BrunoBruno Lafrance: Lafrance: BrunoBruno Lafrance: Lafrance: Structural controls on lode gold deposits
Bruno Lafrance Mineral Exploration Research Centre Laurentian University Manitoba Open House Gold Workshop 2008 Outline
1. Definition of lode gold deposits 2. Formation of fractures and veins 3. Evolution of fault zones 4. Structural controls on mineralization 5. Summary and Conclusions Outline 1. Definition of lode gold deposits 2. Formation of fractures and veins 3. Evolution of fault zones 4. Structural controls on mineralization 5. Summary and Conclusions
Outline
1. Definition of lode gold deposits 2. Formation of fractures and veins 3. Evolution of fault zones 4. Structural controls on mineralization 5. Summary and Conclusions
Outline
1. Definition of lode gold deposits 2. Formation of fractures and veins 3. Evolution of fault zones 4. Structural controls on mineralization 5. Summary and Conclusions
Multiple fault reactivation events
Magnitude Average Rupture Rupture Relative
slip length area frequency
M8 ∼4 m ∼100 km ∼104 km2 N yr-1
M7 ∼1 m ∼30 km ∼103 km2 ∼10 N yr-1
M6 ∼40 cm ∼10 km ∼102 km2 ∼102 N yr-1
M5 ∼10 cm ∼3 km ∼10 km2 ∼103 N yr-1
M4 ∼4 cm ∼1 km ∼1 km2 ∼104 N yr-1
M3 ∼1 cm ∼300 m ∼105 m2 ∼105 N yr-1
M2 ∼4 mm ∼100 m ∼104 m2 ∼106 N yr-1
M1 ∼1 mm ∼30 m ∼103 m2 ∼107 N yr-1
from van der Pluijm and Marshak (1997)
Flin Flon, Manitoba Amisk basalt
Missi Conglomerate
Chloritic laminae
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a N Clockwise dextral rotation of stretching lineation in Missi conglomerate Chloritic lamina in thick quartz vein
Slickenline
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1. Definition of lode gold deposits 2. Formation of fractures and veins 3. Evolution of fault zones 4. Structural controls on mineralization 5. Summary and Conclusions 4. Common structural controls on mineralization I. Dilational and contractional jogs along faults/shear zones II. Intersection of two syn-mineralization structures III. Intersection of faults/shear zones with highly competent and/or chemically reactive rocks IV. In faults/shear zones along lithological contacts between competent and less competent rocks V. Zones that plunge parallel to a stretching lineation VI. Fold hinge zones and limbs I. Dilational and contractional jogs along faults/shear zones
Modified after Cox (2005) I. Dilational and contractional jogs along faults/shear zones II. Intersection of two syn-mineralization structures
Robert and Poulsen (2001)
Ore shoots are parallel to the intersection between the extensional veins and shear veins. II. Intersection of two syn-mineralization structures II. Intersection of two syn-mineralization structures
III. Intersection of faults/shear zones with highly competent and/or chemically reactive rocks
Diabase Iron Formation Sulphide-quartz vein Metasedimentary 0 100 Rocks Feet Diorite Plan of the North Zone, 250-foot level, Hard Rock Mine
III. Intersection of faults/shear zones with highly competent and/or chemically reactive rocks Komis Mine, La Ronge Domain, Saskatchewan
IV. In faults/shear zones along lithological contacts between competent and less competent rocks
F4 Folded carbonate-rich gold-bearing domain parallel to S2
Field of view is 4mm. V. Zones that plunge parallel to a stretching lineation
Timiskaming conglomerate Upper Canada mine – Cross-section
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n VI. Fold hinge zones and limbs
NovaNova ScotiaScotia GeologyGeology
Gold District Avalon Terrane
Cobequid Chedabucto Fault
100 km
Meguma Terrane Halifax Triassic to Jurassic Cambrian to Early Carboniferous Cambrian to Ordovician Late Carboniferous Halifax Formation Goldenville Formation Early Carboniferous Precambrian
Precambrian to Carboniferous: undifferentiated intrusive rocks Courtesy of D. Kontak and R. Horne Meguma Vein Array
BeddingFlexural folding: Concordant bedding-parallel veins slip hinge dilation Saddle Reefs Laminated veins En echelon arrays Massive veins Cross veins Angular veins
Courtesy of D. Kontak and R. Horne Saddle Reefs … represent hinge dilation …product of flexural folding … late in fold development
Ovens Dufferin
Courtesy of D. Kontak and R. Horne En echelon bedding- concordant veins
Courtesy of D. Kontak and R. Horne ns ei v on el h n ec in zo Courtesy of D. Kontak and R. Horne e ri en v o d h te t a n n e i m m a ve L Mo Conclusions 1. The siting of lode gold deposits is controlled by the geometry, orientation, and nature of the host structures and host rocks. 2. Lode gold deposits typically form along host structures, such as faults, which acted as channels for the flow of large volumes of hydrothermal fluids. 3. The deposits occurs in zones of high permeability such as: (I) Fractured damage zones: including contractional jogs, intersection between syn-mineralization structures, competent host rocks intersected or hosted by syn-mineralization structures, lithological contacts, fold limbs (II) dilational zones: including dilational jogs and saddle reef Click to return to menu