Sub- level open stoping method was implemented on an experimental basis in an underground manganese mine situated in central India. The objective was to evaluate its feasibility as a routine method of mining over the conventional cut and fill stoping method. This paper presents the investigations conducted for stability assessment ofthe hang wall and the crown pillar during excavation from this experimental stope vof 22.5 m length and 33.3 m height. The manganese ore body at this mine was 13 to 20 m thick with a dip of around 75–80°. The hang wall consisted of week decomposed quartz free schist whereas the foot wall consisted of a strong quartz muscovite schist and quartzite. Multipoint Borehole Extensometers were installed to monitor the hang wall deformation during the excavation from this stope. The crown pillar stability was monitored through acoustic emission sensors. The monitoring results revealed no significant movement of hang wall rock and crown pillar. The stope was successfully excavated in around thirteen months period and remained fairly stable without any backfilling. This study had critically helped the mine management to evaluate the feasibility of sub level open stoping method in the given geo-mining conditions of this mine.
The Indian Manganese deposits are normally found as bedded sedimentary deposits associated with Gondite series. The manganese mining in India is principally done by Manganese Ore India Limited, a Government of India undertaking company. It has eight underground manganese mines all of which are situated in the central region of India. The geological formation of manganese deposits in all the mines are found to be of same age and hosted by similar rocks.
The common mineral contents are pyrolusite, psilomelane, braunite, bixbyite and mangnite. They are normally fine grained which renders the ore body weaker. The host rocks which are quartz, muscovite schist and quartzite are also not strong at all places. The ore body is steeply dipping and as such, the underground mining is not only difficult but unproductive also due to limited mechanized operations. The conditions are expected to be more severe in the coming years with gradual increase in the depth of workings.
The sub level stoping is a proven method of mining in strong rock condition where the ore body and both hanging wall and foot wall are strong enough to withstand the heavier mining practices. This method is considerably productive, safe and economical.
The cut and fill method of stoping was typically characterized with low productivity and limited mechanization at almost all underground manganese mines in India. This led to the proposal for evaluating the techno economic feasibility of sub level open stoping method on an experimental basis. The Chikla Mine, which was situated in the central region of India was selected for this experiment for its suitable rock conditions.
The cut and fill stoping method was otherwise routinely used at this