Structural-metallogenic evolution of the Garrison gold camp of the Archean southern Abitibi greenstone belt, Ontario, Canada

Abstract

The southern Abitibi greenstone belt in Ontario and Quebec, Canada, stands out as the most prolific fragment of Neoarchean crust within the Superior province. Over 200 Moz gold endowment is attributed to numerous orogenic gold deposits that occur along two major crustal-scale east-trending deformation zones, the Porcupine-Destor and the Larder Lake-Cadillac deformation zones. Most of the current understanding of the geological history and the deposits of the belt come from the world-class and major gold deposits, which are concentrated in giant well-studied gold camps (e.g. the Timmins-Porcupine, Kirkland Lake, and Val-d’Or gold camps). The Garrison gold camp is a smaller camp along the Porcupine-Destor deformation zone ~100 km E of the Timmins-Porcupine gold camp and represents a new orogenic gold discovery. Its structural and metallogenic evolution was studied in detail, because of its unique location along a ~3 km NE-trending transtensional segment of the deformation zone provides an excellent opportunity to unravel processes that occur along NE-trending splays of the Porcupine-Destor deformation zone. These are generally underexplored but may have excellent potential for gold. The ~1.5 million ounces Garrison gold camp comprises four deposits hosted by different structures and rock types. The Buffonta deposit is hosted in mafic volcanic rocks and in brecciated granitic dikes within the Buffonta high-strain zone along the southwestern margin of the 2678 ± 2 Ma Garrison stock, ~3 km south of the Porcupine-Destor deformation zone. Ultramafic volcanic rocks to the north of the Garrison stock host the Porcupine-Destor deformation zone and a subparallel splay, the Munro deformation zone, which host gold-bearing syenite dikes of the 903 deposit and albitite dikes of the Jonpol deposit, respectively. The Garrcon deposit is located between these deformation zones in massive fine-grained sedimentary rocks hosting extensional gold-bearing quartz-carbonate veins. Detailed structural mapping, indicates that the three deposits north of the Garrison stock exist within a sinistral transtensional zone developed as a result of the emplacement of the ~2678 Ma Garrison stock. Sinistral transtension occurred at 2657 Ma, based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb analysis of hydrothermal monazites. This age may represent the age of sinistral shear along other segments of the Porcupine-Destor deformation zone. U-Pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS) data show that ~2683 Ma to ~2672 Ma igneous activity occurred within the camp and localized later strain, hydrothermal alteration and gold deposition. Timing of ore genesis was coeval with, or late during the 2657 Ma main generation of deformation. Re-Os molybdenite and U-Th-Pb electron microprobe monazite ages suggest that the main gold mineralization event occurred at ~2671 Ma, which is similar to the age of mineralizatoin in the Timmins-Porcupine gold camp. At the Garrison gold camp, this was followed by a separate phase of gold mineralization at 2610 ± 38 Ma, which is less well recognized elsewhere. Gold-bearing quartz veins from the Garrcon deposit were investigated in detail using optical microscopy, hot cathodoluminescence (CL) microscopy, electron probe micro-analysis (EPMA) and electron backscatter diffraction (EBSD), in order to assess their internal structure, and to evaluate the significance of CL textures in recrystallized hydrothermal quartz. Results indicate that in fully recrystallized hydrothermal quartz, which is typical in orogenic settings, CL textures and inclusion trails may preserve early crystal structures, even if completely overprinted by recrystallization.