The Geology and Mineralogy of Bentonites and Associated Rocks of the Chuckanut Formation, Mt

Western Washington University Western CEDAR

WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship

Summer 1981

The Geology and Mineralogy of Bentonites and Associated Rocks of the Chuckanut Formation, Mt. Higgins Area, North Cascades, Washington

Susan Kinder Cruver Western Washington University, [email protected]

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Recommended Citation Cruver, Susan Kinder, "The Geology and Mineralogy of Bentonites and Associated Rocks of the Chuckanut Formation, Mt. Higgins Area, North Cascades, Washington" (1981). WWU Graduate School Collection. 645. https://cedar.wwu.edu/wwuet/645

This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. THE GEOLOGY AND MINERALOGY

OF BENTONITES AND

ASSOCIATED ROCKS OF THE CHUCKANUT FORMATION,

MT. HIGGINS AREA,

NORTH CASCADES, WASHINGTON

A Thesis

Presented to

The Faculty of

Western Washington University

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

by Susan Kinder Cruver MASTER’S THESIS

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Susan Kinder Cruver February 15, 2018 THE GEOLOGY AND MINERALOGY

OF BENTONITES AND

ASSOCIATED ROCKS OF THE CHUCKANUT FORMATION,

MT. HIGGINS AREA,

NORTH CASCADES, WASHINGTON

Susan Kinder Gruver

Accepted in Par-tial Completion

Of the Requirements for the Degree

Master of Science

Dean of, Graduater School

Advisory Committee

Chairperson i

ABSTRACT

In the Mt. Higgins area, the Chuckanut Formation is in probable

fault contact with pre-Tertiary metamorphlc rocks. The Chuckanut is over-

lain by Oso volcanics (zircon fission track age of 43.2 * 1.9 MY). A

diorite body (k/At date = 53 * 8 MY) crops out in the Granite Lake area

and is thought to be intrusive into the Chuckanut.

Sedimentary rocks of much of the study area are dominantly thick-

bedded arkoses that are generally cross-bedded, and resemble the Chuck

anut type section. Sediments cropping out along and near Deer Creek are

different; black, bituminous shale is the dominant rock type, and several

bentonite beds are also present. Some bentonites are only a few centi

meters thick and are not lithified, whereas others are thicker, lithifled

and composed of amalgamated beds, some of which are graded. Glass shards

and other volcanic detritus of the air-fall tephra have altered to form

K-rectorlte upon heating to 275-285°C. A mld-Eocene date of 44.5 MY was

obtained by fission track dating of zircons from one of the bentonites.

It is proposed that the Deer Creek area sediments were deposited in lakes

and other low energy environments on a swampy floodplain.

Kalkberg-type mixed-layer illlte/smectite is found elsewhere in the

Mt. Higgins area, and is probably indicative of higher temperatures than

those which created the K-rectorite. On Mt. Higgins, the presence of

andalusite suggests temperatures near 400°C. Cordlerite-bearing sediments

indicate temperatures of 500°C.

Heating was a result of a large geothermal system initiated by the

intrusion of the Granite Lake diorite and possibly other related intrusions, and may be associated with Oso volcanlsm. Magmatic activity may have af fected the area for several million years, perhaps sporadically. li

TABLE OF CONTENTS

ABSTRACT 1

TABLE OF CONTENTS ii

LIST OF FIGURES Iv

LIST OF TABLES vii

ACKNOWLEDGMENTS ix

INTRODUCTION 1

Geologic Setting 1

Statement of Problem 1

Previous Work 1

METHODS OF INVESTIGATION 7

Field Methods 7

Laboratory Methods 7

RESULTS OF INVESTIGATION 10

Lithology and Mineralogy of Rocks in 10 the Mt. Higgins Area

Rocks of the Western Ridge of Finney Peak I3

Rocks of the Deer Creek Area I7

Bentonites of the Deer Creek Area 29

Rocks of the Higgins Creek Tributary Area 38

Rocks of the North Lake Area 38

Rocks of the North Face of Mt. Higgins

Rocks of the Granite Lake Area 4i

Clay Mineralogy 49

K-rectorite 30

Kalkberg-type illlte/smectite 35

Chlorite 53

Illlte ^7 TABLE OF CONTENTS (CONTINUED)

Contact Metamorphic Minerals and Assemblages 58

DISCUSSION 69

Depositional Environment of Rocks of 69 the Deer Creek Area

Vitrlnite Reflectance and Paleotemperature 73

Alteration Mineralogy and Paleotemperature 73

Metamorphic Zonation and Interpretation 88 of the Hydrothermal History of the Mt. Higgins Area

Mineral Zonation 88

Hydrothermal History of the 9I Mt. Higgins Area

CONCLUSIONS 96

REFERENCES 98

GEOLOGIC MAP OF THE MT. HIGGINS AREA back cover

SAMPLE LOCATION MAP back cover iv

LIST OF FIGURES

Figiire Page

1. Index geologic map of part of the western North Gas- 3 cades (modified from the compilation of Haugerud, 1979) showing the location of the study arrea.

2. Topographic map of the Mt. Higgins study area showing 12 subdivisions referred to in the text.

3. Photomicrograph of partially chloritized biotite in a Mt. Higgins area sandstone. Crossed nicols, bar is 0.05 mm. Sample SK-35* T33N| R8E, SWyN¥-|- section 6.

4. Contact between Ghuckanut sediments and Oso volcanics 15 in cliff along Deer Creek. Location is approximately 1.3 km east of the confluence of Higgins Creek and Deer Greek. T33N, R8E, SE^wf section 9-

5. Cliff outcrop of Tertiary fine-grained sediments and 19 bentonite located along an unnamed tributary to Deer Greek. Top of section in figure 6 is at very top of photo. T33N, R8E, center of SW^ section 9-

6. Stratigraphic column depicting measured section of 20 cliff located along an unnamed tributary to Deer Greek. The cliff is pictured in figure 5* T33N| R8E, center of SW-|- section 9*

7. Stratigraphic column depicting measured section of 23 roadcut located along Forest Service road. 331^• T33N, R8E, NE^wi section 9-

8. a) Black, bituminous shale, bentonites and sandstone 2k in roadcut along Forest Service road 331^• T33N> R8E, NE-|SW-5- section 9- This roadcut is the site of the measured section shown in figure 7* X's mark top and bottom of section measured, b) Gloseup of black, bituminous shale and unconsolidated white bentonite at roadcut pictured in figure 7a-* Yellow color is lepidocrocite.

9. Overturned anticline which has developed into a small 25 thrust fault. Location is a few meters upstream from the cliff pictured in figure 5- Length of upper branch of stick is approximately one meter. T33N, R8E, center of SW-^ of section 9*

10. Sketch of fault at edge of Oso volcanics along unnamed 26 tributary of Deer Greek (see fig. 2 for location of creek). Location is approximately 100 meters west-southwest of the Oso-Ghuckanut contact on Deer Greek which is pictured in figiare 4. T33N» R8E, SE-|NEy section 8. V

LIST OF FIGURES (CONTINUED)

Figvire Page

11. Closeup of thick, lithifled bentonites. Location is 30 cliff section pictured in figure 5- T33N, R8E, cen ter of SW-|- section 9-

12. a) Photograph of a graded bentonite (one complete 3I graded bed and the lower portion of another graded bed axe present, b) Sketch of an idealized graded bed.

13. Textures of quartz grains in the thick, lithlfied 32 bentonites, a) nearly eiohedral quartz crystal. b) broken quartz grain, c) embayed quartz. Sample number SK-39A3H middle. Bars on all photo graphs are 0.25 mm, crossed polaxs. T33Ni R8E, center of SW-|- section 9«

14. Photomicrographs of a lithlfied bentonite, sample 33 DP-10. Note altered glass shards, bubbles. T33Nf R8E, center of SW-|- section 9. a) Bar is 0.1 mm, crossed nicols. b) Enlargement of upper left center part of l4a showing a well-preserved shard. Crossed nicols, bar is 0.05 nun. c) Enlargement of l4b showing K-rectorite crystals replacing shaDxis. Crossed nicols, bar is 0.01 mm.

15. Sericitic Kalkberg-type mixed-layer illite/smectlte. 39 Grossed nicols, bar is 0.01 mm. Sample DP-14X. T33N| R8E, center of section 21.

16. Scinidine (?) crystal altered to Kalkberg-type illite/ 39 smectite. Plane light, bar is 0.05 mm. Sample SK-33* T33N, R?E, center of S-|^NE-|- section 12.

17. Andesite dike cutting hornfelsed Ghuckanut Formation 44 rocks, Mt. Higgins. T33Ni R8E, NEy section 33*

18. Photomicrograph of hornfelsed Ghuckanut rock, Mt. Hig- 45 gins. White material is cordierite, brown and dark material is biotite. Grossed nicols, bar is 0.05 mm. Sample DP-21. T33N, R8E, SWlSE^ section 28.

19. Photomicrograph of hornfelsed black shale, Mt. Higgins. 45 Ghiastolite (andalusite) crystal is pictured at center. Plane light, bar is O.Ol^mm. Sample SK-4?. T33N, R8E, NW^NwInEt section 33.

20. Photomicrograph of hornfelsed bentonite from Mt. Higgins. 46 Note shard at upper left edge of photo. Glay is com pletely unexpandable Illite. Grossed nicols, bar is O.O5 mm. Sample SK-48. T33N, R8E, NwlNWf section 28. vi

LIST OF FIGURES (CONTINUED)

Figure Page

21. Photomicrograph showing spotted texture present in 46 many homfelsed siltstones and shales of Mt. Higgins. Crossed nlcols, bar is 0.25 mm. Sample DP-23. T33N, R8E, SW^SW^Et section 28.

22. Photomicrograph of dlorite from the Granite Lake area. 48 Zoned andesine is seen in upper left, corroded hornblende crystal is shown at right center. Grossed nlcols, bar is 0.25 mm. Sample SK-34. T33N, R?E, center of SW-^ section 12.

23. Photomicrograph of alteration of diorlte. G = chlorite, 48 Q = q.uartz, M = muscovite, B = biotite. Green needles may be chlorite or actinolite. Crossed nlcols, bar is 0.05 mm. Sample SK-34.

24. X-ray diffractograms of oriented <2^m fraction of ben- 52 tonite from the Deer Greek area. Cu radiation, C = chlorite, all other peaks are K-rectorlte. Sample DP-10.

25. X-ray diffractograms of oriented -cO.2 ^m fraction of 53 siltstone from the western ridge of Finney Peak. Gu K radiation, C = chlorite, Q = quartz, ML = mixed- layer illlte/smectite (rectorite?). Sample SK-4A.

26. MacEwan direct Fourier transform of K-rectorite. Sam- 55 pie DP-10.

27. Actual (lower pattern) and calculated (upper pattern) 56 X-ray diffractograms of ethylene glycol-treated, oriented K-rectorlte. See text for explanation. Sam ple DP-10.

28. X-ray diffractogram of random, <0.2 /im fraction of 57 purified K-rectorite. Peak positions and absence of peaJcs between 30 33 20 (characteristic of 2M polytype) show the clay to be IM polytype. Sample DP-10.

29. X-ray diffractograms of oriented yum fraction of 60 tuff from north lake area. Cu K<=t radiation, K = Kalkberg-type illite/smectite, G = chlorite, Q = quartz. Sample SK-33-

30. MacEwan direct Fourier transform of Kalkberg-type 62 Illlte/smectite. Sample SK-33.

31. Actual (lower) and calculated (upper pattern) X-ray 63 diffractograms of ethylene glycol-saturated, oriented Kalkberg-type illite/smectite See text for explanation. Sample SK-33* vii

LIST OF FIGURES (CONTINUED)

Figure Page

32. X-ray dlffractogram of random 0.2-2 pm fraction of 64 bentonite from the Deer Creek area. Cu Ko<^ radiation, Q = quartz, C = chlorite, R = K-rectorite. Sample DP-10.

33* Relations among the metastable iron hydroxides and 7I siderite at 25 C ard 1 atm total pressure. Total activity of all dissolved species = 10” molal. Total dissolved carbonate species = 0.01 molal. Iron data from Garrels and Christ (1965)- Dotted area encloses conditions typical for peat-forming environments (Baas Becking and others, I960).

34. Reflectance of vitrinite from coals and from lignitlc 74 shale altered by laboratory reactions and of dispersed vitrinite from deep boreholes. 0 = Carboniferous, Arkoma Basin, Oklahoma - maximum present depth 3750 m, E = Lower Cretaceous, Angelina Co., Texas - maoc. present depth 3500 m, W = Upper Jurassic and Lower Cretaceous, La Salle Co., Texas - max. present depth 6250 m. S = Salton Sea geothermal field, California - max. present depth 2460 m. Taken from Bostick (1979)> Vitrinite reflectance of Deer Creek anthracite plotted with the Salton Sea data.

35- Correlation of the temperature dependent mineral assem- 79 blages in shales, sandstones and volcajiogenic rocks. Temperatiires do not represent equilibrium but are ap plicable (with caution) to lower Tertiary and Mesozoic pre-greenschist facies rocks. Taken from Hoffman and Hower (1979).

36. Schematic diagram of influence of l/S clay reactions on 81 Wilcox sandstone cements. Vertical arrows depict ion transfer between l/S clay reactions and phases in sand stone. Taken from Boles and Franks (1979).

37- Relationship between vitrinite reflectance, maximum 83 rock temperature and burial time. ’’Effective time” means the duration of burial of a rock within 15°C of the maximum temperature in its history. Taken from Bostick and others (I978). Deer Creek area an thracite is plotted (large dot on 275°G line) on diagram.

38. Pressure - temperature diagram showing contact meta- 87 morphic facies, reactions important for Mt. Higgins rocks and Mt. Higgins metamorphic assemblages. All facies divisions ajid reactions, except the andalusite reaction of Hemley and others (198O) and the triple point of Holdaway (l97l)> taken from Hyndman (1972).

39" Map showing location of metamorphic zones in the Mt. 90 Higgins area. vill

LIST OF TABLES

T3(LL6 B3(^0

1. Mineralogy of rocks of the western ridge of 16 Finney Peak.

2. Mineralogy of rocks of the Deer Greek area. 27

3. Mineralogy of bentonites of the Deer Creek area. 36

4. Mineralogy of rocks of the Higgins Creek ij-0 tributary area

5. Mineralogy of rocks of the north lake area. 40

6. Mineralogy of rocks of the Mt. Higgins area. 42

7. Mineralogy of Mt. Higgins dike rocks. 43

8. Chemical composition of K-rectorltes and 58 bentonites.

9. Chemical analyses and structural formulas of 66 some dioctahedral chlorites.

10. Comparison of clay mineralogy of rocks of the 85 Mt. Higgins area and rocks of some active geothermal areas. ix

ACKNOWLEDGMENTS

Dr. David R. Pevear merits special thanks for his advice, assistance and suggestions during the course of this study and for his critical evalu ation of the manuscript. I deeply appreciate the contributions of Drs.

Christopher A. Suczek and Antoni Wodzicki, who not only critically read this manuscript, but also shared their knowledge and expertise with me on many occasions. I am grateful to Dr. R. M. Bustin of the University of British Columbia for providing vitrinite reflectance data and aiding in its interpretation. I thank Dr. Joe Vance of the University of Washing ton for dating a bentonite sample.

Completion of this study would not have been possible without the help of my husband. Jack Cruver, who provided financial support as well as assistance in the field and lab, and I am deeply indebted to him.

Doug Hurcomb, Eric James and Bob Brown are thanked for assisting in the field. Thanks are extended to George Mustoe for his advice regarding laboratory and photographic techniques. I am grateful to Roger Nichols of the Mt. Baker Technical Center, U. S. Forest Service, Sedro Woolley, for providing base maps and sharing his knowledge of the rocks of the area. INTRODUCTION

Geologic Setting

The Ghuckanut Formation consists of continental sediments that were deposited in a Tertiary arc-trench gap (Dickinson, 1976) that was intense

ly block faulted, producing several separate depositional basins (Suczek,

1981). The Ghuckanut and the similar Swauk Formation crop out in a dis

continuous belt from the Bellingham-Mt. Baker area southeast to the

Wenatchee area.

The Mt. Higgins study area is located approximately 12 km west-

northwest of Darrington, Washington (fig. l). Here the Ghuckanut Forma

tion is composed of sandstone, siltstone, shale, bentonite and minor coal.

Statement of Problem

The purpose of the study is to investigate the stratigraphic rela

tions, mineralogy, history and paleotemperatures of the bentonites and

associated rocks within the Ghuckanut Formation in the Mt. Higgins area.

The bentonites are especially significant because they contain mixed-layer

clays replacing glass shards that provide a record of the thermal history

of the area, and because they contain dateable materials which can be used

to establish a time link between sedimentary deposition and Gascade plu

tonism and volcanism.

Previous Work

Sedimentary rocks of the Bellingham area were first called Ghuckanut

Formation by McLellan (192?). The name was given to rocks foimd on the

north end of Lumml Island and the eastern shore of Bellingham Bay that

previously had been assigned to the Puget Group. Glover (1935) measured

two type sections, one along Ghuckanut Drive and the other along the

western shore of Lake Whatcom, obtaining thicknesses of 9484 feet (2891

1 Figure 1. Index geologic map of part of the western North Cascades (modified from the compilation of Havigerud, 1979) showing the location of the study area.

4 meters) and 8800 feet (2682 meters) respectively. Weaver (193?) remea sured the two sections, obtaining Identical results for the Lake Whatcom section and a slightly greater thickness for the Chuckanut Drive section,

11,272 feet (3436 meters). Miller and Misch (19^3) estimated a thickness of 15,000 to 20,000 feet (4572-6096 meters) for the Chuckanut Formation in the area east of American Sumas Mountain. Weaver (1937) considered the

Chuckanut to be of fluvial origin, deposited on a large alluvial plain that stretched from the Canadian border through the Willamette Valley in

Oregon. More recent research (Suczek, I98I) suggests that several fault- bounded depositional basins were present.

Fossil floras identified by Pabst (I968) and palynological studies by Griggs (I966) Indicate to the above authors that the formation was deposited from uppermost Cretaceous through Eocene time. Fossil leaves from the Mt. Higgins area were dated for Jones (1959) by Roland W. Brown

of the U. S. Geological Survey as "clearly Eocene in age" but Brown could

not determine which part of the Eocene. A rhyolitic clast collected from a conglomerate which crops out near Chuckanut Drive gave a zircon fission track age of 49-8 + 1.4 million years, a mld-Eocene age (Frizzell, 1979)*

On American Sumas Mountain Miller and Misch (I963) found the Chuckanut to be unconformably overlain by the Huntlgdon Formation, considered to be

middle Eocene in cige. Rouse, in a personal communication with Griggs

(1966), states that his work with microfossil flora indicate the Hunting don may be as young as Late Eocene to Ollgocene. New palynomorph data

from Reiswig (oral communication, I98I) and Rouse (oral communication to

Pevear, 1981) suggest that the lower part of the section in the Chuckanut

type area is Paleocene, but the upper part is mid-Eocene.

There is no agreement among workers about what to call the sediments

in the Mt. Higgins area. Jones (1959) considers the Chuckanut and Swauk 5

Formations to be the same, and states in the introduction to his thesis that he will call the rocks Swauk Formation. Earlier University of Wash ington Ph.D. students including Vance (1957) had used the name Swauk

Formation for sediments that crop out to the south of Mt. Higgins. Mlsch

(1977) used the name Ghuckanut Formation for the Mt. Higgins sedimentary rocks. Frizzell (1979) used the term "isolated arkosic bodies" for all

Tertiary sedimentary rocks of fluvial origin that are found outside the type localities for the Ghuckanut and Swauk Formations. In this study the sedimentary rocks of Mt. Higgins will be termed Ghuckanut Formation as they are located closer to the Ghuckanut type section.

In the Mt. Higgins area the Ghucanut Formation was first studied by Robert W. Jones as part of a Ph.D. thesis at the University of Wash ington (Jones, 1959)* Jones mapped an area bounded by Deer Greek at the west and northwest, Finney Greek at the north, the Sauk River at the east and the North Fork of the Stillaguamlsh River at the south, which includes the field area for this study. In the Mt. Higgins area Jones determined that the Ghuckanut Formation unconformably overlies older metamorphic rocks. The volcanics described by Jones (1959) to lie between the metamorphics and the Ghuckanut could not be found, althoiigh they were dilligently searched for. Volcanics ranging in composition from basalt to rhyolite, but dominantly dacite, overlie the Ghuckanut Formation (Jones,

1959)* Vance (oral communication, I98O) has Informally named these rocks the "Oso volcanics". Zircons in one of the volcanic units in the study area that was sampled by Vance yielded a fission-track date of 43.2 ±

1.9 million years (Vance, oral communication, 1980). Porphyry dikes cut the Ghuckanut on Mt. Higgins and are possibly associated with a "leucogabbro" intrusive that crops out in the Granite Lake area and may have fed the overlying volcanics (Jones, 1959). Hornblende from this intrusive 6

provided a potassium/argon date of 53 * 8 million years (Bechtel, Inc.,

1979).

Jones (1959) reported the Chuckanut in the Mt. Higgins area to con

sist of conglomerate, sandstone (mainly arkose), siltstone, shale and some

thin seams of coal. Siltstone is the dominant fine-grained sediment.

Micas found in the siltstones sampled by Jones are all sericite or sericiti

form biotite. He suggested nearby intrusives as the source of the heat

required to recrystallize the biotite. Jones also found bleached and

chloritized biotite in arenltes. The top of the section was reported to

be composed dominantly of thin bedded shale, much with high organic con

tent. This less-competent part of the section is more tightly folded

than the more competent sandstone of the lower part (Jones, 1959).

Pevear (oral communication, I977) sampled bentonites from the top of the

section described by Jones and determined they are composed mainly of rectorlte, a regularly interstratified mixed-layer illite/smectite.

Bentonites are deposits composed mainly of smectite, formed by the altera tion of volcanic material, most commonly volcanic ash (Grim and Giiven,

1978). Smectite altered to rectorite is Indicative of burial metamorphic temperatures of 100-190°C (Hoffman and Hower, 1979). At burial meta morphic temperatures of 200-225 G the clay collapses completely to form illlte (Hower and others, 1976; Hoffman and Hower, 1979). Temperatures of up to 290°C are required to complete the illite/smectite to illlte reaction in hydrothermal systems (McDowell and Elders, I98O). Laumontite has been reported in some Chuckanut sandstones outside the study area

(Pongsapich, 1970; Pevear, oral communication, 1979). Laumontite is also indicative of burial metamorphic temperatures in the 100-190°C range ac cording to Hoffman and Hower (1979). METHODS OF INVESTIGATION

Field Methods

Fifty locations were sampled by the author and twenty-eight sites were sampled by D. R. Pevear. Fieldwork was accomplished in the summers of 1978 and 1979* All accessible outcrops were sampled, but fine-grained rocks were more intensely sampled than coarse-grained rocks as the former alter more readily and are more useful for diagenetic studies.

Some geologic mapping was done to add detail to the work of Jones

(1959)• U. S. Forest Service maps with four inch to the mile scale were employed as base maps.

Two sections were measured in the areas where bentonites crop out.

Thickness of each individual sedimentary layer was measured and each layer was sampled. Several samples at different stratigraphic levels were taken of the thicker bentonite beds.

Laboratory Methods

Samples for which the whole-rock mineralogy could not be studied by thin section petrographic methods were ground in a Spex ball mill to pass through a 0.05 mm nylon screen. The 0.05 mm powder was x-rayed in a ran dom orientation to determine mineralogy.

To prepare samples for analysis of size fractions smaller than 2^m, the rocks was initially broken into pea size pieces using a mortar and pes tle. Each sample was then ultrasonically disaggregated and the less than

2pn fractions were obtained by centrifugation using the speed and time data from Jackson (197^)* The less than Ipm and the less than 0.2jam fractions were obtained and analyzed for a few samples. For some of those samples, the Sharpies supercentrifuge was employed. Oriented mounts were made and x-rayed. Random mounts were made of dried and powdered less than 8

2ym mixed-layer clays and x-rayed to study the non-basal reflections, which are importaint in the determination of polytype.

Cailorite-bearing samples were treated with lithium and DMSO by the

technique of Abdel-Kader and others (19?8) to check for the possible presence of kaolinite. Samples rich in organic material and free iron

oxides were treated with clorox and CBD (Jackson, 19?4; technique modified by Pevear, written communication, 1978).

Oriented samples were prepared by using a vacuum to suck the sus pension through porous ceramic plates. Samples were x-rayed as follows:

1) untreated, 2) glycolated and 3) heat treated to 300°G for one hour and after x-raying reheated to 550°C for one hour. Some samples were heated to 2^0 G, 350°G and 450°G and x-rayed after each heating. Heated samples were stored in a desiccator to prevent rehydration.

Samples were analyzed using a General Electric XRD-5 diffractometer at 35 kv and 15 ma using nickel-filtered Gu K

2 26/mlnute with a beam slit of 1° and a counter slit of 0.1° were used.

Range and time constants were vanied to obtain optimum diffractograms.

Standard techniques were used in preparing thin sections. Thin sec tions were stained for plagioclase and potassium feldspar and analyzed with a petrographic microscope to provide mineralogical and textural data.

Purified mixed-layer clays, less than 2um size fractions of bentonites, and two whole rocks were analyzed for major elements. The first step in clay sample preparation was separation of the fine size fraction by the methods detailed above. Ghlorite was dissolved from the clay fraction using warmed HGl and KOH by the method of Bohor ard Gluskoter (1973).

The clay was then concentrated by continous-flow centrifiagation with a

Sharpies Supercentrifuge using time and speed data of Jackson (1974) and 9

dried. Whole rocks were ground to less than 0.1 mm and dried. 0.100 g

of sample and 0.600 g of lithium metahorate were weighed on an analytical

balance and mixed. The mixture was fused at 1000°C for fifteen minutes

and dissolved in 70 ml of HGl. The dissolved sample was then carefully poured into a 100 ml volumetric flask and diluted to 100 ml. Samples were then analyzed for Si, Al, Ti and Mn using a Perkln-Elmer 306 Atomic

Absorption spectrometer. 10 ml of solution was then removed to another

100 ml volumetric flask. 10 ml of lithium-lanthanum solution was added and the sample was brought to volume with distilled-deionized water.

Analysis for Ca, Na, K, Fe and Mg followed. Rocks of known composition were i^sed as standards. Raw data was reduced to oxide percentages using a computer program.

Two coal samples were sent to Dr. Marc Bustln of the University of

British Columbia where pellets were made and maximum vitrinite reflectance in oil was measirred. RESULTS OF INVESTIGATION

Lithology and Mineralogy of Rocks in the Mt. Higgins Area

Roadcuts, streambeds and cliffs provide most of the rock exposures in the Mt. Higgins study area. As a result, outcrops are concentrated in a few distinct areas. Differences in lithology and mineralogy of the rocks of different outcrop areas has been noted in the course of this study and for this reason it is useful to consider each of the areas separ ately in the presentation of results.

Figure 2 is a map of the study area showing the locations of the geographical divisions and the Informal names that will be used in this and other'sections of this thesis. "Western ridge of Finney Eeak", a term previously used by Jones (1959). distinguishes the hill in the northern part of the present study area. The western ridge of Finney Peak is bounded by Finney Peak to the northwest and Deer Greek to the south and southwest. The summit of Finney Peak is located a few kilometers to the east of the study area. "Deer Greek area" will be used for the grouping of outcrops along the southern bank of Deer Greek and east of the con fluence of Higgins Greek and Deer Creek. This area includes outcrops found along the unnamed tributary to Deer Greek (see fig. 2) and exposures in roadcuts nearby. A few kilometers to the south, outcroppings of Chuck- anut Formation-rocks are foimd along an unnamed tributary which flows westward into Higgins Greek, and in a few roadcuts. This area will be referred to as the "Higgins Greek tributary area" Across Higgins Greek to the west, outcroppings of plutonic rock are found in the "Granite Lake area". Oso volcanic rocks and Chuckarut Formation sediments crop out at a few sites between Granite Lake and Deer Greek to the northeast. This area will be called the "north lake area". Good exposures of Chuckanut

10 Topographic map of the Mt. Higgins study area showing subdivisions referred to in the text.

Formation rocks and aindeslte dikes &re found on cliffs and in streambeds on Mt. Higgins, the east-west trending ridge which comprises the south ernmost part of this study area. This portion of the study area is re ferred to as the "north face of Mt. Higgins". "Mt. Higgins area" de scribes the entire geographic area covered by this study and named for the area's dominant topographic featiare.

Rocks of the Western Ridge of Finney Peak

The northern portion of the study area includes a high angle contact between rocks of the Ghuckanut Formation and older metamorphic rocks of the Shuksan suite (Misch, 1977; Morrison, 1977) and possibly the Chilli wack Group (Morrison, 1977)*

Morrison (1977) mapped three northwest plunging folds in the Ghuckanut rocks of the western ridge of Finney Peak. The westernmost anticline and central syncline were also sampled and mapped as part of this study. The

Ghuckanut folds are truncated by the aforementioned high angle contact between the Ghuckanut Formation and the older metamorphic rocks, suggesting the contact is a fault.

Ghuckanut Formation rocks of this area closely resemble rocks of the

Ghuckanut Drive type section. Gross-bedded arkosic sandstones are com

mon, with massive and laminar-bedded sandstones also present. Sandstones

are generally a few meters thick. Sandy to shaly siltstone was observed,

as well aJ5 a few fine, coaly siltstone layers. Fossil leaves are often

present in siltstones and fossil palm fronds were observed in sandstones

at the crest of the ridge. No shale or conglomerate was observed.

Table 1 shows mineralogy of rocks from this area. Sandstones are

composed of quartz, alblte, muscovite,■blotite (often chlorltized, fig. 3)i

calcite (as cement and replacement of mineral and/or rock grains), phyllite 14

Figure 3. Photomicrograph of partially chloritized biotlte in a Mt. Higgins area sandstone. Crossed nicols, bar is 0.05 mm. Sample number SK-35. T33N, R8E, SW-|- NW-|- section 6. 15

Figure 4. Contact between Chuckanut sediments and Oso volcanics in cliff along Deer Creek. Location is approximately I.3 km east of the confluence of Higgins Creek and Deer Creek. T33N, R8E, SE-|- NW-| section 9- Table 1. Mineralogy of rocks of the western ridge of Finney Peak.

3 C 0

DP-11 X X X X X X clay and lithics ss SK-14A X X X X X X clay and lithics si SK-16C X X X X X X clay and lithics si SK-35 X X X X X X lithics ss

^ 2jum frac tion, XRD analysis

SK-2 X X XXX si SK-4A X X XXX si SK-4B X X XXX si SK-5A X XXX si SK-6 X XXX si SK-7A XXX si SK-36 X XXX

rock type abbreviations; ss = saindstone si = siltstone

16 17 and siltstone fragments. Jones (1959) sampled six sandstones from this ridge and determined (by staining rock chips with sodium cobaltinitrate) that four contained potassium feldspar. Three contained potassium feld

spar in amounts ranging between a trace and five percent, whereas the

fourth contained 15 percent potassium feldspar (Jones, 1959)• Sandstones

sampled by Jones were derived from locations to the east of sample sites

in this study,, so apparent discrepancies in results from the present

study and Jones' work may be of no Importance.

The less than 2^m fraction of siltstones contains chlorite, illite,

mixed-layer illite/smectite, * quartz and albite.

Rocks of the Deer Greek Area

To the south of the western ridge of Finney Peak, outcrops along

the southern bank of Deer Creek, its small unnamed tributary and the 331^

U. S. Forest Service road south of Deer Greek (see fig. 2 for location)

expose the upper part of the Chuckanut section as described by Jones (1959)

Fine-grained sediments are dominant here, unlike the western ridge of

Finney Peak or the Chuckanut Formation type section. Black, bituminous

shale, gray shale and gray clayey siltstone are common rock types. Sandy

siltstone, a few thin-bedded gray sandstone layers, one coal bed and

several bentonites comprise the rest of the sedimentary rocks of this

area. A detailed description of the Deer Greek area bentonites is pre

sented in the following section.

Exposures of rocks that may be the stratigraphlcally lowest of this

part of the section are found along the south side of Deer Greek. Most

of the sandstones are found here, along with siltstones, a few black

shales ard gray shales. Unlike the rocks on the western ridge of Finney

Peak, these are thin-bedded . The largest outcrop on Deer Greek is a cliff

capped by Oso volcanics (fig. 4). 18

Up the previously mentioned tributary to Deer Creek (see fig. 2 for location), shale becomes the dominant rock type. A cliff along the tributary creek and readouts expose the black, bituminous shale with interbedded bentonite, plus several beds of gray clayey siltstone and two beds of gray sandstone which contain appreciable amounts of silt and clay. A few of the black shales are very thick, in contrast with the rest of the beds which crop out in this area. At one, outcrop, the top of one sandstone bed is ripple-marked. Fig. 5 is a photograph of the above- mentioned cliff. Stratigraphic columns of the sections measured at this cliff outcrop and a roadcut are shown in figures 6 and 7i respectively.

The roadcut section appears to be correlative with the lower portion of the cliff section. The roadcut exposing black, bituminous shales and associated rocks is pictured in figure 8.

Siltstone, sandstone and shale in the area all contain quartz, K- rectorite and chlorite. Albite, illite, muscovite, biotlte, siderlte

(some black shale horizons contain abundant siderlte concretions) and calclte are also common. Some samples contain anatase, zircon, ankerite, opaques, shale, siltstone and volcanic rock fragments, and hornblende.

Table 2 lists mineralogy of rocks in this area.

The single coal bed is also located along the same tributary creek.

Two samples of the coal were analyzed for maximum vitrinlte reflectance

(R^ max) in oil and were foimd to be anthracites with max of 3.19 ±

0.192^ and 2.95 ± 0.255^. Cell structure is still evident in the anthra cite, indicating heating of the area was a short-term event (Bustin, oral communication to Pevear, I98I). The coal bed is intensely folded and sheared. The coal outcrop is located in T33N, R8E, Nwfswf section 9.

The other fine-grained sediments in this part of the study area also are intensely folded. The small tributary to Deer Greek is located on the

..iM 19

Figure 5. Cliff outcrop of Tertiary fine-grained sediments and bentonite located along an unnamed tributary to Deer Greek. Top of section in figure 6 is at very top of photo. T33N, R8E, center of S¥r sec tion 9. Figure 6. Stratigraphic column depicting measured section of cliff located along unnamed tributary to Deer Creek. The cliff is pictured in figinre 5- T33N| R8E, cen ter of SW|- section 9- 20 ro? |VWV*| 5* i'57U etorlc. Arau vLntcw^oli'dftlfdi t*.nh>N +6 ^K-bU 9L-57V tncdiuj* 0rtu^n^iv& 9»;.-57I f»d.iim qrw UAJd-f k)^LmV4u^ t»'U> tloijtt^ siHebtnC' IcnurtfLt' lxMii«A

I5i:-57fi . «jiarV.

St:*51A5 4tf lufJ'artUI St^'btp flrtUi-broWA lM«>mr UnUn'k'. Gr»M n^ivt cJ^ij ^'k^hno huawiv^, anu be«it>nife. uji 'h *. tpl»«r kJIa^Wi, -k>- ckA- flww\ of b*tfi>»»» b«<^b«#( ^ j

5K--57K. wdiuiw gnw •noA^ivc. cJoY»j»lyWfc

ii mmI Idai^^ra^' Cow^Hcbkel i»ew m St-31f fvwdiuworiu pwriij. Ii| ^ori^ r^WivC volc4.Hic(A>Hc/ 5tth^4brt, Sk.'57L W*dt-,tikuwinBu> W: UcW!«^ • *VQ?

tbtk./ tiilUkilVU^ iMUthAV »hi06 ^ S: dP blact, b«Hiii>tiu7M.5 ohAle 5jt.-57f. v'e>lcanicifts>h'6 SlC’blU. f**e

5fc-576 r blaek.^ SWlI^ UOiUt. bdi'irv^ ortf/ r*\tAty

•Ww 21

S^'43 btoitiWxl^

tvwv^ 4tdU£;

SIL-Hl. u>W*k, umwKiolJilaiQf bciU«fiii€'

Ud^,bUuMirtDvi£>>

e^£'

irvlflW, ti' h/AiuV^ OriiM^ , K** ’M -' Figure ?. Stratigraphic column depicting measured section of roadcut located along Forest Service road 3314. T33N, R8E, NEiSWi section 9- 23

Tof’ OF qs-'SiissWiac-**'**^

yiotk iUiO

W WKk, Wurnmi, 5*C'M1c um^fsm&oli'Jialei) U«i^\nar bedkiicd ' t«ia«*v>te. i«iM». ICpaMrvfiK 5^ins

SIC-'HU WtcJi.^ biVtm'inn* beidkA sWb «o«k^ SitUntC' t»r>C^4H*W&

uAtcm&oUdlOiA oVik/ bcMo'vik' K^iAci4«iui€', 5+«.iw^ft bM cntiU,

SK.-M'^Ar Ami, •filf»C'flr4i»'dA/ Ski-H^P block,fc>^nOU5 Oew«^>^ ier«A ^kvte»tW.. *:>:?*?• w€oU«et^ Wbu >v \

p>:

J'l>U-e>’V«JL eP r.'v-^'.

j •f' u«\irti\Sel*"

IM ^®ttok >v Ob &EoaoNi

5K-‘rtF biotic.

0K)5

Hi'tiie ix*tortd^d0icA icWic werER, be»4o»vite. ^talMni Kj^iJipaoc'Ae.

SK-HIP bkxfik., bikiwuWMS Sb>ol£< u>it(A. |«L»MV«v bc^'vi^ 24

Figure 8. a) Black, bituminous shale, bentonites and sand stone in readout along Forest Service road 3314. T33N, R8E, NE^W'I’ section 9« This readout is the site of the measured section shown in figure ?. X s mark top and bottom of section measured, b) Closeup of black, bituminous shale and uncon solidated white bentonite at readout pictured in figure 7a* Yellow color is lepidocroclte. 25

Figure 9* Overturned anticline which has developed into a small thrust fault. Location is a few meters upstream from the cliff pictured in figure 5* Length of upper branch of stick is approximately one meter. T33N, R8E, center of SW^- of section 9* Figure 10. Sketch of fault at edge of Oso volcanics along unnamed tributary of Deer Creek (see fig. 2 for location of creek). Location is approximately 100 meters west-south west of the Oso-Chuckanut contact on Deer Creek which is pictured in figure 4. T33N, R8E, section 8.

26 Table 2. Mineralogy of rocks of the Deer Creek arrea.

0 H j rite e k n a e t i r e d i s ysis s ly a n a (D S' se ta a n a method 0 o' 0 p C+* H- H- p sample number o' hi H ct- 0 hi H* H- H" p. p. p. 0 and rock type C+ d" d" c+ c+ c+ c+ 0 tsi (D (D (D (D (D (D 3 other DP-8 TS2 X X X X X X sh DP-8SS TS X X X X si and sh fragments ss DB-8A TS2 X X X X X X sh DP-18A TS X X X X X si DP-18G TS2 X X X X X si SK-22 TS2 X X X X X X sh fragments si SK-29 TS X X X XXX hematite, detrital si hornblende SK-31B TS X X X X X X X si SK-32 TST X X X X X si SK-32B TST X X X X X X X si SK-37A TST X X X X X sh fragments si SK-37D TST X X X X X si SK-37F TS X X X X X X ss SK-37I TS X X X X XXX X si SK-37K TS X X X X opaques si SK^l TST X X X X hematite sh SK-43 TST X X X X X X sh fragments ss SK-49A TS X X X sh ajid pumice frag. ss SK-49B TST X X X X X X hematite from weather si + sh ing of siderite

rock type abbreviations: analysis method abbreviations; ss = scindstone TS = thin section petrographic analysis. si = siltstone TS2 = thin section petr. & XRD of-«J2pm frac. sh = shale TST = thin section petr. & XRD of < 2pim frac. and whole rock powder.

2? Table 2. Continued CD W tc) I H- CD Q. O c S' 0 § O tr O P CJ' w CD H* h-> P> hi I-'* H- o 3 Pi g pjH gCD c tl O o H O M o o P> 0 a" H H O o M c+ < c+ sample numberm ^ ^ H* H- H- H- H- H- W- c+ €+ c+ t+ c+ c+ c+ C+’ c+ c+ and rock typem n 0 CO CD (D CD CD CD 0 CD 0 other

SK-llB XR2 X X X si SK-llC XR2 X X X sh SK-llD XR2 X X X sh SK-llE XR2 X XX X sh SK-llF XR2 X sh SK-12 XR2 X XX X si SK-13 XR2 X X X sh SK-13B TS X X X X X X X X X sh freigments si SK-27A TS X X X X X X X replaced glass ss shards SK-27C TS X X X X X X X sh, chert ajid vole. si rock fragments SK-28 TS X XXX X shards, pumice si SK-28B XR2 X X X X X si SK-28C TS X X X X X XXX sh, si and vole, ss rock fragments

Oso volcanic rocks

DP-4 TS2 X XX X

DP-25A TS2 X XX X ankerite

DP-25B TS2 X XXX X

DP-26A TS X X X

DP-26C TS X X X X magnetite

analysis method abbreviations; rock type abbreviations TS = thin section petrographic analysis. ss = sandstone XR2 = XRD analysis of <2^m fraction only. si = siltstone TS2 = thin section petr. anal. & XRD of sh = shale <2um fraction.

28 29

axis of an overturned anticline which has developed into a small-scale

thrust fault (fig. 9)* Areas capped by the more competent volcanic rocks

are much less deformed. At one edge of the volcanics, the sedimentary

rocks are apparently faulted upward (fig. lO). As the sediments that are

protected by a cap of volcanic rocks show little deformation while the

unprotected sediments are intensely folded, it is suggested that the

event which produced the folding postdates the deposition of the Oso volcanic rocks.

Jones (1959) proposed a fault along Deer Greek, separating the sand

stone of the western ridge of Finney Peak from the shales and volcanics south of Deer Greek. The differences between lithologies and bedding attitudes across the creek support Jones' suggestion.

Bentonites of the Deer Greek Area

Bentonites that crop out in the Deer Greek area are of two appearances

Bentonites a few centimeters or less in thickness are unconsolidated.

These bentonites are very fine-grained, containing no grains large enough to identify in hand specimen. They are light gray to white in color and often are stained by lepidocroclte (see figure 8). It is possible that the lack of consolidation is due to weathering.

Thick bentonite beds are also found in the area. These bentonites are lithlfied and contain q^uartz, feldspar and pumice fragments identi fiable in hand specimen. Golor is light to dark gray (fig. 11). In thin section, the thick, lithifled bentonites were found to be composed of many graded beds (fig. 12) and a few layers which show no apparent grading. Grim and Giiven (1978) state that thick bentonites are commonly composed of many thinner layers. Dark gray coloring is most common at the bottom of graded beds. No mineralogical differences were found be- 30

s e c tio n

c l i f f

i s

s e c tio n

Swf

o f L o catio n

c e n te r

E, 8 R bentonites.

T33N,

5. l i t h i f i e d

fig u re th ic k ,

in o f

G loseup p ic tu re d

11.

F ig u re 31

12b.

Figure 12. a) Photograph of a graded bentonite (one complete graded bed and the lower portion of another graded bed are present. b) Sketch of an idealized graded bed. 13c.

Figure 13. Textures of quartz grains in the thick, lithified bentonites, a) nearly euhedral quartz crystal, b) broken quartz grain, c) embayed quartz. Sample number SK-39A3H middle. Bars on all photo graphs are 0.25 nun> crossed polars. T33N, R8E, center of SWy section 9> Figure 14. Photomicrographs of a lithlfled bentonite, sample DP-10. Note altered glass shards, bubbles. T33N, R8E, center of SWp- section 9. a) Bar is 0.1 mm, crossed nlcols. b) Enlargement of upper left center part of l4a showing a well-preserved shard. Crossed nlcols, bar is 0.05 mm. c) Enlargement of l4b showing K-rectorite crystals replacing shards. Crossed nlcols, bar is 0.01 mm. 34 35

tween light and dark portions of the bentonites, indicating coloration

may be due to organic material. Crystal fragments and large shards are

concentrated in the lower portion of graded beds. The size of shards

decreases upward, whereas the percentage of pumice fragments commonly in

creases upward. All shards, formerly volcaric glass, are now altered to

K-rectorite, chlorite and q^uartz. With the exception of higher percentages

of alblte and coarse-grained quartz in the lower part of any single graded

bed, mineralogy does not vary with respect to stratigraphic positon

within the beds. There is no variation in mineralogy between different

graded beds. Lithification of the thick bentonites may be the result of

calcite and/or quartz cementation as both fine-grained calcite and fine

grained quartz are found in the matrix of thick bentonites. The fine

grained quartz was likely formed from the reaction of smectite to K-

rectorite, which liberates silica.

Contacts between the bentonites and other rocks are sharp. Euhedral,

broken and embayed quartz grains (fig. I3) are present in the thick, lith-

ifled bentonites. No detrital components were apparent in thin section.

The sharp contacts and lack of rounding of clasts indicate these are air- fall deposits. The thick, coarser-grained bentonites, as opposed to the thin, fine-grained bentonites, may be indicative of closer proximity to the volcanic vent, or the size differences may be explained by varying energy

of eruption (Lajoie, I98O).

Bentonite mineralogy, as determined by thin section petrography and x-ray diffraction analyses, is quartz, chlorite and K-rectorlte, * calcite

(as a fine-grained dusting in the matrix and also single crystals or ag gregates replacing plagioclase and possibly other phenocrysts), albite, siderite and lepidocrocite (from outcrop weathering), with anatase, zircon and apatite commonly present in trace amounts. Figure 14 shows photomicro- Table 3. Mineralogy of bentonites of the Deer Greek area

SK-3IC XRT X X X X SK-37C-2 XR2 X X X SK-37C-3 XR2 X X X SK-37E XR2 X X X SK-37G XR2 X X X X X SK-37H XR2 X X X X SK-37J XR2 X X X SK-37L XR2 X X X X SK-39A1 XR2 X X X X X SK-39A2 XR2 X X X SK-39A3A XR2 X X X SK-39A3B XR2 X X X SK-39A3G TST X X X X X X SK-39A3Dtop TST X X X X X SK-39A3Dbot. TST X X X X X SK-39A3Etop TST X X X X SK-39A3Ebot. TST X X X X SK-39A3F TST X X X X X X SK-39A3G XRT X X X X SK-39A3Htop TST X X X X SK-39A3Hmid. TST X X X X X SK-39A3Htop TST X X X X of bottom SK-39A3Hbot. TST X X X X X of bottom SK-40A XR2 X X X SK-40Btop TST X X X X SK-40Bbot. TST X X X X X analysis method abbreviations; XR2 = XRD analysis of 42jum fraction only. S - ^alyses of whole rock powder and ^2pm fraction. thin section petrographic analysis & XRD of whole rock & <2p fraction.

36 Table 3* Continued.

CD w >4 H) 1 H- 4 p- § (D o o O tr o o <“ i * “ p <+ H 4 M (D c M o o o H £t o' 4 4 o o c+ ^ !T H H- H* H- H" H* 5+ c+ <+ C+" c+ sample number m p- n

SK-40Ctop TST X X X X SK-40Cmld. XR2 X X X SK-40Cbot. XR2 X X X SK-^2 XR2 X X X X SK-49A XR2 X X X A SK-49E XR2 X X X X SK-49G XR2 X X X DP-10 TST X XXX X tr. zircon

Analysis method abbreviations: XR2 = XRD analysis of <2^m fraction only. TST = thin section petrographic analysis & XRD of whole rock & <2^ frac.

37 38 graphs of a bentonite. Mineralogy of bentonites is listed in Table 3 .

Clay mineralogy will be discussed in detail in a later section.

A fission track date of zircon from one of the thick bentonites (T33 N,

R8 E, center of Swf section 9) gave an age of 44.5 * 2.0 million years

(Vance, oral communication, I98 O).

Rocks of the Higgins Creek Tributary Area

Three kilometers south of the Deer Creek outcrops, exposures of sedimentary rocks are present in a "window" in the overlying volcanic rocks along an unnamed tributary to Higgins Creek (see fig. 2 for location).

Gray siltstone, light gray and black shale, arkosic sandstone and one quartz sandstone were sampled.

Mineralogy of the samples is listed in Table 4 and is summarized as follows: Quartz, Kalkberg-type mixed-layer illlte/smectlte, chlorite and albite, * detrltal blotite, detrltal muscovite, epldote, trachyte fragments and calcite. The Kalkberg-type clay has serlcitic texture in one sample (fig. 15). Myrmekitic intergrowths of quartz and feldspar are found in some sandstones. Calcite is present in a much lesser amount than in the rocks of the Deer Creek airea.

Rocks of the North Lak:e Area

Outcrops in the north lake area (the area is north of Granite LaJce; see fig. 2 for location) are unfortunately minimal. A few outcrops of massive, very well Indurated arkosic sandstone are found in lower areas of the north and west parts of the hill that makes up the area. Volcanic rocks crop out near the top of the hill at the southern edge of the north lake outcrop area, and two units were observed. The lower volcanic unit is a dark, purplish fine-grained rock identical in appearance to a partially devitrified Oso volcanic rock found in roadcuts in the Deer 39

Figure 15. Sericitic Kalkberg-type mixed-layer illite/ smectite. Crossed nicols, bar is 0.01 mm. Sample DP-14X. T33N, R8E, center of section 21.

i Table k. Mineralogy of rocks of the Higgins Creek tributary area,

o 1 S“ S' M CD g 3 P H H* O hd s 0 M O o O H- !-■ P c+ O' o' hi c+ < P- O c+ rr CD H- H* H- o H* P o c+ c+ H c+ c+ c+ c+ C+" W Pj 0 OC) (D 0 CD CD CD CD other

DP-12A sh TS X X X X X DP-12B sh XR2 X X X X DP-12C sh XR2 X X X DP-14 sh XR2 X X X DP-14-2 si TS X X X X X X DP-14X si TS X X X X X X DP-14Z ss TS X X X abundant chert fragments

Table 5- Mineralogy of rocks of the north lake area.

o i-b o p p" o P p H h-' P P p H N' o H P H (D cf o' R O c+ sample number m S' R H* CD H- H* P c+ c+ 4 c+ c+ m and rock type ^ ^ N 0 on CD CD CD other

SK-33 t TST X X XXX DP-15A sh XR2 X X X SK-20 ss TS X X X ankerite, myrmekite

Rock type abbreviations: Analysis method abbreviations: ss = sandstone TS = thin section petrographic analysis si = siltstone XR2 = XRD analysis of <2pm fraction only sh = shale TST = thin section petrographic analysis & t = tuff XRD of whole rock and <2^m fraction

40 Greek area. The upper unit is a light green tuff that has not been

observed elsewhere.

The light green tuff contains phenocrysts of sanidine (?) that have

altered to Kalkberg-type illite/smectite (fig. 16). Mineralogy of the

north lake area rocks is shown in table 5.

Rocks of the North Face of Mt. Higgins

Ghuckanut rocks similar to those found both north and south of Deer

Greek (cross-bedded and massive gray, tan and brown sandstones, gray silt-

stones, black shales and bentonite) are exposed in cliffs and streambeds

on Mt. Higgins, the difference being that all the rocks on Mt. Higgins

have been homfelsed. Dikes of altered porphyritlc andesite cut the horn-

felsed sedimentary rocks (fig. 1?).

Mlneraloglcal data for the homfelsed rocks is shown in table 6.

Alteration minerals present in the sedimentary rocks sampled include quartz, alblte, muscovite, blotite, chlorite, andaluslte, cordlerite, tourmaline (schorl and dravlte), graphite and minor epidote. Figures

18, 19 and 20 are photomicrographs of the homfelsed rocks. Many rocks have a spotted texture, common in contact metamorphlc rocks.

The porphyritlc andesites contain quartz, albite, chlorite and actlnolite as alteration minerals. Mineralogy of these rocks is listed in table 7 -

Rocks of the Granite Lake Area

On the western arm of Mt. Higgins, at and around Granite Lake (see figure 2) are exposures of a diorltic body (termed "leucogabbro" by Jones,

1959) believed to be intrusive into the Ghuckanut Formation. Jones (1959) found that the contacts between the diorite and the Ghuckanut are obscured, but the Ghuckanut rocks nearest to the southeast contact dip away from the Table 6. Mineralogy of rocks of Mt. Higgins.

o Hj B P o O PJ & Pj a w cy

rock type abbreviations analysis method abbreviations; ss = sandstone TS = thin section petrographic analysis si = siltstone section petr. anal. & XRD whole rock sh = shale iSI = thin sec. petr. anal. & XRD whole r., <2um b = bentonite Ct = silicate dissolution & XRD (for graphite) ’

42 Table ?• Mineralogy of Mt. Higgins dike rocks.

rr £U o o S- c+ H- COI ch p) H- O o M H- •p p o o O O P o !-■ < hi CD o c+ c+ H PJ H" H- a H- p. p. sample number ^ CO C*" c+ Pj c+ c+ c+ c+ (0

DP-24C XX XX X X

DP-24D X X X X X XXX plag. = andesine

DP-24H XX XX X

Method of analysis = thin section petrography all rocks are hydrothermally altered andesite porphyry

^3 44

Figure 1?. Andesite dike cutting hornfelsed Ghuckanut Formation rocks, Mt. Higgins. T33N, R8E, NEif section 33* 45

Figirre 18. Photomicrograph of hornfelsed Chuckanut rock, Mt. Higgins. White material is cordierite, brown and dark material is biotite. Grossed nicols, bar is 0.05 mm. Sample DP-21. T33N, R8E, SW^SEt sec. 28.

FigLire 19. Photomicrograph of hornfelsed black shale, Mt. Hig gins. Chiastolite (andaluslte) crystal is pictured at center. Plane light, bar is 0.01 mm. Sample SK-4?. T33N, R8E, N¥-^NW:5NE-|- section 33* 46

Figure 20. Photomicrograph of hornfelsed bentonite from Mt. Hig gins. Note shard at upper left edge of photo. Clay replacing shards is completely unexpandable illite. Crossed nicols, bar is 0.05 mm. Sample SK-48. T33N, R8E, NW-^NWy section 28.

Figure 21. Photomicrograph showing spotted texture present in many homfelsed siltstones and shales of Mt. Higgins. Grossed nicols, bar is 0.25 mm. Sample DP-23. T33N, R8E, SW:^W^E^ section 28. 4? dlorite. Due to this relationship, "argillltlzation" of Chuckanut rocks and the hypahyssal nature of the dlorite, Jones tentatively regarded the

Granite Lake diorite to he intrusive into the Chuckanut Formation (Jones,

1959)• No direct evidence to support this idea has been found to date, but the primary mlneralogic composition of the dike rocks which cut the

Chuckanut Formation on Mt. Higgins is identical to the mineral composition of the diorite, indicating the dikes may be related to the diorite body.

The dlorite is composed primarily of andesine plagioclase and horn blende (fig. 22). Hornblende is generally partly or totally altered to

chlorite and biotlte. Muscovite, quartz, fine-grained chlorite and a green

mineral with needle-like habit (possibly actlnolite or chlorite) are also present as alteration minerals (fig. 23). 48

Figure 22. Photomicrography of diorite from the Granite Lake area. oned andesine is seen in upper left, corroded hornblende crystal is shown at right center. Crossed nlcols, b^ IS 0.25 mm. Sample SK-34. T33N, R?E, center of SW:^- section 12.

Figure 23. Photomicrograph of alteration of diorite. G = chlorite Q quartz, M - muscovite, B = blotlte. Green needles ’ may be chlorite or actinolite. Crossed nicols. bar is 0.05 mm. Sample SK-34. Clay Mineralogy

Mixed-layer illite/smectite, chlorite and illite are the clay

minerals found in rocks of the Mt. Higgins area. Illite is a detrital

constituent of many sandstones, siltstones and some shales, also appearing

as a metamorphic phase in homfelses cropping out on Mt. Higgins. Chlorite

is present in nearly all the sedimentary rocks in the area. Fine-grained

chlorite is a detrital constituent of some siltstones and shales and

occurs as an alteration product in many rocks of the study area. Including

the bentonites of the Deer Creek area. Metamorphic chlorite is found in

homfelses of Mt. Higgins. Two mixed-layer illite/smectite minerals are

present in rocks of the Mt. Higgins area. K-rectorite has formed from the

alteration of shards and other glassy volcanic material present in ben

tonites and other sediments cropping out in the Deer Creek area. Rec-

torite is also found in siltstones of the western ridge of Finney Peak.

Kalkberg-type mixed-layer illite/smectite is found in rocks which crop

out in other parts of the study area.

The smectite to mixed-layer illite/smectite to illite reaction series

results from a well-established diagenetic and metamorphic reaction

(Dunoyer de Seconzac, 1970; Frey, 1970; Hower and others, 1976; Eberl,

1978a)• In response to heat from burial or hydrothermal soiarces, smec

tite layers alter to form Illite by acquiring more tetrahedral and octa

hedral aluminum and more interlayer cations. Not all the smectite layers

alter to form Illite at one time, rather a mixed-layer phase develops

with a certain percentage of illite layers. With increasing time and/or

temperature, the percentage of illite layers increases and the Inter-

layering of the two minerals becomes ordered rather than random. One kind of ordering is the IS type present in rectorlte (also known as allevardite), where packets of illite and smectite pairs occur amidst randomly

49 50

placed layers of the excess mineral (as the two components are not often

present in equal amounts). At least 45% lllite layers are necessary for

IS ordering to he possible• With incresing temperature and thus a greater

percentage of illite layers (usually 85-99%) i ISII t3?pe ordering occurs t

Packets of three illite layers and one smectite layer occur randomly

amidst excess illite layers in clays which have this type of ordering.

The reaction series is complete when all of the smectite reacts and the

mineral contains 100% illite layers. Mixed-layer llllte/smectltes are

distinguishable from smectite and illite as the XRD peaks resultant from

their basal spacing are non-integral and represent spacings between those

of illite and smectite. Peak positions vary with percentage of illite

layers and degree and type of ordering.

For a detailed discussion of mixed layering in clays, readers are

referred to Reynolds and Hower (19?0), upon which the above discrlption

is based.

K-rectorite

It has been stated by Kodama (1966) that the term rectorite (= alle-

vardlte) should be limited to regular Interstratification of Na-mica and

smectite with close to 50% of each component. Others (Eberl, 1978a;

Pevear and others, 1980) have used the mineral name more loosely to in

clude all regularly interstratified illite/smectites with IS ordering of

Reynolds and Hower (19?0), regardless of interlayer cation or percentages of components. In this study, "K-rectorite" (Eberl, 19?8a) will be em ployed for all regularly interstratified illite/smectite minerals with IS ordering and potassium present as the major interlayer cation, regardless of the percentage of each type of layer.

The bentonites and all other sedimentary rocks that crop out in the

Deer Creek area contain K-rectorlte. As previously mentioned, thin sec- Figure 24. X-ray diffractograms of oriented <2^m fraction of bentonite from the Deer Greek area. Cu K«, radia tion, C = chlorite, all other peaks are K-rectorite. Sample DP-10. 52

I 53

\o.^K

Figure 25. X-ray diffractograms of oriented <0.2 ;im‘fraction of siltstone from the western ridge of Finney Peak. Cu Ko< radiation, C = chlorite, Q = quartz, ML = mixed- layer illite/smectite (rectorite?). Sample SK-4A. 54

tion petrographic analyses of the bentonites show that K-rectorite has

replaced glass shards. K-rectorlte is also present in the less than

2pm fraction of Chuckanut siltstones from the western ridge of Finney Peak.

Comparison of XRD patterns (fig. 24) of the K-rectorite from ben

tonites with the data of Reynolds and Hower (19?0) shows the Deer Greek

area mineral to be regularly Interstratified illlte/smectite with IS or

dering and 65% llllte layers. Results are the same using Srodon's (I980)

methods which use the difference in spacing between certain peaks.

Exact determination of percent illite in rectorites from siltstones of

the western ridge of Finney Peak was impossible. Comparison with the data

of Reynolds and Hower (19?0) suggests the clay to be composed of at least

50% Illite layers. The Srodon (I98O) method could not be used due to

overlap of a rectorite peak and a broad illite peak. The XRD pattern of the 550°G-treated sample shows the principal peak to be a 10.3 A rather o than 10 A (fig. 25). This persisted even with heating at ?50°C for one o hour. The collapsed peak position at 10.3 A indicates the possible pre

sence of some interstratified chlorite layers in the clay.

XRD data of a K-rectorite separated from a bentonite were analyzed

by the direct Fourier transform method of MacEwan (1956) (fig. 26). Six

•^^^^^^ction peaks from an ethylene glycol-treated oriented moimt were

utilized. The baseline on fig. 26 is adjusted so that the observed heights at 10 1 (illite) and 17 A (ethylene glycol-smectite) are O.65 and O.35

respectively. Heights of the other maxima were measured ajid compared to

calculated heights. The calculated height was computed on the basis of

the above probabilities O.65, Pg^^e^tlte" with the

constraint that no two smectite layers occur together, a condition de

manded by the type of ordering and presence of excess illite layers.

Agreement between calculated and observed values is good with the except- Cal^. H+. 0.30 6.70 0.N 0.b7 0.0<> o.n Obs^rveA 0.45 0.M 0.31 0.I4> 0.7fc 0.0^ 6.01 0.&5 P'Co.k. t S 11 IS nl rsi XKX SIS ISIX

Figure 26. MacEwan direct Foiirier transform of K-rectorite. Sample DP-10. 56

Figure 27. Actual (lower pattern) and calculated (upper pattern) X-ray diffractograms of ethylene gly col-treated, oriented K-rectorite. See text for explanation. Sample DP-10. 57

Figure 28. X-ray diffractogram of random, <0.2 fraction of purified K-rectorite. Peak positions and absence of peaks between 30 and 33 20 (characteristic of 2M polytype) show the clay to be IM polytype. Sample DP-10. J Table 8. Chemical compostionof K-rectorite aiid bentonites.

1 2

SiO^ 51.08 64.78 66.15

AI2O3 32.45 10.22 17.01

^^2°3 0.41 1.95 2.23

MnO tr 0.15 0.01

CaO 1.49 6.30 0.28

MgO 0.71 0.55 0.43

Na^O 0.92 0.35 1.08

K2O 4.55 1.54 3.51

TiO^ 0.08 0.19 0.50

H2O " 4.14 1.91 0.20

7.46 7.61 2.93

TOTAL 99.15^ 93.64^ * 94.1:^

1. DP-10 : purified K-rectorite from a Deer Greek bentonite.

2. SK-39A3H middle; whole rock powder of a Deer Creek bentonite.

3. SK-48; whole rock hornfelsed bentonite, Mt. Higgins.

* low totals due to incomplete dissolution of samples.

58 59

tion of the peak at 4? A.O Lack of agreement of values for the 4? AQ peak

(3 illite layers + 1 smectite layer) may indicate an Increased tendency

to form the ISII or Kalkberg-type superlattice.

A modified version of a computer program (M0D4) written by R. C.

Reynolds (Reynolds, 1980) was used to produce a computer profile based on

probability conditions for IS ordering, 65^ illite layers and diffracting

domains (n ) 10-14 layers thick. The computer profile closely resembles

the diffraction pattern of the K-rectorlte from Deer Greek area bentonites

(fig. 27).

A chemical analysis of the 2-0.2^m fraction of neairly pure K-rectorite

given in table 8 was used to yield the structural formula given below;

Also shown in table 8 are whole rock chemical analyses of a Deer Creek

bentonite and a bentonite from Mt. Higgins.

Comparison of peaks from the XRD pattern of purified and powdered less than 0.2pm K-rectorite with data given by Chen (197?) and Bradley and Grim (l96l) shows the rectorite to be IM polytype (fig. 28).

Kalkberg-type illite/smectite

Kalkberg-type regularly interstratlfled illite/smectite is found in siltstones, shales and volcanic rocks which crop out a few kilometers north of Mt. Higgins and north of Granite Lake. The term Kalkberg-type has been employed for regularly interstratified Illite/smectite minerals with ISII ordering of Reynolds and Hower (1970).

Comparison of data from diffraction patterns of the Kalkberg-type clay (fig. 29) with data of Reynolds and Hower (1970) shows the mineral to have ISII ordering and between 90 and 95% illite layers.

The direct Fourier transform method of MacEwan (1956) was again em ployed to analyze diffraction data (fig. 30). Seven diffraction maxima 6o

fo.o4^

7e 5 !0 i5 ■ZO 15 50

Figiare 29. X-ray diffractograms of oriented <2 ;Lim fraction of^tuff from north lake area. Cu radiation, K - Kalkberg-type illite/smectite, C = chlorite, Q - quartz. Sample SK-33. Figure 30. MacEwan direct Fourier transform of Kalkberg-type illite/smectite. Sample SK-33> Calc. MK tic • W 7*?

ISI Till ISII rini rsin iitxii 63

2.©

Figure 31* Actual (lower) and calculated (upper pattern) X-iray 'iiff’ractograms of ethylene glycol-saturated, oriented Kalkberg-type illite/smectite. See text for explanation. Sample SK-33- 64

deqr-us Z O 65

from an ethylene glycol-treated oriented mount were used. The baseline

of figure 30 was adjusted so that observed heights of the fundamental

spacings at 10 A (illite) and I6.5 A (smectite) are O.93 and 0.0? respec

tively. The calculated height was computed on the basis of these funda

mental probabilities and again with the constraint that no two smectite

layers occur in contact. Observed and calculated heights closely agree

for all spacings.

An XRD pattern was calculated using a modified version of Reynold's

(MOD 4) computer program (Reynolds. I98O). The computer profile is based

on probabilltiy conditions for ISII order, 93^ Illite and diffracting do

mains (N) 7-13 layers thick. Peak positions agree with those present on

the diffractogram and peak intensities are similar (fig. 31).

Chlorite

An x-ray diffractogram of the powdered less than 2jxm fraction of one

of the Deer Greek area bentonites, composed of rectorite, chlorite and

quarts, is shown in figure 32. Figure 24 presents patterns of an oriented

mount of the same material.

The OOl^peak at 14.2 A (fig. 32) is of much lower intensity than the

002 at 7.13 A. The OO3 peak is at 3.55 A. The peak at 1.499 A apparently

is a combination of 060 peaks from both K-rectorite and chlorite, and indicates the chlorite is dioctahedral. As chlorite could not be sepa rated from the other minerals present except by dissolution, an estimate of the chemical composition of the chlorite was made by indirect methods.

Chemical analyses were made of less than 2jxm samples from a bentonite with chlorite present and with the chlorite completely dissolved. Data produced from two runs were averaged. Estimation of percent chlorite in the sample was made using the technique of Schultz (1964) and found to be 10 percent. Percent quartz was also estimated using Schultz's (1964) Table 9. Chemical analyses and structural formulas of some dioctahedral chlorites.

1 2 3 4 ^ SiO^ 29.59 35.63 39.01 A1203 34.88 34.87 32.15 20.78^ 5.01 0.90 FeO 0.43 0.10 MgO 3.75 8.63 10.14 HpO 11° 14.15 14.15

Total 100.00 100.60“^ 99.50'^ ’°

Tetrahedral

Si 2.76 3.26 3.24 3.3 A1 1.24 0.74 0.78 0.7 Octahedral

2.60 3.01 3.04 2.7 1.46 0.34 0.04 Fe n.d. Mg 0.52 1.18 1.59 2.3

1. P^^2^^^2.76^^1.24^°10^°^^2]C^0.52'^^ 0.60^°1?46*'°^^6'^

2. jAlgCSl^ 25^^0.74^° lo(OH)2][Mgi.i8Al1.01^®0?34^°^^6]

3* [^^^^^3.24^^0.78^° 1.04^°0?04^°^^^

4 .

1. Hydrothermal chlorite, Deer Greek area. 2. Sudo and Sato (I966); Chlorite associated with hydrothermal ore body, Aomori, Japan.^

3. Sudo and Sato (I966); Hydrothermal chlorite around gypsum deposit, Akita, Japan.^

4 . Eggleston and Bailey (I967); Hydrothermal chlorite, Tracy Mine, Michlgcin. a Analysis determined by examination of the chlorite structure. See Eggleston and Bailey (I967) for details, b Total Fe as Fe^O^. c See text for method of determination. d Includes 0.42 ^ S. e Na and K included in the total. f Reported in Heaver and Pollard (1973). 66 6?

method and the appropriate amount of SiOg was subtracted from both chemi cal analyses. The rectorite component, known form the analyses of sam ples treated to dissolve chlorite, was assumed to be 30fo of the untreated sample. Rectorite oxide percentages were adjusted and subtracted from

the oxide percentages of the averaged analyses. The resultant amounts

were normalized to 89%, allowing 11% structurally bound water. The ap

proximated analysis of the chlorite appears in table 9- Although this

data cannot be assumed to be exact, or as reliable as a chemical analysis

of a pure chlorite, it provides a useful approximation of the composition

of the mineral.

A structural formula of the chlorite, divided into component layers,

appears in table It is a di,trioctahedral chlorite, which means the

2:1 (mica-like) layers is dioctahedral and the interlayer (glbbsite- or

brucite-like layer) is close to trioctahedral (Bailey, 1980). The chemi

cal composition and structural formula of the Deer Greek area chlorite

compares favorably with analyses and structioral formulas of sudoites,

also shown in table

Sudoite is a magnesian dl,trioctahedral chlorite, known to occur as

fine-grained material associated with hydrothermal ore deposits (Eggles

ton and Bailey,196?). There are some differences between the sudoite

formulas reported in the literature and the Deer Creek chlorite formula,

the chief difference being that the Deer Creek chlorite contains consi

derably more iron than magnesium. "Fe-sudoite” may be the most appropri

ate name to attach to the chlorite found in rocks of the Deer Creek area.

I Hite

Authlgenic lllite is found in some fine-grained rocks which crop

out on Mt. Higgins. The clay is completely unexpandable when treated with

ethylene glycol. In thin section the lllite has sericitic texture. Contact Metamorphic Minerals and Assemblages

Hornfelsed sedimentary rocks which crop out on Mt. Higgins contain quartz, albite, epidote, muscovite, biotite, chlorite, andalusite, cordierite, tourmaline and graphite as alteration minerals. Andesite por phyry dike rocks which intrude the Ghuckanut rocks in this area also show alteration, including the presence of actinolite, chlorite, albite and quartz. Hornblende, albite and muscovite occur coating fractures of a few of the hornfelsed sediments and laumontite coats some fracture sur faces of the altered dike rocks.

Two assemblages commonly assigned to the albite epidote hornfels facies present in some hornfelsed dandstones, siltstones and shales are as follows;

muscovite - chlorite - andalusite (+ albite + quartz)

muscovite - chlorite - biotite (+ albite + quartz).

A few siltstones and shales contain an assemblage of the hornblende horn fels facies;

muscovite - biotite - cordierite (+ quartz).

No rocks containing mineral assemblages indicative of higher tem perature contact metamorphic facies were sampled. Sampling was not under taken in areas close to the southeastern contact between the Granite LaJce diorite and the Ghuckanut Formation. DISCUSSION

Depositlonal Environment of Rocks of the Deer Creek Area

In the area around Deer Creek, where the upper part of the exposed

Chuckanut section crops out, sediments are dominantly fine-grained. This suggests that these sediments were deposited in a different sedimentary environment than the sandstone-rich western ridge of Finney Peak and the

Chuckanut Formation type section. Two different sandstone beds are found in the sections that were measured in the Deer Creek area. One is a mas sive, medium gray, volcaniclastic sandstone which is 179 cm thick, by far the thickest sandstone in the upper part of the Chuckanut section. The other sandstone crops out in both measured sections. It is a medium to dark gray fine-grained sandstone which weathers brown. In the readout sec tion the bed is 60 cm thick, thinning to 20 cm in the cliff section. Other sandstones found stratigraphically lower in this part of the section are also much thinner than the 179 cm bed. All sandstones from the top of the section contain large percentages of silt and clay. One outcrop of a medium to dark gray fine sandstone is a dip slope with small assymetri- cal ripples present on the bedding surface.

Massive, gray, shaly siltstone is also widely present in the upper part of the section. Thicknesses vary from a few tens of centimeters to one and a half meters. One coal bed was observed.

Black, bituminous, laminated shale is the most abundant rock found in the two measiared sections. Each lamina is less thaji one millimeter thick. Several layers of siltstone a few centimeters or less in thick ness are intercalated in the shale. Siderlte concretions are found in some horizons.

Siderite concretions are commonly found in association with coals.

69 70 peats ajid organic-rich sediments. Postma (197?) reports finding siderite concretions in peat bogs currently forming in Denmark, suggesting the concretions are formed syngenetically and not dicigenetically.

Presence of siderite precludes the possibility of deposition in ma rine or brackish water. The concentrations of calcium and sulfate ions present in sea water are high enough to cause the preferential precipi tation of calcite and iron sulfate minerals (Berner, 1971)* Siderite is formed in reducing conditions and medium pH range, which is also suitable

for the formation of peat (fig. 33)■

No channels, cross-beds or conglomerates were found in this part of

the Chuckanut section. Laminar-bedding of the black shale and small rip

ples on one sandstone bed are the only sedimentary structures noted in

this part of the Chuckanut section.

The high percentage of volcanic detritus present in rocks of the

upper part of the section illustrates a change in provenance for this

part of the Chuckanut Formation. Frizzell (1979 ) states in his study

of the petrology and stratigraphy of Paleogene non-marine sandstones of

the Cascades that these rocks have a mixed plutonic and tectonic source

of continental block tectonic provenance. Plutonic and metamorphic rocks

would be likely source materials. In other parts of the study area,

polycrystalline quartz and metamorphic rock fragments are abundant along

with plutonic quartz and myrmekitic intergrowths of quartz and feldspar.

The change in provenance may indicate the onset of volcanism which pro

duced the Oso volcanics. Frizzell (1979) noted that the younger Paleogene

sediments of the Cascades contain a greater amount of volcanic material

than the older sediments, indicating the presence of a magmatic arc.

The dominance of fine-grained material, high organic content, vir

tual absence of sedimentary structures other than laminar bedding, pre- 71

pU Figure 33* Relations among the metastable iron hydroxides and slderite at 25 C and 1 atm total pressure. Total activity of all dissolved species = 10“° molal. Total dissolved carbonate species = 0.01 molal. Iron data from Garrels and Christ (I965). Dotted area encloses conditions typical for peat- forming environments (Baas Becking and others, I960) 72 sence of siderite and coal all point to deposition in a swamp or lake on a floodplain (Reineck ajid Singh, 1975) •

Sedimentation may have been the result of flooding initiated by mud

flows and debris flows upstream. The thick, volcaniclastic sandstone

associated with the thick bentonite beds suggests volcanic activity closer

to the bog. Volcanic rocks found capping the sediments indicate sub

sequent inundation of the sedimentary basin by volcanic flows and pyro-

clastics.

Stratigraphic relationships between the sedimentary rocks of the

Deer Greek area and the nearby Ghuckanut Formation rocks axe impossible

to determine due to faulting and lack of exposures. It is not known if

there is a gradual transition between the Ghuckanut rocks which contain

little or no volcanic detritus and the dominantly volcanigenic Deer Greek

area rocks, or if the relationship is unconformable . As previously stated,

Frizzell (1979) reports increases in percentage of volcanic detritus in

younger portions of other Eocene strata in the Gascades. The sedimentary

rocks of the Deer Greek area may not be part of the Ghuckanut Formation,

but are tentatively assigned to that formation due to close geographical

association, presence of both volcanic-rich and volcanic-poor sedimentary

rocks on Mt. Higgins, and the increase in volcanic detritus in the upper

parts of other Eocene sedimentary sections noted by Frizzell (1979)•

Recent stratigraphic and petrologic studies of Ghuckanut sediments

in Whatcom Gounty and other Tertiary sediments of the North Gascade area

indicate that Tertiary block faulting was important in the formation of depositional basins, as well as influencing sedimentation (Suczek, 1981;

Johnson, 1981; Frizzell, 1979)* Tertiary block faulting affected the

entire North Gascades area (Davis, 1977)- Vertically stacked sandstone

and conglomerate bodies found in the middle part of the Ghuckanut section 73 along Bellingham Bay are interpreted as braided stream deposits resulting

from uplift of the sediment source area (Johnson, 1981). Upper and lower

intervals of the Bellingham Bay section contain fining upwards cycles of

inferred meandering stream origin (Johnson, 1981).

Similar changes in style of sedimentation were not noted in the Mt.

Higgins Chuckanut section, however, a basin created by block faulting

cannot be ruled out. No conglomerates were found in the study area, but

are reportedly found in nearby Chuckanut outcrops (Jones, 1959). Sug

gested Tertiary dip-slip reactivation of the Straight Greek fault (Davis,

1977) could have created the basin in which the Mt. Higgins area sediments

were deposited. It is possible that the lower parts of the section, which

may contain deposits indicative of source axea uplift, are not exposed

in the Mt. Higgins study area, especially considering that the only con

tact between Chuckanut sediments and older rocks is a fault contact. This

study has not produced conclusive evidence either supporting or disproving

the existence of a Tertiary fault basin in this area.

Vitrinite Reflectance and Paleotemperature

Vitrinite reflectance data from coals in the area of K-rectorlte-

bearlng bentonites can be compared with data from other areas and used

to estimate temperatiire of metamorphism. Vitrinite reflectance (Rq ) is

especially useful in determination of paleotemperatiires as Rq is affected

only by temperature and time, unlike silicate minerals which are also in

fluenced by rock and fluid composition (Bostick, 1979). Length of reaction

time is an important vaxiable. A high vitrinite reflectance suggests a

lower temperature for burial metamorphic rocks with long reaction times

than it does for hydrothermal rocks, which have much shorter reaction times.

Srodon (1979) has compared vitrinite reflectances and mixed-layer Figure VITRINITE REFLECTANCE (OIL-IMMERSION METHOD). IN PERCENT

•

Basin, Reflectance vitrinite Salle depth 2460 Lower ton shale of ------

Deer

Sea

altered 3500 Cretaceous, Co.,

Oklahoma Phytoclasts Coal-coking Dispersed geothermal Creek

Taken

one reaction millions

from

Texas m, of

month's ajithracite ¥ "by

vitrinite deep from

= vitrinite - of

time

- la'boratory in and

Angelina Upper maximum EXPLANATION years

field, max. lignitic

Bostick 'boreholes. reaction

74 bomb

in ’

reaction

present Jurassic rocks shale

plotted from

experiment; present

California time

Co. reactions (1979)*

from

coals time ,

depth Texas 0

borehole with and hydrothermal depth =

a and

Carboniferous,

few

Vitrinite Lower - and the 6520 -

max.

from maoc. 3750 hours' samples:

Salton

m. Cretaceous,

bombs; present

dispersed present m, lignitic

reflectance S E

Sea =

= Arkoma Sal-

depth

data.

clay mineralogy of samples from the Carboniferous Upper Silesian Basin of

Poland. Highest vitrinite reflectance measiared in this study of burial

metamorphic rocks was 2.,2,% and corresponds to ISII ordered mixed-layer clay with 90^ llllte layers sampled at the same depth (Srodon, 1979).

Vi^^inite reflectances of coals sampled in the Mt. Higgins area average

3.07^ and clays from the area of coal outcrop have IS (K-rectorite) or

dering and 65^ illite layers. It is likely that difference in reaction

time is the major reason for the seemingly discordant results, but solu

tion chemistry may also be a factor and will be discussed in the following

section.

Bostick (1979) plotted vitrinite reflctance vs. present temperature

(in the wells from which the samples were derived) for long burial, short

burial and hydrothermal conditions (fig. 3^). Comparison of vitrinite reflectances from Mt. Higgins to those of the Salton Sea grothermal area

(Bostick, 1979) yields a temperature of 275°C ± 25°C (assuming maximum temperature sustained for 0-5 million years). It must be noted that some geologists do not consider vitrinite reflectance to be a good geothermometer.

Foscolos and others (1976) correlated vitrinite reflectance and clay mineralogy for samples of the Lower Cretaceous Sully-Leplne Series and the

Buckinghorse Formation of northeastern British Columbia. Here coals with vitrinite reflectance of 2.20% were foimd at the same depth as mixed- layer clays with 64-68% illite. Comparison to vitrinite reflectances of

Lower Cretaceous samples plotted by Bostick (1979) suggests a temperature of 140°C for these rocks.

Alteration Mineralogy and Paleotemperature

Estimation of temperatures attained diiring metamorphism in the study area can be made by comparison of the alteration mineralogy in the Mt.

Higgins area with that of areas for which the temperature of metamorphism 76 has been established. As the rocks of the Mt. Higgins area appear to be hydrothermally metamorphosed; as evidenced by the contact metamorphic rocks found on Mt. Higgins, the presumably intrusive nature of the diorite-

Chuckanut contact, retention of cell structure in anthracites of the Deer

Creek area (indicating short-term heating) and abundant q_uartz and calcite veining in many of the sedimentary rocks; it is especially useful to com pare the mineral assemblages of Mt. Higgins rocks with data from active geothermal fields. Studies of the Salton Sea geothermal area are (lulte useful for comparison as the alteration found there is the most similar to Mt. Higgins area alteration. Studies of burial metamorphism are also used for comparison.

Mineral assemblages indicative of the lowest paleotemperatures in the

Mt. Higgins area are found in the Deer Creek area rocks. The alteration assemblage is K-rectorlte - chlorite - calcite (dominantly) and/or ainkerlte

(+ quartz + albite). It is interesting to note that the alteration here is clay-carbonate type rather than the zeolltic alteration common in geothermal systems in New Zealand and elsewhere. Zen (197^) suggests that clay- carbonate alteration occurs when carbon dioxide is abundant, whereas zeo lite minerals are formed when concentrations of CO2 are low.

In addition to the K-rectorlte - chlorite - carbonate assemblage found in the Deer Creek area bentonites and associated sediments it is important to note the absence of certain minerls in Mt. Higgins area rocks that are found in Tertiary sedimentary rocks elsewhere in northwest Washington. All plagioclase in Chuckanut sediments of the study area has been albitized.

Potassium feldspar minerals and kaollnite are found in other Chuckanut rocks

(Kelly, I97O; Marcus, 1981; Pevear, oral communication, I98O) and rocks of the Huntingdon Formation (Horton, 1978), but are absent in Mt. Hig gins rocks. Other Tertiary bentonites of Washington and British Colum- 77 bia contain kaollnite occurring with smectite (Centralia coal field of southwestern Washington; L. Reinink-Smlth , oral communication, I98O) or kaolinite with smectite or K-rectorite with up to 55^ illlte (Tulameen,

B. C., coalfield; Pevear and others, 1980). It seems quite possible that kaolinite was involved in the reaction which formed chlorite in the Deer

Greek area rocks.

Three chlorite-forming reactions are suggested to be possible for the Deer Greek area rocks. The first reaction, determined by Hutcheon and others (I98O) to be the chlorite-forming reaction in the burial meta morphosed sandstones of the Gretaceous Kootenay Formation of British Golum- bia and Alberta, is as follows:

1. 5 CaMg( 003)2 + Al^Si^Oj + SIO2 + H^O =

”®5 *l2®^30lo(OH)8 chlorite calotte *

This reaction is similar to one si:iggested by Zen (1959, I960) to explain the calcite - chlorite assemblage found in low grade regionally metamor phosed rocks of the Gastleton, Vermont area. Muffler and White (I969) proposed a similar reaction for rocks of the Salton Sea geothermal area.

This reaction is as follows:

2. CaJIgCOOj)^ t 5 CaHg„^^Fe„^^(C03)2 + 2.5 Al2Sl203(0H)^

fcaollnite Fe chlorite

^ calcite 9003.

Examination of data presented by McDowell and Elders (I980) suggests this reaction may have been important in the Salton Sea rocks they studied. It was noted that dolomite and ankerite disappear whereas calcite and chlorite are first found at depths corresponding to 190°G (McDowell and Elders,

1980). A third reaction was proposed by Boles and Franks (1979) for the 78 burial metamorphlc formation of aluminous chlorites in the Wilcox sand stones of southeast Texas. Their reaction follows:

3. + 3-5Hg*^ + 9H2O + 3 Al2Sl205(0H)^ kaollnite =

''"?^3 V^6Si6°2o(™>l6 chlorite

A similar reaction can be written for the formation of the Deer Greek area

chlorite:

1.46Fe''3 = + ZAljSljOjCOH)^ kaollnite '

chlorite * quarts,

+ 4.96 h"^.

All of the above-mentioned chlorite producing reactions could have

occurred in the Deer Greek area rocks. Iron and magnesium consumed in the

reaction modeled after the Boles and Franks (1979) chlorite reaction could

have been made available by dissolution of dolomite and ankerite, disso

lution of ferromagnesicin minerals, or the smectite to illite reaction.

Ankerite is found in some of the Deer Greek area rocks. Also found in

some Deer Greek area rocks is calcite with hematite strung out along

planes within the crystals, indicating it possibly formed from ankerite.

The smectite to K-rectorite reaction is also important in the deter

mination of the paleotemperature of the Deer Greek area. Figure 3^ is

taken from the work of Hoffman and Hower (1979) and shows mineralogical

changes with increasing burial metamorphic temperatures. The K-rectorite

(= allevardite) observed in the Mt. Higgins arrea corresponds to burial

metamorphic temperatures of 100-175°G. Gomplete reaction of kaollnite

to form chlorite requires temperatures of at least 135°C (Hoffman and

Hower, 1979). Kalkberg-type mixed-layer illlte/smectite corresponds to

temperatures of 175~210°G (Hoffman and Hower, 1979)* 79

-I------1------1------— SMECTITE SHALES ------(I/S) RANDOM

(I/S) ALLEVARDITE (= REGTORITe) ------(I/S) KALKBERG ------1 LUTE 2M MICA CHLORITE------? KAOLIN K-FELDSPAR

----Ib(j CHLORITE SANDSTONES ------lb CHLORITE Mb CHLORITE------? HALLOYSITE/KAOLIN d ------KAOLINITE ------? DICKITE/NACRITE -? CORRENSITE

LAUMONTITE------VOLCANICS PREHNITE------

—— PUMPELLYITE ------___ HEULANDITE ------^------ANALCITE TEMPERATURE(OC) ------^------1------1______L------1______1______100 150 200 250 300 350 Figure 35 . Correlation of the temperature dependent mineral assemblages in shales I sandstones and volcanogenic rocks. Temperatures do not represent equilibrium but are applicable (with caution) to lower Tertiary and Mesozoic pre-greenschist facies rocks. Taken from Hoffman and Hower (19?9). 80

Data of Hoffman and Hower (1979) shown in figure 35 also Indicate that dissolution of potassium feldspar begins at temperatures as low as 100°C. This corresponds to the onset of ordering in mixed-layer illite/

smectites and is siiggested to be a soiirce of potassium for the conversion

of smectite to illite (Hoffman and Hower, 1979; Hower and others, 1976;

Pevear and others, I98O). Dissolution of potassium feldspar may also be a source of potassium in the Mt. Higgins area. Figure I6 is a photomic rograph of a tuff showing the replacement of probable sanidine by Kalk- berg-type illite/smectlte. Another source of potassium in the Mt. Higgins area is the widespread chloritization of biotite, as shown in figure 3.

Findings similar to those of Hoffman and Hower (1979) are reported by

Boles and Franks (1979) in a study of southeast Texas borehole samples

(fig. 36). Breakdown of potassium feldspar and micas liberated the potas sium necessary for the transformation of smectite to illite in the for mation of mixed-layer clays.

Reaction times are much shorter in hydrothermal systems, which are thought to be active for only a few million years or less (Browne, I978).

Therefore, reactions do not go to completion and assemblages are indica tive of higher temperatures than suggested by the same assemblage in burial metamorphic rocks. Comparison of alteration mineralogies found in the Mt.

Higgins area with those of other hydrothermal areas is most effective for determination of paleotemperature.

Conversion of mixed-layer lllite/smectite to illite was found to occur at 210 C in the Salton Sea geothermal field (Muffler and White,

1969). As discussed in a previous section, vitrinite reflectances of anthracites cropping out in the K-rectorite bearing area (average =

3.07^) corresponds to temperatures of 275-285°C attained at the Salton

Sea (Bostick, 1979; see fig. 34 ). 81

^ ICO IS) 2tc TEMTfefATLUee: ®C Figure 36. Schematic diagram of influence of l/s clay reactions on Wilcox sandstone cementst Vertical arrows depict ion transfer between l/s clay reactions and phases in sandstone. Taken from Boles and Franks (1979)* 82

In a later Salton Sea study of Borehole Elmore 1, McDowell and El

ders (1980) found thatmr>ed-layering persisted at temperatures up to 2?5°C

in sandstones and 290 G In shales. Mixed-layer lllite/smectlte from shales

contains up to smectite layers at 185°G, corresponding to the depth

at which samples were first recovered (McDowell and Elders, I98O). As

mentioned previously, dolomite and ankerite disappear, with chlorite and

calcite first appearing, at 210°C.

Interpretation of Steiner's (I968) data from the Wairakei geothermal

field of New Zealand indicates temperatures of 180-230°C for rectorlte

and 230-240°C for Kalkberg-type illlte/smectite.

Calcium was abmdant during hydrothermal metamorphism in the Mt. Hig gins area, as evidenced by the presence of up to 20^ calcite in some ben

tonites and calcite veins in many rocks. Experimental work by Eberl (1978b)

suggests that the presence of calcium can retard the reaction of rectorites to higher grade minerals. Also it seems possible that the rocks in the area did not contain an abundance of potassium-bearing minerals. Lack of sufficient amounts of potassium could also retard the smectite to lllite reaction. These differences in fluid and rock chemistry could explain the differences in values reached by comparing Mt. Higgins clays and to data from the Salton Sea geothermal field. Comparison of clays suggests a tem perature of less than 210 G while vitrinlte reflectance comparisons yield temperatures of 275-285°G. Temperatures in the K-rectorite zone were be tween 200 C and 283 G, but the temperatures of 275~285*^G indicated by values may be more reliable as is unaffected by fluid composition, which appears to be a factor for the Mt. Higgins rocks.

Bostick and others (1978) have plotted the relationship between vitrinite reflectance, maximum rock temperature and effective time (duration of rock temperature within 15°C of the maximum temperature of its history) Figure

m axim um temperature in DEnni ES CFI'-.IUS

37*

Relationship between plotted ture maximum others of "Effective EFFECTIVE a

rock in

(1978).

rock its TIME (leirge

within

time" IN history.

temperature

MILLIONS

dot

Deer

means 15°G 83

OF vitrlnite 275°C Creek

Taken

of YEARS the

I and the

area duration

from line) burial maximum

reflectajice

anthracite

Bostick on

time.

of diagram. tempera

burial

and

shown in figure 37. The 275°C temperature estimated for the Deer Creek

area and the value of approximately % indicate the hydrothermal system

was active in the study area for approximately one million years. Browne

(1978) comments that hydrothermal activity in the Steamboat Springs, Nevada,

area has been occurring for at least one million years and probably as long

as four million years, but that the intensity and location of activity

may change with time. Data of Briggs and Naeser (1979) suggests that tem

peratures as low as 3OO G, effective for one million years, may reset zir

cons. Thus, it seems possible that the 44.5 * 2.0 million year zircon

fission track date obtained for a bentonite from the Deer Creek area may

be a metamorphlc date. The temperature in the area was somewhat lower

than the temperature quoted by Briggs and Naeser (1979), so it may be

possible that the zircons were not reset.

Temperatures affecting the Kalkberg-bearlng areas are assumed to be higher than the 275~285 C temperature indicated for the Deer Creek area, but cannot be pinpointed. Completely unexpandable illite is found in rocks from Mt. Higgins, indicating a temperattire even higher than the Kalkberg- bearlng rocks, or that more potassium was available. A comparison of clay mineralogy of rocks of the Mt. Higgins area and rocks of some active geo thermal areas is foimd in table 10.

The presence of andalusite in rocks on Mt. Higgins is significant and can be used to estimate paleotemperature of those rocks. Winkler (1976) states that the upper stability limit of pyrophyllite is important as the first appearance of an mineral in quartz-bearing rocks requires reaching or exceeding that upper stability limit of pyrophyllite even if the Al2Si20^-phase is not formed from pyrophyllite. Winkler (I976) cites research which indicates andalusite can be produced from pyrophyllite at 400 C and 1.0 kb. At higher pressures still within the andalusite sta- Table 10. Comparison of clay mineralogy of rocks of the Mt. Higgins area and rocks of some active geothermal areas.

b Mt. Higgins Wairakei, Salton Sea ’ 3. Borehole Area New Zealand Elmore 1, Salton Sea*^ 175°G

No rectoriteI mixed-layer data lllite/smectite 200°G

225°G mixed-layer lllite/smectite, Kalberg-type lllite lllite/smectite, 85-100^ 85~95^ lllite layers lllite layers 250°G

•? illite - K-rectorite,i 275 G 65% lllite I r

Kalkberg-type 300°G illlte/smectite, 90-9^ illite layers lllite (exact temp, unknown)

■7I 325°C i illite (temp, of for mation <400°C)

a Wairakei, N. Z.: Steiner, I968. b Salton Sea; Muffler and White, I969. c Borehole Elmore 1, Salton Sea; McDowell and Elders, I98O.

85 Figure 38• Pressure - temperature diagram showing con tact metamorphlc facies, reactions Important for Mt. Higgins rocks and Mt. Higgins meta morphlc assemblages. All facies divisions and reactions, except the andaluslte reaction of Hemley and others (I98O) and the triple point of Holdaway (l97l), taken from Hyndman (19?2). 8? 88

bility range, temperatures of up to 430°C are required for the reaction.

More recent work by Hemley and others (I98O) indicates lower temperatures

for the pyrophyllite - andaluslte reaction. At one kilobar, the tempera

ture of reaction is 365-370 C. Presence of excessive amotints of quartz,

which is the case for the Mt. Higgins rocks, inhibits the reaction, neces

sitating higher temperatures for the formation of andaluslte (Hemley and

others, I980). Figure 38 is a pressure - temperature diagram upon which

this and other important reactions are plotted.

Cordlerite is also useful in the determination of paleotemperature.

Plotted on figure 38 is the cordlerite-forming reaction of Schreyer and

Yoder (reported in Hyndman, 1972) which indicates cordierite-bearing rocks

of Mt. Higgins attained temperatures close to 500°C.

Metamorphic Zonation and Interpretation of the Hydrothermal History of the Mt. Higgins Area

Metamorphic Zonation

Caianges in the metamorphic mineralogy and grade with respect to geo graphical location within the Mt. Higgins study area are apparent, enab ling designation of metamorphic zones (fig. 39). They are as follows:

1) A zone in the northern part of the study area, defined by the presence of rectorlte and abundant calcite. Aluminous Fe-sudoite (chlorite), quartz, ankerlte and albite are also present as alteration minerals in rocks of this zone. Maximum metamorphic temperature reached in this area was between 275°G and 285°G.

2) To the south and southwest of the above-mentioned rectorlte zone,

Kalkberg-type illlte/smectite replaces rectorlte. The Kalkberg zone mineralogy was produced by higher metamorphic temperatures than were ac tive in the rectorlte zone, but those temperatures cannot be-closely es timated. Figure 39. Map showing location of metamoiphic zones in the Mt. Higgins area.

Other metamorphic minerals present in rocks of this zone are quartz,

chlorite, albite, calcite and possibly epidote, although it could not be

determined whether the epidote is detrital or diagenetic. Epidote is

present in trace amounts. Calcite occurs in much lower percentages than

in the rectorite zone rocks.

3 ) Albite-epidote hornfels facies rocks form a zone on the eastern

arm of Mt. Higgins and the upper Higgins Greek valley. Andalusite assem

blages found in some of these rocks suggest temperatures of around 400°C.

4) Rocks bearing mineral assemblages of the hornblende hornfels

facies crop out on the western arm of Mt. Higgins. The presence of cor-

dierite in these rocks indicates metamorphic temperatures of 500°C.

Hydrothermal History of the Mt. Higgins Area

Interpretation of the hydrothermal and geological history of the Mt.

Higgins area involves several considerations. They are as follows:

1) Metamorphic grade generally increases toward the Granite Lake

pluton, but mineral zones are not arranged in an ideally concentric pat tern. Rocks of the albite-epidote hornfels and hornblende hornfels zones do no crop out to the north of the diorite body.

2) Post-Chuckanut faulting in the area complicates the interpretation of the hydrothermal alteration present in the area.

3 ) Age of the Granite Lake diorite is established as 53 * 8 million years (Bechtel, 1979; K/A t date of hornblende), a date which barely over laps the 44.5 * 2.0 million year zircon fission track date of metamorphosed bentonites in the area, and for the Oso volcanics.

4) Diorites with compositions similar to the Granite Lake diorite are present on and near Round Mountain, adjacent to the eastern edge of the study area, ard may be intrusive into the Chuckanut Formation (Jones,

1959)• Homfelsed rocks were noted in the area (Jones, 1959). 92

5) The alteration aureole in the Mt. Higgins area is much larger than aureoles created hy the intrusion of magmatic bodies of similar size and composition to the Granite Lake diorlte into sedimentary rocks.

In short, a simple Interpretation of events which occurred in the area may not be the most reasonable one.

H. P. Taylor, Jr., who pioneered oxygen and hydrogen Isotope studies of hydrothermally altered rocks and proved the existence of alteration aureoles resultant from large-scale Interaction between meteoric waters

(heated by intrusions) and intruded rocks on the basis of isotope data, encountered similar problems in the study of hydrothermal alteration caused by the intrusion of Tertiary granodiorites in the western Oregon Cascades

(Taylor, 1971; Taylor, 1979)* Taylor found that the alteration aureoles caused by the intrusions were much larger than expected (based on data suggesting that a cylindrical stock contains only enough heat to produce an alteration aureole approximately 0.^ to 0.5 stock diameters wide, which is confirmed by field studies in many areas) and often the mineral zonation patterns were not symmetrical (Taylor, 1971 and 1979). Taylor proposed reasons explaining these phenomena. The western Oregon stocks may broaden in cross-section at depth. The alteration zones may be underlain by hid den Intrusions. It is also possible that the intrusions do not represent a single injection of magma, but result from episodic addition of new mag ma from below, as would be expected in a volcanic conduit to the surface

(Taylor, 1979).

These ideas may also be applicable to the hydrothermal history of the

Mt. Higgins ai‘ea. The area was part of a broad magmatic arc active during

Eocene time (Snyder and others, 1976; Davis, 1977; Ewing, I98O) and other igneous rocks of similar age to the Oso Volcanics (^3.1 *1.9 million years) and the Granite Lake diorite have been found within a few miles 93 of the Mt. Higgins cirea, including a basaltic dike from Finney Creek

(just north of the study area) dated as 46 * 8 million years (Bechtel,

1979)• In light of this data and the work of Taylor (1971 and 1979)i it is possible that intrusions are present beneath ard near the study area, and may crop out in the Round Mountain area just east of Mt. Higgins.

Magmatic activity may have begm in the Mt. Higgins area prior to the deposition of the volcanigenic sediments of the Deer Greek area.

Intrusion of the Granite Lake diorlte resulted in high temperature meta morphism of the rocks of Mt. Higgins. Volcanic activity began in or near the study area, producing dikes, the Oso volcanics, and the bentonites and associated volcanigenic sediments which crop out in the Deer Creek area. Magmatism may have been episodic and possibly was active for several million years, creating hydrothermal systems which perhaps affected various parts of the area at various times. The diorite which crops out in the

Round Mountain area is very possibly part of the intrusive group that contributed to metamorphism. The Oso volcanics could have produced a relatively impermeable Insulating cap on the hydrothermal system. Al though this explanation is more complex than a single intrusion model, it may be more realistic considering the time span of magmatism in the area, Taylor's study of the western Oregon Cascades and the knowledge that many intrusive bodies, notable examples being the Sierra Nevada Batholith of California and the Chilliwack Composite Batholith of Washington and

British Columbia, are composed of many smaller intrusions emplaced at different times.

One part of the study area deserves special consideration. The north lake area (see fig. 2 for location), just to the north of the Granite

Lake diorite, contains no rocks of the albite-epldote hornfels or horn blende hornfels facies. The outcrop closest to the northernmost diorite 9^ outcrop is the light green tuff containing Kalkberg-type mixed layer clay with 9^0 illite layers. Ghuckanut formation rocks which crop out to the north are somewhat hornfelsed, but contain no minerals from which definite paleotemperatures could be established. Three possible explanations are presented as follows:

1) The contact between the dioritic body and the rocks to the north may be vertical, while the southeastern Intrusive contact dips gently. This would cause the width of metamorphic zones in the southeast to appear much wider than they are, while the pattern of zonation to the north would re flect the true widths. The narrow hornblende hornfels ajid albite-epidote hornfels zones are assumed to be covered.

2) The northern contact is a fault contact, possibly a continuation of the dip-slip fault mapped to the east. The Kalkberg zone has been faulted down from an original location more distant from the intrusive contact.

3) The tuff is younger than the intrusive body. Either the dlorlte had cooled significantly when the tuff was deposited or metamorphism was the result of a hydrothermal system set up by the intrusion of another pluton or a later phase of the Granite Lake stock.

The first possibility does not seem to be likely considering the large geographical extent of alteration in the study area. Explanation number three may also be improbable. The lowest outcrop of Kalkberg zone volcanic rock is at an elevation of around 2400 feet, while the northern most outcrop of dlorlte is at an altitude of 3200 feet. If the volcanics are Indeed younger than the diorlte, either extensive erosion prior to deposition of the volcanics or tilting after deposition would be necessary.

The well-exposed Ghuckanut rocks do not display tilting to the extent neces sary for the volcanics to be deposited atop the diorite body. 95

The second explanation, that the contact Is a fault, seems most likely of the three possibilities. CONCLUSIONS

1) In the Mt. Higgins area, the Chuckanut Formation is in nearly vertical contact with older metamorphic rocks. It is likely the contact is a fault. The sediments are capped by Oso volcanics of Vance (oral com munication, 1980) and a diorite crops out in the Granite Lake area. It is suggested that the diorite is intrusive into the Chuckanut and is at least partly responsible for the thermal metamorphism evident in the area.

2) The upper part of the Chuckanut section crops out in the Deer

Creek area and is composed of dominantly fine-grained volcanigenic sediments, unlike the thick-bedded sandstones of the rest of the Chuckanut section.

Bentonites from this area are composed primarily of K-rectorite (which replaces shards and other glassy volcanic detritus), quartz, chlorite and volcanic rock fragments. The bentonites are altered air-fall tephra.

The rocks were deposited in a swampy floodplain. The sedimentary basin

in which the rocks of the Mt. Higgins area were deposited may have been formed by Tertiary block faulting.

3) The K-rectorite is a regularly Interstratified illlte/smectlte

with IS order, illite layers and diffracting domains 10-14 layers -j-o -}-2 tAl. ooFe„ oft -0.76 +0.70 ^^^3.37^^0.63^°10^°^^2^ ^3-0.10^^0.12^0.38^ ‘

4) In areas which were exposed to greater temperatures, the mixed-

layer illite/smectite present is the higher grade Kalkberg-type clay. The

Kalkberg-type clay has ISII ordering, 93~95% illite layers and diffracting

domains approximately 12-18 layers thick.

5) Hornfelsed Chuckanut rocks crop out on Mt. Higgins. Mineral as

semblages of both alblte-epidote homfels facies and hornblende hornfels

facies have been identified.

96 9?

6) The Mt. Higgins area is divided into four metamorphic zones:

a) K-rectorite zone with assemblages resultant from temperatures of 2?5-

285°C, b) Kalkberg zone, c) Albite-epidote hornfels facies suggesting

temperatures around 400°C, and d) Hornblende hornfels facies indicating

temperatures around 500°C.

?) It is suggested that either the Mt. Higgins area is underlain by

another intrusion or the Granite Lake diorite is the exposed tip of a lar

ger intrusive complex. A diorite similar to the Granite Lake diorite crops

out east of the study area and may be an extension of the above-mentioned

intrusive complex. Intrusion may have been episodic. Deposition of vol-

canigenic sediments may have continued after the Initial intrusion and

until the volcanics Inundated the depositional basin. The volcanics may

have provided an insulating cap on the hydrothermal system. Hydrothermal

activity may have continued sporadically for several million years, but

the locus of heating may have changed through time.

8 ) The hornblende hornfels facies and albite-epidote hornfels facies zones extend several kilometers to the southeast of the Intrusive contact, but are not present to the north of the diorite. It is likely that the northern contact is a fault, possibly an extension of a previously mapped fault in the eastern part of the area. REFERENCES

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