Figure 7.

Major events in the depositional and diagenetic history of rocks at the Oudam drill site. (1) Deposition of Hartmann's Valley (HV) basaltic sands; (2) lithification/burial resulting in dissolution of Fe‐Mg‐silicates to form Fe‐oxides and amorphous silica, erosion of HV, and deposition lithification/burial of Stimson (ST) sands; (3) hydrothermal fluids flow along the HV/ST contact causing dissolution of amorphous silica and reprecipitation as opal‐CT, Fe‐oxide/oxyhydroxide precipitation and/or recrystallization to gray hematite, formation of minor Fe‐pyrophyllite (or degradation of nontronite), and precipitation of anhydrite; (4) influx of low‐temperature groundwaters resulting in partial rehydration of anhydrite to gypsum and precipitation of minor Mg‐ and Fe‐sulfates; and (5) veinlet formation due to late‐stage fracturing and subsequent infilling by Ca‐sulfates can be concurrent with Step 4 if fractures were the result of volume expansion induced by the partial rehydration of anhydrite to gypsum. See Figure 1 for lithology legend.