The overall alteration pattern in the drill hole at Reydarfj¿rdur is very similar to alteration patterns observed in Icelandic geothermal areas and in low-grade metamorphosed basalts in deep crustal sections elsewhere in Iceland. However more detail in obtained by the study of the IRDP drill core than by study of drill cuttisgs sampled in previous drill holes in Iceland. A comparatively high fossil thermal gradient is obtained at Reydarfj¿rdur by a combination of mineral stability data and the observed occurrence of secondary minerals. This high gradient is consistent with the measured dike dilation at the drill site and the location of the drill site adjacent to a central volcano.