Hydrothermal Scheelite Associated with Upper Cretaceous Intrusions in Romania: A Mineralogical Insight to the W Metallogeny

Hydrothermal scheelite from three Romanian occurrences was analyzed in order to ascertain its structural, physical, vibrational, paragenetic, and crystal-chemical peculiarities as an important tool for characterizing the metallogenetic behavior and facilitating the ore-processing. All three occurrences, i.e., Ciclova and Oravița in Banat and Băița Bihor in the Bihor Mountains, are related to skarn deposits developed at the contact of Upper Cretaceous granodioritic bodies with Mesozoic calcareous deposits. Typical crystals show {001}, {111}, and {101} forms and are up to 15 mm across. The structure was successfully refined as tetragonal, space group I41/a, with R1 = 0.0165 (Ciclova), 0.0204 (Oravița), and 0.0237 (Băița Bihor), respectively. The cell parameters refined for the same samples are a = 5.2459(10) Å and c = 11.3777(5) Å at Ciclova, a = 5.2380(2) Å and c = 11.3679(8) Å at Oravița, and a = 5.2409(2) Å and c = 11.3705(6) Å at Băița Bihor. The multiplicity of bands in both infrared absorption and Raman spectra is consistent with the S4 punctual symmetry of the tungstate anion, agreeing with the structural data. In all cases, the analyzed scheelite is close to the CaWO4 end-member. Cathodoluminescence peculiarities at the level of single crystals suggest that they crystallized in a slightly oxidizing to reducing environment from late hydrothermal solutions. Textural and paragenetic peculiarities suggest that scheelite from the three occurrences crystallized from epithermal, low-temperature, fluoride- and boron-bearing aqueous solutions.