Vancouver Campus

Late Cenozoic post-subduction tectonic, magmatic and metallogenic evolution of the Anatolide-Tauride Orogenic Belt, Turkey

Abstract: The termination of the northward subduction of the Southern Neotethyan oceanic slab beneath the Anatolide-Tauride Block in Turkey led to the onset of the Arabia-Eurasia continental collision in the Oligocene. The subducting Southern Neotethyan slab was affected by post-subduction segmentation manifested by slab break-off (central-eastern Anatolia) and tearing (western Anatolia) during the late Cenozoic. Many igneous complexes formed in the late Cenozoic and some of them host gold-rich porphyry and epithermal prospects and deposits.
New temporal (U-Pb, 40Ar/39Ar and Re-Os dates), spatial (field observations and GIS) and geochemical data (elemental and Sr-Nd-Pb isotopic analyses) provide robust constraints on the genetic relationship between late Cenozoic slab segmentation tectonic events, Anatolian magmatism and associated gold mineralization.
The newly-defined Eastern Anatolian Magmatic Belt formed in response to the slab break-off initiation at ca. 25 Ma, window opening, westward break-off propagation to central Anatolia and induced asthenospheric flow. The slab break-off-related igneous units were subsequently covered by widespread volcanic products in eastern Anatolia (12 Ma-Present) that resulted from the long-lived asthenospheric heating, destabilization of the thickened Anatolian lithosphere root and its partial removal by convective dripping. Magmatic sources include the shallow melting of the previously-metasomatized Anatolian subcontinental lithospheric mantle and asthenosphere by decompression due to impingement of the Arabian
and African sub-slab asthenospheric mantles.
Late Cenozoic Anatolian magmatism produced porphyry and epithermal prospects and
deposits that cluster in nine isolated mineral districts controlled by graben, transtensional corridors and pull-apart basins. The bulk of gold mineralization (33 Moz Au) peaked at the beginning of the slab break-off event at 25 Ma in central and eastern Anatolia, and slab tear at 15 Ma in western Anatolia.
The late Cenozoic trench-parallel and -perpendicular migrations of slab rupture and
window opening in Anatolia 1) allowed toroidal and poloidal flow of asthenosphere beneath
Anatolia, 2) caused the migration of melting source and associated igneous complexes and mineral deposits in the overriding crust, 3) destabilized the Anatolian lithospheric mantle, which reduced the amount of available volatiles and metals, and therefore 4) increased the production of barren, drier and mantle-dominant volcanism through time that partially covers fertile igneous units.

The geology and genesis of the Coffee gold deposit in west-central Yukon, Canada : implications for the structural, magmatic, and metallogenic evolution of the Dawson Range, and gold deposit models

The Coffee gold deposit, located in the Dawson Range, west-central Yukon, Canada, is an example of structurally-controlled, gold-only mineralization with a global resource of ~4 Moz gold. Establishing the controls on ore distribution enhances exploration potential, and provides implications for the tectonic and metallogenic evolution of the northern Cordillera, and global gold deposit models. The controls on ore distribution were identified by drill core logging, field mapping, petrography, and analytical techniques that included geochemistry, shortwave infrared spectroscopy, and geochronology. The results from these analyses allowed the geological and structural framework, and a hydrothermal model for ore formation to be established. Furthermore, a genetic model for hydrothermal events and exhumation within the Dawson Range was developed. Coffee is hosted in metamorphic rocks of the Yukon-Tanana terrane, and mid-Cretaceous plutonic rocks. Metamorphic rocks include psammitic to semi-pelitic schist and K-feldspar augen-bearing orthogneiss that were metamorphosed to lower amphibolite in the Permian. Plutonic rocks include biotite granite of the ca. 100 Ma Coffee Creek pluton, and coeval intermediate dykes. The east-trending dextral strike-slip Coffee Creek fault exerts an important control on mineralization, which is disseminated in the wall rock of high order faults and fractures, and ~1m wide breccia corridors. Mineralization comprises auriferous sulphides that are associated with an alteration assemblage of quartz-muscovite-illite-kaolinite-carbonate, which sulphidize host rock muscovite and biotite. Age determinations from hydrothermal white mica constrains mineralization to ca. 97 Ma, and the coexistence of alteration and ore minerals constrains the character of the hydrothermal fluid to ~250°C and pH ~5. Isotope data provides evidence for decoupled metal sources, and low temperature thermochronology constrains the depth of mineralization to ~5km. Coffee occurs in close spatial and temporal proximity to orogenic gold mineralization. This spatial association, the ore fluid characteristics, and the mid-Cretaceous tectonic regime argues for ore fluids sourced from metamorphic devolatilization of likely siliciclastic rocks at depth. Coffee is interpreted as an epizonal orogenic gold deposit, the result of a regionally significant gold mineralizing event. This interpretation has implications for the metallogeny and exploration of orogenic gold mineralization in the Dawson Range and northern Cordillera, as well as globally.