The Babbitt Copper-Nickel Deposit: Part C: Igneous Geology, Footwall Lithologies, and Cross-Sections

Abstract

Twenty-five cross-sections are presented that display the detailed igneous geology for several areas of the Babbitt Cu-Ni deposit. Shown in the cross-sections are the stratigraphic relationships of at least seven major igneous units - Units I through VII of the Partridge River Troctolite Series (PRTS). However, not all seven units are equally present throughout the deposit due to "pinch-out" relationships and lateral gradational rock type changes. In addition to these seven units, three new units are briefly discussed and include the: 1) Bathtub Layered Series (BTLS) of Hauck (1993); 2) Basal Ultramafic Unit (BU Unit) of Severson (1994); and 3) Upper Layered Series (ULS). Small plug-like bodies of Oxide-bearing Ultramafic Intrusions (OUIs) are also locally present within the Babbitt deposit. They intrude the rocks of the PRTS and are often positioned adjacent to, or within, fault zones. Rock types found within the footwall rocks beneath the Complex at the Babbitt deposit are also described. Metamorphic textural variations are described for select units within the Virginia Formation (RXTAL, DISRUPTED, and BDD PO units). These textural variations indicate that the effects of structural deformation, recrystallization, and partial melting are more pronounced than previously thought. The exact origin of the textures is unknown, but is believed to be associated with early stages of Duluth Complex emplacement. Also present within the basal portion of the Virginia Formation are early intrusive rocks that predate emplacement of the Partridge River intrusion (PRI). These early intrusive rocks are referred to as the Virg Sill and "Massive Gray" Unit ("MG" Unit); both are interrelated and are submembers of a single composite sill. At least three major structural features are present in the footwall rocks and include the: Local Boy Anticline, Bathtub Syncline, and Grano Fault (for a more detailed discussion see Part B - Severson et al., 1994). During intrusion of the Partridge River intrusion, specifically during emplacement of the lowest unit (Unit I), the Local Boy Anticline and Bathtub Syncline were important factors controlling how the base of the Complex was formed (see Part B). In addition, these same structures also appear to have been repeatedly reactivated during continued emplacement of the Complex and affected the distribution of specific units within overlying Unit III and the BTLS. Also, the distribution of the "MG" and Virg Sill units are affected by these same two structures. These relationships suggest that reactivation of the structures created "void spaces" into which specific PRTS units were emplaced. The exact details and of this complicated emplacement history have yet to be unraveled.