## 5 Discussion
### Experimental Results
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **0 days** & **1 Day** & **4 Days** & **16 Days** & **64 Days** \\ \hline \multicolumn{2}{c}{**Primary Phases**} & \multicolumn{4}{c}{**Secondary Phases**} \\ \hline \multirow{6}{*}{Modelling} & & & & Calcite & \((4.8\times 10^{-5})\) & Smectite \((2.13\times 10^{-6})\) \\  & & & SO\({}_{2}\) am. & Dolomite & Calcite \((8.85\times 10^{-2})\) \\  & Clinopyroxene (\(\bar{\text{52}}\)) & Kaolinite & \((2.13\times 10^{-6})\) & \((5.28\times 10^{-5})\) & Dolomite \((8.32\times 10^{-4})\) \\  & Orthopyroxene (\(1.2\)) & \((2.07\times 10^{-5})\) & Kaolinite & SiO\({}_{2}\) am & Magneste \((5.92\times 10^{-5})\) \\  & Olivine (\(10\)) & Ca-zeolites & \((2.4\times 10^{-5})\) & \((5.92\times 10^{-6})\) & Siderite \((2.77\times 10^{-4})\) \\  & Plagioclase (\(11\)) & \((2.82\times 10^{-3})\) & Ca-zeolites & Kaolinite & Ca-zeolites \((5.54\times 10^{-2})\) \\  & & & \((4.16\times 10^{-3})\) & \((2.42\times 10^{-5})\) & SiO\({}_{2}\) am. \((1.34\times 10^{-5})\) \\  & & & & Ca-zeolites & Kaolinite \((2.75\times 10^{-5})\) \\  & & & & \((4.36\times 10^{-3})\) & \\ \hline \multirow{6}{*}{Experimental} & Clinopyroxene & & & & Smectite \\  & (45–55) & Gypsum & Gypsum & Gypsum & (GXRD) \\  & Olivine (15-20) & Halite & (SEM-EDS) & (SEM-EDS) & Gypsum \\  & Amphibole (10–15) & \multirow{2}{*}{(XRD + SEM-EDS)} & Halite & Halite & (GXRD + SEM-EDS) \\  & Plagioclase (5–10) & \multirow{2}{*}{(SEM-EDS)} & \multirow{2}{*}{(SEM-EDS)} & Halite & (GXRD + SEM-EDS) \\  & & Iminetic (5) & & & (GXRD + SEM-EDS) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparative summary of modelled and experimental mineral phases from cumulate gabbro (GXRD: grazing incidence geometry XRD; phases expressed as vol %). behavior of Mg\({}^{2+}\) and total Fe, what is generally described is an increase in its concentration. This was also observed with the GD experiments. * The Ca\({}^{2+}\) (aqueous) decrease can be explained by the high content of this ion in the initial brine. Under the experimental conditions, Ca\({}^{2+}\) should be consumed when forming secondary minerals (Ca-Al-Si; calcium aluminum silicates), as predicted by the modelling. The hypothesis that precipitation of gypsum within the autoclave could account for the Ca\({}^{2+}\) decrease should be discarded, since the sulphate ion concentration is not sufficiently high. Modelling results indicate that for gypsum to precipitate the sulphate concentration should be at least double. * The 0.4 wt. % increase in CaO in the total rock composition after a 64-day run seems to reflect not only its incorporation in the structure of Al-silicates but also the crystallization of gypsum during the drying process, after concluding the run. * Increases of iron and magnesium in solution are in accordance with the decrease, albeit reduced, of these elements (0.4 wt. % FeO and 0.1 wt. % MgO) in the whole rock composition after 64 days. These observations are also in agreement with the textural observations, where the Fe-Mg mineral phases are the first to react with acidified brine, releasing these components into the solution. Regarding the experiment with GD, the variation of Ca\({}^{2+}\) and Mg\({}^{2+}\) concentrations in brine shows a very small increase, or a tendency to remain constant. The increase is in line with what is described in the literature [25]. Such an increase in solution is reflected in the decreasing concentrations of CaO (0.42 wt. %) and MgO (0.21 wt. %) in total rock for the 64-day run specimens. FeO shows a similar trend, decreasing by 0.3 wt. % in the same specimens.