Mapping Log Pd/Cu Ratios in Vulcan and Investigation into the Origin of the Magenta Zone in the NorthMet Deposit: Hoyt Lakes Minnesota, USA
The purpose of this research is to investigate the origin of the PGE-rich Magenta Zone, a geologic feature within the NorthMet Deposit; a Cu-Ni-PGE deposit within a layered intrusion at the base of the 1.1 Ga Duluth Complex. The hypothesis is that a late-stage silicate magma containing dispersed sulfide droplets had infiltrated a permeable crystal mush resulting in the emplacement of the Magenta Zone. While mineralization is typically found along the base of the Duluth Complex, the Magenta Zone lies ~200 m above typical mineralization. Previous research has shown that the Magenta Zone cross cuts the younger concordant units. To build on this previous research we (1) created a block model to map Log Pd/Cu ratios in order to evaluate a magma flow history, (2) performed petrographic analysis of the samples in and around the Magenta Zone, and (3) Mapping of Mg number around the Magenta Zone of data gathered from SEM analysis. The spatial analysis of the Log Pd/Cu ratios have been used in exploration as a proxy for understanding magma flow trajectories. The block model created in this research revealed that the Log Pd/Cu ratio is highly variable and cannot be explained as one pulse of magma resulting in the creation of the Magenta Zone. Instead, the Magenta Zone was infiltrated by magmas that were characterized by differing R-factors that had affected the current distribution of the Log Pd/Cu ratios likely caused by multiple pulses of magma. The petrographic observations reveal a “needle point” texture that supports dissolution/reaction texture of two chemically different magmas. Although the SEM investigations did not demonstrate geochemical differences between the olivine grains in the mineralized versus unmineralized samples, most of the evidence supports a model in which late sulfide plus silicate magma had infiltrated a crystal mush resulting in the present-day mineralization hosted within the Magenta Zone.
Date of Degree
Master of Science (MS)
Social and Behavioral Sciences
Bauer, P. M. C. M. (2022) Mapping log Pd/Cu ratios in Vulcan and investigation into the origin of the Magenta Zone in the NorthMet Deposit: Hoyt Lakes Minnesota, USA [Master’s thesis, Minnesota State University, Mankato]. Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato. https://cornerstone.lib.mnsu.edu/etds/1195/
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