Geology and Genesis of Shear-Zone-Hosted Gold-Base Metals Mineralization in May Hibey in Tigray, Northern Ethiopia
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Date
2013-05-05
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Addis Ababa University
Abstract
Gold-base metal deposit at the May Hibey in northern Tigray occur within the Greenstone Belt, consists of gold intergrown with quartz and/or sulphide mineral and iron oxides in deformed and structurally complicated rocks. The gold-base metal mineralization in the area is hosted almost exclusively within a series of disconnected bands and lenses of quartz veins. These units which are hosted by sequences of metasedimentary and metavolcanic rocks including sericite quartz schist, chlorite mica schist, gossaniferous quartzite, quartz feldspathic schists, quartz porphyry and basic volcanic. Two types of ores have been observed in the field: Primary ore and oxidized ore. Mineralogicaly, the primary ore is marked by gold and sulphides (pyrite, pyrrhotite, galena, sphalerite, pyrrhotite). The oxidized ore is dominated by gold and oxides (hematite, ilmenite, limonite and goethite) facies.
The main alteration processes is represented by silicification, seritization, chloritization, epidotization and sulphidation. Sulphidation involved pyrite, pyrrhotite, galena, sphalerite and chalcopyrite.
The ore bodies occur in the form of veins, vein-lets, intervening silicified rocks, stringers and stockworks.
The mineralization is defined by a complex paragenesis of gold in association with Cu-Pb-Zn- Fe- sulphides and iron oxide minerals.
Field geological observations and laboratory analyses shows that: (1) interbanding of ores of contrasted composition within the greenstone belts, (2) presence of cross-cuttings veins, (3) variation of ore mineralization with variation in meta-volcanic-sedimentary facies, (4) metamorphism of both the ores and the host rocks, (5) intense brittle-ductile shearing along the ore zone, and (6) wall rock alteration:
Suggest that gold and base metals mineralization were deposited by reaction of hydrothermal fluids with iron oxides and sulphides in the host during deformation and metamorphism.
Three recent discoveries of VMS-type Cu-Zn-Pb-Au-Ag at Terer, Terakimiti, Adi Bladie in northern Tigray, along with the May Hibey Au and base-metals discovery, indicate good potential for base and precious metal resources in northern Tigray region.
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Meta-Sedimentary Rocks, Primary Ore, Sulphide Minerals, Oxidized Ore, Ore Minerals, Orebody, VMS