Istituto di Geoscienze e Georisorse     
Cavarretta G., Gianelli G., Puxeddu M. Formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the Larderello-Travale geothermal field. In: Economic Geology, vol. 77 (5) pp. 1071 - 1084. Society of Economic Geologists, 1982.
Different authigenic mineral assemblages and mineral compositions have been found in different areas of the Larderello-Travale geothermal field. In the peripheral areas the most abudant authigenic minerals are quartz, calcite, chlorite, and sulphides. They formed in a temperature range of 150 to 250C and with a PCO2 range of 0.1 to 1.0 atm. In a hotter part of the field, at depths between 200 and 1300 m, where the main productive fractures are located, the most important authigenic minerals are quartz, chlorite, calcite, K-feldspar, and K-bearing mica, with which wairakite, hematite, anhydrite, and barite are sometimes associated. Deposistion of all these minerals occurs in a temperature range of 200 to 300C under Pco2 of about 1 atm, and relatively high PO2 , in fluids sometimes characterized by silica oversaturation. Below the 1300 m depth in the hottest part of the field K-feldspar, chlorite, epidote, sulfides, with minor sphene, prenhite, clynopyroxene, and clinoamphibolite are present. These minerals form in a tempertaure range of 250 to 350C under Pco2 of less than 1 atm and a PO2 ranging from 10-40 to 10-33 atm and reasonably reflect the physicochemical parameters of geothermal fluid before exploitation. Evidence of an earlier hydrothermal stage characterized by higher temperatures can be seen in the occurence of relic wollastonite and andradite
URL: http://www.segweb.org/
Subject petrography and mineralogy
rocks: chemical and petrographical data

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