Reopening and retrograde dissolution in the early quartz veins of the Altar porphyry Cu-(Au-Mo) deposit (Argentina)

MAYDAGÁN LAURA; FRANCHINI, MARTA; RÍOS, JAVIER; LENTZ, DAVID

Upsala

Congreso; 12th Biennial SGA Meeting; 2013

The Society for Geology Applied to Mineral Deposits (SGA)

  Cathodoluminescence (CL) images and fluid inclusion analysis in the early quartz veins of the Altar (31º 29' S, 70º 28' W) porphyry Cu-(Mo-Au) (Argentina) have yielded preliminary results on the characteristics of the hydrothermal fluids of the Altar system. Early type 2 veins show a complex growth history that revealed the existence of three generations of quartz: bright luminescence quartz (Ql), moderate luminescence quartz with euhedral growth zoning (Qmz), and reddish and low luminescence quartz (Qr); and textures that indicate processes of reopening, dissolution, and corrosion. Primary and pseudo-secondary fluid inclusion assemblages hosted in Qmz and Qr quartz generations suggest two episodes of unmixing (boiling) of the hydrothermal fluids. The last episode of fluid unmixing occurred between 350° and 370 °C and ~150 bars and correlated with the dissolution of the Qmz quartz, followed by the precipitation of Qr quartz. The youngest quartz generation (Qr) precipitated with chalcopyrite ± pyrite ± Au (capillary thin type 2b veinlets) that, together with disseminated mineralization in the potassic alteration, constitute the first pulse of Cu-Au-bearing fluids.