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Perkoa

Burkina Faso

Main commodities: Zn Ag Ba Pb
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The massive sulphide Zn-Ag-Ba deposit is located in western Burkina Faso (12°22'N, 2°36'W), west Africa.

It is hosted by the Paleoproterozoic Birimian Supergroup of west Africa and comprises a main orebody, containing >90 percent of the reserves, with various satellite bodies, and is hosted by andesitic dykes, sills, breccias, tuffs, tuffite and dioritic to granitic dikes, structurally overlain by andesite, cumulate rich basic rocks and carbonaceous schist.

The main orebody is semitabular with dimensions of 400x450 m, with an average thickness of 10 m. The satellite orebodies have an average thickness of 4 m.

The immediate hosts are tuffaceous, and are intruded by a 2175±1 Ma quartz diorite in the structural footwall (stratigraphic hanging wall). The main orebody is subparallel to, and is on average 15 m from, the steeply dipping intrusive contact. The satellite orebodies are discontinuous but also show a preferred orientation subparallel to the intrusive contact, on average 75 m stratigraphically below the intrusion.

The massive sulphide ore is predominantly composed of Fe-rich sphalerite (30%), pyrite (25%), barite (10%), hexagonal pyrrhotite (5%), magnetite (5%), and white mica. Quartz is mainly present as host rock relics. Significant quantities of hydrothermal quartz were developed in the structural footwall of the deposit, where the main orebody is close to the quartz diorite (0.5 m away). Albite, (Ba, K) feldspar, Ba rich biotite, chlorite, tourmaline, andradite rich garnet, ilmenite, rutile, titanite, and galena are subordinate. Trace amounts of chalcopyrite, arsenopyrite, Ag rich tetrahedrite, and molybdenite are also found within the massive sulphide ore. A strongly altered quartz-microdiorite dyke containing disseminated zinc spinel + magnetite ± Fe-poor sphalerite occurs adjacent to the massive, Fe-rich sphalerite ore of one of the satellite orebodies.

The magmatic rocks in the Perkoa area have a juvenile character according to the Nd-Sm isotopic data, like most Birimian rocks, although the Perkoa basalts show the influence of a subduction component in various discrimination diagrams. Birimian basalts from other areas have geochemical signatures of MORB or oceanic, within-plate basalts. The massive sulphide ore has been metamorphosed during a regional thermal event under predominantly isotropic stress, probably 100 to 200 m.y. after the emplacement of the quartz diorite. Sphalerite and magnetite were remobilized, whereas pyrrhotite formed at the expense of pyrite. Peak metamorphic temperatures of >460°C at pressures of >1 kbar are indicated by almandine rich garnet, the presence of andradite, and geothermometers involving arsenopyrite and pyrrhotite. Due to the metamorphic modifications of the ore and host rock, however, it is not possible to establish the age relationships between the main ore forming event and granitoid intrusions. As a result, it is not known whether ore deposition took place close to a palaeo sea floor or in a subvolcanic environment (i.e., a skarn).

The estimated ore reserves are 5.7 Mt @ 18.2% Zn, 10% BaSO4, 0.06% Pb, and 26 g/t Ag (50 ppm Cu). For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2003.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Schwartz M O, Melcher F  2003 - The Perkoa Zinc Deposit, Burkina Faso: in    Econ. Geol.   v98 1463-1485


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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