Heap bioleaching of low grade chalcopyrite (CuFeS2) was carried out in 1000 tons scale over a time period of 383 days. Bacterial solution was prepared and re-circulated in specially designed BACFOX (BACterial Film OXidation) tank The micro-organisms used in the pilot scale were a mixed culture of acidophilic bacteria predominantly of the Acidithiobacillus ferrooxidans strain. Effect of rest period, solution recirculation, acid concentration, frequency of solution transfers and seasonal effects on copper recovery were monitored. The leaching studies showed a cumulative copper dissolution rate of 0.14% per day (2.37 kg d(-1)). The overall recovery of the heap was 30%. Variation in leaching efficiency and some of the precautionary measures to improve performance of heap bioleaching are also discussed. (C) 2012 Elsevier B.V. All rights reserved.