Geochemistry and Formation Conditions of Milk-White Quartz Veins in the Maksyutovo Metamorphic Complex, Southern Urals

— Milk-white vein quartz from the Novotroitskoe deposit was studied using inductively coupled plasma atomic emission spectrometry of bulk samples (ICP-OES), grain laser ablation (LA-ICP-MS), electron paramagnetic resonance (EPR) spectroscopy, (IR), and Fourier-transform infrared (FTIR) spectroscopy; and microthermometric data were acquired on the fluid inclusions hosted in this quartz. It is shown that the veins were formed at temperatures of 360–120°C by K- and Na-rich aqueous chloride fluid with a wide range of salinity values (0.9–9.3 wt % NaCl-equiv.). The gross content (ICP-OES) of Al, the dominant admixture in the vein quartz, is in the range of 25–400 ppm, whereas local determinations (LA-ICP-MS) give a range of 11–180 ppm, and the structural form accounts, according to EPR and IR data, for 6–12 ppm. Comparison of analytical data on the Ge admixture in the bulk samples and in spot EPR determinations showed that Ge is contained by the quartz mostly in the form of an isomorphic component, in contrast to Ti, which is hosted mostly as mineral inclusions of titanite. It has been established that the main petrogenetically informative elements in quartz (K, Na, Mg, Mn, Fe, Ca, and Li) belong to a nonstructural form and are contained as mineral and fluid inclusions. High contents of alkalis (ICP-OES and LA-ICP-MS data), molecular H 2 O, and CO 2 (FTIR spectroscopy) are typical of veins of hydrothermal origin with a high content of fluid inclusions.