The sulfide mineral assemblage in cores from Hole 1268A changes downsection, potentially reflecting changes in sulfur and/or oxygen fugacity as fluid migrates through the section. Figure F4 illustrates the changes in the sulfide assemblage downsection compared to total sulfide mineral vein fraction and lithology. The sulfide assemblage that suggests precipitation at relatively high sulfur and oxygen fugacities (polydymite and millerite) yields downsection to progressively lower sulfur and oxygen fugacity assemblages (millerite + pyrrhotite, pyrrhotite + pentlandite, and eventually only pentlandite). This series is interrupted by the reappearance of millerite and polydymite coincident with a breccia interpreted to represent the remnants of a gabbroic intrusion, suggesting a coincident increase in sulfur and oxygen during the precipitation of sulfide minerals in this interval. Sphalerite also appears in the mineral assemblage only in the lowermost part of the intrusion breccia. Below the intrusion breccia, the sulfide mineral assemblage is dominated by pentlandite. Even lower sulfur and oxygen fugacity assemblages (pentlandite + awaruite and awaruite + heazelwoodite) tentatively identified during shipboard analysis were not detected in these samples.