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Description and Origin of Carbonate Minerals in the Upper and Lower Cherty Members of the Biwabik Formation, Minnesota Leslie R

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Description and Origin of Carbonate Minerals in the Upper and Lower Cherty Members of the Biwabik Formation, Minnesota Leslie R University of North Dakota UND Scholarly Commons Theses and Dissertations Theses, Dissertations, and Senior Projects 1973 Description and origin of carbonate minerals in the upper and lower cherty members of the Biwabik Formation, Minnesota Leslie R. Honeyman University of North Dakota Follow this and additional works at: https://commons.und.edu/theses Part of the Geology Commons Recommended Citation Honeyman, Leslie R., "Description and origin of carbonate minerals in the upper and lower cherty members of the Biwabik Formation, Minnesota" (1973). Theses and Dissertations. 142. https://commons.und.edu/theses/142 This Thesis is brought to you for free and open access by the Theses, Dissertations, and Senior Projects at UND Scholarly Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UND Scholarly Commons. For more information, please contact [email protected]. DESCRIPTION AND ORIGIN OF CARBONATE NEIERALS IN THE UPPER. AND LOWER CHER.TY ?•IF1'-fBERS OF THE :BIWABIK FORE,\.TION, HI:l:\1{ESCTA Leslie R. Honeyman, Master of Science The University of North Dakota, 1973 Faculty Advisor: Professor Frank Karner This study was done for the Erie Mining Company after periodic problems with the quality of pellets from taconite of the Biwabik Fonna­ tion had been linked to the presence of carbonate minerals. The carbon­ ates fouad in the cherty members of the Precambrian Biwabik Formation are predominantly side~ite, ankerite, and calcite. Siderite is the only primary carbonate mineral and occurs in three forms: microgran­ ular, granular (oolitic), and crystalline aggregates (recrystallized). Ankerite is a secondary mineral occurring as crystalline aggregates and alteration rims on granular siderite. Calcite is found only in fractures and fault zones. Siderite formed from the original precip­ itate and early in the diagenetic history of the rock. The alteration of siderite to fine-grained, euhedral magnetite appears to be the major part of the pellet-quality problem at Erie. The fine-grained magnetite causes small amounts of siderite to be incorporated with magnetite in the magnetic separation process. This siderite breaks down when the pellet is roasted and carbon dioxide is given off causing the pellet to disintegrate. Ankerite formed in two periods: the ankerite rims on siderite granules formed early in epigenesis and the crystalline ankerite formed much later, Calcite formed late in the epigenetic l history of the formation. It appears that the carbonates of the cherty members of the Biwabik :b'ormation can be used as indicators of an envi- ronment of deposition having reducing conditions and as indicators of the extent of metamorphism caused by the intrusion of the Duluth Gabbro. 2 DESCRIPTION Al\l) ORIGIN OF CAIGONATE HINEPALS I:~ THE UPPER AND LOWER CHZRTY MEHBERS OF TEE BIWABIK FORM.AT IO?:;, l'IINNESOTA by Leslie R. Honeyman Bachelor of Philosophy, University of North Dakota, 1969 A Thesis Submitted to the Graduate Faculty of the University of North Dakota in partial fulfillment of the requirements for the degree of Master of Science Grand lorks, North Dakota August 1973 This thesis submitted by Leslie R. Honeyman in partial fulfill­ ment of the requirements for the Degree of Master of Science from the University of North Dakota is hereby approved by the Faculty Advisory Committee under whom the work has been done. /- ( Chainnan) · \ ' '· ii DESCRIPTION Ai).:'D ORIGIN OF CARBONATE r-IINER...\.LS IN THE UPPER Al\'1J LOWER CHERTY }I™BERS OF THE BIWABIK Degree -----------------------------------Master of Science In presenting this thesis in partial fulfillment of the requirements for a graduate degree from the University of North Dakota, I agree that the Library of this University shall make it freely r2vailable for inspection. I further agree that permission for extensive copying for scholarly purposes may be granted by the professor who supervised my thesis work or, in his absence,·by the Chairman of the Depart­ ment or the Dean of the Graduate School. It is understood that any copying or publication or othe:c use of this thesis or part thereof for financial gain shall not be allowed with­ out my written permission. It is also understood that due recognition shall be given to me and to the University of North Dakota in any scholarly use which may be made of any material in my thesis. Date iii ACKNOWI ... EDGHE1"'T S The three members of my committee, particularly my com.rnittee chairman Dr. Frank Karner, are gratefully acknowledged for their con­ structive criticism and suggestions during the course of this work. The other two members are ffrs. Walter L. Moore and Lee Clayton. Erie Mining Company, Hoyt Lakes, Minnesota supplied funds for field support, laboratory analysis, and thin sections. Wayne Tuttle, Forrest Boyee, and Joe Evers of the Erie Mining Company supplied immeasurable help and assistance while I was on the Erie property. iv T.ATJLE CF COl.TTENTS ACK?WWLEDGHm!TS iv LIST OF TABLES vi LIST OF FIGURES vii ABSTRACT ix INTRODUCTIQ1(l 1 STR..4.TIGRAPHY 4 General Lower Cherty Hember Lower Slaty 11er:iber Upper Cherty Member Upper Slaty Hember METHODS • 14 CARBONATE PETROGP..APHY • 2S Basic Definiticns Siderite Ankerite Calcite DIFFERENCE IN CONCENTRA.TION OF CARBONATE MINERALS • • • • • • • 42 Lower Cherty Member Upper Cherty Member INTERPRETATIONS OF CHANGES IN CARBONATE CONCE!:.'TRATION AND OCCURRENCE • • • • • • • • • • • • • • • • • • • 48 Siderite Ankerite Calcite CONCLUSIONS 52 APPE'rlillIX. Weight Per,::entage for Sample Interval 57 REFERENCES . .. .. 64 V LIST OF TABLES Table Page 1. Comparison of Hineral Abundances Obtained by X-ray and Point-Count Methods. · 23 2. Precision of X-ray De.termination of Peak Intensities 24 3~ Weight Per~entage for Sample Interval. • • • • • • • • • 58 vi LIST OJ? FI·:;:aRES 1. Location and Geologic Map of Study Area Modified from Erie (1967) ..... 3 2. Geologic Cohu-nn for the Eastern Hesabi Range. from Erie (1967) ........... 6 3. Photograph of Interbedded Carbonate and Magnetite­ Rich Chert in Outcrop .••..••••. 15 4. Locations of Drill Hole and Pit Samples from Areal; Area 6; Area 3; and Area 2-West • • . • 18 5. Photomicrographs Showing the Occurrences of Siderite as (A) Hicrogranular Siderite; (B) Granular Siderite with Hicrogranular Side.rite Cement; (C) Granular Siderite with Chert Cement; and (D) Crystalline Aggregates of Siderite (Recrystallized) . • . •••••. 28 ,,. o. Photomicrographs Showing the Alteration or Replacements of Siderite to (A) Recrystallized Siderite; (B) Magnetite; (C) Ankerite and Hagnetite; (D) Ankerite; (E) Minnesotaite; (F) Stilpncmelane; ((;) Quartz; and (R) Stilpnomelane and Magnetite 31 7. Photomicrographs Showing the Oc.currences of Ankerite as (A) talline Rhombs; and (B) Alteration Rims o~ Siderite Granules. • • • ••• 37 8. Photomicrograph Showing Ankerite Altered to or Replaced by Magnetite •... 39 9. Photomicrograph Shot,ing a Calcite Vein •• 41 10. Triangular Diagrams Showing Vertical and Lateral Changes in the Concentrations of Siderite, Ankerite, and Calcite in the U, T, S, and R Layers of the Lower Cherty Member 44 11. Triangular Diagrams Showing the Vertical and Lateral Changes in the Concentrations of Siderite, Ankerite, and Calcite in the L, K', K, and J Layers of the Upper Cherty Member ••..•...•.• 47 vii 12. The Precipitation and Deposition of Carbonate }faterial in the Biwabik Fon,,.ation (I·fodified from DiElC:Qth and Chauvel, 1973) .. 55 viii This study was done. for the Erie Hining Company after periodic problems with the quality of pellets from taconit2 of the Biwabik Forrr.~- tion had been linked to the presence of carbonate minerals. The. carbon- ates found in the cherty members of the Precambrian Biwabik Formation are predominantly siderite, ankerite, and calcite. Siderite is the only primary carbonate mineral and occurs in three forms: nicrogran­ ular, granular (oolitic), and crystalline aggregates (recrystallized). Ankerite is a secondary mineral occurring as crystalline aggregates and alteration rims on granular siderite. Calcite is found only in fractures and fault zones. (siderite formed from the original precip­ itate and early in the diagenetic history of the rock. The alteration of siderite to fine-grained, euhedral magnetite appears to be the major part of the pellet-quality problem at Erie. The fine-grained magnetite causes small amounts of siderite to be incorporated with magnetite in the magnetic separation process. This siderite breaks down when the pellet is roasted and carbon dioxide is given of£ causing the pellet to disintegrate. Ankerite formed in two periods: the ankerite rims on siderite granules formed early in epigenesis and the crystalline ankerite formed much later. Calcite formed late in the epigenetic history of the formation. It appears that the carbonates of the cherty members of the Biwabik Formation can be used as indicators of an environment of deposition having reducing conditions and as indicators of the extent of metamorphism caused by the intrusion of the Duluth Gabbro. ix INTRODUCTION This study was done for the Erie. Hir1ing after periodic problems with the quality of pellets from taconite of the Biwabik. For-- matio.::1 h2.d been linked to the presenc2. of carbon.:cte minerals. The purpose was to determine the of carbonate minerals present, the relationships of the carbonate minerals to each other, and ultimately to the environ.,.~ent of deposition of the taconite. The area of study is the Erie Mining Company property, extend­ ing from the western edge of Area 1, just north of Aurora, 1'1innesota, to the eastern edge of Area 8, along the western edge of Birch Lake, where the Duluth Gabbro Complex transects the Biwabik Formation (Figure 1). Vertical and lateral differences in carbonate mineralogy were studied in four geologic zones within each of the two cherty members of the Biwabik. Carbonate minerals have been altered to various sili­ cates, oxides, and other carbonate minerals; the difference in carbon­ ate minerals is critical in its effect on pellet quality of the high- vollli~e taconite reining operations.
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