Origin of the "epithermal" deposits

Schmitt, Harrison Ashley

doi:10.2113/gsecongeo.45.3.191

Cited by 6 publications

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“…The correlation of active geothermal systems with those responsible for the formation of a number of epithermal precious and base metal vein systems (e.g., Lindgren, 1933;Schmitt, 1950) has been clearly established by White (1955White ( , 1981 The table in the Appendix compiles Th, Tm, and gas concentration data from a number of epithermal deposits for which fluid inclusion freezing and/or gas extraction data are also available. As noted in earlier reviews by Sillitoe (1977) and Buchanan (1981), epithermal vein deposits containing base metal sulfides have apparent fluid inclusion salinities ranging from 0.1 to over 13 equi¾.…”

Section: Co2 In Fossil Hydrothermal Systemsmentioning

confidence: 99%

The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition

Hedenquist¹,

Henley²

1985

Economic Geology

424

201

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In studies of epithermal precious and base metal ore deposits, estimates of salinity (total dissolved salts) are frequently in error when based on fluid inclusion ice melting measurements in the absence of an independent determination of the CO2 content of the inclusion fluid. For a fluid of known composition, the melting point of ice (Tin) may be calculated from Tm= --• Kimi where Ki is the molal freezing (or melting) point depression constant and mi is the molality of a component i (i = Na +, K +, CI-, CO2, etc.). For fully dissociated solute species such as CI-, in the salinity range considered here, K = 1.72 Kelvin/molal, and for undissociated, nonpolar species such as CO•, K --1.86 Kelvin/molal. Fluid inclusion ice-melting data from New Zealand geothermal fields correlate well with values calculated using the above equation and the measured compositions of discharges from wells from which the inclusion samples were obtained. Loss of the dominant dissolved gas, CO•, during boiling at depth results in large, systematic decreases in apparent salinity (in terms of Tm) in the Broadlands field. Misinterpretation of fluid inclusion freezing data may lead to substantial errors in the reconstruction of the physico-chemical environment of ore formation in fossil systems. For example, in the absence of CO• analyses, inclusion fluids similar in gas content to the Broadlands geothermal fluid (NaC1 = 0.2 wt %, CO2 up to 4.4 wt %) may be interpreted to have salinities of 0.85 wt percent NaC1, leading to errors of 23 percent in the estimated depth of formation at 280øC, -0.5 unit in the estimated pH of the ore fluid, and on the order of 200 times in the estimated solubility of an ore component such as lead. Such errors may be transmitted into subsequent estimation of fluid flux or duration of ore formation.A review of published fluid inclusion studies shows that true salinities of inclusion fluids from epithermal precious metal deposits are coincident with those from the majority of explored geothermal systems but that the salinities of inclusion fluids from epithermal base metal deposits are substantially higher, indicating the presence of an evolved, high-salinity fluid during ore metal transport. In the case of low-salinity epithermal deposits, the extreme range in gold to silver ratios between deposits can be accounted for by variations in the H•S to chloride ratio in the original hydrothermal fluid. These variations (primarily in the total gas) occur between active geothermal systems and can be recognized in epithermal deposits through fluid inclusion freezing and crushing studies.

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Section: Co2 In Fossil Hydrothermal Systemsmentioning

confidence: 99%

The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition

Hedenquist¹,

Henley²

1985

Economic Geology

424

201

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“…Determining the lifespan of hydrothermal systems (i.e., the length of time a flow system has existed) is typically limited to mineral precipitates. The geological record has many examples of “ancient” hydrothermal systems (inactive), such as epithermal ore deposits (Schmitt, 1950; Taylor, 2007). Dating these deposits relies on the mineralization of veins, with many studies suggesting these record <1 Myrs of hydrothermal activity (Henry et al., 1997; Marsh et al., 1997; Sanematsu et al., 2006; Wallace, 2003).…”

Section: Introductionmentioning

confidence: 99%

Determining the Lifespan of Hydrothermal Systems Using Thermochronology and Thermal Modeling

et al. 2021

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Hydrothermal springs (or "hot springs") are the emergence of hot groundwater at the earth's surface (Pentecost et al., 2003;White, 1957). These springs reflect deep circulation of meteoric water that is heated in the upper ∼5 km of the earth's crust and are thought to reflect geothermal anomalies and zones of enhanced crustal permeability (Ferguson & Grasby, 2011;Grasby & Hutcheon, 2001). These systems offer vital information of a region's hydrological, climatic and tectonic histories (Gao et al., 2013;Grasby & Hutcheon, 2001;Lynne, 2012), providing important insight into the interaction between atmospheric and lithospheric processes at and near earth's surface. In recent decades, the desire to transition to carbon neutral electricity production has driven the exploration for geothermal energy resources as a form of renewable energy (Tester et al., 2006), and hydrothermal springs have been used to focus exploration activity. However, our understanding of hydrothermal springs remains incomplete, especially when considering the longevity and resilience of systems through major climatic and landscape changes (Skinner, 1997). In any energy system, the reliability of a resource is vital to the production of electricity and the lifespan of these geothermal

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Epithermal gold deposits in volcanic terranes

Henley¹

1993

Gold Metallogeny and Exploration

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Origin of the "epithermal" deposits

Cited by 6 publications

References 0 publications

The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition

The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition

Determining the Lifespan of Hydrothermal Systems Using Thermochronology and Thermal Modeling

Epithermal gold deposits in volcanic terranes

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