The Bibiani Gold Mine project is managed and operated by Asante Gold Bibiani Ltd. (formerly Mensin Gold Bibiani Ltd.), a Ghanaian subsidiary of Asante Gold Corporation. The Government of Ghana holds a 10% free carried interest in the Bibiani Mine.
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Summary:
The gold deposits at Bibiani are structurally controlled mesothermal lode-type deposits. The mineralisation is associated with quartz veins and quartz stockworks which are hosted within a sequence of Lower Birimian fine to medium grained turbiditic sandstones. The sedimentary turbidite sequence is tightly folded, with west-dipping axial planes and localised development of steep west-northwest dipping shear zones which have acted as conduits for the initial gold mineralisation. Gold is closely associated with arsenopyrite and pyrite. Sericite alteration is also commonly observed, both along mineralised structures, and associated with the felsic intrusives. High-grade veins often occur within graphitic shales which generally contain significant sedimentary/metamorphic pyrite.
The Bibiani Project consists of a multi-deposit complex with essentially three mineralised deposits making up the updated Mineral Resources. The MGBL assets are primarily made up of the Bibiani Main Pit, historically a surface and underground mine, with numerous satellite pits along strike to the northeast and southwest along the Bibiani Shear Zone.
Satellite mineralised deposits situated on the same geological structure include South Hill, Russell (south of Main Pit), Big Mug, Little Mug, Pamunu South, Pamunu North and on identified geological splays off the main structure to the northeast includes Walsh, Strauss South, Strauss, Ahiman, and Grasshopper. The adjacent Walsh and Strauss Pits have been exploited previously as open pit operations and were further exploited by Asante within the last two years.
The license area is interpreted to be underlain by volcanic/volcaniclastic/sedimentary rocks related to the transition zone between the lower and upper Birimian Supergroup. In the southern part of the license the rocks strike about 20º to 30º E and dip steeply to the southeast. Further to the north the strike changes to between 40ºE and 50ºE.
Underground and surface mapping has shown that the mineralisation is bounded by a series of faults-vein breccia lodes of varying size and gold mineralisation grades. The mapping indicates that there are several cross faults that offset the stratigraphy, but there is no clear indication that there is a relationship between these faults and the gold mineralisation. The trend of the Bibiani mineralised deposit appears to continue northwards to the Pamunu River, some 2km to the north of the Bibiani Mine. A parallel splay from the Bibiani trend continues up to the Bibiani North mineralised deposit, which centres about 1km to the north of the Bibiani Mining Lease.
Bibiani Main, Big Mug & South Hill
The Bibiani Main Zone within the open pit and the underground zone is mineralised over a strike length of approximately 2km. At the centre of the mine the deposit strikes 030° to 035° which changes to around 020° at the northern end of the mine. In general, the mineral deposit dips east at 60° to 80°, crossing the regional structural fabric at acute angles.
Wall rocks adjacent to the quartz veining demonstrate fine-grained disseminated iron-carbonate and sericite alteration with associated sulphide mineralisation. These alteration haloes can also contain gold values up to 2g/t Au. Some prominent structures measured in the pit walls and berms of the Main Pit include faults, quartz veins, intrusives, dykes, cleavage planes and bedding planes. These structures have significant control on gold mineralization in Bibiani especially extensional faults that serve as conduit for fluid flow and subsequent mineral deposition.
Big Mug mineralized deposit is located directly north of the Main Pit, underlain by Birimian metasedimentary rocks in the eastern part and by intercalated metasedimentary and metavolcanic rocks in the western part of the Mining Lease area. Big Mug however does not have the tonalite intrusive at the east of the main pit but rather a less continuous dacite dyke that pre-dates the main deformation (as evidenced by a pervasive cleavage absent from the tonalite).
South Hill mineralization located directly south of Main pit, is part of the main Bibiani mineralization trend striking around 450 NE and dipping moderately to the SE. The geology includes the Birimian metasediment intruded by granitoids located east of the main lode. Both lithologies appear to be intruded by quartz veins. High grade gold mineralization is concentrated in strongly foliated and silicified metasediment (breccia) located west of the granitoid. Low grade mineralization, on the other hand, is concentrated locally at zones where quartz veins intercept the granitoid thereby creating dilation zones for gold mineralization. Mineral alterations within these rocks include carbon, sericite, silica and sulphides (mainly pyrite). The mineralized zone exhibits strong shearing and brecciation with abundant quartz veining and increased carbon concentrations which may have structurally contributed to the ore deposition by aiding deformation within the fluid corridor.
Walsh and Strauss
Located immediately east of the Bibiani Main Pit are the Walsh and Strauss satellite pits which have been completely depleted.
Russell
Mineralisation at Russell is hosted in shear zones filled with massive to laminated, stockwork style quartz-ankerite veins with pyrite (+/- arsenopyrite) that crosscut folded metasediments and granitoids. The quartz is affected by pressure dissolution stylolites and grey/black pressure shadows form after the quartz. Subsequently the deposit consists of multiple ore shoots along the strike, similar in characteristics to the Main Pit mineralisation. The footprint of identified mineralisation is about 650m with an average grade of 1.7g/t over a width of circa 8m.
Grasshopper and Aheman
The Grasshopper satellite deposit is situated about 0.8km north of the Aheman pit and less than 2km from the Bibiani Processing Plant. Quartz veins are prevalent and are mostly deformed into boudins along foliations. Although the quartz veins mapped have varied orientation, the majority strike NNE and dip NSE. The veins are sometimes massive forming stockworks within the metasediments. Gold mineralization is hosted in deformed metasediments and quartz veins exhibiting some cataclasis, shearing and mostly bounded by well-defined footwall and hanging structures.
A starter pit at Grasshopper commenced in Q2 2023. In November 2023 Asante issued a News Release regarding the identified resource extension of the historically mined Grasshopper Pit. The constrained Indicated Resource of 1.88Mt @ 1.04g/t for 56.5koz of contained gold within an optimal pit shell of $1,850/oz gold price was reported. The MRE for Grasshopper is supported by approximately 1,000m of historical drilling and 8,800m of recent drilling. Further drilling is planned to grow the mineral resources beyond the current pit shell.
Elizabeth Hill
The Elizabeth Hill mineralised deposit has an investigated strike length of approximately 1km and lies on a splay structure between the current Walsh Pit and Main Pit. Mineralisation is hosted along the contact between metasediments and granitoids. Mineralisation is also associated with quartz rich veins within the metasediments and granitoids.