History and Results of VC-1, the First CSDP Corehole in Valles Caldera, New Mexico

Abstract

Valles Caldera #1 (VC-1) is the first Continental Scientific Drilling Program (CSDP) core hole drilled in the Valles caldera and the first continuously cored hole in the caldera region. The objective of VC-1 were to penetrate a hydrothermal outflow plume near its source, to obtain structural and stratigraphic information near the intersection of the ring fracture zone and the precaldera Jemez fault zone, and to core the youngest volcanic unit inside the caldera (Banco Bonito obsidian, 0.13 Ma). VC-1 penetrates 298 m of moat volcanics and caldera fill ignimbrites, 35 m of precaldera volcaniclastic breccia, and 523 m of Paleozoic carbonates, sandstones, and shales, with over 95% core recovery. Hydrothermal alterations are concentrated in sheared, brecciated and fractured zones form the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth. Alterations consist primarily of clays, calcite, pyrite, quartz, and chlorite, but chalcopyrite has been identified in a fractured zone at 847 m. Thermal aquifers were penetrated at various intervals from about 510 m on down.