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Typomorphic features of placer gold of the Anabar region were studied as predictive-exploration criteria. The target of the study was to determine the typomorphic features of placer gold related to the intermediate sources (paleo-placers) and the supposed nearby primary ore occurrences. Two varieties of placer gold were identified. The first variety is well-rounded high-fineness lamellar gold with a highly modified internal structure. This native gold is associated with intermediate sources, Neogene–Quaternary watershed pebble beds. The second type includes slightly rounded gold with a wide variation in fineness (494‰–999‰). Its indicator is a block heterophase internal structure. The set of typomorphic features of this variety of placer gold indicates the vicinity of the primary source, what was the prerequisite for constructing prospecting traverses in order to find ore occurrences. As a result of these studies, hydrothermal-metasomatic formations with gold-sulfide mineralization were identified. The main primary substrate for them is fractured near-fault carbonate rocks of the Cambrian and Vendian–Cambrian age. Along with this, hydrothermalites developed on slightly cemented fine-pebble quartz conglomerates of the Middle Permian age were found in the core of exploration wells. Two types of metasomatic rocks are identified: quartz-potassium feldspar and jasperoid. The main ore minerals were galena and pyrite, different ratios by sites were revealed. Gold was identified in the form of small particles in the carbonate and siliceous substrate of hydrothermal-metasomatic formations. The lithological factor was one of the leading favorable factors for the ore formation due to the presence of near-fault highly permeable fractured carbonate and slightly cemented terrigenous rocks. The structural control of the studied ore occurrences is determined by their localization in the Mayat–Logoy and Dogoy–Kuoy faults of the Molodo–Popigay system of discontinuous faults. We assume a two-stage formation of the gold ore occurrences: during the first stage, the ore components in the form of primary hydrothermal-sedimentary ores in the near-gault zones were formed. The second stage was related to the processes of the Mesozoic tectonic-magmatic activation, when the intrusion of basite dikes initiated the mobilization of ore components the gold-sulfide occurrences were formed in the near-fault zone as a result of silicic-potassic metasomatosis of the carbonate and terrigenous rocks. [ABSTRACT FROM AUTHOR]

The relevance of the research. Poor knowledge and economic attractiveness make the problem of forecasting and prospecting for epithermal high-sulfidation gold-silver deposits within the volcanogenic belts of the Russian Federation topical. The main goal of the work was to develop criteria for forecasting and prospecting for epithermal acid-sulfate gold mineralization within the Ulinsky trough of the Okhotsk-Chukotka volcanic belt. Methods: interpretation of space materials ASTER, Landsat ETM+, Sentinel and digital elevation model according to Shuttle radar topographic mission data, interpretation of airborne geophysical data of magnetometric and gamma-ray spectroscopic surveys with the construction of structural geological schemes; modeling of geochemical fields using multivariate statisticals methods based on lithochemical data, including rank correlation, factorial and cluster analysis. The following main conclusions: the Svetloe ore field has characteristics typical of epithermal deposits of acid-sulfate gold mineralization: it is located in a volcanic belt, confined to central-type volcanic apparatuses controlled by faults; gold mineralization is accompanied by advanced argillic and quartz altered rocks: secondary quartzites of zonal structure, were drawn. The characteristics of structural control and metasomatic zoning are well defined in interpretation of data from remote sensing, airborne magnetic surveys, and gamma ray spectrometry. Furthermore, the distribution of chemical elements in the secondary stray field makes it possible to establish a concentric zonal structure characteristic of hydrothermal gold deposits, with a spatiotemporal change in geochemical associations from the central zone of ore formation to the periphery at the local level of generalization: Au, Mo→Au, Ag, Pb→K, Na, Al→V, Zn, (Co, Ni, Cr, Mn, P). Moreover, within the mineralized zones, the following sequence of formation of geochemical associations is established (from the central part to the periphery): Au-Ag→Ag, Pb, Sb→As, Mo, Ba→Co, Cr, Mn, V, Zn, P.

The methods of mathematical statistics were used to distinguish outliers, such as the Grubbs test and the Dixon test. These methods have not completely identified outliers for statistical tests of the analytical results for constant gold standard samples. An outlier statistical recognition method based on the multiple analysis of relative deviation for constant gold, including the arithmetic mean of gold in the samples, its relative deviation allowable limits in accordance with DZ/T 130.3—2006 and determination of qualified interval of the measurement results in order to identify and remove outliers has been established. After removing the furthest outliers, the whole process was conducted for the next round to remove less obvious outliers until no more outliers were found. The arithmetic mean and its fluctuation range of the gold measurement results were produced. 15 artificial ore gold standard samples were assigned to different laboratories and analyzed with passwords by using the standard sample analysis method. A total of 10 sets of independent analysis results were collected. According to the established method to remove outliers, the obtained arithmetic mean value was closer to the certified value than that by the Grubbs test and the Dixon test. The relative deviation of the quality fraction was 0.35, which was excellent. However, the relative deviations of the quality fraction by either Grubbs test or Dixon test and the median value method respectively were 0.42 and 0.40, which were also good. The quality fraction level has been significantly improved by the outlier statistical recognition method described in this paper, which enhanced the effectiveness of statistical analysis of data.