Geotechnical Investigations - A Tool for Deciding Mining Method for Chromite Deposits in Odisha State, India

Abstract

The Chromite deposits of Sukinda valley, Odisha, India are of strategic importance for the development of ferro-alloy industries. Around 90% of the India’s chromite ore production derived from two important chromite bearing belts, namely the Baula-Nuasahi belt and Sukinda valley ultramafic complex deposit. In terms of rock strength properties, the host rocks and ore body at Baula – Nuasahi chromite belt are hard and compact, with some structural defects such as joints, faults and dykes. After extracting the chromite ore by surface mining up to the economic pit bottom, the remaining reserves were being mined by underground method. In the Sukinda valley chromite deposits, both the wall rocks and ore body are weak, highly weathered. These mines were operated by opencast method. As most of the working mines in Sukinda valley reached their economic pit limit and there is no further scope to extract the ore by opencast mining. Since the chromite ore bodies are having considerable mineable strike length, width, and depth persistence, there is no option except to convert them into underground mines to increase the life of the mines. The chromite ore bodies were proved up to depth of 270m by exploratory drilling. Some major mining companies are planning for underground mining operations, due to constraint of limited space available for waste dumping, working with common lease boundary, slope instability, high volume of stripping ratio. To overcome such problems, the basic step is to conduct the detailed geo-technical investigations to avoid any unexpected consequences during mine development and stoping operations. The geo-technical investigations comprised of geotechnical mapping of existing mined out benches using scan line surveys, geo-technical drilling and logging of cores for the estimation of RQD, structural discontinuities, testing of cores for material properties followed by performing numerical modeling to evolve a suitable stoping method and excavation geometry. The paper deals with the results of the geo-technical investigations carried out for the planning and design of underground mine workings, design of stope parameters based on the geo-mining conditions.