This paper presents the results of the excavation of an ore grinding watermill brought to light in Sector B 121 of the industrial quarter of the mining town of Brandes (Isère, France). The mill, dated by dendrochronology the 13th century AD, was driven with water channelled from the Font-Morelle spring. The head-race and spillway are examples of the opportunistic reuse of earlier anthropic (canal and mining trench) or natural (faults and karsts) features. The tail-race was not totally excavated. The mill-house (drywall and timber construction) is poorly conserved and the millstone driving mechanisms are difficult to interpret. A series of features suggest the use of a horizontal water wheel driven counterclockwise by a jet of water guided through a flume. A large number of millstone fragments and flakes were studied in a previous article.