Petrogenesis and associated mineralization of Acadian related granitoids in New Brunswick

Abstract

The Acadian-related granitoids of New Brunswick are herein divided into geochemically defined groups to ascertain whether magmatic process related trends differentiate barren from mineralized granitoids. The Juniper Barren and Lost Lake granites have some similar characteristics (i.e. lowest SiO2, highest transition element contents, high-K calc-alkaline, metaluminous), but do not constitute a defined geochemical group. They have the characteristics of unfractionated (oxidized) I-type granites, and neither are associated with significant mineralization. Group NB-1 granites are metaluminous to peraluminous, high-K calc-alkaline, light rare-earth element (LREE) enriched with small negative Eu anomalies, and high Nb/Ta and Zr/Hf ratios. Group NB-1 intrusions are interpreted to be unfractionated reduced I-type granite formed via partial melting in an arc system and subsequently contaminated by reducing crustal rocks. The reduced component is critical for the formation of tungsten mineralization. Group NB-2 granites are high-K calc-alkaline, metaluminous to peraluminous I-type granite characterized by K2O contents greater than Na2O, and are LREE enriched with pronounced negative Eu anomalies. Group NB-2 granites are unfractionated to weakly fractionated I-type granite generated from different degrees of partial melting of mixed mantle - older crustal protolith with an igneous quartzo-feldspathic composition. Group NB-3 granites include the most evolved intrusions examined during this study. They are characterized by the highest SiO2 content, Gottini index and K/Rb ratio, and have the lowest Zr/Hf, Nb/Ta, La/Sm and Eu/Eu* ratios. They are considered highly evolved I-type granite formed via crustal thinning related to crustal delamination following the juxtaposition of crustal terranes during the Acadian Orogeny.