The licence area, together with the entire northsouth-trending Yanfolila corridor (that stretches from Guinea in the south to Selendougou in the north), was explored by BHP between 1992 and 1997 and subsequently by Randgold. The latter company relinquished the properties in the mid-2000.
The area is covered by a regional soil survey, completed by BHP in 1993-94. Most of the gold occurrences are concentrated within the eastern sector of licence area which corresponds to the highest potassium anomalies.
In 2002, a regional airborne radiometric survey was undertaken by Fugro Airborne Surveys over the Yanfolila area which included the Sindo licence. On 7 October 2004, SODOFI obtained an Authorisation d'Exploration for the area, and produced a compilation report on all the available geophysical, geochemical and geological data summarised above, together with some additional soil sampling.
There appears to have been no major gold production from the area. However, significant artisanal workings are present within the property boundaries. To the east of Sindo village, a northeast-southwest trending ridge is currently being exploited by local artisanal miners. The operations involved constitute by far the largest artisanal gold mining activities that have observed in any of the licence areas held by Medoro in Mali.
The Sindo licence area is located within the Bougouni region of the West African craton, where generally north-south trending belts of Birimian metavolcano-sedimentary and metasedimentary rocks and orogenic granitoids of Early Proterozoic age crop out. The published geological mapping of the area indicates that the licence area encompasses Birimian metasediments, including quartzitic schists and metagreywackes in the eastern and western parts of the property, all with roughly northeast-southwest strikes. A large body of granodiorite is present in the centre of the licence area and some basic igneous rocks are present in the far northwestern corner of the property, near the banks of the Sankarani Lake. The area is traversed by a series of northeast-southwest and north-northeast-south-southwest trending structures relating to the D2 and D3 transcurrent deformations. There is very little outcrop in the region, with the area covered by thick lateritic weathering profiles. Rock fragments of metapelite and quartzite with hematite staining within the material were observed being recovered from the artisanal workings on the prominent ridge in the eastern part of the licence area, to the northeast of Sindo village.
In the artisinal workings east of Sindo village, the pits reach depths of up to 15 metres. The excavations intersect a typical lateritic profile of ferricrete, red, oxidised clay, mottled clay and saprock present above metapelitic rock (from which the saprock is derived), and a white, sugary quartzite with some black hematite. According to the local miners, the best grades occur between 4 and 12 metres depth, with the quartzite being particularly auriferous. The red oxidised clay was also apparently gold-bearing, with the observed washings being undertaken on this in addition to the quartzite gravel. At the base of the western side of the ridge, a small settlement is present where the gold is traded. There was evidence in some of the gold observed that at least some of it is associated with the hematite found within the white quartzite. The mineralisation contained within the rocks that make up the ridge is therefore primary in nature and not elluvial or alluvial. However, some of the occurrences at the base of the ridge on the eastern side near the river are most likely elluvial. Most of the known gold occurrences in the area are concentrated within the eastern sector of licence which corresponds to the highest potassium anomalies. They also appear to be associated with the contacts between the felsic and the mafic volcano-sediments and between the syn-tectonic granitoids and the meta-greywacke. In addition, the most prominent soil anomalies are also present in areas with high potassium anomalies.
Exploration activity within the past 20 years includes regional soil sampling by BHP and airborne geophysics and radiometrics surveys. Medoro's current joint venture partner SODOFI undertook a limited additional soil sampling program, which involved a series of 13 traverses perpendicularly across a northeast-southwest trending belt of orpillage pits in the eastern part of the licence area. Gold values of up to 500 parts per billion (ppb) corresponded well to the northeast-southwest trend and also correlated well with antimony and bismuth, and to a lesser extent arsenic and silver.
Presently, the Sindo licence is bordered by Research Permits held by Glencar Mining Plc, with the Sanoumalé licence area directly to the north, which covers the town of Siekorole, the Solona licence to the south, and the Komana licence to the south west. At the Komana licence, Glencar has released drill results that include a 1 metres intercept at 733 grams per tonne (g/t) and 17 metres at 2.99 g/t. At Solana, into which the northeast-southwest structures in the eastern part of Sindo run, Glencar has announced gold mineralisation in 8 of 13 holes drilled with the best intersections reportedly containing 8 metres at 2.62 g/t and 2 metres at 25.2 g/t.
The Sindo licence area is located on typical West African cratonic terrane of Brimian metasediments with granitoid intrusions. The geophysical data reveals the general structural and lithological trend across the whole licence area to be northeast-southwest striking. Most of the known gold occurrences within the area are present in the eastern sector of the licence and correspond with high potassium anomalies along these northeast-southwest trends. The anomalies are likely to be related to sericite alteration along the tectonic contact between the metagreywackes and metapelites and volcanics. In terms of current artisanal mining activity, Sindo is by far the most active of all the licence properties within the portfolio. The volume of activity in the area to the immediate east of Sindo village constitutes a primary target. Based on information from the miners, plus evidence of the association of the gold being traded, primary gold mineralisation appears to be hosted within a hematite-bearing quartzite along the ridge. In addition, the clay zone appears to be gold bearing, with further elluvial deposits on the eastern foot of the ridge, on the banks of a branch of the Sankarani Lake. Gold was observed being washed from both the quartzite gravel material and the red clay. The ridge to the east of Sindo village represents a justified drill target for primary gold mineralisation. A second target area occurs at a structural intersection in the southwestern corner of the licence. The area is associated with high potassium anomalies and has similar lithologies and structures to the Siekorolé target of Glencar, 6 km north-eastward along the same strike. The soil geochemistry in this area appears barren. However, this may be due to gold mineralisation, if present, being hosted by a conjugate fault system subordinate to the main north-northeast regional trend, and thus easily missed by the wide-spacing eastwest soil lines if oriented more parallel to them. A further target may be located to the north of this, where some high soil anomalies are coincident with high potassium anomalies. The Sindo licence area is considered to be highly prospective for gold mineralisation and deserves further exploration for the following reasons:
- the presence of large-scale artisanal mining with proven gold production;
- known gold occurrences along favourable geological structures; and
- good access to the site from the town of Yanfolila (20 km to east), with water sources within the licence boundary (Lake Sankarani).