Lafrance.pdf

Bruno Lafrance: Bruno Lafrance: Bruno BrunoLafrance: 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 ein v z t uar q d e

Thi ck q

uar t

z ve in

-fold Z row r a N

Clockwise dextral rotation of stretching lineation in Missi conglomerate

Chloritic lamina in thick quartz vein

Slickenline

σ3

in

ar v ein

E

ve l a on i s n xte

She

σ1

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

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

0

Feet

100

Diabase

Iron Formation

Sulphide-quartz vein

Metasedimentary Rocks

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 Upper Canada mine – Cross-section

Timiskaming conglomerate

ng Stretchi lineation

VI.

Fold hinge zones and limbs

Nova Scotia Geology Gold District Avalon Terrane Cobequid

Chedabucto Fault 100 km

Meguma Terrane

Halifax Triassic to Jurassic Late Carboniferous Early Carboniferous

Cambrian to Early Carboniferous Cambrian to Ordovician

Halifax Formation Goldenville Formation Precambrian

Precambrian to Carboniferous: undifferentiated intrusive rocks

Courtesy of D. Kontak and R. Horne

Meguma Vein Array Flexural folding: bedding-parallel Bedding Concordant 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 beddingconcordant veins

Courtesy of D. Kontak and R. Horne

en

ec

he lo

La m

ina te

Mo

v em

en t

dv

ho

nv ein s

e in

rizo

n

Courtesy of D. Kontak and R. Horne

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

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