Geochemical evidence for multiple magma injections in the formation of the Spruce Road Cu-Ni deposit, Duluth Complex, Minnesota
- Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences
The Spruce Road Cu-Ni deposit is located in the northeast portion of the Duluth Complex, and consists of disseminated sulfide mineralization within gabbroic to troctolitic rock types. Mineralization occurs along basal contacts with footwall rocks of the Giants Range Massif, and is in general similar to that found in other basal zone deposits located to the southwest. Sulfide mineral assemblages are composed principally of chalcopyrite, pyrrhotite, cubanite, and pentlandite. Several distinct zones are recognized in drill core 34870-A (740 m in length) based on mineral modes and textures, plus major and trace element variations. Unit 6 exhibits well-defined trends related to in situ fractional crystallization. Sulfide is thought to have accumulated at the base of this pulse due to gravitational segregation of an immiscible sulfide liquid. Unit 5 represents emplacement of a more evolved, but sulfide-free magmatic pulse. Unit 4 is composed of two well-differentiated pulses, whereas Unit 3 appears to have fractionated very little, but may have been saturated in sulfide at the time of emplacement. Unit 1 is a more evolved and sulfide-rich pulse (or series of pulses) that may have mixed with more primitive magma of Unit 2. Sulfur in Units 1, 3, and 6 is characterized by [delta][sup 34]S values of 4.1 to 10.2 per mil CDT, and is thought to have been derived from crustal sources. The sequence in the Spruce Road area represents periodic emplacement of magmas that had undergone various degrees of fractionation and crustal contamination in sub-volcanic staging chambers.
- OSTI ID:
- 7206973
- Report Number(s):
- CONF-9303210-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:3; Conference: 27. annual Geological Society of America (GSA) North-Central Section meeting, Rolla, MO (United States), 29-30 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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