Quartz-eye-bearing porphyroidal rocks and volcanogenic massive sulfide deposits

This paper presents data supporting the conclusion that the combined association of (1) pyrite-rich stratigraphic units and (2) a characteristic style of quartz-eye porphyry is closely related to the occurrence of volcanogenic massive sulfide deposits.Textural observations on the quartz-eye porphyries suggest that the origin of this rock type may be more complex than that comprising simple metamorphism of a crystal tuff, acid flow, or intrusive rock type. Data are interpreted as suggesting that the quartz eyes are porphyroblastically overprinted on the schistose matrix of these rocks. Quartz eyes are also developed in wall rocks marginal to these quartz-eye porphyries.Because (1) the regional schistosity is steeply oriented and is related to a regional first phase of deformation, and (2) there is a range of strain states of the quartz eyes from highly deformed to undeformed within the same matrix, it is implied that these quartz eyes have grown in an actively deforming matrix and that the quartz-eye porphyries are metasomatically altered acid melts which were previously syntectonically intruded.In the genesis of massive volcanogenic sulfide deposits it is necessary to reconcile the complex origin of these porphyroidal rock types with that of the sedimentary origin of the pyritic units.