231-5 Magnetic Attraction: The Search For Critical Minerals in Iron Skarn Deposits

Session: Critical Mineral Resources and Recovery in the Americas: Emerging Methods in Exploration and Sustainable Extraction (Posters)

Presenting Author:

Authors:

Abstract:

Critical minerals are the foundation of modern technological development worldwide. Elements such as iron, cobalt, gold, and copper have been crucial in the expansion of humanity's grasp across multiple science, defense, and infrastructure sectors. The relationship between critical mineral deposits and large igneous provinces (LIPs) makes their study crucial for understanding the complex geodynamic processes that control their emplacement in the Earth’s crust. One of the largest LIPs, the Central Atlantic Magmatic Province (CAMP), extends along the east coast of North America, Northern Africa, and the northernmost part of South America and is closely linked to important events in geologic history, such as the breakup of Pangea and the End-Triassic Extinction. Within CAMP, Cornwall-type skarn deposits are of particular economic and scientific interest. These particular skarn deposits form when Mesozoic diabase intersects Paleozoic limestones and shales, resulting in the emplacement of iron, cobalt, and copper minerals. Despite extensive documentation resulting from centuries of mining, questions about the origin and mechanics of these deposits persist. Previous models pose varying fluid dynamics, ranging from a single, continuous fluid pulse to multiple fluid pulses. The origin of the iron within these skarn deposits remains debated, with experts proposing that the magnetite was carried and emplaced by the intrusion.  

In contrast, others suggest that the magnetite was leached from the host rock via contact metamorphism. Using samples acquired from and around a magnetite vein in Cornwall Mine (1739-1972) in Pennsylvania, I performed chemical analysis employing an Electron Probe Microanalyzer (EPMA) to characterize zoned magnetite crystals. The variations in the magnetite zones, including a solid solution between Mg-Al spinel and Fe spinel, yielded valuable information about the crystals’ growth, implying multiple hydrothermal fluid pulses or growth events with varying compositions throughout the deposits’ emplacement. The origin of magnetite, whether it is derived from the diabase intrusion or leached from the carbonate host rock, will be determined by analyzing the distribution of magnetite in relation to the sampled magnetite vein in Cornwall Mine. This will involve developing detailed interactive maps for crystals in both the vein and the host rock using ThermoFisher’s Maps Min, an automated mineralogy software, to detect chemical and structural variations in the magnetite, including inclusions or the presence of other critical minerals such as cobalt or copper.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8427

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.