T25 Structural and Stratigraphic Architecture of Gold Deposits and Mining Districts

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

TIMING OF NEOARCHEAN GOLD MINERALIZATION IN THE MALARTIC CAMP AND IMPLICATIONS FOR GOLD METALLOGENY ALONG THE LARDER LAKE – CADILLAC FAULT ZONE, SUPERIOR PROVINCE

Paper number: T25-3
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

The Malartic gold camp straddles the Larder Lake – Cadillac fault zone (LLCfz), which is located between supracrustal rocks of the Pontiac Group and the Abitibi greenstone belt in the Superior Province. Recent work on the Canadian Malartic deposit, the largest of the camp (26.2 Moz Au past-production, reserves and resources), has improved our understanding of ore-forming processes, timing of events and gold endowment in the area. The Canadian Malartic deposit comprises pyritic disseminated-stockwork replacement-style mineralized zones in greenschist facies 2685-2682 Ma turbidites of the Pontiac Group and subalkaline to alkaline porphyritic quartz monzodiorite and granodiorite south of the LLCfz. The intrusions, dated at ~2678 Ma, were coeval with fluvial-alluvial Timiskaming sedimentation, from <2679 to <2669 Ma, and are affected by regional deformation (D2) and associated Barrovian metamorphism at ~2665-2650 Ma. The deposit occurs along a bend in the LLCfz, and consists of two mineralized trends that are subparallel to the NW-striking S2 cleavage and the axial surface of F2 folds, and to the south-dipping Sladen fault. Gold-associated molybdenite and titanite were dated at ~2664 Ma (Re-Os) and ~2661 Ma (U-Pb), respectively. These ages are within error of the ~2660-2658 Ma age for peak amphibolite facies metamorphism in the Pontiac Group south of the mine. Smaller deposits (<1.7 Moz) in the Malartic camp include auriferous disseminated-stockwork zones, quartz ±carbonate-pyrite veins and breccias along fault zones in chemically and mechanically favorable rocks. Field relationships suggest that the formation of these small deposits was incremental and can be bracketed between the end of volcanism (~2698 Ma), and waning stages of D2 deformation (~2640 Ma). Nevertheless, the bulk of the gold in the camp is concentrated in the Canadian Malartic deposit, which formed along the LLCfz and related second order faults. It is compatible with north-south shortening and regional metamorphism, and is therefore attributed to the orogenic class of gold deposits. Hence, the specific timing, location, and brittle-ductile nature of the mineralized structures along the LLCfz have played a major role in concentration of the gold endowment. NSERC-CMIC Mineral Exploration Footprints Project Contribution Number #229.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359977

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