There are many examples of spatially associated porphyry and epithermal ore deposits; a genetic connection has been suggested for some and argued against for others. Nowhere is this spatial association better demonstrated than in the Mankayan district of northern Luzon, Philippines, where the Lepanto high-sulfidation epithermal Cu-Au deposit is superadjacent to the Far Southeast porphyry Cu-Au orebody; together they contain >3.8 million tons (Mt) Cu and >550 t Au. Quartz diorite porphyry dikes intruded Miocene basement rocks of metavolcanic and volcaniclastic rocks to a 300-m elevation. These intrusions postdate the Pliocene volcanic breccia and dacite porphyry that host much of the epithermal ore. K silicate alteration, consisting of biotite-magnetite and minor K feldspar, is centered on the quartz diorite porphyry. K-Ar ages of the biotite are 1.41 _+ 0.05 Ma (n-6). Vitreous, anhedral quartz veins are associated with this early alteration and contain vapor-rich and hypersaline liquid inclusions with maximum homogenization temperatures of 450 ø to 550øC (and 50-55 xvt % NaC1 equiv salinities). Lithostatic pressure estimates indicate a palcosurface at a >-l,500-m elevation. Advanced argillic alteration formed over the top of the porphyry and consists of quartz-alunite, dated at 1.42 _+ 0.08 Ma (n = 5), synchronous with K silicate alteration. The lower limit of extensive quartz-alunite alteration is at a m600-m elevation. Similar alteration and a core of leached, silicic alteration extend northwestward >4 km along the basement dacite contact, localized by the Lepanto fault. Chemical and S isotope zoning of alunite along strike indicates progressively lower temperatures away from the porphyry, from 350 ø to 200øC. K silicate alteration is overprinted by alteration consisting of chlorite plus hematite and/or serieite-illite, with a marginal zone containing pyrophyllite and an outer zone of propylitic alteration. The chlorite-sericite alteration is cut by veins of euhedral quartz that locally fill reopened anhedral quartz veins. The euhedral quartz veins contain anhydrite-white mica-pyrite _+ chalcop)q'ite _+ bornRe and have halos of sericite; illite separated from these halos has ages of 1.30 _+ 0.07 Ma (n = 10). Fluid inclusions provide evidence for boiling on inception of this fracturing event (Th = 350øC, 5 wt % NaC1 equiv) and indicate a depth of 1,500 to 2,000 m below the palcowater table. This brittle-fracture event was followed by cooling and dilution of the hydrothermal fluid. The elevation of the enargite Au epithermal ore and its host of silicic alteration increases as the unconformity between the basement and dacite breccia rises from a 700-to 1,200-m elevation xvith increasing distance from the porphyry. Published data on enargite-hosted fluid inclusions (Th = 295ø-200øC, 4-2 wt % NaC1 equiv) indicate that the temperature and salinity both decrease with increasing distance from the porphyry. Epithermal ore consists of stage 1 euhedral pyrite-enargite-luzonite, and subsequent stage 2 Au is accompanied by ...

The Rodalquilar epithermal Au alunite deposit occurs within the Rodalquilar caldera complex in the Miocene Cabo de Gata volcanic field in southeastern Spain. The Rodalquilar caldera formed by eruption of the rhyolitic Cinto ash-flow tuff at about 11 Ma; continued resurgence of the core of the caldera resulted in structural doming and was followed by emplacement of large ring domes, eruption of the Lfizaras ash-flow tuff, and development of the smaller, nested Lomilla caldera. Hydrothermal circulation associated with the emplacement of shallow hornblende andesitic intrusions late in the evolution of the caldera led to formation of the epithermal deposits along fractures related to multistage caldera collapse and resurgence.Ore deposits within the Rodalquilar caldera complex consist of low-sulfidation Pb-Zn-(Cu-Ag-Au) quartz veins and the economically most important high-sulfidation Au-(Cu-Te-Sn) ores. The latter are enclosed in areas of acid sulfate alteration present on the east margin of the Lomilla caldera. Drilling indicates that hydrothermally altered rocks are present to depths of >900 m, with a gradational change with depth from silicic, to advanced argillic, to intermediate argillic, to sericitic zones; an envelope of propylitic alteration surrounds these zones. The sericitic zone is present at depths >400 m and occurs under the advanced argillic (stage i alunite, diaspore, zunyite, pyrophyllite) and silicic (vuggy silica and massive silicified rock) zones, which are well developed to present depths of •300 and 100 m, respectively. Vuggy silica and massive silicified rock are structurally controlled and spatially related to the Au deposits. K/Ar dating of stage i alunite and hydrothermal illitc indicates an age of mineralization of about 10.4 Ma.The results of paragenetic, fluid inclusion, and stable isotope studies indicate an evolution of the hydrothermal system, consisting of an early period of acidic wall-rock alteration and a late period of Au mineralization. A significant magmatic fluid component was present throughout, contributing acidity in the form of H2SO4 and HC1. Salinities in some samples of deep, hot (>400øC) fluids exceeded 40 wt percent NaC1 equiv, consistent with the presence of a magmatic brine. In addition, the O and H isotope ratios of hypogene alteration minerals (alunite, kaolinitc, sericite, and hydrothermal quartz) indicate that hydrothermal fluids (6•SO = 7 ___ 3%0, 6D = -20 ___ 10%o) during the main period of wall-rock alteration were dominantly magmatic in origin. The 634Szs was •9 per mil and H2S/SO4 of the bulk hydrothermal system during acidic alteration was •5. The 634S values of stage 1 alunite (22.3-31.0%o) and pyrite (0.3-8.0%0) in the advanced argillic zone reflect isotopic equilibrium between sulfate and sulfide at T --220 ø to 330øC, with the lower values corresponding with present-day surface samples. * Present address: Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305 Japan. 0361-0128/95/1704/795-2854.00 795 796 ,4RRIB,•S, JR. ET ,•L. Gold mineralization extend...

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