## 2 Methodology
### Screening and Ranking Criteria
For each geological formation, the fracture density was assessed by fracture pattern studies in outcrops and quarries using a scanline approach with measurement of fracture frequency. The massifs were divided into three categories: more than 10 fractures/m, 3-10 fractures/m, and fewer than 3 fractures/m, to which indices 9, 6, and 1 were assigned, respectively. * Socioeconomic and environmental constraints
* Distance to CO2 sources--transport of CO2 over long distances is a highly penalizing factor. Thus, for this criterion, three categories were defined as a function of the distance to which values 9, 6, and 1 were assigned, respectively, for distances of less than 10 km, between 10 and 100 km, and over 100 km. * Social and demographic situation--building an industry for in situ carbonation will not be well accepted in urban areas. For this criterion, two categories were defined, wherein an index of 3 was assigned to rural regions and zero was assigned to urban areas. * Existence of productive aquifers--groundwater is a value that must be preserved. Thus, geological units that correspond to productive aquifers were completely excluded on the basis of this criterion. * Environmental restrictions--this type of project is prohibited in natural parks and other protected areas. This criterion was considered, but no geological formations favorable to in situ carbonation were identified in protected areas. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Criteria** & **Classes** & **Weight** \\ \hline \multicolumn{3}{c}{**Geological conditions**} \\ \hline \multirow{3}{*}{**CI—Lithological composition**} & Ultramafic—more than & \multirow{3}{*}{9} \\  & 90\% of mafic minerals & \\ \cline{2-3}  & Mafic—40–90\% mafic minerals & \\ \cline{2-3}  & Intermediate—10–39\% of & \\ \cline{2-3}  & mafic minerals & \\ \hline \multirow{3}{*}{**C2—Outcropping area**} & Over 20 km\({}^{2}\) & 3 \\ \cline{2-3}  & From 10 to 20 km\({}^{2}\) & 2 \\ \cline{2-3}  & Less than 10 km\({}^{2}\) & 1 \\ \hline \multirow{3}{*}{**C3—Expected volume**} & Over 20 km\({}^{3}\) & 6 \\ \cline{2-3}  & From 10 to 20 km\({}^{3}\) & 3 \\ \cline{2-3}  & Less than 10 km\({}^{3}\) & Eliminatory criterion \\ \hline \multirow{3}{*}{**CI—Eexistence of a seal unit**} & Existent & 3 \\ \cline{2-3}  & Not known & 0 \\ \hline \multirow{3}{*}{**CS—Fracture density**} & More than 10 fractures/m & 9 \\ \cline{2-3}  & 3–10 fractures/m & 6 \\ \cline{2-3}  & Fewer than 3 fractures/m & 1 \\ \hline \multicolumn{3}{c}{**Socioeconomic constraints**} \\ \hline \multirow{3}{*}{**C6—Distance to CO2 sources**} & Less than 10 km & 9 \\ \cline{2-3}  & From 10 to 100 km & 6 \\ \cline{2-3}  & Over 100 km & 1 \\ \hline \multirow{3}{*}{**C7—Social and demographic situation**} & Urban area & 3 \\ \cline{2-3}  & Rural & 0 \\ \cline{2-3}  & No & 3 \\ \cline{2-3}  & Yes & Eliminatory criterion \\ \hline \multirow{3}{*}{**C9—Environmental restrictions**} & No restrictions & 0 \\ \cline{2-3}  & Protected areas & Eliminatory criterion \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Screening and ranking criteria. The shaded bars represent the relative importance of the class in each criterion. The final ranking results from the sum of the weight obtained in each criterion. If any massif was assigned the class “eliminatory criterion” it was not further considered in the screening and ranking procedure. The final ranking of the rock massits was obtained by adding the weights assigned to each criterion.