Stages of gold mineralization in the oxidation zone in Wadi Hammad, Eastern Desert, Egypt

Three stages of gold mineralization are identified in the zone of oxidation at the contact between porphyritic andesite and granite at Wadi Hammad. The earliest started with the mobilization of silver and gold from their parent galena and redistributed them into microfractutres in quartz. This gold (electrum), is characterized by a very high Ag-content up to 38.5 wt.% and a Pb-content of 2.65 wt.%. The second stage is characterized by the formation of botryoidal goethite and plumboferrite within which very fine blebs of gold are found. This gold contains up to 15.37 wt.% Ag with Pb-content (0.35 - 1.2 wt.%). The third stage is related to carbonate facies formed after the oxides. Here, the gold is finer and shows bimodal characteristics in which the inner part is Ag-rich while the outer part is Ag-poor. These stages were developed under supergene conditions.