Looking for the Blake River in the Swayze : characterization of volcanic rocks in the Swayze Area, Abitibi Greenstone Belt, Ontario

Abstract

The Abitibi Greenstone Belt’s VMS mineralization has been largely constrained to several key chronostratigraphic volcanic assemblages. The most productive of these is the Blake River assemblage (2704 – 2695 Ma). Blake River volcanism in the Swayze area has long since been identified by other workers, however no economic VMS deposits have been identified. The study area for this project comprises two large felsic volcanic packages in the central Swayze area in the western Abitibi, previously mapped as part of the Blake River. A sub-economic VMS occurrence hosted in the southern package. This study found that these two packages of rock have distinctly different chemical characteristics from each other, indicating a genetic relationship between them is unlikely. The two groups show (i) differing levels of HREE depletion and LREE concentration, (ii) different zircon trace element fractionation trends, (iii) and are of different ages. Neither of these groups of samples display REE signatures of felsic volcanics that are typically associated with Archean VMS deposits (e.g., FII, FIIIa, and FIIIb rhyolites). Furthermore, zircon U-Pb CAID-TIMS indicate that these two volcanic packages are not Blake River aged, but in fact belong to the assemblages that temporally flank the Blake River: the Tisdale and Porcupine assemblages. This study exemplifies the powerful synergy of using whole rock geochemistry, zircon trace element chemistry, and zircon U-Pb dating to distinguish between nearby volcanic assemblages in the Abitibi Greenstone Belt.