As the hot hydrothermal fluid flows through this mud, it «cooks» organic material, forming methane (natural gas) and oil - like hydrocarbons. (sciencedaily.com)
Marbles in metamorphic aureoles and iron - rich skarns appear to be favored sites for gold mineralization in these deposits, perhaps due to the rheological character, permeability after fracturing, and chemical reactivity of those rocks to alteration by hydrothermal fluids. (paramountnevada.com)
They hypothesize that hot hydrothermal fluids migrating upward through the thick sediments of the Pescadero Basin «cook» organic matter in the sediment, converting it into petroleum - like hydrocarbons — a process that has been observed at several other vents in the Pacific. (sciencedaily.com)