Typomorphism of Autigenic Gold in Riphean Sandstones of the Kyvvozhskoye Goldfield (Volsko-Vymskaya Ridge, Middle Timan)

Abstract

The results of a comprehensive study of the morphology, composition and the internal structure of fine autigenic gold, first discovered in bedrock on the area of the Kyvvozhskoye goldfield, are presented. It has complex specific rounded-lumpy, lumpy-branched aggregate forms and a smooth growth surface without traces of mechanical wearing. X-ray studies (Debye-Scherrer method) show that reflexes in the form of dashed rings are characteristic of debyeograms of this native gold, which, according to the authors, indicates the absence of exogenous deformations of it. The internal structure of all the studied gold pieces is characterized by a relatively homogeneous inner area and a thin (~1 µm) contrasting enriched with silver low-grade rim. All the particles of the studied native gold have approximately the same average fineness (899–918‰). As a mechanism for the formation of the found autigenic gold, its crystallization is assumed by filling of the free pore space of the host sandstones. Its presence in Riphean rocks is considered as an indicator of the primary dispersion halos and is a direct search sign of the development of potentially productive gold mineralization in this part of the Middle Timan.