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Hydrothermal Systems in Manganese-Rich Iron-Formation Ofthe Cuyuna North Range, Minnesota: Geochemical and Mineralogical Study of the Gloria Drill Core

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Hydrothermal Systems in Manganese-Rich Iron-Formation Ofthe Cuyuna North Range, Minnesota: Geochemical and Mineralogical Study of the Gloria Drill Core MINNESOTA GEOLOGICAL SURVEY D.L. SOUTHWICK, Director HYDROTHERMAL SYSTEMS IN MANGANESE-RICH IRON-FORMATION OFTHE CUYUNA NORTH RANGE, MINNESOTA: GEOCHEMICAL AND MINERALOGICAL STUDY OF THE GLORIA DRILL CORE Frank Melcher, G.B. Morey, Peter L. McSwiggen, Jane M. Cleland, and S.E. Brink Report of Investigations 46 ISSN 0076-9177 UNIVERSITY OF MINNESOTA Saint Paul - 1996 HYDROTHERMAL SYSTEMS IN MANGANESE­ RICH IRON-FORMATION OF THE CUYUNA NORTH RANGE, MINNESOTA: GEOCHEMICAL AND MINERALOGICAL STUDY OF THE GLORIA DRILL CORE Copyright 1996 by the Regents of the University of Minnesota The University of Minnesota is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation. CONTENTS f Abstract ................................................................................................................................................................................. 1 Introduction ............................................................................................................................................................................ 2 Regional geologic setting ....................................................................................................................................................... 2 General stratigraphy ............................................................................................................................................................... 3 Mahnomen Formation ..................................................................................................................................................... 3 Trommald Formation ....................................................................................................................................................... 3 Zone A-Thin-bedded silicate-carbonate iron-formation ....................................................................................... 4 Zone B-Thin-bedded oxide iron-formation .......................................................................................................... 6 Zone C-Thin-bedded manganese-oxide iron-formation ....................................................................................... 7 Zone D-Thick-bedded manganese-rich oxide iron-formation .............................................................................. 7 Zone E-Thick-bedded oxide iron-formation ........................................................................................................ 8 Rabbit Lake Formation .................................................................................................................................................... 9 Magnetic susceptibility ........................................................................................................................................................... 9 Geochemistry....... .... ............................................................................................................................................................. 10 Major element attributes ................................................................................................................................................ 20 Minor and trace element attributes ................................................................................................................................ 22 Rare earth element attributes ......................................................................................................................................... 22 Mineralogy ........................................................................................................................................................................... 23 Silicates ......................................................................................................................................................................... 23 Stilpnomelane ........................................................................................................................................................ 23 Chlorite .................................................................................................................................................................. 26 Biotite-like phases of uncertain affinity ................................................................................................................ 26 Muscovite .............................................................................................................................................................. 27 Tourmaline ............................................................................................................................................................ 27 Alkali feldspar ........................................................................................................................................................ 27 Minnesotaite .......................................................................................................................................................... 27 Clay-like minerals ................................................................................................................................................. 27 Carbonates ..................................................................................................................................................................... 27 Iron Oxides ..................................................................................................................................................... , .............. 28 Magnetite ............................................................................................................................................................... 28 Hematite ................................................................................................................................................................ 28 Ilmenite ................................................................................................................................................................. 29 Goethite and martite .............................................................................................................................................. 29 Phosphates .................................................................................................................. , ........................ ,......................... 29 Sulfates .......................................................................................................................................................................... 30 Manganese oxides and oxyhydroxides .......................................................................................................................... 30 Sulfides .......................................................................................................................................................................... 32 Discussion ............................................................................................................................................................................. 34 Evidence for a hydrothermal system ............................................................................................................................. 35 Rare earth element signatures ............................................................................................................................... 35 Discrimination diagrams ....................................................................................................................................... 36 Correlation coefficient analysis ............................................................................................................................. 38 Mass-balance calculations ..................................................................................................................................... 40 111 Paleogeographic implications .............................................................................................................................................. 43 Conclusions ......................................................................................................................................................................... 44 Acknowledgments ............................................................................................................................................................... 45 References cited ................................................................................................................................................................... 45 ILLUSTRATIONS Figure 1. Generalized geologic map of the Cuyuna range showing the location of the Gloria drill site and other localities mentioned in the text ........................................................................................................................ 2 2. Generalized lithologic column of strata intersected in the Gloria core summarizing various nomenclatural schemes used on the North range ..................................................................................................................... 4 3. Stratigraphic summary of chemical data compiled on Tables 1-3 ................................................................
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