A contribution to the ore genesis of the magnesite deposit of Eugui,Navarra (Spain)

In the area of the magnesite deposits of Eugui (Navarra, Spain) studies on illite crystallinity, the degree of graphitization of carbonaceous material, measurements of vitrinite reflectivity, and fluid inclusions have been carried out on dolomites, magnesites, schists, and carbonaceous matter. These rocks have suffered metamorphism of very low to low grade.The magnesite appears generally concordant with the Namurian dolomitic rocks showing a typically banded structure. The genetic model proposed involves an early Mg concentration during sedimentation (syndiagenetic dolomitization), lateral circulation of saline solutions, and formation of diagenetically crystallized rhythmites (DCR), and final compaction. The formation of magnesite took place under the conditions of low pressure and temperatures close to 150°C, very similar to all strata-bound ore deposits. Deformation and regional metamorphism only caused minor removal, recrystallization, and transformation of the clay minerals and carbonaceous matter.