Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Abstract

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

Zircon from Altered Monzonite Rocks Provides Insights into Magmatic and Mineralizing Processes at the Douay Au Project, Abitibi Greenstone Belt

“…This contribution aims to determine the timing of magmatic and hydrothermal events at the Douay project using the chemistry of zircon from an intrusive phase of the Douay intrusion. Zircon chemistry has been used to constrain the oxidation state of magmatic systems and their gold potential [12][13][14], while evaluating the maximum amount of Au that can be dissolved by a magma requires insights into the oxygen fugacity parameter (f O 2 ) and volatile (S, Cl) content of the melt [15]. Zircon, in a mineralized alkaline system, can be U-rich, metamict, and extensively altered, as is the case here.…”

Intrusion-Associated Gold Systems and Multistage Metallogenic Processes in the Neoarchean Abitibi Greenstone Belt

“…Magmatism in this latter period has a limited volume, and there are mostly two main magmatic stages to the evolution of late Archean (3.0-2.5 Ga) greenstone belts [9]. In the Abitibi belt, the oldest rocks of the synvolcanic period correspond to 2.79 Ga felsic volcanic units [10], a~2.80 Ga tonalite intrusion [11] in the northeastern corner of the belt, and 2.74 Ga intrusive rocks [12] in the southwestern corner. The syntectonic period extends from 2690 to 2665 Ma in the southern part of the belt (Figure 1) and from 2701 to 2690 Ma in the Chibougamau area and the northern reaches [4,13,14].…”

“…These are also oxidized magmas, as indicated by the lack of an Eu anomaly, the elevated Fe 2+ /Fe 3+ ratio, and the presence of magmatic magnetite, e.g., the East Sullivan intrusion [52]. Alkaline magmatism is also generally considered oxidized, as indicated by petrogenetic studies [60] and direct measurements of the fO 2 parameter using zircon chemistry [11]. Such magma exsolved oxidized fluids, as indicated by characteristic alteration minerals, such as sulfates, magnetite, and hematite [51,53].…”

“…The mineralizing systems of category A demonstrate that TTG and TTD suites, as well as sanukitoids and other magmas, can generate gold-bearing mineralizing fluids. Much remains to be done to quantify the amount of gold and base metals transported by Archean magmatic systems, including a more systematic evaluation of volatile content and of the fO2 parameter [11,60,90].…”

Editorial for Special Issue “Distribution of Major- and Trace-Elements in Igneous Minerals”

“…Madon et al [9] analyze the genetic links between hydrothermal gold deposits and syntectonic magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada. They study five plutons from the Chibougamau area (Anville, Saussure, Chevrillon, Opémisca, and Lac Line) that are representative of the chemical diversity of synvolcanic, with TTG affinity, and syntectonic, with sanukitoid and alkaline affinity, magmatism.…”