Hypogene

Hypogene refers to geological processes and minerals that originate deep within the Earth's crust, typically below the weathering zone, and are formed by hydrothermal fluids moving through rocks. The term combines hypo- meaning under and genesis meaning origin, and is used in geology and ore-deposit studies to distinguish deep-seated, primary mineralization from surface-related processes.

In hypogene systems, hot, chemically aggressive fluids migrate through fractures and pore spaces, precipitating ore minerals as they interact with ambient rocks. The fluids are often related to magmatic activity, tectonic movement, or metamorphic conditions, and the resulting mineral assemblages commonly include sulfides such as pyrite, chalcopyrite, and sphalerite, as well as quartz, carbonates, and alteration minerals like sericite, chlorite, and epidote. Hypogene processes form the initial, primary ore deposits that may later be modified or overprinted by near-surface events.

Hypogene ore deposits include several major types. Porphyry copper deposits are large, low-grade systems with disseminated sulfides associated with extensive alteration halos. Volcanogenic massive sulfide (VMS) deposits form from hydrothermal vents on the seafloor or at depth and can be rich in copper, zinc, lead, and iron sulfides. Skarn deposits arise from chemical interaction between hydrothermal fluids and carbonate rocks, producing calc-silicate minerals and sulfides. Vein and replacement deposits, including many hydrothermal vein systems, also fall under hypogene classifications, though some near-surface equivalents are described as epithermal.

Hypogene is contrasted with supergene processes, which act near the surface after exposure to meteoric waters, and with epigenetic concepts that describe post-formation alteration.