Summary:
Geologically, the Molo deposit is situated in the Bekily block, (Tolagnaro-Ampanihy high grade metamorphic province) of southern Madagascar. The Molo deposit is underlain predominantly by moderately to highly metamorphosed and sheared graphitic (biotite, chlorite and garnet-rich) quartzo-feldspathic schists and gneisses, which are variably mineralised. Near surface rocks are oxidised, and saprolitic to a depth, usually of less than 5m.
The Molo deposit occurs within the regional Ampanihy Shear Zone. The most conspicuous feature of rocks found within this shear zone is their well-developed northsouth foliation and vertical to sub-vertical nature. Martelat et al. (2000) state that this observed bulk strain pattern is clearly related to a transpressional regime during bulk horizontal shortening of heated crust, which resulted in the exhumation of lower crustal material.
The Project area is underlain by supracrustal and plutonic rocks of late Neoproterozoic age that were metamorphosed under upper amphibolite facies and deformed with upright north-northeast-trending structures. The supracrustal rocks involve migmatitic (± biotite, garnet) quartzo-feldspathic gneiss, marble, chert, quartzite, and amphibolite gneiss. The metaplutonic rocks include migmatitic (± hornblende / diopside, biotite, garnet), feldspathic gneiss of monzodioritic to syenitic composition, biotite granodiorite, and leucogranite.
Descriptions of the individual lithological units identified by the Company, which are relevant to Molo, are included below.
Amphibolitic Gneiss
Dark grey to black, mesocratic to melanocratic, medium to coarse grained, sub-equigranular to porphyroblastic amphibolitic gneiss and amphibolite. Amphibolitic gneiss forms one, or more major continuous bands in the eastern part of the permit, intercalated with quartzofeldspathic gneiss and spatially associated with marble. In the central portion of the detailed map area, amphibolitic gneiss forms local bands, or lenses intercalated with quartzofeldspathic gneiss and marble.
Meta-quartzite
White to greyish white, weakly to moderately layered and foliated, coarse to medium grained quartzite. Brecciated quartzite with isoclinally folded layering is locally associated with dark brown ferruginous gossan. Un-brecciated quartzite very locally contains narrow, concordant, and discontinuous seams of gossan.
Grey-white Chert
Mottled greyish-white, massive to brecciated, hyalocrystalline graphite-bearing chert, (or possibly siliceous rhyodacite). Grey-white chert displays evidence of polyphase brecciation, involving cm to mm scale, angular white siliceous fragments in a relatively early translucent grey siliceous (chalcedony) breccia matrix, and/or a later opaque brown ferruginous gossan breccia matrix.
Brown Fe-carbonate Chert
Tawny (yellowish) brown to reddish brown and chocolate brown, massive, hyalocrystalline opaque, graphite-bearing Fe-carbonate chert, variable biotite, and/or specularite. Brown chert, like grey-white chert, contains a small amount (=1%) of fine-grained disseminated graphite, as well as variably small amounts of fine-grained disseminated biotite and/or specularite. Brown chert represents a widespread Fe-carbonatized alteration facies of greywhite chert, and both occur within the same chert masses. Brown chert is intimately associated with brown marble and ferruginous gossan.
Ferruginous Gossan
Dark purplish brown to black, dense, massive to brecciform and quasi-layered, aphanitic to fine-grained, siliceous ferruginous gossan. The gossan is variably highly siliceous to moderately siliceous and pitted, composed in part of Fe carbonate, (siderite-ankerite), and generally contains disseminated to clustered, fine-grained specularite, biotite, and/or graphite. Siliceous ferruginous gossan occurs as:
- Breccia matrix of late-stage chert breccia and quartzite breccias.
- Concordant layers inter-calated with chert and marble and discontinuous concordant seams in quartzite discordant masses cutting regional structure in quartzo-feldspathic gneiss and marble.
- Siliceous ferruginous gossan is locally associated with cm scale patchy masses of green, opaque calc- silicate, or bright green amorphous and resinous calc-silicate mineral.
Quartz Feldspar Gneiss
Light grey to white, migmatitic, well foliated, and locally lineated, leucocratic to hololeucocratic, generally medium-grained, (to fine, or coarse grained), ubequigranular to porphyroblastic biotite- garnet Quartzo-feldspatic gneiss comprises a mixture of fundamental constituent lithologies, dependent on the relative abundance, or absence of biotite and garnet.
Feldspathic Gneiss
Pinkish grey to pink, migmatitic, foliated, medium to coarse grained, leucocratic (± hornblende / diopside, biotite, garnet) feldspathic gneiss. The feldspathic gneiss is comprised of a mixture of quartz-poor constituent lithologies.
Molo Property Geology
The Molo graphitic zone is delineated over the western, isoclinal antiform of a surficially exposed, steeply plunging (84°), antiform-synform pair consisting of graphitic schist and graphitic gneiss exposed for a strike length of over 2 km and a width of 750m.
The limbs of the Molo antiform are parallel to the regional Ampanihy shear zone, and both dips steeply to the west at 85°. Outcrop mapping and trenching on Molo has shown the surface geology to be dominated by resistant ridges of graphitic schist and graphitic gneiss, as well as abundant graphitic schist float.
Geological modelling has shown that the deposit consists of various zones of mineralised graphitic gneiss, with a barren footwall composed of garnetiferous gneiss. The host rock of the mineralised zones is graphitic gneiss.
Graphite Mineralisation on Molo
Graphite mineralisation on the Molo Project is hosted in schists, believed to originally have been mud stones, silt stones, and sand stones. Graphitic mineralisation in the Molo Project area is bimodally distributed, with low-grade and high-grade zones having carbon cut-off grades of 2% and 4% C, respectively. High-grade mineralization is associated with metamorphosed silt stones and mud stones, while low grade mineralization is associated with rocks interpreted to represent metamorphosed sand stones, which are interpreted to be more favourable hosts for large and jumbo flake graphite (Scherba et al., 2018).
The Molo graphite deposit appears to have resulted from many mineralizing events, which extended over a period of time that may range from ca. 900 to ca. 490 Ma. These include the graphitization during the emplacement of anorthosite complexes, graphitization in a high-strain regime under high pressure and high temperature granulite facies metamorphism during the collision of the Androyen domain with the Vohibory domain, graphite refining and re-crystallization believed to have taken place during East Gondwana and West Gondwana collision, and the formation of post-collisional hydrothermal vein graphite during orogenic collapse. The super-imposition of the tectono-metamorphic history of southern Madagascar on a sedimentary sequence in which the protoliths were rich in organic carbon has resulted in flake graphite mineralization with high carbon purities and large flake sizes (Scherba et al., 2018).