Das Projekt "Study of reactions between dry rocks and heat exchange fluids" wird vom Umweltbundesamt gefördert und von Universität Karlsruhe, Mineralogisches Institut durchgeführt. Objective: To study the reaction between water and rock in order to obtain a better understanding of reactions that happen in a hot dry rock system. General information: reactions between rocks and heat exchange fluid change both the structure and chemical composition of the heated source rocks. Since the surfaces are of foremost interest, the investigations will be mainly concerned with these. The reaction mechanisms will be determined on the basis of measured reaction rates and reaction products. Major and trace elements will be measured in solution as well as surface structures and secondary minerals. Hdo will be used to study the possible replacement of metal cations by h3o+. Solids and liquids will be analysed with sims and mass spectrometry. See also contracts 0001/b, 0079/b, 0002/d, 0057/uk and 0010/f. Advancement: this contract started on 1.10.86 as a continuation of contract 0002/D. Achievements: The aim of the work has been to get closer understanding of water rock interaction at the conditions of hot dry rock energy exploitation by studying its initial reaction. Investigations have been carried out to prove the idea that during the initial phase of the reaction between feldspars and aqueous fluids an exchange between alkali and alkaline earth cations with hydronium ions takes place building a hydronium feldspar at the very outer layers of the mineral. The compositions of the reaction fluids were measured by atomic absorption spectrometry (AAS) and the investigations on the solid samples were carried out by infrared (IR) spectrometry, X-ray diffractometry (XRD), X-ray Guinier camera and secondary ion mass spectrometry (SIMS). Investigations on thin cleaved fragments with the IR method did not show any change of the absorption bands compared to the starting material. XRD investigations on powdered samples gave some evidence for the existence of (D3O) AlSi3O8 by the splitting of the (201) reflection. However these results were not unambiguous. They could not be substanciated with the X-ray Guinier method. SIMS investigations gave a clear direct indication for the incorporation of deuterium in feldspar along with simultaneous depletion of both potassium and aluminium. This result indicates an exchange reaction of deuterium oxide (D3O) for potassium and a disintegration reaction of the (Al, Si)O4 network to occur simultaneously.