SM-ND AND SR ISOTOPE SYSTEMATICS OF SCHEELITE FROM THE GIANT AU(-W) DEPOSIT MURUNTAU (UZBEKISTAN): IMPLICATIONS FOR THE AGE AND SOURCES OF AU MINERALIZATION

Abstract

The application of the Sm–Nd isotope system of scheelite to dating of low-sulfide, quartz-vein hosted Au mineralization is still under discussion. In the present work, new Sm–Nd and Rb–Sr data for scheelite from the giant Muruntau/Myutenbai Au deposit (Kyzylkum, Western Uzbekistan) are discussed. Based on the geological relationship, mineralogical properties, and trace element characteristics, two types of scheelite can be distinguished within the deposit. The first one is represented by early bluish luminescent and weakly coloured scheelite (generation 1) found within strongly deformed flat quartz veins. The apparent isochron defined by this scheelite (351±22 Ma) is interpreted as a mixing line. Typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins (generation 2) defines a Sm–Nd isochron age of 279±18 Ma (εNd=–9.5±0.3; MSWD: 1.5). No evidence for mixing or disturbance by late alteration were found for these scheelites. This Sm–Nd isochron age agrees with the Rb–Sr and K–Ar age range for wall rock alteration in this deposit reported previously. The age of 280 Ma is interpreted to date the high-grade ore formation in the Muruntau deposit. There are currently no reliable age data available on the magmatic events in the Muruntau region. Probably, there is some overlap in time of the Hercynian gold deposition with the intrusion of lamprophyric dykes. The Nd and Sr isotopic signatures of scheelite define the wall rocks (mainly metasiltstones and metasandstones) as the most probable sources for these elements in scheelite.