Mineros, through Mineros Aluvial S.A.S., its wholly owned subsidiary, holds a 100% interest in the Nechí Alluvial Project under two types of mining titles: Recognition of Private Property (Reconocimiento de Propiedad Privada, RPP) and mining concession contracts (contrato de concesion minera).
Summary:
The Nechí Alluvial Project is situated in the alluvial valley and flood plain of the Nechí River lower basin that lies within the foothills of the Central Cordillera of the Andes Mountains.
The Nechí alluvial deposits may be classed as a Tertiary gravel plain gold placer with bordering bench or terrace deposits. The gravel plain style of placer is Mineros’ primary exploration target for dredging. Gravel plain deposits are generally characterized by well-rounded gravels, few boulders, and fine gold distributed vertically and laterally in the pay formations. Such placers are formed in low-velocity shifting stream channels in low-gradient valleys. Gold grades in the Nechí River flood plain are elevated at the mouths of creeks draining the high ground (Segovia batholith) to the east and these areas likely represented the merging of creek or river placers with the main gravel plain. In the upper reaches of the Nechí River, the goldbearing gravel plain placers likely grade into river placers.
Gold in the Nechí alluvial gold deposits consists of free grains that are predominantly No. 4 or smaller. No. 4 grains are very fine (flour or powder gold), with individual grains weighing approximately 0.02 mg. No. 2 and No. 3 gold grains are also present. In terms of grain counting, No. 4, and smaller grains account for 96% of the grains logged in drill hole sampling, however, the weight contribution of No. 3 and No. 4 grains is 86%. As determined from fire assays of bullion, the gold grains are 850 to 900 fine (85% to 90% gold), with approximately 9% silver, 1% iron, and traces of platinum. Mineros currently uses an assumption of 890 fineness for resource and reserve estimation.
Resistate heavy minerals separated from various process streams on the dredges have been studied for potential economic interest as industrial minerals (Lamus et al., 2006). Those present in Nechí River black sands have been identified as magnetite, ilmenite, titanomagnetite, zircon, monazite, and minor hematite, chromite, and rutile. The monazite is sometimes intergrown with xenotime and thorite. Ilmenite averages 49% TiO2 and has elevated Mn. Silicate gangue and other minerals are principally quartz plagioclase, chlorite, clinozoizite, hornblende, ferro-actinolite, and minor muscovite, biotite, and pyrite.