Cerro Lindo Mine, Peru

Cerro Lindo, owned and operated by Compania Minera Milpo S.A., is the largest underground mine in Peru, currently mining more than 20,000 tonnes per day. The mine profitably develops seven volcanogenic massive sulphide (VMS) ore bodies.

To begin mining the secondary stopes in Ore Body 5, and realise the optimal dimension and stope support design while tackling excessive dilution from the walls and roof, SRK conducted a series of field and laboratory investigations to establish a reliable geomechanical model. This included installing 46 geomechanical monitoring stations, three detailed geomechanical transects and re-logging four strategically selected diamond drill holes, comprising a total of 410m.

The frequency of the discontinuities was carefully recorded to estimate the RQD values, and the body’s RMR was also estimated. A total of 104 samples were taken from all lithologies and various mine levels and assigned for laboratory tests to determine the physical and mechanical properties of the intact rock.

Structural mapping and logging allowed for the creation of a new model of the in-situ stress field and for the calculation of the principal stresses using kinematic analysis of faults as well as in-situ stress measurements.

Following dilution reconciliation across different stages of mining, using the equivalent linear overbreak slough (ELOS) criteria, SRK conducted a back analysis of these stopes to establish the optimum stope geometry as well as the key dilution controls.

Using the results of those analyses, SRK developed a mine extraction sequence and a numerical model to ensure that optimum mine stability was attained.

Further back analysis of past fill strengths allowed for the identification of a series of alternate strategies and opportunities.

Finally, SRK oversaw the installation of blast monitoring instrumentation to assess on-going effects and allow for the control of the rock mass behaviour.

Antonio Samaniego: asamaniego@srk.com.pe

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