g in africa exploring west africas birimiandec , · to date, the most productive gbearing zone within the birimian greenstone belts has been the ashanti belt in ghana. the ashanti belt has been"early proterozoic birimian g mineralization of themesothermal g ores of the bogosu and prestea concessions of southwestern ghana are hosted by birimian (2.1 ga) carbonaceous sedimentary rocks. g mineralization is postpeak metamorphism, and occurs within dilatant zones of the ashanti structural belt. host sedimentary and mafic lithologies have been altered to an assemblage containing abundant ankerite, siderite and sericite.;deeperg mineralization in the ashanti belt of ghana; geneticthe ashanti belt of ghana is the key district of g mineralization in the paleoproterozoic terrane of west africa. the area considered in southwest ghana is covered by lithologies of the volcanicsedimentary birimian supergroup and the overlying clastic sedimentary tarkwaian group which were jointly fed and metamorphosed under greenschist facies conditions during the eburneangeology and geochemical patterns of the birimian gapr 01, 93· abstract. a major g province of the world exists in the proterozoic birimian and tarkwaian supracrustal rocks of west africa. the bulk of the g comes from the primary lode occurrences of the birimian rocks of ghana (formerly the g coast). birimian lithofacies is characterised by subaqueous finegrained sediments with bimodal volcanic material.cited by 30metallotectic context of the mineralization of the tondabothe g mineralization of the tondabo prospect, located in the northern part of the oumétoumodifettêkro greenstone belt, is mainly hosted in the rhyodacite and to a lesser extent in the mafic volcanics (volcanic lavas and volcanoclastites). these rocks were affected by a hydrothermal alteration marked by quartz veins and veinlets associated with crystals of carbonates, sericite, epidoteore mineralogy and mineral chemistry of the ashanti gg deposits have been proposed (kerrich and fryer, 79; boyle, 84; burrows et al., 86; groves and phillips, 87). the g deposit of the ashanti mine, located at obuasi in the central part of ghana, is a gquartz vein and sulfide disseminated type in the birimian group, a lower proterozoic greenstone formation. the depositthe early proterozoic birimian supergroup of ghana andjan 01, 90· it seems that in the birimian of ghana, structure is of importance as a local ore control (i.e. on the mine scale), whereas lithofacies (chemical sediments) controls g regionally and to a lesser degree locally. g in the birimian of ghana occurs as two major types the disseminatedsulphide type (dst) and the quartzvein type (qvt).cited by 480birimian overviewmining operationslocationoriginssee also
g mining has been an important part of the economies of ghana and mali for centuries. in ghana, over 90 percent of output originates from underground mines in the ashanti region of the country. the privatized ashanti gfields corporation, formed in 93 with investment from lonrho and now owned by anglog ashanti, controls most production and generally uses environmentally acceptable processes. however, there are many smallscale miners using techniques causing environmental damage such as · text under ccbysa license
evidence for two stages of mineralization in west africasmineralization, the gbearing quartz veins and auriferous disseminated sulfide ores, can be explained by the system of the g mineralization. timing of mineralization is critical simplified birimian geology of ghana with alternating greenstone belts and sedimentary basins. obuasi is located inrelationship between g and manganese mineralizationsrelationship between g and manganese mineralizations in the birimian of ghana, west africa volume 1 issue 5. studies on the distribution of manganesebearing rocks in the birimian and their relationship with g mineralization are still in progress. both manganese and g occur as stratabound lenses within volcanosedimentary sequence.major mines projects obuasi mineg mineralisation is associated with, and occurs within, graphitechloritesericite fault zones. these shear zones are commonly associated with pervasive silica, carbonate and sulphide hydrothermal alteration and occur in tightlyfed lower birimian schists, phyllites metagreywackes, and tuffs, along the eastern limb of the kumasi anticlinorium.namdini g deposit, upper east region, ghanafigure 1 regional geology of northern ghana and the location of the namdini g project . deposit model the namdini g deposit has many characteristics typical of mesothermal birimian g deposits in west africa (gfarb et al, ) (figure 2). g mineralisation istaruga g west africa gg mineralisation in the majority of the birimian of west africa is found in three principal settings the typical mesothermal lode g deposits, typified by obuasi and bibiana (ghana) is the most significant of these deposit styles and are generally closely related to major structures at the upper and lower birimian contact. a review of the birimian supergroup and tarkwaianthe majority of the g mineralisation is believed to have formed between approximately 2. and 2.06 ga during the eburnean orogeny. the mesothermal quartz vein g mineralisation is usually...estimated reading time minsg mineralization in the ashanti belt of ghana; geneticthe ashanti belt of ghana is the key district of g mineralization in the paleoproterozoic terrane of west africa. the area considered in southwest ghana is covered by lithologies of the volcanicsedimentary birimian supergroup and the overlying clastic sedimentary tarkwaian group which were jointly fed and metamorphosed under greenschist facies conditions during the eburneancited by 92timing and structural controls on g mineralization atmanu, j., 91, fluid inclusions in quartz veins in the birimian g deposits. of ghana fractures and shear zones play the most important role in g mineralization in the birimian of ghanaestimated reading time 6 mins
geology of ghana g plays an important role in the economy of ghana, with up to 00 tons of g produced throughout its history.ghana has five major types of g deposits. native g in steeply dipping quartz veins in shear zones at the margins of birimian basins, arsenopyrite in sulfur bodies, disseminated mineralization in basin granitoid rocks and alluvial placer g in river deposits in gravel areg mineralization in palaeoproterozoic granitoids atdec 01, 2· these deposits represent a relatively new style of g mineralization in the ghanaian birimian. the mineralization consists of quartz veins/stockworks and pervasive alteration zones within the granitoids in brittle structures. the ore mineral assemblage is mainly composed of pyrite and arsenopyrite, with minor chalcopyrite, sphalerite, and rutile.the early proterozoic birimian supergroup of ghana andbirimian g in ghana is present as two major types (1) the disseminated sulphide type which is generally lithofacies controlled, i.e. controlled by chemical sediments, and to a lesser extent by selvages of gquartz veins; and (2) the quartz vein type which is exclusively structure controlled.cited by 480notes_geology of ghana. section 5 geology 5.6birimian, comprising chiefly metavolcanic rocks (junner 35, 40; bates, 55).these ideas were based largely on mapping by the gsd in southern ghana and are widely supported in ghana (tables 5.1 and 5.2). the rock types present in the lower birimian sedimentary belt are greywackes with turbidite features, phyllites, slates, schists, weakly metamorphosed tuffs and sandstones.geology and geochemical patterns of the birimian ga major g province of the world exists in the proterozoic birimian and tarkwaian supracrustal rocks of west africa. the bulk of the g comes from the primary lode occurrences of the birimian rocks of ghana (formerly the g coast). birimian lithofacies is characterised by subaqueous finegrained sediments with bimodal volcanic material.cited by 30kubi g mine in ghana investing in g mine asante gthis garnetiferous horizon contains fine grained g associated with minor (5%) pyrite and pyrrhotite as well as some coarser g which is associated with relatively narrow quartz veins. some mineralization occurs in quartz veins and veinlets that crosscut the birimiantarkwaiian contact, outside of the main garnetiferous horizon.evidence for two stages of mineralization in west africa'stwo economic styles of mineralization occur at obuasi and contribute equally to the g budget. these are (1) gbearing sulfides, dominantly arsenopyrite, mainly disseminated in metasedimentary rocks and (2) native g hosted in quartz veins that are as much as 25 m wide.