T100 Fundamental Insights from Field and Laboratory Studies Related to the Genesis and Ore-Forming Processes Associated with Granitoid Generation and Evolution to Their Related Alteration and Mineralization

Tuesday, 27 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

IMPLICATIONS OF ZIRCON PETROCHRONOLOGY OF THE SOUTH MOUNTAIN BATHOLITH (NOVA SCOTIA) FOR SN-W METALLOGENY

Paper number: T100-8
Program: Technical Sessions
Time: 7:15 PM – 7:30 PM

Authors

Abstract

Various models have proposed contrasting metal sources for Sn-W mineralized settings, including deep metasomatized mantle to enriched layers of supracrustal sequences, the latter related to anatexis or contamination. Furthermore, Sn deposits in general form in clusters in areas with multi-stage protracted magmatism. Here we explore these aspects of Sn metallogeny using the South Mountain Batholith (SMB) of Nova Scotia (Canada). This multi-phase, 7300 km2 batholith hosts numerous polymetallic (Sn, W, Mo, Cu, Ta, Nb, Zn) occurrences, but at only one locality (East Kemptville, EK) did significant Sn(-Zn-Cu-Ag-In) mineralization form. To address the Sn metallogeny of the SMB, U-Pb dating was combined with the geochemical (REE) and isotopic (Lu-Hf, δ18O) signatures of zircon from across the SMB to constrain batholith petrochronology.

Zircon and monazite CA-TIMS dating of the two main phases of the SMB indicate a transition from less-evolved granodiorite (378.7 ± 1.2 to 375.4 ± 0.8 Ma) to more-evolved monzo- to leucogranite (375.4 ± 0.8 to 370.8 ± 0.8 Ma), reflecting ~10 Myr of magmatic activity. In situ SHRIMP, LA-MC-ICP-MS, and SIMS analyses of distinct CL-defined zircon domains reveal: 1) autocrysts have ages coincident with CA-TIMS results and δ18O between +7.3 and +9.1 ‰ (V-SMOW), but the EK deposit is hosted by a much younger pluton (365.3 ± 2.3 to 362.2 ± 3.4 Ma); 2) the δ18O for antecrystic domains (+7.1 and +8.9 ‰) are similar to autocrystic rims, but generally record crystallization ages 3–15 Ma older than the autocrysts; 3) abundant xenocrystic cores of varied ages (~420 Ma to 2.2 Ga) with distinct chemical and isotopic signatures; 4) the zircon REE patterns and derived fO2 values are similar across the SMB; and (5) the εHf signature in zircon autocrysts from the EK host pluton is higher (+1.74 to +4.38) than from the rest of the SMB (-2.99 to +1.68).

These new data indicate: 1) batholith construction occurred over a protracted interval spanning 15-20 Myr; 2) variation in SMB zircon δ18O and εHf values suggests a mantle source with elevated δ18O and εHf values, and 3) contamination of the SMB via assimilation of the host Meguma Supergroup clastic rocks is widespread. These data will be used to further explore the origin of Sn in the SMB and localization of significant Sn accumulation to one phase of the SMB.

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

doi: 10.1130/abs/2020AM-358208

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