Hydrovolcanic Breccia Pipe Structures-General Features and Genetic Criteria. I. Phreatomagmatic Breccias

Abstract

Two types of hydrovolcanic breccias are generally accepted: phreatomagmatic and phreatic. Due to their specific characteristics generated during the brecciation, characteristics that control the ore deposition, these breccias represent favourable hosts for mineralization. The depth of formation, the general form and dimensions, the breccia - host rock contact, as well as fragments, matrix, and open spaces altogether control the position and the size of the breccia hosted ore bodies and contribute in different degrees to the rise of the ore grades in phreatomagmatic and phreatic structures. Consequently, the recognition of the genetic type of breccia allows an appropriate strategy in mineral exploration. Describing a breccia necessarily implies a check of its general features, such as environment/depth of formation, general form/geometry, dimensions, breccia- host rock contact, fragments, matrix, alteration, mineralization, surface connection, as well as of its additional features, namely fluidization and facies changes (see Table 2). There are several characteristics with high genetic significance among the abundant descriptive features regarding breccia structures. To point out such evidences means to find out the keys for the genetic intrepretation. A complete list of genetic criteria is proposed for phreatomagmatic breccias (see Table 3).