Physical properties measurements taken on core recovered from Site 1191 (Satanic Mills hydrothermal site) include magnetic susceptibility, natural gamma radiation, compressional wave velocity, thermal conductivity, and standard index properties. The magnetic susceptibility meter and natural gamma radiation device were run on all cores (Cores 193-1191A-1R through 3R) recovered from Hole 1191A using the multisensor track. Where possible, compressional wave velocity measurements were made in only one direction on discrete samples. Thermal conductivity was measured throughout the one lithologic unit recovered from this hole. Index properties were measured on three discrete minicore samples.
Figure F13 shows the downhole profile for magnetic susceptibility from the seafloor to 16 mbsf. The values range from 32.1 × 10-5 to 1168.1 × 10-5 SI, with an average of 416 × 10-5 SI. The magnetic susceptibility is high throughout the core, with the highest values concentrated in Core 193-1191A-2R. Although only small amounts of magnetite were observed in thin section, very fine grains of magnetically susceptible material may be in the groundmass, which could account for the high values.
Natural gamma radiation (NGR) records are summarized in plots of total counts per second (cps) vs. depth (see Fig. F14). NGR values range from 3.1 to 16.2 cps, averaging 10 cps. As with Sites 1188 and 1189, much of the variation may be caused by errors in the measurement process (see "Physical Properties" in the "Site 1188" chapter). The values from this site are on average similar to those of fresh volcanic rocks from the top of Hole 1188A, but are significantly lower than those of fresh, less siliceous, volcanic rocks from the top of Hole 1189A.
Two compressional wave velocity values were obtained from Hole 1191A. Data for these samples are shown in Table T8. Both samples, taken from unaltered dacites that are moderately vesicular, have velocities >5 km/s.
Thermal conductivity measurements for the recovered core span a small range of values, from 1.25 to 1.79 W/(m·K) (Fig. F15). The average value of the measurements, 1.45 W/(m·K), is consistent with measurements from unaltered dacites from Holes 1188A and 1189A.
The data for water content, bulk density, dry density, grain density, porosity, and void ratio are displayed in Table T9. Grain densities measured on ICP-AES powder samples are given in Table T10. There is very little variation in the grain density values of the minicore samples, which range from 2.5 to 2.6 g/cm3. These values are generally consistent with those from other unaltered dacites at Sites 1189 and 1190. They are also generally similar to ICP-AES grain densities, but because ICP-AES samples and minicore samples were taken from different intervals, exact comparisons cannot be made. The porosity values also differ very little, with values ranging from 7.1% to 11.5%.