Figure F82. Net mass gain ("enrichment") or loss ("depletion") of rock components from the most highly altered ("bleached") intervals in Units 18 and 19. The composition of the altered rock was divided by the composition of the least-altered sample (assumed protolith) from that unit. Thus, values greater than unity represent mass gains during alteration, whereas values less than unity represent mass loss. Samples 183-1139A-70R-1 (Piece 2A, 17-20 cm) and 70R-2 (Piece 1F, 141-145 cm) were selected as highly altered and relatively unaltered pairs, respectively, in Unit 18. Corresponding samples from Unit 19 were Samples 183-1139A-71R-7 (Piece 1B, 25-27 cm) and 71R-4 (Piece 11, 135-138 cm). The assumed protoliths have H₂O and CO₂ concentrations of 0.8 to 2.3 wt% and, as a consequence, are only slightly altered. Missing histograms for CaO and MgO reflect cases where concentrations were below detection. For complete chemical analyses for Hole 1139A basement units, see "Igneous Petrology" and Table T11.