Typomorphism of Native Gold (Geological-Industrial Types of Gold Deposits in the North-East of Russia)

Abstract

This study presents the typomorphic features of native gold grains from three different geological-industrial types (GIT) of gold deposits in the North-East of Russia: (1) gold–arsenic-sulfide in black shale strata (Natalka, Degdekan, Karalveem, Maldyak deposits), (2) gold–quartz veins in granitoids (Dorozhnoye, Butarnoye, Shkolnoye, Maltan deposits), and (3) gold–silver adularia in volcanogenic strata (Kupol, Olcha, Kubaka, Burgali, Primorskoe, Dalnee deposits). The reliability of the geological interpretation is directly related to mineral associations, fineness variations, its internal structure and the content of microimpurities. Native gold is a reliable indicator for identifying various GIT of gold deposits at the early geological-prospecting stages of studying gold-bearing areas. Typomorphic features of native gold for each of the considered GIT are stable and do not depend on the age and scale of mineralization. It is shown that using an integrated approach obtains genetic information about a particular ore object, which makes it possible to predict the vertical range of mineralization and outline the technology for processing ores. The information obtained can also be effectively used in the search for placer deposits in nearby watercourses. Identification of typomorphic features of ore and placer native gold opens up wide opportunities for delineating the distribution areas of placer deposits.

Internal Structures of Placer Gold as an Indicator of Endogenous and Exogenous Processes

“…The identified high-grade shells on gold particles with deformation lines are extremely rare (Figure 2e,f). It is known that gold is an inert metal that practically does not change in exogenous conditions; however, we found that when staying in various exogenous conditions for billions of years and repeated redeposition, primary recrystallization and secondary recrystallization of gold occurred with the removal of silver and impurity elements [1,2,4,8]. When studying the internal structure of placer gold from the Quaternary deposits in the east of the Siberian Platform, it was found that almost all flake gold of type I with a size of 0.1-0.25 mm, of high fineness, is characterized by primarily recrystallized and secondarily recrystallized internal structure.…”

“…Thus, the identification of numerous deformation lines in placer gold indicates that these structures were formed in metamorphic strata and are an indicator for predicting ore deposits of gold-ferrous-quartzite mineralization. We draw attention to the fact that, although metamorphogenic gold has been studied earlier [1,3,4,8], this problem needs to be addressed in additional research.…”

“…After each etching procedure, the polished section was washed under a strong stream of water, then dried. Polyphase particles were etched differentially: first, the low-grade phases of gold were etched, and then, with a stronger solution, the high-grade phases [4]. Standard reagents were used for etching (HNO 3 + CrO 3 -kustelite; HCl + CrO 3 + thiourea − electrum; HCl + CrO 3 of various concentrations -medium-grade gold; HCl+4HNO 3 -high-grade gold).…”

“…The indicators of placer gold (morphology, impurity elements, microinclusions, internal structures, etc.) carry extensive information about the nature of native gold, both in endogenous and exogenous conditions [1][2][3][4][5][6][7][8][9][10][11]. In exogenous conditions, the evolution of placer gold occurs, but it retains the "memory" of its primary sources.…”

“…The internal structures of placer gold were first studied by Petrovskaya and Fastalovich [12]. Then, Nikolaeva [2], Popenko [3], Savva and Preis [4], Nikolaeva et al [8] and Savva et al [5,13] studied the internal structures of placer gold. They studied the internal structures of native gold from endogenous sources, as well as zones of hypergenesis and alluvial placers.…”