Abstract The Felbertal scheelite deposit is located in the northern part of the central Hohe Tauern (Austria). It occurs in an up to 400-m-thick section of the Precambrian (?) to Cambrian Habach Group, consisting of fine- and coarse-grained amphibolites, hornblendites, I-type granites, and quartzites. In the present paper, a comprehensive review of the voluminous literature covering the geologic, mineralogical, petrographic, geochemical, microthermometric, tectonic, geochronological, and isotopic aspects of the deposit is given, and then an attempt is made to combine these various aspects into a unifying evolutionary model of ore genesis. The premineralization history of both ore fields of the Felbertal scheelite deposit starts with fine-grained amphibolites, classified as volcanic arc basalts, at 547 ± 21 Ma. Sills of hydrothermally altered pyroxenites and gabbros, followed by I-type granites, intruded the basalts during Cambrian time. This rock suite may have been derived by differentiation and fractional crystallization of a calc-alkaline basaltic magma in an active continental margin setting. Primary scheelite formation is linked to the subsequent emplacement of highly differentiated granitic rocks (with within-plate granite characteristics) some 515 m.y. ago, as indicated in the eastern ore field by a granite gneiss (522 ± 11 Ma) underlying a scheelite-rich quartzite (507 ± 29 Ma.). This elongate quartzite lens, the contiguous granite gneiss lens, and an underlying stockwork zone mark a single feeder system. The rhythmic, fine-grained, and thinly laminated quartzite is interpreted as having been produced by the consecutive filling, under high fluid pressure, of a cavity with quartz and the oldest detectable scheelite mineralization (stage 1 scheelite), periodically interrupted by detachment and sliding phenomena. The feeder system narrows downwards as its WO 3 grade diminishes. The western ore field consists of several orebodies (K 1 to K 8 ). In the K 2 orebody, the emplacement of an I-type granite (older K 2 gneiss: 525 ± 14 Ma) was followed by the deposition of a bowl-shaped quartz mass and the formation of an eruption breccia (510 ± 36 Ma), intruded by a younger granite dike (younger K 2 gneiss: 512 ± 10 Ma). Primary scheelite deposition was coeval with the formation of the quartz mass; it was strongly enhanced during the formation of the eruption breccia, accompanied by elevated F contents, but was only minor in the subsequent intrusion of the small, younger K 2 granite. Primary mineralizing fluids are not preserved in fluid inclusions of scheelite due to metamorphic overprints. However, they may still be characterized by isotopic data of scheelite, which reflect a crustal origin with 87 Sr/ 86 Sr = 0.72 to 0.74, negative ε Nd ratios, elevated 238 U/ 204 Pb ( 206 Pb/ 204 Pb, 207 Pb/ 204 Pb) ratios, δ 18 O values of 8 per mil, as well as enrichments in Rb and Cs. Significant contributions to the fluids were possibly released from micas due to breakdown, leaching, or restructuring reactions, which may occur in deeper sections of a thick continental crust at an active continental margin setting. Such fluids apparently infiltrated a magma chamber of the Habach Group rock suite and caused the subsolidus formation of tschermakitic hornblende (with 87 Sr/ 86 Sr ratios of 0.74) by replacing clinopyroxene (with 87 Sr/ 86 Sr ratios of 0.707). Eventually, they transferred a presumably dissolved W content into the melt. There is no clear geologic record from the time interval between the early Paleozoic (Cambrian) and the emplacement of the late Paleozoic Habach intrusive rocks. One of the latter is represented in the western ore field of the Felbertal scheelite deposit by a horseshoe-shaped granite gneiss intrusion in the K 1 and K 3 orebodies, dated at 336 ± 19 Ma. The total mass of these K 1 -K 3 gneisses is approximately 5 million tons. The gneisses display geochemical and isotopic characteristics of a differentiated, orogenic melt of mixed crust-mantle origin. This melt may have been produced by the injection of mantle-derived magmas into a (thick) continental crust, presumably during a period of crustal relaxation. There is evidence for a K 1 -K 3 granite-related scheelite deposition in these granites, in apical quartz masses, and in their host rocks (mainly fine-grained amphibolites) in the form of quartz veins and small veinlets that are as much as tens of meters from the granite contact. Variscan amphibolite facies metamorphism between 325 and 280 Ma induced a period of pervasive remobilization and caused an ubiquitous, low-grade dispersion of the preexisting early and late Paleozoic scheelite mineralization and the formation of some high-grade enrichments of scheelite porphyroblasts along shear zones (stage 2 scheelite). Several sets of crosscutting, scheelite-bearing quartz veins and veinlets were formed under protracted amphibolite-facies metamorphic conditions. The metamorphic fluid regime further induced an alteration of the geochemical patterns of preexisting rocks (e.g., enrichments of Rb and Cs as well as of U, and 207 Pb, compared to Th, and 208 Pb). Furthermore, elevated 87 Sr/ 86 Sr ratios, possibly released from micas, dominated the isotopic signature of the recrystallizing, metamorphic scheelites. Small lamprophyric dikes were emplaced in Late Variscan time after the intrusion of the Granatspitze central gneiss protoliths, the emplacement of the K 1 -K 3 granite, and the subsequent shear zone formation. A change of the previously prevailing oxidizing conditions occurred, presumably after the intrusion of the lamprophyres. Subsequently, strong reducing conditions are indicated by WS 2 -MoS 2 exsolutions in the preexisting stage 1 and stage 2 “molybdoscheelites.”These scheelites were followed by the coexistence of MoS 2 and of bluish, fluorescent, pure scheelites (stage 3 scheelite), the crystallization of which has been dated by Sm-Nd at 319 ± 34 Ma. Evidence for the reducing conditions during the Late Variscan tungsten remobilization period is provided by a methane component in the fluid inclusions within such scheelites and accompanying quartz. Under Alpine lower amphibolite- to upper greenschist-facies metamorphic conditions, the scheelite remobilization was obviously less intense. It was locally focused along some faults and quartz veins, usually as sparse, but large, whitish-bluish fluorescent crystals with a Sm-Nd age of 29 ± 17 Ma (stage 4 scheelite).

Felsic gneisses, sillimanite schists, and amphibolites in Pelham Bay Park were subjected to three phases of deformation and metamorphism. During the third phase, compositionally distinct layers were produced within the amphibolites as a result of metasomatism. These layers are parallel to each other and range from a fraction of an inch to several feet in thickness and consist of the following assemblages: (a) plagioclase-biotite (muscovite-microcline) [plagioclase-biotite gneiss], (b) plagioclase (hornblende-magnetite-sphene) [plagioclase-rich layers], and (c) calcite-plagioclase (hornblende) [calcite-rich layers]. Plagioclase-biotite gneiss was produced by potash metasomatism of amphibolite (biotite replacing hornblende). Plagioclase-rich layers were produced by soda metasomatism of amphibolite (plagioclase replacing hornblende). Calcite-rich layers were produced by lime metasomatism of either feldspathic amphibolite or plagioclase-rich layers (calcite replacing plagioclase). The metasomatically produced layers superficially resemble primary layering in para-amphibolites and also resemble secondary layering produced by metamorphic segregation operative during an early phase of deformation. Evidence for the metasomatic origin of these layers includes: (a) gradation over short distances, both across and along strike into amphibolite; (b) replacement textures; (c) mineral assemblages unlike those resulting from the metamorphism of common sedimentary and volcanic rocks; and (d) the presence of relict foliations and skialiths. The metasomatically produced layers generally occur either in the hinge zones of F 3 folds or at the ends of amphibolite layers separated by boudinage on the limbs of F 3 folds. These were areas of relatively low pressure toward which fluids rich in potash, soda, and lime migrated, causing metasomatic replacement of amphibolites.