Baja Mining and the operations management team at Minera y Metalurgica del Boleo (MMB) in Mexico recently provided an update on the Boleo project, including the processing plant production ramp-up at both the underground and open-pit operations.
In late October, Boleo shipped a further 2,750 metric tons (mt) of copper cathode (in addition to the 1,919 mt shipped in July) and MMB plant personnel have been working to address process and equipment “issues,” which have become apparent during the ramp-up of copper production. A zinc-cobalt circuit is being commissioned and zinc sulphate production is now expected to commence in December and cobalt metal production in January.
The ramp-up and operation of the Boleo plant was significantly disrupted by the access restrictions imposed by the former president of the municipio of Mulege at the Boleo site in September. The newly elected president removed these restrictions as one of her first acts after taking office.
MMB management is working to increase copper extraction rates to design levels. The sulphur dioxide (SO2) circuit is being prepared for startup and is scheduled to come online on soon, which is expected to improve copper recovery. Plant management is also investigating other parameters such as operating temperature and acid dosage rates affecting copper recovery in order to make process adjustments in the leaching circuit. These adjustments are also intended to reduce high levels of gypsum present in the circuit. It may take several months to make these adjustments, particularly if plant design modifications are required.
The materials handling circuit is functioning satisfactorily and it could achieve design capacity throughput rates. However, certain modifications are being introduced to address material sizing to improve the performance of the scrubber and crusher, which at times have been hampered by excessive clay in the plant feed. A fourth tailings pump has just been installed to provide added flexibility and back-up. Several minor but disruptive equipment failures have occurred, which plant management have rectified, including the replacement of a number of blades on leach tank agitators.
The plant continues to be fed from low-grade stockpiles while the operation is being ramped up. The expected total copper production for 2015 will be approximately 7,500 mt, quite a bit lower than the expected to 20,000 mt.
MMB is evaluating new underground mining methods. Crews are advancing access tunnels in three mines at the manto level, and Mexican contract miners are carrying out trials using short-wall mining techniques. Approximately 140 miners are working on three production shifts.
Underground mining has been constrained by very difficult ground conditions, availability of experienced personnel and equipment. Underground production is averaging approximately 450 mt/d. MMD hopes to increase that rate to a level of 1,000 mt/d before the end of the year when new equipment arrives this month.
Surface mining continues to provide the bulk of the material delivered to stockpiles. Year-to-date through September, the surface mine has added approximately 260,000 mt to stockpiles with an average grade of 1.43%. Mining strip ratios are currently between 7:1 and 8:1, with an average haul distance of approximately 6 km.