Formation of Mg-carbonates and Mg-hydroxides via calcite replacement controlled by fluid pressure

Duan, Gan; Brugger, Joël; Etschmann, Barbara; Ram, Rahul; Frierdich, Andrew J.; Micklethwaite, Steven

doi:10.1007/s00410-020-01755-4

Cited by 9 publications

(3 citation statements)

References 53 publications

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“…While the catalytic role of hydrothermal fluids in the marcasite to pyrite transformation requires further detailed studies, it is likely that the rapid transformation is due to CDR mineral replacement reactions rather than solid-state transformation. This is because at low temperatures, CDR is much faster than solid-state reactions, as has been demonstrated in numerous hydrothermal mineral phase transformations in sulfides, ,− tellurides, , phosphates, , carbonates, − oxides, , and silicates. , …”

Section: Discussionmentioning

confidence: 97%

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection

Yao

Xia

Brugger

et al. 2021

ACS Earth Space Chem.

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Pyrite is the most abundant metal sulfide in the Earth’s crust and is also found on Mars. It can form by direct hydrothermal precipitation or by polymorphic phase transformation from marcasite. However, the control on the dynamics of hydrothermal pyrite precipitation is poorly understood, and the kinetics of the hydrothermal transformation from marcasite to pyrite is unknown. To address these issues, we quantified pyrite and marcasite formation in hydrothermal fluids at pH 1, using pyrrhotite as a precursor mineral to produce supersaturated solutions. In situ powder X-ray diffraction experiments at 190 °C showed that hydrothermal fluids rich in ΣS(-II) (0.2 molal) favored the precipitation of nanocrystal pyrite (∼20 nm) due to a high saturation index (>105), while ΣS(-II)-free fluids produced a mixture of marcasite and pyrite nanocrystals (21–46 nm) due to a low saturation index (<104). The fluid/rock ratio (70 and 120 g/g at 210 °C) can also affect the saturation indices of these fluids, influencing nucleation and crystal growth dynamics of pyrite and marcasite and resulting in complex evolution of crystallite size, phase abundance, and the pyrite/marcasite ratio. Ex situ hydrothermal experiments at 210 °C showed rapid transformation from marcasite to pyrite, with around 95% marcasite being transformed to pyrite in 20 weeks, compared to more than 6.3 million years at 210 °C under dry conditions based on extrapolation from previous kinetic studies. These results suggest that saturation index influences hydrothermal precipitation dynamics and controls phase selection between pyrite and marcasite and that marcasite may not survive over geological time in low-temperature (<200 °C), water-saturated environments.

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Section: Discussionmentioning

confidence: 97%

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection

Yao

Xia

Brugger

et al. 2021

ACS Earth Space Chem.

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“…This scenario was also insighted (Gallien et al ., 2007) explaining seemingly marine carbon‐isotope and oxygen‐isotope values in dolostones of the Monzoni Intrusive Complex aureole (about 10 km north‐east of the Latemar platform). This preservation model depends on a suite of factors often overlooked due to their complex nature: protolith composition, effects of volatilization, temperature of exchange, exchange kinetics, fluid isotope composition, fluid pressure and fluid flux/mixture (Baumgartner & Valley, 2001, and references therein; Duan et al ., 2021).…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Constraints on the preservation of proxy data in carbonate archives – lessons from a marine limestone to marble transect, Latemar, Italy

et al. 2021

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This work evaluates an exceptionally complex natural laboratory, the Middle Triassic Latemar isolated platform in the northern Italian Dolomite Mountains and explores spatial and temporal gradients in processes and products related to contact metamorphism, dolomitization and dedolomitization of marine limestones. The relation between petrographic change and re‐equilibration of geochemical proxy data is evaluated from the perspective of carbonate‐archive research. Hydrothermal dolomitization of the limestone units is triggered by dykes and associated hydrothermal fluids radiating from the nearby Predazzo Intrusion. Detailed petrography, fluid inclusion analysis, δ13C and δ18O data and 87Sr/86Sr isotope ratios shed light on the extreme textural and geochemical complexity. Metamorphic and diagenetic patterns include: (i) peak‐metamorphic and retrograde‐metamorphic phases including three dolomite marbles, two dedolomite marbles, brucite, magnesium silicates and late‐stage meteoric/vadose cement at the contact aureole; (ii) four spatially defined episodes of dolomitization, authigenic quartz, low magnesium calcite and late‐stage meteoric cement at the Latemar isolated platform; and (iii) kilometre‐scale gradients in δ13C values from the contact aureole towards the platform interior. Results shown here are relevant for two reasons: first, the spatial analysis of alteration products ranging from high‐grade metamorphic overprint of marbles at temperatures of 700°C in the contact aureole to moderately altered limestones in the platform interior at temperatures <100°C, allows the observation of processes that commonly occur along vertical (prograde) gradients from shallow burial to metamorphism at depths >20 km. Second, under rock‐buffered conditions, and irrespective of metamorphic to diagenetic fluid−rock interactions, both marbles, and low‐temperature hydrothermal dolomites have conservative marine δ13C and δ18O values. The fact that metamorphism and hydrothermal dolomitization of precursor limestones and early diagenetic dolostones did not per se reset environmental proxy data is of interest for those concerned with carbonate archive research in Earth’s deep time.

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“…Plümper et al 10 highlighted the importance of the coupling between nano-scale reaction mechanism that forms a transient reaction-induced porosity, and macro-scale fluid flow, for explaining pervasive crustal, fluid-present reactions (e.g. metamorphism; dolomitization 46 ). Our results show that the internally and externally driven factors (predictable using equilibrium thermodynamics) at the macro-scale, may contribute to explaining the widespread occurrence of albitisation, as well as the common occurrence of potassic alteration overprinting this sodic alteration.…”

Section: Discussionmentioning

confidence: 99%

Kinetically driven successive sodic and potassic alteration of feldspar

et al. 2021

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The dynamic evolutions of fluid-mineral systems driving large-scale geochemical transformations in the Earth’s crust remain poorly understood. We observed experimentally that successive sodic and potassic alterations of feldspar can occur via a single self-evolved, originally Na-only, hydrothermal fluid. At 600 °C, 2 kbar, sanidine ((K,Na)AlSi3O8) reacted rapidly with a NaCl fluid to form albite (NaAlSi3O8); over time, some of this albite was replaced by K-feldspar (KAlSi3O8), in contrast to predictions from equilibrium reaction modelling. Fluorine accelerated the process, resulting in near-complete back-replacement of albite within 1 day. These findings reveal that potassic alteration can be triggered by Na-rich fluids, indicating that pervasive sequential sodic and potassic alterations associated with mineralization in some of the world’s largest ore deposits may not necessarily reflect externally-driven changes in fluid alkali contents. Here, we show that these reactions are promoted at the micro-scale by a self-evolving, kinetically-driven process; such positive feedbacks between equilibrium and kinetic factors may be essential in driving pervasive mineral transformations.

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Formation of Mg-carbonates and Mg-hydroxides via calcite replacement controlled by fluid pressure

Cited by 9 publications

References 53 publications

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection

Constraints on the preservation of proxy data in carbonate archives – lessons from a marine limestone to marble transect, Latemar, Italy

Kinetically driven successive sodic and potassic alteration of feldspar

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Formation of Mg-carbonates and Mg-hydroxides via calcite replacement controlled by fluid pressure

Cited by 9 publications

References 53 publications

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS2 Precipitation Dynamics and Phase Selection

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS2 Precipitation Dynamics and Phase Selection

Constraints on the preservation of proxy data in carbonate archives – lessons from a marine limestone to marble transect, Latemar, Italy

Kinetically driven successive sodic and potassic alteration of feldspar

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Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS₂ Precipitation Dynamics and Phase Selection