ACCESSORY GOLD-SILVER MINERALIZATION FROM CHROMITITES OF KHARCHERUZ ULTRAMAFIC MASSIF (THE POLAR URALS)

Abstract

The relevance of the work is caused by weakly elaboration of mineralogical aspects of ultramafic restitic massifs, which does not allow their generalization at mineralogical level and restoration of complete history of their formation and transformation, as well as solution of number of controversial questions of petrology of these objects. The mineralogy of accessory ore mineralization from restitic ultramafites is poorly studied direction. The main aim of the research is to study the accessory gold-silver mineralization in massive chromitites of Kharcheruz ultramafic massif of the Polar Urals, reconstruction of mechanism of its formation. Methods: study of ore mineralization in polished sections using a polarizing microscope AxioScope Carl Zeiss; determination of chemical composition of ore mineralization by the method of X-ray spectrum microanalysis using scanning electron microscope Tescan Mira 3 LMU with energy-dispersive spectrometry UltimMax100 (Oxford Instruments). The results. For the first time in medium- and densely disseminated chromitites of Kharcheruz ultramafic massif of the Polar Urals, accessory gold-silver mineralization was diagnosed, represented by three-component solid solution Au–Cu–Ag, corresponding in chemical composition to cuprous gold (cuproauride), and silver sulphide – acanthite (Ag2S). Formation of revealed acanthite was obviously associated with superimposed metamorphic processes of transformation of original ultrabasic rocks. However, question of the genetic nature of identified Au–Cu–Ag three-component natural triad is not so unambiguous and requires additional, more in-depth study. It is not excluded that the revealed finds of cuprous gold directly in chromitites may belong to primary mantle type, in genesis of which metamorphic crustal processes associated with borrowing of metals dispersed in restite ultramafic rocks or host rocks of frame did not play any significant role. This is also evidenced by close composition of revealed cuproauride with cuprous gold from the chromitites of Voikaro-Synyinsky massif, which along with Kharcheruz massif is a part of the Khadatinsky ophiolite belt and, apparently, has common deep mantle source.

Keywords

• the polar urals
• kharcheruz massif
• restitic ultramafites
• chromitites
• au–cu–ag alloy
• acanthite
• chemical composition
• genesis