Project Description and Location
Falea uranium, silver, and copper deposit (the Project or the Property) is located in Mali, West Africa in the Prefecture of Kenieba, District of Kayes.
The Property is approximately 350 km west of Bamako, the capital of Mali, and
approximately 240 km south of the city of Kayes. The nearest town is Kenieba, which is an
80 km drive north from the Property. The Project is located approximately 80 km to the east
of AREVA's Saraya East uranium deposit in Senegal and approximately 13 km along trend
from Merrex Gold Inc.’s Siribaya gold deposit.
GoviEx acquired the Property from Denison Mines Corp. (Denison) in June 2016. Denison acquired the Property following completion of the acquisition of 100% of Rockgate Capital Corp. (Rockgate) in January 2014.
The Property comprises three contiguous exploration permits, namely the Falea, Bala, and
Madini Permits. The Mineral Resources occurring within the Bodi, Central, North, and East
Zones are wholly contained within the Falea Permit.
The total surface area of the Falea Permit in terms of the Exploration Rights is approximately 7,500 ha. The Madini Permit adjoining to the east covers an area of 6,700 ha and the Bala Permit adjoining to the south covers an area of 12,500 ha.
Geology and Mineralization
Mineralization at the Property is hosted in the Neoproterozoic to Carboniferous sedimentary
sequence of the Taoudeni Basin, a shallow interior sag basin with flat to very shallow dips.
The Taoudeni Basin is located over a large portion of the West African Craton between the Reguibal Shield to the north and the Leo Shield to the south and encircles the Pan-African
Belts to the west and east. The Taoudeni Basin is underlain by the Birimian greenstones
which have been intruded by uranium-bearing Saraya granites.
The deposition of the Taoudeni Basin sedimentary sequence within the Project area was
largely controlled by north-south and east-southeast trending structures. The orientation of
the structural trends is coincident with the structural orientations within the Birimian
greenstones. A dolerite sill ranging in thickness from a few metres to more than 160 m is
present throughout most of the basin, intruding 65 m to 120 m above the Kania sandstone
and forming prominent cliffs in the area.
Most of the mineralization at Falea occurs in the flat lying Kania sandstone, which is
underlain and overlain by argillaceous units. The Kania sandstone is located near the
bottom of the Taoudeni Basin sequence. The mineralization is interpreted as an
unconformity type uranium deposit, since it is associated with the unconformity between the
Kania sandstone and the underlying Birimian greenstones.
Four main mineralized areas have been identified, the North Zone, the Central Zone, the
East Zone, and the Bodi Zone. The North, Central, and Bodi zones are further subdivided
into the North Upper and North Deep, the Central Upper and Central Deep, and the Bodi
Upper and Bodi Deep areas. The subdivisions of the Upper and Deep areas are based on
their positions relative to the cross-cutting Road Fault.
Some of the highest grade uranium mineralization occurs in the Plateau Edge Structure
(PES), a northwest trending zone of higher grade uranium-silver-copper mineralization which
extends from the southeastern flank of the North Upper Zone, past the Road Fault, to the
plateau edge and then parallel to it. Higher grade silver mineralization seems to be related to
areas where northeast trending structures intersect the PES.
Exploration and Development History
Uranium, silver, and copper mineralization at Falea was first discovered by COGEMA in the
1970s at the Central Zone. Drilling by Rockgate began in the Central Zone and progressed
northward, resulting in the discovery of the North Zone in late 2007 and the high-grade Plateau Edge Structure (PES) in late 2009.
The North Zone discovery was significant because it hosts higher uranium grades than Central Zone in addition to strong silver grades associated with native silver mineralization throughout much of the zone. The PES is a northwest-trending zone of thick, high-grade uranium-silver copper mineralization running along the northeastern margin of the North Zone. The zone hosts higher grades and thicknesses than North Zone proper and sits adjacent to the plateau edge.
From January to August 2011, 160 diamond drill holes totalling 45,691 m focused on resource definition in the North Zone and initial exploration drilling at Bala, south of Central Zone, East Zone, and Road Fault. The program resumed in October 2011 running through July 2012 and comprised 398 diamond drill holes totalling 88,350 m. Drilling continued to infill and step-out on the North Zone, and expanded north into the Bodi Zone. An additional 44 diamond drill holes were completed at the East Zone and 19 more at the Central Zone as part of an expanded resource definition program.
In October and November 2012, a total of 15,936 m was completed in 66 diamond drill holes
located in the Bodi and North Zone areas. Almost all work to date has been completed on the
The Falea deposit is interpreted as an unconformity-associated uranium
deposit, using a polymetallic egress model for the geological model. The unconformity at
Falea is between the Birimian and overlying sedimentary sequences. The egress model was
applied due to the presence of the Road Fault, which could have introduced fluids into the
Unconformity-associated deposits are high-grade concentrations of uranium that are located
at or near the unconformity between relatively undeformed quartz rich sandstone basins and
underlying metamorphic basement rocks.
The compositional spectrum of unconformity-associated uranium deposits can be described
in terms of monometallic (simple) and polymetallic (complex) end-members on the basis of
associated metals. Polymetallic deposits are typically hosted by sandstone and
conglomerate, situated within 25 m to 50 m of the basement unconformity. Polymetallic ores
are characterized by anomalous concentrations of sulphide and arsenide minerals containing
significant amounts of nickel, cobalt, lead, zinc, and molybdenum. Some deposits also
contain elevated concentrations of gold, silver, selenium, and platinum-group elements.
MINERAL PROCESSING AND METALLURGICAL TESTING
In March 2010, Rockgate commissioned SGS South Africa (Pty) Ltd (SGS) to perform
mineralogical characterization and deportment analysis of a composite sample from the
Falea Project. The Summary and Discussions and Conclusions sections of the SGS
report (SGS, 2010) focuses on the liberation characterization, flotation response and/or
leaching efficiency in general of the sample, and how this could impact the mineral
processing at Falea.
The grading analysis completed indicates that uranium, silver, sulphur, and base metals
preferentially upgrade into the finer fractions. The silver displays no up- or downgrading in
the 106 μm fraction.
The uranium-phases are dominantly U-silicates and U-oxides, both of which are readily
leachable by acid leaching. Leach tests indicated approximately 90% dissolution of
uranium after 48 hours, however, after six hours, the uranium dissolution was already at
The silver is present as native silver and silver-sulphide. Both minerals will dissolve in a
cyanide solution, however, the silver-sulphide (acanthite) dissolves at a much slower rate
than native silver. Only 77.56% of the silver was dissolved after 48 hours during the leach
testwork. The leach kinetics may be improved by employing a stronger cyanide solution, however, the presence of chalcopyrite and pyrite may increase ferricyanide
consumption. Due to the very fine-grained nature of the silver-phases, it is expected that
finer grinding (to approximately 80% -65 μm) will improve silver recoveries.
Copper is present in low concentrations (approximately 0.16%). Copper is predominantly
hosted by chalcopyrite and lesser chalcocite/covellite. A small amount of copper is also
hosted in a silver-sulphide phase. Since chalcopyrite is not acid soluble, the acid leach
recovery of copper is poor (approximately 17% after 48 hours), however, at a grind of
80% -75 μm, chalcopyrite is well liberated (>90% liberated and high middlings). Pyrite,
the main sulphide mineral, exhibits similar degrees of liberation at this grind. Therefore,
sulphide and copper recovery by flotation is expected to be high. Preliminary flotation
tests indicated approximately 95% copper recovery with a mass pull of 11%, resulting in
a copper grade of approximately 1.7%. Cleaning of this rougher concentrate to achieve
the required saleable grades appears possible.
In March 2011, the Australian Nuclear Science and Technology Organisation (ANSTO) was
appointed to complete the metallurgical testwork for the Falea Property. The following>
summary of mineralogy and metallurgical testwork commissioned by Rockgate is taken from
Rockgate’s 2013 Annual Information Form.
The Falea deposit is polymetallic, containing significant quantities of uranium, silver, and
copper. The uranium is present as an oxide (U3O8) and is leachable with either acid or
alkaline. The silver is present as either elemental or sulphide. The copper is present as both
leachable and non-leachable (refractory) forms in varying proportions.
For the current flowsheet proposed the first step would be flotation of the ore and then an alkaline leach on both the flotation concentrate and the flotation tails.
Subsequent work indicated that the most suitable process would be Alkali leach, followed by Counter Current Decantation (CCD), Ion Exchange (IX) and Sodium Diuranite (SDU). The testwork indicated an overall recovery of 90% uranium, including 99% recovery from the sulphide concentrate, using MgO as the precipitant. The precipitated uranium is recycled to the alkali circuit. Overall silver recovery of 88% has been achieved, including 97% silver recovery in the cyanide leach. Overall copper recovery of 73.5% has also been achieved, including 90% recovery from solvent extraction from the float concentrate.