Structural Evolution of Auriferous Veins at the Endeavour 42 Gold Deposit, Cowal Mining District, NSW, Australia

A. D. Henry; P. McInnes; R. M. Tosdal

doi:10.2113/econgeo.109.4.1051

Low-temperature thermal history of the Gilmore Dome area, Fairbanks Mining District, Alaska

Canadian Journal of Earth Sciences ◽

10.1139/e93-062 ◽

1993 ◽

Vol 30 (4) ◽

pp. 764-768 ◽

Cited By ~ 6

Author(s):

John M. Murphy ◽

Arne Bakke

Keyword(s):

Gold Deposit ◽

Fission Track ◽

Hydrothermal Fluids ◽

Mining District ◽

Cooling Path ◽

Alteration Assemblage ◽

Zircon Fission Track ◽

History Of ◽

Maximum Temperatures ◽

Fission Track Ages

Eight apatite and two zircon fission-track ages provide evidence of complex Tertiary thermal overprinting by hydrothermal fluids in the Gilmore Dome area. Five ages on apatite from the Fort Knox gold deposit average 41 Ma, one from the Stepovich prospect is 80 Ma, and two from Pedro Dome average 67 Ma. Elevations of these samples overlap but their ages do not, indicating that each area experienced a different thermal history.Ages of apatite from the Fort Knox gold deposit decrease with elevation from 42 to 36 Ma but have data trends indicative of complex cooling. Two ~51 Ma ages on zircon indicate that maximum temperatures approached or exceeded ~180 °C. An alteration assemblage of chalcedony + zeolite + calcite + clay in the deposit resulted from deposition by a paleo-hydrothermal system. The data suggest that the system followed a complex cooling path from > 180 to < 110 °C between 51 and 36 Ma, and that final cooling to below 60 °C occurred after ~25 Ma.The 80 Ma age from Stepovich prospect either resulted from cooling after intrusion of the underlying pluton (~90 Ma) or records postintrusion thermal overprinting sometime after ~50 Ma. The 67 Ma samples from Pedro Dome may also have experienced partial age reduction during later heating. The differences in the data from the different areas and the presence of a late alteration assemblage at Fort Knox suggest that the fluids responsible for heating were largely confined to the highly fractured and porous Fort Knox pluton.

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Structural evolution of the Hemlo greenstone belt in the vicinity of the world-class Hemlo gold deposit

Canadian Journal of Earth Sciences ◽

10.1139/e03-004 ◽

2003 ◽

Vol 40 (3) ◽

pp. 395-430 ◽

Cited By ~ 8

Author(s):

T L Muir

Keyword(s):

Gold Deposit ◽

Greenstone Belt ◽

Structural Evolution ◽

Small Scale ◽

Structural Elements ◽

Shear Sense ◽

History Of ◽

Brittle Fractures ◽

World Class ◽

Dextral Shear

A complex history of volcano-sedimentary deposition, polyphase strain, multiple intrusive events, and various stages of porphyroblastesis is indicated for the Hemlo gold deposit area within the Hemlo greenstone belt. Structural elements can be assigned to at least six stages of development (D1D6). D1 generated small-scale folds and low-angle faults (thrusts?) with no planar fabric, except within strain aureoles around the earliest intrusions. D2 was a progressive event resulting from northeast-directed compression, which generated regional, predominantly S-shaped folds (early D2); penetrative planar and linear fabrics, overturned stratigraphy, and formation of an inflection in the strike of the greenstone belt (mid-D2); and development of high-strain zones with dominant sinistral and local dextral shear sense (late D2). D3 was a distinctly separate progressive event resulting from northwest-directed transpression, which generated variably penetrative east- to northeast-striking foliation (S3), ductile dextral shear fabrics, and small-scale Z-shaped folds (early D3), followed by brittleductile to brittle development of cataclasite and pseudotachylite in layer-parallel zones (late D3). D4 resulted in contractional kinks and brittle fractures, locally in conjugate sets. D5 and D6 are represented by brittle to brittleductile faults, which overprint Paleoproterozoic and Mesoproterozoic dikes, respectively. Four granitoid magmatic events span the interval 27202677 Ma, with emplacement mainly during D2, between ca. 2690 and ca. 2684 Ma. A protracted period of regional medium-grade metamorphism likely spanned the D2D3 stages. The Hemlo gold deposit was emplaced during mid-D2 and was largely controlled by D2 structural elements and competency contrast between rock units.

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