A different and relatively frequent structure in both the Mine and the surrounding area are quartz structures called "Seixo Bravo". This connotation is mainly due to the hardness it presents and to the fact that they do not present useful mineralization. These are lenticular, irregular, with sub-vertical inclination, structures whose arrangement is in agreement with the main schistosity and there width can easily reach 3m. It is an exudation quartz, barren, product of segregation and recrystallization of quartz by regional metamorphism. They are prior to mineralized veins and often form 90º angles.