160 Ma of magmatic/hydrothermal and metamorphic activity in the Gällivare area: Re–Os dating of molybdenite and U–Pb dating of titanite from the Aitik Cu–Au–Ag deposit, northern Sweden |
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Authors: | Christina Wanhainen Kjell Billström Olof Martinsson Holly Stein Roger Nordin |
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Institution: | 1. Division of ore geology and applied geophysics, Lule? University of Technology, 97187, Lule?, Sweden 2. LIG, Swedish Museum of Natural History, Box 50007, 10405, Stockholm, Sweden 3. AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO, 80523-1482, USA 4. Boliden Mineral AB, 93681, Boliden, Sweden
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Abstract: | Host rocks to the Aitik Cu–Au–Ag deposit in northern Sweden are strongly altered and deformed Early Proterozoic mica(-amphibole)
schists and gneisses. The deposit is characterised by numerous mineralisation styles, vein and alteration types. Four samples
were selected for Re–Os molybdenite dating and 12 samples for U–Pb titanite dating in order to elucidate the magmatic/hydrothermal
and metamorphic history following primary ore deposition in the Aitik Cu–Au–Ag deposit. Samples represent dyke, vein and alteration
assemblages from the ore zone, hanging wall and footwall to the deposit. Re–Os dating of molybdenite from deformed barite
and quartz veins yielded ages of 1,876±10 Ma and 1,848±8 Ma, respectively. A deformed pegmatite dyke yielded a Re–Os age of
1,848±6 Ma, and an undeformed pegmatite dyke an age of 1,728±7 Ma. U–Pb dating of titanite from a diversity of alteration
mineral associations defines a range in ages between 1,750 and 1,805 Ma with a peak at ca. 1,780 Ma. The ages obtained, together
with previous data, bracket a 160-Ma (1,890–1,730 Ma) time span encompassing several generations of magmatism, prograde to
peak metamorphism, and post-peak cooling; events resulting in the redistribution and addition of metals to the deposit. This
multi-stage evolution of the Aitik ore body suggests that the deposit was affected by several thermal events that ultimately
produced a complex ore body. The Re–Os and U–Pb ages correlate well with published regional Re–Os and U–Pb age clusters, which
have been tied to major magmatic, hydrothermal, and metamorphic events. Primary ore deposition at ca. 1,890 Ma in connection
with intrusion of Haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism. Early
metamorphism at 1,888–1,872 Ma overlapping with Haparanda (1,890–1,880 Ma) and Perthite-monzonite (1,880–1,870 Ma) magmatism
clearly affected the Aitik area, as well as late metamorphism and Lina magmatism at 1,810–1,774 Ma and TIB1 magmatism at 1,800 Ma.
The 1,848 Ma Re–Os ages obtained from molybdenite in a quartz vein and pegmatite dyke suggests that the 1,850 Ma magmatism
recorded in parts of northern Norrbotten also affected the Aitik area. |
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Keywords: | Aitik Cu– Au– Ag deposit Titanite Molybdenite Re– Os and U– Pb dating Northern Norrbotten ore province Sweden |
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