The Bent Hill drill holes followed a generalized stratigraphy from the surface to depth as follows: clastic sulfide, massive sulfide, sulfide feeder system with an underlying deep copper zone (DCZ), sediments, and basaltic sill and flow complex (Fig. F3). Each group has been further subdivided into subunits that are described in the Leg 169 Initial Reports volume (Fouquet, Zierenberg, Miller, et al., 1998). Because this paper details the evolution of the sulfide feeder units, these units will be described below. In the Leg 169 Initial Reports, the sulfide feeder system, Unit VI, is divided in three subunits based on the degree of sulfide mineralization (Fouquet, Zierenberg, Miller, et al., 1998). Subunit VIA is sulfide-veined sediment where sulfides are predominant in the veins but are also present as fine-grained disseminations. The total sulfide content in Subunit VIA ranges from 10 to 50 vol%. The major sulfides in these units are isocubanite, chalcopyrite, pyrrhotite, with minor pyrite and traces of marcasite and galena. Subunit VIB is defined as sediment with sulfide veins and/or impregnations. This unit is only weakly mineralized, and the dominant sulfides are pyrrhotite, chalcopyrite/isocubanite, and pyrite with minor sphalerite. The sulfide mineralogy is not consistent in this unit and may change from section to section downhole. The final subunit in the sulfide feeder system, Subunit VIC, is characterized by sulfide bands and impregnations in sandstone. This unit is predominantly CuFe-sulfide rich, and sulfides commonly mimic primary sedimentary structures. A DCZ falls within this subunit and is identified by a predominance of CuFe sulfides and the relative absence of any other sulfide minerals.