The effects of amphibolite facies metamorphism on the trace element composition of pyrite and pyrrhotite in the Cambrian Nairne Pyrite Member, Kanmantoo Group, South Australia

The trace element composition of pyrite has been used to explore for hydrothermal ore deposits and to understand ore-forming processes. However, the effects of metamorphism on the trace element distribution in pyrite have received relatively limited attention. In this study, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of pyrite and pyrrhotite, along with minor amounts of sphalerite, chalcopyrite, and galena, are used to evaluate the effects of amphibolite facies metamorphism on the trace element distribution and remobilization of metals in iron sulfides in the clastic sediment-hosted Cambrian Nairne Pyrite Member (NPM), South Australia. The NPM and the Mt. Torrens Pb-Zn-Ag prospect, which occur near the base of the Kanmantoo Group, preserve irregularly zoned subhedral to euhedral metamorphic pyrite (Py1) and anhedral pyrrhotite (Po1), along with relatively minor quantities of remobilized anhedral pitted and cataclastic pyrite (Py2a) in quartzofeldspathic rocks and anhedral inclusion-poor pyrite (Py2b) in calc-silicate rocks that armor or cross-cut earlier formed Py1. Rare anhedral secondary melnikovite pyrite (Py3) locally formed on the margins of Py1 and Py2a. Trace element studies show that Py1 in the NPM at Brukunga and Ironstone Ridge contains mean values of 1254 ppm Co, 123 ppm Ni, 2167 ppm As, 16 ppm Se, 10 ppm Cu, 25 ppm Zn, and 15 ppm Pb, whereas Py1 in the Mt. Torrens prospect contains mean values of 2312 ppm Co, 263 ppm Ni, 1835 ppm As, 95 ppm Se, 9 ppm Cu, 6 ppm Zn, and 9 ppm Pb. Rare inclusion-rich cores of Py1 show higher concentrations of trace elements than inclusion-free rims with minor amounts of chalcopyrite, galena, and sphalerite forming along grain boundaries or in fractures within pyrite. This is interpreted to be the result of the release of Cu, Pb, and Zn from pyrite as it recrystallized. Remobilization of these elements then formed discrete sulfides at the millimeter to centimeter scale, with some exceptions at the meter scale where chalcopyrite, sphalerite, and galena, along with other sulfides and sulfosalts, formed in veins and tension gashes. These observations suggest that remobilization of trace metals, including Cu, Pb, and Zn, did not migrate more than a few meters at most. Moreover, despite the recrystallization of pyrite and pyrrhotite and subsequent remobilization of some trace elements (i.e., Co, Ni, As), which were structurally bound in these Fe sulfides, still retain elevated concentrations at amphibolite facies conditions. Remobilization of metals from the NPM during metamorphism to form Cu-Au (e.g., Kanmantoo) and Pb-Zn- Ag-(Cu-Au) (e.g., Angas, Wheal Ellen) deposits in the Tapanappa Formation stratigraphically higher in the Kanmantoo Group seems unlikely. However, it is possible that one source of metals for these deposits could have been leached from the NPM and carried in large hydrothermal cells prior to metamorphism. Such a scenario is consistent with previously published sulfur isotope data for sulfides from the NPM, and Cu-Au and Pb-Zn-Ag- (Cu-Au) deposits, which indicate that sulfur derived from the NPM and pyritic schists in the Kanmantoo Group was a likely source of sulfur for the base and precious metal deposits

Boron isotopes as a proxy of weathering mechanisms and balance in soil minerals

L’objectif de cette thèse est d’estimer la capacité du bore et de ses isotopes à évaluer les mécanismes et bilans de l’altération des minéraux dans les sols. Pour ce faire, trois axes ont été développés : 1) une approche expérimentale, durant laquelle un minéral-test (la biotite) est soumis à l’action de différents agents altérants représentatifs de ceux trouvés dans les sols. 2) une approche in-situ dans un sol forestier acide, menée sur des minéraux séparés (biotite, muscovite,feldspath potassique et albite), au cours de leur altération à différentes profondeurs (site de Breuil-Chenue, France). L’objectif de cette étude est de déterminer la sensibilité du bore aux processus de la formation des sols. 3) une seconde approche in-situ sur le même site expérimental, menée cette fois-ci sur les horizons superficiels (horizon A et horizon d’accumulation des oxy-hydroxydes d’aluminium), dont le but est de déterminer la sensibilité du bore et de ses isotopes aux processus liés à la proximité de la végétation (variations saisonnières, proximité des racines). Le bore permet, grâce à sa très grande réactivité durant les mécanismes d’altération par rapport aux éléments majeurs constitutifs du réseau cristallin (observable aussi bien en conditions expérimentales qu’en milieu naturel), de tracer avec une grande sensibilité les mécanismes de dissolution ou de transformation des différents minéraux primaires, et ouvre de nouvelles perspectives quant à la compréhension et la modélisation des sols.The objective of this thesis is to estimate the ability of boron and its isotopes to evaluate mineral weathering budgets and mechanisms in soils. In this goal, 3 different approaches were conducted:1) an experimental approach during which a test-mineral (biotite) undergoes the action of different weathering agents, representative of those found in soils.2) an in-situ approach in an acid soil profile led on different minerals (biotite, muscovite, K-feldspar and albite) handpicked at various depths and weathering state (Breuil-Chenue forest experimental site, France).The objective of this study is to determine the sensitivity of boron to soil formation processes.3) an second in-situ approach conducted on the same study site but this time on sub-surface horizons (horizon A and Al-oxi-hydroxides accumulation horizon), which aim is to evaluate the sensitivity of boron and its isotopes to mechanisms in close vicinity to vegetation (seasonal variations, vicinity of the roots). B and its isotopes able, thanks to its high reactivity during weathering mechanisms in comparison to major elements that constitute the crystallographic network (observed in experimental as well as in in-situ approaches), to trace with a great sensitivity primary minerals dissolution or transformation mechanisms, and opens new insights for the comprehension of soils

Boron isotopes as a proxy of weathering mechanisms and balance in soil minerals

L’objectif de cette thèse est d’estimer la capacité du bore et de ses isotopes à évaluer les mécanismes et bilans de l’altération des minéraux dans les sols. Pour ce faire, trois axes ont été développés : 1) une approche expérimentale, durant laquelle un minéral-test (la biotite) est soumis à l’action de différents agents altérants représentatifs de ceux trouvés dans les sols. 2) une approche in-situ dans un sol forestier acide, menée sur des minéraux séparés (biotite, muscovite,feldspath potassique et albite), au cours de leur altération à différentes profondeurs (site de Breuil-Chenue, France). L’objectif de cette étude est de déterminer la sensibilité du bore aux processus de la formation des sols. 3) une seconde approche in-situ sur le même site expérimental, menée cette fois-ci sur les horizons superficiels (horizon A et horizon d’accumulation des oxy-hydroxydes d’aluminium), dont le but est de déterminer la sensibilité du bore et de ses isotopes aux processus liés à la proximité de la végétation (variations saisonnières, proximité des racines). Le bore permet, grâce à sa très grande réactivité durant les mécanismes d’altération par rapport aux éléments majeurs constitutifs du réseau cristallin (observable aussi bien en conditions expérimentales qu’en milieu naturel), de tracer avec une grande sensibilité les mécanismes de dissolution ou de transformation des différents minéraux primaires, et ouvre de nouvelles perspectives quant à la compréhension et la modélisation des sols.The objective of this thesis is to estimate the ability of boron and its isotopes to evaluate mineral weathering budgets and mechanisms in soils. In this goal, 3 different approaches were conducted:1) an experimental approach during which a test-mineral (biotite) undergoes the action of different weathering agents, representative of those found in soils.2) an in-situ approach in an acid soil profile led on different minerals (biotite, muscovite, K-feldspar and albite) handpicked at various depths and weathering state (Breuil-Chenue forest experimental site, France).The objective of this study is to determine the sensitivity of boron to soil formation processes.3) an second in-situ approach conducted on the same study site but this time on sub-surface horizons (horizon A and Al-oxi-hydroxides accumulation horizon), which aim is to evaluate the sensitivity of boron and its isotopes to mechanisms in close vicinity to vegetation (seasonal variations, vicinity of the roots). B and its isotopes able, thanks to its high reactivity during weathering mechanisms in comparison to major elements that constitute the crystallographic network (observed in experimental as well as in in-situ approaches), to trace with a great sensitivity primary minerals dissolution or transformation mechanisms, and opens new insights for the comprehension of soils

Contribution des isotopes du bore à l'étude des mécanismes et bilans de l'altération des minéraux des sols

The objective of this thesis is to estimate the ability of boron and its isotopes to evaluate mineral weathering budgets and mechanisms in soils. In this goal, 3 different approaches were conducted:1) an experimental approach during which a test-mineral (biotite) undergoes the action of different weathering agents, representative of those found in soils.2) an in-situ approach in an acid soil profile led on different minerals (biotite, muscovite, K-feldspar and albite) handpicked at various depths and weathering state (Breuil-Chenue forest experimental site, France).The objective of this study is to determine the sensitivity of boron to soil formation processes.3) an second in-situ approach conducted on the same study site but this time on sub-surface horizons (horizon A and Al-oxi-hydroxides accumulation horizon), which aim is to evaluate the sensitivity of boron and its isotopes to mechanisms in close vicinity to vegetation (seasonal variations, vicinity of the roots). B and its isotopes able, thanks to its high reactivity during weathering mechanisms in comparison to major elements that constitute the crystallographic network (observed in experimental as well as in in-situ approaches), to trace with a great sensitivity primary minerals dissolution or transformation mechanisms, and opens new insights for the comprehension of soils.L’objectif de cette thèse est d’estimer la capacité du bore et de ses isotopes à évaluer les mécanismes et bilans de l’altération des minéraux dans les sols. Pour ce faire, trois axes ont été développés : 1) une approche expérimentale, durant laquelle un minéral-test (la biotite) est soumis à l’action de différents agents altérants représentatifs de ceux trouvés dans les sols. 2) une approche in-situ dans un sol forestier acide, menée sur des minéraux séparés (biotite, muscovite,feldspath potassique et albite), au cours de leur altération à différentes profondeurs (site de Breuil-Chenue, France). L’objectif de cette étude est de déterminer la sensibilité du bore aux processus de la formation des sols. 3) une seconde approche in-situ sur le même site expérimental, menée cette fois-ci sur les horizons superficiels (horizon A et horizon d’accumulation des oxy-hydroxydes d’aluminium), dont le but est de déterminer la sensibilité du bore et de ses isotopes aux processus liés à la proximité de la végétation (variations saisonnières, proximité des racines). Le bore permet, grâce à sa très grande réactivité durant les mécanismes d’altération par rapport aux éléments majeurs constitutifs du réseau cristallin (observable aussi bien en conditions expérimentales qu’en milieu naturel), de tracer avec une grande sensibilité les mécanismes de dissolution ou de transformation des différents minéraux primaires, et ouvre de nouvelles perspectives quant à la compréhension et la modélisation des sols

Boron as a proxy of the evolution of primary mineral weathering mechanisms: from the bedrock to the surface

International audienc

Contribution des isotopes du bore à l'étude des mécanismes et bilans de l'altération des minéraux des sols

L objectif de cette thèse est d estimer la capacité du bore et de ses isotopes à évaluer les mécanismes et bilans de l altération des minéraux dans les sols. Pour ce faire, trois axes ont été développés : 1) une approche expérimentale, durant laquelle un minéral-test (la biotite) est soumis à l action de différents agents altérants représentatifs de ceux trouvés dans les sols. 2) une approche in-situ dans un sol forestier acide, menée sur des minéraux séparés (biotite, muscovite,feldspath potassique et albite), au cours de leur altération à différentes profondeurs (site de Breuil-Chenue, France). L objectif de cette étude est de déterminer la sensibilité du bore aux processus de la formation des sols. 3) une seconde approche in-situ sur le même site expérimental, menée cette fois-ci sur les horizons superficiels (horizon A et horizon d accumulation des oxy-hydroxydes d aluminium), dont le but est de déterminer la sensibilité du bore et de ses isotopes aux processus liés à la proximité de la végétation (variations saisonnières, proximité des racines). Le bore permet, grâce à sa très grande réactivité durant les mécanismes d altération par rapport aux éléments majeurs constitutifs du réseau cristallin (observable aussi bien en conditions expérimentales qu en milieu naturel), de tracer avec une grande sensibilité les mécanismes de dissolution ou de transformation des différents minéraux primaires, et ouvre de nouvelles perspectives quant à la compréhension et la modélisation des sols.The objective of this thesis is to estimate the ability of boron and its isotopes to evaluate mineral weatheringbudgets and mechanisms in soils. In this goal, 3 different approaches were conducted:1) an experimental approach during which a test-mineral (biotite) undergoes the action of differentweathering agents, representative of those found in soils.2) an in-situ approach in an acid soil profile led on different minerals (biotite, muscovite, K-feldspar andalbite) handpicked at various depths and weathering state (Breuil-Chenue forest experimental site, France).The objective of this study is to determine the sensitivity of boron to soil formation processes.3) an second in-situ approach conducted on the same study site but this time on sub-surface horizons(horizon A and Al-oxi-hydroxides accumulation horizon), which aim is to evaluate the sensitivity of boron andits isotopes to mechanisms in close vicinity to vegetation (seasonal variations, vicinity of the roots).B and its isotopes able, thanks to its high reactivity during weathering mechanisms in comparison to majorelements that constitute the crystallographic network (observed in experimental as well as in in-situapproaches), to trace with a great sensitivity primary minerals dissolution or transformation mechanisms, and opens new insights for the comprehension of soils.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

From bulk soil to intracrystalline investigation of plant-mineral interaction

International audienc

Mechanisms of primary mineral weathering inferred from boron isotopes

Mechanisms of primary mineral weathering inferred from boron isotopes. European Geosciences Union General Assembly 201

Insight into biotite weathering rate using U-series isotopes

International audienc

The effects of amphibolite facies metamorphism on the trace element composition of pyrite and pyrrhotite in the Cambrian Nairne Pyrite Member, Kanmantoo Group, South Australia

The trace element composition of pyrite has been used to explore for hydrothermal ore deposits and to understand ore-forming processes. However, the effects of metamorphism on the trace element distribution in pyrite have received relatively limited attention. In this study, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of pyrite and pyrrhotite, along with minor amounts of sphalerite, chalcopyrite, and galena, are used to evaluate the effects of amphibolite facies metamorphism on the trace element distribution and remobilization of metals in iron sulfides in the clastic sediment-hosted Cambrian Nairne Pyrite Member (NPM), South Australia. The NPM and the Mt. Torrens Pb-Zn-Ag prospect, which occur near the base of the Kanmantoo Group, preserve irregularly zoned subhedral to euhedral metamorphic pyrite (Py1) and anhedral pyrrhotite (Po1), along with relatively minor quantities of remobilized anhedral pitted and cataclastic pyrite (Py2a) in quartzofeldspathic rocks and anhedral inclusion-poor pyrite (Py2b) in calc-silicate rocks that armor or cross-cut earlier formed Py1. Rare anhedral secondary melnikovite pyrite (Py3) locally formed on the margins of Py1 and Py2a. Trace element studies show that Py1 in the NPM at Brukunga and Ironstone Ridge contains mean values of 1254 ppm Co, 123 ppm Ni, 2167 ppm As, 16 ppm Se, 10 ppm Cu, 25 ppm Zn, and 15 ppm Pb, whereas Py1 in the Mt. Torrens prospect contains mean values of 2312 ppm Co, 263 ppm Ni, 1835 ppm As, 95 ppm Se, 9 ppm Cu, 6 ppm Zn, and 9 ppm Pb. Rare inclusion-rich cores of Py1 show higher concentrations of trace elements than inclusion-free rims with minor amounts of chalcopyrite, galena, and sphalerite forming along grain boundaries or in fractures within pyrite. This is interpreted to be the result of the release of Cu, Pb, and Zn from pyrite as it recrystallized. Remobilization of these elements then formed discrete sulfides at the millimeter to centimeter scale, with some exceptions at the meter scale where chalcopyrite, sphalerite, and galena, along with other sulfides and sulfosalts, formed in veins and tension gashes. These observations suggest that remobilization of trace metals, including Cu, Pb, and Zn, did not migrate more than a few meters at most. Moreover, despite the recrystallization of pyrite and pyrrhotite and subsequent remobilization of some trace elements (i.e., Co, Ni, As), which were structurally bound in these Fe sulfides, still retain elevated concentrations at amphibolite facies conditions. Remobilization of metals from the NPM during metamorphism to form Cu-Au (e.g., Kanmantoo) and Pb-Zn- Ag-(Cu-Au) (e.g., Angas, Wheal Ellen) deposits in the Tapanappa Formation stratigraphically higher in the Kanmantoo Group seems unlikely. However, it is possible that one source of metals for these deposits could have been leached from the NPM and carried in large hydrothermal cells prior to metamorphism. Such a scenario is consistent with previously published sulfur isotope data for sulfides from the NPM, and Cu-Au and Pb-Zn-Ag- (Cu-Au) deposits, which indicate that sulfur derived from the NPM and pyritic schists in the Kanmantoo Group was a likely source of sulfur for the base and precious metal deposits.This article is published as Conn, C. Dakota, Paul G. Spry, Dan Layton-Matthews, Alexandre Voinot, and Alan Koenig. "The effects of amphibolite facies metamorphism on the trace element composition of pyrite and pyrrhotite in the Cambrian Nairne Pyrite Member, Kanmantoo Group, South Australia." Ore Geology Reviews 114 (2019): 103128. doi:10.1016/j.oregeorev.2019.103128.</p