摘要
Host rocks to the Aitik Cu8211;Au8211;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 Re8211;Os molybdenite dating and 12 samples for U8211;Pb titanite dating in order to elucidate the magmatic/hydrothermal and metamorphic history following primary ore deposition in the Aitik Cu8211;Au8211;Ag deposit. Samples represent dyke, vein and alteration assemblages from the ore zone, hanging wall and footwall to the deposit. Re8211;Os dating of molybdenite from deformed barite and quartz veins yielded ages of 1,876卤10 Ma and 1,848卤8 Ma, respectively. A deformed pegmatite dyke yielded a Re8211;Os age of 1,848卤6 Ma, and an undeformed pegmatite dyke an age of 1,728卤7 Ma. U8211;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 (1,8908211;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 Re8211;Os and U8211;Pb ages correlate well with published regional Re8211;Os and U8211;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 1,8888211;1,872 Ma overlapping with Haparanda (1,8908211;1,880 Ma) and Perthite-monzonite (1,8808211;1,870 Ma) magmatism clearly affected the Aitik area, as well as late metamorphism and Lina magmatism at 1,8108211;1,774 Ma and TIB1 magmatism at 1,800 Ma. The 1,848 Ma Re8211;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.