Pectolite, stevensite, pyroaurite, calcite, and aragonite are described from cavities, veins, and groundmass of an ophiolite-derived late Quaternary debris flow deposit. The debris flow occurs in an area devoid of hydrothermal activity and therefore the authigenic minerals must have formed under essentially surficial P-T conditions. Pectolite formed in the debris flow appears to be more fibrous than pectolite formed at higher temperatures. Stevensite occurs as veins and as a replacement of pectolite. Pyroaurite occurs as fibrous mats.