The optimal windows for seismically-enhanced gold precipitation in the epithermal environment

Sánchez-Alfaro, Pablo; Reich, Martín; Driesner, Thomas; Cembrano, José; Arancibia, Gloria; Pérez-Flores, Pamela; Heinrich, Christoph A.; Rowland, J. V.; Tardani, Daniele; Lange, Dietrich; Campos, Eduardo

doi:10.1016/j.oregeorev.2016.06.005

Cited by 26 publications

(18 citation statements)

References 44 publications

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“…The scales can contain high concentrations of Au and Ag [36,61,65]. Theoretical considerations by Sanchez-Alfaro et al [66] confirm that flashing is an effective mechanism for Au precipitation.…”

Section: Silica Deposition In Ore-bearing Bandsmentioning

confidence: 97%

“…The study of low-sulfidation epithermal deposits has shown that mineral deposition in the epithermal environment can occur by three processes, namely cooling, boiling, and flashing of the thermal chloride waters [37,64,66,71]. Each of these processes may be responsible for, or contribute to, the observed compositional difference between adjacent ore-bearing colloform quartz bands and the apparent decoupling of Au, Ag, and other metals.…”

Section: The Banded Quartz Veins In Low-sulfidation Epithermal Deposimentioning

confidence: 99%

“…Cooling of the near-neutral thermal waters results in a reduction of Au solubility, with the Au being dominantly transported as [Au(HS) 2 ] − . Sanchez-Alfaro et al [66] demonstrated that a temperature decrease of 160 • C from the reservoir temperature results in the deposition of 95% of the Au.…”

Section: The Banded Quartz Veins In Low-sulfidation Epithermal Deposimentioning

confidence: 99%

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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

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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...

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Section: Silica Deposition In Ore-bearing Bandsmentioning

confidence: 97%

Section: The Banded Quartz Veins In Low-sulfidation Epithermal Deposimentioning

confidence: 99%

Section: The Banded Quartz Veins In Low-sulfidation Epithermal Deposimentioning

confidence: 99%

See 1 more Smart Citation

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

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“…This process of metal deposition is observed in modern geothermal systems where sharp decreases in pressure occur such as on back-pressure plates in surface pipes of geothermal power plants [9]. Sanchez-Alfaro et al [87] showed that flashing is a more effective mechanism of gold precipitation than gentle boiling.…”

Section: Implications For Ore-forming Processesmentioning

confidence: 98%

“…Therefore, textural analysis on epithermal veins could be used to identify hydrothermal systems that underwent transient periods of fluid flashing. These systems are likely to be associated with veins having high gold grades, as fluid flashing represents the most efficient process of gold deposition in the epithermal environment [9,87]. Conversely, hydrothermal systems in which fluid ascent is only accompanied by gentle boiling or cooling (cf.…”

Section: Exploration Implicationsmentioning

confidence: 99%

Textural Characteristics of Noncrystalline Silica in Sinters and Quartz Veins: Implications for the Formation of Bonanza Veins in Low-Sulfidation Epithermal Deposits

Taksavasu

Monecke

Reynolds³

2018

Minerals

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Abstract:Silica sinters forming at the Wairakei geothermal power plant in New Zealand are composed of noncrystalline opal-A that deposited rapidly from cooling geothermal liquids flashed to atmosphere. The sinter is laminated with alternating layers of variably compacted silicified filamentous microbes encased by chains of fused silica microspheres. Microscopic inspection of bonanza quartz vein samples from the Buckskin National low-sulfidation epithermal precious metal deposit in Nevada showed that colloform bands in these veins exhibit relic microsphere textures similar to those observed in the silica sinters from the Wairakei power plant. The textural similarity suggests that the colloform bands were originally composed of noncrystalline opal-A that subsequently recrystallized to quartz. The colloform bands contain dendrites of electrum and naumannite that must have grown in a yielding matrix of silica microspheres deposited at the same time as the ore minerals, implying that the noncrystalline silica exhibited a gel-like behavior. Quartz bands having other textural characteristics in the crustiform veins lack ore minerals. This suggests that ore deposition and the formation of the colloform bands originally composed of compacted microspheres of noncrystalline silica are genetically linked and that ore deposition within the bonanza veins was only episodic. Supersaturation of silica and precious metals leading to the formation of the colloform bands may have occurred in response to transient flashing of the hydrothermal liquids. Flashing of geothermal liquids may thus represent a key mechanism in the formation of bonanza precious metal grades in low-sulfidation epithermal deposits.

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Auriferous pyrite formed by episodic fluid inputs in the Akeshi and Kasuga high-sulfidation deposits, Southern Kyushu, Japan

et al. 2021

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Pyrite geochemistry has proven useful for tracking changes in the composition and physico-chemical conditions of hydrothermal fluids in ore-forming environments. Here, we investigated the microtextural features and chemical composition of pyrite, a main Au-bearing phase in the Akeshi and Kasuga deposits (Southern Kyushu, Japan), to better constrain the ore-forming processes in these high-sulfidation epithermal Au deposits. Despite the widespread distribution of Au-bearing pyrite in both deposits, no visible Au minerals coexist with pyrite. However, in situ laser ablation inductively coupled plasma mass spectrometry results show that Au concentrations in pyrite vary from below the detection limit to 41 ppm and are positively correlated with Cu (r = 0.4; up to 7400 ppm) and Bi concentrations (r = 0.44; up to 640 ppm). In both deposits, high Cu and Au concentrations occur in small (< 25 μm) anhedral grains of pyrite, which are interpreted to have rapidly crystallized from the ore-forming hydrothermal fluid. In addition, dissolution–reprecipitation textures and thin, concentric, Cu-rich overgrowths were identified in a number of larger (> 25 μm) pyrite grains and aggregates. These abrupt changes in the trace element compositions of pyrite grains likely record episodic metal-rich fluid inputs. We also propose that gold adsorption onto growing pyrite surfaces played a key role in the mineralization of these deposits.

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The optimal windows for seismically-enhanced gold precipitation in the epithermal environment

Cited by 26 publications

References 44 publications

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

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

Textural Characteristics of Noncrystalline Silica in Sinters and Quartz Veins: Implications for the Formation of Bonanza Veins in Low-Sulfidation Epithermal Deposits

Auriferous pyrite formed by episodic fluid inputs in the Akeshi and Kasuga high-sulfidation deposits, Southern Kyushu, Japan

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