4. The study area
The Dharapani Magnesite Mine is situated about 7 km from Pithoragarh town of Uttaranchal State in India. The mining area is hilly, having high ridges and hillocks separated by valley and depression. The area comprises mainly meta-sedimentary and metamorphic rocks. The area stratigraphically belongs to the lesser Himalaya, which is considered to be young dynamic mountain chain. The thickness of rock unit is variable from 5 to 8 m. Magnesite bands occur in the form of discontinuities bands spreading over the length and breadth of the area [11]. The magnesite ore bodies are associated with dolomitic rock. The general dip of ore bodies and associated formation varies, from 20° to 60° (with local variation) is towards the North-East. Isoclinal folds and joints have been observed on the exposed face of the mine.
The deposit is being worked by opencast mining method with 7–8 benches. The 6–7 m high benches are excavated by drilling and blasting. The explosive used in mine is indomite (slurry) cartridges and blasted simultaneously in staggered pattern of drilling (Fig. 2 and Fig. 3). The mine produces approximately 30,000 t/year magnesite. The 75 blast events were monitored and recorded on different locations with the help of SINCO-6 seismograph having two transducers for PPV measurement and one additional for air blast [12]. These data sets were used for prediction, training and validation. The 10 blast events (20 data sets) further recorded were used for the estimation as well as for ANN validation with predictors.
The two villages Bhurigon and Tarigon are 300–350 m away from the blast site and always vulnerable and suspicious about the blast vibration. Mines management always received complaint from the villagers regarding blast vibration. To overcome from the difficulties, the blasts were monitored and safe charge of explosive was estimated.