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Sublevel caving is an underground mass mining method used for extracting different types of ores from the earth crust. Mines using sublevel caving (SLC) as the primary mining method are generally highly mechanized with standardized and independent unit operations. Mine development for caving operations are similar to other underground mining methods, however, the scale of production drilling and blasting performed in caving operations including SLC are larger than many other underground mining methods (such as room and pillar or cut and fill). Loading of the material from the production face in sublevel caving is facilitated by the flow of material under gravity into the production face. A large amount of material is loaded from a limited opening termed as the draw point. Different unit operations (drilling, blasting, loading and transportation) are performed in isolation with each other which leads to standardized procedures and safe operation. The mine design allows for operational agility with respect to ore geometry and inclination. These features give SLC an advantage over other mining methods. However, SLC demands a caving conducive geology along with a large ore footprint. The mining method also registers higher percentage of dilution and ore loss compared to non-caving mining methods. Material flow in SLC has been studied extensively in the past five decades and different methods have been used to simulate material flow in caving operations. Physical models of different scales has been designed for simulating material flow by using sand, gravel or rocks and studying the movement of material inside the model. Initial physical models showed an ellipsoidal zone above the draw point from which material flowed into the draw point. However, subsequent modelling results disagreed with this notion of material flow. Numerical modelling techniques have also been applied to simulate material flow. The models were calibrated against mine or mill production data for optimization. Currently, marker trials are being used to understand material flow in SLC. Markers (numbered steel rods, RFID enabled markers) are installed in boreholes drilled inside the burden of a production ring and based on the recovery sequence of markers, material flow is predicted. Results from physical models, numerical models and marker trials along with mine experience have been used in the past to design draw control strategy for SLC operation. Initial draw control techniques were based on the assumption of uniform flow of material. But with the advancement in modelling techniques, draw control strategies have also changed. Ore flow simulation techniques developed to simulate material flow are being applied to predict the ore grade at draw point and hence help in draw control during the loading process. Recent draw control strategies in some mines have evolved to include production data and metal prices to optimize the loading process in SLC. Monitoring of the ore grade at the draw point is crucial in controlling dilution and increasing ore recovery. Present draw point monitoring technique predicts ore grade by exploiting the differences between ore and waste. The difference between ore and waste can be detected through visual observations, assay sampling or weight measurements. Draw point monitoring gives data for both regulation and calibration of draw control strategies, and provides important information regarding dilution and ore recovery during the loading process. Understanding material flow is vital for improving different aspects of SLC operation but draw control for SLC is an operational activity which regulates the loading process for a given mine design and material flow conditions. Therefore, an effective draw control requires a constant monitoring system and a constant calibration of the loading criteria’s through draw point monitoring for reducing dilution and improving ore recovery. För godkännande; 2016; 20160829 (gurshe) |
