학술논문
The Mittersill scheelite deposit, Austria.
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Abstract
The deposit consists of two parts, the Ostfeld open pit and the Westfeld underground mine. The scheelite-bearing metavolcanic sequence represents an imbricated stack of several thrusted hornblendite units and metavolcano-sedimentary units. The hornblendite units consist of hornblendites, coarse-grained amphibolites and intercalations of rhyolitic to dacitic gneisses. The metavolcano-sedimentary units contain associated fine-grained amphibolites and gneisses. The entire sequence has undergone multiple metamorphism (up to 530 degrees C and 5-6 kbars) and deformation. The tungsten and its associated sulphide-sulphosalt mineralisation occurs within the entire metavolcanic sequence but is of subeconomic importance (less than 0.3% WO3). Mineable tungsten concentrations (1% WO3, maximum 15% WO3) occur exclusively in the hornblendite units and are hosted in both concordant felsic gneisses and fabric parallel as well as fabric crosscutting quartz veins. Isotopic evidence shows conclusively that mafic and felsic rocks of the hornblendite units, as well as the mineralisations, are cogenetic. It is proposed that preconcentration of tungsten took place in boninitic melts within a back-arc environment. The magmatic preconcentration was followed by intense mobilisation and accumulation of tungsten into a complex system of quartz veins and lenses during two metamorphic events.
The deposit consists of two parts, the Ostfeld open pit and the Westfeld underground mine. The scheelite-bearing metavolcanic sequence represents an imbricated stack of several thrusted hornblendite units and metavolcano-sedimentary units. The hornblendite units consist of hornblendites, coarse-grained amphibolites and intercalations of rhyolitic to dacitic gneisses. The metavolcano-sedimentary units contain associated fine-grained amphibolites and gneisses. The entire sequence has undergone multiple metamorphism (up to 530 degrees C and 5-6 kbars) and deformation. The tungsten and its associated sulphide-sulphosalt mineralisation occurs within the entire metavolcanic sequence but is of subeconomic importance (less than 0.3% WO3). Mineable tungsten concentrations (1% WO3, maximum 15% WO3) occur exclusively in the hornblendite units and are hosted in both concordant felsic gneisses and fabric parallel as well as fabric crosscutting quartz veins. Isotopic evidence shows conclusively that mafic and felsic rocks of the hornblendite units, as well as the mineralisations, are cogenetic. It is proposed that preconcentration of tungsten took place in boninitic melts within a back-arc environment. The magmatic preconcentration was followed by intense mobilisation and accumulation of tungsten into a complex system of quartz veins and lenses during two metamorphic events.
The deposit consists of two parts, the Ostfeld open pit and the Westfeld underground mine. The scheelite-bearing metavolcanic sequence represents an imbricated stack of several thrusted hornblendite units and metavolcano-sedimentary units. The hornblendite units consist of hornblendites, coarse-grained amphibolites and intercalations of rhyolitic to dacitic gneisses. The metavolcano-sedimentary units contain associated fine-grained amphibolites and gneisses. The entire sequence has undergone multiple metamorphism (up to 530 degrees C and 5-6 kbars) and deformation. The tungsten and its associated sulphide-sulphosalt mineralisation occurs within the entire metavolcanic sequence but is of subeconomic importance (less than 0.3% WO3). Mineable tungsten concentrations (1% WO3, maximum 15% WO3) occur exclusively in the hornblendite units and are hosted in both concordant felsic gneisses and fabric parallel as well as fabric crosscutting quartz veins. Isotopic evidence shows conclusively that mafic and felsic rocks of the hornblendite units, as well as the mineralisations, are cogenetic. It is proposed that preconcentration of tungsten took place in boninitic melts within a back-arc environment. The magmatic preconcentration was followed by intense mobilisation and accumulation of tungsten into a complex system of quartz veins and lenses during two metamorphic events.