An occurrence of chrysotile asbestos in the Usushwana river valley some 10 miles west of Mbabane, has been sporadically prospected since its discovery in 1946. No fibre of economic grade has, however, been discovered but certain features concerning the genesis of this deposit are described and may prove of value in the further search for this valuable mineral.
Cross-fibre asbestos is confined to narrow mylonitized apple green serpentinite (totally serpentinized) occurring as sharply demarcated bands in dark blue-green serpentinite (partially serpentinized). As these mylonitized bands decrease in width they pass out into fractures less than an inch thick filled by verde antique, sometimes with traces of slip fibre. The widest mylonitized band located was 18 inches wide in which were up to a dozen seams of fibre of maximum width ½ in.
The features of the occurrence suggest that fault or shear action has been primarily responsible for the localization of this deposit.