## 4 Results
### Brine Evolution  
Before starting the carbonation experiments, the composition of the brine was analysed using a combination of techniques (see Tables 6 and 7, \"Pure Brine\" column). The brine used in each run of experiments was recovered immediately after the end of the run for a comparative chemical analysis. Figure 6: (**a**) Backscattered electron image of a detail of carbon-rich particles (om—organic matter) associated with halite (hal); (**b**) ATR-FTIR spectra of gabbro-diorite (GD) at 0 days (blue) and 16 days (pink). The calcite reference spectrum is also shown for comparison (yellow; STJapan Inc. database). The insets are the spots of analysis. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **CG (w. \%)** & **Stat. Error** & **CG 64 (w. \%)** & **Stat. Error** & **GD 0 (w. \%)** & **Stat. Error** & **GD 64 (w. \%)** & **Stat. Error** \\ \hline
**SiO\({}_{2}\)** & 42.30 & \(\pm\) 0.0344 & 42.20 & \(\pm\) 0.0345 & 49.00 & \(\pm\) 0.0356 & 49.50 & \(\pm\) 0.0356 \\
**TiO\({}_{2}\)** & 3.34 & \(\pm\) 0.0175 & 3.20 & \(\pm\) 0.0175 & 3.26 & \(\pm\) 0.0176 & 3.16 & \(\pm\) 0.0176 \\
**Al2\({}_{3}\)** & 9.40 & \(\pm\) 0.0295 & 9.50 & \(\pm\) 0.0300 & 16.20 & \(\pm\) 0.0368 & 16.40 & \(\pm\) 0.0369 \\
**Fe2\({}_{3}\)** & 15.50 & \(\pm\) 0.0133 & 15.10 & \(\pm\) 0.0135 & 11.20 & \(\pm\) 0.0115 & 10.90 & \(\pm\) 0.0115 \\
**P2\({}_{3}\)** & 0.28 & \(\pm\) 0.00427 & 0.34 & \(\pm\) 0.00439 & 0.85 & \(\pm\) 0.0056 & 0.74 & \(\pm\) 0.00494 \\
**MnO** & 0.40 & \(\pm\) 0.005 & 0.40 & \(\pm\) 0.005 & 0.32 & \(\pm\) 0.005 & 0.31 & \(\pm\) 0.005 \\ MgO & 12.90 & \(\pm\) 0.0506 & 12.80 & \(\pm\) 0.0503 & 4.48 & \(\pm\) 0.0349 & 4.27 & \(\pm\) 0.0344 \\ CaO & 12.70 & \(\pm\) 0.0428 & 13.10 & \(\pm\) 0.0444 & 8.33 & \(\pm\) 0.0375 & 7.91 & \(\pm\) 0.0371 \\
**BaO** & 0.23 & \(\pm\) 0.013 & 0.20 & \(\pm\) 0.013 & 0.28 & \(\pm\) 0.013 & 0.27 & \(\pm\) 0.013 \\
**Na\({}_{2}\)O** & 0.84 & \(\pm\) 0.0519 & 0.88 & \(\pm\) 0.0512 & 3.46 & \(\pm\) 0.0607 & 3.59 & \(\pm\) 0.0612 \\
**K2\({}_{0}\)** & 0.19 & \(\pm\) 0.0345 & 0.23 & \(\pm\) 0.0356 & 1.42 & \(\pm\) 0.0395 & 1.42 & \(\pm\) 0.0396 \\
**S** & 0.19\% & \(\pm\) 0.00172 & 0.24\% & \(\pm\) 0.00178 & 0.15\% & \(\pm\) 0.00162 & 0.23\% & \(\pm\) 0.00174 \\
**LOI** & 0.89 & & 0.95\% & & 0.03\% & & 0.25\% \\
**total** & 99.17 & & 99.14\% & & 98.98\% & & 98.95\% \\ \hline  & **(ppm)** & **(ppm)** & **(ppm)** & **(ppm)** & **(ppm)** & \\ \hline  
l** & 43 & \(\pm\) 0.364 & 54 & \(\pm\) 0.371 & 53 & \(\pm\) 0.359 & 70 & \(\pm\) 0.383 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Whole-rock geochemistry before and after runs of 64 days for cumulate gabbro (CG) and gabbro-diorite (GD). The variation in the brine chemistry with time for both experiments--Experiment 1 with CG and Experiment 2 with GD--is shown in Tables 6 and 7. The pH, measured just after concluding each run, is more acidic for Experiment 1 (with CG). In fact, the initial pH of 6.85 dropped to 4.5, 4.87, 5.1 and 5.5, after one, four, 16 and 64 days, respectively, in the brine-rock-CO\({}_{2}\) system (Table 1) whereas for Experiment 2 (with GD) the pH decreased from 7 (brine without CO\({}_{2}\)) to 5.81, 5.61, 6.38 and 6.61. In Experiment 2, the number of specimens was doubled (higher rock/brine ratio), but there was not a clear increase in the concentration of ions in solution, as suggested by similar values of conductivity for both experiments. For Experiment 1 (CG), in general, the behavior of cations in solution was variable, despite the tendency of Ca\({}^{2+}\) decreasing, whereas K\({}^{+}\), Mg\({}^{2+}\), SiO\({}_{2}\) and total Fe increased. For Experiment 2 (GD), besides Na\({}^{+}\), all other analysed cations had lower concentrations in solution when compared to Experiment 1. Furthermore, the analysed elements did not always show the same behavior as described for Experiment 1. After an increase until the four-day run,