Sulfide. Mineralization In The Lega Dembi Primary Gold Deposit Sidamo Southern Ethiopia

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Sulfides in the LDPGD are found in small quantity. The deposit is a lowsulfide-rngold quartz deposit which specifically belongs to the pyrite-arsenopyrite-galenarnassemblage type of "Volcanic precious metals tellurides association" which is typicalrnof volcanic to subvolcanic settings. It is hosted in volcano sedimentary successionrnmetamorphosed to greenschist to lower amphibolite facies. It spatially coincides withrnthe nearly N-S trending shear zone restricted to its hanging wall. Types and detailsrnof features of the enclosing rocks are ·discussed. Structures dominating in the arearnand their possible relation to the mineralizing process are described.rnThe ore zone and ore accommodating structures (fractures, veins, lenses,rnstringers and stockworks) are localized to the shear zone and generally trendsrnparallel to major and minor structures in the area. The mineralization seems to bernhighly influenced by structures than lithology and other physico-chemical factors.rnPeculiarities related to the ore zone and ore bodies are elaborated.rnExtensive metasomatic alterations are developed in the enclosing rocks. Theirrntypes, disposition and relations to the mineralized zone and mineralization processrnare explained.rnDifferent ore minerals sulfides, sulfosalts, tellurides, tungestate and gold arernidentified. Their structure, texture, parageneses and zonal arrangement (especiallyrnthe vertical one) are treated oased on field and laboratory (using polished sections)rnstudies.rnSince sulfides are scarcely encountered, the treatment of geochemical data ofrnsulfide forming metals was critical. This study was employed to systematically explainrnthe nature of distribution of the sulfides. The most important sulfide formingrnelements (Pb, Zn, Cu, Ag, As, Sb, Mo, Co, Ni), their distribution (which canrnreasonably be explained by the presence or absence of their sulfides or sulfides ofrnother metals which can host them) in relation to different lithologies andrnenvironments, their association in different environments and lithologies and theirrnzonal arrangement along dip, strike and across the strike of the ore zone arernexplained. The distribution of the elements in relation to the distribution of the sulfides, the significance of each element as a tracer or best associate of gold arerngiven. TIle details about spatial distribution and character of gold and sulfide richrnzones are treated in this work.rnThe mineralization is believed to be the result of regional metamorphismrnfurnishing hydrothermal fluids which resulted in extensive metasomatic alterationsrnand subsequent emigration, remobilization and redeposition of metals in the form ofrntheir sulfides. The reprecipitation was facilitated by the formation of low poT regimernwithin and around dilatant zones created by movements along the eastern shear zone.rnRecommendations as what is to be done concerning further studies on therndeposit and possible prospecting guides for gold in Adola area are suggested.

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Sulfide. Mineralization In The Lega Dembi Primary Gold Deposit Sidamo Southern Ethiopia

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