| الوصف: |
The lowermost, discontinuous units of the impact-generated Sudbury Igneous Complex (SIC), Sublayer, Footwall Breccia (FWBX), and Inclusion Quartz Diorite (IQD), are distinguished from overlying Main Mass norite rocks by the presence of abundant inclusions and Ni-Cu-PGE (PGE – platinum group element) mineralization. The majority of the felsic-mafic inclusions appear to be derived from exposed country rocks, but volumetrically important mafic-ultramafic inclusions have only rare equivalents in the surrounding country rocks and appear to be preferentially associated with sulfide mineralization. Establishing the petrogenesis of the mafic-ultramafic inclusions and the nature of their association with the Ni-Cu-PGE mineralization are therefore critical to understand the evolution of the impact melt, genesis of Sublayer, FWBX, and IQD, and the formation of one of the world’s largest accumulations of Ni-Cu-PGE mineralization. Petrographic, mineralogical, geochemical, and Sm-Nd and Re-Os isotopic data indicate three origins for the olivine-bearing mafic-ultramafic inclusions: (1) Anteliths, comprising olivine melanorites and olivine melagabbronorites in the Whistle and Levack embayments on the North Range, which are characterized by igneous textures, Zr/Y, Zr/Nb, Nb/U, and Zr/Hf ratios similar to igneous-textured Sublayer matrix (ITSM), unradiogenic εNd1850 Ma values (-8 to -5), and slightly unradiogenic to radiogenic γOs1850 Ma values (-8 to +94). They likely crystallized from a local mixture of SIC impact melt and a more mafic melt derived by melting of the widespread Huronian volcanic and subvolcanic units in the region. (2) Local xenoliths, comprising wehrlites and olivine clinopyroxenites in the Levack embayment and olivine melanorites in the Foy Offset on the North Range, which are characterized by shock mosaic and recrystallized textures, and trace element patterns (e.g., negative Th-U, Nb-Ta-(Ti), Sr, and Zr-Hf anomalies) similar to and Nb/U ratios overlapping with a layered mafic-ultramafic intrusion in the ... |
