Characteristics of Supergene Gold of Karst Cavities of the Khokhoy Gold Ore Field (Aldan Shield, East Russia)

Abstract

Typomorphic features of supergene gold in karst cavities were studied in the recently discovered Au–Te–Sb–Tl deposit within the Khokhoy gold ore field of the Aldan-Stanovoy auriferous province (Aldan shield, East Russia). Two morphological types of supergene gold, massive and porous, are recognized there. The first type is represented by gold crystals and irregular mass, with the fineness ranging from 835 to 1000‰. They are closely associated with goethite, siderite, unnamed Fe, Te, and Tl carbonates, Tl tellurites/tellurates and antimonates, as well as avicennite with a Te impurity. The second type is represented by mustard gold of two types with different internal structure: microporous and dendritic. The supergene gold is characterized by persistently high fineness. Along with Ag, it invariably contains Hg (up to 5.78 wt%) and Bi, and, rarely, Pb, Cu, and Fe. The supergene gold is chemically homogeneous, and its particles are all marked by high fineness, without any rims or margins. The obtained characteristics made it possible to prove the existence of two genetic types of supergene gold. Mustard microporous gold is the result of the decomposition of the associated minerals—goethite, Tl oxides, tellurium, Fe, Mn and Tl carbonates and antimonates, containing microinclusions of gold. Massive gold and dendrites are newly formed. The decomposition, remobilization, and reprecipitation of residual gold nanoparticles and their aggregation led to the formation of dendrites, and with further crystal growth and filling of pores, to gold of massive morphology. In terms of morphology, internal structure, fineness, and trace element composition, supergene gold of the Khokhoy gold ore field is comparable to gold from the Kuranakh deposit (Russia) and the Carlin-type gold deposits. It also is similar to spungy and mustard gold from Au–Te and Au–Sb deposits, weathering crusts, and placers. Its main characteristic feature is a close paragenesis with Tl minerals.

Types of Tellurium Mineralization of Gold Deposits of the Aldan Shield (Southern Yakutia, Russia)

“…The Kuranakh and Khokhoy deposits have features of Carlin-type mineralization: they are located in the area of tectonic-magmatic activation, are conjugated with intrusions of monzonite-granodiorite series, and are of normal and high alkalinity, strata of carbonate rocks, stratoidal disseminated deposits, presence of jasperoids, low content of sulfides, finely-dispersed gold in pyrite, typomorphic elements-Au-Tl-As-Hg-Sb-Te-Ba-F [4,33,40].…”

“…The extensive and diverse list of associated minerals includes selenides (clausthalite (PbSe), naumannite (Ag 2 Se), tiemannite (HgSe)); sulfides (cinnabar (HgS), stibnite (Sb 2 S 3 ), orpiment (As 2 S 3 ), acanthite (Ag 2 S), uytenbogaardtite (Ag 3 AuS 2 )); Ag chlorides and bromides (chlorargyrite (AgCl), bromargyrite (AgBr)); emphasizes the epithermal of Au-Ag-Te type ores. This mineral type also includes the low-temperature thallium mineralization of the Khokhoy deposit of the Verkhneamginsky cluster, represented by thallium tellurates and telluroantimonates with weissbergite (TlSbS 2 ), avicennite (Tl 2 O 3 ) and thallium antimonates (Table 7) [33,40]. A characteristic feature of ores bearing Au-Ag-Te mineralization is the susceptibility to supergene changes.…”

“…Native gold, which is associated with tellurides, is of a usually porous structure. Spongy and mustard gold is often found in Au-Ag-Te deposits (Figure 4) [14,33,41,42]. The grain size varies, and relatively large gold is typical for the Au-Bi-Te type.…”

“…In addition to the well-known tellurium and selenium minerals, new mineral types of tellurates have been established: kuranakhite [13], yafsoanite, kuksite, cheremnykhite and V, Si-dugganite [14][15][16][17]. Recently, new information has appeared on tellurium mineralization in the deposits and ore occurrences of the CAD in the ores of Lebedinsky [18,19], Elkonsky [20][21][22], Dzhekondinsky [23,24], Yukhtinsky [25,26], and the Nimgerkansky [27] ore fields, as well as a number of other gold ore objects outside the CAD-Verkhne-Tokkinsky [28,29], Verkhneamginsky [30][31][32][33][34], Tyrkandinsky, Guvilgrinsky, Altan-Chaidakhsky, and Verkhnealgominsky [35][36][37][38] (Figure 1). Figure 1.…”

Gold in the Oxidized Ores of the Olympiada Deposit (Eastern Siberia, Russia)

“…The occurrence of spongiform gold in the Lower Zone is explained by the process of leaching of impurities (de-alloying), which is experimentally demonstrated in the work [79]. The formation of spongiform gold was also repeatedly observed in nature, as in the supergene zone during oxidation and decomposition of gold tellurides and antimonides, as well as AuAg alloys [80][81][82][83] and under hypogene conditions under the influence of alkaline and neutral fluids with temperatures of 140-200 °C [84,85]. The liberation of gold from impurities in this process is accompanied by an increase in its free surface, which contributes to its further dissolution.…”