Volatile Composition of Fluid Inclusions in Gold-Bearing Quartz Veins Analyzed by Solid-Mass Spectrometry: Method and Contributions to the Orogenic Metallogenic Model and Exploration

Abstract

This chapter provides details about the analytical procedures and examples from published papers of the contributions of this technique to the understanding of, (1) the signification of ethane; (2) the hydrothermal reactions; (3) the water-poor and CO2-rich fluids; and (4) the source of gold. Gold deposits used as examples range in age from the Archean to the Paleozoic era. Ethane was established as an indicator (proxy) of organic thermal maturation at depth. Hydrothermal reactions inducing graphite precipitation in the host rocks and mineralized structures and consumption of CO2 and CH4 were documented in the Otago Schist district in New Zealand, accounting for the low-CO2 mineralizing fluids, and in the Keraf Zone in Sudan, accounting for the various fluid signatures. Water-poor and CO2-rich fluids associated with high-grade gold or world-class gold deposits also result from hydrothermal reactions involving the consumption of water and ethane. Gold transport as nanoparticles or as hydrocarbon-gold complexes is related to water-poor, hydrocarbon-rich fluids and associated with high-grade gold mineralization. The sedimentary source of gold is demonstrated by the presence of ethane, which is a tracer of organic matter metamorphism in deep sedimentary rocks at amphibolite facies, providing gold extraction from nodular pyrite during transformation to pyrrhotite.