structural controls on lode gold deposits
DESCRIPTION
Structural controls on lode godTRANSCRIPT
Bruno Lafrance:Bruno Lafrance:Bruno Lafrance:Bruno Lafrance:
Structural controls on lode gold deposits
Bruno LafranceMineral Exploration Research Centre
Laurentian UniversityManitoba 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
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)
Multiple fault reactivation events
Flin Flon, Manitoba
Amisk basalt
Missi Conglomerate
Narrow Z-folded quartz vein
Thic
k qu
artz
vei
n
Chloritic laminae
Clockwise dextral rotation of stretching lineation in Missi conglomerate
Slickenline
Chloritic lamina in thick quartz vein
Extensional vein
Shea
r vei
n
σ1
σ3
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
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
Modified after Cox (2005)
I. Dilational and contractional jogs along faults/shear zones
I. Dilational and contractional jogs along faults/shear zones
II. Intersection of two syn-mineralization structures
Ore shoots are parallel to the intersection between the extensional veins and shear veins.
Robert and Poulsen (2001)
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
Sulphide-quartz vein
Diorite
Iron Formation
MetasedimentaryRocks0 100
Feet
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.
Upper Canada mine – Cross-section
V. Zones that plunge parallel to a stretching lineation
Timiskaming conglomerate
Stretching lineation
Nova Scotia GeologyNova Scotia Geology
Precambrian to Carboniferous:undifferentiated intrusive rocks
Precambrian
Cambrian to Ordovician
Halifax FormationGoldenville Formation
Cambrian to Early Carboniferous
Early Carboniferous
Triassic to Jurassic
Late Carboniferous
100 km
Avalon Terrane
Halifax
Chedabucto Fault
Meguma Terrane
Cobequid
Gold District
VI. Fold hinge zones and limbs
Courtesy of D. Kontak and R. Horne
Meguma Vein Array
Bedding Concordant veinsSaddle ReefsLaminated veinsEn echelon arraysMassive veins
Cross veinsAngular veins
Flexural folding: Flexural folding: beddingbedding--parallel parallel slipslip hinge dilationhinge dilation
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
Movement horizon
Laminated vein
en echelon veins
Courtesy of D. Kontak and R. Horne
Conclusions1. 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 contractionaljogs, intersection between syn-mineralization structures, competent host rocks intersected or hosted by syn-mineralization structures, lithologicalcontacts, fold limbs
(II) dilational zones: including dilational jogs and saddle reef
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