Structural controls on an orogenic gold system: The world-class Siguiri gold district, Siguiri Basin, Guinea, West Africa

    Research output: Contribution to journalArticle

    9 Citations (Scopus)

    Abstract

    Orebodies in the Siguiri district, a world-class Paleoproterozoic orogenic gold camp located in the Birimian of northeastern Guinea, are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins. Although no large regional fault system was recognized, observations from five representative deposits of the Siguiri district (Sanu Tinti, Bidini, Kami, Kosise, and Sintroko PB1) show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains. Two shale-dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium- to coarse-grained graywacke and this domain hosts the bulk of the gold endowment of the district. The three domains exhibit similar structural elements that can be described within a four-stage deformation scheme. The first deformation event (D1S) is poorly constrained and interpreted to have been an N-S compressional event. It included development of minor folds with W- to WNW-gently plunging fold axes without a clear axial planar cleavage. The main and second deformation event (D2S) is interpreted to have been associated with E-W to ENE-WSW-directed compression. The D2S event was responsible for forming the dominant N-trending structural grain of the district and creating interference patterns between F1S and F2S folds. The third event (D3S) developed progressively from D2S compression into an early-D3S E-W- to ENEWSW-directed transpression and a late-D3S NNW-SSE-directed-transtension responsible for most of the gold mineralization in the Siguiri district. The fourth and last event (D4S) was an NW-SE-oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping NNE-SSW ductile cleavage. Late-D3S gold-bearing mineral occurrences formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D3S. Mineralization is expressed as mineralized shear zones or subvertical damage zones, characterized by a 10- to 15-m-wide zone of dense quartz-carbonate-sulfide veining, or disseminated gold-bearing sulfides. The mineralized veins consistently strike ENE-WSW, are steeply dipping, and commonly have a conjugate geometry at the mesoscale. Finite strain analysis of deformation, including analysis of folds, faults, and conjugate mineralized vein sets, is consistent with a stress switch from a compressional (D2S) to transpressional deformation (termed early-D3S). Results of paleostress analysis on conjugate mineralized vein sets that formed late during D3S indicate that the stress field ranged from extensional to strike-slip, sometimes within the same vein locality. The late-D3S deformation is interpreted to have been a transtensional event. The first change in the orientation of the principal stress axes is related to a switch from a far field-dominated to a body force-dominated stress field reducing the deviatoric component on the stress tensor. The second change in the orientation of the principal stress axes, from early-D3S transpression to late-D3S transtension, suggests that ó1 and ó2 were similar in magnitude, which facilitated localized stress switches. In the Siguiri district, the early-D3S and late-D3S stress switches, which occurred at both a local and regional scale, enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world-class gold system.

    Original languageEnglish
    Pages (from-to)73-98
    Number of pages26
    JournalEconomic Geology
    Volume112
    Issue number1
    DOIs
    Publication statusPublished - 1 Jan 2017

    Fingerprint

    Guinea
    structural control
    Gold
    gold
    veins
    basin
    fold
    transtension
    Bearings (structural)
    switches
    transpression
    Switches
    stress field
    cleavage
    shear zone
    Sulfides
    dipping
    compression
    sulfide
    Birrimian

    Cite this

    @article{b29a671a9ce3488180c0895cd9c53823,
    title = "Structural controls on an orogenic gold system: The world-class Siguiri gold district, Siguiri Basin, Guinea, West Africa",
    abstract = "Orebodies in the Siguiri district, a world-class Paleoproterozoic orogenic gold camp located in the Birimian of northeastern Guinea, are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins. Although no large regional fault system was recognized, observations from five representative deposits of the Siguiri district (Sanu Tinti, Bidini, Kami, Kosise, and Sintroko PB1) show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains. Two shale-dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium- to coarse-grained graywacke and this domain hosts the bulk of the gold endowment of the district. The three domains exhibit similar structural elements that can be described within a four-stage deformation scheme. The first deformation event (D1S) is poorly constrained and interpreted to have been an N-S compressional event. It included development of minor folds with W- to WNW-gently plunging fold axes without a clear axial planar cleavage. The main and second deformation event (D2S) is interpreted to have been associated with E-W to ENE-WSW-directed compression. The D2S event was responsible for forming the dominant N-trending structural grain of the district and creating interference patterns between F1S and F2S folds. The third event (D3S) developed progressively from D2S compression into an early-D3S E-W- to ENEWSW-directed transpression and a late-D3S NNW-SSE-directed-transtension responsible for most of the gold mineralization in the Siguiri district. The fourth and last event (D4S) was an NW-SE-oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping NNE-SSW ductile cleavage. Late-D3S gold-bearing mineral occurrences formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D3S. Mineralization is expressed as mineralized shear zones or subvertical damage zones, characterized by a 10- to 15-m-wide zone of dense quartz-carbonate-sulfide veining, or disseminated gold-bearing sulfides. The mineralized veins consistently strike ENE-WSW, are steeply dipping, and commonly have a conjugate geometry at the mesoscale. Finite strain analysis of deformation, including analysis of folds, faults, and conjugate mineralized vein sets, is consistent with a stress switch from a compressional (D2S) to transpressional deformation (termed early-D3S). Results of paleostress analysis on conjugate mineralized vein sets that formed late during D3S indicate that the stress field ranged from extensional to strike-slip, sometimes within the same vein locality. The late-D3S deformation is interpreted to have been a transtensional event. The first change in the orientation of the principal stress axes is related to a switch from a far field-dominated to a body force-dominated stress field reducing the deviatoric component on the stress tensor. The second change in the orientation of the principal stress axes, from early-D3S transpression to late-D3S transtension, suggests that {\'o}1 and {\'o}2 were similar in magnitude, which facilitated localized stress switches. In the Siguiri district, the early-D3S and late-D3S stress switches, which occurred at both a local and regional scale, enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world-class gold system.",
    author = "Erwann Lebrun and John Miller and Nicolas Th{\'e}baud and Stanislav Ulrich and McCuaig, {T. Campbell}",
    year = "2017",
    month = "1",
    day = "1",
    doi = "10.2113/econgeo.112.1.73",
    language = "English",
    volume = "112",
    pages = "73--98",
    journal = "Economic Geology",
    issn = "0361-0128",
    publisher = "Society of Economic Geologists",
    number = "1",

    }

    TY - JOUR

    T1 - Structural controls on an orogenic gold system

    T2 - The world-class Siguiri gold district, Siguiri Basin, Guinea, West Africa

    AU - Lebrun, Erwann

    AU - Miller, John

    AU - Thébaud, Nicolas

    AU - Ulrich, Stanislav

    AU - McCuaig, T. Campbell

    PY - 2017/1/1

    Y1 - 2017/1/1

    N2 - Orebodies in the Siguiri district, a world-class Paleoproterozoic orogenic gold camp located in the Birimian of northeastern Guinea, are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins. Although no large regional fault system was recognized, observations from five representative deposits of the Siguiri district (Sanu Tinti, Bidini, Kami, Kosise, and Sintroko PB1) show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains. Two shale-dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium- to coarse-grained graywacke and this domain hosts the bulk of the gold endowment of the district. The three domains exhibit similar structural elements that can be described within a four-stage deformation scheme. The first deformation event (D1S) is poorly constrained and interpreted to have been an N-S compressional event. It included development of minor folds with W- to WNW-gently plunging fold axes without a clear axial planar cleavage. The main and second deformation event (D2S) is interpreted to have been associated with E-W to ENE-WSW-directed compression. The D2S event was responsible for forming the dominant N-trending structural grain of the district and creating interference patterns between F1S and F2S folds. The third event (D3S) developed progressively from D2S compression into an early-D3S E-W- to ENEWSW-directed transpression and a late-D3S NNW-SSE-directed-transtension responsible for most of the gold mineralization in the Siguiri district. The fourth and last event (D4S) was an NW-SE-oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping NNE-SSW ductile cleavage. Late-D3S gold-bearing mineral occurrences formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D3S. Mineralization is expressed as mineralized shear zones or subvertical damage zones, characterized by a 10- to 15-m-wide zone of dense quartz-carbonate-sulfide veining, or disseminated gold-bearing sulfides. The mineralized veins consistently strike ENE-WSW, are steeply dipping, and commonly have a conjugate geometry at the mesoscale. Finite strain analysis of deformation, including analysis of folds, faults, and conjugate mineralized vein sets, is consistent with a stress switch from a compressional (D2S) to transpressional deformation (termed early-D3S). Results of paleostress analysis on conjugate mineralized vein sets that formed late during D3S indicate that the stress field ranged from extensional to strike-slip, sometimes within the same vein locality. The late-D3S deformation is interpreted to have been a transtensional event. The first change in the orientation of the principal stress axes is related to a switch from a far field-dominated to a body force-dominated stress field reducing the deviatoric component on the stress tensor. The second change in the orientation of the principal stress axes, from early-D3S transpression to late-D3S transtension, suggests that ó1 and ó2 were similar in magnitude, which facilitated localized stress switches. In the Siguiri district, the early-D3S and late-D3S stress switches, which occurred at both a local and regional scale, enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world-class gold system.

    AB - Orebodies in the Siguiri district, a world-class Paleoproterozoic orogenic gold camp located in the Birimian of northeastern Guinea, are typically represented by cryptic subvertical damage zones that host a high density of mineralized veins. Although no large regional fault system was recognized, observations from five representative deposits of the Siguiri district (Sanu Tinti, Bidini, Kami, Kosise, and Sintroko PB1) show that these orebodies are locally controlled by incipient structures and spread across three distinct structural and lithostratigraphic domains. Two shale-dominated peripheral domains adjoin a central domain whose lithostratigraphy is dominated by medium- to coarse-grained graywacke and this domain hosts the bulk of the gold endowment of the district. The three domains exhibit similar structural elements that can be described within a four-stage deformation scheme. The first deformation event (D1S) is poorly constrained and interpreted to have been an N-S compressional event. It included development of minor folds with W- to WNW-gently plunging fold axes without a clear axial planar cleavage. The main and second deformation event (D2S) is interpreted to have been associated with E-W to ENE-WSW-directed compression. The D2S event was responsible for forming the dominant N-trending structural grain of the district and creating interference patterns between F1S and F2S folds. The third event (D3S) developed progressively from D2S compression into an early-D3S E-W- to ENEWSW-directed transpression and a late-D3S NNW-SSE-directed-transtension responsible for most of the gold mineralization in the Siguiri district. The fourth and last event (D4S) was an NW-SE-oriented compressional event responsible for the localized overprinting of veining by a steep to shallowly dipping NNE-SSW ductile cleavage. Late-D3S gold-bearing mineral occurrences formed along subvertical N-S reverse faults, NE-trending dextral shear zones, WNW-trending sinistral faults, and E-trending normal relay faults developed or reactivated early-D3S. Mineralization is expressed as mineralized shear zones or subvertical damage zones, characterized by a 10- to 15-m-wide zone of dense quartz-carbonate-sulfide veining, or disseminated gold-bearing sulfides. The mineralized veins consistently strike ENE-WSW, are steeply dipping, and commonly have a conjugate geometry at the mesoscale. Finite strain analysis of deformation, including analysis of folds, faults, and conjugate mineralized vein sets, is consistent with a stress switch from a compressional (D2S) to transpressional deformation (termed early-D3S). Results of paleostress analysis on conjugate mineralized vein sets that formed late during D3S indicate that the stress field ranged from extensional to strike-slip, sometimes within the same vein locality. The late-D3S deformation is interpreted to have been a transtensional event. The first change in the orientation of the principal stress axes is related to a switch from a far field-dominated to a body force-dominated stress field reducing the deviatoric component on the stress tensor. The second change in the orientation of the principal stress axes, from early-D3S transpression to late-D3S transtension, suggests that ó1 and ó2 were similar in magnitude, which facilitated localized stress switches. In the Siguiri district, the early-D3S and late-D3S stress switches, which occurred at both a local and regional scale, enhanced the fracture permeability and were critical for the establishment of active fluid pathways leading to the formation of a world-class gold system.

    UR - http://www.scopus.com/inward/record.url?scp=85015995543&partnerID=8YFLogxK

    U2 - 10.2113/econgeo.112.1.73

    DO - 10.2113/econgeo.112.1.73

    M3 - Article

    VL - 112

    SP - 73

    EP - 98

    JO - Economic Geology

    JF - Economic Geology

    SN - 0361-0128

    IS - 1

    ER -