T100 Fundamental Insights from Field and Laboratory Studies Related to the Genesis and Ore-Forming Processes Associated with Granitoid Generation and Evolution to Their Related Alteration and Mineralization

Tuesday, 27 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

MAGMATIC EVOLUTION OF A NEOARCHEAN GREENSTONE BELT: THE EXAMPLE OF THE CHIBOUGAMAU AREA, ABITIBI SUBPROVINCE

Paper number: T100-2
Program: Technical Sessions
Time: 5:45 PM – 6:00 PM

Authors

Abstract

In Archean granitoid-greenstone belts, the relationship between magmatism and mineralizing processes remains controversial. In the Neoarchean (>2.79 to ~2.65 Ga) Abitibi greenstone belt of the Superior craton, Canada, Cu-Au porphyry systems are associated with synvolcanic tonalite–trondhjemite–diorite (TTD) suites rather than the more common tonalite–trondhjemite–granodiorite (TTG) compositions. Syntectonic intrusions, in contrast, may have a petrogenetic connection to intrusion-related gold systems (IRGS). The importance of TTG versus TTD suites in the evolution of greenstone belts, the late onset of K-bearing magmatism and the importance of related mineralization has to date been poorly constrained. This contribution presents preliminary results that describe the chemistry and distribution of tonalite-dominated magmatism in the Abitibi greenstone belt, and provides new insights into physico-chemical parameters such as pressure, temperature, and oxygen fugacity (ƒO2). Comprehensive lithogeochemical data across the belt are used to evaluate the petrological evolution of TTG and TTD suites, revealing two coeval and differentiated trends of Neoarchean magmas: 1) a HREE-depleted tonalitic magma from high pressure melting of a hydrated basalt source (TTG suite); and 2) a hybrid HREE-undepleted magma that may be a mixture of mantle-derived and tonalitic melts (TTD suite). Synvolcanic, tonalite-dominated magmatism in the Abitibi greenstone belt comprises crustal melts as well as a significant proportion of mantle-derived magma (i.e., diorite) which may have been essential for establishing Cu-Au magmatic-hydrothermal mineralizing systems. In synvolcanic and syntectonic plutons, apatite and zircon chemistry preserve a marked increase in magmatic ƒO2 and provide preliminary insights into the S and Cl content of Neoarchean magmas. The increase in magmatic ƒO2 and K-content recorded in later, syntectonic plutonism may indicate a metasomatised mantle source that could be critical for IRGS metallogeny.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-349135

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