The Strata-Bound Magnesite Deposit of Eugui-Asturreta in the Spanish Pyrenees

Summary

A detailed lithological survey of the Asturreta magnesite deposit, carried out for practical reasons, led to the result that a correlation of the individual strata of magnesite and dolomite was not possible even for short distances. This phenomenon, unusual in marine-sedimentary deposits, can perhaps be explained by postdiagenetic and metamorphic mobilization processes. A study of the layered structure and microchemical analyses indicates a sedimentary genesis in a subsalinary environment. This is confirmed by the observation of some gypsum pseudomorphoses. Most convincing is the geological evidence, gained by reconstructing the original basin of sedimentation: the geometrical flattening of the folded carbonate rock series discloses a clear coincidence of greatest thickness and magnesite enrichment. The first sedimentary theory of de Llarena (1950) thus gains strong support.