Evolution of a Vertically Zoned Magmatic–Hydrothermal Gold System: The Marmato Deposit, Colombia

The Marmato gold deposit in Colombia’s Middle Cauca Belt records a late-Miocene magmatic–hydrothermal system extending vertically for >1.4 km. Integrated structural, paragenetic, geochronological, and fluid-inclusion data constrain its zonation and the processes of gold transport and precipitation. Later upper-system veins crosscut and locally reopen lower system veinlets, documenting their succession, spatial overlap, and pathway reuse. Stages 2 and Stage 5 adularia ages (~6.05 and ~5.96 Ma) provide approximate temporal anchors but do not constrain the intervening stages or total duration. Reduced lower-system quartz–pyrrhotite veinlets contain native gold and native bismuth within a Au–Bi–Te association, whereas upper-system veins contain pyrite-rich polymetallic assemblages and electrum. Lower-system liquid-bearing inclusions yield a Q1–Q3 homogenization-temperature range of 350–387 °C and higher apparent salinities and calculated pressures than upper-system inclusions, which yield a Q1–Q3 range of 314–345 °C. Aqueous Au–HS complexes likely dominated gold transport. The lower-system Au–Bi–Te association is compatible with, but does not demonstrate, Au partitioning into a Bi-rich melt. Upper-system electrum precipitation is inferred to reflect cooling and chemical evolution, with pressure fluctuations and possible phase separation as additional controls. Marmato is interpreted as a single vertically and paragenetically zoned magmatic–hydrothermal system, combining selected porphyry and reduced intrusion-related affinities below with strong low- to intermediate-sulfidation epithermal affinity above.