In the Touissit - Bou Beker - El Abed MVT district the distribution of δ³⁴S values of the main stage mineralization can be essentially interpreted as the result of mixing between a heavy and a light δ³⁴S reservoir. The results suggest that thermochemical reduction of Triassic sulphate and, possibly, pyrites disseminated in the sedimentary sequence (and/or leaching of basement sulphides) constitute the sources of the two sulphur types. A zonation with δ³⁴S values for main stage sphalerite and galena increasing systematically eastwards has been recognized at the district scale. Temperatures calculated from coexisting sphalerite-galena pairs range from 70 °C to 135 °C and are in good agreement with geological and fluid inclusion data.