الفهرس 
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Abstract
. Cu-Ni-PGE mineralization at Abu Swayel occurs in discontinuous bodies and lenses of amphibole rocks of unusual petrographic and geochemical composition which are mtercalated into metasediments of Proterozoic age. Two distinct types of amphibole rocks lledistinguished both showing chemical similarities with komatiitic or high-Mg basaltic lOCks. Sulphides and PGM are concentrated in the lower part of the more magnesian coarse ~ained variety and along a synmctamophic shear zonc. Mincrali7.ation in the shear zone is losted by a plagioclase-garnet rock showing coarse-grained pegmatitic texture and oontaining minor hornblende, Fe-Mg amphiboles and chlorite.
2. Metapelites containing assemblages of garnet-biotite-sillimanite+quartz ±staurolite !plagioclase ±alkali feldspar indicate amphibolite facies conditions. These were confimled yresults of geothermobarometry giving maximum P-T conditions of ca. 650°C at 4-6 kbar. is important to note that the mafic- ultramaf~c unit was affected by the same high-T,
nedium-P event. There it resulted in formation of complex amphibole-dominated scmblagl:s (sl:vl:ral cUl:xistillg calcic alllpllilJulcs alld/ur l;l:-Mg tlillphibuks, ±chlurite, lagioclase etc.).
3. Fluid flow along the synmetamorphic shear zone resulted in alteration (alkali tasomatism with increase in Si, alkali elements) of the magmatic precursor rocks and the
ation of the garnet-plagioclase pegmatitic zone. A systematic increase in Si, Fe/Mg and rease in HFS elements (e.g. Ti,’ Cr, V) toward this pegmatitic zone is recorded in a mical profile across this zone. Petrographically this pre- to synmetamophic alteration is rressed by variation in modal contents of amphiboles. chloritc and plagioclase and by iation of amphibole and chlorite composition. Total Fe contents of Fe-Mg minerals rease towards the mineralized zone.
4. The geotectonic setting and ages of the ultramafic-mafic host rocks and of amphibolite ’es metamorphism are equivocal. The metamorphic mafic- ultramafic rocks are older than 820 Ma. and are thus older than typical ophiolites in the Eastern Desert. A sill like sion is recommonded.
5. The close association of the Cu-Ni-PGE mineralization with mafic-ultramafic units of Komatiitic affinity in the Abu Swayel area suggests a primary magmatic origin of the mineralization. Mineral assemblages and ore textures (e.g., sulphides occuring interstitial to metamorphic hydrosilicates) reveal a strong metamorphic overprint.
6. The present geological position, textural features, and mineralogical composition of the Cu-Ni ores is the product of amphibolite facies metamorphism and hydrothermal remobilization of the primary mineral associations. The hydrothermal solutions could have been derived from the metasediments during metamorphism.
7. The Abu Swayel deposit is enriched in Cu, Pd, and Au (the most mobile elements) and is strongly depleted in IPGE (the least mobile elements). The general increase of S, Cu, Pd and Au contents towards the shear zone suggests that these elements were redistributed by metamorphic fluids.
8. PGM are represented by Pd-bismuthotellurides which are considered characteristic for low-temperature hydrothermal deposition, could have formed during cooling stage after the peak of amphibolite facies metamorphism. The precipitation of PGE took place over a wide range of temperatures.
9 . The formation of Fe3+ rich hydrosilicates and almandine-rich garnet in the vicinity of
mobilized sulphides suggests that the hydrothermal solutions were oxidizing and implying metal transport as chloride complexes.
1. The Urn Samiuki massive sulphide mineralization occur at the top of felsic volcanic rocks of Cycle I volcanics of H~amid Group. These felsic volcanics foml part of the Shadli
Metavolcanics which comprises the Urn Samiuki and Hamamid Group. These metavolcanics
were erupted in an extensional regime -710 Ma ago. The Hamamid group was erupted in two magmatic cycles; Cycle I and Cycle II volcanics.
2. The massive sulphide bodies are underlined by a pipe like alteration zone. Four distinct types are recognized: a) quartz-tale-chlorite; b) quartz-talc-tremolite; c) talc-rich; and d) serpentine-tremolite-talc-calcite. The circulation of Mg-rich seawater in the erupted, penneable, rhyolite removed alkalies, AI, (and Si) and formed the alteration zones.
3. Three ore types are identified; black, galena-rich, and yellow ore. Sphalerite, chalcopyrite, pyrite, galena, and bornite are major sulphide minerals. Tetrahedrite-tennantite series, arsenopyrite, pyrrhotite, and molybdenite are minor or accessory minerals. Covellite and digenite are common supergene minerals. The microprobe analyses of bornite and covellite revealed high contents of Ag. A compositional range extending accross the entire tennantite (Cu 12As4S 13)-tetrahedrite (Cu12Sb4S 13) solid solution is revealed in fahlore minerals
4. Six silver minerals are identified for the first time from Urn Samiuki; hessite (Ag2 Te), electrum (Au,Ag), acanthite (Ag2S), mckinstryite (Ag1.2CuO.8S), freibergite (Ag,Cu,Fe,Zn)12 (Sb,As)4 S 13’ and native silver (Ag). Silver was deposited at the early stage of mineralization as solid solution in fahlore minerals. At high temperatures it was deposited as solid solution in bornite and as hessite and electrum. The greenschist facies metamorphism and defromational events liberated silver from early deposited minerals, remobilized and redeposited it as solid solution in covellite and low temperature silver minerals e.g., acanthite and mckinstryite.
5. The Urn Samiuki ores are rich in Zn, Cu, and Pb with an average consistent with Zn dominated deposits. High Ag contents (up to 600ppm), Au (up to 3ppm), and Cd (up to 0.2 wt. %) are recorded in the massive sulphide ores.
6. The chemical and geological criteria suggest that the Urn Samiuki metals were derived from two sources; magmatic and from footwall rocks. The base metals were concentrated in the most fractionated part of a depleted mantle magma and were carried to the surface at the last stage of magmatism following the eruption of Cycle I felsic rocks. Additional metals were leached from the footwall rocks (mainly rhyolite) by seawater-rock interaction.