mineral reaction
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2022 ◽  
Vol 3 ◽  
Author(s):  
Pei Li ◽  
Hang Deng ◽  
Sergi Molins

In various natural and engineered systems, mineral–fluid interactions take place in the presence of multiple fluid phases. While there is evidence that the interplay between multiphase flow processes and reactions controls the evolution of these systems, investigation of the dynamics that shape this interplay at the pore scale has received little attention. Specifically, continuum scale models rarely consider the effect of multiphase flow parameters on mineral reaction rates or apply simple corrections as a function of the reactive surface area or saturation of the aqueous phase, without developing a mechanistic understanding of the pore-scale dynamics. In this study, we developed a framework that couples the two-phase flow simulator of OpenFOAM (open field operation and manipulation) with the geochemical reaction capability of CrunchTope to examine pore-scale dynamics of two phase flow and their impacts on mineral reaction rates. For our investigations, flat 2D channels and single sine wave channels were used to represent smooth and rough geometries. Calcite dissolution in these channels was quantified with single phase flow and two phase flow at a range of velocities. We observed that the bulk calcite dissolution rates were not only affected by the loss of reactive surface area as it becomes occupied by the non-reactive non-aqueous phase, but also largely influenced by the changes in local velocity profiles, e.g., recirculation zones, due to the presence of the non-aqueous phase. The extent of the changes in reaction rates in the two-phase systems compared to the corresponding single phase system is dependent on the flow rate (i.e., capillary number) and channel geometry, and follows a non-monotonic relationship with respect to aqueous saturation. The pore-scale simulation results highlight the importance of interfacial dynamics in controlling mineral reactions and can be used to better constrain reaction rate descriptions in multiphase continuum scale models. These results also emphasize the need for experimental studies that underpin the development of mechanistic models for multiphase flow in reactive systems.


2021 ◽  
Author(s):  
Ane K. Engvik ◽  
Claudia A. Trepmann ◽  
Håkon Austrheim

<p>The Proterozoic gneisses of the Bamble lithotectonic domain (south Norway) underwent intense scapolitisation caused by K- and Mg-rich fluids and extensive albitisation with formation of numerous ore deposits.</p><p>By detailed studies of mineral reaction fabrics we document release of the chemical active Mg, K and Fe-components forming the metasomatic fluid: Breakdown of biotite to muscovite releases K, Mg, Fe, Si and H<sub>2</sub>O. As reaction products tiny Fe-oxide needles are present in the transforming rock. H<sub>2</sub>O is reacting with K-feldspar to produce additional amounts of white mica and quartz. During a subsequent reaction muscovite is replaced to sillimanite again releasing quartz and a K-rich fluid. The reactions form the peculiar sillimanite-nodular quartzite, but also well-foliated sillimanite-mica gneiss.</p><p>Optical and EBSD microfabric studies reveal a shape preferred orientation for quartz, but despite of a pronounced foliation, quartz does not show a crystallographic preferred orientation. A crystallographic preferred orientation is present for mica and sillimanite. Coarse micas show sutured boundaries to quartz, implying low nucleation rates, no crystallographic or surface-energy control during growth and no obvious crystallographic relationship to quartz.</p><p>Our study illustrates the transformation of a quartzofeldspatic lithology into sillimanite-bearing quartzite. The mineral replacement and deformation show ongoing metamorphic reactions during deformation. The microfabric data indicates reaction at non-isostatic stress condition. The deduced mineral replacement reactions document a source of K-, Mg- and Fe-rich metasomatic fluids necessary to cause the pervasive scapolitisation and Fe-deposition in the area. The mineral reactions and deformation produce rocks with a new mineralogy and structure; an increased understanding of these processes is important for the modelling of crustal building and geological history.</p>


2020 ◽  
Author(s):  
Gan Duan ◽  
Joel Brugger ◽  
Rahul Ram ◽  
Yan Xing ◽  
Barbara Etschmann

Abstract The evolution of hydrothermal fluids during metasomatic and/or hydrothermal processes is responsible for the formation of ore deposits and associated alteration. In systems with well-developed breccia and fractures, mineral reactions are largely driven by decompression boiling, fluid cooling or external fluid mixing, but in less permeable rocks, elements exchanges occur at fluid-mineral interfaces, resulting in a self-evolved fluid-mineral reaction system. However, the dynamic fluid evolution leading to large-scale (km) alteration remains poorly understood. We observed experimentally that the sequential sodic and potassic alterations associated with mineralization in large ore deposits, in particular Iron Oxide Copper Gold (IOCG) deposits, can occur via a single self-evolved, originally Na-only, hydrothermal fluid, driven by a positive feedback between equilibrium and kinetic factors. Albite formed first upon reaction of sanidine ((K,Na)AlSi3O8) with a NaCl fluid at 600˚C, 2 kbar. However, with increasing reaction time, some of the initially formed albite was in-turn replaced by K-feldspar (KAlSi3O8). Fluorine accelerated the process, resulting in nearly complete back-replacement of albite within 1 day. These experiments demonstrate that potassic alteration can be induced by Na-rich fluids, and pervasive sequential sodic and potassic alterations do not necessarily reflect near-equilibrium, externally-driven changes in fluid alkali contents.


2020 ◽  
Vol 10 (1) ◽  
Author(s):  
R. A. Wogelius ◽  
A. E. Milodowski ◽  
L. P. Field ◽  
R. Metcalfe ◽  
T. Lowe ◽  
...  

2020 ◽  
Author(s):  
Robert G. W. Seidel ◽  
John C. Bridges ◽  
Thomas Kirnbauer ◽  
Sarah C. Sherlock ◽  
Susanne P. Schwenzer

<p>We present results of an ongoing petrologic and modelling study of a new Martian analogue rock: The Frankenstein Gabbro (Odenwald, Germany). Our aim is to predict mineral reaction paths and fluid properties during hydrothermal alteration of basaltic host rocks on Mars – thought to be a common by-product of impact cratering – in order to assess the habitability of the fluids for the potential of Martian life, and establish a link between habitable fluid conditions and secondary mineral assemblages.</p><p>Primary minerals of the analogue are mostly plagioclase (~70 vol.%) and clinopyroxene (~20 vol.%) with lesser percentages of amphiboles and Fe-oxides. We focus on a chloritic-propylitic alteration event associated with hairline fault planes and mineral veinlets. The secondary mineralisation shows strong small-scale variability, depending on host mineral and type of fluid pathway: For plagioclase hosts, fault planes are dominated by chlorite with additional epidote and prehnite, while mineral veinlets consist of albite ± calcite ± chlorite ± epidote ± K-feldspar ± mica. For clinopyroxene hosts, fault planes consist of actinolite with additional chlorite or vermiculite, while mineral veinlets consist of prehnite and vermiculite.</p><p>We use the software CHIM-XPT to model mineral reaction paths, with published XRF bulk rock data, EMP analyses of single minerals, and a starting fluid enriched in Na, K, Mg and Si for input, the latter based on calculated element budgets of mineral replacement reactions. Our models reproduce secondary assemblages related to plagioclase-hosted fault planes (chlorite–epidote–prehnite) and veinlets (albite–chlorite–epidote–K-feldspar–mica), as well as alteration rims around clinopyroxene related to fault planes (actinolite–chlorite). Corresponding fluid conditions are ~200–250 °C, pH ~6.5–8.0, at water/rock ratios >3000, in agreement with pre-model constraints by mineralogy. The breakdown of clinopyroxene and plagioclase releases large amounts of Ca, with calcite inferred to be a late-stage product of cooling. Fluid redox state is shown to be largely controlled by host minerals, and in turn exerts strong influence on secondary mineral formation: clinopyroxene releases Fe<sup>2+</sup> during alteration, which is taken up by chlorite; in contrast, plagioclase contains up to 0.5 wt.% Fe<sup>3+</sup> substituting for Al, which is taken up by epidote. Prehnite, of the same elemental composition except for Fe, is inversely correlated with epidote. Thus, the relative percentages of chlorite, epidote and prehnite can serve as indicators of redox state in similar types of rock.</p><p>Our models match key petrological observations and provide information about the alteration process beyond what may be directly observed. They illustrate the need to account for small-scale variability, and to adjust models on a case-by-case basis. This has important implications for models of Martian habitability, where similar features may be expected. Next, we will apply these reaction pathways to Martian rocks (shergottitic basalts), focusing especially on small-scale distribution of dissolved iron species, a suggested energy source for hypothetical microbial Martian life.</p>


Fuel ◽  
2018 ◽  
Vol 229 ◽  
pp. 241-247 ◽  
Author(s):  
Jianrui Zha ◽  
Yaji Huang ◽  
Wenqing Xia ◽  
Zhipeng Xia ◽  
Changqi Liu ◽  
...  

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