Several types of rock enclose the tungsten skarn deposit of Salau, including alternations of marbles and pelitic schist. A detailed mineralogical and petrographical study has been undertaken in order to characterize the different stages of transformation of these rocks as induced firstly by the intrusion of granodiorites and then by the action of mineralizing fluids. The different episodes are as follow : 1 -A contact metamorphism, which causes the formation of the calc-silicate hornfelses. The main process involved at this stage is a diffusion metasomatism between marble and pelitic beds. The following zoning is observed sphene + C-zoïsite | C-zoïsite | salite | calcite. Locally, other minerals appear ; they are : garnet, idocrase and wollastonite. Moreover, geochemical studies show a local enrichment in iron due to slight mobility within the rock. On the whole rock scale, the metamorphism is isochemical. 2 -Infiltration metasomatism is common in the Barregian Formation and in pure limestone. It is characterized by an addition of iron, aluminium and manganese leading to the crystallization of calcic pyroxene and garnet. When affecting pure marble, the zoning is : garnet | pyroxene | calcite. In the calc-silicate hornfelses, this zonation depends on the primary zone affected. Thus, when the sphene + clinozoïsite as well as the clinozoïsite zones are affected, the zoning is : garnet | C-zoïsite When the salite zone is affected, the zoning is : garnet | hedenbergite | salite Hedenbergite composition varies according to the mineral which has been transformed : more ferrous when formed on calcite (Hed. 90, Dio. 6, Joh. 4), it appears more magnesium rich when formed on salite : (Hed. 70, Dio. 27, Joh. 3). The garnet solid solution shows, at this stage, slight variations around Gross. 80, Spess. 17, Alm. 19, Andr. 4. In detail, its composition depends on that of the primary mineral. 3 -Hydrothermal alteration affects all rock-types occurring in the deposit : sedimentary rocks, igneous rocks and skarns. We shall subdivide this stage into two parts. — a silicification characterized by rock dissolution and quartz and scheelite crystallization when developed in sedimentary rocks, — a sulphidization at the end of scheelite deposition, characterized by an addition of iron.