Porphyry to Epithermal Transition in the Altar Cu-(Au-Mo) Deposit, Argentina, Studied by Cathodoluminescence, LA-ICP-MS, and Fluid Inclusion Analysis

MAYDAGÁN LAURA; FRANCHINI, MARTA; RUSK, BRIAN; LENTZ, DAVE; MCFARLANE, CHRISTOPHER; IMPICCINI, AGNES; RÍOS, JAVIER; REY, ROGER

ECONOMIC GEOLOGY AND THE BULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS

SOC ECONOMIC GEOLOGISTS, INC

Año: 2015 vol. 110 p. 889 - 923

0361-0128

The middle to late Miocene Altar porphyry Cu-(Au-Mo) deposit, located in the Andean Main Cordillera of San Juan Province (Argentina), is characterized by the superposition of multiple vein generations consisting of both porphyry-type and high sulfidation epithermal-style alteration and mineralization. We constrain the physical and chemical evolution of the hydrothermal fluids that formed this deposit, based on description and distribution of vein types, scanning electron microscopy, cathodoluminescence imaging, trace elements in quartz veins, and fluid inclusion microthermometry.Quartz CL textures and trace elements (chiefly Li, Al, Ti, and Ge) discriminate among quartz generations precipitated during different mineralization and alteration events. Early quartz ± chalcopyrite ± pyrite veins and quartz ± molybdenite veins (A and B veins) show considerable complexity and were commonly reopened, and some experienced quartz dissolution. Early quartz ± chalcopyrite ± pyrite veins (A veins) are dominated by equigranular bright-CL quartz with homogeneous texture. Most of these veins contain higher Ti concentrations than any other vein type (average: 100 ppm), and have low to intermediate Al concentrations (65-448 ppm). Quartz ± molybdenite (B veins) and chlorite + rutile ± hematite (C veins) veins contain quartz of intermediate CL intensity that commonly shows growth zones with oscillatory CL intensity. Quartz from these veins has intermediate Ti concentrations (~20 ppm) and similar Al concentrations as A veins. Quartz from later quartz + pyrite veins with quartz + muscovite ± tourmaline halos (D veins) has significantly lower CL intensity, low Ti (