Typomorphism of fine placer gold and potential primary sources of the Anabar mineral subprovince (North-eastern Siberian Platform)

Abstract

Typomorphic features of placer gold of the Anabar and Bolshaya Kuonamka river basins are studied with the aim of determining its indicators and forecasting potential primary sources. All analytical work was carried out in the department of physico-chemical methods of analysis IGABM SB RAS. A detailed study of the morphology, surface microrelief, photographing was performed on a JSM - 6480 LV scanning (microscope) microscope of JEOL company with Oxford Instruments analytical prefixes (wave and energy dispersive spectrometers). Gold fineness is determined on Camebax-micro X-ray microanalyzer a «Cameca» firms. It is shown that the main sources for the gold are auriferous reservoir rocks of Neogene-Quaternary age. The indicator typomorphic features of the gold include a small size (-0.5 mm), scaly and platy forms, rough shagreen surface with casts of minerals pressing, and high fineness (900-999%o). The most highly informative feature is a strongly modified internal structure of the gold showing evidence of granulation and recrystallization. Autochthonous gold of ore habit is also found. Characteristic features of this type of gold are a very small size (-0,2 mm), angular-cloddy forms of individual particles, rough porous surface, widely ranging fineness (535 to 999% ), heterogeneous chemical composition, and a complex, multi-phase internal structure. This indicates the presence of neighboring primary sources. Hydrothermal-metasomatic formations with disseminated gold-sulfide mineralization, discovered at the places of tectonic jointing of carbonate rocks, developed in fault zones could be such sources. Considering epigenetic mineral associations, quartz-potassium feldspar and quartz hydrothermal-metasomatic formations are identified. Ore mineralization of disseminated type is represented by (in decreasing order) pyrite, gold, chalcopyrite, galena, sphalerite and silver. Gold is found in native form and in association with pyrite (quartz metasomatites) and potassium feldspar metasomatites). Thus, as a result of performed studies, indicator typomorphic features of autochthonous fine gold are identified. Near-fault hydrothermal-metasomatic formations with gold-sulfide disseminated mineralization are discovered in the studied area for the first time and examined.