The paper presents process layouts for excavation of zones near pit envelope based on the analysis of findings of the ore loss study in case of open-pit mining, as well as the results of field measurements in the quarry faces in Muruntau and Myutenbai open pits. In the course of the field measurements, parameters of the quarry faces at Muruntau and Myutenbai open pits were determined under the following working conditions of an excavator: at full bench with shotpile height of 19–21 m; at full bench with shotpile height of 12–14 m at excavation of the “blast cap”; at heading face and taking ramp material. In all the above-listed quarry faces, the slope angles and the ore mass shotpile height when excavating were measured. Besides, the used excavator type (dragline or hydraulic) was taken into account. For each face, 2–3 measurements were performed, and the average slope angle at the ore mass excavation was determined for each type of excavator. At the next stage of the field measurements, the bench height in the rock mass and the shotpile parameters were measured before and after blasting operations under the following arrangements for preparing the rock mass for excavation: a) under normal conditions, when the ore mass blasting is performed for the selected face or relieving wall of the required thickness; b) in compression with a “blast cap” formation; c) in the marginal parts of the bench. Based on the results of the actual bench height and the blasted rock shotpile parameter field measurements, the following conclusions were drawn: a) the actual slope angles of the quarry faces were 49° when excavating the “blast cap” using dragline excavators, and 53° when excavating the ore mass at full bench regardless of the excavator type used; the slope angles of 49° for the dragline excavator and 53° for the hydraulic excavators were taken for further calculations; b) the width of the marginal (near-envelope) zone, where losses and dilution of balance ore are generated, increased from 7 to 13.0 m (at 49°) and from 7 to 11.3 m (at 53°); as a result, the areas of loss and dilution triangles have increased; c) when blasting in compression conditions, in the upper part of the shotpile, intense mixing of the involved rock and all ore grades occurs, therefore, when excavating the “blast cap”, bulk ore mass mining is only possible. The lower part of the blasted bench preserves the geological structure of the rock mass to a greater degree and can be selectively excavated with separation of the ore mass by grade; d) when blasting the rock mass, to maintain the required pulse direction and the blasting sequence, barren boreholes are included in the breaking outline, which increase the balance ore dilution, and structural dilution arises, which should be taken into account when drawing up the "Methods for determining, limitation and accounting for ore losses and dilution in the course of the Muruntau and Myutenbai (the fifth stage) open-pit mining"; e) when compiling the "Methods ...", the option of dividing a bench of 15 m high into two sub-benches of 7.5 m should be considered.
Open Pit Mining