| 1. |
- Abdelnasser, Amr, et al.
(författare)
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REE geochemical characteristics and satellite-based mapping of hydrothermal alteration in Atud gold deposit, Egypt
- 2018
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Ingår i: Journal of African Earth Sciences. - : Elsevier. - 0899-5362 .- 1464-343X. ; 145, s. 317-330
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Tidskriftsartikel (refereegranskat)abstract
- New geochemical data of the hydrothermal alteration zones associated with gold-bearing quartz veins at Atud mine are used for better understanding the ore evolution and exploration vectoring. ASTER and Landsat 8 OLI data are used to elucidate the distribution of gold-associated alteration zones. Three alteration zones are defined; zone 1 (sericite-kaolinite-quartz-pyrite), zone 2 (quartz-sericite-albite-pyrite), and zone 3 (chlorite-carbonate-epidote ± pyrite). Sericite and hydrothermal quartz are confined to the mineralized quartz veins. Fe-OH and OH-bearing minerals are observed along NW- and NE-trending shear zones in the Main Atud mine. The association of gold-bearing quartz veins and sericite alteration is constrained by processing ASTER- and OLI-imagery data. The geochemical data of the ore-enveloping hydrothermally altered rocks are used to assess the behavior of the REEs during the mineralization process. Mild enrichment in LREE and significant enrichment in the HREE are associated with sericite in zones (1) and (2) alterations. Carbonate alteration (zone 3) is enriched in LREE and in immobile HREE. Moreover, LREE and Eu anomalies have negative correlated with the Alteration Index (A.I.) and K2O index (K.I.) in zones 1 and 2, suggesting high mobility of LREE in K-rich hydrothermal fluids. On the other hand, HREE anomalies with increasing MgO index (M.I.) in alteration zone 3 may imply low solubility of these elements in alkaline solutions. Au anomalies linked to sericite/silica alteration is a rather meaningful vector for further exploration in the area.
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| 2. |
- Zoheir, Basem, et al.
(författare)
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Granitoid-associated gold mineralization in Egypt : a case study from the Atalla mine
- 2018
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 53:5, s. 701-720
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Tidskriftsartikel (refereegranskat)abstract
- Gold-bearing sulfide-quartz veins cutting mainly through the Atalla monzogranite intrusion in the Eastern Desert of Egypt are controlled by subparallel NE-trending brittle shear zones. These veins are associated with pervasive sericite-altered, silicified, and ferruginated rocks. The hosting shear zones are presumed as high-order structures of the Najd-style faults in the Central Eastern Desert (similar to 615-585 Ma). Ore minerals include an early pyrite-arsenopyrite (+/- pyrrhotite) mineralization, partly replaced by a late pyrite-galena-sphalerite-chalcopyrite (+/- gold/electrum +/- tetrahedrite +/- hessite) assemblage. Gold occurs as small inclusions in pyrite and arsenopyrite, or more commonly as intergrowths with galena and sphalerite/tetrahedrite in microfractures. Arsenopyrite geothermometry suggests formation of the early Fe-As-sulfide mineralization at 380-340 A degrees C, while conditions of deposition of the late base metal-gold assemblage are assumed to be below 300 A degrees C. Rare hessite, electrum, and Bi-galena are associated with sphalerite and gold in the late assemblage. The early and late sulfide minerals show consistently a narrow range of delta S-34 aEuro degrees (3.4-6.5) that overlaps with sulfur isotopic values in ophiolitic rocks. The Au-quartz veins are characterized by abundant CO2 and H2O +/- CO2 +/- NaCl inclusions, where three-dimensional clusters of inclusions show variable aqueous/carbonic proportions and broad range of total (bimodal) homogenization temperatures. Heterogeneous entrapment of immiscible fluids is interpreted to be caused by unmixing of an originally homogenous, low salinity (similar to 2 eq. mass % NaCl) aqueous-carbonic fluid, during transition from lithostatic to hydrostatic conditions. Gold deposition occurred generally under mesothermal conditions, i.e., 1.3 kbar and similar to 280 A degrees C, and continued during system cooling to < 200 A degrees C and pressure decrease to similar to 0.1 kbar. Based on the vein textures, sulfur isotope values, composition of ore fluids, and conditions of ore formation, we suggest that the Atalla monzogranite intrusion acted only as a competent structural host for ore deposition from shear-related, metal-rich fluids migrated up from depth. This model is also presumed for most granitoid-associated Au deposits in the region, considering the similarity in their structural control, alteration pattern and mineralogy, and chemistry of the ore fluids.
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| 3. |
- Zoheir, Basem, et al.
(författare)
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Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt
- 2014
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Ingår i: Journal of African Earth Sciences. - : Elsevier BV. - 1464-343X .- 1879-1956. ; 99:1, s. 165-187
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Tidskriftsartikel (refereegranskat)abstract
- The auriferous quartz±carbonate veins at Dungash mine, central Eastern Desert of Egypt, are confined to ∼E-trending dilation zones within variably foliated/sheared metavolcanic/volcaniclastic rocks. The vein morphology and internal structures demonstrate formation concurrent with a dextral shear system. The latter is attributed to flexural displacement of folded, heterogeneous rock blocks through transpression increment, late in the Neoproterozoic deformation history of the area. Geochemistry of the host metavolcanic/metavolcaniclastic rocks from the mine area suggests derivation from a low–K, calc–alkaline magma in a subduction-related, volcanic arc setting. In addition, chemistry of disseminated Cr-spinels further constrain on the back-arc basin setting and low-grade metamorphism, typical of gold-hosting greenstone belts elsewhere.Mineralogy of the mineralized veins includes an early assemblage of arsenopyrite-As-pyrite-gersdorffite±pyrrhotite, a transitional pyrite-Sb-arsenopyrite±gersdorffite assemblage, and a late tetrahedrite-chalcopyrite-sphalerite-galena-gold assemblage. Based on arsenopyrite and chlorite geothermometers, formation of gold-sulfide mineralization occurred between ∼365 and 280°C. LA-ICP-MS measurements indicate the presence of refractory Au in arsenian pyrite (up to 53 ppm) and Sb-bearing arsenopyrite (up to 974 ppm). Abundant free-milling gold associated with the late sulfide assemblage may have been mobilized and re-distributed by circulating, lower temperature ore fluids in the waning stages of the hydrothermal system.Based on the isotopic values of vein quartz and carbonate, the calculated average δ18OH2O values of the ore fluids are 5.0±1.4‰ SMOW for quartz, and 3.3±1.4‰ for vein carbonate. The measured carbonate δ13C values correspond to ore fluids with δ13CCO2= -6.7±0.7‰ PDB. These results suggest a mainly metamorphic source for ore fluids, in good agreement with the vein morphology, textures and hydrothermal alteration. The calculated δ34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (∼1.5 to 3.6 ‰), (∼0.4 to 1.0‰), and (–3.7 to –1.9‰), respectively. The systematic evolution towards lighter δ34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions.The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.
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| 4. |
- Zoheir, Basem, et al.
(författare)
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Trace elements and isotope data of the Um Garayat gold deposit, Wadi Allaqi district, Egypt
- 2019
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 54:1, s. 101-116
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Tidskriftsartikel (refereegranskat)abstract
- Trace element composition of sulfides and O, C, Sr and S isotopic data are assessed to constrain the evolution and potential fluid and metal sources of the Um Garayat gold deposit. Ore microscopy and BSE investigations of quartz veins show blocky arsenopyrite and pyrite replaced in part by pyrrhotite, chalcopyrite, sphalerite, galena, and gersdorffite. Free-milling gold occurs commonly in close association with the late sulfides, and along fractures in pyrite. On the other hand, recrystallized pyrite is disseminated in host metavolcaniclastic/metasedimentary rocks that commonly contain carbonaceous material. In situ LA-ICP-MS analysis of sulfides shows the recrystallized pyrite enriched in most trace elements, while blocky pyrite contains only some traces of arsenic. Detected concentrations of gold (up to 17ppm) were only reported in arsenopyrite disseminated in quartz veins. The S-34 values of blocky pyrite and pyrrhotite in quartz veins define a narrow range (1.6 to 3.7 parts per thousand), suggesting a homogenous sulfur source which is consistent with the dominantly mafic host rocks. The recrystallized pyrite has a distinctive sulfur isotope composition (S-34 -9.3 to -10.6 parts per thousand), which is rather comparable to diagenetic sulfides. Hydrothermal carbonate in quartz veins and wallrock have nearly constant values of O-18 (10.5 to 11.9 parts per thousand) and C-13 (-4.2 to -5.5 parts per thousand). Based on constraints from mineral assemblages and chlorite thermometry, data of six samples indicate that carbonate precipitation occurred at similar to 280 degrees C from a homogenous hydrothermal fluid with O-18(H2O) 4.4 +/- 0.7 parts per thousand and C-13 =3.7 +/- 0.8 parts per thousand. Strontium isotope values of two samples (Sr-87/Sr-86 = 0.7024 and 0.7025) are similar to the initial Sr-87/Sr-86 ratios of island arc metabasalts (similar to 710Ma) in the South Eastern Desert. The generally homogenous sulfur, C, O, Sr isotope data are suggestive of metamorphogenic fluids, likely produced from dominantly mafic volcanic rocks at the greenschist-amphibolite facies transition.
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