A review of intrusion-hosted gold systems of the Palaeoproterozoic Birimian terrane of Ghana

Intrusion-hosted gold deposits within the Birimian terrane in Ghana have become attractive targets for exploitation. However, similarities between intrusion-related gold deposits (IRGDs) and orogenic gold deposits (OGDs) generally result in misclassification of these deposits. This paper reviews the literature on gold deposits hosted in intrusions of the Birimian terrane of Ghana, and in addition applies multivariate statistics of geochemical data, to ascertain their classification. The host intrusions can be linked to the two different magmatic pulses (2179 ± 2 to 2136 ± 10 Ma) and (2125 ± 2 to 2088 ± 1 Ma) that intruded the volcanic belts and sedimentary basins, respectively. Intrusion emplacement and gold deposition in the Birimian of Ghana are products of large-scale compressional to transpressional activity, the Eburnean tectonothermal event (ca. 2.1 Ga). Mineralization within sedimentary basin-type intrusions is concomitant with intrusion emplacement, while volcanic belt-type intrusions significantly predate mineralization. Low salinity (< 10 wt % NaCl equivalent), reduced fluids with H₂O–CO₂-rich and minor methane (CH₄) and nitrogen (N₂) compositions are responsible for gold emplacement at crustal depths of 4–6 km. The trapping temperature and pressure for hydrothermal fluids usually range between 180 and 350 °C and between 1 and 3 kbar, respectively. Trace element geochemistry has revealed anomalous concentrations of granophiles in some of the deposits and consistent low base metal concentrations associated with gold. The tectonic setting of the deposits, among other factors, aligns the intrusion deposits to the OGDs. Nonetheless, after analysing the distinguishing attributes of the deposits, it cannot be disregarded that magmatic fluids play a role in the overall hydrothermal fluid budget.

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