Two genetic types of volcanic-hosted massive sulfide mineralizations from the Eastern Desert of Egypt |
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Authors: | Ahmed G Abd Allah |
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Institution: | (1) Geology Department, Faculty of Science, Minia University, Minia, Egypt |
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Abstract: | Volcanic-hosted (Cu–Zn–Pb) massive sulfide mineralizations are described from four prospects in the Eastern Desert: Helgate,
Maaqal, Derhib, and Abu Gurdi. Helgate and Maaqal prospects are hosted in island arc volcanics in a well-defined stratigraphic
level. Massive sulfides form veins and lenses. Although these veins and lenses are locally deformed, sulfides from Helgate
and Maaqal prospects show primary depositional features. They form layers and colloidal textures. Sphalerite, pyrite, chalcopyrite,
and galena are the major sulfides. Gangue minerals are represented by chlorite, quartz, and calcite. The sulfide mineralizations
at Helgate and Maaqal are Zn-dominated. Derhib and Abu Gurdi prospects occur as disseminations, small massive lenses, and
veins along shear zones in talc tremolite rocks at the contact between metavolcanics and metasedimentary rocks. The host rocks
at Derhib and Abu Gurdi are metamorphosed to lower amphibolite facies as revealed by silicate mineral assemblage and chemistry.
Chalcopyrite, pyrite, sphalerite, and galena are the major sulfide minerals while pyrrhotite is less common. Recrystallization,
retexturing and remobilization of sulfide minerals are reflecting postdepositional metamorphic and structural modifications.
Electrum and Ag–Pb–Bi tellurides are common accessories. Gangue minerals comprise amphiboles of actinolite and actinolitic
hornblende composition, talc, and chlorite. The ores at Derhib and Abu Gurdi are Cu–Zn and Zn-dominated, respectively. The
distinct geological, petrographical, and geochemical differences between sulfide mineralizations at Helgate–Maaqal on one
hand and Derhib and Abu Gurdi on the other hand suggest two genetic types of sulfide mineralizations; Helgate–Maaqal prospects
(type 1) are similar to the Archean analogs from Canada (Noranda type), while Derhib and Abu Gurdi (type 2) show similarity
to ophiolite-associated deposits similar to those described from Cyprus, Oman, and Finland. In genetic type 1, ore minerals
were deposited on the seafloor; the role of postdepositional hydrothermal activity is limited. In genetic type 2, base metals
were part of the ultramafic rocks and were later redistributed and mobilized during deformation to be deposited along shear
zones. The dominance and diversity of tellurides in genetic type 2 highlight the role of metamorphic–hydrothermal fluids. |
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