 Most deposits fit the model of having been formed late in the basin history and in most cases feeder systems and metal zonation support exhalative models.However, in the case of diatreme related deposits, such as the giant low-grade Abra deposit, the mineralization is intra-formational, lacks sedimentary textures (is epigenetic and replacement type) and is too low in the basin profile (i.e.in the basal formation).