Rb-Sr isotopic study of the Muruntau deposit: Magmatism, metamorphism, and mineralization

The results of Rb-Sr isochrone isotopic-geochronological studies of metamorphic and igneous rocks in the vicinity of the Muruntau deposit, central Kyzyl Kum Desert, are reported. Combined with the previously published data for the hydrothermal-metasomatic rocks [1, 2], this study outlines the chronology of this gigantic deposit. Greenschist-facies metamorphism of the ore-hosting Besapan Formation is dated at 401 +/- 11 Ma. The main stage of productive hydrothermal activity at the Muruntau deposit was coeval with the formation of Stage II igneous rocks (273.1 +/- 1.6 Ma), but not coeval with the emplacement of Stage I granitoids. The temporal association of the early productive metasomatites and Stage II dykes indicates that Stage II magmatism and early metasomatism had a common source of energy. Subsequent ore redeposition occurred in discrete pulses at 257.6 +/- 2.2, 230.2 +/- 3.5, and 219.4 +/- 4.2 Ma, which were due to the pulses of regional tectonic activity. The strontium of the ore metasomatites, quartz-scheelite, quartz-tourmaline, quartz-arsenopyrite, quartz-adularia, and carbonate veins was derived from metamorphic rocks of the Besapan Formation. There is no evidence for the input of less radiogenic Sr from the magma chamber, but the situation may be different in the case of other elements such as Au and W whose geochemical behavior substantially differs from that of Sr.