Liberia

Dugbe Project

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Overview

Mine TypeOpen Pit
StagePermitting
Commodities
  • Gold
Mining Method
  • Truck & Shovel / Loader
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SnapshotThe Dugbe Gold Project is in southern Liberia within one of the last remaining genuinely under-explored parts of the Birimian geological province which is host to the majority of West African gold deposits.

A mineral development agreement issued by the Government of Liberia for the project secures mining rights and terms for 25 years.

Owners

SourceSource
CompanyInterestOwnership
Hummingbird Resources plc 51 % Indirect
Pasofino Gold Ltd. (operator) 100 % Indirect
On December 12, 2023, Pasofino, through its wholly-owned subsidiary, consolidated its interest in the Dugbe Gold Project and currently owns 100% of the Dugbe Gold Project (prior to the issuance of the Government of Liberia's 10% carried interest).

Hummingbird Resources plc now has a controlling interest in Pasofino Gold Limited, who is the owner of the Dugbe Gold Project in Liberia.

Contractors

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Deposit type

  • Metamorphic
  • Orogenic

Summary:

Boadi (1991) determined that the pyroxene-garnet gneisses are of volcanic and volcano-sedimentary origin and that the protoliths would therefore be consistent with typical Birimian lithologies; however, this protolith assessment does not categorically exclude Archaean protoliths.

The Tuzon and Dugbe F deposits can be broadly classified as being highly metamorphosed “orogenic type” deposits. Whilst orogenic gold deposits typically exhibit strong structural controls on mineralisation and are generally hosted within veins or shear zones or zones, these are not obvious at Tuzon and Dugbe F. Orogenic deposits elsewhere within the Birimian of West Africa belong to the mesozonal class and typically have structural controls of the brittle-ductile type. It is apparent that Tuzon and Dugbe F were subject to lower crustal hypozonal conditions with higher temperature and pressure within the ductile zone.

The upper amphibolite to granulite facies gneissic host rocks and the absence of wall-rock alteration at Dugbe F and Tuzon is atypical of Birimian deposits. Alteration may have been ‘obliterated’ by the high temperature metamorphism that post-dated the gold mineralisation. High-strain fabrics, possible ‘relic’ sheared intervals and micro-shearing at a crystal-scale, may be indicative of a major shearing event which is less obvious being ductile (without brittle aspects) which affected the bulk of the rock-mass of the host and immediate country rocks. It may be that due to the high temperature and high-pressure events that the original deposit characteristics have been largely destroyed.

A more appropriate classification of the Tuzon and Dugbe F deposits may be a “granulite facies gold deposit type” (CSA, 2020). This could be considered a modifying classification, i.e. an orogenic gold deposit with later granulite facies modification. Granulite facies gold deposits are less common but are known from the Superior Province in Canada, the North China Craton and the Yilgarn and Gawler cratons in Australia.

Both Tuzon and Dugbe F are characterised by the continuity of the mineralised zone and at Dugbe F this resembles a stratiform layer although this form could be due to extreme structural transposition. Mineralogical investigations conducted by SRK (Brough and Bowell, 2013) suggest that the Tuzon deposit in its current form resulted from the deformation, metamorphism and remobilisation of a pre-existing gold deposit which is consistent with the view that it may have been orogenic originally and with quite different characteristics.

The Dugbe F deposit has a surface footprint of approximately 3,400m x 1,500m and has a long axis with orientation 020°. The deposit is hosted by a single layer with overall gentle (5 –20°) south- east dip which crops out or sub-crops along its north-western ‘up-dip’ edge. The layer is undulating and to date two large isoclinal or near-isoclinal recumbent folds have been identified from drillcore interpretation, one in the north-east of the deposit and one in the south-east. They cause thickening and repetition of the mineralised layer.

The mineralised zone has a stratiform geometry. The host-rock is sulphide-bearing orthopyroxene gneiss (OSG), which is essentially the upper part of a thick orthopyroxene gneiss unit mostly without sulphide which is referred to as the footwall gneisses. The mineralised layer is typically close to the contact with the overlying orthopyroxene-garnet gneiss and feldspar-biotite gneiss units. A sub-concordant granite sheet occurs 20m – 80m above the mineralised layer over the south and east part of the deposit.

Where not folded, the mineralised zone has a thickness ranging from less than 1m up to 20m, with an average of 10 - 12m, and it thickens and thins, both along strike and down dip. The mineralised layer has good geological continuity, typically only interrupted where cut by younger pegmatites and rare structures. The pegmatites are abundant ranging from centimetres to tens of metres thick; some cut out the mineralised layer completely. A single steeply dipping ±10m thick dolerite sheet cuts the deposit from south to north approximately midway along the deposit extent.

The Tuzon deposit has a length of 1,800m and an average strike of 030°. Mineralised drillhole intersections extend a further 375m to the SW. The mineralised footprint is typically over 150m and up to 375m wide. The deposit outcrops at surface over most of the strike length of the deposit and the deepest part of the current MRE is approximately 390m below surface.

The rock types and their sequence are the same as those at the Dugbe F deposit. The host rock is orthopyroxene-sulphide gneiss (OSG). This is essentially the upper part of the footwall gneisses which is a thick series of OXG with lesser OSG intervals. Above the host rock are orthopyroxene- garnet gneiss (OGG) and feldspar-biotite gneiss (FBG) units (Figure 7-8) which are referred to as the hangingwall gneisses. Due to folding at Tuzon the sequence may be overturned depending on position on the fold structure. Narrow layers of OGG may be found within the mineralised layer but are generally low grade or barren.

The overall form of the Tuzon deposit is that of a SW plunging refolded synform. The average plunge over the length of the deposit is approximately 12°. There is a distinct flexure in the strike of the deposit approximately mid-way position; the northern half of the deposit has an orientation of 18° and the southern half, 38°.

Most of the work to date has focused on the Tuzon deposit and the following description is based on the large amount of work completed for this deposit. The gold mineralogy at Dugbe F appears to be very similar and in SRK’s opinion Dugbe F and Tuzon represent parts of the same mineralised body which has been folded on a large scale and subsequently eroded to result in two present day mineralised deposits.

The gold mineralisation is spatially associated with elevated levels of sulphide; principally pyrrhotite and arsenopyrite. There are minor amounts of chalcopyrite. The sulphides are very finely disseminated, but can occur as coarser angular blebs, thin folded monomineralic laminae and stringers as well as remobilised coarser fracture fill. The pyrrhotite is weakly magnetic and it has been noted that mineralisation generally coincides with the higher magnetic readings. Gold is associated with elevated arsenic reflecting the association with arsenopyrite but arsenopyrite and pyrrhotite may persist below the level of gold mineralisation. An antipathetic relationship between the presence of gold and graphite has been observed (Harrison, 2014) - the sulphide zones associated with graphite generally do not carry gold. These are typically above or below the gold mineralised layer.

The mineralised zones in general appear to contain less felsic portions or neosomes (Harrison, 2014) and macroscopically the mineralisation appears to be better developed in orthopyroxene- biotite-rich or more maficrich melanosomes, whilst the neosomes are weakly mineralised or barren. The sulphide mineralisation and associated gold mineralisation is not associated with any macroscopically recognisable wall rock alteration.

Most of the gold is fine (<10µm with most <5µm). The coarsest grains tended to be located at grain boundary (junction) locations, but all the fine minerals were hosted within coarser minerals. The majority of these gold grains could be classed as lying along internal grain boundaries (grain boundaries between quartz and quartz) or lying along alteration patches within the grains. Metallurgical testwork for samples from the Dugbe F and Tuzon deposits for the FS suggest that there may be subtle differences in the gold mineralogy or textural position causing the recovery of gold being slightly lower at Dugbe F. More work is required to understand these differences.

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Comminution

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Processing

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Production

CommodityUnitsAvg. AnnualLOM
All production numbers are expressed as metal in doré.

Operational metrics

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* According to 2022 study.

Production Costs

CommodityUnitsAverage
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* According to 2022 study / presentation.

Operating Costs

Currency2022
OP mining costs ($/t milled) USD 11.5 *  
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* According to 2022 study.

Project Costs

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Processing OpEx $M USD 710
G&A costs $M USD 957
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Personnel

Mine Management

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