The distribution of rare earth elements in albites from Sarule-Ottana area (central Sardinia, Italy) | La distribuzione delle terre rare nelle albititi dell'area di Sarule-Ottana (Sardegna Centrale, Italia)

Several albitite lenses occur over an area of 90 Km2 in Central Sardinia within Hercynian granitoids: The albitites were studied in the past years as concerns mineral association, distribution and fractionation of Rare Earth Elements (REE). The papeper reports on the results of the prospection carried in the Sarule-Ottana sector. The Hercynian granitoids, mainly granodiorites, consist of quartz, plagioclase and K-feldspar; biotite and allanite are the main accessory minerals. The paragenesis of albitites mainly consists of rarely zoned plagioclase and quarts. Subordinate minerals are K-feldspar, biotite, chlorite, epidote, titanite and muscovite. Three main lithitypes were recognized based on different mineralogical associations: albite s.s., quartz bearing albite and chlorite-bearing albitite. Compared to unaltered rock, albitite s.s. shows higher Na2O and Al2O3, quartz-bearing albitite higher content in Sr and Na2O, and chlorite bearing in Na2O and MgO. All these lithotypes are generally depleted in Fe, K, Rb and Ba, this suggesting that plagioclase, K-feldspar and biotite were affected by remarkable chemical-structural transformations. The mobilization of REE, essentially due to metasomatic processes, caused a re-distribution of these elements into the albitites, enriching the epidote-bearing facies in LREE. A number of studied quartz veins were found to be very low in REE. Epidote and titanite are the REE-bearing minerals of albitites. Epidote shows a variable composition ranging from LREE-free to LREE-bearing to allanite-(Ce). Titanite contains variable amounts of of Y along with subordinate HREE. Geological, mineralogical and petrographic evidences and REE mobility considerations suggest that metasomatic processes may be related to seawater circulating through the metasedimentary basement.