Thanks to various projects funded or co-funded by CNR and to the scientific
collaboration with ENEL, IGG has taken an active part in the investigation of
southern Tuscany, in particular for geothermal exploration. We will give an overview
of the most recent results of the many activities and research, underlying the
multidisciplinarity of our Institute, taking as example the famous Larderello area.
Metamorphic and granitic rocks hosting the deep geothermal reservoir have been
studied from various perspectives. Geochemical and petrographic methods have been
applied to core samples to study magmatic and hydrothermal minerals and fluid
inclusions, and together with geophysical methods were applied to study the signature
of geothermal fluid circulation. These studies provided important information
regarding the geothermal system and its evolution with time.
Geological surveys and structural analysis of major structures integrated with
analogue modelling studies provide useful insights into the understanding of the
Larderello tectono-magmatic evolution.
Contact metamorphic isogrades were defined at Larderello, as well as ages of granites
and contact metamorphic rocks.
Fluid geochemistry provided reservoir temperature and origin of noble gases.
Isotopic composition of oxygen, carbon and hydrogen in steam and carbon dioxide can
provide useful information about origin of water and gases.
Noble gases isotopes in fluids from geothermal wells, fumaroles and fluid inclusions
allow to trace the different sources (mantle, crust and air) and the evolution in
space and time of the hydrothermal system.
Source and evolution of crustal magmas have been studied using isotopic geochemistry.
Chemical and isotopic characteristics of fluids (geothermal, surface and ground
water, thermal and cold springs) are investigated to identify the origin of some
geochemical anomalies that are peculiar for local groundwater. Connected study on
Quaternary alluvial sediments provided significant information on the role that the
geothermal fluids had on the geochemical signature of the local sediments.
Heat flow and thermal gradients have been defined, and thermal models allowed the
reconstruction of temperature distribution in the crust, providing also indication of
Magnetotelluric method has provided a useful contribution to geothermal exploration
and exploitation; data interpretation has revealed a good correlation between the
feature of the geothermal field and the resistivity distribution at depth: low
resistivity corresponds to productive areas under exploitation. Medium-deep crustal
decrease of resistivity has also been defined.
The changes over time of R/Ra and its spatial distribution have given indication
regarding both the evolution of fluid circulation and temperature and the origin of
fluids. Comparison of geochemical and geophysical data have provided important
information regarding transport mechanism in the crust.
Fluid distribution and processes in the geothermal reservoir have been studied using