Open pit mining usually covers the whole boundaries. Horizontal slices with certain thickness are defined to extract ore from top to bottom until reaching the ultimate or temporary boundary and forming the ultimate or temporary slope.
The stripping method usually includes the positioning of open trench, advancing direction, and the arrangement and factors of working face. It impacts both the production technologies and economic benefits in the initial stage. Applying appropriate stripping methods to orebodies with different technical conditions can reduce the amount of capital construction, accelerate the project schedule and gain better initial economic results.
1. Determine the slice height (bench height) according to the equipment capability. The bench height is usually between 6m and 15m: the bigger the mine, the larger the value. And the bench height for medium-to-large mines is usually 10m or 12m.
2. Determine the ultimate slope angle and integrant parts of ultimate pit slope according to the rock property, geologic structure, hydrogeology and mining depth around the boundaries. The ultimate slope angle is usually between 30° and 55°: bigger values should be chosen if rock stability is better and mining depth is small, and vice versa.
3. Calculate the economic reasonable stripping ratio according to the techno-economic indicator for open pit mining, and then determine the boundary stripping ratio based on the principles of boundary delineation. The boundary stripping ratio is usually between 4 and 10 (m3/m3): smaller values should be chosen if the mine is small, and vice versa.
4. Determine the road layout and parameters according to development and transport mode.
5. The ultimate pit slope is composed of bench height, bench slope angle, cleaning berm, safety berm and transport berm. The slope angle should be the ultimate slope angle.
The development and transport mode is an important part of open pit mining design. It aims to build the transport roads between the ground and benches and between all benches, links up the open pit with the ore site, waste dump and industrial sites, and makes new working levels ready. The scope covers the layout types of pit line development and the establishment of a sound transport system, with consideration given to the overall plan of deposit development and mine engineering.
There are two common development and transport modes.
1. Single development and transport
This includes road transport and railway transport.
2. Combined development and transport
This includes road-railway transport, road (narrow gauge railway)-footrill and orepass transport, road (narrow gauge railway)-ramp transport, and road-crushing station-belt conveyor transport.