Distribution of Hydrothermal Minerals in Larderello-Travale and Mt. Amiata Geothermal Fields (Italy)

Abstract

At Larderello an older phase of hydrothermal activity (350°-580°C) was characterized by wolastontie, andradite, clinopyroxene, plagioclase (an 1-60%), biotite, tourmaline and sulphides. In a more recent phase (150°-450°C), K-feldspar, ablite, epidote, chlorite, sphene, tremolite-actinolite, cliopyroxene and sulphides were deposited. The first appearance of K-feldspar (230°-270°C), epidote (230°-290°C), tremoite-actinolite (290°-340°C) and albite (T 330°C) gives vertical distribution patterns of temperatures in good agreement with the present day isotherms. In maps showing the present day temperatures distribution at 1 and 2 km depth, the same minerals were found within the isotherms of 250°C and 280°C respectively, i.e., in the most productive areas. In the Mt. Amiata field albite, calcite, K-mica, quartz, K-feldspar, chlorite were deposited in the range o250°-350°C. In the well PC29 epidote, quartz, albite and K-feldspar appear at T - 350°C. The widespread occurrence of calcite instead of epidote confirms the present day high P CO2.