.i‘I‘ II‘H I"I I III I I I I II I I III I II I I II I II II :II ’ MINERALQGY ANS PETRQGRAFHY OF ERON FQRMATIC‘N AT LAKE ALSANEL QLEESEEC, CANADA ?52319 {or the Dag?” of M. S. MECBEG‘I‘LN W"??? INHBSITI’ why“. Lu“ RudOIPh K. Hogberg 1957 TH EEEE U IIIIIIIIIIIIIIIIIIIIIIIIIIIIII IA AUC29W3’ MINERALOGY AND PETROGRAPHY OF IRON FORMATION AT LAKE ALBANEL, QUEBEC, CANADA By RUDOLPH K. HOGBERG A THESIS Submitted to the School of Science and Arts of Michigan State Universit of A riculuture and Applied Science. in partial ulfil ment of the requirements for the degree of MASThR OF SCIENCE Department of Geology 1957 ABSTRACT The Temiscamie River area, on Lake Albanel, is located in the Precambrian shield of westecentral Quebec, Canada. Results of laboratory examination of forty three thin sections, from diamond drill core fragments, revealed certain conclusions relative to textural relationships and mineralogic content of an iron formation. Macrosconic study pointed out three divisions of the Temiscamie iron formation. Two divisions, the "Upper slate" and the "Lower slate", were used in background study. Micro- ,scopic examination of both the "slate" members indicates a striking similarity of alternating light chert and dark extremely fine grained carbonate bands. The middle division, or "Iron formation", consists of anhedral carbonate grains in irregular patches and bean shaped granules composed entirely of carbonate or with varying amounts of chart, all surrounded by an equal-grained chert matrix. Magnetite occurs as irregular aggregates of anhedral and subhedral shaped grains and as rice-like grains in inter- locking fabrics. Minor amounts of minnesotaite, stilpnomelane and muscovite were observed. Petrographic modal analyses of twenty one thin sections from eleven diamond drill holes were made upon two arbitarily selected horizons at approximately uniform positions above 11 the stratigraphic "footwall" boundary. The estimates of mineral volume percentages determined from modal analyses were found to be valid upon comparison with metallurgical test results. Correlation of the total iron computations from model analyses with metallurgical test total iron findings revealed the carbonate to be siderite and also that magnetite constitutes the overwhelming majority of the iron of the "Iron formation". No observable mineralogic changes were observed along the "oxide bearing member". The general SBQJEHCG of crystallization of a colloidal gel from an initial crystallized stilpnomelane to a finally crystallized fine grained chert groundmass is suggested. A reducing environment is postulated for the formation of magnetite from ore-existing iron-rich minerals. Secondary alteration of the formations, from carbonate and magnetite to limonite and martite, is probably due to the influence of the present weathering surface. iii ACKNOWLhDGMbNTS The author wishes to express a most sincere thanks to Dr. J. Zinn, Dr. J. W. Trow and Dr. H. B. Stonehouse for their guidance and aid in this study; also to Dr. B. T. Sandefur and Mrs. J. E. Smith for much appreciated constructive criticisms. He is also deeply indebted to the Albanel Minerals Limited for financial assistance, equipment, samples and much of the information used in the problem. In this con- nection the cooperation and suggestions of Mr. B. H. Boyum and Mr. E. J. Rex were invaluaole. iv TABLE OF CONILNTS INTRODUCTION ............................ Location and Accessibility ...... Physical Features and Climate ............ Exploration History ............... Regional Geologic Setting ....... Purpose and Scope ................ Glossary of Abbreviations for Tables II through X ............. ........... . ...... .......... Tilt. 'I'hlleSCAulfli IRON FOR....¢.1‘IO.I . . . . . . . . . . . . Introduction .............. Methods and Procedures ,5............. Minerals ................ lQaartZ OOoOooooooooaooooo. Carbonate ............. magnetite 00.00.00.000... Minnesotaite ........... Stilpnomelane ......... Limonite ... .................................... . Hematite ...... ......................... Muscovite .............. Pyrite OI... ...... O..- "UDper and Lower Slates" ... Graphite ........... .................... .. ..... .. "Iron Formation" .......... Page CONCLUSIONS ......................................... 42 SUGGESTIONS FOR FURTHER STUDY . . . . . . . . . . . ...... . . . . . . r34 REFERENCEIS OOOOOOOOOOOOOOOOOIOO ....... 00.00.000.00... 45 vi TABLE I. II. III. IV. VI. VII- VIII. IX. X. LIST OF TABLES Stratigraphic Column of the Temiscamie River Area 0.0.0... ......... ......OOO......... Analyses of 100' Horizon of "Iron Formation" ........ ............ . ..... ... Analyses of 100' Horizon of "Iron Formation" (Cont.) ..................... analyses of 50' Horizon of 'Iron Formation” ......... ........... ......... Analyses of 50' Horizon of "Iron Formation" (Cont.) ..................... Analyses of Samples of "Iron Formation" ...... Analyses of Samples of "Iron Formation" (cont.) ....... ..... .......................... Analyses of Samples of "Upper Slate" ......... nal sea of Samples of "Upper Slate" can.) 00.0.0000.00.0000000000000000.0.000... Analyses of Samples of "Lower Slate" ......... vii Page 17 18 19 LIST OF FIGURhS Figire Page 1. Location of the Temiscamie River Area ......... l 2. Picture of the southwest portion of the Temiscamie River area ..................... 2 3. Temiscamie River Area, Mistassini Territory, Quebec, Canada ..................... (A 4. Geologic Map of Sandspit Sheet, Temiscamie River Area, Quebec, Canada .................... 9 5. Geologic Map of Albanel Sheet, Temiscamie . River Area, Quebec, Canada .................... 10 6. Vertical Cross Section of Diamond Drill Holes, Sandspit Sheet, Temiscamie River Area, Qlebec’ canada C.......OOOCO..... ..... .0. 11 7. Vertical Cross Section of Diamond Drill Holes, Albanel Sheet, Temiscamie River Area, glebec, canada .........0.....0.......... 12 8. Photomicrograph of Al-fil5-22' showing banding of dark carbonate and light Chert layers .........OOOOOOOQOOOQOOOOOI.000... 50 9. PhotomicrOgraph of Al-#18-l40'-150' ShOWiflE stilpnomelane blades in chert ................. 30 10. Photomicrograph of Al-filS-d' showing the contact of chert and carbonate layers. Magnetite (black) is in carbonate ............. 32 ll. Photomicrograph of Ss-fiES-llO' showing minnesotaite blades, carbonate, stilp- nomelane (dark gray) and magnetite in chert ... 52 12. Photomicrograph of Ss-fi24-20A showing small anhedral and large rhombs of carbonate. Stained rings are limonite ........ 54 13. Photomicrograph of Al-fiZO-ea' showing carbonate granules in chert.‘ Staining is limonite .............. ....... . ..... . ....... S4 viii Figure page 14. Photomicrograph of Al-#15—157' showing poikilitic texture of the carbonate and magnetite in irregular masses ................. 06 15. Photomicrograph of Ss-fi24-125' showing stilpnomelane (medium gray) and carb- onate replaced by magnetite all in chert groundmass 3'3 16. Photomicrograph of Al-#15-lea' showing stilpnomelane (medium gray) at border or magnetite blinds ......OCOO 00.00.000.000..... 38 17. Photomicrograph of Al-filS-S?’ showing a granule of carbonate (medium gray) and muscovite (light gray) ringed by magnetite in chert matrix ............................... 58 ix INTRODUCTION Location and Accessibility Exposures of iron bearing sedimentary formation have been found at Lake Albanel in west-central Quebec. Many geologists are now of the opinion that these rocks are a con- tinuation of a trend that may be traced 400 miles southwest from similar sedimentary iron occurrences in the Labrador trough. The Albanel lake area is in the Mistassini Territory, Fig. 1 Location of the Temiscamie River Area \ N3 Province of Quebec, Canada, approximate1y 250 miles directly east of the southern extremity of James Bay. Lake Albanel is the smaller and more southeasterly of two large northeast trending lakes; the other is Lake Mistassini. These lakes are the headwaters of the Rupert River which flows into James Bay. A 145-mile gravel road from Lake St. John to Chibougamau affords access to a point 90 air miles southwest of the area. The inhabitants, a Mistassini Cree band of Indians, exploit the natural resources of fish and game for food and other means of livelihood. Physical Features and Climate This region displays moderate relief and poorly integrated drainage, both are characteristic of the Canadian Fig. 2 Picture of the southwest portion of the Temiscamio River area TEMISCAMIE RIVER AREA 3 8 p a msnssml TERRITORY cuesec, CANADA V ‘7 Scale. in ulee o g 5? l O I 2 R. K H. May I957 one! Quebec 529 . Dept. of Mines :2 .‘3 ‘6 g _ I 7 O a {P OJ AND§PIT SHE T w - I Q? fl 3 '73. OC' Fla 3 shield. Figure 2 is a aerial photograph showing the general land forms of the area. Glacial deposits, variable in thickness, conceal the bed rock with "sand plains", drumlins and discontinuous eskers. Heavy forests of black spruce and balsam envelop the region, except in the muskeg portions. White birch grows upon the low glacial ridges. The summer season is short. Ice on the large lakes breaks up in early June, and these bodies of water freeze again in October. At times strong southwest winds make canoe travel on the large lakes impossible. Summer rain- fall is quite heavy and frequent and temperatures are moderate. The winters are cold with temperatures ranging down to - 40° F. Exploration History This region was first mentioned in the literature by explorers, missionaries and traders in their records of quests for a route west from Lake St. John to James Bay (Mawdsley and Norman, 1955). Early reports on the geology of the region were written by Richardson in 1871 who reported flat lying limestones at Lake Mistassini, and by Low in 1886, who called the sedimentary formation Cambrian in age because of the resemblance to Cambrian age strata on the east side of Hudson Bay. Barlow, in 1910, called the sediments Ordovician upon finding possible biogenetic structures (Neilson, 1953). In more recent geological exploration, Norman (1940) described the contact of the sedimentary sequence with the Grenville sub—province. Neilson and Wahl mapped the geology of the Albanel and Temiscamie River areas in 1947 and 1948. Their reports (Neilson, 1953 and Wahl, 1953) are a description of the igneous and metamorphic rocks, the stratigraphy of the Precambrian Mistassini series,> structural features, and the economic potential of the two areas. Regional Geologic Setting This discussion of the general geology is a summary of the works of‘Neilson (1953 , Norman (1940) and Wahl (195%). Rocks of the region consist of sedimentary strata overlying a granite and gneiss complex. The sediments and basement rocks are intruded by pegmatites, and alkaline and basic plutons (Table I). The basement complex of early Precambrian granites, orthogneisses and paragneisses is exposed in the southeast portion of Figure 3. TABLE I STRATIGRAPHIC COLUMN OF THE ThMISCAMIE RIVER AREA Rock unit Character of unit thickness in feet Pleistocene Stratified sands and gravel, varies till Uhconformigy Intrusive Alkaline and basic intrusives complex Pegmatite "Upper slate"- cherty carbonate and graywacke 2 Temiscami "Iron formation"- cherty iron . 220' ya iron carbonate 3. formation 9 "Lower slate”- cherty carbonate *4 and argillite 50' -S Quartzite 55' . $——————- Disconformity ? 4 ‘3 Upper n Albanel Sandy gray dolomite 2000' g formation * Disconformity ? Lower Shaly gray dolomite 4000' Albanel Massive gray dolomite to ? formation 7800' Uhconformity ? Granite Granite and gneiss Orthogneiss complex Paragneiss after Neilson (1953) and Wahl (1953) During later Precambrian time dolomites and "Iron formation" of the Mistassini series were deposited. The dolomite succession is divided into two well stratified members by a disconformity. The Lower Albanel formation consists of dark gray, ferruginous and shaly beds and is limited areally to the Mistassini lake basin. The Upper Albanel formation, confined to the Lake Albanel area, is composed of sandy dolomites. The uppermost member of the Upper Albanel formation contains possible cryptozgon structures. Overlying and separated by another disconformity is the basal quartZite of the Temiscamie iron formation.. This pure quartzite is persistent in the vicinity of Lake Albanel. It is followed by the argillite and cherty carbonate beds of the "Lower slate", which in turn grades into the "Iron formation". The "Upper slate" is composed of fine grained cherty carbonate and graywacke. The sediments of the Mistassini series strike northeast and dip gently to the southeast. This simple structure is interrupted locally by small synclines, anticlines and faults. The angle of dip of the beds increases very rapidly southwestward towards a zone of intense shearing and crush- ing which marks the so called "Grenville front". It is generally agreed that the Grenville gneisses in this area have been thrust northwestward over the sedimentary strata. Presently the correlation of the rocks of the area with similar occurrences is obscure. Lack of field mapping between the Albanel region and other geological provinces which contain iron formation necessitates considering this region as isolated geologically until more information can be gathered. Purpose and Scope This problem was suggested by Albanel Minerals Ltd. upon request by the author. An interest was developed in a detailed examination during the course of field work on the "Iron formation" in the Albanel lake area during the summer of 1956. Anomalous fluctuations in the hematite/mag- netite ratio pointed out the Albanel and Sandspit Sheets of the Temiscamie River area as critical areas for further examination (Figures 4 and 5). This thesis reports the results of a laboratory study of core fragments from 11 selected diamond drill holes (Figures 6 and 7). The cores were relogged by the author and sampled in certain horizons. Forty three thin sections were studied. The author also determined modal analyses of 21 thin sections. The purpose of this investigation is to ascertain the 'petrography and significant mineralogic gradation of the "oxide bearing member" of the Temiscamie iron formation. GEOLOGIC MAP OF SANDSPIT SHEET TEMISCAMIE RIVER AREA QUEBEC, CANADA . MISTASSINI SERIES Scale? In fact SEE: E SLATE a sRAvacxs 2000 0 2000 4000 m CHERTY CARBONATE 0.1m. o STRIKE a DIP ,. FAULT - - m mo" FORMT'ON E CHERTY CARBONATE a ARGILLITE R.K.H. May 1957 after Albonel [:1 QUARTZ.” Minerals Ltd. m DOLOMITE Fig 4 10 GEOLOGIC MAP OF ALBANEL SHEET TEMISCAMIE RIVER AREA QUEBEC, CANADA Scale 2 in feel 2:15:51! 2000 0 2000 4000 D.D.H. o STRIKE a DIP -.— FAULT -- -— R. K. H. May l957 after Albanel Minerals Ltd. MISTASSINI SERIES SLAT E 8 GRAYWAC KE CHERTY CARBONATE "IRON FORMATION " CHERTY CARBONATE a ARGILLITE OUARTZITE DOLOMITE BBWEEM Fig. 5 11 24 VERTICAL I": Ioo' HORIZONTAL l"=4000' v. E = 40 TO I SAMPLE LOCATIONS . Ioo' HORIZON —- — 50' HORlZON — - .— R. K. H. 25 35 300' . ". 30d ‘ /V’. . \ 29 / / , \ / / I. \ 200' . // I,”’ . \'\ ~—zoo me E —i00" 0' Lake Albanel (Izas‘) 0' VERTICAL CROSS SECTION OF DIAMOND DRILL HOLES SANDSPIT SHEET TEMISCAMIE RIVER AREA QUEBEC,CANA0A Scale T EMISCAMIE IRON FORMATION 7/4 CHERTY CARBONATE @ “IRON FORMATION " E CHERTY CARBONATE a ARGILLITE permisson of Albanel Minerals Ltd. May IS 57 Fig. 6 L; ' 12 22 ...- \ '20 '3-..»- \ ’ II '5 o '3 a \3 l9 - , \ \ - / 200' —— , —-/ -200' ~ \ ' I / \ \ / L, \ :0: . \ \ a _ ._ _ ._ ‘ ‘ ‘ 3 I00' , El ~. _ -Ioo' i I 0' Lake Albanel (l289') VERTICAL CROSS SECTION OF DIAMOND DRILL HOLES ALBANEL SHEET TEMISCAMIE RIVER AREA QUEBEC, CANADA Scale VERTICAL I": IOO' TEMISCAMIE IRON FORMATION HORIZONTAL I": 4000' r v. E, -. 40 TO . OHERTY CARBONATE SAMPLE LOCATIONS m "IRON FORMATION' E CHERTY CARBONATE a ARGILLITE IOO' HORIZON -— — 50' HORIZON - —- — permisson Of Mayl957 Albanel Minerals Ltd. R. K. H. Fla. 7 13 GLOSSARY OF ABBREVIATIONS FOR TABLES II THROUGH X Al - Albanel Sheet alt - secondary oxidation and hydration anh - anhedral av - average bd and bds - band and bands brn - brown Garb - carbonate CONT. - continued dia — diameter euh - euhedral grn - green irr - irregular Lim.— limonite ny mag - normally magnetic 1t — light Mag - magnetite mag - magnetic maj - majority max - maximum med - medium Minn - minnesotaite Muse - muscovite ny mag - normally magnetic Qtz - quartz Stilp - stilpnomelane subh - subhedral tr - trace Ss - Sandspit Sheet vy 1y mag - very leanly magnetic X - crossed yel - yellow Banding thin banded - less than 1/8” medium banded - 1/8" to s/a" thick banded - 5/8" to 6" massive - over 6" 14 I uo>aa Inc one: Abv wcoH ES m. NMMOEM pa mecca a E b canIHOh usage a new. sswlaos an _ meannesfismwfis noses as“ a.“ DOUG pHQ U G wqo OMHG Q HH WHHOH SE ”Con oaoanoooaa Onwaa a em m >aH copoeah Rafi moacoo. 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H .mmmnakmmw mwmpm ocSm GS SE mmH.o 0S S0S0 mm H.0 h :OSS00m 0S unawaau Adv 0S0 hocSE AHV as 00.0 Adv >0 NS0S0E AHV_ 0S0B 002 no 0 0000.90 000 h>0k nfi0S _ 000 0S00 0000 «KS0S0E hmhww 000000 0000 0000 0000 -0000 00 0000 0000 «00Et000 SH «002-000 0&0 “005 ha 00 0000 .mmlflflhfi .NNlmdfi .mmtqul .mfllqm H0 H4 H0 H4 .000ha000 nOSS00m cfina 000 0000 0.02000 gmy0 0000000000000 0000 000000 00: s00§u0< 00 00005 000 u000n0< 00 000-000 a 100 BE 000.0.50 000 000 .000 0000500 000 00000 0000500 000-000 0000 00000005 0000 A00 0002 000 ,I.0«0|@0*IH< .omms.bom a 000000: .000-.mm%¢0m 00000 000 0000000 a 00090 Ame 00 W0 0000000 00_ -000u00 00.0000 -0000 0000.0000000 000 00 0000000 0 000 00 0000 0002 000 00 000000 0000 0000000 000 00000000 000 000080 00000o0oouo00 x 0000000 002 000 00000000 Av. .000: 00000 000 0000005 0000 Ami 00000000 000 0000000 0000 0000 Amv .000u.mm*umm_bomc00%¢0< 00 000 0005000 000008 00000 0000 00000 000000 00000 000 00 0000500 Am“ 0000800 002000000000 Amy 000 0000 Amy n.0mmumm 00000 00:000 ANH . .000 .000-.000 .000-.000 000 00 000.0 0000000 000 000000 000 00000000 00.0.00 00 -0000. 0 00 00000000 00 N 000000 00 00 00.0 5 0000000 00 0000000 000 0000000 000 00 000 000 00 000000 000 00000 000 00 000.0 000 0000 0000 000000 #0000 000000000 0000000 0000 00 0000 0000 .0000-000 0» 0000000 5000 .0001000104 00 000000 00000 0000 0000 008 #000000 00000 005 “m0ascoc 0000000 0005 h0 “was 50 »> «maaunoz 00 0000-000 0000 ¥000-.000-000 .000-000 .000-000 .000-.000-000 .000-.000-000 .0000000 00 00 .IH4 _ 00 _ 00 “mm 00000000 000000m-0000 000 000m- , =00000 00000: 00 00000000 x 00000 THE Th.a’.ISCMaIb IRON FORMaTICN Introduction The cores upon which this study is based were drilled during the summer field season of 1954. At that time the company retained representative core sections and used the remaining portions for metallurgical testing. For the investigation the author selected samples from diamond drill holes with the greatest footage in the "Iron formation". A detailed macroscopic examination of the core fragments from 11 holes revealed three Stratigraphic divisions. Two of the divisions, the "Upper slate" and the "Lower slate", are considered separately from the "oxide bearing member". Thin and polished sections available for examination, were previously prepared for a cursory survey, by the company, of the formation in the Sandspit and Albanel Sheet areas. The writer compared the distribution of the various sampled horizons with the recognized stratigraphic divisions. This information was consolidated with studies of additional thin and polished sections to provide an adequate coverage for the problem. Samples of the "Iron formation" at approxi- mately 50' and 100' positions above the stratigraphic "footwall" boundary were chosen for microscopic study and petrographic modal analyses. Additional random rock sections from the "oxide bearing member" provided further data. Core fragments from the two "slate" members were selected for background microscopic examination. Methods and Procedures The author examined the thin sections by the common oetrographic procedures. Study of polished sections and core sections supplemented the thin section work. a six-spool continuous line integrating stage was employed for the modal analyses. Lines were run perpendicular to the sedimentary banding at two millimeter intervals. To determine satisfactory length of traverse for reliable measurements, the author computed the percentages of each mineral on every component line. The traversing was terminated when more than six lines were completed and the percentages of all the minerals on any two-consecutive lines held constant. Total traverse lengths varied from 77.89 to 167.02 millimeters and averaged 114.66 millimeters. If less than 0.5 % of a mineral was measured it was listed as a trace in the modal analyses tabulations. Petrographic modal analysis is based on the theory that parallel line traverses of thin sections are consistent 25 estimators of true population or mineral mean. The analysis is unbiased if the traverse length is sufficiently large. Chayes (1956) describes two types of errors in the estimation of the mean of minerals in rocks analyzed by the continuous line integrator. The reproducibility or counting error of the thin section is a combination of process, instrument, identification and tabulation conventions. To limit this error the same procedures were followed on each component line. The minerals were easily identified and tabulation conventions were consistent. The second or analytical type is the random error of the analysis in estimating the mineral composition of the core from which the thin section was cut. Finally the estimate of volume of each mineral from thin section analysis is what Chayes (1956) has named the Ebllesse or area-volume relation. He states: "Thus, the ratio of the area occupied by mineral A to the area occupied by all minerals (the total measurement area) is a consistent estimate or the volume percentage of mineral A in the rock." Minerals The minerals observed in thin section examination are here described by their diagnostic characteristics and listed in the order of decreasing abundance. Quartz (Chert) - Chert is defined for this study as a chemically precipitated silica which has been recrystallized 26 to microscopic quartz grains. The grains are colorless in plain light and exhibit undulatory extinction between crossed nicols. The diameter of the average quartz grains is 0.006 mm. but extremes in grain Size ranging from 0.005 mm. to 0.3 mm. in diameter were noted. Chert is the major constituent of the ”oxide bearing member" and exists in massive to thin. layers interbedded with carbonate. Carbonate - The predominant amount of carbonate is of anhedral grains usually less than 0.6 mm. long and one-half as wide. Uhder plain light it is cloudy gray to colorless and between crossed nicols a gray brown. The author observed a minor quantity of colorless to high interference order white rhombs in association with fine to medium grained chert. These euhedral grains are up to 0.2 mm. long. Both varieties usually exhibit rhombohedral cleavage lamellae. Magnetite - Minor amounts of this mineral are in individual opaque octahedrons or dodecahedrons. Most of it however, occurs as subhedral, anhedral and rice—like grains. ginnesotaite - This hydrous iron silicate appears as radiating bundles of needles or plates, averaging 0.03 mm. long, scattered in the chert layers. It is colorless or may be gray-green to yellowish. Parallel extinction, high birefringence and little pleochroism are distinctive optical properties of minnesotaite. According to Gruner (1944B) minnesotaite varies between considerable limits in the ratio 27‘ of F8" to Fe"'to Mg. This mineral has a talc crystal structure revealed by X rays. Gruner (1944B) assigns the following chemical formula to minnesotaite: (011)“ (Fe", Mg)ll (Si, Al. Fe"')16 057 Stilpnomelane - This mineral is abundant in the two "slate" members and appears in minor amount in the "Iron formation". In core pieces it is seen as green to black needles, in crushed core as green-black plates or blades and in thin rock section as blades averaging 0.2 mm. long. It occurs in the chert and carbonate as sheathes and irregular fibers of yellow-green ferrous and yellow-brown ferric forms. Pleochroism of stilonomelane is distinct, except in places where finely grained crystals are not aligned parallel to each other. In the latter instances it is impossible to distinguish stilpnomelane from the other hydrous iron silicates. It crystallizes as a mics and chlorite unit cell structure. The chemical formula proposed by Gruner (1944A) for stilp- nomelane is (0H)4 We", Mg, A1, Fe"')7-8 SilBOZS-Eél 2-4 H20 Limonite - Limonite is described by Dana (1944) as a cryptocrystalline goethite containing absorbed water. A portion of the staining is probably lepidocrocite, which is dimorphous with limonite. This hydrous ferric mineral is observed as yellow to orange-red colored staining under reflected light and is semiéopaque in plain light. Hematite (Martite) - The hematite observed is pseudo- morphous after magnetite. Han (1957) describes martite as: ". . . actually a hematite aggregate, usually containing variable amoun s of magnetite and occasionally goethite and pyrite, which is contained within the crystal form of magnetite or pyrite . . ." - Han states further that it is formed by diffusion of oxygen along the fine grained crystal boundaries of the magnetite crystals. Martite is observed as a ruby red colored mineral under reflected light. Muscovite - Muscovite is present in minute amounts associated with quartz, carbonate and magnetite. It is colorless in thin section with plain light and the grains appear as low relief blades and scales. Muscovite exhibits very little pleochroism, but has marked interference colors of violet, blue, green and red. Optically it has a small 2V and is negative in sign. gyrite - This iron sulfide occurs in small irregular grains in the extremely fine grained carbonate bands. Also a very small quantity was seen in the chert layers Graphite - The author observed minor amounts of minute plates of a black opaque mineral thought to be graphite in the fine grained carbonate layers. "Upper and Lower Slates" The upper and lower "slate" members are very similar in mineral content and textural appearance. They both are non-magnetic to only slightly magnetic, usually thin to medium banded and composed of fine to very fine grains. The bands generally consist ofalternating light chert layers and extremely fine grained dark carbonate bands. Minor quantities of pyrite and apparently some graphite are associated with the carbonate layers. Carbonate occurs generally as masses of very small anhedral grains. a relatively large amount of individual carbonate rhombs averaging 0.6 mm in length are located in portions of the "Upper slate". Bradshaw (1956) has noted that the carbonate in bands is anhedral while that occurring in the adjacent chert is euhedral in grain boundaries. This» he explains, is because of its greater power of crystallization and/or recrystallization of the carbonate during diagenesis and lithification. Quartz, carbonate, stilpnomelane and minnesotaite constitute the major mineral components of both of the "slate" members. Minnesotaite is abundant in the chert as colorless needles and also in minor proportions of light green irregular patches. Blades, sheathes and stringers of stilpnomelane occur in the chert and carbonate groundmasses. An insignificant quantity of magnetite was observed in the "Upper slate". 30 Figure 8. Photomicrograph of A1-#15-22' showing banding of dark carbonate and light chert layers. Plain light, x40 diameters.. Figure 9. Photomicrograph of Al-318-1fl0L150' showing stilpnomelane blades in chert. Plain light, x200 diameters. Considerable hydration of carbonate to limonite was observed in diamond drill holes Al-fizo-od' and Al-#ll-60'-65'. This secondary alteration indicates probable recent hydration from the present weathering surface. "Iron Formation" The color of the "Iron formation" is light to dark gray but at various places it is altered to a brown-gray, yellow-gray and very frequently to a pink gray. The formation is normally of fine grained material with dis- seminated larger crystals, plates and stYlolitic-like thin wavy bands of magnetite. Also distinctive yellow-buff patches and bands of carbonate are common. From field evidence it is apparent that magnetic attraction changes with different concentrations of magnetite. The majority of the rock is composed of chert.commonly with an average diameter grain size of 0.006 mm. Carbonate is overwhelmingly of anhedral grains in layers and irregular patches. Interspersed oval to bean shaped granules are composed entirely of carbonate or varying amounts of chert and carbonate. Individual carbonate rhombs are surrounded by fine grained chert and commonly have a poikilitic texture with inclusions 0f quartz grains. This texture may be due to recrystallization of quartz and carbonate, although an 32 Figure 10. Photomicrograph of Alq#15— 5' showing the contact of chert and carbonate la ers. Magnetite (black) in carbonate. P ain light, x200 diameters. Figure 11. Photomicrograph of Ss-#25- llO' showing minnesotaite blades, carbonate, stilp- nomelane (dark gray) and magnetite in chert. Plain light, x200 diameters. interstitial introduction of both can be speculated. Magnetite exists as irregularly shaped aggregates of anhedral grains and-interlocking rice—like grains in distorted fabrics. Magnetite very frequently is observed to partially P301808 the Peripheral portions of the carbonate granules. The substituted parts of the carbonate grains are anhedral to rice-like in shape, which points out an extensive replace- ment of pre-existing carbonate by magnetite forming what are now predominant textures in some horizons of the "oxide bearing member". A small amount of euhedral grains of magnetite are present. There is a minor amount of minnesotaite and stilpnomelane in the iron formation compared with the "slate" members. A small quantity of the rice-like grains of magnetite may be pseudomorphous after minnesotaite needles and plates. The author viewed several location in thin section where stilpnomelane was partially replaced by sibhedral to anhedral grains of magnetite. The muscovite content of the "Iron formation" appears to be confined to occurrences in the Albanel Sheet area. It was observed in four rock thin sections, three of which were at the 100' horizon. Under high magnification miscovite has a clean boundary with the associated chert, carbonate and magnetite. The scales of muscovite are differentiated by their brilliant colors between crossed nicols. Needles of chlorite appear in the muscovite scales. The rounded 34 Figure 12. Photomicrograph of Ss—fi24-20A showing small anhedral and large rhombs of carbonate. Stained rings are limonite. Plain light, x200 diameters. Figure 13. Photomicrograph of A1-#20-38' showing carbonate granules in short. Staining is limonite. Plain light, x200 diameters. 35 form of the scales denotes a probable clastic origin. Incipient hydration shown by yellow to orange-red. semi-opaque smears and stains of limonite abound in the carbonate masses. Thin section 83-329-4' displays unlSlal oval rings, probably of limonite, which appear to cut across the equal grained chert when viewed between crossed nicols- The ring-like nature and apparent penetration of these stains may be explained by the fact that a thin section consists of more than on plane. Thus the rings could be above the chert it seems to out. Also during original formation an iron bearing mineral was collected around granules composed of chert and carbonate. A matrix of grains very similar in size to the chert of the granules were later crystallized in a surrounding groundmass. Hydration of the iron took place at a later time. Martite is observed as a rim replacement of large magnetite grains, and as pseudomorphs after dust size euhedral magnetite grains. The magnitude of secondary alteration can be only roughly estimated and this is tabulated in Tables II through X. The amount of hydration and oxidation observed is attributed to shallow burial or exposure to the present land surface. The proceeding paragraphs are a summary of the textures, mineral composition and relationships of the "Iron formation" that are included in Tables II through x, Figure 14. Figure 15. PhotomicrOgraph of A11#15—137' showing poikilitic texture of the carbonate and magnetite in irregular masses. Plain light, x200 diameters. Photomicrograph of Ss-#24-l25' showing stilpnomelane (medium gray) and carbonate replaced by magnetite all in chert ground- mass. Plain light, x200 diameters. 37 To estimate the mean volume percentages of the mineral constituents, especially the magnetite, the author made a petrographic modal analyses on approximately 50' and 100' horizons of diamond drill core fragments in the "oxide bearing member". The selection of the two horizons was made as randomly as possible to be consistent in finding the unbiased means of minerals of theformation. In each case the sample nearest the selected horizon was analyzed. The estimated volume percentages are listed in Tables II through IV. An attempt was made to predict the variance of the estimates from the means of the minerals. Thin section Ss-#35-65' was selected to test the reproducibility error, because it was a slide of excellent random.spacing;of minerals. Theoretically this rock section shoild mark the upper limit of accuracy in the counting method. The writer determined an average deviation of 1.3 % from the mean of each mineral on three equal length traveres made on separate occasions. An error possibly greater than 1.3 % per mineral would therefor be inherent in counting, if compensating errors are neglected in our measurements. It is difficult to estimate the analytical error due to inconsistent banding and the bladed nature of minerals as compared to the ideal oval shaped grains. The analytical error is then an unkown increment added to the counting error and as a result the combined total error could not be estimated. However chert, carbonate 38 Photomicrograph of Al-filS-IBZ' showing stilpnomelane (medium gray) at border of magnetite.bands. Plain light, x200 diameters Figure 16. Figure 17. PhotomicrOgraph of A1-#15-57' showing a granule of carbonate (medium gray) and muscovite (light gray) ringed by magnetitein.chert matrix. Crossed nicols, x200 diameters. and magnetite compose the overwhelming percentage of the cores and their respective estimates should have merit. The validity of estimatzs of magnetite is proved by comparison of modal analyses computations and metallurgical test results of the same cores. The author assumed the iron content of magnetite to be 72 % and that of carbonate 48 %. The average total iron percentages, in correlation of modal analyses computations with the average listed percentages of 100 mesh metallurgical tests, differed by 2 %. It follows that the magnetite, carbonate and chert volume percentages from modal analyses are valid. The congruence of results indicates the carbonate to be of the variety siderite. Also that the secondary alteration minerals and iron silicates contain a very insignificant amount of the total iron of the formation. No perceivable mineralogic gradation appears-in comparing the two horizons in tracing them from west to east. The computed means of the minerals in the horizons indicate that the upper one has less chert than the 50' horizon. Thus the 100' horizon has a favorable gain in magnetite and silicate minerals.‘ The volume percentages of the major minerals are generally constant throughout the horizons analyzed. In view of this average content a suitable "mill feed" for concentration may be planned by by metallurgists for the "oxide bearing member" of the Temiscamie iron formation. 40 In detailed examination of slides from cores of the Sandspit and Albanel Sheet areas the writer observed a sequence of development to the present mineralogic content. Stilpnomelane appears in both the chert and carbonate masses. Minnesotaite is observed along the boundaries of the carbonate in the chert. additional stilpnomelane, carbonate and minor amounts of euheeral grains of magnetite also occur in the chert. This sequence of crystallization from stilpnomelane to the chert probably took place during diagenesis. The author favors Gruner's explanation of the paragenesis of the minerals and thinks it may apply to the Temiscamie iron formation. Gruner (1946) writes: "As stilpnomelane is from, let us assume, a colloidal gel, it will take the ions in its neighborhood which are most convenient and of the necessary charge. If it cannot find any more it will stop growing. The leftover gel material, then, may be of the proper composition to form minnesotaite or greenalite, or quartz and siderite, 1r Co is available in considerable concentration." 2 The magnetite in the "Iron formation" appears to have more than one generation of development. Euhedral grains in the chert may be of primary origin. However the predominant amount of the magnetite is secondary. With further research a more complete genesis of the magnetite might be determined. The writer would like to suggest an idea on the formation of magnetite from Dre-existing carbonate and stilpnomelane. James (1954) describes a burial environment possessing a lower redox potential than a deposition environment. With less available oxygen, and at the same time the action of 41 the organic material present in the original material: reduction of the iron oxides in the mud takes place as the material is isolated from the oxygenated waters by burial. CONCLUSIONS Detailed laboratory examination cu‘ core samples revealed certain conclusions relative to the textural relationships and mineralogic content of the "Iron formation”. Macroscopic study pointed out three divisions in the Temiscamie iron formation. The "Upper slate" and "Lower slate" members consist generally of interbedded light cherty and dark extremely fine grained carbonate. Minnesotaite and stilpnomelane are found abundantly in some portions. These two divisions were considered only as a background microscopic study for the "oxide bearing member" and are named "slate" because of their field appearance. The ”Iron formation" is usually gray colored but often tinted pink. Microscopic examination of thin sections indicates irregular patches of anhedral carbonate and bean shaped granules composed of carbonate with minor amounts of chert in an equal- grained chert matrix. A small quantity of minnesotaite and stilpnomelane occurs in the "oxide bearing member" Muscovite in minute amounts was observed in certain horizons. A sequence of crystallization of the formation from.a colloidal gel with initially crystallized stilpnomelane to a finely crystallized.chert groundmass is thought to have taken place during diagenesis. Poikilitic textures of rhombs of carbonate, with included quartz grains, indicates a possible post diagenetic recrystallization of carbonate and quartz. 42 45 Magnetite is predominantly of secondary origin. The pre-existing carbonate is replaced by an abundance of rice- like and anhedral grains composing irregular aggregates occurring throughout the "Iron formation". Development of the magnetite is thought to have been in a reducing environment. Petrographic modal analyses made upon thin sections from core fragments at approximately 50' and 100' horizons of the "oxide bearing member". The modal analyses estimation of volume percentages of the major minerals were found to be valid upon comparison with metallurgical test results from the same diamond drill cores. The total iron computations from modal analyses indicated the carbonate to be of the variety siderite. Also an insignificant amount of the total iron of the "Iron formation" is from the combined iron content of limonite, martite and the hydrous iron silicates. No observable mineralogic gradations from the estimates of modal analyses were delineated along the strike of the "Iron formation". Patches of color variations are not related to essential differences in mineralogic composition. The lack of variance of the chert, carbonate and magnetite minerals suggests that the "oxide bearing member" is uniform and will lend itself to large scale exploitation in the Sandspit and Albanel Sheet areas. SUGGESEIONS FOR FURTHER STUDY This detailed examination of drill cores has delineated several problems for further study. Among the most fertile for research are the following. 1. An intensive laboratory investigation of the Mistassini series sediments to determine the paragenesis might prove valuable. Priority should be placed on the study of the "Iron formation" with the determination of the genesis of the magnetite emphasized. 2. A trace element study of the Temiscamie iron formation may suggest important implications on the source material and the environment of deposition of the iron-rich sediments . 3. Identification of the suite of hydrous iron silicates appearing in thin sections may be confirmed by X ray work. 4. Possible effects of structural features upon exploitation of the "oxide bearing member" might possibly be pointed out by careful field mapping. 5. A petrofabric study by plotting c-axes 0f the quartz grains may provide further evidence for secondary recrystallization of the formations of the region. 44 REFERENCES BRADSHAW, B. A. (1956) Petrologic comparison of Lake Superior iron formations: Toronto Univ., Unpublished PhD. thesis. CHAYES, F. (1956) retrographic modal analysis: John Wiley and Sons, Inc., New York. DANA, J. 0., and E. S. (1944) System of Mineralogy: 1, ed. 7, by Palache, C., Berman, H., and Frondel: John Wiley and Sons, Inc., New York. GRUNER, J. W. (1944A) The structure of stilpnomelane reexamined: Am. Mineralogist, vol. 29, pp. 291-298. (19448) The composition and structure of min- nesotaite - a common iron silicate in iron . formations: Am. Mineralogist, vol. 29, pp. 565-572. : —-—- (1946) The mineralogy and geology of the taconites and iron ores of the Mesabi range, Minnesota: Office of the Commissioner of the Iron Range Resources and Rehabilitation, St. Paul, Minnesota. HAN, TSU—MING (1957) The genetic relaionships between magnetite and hematite with a special note on martite: from paper presented at The 5rd Annual Institute on Lake Superior Geology, East Lansing, Michigan. JAMES, H. L. (1954) Sedimentary facies of iron formation: Econ. Geol., vol. 49, pp. 255-295. MAWSSLEY, J. B., and NORMAN, G. W. H. (1955) Chibougamau lake map-area, Quebec: Geol. Surv. Can., Mem. 185. NEILSON, J. M. (1955) Albanel area, Mistassini Territory: Quebec Dept. of Mines, G. R. 55. NORmAN, G. W. H. (1940) Thrust faulting of Grenville gneisses northwestward against the Mistassini series of Mistassini lake, Quebec: Jour. Geol., V01. XLVIII, no. 5, pp. 512-525. 45 WAHL, W. G. (1955) Temiscamie River area, Mistassini Territory: Quebec Dept. of Mines, G. R. 54. Demco-293 Date Due "Iilliliiill'lil'iilr