Fluid inclusion evolution at the La Verde porphyry copper deposit, Michocan, Mexico

Abstract

La Verde porphyry copper deposit presents Ca-Na-K hydrothermal alteration, which is typical of porphyry copperdeposits. The temperature of homogenization (Th) in quartz from the potassic zone are Th=480-780 °C and melting temperatures (Tm) of the NaCl range from 430 to 570 °C, which correspond to salinities between 50 and 65 wt.% NaCl. In the stockwork zone, both subsaturated and saturated fluids are present Th range from 180 to 480 °C and salinitie group around 11–14 eq. wt.% CaCl2 and 22–54 wt.% NaCl. It is possible that these conditions reflect a plastic-brittle phase transition that characterizes porphyry copper deposit formation. In the propylitic alteration zone, the fluids are undersaturated, the salinities are 9–10 eq. wt.% CaCl2 and 5–23 eq. wt.% NaCl with Th range from 185 to 395 °C. Calcite in late-stage veinlets has salinities of 12.8–22.3 eq. wt.% NaCl. with Th range from 150 to 265 °C. La Verde porphyry copper deposit data present boiling in the mineralized zone caused by a drop in pressure from 1200 bars (equivalent to ca. 4.8 km) to 345 bars. Late-stage fluids show dilution by non-magmatic waters. 6345 values range from + l.15 % to +2.50 %o and 613C in calcite from −6 %o to −2the features are characteristic of magmatic fluids.