Contents of F, Cl, Li and B in the granite intrusions of Larderello, Italy

The active geothermal system of Larderello was originated by Pliocene-Quaternary granite intrusions more or less differentiated. A fluorine content in the magma has been estimated of approximately 1-1.5 wt%, with values up to 2.7 wt%. Boron shows high values only in tourmaline-bearing granites, and a content in the magma of at least 1 wt% is a realistic estimate. Lithium shows a slight positive anomaly and mainly concentrates in micas. Chlorine shows values which can be considered normal for granitic rocks. The amount of F and B suggests low solidus temperatures, and hence the possible occurrence of molten granite at very shallow crustal depth below Larderello. The origin of Cl and B in the present day geothermal steam of Larderello may be magmatic.