Ghana

Bogoso-Prestea Mine

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Overview

Mine TypeOpen Pit & Underground
StatusActive
Commodities
  • Gold
Mining Method
  • Truck & Shovel / Loader
  • Shrinkage stoping
  • Longhole open stoping
  • Alimak
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SnapshotBogoso Prestea Mine is an established gold mining operation located within West Africa’s premier Ashanti Gold Belt. Bogoso Prestea Mine is one of the largest and most famous gold mines in Ghana.

Bogoso Prestea has been producing gold for over 100 years comprised of both open pit and underground operations.

Owners

SourceSource
CompanyInterestOwnership
Government of Ghana 10 % Indirect
Future Global Resources Bogoso Prestea Ltd. (operator) 90 % Direct
Blue International Holdings Limited 90 % Indirect
The gold producing Bogoso Prestea Mine, was acquired in October 2020 from Golden Star Resources by Blue International Holdings Limited, through its locally (Ghana) registered entity, Future Global Resources Bogoso Prestea Limited (FGRBPL).

Per the acquisition, FGRBPL owns 90% of Bogoso Prestea Mine, with the Government of Ghana holding the remaining 10% interest. Blue International Holdings Limited is a UK registered company, although its corporate operations are led out of its Accra Office which it shares with its subsidiary FGRBPL.

Contractors

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Deposit type

  • Vein / narrow vein
  • Orogenic
  • Mesothermal

Summary:

The Prestea-Bogoso area occurs at the southern termination of the Ashanti Belt, where the gold deposits, mined or under exploration, are localised principally along two steep to subvertical major crustal structures referred to as the Ashanti trend and the Akropong trend. The principal structures are graphitic shear zones and mineralised fault filled quartz veins. The Bogoso Prestea section of the Ashanti Trend shows a range of mineralisation styles associated with graphitic shear zone, which represents the principal displacement zone of a regional-scale shear zone that defines the mineral belt. These styles include laminated quartz vein deposits containing free gold, highly deformed graphitic shear zones containing disseminations of arsenopyrite as the principal gold bearing phase (e.g. Buesichem, Chujah-Dumasi and Bogoso North) and disseminations of sulphides in mafic/intermediate volcanic rocks generally found in the footwall of the main shear zone.

The Bogoso Prestea deposits can be classified as a lode gold deposits or orogenic mesothermal gold deposits, which are the most common gold systems found within Archean and Paleoproterozoic terrains. In the West African shield, orogenic gold deposits are typically underlain by geology considered to be of Eburnean age and are generally hosted by volcanosedimentary sequences. The Ashanti belt is considered prospective for orogenic mesothermal gold deposits and hosts numerous other lode gold deposits such at the Obuasi mine.

The Prestea concession lies within the southern portion of the Ashanti Greenstone Belt along the western margin of the belt. Rock assemblages from the southern area of the Ashanti Belt were formed between a period spanning from 2,080 to 2,240 Ma as illustrated in Figure 6, with the Sefwi Group being the oldest rock package and the Tarkwa sediments being the youngest. The Ashanti Belt is host to numerous gold occurrences, which are believed to be related to various stages of the Eoeburnean and Eburnean deformational events.

The geology of the Prestea concession is divided into three main litho-structural assemblages, which are fault bounded and steeply dipping to the west. This suggests that the contacts are structurally controlled and that the litho-structural assemblages are unconformable. From the eastern footwall to the western hanging wall, these packages are represented by the Tarkwaian litho-structural assemblage, the tectonic breccia assemblage, composed of sheared graphitic sediments and volcanic flows, and the last assemblage is composed of undeformed sedimentary units of the Kumasi Basin, which is located to the west of the Ashanti fault zone.

The various authors interpret the Main and West Reef structures to represent reactivated Eoeburnean reverse faults. However, there is some debate about when quartz veining, i.e., emplacement of the lode deposits, took place. Undoubtedly, there are several generations of quartz veining spawning over an extended period of time, most likely from the Eoeburnean orogeny to the end of the Eburnean reactivation. Gold within the West and Main Reefs is associated with smoky grey quartz veins which re-fracture the milky quartz veins that comprise the majority of the reef structures that are evidences of multiple fluid pulses along the major faults and most likely of Eburnean timing. To date, there has been no geochronological dating on the Prestea mineralization, but gold emplacement has been interpreted to be of syn-D3 to syn-D4 Eburnean timing.

Davis and Allibone (2004) show the Main Reef to be deformed in a variety of styles, including being affected by folding and boudinage associated with sinistral deformation and a third subordinate folding event.

The margins of the West Reef mineralized quartz vein are strongly sheared and comprise a brittleductile zone of deformation in the graphitic schists a few centimetres to up to 2 m in width on both sides of the vein at any locality. The deformation along the margins of the vein is interpreted to be due to post-mineralization deformation nucleating on the margins of the vein, which represents a strong competency contrast with the graphitic wall rocks. The kinematics of this deformation appears to be dextral. Over the length of the vein exposed on 17 L, several subsidiary shears were observed to cut through the vein which either caused the vein to be duplicated, causing local thickening of the mineralized vein over approximately 0 to 10 m, or caused extensional offsets of the vein. One 10-metre gap in the continuity of the resource on 17 L could be attributed to one of these shears. Overall however, these are relatively minor disturbances which just cause local irregularities in the vein and there should be no overall material loss.

Two distinct styles of mineralization are found on the Prestea mine site. The more extensive of the two mineralization styles are laminated fault fill quartz veins (Reef style mineralization), bound to the Main Reef fault or to the second order faults found in the Kumasi sedimentary hanging wall. The second mineralization style, which has never been mined in the past, consists of arsenopyrite rich, brecciated, and altered volcanic lenses.

Gold mineralization between Marlu and Bogoso North is restricted to a narrow graphitic fault zone located in the sedimentary hanging wall of the deposits with the footwall composed of volcanic lenses and sheared sedimentary rocks. The Bogoso North deposit consists of two splays of the main shear zones, a quartz vein dominated hanging wall splay, and a highly graphitic footwall structure. The two splays of the main shear zone at Bogoso North extend for approximately 500 m along strike and range in true width from 5 to 15 m. Gold mineralization at Bogoso North dips moderately to the northwest at 40 to 50º. The mineralisation is modelled over a 2 km strike at Bogoso North and an additional 2.7 km northwards to a depth of some 300 m. Bogoso North gold mineralization is associated with either quartz veins or graphitic cataclasites.

Quartz vein hosted gold mineralization generally is coincident with relatively high gold tenors, typically between 5 to 15 g/t Au. Vein gold is associated with abundant disseminated arsenopyrite in and around slices of graphitic mylonitic rock within the quartz veins. Although visible gold is occasionally observed in the veins at Bogoso North there are not abundant amounts of free gold as at Prestea and Ashanti. The quartz veins mark dilatant fractures, which focussed gold-bearing fluids, although gold deposition appears to have been promoted by interaction with adjacent wall rock fragments.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityUnits20222021202020192018201720162015
Gold oz  ....  Subscribe  ....  Subscribe  ....  Subscribe47,60375,087130,33189,673114,150
All production numbers are expressed as metal in doré.

Operational metrics

Metrics202120192018201720162015
Plant annual capacity  ....  Subscribe
Waste  ....  Subscribe767,106 t928,457 t3,522,451 t4,039,768 t3,603,153 t
Ore tonnes mined  ....  Subscribe646,254 t502,266 t1,494,347 t1,499,656 t1,710,916 t
Tonnes processed  ....  Subscribe719,449 t1,301,976 t1,632,979 t

Production Costs

CommodityUnits202220212020201920182017
Cash costs Gold USD 1,484 / oz   1,292 / oz   632 / oz  
All-in sustaining costs (AISC) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 1,937 / oz  

Financials

Units202220212020201920182017
Capital expenditures M USD 13   11.4   48.1  
Revenue M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe 60.9   89.9   148.1  

Heavy Mobile Equipment

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Personnel

Mine Management

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Total WorkforceYear
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Aerial view:

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