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

The application of the Sm-Nd isotope system of scheelite to dating of low-s ulfide, 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 Mur untau/Myutenbai Au deposit (Kyzylkum, Western Uzbekistan) are discussed. Ba sed on the geological relationship, mineralogical properties, and trace ele ment characteristics, two types of scheelite can be distinguished within th e deposit. The first one is represented by early bluish luminescent and wea kly coloured scheelite (generation 1) found within strongly deformed flat q uartz veins. The apparent isochron defined by this scheelite (351 +/- 22 Ma ) is interpreted as a mixing line. Typically brownish to orange and yellowi sh luminescent scheelite from steeply dipping veins (generation 2) defines a Sm-Nd isochron age of 279 +/- 18 Ma (epsilon (Nd) = -9.5 +/- 0.3; MSWD: 1 .5). No evidence for mixing or disturbance by late alteration were found fo r 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 M uruntau 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 dy kes. 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.