RB-SR ISOTOPIC STUDY OF THE MURUNTAU DEPO SIT - MAGMATISM, METAMORPHISM, AND MINERALIZATION

The results of Rb-Sr isochrone isotopic-geochronological studies of me tamorphic and igneous rocks in the vicinity of the Muruntau deposit, c entral Kyzyl Kum Desert, are reported. Combined with the previously pu blished 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 Murun tau deposit was coeval with the formation of Stage II igneous rocks (2 73.1 +/- 1.6 Ma), but not coeval with the emplacement of Stage I grani toids. The temporal association of the early productive metasomatites and Stage II dykes indicates that Stage II magmatism and early metasom atism had a common source of energy. Subsequent ore redeposition occur red 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. Th e strontium of the ore metasomatites, quartz-scheelite, quartz-tourmal ine, quartz-arsenopyrite, quartz-adularia, and carbonate veins was der ived from metamorphic rocks of the Besapan Formation. There is no evid ence for the input of less radiogenic Sr from the magma chamber, but t he situation may be different in the case of other elements such as Au and W whose geochemical behavior substantially differs from that of S r.