TRACING FOSSIL AND PRESENT-DAY FLUIDS IN ROCKS - APPLICATION OF THE NUCLEAR MICROPROBE

Geological fluids contain water, chlorides and Na as major components, and metals, CO2 gas and CH4 gas as minor or major components. Quantit ative analysis of geological fluids in fluid inclusions and hydrotherm al minerals is vital to the characterization of fluid-rock interaction s. The presence and quantity of trace and minor elements can be determ ined in fluid inclusions and minerals by Proton-induced-X-ray-emission (PIXE) and Proton-induced-gamma-ray-emission (PIGE) with EDS analysis , based on computer-aided interpretation of X-ray spectra. A feature o f the PIXE-PIGE method is the long range (deep penetration) of protons in light matrices, which allows near-surface inclusions to be analyse d. The applications presented here concern samples from submarine hydr othermal deposits (Red Sea, Lau Basin), and from skarns in Central Mor occo. In submarine hydrothermal processes, PIXE data show trace-elemen t-bearing-mineral(s) in assemblages with bulk geochemical anomalies, e .g. Co- and Pb-contents in the 1000 ppm range in chalcopyrite from the Hine-Hina field, Lau basin. PIXE data for high T chimneys of the Atla ntis II deep record trace element perturbations due to boiling. Hypers aline magmatic fluids in the Sn-skarns of El Hammam contain more than 1000 ppm Cu and Pb but no Zn. A Sn-borate: nordenskioldine, has been i dentified in the high T-skarns, trapping a Li-bearing concentrated bri ne. (C) 1997 Elsevier Science B.V.