Hydrothermal ore deposits are commonly surrounded by an inner halo of hydrothermal alteration, a wider halo of unaltered rocks enriched in mobile trace elements, and a halo formed by the nearly spent solutions. The streaming-through halo is characterized by an abundance of submicroscopic - secondary liquid-gas inclusions, but has no other, distinctive chemical or petrographic properties. A decreptoacoustic method, with which samples of gangue or wall rock minerals are heated to 700°C while the number of decrepitations are counted, has-been developed to study rock samples or the light fraction of sediments derived-from a mineralized area. This method, when used in conjunction with geochemical and other standard methods, shows promise of becoming a powerful prospecting tool. -- E. Ingerson.
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