Arburese, South Sardinia Province, Sardinia, Italyi

Regional Level Types
Arburese	Mining District
South Sardinia Province	Province
Sardinia	Autonomous Region
Italy	- not defined -

Arburese is a geographical area and a mining district of South West Sardinia, bounded on the east by the Campidano Plain, on the south by Iglesiente, on the west by the Sea of Sardinia, and on the north by the Gulf of Oristano. Sometimes this region is also referred to as the Upper Iglesiente (Alto Iglesiente in Italian; Igresienti de susu or Muntangia in Sardinian) or Guspinese.

From a geological point of view, Arburese consists of a Palaeozoic basement, deformed and metamorphosed by the Hercynian orogeny and intruded by late-Hercynian granitoid plutons, locally overlaid with sedimentary and volcanic covers spanning from the Permo-Carboniferous to Oligo-Miocene and Quaternary.

The Arburese region is characterised by two late Variscan intrusions, which differ in age and composition: the Arbus (or Arburese) and the Monte Linas pluton, aging 304 ±1 Ma, and 289 ±1 Ma respectively. They emplaced at shallow crustal levels and crosscut the basal thrust between the alloctonous prism and the foreland of the Variscan belt of Sardinia. The Arbus Pluton (AP) is a composite intrusion of piroxene- and amphibole-granodiorites hosting minor amounts of monzogabbroic rocks and cordierite-bearing granites with a wide core of leuco-monzogranites. Tourmaline greisens and pegmatites garnish the contact between the border facies and the host metamorphic rocks. The Monte Linas Pluton (MLP) has biotite monzogranite composition. The pluton is internally zoned, from medium grained monzogranite in the core to hololeucocratic fine-grained rock-types at the top, where often F-greisen, fayalite-pegmatite pods and sill are common. In both plutons the igneous associations are high-K ilmenite series, suggesting derivation from low- fO2 magmas possibly linked to a common crustal contribution; however, in the Linas Pluton magnetite in the fine-grained facies may indicate an increase in oxygen fugacity.

Small Sn deposits are hosted in low-grade metamorphics close to the contacts with intrusives. The AP-related Sn ores consist of high-temperature As-Sn quartz veins. They are vertically zoned, from quartz-chlorite-cassiterite to large quartz-arsenopyrite veins. Ore microscopy and SEM-EDS analyses evidenced a vein texture made of thick idiomorphic and frequently twinned cassiterite crystals, alternated with several generations of banded/geodic quartz. Clinochlore aggregates are included into the quartz. The arsenopyrite ore shows alternating bands of microgranular to crystalline millimetric arsenopyrite with quartz. Field and analytical data suggest genetic mechanisms dominated by mobilization of residual Sn by chloride and other complexes in reducing, As- and S- rich, low- fO2 juvenile fluids. Cassiterite and successive arsenopyrite precipitation occurred under changing physicochemical conditions (e.g. oxygen contents; temperature decrease; pH).
The MLP Sn metallogeny include Sn- Pb-Zn-Cu veins (e.g. Canale Serci old mine). Cassiterite occurs as fine-grained corroded crystals. Optical and SEM-EDS analyses evidence a high-temperature oxide stage (quartz-chlorite-cassiterite) followed, after brecciation, by mesothermal sulfide stages, with progressive deposition of sphalerite, pyrite, chalcopyrite, tetrahedrite, galena, and marcasite. Naitza et al. (2015) considered a possible derivation of the ore from residual, reducing juvenile fluids, capable to carry Sn- complexes from monzogranite magmas from which cassiterite precipitated in consequence of an increasing in fO2.

A really important occurrence is the huge mesothermal lode system of Montevecchio-Ingurtosu-Gennamari, which borders the northern and western sides of the Arburese Pluton. This system includes both radial bodies, generally of minor economic importance, and kilometre-sized peripheral bodies, forming sub-systems roughly parallel to the border of the batholith, with an overall longitudinal extension of some 12 km. The mineral assemblage mainly includes Fe-bearing sphalerite (marmatite), galena, and pyrite, in variable proportions, and minor chalcopyrite and other sulphides and sulphosalts; the main gangue minerals are quartz and ankerite. The mines that exploited these lodes mainly produced Pb and Zn, besides minor, but very important, quantities of Ag and Cd that were regularly recovered from the metallurgical treatments of, respectively, the Pb and Zn concentrates. Montevecchio, the easternmost of the mines that was operated here, is the most important.

Fossils

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References

Localities in this Region