U–Pb Geochronology of the Syn-Orogenic Knaben Molybdenum Deposits, Sveconorwegian Orogen, Norway
Geol. Mag. 152 (3), 2015, pp. 537–556. c Cambridge University Press 2014 537 doi:10.1017/S001675681400048X U–Pb geochronology of the syn-orogenic Knaben molybdenum deposits, Sveconorwegian Orogen, Norway ∗ BERNARD BINGEN †, FERNANDO CORFU‡§, HOLLY J. STEIN§¶ & MARTIN J. WHITEHOUSEࢱ ∗ Geological Survey of Norway, 7491 Trondheim, Norway ‡Department of Geosciences, University of Oslo, 0316 Oslo, Norway §Centre for Earth Evolution and Dynamics, University of Oslo, 0316 Oslo, Norway ¶AIRIE Program, Colorado State University, Fort Collins, CO 80523-1482, USA ࢱSwedish Museum of Natural History, 104 05 Stockholm, Sweden (Received 29 March 2014; accepted 4 August 2014; first published online 11 November 2014) Abstract – Paired isotope dilution – thermal ionization mass spectrometry (ID-TIMS) and secondary ion mass spectrometry (SIMS) zircon U–Pb data elucidate geochronological relations in the historically important Knaben molybdenum mining district, Sveconorwegian Orogen, south Norway. This poly- phase district provided c. 8.5 Mt of ore with a grade of 0.2 %. It consists of mineralized quartz veins, silica-rich gneiss, pegmatites and aplites associated with a heterogeneous, locally sulphide-bearing, amphibolites facies gneiss called Knaben Gneiss, and hosted in a regional-scale monotonous, com- monly weakly foliated, granitic gneiss. An augen gneiss at the Knaben I deposit yields a 1257 ± 6Ma magmatic zircon age, dating the pre-Sveconorwegian protolith of the Knaben Gneiss. Mineralized and non-mineralized granitic gneiss samples at the Knaben II and Kvina deposits contain some 1488– 1164 Ma inherited zircon and yield consistent intrusion ages of 1032 ± 4, 1034 ± 6 and 1036 ± 6 Ma. This age links magmatism in the district to the regional 1050–1020 Ma Sirdal I-type granite suite, corresponding to voluminous crustal melting during the Sveconorwegian orogeny.
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