gold mine there is a NW-SE trending 12.5 km long metagabbro-diorite complex which encloses rafts of the surrounding metasedimentary rocks. The rock association, tectonic contacts and flat REE patterns of the meta-gabbrodiorite are interpreted to indicate that they, with the enclosed and enclosing metasedimentary rocks, constitute an extensive ophiolitic mélange (El Mahallawi, 1995). The serpentinites are extensively sheared by NW, NNE, ENE and E‐W structures, and are cut by large, nearly vertical quartz‐carbonate dyke‐like bodies up to 3 m thick. The pelitic to psammo‐pelitic schists of the mélange are more common to the northeastern and central parts of the mineralised area where they show well developed preferred NW‐SE and east-west striking orientation and mainly dip north (Sakran et al., 2009; Helmy and Kaindl, 1999).
The Shait granite (Schurmann, 1953), which is >3 km in diameter, is exposed ~1 km SW of the Hamash gold mine and intrudes the metagabbro-diorite (El Gaby and El Aref, 1977). Both are metamorphosed to upper greenschist facies.
Metavolcanic rocks occupy the northern part of the Hamash area. They have chemical characteristics consistent with calc-alkaline continental arc setting (El Gaby et al., 1988), are metamorphosed to lower greenschist facies (Stern et al., 1984) and are younger than the Shait granite. Within the major strike slip fault zones, they have well developed mylonitic and shear foliations striking NW‐SE. They include meta-basalts,
meta-andesites and meta-dacites as well as equivalent meta-pyroclastics. Some have well developed porphyritic texture with plagioclase phenocrysts (Sakran et al., 2009; Helmy and Kaindl, 1999).
The Hamash cluster of deposits straddle the northern contact between the metavolcanic sequence to the NE and and the a semi-circular, 4.5 x 3.2 km intrusion (to the SW) of coarse grained pink granite and granodiorite which contains large inclusions of meta-gabbro. While Helmy and Kaindl (1999) describe this intrusion as a coarse grained granite and granodiorite, Sakran et al. (2009) detail a the same intrusion as tonalite and quartz diorite, which occur as large elliptical, exfoliating intrusions that are leucocratic, coarse‐grained, with an equigranular hypidiomorphic texture, composed of plagioclase, biotite and quartz. These rocks are cut by numerous dykes mainly of granitic composition but more alkaline in composition and by extensive quartz veining throughout (Sakran et al., 2009; Helmy and Kaindl, 1999).
The Hamash gold mine lies on the northeastern margin of the 500 to 750 m diameter Hamash Granite intruded into the northern margin of the larger granite described immediately above. It is essentially a leucogranite and encloses numerous xenoliths the older calc-alkaline volcanic arc and ophiolitic rocks. Near the Hamash mine area, it cuts across the ophiolitic meta-gabbro to the south and the metavolcanics to the north. At the Hamash gold mine site, the
quartz veins cutting this granite have pronounced alteration halos rich in gold and sulphides, and in the oxide zone are mostly iron oxide stained (Sakran et al., 2009).
Small creamy white trachyte plugs, some with porphyritic textures, are found mainly in the central part of the deposit area and have high relief. Further south, these rocks form a large mass, and intrude highly sheared Shait granite (Sakran et al., 2009; Helmy and Kaindl, 1999).
Mafic and felsic dykes which crosscut the arc volcanics and Hamash Granite, although their relationship to the trachyte plugs is unknown. The mafic dykes are a medium‐grained, equigranular and dark colored dolerite with greenish hues due to the abundance of ferromagnesian minerals. The felsic dykes are mainly in the Hamash gold mine area. They are aplitic to rhyolitic, fine grained and light coloured with a pink to reddish tint indicating the predominance of alkali‐feldspars, and are strongly jointed, with the latter being filled with brownish red iron oxides (Sakran et al., 2009; Helmy and Kaindl, 1999).
The Hamash cluster of deposits area lies in the southwestern part of the major ENE oriented, dextral Idfu‐Marsa Alam shear zone in which the Sukari deposit is also located. This shear zone displaces the ophiolitic mélange, volcanic arc rocks and granitic rocks with a lateral offset of ~1500 m. The same rocks cut by a series of ENE-WSW to east-west oriented, SE vergent thrusts as well as north-south, NE‐SW and NW‐SE strike‐slip faults. The thrusts are concentrated at the contact zone between the ophiolitic mélange and volcanic arc rocks, and cut and juxtapose the two units. These thrusts are all parallel to the axial plane of a major anticline that deforms the volcanic arc rocks to the north of the deposit area with 'right-way-up' limbs dipping at 60 to 70° NW and SE. This structural pattern is overprinted in the deposit area by two dextral WNW-ESE to NW-SE orientation shears. The structural interaction resulted in the formation of a dilatation zone with NW oriented normal faults as well as extensional fracture swarms which facilitated the intrusion of Hamash granite (Sakran et al., 2009).
Four stages of veining, Q1 to Q 4 inclusive, have been identified at the Hamash Gold Mine (Helmy and Kaindl, 1999):
• Q1 veins, which are barren and up to 7 m, averaging ~60 cm thick, with a pale red colour due to iron oxides along cracks. Most trend east-west, dip at 60 to 70°N, and extend over lengths of several hundred metres. They are up to 95% composed of milky quartz, and typically cut by an anastomosing network of brown-blue iron- and copper-stained fractures. Locally open vugs are developed into which quartz crystals up to 0.7 cm in length protrude. They are almost devoid of fresh sulphide, except for a few coarse-grained pyrite crystals. Hematite is abundant and replaces pyrite, whilst relicts of chalcopyrite are evident. The veins are flanked by alteration zones that are generally <5 cm wide.
• Q2 veins, which comprise massive, banded and brecciated, predominantly anhedral milky quartz, with an outer margin of fine grained quartz and associated thin veinlets in the alteration halos. They are grey-white in colour with grains and aggregates of anhedral coarse-grained and finer euhedral, pyrite. The coarse grained pyrite (Py1) is deformed and contains inclusions of chalcopyrite and gold (G1). The finer pyrite is undeformed and devoid of gold. Chalcopyrite occurs as small anhedral grains intergrown with quartz and pyrite and commonly contains pyrite inclusions. Gold also occurs as fracture fillings in PI (GI).
• Q3 veins, which are up to 5 cm thick and composed of grey to transparent, coarse-grained euhedral quartz and similarly coarse-grained euhedral chalcopyrite crystals and finer fracture fillings. The coarse grained chalcopyrite crystals are up to 3 cm in diameter and occupy up to 35 vo1.% of the veins. The chalcopyrite is partially replaced by chalcocite, with secondary bornite forming fine elongate grains along the contacts between chalcopyrite and chalcocite, and associated with a second generation of pyrite (P2). Pyrite, totalling <4%, occurs as small idiomorphic inclusions in quartz and chalcopyrite. Digenite is also a secondary product after pyrite and chalcopyrite.
• Q4 veins, composed of fine-grained milky quartz and pyrite, with gold occurring as small veinlets crosscutting deformed pyrite crystals. Coarser gold grains contain small pyrite (P3) inclusions. The paragenetic sequence sequence is interpreted to be quartz → sulphide → gold precipitation.
In the Hamash Gold Mine, the mineralised quartz veins Q2 to Q4 trend NNE-SSW and dip steeply at 80 to 90°WNW. Q3 and Q4 veinlets occur within Q2 quartz veins and are not observed in contact with the host granite. Sometimes Q4 quartz veintets intersect Q2 and Q3 veins. The veining of the Hamash Gold Mine is restricted to the eastern margin of the Hamash Granite, whilst the other occurrences of the cluster occur within structure in the volcanic arc and other granitic rocks (Helmy and Kaindl, 1999).
At the Hamash Gold Mine, the different types of quartz veins have well-developed alteration halos with variable thicknesses, ranging from few cm up to half a metre. Two types are recognised (Helmy and Kaindl, 1999):
• Quartz-sericite-pyrite, which is developed adjacent to the mineralised veins and comprises large quartz crystals, surrounded by finer anhedral quartz grains. Associated fine grained aggregates of K-mica (sericite and less commonly muscovite) constitute ~45 vol.% of the alteration and replaces primary igneous feldspars and mafic minerals. Small euhedral crystals of epidote occur in the sericite matrix. The fine quartz veinlets found within the halo comprise more than 60% of the alteration assemblage. Small euhedral pyrite cubes (up to 10 vol.%) occur within the sericite matrix, whilst chalcopyrite occurs as small isolated irregular grains.
• Chlorite-epidote-pyrite-sericite, occurs peripheral to the quartz-sericite-pyrite zone and quartz vein and contains minor pyrite and chalcopyrite.
NOTE: While information on the geology, structure and veining is available, no detailed descriptions of the actual deposits has been encountered, including vein dimensions, single or multiple, and if the latter, the density and spacing.
Ore Reserve estimates are as follows (Abouzeid and Khalid, 2011):
Hamash Gold Mine - 2.02 Mt @ 2 to 4 g/t Au;
Um Tondob (or Um Tundub) - 120 Mt @ 0.83 g/t Au;
Ara - 5 Mt @ 1.5 g/t Au;
Abou Tarda - 0.348 Mt @ 1.5 to 5 g/t Au;
TOTAL Proved Ore Reserves - 127.37 Mt @ 0.9 g/t Au for ~ 115 t of contained gold, before an estimated heap leach recovery of 46%.
The most recent source geological information used to prepare this decription was dated: 2011.
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.
Hamash gold mine
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Helmy, H.M. and Kaindl, R., 1999 - Mineralogy and fluid inclusion studies of the Au-Cu quartz veins in the Hamash area, South-Eastern Desert, Egypt: in Mineralogy & Petrology v.65 pp. 69-86.
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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.
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Sakran, SH.M., Said, A., El Alfy, Z. and El Sharkawi, M.A., 2009 - Hammash releasing bend and its control of gold mineralization, Hammash Gold Mine area, South Eastern Desert, Egypt: in Egyptian Journal of Geology, v.53, pp. 87-99.
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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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