TY - JOUR
T1 - Synchronous solid-state diffusion, dissolution-reprecipitation, and recrystallization leading to isotopic resetting
T2 - insights from chalcopyrite replacement by copper sulfides
AU - Chaudhari, Alok
AU - Brugger, Joël
AU - Ram, Rahul
AU - Chowdhury, Priyadarshi
AU - Etschmann, Barbara
AU - Guagliardo, Paul
AU - Xia, Fang
AU - Pring, Allan
AU - Gervinskas, Gediminas
AU - Liu, Amelia
AU - Frierdich, Andrew
PY - 2022/8/15
Y1 - 2022/8/15
N2 - Reactions among minerals occur via solid-state diffusion or fluid-induced, interface-coupled dissolution-reprecipitation (ICDR). Both mechanisms can coexist under conditions where the rates of both processes are similar, depending mainly on the nature of the mineral, temperature, and fluid composition. To clarify the synergies between these reaction mechanisms, we investigated the replacement and recrystallization reactions of chalcopyrite in the presence of a 65Cu-enriched aqueous fluid. The replacement of chalcopyrite by secondary copper sulfides follows a paragenetic sequence, whereby chalcopyrite is initially replaced by covellite, and then by digenite, with some of the digenite replacing covellite in longer duration experiments. The replacement reactions proceed via ICDR along with solid-state diffusion of 65Cu from the fluid into product minerals, with both mechanisms occurring at similar rates. Over time, chalcopyrite is completely replaced, and the secondary copper sulfides attain isotopic equilibrium with the fluid. Depending on temperature, thermal history, and fluid-mineral ratio, the reaction products may preserve kinetic or equilibrium signatures. We have identified a new geochemical process of ‘porosity-aided recrystallization’, which may result in a re-equilibration or perturbation of mineral isotopic/trace element compositions due to exchanges between the mineral and fluid facilitated by extensive micro- to nano-scale porosity created by ICDR reactions. Porosity-aided recrystallization will affect any mineral-fluid system where mass transfers via solid-state diffusion and ICDR operate at similar rates, causing rapid (days-weeks) ‘resetting’ of the original isotopic abundances and trace element contents of the affected minerals. In copper sulfides, porosity-aided recrystallization occurs at lower temperatures (<300 °C) due to fast cation diffusion rates (log10D ≈ –13.6, 300 °C), but also takes place across other mineral systems where diffusion rates are faster at high temperatures. The open-system isotopic and trace element exchanges associated with porosity-aided recrystallization could lead to erroneous petrological interpretations, especially where these markers are used as a proxy for reconstructing geological evolution.
AB - Reactions among minerals occur via solid-state diffusion or fluid-induced, interface-coupled dissolution-reprecipitation (ICDR). Both mechanisms can coexist under conditions where the rates of both processes are similar, depending mainly on the nature of the mineral, temperature, and fluid composition. To clarify the synergies between these reaction mechanisms, we investigated the replacement and recrystallization reactions of chalcopyrite in the presence of a 65Cu-enriched aqueous fluid. The replacement of chalcopyrite by secondary copper sulfides follows a paragenetic sequence, whereby chalcopyrite is initially replaced by covellite, and then by digenite, with some of the digenite replacing covellite in longer duration experiments. The replacement reactions proceed via ICDR along with solid-state diffusion of 65Cu from the fluid into product minerals, with both mechanisms occurring at similar rates. Over time, chalcopyrite is completely replaced, and the secondary copper sulfides attain isotopic equilibrium with the fluid. Depending on temperature, thermal history, and fluid-mineral ratio, the reaction products may preserve kinetic or equilibrium signatures. We have identified a new geochemical process of ‘porosity-aided recrystallization’, which may result in a re-equilibration or perturbation of mineral isotopic/trace element compositions due to exchanges between the mineral and fluid facilitated by extensive micro- to nano-scale porosity created by ICDR reactions. Porosity-aided recrystallization will affect any mineral-fluid system where mass transfers via solid-state diffusion and ICDR operate at similar rates, causing rapid (days-weeks) ‘resetting’ of the original isotopic abundances and trace element contents of the affected minerals. In copper sulfides, porosity-aided recrystallization occurs at lower temperatures (<300 °C) due to fast cation diffusion rates (log10D ≈ –13.6, 300 °C), but also takes place across other mineral systems where diffusion rates are faster at high temperatures. The open-system isotopic and trace element exchanges associated with porosity-aided recrystallization could lead to erroneous petrological interpretations, especially where these markers are used as a proxy for reconstructing geological evolution.
KW - Chalcopyrite
KW - Copper isotopes
KW - Copper sulfides
KW - Diffusion
KW - Interface coupled dissolution reprecipitation
KW - Isotope tracer
KW - Porosity-aided recrystallization
UR - http://www.scopus.com/inward/record.url?scp=85132767494&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2022.06.005
DO - 10.1016/j.gca.2022.06.005
M3 - Article
AN - SCOPUS:85132767494
SN - 0016-7037
VL - 331
SP - 48
EP - 68
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -