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TitleTriangle zone thrust geometry as a natural focusing mechanism in orogenic gold systems
AuthorBleeker, WORCID logo; Honsberger, I WORCID logo
SourceAbstracts, GAC-MAC-IAH-CNC-CSPG 2022 Halifax; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 45, 2022 p. 75-76, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220655
PublisherGeological Association of Canada-Mineralogical Association of Canada
MeetingGAC-MAC-IAH-CNC-CSPG; Halifax; CA; May 15-18, 2022
Mediapaper; digital; on-line
File formatpdf
Subjectsgeochemistry; gold geochemistry; gold; orogenic regions; faults
ProgramTargeted Geoscience Initiative (TGI-6) Ore systems
Released2022 07 19
AbstractOrogenic gold mineral systems are typically associated with deep-reaching fault systems active at the peak of, or late during, a major orogenic shortening episode. Although often steepened or even overturned by later deformation, and overprinted by late strike-slip movements, the critical faults acted as thick-skinned thrusts during the onset of mineralization, thus promoting large-scale fluid advection. This can be shown by detailed structural and kinematic studies, but, where severely overprinted and confused by later strike-slip movements, it is also indicated by preferential preservation of upper crustal syn-orogenic clastic deposits in footwall panels or synclines on one side of the major faults. Gold endowment is also typically asymmetric across these faults, with higher gold endowment on the more completely preserved footwall side of these fault systems, with complementary parts having been removed by uplift and erosion on the hanging-wall side. Type examples of this setting are the highly endowed Timmins and Kirkland Lake gold camps of the Abitibi greenstone belt. Other camps with essentially identical setup, across geological time, are the Barberton greenstone belt (3.2 Ga), the Yellowknife belt (2.7-2.6 Ga), systems in the Trans-Hudson orogen (1.8 Ga), the central Grenville orogen (1.1 Ga), the gold belt of central Newfoundland (0.4 Ga), and even younger systems such as the Motherlode system (0.1 Ga) of California. We are engaged in an in-depth comparative study among some of these settings, specifically between the Archean Abitibi systems and the emerging gold belt of central Newfoundland. These two well-endowed settings, on either end of the temporal spectrum, show amazing similarities in overall structural and lithological architecture, and in terms of key processes and rates. Gold is spatially associated with narrow panels or belts of syn-orogenic clastic deposits, preserved in the structural footwalls of first-order thrust systems. Bimodal syn-orogenic magmatism occurred prior to thick-skinned thrusting, suggesting that the first-order thrust faults inverted earlier extensional fault systems. A potentially critical insight of our comparative study is the realization that the key thrust faults also wedged into the orogenic foreland, in a "triangle zone"-like geometry, forcing reactivation of older thrust systems of opposite dip. Importantly, this geometry sets up an upward-converging geometry of active faults where advecting fluids are naturally contained and focused, to create a narrow domain affected by cyclic fluid over-pressuring. We hypothesize that this triangle zone geometry is critical to forming some of the world's richest orogenic gold districts.
Summary(Plain Language Summary, not published)
This contribution presents a unifying model to explain the formation of orogenic gold deposits along fault zones.

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