GEOLOGIC OVERVIEW OF STURGEON LAKE GREENSTONE BELT GRANITOID PLUTONS, WESTERN WABIGOON SUBPROVINCE

Analyzing petrographic and geochemical data of granitoid plutons provides an important perspective of the metallogeny of greenstone belts when comparing between metal-endowed belts and metal-poor belts. Felsic plutons within Archean greenstone belts record geodynamic histories and constrain deformational events since they occur throughout the formational history of the belt. Granitoid plutons differ geochemically and petrographically due to the origin of the melt, melting mechanisms, crust-mantle interactions, and subsequent magmatic-hydrothermal activities. The granitoid plutons in the Sturgeon Lake greenstone belt are divided into three classes based on fabric development and influence on regional structure: pre-, syn-, and post-tectonic. This study contributes to petrographic and geochemical data of granitoid plutons and improves petrogenetic, tectonic, and metallogenic models for the belt. Preliminary observations indicate that there are limited petrographic differences between mineralized and non-mineralized plutons. Several Cu-Mo showings were observed in the field, which suggests magmatic-hydrothermal systems playing significant role in the region. Petrographic observations reveal that amphiboles, commonly hornblende, a primary mineral of the syn- and post-tectonic plutons, mostly lack post-crystallization metamorphic and/or hydrothermal alterations. Pre-tectonic plutons contain biotite ± hornblende, indicating biotization of mafic minerals as they are more affected by metamorphic and/or hydrothermal alterations. Additional differences between the different classes of plutons are highlighted by trace element geochemistry. Many pre-tectonic plutons were observed containing quartz ± pyrite veins that may be associated with the mineral deposition in the region. Geochemical analyses reveal similarities between non-mineralized and mineralized plutons. Most plutons contain relatively similar compositions of SiO₂ and REEs, with notable outliers in specific plutons. The Sturgeon Lake greenstone belt felsic plutons compare with plutonic suites which appear near the end of accretionary tectonic systems elsewhere in the Superior Province. Pre-tectonic plutons align with TTG compositions and syn- to post-tectonic plutons align with hybrid granite compositions.