GEOLOGY OF SOLID ROCK - PLOT 303 & 304
Most of the plots are covered by thick eluvial and colluvial material. The A-horizon is up to 1.3m, whilst the laterite B-horizon can be up to 12m thick. The solid geology is exposed in the main pit in Plot 304 (grid reference 626840 8557491, UTM coordinates). Several pits in both 303 and 304, have exposed talc-chlorite-magnetite+haemalite schist, mica schist, tourmaline veinlets and phlogopite-biotite schist band of the Muva Supergroup. The mica schist is generally reddish-yellow medium grained and composed of quartz and muscovite. In Plot 304 the TCMS bands overlain by 3m thick phlogopite schist. However, the adjacent plots 260, 254 and 253 (Fig. 1b) have geological information that can be used for inference and correlation. Talc-chlorite-magnetite schist, quartz-schorl veins and phlogopite-biotite schist have been exposed in the plots on the southern side. Greenish fractured beryl/emerald crystals are sometimes found embedded in the clear quartz-schorl rock. The stratigraphy in plots 303 & 304 have laterite at the top being underlain by mica schist. The mica schist is underlain by biotite-phlogopite schist (cover) which is in contact with talc-chlorite-magnetite schist. The sequence is complete at about 35m depth.
Quartz-black tourmaline (schorl) veins occur in the plot and are exposed in the main pit and at grid reference 3 626960 8557473, 6268788 8557604, 626759 8557402. The veins in the main pit are thin. The quartz in the veins reddish brown due to iron oxide staining. The emerald mineralisation is always associated with these quartz-schorl veins. The emeralds occur at the contact between the talc-chlorite-magnetite schist and the veins. The veins are zones with border zones comprising banded quartz-schorl (tourmalinite) and core zones of quartz. The border zones can comprise up to 80% schorl.
Emerald mineralisation has been found in the main pit of Plot 304. The emerald is associated with NNE-N-trendi quartz-tourmaline, tourmalinite and quartz veins intruding greenish-grey talc-chlorite-magnetite-tremolite schist. The schist is soft and green with spots of biotite and quartz. Biotite also defines shear zones. The emerald is found in quartz-tourmaline (schorl) veins and at the biotite-phlogopite-rich contacts (Njamu and Sakungo, in press; Sliwa and Nguluwe, 1984). It has been noticed that steep veins are usually barren or host low quality beryl, with shallow-dipping veins are associated with good quality emeralds. The veins have intruded into shear zones, which are now biotite-phlogopite-rich due to the alteration of the original amphibolite rocks. The main TCMS band trends roughly east-west and are displaced by faults or gently folded.
There presence of quartz-tourmaline (schorl or 'firestone') and quartz-muscovite veins and TCMS indicates that the plot has high emerald potential. So far, the main pit has been opened-up. The availability of gem-quality emerald is very high and real.