Bioleaching is a complex process which utilizes the earth's natural micro flora for the recovery of insoluble minerals. The process is principally simple although the massive dimensions of the "bioreactor" make the operation and control of heap leaching process demanding. A multivariate analysis was performed to data collected from Talvivaara Mine's bioleaching heaps. Data were analysed by correlation matrices and principal component analysis. In addition, cross correlation was used to determine a process delay of the bioleaching heaps. Examined process variables were metal contents, pH, temperature and microbial content of the pregnant leaching solution. The most important irrigation variables of the bioleaching process proved to be pH and temperature, together with the Al and Fe concentrations of the irrigation solution. Process delay between irrigation pH and Ni of pregnant leaching solution was found to be 60 days. Used methodologies provided powerful tools for the investigation of phenomena related to bioheapleaching processes. (C) 2016 Elsevier Ltd. All rights reserved.