Fig. 6

SEM and optical microscope micrographs of volcanic rocks affected by fracture-controlled alteration in CP2A and CP5A wells of the CP geothermal system. a Massive crystallization of adularia (Adl) with minor albite (Alb) in altered dacitic tuffs sampled close to a major FZ at 445 m depth in CP5A well. SEM observations in backscattering mode evidence chemical zoning in K-feldspars related to solid solution between adularia and celsian (Ba-rich Adl). b Quartz (Qtz) and adularia veinlets in strongly altered dacitic tuffs sampled at 445 m depth in CP5A well with later illitization (Ill) of adularia and deposition of hematite (Hem) in the wall rock. c feathery texture of quartz crystallized in veins with calcite and adularia in strongly altered dacitic tuffs sampled at 445 m depth in CP5A well d Radial pattern of adularia needles typical of the flamboyant texture as fracture infillings in the dacitic tuffs sampled at 445 m depth in CP5A well. e Chemical zoning related to Ba for K substitution in outer part of adularia crystals at the wall of the open spaces in the strongly altered dacitic tuffs sampled at 445 m depth in CP5A well. f Late crystallization of illite (Ill), chlorite (Chl), and hematite (Hem) after deposition of adularia and quartz in the strongly altered dacitic tuffs sampled at 445 m depth in CP5A well. g Dissolution of adularia crystals followed by crystallization of illitic clay minerals in the dacitic tuffs sampled at 550 m depth in CP5A well. h Quartz-hematite veinlets with intense alteration in wall rock consisting in the replacement of andesitic tuffs by illitic minerals and carbonates (calcite with minor inclusions of dolomite), close to a major FZ at 1540 m in CP2A well