Skiff Bank is a bathymetric and gravimetric high located ~350 km southwest of the Kerguelen Islands in the northern portion of the Kerguelen Igneous Province (KIP). Ocean Drilling Program Site 1139 was drilled at a water depth of 1415 m on Skiff Bank's western edge. Hole 1139A penetrated to a depth of 695 meters below seafloor (mbsf) with sediment recovered from the upper 462 m and igneous basement recovered from the lower 233 m. A total of 19 basement units were identified, including variably welded trachytic to rhyolitic volcanic and volcaniclastic rocks (Units 1-5) and 14 lava flows with intermediate to mafic compositions (Units 6-19) (Shipboard Scientific Party, 2000, doi:10.2973/odp.proc.ir.183.101.2000).To better assess the mass transfer of major elements associated with these unique alteration patterns, we have conducted a detailed chemical analysis of both major and trace elements in samples from the basement units of Hole 1139A. These data are reported here, along with whole-rock analyses for carbon, sulfur, and ferrous/ferric ratios (Table T1). Downhole trends for SiO2, C, Fe3+/Fe total, and loss on ignition (LOI) are shown. The trends serve to quantify the distinct alteration observed in some basement units within Hole 1139A. For example, carbon increases dramatically below 570 mbsf and shows large enrichments in basement Units 5-19. The data also show that iron becomes more reducing with depth overall, with Fe3+/Fe total ratios dropping to as low as 0.13 in basement Unit 18. The large variations in this ratio with depth probably reflect alteration zones with variable amounts of hematite and siderite. These unique alteration assemblages and whole-rock compositions were likely produced by CO2-rich hydrothermal fluids interacting with intermediate to felsic volcanic rocks at high water-to-rock ratios. The fluids involved were probably unlike hydrothermal fluids that affected other parts of the KIP.