Emerald mineralization. in the Gacha/a region is emplaced in breccias, veins, and also in fault walls, these faults having a N-NE strike, and affecting lower Mesozoic strata. Sedimentary rocks of Paleozoic age are also present in the area. Mineralization is intimately related to the black shales, showing a high degree of metasomatic alteration. This alteration consists of repbcement of the host rock and cavity filling by oligoclase, dolomite, and pyrite, some calcite, and traces of rutile and fluorite. M ineralizing solutions could have been originated by meteoric and/or connate water from sediments, this water leaching the necessary ions on their way through the host rocks. Many features suggest a e lose relationship between eooporitic sequences and emerald mineralization, contributing the former, by solution, some of the ions required to the formation of the latter. Some emerald exploration guides are proposed, based on the knowledge of structural, lithologic, and geochemical characteristics. Different methods are applicable in ali exploration steps, from a regional scale, to the orientation of mining works.