In this paper we are proposing a new type of bioreactor for the biological oxidation of refractory gold ores. In order to reduce the intraparticle friction, to reduce the energy consumption and increase the volumetric rate of oxygen transfer, the sulfide particles are entrapped into the pores of an inert material (non-woven textile). It was named immobilized ore bioreactor. It has been shown that this reactor can handle up to 40% w/v of pyrite, which is twice the typical value for classic slurry bioreactors. The volumetric rate of pyrite oxydation by Thiobacillus ferrooxidans in the new reactor was 2.5 times higher than that in a slurry bioreactor operating under similar initial conditions.