A complex, polymetallic ore with approximately 6 wt% organic carbon and 3 wt% inorganic carbon (calcite) was bioleached using mixed cultures of mesophilic and moderately thermophilic microorganisms enriched from materials obtained from an auto-heating coal mine. The microorganisms adapted readily to the ore despite the organic carbon content. Two characteristics of the pyrite-rich ore, a porous organic-sericite phase that allowed the lixiviant and oxidant to penetrate particles and contact sulfide grains and a quartz-feldspar phase that partly occluded the acid-consuming carbonate phase, facilitated rapid and efficient metal (Co, Ni, Cu and Zn) extraction. Metal extractions showed little temperature or acid dependence. Extractions of Co, Ni, Cu and Zn in inoculated tests were higher than in uninoculated tests under the same conditions, indicating at least partial association of the metals with sulfide minerals and highlighting the roles of microorganisms in enhancing bioleaching. Approximately 40-60 wt% of the metals were acid soluble. The oxidation of pyrite with concomitant acid generation was a key parameter in lessening acid consumption during leaching. On the basis of solution monitoring data and leached residue analyses of the carbonate contents and sulfur speciation, it is concluded that leachate free acidity is also an important parameter in metal extraction. Both parameters relate directly to acid use in bioleaching systems and impact on the economics of proposed processes. The microbial communities in the inocula and bioleaching samples contained three archaeal and five bacterial species. The archaeal species detected were related to Ferroplasma (Fp.) acidiphilum, Thermogymnomonas (T.) acidicola and Metallosphaera (M.) hakonensis. The bacterial species detected were related to Leptospirillum (L.) ferriphilum, Acidithiobacillus (At.) thiooxidans, Ferrimicrobium (Fm.) acidiphilum, At. caldus and Acidimicrobium (Am.) ferrooxidans. The Ferrimicrobium acidiphilum-related species was the only species present in the 35 degrees C and possibly the 50 degrees C columns thought to be native to the ore. (C) 2014 Elsevier Ltd. All rights reserved.