Mineral-fluid interactions in the Broadlands-Ohaaki geothermal system, New Zealand

Abstract

The primary textures and the distribution and composition of secondary minerals combined with drilling data on circulation losses were used to identify flow paths, less permeable rock units, upflow zones, and the descent of cooler waters in the Broadlands-Ohaaki geothermal system, New Zealand. Changes in the secondary mineralogy and mineral and fluid composition in most of the permeable flow zones and in fractures in less permeable rock units are in response to boiling, steam loss, and cooling with a concomitant increase in pH, fO2, fS2, and H2S/H2 and decrease in fCO2. Alteration mineralogy and mineral compositions in some of these less permeable rock formations are the best indicators of the nature of the deep, high temperature fluid. -from Authors