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1987 Metamorphism in the Wabigoon Subprovince in the vicinity of Vermilion Bay and Sioux Lookout, Ontario Christine K. Roob University of North Dakota
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Recommended Citation Roob, Christine K., "Metamorphism in the Wabigoon Subprovince in the vicinity of Vermilion Bay and Sioux Lookout, Ontario" (1987). Theses and Dissertations. 249. https://commons.und.edu/theses/249
This Thesis is brought to you for free and open access by the Theses, Dissertations, and Senior Projects at UND Scholarly Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UND Scholarly Commons. For more information, please contact [email protected]. METAMORPHISM IN THE WABIGOON SUBPROVINCE IN THE VICINITY OF VERMILION BAY AND SIOUX LOOKOUT, ONTARIO
by Christine K, Roob Bachelor of science, North Dakota state University, 1982
A Thesis ·submitted to the Graduate Faculty of the University of North Dakota in partial fulfillment of the requirements for the degree of Master of Science
Grand Forks, North Dakota
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December 1987 This thesis submitted by Christine K. Roob in partial fulfillment of the requirements for the degree of Master of Science from the University of North Dakota has been read by the Faculty Advisory Collllllittee under whom the work has been done, and is hereby approved.
(Chairman)
This thesis meets the standards for appearance and conforms to the style and format requirements of the Graduate School of the University of North Dakota, and is hereby approved.
Dean of the Graduate School
ii 628547 -
Permission
Title: Metamorphism in the Wabigoon Subprovince in the Vicinity of Vermilion Bay and Sioux Lookout Ontario
Department: Geology and Geological Engineering
Degree: Master of Science
In presenting this thesis in partial fulfillment of the requirements for a graduate degree from the University of North Dakota, I agree that the library of this University shall make it freely available for inspection. I further agree that permission for extensive copying for scholarly purposes may be granted by the professor who supervised my thesis work, or in his absence, by the chairperson of the department or the Dean of the Graduate School. It is also understood that any copying or publication or other use of this thesis or part thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and the University of North Dakota in any scholarly use which may be made of any material in my thesis.
Signature LnSJ-1Dfu.O J\~ Date------
iii TABLE OF CONTENTS LIST OF ILLUSTRATIONS • ...... vi LIST OF TABLES •• ...... vii ACKNOWLEDGMENTS • . . . ,...... viii ABSTRACT .•...... ' ...... • ix
STATEMENT OF PROBLEM. •• • • ..1 Introduction ••.• . . • ...... 2 Previous Works •• • • • • • .5 Geology of the Thesis Area. • • .6 OTHER GREENSTONE BELTS • ...... 15
PETROI,OGY • ...... • . . .26 Metasediments .•••...••••.••••.••••.••• ,26 Metamorphosed Pelitic Sediments. • .26 Quartz-Amphibole-Epidote Gneiss. .31 Metamorphosed Psammitic Sediments. . . • .32 Alllphibole-rich Meatmorphosed Sediments. • ,34 Metamorphosed Conglomerates. .. . • .34 Slate ...... • • • .36 Iron-rich Metasediments. • • • • .36 Metaquartzites •.•.•.....• • . . ••• .36 Metavolcanics •..••••.•..•.•.•• • .37 Metamorphosed Aphyric Basalt. • . .. ,37 Metamorphosed Basalt Porphyry. . . • .38 Metabasite •••••• ...... • ,39 Pillowed Basalt •• ...... 39 Felsic Tuff ••••• • . . .40 METAMORPHISM .•••••••.••• .. • . . • • .. .. ,41 Andalusite Isograd. • . .. .• • • • .50 Garnet Isograd .••••• • • .. • • ,51 Sillimanite-K-feldspar Isograd. .. .52
GEOTHERMOMETRY/GEOBAROMETRY •••.•.•.••• . .. . • • • .. • • 54 Biotite-Garnet Geothermometery ••• ..... • .54 Garnet-Cordierite Geothermometry. • • .55 Cordierite-Biotite Geothermometry •• .. • • • 62 Garnet-Cordierite Geobarometry .••• • ••••• • • 62 Garnet-PLagioclase-Sillimanite-Quartz Geobarometry •• 65 DISClJSSION ...... , ...... 70
iv CONCLUSIONS...... " ...... 76 APPENDICES •••••• ...... " ..... • • . . •• 78 Appendix A: Sample Locations •••• • • • • • • .79 Appendix B: Microprobe Analyses. • • • • • • • .89 Appendix c: Mineralogy of Thin Sections ••• .103
REFERENCES ••• ...... • 110
V - LIST OF ILLUSTRATIONS Figure
1. Superior Province, in Ontario, showing major lithologic and subprovince boundaries ••••••..••• 3 2. PrOJDinant lithologies and structural features of the study area ...... 7
3. comparative sections of Archean stratigraphy in Canada (Kakagi Lake, Stormy Lake, Shebandowan), South Africa (Barberton) and Western Australia (Scotia) ...... 18
4. Comparison of the Archean shields in Canada, Australia and Rhodesia .••...•...... 20
5. Mineralogical phase equilibria ••••..••••••••••... 42
6. Low-grade metamorphism in the Wabigoon subprov!nee ...... •...... 4 4 7. Isograds in the Vermilion Bay-Dryden area •••••••• 46
a. Isograds in the Dryden-Thunder Lake area .•••••••. 48
9. Temperature trends in the Vermilion Bay-Dryden area ...... 5 7
10. Temperature trends in the Dryden- Dinorwic area ...... 59
11. Pressure trends in the Vermilion Bay-Dryden area • •..•.••.•••..•...•••.•..•.•.•• 68 12. Location of Townships in the study area ••••••... 80
13. Sample locations, vermilion Bay to Dryden •.••••. 83
14. Sample locations, Dryden to Sandybeach Lake ••••• 85
15. Sample locations, Sandybeach Lake to Superior Junction ...... , ...... 87
vi
'! LIST OF TABLES Table 1. Correlation and comparison of stratigraphic units •• 9 2. comparison of stratigraphic units and rock types •• 27
3. Biotite-Garnet Thermometry •.•••••..•••.•.•.•.••••• 56 4. Garnet-cordierite Geothermometry •••••..•••.••••••• 61
5. Biotite-cordierite Geothermometry ••.•••••••..••.•• 61 • 6. Garnet-cordierite Geobarometry •••••••.•••••••.•.•• 64 7. Garnet-Cordierite Geobarometry ••••.••••••••••.•••. 64 a. Garnet-cordierite-Sillimantite-Quartz The~ometry ...... 66
9. Garnet-Plagioclase-Sillimantite-Quartz Geobarometry ...... •...... •..... 66
10, Scanning Electron Microscope/Electron Probe Microanalyzer Precison·and Accuracy •.•..•••.••• 93
vii ACKNOWLEDGEMENTS There are several people I must thank for helping me with this study. First and foremost, Dr. Dexter Perkins, whose time, knowledge, and immense patience helped me get through this. Dr. Will Gosnold and Dr. Frank Karner I thank for their critical reviews of the manuscript. I would like to thank the Beta zeta Chapter of Sigma Gamma Epsilon and the University of North Dakota Graduate School for financial assistance. I am grateful to the Professors at North Dakota State University for their help in the later stages of thesis reproduction. A special thanks goes out to Steve Giddings whose knowledge and data of his ajoining area was so freely shared. Last but not least I would like to thank my family who have stood by and given me their love, encouragement and support.
viii
..,' /, ABSTRACT
The Wabigoon-English River subprovince boundary has been proposed by various workers to be either a fault, an unconformity, an intrusive contact or a gradational boundary. North of the Wabigoon Fault, in the Vermilion Bay-Dryden area, migmatization and partial melting of meta sediments have produced a variety of metatexitic and diatexitic migmatites. Because migmatites are not encountered in the Wabigoon subprovince proper and the area north of the Wabigoon fault is so different from the rest of the subprovince, it is thought that the area may constitute the southernmost part of the English River sub province. The Wabigoon Subprovince is a volcanic-plutonic belt located within the Superior Province of the canadian Shield. The subprovince contains metavolcanic rocks with small amounts of metasedimentary rocks which have been intruded by granitoid rocks. The study area is located along the northernmost edge of the Wabigoon Subprovince extending from vermilion Bay to Sioux Lookout, Ontario. Three isograds can be mapped in the field: l) an area of medium-grade, andalusite-bearing, metamorphosed pelitic sediments, 2) an area of medium-grade, garnet-bearing, metamorphosed pelitic sediments, and 3) an area of high-
ix grade, metamorphosed pelitic sediments containing metastable sillimanite. The isograds are on the average 2 to 4 Km apart. Results from the application of three geothermometers ( biotite-garnet, garnet-cordierite and biotite cordierite) geothermometry indicate there is a gradual temperature increase from 4Sa°C in the southern half of the study area to 6ao0 c in the northern half. Pressures calculated by applying two geobarometers (garnet-cordierite and garnet-plagioclase-sillimanite-quartz) for the northern half of the study area ranged from 3.9 to 4.8 Kb; those in the southern half are less than 3.9 Kb. The observed changes in mineralogy, geobarometry and geothermometry, are characteristic of a regular progressive increase in metamorphic grade from the Wabigoon fault north to the start of migmitization. There is a gradual increase in temperature and pressure, with no major jumps or breaks, from south to north. The study area represents either a part of the English River Subprovince or a transitional zone between the Wabigoon and English River Subprovinces.
X STATEMENT OF PROBLEM The Wabigoon-English River subprovince boundary has been proposed by various workers to be either a fault, an unconformity, an intrusive contact or a gradational boundary (Blackburn et al., 1985). North of the Wabigoon Fault, in the Vermilion Bay-Dryden area, migmatization and partial melting of metasediments have produced a variety of metatexitic and diatexitic migmatites (Breaks et al., 1978). Because migmatites are not encountered in the Wabigoon subprovince proper and the area north of the Wabigoon fault is so different from the rest of the subprovince, it is thought that the area may constitute the southernmost part of the English River subprovince (Bartlett, 1978). The Wabigoon-Quetico boundary is poorly defined. The current school of thought (Mackasey et al., 1974; Blackburn and Mackasey, 1977), is that the boundary is stratigraphic rather than structural, and that the interface has been offset later by fault movements. The objective of this study was to determine the metamorphic conditions recorded by the rocks and investigate the transition zone between the English River and the Wabigoon Subprovinces. The area which is located along the northernmost edge of the Wabigoon Subprovince and the southernmost edge of the English River Subprovince, extends from Vermilion Bay to Sioux Lookout, Ontario.
1
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Samples were collected along the Trans-Canada Highway (17), Highway 72 and numerous township and lumber roads (Figure
1) • The plan of this study was to make general descriptions of the rock types encountered, determine metamorphic mineral assemblages, estimate possible reactions, using petrographic studies, and make estimations of metamorphic pressures and temperatures using known metamorphic reaction data. The results of these investigations were used to determine general trends of metamorphism, t~perature, and pressure for the area. Published results of studies of other greenstone belts were compared to the study area. Introduction The Archean superior Province is a major tectonic division of the Canadian Shield. Rocks of the province have U-Pb zircon ages ranging from 2.6-J.O G.A. with most in the range 2.6-2.7 G.A. The province has been divided into several subprovinces based on tectonic features, lithologic associations, and metamorphic grade (Condie, 1981). The subprovinces in the western part of the province occur as large linear belts of alternating volcanic plutonic and sedimentary-plutonic rocks (Condie, 1976). From north to south the volcanic-plutonic belts are the Sachigo, Uchi, Wabigoon, and Wawa; the sedimentary-plutonic belts are the Berens River, English River, and Quetico 3
I I I
Figure 1. superior Province, in Ontario, showing major lithologic and subprovince boundaries. Enlargement depicts the study area. HUDSON BAY
PHANEROZOIC
JAMES SACHIGO COVER BAY
UCHI
' ' ' 10 KM ' ' ' ' 5
(Figure 1). The Wabigoon subprovince is a volcanic-plutonic green stone belt. U-Pb dates on sphene and zircon in meta volcanic and plutonic rocks of the subprovince, suggest an age of 2750-2700 M.A. (Hart and Davis, 1969; Krogh and Davis, 1971; Davis et al., 1980; Davis et al., 1982; Davis and Trowell, 1982). The subprovince contains predominantly metavolcanic rocks with small amounts of metasedimentary rocks; both of which have been intruded by granitoid rocks. Bordering the Wabigoon subprovince to the north and south are assemblages of metasedimentary rocks, migmatites and granitic rocks which make up the English River- and Quetico-subprovinces, respectively. Previous Works Many studies have been conducted on small portions of the thesis area. The Vermilion Bay area was studied by Blackburn (1977), Westerman (1978), and Breaks et al. (1978). The geology of the Eagle River area was mapped by Moorhouse (1939); and Bartlett (1978) determined metamorphic grade. The geology of the Dryden-Wabigoon area was mapped by Satterly (1943). Pettijohn (1939 and 1940) concentrated on the geology in the Thunder Lake area. Palonen and speed (1977) examined the geology of the sandybeach area. Detailed mapping of Echo Township was done by Armstrong (1950). Johnston (1972) mapped the geology of the Vermilion-Abram Lakes area. The Sioux Lookout• area has 6 been mapped by several authors: Hurst (1932), Pettijohn (1934), Skinner (1968), Walker and Pettijohn (1971), Turner and Walker (1973), and Page and Clifford (1977), Regional studies of the area were conducted by Mackasey et al. (1974), Trowell et al. (1980), and Blackburn et al. (1982). Geologic maps were constructed by Breaks et al. (1976 a and b, and 1978). Geology of the Thesis Area A number of easterly trending metasedimentary and metavolcanic belts, all intruded by granitic stocks are found in the thesis area (Figure 2). The major metasedimentary and metavolcanic belts are: Wabigoon Volcanic Belt, Zealand Sediments, Thunder River Volcanics, Thunder Lake·sediments, Brownridge Volcanics, Brownridge Sediments, southern volcanic Belt, Minnitaki group, Central Volcanic Belt, Abram group, and Northern Volcanic Belt (Figure 2). The Zealand Sediments, Thunder River Volcanics, and the Thunder Lake Sediments are located in the Dryden area. The Brownridge Volcanics and Sediments are located north of Thunder Lake. southern Volcanic Belt, Minnitaki group, central Volcanic Belt, Abram group, and the Northern Volcanic Belt are in the eastern half of the area. Table l shows how these correlate from one end of the study area to the other. The following descriptions of these belts are a summary of the work done by the authors listed in the p
7 r
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Figure 2. Prominant lithologies of the study area. (Modified from Blackburn, 1980)
[]Volcanic Belts 1. Wabigoon Volcanic Belt 2. Thunder River Volcanics 3. Brownridge Volcanics 4. Southern Volcanic Belt 5. Central Volcanic Belt 6. Northern Volcanic Belt []sedimentary Belts 7. Zealand Sediments 8. Thunder Lake Sediments 9. Brownridge Sediments 10. Minnitaki Group 11. Abram Group
~ Granitoid Rocks ; ., I'' •• • • ~ .. ~ ~ ..·~ ~ ... ,.. <•" ~. -~ 1 • •1
z \
~ :,,: 0... TABLE 1
CORRELATION AND COMPARISON OF STRATIGRAPHIC UNITS
Moorhouse 1939 SATTERLY . 1943 TURNER AND WALKER 1973 Keweenawan: Keweenawan: Diabase Dikes Quartz Diabase Dikes
Algoman (?): Algoman (?) : Granitic Intrusives Granitic Intrusives Hybrid Intrusives Hybrid Intrusives
Hailyburian (1): Hailyburian (?): Basic Intrusives Basic Intrusives
Timiskaming (?): Sedimentary Series
Keewatin: Keewatin: Volcanic Complex Wabigoon Volcanics
Zealand Sediments
Thunder River Volcanics Minnitaki Group
Thunder Lake Sediments ---fault bounded Brownridge Volcanics Central Volcanic Belt ---fault Brownridge Sediments Abram Group ---unconformity Northern Volcanic Belt 10 previous works section. The Wabigoon Volcanic Belt.is composed of thick sequences of metavolcanics, either mafic pillowed flows or intermediate to felsic pyroclasts, with small amounts of chemical and elastic sediments. The Wabigoon Volcanic Belt has been divided into an upper and lower sequence. The lower Wabigoon volcanics are a mixed sequence of pillowed mafic flows, heterogeneous assemblages of tuff and lapillii-tuff pyroclastics and minor interflow sediments. Felsic pyroclastics and flows appear to be concentrated toward the top of the lower sequence. A Jensen cation plot of the volcanics shows a complete variation from tholeiitic to calc-alkaline flows and pyroclasts (Trowell et al., 1980). The predominantly north facing upper Wabigoon volcanics are a sequence of mafic pillowed flows, which are characteristically amygdaloidal with intercalated tuffs and cherty interflow sediments. The volcanics fall in the region of Fe-tholeiitic flows in a Jensen cation plot (Trowell et al., 1980). Zealand Sediments comprise fine to-medium-grained, well bedded greywacke, impure quartzite, pebble conglomerate, iron formation and minor slate. Thunder River Volcanics are intercalated with the Zealand and Thunder Lake sediments and pinch out to the west. They are composed of schistose, ellipsoidal green stone, and sheared and altered intrusives of diorite and 11 basic rocks. To the east they are divided and cut off by the Sandybeach granite mass. The Thunder Lake Sediments consist of greywacke, quartzite, conglomerate, arkose, and garnet-biotite schist. Interbedded with the garnet-biotite schist layer is a highly crystalline iron formation. The Zealand sediments join the Thunder Lake sediments in McAree Township to become the Minnitaki Belt (Satterly, 1943). To the west, they appear to be the same as the Timiskaming sedimentary series described by Moorhouse (1939) (Satterly, 1943) (Table l}. The Brownridge Volcanics are composed of intermediate to mafic pillowed lavas, minor felsic lavas, and agglomerates: The Brownridge Sediments consist of grey wacke, quartzite, and conglomerate. Unlike other sediments of the area they contain no iron formation. The Southern Volcanic Belt is a mafic volcanic unit consisting of massive, pillowed, amygdaloidal, and plagioclase-phyric flows with inter-flow beds of metasediments and intermediate to felsic tuffs. Detailed mapping in Avery and MacFie Townships is insufficient for correlation between the metavolcanics of the Southern Volcanic Belt and the Wabigoon Volcanic Belt. They do appear to correlate in part with the Central sturgeon Lake Volcanics further north (Trowell et al.,
1980). 12
The Minnitaki group is predominantly composed of interbedded wacke-siltstone, arkose, black fissle slate, banded iron formation and oligomictic conglomerates. The oligomictic conglomerates contain granitoid clasts which are predominatly quartz-feldspar porphyritic trondhjemite and equigranular trondhjemite. Detailed mapping of East Bay area on Minnitaki Lake (Walker and Pettijohn, 1971), shows five distinct interbed ded, stratigraphically unrestricted facies. These are: a white arkosic facies, slate facies, greywacke facies, granite bearing conglomerate and siliceous facies. These correlate with the Zealand-Thunder Lake sediments in the Dryden-Wabigoon area (Satterly, 1943). The Central Volcanic Belt is composed dominantly of mafic and intermediate metavolcanic flows with fragmental rocks and redeposited volcanic fragmental rocks. The belt has been divided into two units. The lowest unit is a sequence of felsic to intermediate flows, pyroclastic and autoclastic breccias and subvolcanic intrusions which are intercalated with and overlain by mafic metavolcanic flows. The upper unit consists of a sequence of magnesian to slightly iron-rich tholeiitic metavolcanic flows which are massive to pillowed and finely amygdaloidal. The Central Volcanic Belt appears to correlate with the Brownridge Volcanics. The Abram Group consists of three formations: Ament 13
Bay, Daredevil and Little Verl!lilion. The Ament Bay For mation is composed of granitoid-clast conglomerate with some interbedded arkosite. The granitoid-clast conglom erate contains medium-grained equigranular plutonic clasts composed of trondhjemite and microcline, and porphyritic granodiorite to quartz monzonite. Arkosic units are com posed of greater than 25 to 30 \ sand sized quartz (Blackburn et al., 1982). The Daredevil Forl!lation consists of inter1Dediate to felsic tuff and minor lapillii tuff, and wacke-siltstone. This forl!lation is intercalated with and overlies the Ament Bay Forl!lation. The Little Verl!li~ion For1Dation is composed of thickly bedded wackes and pebbly wackes, thinly bedded wacke-siltstone and shales, and a sediment clast conglomerate. The Abram Group sediments appear to correlate with the Brownridge Sediments mapped by Satterly (1943). There has been some discussion on the relationship between the Abram and Minnitaki groups. Johnston (1972) contends that the Abram and Minnitaki groups are folded and/or faulted equiv alents, while Turner and Walker (1973) contend they are not. The Northern Volcanic Belt is divided into the Botham Bay Volcanics and the Patara Sediments. The Botham Bay Volcanic sequence is the lower unit and is composed of mafic volcanic flows. Flow structures and textures, such as vesicularity and pillow forl!I, are used to subdivide the 14 volcanics into; high-magnesian flows, which predominate, and high-iron flows. An interbedded chert and quartz magnetite ironstone unit is found at the top of the Bothall! Bay Volcanic sequence. The Patara Sediments consist of a sequence of water laid material derived mainly from a volcanic source. several units have been identified: a mafic volcanic breccia unit forms the base; a mafic volcanic-clast conglomerate unit; a conglomerate-wacke-mudstone unit; an interbedded mudstone-siltstone unit; a quartz pebble con glomerate; a pebbly arkose to conglomerate unit follows with a felsic volcanic breccia facies found at the top. No formation in the Vermilion Bay-Dryden area correlates with the Northern Volcanic Belt. Granitic intrusives into the area are compositionally variable. Compositions range from diorite, quartz hornblende diorite, grey quartz-biotite diorite, granodiorite, pink granite and granodiorite, pegmatite quartz porphyry, quartz-feldspar porphyry, to quartz monzonite. These granitic intrusives were emplaced as batholiths, stocks, dikes and sills. OTHER GREENSTONE BELTS Greenstone belts are found nearly all over the world, Although there is a great deal of diversity among the belts, all share some similar characteristics. Greenstone belts are linear-to irregular-shaped, the supracrustal sequences can range in width from 5 to 250 I<:Jn and in length up to several hundred kilometers (Condie, 1981), Low-grade greenschist facies metamorphism is typical of most greenstone belts. Preservation of original volcanic and sedimentary-features is common, especially away from the contacts (Anhaeusser et al., 1969). The greenstone belts have a general idealized strati graphy that ranges from lower ultramafic/mafic volcanics to an upper largely elastic, sedimentary group capped with chemically precipitated banded iron formations and cherts (Windley, 1973). Volcanic rock types includes: ultramafic, mafic and intermediate lavas, with the mafic suite predomin ating. The volcanics frequently display pillow structures. Subordinate interbedded sedimentary horizons are characteristically associated with the volcanics. Often occuring as apparently intrusive, sill-like bodies are a wide variety of ultramafic rock types (Condie, 1981). The upper sedimentary group displays a wide array of rock types, with greywackes, shale, banded ironstones, jaspilites and cherts being particularly characteristic. In addition, conglomerates, breccias, quartzites,
15 16
Wilson et al. (1974), Wilson et al. (1976) and Wilson and Morrice (1977) noticed that volcanic belts in each shield contained similar volcanic sequences with similar lava types. Four Archean volcanic sequences were recognized: lower mafic, middle mafic, middle felsic and upper diverse. The lower mafic group is characterized by pillowed and massive, nonvesicular and unbrecciated, basalt flows and laterally extensive ultramafic sills and possibly flows. The middle mafic group is also characterized by pillowed and massive basalt flows but these are commonly vesicular and have flow-top breccia and are more iron-rich. The middle felsic group is characterized by fragmental volcanic rocks varying in composition from andesite to rhyolite. The upper diverse group is composed of volcanic rocks ranging in composition from basalt to rhyolite and including both flows and pyroclastic units (Blackburn and others, 1985). Within the study area the Northern Volcanic belt constitutes the lower mafic sequences. The lower Wabigoon Volcanics, southern Volcanic belt and Brownridge Volcanics make up the middle mafic to middle felsic sequences. The upper Wabigoon Volcanics is equivalent to the upper diverse sequence. In the western Wabigoon Subprovince, detailed stratigraphy of six sequences suggests that there was a consistent evolution through time from mafic, tholeiitic,
,- ,..,,., '~' ' 17 quiescent, submarine flows to more silicic, calc-alkaline, pyroclastic in part subaerial volcanism (Blackhurn a~d others, 1985). Comparisions of these sequences in Canada, south Africa and Western Australia are displayed in figure 3. Partucularly prominent in the Barberton belt are ultramafic successions, but the ultramafic assemblage is not always encountered in greenstone belts, particulary those in Canada. Instead, andesitic volcanics appear to be prominent in the Canadian belts. The similarity of Archean shields in Rhodesia, Australia and Canada is shown in figure 4. Looking at the. greenstone belts they show a roughly parallel, linear orientation, The volcanic-sedimentary greenstone belts are intruded by oval-shaped granitic-diapirs giving them arcurate, cuspate and synformal shapes. The structural features and size of the features are similar and each shield contains similar stratigraphic sequences. Regional metamorphic grade, within the Rhodesian, Australian and Canadian greenstone belts, is generally of the greenschist or amphibolite facies. Local increases in the metamorphic grade may occur in traveling from the center of the greenstone belt to the edges of many individual belts or around intrusive granitic stocks within the belts. The usual effects are a coarsening of textures towards the margins of the belts and the formation of
- 18
I I t I
II Figure 3. Comparative sections of Archean stratigraphy in Canada (Kakagi Lake, Stormy Lake, Shebandowan), South Africa I (Barberton) and Western Australia 'i l (Scotia). (Wilson et al., 1976) !; Kakagi Lake, Stormy Lake, and Shebandowan stratigraphic sections are from the southern half of the Wabigoon Subprovince. I< m. 30
. .
lil!lli'lll GRE'l'W~CKE 25 I ~ RH,01.JTE lilD!J ANOESITE-OACITE FRM UPPER DIVERSE mxJ BASALT cm:::ra ANORTHOSITIC GASBRO 20 - SERPENTIN'1E
,.,,,,,,4------GA98RO-PERIOOTfTE z MIDDl E .. Ll:>3\:1 AN0ESITE-OACITE FEtSIC "' fRAGMENl/lLS 15 " "'a ~ GABBRO a MIDDLE -" - SERPENTINITE z rJlllllJ BASALT MAF IC ,r 10 ~ ------./ij - SERPENTINITE LOWER ,' ~ BASALT MAFIC "'· INTRUSl\l'E CONTACT l! :J mr!m GRANITE '"> KAKAGI L. :i; ~ "'::, 0: w "' 0 i SCOTIA m
~ 20
Figure 4. comparison of the Archean shields in Canada, Australia and Rhodesia. (Wilson, 1971)
22 hornblende instead of actinolite in mafic volcanic rocks, together with the formation of andalusite, kyanite and sillimanite in aluminous pelitic rocks (Anhaeusser et al., 1969). The actual contacts of the greenstone belts with the high-grade gneiss complexes are often disrupted by later granitoid intrusions and major structural breaks (Windley, 1973 and Gorman, Pearce and Birkett, 1978). Within the Superior Province itself several areas show the same metamorphic progression as the study area. The Uchi subprovince is characterized by a gradational change from greenschist- to amphibolite-facies metamorphism. Several workers have documented a progressive increase in metamorphic grade when traveling from. the Uchi subprovince southwards into the English River subprovince {McRitchie and Weber, 1971 and Breaks et al., 1978). Intact progressive metamorphic zonations are apparent in the St. Joseph-Papaonga Lake area and in the Rice Lake region (McRitchie and Weber, 1971 and Breaks et al. 1978), The patterns resemble those found in the study area. The same progressive increase in metamorphic grade has been found when traveling southward away from the Wabigoon subprovince into the Quetico subprovince. In the Atikokan Sapaw, Crooked Pine Lake, Jellicot, Planet-Huronian and de Courcey and Smiley Lake areas the grade of metamorphism increases from greenschist- to amphibolite-facies to anatexis southward away from the subprovince boundary. 23
Metamorphic zones are broadly parallel to structural and lithologic trends (Kehlenbeck, 19761 Pirie and Mackasey, 1978 and Blackburn et al., 1985) much like those in the study area. The Kaapvall and Rhodesian Provinces are located in south Africa. The major greenstone belts of the Kaapvall Province are the Barberton, Murchison and Pietersburg belts. Metamorphic grade in the Kaapvall Province ranges from greenschist to amphibolite facies. Of all the green stone belts of the world the Barberton belts contains the most complete and one of the best preserved greenstone successions known (Condie, 1981). The metamorphic zoning includes an amphibolite facies adjacent to granities and pegmatites, grading way from the contacts into various subfacies of greenschist metamorphism (Anhaeusser and Wilson, 1981). The major difference between the study area and the Barberton belt is that the Barberton belt contains ultramafic successions while the study area does not. Another difference is that the metamorphic grade is much lower in the Barberton Belt than the study area. The metamorphic grade prevalent,in the Murchison greenstone belt is the greenschist facies. Only along some of the granite-greenstone contacts does the metamorphic grade increase to amphibolite facies. In the Pietersburg green stone belt most of the sequences display low-grade green schist facies metamorphism except at some granite contacts 24
where amphibolite facies assemblages occur (Anhaeusser and Wilson, 1981). Again the major difference is in metamorphic grade and zoning. Greenstone belts in the Rhodesian Province seem to share the same regional metamorphic imprint. The overall grade increases outward fron the center of the province ranging from prehnite-pumpellyite to amphibolite facies.
A few remnants of granulite facies terrains have also been reported (Condie, 1981). Most workers record a distinct and rapid increase in metamorphic grade as granite contacts are approached. The Yilgarn and Pilbara Provinces of Australia contain granite-greenstone terrains. The Yilgarn Province has been divided into three subprovinces based on tectonic style, metamorphic grade and lithologic abundances, much like the superior Province. The three subprovinces are: Eastern Goldfields, ·Murchison and Southwestern. Metamorphic grades in greenstone belts in both the Murchison and Eastern Goldfields subprovinces range from prehnite-pumpellyite facies to upper amphibolite facies. The southwestern sub province is composed chiefly of high-grade terrains (Hallberg and Glikson, 1981). In the Pilbara Province there is no distinct structural trend, much like the Abitibi subprovince in the Superior Province. Progressive transitions take place from heavily sheared, amphibolite facies granit-intruded (or faulted) margins of the green- 25 stone belts into little deformed lower greenschist or prahnite-pumpellyite facies in the core (Hallberg and Glikson, 1981). PETROLOGY Metasediments samples were collected from most of the metasedimen tary belts of the study area (Table 2). Metamorphosed equivalents of the following rock types were collected and described: pelitic sediments, psammitic sediments, conglom erates, amphibole-rich sediments, shales, and quartzites; Metamorphosed Pelitic Sediments (Pelitis Schists) The bulk of these rocks are concentrated between Dryden and Vermilion Bay within the Thunder Lake/Zealand sediments. Previous studies indicate metamorphic grade increases from the Wabigoon fault northward. Evidence of this increase in metamorphic grade for south to north is a coarsening of the matrix and the introduction of leucocratic material as stringers, pods and layers. common lithologic types are quartz-biotite+/-garnet +/-cordierite+/-andalusite schists and migmatitic gneisses. These sediments are commonly interbedded with metamorphosed psammitic sediments. The metapelitic rocks are medium to coarse grained, moderately to strongly foliated, with some crenulation folding and are often porphyroblastic in nature. Porphyroblastic minerals include garnet, cordierite, ·andalusite, and biotite, which in turn are often very poikiloblastic. Large (1.0-1.5 cm) "knots" of andalusite and cordierite with inclusions of quartz, biotite,
26 27
TABLE 2
COMPARISON OF STRATIGRAPHIC UNITS AND ROCK TYPES
Wabigoon Zealand Minnitaki Central Abram Volcanics Thunder seds volcanics Group Lake seds Metamorphic------Pelitic Seds X X Quartz------Amphibole X Gneiss Metamorphic------Psammitic X X Sediments Amphibole------rich seds X Metamorphic Conglomerate X
Slate------X X
Iron-rich seds X Meta quartzite X Metamorphic------Aphyric Basalt X X Basalt Porphyry X ------Pillowed Basalt X .Falsie Tuff X X Metabasite------X ------
.. ~' 28 muscovite and opaques occur in samples from the Eagle River area. Weathered surface colors are rusty to light brown, while fresh surface colors are medium to dark grey. Typical mineralogy of the sediments is quartz plagioclase-biotite +/-garnet+/-cordierite+/-sillimanite. Accessory minerals include apatite, zircon, tourmaline, monazite, opaques, and sphene. Chlorite is a secondary alteration product of biotite and garnet. Textures such as myrmekite and other symplectic intergrowths are more common in the northern half of the area. The leucocratic material of the migmatitic gneisses occur as stringers, pods and layers ranging in thickness from 1.0 cm up to several metres. They are coarse grained and granoblastic, with little to no folation. Colors range from white to light pink. Typical mineralogy is quartz plagioclase-alkali feldspar-biotite+/-garnet+/-cordierite. Composition ranges from quartz monzonite to granite. Plagioclase crystals range in composition from An22 to
An33. They often show albite and Carlsbad twinning with albite being the most common. Alteration of plagioclase to sericite occurs along twinning planes and in the cores of grains. Zonation occurs in only a few samples. Infiltra tion and replacement by alkali feldspar and quartz are common, especially in the northern half. Inclusions of quartz and biotite also occur. Biotite is the dominant mafic mineral of the rocks. 29
It is strongly pleochroic and contains pleochroic halos surrounding inclusions of zircon and apatite. Many grains are infiltrated along edges and cleavage planes by K-spar, plagioclase, and quartz. The garnets occur as poikiloblastic porphyroblasts ranging in size from 0.3 to 5.0 mm, which contain quartz, biotite and opaques. Crystals range from clear to light pink in plane polarized light and display rounded to hexagonal outlines. Many are elongated and flattened. Composition of analyzed garnets indicate they were for1I1ed from a solid solution series of almandine-pyrope with grossular and spessartine components (Appendix B). They do not show any significant compositional zonation. Cordierite generally occurs as poikiloblastic porphyroblasts 0.5 to 5.0 mm in size which contain sillimantite, quartz, biotite and plagioclase. Pinitization of the cordierite forms a yellowish alteration along the edges and fractures of the grain. Usually the cordierite is concentrated close to, or in the leucocratic material of the migmatitic gneisses, but it can also occur as discrete grains or as large ''knots" within the matrix. The cordierite that occurs as "knots" in the Eagle River area, are elongated porphyroblasts, 1.0 to 1.5 cm in size. These porphyroblasts are much more poikiloblastic than those that occur in other locations of the study area. Inclusions of quartz, biotite, plagioclase, pyrite and
..,.,. - 30 ilmenite are common. Composition of the analyzed cordierite range from 0.57 to 0.66 Mg/Mg+Fe (Appendix B). Sillimanite, when found, occurs as either needles, usually in the cores of cordierite, or as mats of fibrolite. Andalusite occurs as porphyroblasts 1.0 to 1.5 cm in size, containing inclusions of quartz, chlorite, muscovite, pyrite and monazite. Alkali fe1dspar occurs as anhedral crystals of micro cline and/or perthite. It is found mainly in the leucocratic material of the migmatitic gneisses, and often contains inclusions of quartz and plagioclase. Occuring as accessory minerals in the rocks are apatite, zircon, tourmaline, opaques, sphene and monazite. Apatite crystals are generaly subhedral to euhedral prismatic and hexagonal cross sections up to 0.5 mm in size. zircon crystals are usually less than 0.2 mm in size and are enclosed in biotite. Tourmaline crystals are less than 0.2 mm in size and generally show hexagonal cross sections. Opaques, usually pyrite and ilmenite, range from 0.2 to 1.5 mm in size. The crystals are generally sub- to euhedral cubic cross sections and are often associated with the biotite and garnets. Sphene crystals are not very common, but when found are less than 1.0 mm in size and typically show euhedral diamond-shaped or wedge-shaped forms. Monazite crystals are usually anhedral and less than 0.1 mm in size, 31
Quartz-Alnphibole-Epidote Gneiss Quartz-amphibole-epidote gneisses are fonud near Thunder Lake and are characterized by alternating layers of felsic material and mafic material, 3.0 to 10.0 mm thick. Felsic material occurs, not as a continous layer but as stringers and blebs within the layer. Felsic layers are composed of clots of anhedral, granoblastic, quartz plagioclase+/-kspar+/-carbonate+/-epidote. These are sur rounded by an interlocking matrix of quartz-plagioclase epidote+/-amphibole+/-biotite+/-sphene+/-riebeckite. Mafic layers are composed of biotite-epidote-quartz-feldspar opaques+/-amphibole. Plagioclase crystals are albite and Carlsbad twinned. Many are altered to sericite and are being infiltrated and replaced by quartz. Epidote-clinozoisite crystals occur as anhedral aggregates and euhedral prismatic forms. Biotite is bladed, containing pleochroic halos and inclusions of zircon and epidote. Alnphibole, when present, is highly infiltrated and replaced by epidote and quartz. They are poikiloblastic and bladed in form. composition was determined to be ferro-hornblende (Hawthorne, 1983). Opaques are anhedral in form, 0.3 to 0.5 mm in size. Sphene occurs as anhedral aggregates associated with amphibol.e and epidote. Riebeckite is found in minute traces, it is bladed, 0.1 mm in size, randomly oriented, and has been infiltrated and replaced by the matrix, it's 32 pleochroic in blue-violet colors. Metamorphosed Psammitic Sediments The occurrences of these rocks are more widespread than those of the metamorphosed pelitic sediments. The common lithologic type is a phyllite. The metamorphosed psammitic sediments are fine-to medium-grained, moderately foliated and generally lack porphyroblasts. Characterized by subangular to angular megacrysts of quartz, feldspar, and rock fragments, o.s to 1.0 mm in size, in a fine grained matrix of quartz, feldspar, biotite, white mica, chlorite and carbonate. Weathered surfaces are rusty to light brown in color, while fresh surfaces are medium grey in color. Relict bedding is often observed. The original rock is believed to have been as arkosic arenite or wacke according to Gilbert's 1955 classification scheme (Gilbert, 1955). Typical mineralogy is quartz-plagioclase-biotite+/ white mica+/-alkali feldspar. Accessory minerals include apatite, tourmaline, zircon, epidote, and opaques. Chlorite, carbonate and muscovite also occur as secondary minerals. carbonate veins, as well as quartz-feldspar veins cross cut the rocks. Rocks in the eastern half of the study area are less metamorphosed than those of the western half. As a result the grains are more angular in the east and there is little to no biotite present. Plagioclase megacrysts are subrounded to subangular, 33 o.5 to 1.0 mm in size. They are characterized by both albite and Carlsbad twinning. Many are altered to sericite, while others are very poikilolitic containing quartz and biotite. Alkali feldspar megacrysts are very rare. They are anhedral, 0.2 mm in size, composition is that of microcline. The megacrysts are very poikiloblastic and are being altered. Biotite grains are bladed, 0.5 mm in size, and are pleochroic. Many grains are infiltrated along cleavage planes and grain boundaries and are being replaced by opaques, plagioclase, and quartz. Accessory minerals are apatite, zircon, tourmaline, epidote-clinozoisite, and opaques. Apatite crystals are generally subhedral, exhibit prismatic cross sections and are 0.1 mm in size. Zircon crystals occur only in biotite, are generally less than 0.1 mm in size and commonly possess alteration halos. Tourmaline crystals are generally euhedral, exhibiting hexagonal cross sections, 0.1 mm in size. Epidote-clinozoisite crystals generally occur as anhedral aggregates. Opaques, pyrite, are generally euhedral and exhibit cubic shaped forms, 0.2 to 0.3 mm in size. They are intimately associated with epidote and biotite. Secondary carbonate crystals occurs in the matrix as small anhedral blebs and in veins as anhedral crystals 1.0 34 mm in size. Secondary chlorite is found in the matrix as fine bladed grains and as an alteration product of biotite. Muscovite, secondary in origin, occurs in single euhedral blades, 1,0 mm in size that are randomly orientated throughout. Amphibole-Rich Metamorphosed Sediments The amphibole-rich rocks are fine grained and phyllitic. Fresh surfaces are medium grey in color, weathered surfaces are medium dark grey to yellowish brown in color. Some relict bedding is observed. Thin carbonate -quartz-plagioclase veins, 1.0 to 2.0 mm in size, run parallel to foliation. Typical mineralogy is quartz feldspar-biotite-amphibole. Accessory minerals are epidote, opaques, zircon, and carbonate. Possible precursor rock type is a dirty sandstone or argilleaceous rock. Biotite is strongly pleochroic and contain pleochroic halos surrounding inclusions of zircon. Many grains are infiltrated and replaced by amphibole and plagioclase. Amphibole grains are sub- to euhedral and display bladed forms and prismatic sections showing typical amphibole cleavages. They are poikiloblastic containing quartz, feldspar, biotite, and opaques. Composition was determined to be ferro-hornblende (Hawthorne, 1983). Metamorphosed conglomerates All conglomerates were collected from the Sioux 35
Lookout area. Granitoid and volcanic clasts are predominent in these conglomerates. Depending on the type of clasts present, these conglomerates were called granitoid clast conglomerates or granitoid-volcanic clast conglomerates. The clasts are subrounded to subangular, pebble to cobble size and have been elongated. These are matrix supported conglomerates.
Granitoid clasts are of two textural types: 1) coarse grained equigranular type and 2) a fine grained equi granular type. Type 1 is composed of quartz-plagioclase biotite-opaques. The plagioclase grains have been altered to sericite and carbonate. Type-2 is composed of quartz feldspar-biotite-amphibole. Amphibole grains are poikilo blastic containing biotite, feldspar, opaques, and display bladed forms and prismatic sections showing typical amphibole cleavages.
Volcanic clasts are composed of phenocrysts of plagio clase in a felty matrix of epidote, chlorite, carbonate and opaques. Plagioclase phenocrysts are characterized by
Carlsbad twinning, 1.0 mm in size and are being altered to carbonate and sericite.
The matrix is medium to fine grained, moderately foliated, and composed of biotite, amphibole, epidote, chiorite, and opaques. Amphibole grains are euhedral, O.J to 2.0 mm in size, and display bladed forms and prismatic sections showing typical amphibole cleavages. These are 36 poikiloblastic, containing biotite, feldspar and opaques and are being altered to chlorite and carbonate. Epidote grains are euhedral, generally less than o.5 mm in size and display prismatic forms. Slate Slate samples are very fine grained with a slaty texture. Fresh surfaces are dark grey in color, weathered surfaces are medium dark grey to reddish brown in color. Thin veins of quartz and feldspar run through the sample. Being so fine grained it was hard to determine what minerals are present. Under high magnification quartz, feldspar, biotite, muscovite, epidote, and opaques were identified, Iron-Rich Metasediments Iron-rich metasediments are composed of two bands of material, the first band contains small anhedral grains of quartz, feldspar, muscovite, and opaques. The second band is composed prinipally of opaques, pyrite and pyrrhotite, with lenticules of coaser grained quartz and feldspar. The first band is foliated and on a fresh surface is white to cream in color. The second band is massive and on a fresh surface is gold in color. weathered surfaces are stained reddish orange due to oxidation of the iron bearing minerals. Metaquartzites Composed principally of quartz, the metaquartzites are 37 phyllitic and very fine grained. Fresh surfaces are medium light grey in color, weathered surfaces are medium dark grey in color. The matrix is composed of granoblastic quartz, feldspar, biotite, muscovite, tourmaline, opaques, epidote, chlorite, and carbonate. Biotite and opaques, concentrated in streaks, give a flaser-like texture to a few of the samples. Metavolcanics A majority of the metavolcanic samples are from the Central Volcanic Belt and have been metamorphosed to chloritic schists, phyllites and massive greenstones. Metamorphosed Aphyric Basalt Aphyric basalts are fine grained, fairly massive to phyllitic. Fresh surfaces are greenish grey colored, weathered surfaces are dark greenish grey to buff colored. carbonate veins and stringers, along with quartz-feldspar veins cross cut the samples. The groundmass is aphanitic to fine grained and has a "felty" texture. The principle groundmass mineral is chlorite with varying amounts of epidote-clinozoisite, quartz, feldspar, carbonate, opaques and sphene. Chlorite occurs as small blades. Epdiote-clino zoisite occur as aggregates of rounded grains and as single euhedral prismatic crystals. both in the matrix and as grains lining veins. Both quartz and feldspar occur as small anhedral grains less than 0.1 mm in size. Carbonate 38 occurs as small anhedral grains in the matrix and as large anhedral grains in veins. Pyrite occurs as sub-to euhedral cubic crystals, 0.1 to 0.3 mm in size. Sphene occurs as brown grungy masses. Metamorphosed Basalt Porphyry Basalt porphyries are phyllitic to slightly schistose. The matrix is fined grained with feldspar phenocrysts, and/or altered pyroxene or olivine phenocrysts, ranging from 1.. o to 15. O mm in size. Fresh surfaces are greenish grey in color, weathered surfaces are medium grey in color. Carbonate-quartz-feldspar veins, 1.0 mm in thichness cross cut the samples. The fine grained matrix is composed of chlorite, epidote-clinozoisite, carbonate, opaques, quartz, feldspar, and sphene. Epidote-clinozoisite occur as aggregates of rounded grains or euhedral prismatic crystals. Carbonate crystals are anhedral and less than 0.1 mm in size. Opaques occur as sub- to euhedral, cubic crystals 0.1 to 0.4 mm in size. Sphene occurs as brown grungy masses. Plagioclase phenocrysts are 1.0 to 2.0 mm in size and compose 30 to 40 percent of the rock. Crystals are euhedral laths of rounded and are generally Carlsbad twinned. Many of the phenocrysts are altered to sericite, carbonate and chlorite. Phenocrysts of possible pyroxene or olivine have been completely altered to actinolite with inclusions of quartz 39
and plagioclase. They are anhedral, 1.0 to 2.0 mm in size. Metabasite Metabasite samples are fine grained, massive to weakly foliated, with nematoblastic texture. Fresh surfaces are dark greenish grey in color, weathered surfaces are dark grey in color. Typical mineralogy is amphibole-chlorite feldspar-quartz-epidote-opaques+/-carbonate +/-biotite. Amphibole crystals are 0.5 to 1.5 mm in size, fairly euhedral displaying bladed forms and prismatic sections, showing typical amphibole cleavages. They comprise greater than 50 percent of the rock. Many contain inclusions of opaques and zircon. Some amphiboles have a "fibrous" (or feathered) appearance, others are zoned (hornblende cores, actinolite edges). Chlorite, finely bladed and occurs in the matrix, as the alteration product from biotite, and as radiating blades in veins. Quartz and feldspar occur as anhedral grains less than 0.2 mm in size. Epidote/clinozoisite occur as aggre gates of rounded grains or as euhedral prismatic crystals. Ilmenite and pyrite are anhedral to euhedral cubic forms. Commonly these are associated with amphibole and biotite. Carbonate occurs as anhedral grains less than 0.2 mm in the matrix. Biotite is strongly pleochroic, reddish-brown in color. Pillowed Basalt Pillow ellipsoids are, on the aver~ge, 15 to 20 cm in
.,, 40 length. Selvages are dark green in color, while the interior is greyish green in color. vesicles occur along the outer edges of the ellipsoids. Vesicles are composed of fine grained quartz, epidote, and a trace of chlorite. The interior is composed of a "felty" matrix of quartz, feldspar, and epidote, with a small amount of chlorite, opaques and carbonate. Felsic Tuff Tuffs are slightly schistose and fine grained. They contain both light and dark fragments. Weathered surfaces are brownish grey in color, fresh surfaces are very light grey in color. The fined graine~ elastic groundmass is composed of quartz, feldspar, sericite, epidote, carbonate, and opaques. ·within this matrix are porphyroclasts of subangular quartz, plagioclase, and mafic to felsic rock fragments. METAMORPHISM A modified version of the metamorphism classification scheme proposed by Winkler (1979) was used in this study (Figure 5). In Winkler's system, the fluid pressure is accepted to approximate load pressure. The grade of metamor phism in the study area was generally found to be of upper greenschist-to upper amphibolite-facies. Three isograds were identified and mapped from the mineral assemblages described in the previous section and from the use of mineral reaction data of other authors. Low-grade metamorphism is confined to the metavolcanic sequences of. the Wabigoon subprovince (Figure 6). A characteristic mineral assemblage typical of these low grade metamorphic rocks is: chlorite+zoisite/clinozoisite+/-actinolite+/-quartz These minerals coexist with plagioclase, biotite, muscovite or phengite and calcite. This assemblage is typical for the greenschist facies observed in rocks that have originated from basalts and tuffs, marls, certain pelites and greywackes (Winkler, 1979). The boundary between the low-grade and medium-grade division of metamorphism is defined by the first appearance of staurolite or cordierite (Winkler, 1979). Andalusite and garnet isograds are found within the temperature range of medium-grade metamorphism. The second sillimanite isograd marks the beginning of high-grade metamorphism
41 42
Figure 5. Mineralogical phase equilibria: (Chipera, 1985)
~ Ab = Albite AS = Al2Si05 B = Biotite Chl = Chlorite Cord = Cordierite Gt = Garnet Ksp = IC-Feldspar Ms = Muscovite OPX = Orthopyroxene Q = Quartz St = staurolite Stlp Stilpnomelane V = H20 Vapor Pyp -= Pyrophyllite MINERALOGICAL REACTIONS;
1 Pyp =As+ Q + V (Holdaway, 1971) 2 Stlp +Mu= B + Mu (Winkler, 1979) 3 Chl + Mu - st+ B + Q + V (Hoschek, 1969) 4 Chl +Mu= Cord+ B +AS+ Q (Winkler, 1979) 5 Mu+ St+ Q = B + AS (Hoschek, 1969) 6 Mu+ Q = Ksp + AS (Winkler, 1979) 7 Ab+ Mu+ Q + V =AS+ Melt (Winkler, 1979) 8 Ab+ B +AS+ Q + V =Cord+ Gt+ Melt(Wet) (Grant, 1973) 9 Ab+ B +AS+ Q =Cord+ Gt+ Melt(Dry) (Grant, 1973) 10 Granite Minimum Melt (Winkler, 1979) 11 B +Gt= Ksp +Cord+ OPX + Melt(Dry) (Grant, 1973) 12 Holdaway's aluminosilicate triple point (Holdaway, 1971) 0 0 cc
0 0,... 0 0 0 a:, Q. :E w I- 0 0 IO . " ~m Figure 6. Low-grade metamorphism in the Wabigoon subprovince. A Amphibole 8 Chlorite [] Volcanic Belts [ill Sedimentary Belts ;_,;_ >< ::, 0 0) z ' 46 Figure 7. Isograds in the Vermillion Bay-Dryden area. 0 0 0 Second Sillimanite Isograd a • a Garnet Isograd I\ I\ J\ Andalusite Isograd D, Cordierite • Andalusite 0 Garnet 0 Sillimanite .. Amphibole s Staurolite ,,.:.1;._,u;,t .,;,.,Fim0.2; IN 10 KM " 48 Figure a. rsograds in the Dryden-Thunder Lake area. ,. . . Garnet Isograd O Garnet 6 Amphibole a Chlorite - z ' w ..."< z 0 0 C, m < 3' 50 (Figures 7 and 8). Andalusite Isograd There have been several reactions proposed for the formation of andalusite porphyroblasts: 1. pyrophyllite=andalusite+quartz+H20 (Holdaway, 1971; Winkler, 1979) 2. chlorite+muscovite+quartz=andalusite+biotite+H2o. (Winkler, 1979) If pyrophyllite is present the first possible appearance of andalusite occurs under the conditions of equation i. (curve 1, Figure 5). Andalusite produced under the conditions of equation 2 will occur to the right of curve 1 in figure 5. Porphyroblasts of cordierite occur with andalusite. - cordierite does not col!llllonly appear in metapelitic rocks unt~l the garnet-chlorite, chlorite-staurolite or chlorite-Al2Si05 tie lines are broken (Hess, 1969, p. 199). Typical bulk compositions of pelitic rocks contain appreciable amounts of iron so cordierite becomes stable only after the chlorite-Al2Si05 field is breached (Hess, 1969). The most common reaction producing cordierite is: 3. chlorite+muscovite+quartz=biotite+cordierite+Al2Si05+H20 (Winkler, 1979) (see curve 4, Figure 5) at temperatures from less than 510° to 5so0 c (Hess, 1969; Winkler, 1979; toomls, 1986). There is only one occurrence of staurolite (sample VH 3, labled sin Figure 7). The fonnation of staurolite depends on the bulk chemical composition. several reactions proposed for the formation of staurolite: 51 4. chlorite+muscovite-staurolite+biotite+quartz+H2o (Winkler, 1979) s. chlorite+:muscovite+almandine=staurolite+biotite+quartz+ H20 (Winkler,1979) 6. chloritoid+quartz=staurolite+almandine+H2o (Hoschek, 1969) 7. chloritoid+Al2Si05=staurolite+quartz+H20. (Hoschek, 1969) · There is no evidence that chloritoid was ever present, thus equations 6 and 7 do not apply. Both garnet and staurolite occur in sample VH3. However they occur in different layers and not together. Equation 5 may apply for the formation of staurolite, because all the phases are present. Equation 4 is the most probable cause for the formation of staurolite in sample VH3. In either case, conditions for the formation of staurolite would be possible to the right of curve 3 in Figures. Garnet Isograd The appearance of garnet is very sensitive to bulk composition, pressure and water pressure and oxidation state. The following reactions have been proposed for the formation of almandine: s. muscovite+biotite+quartz=almandine+k-spar (Loomis. 1986) 9. cordierite+biotite=garnet+muscovite+quartz (Loomis, 1986) 10, chlorite+muscovite+quartz=garnet+biotite+H20 (Winkler, 1979) 11. chlorite+biotite(l)+quartz=garnet+biotite(2)+H20• (Winkler, 1979) Equation 8 can be ruled out because k-spar is not present in the samples at the garnet isograd. Equations 9, 10, and 11 are all possible in the formation of almandine and would .~. 52 occur to the right of curve 4 in Figure 5. Hornblende has been identified in severals areas as the dominate amphibole (Giddings, 1986). Field observations suggest that actinolite changes to hornblende at about the same P-T conditions of formation as almandine garnet in metapelitic rocks at medium and high pressures. Therefore hornblende bearing assemblages could have been metamorphosed under medium-grade metamorphic conditions. The breakdown of muscovite in the presence of quartz and plagioclase defines the boundary between medium-grade and high-grade metamorphism (curve 6, Figure 5). If a pressure of 3 Kbars is assumed, the breakdown of muscovite in the presence of quartz to form K-spar and sillimanite (the second sillimanite isograd) marks a minimum temperature of approximately 6350 c (Bartlett, 1978). At higher pressures, greater than 3.5 Kb, anatexis takes place (curve 10, Figure 5). During the process of anatexis muscovite furnishes Al2Si05 and K-feldspar component, which together with the components of previously crystalline quartz and plagioclase constitute the anatectic melt (Winkler, 1979). The leucocratic material contains quartz+plagioclase+K-feldspar+/-biotite+/-cordierite+/ garnet+/-sillimanite. Sillimanite-K-Feldspar Isograd Fibrolite is the common variety of sillimanite at and above the isograd. Fibrolite is a metastable mineral which 53 probably forms from the reaction of a mineral or mineral assemblage which has been made unstable by overstepping of the equilibrium boundary (Holdaway, 1971). Formation of fibrolite from andalusite can be ruled out because of the large amount of overstepping required (Holdaway, 1971), Almandine only occurs with cordierite under muscovite stable conditions if the rocks are K-deficient or if almandine is stabilized by high Mn or Ca (Holdaway and Lee, 1977). The garnet-cordierite assemblage becomes stable by the common reaction: biotite+sillimanite=garnet+cordierite at 600° C at 2 Rb total pressure and.. lRb water pressure (Loomis, 1986). This agrees with P-T-X relations deter mined by Martignole and sisi (1981) and Lonker (1981). As total pressure and water pressure increase so will the temperature at which the reaction becomes stable (Loomis, 1986). GEOTHERMOMETRY/GEOBAROMETRY The microprobe analyses in Appendix B were applied to three geothermometers (biotite-garnet, garnet-cordierite, and biotite-cordierite) and two geobarometers (garnet cordierite and garnet-plagioclase-sillimanite-quartz) which were used to estimate temperature and pressure conditions during metamorphism of the area. Biotite-Garnet Thermometry Biotite-garnet thermometry is based on the temperature-sensitive exchange of Fe and Mg between coexisting phases. Biotite becomes more Fe-rich and garnet more Mg-rich with increasing temperature. The continous exchange reaction is: Fe-garnet+ Mg-biotite =Mg-garnet+ Fe-biotite The change in volume for the reaction is small, thus the reaction is essentially pressure independent and temperature dependent. This thermometer is widely used because it is a common assemblage in many metamorphic rock types. Biotite-garnet geothermometer calibrations of Thompson (1976), Ferry and Spear (1978), Goldman and Albee (1977), • Perchuk and Lavrent'eva (1983), Ganguly and Saxena (1984), and Indares and Martignole (1985a) were used in this study. For a given lnK (lnK = ln((XMg/Xpe)Gt/(XMglXFe)bio)), variations in temperature values exist between the various biotite-garnet geothermometer calibrations. See Chipera 54 55 (1985) for a discussion on the calibration and relation ships of these geothermometers. Results from the application of the thermometers are in Table 3. The Ferry and Spear, Perchuk and Lavrent'eva, Thompson, and Ganguly and Saxena thermometers produce temperatures that are within+/- 50° C of each other. Goldman and Albee and Indares and Martignole produced temperatures lower than the others. Ferry (1980) found that although the Goldman and Albee calibration qualitatively corrects for compositional effects, it may occassionally overcompensate for them. This condition may also be true for Indares and Mar~ignole calibrations. Although the temperatures differ between the various thermometers, higher temperatures were recorded in the northern half of the study area with a decrease southwards toward the Wabigoon subprovince (Figures 9 and 10). Garnet-Cordierite Geothermometer The garnet-cordierite thermometer is nearly identical to the biotite-garnet geothermometer, and is based on the exchange reaction: Fe-cordierite +Mg-garnet= Mg-cordierite + Fe-garnet Thompson (1976) and Perchuk and Lavrent'eva (1983) thermometers were used and the results are in table 4. Thompson's thermometer produced temperatures that varied +/- so0 c than those calculated from biotite-garnet geother mometry, Perchuk and Lavrent'eva produced temperatures 60 ------~- 56 TABLE 3 BIOTITE-GARNET THERMOMERTRY Temperature in Degrees C Mg/Mg+Fe SAMPLE Gt Bio lnK. FS PL TH GS GAl GA2 !Ml IM2 ------M2 0,083 0,299 -1.55 640 630 620 680 560 480 560 530 M3 0.136 0.426 -1.55 650 630 620 630 560 540 560 570 S4 0.128 0,425 -1.61 620 610 600 620 550 520 540 570 S6B 0,124 0.371 -1.42 700 650 650 720 580 580 600 680 S7 0.139 0.473 -1.71 590 600 570 580 530 520 530 560 sac 0.176 0,481 -1.47 680 640 640 610 580 580 600 620 S9A 0,146 0.477 -1.68 600 600 580 570 530 520 540 560 A4 0.150 0,516 -1.79 560 580 550 580 510 580 520 620 AlO 0.090 0.288 -1.41 700 660 660 760 590 540 610 680 VH3B 0.059 0.342 -2.12 460 520 480 540 460 410 450 490 Z4B 0.088 0.460 -2.17 450 520 470 550 460 520 470 590 Z7 0.071 0.337 -1.89 530 560 530 570 500 420 500 490 MAl 0.097 0.452 -2.14 460 520 480 510 460 440 430 490 ------lnK ln((XMg/XFe)Gt/(XMj/XFe)Bio) FS -= Ferry and Spear (l 78) PL = Perchuk and Lavrent'eva (1983) TH = Thompson (1976) GS = Ganguly and Saxena (1984) GAl = Goldman and Albee (1977) second parameter solution GA2 = Goldman and Albee (1977) fifth rank solution IMl = Indares and Martignole (1985a) using thermodynamic data only IM2 = Indares and Martignole (1985a) using both thermodynamic and empirical data 57 Figure 9. Temperature trends in the Vermilion Bay-Dryden area. - ,,,,,,_ ···,'cs;:,,,~ 1N 10 KM 59 Figure 10. Temperature trends in the Dryden-Dinorwic area. () z \ Ill <"' I ... I I z 0 0 o I (ll ' m g < :t «>' ,, 61 TABLE 4 GARNET-CORDIERITE GEOTHERMOMETRY Mg/(Mg+Fe) Perchuk SAMPLE GARNET CORDIERITE lnK Lavrent'eva Thompson (1983) (1976) ------M3 0.136 0.663 -2.53 520 730 54 0.128 0.609 -2.36 560 570 S6B 0.124 0.566 -2.22 590 600 S9A 0.146 0.630 -2.30 570 580 ------ TABLE 5 BIOTITE-CORDIERITE GEOTHERMOMETRY Mg/(Mg+Fe) Perchuk SAMPLE BIOTITE CORDIERITE lnK Lavrent•eva (1983) ------M3 0.426 0.633 -0.975 1070 S4 0,425 0.609 -0,745 700 S6B 0,371 0.566 -0.793 760 S9A 0.477 0.630 -0.624 580 S2C 0.452 0.632 -0.733 690 T4 0.465 0,640 -0.716 670 TS 0.482 0,660 -0.735 690 62 to 100°c lower than those calculated from biotite-garnet geothermometry. Newton and Wood (1979) and Martignole and sisi (1981) point out that the water content in the cordierite has a profound effect on the garnet-cordierite equilibria but the effect has yet to be thoroughly evaluated. Neither geothermometer take the water content of cordierite into consideration and may be the cause of the discrepency in temperatures. Cordierite-Biotite Geothermometry The cordierite-biotite thermometer is dependent on the exchange of Fe and Mg between coexisting phases and is based on the exchange reaction: Fe-cordierite + Mg-biotite = Fe-biotite + Mg-cordierite Perchuk and Lavrent'eva (1983) thermometer was applied and the results are in Table 5. The calculated temperatures are 60 to 100°c higher than those calculated by the other geothermometers. Both cordierite and biotite are hydrous minerals and their water contents were not taken into consideration. Of all the various geothermometers the biotite-garnet geothermometer seems to be the most consistent with metamorphic reaction data. Garnet-Cordierite Geobarometery Garnet-cordierite geobarometry is based on the reaction: 3Fe-Mg cord= 2Fe-Mg Garn+ 4Sill + 5Quartz +/- H20 Since there is no stable sillimanite found in the samples 63 the geobarometers will be recording maximum possible pres sures. Newton and Wood (1979), Martignole and Sisi (1981) and Hutcheon et al. (1974) geobarometers were used. Newton and Wood (1979) using Mirwald-Schreyer (1977) cordierite hydration data, corrected quantitatively for the hydration state in deriving standard state thermodynamic properties of Mg-Cord from experimental data taken at conditions of PH20 equal to PoroTAL (Table 6). Because PH20, is an unknown varible, the mineral assemblage can be used only to estimate a range of metamorphic pressures. The range is 4.3 to 5.6 with lower and upper limits corresponding to conditions of Pff20-o and Pff2o•PoroTAL (Ferry, 1980). The pressures determined from the cordierite isopleths were generally 1 :Kbar greater than those determined from the garnet isopleths. Theoretically both the garnet and cordierite isopleths should give the same pressure. Martignole and Sisi (1981) re-evaluated the geobarometer and Mg/(Mg+Fe) isopleths were derived for cordierites of varying nH20 (O,S, 0.5, and O.O). They also found that there are three variables which will determine the pressure a rock will record: temperature, amount of water with which the cordierite equilibrated and the mole fraction of Mg in garnet and cordierite. Pressures varied from 5.4 to 7.0, 3.6 to 4.8 or 2.6 to 3.6 :Kbars depending on how much water was assumed to exist in the cordierite 64 TABLE 6 GARNET-CORDIERITE GEOBAROMETRY (Newton and Wood, 1979) Pff2o=i>TOTAL Pff2o=O Mg/Mg+Fe GARNET CORD GARNET CORD SAMPLE TEMP GARNET CORD Kbars Kbars Kbars 10::>ars ------M3 600 0,136 0.663 4,3 5.6 3.3 4.3 S4 600 0,128 0.609 4.3 5.4 3.2 4.1 S6B 700 0.124 0.566 4.2 5.2 3.3 4.1 S9A 600 0.146 0.630 4.3 5,5 3,3 4.1 ------ TABLE 7 GARNET-COROIERITE GEOBAROMETRY (Martignole and Sisi, 1981) nH20=0.8 nH20=0.5 nH20=0 Mg/Mg+Fe GAR CORD GAR CORO GAR CORD SAMPLE TEMP GARNET CORO Kb 10:) Kb Kb Kb Kb ------M3 600 0,136 0,663 5.3 5.9 3.6 4,2 2,8 3.2 S4 600 0.128 0.609 5.0 5.4 3.4 3.8 2.6 2.8 S6B 700 0.124 0,566 6.8 7.0 4.4 4.8 3.4 3.6 S9A 600 0.146 0.630 5,2 5.5 3.8 3.9 2.8 3.0 ------~------65 (Table 7). Hutcheon et al. (1974) thermometer/barometer assumes ideal ionic solution in garnet and cordierite and that the stability of cordierite is independent of water content. Pressures of 2.5 to 3,3 Kbars is consistant with the other barometers but the temperatures are 30o0 c lower than those produced by the biotite-garnet geothermometer again because of the water content of cordierite (Table 8). Garnet-Plagioclase-Sillimanite-Quartz Geobarometry Garnet-plagioclase-sillimanite-quartz barometry is based on the reaction: Janorthite - grossular + 2sillimanite + quartz Since there is no stable sillimanite present, this barometer records the maximum possible pressures of equilibriation. Geobarometer calibrations of Ghent {1976), Perchuk et al, {1981), and Chipera {1985) were used. Ghent (1976) uses a value of 1.276 for the activity coefficient of anorthite and a value of W=lOOO for the activity of grossular, Perchuk et al. (1981) used a pressure formula from Aranovich and Podlesskii {1980). Chipera (1985) used Newton's (1983) activity model for anorthite and Ganguly and Saxena's (1984) activity model for garnet. When these barometers were applied to rocks from the study area.it. was found that Ghent (1976) produced pressures 1.1 to 3,4 Kbars and was lower than the others. 66 TABLE 8 GARNET-CORDIERITE-SILLIMANITE-QUARTZ THERMOMETRY (Hutcheon, Froese and Gordon 1974) Hutcheon Hutcheon Mg/Mg+Fe et al. et al. SAMPLE CORD GARNET TEMP Rbars ------M3 0.663 0.136 330 3.0 S4 0.609 0.128 380 2-6 S6B 0.566 0.124 430 3.2 S9A 0.630 0.146 400 3.3 ------TABLE 9 GARNET-PLAGIOCLASE-SILLIMANITE-QUARTZ GEOBAROMETRY SAMPLE TEMP Xan Xgr Xal lnK G p C ------M3 600 0.254 0.029 0.121 0.763 -9.6 1.2 3.0 2.4 S4 600 0.245 0,026 0.111 0.751 -9.4 1.1 2.1 2,3 S6B 700 0.217 0.023 0.099 0.699 -9.0 3.2 3.8 3,9 S9A 600 0.299 0.028 0.129 0,758 -9.3 1,5 3.2 2.8 Z4B 500 0.326 0.181 0.050 0.516 -3.3 6.1 8.3 9.1 A4 550 0.256 0.045 0.110 0.623 -7.7 2.5 4.3 4.4 VH3B 500 0.232 0.080 0.047 0.762 -6.l 3.4 5.1 5.6 ------lnK • ln( (~r)/ (Aan) 3) Xan = Ca/Ca Na+K in Plagioclase Xgr = Ca/Ca+Fe+Mg+Mn in Garnet G = Ghent (1976) p = Perchuk et al. (1981) C - Chipera (1985) 67 Perchuk et al. {1981) produced pressures of 2.7 to 5.1 I I I I Figure 11. Pressure trends in the Vermilion Bay-Dryden area. I 1 I I 1N 10 KM 5 <:: C } I ~ERMIL~ON Q f'\ U \ ,rr::c: ( _..::.._,_ ~4-5 l~-5 --- DISCUSSION The bulk chemical composition of rock types is important in the formation of metamorphic index minerals. A petrographic study of all the various lithologies shows that the major minerals, quartz, plagioclase, and biotite; and the accessory minerals, iron oxide, zircon and apatite, are common throughout the study area. Assuming that the minerals in the various lithologies were formed previous to, or at the same time as, the peak of metamorphism, the temperatures obtained should reflect the maximum thermal conditions. Approximate minimum temperatures can be deduced from observations of changes in mineralogy and .known metamorphic reaction data. Three isograds were identified from the appearance and disappearance of metamorphic index minerals: andalusite, garnet, and second sillimanite. The most southerly isograd is the andalusite isograd which is north of the I metasediment-metavolcanic contact. At the andalusite isograd cordierite and andalusite porphyroblasts are the key index minerals. The presence of andalusite indicates pressures of less than 4 Kb and temperatures of greater 400 0 C. Cordierite indicates pressures and temperatures of 1 to 3.5 Kb and soo0 c to 54o0 c respectively. The garnet isograd was determined by the first appearance of garnet and the disappearance of andalusite and cordierite. The presence of almandine indicates 70 71 pressures and temperatures of 3.5 to 4 Kb and 5oo0 to 60<:fc respectively. Hsu {1968) found that reducing conditions are essential for the formation of almandine. The amount of Mn and Ca influences the stabilization of almandine-rich garnets. The more Mn and Ca the lower the temperature for formation {Loomis, 1986). In common rocks the pressure must exceed 4 Kb when almandine is formed at temperatures of about. soo0 c {Winkler, 1979). The breakdown of muscovite in the presence of quartz and plagioclase defines the boundary between medium- and high-grade metamorphism which is represented by the second sillimanite isograd. North of the isograd an increase in the abundance of granitic rocks is seen: apparently due to an increase in the degree of anatectic melting~ This would indicate that the temperatures within the melting range are being approached. The cordierite, biotite and garnet present in the granitic rocks exposed along Highway 17, and areas north of it in the Vermilion Bay and Dryden area, are assumed to have melted out from the metasedimentary rocks. The first appearance of garnet in the presence of cordierite is dependent upon both pressure and the bulk composition of the rock. Most natural cordierites are magnesium-rich and the amount of iron end member that can be incorporated into the cordierite structure is limited {Holdaway and Lee, 1977). When the FeO/MgO ratio exceeds this limit garnet must appear. Also if the garnet has 72 sufficent amounts of Mn and Ca it will be stabilized at lower temperatures and pressures. This may account for the reason why cordierite and almandine garnet are occuring together at lower temperatures and pressures than those published by other authors. Following Winkler's (1979) metamorphism classification scheme the andalusite and garnet isograds represent areas of medium-grade metamorphism. The reasonable pressure temperature estimates might be less than 3.5 Kb and 6oo0 c here. At the boundary between medium- and high-grade the pressure and temperature lie very close to 3.5 Kb and 63o0 c respectively. A pressure increase to 4 to 4.5 Kb occurs northwards as well as an increase in temperature to that necessary for ·the formation of migmatites. Three geothermometers (biotite-garnet, garnet cordierite, and biotite-cordierite) were used to estimate thermal conditions during metamorphism of the area. Of the three the biotite-garnet geothermometer gave results most consistant with those estimated from mineral assemblages and reactions. The garnet-cordierite and biotite cordierite geothermometers produced temperatures that varied+/- 50 to 100°c from those produced from biotite garnet geothermometry. Cordierite is a hydrous mineral and the water content was not taken into consideration, possibly causing the discrepency in temperatures. Temperatures estimated from geothermometry are 73 consistant with temperatures estimated from the petrographic studies. The medium-grade areas ranged from 490°c in the southernmost half to 58o0 c just below the second sillimanite isograd. Temperatures of 600° to 66c:f'C were calculated from samples in the northern half of the study area. Two geobarometers (garnet-cordierite and garnet plagioclase-sillimanite-quartz) were used to estimate pressure conditions during metamorphism of the area. In the garnet-cordierite geobarometers nH20 was varied depending on how much water was assumed to exist in the cordierite. When PH20 was assumed to be less than PToTAL, calculated pressures for the northern half of the study area (above the second sillimanite isograd) ranged from 3.9 to 4.8 Kb, consistant with those derived from mineral assemblages and reactions. Garnet-plagioclase-sillimanite-quartz calibrations of Ghent (1976), Perchuk and others (1981) and Chipera (1985) were used. Calculated pressures were at least 1 Kb lower than those calculated from garnet-cordierite geobarometry. Of the three Perchuk and others {1981) calibration was most consistant with those derived from mineral assemblages and reactions. The observed changes in mineralogy are characteristic of a regular progressive increase in metamorphic grade. Geothermometer and geobarometer calculations support this M •~• 'I 74 statement by showing a gradual increase in temperature and pressure with no major jumps or breaks from south to north. The metamorphic history of the area can be summarized by three metamorphic events. The first metamorphic event produced the main regional metamorphic zones with the growth of biotite, muscovite, garnet, andalusite, cordierite and sillimanite poikiloblasts. The second metamorphic event resulted in the formation of the main schistosity of the area, and is defined by the wrapping of biotite and muscovite around porphyroblasts. The coarsening of the matrix occurred at this time. The third metamorphic event produced deformation features such as the kinking of biotite. Emplacement of quartz veins occurred, as well as fracturing of the rocks, thereby allowing the passage of fluids through the rock system. This resulted in the alteration of many of the mineral grains such as the pinitization of cordierite and the sericitization of plagioclase. The metamorphic zonation in all greenstone belts is quite close to each other. Each show low-grade metamorphism in the cores of the belts increasing to higher-grade metamorphism along their margins. Most contacts between greenstone and gneissic terrains have been disrupted by later granitoid intrusions or complicated by major structural breaks. Most authors have come to the conclusions that certain 75 geologic features such as, stratigraphy, structure, metamor -phism, relationship to shield granites and the geotectonic setting, are common to all greenstone belt with minor variations from belt to belt caused by variations in tectonic style, erosional level and thickness of Precambrian crust. CONCLUSIONS Metamorphosed pelitic sediments, migmatitic gneiss, metamorphosed psalmllitic sediments, amphibole-rich sediments, metamorphosed conglomerates, slate, iron-rich sediments and metaquartzites comprise the sedimentary sequences. Metamorphosed aphyric basalts, metamorphosed basalt porphyries, metabasites, pillow basalts and felsic tuffs comprise the volcanic sequences. The results from the application of several geobaro meters indicate that the pressures ranged from 3 to 4,5 Rbars and were fairly constant throughout the study area. Temperatures attained from the application of several gee thermometers indicate there is a gradual increase from 45o0 c in the southern half of the study area to 65o0 c in the northern half. There are no discontinuities in the isobars or isotherms. Several isograds were determined amd mapped. These divide the area into: 1.) an area of medium-grade, andalusite-bearing metamorphosed pelitic sediments, 2.) an area of medium-grade, garnet-bearing metamorphosed pelitic sediments, and J.) an area of high-grade metamorphosed pelitic sediments containing metastable sillimanite. Trends of the isograds generally parallel the metavolcanic metasedimentary contact between the Wabigoon and English River Subprovinces. Metamorphic grade ranges from middle greenschist- to upper amphibolite-facies. 76 77 The study area represents either a part of the English River subprovince or a transitional zone between the Wabigoon and English River Subprovinces. Greenstone belts are not all the same; minor differences of sequence and facies changes together with local unconformaties are commmon. The study area is a variation from the other greenstone belts of the world. ,. •.• ~ APPENDICES 79 APPENDIX A SAMPLE LOCATIONS 80 Figure 12. Location of Townships in the study area. I I I I lj .. ',,',-.;,' BLOCK NO. 10 SIOUX LCOKOU1' t ' .. RUGBY I BAIT'(ON ECHO I 11 I I I I I I------I I /llf G~ SANFORD! ETON ROWNRIDG V WIC AVERY 82 Sample Localities Langton Eton Brownridge Block 10 Ll El Bl SLl0-1 L2 E2 SLl0-2 E3 south Worth SLl0-3 Mutrie SWl SLl0-4 Ml Wainwright SW2 SLl0-5 M2 Wl SLl0-6 M3 W2 Hartman SLl0-7 M4 W3 Hl SLl0-8 MS W4 H2 SLl0-9 M6 WS HJ SLl0-10 W6 H4 Temple W7 HS Echo Tl WB H6 (collected T2 W9 H7 by Steve T3 WlO Giddings) T4 Wll McAree HW 3 TS MAl HW 3A T6 Van Horne HW 4 T7 VHl Pickerel HW 7 VH2 US1 OA 9 Aubrey VH3 US2 z2-2 Al VH4 US3 Z2-18 A2 VHS US4 A3 VH6 USS A4 VH7 US6 AS US7 A6 Zealand USS A7 Zl. AS Z2 Jordon A9 Z3 Jl Al.O Z4 J2 All. ZS JJ Al2 Z6 J4 Z7 JS Sanford ZB J6 Sl Z9 J7 S2 Zl.O S3 Zl.l. Drayton S4 Zl.2 01 SS Zl.3 02 S6 Zl4 S7 ZlS SS Zl.6 S9 Zl.7 Sl.O Zl.B Sl.l. Zl9 Sl.2 Z20 Sl.3 Z21 83 Figure 13. Sample locations, Vermilion Bay to Dryden • Thin sectioned samples 0 Uncut samples 'c,;,.v·, - I • rw:r.i ,f :f'ftl'iilf!j'fe/'ialldi!l'[f~. IN 10 KM E1 w A12 A11 I 85 l Figure 14. Sample locations, D:r:yden to Sandybeach Lake. • Thin sectioned samples O Uncut samples -. ·,·. ":,.' ',,Ail its !~ :, *' ,.. -,, ·;r:.-'\ ff''· I'd>: jN qi •Zt9 oz21 WABIOOON LAKE ~GOON 10 KM 87 Figure 15, Sample locations, Sandybeach Lake to Superior Junction. • Thin sectioned samples O Uncut samples z 0 "'0 => :c z ' APPENDIX B MICROPROBE ANALYSES 90 OBTAINING CHEMICAL DATA Mineral analyses were obtained from polished thin sections using a JEOL 35C scanning electron microscope equipped with a Li drifted silicon detector. Standard operating conditions were 15 Kev (accelerating voltage) and 1000 picoamps (beam current). Energy dispersive spectra were processed by a Tracor Northern (TN2000) operating system and corrected using~ Bence-Albee correction program. A counting time of 120 seconds was used. Natural garnets, biotites, and feldspars were used as standards. In mafic minerals garnet R-1134 was used to standardize for Si-Al-Fe-Mg-Ca; rhodonite R-1826 was used to standardize for Mn; Biotite 4-166 for Ti and K. In feldspars, standards were Tib Albite for Na; Orthoclase OR-lA for K and Barton Ang5 Ab15 for ca. Relevant chemical data for the standards (wt%) are as follows: Garnet R-1134 Tib Albite Si = 40.067 Na= 11.810 Al = 22.233 Fe = 23.138 orthoclase OR-lA Mg = 9.110 K = 14.920 Ca = 5.866 Barton An85 Abl5 Biotite 4-166 ca= 17.140 Ti .. 3.200 K = 9.222 Rhodonite Mn,. 45.150 The standards were analyzed prior to unknowns. Six spectra w~re collected for each standard and regressed 91 individually to see if any points were anomalous. All consistent spectra were averaged together and corrected using the Bence-Albee correction program. If the ' calculated weight percentages didn't match those of the reference compositions of the standards above, the correction factors in the XML fitting program were manually changed. A new correction factor was calculated from the equation: reference weight percentage/ calculated weight percentage x old correction factor= new correction factor then refit using the Bence-Albee correction program. This process was repeated until the calculated weight percentage of all elements remained consistant {usually requiring two iterations) • Precision and accuracy of 14 natural and synthetic standards are listed in Table 10. Six analyses per standard were averaged, after standardizing by the method described above. The results were compared to the reference compositions of the standards given above. Relative error and one standard deviation were calculated for each standard and element. Some heterogeneity in the standards and occasional inclusions may account for the observed discrepancies. Minor differences at low concen trations account for the large relative errors. For minerals in thin sections, 3 to 4 analyses on 3 to 4 grains were obtained and averaged together. Garnet cores and matrix biotite isolated from garnet were probed. These - 92 are believed to be least affected by late Fe-Mg re-equili bration (Tracy et. al., 1976; Indares and Martignole, 1985b). ::,; ;; :i.e 8~1 U, 1~ ~~ !. .;..;,; ~~ '· ~.;~ ~~,. ~·; ••• O'Oi' ,i ,i t ~~·.99 • ... :: .. .: ... ..~i " ' • eM ~;:; , .. :=::s ~~~ :;s:: ~:;; "!:-:-: ;; ~2: "':1:l!'"t i: ;•; .:,;i:: -··-u: '! J. -·~-- ' ' ••i - ' - . • & -··- -·-- • ··- -·· :: == ~~:; =u ~1!; :;;~ ~ !!;; ~~ '· s~$ === .:o.;=•= ..:oo .. , ti O,i ... ;::07 om7 ••• .-·- ' 7 • - ' :=:i= =:,u: ::g=: a:;:: ;u .,; if 8 :==.,,;.,;..; =··.'":"!: ~~ '· l>l-= ~d; .. , ..:01 - ;:o !; ci D 8 ••• .. , . 7 ··~ :u;a: :.; ;It 88. 88, :: ... ~~ •. :ss ~~=i :;~~ --- o•g !!o; 001 ... • ~ i•i ••• :t•i: ••• ·- 7 .. j 88, ··~:s::: ::!!~ 11 ~= ~st~ 00 .•• "!"!"! "!":"l: ~~~ ~~,. ~~·. i ,: .. ;t Ci 'f -·--01 -·- .;.; i =Qi 60~ ••• ••• ! £ i . ~ =·~ t •• .. • •: ' • I! =;; U, ~~=: 118 ~;8 !t:8 :i:t :: g 11•-.. ! i .. ~: ;•; oot ... 00 f ciO=i ci.; 8 ! i s! ••i ••i ! ii - ' ~ ··-' ::s I ! 7 • : - : f 2 :! • !.. ! ! ;::; 8S, U, 88. !: 2; ~2= 88, i l 1 J H 1· .;.,; ; ,i. ~~\ GO ,' ' 1 • = r • ! ua ~\ ;•i ••= t ••• :oi ..:o~ £ •• ] =~ .i"i .... ;• ! . i = ! lg!i • UM • ~ i • ,, ! •• ::::; ;;gg ::::: ::: ~~~ sa8 :;~; g:; : : : 1. ~1 i.•i .: • i :::•, ~5 :• 00i $:.:, --·...... = = ,!jj "3 T ··~ 7 • --~• f f f i ...C:l =. 1~ • ~ ='a :. ... ••• 8!:1 8:!:, i ":"':"l ~;,. "'l~"': It~ 1. .;=~, ,,; t 00{ ·-· === j HJ !I :0s; ••• =°'~; ••• 00/ -··---; i.Oi ! l! ! : '• . n, I~, A~ =~= ~~~ ~;=; ~~\oo, ~! !· ao; ~~ '• ~~; oo; -=$ ;•; ••• -·~- . ••• -·-- " ~~~ ij;~ ::~= ~~:; 211 ~'!~ ::as ::ss l::?:t OOi •00 .. ~ ... 'i' . ..; :i•; .. , oo: oos iOf ;.. - T • . ' :;;:~ II"" :::=: :u:i "M =~g •·s ;::g :; ~~~ ~"t"'t 000 ;;;; 8 ao..: .,... ' ;iOi ftO,j-· .i_O~ ... ..,': ; - . ••: 7 • -·- " • :::,:a : lt!I 88, =~ ~;~ ~~ \ ::;~~ ;=:~ ,,; .; i' ~~ 1. ;: 90' ~ ... o ,! :• .:.oo ... ••• Q~ '"' ::-, i' ;:: I :N I • ~.- ~ - I I 3 • ·-- 94 XMg = Mg/Fe+Mg XFe = Fe/Fe+Mg Xan = Ca/Ca+Na+K Xab = Na/Ca+Na+K Xor = K/Ca+Na+K Xpy = Mg/Mg+Fe+Ca+Mn Xal = Fe/Mg+Fe+ca+Mn Xsp - Mn/Mg+Fe+ca+Mn Xgr = Ca/Mg+Fe+Ca+Mn / -: * Calculated as Fe+2 95 MICROPROBE ANALYSES GARNET ~ Ml li S6B Ill sac ~ ., --.~ Si02 38.87 37.31 37.84 37,56 37,81 38,06 37.80 Al203 22.32 21.18 21,62 21. 43 21.28 21.42 FeO 21.43 '.) 40.78 34.28 33.78 30,93 32.51 32.40 34.05 MnO 1.21 3.87 5.00 7.86 5.12 3.51 3.88 MgO 2.07 3.04 2.79 2.46 2.96 3.88 3.26 Cao 0.78 1.02 0,93 0.77 1.06 1.03 0,87 TOTAL 106,03 100.70 101.96 101.01 100.74 100.30 101.29 NORMALIZED MOLES BASED ON 8 TOTAL CATIONS Si 2.98 2.99 3.oo 3.01 3.03 3.04 3.01 A1IV 0.02 0.01 o.oo o.oo o.oo o.oo AlVI o.oo 2.00 1.99 2.02 2.02 2.01 2.01 2.01 Mg 0.24 0.36 0.33 0,29 0.35 0.46 0,39 Fe* 2,62 2.30 2,24 2.07 2,18 2.16 2.26 Mn 0.08 0.26 0.34 0.53 0,35 0.24 0.26 Ca 0.06 0.09 0.08 0.07 0.09 0.09 0.07 TOTAL 8.oo 8.00 8.00 8.00 8,00 8.oo 8.oo 0 11,99 11.99 12.01 12.02 12,03 12.04 12.01 Xpy 0.08 0.12 0.11 0.10 0.12 0.16 0.13 Xal 0.87 0.76 0,75 0.70 0,73 o. 73 0.76 Xsp 0.03 0.09 0.11 0.18 0.12 0.08 0.09 Xgr 0.02 0.03 0,03 0.02 0.03 0.03 0.02 96 MICROPROBE ANALYSES GARNET A4 AlO Yru.D li.B ll HP.! ~ Si02 37.73 37.33 37.96 38.96 37.75 37.54 37.92 Al203 21.30 21. 48 21.40 21.91 21.04 21.06 21.52 FeO 27 .20 33.49 33.45 23.19 ,.' 38.85 29.83 35.32 MnO 9.57 6.99 4.80 11.22 0.39 6.38 2.47 MgO 2.70 1.86 1.17 1.26 1.67 1.63 3.34 cao l..55 0.68 2.75 6.36 1.74 1.56 0.37 TOTAL 1.00.05 1.01. 83 l.01.. 53 l.02.90 l.01..44 98,00 l.00.94 NORNALIZED MOLES BASED ON 8 TOTAL CATIONS Si 3.04 2.98 3.04 3.05 3.03 3.10 3.02 A1IV o.oo 0.02 o.oo 0.00 o.oo o.oo 0.00 A1VI 2.02 2.01. 2.02 2. 02 l..99 2.05 2.02 Mg 0.32 0.22 0.1.4 O.l.5 0.20 0.20 o. 40 Fe• 1.83 2.24 2.24 l..52 2.61. 2.06 2.36 Mn 0.65 0.47 0.33 0.74 0.03 0.45 0. l. 7 Ca 0.13 0.06 0.24 0.53 0.1.5 0.14 0,03 TOTAL 8.00 8.00 8.00 s.oo 8.00 s.oo s.oo 0 12.05 12.00 12.05 12,06 12.02 l.2.13 12. 04 Xpy 0.11 o. 07 0.05 0.05 0.07 0,07 0.13 Xal 0.62 0,75 0.76 0.52 0.87 0.72 0.80 Xsp 0.22 0.16 0.11 0.25 0.01 0.16 0.06 Xgr. 0.05 0.02 0.08 0.18 0.05 0.05 0.01 - 97 MICROPROBE ANALYSES BIOTITE ~ H.J. li §.fill fil. ~ ~ Si02 34,88 34.37 34.69 35,52 35.46 35.73 34.78 Ti02 2,59 2.81 2,87 2,74 2.17 2.39 1.88 Al203 19.21 18,46 18.94 19.51 18.61 18.90 19,06 Feo 23.25 19,27 20,45 21.89 19.13 18.36 18.97 MnO 0.13 0.22 0.23 0,41 0.20 0,16 0.19 MgO 5.56 8.02 8.47 7,24 9,63 9.56 9.71 cao 0,16 Q.13 0.15 0.12 0.10 0,14 0.20 Na20 0.16 0.04 0,04 0.11 0.09 o.oo 0.24 K20 9.14 9,19 8.90 9,23 8.91 9,28 9.13 TOTAL 95.08 92,51 94.74 96.77 94.30 94 .52 94.16 NORMALIZED MOLES BASED ON (01o(OH)2) Si 2.71 2.70 2.67 2.69 2,72 2,72 2,68 A1IV 1.29 1.30 1,33 1.31 1,28 1.28 1, 32 A1VI 0.46 0.41 0,39 0.43 0.40 0.42 0.41 Ti 0.15 0.17 0,17 0.16 0.12 0.14 0.11 Fe* 1.51 l,27 1,32 1.39 1,23 l.17 1.22 Mn 0.01 0,01 0.01 0.03 0.01 0.01 0.01 Mg 0.64 0.94 0,97 0,82 1.10 l.09 1.11 Ca 0.01 0.01 0.01 0.01 0.01 0.01 0.02 Na 0.02 0.01 0.01 0.02 0.01 o.oo 0,04 K 0.91 0,92 0,87 0.89 0.87 0.90 0.90 TOTAL 7,72 7.74 7.75 7.74 7.76 7.74 7,82 XMg 0.30 0.43 0,42 0.37 0.47 0.48 0.48 XFe 0,70 0.57 0,58 0.63 0,53 0.52 0,52 98 MICROPROBE ANALYSES BIOTITE M A1Jl ~ Z4B Z7 MA! S2C Si02 35.35 35.25 34.45 35.93 34.05 35.80 35.21 Ti02 1.49 2,57 1.61 1.68 1.52 1.52 1.94 Al203 19.09 18,72 17, 19 17.77 16.57 18.98 19.61 FeO 17.00 24.17 24.92 19.70 25.43 20.66 19.42 MnO 0.35 0,39 0.11 0.36 0.13 0.20 0.19 MgO 10.11 5.50 7.26 9.40 7.24 9.57 8.98 cao 0.11 0.15 0.10 0.15 0.25 0.14 0.11 Na20 0.15 0.19 0.22 o.oo 0.35 0.19 0.10 IC20 8.73 9.24 8,41 9.25 7. 62 9.05 8.91 TOTAL 92.38 96.18 94,27 94.24 93,16 96.11 94.47 NORMALIZED MOLES BASED ON (01o(OH)2) Si 2.74 2,72 2,72 2.77 2.73 2.11 2.69 A1IV l. 26 1.28 1.28 1.23 1.27 1.29 1. 30 AlVI 0.48 0.43 0.33 0.39 0.29 0.40 0.47 Ti 0.09 0,15 0.10 0.10 0.09 0.09 0.11 Fe* 1.10 1.56 1.65 1.27 1.10 1.31 1.24 Mn 0.02 0,03 0.01 0.02 0.01 0.01 0.01 Mg 1.17 0.63 0.86 1.08 0.86 1.08 1.03 ca 0.01 0.01 0.01 0.01 0.02 0.01 0.01 Na 0.02 0.03 0.03 o.oo 0.05 0.03 0.01 K 0.86 0.91 0.85 0.91 o. 78 0,87 0.87 TOTAL 7. 75 7.75 7.82 7.78 7.82 7.81 7.75 XMg 0.52 0,29 0.34 0.46 0.34 0,45 o. 45 Xpe 0.48 0.71 0.66 0.54 0.66 0.55 0.55 99 MICROPROBE ANALYSES BIOTITE Si02 35.52 35.60 Ti02 l.73 1.63 Al203 19.93 19.29 FeO 18.86 18.90 MnO 0.12 0.07 MgO 9.21 9.87 cao 0.08 0.11 Na20 0.16 0.19 K20 8.65 8.63 TOTAL 94.26 94.29 NORMALIZED MOLES BASED ON (01o(OH)2) Si 2. 71 2.72 AtIV 1.29 1.28 AtVI 0.50 0,45 Ti 0.10 0,09 Fe* 1.20 1,21 Mn 0.01 o.oo Mg 1,05 1.13 Ca 0.01 0.01 Na 0.02 0.03 K 0.84 0.84 TOTAL 7.73 7.76 XMg 0.47 0.48 XFe 0.53 0.52 100 MICROPROBE ANALYSES CORDIERITE IQ .Ii! S6B ~ ~ li l'.2. Si02 49.92 48.42 48.08 48.88 48,34 49.04 48.62 Ti02 o.oo 0.05 0.03 o.oo 0.02 0.02 0.03 Al203 33.46 32.64 31. 63 32.68 32.73 32.73 32.86 FeO 7.58 8,52 8.95 7.96 7.87 7.09 7.45 MnO 0.34 0.41 0.77 0.24 0.35 0.30 0.39 MgO 8.43 7.46 6.56 7.64 7.54 7.09 8.16 cao 0.05 0.07 0.07 0.06 0.05 0.09 0.07 Na20 o.os 0.19 0.72 0.29 0.26 0.54 0.17 K20 o.oo o.oo o.oo o.oo 0.01 o. 02 0.01 TOTAL 99.83 97.76 96.81 97.75 97.17 96.92 97.75 NORMALIZED MOLES BASED ON 11 TOTAL CATIONS Si 5.05 5. 03 5.05 5.06 5.04 5.11 5.02 AlIV 0.95 0.97 0.95 0.94 0.96 0.89 0.98 AlVI 3. 04 3.02 2.96 3.05 3.06 3.13 3.03 Ti o.oo 0.01 o.oo o.oo 0.00 o.oo . o. 00 Mg 1.27 1.15 1.03 1.18 1.17 1.10 1.25 Fe• 0.64 0.74 0.79 0.69 0.68 0.62 0.65 Mn 0.03 0.04 0.07 0.02 0.03 0.03 0.03 Na 0.01 0,04 0,15 0.06 0.05 0.11 0.03 ca 0.01 0.01 0.01 0.01 0.01 0.01 0.01 K o.oo o.oo 0.00 o.oo 0.00 o.oo o.oo TOTALll.00 11.01 11.01 11.01 11.00 11.00 11.00 0 18.04 18.01 17.93 18. 03 18.02 18.07 18.01 XMg. 0.66 0.61 0.57 0.63 0.63 0.64 0.66 XFe 0,34 0.39 0.43 0.37 0.37 0.36 0.34 101 MICROPROBE ANALYSES PLAGIOCLASE ~ lU Zil .a.§B gs M Yl:iJ.B Si02 61,75 61.89 59.28 62.92 62,15 61.47 62.78 Al203 24.29 24.51 25.09 25.27 23.72 24,33 23,87 eao 5.26 5.32 6.71 4.52 4.84 5,44 4.87 Na20 8.85 8.53 7.66 8.97 8.78 8,68 8.85 K20 0.17 0.23 0.10 0.13 0.28 0,11 0.09 TOTAL 100.32 100.48 98.84 101.81 99.77 100.03 100.46 NORMALIZED MOLES BASED ON 5 TOTAL CATIONS Si 2,72 2.73 2.67 2.73 2. 76 2.72 2.77 Al 1.26 1.28 1.33 1.29 1,24 1.27 1.24 Na 0.76 0.73 0.67 0.75 0.75 0.74 0,76 Ca 0.25 0,25 0.32 0.21 0.23 0.26 0.23 K 0.01 0.01 0,01 0.01 0.02 0.01 0.01 TOTAL 5.00 5.00 5.00 4.99 5,00 5.00 5.00 0 7,97 8.00 8.00 8.00 7.99 7.98 7.82 Xan 0,24 0.25 0,33 0.22 0.23 0.26 0,23 Xab 0,74 0.73 0,67 0.77 0,75 o.74 0,76 Xor 0.01 0.01 o.oo 0.01 0.02 o.oo 0.01 , 102 MICROFROBE ANALYSES PLAGIOCLASE Si02 61,04 Al203 25.76 Cao 6.61 Na20 8.05 K20 0.07 TOTAL 101.53 NORMALIZED MOLES BASED ON 5 TOTAL CATIONS Si 2,67 Al 1.33 Na 0.68 Ca 0,31 K 0.00 TOTAL 4.99 0 8.00 Xan o.31 Xab 0,69 Xor o.oo - ' I 103 ! I i i i APPENDIX C MINERALOGY OF THIN SECTIONS I ! L, L ------ 104 EXPLANATION OF ABBREVIATIONS USED IN APPENDIX C AMPH = AMPHIBOL MYRM = MYRMEKITE APAT = APATITE OPAQ = OPAQUES BIOT = BIOTITE OTHR = OTHERS CARB = CARBONATE Pt.AG = PLAGIOCLASE CHLR = CHLORITE QTZ = QUARTZ CORD = CORDIERITE SILL = SILLIMANITE EPID = EPIDOTE GROUP SPH = SPHENE GARN = GARNET TOUR = TOURMALINE KFSP = K-FELDSPAR ZIRC .. ZIRCON MUSC = MUSCOVITE X .• PRIMARY ORIGIN 2 . SECONDARY ORIGIN V . VEIN MATERIAL T : TRACE R .• RIEBECKITE M MONAZITE A . ANDALUSITE s : STAUROLITE MPS : METAMORPHOSED PELITIC SEDIMENTS MWS METAMORPHOSED PSAMMITIC SEDIMENTS I MAS : METAMORPHOSED AMPHIBOLE-RICH SEDIMENTS MC . METAMORPHOSED CONGLOMERATES MQ : METAMORPHOSED QUARZITE I MAB .• METAMORPHOSED APHYRIC BASALT MB METABASITE MBP : METAMORPHOSED BASALT PORPHYRY PILB : PILLOWED BASALT UGR : UNDIVIDED GRANITIC ROCKS GN : QUARTZ-AMPHIBOLE-EPIDOTE GNEISS MFT METAMORPHOSED FELSIC TUFF 105 PKBMGCSACCEAZTO 0 M QLFIUAOIMHAPPIOPSTY TASOSRRLPLRIARUAPHR I SAMPLE Z G P T C N D L H R B D T C R Q H R M LITHOLOGY ------I Ll X xx X 2 XX X X MB I..2B XX XX xx X X MPS 1 M1A XX X X X X MX MPS I M2 XX X X X 2 X M UGR M3 X X XX X xx X X X M X MPS I Tl X XX X X 2 X XX X M MWS I T4 xx X T XA xx X M MWS l T5 -X X X 2 X A XXX M MWS AlA xx X 2 X 2 X X MWS I AlB XX X X X UGR I AlD XX X X X X XXX MPS AlE XX X 2 XA 2 xx X MPS AlF XX XX XA 2 XX XX MPS A2A XX XX X 2 2 X X MWS I A2B xxxxx X X X MWS l A2C X X X 2 XX X X MWS A4 XX XX X XX X MPS I AlO XX XX XX X X UGR l Sl XXXXTX 2 X X UGR S2A XXXXXR XX X UGR l S2B XX X X 2 XX XX MPS S2C XX XX X X X X X X MPS S3 X X X XX X MPS ------ .. 106 P K B M G C S A C C E A Z T O O M Q L F I U A O I M H A P P I O P S T Y T A S O S R R L P L R I A R O A P H R SAMPLE Z G P T C N D L H R B D T C R Q H R M LITHOLOGY S4------XX X XXX XX X M MPS ss XX X T 2 XX X MPS S6B xx xxxxx X T X MPS S7 XX X X X MPS sac XX X X XX X M MPS S9A XX X XX XX T MPS S9B XX X XX X X MPS I S12B XXXX XXX 2 X X UGR E1 XX XX X XX XX X UGR I E2A XX X XX X T MPS I E3A X X X X X XX X X MAS ws XX XX X X X X UGR VH1A X X X X V X X MWS VH1B XX X 2 X MWS VH2A XX X 2 2 X X X MPS VH2B XX X 2 XX X X MWS VH3A XX X 2 A 2 X XX S MPS VH3B XX X X 2 X X X X MPS VH4 XX X X V X X X MAS VHS XX X X 2 X M MAS VH6 XX X XX X MWS VH7 XX X XX X MWS VHS XX XX 2 X MWS ------107 P K B M G C S A C C E A Z T O O M Q L F I U A O I M H A P P I O P S T Y TASOSRRLPLRIARUAPHR I SAMPLE------·------Z GP TC ND L HR B D TC R Q HR M LITHOLOGY I Zl X T X X 2 X X MB Z2A XT X 2 V X X MB l Z2B XX X X X MB I ZJA XX XX 2 XX X MWS ZJB XX X 2 XX X MWS I Z4A XX XX 2 XX XX MPS Z4B XX X TX 2 XX XX MWS I ZS XX X T 2 VT MWS Z6A XX XX 2 X X X MWS l Z6B XX XX 2 XX XX MWS I Z7 XX X X 2 X X MPS ZS XX X X 2 2 X MB Z9 X X X 2 2 XX X MWS ZlO XX XX 2 X X X MWS Zl2 XX X T XX XX MWS Z13 XX X 2 XX X MWS Zl4 XX X 2 XX XX X MWS Z15 XX X T XXXX X R GN Zl6 XX X X 2 V X X X X MB Z17A XX XX 2X XX XT GN Z17B XX XX X XXXX XXR GN ZlS XX XX T X X MPS Z19 xxxxx 2 X X UGR ------ - 108 PKBMGCSACCEA Z T O OM QLFIUAOIMHAPP I O P S T Y TASOSRRLPLRIA RUAPHR SAMPLE ZGPTCNDLHRBDT CRQHRM LITHOLOGY ------Bl xx X X X X X X XX UGR SWl XX X 2 2 X ·x MB SW2 X X X XX X MFT HlA xx X TX T XX T X UGR HlB XX X X 2 2 2 XX X XX UGR H2 X X X X X XX UGR I HS X X X 2 X X MB H7 XX xx X 2 X X xx X UGR I MAl XX XX X 2 X XX X MPS I USl XX X 2 XX SLATE US2 X X x_ 2 2 X X MBP I US3 XX XXX XX MAB US4 X X X 2 2 XX MAB US6 X X X XX XX PILB US7 X X X V X XX MBP usa X X 2 2 2 X X R MFT Jl xx xx X X MAB J2 XX 2 2 X X MAB J3 XX 2 X XX MBP J4 X X 2 X XX MBP J5 X X 2 X X X MBP J6 X X 2 2 X X MBP J7-1 X X X X X X MAB ------109 P K B M G C S A C C E A Z T O O M Q L F I U A O I M H A P P I O P S T Y T A S O S R R L P L R I A R U A P H R SAMPLE Z G P T C N D L H R B D T C R Q H R M LITHOLOGY J7-2------X X X X X X MAB Dl X X X X X TT X X MC D2 X xvx XX MAB SLl0-2 X X X XX X MWS SL103A XX X XXVX X X MC SL103B XX X 2 X2VXXXXX MWS SLl0-4 X X X X 2 X MC SLl0-5 X X X X 2 X X X X MC SLl0-6 XX X X 2 V X X MC SLl0-7 X X X XX X MC SL10-8 X X xvx XX MAB SLl0-9 X X XX X X MC SLl0-10 X XX X XX SLATE HW-3 X X X 2 X FE SED HW-3A X X 2 2 X X MFT HW-4 X X X T 2 X X MFT HW-7 xx X 2 V X MFT OA-9 XX X 2 2 X X MQ z2-2 X X XX 2 V XX XX MQ Z2-18 X X X X 2 X X X MQ ------I REFERENCES ti f .·.· I It I 111 Anhaeusser, C.R., Mason, R., Viljoen, M.J., and Viljoen, R.P., 1969, A reappraisal of some aspects of Precambrian Shield Geology: Geological Society of America Bulletin, v. 80, p. 2175-2200. 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