A mixer especially suited for treating a mixture of mineral substrate particles and hydrocarbon compounds, especially tar sands and contaminated soils, to recover a hydrocarbon portion and a cleaned substrate portion. Hydrocarbonaceous rock, sand, ore, or soil containing bitumen, petroleum, and/or kerogen is crushed or otherwise comminuted as needed to the particle size of sand or smaller. The comminuted ore is mixed with water to form a slurry, is heated to between 60.degree. C. and 100.degree. C., and is agitated with an oxidant in aqueous solution, preferably hydrogen peroxide, in a flow-through mixer having a low axial flow rate and a high radial flow rate. Both free interstitial hydrocarbons and those hydrocarbons bound electrostatically to the surfaces of clay-like particles in the ore are released from the mineral substrate. Some of the released hydrocarbon compounds may be controllably cleaved by the oxidant to yield organic compounds having lower average molecular weights which are suitable for refining as oil after separation from the process water phase and the residual particulate mineral substrate. The water and mineral tailings from the process are substantially free of hydrocarbon contamination and are environmentally suitable for landfill disposal.