Aplite Hosted Reichenspitz-Type Molybdenite Mineralization in the Central Tauern Window, Salzburg/Tyrol

Research output: ThesisMaster's ThesisResearch

Abstract

Vein-type Mo mineralization is known from the Subpenninic Central Gneis units in the Tauern Window of the Eastern Alps; the type locality is located at the Alpeinerscharte in the Tux gneiss core. The aplitic granite (known as Reichenspitzgranit) building up the Reichenspitze at the border Salzburg/Tyrol (Austria) is host to low-grade molybdenum mineralization showing slightly differing structural and mineralogical attributes. It is bound to the area Reichenspitze-Gabler-upper Mannlkar-upper Roßkar and the ridge N-Zillerscharte to Zillerplattenscharte. Both areas yield variably sized aplitic stocks. Significant glacial retreat of the last 60 years made an update of the geological map necessary, as additional aplite bodies and faults became exposed. The post-orogenic A-type aplitic granites intruded at 282±6 Ma (Besang et al., 1968) into older Variscan I-type plutons. SiO2 contents of the aplites range from 73-77%, clearly distinguishable from 70-73% SiO2 of the gneisses. Both lithologies are low in CaO (1-3% for the gneisses; below 1% for the aplites), and the aplites are enriched in K2O compared to the gneisses (3-4% for the gneisses; 4-6% for the aplites). The aplites have a high content of high field strength elements and a negative Eu anomaly (chondrite normalized). In the pneumatolytic stage, a low-grade low fluorine calc-alkaline molybdenum porphyry system developed, probably similar to the Endako porphyry in British Columbia. The molybdenite formed in quartz veins and impregnations, that are often associated with ENE-WSW trending regional faults. Accessory minerals are pyrite, traces of chalcopyrite, minor Bi-Te minerals (native bismuth, bismuthinite and other phases), uraninite and thorite. The mineralization is enriched in Mo, Cu, Y, Ce, Rb, Th and U, and depleted in Ba, Sr and Li with respect to the host rocks. The Oligocene thermal event (Tauernkristallisation) of the Alpine orogenesis reached at least upper greenschist facies conditions and produced a widespread saussuritisation of plagioclase. During this event, a complex assemblage of secondary Mo-bearing minerals, rare earth element-bearing minerals (e.g., a conspicuous allanite-zircon-thorite assemblage) and a variety of poorly characterized Bi-bearing phases formed due to remobilization.

Details

Translated title of the contributionAplitgebundene Molybdänitmineralisation vom Typ Reichenspitze im zentralen Tauernfenster, Salzburg/Tirol
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
Supervisors/Advisors
Award date14 Dec 2018
Publication statusPublished - 2018