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The Cu-Mo (and Zn-Fe-Pb) mineralisations of central Sardinia (Ogliastra) represent an important stage of evolution of mineralising processes in the Sardinia microplate. The cre-association (Cu-Mo), the calc-alkaline trends of Hercynian granitoid stocks, the geodynamic environment of the palaeomargin are parameters in agreement with a porphyry copper mineralisation mode. However, the absence of typical zoning both of metals and hydrothermal alteration as well as that of a large calc-alkaline volcanic cycle, the prevalence of Zn over Cu and the low grade of Mo are parameters restrict the applicability of such a model. The mineralising fluids deposited a clear geochemical halo around the orebodies and the host rocks are primarily granodiorite with subordinate granite. The mineralisation consists of small bodies with disseminated sulphides and oxides in a stockwork texture. Quartz veins with disseminated mineralisation, are also present., The Cu-Mo (and Zn-Fe-Pb) mineralisations of central Sardinia (Ogliastra) represent an important stage of evolution of mineralising processes in the Sardinia microplate. The cre-association (Cu-Mo), the calc-alkaline trends of Hercynian granitoid stocks, the geodynamic environment of the palaeomargin are parameters in agreement with a porphyry copper mineralisation mode. However, the absence of typical zoning both of metals and hydrothermal alteration as well as that of a large calc-alkaline volcanic cycle, the prevalence of Zn over Cu and the low grade of Mo are parameters restrict the applicability of such a model. The mineralising fluids deposited a clear geochemical halo around the orebodies and the host rocks are primarily granodiorite with subordinate granite. The mineralisation consists of small bodies with disseminated sulphides and oxides in a stockwork texture. Quartz veins with disseminated mineralisation, are also present.

Large kaolin deposits hosted by Miocene silicic pyroclastic rocks represent hydrothermal alteration within 200 m of the Miocene palaeosurface as boiling hydrothermal fluids ascended steeply dipping faults. The broadly stratiform deposits constitute advanced argillic alteration produced in a steam-heated zone near the surface, while the deeper deposits represent two types of epithermal systems: weakly acidic low-sulphidation at Tresnuraghes and acidic high-sulphidation at Romana. The size of the systems suggest that the deeper parts may be prospective for precious metals., Large kaolin deposits hosted by Miocene silicic pyroclastic rocks represent hydrothermal alteration within 200 m of the Miocene palaeosurface as boiling hydrothermal fluids ascended steeply dipping faults. The broadly stratiform deposits constitute advanced argillic alteration produced in a steam-heated zone near the surface, while the deeper deposits represent two types of epithermal systems: weakly acidic low-sulphidation at Tresnuraghes and acidic high-sulphidation at Romana. The size of the systems suggest that the deeper parts may be prospective for precious metals.

The deposit is hosted by the upper pyroclastic facies of an Oligocene-Miocene calcalkaline volcanic unit. Measured reserves are estimated as about 1 000 000 t, with montmorillonite and K-feldspar the main minerals and minor quartz, illite and plagioclase. Chemical analysis has shown that the minerals are mainly of the Ca-Mg type. Their physical and chemical characterstics make them suitable for foundry use, for the production of animal feed and litter, as carriers and diluents in pesticide and fertiliser preparation, in iron-ore pelletising, for treating waste water, in the production of detergents and as waterproofing in waste disposal sites., The deposit is hosted by the upper pyroclastic facies of an Oligocene-Miocene calcalkaline volcanic unit. Measured reserves are estimated as about 1 000 000 t, with montmorillonite and K-feldspar the main minerals and minor quartz, illite and plagioclase. Chemical analysis has shown that the minerals are mainly of the Ca-Mg type. Their physical and chemical characterstics make them suitable for foundry use, for the production of animal feed and litter, as carriers and diluents in pesticide and fertiliser preparation, in iron-ore pelletising, for treating waste water, in the production of detergents and as waterproofing in waste disposal sites.

Detailed prospecting and sampling of the deposits has been carried out to test their quality and possible use in the ceramics industry. The deposits are mainly welded aeolian and fluvial quartz-feldspar sands. The samples were analysed by X-ray diffraction and X-ray fluorescence techniques and tested for use in stoneware and porous tiles. The sand was found to have suitable properties for use in ceramics, with some restrictions due to the presence of Fe oxides and smectites. Their quality could be improved, however, by simple washing and riddling. The technological behaviour of the sands was comparable with that of quartz-feldspar sands from Sassuolo., Detailed prospecting and sampling of the deposits has been carried out to test their quality and possible use in the ceramics industry. The deposits are mainly welded aeolian and fluvial quartz-feldspar sands. The samples were analysed by X-ray diffraction and X-ray fluorescence techniques and tested for use in stoneware and porous tiles. The sand was found to have suitable properties for use in ceramics, with some restrictions due to the presence of Fe oxides and smectites. Their quality could be improved, however, by simple washing and riddling. The technological behaviour of the sands was comparable with that of quartz-feldspar sands from Sassuolo.

The fluorite-bearing hydrothermal mineralisation occurs mainly within Palaeozoic volcanic and metasedimentary rocks, with only three occurrences being located in Cainozoic volcanic and siliciclastic rocks. Most of the fluorites exhibit relatively high rare-earth and Y (REY) contents, strong positive Y anomalies, slightly negative Ce and generally positive Eu anomalies indicating that the REY were mobilised mainly from non-carbonate rocks. Mixing probably occurred between diluted surficial waters and brines circulating mainly through the Lower Palaeozoic metasedimentary basement. The Cainozoic fluorites exhibit chemical and isotopic features similar to those of the Palaeozoic fluorites, but the Nuraghe Onigu fluorite displays a possible contribution of Sr from Cainozoic magmatic rocks. The data suggest that radiogenic Nd was provided to the fluids from the Ordovician siliciclastic basement, except for three deposits where the potential source rocks of Nd were mainly Ordovician acidic magmatic rocks. The results for the Cainozoic fluorites suggest a provenance of Nd essentially from the leaching of Variscan granitoids., The fluorite-bearing hydrothermal mineralisation occurs mainly within Palaeozoic volcanic and metasedimentary rocks, with only three occurrences being located in Cainozoic volcanic and siliciclastic rocks. Most of the fluorites exhibit relatively high rare-earth and Y (REY) contents, strong positive Y anomalies, slightly negative Ce and generally positive Eu anomalies indicating that the REY were mobilised mainly from non-carbonate rocks. Mixing probably occurred between diluted surficial waters and brines circulating mainly through the Lower Palaeozoic metasedimentary basement. The Cainozoic fluorites exhibit chemical and isotopic features similar to those of the Palaeozoic fluorites, but the Nuraghe Onigu fluorite displays a possible contribution of Sr from Cainozoic magmatic rocks. The data suggest that radiogenic Nd was provided to the fluids from the Ordovician siliciclastic basement, except for three deposits where the potential source rocks of Nd were mainly Ordovician acidic magmatic rocks. The results for the Cainozoic fluorites suggest a provenance of Nd essentially from the leaching of Variscan granitoids.

Prospecting for REE mineralisation has been carried out in the sandstones of Punta Serpeddi which host heavy minerals concentrated in placers. The results are presented of detailed investigations from six zones in the Dolianova sector which were carried out on bulk and preconcentrate samples. Rutile, monazite, zircon and ilmenite are the most important minerals present with apatite present as a subordinate mineral. Chemical characterisation by microprobe analysis demonstrates that monazite is the most important REE-bearing mineral; it is present in the magnetic classes between 0.5 and 1.3 tesla., Prospecting for REE mineralisation has been carried out in the sandstones of Punta Serpeddi which host heavy minerals concentrated in placers. The results are presented of detailed investigations from six zones in the Dolianova sector which were carried out on bulk and preconcentrate samples. Rutile, monazite, zircon and ilmenite are the most important minerals present with apatite present as a subordinate mineral. Chemical characterisation by microprobe analysis demonstrates that monazite is the most important REE-bearing mineral; it is present in the magnetic classes between 0.5 and 1.3 tesla.

A new bentonite deposit has been discovered in Iscala Ezza. It is hosted by Oligocene-Miocene calc-alkaline volcanites. The mineralisation averages 5 m in thickness and is localised in the upper part of a pyroclastic-cineritic formation about 50 m thick in outcrop. Montmorillonite is the main bentonite mineral with cristobalite, sanidine, quartz and illite as the main accessory minerals. Ematite and goethite occur in the superficial parts of the mineralisation. The main exchangeable cations are Ca and Mg. The origin of the deposit has been proposed as deuteric alteration. This agrees with the observed retention of relict texture by the bentonites. There is also no evidence that weathering and hydrothermal process had significant roles in bentonite formation. The bentonite has good physical and chemical properties for industrial use., A new bentonite deposit has been discovered in Iscala Ezza. It is hosted by Oligocene-Miocene calc-alkaline volcanites. The mineralisation averages 5 m in thickness and is localised in the upper part of a pyroclastic-cineritic formation about 50 m thick in outcrop. Montmorillonite is the main bentonite mineral with cristobalite, sanidine, quartz and illite as the main accessory minerals. Ematite and goethite occur in the superficial parts of the mineralisation. The main exchangeable cations are Ca and Mg. The origin of the deposit has been proposed as deuteric alteration. This agrees with the observed retention of relict texture by the bentonites. There is also no evidence that weathering and hydrothermal process had significant roles in bentonite formation. The bentonite has good physical and chemical properties for industrial use.

In the southwestern part of Sardinia some subvolcanic andesitic bodies occur, related to rift structures. Weak alteration phenomena and the presence of pyrite disseminations led to the investigation of the area through petrographical studies and geochemical prospecting of rocks and soils. The geochemical survey showed that, given the local morphological and climatic conditions, rock and soil sampling is well correlated; furthermore, correlations relating Cu with Ba and Sr proved effective in defining the anomalous areas. The main anomaly area found by these studies could represent a porphyry copper body., In the southwestern part of Sardinia some subvolcanic andesitic bodies occur, related to rift structures. Weak alteration phenomena and the presence of pyrite disseminations led to the investigation of the area through petrographical studies and geochemical prospecting of rocks and soils. The geochemical survey showed that, given the local morphological and climatic conditions, rock and soil sampling is well correlated; furthermore, correlations relating Cu with Ba and Sr proved effective in defining the anomalous areas. The main anomaly area found by these studies could represent a porphyry copper body.

X-ray, optical microscope, and electron microprobe analyses on about 50 samples were carried out. A VLF electromagnetic study was also carried out to achieve a higher structural and attitudinal definition of the mineralised area. The spectral analysis of the electromagnetic signal was done by the Maximum Entropy Method. By the data filtration and interpolation a bi-dimensional representation of the VLF anomalies was obtained., X-ray, optical microscope, and electron microprobe analyses on about 50 samples were carried out. A VLF electromagnetic study was also carried out to achieve a higher structural and attitudinal definition of the mineralised area. The spectral analysis of the electromagnetic signal was done by the Maximum Entropy Method. By the data filtration and interpolation a bi-dimensional representation of the VLF anomalies was obtained.

Chemistry of the rocks analysed shows that the emplacement of the Mo ores was accompanied by weak alteration of the host rocks, that was performed by acidic fluids closely connected as origin with the intrusion of the granitic magmas. Alteration is characterised in most rocks by an increase of SiO2 and a decrease of Al2O3, all other major elements exhibit no characteristic variations. TiO2, MnO and P2O5 exhibit lower contents in most rocks with respect to unaltered rocks of similar SiO2 content. Finally, among trace elements, only Ba and to a lesser extent Sr, decrease with increasing SiO2, all other trace elements display constant abundances in most rocks., Chemistry of the rocks analysed shows that the emplacement of the Mo ores was accompanied by weak alteration of the host rocks, that was performed by acidic fluids closely connected as origin with the intrusion of the granitic magmas. Alteration is characterised in most rocks by an increase of SiO2 and a decrease of Al2O3, all other major elements exhibit no characteristic variations. TiO2, MnO and P2O5 exhibit lower contents in most rocks with respect to unaltered rocks of similar SiO2 content. Finally, among trace elements, only Ba and to a lesser extent Sr, decrease with increasing SiO2, all other trace elements display constant abundances in most rocks.