| Summary: | Lithogeochemical or whole-rock chemical analysis has been widely used in the field of ore geology, but its application to study geothermal alteration in active geothermal systems remains uncommon. Within the framework of the GECO project, lithogeochemical characterization was proposed to assess the feasibility of the permanent storage of CO2 in the Nesjavellir high-temperature geothermal system in Iceland, using the CarbFix technology. Whole-rock chemical analyses were performed on samples at variable depth from 9 boreholes and 5 surface locations to determine the total and elemental mass change with respect to the unaltered precursor lithology. These values were employed to represent the distribution of components in the subsurface of Nesjavellir in 3D with the software Leapfrog. The results showed that, despite alteration controlling the distribution of most components, the variation in concentration of key cations for the CarbFix process rarely exceed the background values for Icelandic basalts. However, it was made evident that large quantities of carbon and sulfur are being captured in proximity to the surface and along faults, respectively. Redistributions of carbon and sulfur in the system cannot alone explain the large enrichments. Thus, the present study suggests that it is likely that these components derived, at least partially, from an external source (e.g., from magma degassing). The consideration of ongoing storage of natural CO2 and H2S, their remobilization and the redistribution of hazardous elements are recommended for future greenhouse gases injection campaigns. Efnagreiningar á heildarefnasamsetningu berggerða eru víða notaðar á sviðum jarðfræðinnar tengdum málmgrýtum en hingað til hefur ekki tíðkast að nýta aðferðarfræðina til að rannsaka ummyndun í virkum jarðhitasvæðum. Innan GECO verkefnisins hefur verið lagt til að notast við heildarefnasamsetningu berggerða til að meta áreiðanleika þess að binda CO2 innan jarðhitasvæðisins á Nesjavöllum með aðferðum CarbFix verkefnisins. ...
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