Exploration for antimony deposits in southern Tuscany, Italy

Abstract

The idealized prototype of a southern Tuscan antimony deposit can be described as follows: The irregular mineralization is situated in the upper part of the highly porous Calcare Cavernoso, overlain by an impermeable unit, normally a flysch-type rock. The deposits are bound to the edge of horst positions and also to areas of elevated geothermal gradient and resulting hydrothermal activity. These observations were used as variables for statistical probability calculations for antimony-deposit formation. Within the areas determined to be of high probability, 47 target areas were selected for geochemical soil sampling. Positive correlation of antimony with barium, strontium and lead, corresponding to gangue and accessory ore minerals in the deposit was found. Local distribution of Sb of 3 representative areas are discussed in detail. Although no high anomalies so far unknown were identified, known mineralizations were extended or neighbouring anomalies found. Regional correlation with horst structures and especially their fault margins (e.g. eastern margin of the ridge of Monticiano) was confirmed. The high density of mineralizations in the Tafone area is also reflected in the geochemical results of the soil sample prospection. A possible explanation for this accumulation may be seen in the large outcrops of pre-Carboniferous rocks, which generally are expected to be the primary source of antimony. From these pre-Variscan units antimony was remobilized and transported hydrothermally to its present position.