In the Western Greywacke Zone E of Saalfelden in the municipal area of Maria Alm SW of the village Hinterthal an area of around two square kilometers was mapped geologically in the scale of 1:1000. There the sparry magnesite occurrence of Entachen is hosted in dolomites above Silurian metapelites, metapsammites and lydites. The magnesite is developed by an exploration gallery of 174 m which was mapped in the scale of 1:500 and chipsampled. Every gross sample represents the quality of the magnesite along 5 m of the gallery. In addition further hand samples were taken from the surface of the mapping area. A total number of 50 magnesite, 10 dolomite and 8 host rock samples were geochemically investigated in respect to major and trace elements. Petrographically 3 magnesite types with 18 subtypes, 3 magnesite-dolomite mixed or transition types and 5 dolomite types were determined from the carbonate rocks. The average crystal size of the sparry magnesite is about 1 mm. Typical for the Hinterthal magnesite are the frequently occurring red colour and flaserbedding produced by up to a few mm-thick layers of phyllosilicates parallel to the bedding of the carbonate rocks. The quality of the magnesite was determined along the the exploration gallery by geochemical parameters of MgO, SiO2, CaO, Fe2O3 and LOI. The geological mapping confirmed the 3 already known parts of the magnesite occurrence. The major part of the occurrence is formed by the big Entacher and smaller Pirnbach ore bodies. The Baleiten ore body is the smallest of all and separated by a valley from the other ones. The magnesite has distinct bedding in the cm scale up to dm scale and dips flat to the north with 12 degrees on average. Typically, the ore body is affected by faults parallel to the bedding planes and a set of steep E-W striking faults. The transition to the country rock is often characterized by clayish material and gouge. Generally Late Silurian lydites are developed in the foot wall of the magnesite. The rest of the surrounding rocks are metasandstones and metapelites forming vast areas of the mapped area. Field evidence, petrography and geochemisty suggest a metasomatic origin of the magnesite. The computer aided geological modeling determined the total amount of inferred resources for the magnesite occurrence.