Le Geotop - Dr. Lyndsay Moore: Intracaldera facies... (10-03-2017)

Dr. Lyndsay Moore: Intracaldera facies... (10-03-2017)

 

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Dr. Lyndsay Moore, Earth & Planetary Science - McGill University

Intracaldera facies of the Rouyn-Pelletier caldera complex and associated mineralization; Abitibi greenstone belt, Québec, Canada

Vendredi 10 mars 2017 à 15h30 / Friday, March 10, 2017, 3:30 pm

Redpath Museum Auditorium, 859 Rue Sherbrooke O, Université McGill

Résumé / Abstract:

Sub-vertically-dipping strata provide an opportunity to observe the internal organization and architecture of ancient submarine volcanic complexes. The Abitibi greenstone belt, and more specifically the Blake River Group (BRG), hosts numerous cross-sectional views through such complexes. The Blake River Group is composed of a megacaldera complex (the Blake River megacaldera complex – BRMCC) with an initial shield phase known as the Misema caldera and two nested graben-type structures known as the New Senator and Noranda calderas. The southern sector of the New Senator caldera (SNSC) is of particular interest because it hosts the 54 Mt Horne Au-rich volcanogenic massive sulfide (VMS) deposit. Host volcanic units of the deposit, those within the Horne block, have poorly correlated across the Horne Creek fault with the neighbouring “Noranda camp” and their exact stratigraphic relationship was unclear.

A multifaceted approach is employed at numerous outcrop localities in the city of Rouyn-Noranda, Quebec and uses detailed facies mapping combined with geochemical and geochronological analysis to define the stratigraphy of the SNSC. With these techniques, the stratigraphy of the SNSC is shown to be dominated by subaqueous effusive mafic volcanic facies with local effusive felsic complexes. Incorporating structural data, synvolcacnic faults and dyke complexes, stratigraphy is divided into specific volcano-stratigraphic blocks herein identified as the Pelletier, Senator, Glenwood, Évain, Stadacona and Chadbourne blocks. These blocks, along with the previously identified Horne block, compose the Rouyn-Pelletier caldera complex.

Geochronological analysis shows that felsic volcanic facies of the Glenwood block are the same approximate age as felsic facies of the Horne block and neighbouring Quemont and Delbridge felsic complexes (~ 2702 Ma). These late-stage felsic complexes host significant base metal deposits with notable gold and silver mineralization. Ongoing research focuses on comparing volcanic and intrusive facies, alteration phases and styles of mineralization of each complex. In doing this, we aim to better define the relationship between Archean-aged submarine felsic volcanic complexes of the SNSC and their associated polymetallic deposits.