Formation and Aggregation of Gold (Electrum) Nanoparticles in Epithermal Ores

Saunders, James A.; Burke, Michelle

doi:10.3390/min7090163

Cited by 54 publications

(26 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The non-classical pathway of gradual nucleation within a dense droplet and crystal growth, arrested possibly due to a lack of solutes accumulated within other liquid species, is believed to prevent crystallization of gold chalcogenides and results in their compromised structure inclined to decompose to metallic gold. Such reactions can play a role in the deposition of gold colloids in several types of ores [62,63], even although the hydrothermal processes proceed at higher temperatures and in a different time scale, resulting, in particular, in crystallization and annealing of the solid phases. The formation of crystalline gold selenide, including the nanoparticles which are interesting also for materials science, is possible under ambient conditions but it may require stabilizing agents.…”

Section: Discussionmentioning

confidence: 99%

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

et al. 2018

View full text Add to dashboard Cite

The reactions of aqueous gold complexes with H 2 Se and H 2 S are important for transportation and deposition of gold in nature and for synthesis of AuSe-based nanomaterials but are scantily understood. Here, we explored species formed at different proportions of HAuCl 4 , H 2 Se and H 2 S at room temperature using in situ UV-vis spectroscopy, dynamic light scattering (DLS), zeta-potential measurement and ex situ Transmission electron microscopy (TEM), electron diffraction, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Metal gold colloids arose at the molar ratios H 2 Se(H 2 S)/HAuCl 4 less than 2. At higher ratios, pre-nucleation "dense liquid" species having the hydrodynamic diameter of 20-40 nm, zeta potential −40 mV to −50 mV, and the indirect band gap less than 1 eV derived from the UV-vis spectra grow into submicrometer droplets over several hours, followed by fractional nucleation in the interior and coagulation of disordered gold chalcogenide. XPS found only one Au + site (Au 4f 7/2 at 85.4 eV) in deposited AuSe, surface layers of which partially decomposed yielding Au 0 nanoparticles capped with elemental selenium. The liquid species became less dense, the gap approached 2 eV, and gold chalcogenide destabilized towards the decomposition with increasing H 2 S content. Therefore, the reactions proceed via the non-classical mechanism involving "dense droplets" of supersaturated solution and produce AuSe 1−x S x /Au nanocomposites.

show abstract

Section: Discussionmentioning

confidence: 99%

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

et al. 2018

View full text Add to dashboard Cite

show abstract

“…So, what is the formation mechanism of dendrites? Interesting data on the formation of native gold dendrites in epithermal ores are presented by Saunders [32][33][34]. Author showed a scanning electron microscope (SEM) image of electrum dendrites that appeared to have formed from aggregation of smaller colloid-sized particles.…”

Section: Discussionmentioning

confidence: 99%

“…The most intricate forms of gold are seen in a very rare mineral avicennite (Tl 2 O 3 ), an oxide of thallium with a Te impurity ( Figure 5d, Table 3; Nos. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Sometimes massive gold occurs in assemblage with siderite ( Figure 5e,f, Table 3; Nos.…”

Section: Massive Goldmentioning

confidence: 99%

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

Anisimova¹,

Kondratieva²,

Kardashevskaia³

2020

Minerals

View full text Add to dashboard Cite

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.

show abstract

“…The observation that ginguro and gankin bands show distinct microtextural characteristics suggests that the ore-bearing bands were formed by unique processes. The original presence of a noncrystalline silica precursor in these bands suggests that silica deposition occurred as a result of supersaturation (with respect to quartz), which could have been achieved due to vigorous boiling or flashing of the thermal waters [26,37,38,53,54]. Vigorous boiling or flashing events in geothermal systems can be seismically triggered [55] and result in the formation of hydrothermal eruptions on surface [56][57][58][59].…”

Section: Silica Deposition In Ore-bearing Bandsmentioning

confidence: 99%

The Distribution of Precious Metals in High-Grade Banded Quartz Veins from Low-Sulfidation Epithermal Deposits: Constraints from µXRF Mapping

Tharalson

Monecke

Reynolds³

et al. 2019

Minerals

View full text Add to dashboard Cite

High-grade ore zones in low-sulfidation epithermal deposits are commonly associated with the occurrence of banded quartz veins. The ore minerals in these veins are heterogeneously distributed and are mostly confined to ginguro bands, which can be identified in hand specimen based on their distinct dark gray to black color. Micro-X-ray fluorescence element maps obtained on representative samples of banded quartz veins show that Au occurs together with Ag minerals in some of the ginguro bands, but Au can also be present in quartz bands that are light gray to white and cannot be macroscopically distinguished from barren bands. The occurrence of compositionally distinct ginguro and gankin bands, the latter being a new term coined here for colloform quartz bands containing primarily electrum or native gold, can be explained by temporal changes in the composition of the ore-forming thermal waters or variations in the conditions of ore deposition. Textural relationships, including the dendritic shape of ore minerals that appear to have grown in a matrix of silica microspheres, suggest that the ginguro and gankin bands have formed as a result of rapid deposition associated with vigorous boiling or flashing of the thermal waters.Minerals 2019, 9, 740 2 of 23 in Japan [15]; Ivanhoe in Nevada [14]; Koryu in Japan [7,12]; Kushikino in Japan [5]; and Midas in Nevada [9]. Some of the best examples of ginguro bands occur at the high-grade Hishikari deposit of Kyushu in Japan [6,8,10,16,17]. At all of these deposits, ginguro bands are characterized by extremely high precious metal grades and can contain thousands of ppm Au and Ag. Many low-sulfidation epithermal deposits would not be economically viable without the occurrence of these high-grade ore bands [11].This contribution reports on the distribution of precious metals in banded low-sulfidation epithermal veins as constrained by micro-X-ray fluorescence (µXRF) mapping of hand specimens. Combined with optical petrography, this study shows that native gold or electrum do not always occur together with Ag sulfides or selenides in ginguro bands, but can also be present in significant quantities in other quartz bands. These Au-bearing quartz bands cannot be visually distinguished from barren quartz bands. The findings highlight that comprehensive petrographic studies are required to fully characterize low-sulfidation epithermal deposits as macroscopic vein characteristics only provide limited information on the location of ore minerals within the veins. Implications for the current understanding of the ore-forming processes are discussed. Materials and Methods Sample LocationsThis study focuses on three representative hand specimens of epithermal ores collected from the Hokuryu deposit of Hokkaido in Japan, the Midas deposit in Nevada, and the Sado Kinzan deposit in Japan.The Hokuryu deposit in the Omu mining camp of Hokkaido in Japan represents a small low-sulfidation epithermal deposit that produced a total of~300,000 metric tons of ore for an estimated 68,000 oz Au and~370,00...

show abstract

Formation and Aggregation of Gold (Electrum) Nanoparticles in Epithermal Ores

Cited by 54 publications

References 55 publications

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

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

The Distribution of Precious Metals in High-Grade Banded Quartz Veins from Low-Sulfidation Epithermal Deposits: Constraints from µXRF Mapping

Contact Info

Product

Resources

About