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- Title
Portable-XRF geochemistry and EDS mineralogy of the Maple-Hovey manganese deposit, northern Maine, USA.
- Authors
MADSEN, LAUREN E.; CHUNZENG WANG; YATES, MARTIN; LENTZ, DAVID R.; WHITTAKER, AMBER H.; CRUZ-URIBE, ALICIA M.
- Abstract
The Silurian Aroostook County manganese district in northern Maine consists of northern, central, and southern sub-districts. Collectively, they represent the largest manganese reserve in the United States. This study focuses on the central sub-district where the largest known deposit, the Maple-Hovey deposit, is located. Detailed field mapping, cross-section characterization and sampling across two continuous exposures of the primary ore zone, portable-XRF analyses, petrography, and preliminary energy dispersive spectroscopy (EDS) mineral identification via electron microprobe have been conducted to characterize the lithogeochemistry, chemostratigraphy, and mineralogy in the deposit to better constrain its metallogenesis. Field observations show that the manganese deposit is presented as a continuous but swell-and-pinch layer, and the primary ore zone consists of thinly laminated, very fine-grained manganese ironstone. The ore and surrounding host rock are dominated by a layered sequence with varying mineralogy. Petrographic observations and EDS spectra reveal a chlorite-rich host rock, Fe-rich layers largely consisting of hematite with lesser magnetite and pyrite, Mn-rich layers of varying compositions of Mn-silicates, oxides, and carbonates, and P-rich layers occurring in the primary Mn ore zone. Cross-cutting veinlets containing a Mn-silicate (possibly rhodonite, MnSiO3), albite, and other minerals indicate minor hydrothermal activity. Spessartine garnet occurs as a major Mn-silicate, indicating high Mn and Al concentrations allowed its formation at low temperatures and greenschist-facies peak metamorphism. Initial results from portable-XRF data show that Fe and Mn are generally found in discrete layers. Barium, Ni, and Ti are of varying but relatively high concentrations both within and surrounding the ore zone. These observations support the interpretation that the Maple-Hovey Fe-Mn Deposit represents a sedimentary accumulation with similarities to the well-characterized Silurian Woodstock Fe-Mn deposits in New Brunswick, Canada, and other Fe-Mn deposits worldwide.
- Subjects
MAINE; NEW Brunswick; MINERALOGY; GEOCHEMISTRY; MANGANESE; METALLOGENY; PETROLOGY; ELECTRON probe microanalysis
- Publication
Atlantic Geoscience, 2023, Vol 59, p54
- ISSN
2564-2987
- Publication type
Article
- DOI
10.4138/atlgeo.2023.002