STRATIGRAPHY AND STRUCTURE OF A PORTION OF THE menmmmou AT LAKE ALBANEL, QUEBEC Thesis {or the Degree of M. S. MICHIGAN STATE UNIVERSlTY James T. Neal 1959 r’vub .3. _ st am: .. . u... a (5.. ..v9QOYJ'AA‘“’ g .u 9.. STRATIGRAPHY AND.STRUCTURE OF A PORTION OF THE IRON-FORMATION AT LAKE ALBANEL, QUEBEC BY James T. Neal A THESIS Submitted in partial fulfillment of the requirements for the degree of Easter of Science in Michigan State University East_Lansing, Michigan 1959 ABSTRACT The Lake Albanel iron range is located in central Quebec approximately hOO miles north of Montreal. It is felt by many geologists that the sedimentary sequence in this area is a continuation of the Labrador trough, located to the. northeast. L A portion of the range, known collectively as the "B" Group area, has been studied because stratigraphic and struc— tural trends were previously somewhat indeterminate due to complex folding and faulting. It is believed that the Grenville orogeny may be responsible for these dieturbances subsequent to the deposition and lithifaction of the rocks. Core specimens and thin and polished sections from 23 diamond drill holes were examined. The stratigraphic suc- cession consists of sediments of the Mistassini series which overlie older gneisses and granites, and associated igneous and metamorphic rocks. From oldest to youngest, the rocks encountered in the "B" Group are: (1) Upper Albanel dolomite formation; (2) Boulder Bay quartzite formation; (3) Temiscamie iron-formation which consists of (a) lower argillite member, (b) lower sideritic chart and iron silicate member, (c) mag- netitic hematitic sideritic-dolomitic chert member, (d) up- per stilpnomelane argillite member, (6) upper sideritic chert member, (f) fine-bedded magnetitic iron silicate member; (h) Kallio slate and graywacke formation. Although the upper and lower sideritic cherty and arg- ii‘ illitic members have similar lithologic characteristics, studies reveal that they usually can be distinguished by their own distinctive mineralogic assemblages and textural varia- tions. Structurally, the "B" Group displays a series of trun- cated, sometimes overturned, anticlines and synclines. They strike generally to the northeast and are complexly faulted in some places. Stratigraphy in the "B" Group portion of the range has been compared with that found in.other parts. Consistent . variations have been observed. The iron-formation has characteristics similar to that of the extensively studied "Lake Superior type" iron form- ations. It seems highly probable that the Temiscamie forma- tion was deposited under similar conditions and possibly at the same time in geologic history. 111 ACKNOWLEDGMENTS The author wishes to express a most sincere thanks to those who have aided in this study. Special thanks goes to Dr. Terence T. Quirke, Jr. for much advice and information which laid the foundation for the investigation. The following members of Michigan State University's departmemnt of geology have been of immeasurable assistance: Dr. Justin Zinn has given much advice and constructive crit- icism, and valuable suggestions have been.made by Dr. James Trow and Dr. B. T. Sandefur. Dr. H. B. Stonehouse has aided in x-ray determinations, and Mrs. Jane E. Smith has donated much time and help in preparing the photomicrographs. He is also deeply indebted to the Cleveland-Cliffs Iron Company for financial assistance, samples, and equipment. In this connection the suggestions and c00peration of Mr. Burton H. Boyum were invaluable. iv TABLE OF CONTENTS Page INTRODUCTION ....................................... 1 Location and Accessibility ....................... 1 Physical Features and Slimate .................... 1 Exploration History .............................. 3 hegional Geology ................................. h Purpose and Scope ................................ 8 Procedure ........................................ 11 "B" GROUP STRATIGRAPHY ............................. 12 Upper Albanel Dolomite Formation ................. 1h Boulder Bay quartzite Formation .................. 15 Lower Argillite Member ........................... 17 Lower Sideritic Chert and Iron Silicate Member ... 2O Nagnetitic Hematitic Sideritic-Dolomitic jhert P’ember 00.0.0000...0.0.0...0.000.000.0000... 21!- Upper Stilpnomelane Argillite Nember ............. 38 Upper Sideritic Chert Member ..................... Ml Fine-Bedded Nagnetitic Iron Silicate Member ...... hS Kallio Slate and Graywacke Formation ............. Mg STRATIGRAPHIC DISTINCTIONS ......................... 51 COMPARATIVE STRATIGRAPHY ........................... Sh Boulder Bay Quartzite Formation .................. 5h Lower Argillite Member ........................... 5h Lower Sideritic Chert and Iron Silicate Member ... 5h Magnetitic Hematitic Sideritic-Dolomitic Chart yember 0.00............OOOOOOOOOOOOI.0...... 55 Upper Stilpnomelane Argillite Member ............. S7 Page Upper Sideritic Chert Member .................... 57 Fine—Bedded Nagnetitic Iron Silicate Member ..... S7 STRUCTURAL INTERPRETATION ......................... 58 ORIGIN OF THE IRON FORMATION ...................... 69 CONCLUSIONS ....................................... 72 SUGGESTIONS FOR FURTHER STUDY ...................... 73 fig-:G‘EFIETJSES ..........OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 7h vi Figure pr \0 co «I O‘U'l 10 11 Table 1 LIST OF FIGURES Location of the Thesis Area .................... Location Nap of the Lake Albanel Iron Range, Quebec .0000000000.0000000000000000.00000.000000 Geologic Map of the "B" Group .................- Composite Stratigraphy and Attitudes of "B" Group Drill Holes .......................... Structural Cross-Section Along Structural Cross—Section Along Structural Cross—Section Along Structural Cross-Section Along Structural Cross-Section Along Structural Cross-Section Along Structural Cross-Section Along TABLES Line Line Line Line Line Line Line 9000' 6000' 3000' 0' N 2000' 3000' 6000' S S S N N N Stratigraphic Column of the Area -............. vii Page 2 10 13 59 so 62 63 61; ee 67 Page 5 LIST OF PLATES Plate Page 1 Photomicrograph of 8-11 at 69' showing rounded chert grains within lower argillite member ......OOCOCOOOOO......OIOCCO... 19 2 Drill cores of cherty taconite ................ 2S 3 Drill cores of irregularly banded cherty taconite ...00.0.0000......OOOOOOOOOOOOOOOOOOOO 2? h Drill cores of oolitic and granular cherty taconi-te ......O......OCCOOCOCOCOCCC0.00.0.0... 27 Drill cores of mottled cherty taconite ........ 27 Photomicrograph of 8-18 at 303' showing chains of euhedral magnetite in chart matrix 00.000.00.00...........OOOOOOOOOOOOOOCOC 29 7 Photomicrograph of B-18 at 303' showing relations of chart within magnetitic member ... 29 8 Photomicrograph of B-lS at 187' showing granules with magnetite rims in chart ......... 30 9 Photomicrograph of B-ll at 392' showing relations of magnetite, carbonate and chart ... 30 lO Photomicrograph of polished section from 8-22 at 22h' showing relations of hematite and magnetite bands .........OCOOCOOCOOOCOOCOOO 31 ll Photomicrograph of 8-13 at 31' showing hematite (martite) alteration from magnetite in the rims of granules ............. 32 12 Photomicrograoh of 8-19 at 293' showing blades of green stilpnomelane in Carbonate .... 3h 13 Photomicrograph of 3-11 at hh?’ showing brown stilonomelane near magnetite nCtthdI'éi .....OOOOOOO........OOOOOOOOOODOOOOOO 31‘- 1h Photomicrograph of 8-25 at 77' showing confused fibrous aggregates of minnesotaite in Cher't 00000000000000.0000...000000.00.000.00 1?; 15 Photomicrograph of upper argillite showing stilpnomelane needles in carbonate matrix ..... 39 viii Plate 16 17 18 P Photomicrograph showing relic oolites in Chart 0.00.00.00.00........OOOOOOOOOOOOOOO0.... Drill-cores of fine—bedded cherty taconite .... Photomicrograph of B-lQ at 98' showing finely bedded magnetite and hematite in matrix of carbonate ........................... ix INTRODUCT ION Location and Accessibility The area under consideration is situated in Mistassini territory, Quebec, and is bounded by Lake Albanel on the west and the Temiscamie River on the east (Fig. 1). Approximately 250 miles due east of the southernmost extremity of James Bay and 175 miles north of the agricultural region of Lake St. John, the area lies on the contact between Precambrian sed- iments and the underlying complex of granite gneisses which are thought.to be of early Precambrian age. Access to the area in 1957 was most easily accomplished by a 100 mile flight from Chibougamau, which lies to the southwest. Abundance of bodies of water makes accessibility by float planes relatively easy. Physical Features and Climate The region exhibits the moderate relief typical of the Canadian Shield. Maximum relief in the map area is 350 feet. Minor streams and small bodies of water are everywhere. Drainage is via Lakes Albanel and Mistassini and thence by the Rupert River to James Bay. ' The topography is clearly an expression of the bedrock, however glacial deposits conceal rock exposures. Many eskers, drumlins, and outwash plains are evident in the area. E 3 O O f: :3 JAMES BAY 52°N a . 52°N // /. P ' . a u ... R TEMISCAMIE 5 «A QUEBEC L o 750 N , §L°N CHIBOUGAMAU (l)— 410 BIO L. ST. JOHN me Q 03' 03 t J.T.N. L958 3 F'lG.l LOCATION OF THE THESIS AREA Vegetation consists of heavy forests of black spruce and balsam on high ground and muskeg sections in swampy areas. Jack-pine, tamarack, and white birch stands are also abun- dant. The climate is characterized by short, rainy summers and long, cold winters. Average annual rainfall is 35 inches and the mean annual temperature is 31.h°F., yet winter temper- atures as low as -60°F. have been reported. Exploration History Earliest reports of the region have come from the ac- counts of missionaries, traders, and explorers in their search for a route from Lake St. John to James Bay (Mawdsley and Norman, 1935). Richardson visited the district in 1870-71 and reported the presence of flat-lying limestones at Lake Mistassini. A. P. Low in 1886 called the Mistassini series Cambrian be- cause of similarity to rocks exposed on the east side of James Bay which were at that time thought to be Cambrian. Because of algal structures, Barlow in 1910 classified the sediments as Ordovician (Neilson, 1953). More recently, Norman (19h0) described the contact between the sediments and the gneisses of the Grenville sub- province. Neilson (1963) and Wahl (1953) mapped and described the geology of the Lake Albanel and Temiscamie River areas. Their reports are the most recent published information on the area. h Regional Geology Neilson (1951, 1953) and Wahl (1953) have described the regional stratigraphy Of the area. The oldest rocks in the area (commonly referred to as the basement complex) are a complex of granites, orthogneisses, and paragneisses. Unconformably overlying this complex are sedimentary strata of younger age (see Table 1). These sediments and the complex of gneisses have been intruded by pegmatites, and alkaline and basic plutons. The basement complex or rocks similar to it are exposed east of the Temiscamie River (Fig. 2) which many geologists feel is the boundary of the so called "Grenville front". This is the tremendous fault zone that is considered to sep- arate "Huronian type" sediments from "Grenville type" rocks. This fault is believed to continue on to the region of the Labrador trough. It is thought that the Grenville gneisses in this area have been thrust northwestward over the sediment- ary strata. Sediments of the Papaskwasati group (Neilson, 1951) rest with angular unconformity upon the basement complex of gran- ites and gneisses. Papaskwasati sediments are only found north of Lake Mistassini. With conformable relations, dolo- mites of the Mistassini series” were then deposited during later Precambrian times. The dolomite succession is divided * Neilson (1953) feels that "group" is a better term than "series" according to stratigraphic usage. Series has been retained to avoid confusion since it has already appeared in the literature. TABLE 1 STRATIGRAPHIC COLUMN 0? THE AREA Rock units Lithic character Thickness Pleistocene Stratified sands and gravel, till variable Great unconformity ? Grenville progeny ? (Quirke, 1958) Intrusive Basic and alkaline intrusives contact Kallio fm. Slate, graywacke 4800' 16) Fe-sil. iron-formation 0-150' (5) Upper aid. chert 309' (h) Upper stilp. argillite 3-;0' :25 3 TeTiggamie T3) ifagnetitic Fe-carb. 0-200' :z *4 formation cherty iron-formation gi 3 (2) Lower sideritic chert 5-50' <£ m 1) Lower argillite 15-50' J_ t) "w m *4 Boulder Efi .E Bay fm. guartzite, siltstone 20—110' , m ——————-Disconformity 55 3 Upper 6* -§ Albanel Arenaceous dolomite 2000' S --3 formation 2 Disconformity ? Lower h000'- Albanel Shaly dolomite 7800' (?) formation Papaskwasati Quartz sandstone, pebble group conglomerate Unconformity gym,Granite and Granites, Neilson 53:5 gneiss orthogneiss, (1953) 8: Egg complex paragneiss Wahl (1953) after Neilson (1951, 1953). Wahl (1953). and Quirke (1958) 5/000’1'] $NONJHO£(:> 1 5:. A ~o TRour POINT p SCALE: ll I :.: Io,ooo’ [/73'OO’N ’ / LAKE //ALBAN£'/__ . ‘ POINI‘ DE ,4 BA" / L'RFFLE'URMENT' P'TAOE ace/105A KU ' 6" POINT or L'fS/c’ffi? S LAC [/zvfl? PLAT'E'AU s KALL/o LAKE CAN 0 LAN: BAY RUTH ‘O Inga.“ LAKE TEM/SCAM/f R/Vf’q coom ‘55 LAKE /'--'—-.‘-:\\ / ' l 0” ‘ N£MINE v99 JV“ / , /dq> ) AIL W1.» W WW \ INFERRED QRENVILLE FR / / 73°oo’w/ 5/°oo'/v FIG. 2 LOCATION MAP OF THE .LAKE ALBANEL IRON RANGE, QUEBEC ~ by a disconformity into two well stratified members: (1) the Lower Albanel formation which contains dark gray, ferruginous and shaly beds and is exposed in the Mistassini lake basin; (2) the Upper Albanel formation which consists of sandy dolo- mites and is exposed in the Lake Albanel area. Disconformably overlying the dolomite succession is the Boulder Bay quartzite formation, the Temiscamie iron-form- ation, and the Kallio slate and graywacke formation. A com- plete description of these rocks is found in a later section of this paper.) The Mistassini sediments strike northeast and dip gently to the southeast. The regional structure is inter- rupted locally by small folds and faults. Approaching the inferred "Grenville front", the angle of dip of the beds increases rapidly. Correlation with similar rocks elsewhere is exceedingly difficult, if at all possible, due to the lack of mapping between areas where more geologic information is available. Neilson (1953) has pointed out the lithologic similarity between the Temiscamie iron—formation and the Animikie (Upper Huronian) formations of the Lake Superior region. It must be pointed out that this can be no more than a tentative classification until further work is done in surrounding areas. A’I'O/Kho dating on several selected samples was under- taken by T. T. Quirke, Jr. under the supervision of S. S. Goldich of the Department of Geology and Mineralogy, Univer- sity of Minnesota. Dates obtained reveal that the Grenville type rocks exposed at Lake Albanel compare favorably with dates obtained from the Grenville elsewhere; however, the metamorphism of the Grenville is apparently younger than the Temiscamie iron formation. This demonstrates that the Gren- ville complex cannot be considered older than the Mistassini _series as intimated by Neilson and Wahl (Table 1). Dates on the iron-formation indicated a younger age than the Huronian iron-formations of the Mesabi type. It is thought by many geologists that the Mistassini trough is an extension of the Labrador trough. If these dates are absolute, then the Quebec iron-formations are post- Huronian. T. T. Quirke, Jr. has suggested that subsequent metamorphism has reduced the argon content of the Mistassini series and that possibly the ages are only apparent, inti- mating that the Temiscamie iron-formation.may be the same age as Lake Superior iron-formations. Certainly further dating will have to be done before any true ages may be ascertained. Purpose and Scope During the field season of 1957, the writer became in- terested in the iron formation exposed at Lake Albanel. Mr. N. R. Sutton of Albanel Minerals Limited has suggested the following problem in order to obtain more information. Be- cause of apparent economic possibilities for the "B" Group portion of claims (see Fig. 2), an adequate structural in- terpretation is essential in preliminary exploration. Inadequacy of surface exposures has necessitated a detailed study of diamond drill cores to reveal more clearly the structure and stratigraphy. Twenty-three diamond drill holes were drilled during the field season of 1957 (Fig. 3). Un- fortunately, criteria for distinguishing between the differ- ent units of the Temiscamie iron-formation have not been firmly established. Preliminary studies reveal that the sideritic cherty and argillitic members underlying and over- lying the magnetitic member reveal clues for distinguishing them. In an effort to establish more definite criteria for their prooer stratigraphic sequence in the "B" Group, a micro- scopic examination was undertaken of cores from each of the diamond drill holes. In an effort to ascertain variations of the iron-rich layers, thin and polished sections of these horizons have been examined. The mineralogy, texture, and other features were studied to see what changes the "B" Group might have as compared with other parts of the iron-formation. Overall stratigraphy of the "B" Group has been compared with other portions of the iron-formation to point out dis- tinctions which should facilitate future exploratory work. Structural interpretations, dependent on the stratigraph- ic interpretations, have been made. This work combines with field mapping which was done by T. T. Quirke, Jr. and others (see Fig. 3). LEGEND 4 KALLK) SLATE FORMATKnJ 3 TEMiSCAMfiE IRON-FORMATION f. fine-bedded mogFe sil. mbr. e. upper siderific Cher? mbr. d. upper sfilp. argillife mbr. c. mog.hem. sid.—do|. Cheri mbr. {a lower sid. Cheri *8 Fe sil. mbr. a. lower orgiHife mbr. 2 BOULDER BAY QUARTZH‘E FM. 1 UPPER ALBANEL DO’L. FM. —+—- SYNCLMEL -F+ U , PLUNGMKS —+—— ANTKHJNE ~4—+ " ,PLUNGWKS —$%— " ,OVERTURNED ~R—- SYNCUNE, " ,1“ STmKE AND ow or BEDS “a " " ,OVERTURNED WLITHIC BOUNDARY ““ —‘— AXIAL TRACE OF FOLD W W FAULT d-/ o DIAMOND DRILL. HOLE d '9 O 500 IOOO L _J J FEET “B” GROUP GEOLOGY offer T.T. QuirkeIJr. (I958) 11 Procedure A complete visual re-logging of the skeleton drill cores was undertaken in each of the 23 diamond drill holes. This was done in order to determine any additional lithologic or textural variations not previously noted and to choose logical points where microscopic examination would be of value. Fifty-five thin sections were prepared and examined from the argillitic and sideritic cherty members. Thirty thin sections and seventeen polished sections were examined from the iron-rich portions. Sixteen additional sections from the Upper Albanel dolomite formation, Boulder Bay quartzite formation, and Kallio slate and graywacke formation were also studied. Thin sections were prepared from chips cut normal to the bedding. Commonly accepted petrographic techniques were employed throughout the investigation. 12 "B" GROUP STRATIGRAPHY The following account is a description of the rocks en- countered in "B" Group drill holes (Fig. 3). Log records of these holes are presented graphically in Fig. h. Only one hole (B-21) was drilled deep enough to reach the Upper Albanel dolomite formation, however several holes penetrated the Boulder Bay quartzite formation. A somewhat brief de- scription of these formations is given because they are gen- erally easy to recognize when found. At times, however, the lower chert member could conceivably be confused with the Boulder Bay quartzite formation. figmenclature- Chert is defined in this study as micro- crystalline quartz that has crystallized from a colloidal gel. Size distinction would include those sizes less than 0.03 mm. The terms mosaic quartz and quartz are reserved for the larger sizes. The general term "carbonate" is used in some instances where mineralogic distinction is nearly impossible due to extremely fine sizes, as well as intermixing between differ- ent varieties. At least two carbonates have been identified. X-ray determinations by both quirks (1968) and the author reveal that siderite and dolomite are present. fiefractive index measurements on the no of the dolomite suggest it should be placed in the ankerite class. Indices of the nO between 1.70 and 1.80 as well as association with iron-rich minerals support this conclusion. I I? I— U . ‘fi 3‘ B—l B—2 B—3 B—4 B—e 'B—7 B—B B-e B—Io B—II B—I2_ B—I3 B-I4 B—I5 B-I6 B—IB B—Ie B~2o B—2I B—22 B—24 B—25 B—2e o LEGEND 0' )Sf 31 X )1 id 131’ )sf )6 )8f )1 31 )1 )1 0I .... - .E _. ... “‘ __ ~-*“ t“ .... I:- .... , _ .... .. L; .... i ~ B e I L , -' .. 2:: ° ' o 4 == we _ M :1: o O STRATIGRAPHIC DIRECTION YOUNGEST To I O 7 % A E- 1} o , o- I .E. II E; 7: . ? OLDEST) I "T‘ 0 IE é -—- E g - ..Q --‘-I _ . )1 o :2: _ .. : f / E :7; E *5- x: —' [3] THIN SECTION :2"— O - E o _ 5E * ‘— I :0 V " . _200. a: 5' 3‘ ____ E ° ~ --200' [T] POLISHED SECTION 0 _E g g 0 90 . o E E __?__ * ‘ OVERBURDEN : O :5; 'M hi— 0 . Q L b— - VI'S' I _3O_OI I... 9 o . O -300 - KALLIO SLATE AND GRAYWACKE FM. ____ 1 :0" IV“ 1 E E UPPER SIDERITIC CI—IERT MBR. _.___ . 755 o < v25: -- .2 _ . E FINE BEDDED MAGNETITIC IRON —400' a. o i :z: ; _o v *1 400 g SILICATE MBR. O In: _ 0-.- ‘. a C23 UPPER STILPNOMELANE ARGILLITE MBR. a. -—-+ i - V *-- D: L__ . _ _ —500' -3. a - -500' m MAGNETITIC HEMATITIC SIDERITIC— 1r ; as 5 DOLOMITIC CHERT MBR.‘ _.‘__ 4 E 5n) LOWER SIDERITIC CHERT AND IRON :— SILICATE MBR. I LAJ 1500. -600 I— LOWER ARGILLITE MBR. BOULDER BAY QUARTzITE FM. ;7oo' v —700' C] UPPER ALBANEL DOLOMITE FM. SIGNIFIES INTERBEDDING ‘J.T.N. I958 FIG4 COMPOSITE STRATIGRAPHY AND ATTITUDES OF “B” GROUP DRILL HOLES 1h The general term "iron silicates" is also used in some instances where distinction is doubtful. It is often diff- icult to distinguish the iron silicates because of intimate intermixing and fine grain sizes. Minnesotaite and stilp- nomelane have both been recognized and verified by x-ray diffraction patterns. A complete description of these min- erals will follow in a later section of this paper. The word "minor" is used in a compositional sense when the constituent amounts to less than 5% of the rock. Upper Albanel dolomite formation Surface exposgres- The Upper Albanel dolomite is found along the east shore of Lake Albanel on promontories and small cliffs. It is exposed in the "B" Group, apparently because of folding and faulting, near the Temiscamie River. Negascopic description— Appearance in specimens gener- ally shows a dark gray, quite massive, fine grained rock. Sometimes it is banded; the different beds are of differing grain size. Outcrops weather to buff or gray and may exhibit differential weathering along silica-rich bands. Microscopig description- Two thin sections were studied from the "B" Group. Generalizations perhaps should not be made, however the uppermost portion of the formation, although largely dolomitic, clearly is not as pure as that encountered at depth. Graphite and possibly some clay minerals were ob- served in the upper part. The deeper section exhibited 15 minor chlorite and quartz veinlets scattered through the dolomite. Grain size is commonly 0.03 mm or less. Boulder Bay quartzite formation Sgrfgqg equgurgs- The Boulder Bay quartzite formation is found at the surface in several outcrops in the "B" Group where folding and faulting have occurred. The river front and the broad plunging anticline (see Fig. 3) in the north- western portion of this area are locations where the form- ation is exposed. The quartzite can be found elsewhere in the iron range along the lake front and in several other locations. fiegasqqpic descgiptign- When seen by the unaided eye, this formation is nearly always fine grained and usually quite massive although bedding may be observed. Color varies from a very pure whitish-gray to a light greenish-gray, the latter of which seems to most common. A blackish-gray variety is also present. Microscopic; dg§_§1 tign- Several distinct varieties of quartzite are readily apparent in thin section. Most common- ly observed is a very chloritic and impure variety. Quartz content varies from h0¢ to 60 %. Individual grains are ex- ceedingly diverse in both siZe and shape. Grain size ranges from 0.01 mm to a maximum of 1 mm, although an average would be closer to 0.1 mm. Grains generally exhibit maximum angular- ity, although well rounded shapes may also be present. 16 Carbonate is present in the matrix in anhedral grains and may make up as much as 20% of the rock. Chlorite is also oresent in the matrix in variable amounts and explains the greenish cast seen in core specimens. Graphite occurs as a very fine dusty material in minor amounts in the matrix and also imparts darker colors to some of the rock, depending on the amount present. Small grains of microcline and plagioclase may be observed in minor amounts. Small anhedral grains (0.05 mm) of feldSpar are present in several slides in minute amounts. The other (second) type is nearly pure quartzite, but contains minor amounts of chlorite and carbonate. Quartz grains are larger; commonly 0.3 mm in diameter. Very distinct undulant extinction is present in quartz taken near inferred faults. Sutured textures are prominent, and secondary de- velopment of individual grains may be observed. It appears that chalcedonic interstitial material may have been present but has crystallized and now is part of the grains. Minor fragments of micro-crystalline quartz are present as aggre- gate grains. Bglationghips— The Boulder Bay quartzite appears to change gradually into the overlying Temiscamie iron-formation. Ninor interbedding of the two types may occur. There appears to be a tendency for finer quartz grain sizes as well as in- creased chlorite content to appear near the tOp of the form- ation. Angularity of quartz grains also increases. Siltstone is probably a more appropriate name for this type of rock. 17 The second facies described (pure quartzite) appears near the bottom of the formation. The variety of lithologic types reflects conditions of sedimentation that existed dur- ing deposition. Only one drill hole transected the entire formation. Average thickness appears to be about 110 feet. Lower argillite member Sgrfagg expgguges- Outcrops of this member are seldom seen due to the apparent susceptibility of the member to weathering. It is encountered in many of the diamond drill holes, however. Eggggqqgig dgscriptigg- Appearance of the lower argil- lite member in core or hand specimen nearly always shows a very dense and clay-black rock. It is generally very fine grained and often exhibits fine bedding. In some places it is quite massive. Slaty cleavage is not present, although minor slip cleavage was observed in one thin section (Plate 1). Pyrite is frequently observed im minor amounts as euhedral crystals or in layered anhedral masses. Fracturing along graphitic layers occurs frequently in drill core specimens. This member is often interbedded with the overlying lower sideritic cherty member. When this occurs, it is some- times difficult to assume a definite stratigraphic horizon. The lower argillite member is usually non-magnetic, but in several places it is faintly but discernibly magnetic. 18 It appears that distinction between the upper and lower argillite members on the basis of magnetism may have some value when considered with other criteria, but not by itself. Magnetism as a basis for identification will be discussed in a later section of this paper. Eicroscopic dgscription- In thin section the reason for the denseness of the member is readily apparent. Graphite is finely intermixed in a sideritic, chloritic, sometimes ser- icitic groundmass. Very thin layers of graphite with an average width of 0.00% mm account for the easily visible bed- ding. The graphite is opaque in thin section and its presence is readily apparent. It is also found disseminated in the groundmass. Lighter colored carbonate minerals often exist as distinct beds. In most cases the differing shades of gray and black are seen to be a function of the percentage of graphite. The main constituent is exceedingly fine grained (0.01 mm or less) anhedral carbonate, probably of the variety siderite although ankerite also occurs. Some sections are almost en- tirely light-colored carbonate when interbedded with the lower sideritic cherty member or when in proximity to it. In these carbonate-rich sections, both siderite and ankerite are present. Ankerite occurs as euhedral rhombs in a fine grained matrix of chart. Angular quartz grains generally occur in minor amounts, but in a few places constitute a greater part of the rock. Graywacke or siltstone would be a more appropriate name for 19 these horizons. This type is considered as a more clastic facies of the member. Sodic plagioclase grains were seen infrequently in sev- eral thin sections from place to place along the strike. Magnetite frequently occurs in exceedingly fine layers (0.005 mm and less in width), intimately associated with graphite layering. Generally this is not a sufficient amount to make the core specimen.magnetic, even when a strong labor- atory magnet is used. At several places in the group slides show exceedingly well rounded grains of chert interbedded in the normal arg- illite (see Plate 1). Often chlorite occurs in the interiors Plate 1. Photomicrograph of 8-11 at 68' show- ing rounded chert grains contained within the lower argillite member. Bedding horizontal; minor slip cleavage inclined. without analyzer, x32. 20 of these grains in minor amounts. The origin of these is not clear, but due to the extreme roundness and occasional fracturing, the suggestion is offered that they may be oolitic in nature and have suffered some abrasion. jhlorite and sericite occur frequently in the ground- mass. Chlorite is usually disseminated but also occurs in thin bands and layers. Iron silicate minerals generally are lacking, yet where the argillite member is interbedded with the lower sideritic cherty member, minnesotaite may be present in minor amounts. It is then associated with chert-rich portions. Stilpnomelane blades were seen in one of the slides. Relatiqnships- The lower argillite member appears to be gradational into both the overlying and the underlying units. True estimates of thickness are thus quite difficult, if at all possible. The combined thickness of the lower members would probably average about 70 feet. Lower sideritic chert and iron silicate member Surfage expgsgres- This member is observed frequently throughout the iron-formation. Principal exposures are ob- served along the scarp paralleling the shore of Lake Albanel. Outcrops are more frequent where the member is capped by the overlying magnetitic member. "B" Group exposures are fairly numerous and observable in various locations. EEEESCOQLE.QEQQELRELQE‘ When seen in drill core spec- 21 imens the member is typically a dirty buff-gray, quartzitic appearing rock. It is usually well bedded and the basal portion frequently is interbedded with the underlying arg- illite member. Alternating dark gray and lighter colored buff-gray beds are common. Fassive varieties are also present but less common than those exhibiting bedding. Carbonate O content and other compositional variations seem to be the principal factors causing different appearance in core and hand Specimens. When minnesotaite is present, the rocks are greenish-gray. Stilpnomelane, when present, may be detected by very small greenish-black needles visible to the unaided eye. Beds of pure siderite up to several inches in thick- ness may be observed. Pyrite and chlorite are present but occur irregularly. Core specimens may or may not be magnetic. In some cases slight magnetism can be detected with the aid of a laboratory magnet. Nagnetism occurs most frequently when the sample is taken from near the overlying magnetic member. Eigrggqqgiq degcriptigg- Quartz and chert are the most .abundant minerals and occur together in a mosaic texture. Distinction between the two is on the basis of size, although the larger grains are considered to have crystallized from the same original material. Grain sizes of the chert average - 0.01 mm, and the larger quartz grains are usually less than 0'1 mm in diameter. Although quartz comprises 603 of this member, individual sections may show almost all or no quartz. Carbonates are the other major constituents of the member. 22 Siderite and ankerite are present and may occur together or individually, although the former seems more typical. Sid- erite and ankerite occur in anhedral masses with chert with grain sizes averaging only a few hundredths of a millimeter. Larger grains, up to several tenths of a millimeter, are common and may be present within the quartz and carbonate matrix or within quartz-rich portions. Ankerite may constitute the greater majority of some beds. In this situation, it occurs in fairly large subhedral crystals. It occurs also in euhedral rhombs in quartz and with quartz in thin veinlets transecting the rock. Siderite occurs in very small, dust outlined, anhedral masses with quartz, in larger anhedral to subhedral crystals, and.sometimes as rims of granules. ‘ Contacts between carbonate-rich and quartz-rich portions are highly irregular and exhibit extensive replacement of the carbonate by quartz and chert. Minnesotaite* occurs in small amounts in some of the sections with no apparent regularity. It occurs most common- ly in quartz as microscopic bundles or sheaves of radiating fibers, although individual needles may also be observed. .Parallel extinction, general lack of pleochroism, birefring- ence about equal to that of sericite, and general lack of color (it may also be light green) are the chief criteria for recognition. * Similar occurrences of the iron silicate minerals may be observed in Plates 12 & 1h, although these actually are photo- graphs of the magnetitic member. 23 Stilpnomelane occurs as fine blades in the carbonate, occasionally in chert, and sometimes in the darker carbonate beds. In one slide, a confused fibrous aggregate of the min- eral had granule outlines. In several others, siderite rims enclosed stilpnomelane granule interiors. Stilpnomelane may be either brown or green, depending on the relative amounts of ferric and ferrous iron present. The green variety is most common. Roth exhibit strong pleochroism which is the chief criterion for recognition. Green chlorite is present as veinlets in several sections. Dark cloudy material, presumably graphite, is present mainly as dust and appears to be associated more with carbonate than chert. Very thin layers of graphite are present in the darker beds and also in stylolite seams. In the darker beds (visible in hand specimen), exceed- ingly fine grained carbonate rich in graphite is the main essential mineral. Stilpnomelane may be present in minor quantities as blade-like fibers in the groundmass. Minor disseminated chlorite particles may also occur. Relationships- The change in lithology between both underlying and overlying members appears to be relatively abrupt, although interbedding between both units is common. Lithology appears to be quite uniform, both laterally and vertically. The appearance of stilpnomelane granules seems to be restricted in the field to the broad plunging anticline at the northwest end of the group, however. Further studies may reveal occurrence of those elsewhere. Magnetitic hematitic sideritic-dolomitic chert member §E££§9§.9§29§B£2§' Because of the resistant nature of this member to weathering, it is frequently encountered throughout the iron-formation. It forms prominent ridges in the "B" Group as is the case in many other areas. OutcrOps are peck-marked where carbonates are dominant and they common- ly exhibit goethite staining. This is the member of the Temiscamie iron-formation that has economic significance. Negascopic descriptiqn- The rocks of the magnetitecrich portion may all be included under the general name taconite as used in the Mesabi range of Minnesota and elsewhere. The essential minerals are chert, magnetite, iron carbonates, and iron silicates. All of the rocks are of varying shades of gray when seen in drill cores or on fresh surfaces in hand specimens. Magnetite-rich portions give blackish colors and may be seen in bands, granules, or finely disseminated in the chert groundmass. Chert and carbonate, where dominant, show light gray to light yellow colors. The iron silicates, when abun- dant, impart light green, yellow-green, and dark green colors to the rocks. Hematite ray be seen from place to place in minor amounts and its presence can be detected by steel-gray colors or by pinkish tint in specimens. Several distinct varieties are: (1) Cherty taconite (Plate 2). (2) Irregularly banded cherty taconite (Plate 1). 25 Plate 2. Drill cores of cherty taconite. Typical occurrence shows finely disseminated chert, magnetite, and carbonate. One and one- fourth natural size. Plate 3. Drill cores of irregularly banded cherty taconite. Black bands are magnetite, lighter bands carbonate. Nassive beds between bands are cherty taconite. One and one-fourth natural size. (I) Granular and oolitic cherty taconite (Plate h). (H) Yottled cherty taconite (Plate q). It is important to note that all gradations of the diff- erent varieties are present and may occur together or sepa- rately. In addition to these varieties, very thin bedded and more regularly banded types are also present. Cherty taconite (Plate 2) is the name given to those massive varieties where banded layers are absent. Typically, chert, magnetite, and carbonate are finely disseminated and intimately intermixed. This is the most common variety. Irregularly banded cherty taconite (Plate 3) is common and seen in all of the drill holes (excepting B-lg and B-lq which contain the fine-bedded magnetitic iron silicate member). Individual magnetite bands are usually half an inch or less in thickness but may range up to several inches thick. These bands alternate with cherty and granular massive layers and carbonate or iron silicate layers. In some places these bands are more regular than in others. Granular and oolitic varieties (Plate h) exhibit granules and oolites which are most readily apparent in drill core specimens. Individual granules or oolites usually average 1 mm in diameter and may constitute the major percentage of some rocks or be only a minor constituent in others. They may be well formed or highly irregular in shape. Fottled cherty taconite (Plate 4) exhibits rounded blebs of magnetite within the cherty taconite, These vary in size from one-quarter to an inch in diameter. Although these are 27 Plate h. Drill cores of granular and oolitic cherty taconite. Center specimen shows conspic- uous granules with magnetite rims; left and right specimens exhibit more deformrd types. One and one-fourth natural size. Plate 5. Drill cores of mottled cherty taconite. Dark blebs of magnetite visible in cherty taconite. One and one-fourth natural size. 28 by no means as abundant as the other varieties, they are found throughout the member. Eigrgscopig descriptign— Chert and quartz are the major minerals of the matrix in which the oxides, carbonates, and silicates occur. The average size of the chert is 0.01 mm, but the range is from 0.00% mm to 0.1 mm (quartz). Interiors of granules frequently exhibit a crystal mosaic of quartz of larger grain size than in the chert matrix. Nagnetite occurs in concentrations of euhedral grains, as individual euhedra disseminated in the matrix, as masses of euhedra, in chains of euhedra (Plates 6 a 7), as rims of granules in euhedral form (Plate 8), and in less perfectly developed subhedral and anhedral forms. When concentrated in bands it is seldom pure (Plate 9), and usually is interbedded with chert, carbonates, and sometimes iron silicates. The size of these different forms is quite variable. Individual octahedra are commonly 0.03 mm in diameter but may be considerably smaller or slightly larger. Chains generally are in the order of half a millimeter in length but may be smaller or larger. Granules commonly are 1 mm in diameter. Hematite is frequently observed but is by no means as abundant as magnetite. Its presence often may be detected only by orange colored dust in chert or carbonate when exam- ined under reflected light. This dust forms ”clouds" in chert (Plate 8), occurs as concentric layers in oolites, and as small irregular masses from place to place. These small amounts are generally sufficient to color the rock a very 29 Plate 6. Photomicrograph of B-lB at 303' show- ing chains of euhedral magnetite in chert matrix. dithout analyzer, x ?2. ,,-_. ,. -— -1- ,—_—-_-_ _. Plate 7. Same as above under crossed nicols; showing relations of chert. Larger medium-gray particles are carbonate. x 32. 30 Plate 8. Photomicrograoh of B—18 at 187' showing granules with magnetite rims in chert. Dust in chert is exceedingly fine grained hematite. Siderite grains (gray) at left and right margin. Without analyzer, x $3. Plate 9. Photomicrograph of 8-11 at ?92' showing relations of magnetite (black), carbonate (gray), and chert (white). Without analyzer, x 32. 31 light Dink. Netallic hematite lenses may be observed in close assoc- iation with magnetite bands. These contacts are seldom sharp and exhibit intermixing of the hematite in magnetite (Plate 10). These layers are not abundant yet may be seen in many drill cores. Lenses of hematite are never pure, and usually con- tain intermixed chert and carbonate. Plate 10. photomicrograph of polished section from 8-22 at 22h"showing relations of hematite (whitel and magnetite (light gray) bands. Darker gray is quartz. Reflected light, x 25. Hematite (martite) may be seen on the margins of magnet- ite in some granules (Plate 11) and occasionally in anhedral grains intermixed with magnetite. This is not typical but other sections might show that it is more common. The size of the individual anhedral grains is usually 0.02 mm or less in diameter. 32 Plate 11. Photoricrograph of 3-1? at 33' (polished section) sh0wing hematite (nartite) alteration from magnetite in the rims of granules. Hematite (white), maznetite (light gray), chert (darker gray). Reflected light, x 6?. The carbonates occur in a numerous variety of forms. They are usually anhedral to subhedral, yet well-formed rhombs may be observed (Plate 9). They are seen in the interior of granules, interbedded with magnetite (Plate 9), intermixed with chert and quartz, or can make us entire layers. Some sections reveal that it is entirely absent or nearly so (Plates 6 a 7). Ankerite and siderite are both present and may occur together or seoarately. The iron silicates minnesotaite and stilpnomelane are abundant in some sections and may constitute the greater majority of some beds. Often they are intimately associated, and where this occurs, distinction between the two becomes 33 exceedingly difficult. To account for this, Gruner (lqhé) states: "As stilpnomelane forms from, let us assume, a colloidal gel, it will take the ions in its neigh- borhood which are most convenient and of the neces- sary charge. If it cannot find anymore it will step growing. The leftover gel material, then, may be of the procer composition to form minnesotaite or greenalite, or quartz and siderite, if 002 is available in considerable concentration." Stilpnomelane may be seen as individual blades in car— bonate or quartz and chert, as massive layers interbedded with magnetite, as confused radiating fibrous aggregates in granules, or in irregular sheaves (Plate 12) in carbonate or quartz and chert. When associated with carbonate or quartz it is nearly always green (containing mostly ferrous iron), while near magnetite (Plate 13) it is usually brown (contain- ing mostly ferric iron). Frequently the gradation from green to brown, or from brown to green stilpnomelane is evident. Minnesotaite occurs in chert usually as exceedingly small colorless to light green aggregates of radiating fibers (Plate in). It may also be in close association with carbon- ate or magnetite. Quirks (10§8) has reported the presence of talc (verified by x-ray diffraction pattern) in one instance. Because of the exceedingly fine grain sizes and possible confusion with sericite or minnesotaite, its presence is somewhat indeterm- inate, unless x-rays are used. Green chlorite is found in very minor amounts usually as small irregular grains in the matrix, or as small veinlets from place to place. In a few instances, very small irregular 3’1 Plate 12. Photomicrograph of 8-18 at 383' showing blades of green stilonomelane in carbonate. Clear white color is quartz, black octahedra are magnetite. Plain light, x 63. Plate 1?. Photomicrograph of 8-11 at hh?‘ showing brown stilonomelane (dark gray) near magnetite octahedra (black). Clear white is quartz, stiooled white is carbonate. Without analyzer, x 216. In ' ._ o ‘1: ”if L11 I i 0 a", i . “a. ' W _ o . .Iania .- fl——.'_ ».- 35 Plate 1h. Photomicrograoh of B-2q at 77' showing confused fibrous aggregates of minnesotaite in chert (white). Euhed- ral magnetite 'black) in chains and irregular masses. Without analyzer, x 63. grains exhibit interference colors of the second order. It may be that this is green biotite which has the aaoearance of a chlorite, yet has not completely changed to chlorite, and thus retains the birefringence of biotite. It is not a common occurrence. Discussion of features- Trequently in records of drill holes, the adjective ”oolitic" appears. Thin sections demon- strate that true oolites (showing concentric layering) are not common, although they are present in minor amounts. Where present, they seldom exhibit good concentric layering of the constituent minerals. Granules are common and may be associated with oolites. It is possible that conditions 36 favoring formation of these may be similar, or that granules at one time may have been oolites which subsequently changed character during diagenesis. The word jasper is found freiuently in drill hole records. Thin sections show that true jas,er is not present. Usually these pink rocks contain very minor amounts of randomly dis- seminated dust size hematite. One of the most common occurrences of magnetite is in the form of chains (Plates 6 a 7). It seems likely, due to intimate association with granules and their general rounded form, that they formed parts of granules at one time. Dessication textures are apparent in the chert in many places. Their presence is indicated by the occurrence of orange-red hematite dust in cracks in the chert. Presumably, they are formed by loss of water in the original gel uoon lithifiCation. Relationshipg- A study of ”B” Group drill cores and thin sections reveals that granules and oolites (or oolitic appearing textures) are most typical of the upper half of the member. Oftentimes they are restricted to the uioer one- third. Some thin sections and drill cores show minor amounts near the base of this member. Pagnetite bands may occur anyplace in the member, however they are nearly always prevalent in the bottom half. Usually they become finer and better developed with depth. The iron silicates are abundant in the lower one-fourth of the member, although stilonomelane may occur in minor amounts in other horizons. Ninnesotaite is abundant in the majority of cases in the lowermost portions. The carbonates anoear to follow no regularity either in abundance or mode of occurrence. Drill hole records show that in most of the drill holes there are definite rich and lean zones, however no generalizations can be made from cresent information due to the high variation in individual drill holes. iematite, too, follows little regularity. It has been reported in many holes and at different nositions within the member. Nevertheless, it appears that it is more common in the middle and lower parts of the member. Because it is gen- erally a minor constituent, and oftentimes goes unnoticed, it might be shown in further studies that there are more def- inite hematite zones in the member than have so far been recog- nized. Chert and quartz are quite uniform throughout the member. The average size of the chert is generally 0.01 mm, although in a few slides there was a suggestion that the chert might be slightly more recrystallized near the base. Average size in these cases was about 0.02 mm. Seldom is the chert and quartz uniform in rescect to size and nearly always larger quartz grains (up to 0.1 mm) are found intimately intermixed with chert. Nagnetite is euhedral in nearly all of the thin sections. It accears that with denth the grains become less perfectly develoned and may occur in subhedral shapes. It is a rarity when crystal boundaries cannot be recognized, although they 33 are highly imperfect in places. Euhedral magnetite may occur at the bottom of the member which shows that no definite relations regarding crystal shapes can be established, although the suggestion that it becomes more subhedral with depth is evident in thin sections. Grain sizes diminish slight- ly with depth. This is anoarent in many sections. As mentioned previously, the member may be somewhat interbedded with the underlying and overlying members. An average thickness in the "B” Group is somewhat difficult to measure because of highly complex faulting. The average seems to be in the neighborhood of 200 feet. Upper stilonomelane argillite member Surface exoosures- This member is observed on the surface infrequently as is the case with the lower argillite member. It is apparently very susceptible to weathering. fleaascooic description- Drill core specimens are tyoical— ...—L 1y greenish-gray to greenish-black finely crystalline mudstcnes. Thin beds can be observed between more common massive layers. Very fine needles of stilonomelsne are visible in gray specimens and may be detected in the blacker varieties by the presence of fine crystalline texture. Oolites may be observed in chert in those portions interbedded with the magnetic member. The name "stilpnomelane-carbonate member" would be a more aoorooriate name for this member than argillite. The word argillite is retained to avoid confusion and is in keeping with past usage. 39 Core soecimens of the upper argillite were found to be magnetic in 001 of the cores examined, but in some of the cases magnetism is barely discernible, even when using a strong laboratory electro-magnet. Fagnetism is more pronounced near the contact of the underlying magnetic member. This may have significance in economic considerations. Eicroseooic desgrigtlon- When seen in thin section, this member consistently shows an abundance of iron carbonates, stilpnomelane, and euhedral magnetite in the portions near the bottom of the member (see Plate 15). Plate 19. Photomicrogreph of upoer argillite show- ing stilonomelane needles in carbonate matrix. Small black euhedra are magnetite crystals. Plain light, x 53. Siderite and ankerite are present as exceedingly fine grained anhedral grains. Coarse grains of both minerals also MO occur in veins and in irregularly shaped lenses. These min- erals form the groundmass for stilpnomelane and magnetite. The groundmass is generally very cloudy. This is probably due to the presence of dust size graphite intermixed with the carbonate. Stilpnomelane occurs abundantly throughout the member. It occurs as a mesh of acicular blades (Plate 1%), sometimes constituting h04 of the rock. It may be either brown or green and sometimes both. Birefringence and pleochroism are quite variable. In some slides it is only a minor constituent and occurs as individual needles in the carbonate. In sections where stilonomelane is dominant, the individual crystals average 0.1 mm long and 0.01 mm wide. Where it is less abun- dant it may be as much as 0.3 mm long and 0.05 mm wide. Stilp- nomelane-rich sections impart a greenish-black color to core and hand specimens. Hagnetite may account for as much as 15% of some sections, although this is the exception. Typically, magnetite occurs in small amounts, evenly disseminated and in very small euhedra averaging 0.01 mm in diameter. Very thin layers are also seen and consist of concentrations of individual euhedra. Graphite occurs frequently in small amounts as very thin layers, in stylolite seams and disseminated in the matrix. Green chlorite is often observed in small amounts with no apparent regularity. Quartz and chert are seldom, if ever, observed except where interbedding with the underlying and overlying units occurs. hl Relationships- Interbedding may occur with both the overlying cherty member and the underlying magnetic member, although it is more pronounced with the former. When inter- bedding occurs, oolites may be observed in cherty carbonate interbedded with the normal argillite. This member appears to be about 15 feet thick on an average, although this is quite variable. Upper sideritic chert member Surface caposures- Due to relative stratigraphic posi- tion, this member is fairly common in outcrop and may be ob- served throughout the iron-formation. "B" Group outcrops are numerous with main exposure areas in the broad plunging anti- cline located in the northwest part of the group. Megascopic description- In hand and core specimens this member is nearly identical with the lower cherty member. Alternating bands of quartz and carbonate, irregular patches of carbonate, and evenly disseminated carbonate in quartz matrix are typical variations. Darker carbonate bands are seen as well as interbedded portions of the upper argillite member. Quartz-rich bands are generally whitish-gray in color. Very small anhedral patches of carbonate, as well as granular forms can be seen in the quartz. Stilpnomelane needles are visible in some specimens. Some of the core specimens are slightly, yet perceptibly, magnetic. As a general rule, however, the member is non- magnetic. h2 MicroscOpic description- This member exhibits diversi- fied texture and mineral composition. Major constituents are quartz and carbonate with minor amounts of stilpnomelane, magnetite, chlorite, pyrite, and graphite. Textures frequent- ly observed are oolitic, granular, and highly irregular poik- olitic. Bedding is commonly seen in thin sections. Quartz and chert are the most common minerals, but the distribution is irregular and can make up nearly all or none of the beds. In beds of highly irregular configuration where quartz and carbonate occur together, mosaic textures of quartz and chert are common. Some sections consist almost entirely of quartz (0.1 mm) while others are entirely chert (0.01 mm). Many slides show evidence of considerable replacement of carbonate by quartz. Carbonates are the other essential constituents of the member. Siderite and ankerite are present and occur in gran- ules, in irregular anhedral masses in beds, finely intermixed in quartz, and as rhombic euhedra in chert. Quirke (1958) has shown that x-ray diffraction patterns indicate the presence of siderite, but that the refractive indices are somewhat low- er than they should be for the mineral. He has suggested that the mineral may have significant amounts of magnesium or man- ganese in the structure. Ankerite usually shows up in masses of subhedral.crysta1s in individual beds. It occurs frequently as euhedral crystals in quartz and chert and may also be in granules. Grain sizes are exceedingly variable and range from 0.01 mm to 0.3 mm in LLB largest diameter, although average 0.1 mm. Siderite occurs in a like manner to ankerite and may be present with it or as a separate constituent. Individual dark beds show exceedingly small (less than 0.01 mm) grain sizes and have considerable amounts of graphitic dust con— tained within the matrix. Where contacts between chert and carbonate beds are examined, abrupt mineralogic change is not always evident and solid carbonate beds often show gradationally decreasing amounts. As the amount of carbonate decreases, crystal out- lines show more perfect develooment. Stilpnomelane blades occur in minor amounts as sheaves in carbonate and also in quartz. It occurs occasionally as a mat of lath shaped crystals in the darker beds, however this may represent interbedding with the underlying upper argillite. Green varieties are most common, although brown needles are also present. There appears to be no regularity in relative amounts present, mode of occurrence, or position within the member. Minnesotaite'may possibly be present (mistaken for stilpnomelane), however none was positevely identified. Magnetite and pyrite are occasionally present in small anhedral grains and constitute less than 1% of the rock. Graphite is present as dust within the darker beds, in very thin layers (0.01 mm), and in stylolite seams. Chlorite may be observed in the interior of some granules, as concentric layers in oolites, and in irregular masses from uh place to place. This is probably derived from some original clay minerals. Granules and oolites were observed persistently through- out the member, with the former being more common. However, in some slides these features are absent. Individual granules may occur entirely within carbonate, in quartz and chert, or in close association with both. Often .these are preserved only as outlines of dust within the an- hedral carbonate matrix. In some cases the interior of gran- ules contains quartz. These granules are nearly always poorly formed. Well shaped spherical forms are the exception. Sizes range from 0.1 mm to 1 mm, with an average of 0.6 mm. Relic oolites may be observed in chert in several sections. Often these are preserved only as concentric layers of dust Plate 16. Photomicrograph showing relic oolites in chert. Concentric layers consist of chlorite (dark) and stilpnomelane (not discernible in picture). Lighter colored layers are dust. Plain light, x 25. 115 within the chert. In others are found concentric layers of chlorite and stilpnomelane (see Plate 16). Chlorite may make up the entire composition in some oolites, although this is uncommon. Chert within the interiors is generally slightly larger in grain size than within the chert matrix.. Relationships- Interbedding with the underlying upper argillite is common, but this member was not observed in con- tact with the younger Kallio slates. No drill holes penetrated the entire thickness of the member. The thiCkness of the upper sideritic chert member has been estimated by Quirks (1958) to be at least 300 feet. Fine-bedded magnetitic iron silicate member _ Surface exposures- The fine-bedded magnetitic iron silicate member has been identified in drill holes 8-15 and B-19 but is seldom seen cropping out at the surface. auirke (19§8) reports that it outcrops just east of Coom Lake (see Fig. 2) and in fault blocks along the Temiscamie River. It may also be found in other areas in the iron formation. Megasoopic description- The most obvious characteristic 'of this member. is the thin, distinctive bedding (Plate 17). Variation in hand or core Specimens commonly is shown to be a. function of the composition and width of bedding. Pink chert is prominent in some layers and may be as much as sev- eral inches thick. Magnetite-rich, carbonate—rich, and sili- cate-rich layers occur in a similar manner, each having their he 7 _____ -_ ...— - l_ -_ _ ‘— _—_, '~Plate 17. Drill cores of fine-bedded cherty tacon- ite. Top specimen exhibits thicker beds. Individual beds vary with chert-magnetite ratio. Band at extreme right is nearly pure magnetite, center is‘a mixture of chert and magnetite. Intermediate gray is pink chert, light color is carbonate. Bottom specimen shows predominately iron silicate layers, magnetite- rich layers, and cherty carbonate layers. One and one-fourth natural size. own characteristic color. Where silicates are prominent, the ‘ bedding is generally thinner and better developed than where magnetite and chert are dominant. Gradations between the different layers are readily apparent in core specimens. Quirke (1958) has noted the similarity with "wavy banded taconites" of the Nesabi range in Minnesota w The name fine- bedded cherty taconite is suggested for this facies of iron- formation at Lake Albanel. MicroscOpic description- Thin sections quickly reveal the fine-bedded nature of this member (Plate 18). Granules, Plate 18. Photomicrograph of 8-10 at 98' show- ing finely bedded magnetite (black) and hematite in matrix of carbonate. Without analyzer, x 25. oolites, chains, or other features are not observed. quartz and chert are the most abundant minerals of the matrix. Chert is slightly finer grained than in the other iron-rich member. fiverage grain sizes are about 0.008 mm. Larger quartz grains are found in intimate association with chert and may vary in size up to 0.06 mm. Chert and quartz usually occur in beds associated with carbonate or minor amounts of iron silicates, although in magnetite-rich beds quartz is seen intermixed with carbonate. Quartz can be ob- served in several slides. Magnetite occurs in euhedral grains and as concentrations of euhedral grains interbedded with carbonate or iron silicates. Grain sizes are smaller than in the main iron-rich member. ’18 Average grain sizes are in the order of 0.015 mm with a range varying from 0.006 mm to 0.0% mm. Ninnesotaite and stilpnomelane are major constituents in some of the layers. Stilpnomelane frequently forms a mesh of blades in which magnetite layers occur. It may also occur in carbonate. Minnesotaite generally is associated with chert in small amounts, yet may constitute entire layers. These layers are easily recognized in hand or core specimens by the characteristic light green color and extremely soft and fibrous nature, similar to talc. The carbonates siderite and ankerite are both present and often form interbeds with magnetite layers (Plate 18). They are also associated with quartz and chert and may contain minor amounts of hematite dust. Hematite is abundant in some portions and is seen to 'occur as orange-red dust in chert and in very small anhedral grains associated with magnetite and the carbonate minerals. In some sections it occurs nearly exclusive of magnetite. Chlorite is observed in very minor amounts in several sections as small anhedral grains. Relationships- From drill core determination, it appears that the member is slightly more than 100 feet thick. Because of intense faulting in the "B" Group, a true stratigraphic position can not be established. The relation- ships in other parts of the iron-formation have been studied by Quirks (19g8) who states: "North of the Temiscamie River and west of Te-Te- Pisca Bay in six drill holes the fine-bedded mag- h9 netitic iron silicate member was consistently above the magnetitic hematitic sideritic-dolomitic chert member. Between these two members is up to 90 feet of argillite, presumably the equivalent of the upper argillite member found along the lake front. Thus, argillite may occur both above or below the fine—bedded magnetitic member. This seems to imply that this member may be considered as either a lens in the upper argillite member or simp- ly as a facies of that member. Except for the abun- dance of magnetite and the absence of graphite in the fine-bedded magnetitic member, the lithologies are similar. The thickest section of the upper argillite along the lake front is no feet. In the fault blocks along the river this member (includ- ing the fine-bedded magnetitic facies) may be up to 275 feet thick. Not counting the fine-bedded magnetitic facies it might still be as much as 175 feet thick. This thickening may be real and might be explained by its paleogeographic position in the basin of deposition or it may be apparent and caused by faulting. The problem cannot be solved from present information." Kallio slate and graywacke formation This formation has been recognized in drill holes 8-15 and 3—19 (Fig. 3). It is also found exposed at the surface immediately west of these holes. Quirks (1958) reports that .it is not found farther west than the east shore of Einer, Kallio, and Ruth lakes (Fig. 2). Bedding and slaty cleavage are usually vertical. Negascopic description- When seen in hand or core spec- imens, these rocks are consistently very dense black in color. Bedding and cleavage are present although they may be widely spaced. Graphite is a major constituent and may be dissemi- nated or in lustrous seams. Pyrite is abundant and may occur k in euhedral cubes, finely disseminated in massive graphitic 50 beds, or in massive layers up to one-half inch in thickness. Microscopic description- Thin sections show several distinct varieties of this formation, although it is not so apparent in hand or core specimens. The amount of graphite is exceedingly high in all of the specimens, however the amount of quartz is variable. Some sections are opaque in thin section due to the high percentage of graphite and relatively small amount of quartz. Quartz , pyrite, and sericite are disseminated in the ground- mass in very small (0.0u mm) particles. Quartz grains (0.1 mm) make up 50% of the rock in other sections. Slaty cleavage is not apparent in these core spec- imens. The groundmass is highly graphitic, sericitic, and pyritiferous. Plagioclase grains are present in minor amounts and small anhedral carbonate grains may be observed. Relationships- Quirke (1958) reports that this formation is somewhat interbedded with the upper sideritic chert member. This is believed to be the youngest consolidated formation of the Mistassini series. Quirks (1958) writes that Neilson estimated the thickness to be about 800 feet. Sl STRATIGRAPHIC DISTINCTIONS The members which are the most difficult to recognize are the upper and lower sideritic cherty and argillitic mem- bers. Quite possibly, in some places, the Boulder Bay quartz- ite formation and the Kallio slate and graywacke formation could be confused with the cherty and argillitic members. Generally, hand or core‘specimens are sufficient for recognition of the latter two units mentioned above. The gray, quite uniform quartzitic appearance of the Boulder Bay formation and the pitch black, extremely graphitic, and abun- dantly pyritic character of the Kallio formation usually leave no doubt in regard to the unit's stratigraphic position. If there is doubt, thin sections quickly reveal the conspicuously detrital nature of these rocks. The two argillite members are similar in appearance and have similar stratigraphic position in that they are both overlain by sideritic chert. Core or hand specimens usually show that the lower member is better and more finely bedded than the upper member. It also is generally blacker (as opposed to the characteristic greenish-gray to greenish-black cast of the upper member) except where interbedding of car- bonates is prominent. With high regularity, very small blades of stilpnomelane are visible to the unaided eye in the upper argillite specimens. Magnetism of these members is noticeably different. In all but a very few of the upper argillite specimens examined, S2 magnetism could be detected, but often only with the aid of a strong laboratory magnet which is capable of identifying very small amounts of magnetite. The lower argillite member, on the other hand, is seldom magnetic, although in about a third of the specimens examined feeble magnetism could be detected. In no case was the lower argillite as strongly magnetic (actually weak magnetism relative to the iron-rich member) as a few of the upper argillite specimens. Since both members sometimes are and sometimes are not magnetic, this can not be used by itself as a basis for differentiation but may have some value when considered with other criteria. Thin sections reveal further clues for distinction. Stilpnomelane is abundant in the upper member, while it was found in only a few instances in the lower member. Here it was interbedded with the lower chert member and perhaps may not be a true representation of the lower argillite. The much denser and blacker appearance of the lower member is a distinguishing characteristic. More graphite, possibly more pyrite, and the occurrence of detrital quartz particles are distinctive features common only to the lower member. The occurrence of extremely well rounded grains of quartz (exhibiting crystal mosaic texture) is found only in the lower member. Distinction between the upper and lower cherty members is less obvious than in the argillite members. Quartz, chert, and carbonate frequently exhibit identical characteristics. In megascopic examination, the writer felt that the chert-rich portions generally showed whiter and purer colors in the upper member. Thin sections give more clues to the identity. It was reported early in 1958 by one worker that oolites and granules rarely, if ever, occurred in the lower member. This is erro- neous, at least in the "B" Group, for granules have been ident- fied. Granules of the upper and lower members generally have different characteristics. Frequently, granules of the upper cherty member are evidenced only by the presence of dust out- lines in massive anhedral layers of carbonate. Granules of the lower member generally contained stilpnomelane or minne- sotaite in the interiors with outer rims of carbonate. Oolites as shown in Plate 16 were found only in the upper member. Minnesotaite was identified in many slides of the lower member as minor amounts in chert. It was not observed in the upper member, although it conceivably might be present. Where these features are absent, which is the case in some specimens, distinction between the two members is not possible. When distinction is doubtful, a study of the relationships with adjoining units and with the magnetic member will prove help- ful. The characteristics of the magnetic member such as gran- ules in the uppermost portion, better banding and the occur- rence of iron silicate minerals near the bottom should aid in understanding the stratigraphic position of the different units. Taken collectively, these characteristics are the criteria for distinguishing the different members of the Temiscamie iron-formation. Sh COMPARATIVE STRATIGRAPHY Differences in stratigraphy are present to a greater or lesser degree in other parts of the iron range- The follow- is a summary of variations observed by Quirks (1958). Place locations may be found in Fig. 2, p. 6. Boulder £31 quartzite formation- This formation is thin- nest at the south end of the range where it may be as little as seven feet thick. Along the lake front it varies from 20 to 50 feet and in the "B" Group it is slightly over 100 feet thick. In some parts of the range a quartzite conglomer. ate is found at the bottom of the formation. The contact with the younger Temiscamie iron-formation is disconformable northeast of Aallio Lake. Most of the contacts observed in drill cores appear to be conformable and in the "B" Group they are gradational. Lower argillite member- This member has apparently simi- lar characteristics throughout the range, although variations in thickness are evident. It is no feet thick in the vicinity of Canso Bay and seems to thicken irregularly northeastward. Lower sideritic chert and iron silicate member- The lnwer chert member becomes thinner towards the southern end of the range in a similar manner to the underlying argillite and Boulder Bay quartzite. At the south end of the range it is consistently less than 20 feet thick._ North of the Temis- camie River mouth the thickness is generally between 20 and no feet. The lithology of the member is quite uniform north of 55 this point. Near the Richmond River and the Snowshoe Islands it contains considerably less minnesotaite and relic granules appear. Granule-like masses of stilpnomelane have also been reported here. Magnetitig hematitic sideritic-dolomitic chert member- The average,thickness of this member is lhO feet as computed from 25 drill holes covering a length along strike of 35 miles but varies in this distance between 72 and 195 feet. Between Kallio Lake and Plateau Lake it is 132 feet and in the "B" Group it is estimated to be about 200 feet thick. Fagnetite occurs throughout the member without any not— iceable variation in abundance. Lenses of abundant hematite are observed from place to place along the strike. In the northern part of the range this mineral is usually in the upper part of the member. This zone is less than 50 feet thick with a concentration near the middle of the lens. In some cases it may exceed magnetite in abundance and in a few cases magnetite is completely absent. Near the Snowshoe Islands two hematite zones have been recognized. One of these is 60 feet thick and near the top of the member, the other is near the middle. Stilpnomelane is found mainly towards the bottom of the member north of Plateau Lake. Between Plateau Lake and Einer Lake it is found throughout the member but seldom exceeds 3% of the rock. It becomes lighter in color and is found in small amounts through the entire member south of the river mouth. Minnesotaite is typical of the lower section of the member 56 associated with chert and quartz, and in some places it is ubiquitous throughout the member. Granules and oolites typify the upper one-third of the member at the northeast end of the range. Bedding is also evident. Dust size hematite is disseminated in chert and sid- erite in the middle third of the member. The lower third is generally bedded and granules or oolites are rare. South of Plateau Lake bedding planes become less prom- inent in the bottom of the member. Bedding occurs at the bottom for several miles farther, yet is also found at other positions within the member. Granules and oolites are most common in the upper two-thirds of the member, however they may be found within a few feet of the bottom. In the Einer Lake area beds of granules may be observed. Between Einer Lake and the Temiscamie River mouth bedding is typical throughout the member. Granules and oolites are most common in the upper half. ~ Southwest of the river mouth on Presqu'ile Chebamonkque the upper portion of the member has been eroded away. The maximum thickness of the remaining part is 130 feet. Drill cores reveal that the lower up to 60 feet is bedded, generally becoming more prevalent with depth. Granules are found above the bedded zone. Between Presqu'ile Chebamonkque and the southern extension of the range there are no significant outcrops. There is little textural difference between the member near the river mouth and that to the south. Bedding and granules are found 57 throughout the member in this portion of the range. £3223 stilpnomelane argillite member- Near Canso Bay this member ranges up to ten feet thick. From this vicinity southwestward the member is thin, entirely absent, or present only as thin layers interbedded with the upper sideritic chert member. The member is best develooed in the Snowshoe Islands area where the maximum thickness is us feet. In the "B" Group the average is about 15 feet. lgppgr sideritic chert member— This member is the thickest member of the Temiscamie iron-formation. No drill holes tran- sected the entire thickness. Structural evidence northwest of Ruth Lake indicate it is at least 300 feet thick. No consistent variations have been detected for this member. Southeast of Kallio Lake the upper portion of it is interbedded with the overlying hallio slate and graywacke formation. Fine-bedded magnetitic iron silicate member- Because the relationships of this member are not well understood, little can be said about stratigraphic variability. However, the true thickness is apparently close to 100 feet where it is found. 58 STRUCTURAL INTERPRETATION Infornation obtained from drill holes (Fig- h) combined with field mapping (Fig. 3) by Quirke (1058) forms the basis for structural cross-sections found in successive pages. The reader is asked to refer to the geologic map for place loca— tions which will be mentioned in the description of the struc- ture. In the southwest portion of the group no surface outcrons exist and the structure must be interpreted on the basis of four widely spaced drill holes. This necessitates a certain amount of conjecture. Fig. 5, a cross-section through drill holes B-21 and B—ZS, shows the simplest interpretation to be a broad, gently dipping anticline. The inference that the magnetitic member continues on under the river is supported by a high magnetic anomaly near the river's edge. Fig. 6, a cross-section through drill holes B-16 and B-18, suggests a far more intricate pattern of folding and faulting, more like the structure to the north. It is felt by the writer that faulting occurred quite late in folding, thus explaining the small amount of the lower part of the magnetitic member found in drill hole B-18. Nagnetic anomalies have been report- ed over each of the positions where the magnetitic member is proposed to emerge, thereby supporting this interpretation. Figa 7, a cross-section through drill holes B-B, B-10, and B-12, apparently represents a similar situation as was found along line 6000' S. An unexpected zone of fifty feet H6. 5 CROSS SET|0N /-\LONG LINE ll: IOOI 9000' S. (LOOKING N 0RTHEAST) JIN. .- / / \ x I i \ '- / ’- / / \ / \ / \ / BASE Luv ‘\ ELEY ,, E \\ ELEV. I400 \ I I4 —‘ \\ 00 ~ \ \ \ —«—— tea \,kTBWSCAMEI WVER \\\\ I300' ‘—-—e ".A ‘\ 1300' ’ -.-., \ i. ' ’ \ \ v. P) \\\\\\\ I . ' 1200 ‘\\\\\ - iTsoo' H00 \\\\\\\ ”00' UPPER ALBANEL FM. I000 I000. |958 ELEV. ISOO' I300I ( BASE LINE ELEV ISOOl UPPER CHERT AND ARGILLITE MEMBERS ‘ ”BRECCIA UPPER ALBANEL FM. I300' .3/2‘ .“ft . I' ‘ , . MINOR BRECCIA IIOO' SUPPER ALBANEL Phi CROSS SECIION MAGNETWKZHEMAHTKng mDEanc—DOLoanc~~ CHERT MEMBER I": I00' . "' .iTN. l958 - _ LOWER CHERT a ARGILLITE MEMBERS FIG. e ALONG LINE woos. (LOOKING NORTHEAST) 61 of the magnetitic member was encountered in drill hole B-10, and seems most readily explained by a small block movement. This small portion is most likely near the too of the member, as attested by the occurrence of well formed granules in core specimens. Magnetic anomalies are reported where the mag- netitic member comes to the surface. Fig. 8, a cross-section through drill holes B-3, B-l, B-6, and B—lh, shows a section through the truncated, over- turned, doubly plunging anticline. The Upper Albanel dolo- mite formation has been exposed southeast of drill hole B-lu apparently by thrust or block faulting. Fig. 9, through drill holes B-2k and B—h, shows essen- tially similar structure near the river as in Fig. 8 except that apparently the axial plane of the anticline dips more gently to the southeast. In the vicinity of drill hole B-Eh only a small amount of the magnetitic member is exposed in the broad, fairly symmetrical, plunging anticline. A cross-section along line 1000' N would demonstrate a compromise between Fig. 8 and Fig. 9, except near drill hole B-26 where lithology and structure are somewhat indeterminate due to limited information. The uppermost portion of this hole contains an impure quartzite, characteristic of the Boulder Bay formation. From there to the middle of the hole there exists highly sheared and brecciated sideritic chert, frequent- ly exhibiting veins of white quartz. Conceivably, this may 1M3 either the upper or lower chert member, however the writer was unable to determine which one it was. From the middle of _ ELEV. l400' ELEV. ‘I400' I200l o _. v M '4. _ A ‘ SIDERITIC MEMBER [200' UPPER CHERT MEMBER I000I \ \ \ \\ UPPER ALBANEL FORMATION I000I .\:¢::ER ARGmLHTZ MEMBER MAG.HEM.SDr;;:\\\\\ CHERT MEMBER PPULDER.BAYJPVE§;I" 800' FIG. 7 CROSS . i r . \ . J . . SECTION ALONG LINE . 3OOO‘ 3 T’::A~#d‘ ..AW— - —. \ BASE LINE ,, ,_- ' * \ / \ ELEV. I6 I _. \\ / co 8 I9 \ \ - // \ I600' \ UPPER CH . \ / ,. x \ , _ .. \ ' f B—II // \ F.—BEDDED . . b ' ~r— _ ~ vvvaM MAG Fe SW MAGNETITIC HEMATITIC . UPPER . ’VVI/MN : MEMBER ‘ SIDERITIC- DOLOMITIC a. CHI . % CHERT MEMBER I400' “st, «in . ' 2‘ L. T g KALLIO FORMATION '~ ~ SHEARWG ‘ UPPER ALBANEL FORMATION Egg/RETR . LOWER CHERT AND I BOULDER BAY ARGILLITE MBRs. \ FORMATION IEOO' u [200! UPPER ALBANEL ’ FM. FIG. II CROSS SECTION ALONG LINE @000 N. ILO0I