SPURRITE, TILLEYITE AND ASSOCIATED MINERALS IN THE EXOSKARN ZONE FROM CORNET HILL (METALIFERI MASSIF, APUSENI MOUNTAINS, ROMANIA)

The high-temperature skarn of Cornet Hill (Apuseni Mountains, Romania) is known as one of the rare occurrences of spurrite and tilleyite worldwide. Both minerals concentrate in the outer skarn zone, corresponding to the exoskarn, at the contact between a monzodiorite-quartz monzonite body of Upper Cretaceous age and Tithonic-Kimmeridgian reef limestones. The Cornet Hill skarn is clearly zoned. The zoning is defined by the predominance of series of mineral species and is, from the outer to the inner part of the metasomatic area, as follows: calcite (marble), tilleyite, spurrite, wollastonite + gehlenite + vesuvianite, wollastonite + grossular, quartz monzonite. The exoskarn is confined to the tilleyite- and spurrite-bearing zones. The mineral associations identified in the exoskarn zone so far include: (1) metasomatic or primary products such as spurrite, tilleyite, and accessory gehlenite, grossular, titanian andradite, monticellite, wollastonite, perovskite, vesuvianite, ellestadite-(OH), and (2) hydrothermal and weathering (secondary) minerals such as afwillite, fukalite, scawtite, thaumasite, hibschite, xonotlite, thomsonite, gismondine, plombierite, tobermorite, riversideite, portlandite, allophane, calcite, and aragonite. Chemical, optical, infrared absorption, and X-ray powder analyses of the primary mineral species, as well as of three secondary species firstly described in the Romanian skarns, i.e. , afwillite, thaumasite, and fukalite, are reported here.