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Neoproterozoic orogenic vein-type gold mineralization is common in the crystalline basement rocks of the Eastern Desert of Egypt, which constitute the northern tip of the Nubian Shield. This chapter delineates the textural and compositional features of different sulfide phases and visible gold in mineralized veins and related alteration zones as well as fresh country rocks from 18 gold deposits located in the Eastern Desert. These data contribute to deciphering the origin of vein-type gold mineralization in the northern tip of the Nubian Shield. Field, careful petrographic investigations, and electron probe microanalysis revealed that gold mineralization has resulted from the circulation of H2O- and CO2-rich fluids related to post-peak metamorphic hydrothermal activity. Sulfide minerals and gold in the investigated mineralizations occur in various generations, constituting variable assemblages with distinct mineral parageneses. Three stages of mineralization have been identified namely; pre-hydrothermal, hydrothermal, and post-hydrothermal. The hydrothermal sulfide phases comprise many generations of pyrite, arsenopyrite, marcasite, pyrrhotite, chalcopyrite, sphalerite, and galena along with minor gersdorffite, tetrahedrite, and altaite. Part of these sulfides was formed as a consequence of the sulfidation of pre-existing rocks. The hydrothermal assemblages of the investigated gold deposits were found to have the main gold budget. Gold occurs in two settings; invisible and visible. The invisible gold is present as submicron and nano-size inclusions in some magmatic sulfides in the fresh rocks and the hydrothermal sulfide phases. Visible gold, on the other hand, is essentially present as tiny particles that fill the microfractures in the deformed hydrothermal sulfides particularly, pyrite and arsenopyrite as well as tiny inclusions in the deformed quartz and oxidized sulfides. Visible gold is distinguished into three generations; each is marked by Au fineness, with Au/Ag ratios decreasing from the early generation to the late-formed gold. The estimated physicochemical conditions (temperature of formation, fS2, and fO2) of gold mineralization, and the factors controlled the multi-stage sulfide deposition and gold enrichment in the investigated deposits have been used to model orogenic hydrothermal gold mineralization in the Eastern Desert.

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Multi-Stage Hydrothermal Processes at Gold Deposits in the Eastern Desert of Egypt: Insights from Petrography and Sulfide Compositions

  • 章节

  • 发表日期：

    2025年

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  • Khalil I. Khalil,
  • Ayman E. Maurice

摘要

Neoproterozoic orogenic vein-type gold mineralization is common in the crystalline basement rocks of the Eastern Desert of Egypt, which constitute the northern tip of the Nubian Shield. This chapter delineates the textural and compositional features of different sulfide phases and visible gold in mineralized veins and related alteration zones as well as fresh country rocks from 18 gold deposits located in the Eastern Desert. These data contribute to deciphering the origin of vein-type gold mineralization in the northern tip of the Nubian Shield. Field, careful petrographic investigations, and electron probe microanalysis revealed that gold mineralization has resulted from the circulation of H2O- and CO2-rich fluids related to post-peak metamorphic hydrothermal activity. Sulfide minerals and gold in the investigated mineralizations occur in various generations, constituting variable assemblages with distinct mineral parageneses. Three stages of mineralization have been identified namely; pre-hydrothermal, hydrothermal, and post-hydrothermal. The hydrothermal sulfide phases comprise many generations of pyrite, arsenopyrite, marcasite, pyrrhotite, chalcopyrite, sphalerite, and galena along with minor gersdorffite, tetrahedrite, and altaite. Part of these sulfides was formed as a consequence of the sulfidation of pre-existing rocks. The hydrothermal assemblages of the investigated gold deposits were found to have the main gold budget. Gold occurs in two settings; invisible and visible. The invisible gold is present as submicron and nano-size inclusions in some magmatic sulfides in the fresh rocks and the hydrothermal sulfide phases. Visible gold, on the other hand, is essentially present as tiny particles that fill the microfractures in the deformed hydrothermal sulfides particularly, pyrite and arsenopyrite as well as tiny inclusions in the deformed quartz and oxidized sulfides. Visible gold is distinguished into three generations; each is marked by Au fineness, with Au/Ag ratios decreasing from the early generation to the late-formed gold. The estimated physicochemical conditions (temperature of formation, fS2, and fO2) of gold mineralization, and the factors controlled the multi-stage sulfide deposition and gold enrichment in the investigated deposits have been used to model orogenic hydrothermal gold mineralization in the Eastern Desert.