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[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]The proposed Piina concession is located at the central part of the Bole-Nangodi gold-bearing tectonic belt. The region is dominated by a relatively broad, highly dissected volcanic belt (up to about 40km wide south of Bolgatanga) which is only well exposed at the north end but mainly overlain by Volta Basin sediments towards the southwest where it joins up with the Bole Belt. The volcanic belt is flanked on both sides by massive granitoid complexes; these granitoids occur in areas where extensive basin sediments were deposited but subsequently eroded to quite deep levels now represented by the granitic terrane – considered to be mainly intrusive complexes developed during the peak Eburnean thermotectonic event (approximately 2100 Ma).
There is also a wide range of Birimian metamorphic units from mafic flows to fine-grained marine elastic sediments. The dominant volcanic units are primarily massive tholeiitic basalts with occasional examples of pillow structures. The mafic units (bvm) occur in fairly well-defined belts and bands but also contain significant interbeds of fine-grained metasediments, including persistent horizons of chemical sediments with manganese, chert, and graphitic material. Amongst the dominantly tholeiitic basalts are subordinate but nevertheless significant amounts of intermediate to felsic metavolcanic units with a calc-alkaline affinity (Sylvester and Attoh, 1992; Melcher and Stumpf], 1994). Exploration work by BHP in the central Nangodi area (BHP Report on the Nangodi concession, May 1994), outlined fairly extensive areas with volcanic breccias (agglomerates), which are presumably quite close to the original vent areas. Within the general vicinity of the town of Nangodi, the belts of primarily metavolcanic units are bounded on their eastern margins with fairly thick sequences of pyroclastic and epiclastic metasediments (bvsm).
There are also several areas in the northern part of the Nangodi belt which feature conglomerates, quartzites and cross-bedded sandstones. The coarse elastic component of the conglomerates consist mainly of phyllite and fine-grained, pink granitoids in a matrix of dark grey sandstone (greywacke). The contacts of these elastic sequences generally feature considerable shearing so that stratigraphic relationships with adjacent units are not very clear. Junner (Gold Coast Survey – Annual Report for 1935-36) originally designated the units as Tarkwaian and this was later supported by Melcher and Stumpf! (1994) who mapped parts of the belt.
Enormous variety of intrusives have been mapped within the Nangodi Belt. These fit reasonably well into the general basin-type and belt-type models well established in southern Ghana. The belt-type intrusives are generally of intermediate (granodiorite) composition but with some phases noticeably more mafic (quartz diorite to diorite); hornblende is the typical mafic mineral and the intrusions are largely devoid of roof pendants and xenoliths of countryrock. In contrast to these are the large granitoid complexes on the margins of the belt, which are also intermediate in composition but with minor felsic phases. The margins of these granitoids usually have conspicuous zones of migmatites and gneisses and, in many areas, feature extensive xenoliths and roof pendants of countryrock. In addition to these two familiar intrusive, the Nangodi Belt also features the Bongo-type intrusive. This is a distinctive pink coloured, massive alkaline granitoid occurring in two main intrusive bodies -the large northern intrusion extends from Bolgatanga northwards to the Burkina Faso border whereas the second is a much smaller plug exposed in prominent hills (up to 100m relief) immediately southwest of Tonga[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”508″ img_size=”large” alignment=”center” onclick=”link_image”][/vc_column][vc_column width=”1/2″][vc_column_text]In the regional geological map, three groups of structures can be basically seen. The first group is spread along NEE direction, i.e., primarily along the White Volta River and quartz sandstone contact zone. Topography is relatively strongly dissected along the White Volta River, which is possibly affected by the napped fault. The second group is spread nearly along NS direction, along the river. This group is napped fault. The third group is a small-scale tension fracture spread along the EW direction, which is well developed in the sandstone, schist and slate region. The auriferous quartz vein is mainly produced in this tension fracture group; it is also the main guide structure and host structure within this area.
Most of the Nangodi Belt features intense structural deformation oriented along prominent NE trending faults. The principal fault passes right through Bolgatanga and is defined by strong cataclastic effects and healed mylonites, which are recognizeable in virtually all of the airborne geophysical data. This fault (herein referred to as the Bole-Bolgatanga Fault Zone) can be traced southwards to the Bole area where it appears to correlate with the fault NW of Bole. Within fairly thick sequences of the Birimian volcanic (Bvm) and volcanic/sedimentary sequences (Bvsm) south of Nangodi, there also appears to be considerable shearing over broad areas, butmuch of it is oriented more in a N-S direction rather than the prominent NE trends seen closer to the Bolgatanga area. There are also some indications of late-stage faulting with minor dislocations and cross-cutting the main NE structural/metamorphic fabric.
Gold is the primary mineralization within the Bole-Nangodi Belt although some minor occurrences of iron ore, base metals and other minerals such as manganese and graphitic metasediments have been reported. The principal prospects and former small producers occur along a strike length of about 14km from Nangodi in the north (approximately 25km ENE of Bolgatanga) to just south of the Pelungu belt granitoid. Along this N to NNE trending zone, there is a northern clusterof deposits (Nangodi, Midas Reef, Money Palaver Reef, Strong Reef) and a second cluster (Zug, Blasted Oak, Dushe) around the SW margin of the Pelungu granitoid.[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]The northern prospects are primarily narrow quartz veins (0.5-2.Sm), often with high (commonly greater than 1 oz/t) but erratic gold values. The hostrocks in the northern cluster are primarily manganiferous phyllites that are highly sheared. The veins appear to pinch at depth {Kesse, 1985) and commonly contain pyrite, arsenopyrite and, in places, conspicuous tourmaline; most of the contained gold appears to be free-milling.
The southern cluster also features quartz veins systems but hosted by various phases/zones of the Pelungu intermediate intrusive. The Zug and Dushe deposits are narrow, steeply dipping veins whereas at Blasted Oak the veins occur in a broad, shallow dipping (to the SW) system. The mineralogy of the veins is similar to the northern deposits. The Widenaba prospect, close to the Burkina Faso border and approximately 14km NE of Nangodi, is a very similar narrow vein system in metasediment- volcanic units, close to the contact of a belt granitoid.
Approximately 6km south of the Pelungo intrusive is a broad, general flat area of metasediments and volcanics where extensive small-scale mining has been underway for several years. This area, also known as Yale, hosts many known quartz veins usually striking N·S and dipping close to 90°. The veins vary from a few centimetres wide up to about 2m. Many of the veins appear to be quite low in value but others contain considerable fine-grained free gold, commonly accompanied by pyrite. In many cases, it is reported (Aurex AB, pers. comm.1999) that veins with quite low values at surface may have significantly higher grades at depths below Sm. The metasediment/volcanic hostrocks contain some gold in areas immediately adjacent to mineralized veins. Figure above shows a plot of the regional geology of Ghana with some major mineral occurrences.[/vc_column_text][/vc_column][/vc_row]