CL for characterizing quartz and trapped fluid inclusions in mesothermal quartz veins: Muruntau Au ore deposit, Uzbekistan

Combined cathodoluminescence (CL) and transmitted light microscopy were use d to characterize quartz from flat and steeply dipping quartz veins and fro m veinlets in banded host rocks from the giant Muruntau Au quartz Vein depo sit, Kyzyl Kum Desert, western Uzbekistan. The CL examinations were carried out using a 'hot-cathode' CL microscope linked to a highly sensitive digit al video camera. The multi-stage deformed flat quartz veins and the steeply dipping hydrothermal formations at Muruntau are characterized by quartz wi th different CL colours, internal structures and degree of secondary altera tion. Primary growth zoning of quartz, indiscernible in conventional polari zed light was found to occur only in steeply dipping veins. The bulk of the high-grade Au mineralized 'central' quartz veins is dominated by one gener ation of hydrothermal quartz; intense brecciation of these veins is indicat ed by the occurrence of fragments of zoned quartz crystals. Primary growth zoning in quartz may be revealed not only by variations in the intensity of blue CL and/or by primary fluid inclusions arranged within the zones, but also by secondary inclusions and recrystallization phenomena developed alon g boundary surfaces between the zones. Using the results from CL imaging an d microstructural analysis of the quartz, fluid inclusions investigated ear lier were assigned to genetic types; the evidence of probably primary inclu sions is of considerable importance for further studies of the geochemical conditions during vein formation. Considering geological and mineralogical data, CL studies of vein quartz may help to reveal the history of precipita tion, deformation and recrystallization processes in the Muruntau Au ore fi eld.