Source of fluids forming distal Zn-Pb-Ag skarns: Evidence from laser ablation–inductively coupled plasma–mass spectrometry analysis of fluid inclusions from El Mochito, Honduras

Abstract

The compositions of fluid inclusions trapped in garnet, pyroxene, and sphalerite, measured with laser ablation–inductively coupled plasma–mass spectrometry, from the distal, dominantly limestone-hosted, El Mochito Zn-Pb-Ag skarn, Honduras, are very similar to those of proximal magmatic fluids in granitoid-related mineral deposits. However, the El Mochito mineralizing fluids are chemically distinct from basinal brines, demonstrating that in distal skarns, magmatic fluids dominate, and that most element concentrations and ratios are unaffected by water-rock interaction. High fluid temperatures (~325–425 °C) throughout the paragenesis are also consistent with this hypothesis. A variety of elements and element ratios (e.g., Rb, Mn, K/Na, Mn/Na, Rb/Na, Zn/Na) clearly discriminates between magmatic fluids and basinal brines. Elevated Ca most likely resulted from carbonate dissolution along the flow path. Zinc and Pb contents indicate that the ore metals were precipitated in the deposit in proportions that approached their ratios in the fluid.