Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland

Matti Poutiainen, Sami Partamies

    Research output: Contribution to journalArticleScientificpeer-review

    7 Citations (Scopus)

    Abstract

    The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.
    Original languageEnglish
    Pages (from-to)196-207
    Number of pages12
    JournalMineralium Deposita
    Volume38
    Issue number2
    DOIs
    Publication statusPublished - 2003
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    Gold deposits
    Finland
    greenstone belt
    fluid inclusion
    Archean
    gold
    deposits
    inclusions
    Fluids
    fluid
    fluids
    veins
    quartz vein
    Quartz
    Gold
    Bearings (structural)
    quartz
    texture
    sulfide
    sulfides

    Keywords

    • Finland
    • Rämepuro gold deposit
    • Greenstone belt
    • Fluid-inclusion petrography
    • Orogenic gold

    Cite this

    @article{503b0545b86f4fb9852db860ca3680bc,
    title = "Fluid evolution of the late Archaean R{\"a}mepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland",
    abstract = "The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The R{\"a}mepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt{\%} NaCl), and (2) H2O–CO2 (≤12 equiv. wt{\%} NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ({"}implosion textures{"}) related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.",
    keywords = "Finland, R{\"a}mepuro gold deposit, Greenstone belt, Fluid-inclusion petrography, Orogenic gold",
    author = "Matti Poutiainen and Sami Partamies",
    year = "2003",
    doi = "10.1007/s00126-002-0303-6",
    language = "English",
    volume = "38",
    pages = "196--207",
    journal = "Mineralium Deposita",
    issn = "0026-4598",
    publisher = "Springer",
    number = "2",

    }

    Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland. / Poutiainen, Matti; Partamies, Sami.

    In: Mineralium Deposita, Vol. 38, No. 2, 2003, p. 196-207.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Fluid evolution of the late Archaean Rämepuro gold deposit in the Ilomantsi greenstone belt in eastern Finland

    AU - Poutiainen, Matti

    AU - Partamies, Sami

    PY - 2003

    Y1 - 2003

    N2 - The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.

    AB - The late Archaean (ca. 2.7 Ga) Ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences. The Rämepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks. It consists of gold-bearing quartz–tourmaline–sulphide veins located mainly within an intensively altered and sheared zone about 20–30 m in width. Two types of fluid inclusions were distinguished in the quartz veins: (1) H2O–CH4 (≤9 equiv. wt% NaCl), and (2) H2O–CO2 (≤12 equiv. wt% NaCl). The two compositionally different fluid-inclusion types occur in separate veins. The compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of Na, S, Ca, Cl, and in lesser proportions of K and Fe. The residues of the type 2 fluid inclusions are dominated by Na, Ca, Cl and minor K. For the type 1 and type 2 fluid inclusions, microthermometric experiments indicate average homogenisation temperatures of 310–350 and 220–250 °C respectively. Both types of fluid inclusions contain 1–3 anisotropic solids (Ca/Mg carbonate?, nahcolite?, tourmaline?). Sulphide daughter minerals occur only in the type 1 fluid inclusions. This fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents. Some type 1 fluid inclusions display distinct morphological features ("implosion textures") related to post-trapping re-equilibration. The presence of the fluid-inclusion re-equilibration textures in some auriferous quartz veins and their absence in other gold-bearing quartz veins suggest an age difference between them. This conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins, indicating a change from reducing (CH4) to a more oxidising (CO2) fluid environment. The fluid-inclusion evidence suggests two separate gold mineralisation events, one related to late Archaean regional metamorphism, the other to Palaeoproterozoic thrusting and metamorphism.

    KW - Finland

    KW - Rämepuro gold deposit

    KW - Greenstone belt

    KW - Fluid-inclusion petrography

    KW - Orogenic gold

    U2 - 10.1007/s00126-002-0303-6

    DO - 10.1007/s00126-002-0303-6

    M3 - Article

    VL - 38

    SP - 196

    EP - 207

    JO - Mineralium Deposita

    JF - Mineralium Deposita

    SN - 0026-4598

    IS - 2

    ER -