Chemical composition of rock-forming minerals in granitoids associated with Au-Bi-Cu, Cu-Mo, and Au-Ag mineralization at the Freegold Mountain, Yukon, Canada

Magmatic and hydrothermal fluid chemistry and petrogenetic implications

Thierry Bineli Betsi, David R. Lentz

    Research output: Contribution to journalArticle

    4 Citations (Scopus)

    Abstract

    The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au-Bi-Cu-As deposit, Revenue Au ± Cu and Stoddart Cu-Mo ± W mineral occurrences, and Laforma Au-Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4-91% Or), whereas plagioclase spans a wide range (4.4-70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu-Mo ± W, Laforma Au-Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au-Bi-Cu-As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10-13 and 10-11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8-7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6-2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520-780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu-Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au-Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.

    Original languageEnglish
    Pages (from-to)657-691
    Number of pages35
    JournalInternational Geology Review
    Volume55
    Issue number6
    DOIs
    Publication statusPublished - Apr 20 2013

    Fingerprint

    hydrothermal fluid
    biotite
    chemical composition
    mineralization
    mountain
    mineral
    rock
    amphibole
    magma
    plagioclase
    fluid
    feldspar
    magnetite
    edenite
    mineral alteration
    fluid composition
    skarn
    ilmenite
    fractional crystallization
    hornblende

    All Science Journal Classification (ASJC) codes

    • Geology

    Cite this

    @article{5253c27d589a4d998427aaf248bea033,
    title = "Chemical composition of rock-forming minerals in granitoids associated with Au-Bi-Cu, Cu-Mo, and Au-Ag mineralization at the Freegold Mountain, Yukon, Canada: Magmatic and hydrothermal fluid chemistry and petrogenetic implications",
    abstract = "The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au-Bi-Cu-As deposit, Revenue Au ± Cu and Stoddart Cu-Mo ± W mineral occurrences, and Laforma Au-Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4-91{\%} Or), whereas plagioclase spans a wide range (4.4-70.07{\%} An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu-Mo ± W, Laforma Au-Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au-Bi-Cu-As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10-13 and 10-11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8-7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6-2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520-780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu-Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au-Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.",
    author = "Betsi, {Thierry Bineli} and Lentz, {David R.}",
    year = "2013",
    month = "4",
    day = "20",
    doi = "10.1080/00206814.2012.731767",
    language = "English",
    volume = "55",
    pages = "657--691",
    journal = "International Geology Review",
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    TY - JOUR

    T1 - Chemical composition of rock-forming minerals in granitoids associated with Au-Bi-Cu, Cu-Mo, and Au-Ag mineralization at the Freegold Mountain, Yukon, Canada

    T2 - Magmatic and hydrothermal fluid chemistry and petrogenetic implications

    AU - Betsi, Thierry Bineli

    AU - Lentz, David R.

    PY - 2013/4/20

    Y1 - 2013/4/20

    N2 - The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au-Bi-Cu-As deposit, Revenue Au ± Cu and Stoddart Cu-Mo ± W mineral occurrences, and Laforma Au-Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4-91% Or), whereas plagioclase spans a wide range (4.4-70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu-Mo ± W, Laforma Au-Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au-Bi-Cu-As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10-13 and 10-11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8-7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6-2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520-780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu-Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au-Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.

    AB - The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au-Bi-Cu-As deposit, Revenue Au ± Cu and Stoddart Cu-Mo ± W mineral occurrences, and Laforma Au-Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4-91% Or), whereas plagioclase spans a wide range (4.4-70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu-Mo ± W, Laforma Au-Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au-Bi-Cu-As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10-13 and 10-11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8-7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6-2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520-780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu-Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au-Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.

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