by Iwan Williams, Exploration Manager Ghana, Lennard Kolff, COO & Abdul-Razak Shaibu Ballah, Senior Geologist Ghana at IronRidge Resources Ltd.
Coinciding with increased interest in lithium and its application in the stored energy space, IronRidge Resources Ltd. (AIM:IRR) commenced a top-down desktop review of the Birimian terrain of West Africa, following the discovery of the Goulamina deposit in Mali. The margins of the Cape Coast batholith were considered prospective for pegmatites, further enhanced by their proximity to operational infrastructure and pro-mining jurisdiction.
Literature review highlighted that pegmatites were first recorded in the area by the Geological Survey in 1916, but it was not until the period 1963 to 1965 that the current site of the Ewoyaa discovery was recognized in mapping, trenching and bulk sampling. A further literature review provided more encouragement through the Master’s thesis by S. Amoako Mensah on the spodumene pegmatite occurrences of Saltpond.
The Ewoyaa Lithium Project (Ewoyaa) was (re)discovered by IronRidge with fieldwork commencing in January 2016. In May 2017 historical trenching over Ewoyaa was located and a discovery drill hole was announced in August 2018 – 128 m (420 ft) at 1.21% Li₂O from 3 m (9.84 ft). This lead to a JORC-compliant maiden mineral resource estimate of 14.5 Mt at 1.31% Li₂O in the inferred and indicated category, including 4.5 Mt at 1.39% Li₂O in the indicated category announced in January 2020. Thick vegetation, deep tropical weathering, localized alluvium cover, rare outcrop and the extreme mobility of lithium in this environment make exploration very challenging.
Through joint venture and application, the Company has achieved a combined lithium portfolio covering 684 km2 (264 mi2) collectively called the Cape Coast Lithium Portfolio. Exploration auger and RC drilling is currently ongoing, testing new targets in order to grow the resource base.
Western Ghana is characterized by a thick sequence of steeply dipping metasediments, alternating with metavolcanic units of the Proterozoic age (2.2-2.3 Ga). These Birimian Supergroup sequences extend for approximately 200 km (124 mi) along strike in a number of sub-parallel north-easterly trending volcano-plutonic belts and volcano-sedimentary basins. The rocks of the volcano-plutonic belts and the volcano-sedimentary basins appear to represent partly contemporaneous lateral facies equivalents, as most of the sediments appear to be derived from the adjacent volcanic belts. The Ewoyaa project sits close to the western margin of the Kibi-Winneba Volcanic Belt within the Cape Coast Basin.
The Eburnean (2.1 Ga) tectono-thermal orogenic event is responsible for the folding and metamorphism of Birimian Supergroup rocks and, at the same time, the development of high-strain zones along the Birimian belt/basin boundaries. The Birimian basins were preferentially intruded by extensive, late and syn-kinematic granitoids of the Eburnean Plutonic Suite (2116-2088 Ma) including the regionally extensive Cape Coastundifferentiated biotite granitoid pluton, the dominant geological feature of this region. The last manifestation of the Eburnean plutonism may be the pegmatite intrusions which are spatially associated with a portion of the pluton’s margin and have been dated to 2072 Ma but could be the result of metasediment anatexis.
Exploration is challenging, where outcropping pegmatite is rare in the region, due to deep tropical weathering with well-developed lateritic soil profiles and localized alluvium cover, combined with ubiquitous impenetrable dense secondary growth vegetation, thus nearly all ground exploration work requires line cutting.
All the granted tenement areas have been flown with high-resolution heliborne magnetic and radiometrics, and soil sampled on a 100 x 100 m grid (328 x 328 ft), and the resultant geophysical and geochemical data interpreted to develop exploration targets. The soil samples have all been prepped and analyzed in-house using bench-mounted PRESS, pXRF and pLIBS providing rapid results and significant cost savings. Man-portable, yet strong, powered auger rigs are used for follow-up prospecting work along hand cut traverse lines, drilling down 5-10 m (16-33 ft) through the laterite, duricrust, stone lines and saprolite to identifiable lithology. Infill auger traverses are used to delineate pegmatite targets at surface, ready for initial RC drilling on broad spaced drill fences.
The pegmatites of the Ewoyaa project predominantly intrude a host rock of biotite/mafic schist, however, the host rock can also be granodiorite or other granitoid where locally developed. Two dominant mineralized pegmatite trends have been observed at the Ewoyaa; the North-Northeast-South-Southwest en-echelon pegmatite array of the ‘Ewoyaa trend’ and the Northwest-Southeast to East-West orientated pegmatite dykes of the ‘Abonko trend’. The Ewoyaa trend pegmatites are subvertical or dip steeply to the east, while the Abonko trend pegmatites range from subvertical to dipping 45o North-East. Individual pegmatites range in thickness from less than 1 to 60 m (3 to 197 ft) and have variable strike length from 150 to 600 m (492 to 1969 ft) but with en-echelon pegmatite dyke arrays collectively extending over 1500 m (4921 ft) of strike open in many directions.
The mineralogy of the spodumene bearing pegmatites is very consistent throughout the Ewoyaa project, with predominantly albite (+/-microcline)-quartz-muscovite with accessory apatite and rare beryl and local secondary Fe-Mn-Li bearing phosphates. Mineralized pegmatite has been classified by grainsize in drill core into geo-domains, with coarse grained (>20 mm (>0.79 in)) P1 being dominant to the finer grained (<20 mm (<0.79 in)) P2. P1 type spodumene crystals in lengths of up to 80 cm (31.5 in) and 20 cm (7.87 in) in diameter have been observed at the Abonko quarry outcrops.
Mineral resource estimate
The 2019 indicated and inferred JORC (2012) compliant resource of 14.5 Mt at 1.31% Li₂O, with 4.5 Mt at 1.39% Li₂O in the indicated category (0.5% Li₂O cut-off) at the Ewoyaa, are the product of 198 RC drill holes totaling 25 574 m (83 904 ft) and eleven diamond holes for 1394.3 m (4574.48 ft) and extends over an area of 2.6 by 2.4 km (1.62 by 1.49 mi). Recent auger and RC drilling has expanded the current footprint of the spodumene mineralized pegmatite swarm to 3.6 by 2.4 km (2.24 by 1.49 mi), a footprint that continues to grow as our exploration team evaluates untested exploration targets within the combined 684 km2 (264 mi2) tenement holding with RC drilling still ongoing at the time of writing.
The Project fundamentals support a robust Scoping study with conventional open cut mining from surface with low stripping ratios and close proximity to logistics and infrastructure – only 1 km (0.62 mi) away from the highway and 110 km (68 mi) by road from the deep-sea port of Takoradi, ensuring low operating costs. Good geological continuity and excellent metallurgy result in simple processing via coarse 6.3 mm (2.48 in) crush and conventional gravity flowsheet producing a premium 6% spodumene concentrate with significant value-add potential from feldspar credits providing for low capital costs.
The Scoping study supports a business case for 2.0 million tonnes per annum production operation over an eight-year life of mine. Meaning production of an average of 295 000 tonnes per annum of 6% Li₂O spodumene concentrate with total revenues exceeding USD 1.55 billion, at a capital cost of USD 68 million with <1 year payback.
The Ewoyaa project has a post-tax net-present value (NPV8) of USD 345 million, internal rate of return of USD 125%, and operating costs of USD 247 per tonne of 6% lithium spodumene concentrate. Thus, the project has an average EBITDA of USD 105 million per annum with a significant potential to extend life of mine.
The Company demonstrates sound ESG initiatives with a strong national Ghanaian team, employment and training within the communities where we operate, environmental rehabilitation programs and hydro-electric, solar and logistic advantages providing for a potential low carbon footprint.
For more information visit: www.ironridgeresources.com.au
Read more articles from Issue #16 of Coring Magazine: