Hydrothermal alteration in Puerto Rican porphyry copper deposits

Journal of Research of the U. S. Geological Survey, 1977, volume 5, issue 6

“…This confirms Seiders' Eocene age for the stock on the basis of the observation that it intruded branches and dikes along fault zones which in turn displaced lower Tertiary rocks (Seiders, 1971). Contact metamorphic chalcopyrite-pyrrhotite deposits are noted in limestones near the southeast contact of this stock (Domenech, 1899, Cox andBriggs, 1973), and chalcopyrite molybdenite mineralization at La Muda (Pease, 1966, p. 109-110;Cox, Larsen, and Tripp, 1973) is closely related to intrusive porphyries of probable Eocene age.…”

“…Eocene intrusive rocks range from equigranular, medium-grained hornblende-quartz diorite and diorite to hornblende-quartz diorite porphyry with a saccharoidal quartz-plagioclase groundmass, and to andesitic and dacitic porphyry with fine to glassy groundmass. The quartz diorite porphyry is spatially and genetically related to the porphyry copper deposits at Tanama and Rio Vivi (Cox, Larsen, and Tripp, 1973) and to weak copper mineralization at Cuyon (Bergey, 1966). All three rock types are found as unmineralized intrusions cutting across the copper orebodies at Tanama and Rio Vivi areas.…”

Journal of Research of the U. S. Geological Survey, 1976, volume 4, issue 1

“…The textures and composition of the quartz oligoclase porphyry at Puerto Maunabo have many of the characteristics and associations of hornblende-quartz diorite porphyry stocks associated with the porphyry copper-type mineral deposits of Puerto Rico (Cox, Larson and Tripp, 1973). They are highly siliceous porphyries that contain finely divided conspicuously reddish-brown hydrothermal biotite and no primary mafic silicates.…”

“…Most of the porphyry-copper-type ore deposits in Puerto Rico, on the other hand, contain, in veinlets, hydrothermal biotite and potassium feldspar in addition to the base metals (Cox, Larson and Tripp, 1973). Although K+ ions are not necessarily required to precipitate base metals from solution, the physical and chemical environment that causes the precipitation of K + ions, either as biotite or potassium feldspar, appears to be very similar to that required for precipitation of base-metal sulfides.…”

Journal of Research of the U. S. Geological Survey, 1975, volume 3, issue 3

“…The geochronology of volcanism, intrusion, and mineralization was studied by Barabas (1971). Cox (1972) and Cox, Larsen, and Tripp (1973) have described the mineralogy and hydrothermal alteration of the deposits.…”