Field Guide to Hydrothermal Alteration 

in the White River Altered Area and in the 

Osceola Mudfl ow, Washington

By David A. John, James J. Rytuba, Roger P. Ashley, Richard J. Blakely, James W. Vallance, 

Grant R. Newport, and Gary R. Heinemeyer

Prepared for the Society of Economic Geologists Field Trip, November 6, 2003

Bulletin 2217

U.S. Department of the Interior

U.S. Geological Survey
1

Bulletin 2217

U.S. Department of the Interior

U.S. Geological Survey

Field Guide to Hydrothermal Alteration 

in the White River Altered Area and in the 

Osceola Mudflow, Washington

By David A. John, James J. Rytuba, Roger P. Ashley, Richard J. Blakely, James W. Vallance, 

Grant R. Newport, and Gary R. Heinemeyer
2

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is 

for descriptive purposes only and does not imply endorsement 

by the U.S. Government.

U.S. Geological Survey, Reston, Virginia: 2003

Electronic copies of this publication are available online at

http://geopubs.wr.usgs.gov/bulletin/b2217/

Additional USGS publications can be found online at

http://geology.usgs.gov/products.html

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS (1–888–275–8747)

World Wide Web: http://www.usgs.gov/

Published in the Western Region, Menlo Park, California

Manuscript approved for publication October 25, 2003
III

Figures

1. Map showing location of the Western Cascades and High Cascades arcs and 

associated mineral deposits, northwestern United States.................................................... 16

2. Map showing areas inundated by Holocene debris flows from Mount Rainier....................... 17

3. Photograph of vuggy silica alteration in the Scatter Creek (James Hardie) silica quarry ..... 17

4. Geologic map of the White River area, showing field trip stops ................................................. 18

5. Heterolithic breccia (lahar) in the Fifes Peak Formation.............................................................. 20

6. Finely bedded tuffs from small outcrop about 0.5 km north of the Superior quarry................. 20

7. Silicified flow-banded dacite showing large flow fold.................................................................. 20

8. Map showing distribution of hydrothermal alteration in the White River area ........................ 21

9. Photo of leached phenocrysts in vuggy silica alteration in the Scatter Creek quarry............ 22

10. Photo showing sharp contact between vuggy silica alteration and advanced argillic 

alteration in the Scatter Creek quarry ....................................................................................... 22

11. Schematic model for high-sulfidation gold deposits, showing zoning of hydrothermal 

alteration assemblages and ore types ...................................................................................... 23

12. Log ƒO2-pH diagram showing fluid relations forming vuggy silica alteration ........................... 23

13. Aeromagnetic anomalies of the White River altered area and surrounding regions.............. 24

14. Cross sections of IP surveys across the White River altered area ............................................ 25

15. Geophysical anomalies of the White River altered area and surrounding regions................. 26

16. Ground magnetic studies of the White River altered area........................................................... 27

17. Ground magnetic profile across White River altered zone.......................................................... 28

18. View of the Superior (Ash Grove) quarry from Taugow................................................................ 28

19. Generalized geologic map of the Superior quarry......................................................................... 29

20. Gray vuggy silica rock with abundant voids after phenocrysts in andesite flow..................... 30

21. Photographs of sulfide minerals in vuggy silica from the Superior quarry ............................... 30

22. Enargite filling funnel-shaped void in white chalcedonic silica in the Superior quarry ......... 30

Contents

Introduction ................................................................................................................................................... 1

Road log from Enumclaw to the White River Altered Area and the Osceola Mudflow along 

the lower White River, Washington ............................................................................................. 2

Part 1: The White River Altered Area ........................................................................................................ 3

Geology of the White River Altered Area ......................................................................................... 3

Economic Geology of the White River Altered Area—Historical Perspective .......................... 4

Hydrothermal Alteration and Mineralization in the White River Area......................................... 4

Geophysical Framework of the White River Altered Area............................................................. 6

Geochemical Exploration Studies of the White River Altered Area............................................. 7

Stop 1: Superior (Ash Grove) Silica Quarry ...................................................................................... 9

Stop 2: Taugow.................................................................................................................................... 10

Stop 3: Scatter Creek (James Hardie) Silica Quarry..................................................................... 10

Part 2: The Osceola Mudflow in the Lower White River...................................................................... 11

General Features of the Osceola Mudflow .................................................................................... 11

Hydrothermal Alteration in the Osceola Mudflow ........................................................................ 12

Stop 4: Osceola Mudflow near Greenwater................................................................................... 13

Stop 5: Osceola Mudflow in the Corliss Gravel Quarry ................................................................ 13

References................................................................................................................................................... 13
IV

23. Tan chalcedony replacing relict flow and devitrification layers in dacite flow in the 

Superior quarry.............................................................................................................................. 31 

24. Massive tan chalcedony cut by hydrothermal breccias with sulfides in gray areas in the 

Superior quarry.............................................................................................................................. 31

25. Felsic porphyry dike in the Superior quarry.................................................................................... 31

26. Hydrothermal breccia with clasts of early stage white chalcedony in tan to gray 

chalcedony with sulfides in gray areas in the Superior quarry ............................................ 32

27. Sulfide-bearing hydrothermal breccia developed in massive tan silicified rock in the 

Superior quarry.............................................................................................................................. 32

28. Massive tan silicified rock cut by stockwork of sulfide-bearing gray chalcedony in the 

Superior quarry.............................................................................................................................. 32

29. Brecciated siliceous hydrothermal sedimentary rocks in the Superior quarry ....................... 33

30. Fault breccia with clay-supported fragments that contains high gold content (1.7 ppm) 

in the Superior quarry................................................................................................................... 33

31. North-striking fault with red clay gouge developed in massive vuggy silica rock .................. 33

32. Red to brown smectite clay zone developed from alteration of bedded tuff ............................ 34

33. Taugow from the Superior quarry .................................................................................................... 34

34. Knob of alunitic alteration on Taugow............................................................................................. 34

35. Leached silicified tuff breccia with relict pyroclastic textures exposed in road cut near 

top of Taugow ................................................................................................................................ 35

36. Narrow fine-grained silicic dike cutting silicified tuff breccia near top of Taugow................ 35

37. Blocks of vuggy silica alteration in hydrothermal breccia near top of Taugow....................... 35

38. Generalized geologic map of the Scatter Creek quarry................................................................ 36

39. Stockpile of sized silica at Scatter Creek quarry ........................................................................... 37

40. Gray vuggy silica rock cut by white quartz and chalcedony veins and hydrothermal 

breccias in the Scatter Creek quarry......................................................................................... 37

41. Voids developed in porphyritic andesite after leached plagioclase and pyroxene 

phenocrysts by acid hydrothermal fluids leaving a residual ground mass of silica.......... 37

42. Northeast-trending rib of orangish-brown vuggy silica alteration in the Scatter Creek 

quarry .............................................................................................................................................. 38

43. “Clay hole” of propylitic alteration in Scatter Creek quarry ........................................................ 38

44. Oxidation in the Scatter Creek quarry.............................................................................................. 39

45. Vuggy silica cut by white chalcedonic hydrothermal breccia and veins in the Scatter Creek 

quarry .............................................................................................................................................. 39

46. Vuggy silica cut by hydrothermal breccias in the Scatter Creek quarry................................... 40

47. Fracture in vuggy silica filled with late stage hydrothermal red clay in the Scatter Creek 

quarry .............................................................................................................................................. 40

48. White outcrops of leached rock formed in the near-surface steam-heated zone in the 

Scatter Creek quarry .................................................................................................................... 41

49. Map showing distribution of the Osceola Mudflow and Paradise lahar................................... 41

50. Dark-gray clay-pyrite rich matrix of the Osceola Mudflow.......................................................... 42

51. Typical outcrop of the Osceola Mudflow along the White River near Greenwater, 

Washington .................................................................................................................................... 42

52. Typical smectite-pyrite alteration of andesite clast in the Osceola Mudflow.......................... 42

53. Back-scattered SEM image of smectite alteration of andesite clast in the Osceola Mudflow..... 43

54. Back-scattered SEM image of smectite-pyrite alteration of andesite clast in the Osceola 

Mudflow.......................................................................................................................................... 43

55. Back-scattered SEM image of advanced argillic altered clast in Osceola Mudflow ............. 43

56. Back-scattered SEM image of advanced argillic altered clast in Osceola Mudflow ............. 44

57. Back-scattered SEM image of intergrown alunite and kaolinite in advanced argillic altered 

clast in the Osceola Mudflow ..................................................................................................... 44
V

58. Back-scattered SEM image of alunite containing P-rich domains in advanced argillic 

altered clast in the Osceola Mudflow........................................................................................ 44

59. Back-scattered SEM image of vug-filling anhydrite/gypsum and fluorite in advanced 

argillic altered clast in the Osceola Mudflow .......................................................................... 45

60. Schematic diagram showing formation of normal zoning by incremental deposition model 

for mass flow deposits ................................................................................................................. 45

61. Exposure of Osceola Mudflow overlying well bedded late Pleistocene glacial-fluvial 

deposits in the Corliss quarry...................................................................................................... 46

62. Partly charred trees protruding from the Osceola Mudflow in the Corliss quarry .................. 46

63. Base of the Osceola Mudflow in the Corliss quarry...................................................................... 46

Tables

1. Mineral assemblages in the White River altered area ................................................................. 47

2. Types of silicic alteration in the White River altered area........................................................... 48
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

1

Field Guide to Hydrothermal Alteration in the White River 

Altered Area and in the Osceola Mudflow, Washington

By David A. John1, James J. Rytuba1, Roger P. Ashley1, Richard J. Blakely1, James W. Vallance2, Grant R. 

Newport3

, and Gary R. Heinemeyer4

Introduction

The Cenozoic Cascades arcs of southwestern Washington 

are the product of long-lived, but discontinuous, magmatism 

beginning in the Eocene and continuing to the present (for 

example, Christiansen and Yeats, 1992). This magmatism is 

the result of subduction of oceanic crust beneath the North 

American continent. The magmatic rocks are divided into 

two subparallel, north-trending continental-margin arcs, the 

Eocene to Pliocene Western Cascades, and the Quaternary 

High Cascades, which overlies, and is east of, the Western 

Cascades (fig. 1). Both arcs are calc-alkaline and are characterized by voluminous mafic lava flows (mostly basalt to 

basaltic andesite compositions) and scattered large stratovolcanoes of mafic andesite to dacite compositions. Silicic volcanism is relatively uncommon. Quartz diorite to granite plutons 

are exposed in more deeply eroded parts of the Western 

Cascades Arc (for example, Mount Rainier area and just north 

of Mt. St. Helens, fig. 1).

Hydrothermal alteration is widespread in both Tertiary 

and Quaternary igneous rocks of the Cascades arcs. Most 

alteration in the Tertiary Western Cascades Arc resulted from 

hydrothermal systems associated with small plutons, some of 

which formed porphyry copper and related deposits, including 

copper-rich breccia pipes, polymetallic veins, and epithermal 

gold-silver deposits (fig. 1). Hydrothermal alteration also 

is present on many Quaternary stratovolcanoes of the High 

Cascades Arc. On some High Cascades volcanoes, this alteration resulted in severely weakened volcanic edifices that were 

susceptible to failure and catastrophic landslides. Most notable 

is the sector collapse of the northeast side of Mount Rainier 

that occurred about 5,600 yr. B.P. This collapse resulted in 

formation of the clay-rich Osceola Mudflow that traveled 120 

km down valley from Mount Rainier to Puget Sound covering 

more than 200 km2

 (fig. 2).

This field trip examines several styles and features of 

hydrothermal alteration related to Cenozoic magmatism in 

the Cascades arcs. The morning of the trip will examine the 

White River altered area, which includes high-level alteration related to a large, early Miocene magmatic-hydrothermal 

system exposed about 10 km east of Enumclaw, Washington 

(figs. 1 and 3). Here, vuggy silica alteration is being quarried 

for silica and advanced argillic alteration has been prospected 

for alunite. Clay-filled fractures and sulfide-rich, fine-grained 

sedimentary rocks of hydrothermal origin locally are enriched 

in precious metals. Many hydrothermal features common in 

high-sulfidation gold-silver deposits and in advanced argillic alteration zones overlying porphyry copper deposits (for 

example, Gustafson and Hunt, 1975; Hedenquist and others, 

2000; Sillitoe, 2000) are exposed, although no economic base 

or precious metal mineralized rock has been discovered to 

date. The afternoon will be spent examining two exposures 

of the Osceola Mudflow along the White River. The Osceola 

Mudflow contains abundant clasts of altered Quaternary rocks 

from Mount Rainier that show various types of hydrothermal 

alteration and hydrothermal features. The mudflow matrix 

contains abundant hydrothermal clay minerals that added 

cohesiveness to the debris flow and helped allow it to travel 

much farther down valley than other, noncohesive debris flows 

from Mount Rainier (Crandell, 1971; Vallance and Scott, 

1997). 

The White River altered area is the subject of ongoing 

studies by geoscientists from Weyerhaeuser Company and the 

U.S. Geological Survey (USGS). The generalized descriptions of the geology, geophysics, alteration, and mineralization 

presented here represent the preliminary results of this study 

(Ashley and others, 2003). Additional field, geochemical, geochronologic, and geophysical studies are underway.

The Osceola Mudflow and other Holocene debris flows 

from Mount Rainier also are the subject of ongoing studies by 

the USGS (for example, Breit and others, 2003; John and others, 2003; Plumlee and others, 2003, Sisson and others, 2003; 

Vallance and others, 2003). Studies of hydrothermal alteration 

in the Osceola Mudflow are being used to better understand 

fossil hydrothermal systems on Mount Rainier and potential 

hazards associated with this alteration.

Overview of Field Trip and Field Guidebook

This one-day trip has five stops, the first three are in the 

White River altered area and latter two are in the Osceola 

Mudflow (fig. 4). The five stops are: Stop 1—Superior silica 

quarry, Ash Grove Cement Co.; Stop 2—Taugow breccia pipe; 

Stop 3—Scatter Creek silica quarry, James Hardie Building 

Products, Inc.; Stop 4—Osceola Mudflow near Greenwater; 

and Stop 5—Osceola Mudflow in the Corliss gravel quarry. 

The first part of the guidebook contains a short road log 

from Enumclaw through the White River altered area and 

along the White River to Greenwater. 

1

U.S. Geological Survey, Menlo Park, California. 

2

U.S.Geological Survey, Vancouver, Washington. 

3

Weyerhauser Company, Federal Way, Washington. 4

Tucson, Arizona.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

2

The second part of the guidebook contains short chapters 

on the geologic setting of the White River altered area, the 

history of economic geology in the area, general features of 

hydrothermal alteration in the area, geophysical features of the 

altered area, and geochemistry of the alteration. These chapters are followed by detailed descriptions of the three field trip 

stops in the White River altered area. 

The third part of the guidebook describes general features 

of the Osceola Mudflow and a preliminary study of hydrothermal 

alteration in the mudflow. These sections are followed detailed 

descriptions of the two field trip stops in the Osceola Mudflow.

Acknowledgments

We want to thank Weyerhaeuser Company for access to 

the Superior and Scatter Creek silica quarries, Scott Corliss 

of Corliss Resources for access to the Corliss gravel quarry, 

Denis Johnson of Weyerhaeuser for computer graphics, Steve 

Box for unpublished field data, and Robert Oscarson for help 

with the SEM. Reviews of the field guide by Ted Theodore 

and Don Singer were very helpful.

Road Log from Enumclaw to the White 

River Altered Zone and the Osceola 

Mudflow along the Lower White River, 

Washington

Elapsed

mileage

0.0 Intersection of Washington State Highways 164 and 

410. Reset odometer to 0.0. Turn left onto Washington State Highway 410 and travel east.

1.1 Gravel quarry on left.

1.5 Corliss gravel quarry on left. We will return to the 

Corliss quarry this afternoon for Stop 5 to look at 

the Osceola Mudflow. The quarry produces sand and 

gravel from glacial kame terraces that were banked 

against the west edge of the cascade Range during 

Pleistocene glaciation.

3.5 The “410” aggregate quarry on left. Andesitic lava 

flows of the Fifes Peak Formation are quarried for 

crushed rock.

5.0 Mud Mountain Road on right. Road runs to the Mud 

Mountain Dam, a U.S. Army Corps of Engineers flood 

control dam. The dam was authorized by Congress in 

1936 after the White River flooded in December 1933 

devastating Tacoma and other parts of the Puget Sound 

lowlands. World War II delayed construction of the 

dam, which was finally completed in 1948.

6.4 Intersection with Scatter Creek Road on left. Turn left 

and pass through gate onto private timber company 

lands.

7.1 Denny-Renton quarry on left. The quarry produced 

small amounts of silica prior to 1936 and after World 

War II. More recently, the quarry has been backfilled 

by large blocks of silicified rock from the Superior 

(Ash Grove) quarry.

7.4 Intersection, turn right toward the Superior quarry.

8.0 Stop 1, Superior (Ash Grove) quarry. See detailed 

description of the Superior quarry below. After the 

tour of the quarry, turn around and exit. Taugow is 

visible at 12:00 when leaving quarry. 

8.6 Intersection; turn right onto main road.

8.8 Intersection; stay to right.

9.7 Intersection; turn left (hard left uphill).

10.2 Optional stop to collect alunite. Good exposures of 

lapilli tuff breccia containing abundant pale pink 

alunite crystals on both sides of road.

10.3 Intersection, turn right.

10.8 Coarse alunitic tuff breccia cut by hydrothermal breccias in low road cuts. Fragments in tuff breccia are 

various types of andesites.

10.85 Stop 2, Taugow. See detailed description of this stop 

below. The rocky knob to west with clump of trees 

is silicified andesitic lapilli tuff. Superior quarry is 

in middle distance to the left (west-southwest) of 

this knob. Examine this knobby outcrop and the low 

roadcuts back down the road.

On clear days, a 360° panorama of the White 

River altered area and the surrounding region is visible 

from the top of Taugow: glacier-covered Mount Rainier is at S. 20° E. The peak to due south is composed of 

the Pleistocene basalt of Canyon Creek that unconformably overlies the late Oligocene to early Miocene 

Fifes Peak Formation. The hill below in the middle 

distance is entirely altered; the outcrops are silicified 

and significant amounts of silicified rock have been 

delineated for possible future mining for silica.

To the west beyond the silicified knob is the 

lower White River Valley with buttes composed of 

Fifes Peak Formation in the distance. Enumclaw lies 

in the lowlands beyond these buttes.

The skyline to the north and northeast with the 

radio towers is Grass Mountain, which was mapped 

by Tabor and others (2000) as the Oligocene Ohanapecosh Formation. The slope in the middle distance is 

porphyritic andesite of Fifes Peak Formation. This area 

marks the northern edge of the White River hydrothermal system. Strands of the White River Fault Zone 

trend west-northwest through the terrain between this 

slope and Grass Mountain, juxtaposing the Fifes Peak 

Formation against the older Ohanapecosh Formation.

To the east is the White River Valley and the 

Naches Pass area is on the skyline. To the southeast 

across White River, the altered area continues. The 

cliff with the trees on top bounding a clear cut, trending downhill to the west, is another major silicified 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

3

zone. Exploration for alunite in the 1940s was in an 

area to the left of this silicified zone.

Clearwater Creek is at S. 45° E. The Fifes Peak 

Formation is exposed in Clearwater Creek canyon. 

The upland areas east of Clearwater Creek are occupied by rhyolite and rhyolite tuff units of Clear West 

Peak. These rocks have been interpreted as being 

related to a caldera (McCulla, 1986).

Turn vehicles around and drive back down road.

11.9 Intersection with main road. Turn left.

12.6 Stop 3, entrance to Scatter Creek (James Hardie) 

quarry. See detailed description of the quarry below.

After tour of the Scatter Creek quarry, turn 

vehicles around and drive back down main road 

toward the paved road.

16.0 Intersection with Washington Highway 410. Turn left 

up the White River Valley. For next 10 miles, the road 

passes in and out of Fifes Peak Formation andesites 

and glacial deposits. Hydrothermal alteration related 

to the White River hydrothermal system ends after 

about 3.5 miles.

27.0 Cross the White River Fault Zone, a major NW–striking high-angle fault that juxtaposes Fifes Peak 

Formation andesite on the south against well-bedded 

andesite to dacite breccia, volcaniclastic sedimentary rocks, and locally abundant altered basalt and 

andesite flows of the somewhat older Ohanapecosh 

Formation.

27.5 Greenwater.

28.5 Fire station on left side of road.

28.8 Gravel road on right side of road to private houses. 

Park along the highway just past the gravel road. 

Stop 4, Osceola Mudflow along White River. Find 

a trail parallel to the highway and walk about 50 feet 

west. Find a place to drop off the high terrace down 

to river level. Continue west about 100 feet to the 

outcrop right at river level. See detailed description of 

the outcrop below.

Return to vehicles, Turn around and drive back 

down Highway 410 toward Enumclaw.

41.6 Scatter Creek Road on right. Continue west on Highway 410 to the Corliss quarry.

46.5 Stop 5, Osceola Mudflow in the Corliss gravel 

quarry. See detailed description of the Corliss quarry 

below. End of road log.

Part 1: The White River Altered Area

Geology of the White River Altered Area

The White River altered area is located in the western 

Cascade Range 8 to 15 km east-southeast of Enumclaw, 

Washington. It comprises two adjacent areas of intensely 

altered volcanic rocks, one covering about 20 km2

 on the north 

side of the White River, and a second covering about 3 km2

 on 

the south side of White River. Alteration is likely continuous 

between these areas beneath surficial deposits in the White 

River Valley.

Bedrock in the area has been included in the Fifes Peak 

Formation by Tabor and others (2000) and McCulla (1986) 

(fig. 4). It consists mainly of porphyritic basaltic andesite and 

andesite flows and breccias (fig. 5). The typical porphyritic 

rock contains plagioclase, clinopyroxene, and orthopyroxene phenocrysts. Many outcrops in the altered area north of 

the White River show relict fragmental textures, and locally 

show compaction or eutaxitic structures, suggesting that the 

original rocks were tuffs and tuff breccias (fig. 6). These 

rocks are shown as a separate subunit of the Fifes Peak by 

Tabor and others (2000) (fig. 4). This subunit was interpreted 

by McCulla (1986) as outflow facies rhyolite tuff related to 

a caldera located about 10 km to the southeast in the Clearwater River drainage. Detailed mapping in the altered area 

has shown that this unit also may contain rhyolite or dacite 

flows, possibly part of a local flow-dome complex (fig. 7; G. 

Heinemeyer and G. Newport, unpub. data, 2003), and sparse 

felsic dikes.

The age range of the Fifes Peak Formation in the Snoqualmie Pass 30 x 60 minute quadrangle is about 20–24 Ma 

(Tabor and others, 2000). Only two samples of the Fifes Peak 

andesite in the vicinity of lower White River have been dated 

isotopically, yielding K–Ar ages of 24.1±0.8 and about 21.5 

Ma (Tabor and others, 2000; Weyerhaeuser Co., unpub. data, 

1994). Intracaldera rhyolite to the south at Clear West Peak, 

which is thought to be related to the extracaldera unit, has 

been dated at about 22 Ma (Mattinson,1977).

The White River Fault Zone is a major fault zone that 

crosses the Cascade Range in the vicinity of Naches Pass, then 

follows the Greenwater and White Rivers in a west-northwesterly direction, passing 2 to 3 km north of the northern part of 

the altered area (fig. 4; Tabor and others, 2000). Rocks north 

of the White River Fault are mapped as part of the Ohanapecosh Formation by Tabor and others (2000). The Ohanapecosh consists of highly altered, well-bedded andesite to 

dacite breccia, volcaniclastic sedimentary rocks, and locally 

abundant altered basalt and andesite flows. It is somewhat 

older than the Fifes Peak, and it is thought to unconformably 

underlie the Fifes Peak Formation. Tabor and others (2000) 

also show a fault in the Clearwater River valley that strikes 

north-northwest into the altered area (figs. 4 and 8).

Quaternary surficial deposits are extensive in the lower 

White River area. They include glacial deposits and mudflows 

from Mount Rainier. Between the two altered areas, the bottom of the valley of the White River is relatively flat and more 

than 1 km wide; it broadens westward to a width of 7 to 8 

km. This low-lying area is underlain by glacial deposits of the 

Vashon stage of Fraser glaciation. Although most exposures 

of glacial material in this area have been mapped as undivided 

Vashon drift (Tabor and others, 2000), till, kame terrace, and 

recessional outwash deposits have been recognized.

Alpine glacial deposits, including till and outwash, 

locally mantle bedrock on the sides of the White River Valley. 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

4

Tabor and others (2000) show a relatively large area of such 

deposits occupying the drainage area of Scatter Creek to the 

northwest of the larger altered area.

The low-lying glacial deposits are mantled by laharic 

deposits originating from Mount Rainier. The Osceola Mudflow (Crandell, 1971; Vallance and Scott, 1997) is the most 

extensive of these deposits.

Economic Geology of the White River Altered 

Area—Historical Perspective

According to Callaghan (1940) and Huntting (1955), 

silicified rock of the White River area was prospected for 

gold in the late 1800s. Two adits, one about 100 m long, were 

driven near the White River just south of the Superior quarry. 

A stamp mill was erected in about 1890 to mill the ore, but it 

was soon abandoned. Assays were said to range from about 

0.03 to 0.07 oz Au/ton. In the late 1920s, alunite-bearing rock, 

initially assumed to be clay, was exposed by the White River 

Logging Company in cuts made in the course of constructing 

a logging railway. Alunite was identified in the early 1930s, 

and subsequently the Kalunite Company of Salt Lake City, 

Utah, explored the area for alunite by drilling and trenching. 

Some public lands within the altered area were explored by the 

Washington Division of Mines and Geology. Exploration done 

in the late 1930s and early 1940s yielded estimated reserves of 

1,140,000 tons of rock containing more than 20 percent alunite 

(Livingston, 1971; Kelly and others, 1956).

The only commodity exploited to date in the White River 

altered area is silica. Although not mentioned in reports on 

the alunite exploration, silica was produced by the DennyRenton Clay and Coal Co. from a small quarry near the west 

edge of the northern altered area (Denny-Renton quarry, fig. 

8) some time before 1936 (Glover, 1936; Valentine, 1960). 

After World War II, Manufacturers Mineral Co. operated this 

quarry. Another small quarry located just north of Washington Highway 410 in Section 7 (T.19 N., R. 8 E.) on the south 

flank of Quarry Hill (fig. 8) was operated by Superior Portland Cement, Inc. in 1948 (Valentine, 1960, described therein 

as in R. 7 E.). This quarry also is known informally as the 

ASARCO quarry, because reportedly silica from this site was 

used as flux by the ASARCO smelter at Tacoma.

Recent quarry operations include the Superior pit, operated by Ash Grove Cement Co., which was started in 1987, 

and the Scatter Creek quarry operated by James Hardie Building Products, Inc., started in 1999 (fig. 8). Features of these 

active quarries are described in detail in this field guide.

Weyerhaeuser Company began exploration for base and 

precious metals in the White River hydrothermal system in 

1986. Work done to date includes geochemical analysis of 

cuttings from many blast holes in and around the active silica 

pits, rotary drill holes to average depths of about 125 m in 

the large areas of silicification, a soil geochemical survey of 

selected areas both north and south of White River, periodic 

detailing mapping of the Superior and Scatter Creek silica 

quarries, isotopic dating, and recently, an IP survey north 

of White River and modeling of existing USGS geophysical data. Preliminary results of this work and other on-going 

geophysical and geochemical investigations are described in 

this guide.

Hydrothermal Alteration and Mineralization in 

the White River Area

Introduction

The White River altered area consists of intensely altered 

rocks that are exposed across an area covering about 25 km2

on both sides of the White River near its confluence with the 

Clearwater River (fig. 8). Most alteration is exposed on the 

northwest side of the White River, and this guidebook focuses 

on a reconnaissance study of hydrothermal alteration in this 

area. The White River altered area displays many characteristic features that are associated with quartz-alunite (high-sulfidation) gold deposits (for example, Ransome, 1909; Steven 

and Ratte, 1960; Arribas, 1995; Hedenquist and others, 2000) 

and with the upper parts of porphyry copper-gold deposits (for 

example, Sillitoe, 2000). 

Previous and Present Studies

McCulla (1986) described general alteration features 

and showed the distribution of some key alteration minerals 

in the White River altered area. Reconnaissance mapping by 

Weyerhaeuser Co. (1996) distinguished areas of argillic and 

advanced argillic alteration and silicification from unaltered 

and propylitized rocks (fig. 8). They performed a limited 

number of x-ray diffraction (XRD) analyses confirming their 

alteration types. The USGS has analyzed about 100 samples 

widely distributed across the north side of the White River 

altered area using infrared spectrometry (PIMA) (fig. 8, table 

1). The sample density is inadequate to define regional-scale 

alteration zoning, if present, but analysis of these samples 

confirms the general types of alteration and identifies some 

previously unknown alteration minerals. Additional petrographic, XRD, geochemical, and geochronological studies of 

these samples are underway.

Description of Hydrothermal Alteration

Hydrothermal alteration on the north side of the White 

River altered area consists of two large bodies of massive 

silica ± alunite that presently are being mined for silica, as 

well as numerous other bodies of silica (fig. 8). The silica 

bodies consist of vuggy silica alteration of andesite lava flows 

and breccias, pyroclastic rocks, and hydrothermal breccias that 

have been overprinted by subsequent stages of hydrothermal 

brecciation and chalcedonic silica veins and vug fillings (table 

2). The silica bodies define two large zones of intense alteration where alkalis and alumina have been leached leaving a 

residual rock with greater than 95 weight percent silica. One 

silica body trends east-west and extends for about 5.5 km and 

another trends northeast for about 7 km. Bordering the zones 

of silica are areas of low relief and limited outcrops of argillic 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

5

and advanced argillic alteration containing kaolinite, dickite, 

alunite, illite, and locally, pyrophyllite (fig. 8). The distribution 

and geochemistry of the silica bodies have been documented 

during exploration, development, and mining of the silica bodies. There is less information on the extent and geochemistry 

of the argillic and advanced argillic alteration that borders the 

silica bodies. The size, continuity, and intensity of silicification and advanced argillic alteration are comparable to other 

large acid-sulfate systems that are associated with high-sulfidation gold-silver deposits and with porphyry copper-gold 

mineralization. 

The acid-sulfate alteration formed in andesite flows and 

breccias assigned to the Oligocene to early Miocene Fifes 

Peak Formation, and in the Superior quarry, an intermediate 

composition (dacite?) flow or flow dome (fig. 7). The latter 

possibly is correlative with the rhyolite of Clear West Peak, 

and bedded tuffs and tuff breccias assigned as a rhyodacite 

tuff member of the Fifes Peak Formation by Tabor and others 

(2000) (figs. 4, 6, and 8). Because of the intensity of the acid 

leaching, the original composition and primary textures of 

many volcanic rocks are not discernable. In the Superior and 

Scatter Creek quarries, vuggy silica alteration locally contains 

numerous small vugs with morphology typical of plagioclase 

and pyroxene phenocrysts in the andesite flows in the Fifes 

Peak Formation (fig. 9). Other areas consist of massive, finegrained silica that may represent alteration of aphyric glassy 

volcanic rock. In the southwest part of the Superior quarry, a 

flow-banded volcanic rock of intermediate composition has 

relict devitrification layers and contains xenoliths of another 

intermediate composition volcanic rock. Sparse felsic dikes 

are present in both the Scatter Creek and Superior quarries and 

on Taugow. 

The advanced argillic alteration consists of massive 

zones of residual silica bordered by alteration assemblages 

composed of kaolinite, dickite, alunite, pyrophyllite, and 

pyrite (fig. 8, table 1). Illite-, montmorillonite-, and chloriterich argillic and propylitic alteration is present outside the 

zone of advanced argillic alteration, but is poorly documented 

because of poor exposure. Residual vuggy silica alteration 

commonly displays relict voids developed after phenocrysts 

and (or) pumice clasts. Enargite and pyrite are present within 

the vuggy silica rock and in hydrothermal breccias, but for 

the most part, the sulfide minerals are oxidized and leached 

at present levels of exposure in the mines. Casts of pyrite 

also contribute to the vuggy texture of the residual silica. In 

the Scatter Creek quarry, fine-grained hematite replaces the 

sulfide minerals and gives the rock a dark gray color. Locally 

in the silica deposits, voids are not present and the silica is 

massive with little remnant texture. The massive nature of the 

silica may in part reflect the massive nature of the original 

rock, as well as late-stage deposition of hydrothermal silica 

that filled voids and fractures. Late-stage deposition of hydrothermal silica and sulfide minerals locally shows sedimentary 

textures and horizontal banding (see section on the Superior 

quarry below). The silica ranges from white chalcedonic 

silica to black chalcedony with darker colors reflecting the 

presence of sulfide minerals and (or) hematite replacement of 

sulfide minerals.

Structural Control of Acid-Sulfate Alteration

Residual vuggy silica alteration typically is structurally 

controlled (for example, Ransome, 1909; Steven and Ratte, 

1960). Elongation of the silica bodies in the northern part 

of the White River altered area (fig. 8) suggests that major 

structural controls are east-northeast- and east-striking faults. 

In addition, some suggestion is present that silicification along 

the edges of the White River hydrothermal system may follow 

minor radial structures developed outward from hydrothermal 

and perhaps local volcanic vents. However, few structures 

controlling vuggy silica alteration are obvious in either the 

Superior or Scatter Creek quarries. On the north side of the 

Scatter Creek quarry, a prominent silicified ridge of vuggy 

silica alteration strikes N. 10° W. The ridge is comprised of 

vuggy silica alteration developed in pyroclastic rocks and 

porphyritic andesites of the Fifes Peak Formation, which 

are cut by numerous, irregular hydrothermal breccia bodies. 

Another narrow silicified rib of vuggy silica strikes N. 70° E. 

and dips 75° NW. The vuggy silica alteration here is bordered 

by narrow zones of alunitic and illitic alteration (fig. 10; also 

see section on the Scatter Creek quarry below). 

Age of Hydrothermal Alteration

Isotopic ages of alunite from the advanced argillic alteration range from 20.4 to 23.5 Ma (McCulla, 1986; Weyerhaeuser Co., 1996). The youngest age, 20.4±0.1 Ma, is from 

Cady Hill (fig. 8) and determined by Ar–Ar methods. Alunite 

from a drill hole near the Superior quarry has a K–Ar age of 

21.0±0.9 Ma, and alunite from Taugow has a K-Ar age of 

22.3±0.9 Ma. Alunite from south of the White River (Bridge 

Camp alunite, fig. 8) has a K–Ar age of 23.5±1.1 Ma. We are 

in the process of dating several additional alunite samples using 

Ar–Ar techniques. It is likely that the entire area of advanced 

argillic alteration formed from the same hydrothermal system.

Inferred Environment of Hydrothermal Alteration

The advanced argillic alteration at White River formed 

from disproportionation of magmatic SO2

 to H2S and H2SO4

during condensation of a magmatic vapor plume (Rye and 

others, 1992; Stoffregen, 1987; Arribas, 1995), as indicated by 

mineral assemblages (table 1), types of silicic alteration (table 

2), and reconnaissance stable isotope data in McCulla (1986). 

The acid condensate leaches most major and minor elements 

from the host rock leaving residual silica and forming zones of 

alunite and kaolinite (or pyrophyllite at higher temperatures), 

illite, montmorillonite, and propylitic alteration progressively 

outward from the residual silica core. This alteration zoning 

results from progressive neutralization and increasing pH of 

acidic magmatic-hydrothermal fluids due to rock buffering 

outward from fluid conduits (figs. 10 to 12; also see description 

of the Scatter Creek quarry). In this magmatic-hydrothermal 

environment, transport of rare earth and other elements, such as 

F, Cl, Ti, and P, leads to formation of minerals, such as zunyite, 

woodhouseite, svanbergite, crandellite, and rutile-anatase, that 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

6

may occur in the zone of alunite-kaolinite alteration. Elevated 

concentrations of F, as much as 0.75 weight percent, and TiO2, 

as much as 3.8 weight percent, are present in the advanced 

argillic alteration at the Superior quarry (fine-grained rutile 

crystals have been observed in the Superior quarry and on Cady 

Hill). Zunyite (Al13Si 5O20 (OH)16 F2Cl) has been identified 

by PIMA in one sample collected about 500 m northwest of 

the Scatter Creek quarry (fig. 8). Gallium concentrations are 

elevated in alunite-kaolinite alteration peripheral to the zone 

of vuggy silica alteration in the Superior quarry, as much as 

101 ppm, and depleted in vuggy silica alteration, less than 0.5 

ppm. The Ga enrichment is typical of that present in zones of 

alunitic alteration formed in the magmatic-hydrothermal environment in other high sulfidation gold-silver deposits (Rytuba 

and others, in press). High Au concentrations, as much as 1.7 

ppm, are present in fault and fracture zones that formed late in 

the hydrothermal system. The Au–enriched fault breccias and 

fractures are filled with red clay consisting of montmorillonite 

± dickite and earthy hematite. 

The acid-sulfate alteration in the White River area is 

inferred to have formed at shallow depths beneath the paleosurface on the basis of sedimentary textures formed during 

late-stage hydrothermal alteration and types of silicic alteration (fig. 11, table 2). Hydrothermal depositional textures and 

the presence of steam-heated acid-leached rocks in the Scatter 

Creek quarry (see section on the Scatter Creek quarry below) 

indicate that the present exposures reflect the upper part of the 

hydrothermal system. Similarly, bedded hydrothermal sediments in the Superior quarry also indicate very shallow levels 

of the exposure of the hydrothermal system (see section on 

the Superior quarry below). Alteration features and possible 

base- or precious-metal mineralization at greater depths are 

unknown, because exploration drilling has been limited to 

shallow (average 125-m-deep), vertical drill holes, mostly 

within the silica quarries.

Geophysical Framework of the White River 

Altered Area

Regional Magnetic Anomalies

Volcanic rocks are typically magnetic and produce distinctive magnetic anomalies. Therefore, intense and pervasive 

hydrothermal alteration of volcanic rocks and the concomitant 

destruction of magnetic minerals sometimes produce negative 

anomalies in low-altitude magnetic measurements. Thus, an 

investigation was initiated to examine existing aeromagnetic 

data from, and conduct ground-magnetic measurements in, the 

White River altered area. 

Figure 13 shows aeromagnetic anomalies surrounding 

the White River altered area. These data were acquired by the 

USGS in 1997 as part of ongoing earthquake hazard investigations of the Puget Lowland (Blakely and others, 1999). Flight 

lines were flown north-south at a nominal altitude of 250 m 

above terrain, or as low as safely possible. Lines were spaced 

400 m apart over the Puget Lowland, but were spaced 800 m 

over outlying regions, including the White River altered area. 

Widely spaced tie lines were flown in the east-west direction 

to facilitate data processing.

Magnetic anomalies (fig. 13A) surrounding the White 

River altered area display short-wavelength, high-amplitude 

patterns characteristic of unmetamorphosed volcanic terrane (fig. 13B). The most pronounced magnetic anomalies 

are associated with volcanic rocks of the Miocene Fifes Peak 

Formation and the Oligocene Ohanapecosh Formation in the 

northeastern and south-central parts of the study area. The 

west-northwest-striking White River Fault Zone, which brings 

these two formations into contact, is evident in the aeromagnetic anomalies, and other anomalies with similar WNW trend 

are related to mapped structures. Aeromagnetic anomalies (fig. 

13A) also display north-northeast trends, possibly indicating faults antithetic to the White River Fault Zone, although 

no ENE–striking faults are mapped in the region (fig. 13B)). 

The White River altered area is located near the intersection 

of WNW– and ENE–trending anomalies, perhaps reflecting 

structural control on the evolution of the hydrothermal system. 

Magnetic anomalies in the immediate vicinity of the 

White River altered area may have implications for mineral 

resource evaluations. A small magnetic high (label A, fig. 

13A) corresponds closely with intense acid-sulfate alteration, exposed silica bodies, and a large shallow zone of very 

high resistivity and high chargeability zone at depth (fig. 14; 

Weyerhaeuser Co., 2003). It seems unlikely that altered rocks 

exposed at the surface contribute significantly to the positive 

magnetic anomaly. The anomaly may reflect an underlying 

intrusive body possibly related to the hydrothermal evolution 

of the White River altered area. 

A broad, polygonal-shaped magnetic low (label B, 

fig. 13A) is also difficult to explain on the basis of regional 

geologic mapping. Sharp gradients around the margins of the 

magnetic low suggest that its source lies near the topographic 

surface. The anomaly is underlain by Fifes Peak Formation, 

which includes rhyolite and rhyodacite tuff. Such rocks commonly have low magnetizations, but exposures of these rocks 

elsewhere in the study area do not show pronounced aeromagnetic lows. The zone of intense acid sulfate alteration overlaps 

the magnetic low on its southeastern margin (fig. 13), suggesting that the anomaly may be caused by the destruction of 

magnetite during alteration of volcanic rocks. If so, the lateral 

extent of the magnetic low would permit mapping the lateral 

extent of intense alteration. Both anomalies A and B were 

investigated in the field during the summer of 2003, and those 

preliminary results are discussed below.

Regional Gravity Anomalies

Figure 15 shows a comparison of aeromagnetic and 

gravity anomalies over the White River altered area. Such 

comparisons are facilitated by first converting aeromagnetic 

anomalies to pseudogravity anomalies (fig. 15A), a linear 

filtering operation that in effect replaces magnetization with 

density in one-to-one proportions (Blakely, 1995). The lack 

of any obvious correlation between pseudogravity (fig. 15A) 

and observed gravity (fig. 15B) throughout the White River 

study area demonstrates that variations in magnetization are 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

7

not obviously linked with variations in density, a common 

observation in volcanic terrane. 

A notable exception is present directly over the altered 

area. Gravity stations are rather sparse in this region, however, 

precluding detailed comparisons of gravity anomalies with 

geology and aeromagnetic anomalies. Nonetheless, a small 

positive gravity anomaly does lie partially within the altered 

zone, approximately corresponding with the positive aeromagnetic anomaly (label A, fig. 13A and 15A), thus adding support 

to the existence of a relatively shallow intrusion possibly 

associated with the White River hydrothermal system.

Field Investigations

Detailed field studies were conducted during the summer 

of 2003 to investigate the near-surface expression of aeromagnetic anomalies in the White River altered area. Studies included three ground-magnetic transects walked along 

logging roads using a portable cesium-vapor magnetometer. 

A base station was established on Taugow to simultaneously 

measure diurnal and transient fields, which were subsequently 

subtracted from the ground-magnetic profiles. In addition, the 

ground-magnetic measurements were judiciously edited to 

remove cultural artifacts and magnetometer dropouts. Magnetic susceptibility measurements also were made at 27 sites 

inside and outside the altered zone using a hand-held susceptibility meter. 

As expected, susceptibility measurements (fig. 16A) show 

a clear correlation between extraordinarily weak magnetization and the exposed zone of intense silicification. This correlation transcends the original rock type, as altered andesite 

flows are just as low in susceptibility as altered pyroclastic 

rocks. The only exception to the correlation is a single site 

(label X, fig. 16A), where high susceptibility was found inside 

the altered zone. This site is located within a quarry excavated 

into a laterally restricted fresh basalt or andesite of apparent 

Fifes Peak age. 

Figure 16B shows magnetic intensity measured along one 

of the ground-magnetic transects. As expected, the general 

aspects of the ground-magnetic profile agree with the aeromagnetic data. Most notable, the western edge of the aeromagnetic high agrees closely with a sharp gradient in the groundmagnetic profile. Surprisingly, the dramatic destruction of 

magnetic minerals, evident in susceptibility measurements 

(fig. 16A), is not obviously reflected in either the aeromagnetic 

or ground-magnetic data. This suggests that the aeromagnetic 

and ground-magnetic anomalies originate from sources below 

the zone of alteration. 

Although the source of the magnetic high is clearly not 

the altered volcanic rocks exposed at the surface, the source 

probably lies at relatively shallow depth. This is evident from 

the sharp magnetic gradient on the ground-magnetic profile 

(arrow, fig. 17). Using a simple graphical technique (Blakely, 

1995, p. 238–239), it is estimated that the source of this gradient lies between 230 and 390 m depth. IP surveys conducted 

independently in the area show high resistivity diminishing 

and high chargeability increasing at depths consistent with an 

inferred magmatic source (fig. 14). It is predicted, therefore, 

that magnetite-destructive alteration lies entirely above these 

depths. Drill holes did not extend to these depths, however.

The pronounced aeromagnetic low to the west of the 

silicified zone (label B, fig. 13A) remains problematic. Several 

explanations are possible. (1) The anomaly is located over a 

region of relatively flat and subdued topography bounded on 

the north, south, and east by higher terrain. The possibility that 

the negative anomaly is caused by variations in aircraft altitude 

and terrain effects was considered, but modeling experiments 

using digital elevation models indicate that this is not the 

case. (2) The anomaly may reflect a subsurface extension of 

hydrothermally altered volcanic rocks, but the lack of correlation between ground-magnetic and aeromagnetic anomalies 

on the one hand and susceptibility measurements and silicified 

rock on the other makes that conclusion difficult to defend. (3) 

The magnetic low may be caused by a thick basin filled with 

relatively nonmagnetic glacial deposits. Such a basin should 

produce a negative gravity anomaly as well, but gravity measurements, although sparse, show a slight positive anomaly. 

(4) The magnetic low may be caused by reversely magnetized 

volcanic rocks that erupted during a time of reversed magnetic 

polarity. Future field studies and magnetic modeling experiments are planned to evaluate these alternative explanations.

Geochemical Exploration Studies of the White 

River Altered Area

Weyerhaeuser Company work has focused on geologic 

mapping and surface exploration sampling programs in 

specific areas, including working mine faces, and on detailed 

geochemical analysis of drill holes. Geochemical sampling has 

targeted zones of intense silicification, hydrothermal breccias, 

areas of outcrop, and locations with soil sample anomalies. 

Additionally, several, large reconnaissance-scale soil sample 

surveys have been completed. Areas with the highest sample 

density and most geochemical data include the Superior quarry 

area, the Scatter Creek quarry area, the Taugow area, the 

Quarry Hill area, and altered areas south of the White River 

(fig. 8).

Many trace elements in the White River altered area 

are elevated to varying degrees in the most siliceous areas. 

Anomalous elements include Au, As, Cu, Sb, Bi, Te, Pb, Zn, 

Mo, Hg and Se. Statistical analysis of geochemical data and 

field observations suggest that in the Superior quarry hill area 

there may be two primary geochemical associations—CuAs±Te, probably related to enargite deposition in vuggy silica, 

and Bi-Sb-Te-Au-Mo-As related to hydrothermal veins and 

breccias.

Experience has shown that sampling of the highly 

leached surface exposures rarely produces geochemical results 

representative of the original trace element composition. In 

fact, samples from surface outcrops commonly are devoid of 

anomalous concentrations. Sampling of subsurface zones with 

abundant limonite or sulfide minerals commonly yields trace 

element contents several orders of magnitude greater than 

leached surface samples. Zones with elevated trace element 

contents commonly are present within 10 meters of the exist-
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

8

ing erosion surface. Although tentative, certain geochemical 

patterns have been recognized along with a distinct elemental 

suite. Anomalous trace elements present at the White River 

prospects and the patterns in which they are present are as 

follows:

Gold

Anomalous gold content, in excess of 100 ppb, was found 

in outcrop by numerous samplers in the 1970s and 1980s. 

Most of these samples were in the Superior quarry and Quarry 

Hill areas. High Au contents (500 to 1,800 ppb) do not tend to 

be present within silicified promontories. Rather, the highest 

concentrations have been found in the following settings:

1. Soil samples from depressions surrounded by silicification. 

The best example is on the south face of Superior quarry 

hill area where a depression surrounded by vertical cliffs 

yielded soil samples with 1,600 ppb Au. Fill-in soil sampling defined the area and later rock chip sampling and 

shallow air-track drilling produced similar values.

2. Advancement of the Superior quarry allowed sampling 

along a strike length of 200 meters in a highly fractured 

zone trending N. 70° W. The fracture zone crosscuts 

silicification and did not crop out prior to mining. At 

each stage of mine advance, the gold contents increased, 

and Au contents in this structural zone are as much as 

1,800 ppb. Associated with this zone are large pockets 

of white hydrothermal kaolinite and small amounts of 

manganese oxide.

3. During excavation of overburden prior to mining near the 

west end of the Superior quarry, Ash Grove uncovered a 

circular depression about 30 m in diameter. The depression had steep sides and a fracture pattern parallel to the 

steep faces, which dipped away in all directions. Excavation, which went to the current pit floor elevation, never 

intersected bedrock in the depression; however, abundant 

highly limonitic material was present. Two samples 

containing 500 and 900 ppb Au were collected along 

lower exposures within the depression. The depression 

also had highly anomalous concentrations of Te, Ba, Sb, 

Bi, Mo, As, Cu, Zn, and Ag. This depression may mark a 

hydrothermal eruption crater.

4. Gold anomalies in soil samples suggest several linear 

trends as much as 400 m long and 15 m wide. Although 

Au anomalies are sometimes spatially associated with 

massive silicification, they are commonly adjacent to or 

cross in and out of silicified rocks in softer zones with 

abundant clay alteration that did not crop out prior to 

mining.

Observations in the Superior quarry hill area suggest that 

the gold anomalies are in softer fracture zones or in pipe-like 

structures cutting silicified rocks. These less resistant rocks 

typically were scoured out by glaciation and filled with glacial 

debris, which may make recognition by soil sampling difficult. 

Anomalous Au contents are present in both sulfide mineralbearing and oxidized, altered rocks.

Silver

Silver is uniformly low in the White River area. The 

highest Ag content in the Superior quarry hill area is 1.55 ppm 

from a sample on the southwest flank of the hill near Washington Highway 410. Here, elevated Ag is associated with high Bi 

and Sb contents.

Arsenic

Elevated arsenic contents in excess of 300 ppm have 

been found in samples collected from numerous locations in 

the White River altered area. Enargite-bearing samples, areas 

with high limonite content, and sulfide zones beneath the most 

intensely leached capping tend to have the highest As contents. 

Maximum values commonly exceed 1,000 ppm. Anomalous As 

is commonly associated with anomalous amounts of Cu, where 

enargite is likely the source mineral. However, some samples 

also contain low Cu contents and high As contents. Samples 

with low Cu contents generally are present in oxidized rocks.

Copper

Elevated copper contents are associated with the abundant limonite and sulfide mineral-rich zones within the 

strongly silicified areas. Concentrations in excess of 100 ppm 

are common with maximum values greater than 12,000 ppm 

(1.2 weight percent Cu) in an enargite-bearing sample from 

the Superior quarry. The most anomalous Cu is in the Superior 

quarry hill area.

Antimony

Antimony contents beneath leached capping in the most 

siliceous core zones average about 25 ppm. Widespread 

values greater than 50 ppm are common and maximum values 

are about 500 ppm. Most anomalous Sb is near the Superior 

quarry hill area, although areas of anomalous Sb also are present south of White River (Sec. 10, T. 19 N., R. 8 E.), where 

several gossan samples have yielded high Sb contents. No 

drilling has been conducted in these areas.

Mercury

High mercury contents are present locally in silicified 

rocks. Samples with greater than 500 ppb Hg are common and 

anomalies from 1,000 ppb to greater than 5,000 ppb are present in the more intensely silicified and pyritized areas.

Bismuth, Tellurium and Selenium

Highly anomalous bismuth, tellurium and selenium 

contents have been found in the Superior quarry hill area. The 

most anomalous values for each element are about 200 ppm 

Se, 200 ppm Te, and 900 ppm Bi. Higher Bi and Te contents 

commonly are associated with high Sb contents.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

9

Molybdenum

A strong molybdenum anomaly in drill holes and surface 

samples is present south of the Scatter Creek quarry. The area, 

bounded by Cady Hill, the east flank of Quarry Hill, and the 

Scatter Creek quarry has yielded anomalous Mo contents in 

surface samples and in two drill holes. Molybdenum contents 

in the drill holes commonly exceeded 100 ppm, and the highest Mo content was 750 ppm. These anomalies are present 

close to anomalous Pb and W (30–40 ppm) contents, but no 

other strong elemental associations were noted. 

The Mo anomalies may reflect a deep source for the 

hydrothermal alteration and mineralization exposed on the 

surface. The near-surface Mo anomaly is coincident with an IP 

chargeability anomaly (fig. 14) and may be located over deep, 

porphyry style copper-gold-molybdenum mineralized rock 

(fig. 11). More work is needed to determine the significance of 

the anomalous molybdenum zone in this area.

Stop 1: Superior (Ash Grove) Quarry

The Superior (Ash Grove) silica quarry is located in 

the southwest part of the White River acid-sulfate alteration 

system (figs. 8 and 18). The massive silica bodies consist 

of vuggy silica that has been crosscut by several stages of 

hydrothermal breccias and overprinted by chalcedonic veining 

and quartz veining and vug filling. The hydrothermal breccias have been rebrecciated and subjected to continued acid 

leaching and vuggy silica development. Intense acid leaching 

of host andesite and dacite flows and tuffs of the Fifes Peak 

Formation by magmatic-hydrothermal fluids has resulted in 

the formation of vuggy silica rock with greater than 95 weight 

percent SiO2

. Aluminum content is generally less than 0.5 

weight percent (Al2O3), and Na, K, Mg and Ca oxides are all 

less than 0.15 weight percent. Iron content as hematite and 

more rarely as pyrite in the silica bodies is variable ranging 

as high as 12 weight percent but more typically is less than 5 

weight percent. Ti oxide content ranges from 0.6 to 1.6 weight 

percent. Mining for silica by the Ash Grove Cement Company 

is by open pit methods, and the silica is crushed and sized on 

site. The silica is used in the production of Portland cement. 

Bordering the silica body exposed in the quarry are areas of 

low relief and limited outcrops of advanced argillic alteration 

consisting of kaolinite and alunite and locally pyrophyllite 

(fig. 18). 

The rocks in the Superior quarry are highly altered and 

it is commonly difficult to discern the original rock type (fig. 

19). Massive and homogenous gray vuggy silica in the central 

and west part of the quarry contains voids where plagioclase 

and pyroxene phenocrysts have been leached from andesite 

flow rock (fig. 20). Pyrite and enargite (figs. 21 and 22) are 

present most commonly in the hydrothermal breccias, and 

also are present locally in the vuggy silica; however, at the 

present mine level, the sulfide minerals are mostly oxidized 

and leached leaving numerous voids. Hematite is the primary 

oxidation product of the sulfides and gives the vuggy silica its 

dark gray color. 

In the southeast part of the quarry, bedded welded tuffs 

have been leached and altered to vuggy silica rock. The voids 

in the vuggy silica were developed from leaching of pumice 

and phenocrysts and are larger than those developed in the 

altered andesite flow rock. Layering within the tuff indicates 

that bedding is subhorizontal.

In the southwest part of the quarry, vuggy silica alteration 

is developed in a porphyritic intermediate composition rock 

(possibly dacite) and associated fragmental volcanic rocks. 

Exposures of altered flow-folded dacite are present on the 

steep scarp just south of the quarry (fig. 7). The dacite shows 

relict flow banding and has textural layers that are interpreted 

to be devitrification textures developed in glassy zones in the 

dacite (fig. 23). Xenoliths as much as several cm in length are 

present in the dacite. Vuggy silica alteration developed in the 

dacite and associated fragmental rocks contains larger voids 

and is less massive and homogenous as compared to vuggy 

silica alteration developed in andesite flow rock. Other areas in 

the pit consist of massive, fine-grained silica that may represent alteration of an aphyric glassy flow rock (fig. 24). Finegrained layering is commonly visible in rocks that have been 

silicified, and these rocks likely were bedded fine-grained tuffs 

and sedimentary rocks that are exposed in outcrops about 0.5 

km north of the quarry (fig. 6).

Also in the steep face on the upper bench along the southwest side of the pit, a narrow, north-northeast striking, felsite 

porphyry dike cuts near horizontal flow foliated dacite. The 

dike cuts the center of the prominent hill and forms the point 

of highest elevation (fig. 25). This dike extends across the pit 

to the northeast. The fine-grained dike rocks are buff-white to 

tan in color and contain sparse 1-2 mm quartz phenocrysts. 

Dike margins commonly exhibit faint flow banding accentuated by weak limonite staining. The dike occasionally is cut by 

irregular, hairline quartz veins. Near its margins, it contained 

appreciable pyrite that is now oxidized. The dike, although 

completely silicified, appears to postdate most massive hydrothermal breccias in the Superior quarry; however, in the northern part of the pit, narrow hydrothermal breccia dikes cut and 

contain fragments of the dike. This indicates the complex and 

multiphase nature of the breccias and associated hydrothermal 

activity. The presence of the felsite porphyry dike is significant 

from several perspectives: 

• It is situated in the center of some of the most massive 

and well-developed hydrothermal breccias; 

• The dike is proximal to zones of abundant limonite and 

gossan that correspond to areas of pyritic hydrothermal 

sediments and associated hydrothermal vents; 

• The dike forms the core of a north-northeast-trending 

zone that contains some of the highest Au, As, Cu, and 

Bi contents; 

• The dike may be a late magmatic feature related to a 

dacite dome in the Superior quarry area (figs. 7 and 23).

Multiple stages of veining and hydrothermal brecciation 

core the vuggy silica zones and silicified rocks in the quarry. 

The earliest stage consists of hydrothermal breccia and veins 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

10

containing white chalcedonic silica (fig. 26). Locally large 

voids created during brecciation of the vuggy silica are filled 

with white chalcedony that forms a massive white rock with 

little or no texture. Later stages of veining and hydrothermal 

brecciation contain various colors of chalcedony ranging 

from tan (fig. 27) to black depending on the amount of sulfide 

minerals present and extent of oxidation of the sulfide minerals. Veins of gray chalcedony cut vuggy silica rock and locally 

develop a stockwork texture (fig. 28). Late stage hydrothermal 

deposition of silica and sulfide minerals commonly show sedimentary textures and horizontal banding indicating near-surface deposition of silica and sulfide minerals in hydrothermal 

vents (figs. 22 and 29). 

In the southwest part of the quarry, a series of north-striking 

high-angle normal faults contain hematite-rich, clay-supported 

breccias and clay-filled fractures are present (figs. 30 and 31). 

Some clay zones are subhorizontal and likely reflect alteration 

of tuffs interbedded with the dacite flow (fig. 32). Gold contents 

as much as 1.7 ppm are present in these fault and fracture zones. 

The clay minerals are montmorillonite ± dickite. Sedimentary 

structures, such as graded and cross bedding, in these open 

fractures indicate near-surface deposition and that the level of 

exposure of the hydrothermal system is relatively shallow.

Detailed geochemical surveys of the silica bodies show 

that anomalous concentrations of As, Au, Bi, Cu, Ga, Hg, Mo, 

Sb, Se, Te, and F are present locally. Elevated concentrations 

of F, as much as 0.75 weight percent, and TiO2

, as much as 

3.8 weight percent are present in the advanced argillic alteration. Fine-grained rutile is present locally. In areas where Au 

is anomalous, higher concentrations of Sn and W also are 

present. This geochemical suite is typical of that associated 

with high-sulfidation gold deposits that are associated with 

porphyry Cu-Au systems (for example, Sillitoe, 2000).

Stop 2: Taugow

Taugow, a hill midway between the Superior and Scatter 

Creek quarries, is named for the Taugow VABM marker near 

the top of the hill (figs. 8 and 33). Rocks exposed on Taugow 

include strongly altered tuff and tuff breccia cut by a narrow 

felsic dike and by hydrothermal breccias. Most pyroclastic rocks 

exposed are silicified or strongly altered alunitically. This brief 

stop will examine these hydrothermal features. In addition, if 

the weather is clear, this stop affords a 360° panorama of the 

White River altered area and Mount Rainier (see road log).

From the parking area (landing at end of road), the small 

knob to the west consists of alunitically-altered tuff and tuff 

breccia containing relatively coarse-grained, pink-colored alunite (fig. 34). Alunite from here has been dated at 22.3±0.9 Ma 

by K–Ar methods (Weyerhaeuser Co., 1996), and a 40Ar/39Ar 

date is in progress. 

The north side of the road cut just before the end of the 

road exposes silicified, well-bedded tuff breccia (fig. 35) 

intruded by a narrow (2 to 3-cm-wide) fine-grained, quartzphyric felsic dike (fig. 36) and cut by hydrothermal breccias. 

This dike and a similar dike mapped in outcrops on the lower 

southwest flank of Taugow are examples of only a few dikes 

that have been recognized in the White River altered area. 

Bedding in the tuff is about N. 10° E. 20° SE. To the south 

across the road from the tuff breccia, hydrothermal breccia is 

well exposed (fig. 37). The matrix-supported breccia contains 

a heterogeneous mixture of subangular blocks as much as 50 

cm wide, including flow-banded lavas and (or) well bedded 

tuffs, felsite, and porphyritic andesite. The blocks are silicified 

and include vuggy silica alteration. The breccia matrix consists of fine-grained silica and hematite. The hematite probably 

replaces sulfide minerals.

Stop 3: Scatter Creek (James Hardie) Silica Quarry

The Scatter Creek (James Hardie) silica quarry produces 

high purity silica, greater than 97 weight percent SiO2, from 

leached and silicified volcanic rocks of the Fifes Peak Formation and cross-cutting hydrothermal breccias (fig. 38). Aluminum content of the silicified rock is generally less than 0.5 

weight percent (Al2

O3), and Mg, Ca, Na, and K oxides are less 

than 0.02 weight percent. Residual Ti oxide is present at as 

much as 0.8 weight percent and Fe oxide as hematite is variable but generally less than 0.5 weight percent. Silica is mined 

by open pit methods and crushed and sized on site (fig. 39) for 

shipment to James Hardie Building Products, Inc., for production into fiber cement-based external siding and backer board 

known as Hardibacker. Silica is stockpiled on site and mining 

is episodic, occurring when stockpiles are depleted. 

Alteration in the Scatter Creek quarry consists of pervasive 

leaching of porphyritic andesite flows and pyroclastic rocks 

to form vuggy silica alteration (fig. 40). In the central part of 

the quarry, vuggy silica alteration is well developed in massive andesite flows and is characterized by voids from 2 to 4 

mm in length formed from the leaching of plagioclase feldspar 

and pyroxene phenocrysts. The morphology of the leached 

phenocrysts is well preserved throughout most of the dark gray 

to black vuggy silica rock (fig. 41). Locally larger voids are 

present where leaching of clots of phenocrysts (glomeroporphyroclasts) has occurred. The large body of vuggy silica alteration 

in the central part of the quarry trends E-W and has elevated 

concentrations of Ag, As, Au, Cu, Hg, F, Mo, Se, Sb and Te. 

The highest concentration of Mo, as much as several hundred 

ppm, is present in vuggy silica in the SE part of the quarry. 

Molybdenum contents in excess of 700 ppm were encountered 

in drill holes just south of the Scatter Creek quarry. In the 

north-central part of the quarry, a rib of vuggy silica alteration 

about 1 meter wide was developed along a N.60–70°E. striking 

fault that localized the upward flow of acid magmatic-hydrothermal fluids (figs. 10 and 42). Bordering this vuggy silica 

is a zoned assemblage of advanced argillic alteration where 

plagioclase and pyroxene phenocrysts have been replaced by 

alunite and kaolinite, grading outward into zones of illite and 

montmorillonite/chlorite (fig. 43). This zoning was developed as 

a result of buffering of the acid fluids by the country rock as it 

moved outward from the fault (figs. 11 and 12).

Most pyrite and other sulfide minerals in the vuggy silica 

alteration have been oxidized to a depth of greater than 125 

m, and relict pods of sulfide minerals are only rarely present. 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

11

Casts after pyrite are common, however, and indicate that as 

much as several weight percent pyrite was originally present. Fine-grained specular hematite is the primary oxidation 

product of pyrite and gives the vuggy silica its dark gray color. 

Within the upper few meters of the surface, hematite has been 

leached from the rock by surface weathering, and the resulting 

vuggy silica is white and distinctive from its generally black to 

gray color (fig. 44).

Multiple stages of hydrothermal breccias and quartz and 

chalcedonic veins cut the vuggy silica rock in and outside the 

quarry. An early stage of hydrothermal breccias cemented by 

white chalcedony and cut by white chalcedony silica veins is 

well developed in vuggy silica present in and outside the quarry 

(fig. 45). On the periphery of the quarry, vuggy silica alteration 

has been hydrothermally fractured and locally more strongly 

brecciated and the resulting fractures and open spaces have been 

filled by white chalcedony. Hydrothermal fracturing and rotation of blocks of vuggy silica during hydrothermal brecciation 

locally developed large voids, as much as 0.5 m, that were filled 

with dense white chalcedony that now form massive bodies of 

white silica. A subsequent stage of hydrothermal breccias and 

veins containing tan (fig. 40) to dark gray chalcedony cut the 

early stage of white chalcedony veins. The later chalcedony 

veins and breccia contained fine-grained sulfides that have been 

oxidized to hematite (fig. 46), and the veins have elevated concentrations of As, Au, Cu, Hg, F, Mo, Sb, Se, and Te. 

High-angle normal faults and fractures cut the vuggy 

silica alteration and are well exposed in the quarry. The most 

prominent fault zone is 3 m wide, strikes N. 10-45° W. and 

dips 80° SW. It is filled with clay-supported fault breccia. 

Red clay-filled fractures, similar to Au–bearing fractures in 

the Superior quarry, are present throughout the Scatter Creek 

quarry. They consist of montmorillonite ± dickite and abundant hematite and are 1 to 12 cm wide (fig. 47). 

An alteration zone of highly leached white rock consisting of cristobalite, opal, and kaolinite is present within a fault 

block in the central part of the quarry (fig. 48). This type of 

hydrothermal alteration is typical of alteration that forms in 

the steam-heated environment above the paleo-ground water 

table. In this environment, H2

S is oxidized by atmospheric 

oxygen to form sulfuric acid that leaches alkalis and aluminum 

from the rock leaving residual silica (for example, Schoen and 

others, 1974; Hedenquist, 1990). Because the alteration forms 

in a near-surface, low temperature environment, the residual 

silica is typically opal and cristobalite. The presence of steamheated acid-leach alteration indicates that the level of exposure 

of the hydrothermal system in the Scatter Creek quarry is 

relatively shallow (fig. 11 and table 2).

Part 2: The Osceola Mudflow in the 

Lower White River

General Features of the Osceola Mudflow 

About 5,600 years ago, an eruption of Mount Rainier 

triggered an edifice (sector) collapse that caused the 3.8–km3

Osceola Mudflow and coeval phreatic and pumiceous magmatic tephras. The phreatic tephras, like the Osceola Mudflow, 

are clay-rich and contain hydrothermal minerals typical of 

acid-sulfate systems. Mineralogy and stratigraphy demonstrate the genetic link between the Osceola Mudflow and its 

tephra and suggests how the hydrothermal system might have 

influenced the eruption (Vallance and Scott, 1997; Vallance 

and others, 2003).

The Osceola Mudflow began as a water-saturated avalanche 

or a series of avalanches during phreatomagmatic eruptions at 

the summit of Mount Rainier. It filled valleys of the White River 

system north and northeast of Mount Rainier to depths of 80 

to 150 m, flowed northward and westward more than 120 km, 

covered more than 240 km2

 of the Puget Sound lowland, covered 

another 160 km2 under the water of Puget Sound and extended 

as much as 20 km under water (figs. 2 and 49). 

Near Mount Rainier, deposits of the Osceola Mudflow 

cap ridges high above the Winthrop and Emmons Glaciers. 

Remnants also are present on top of Steamboat Prow and 

throughout the Inter Fork drainage basin. The homogeneity of these deposits, the lack of hummocky terrain within 

10 km of the summit, and the apparent fluidity suggest that 

the avalanches which initiated the Osceola Mudflow mixed 

thoroughly within 2 km of their source and abruptly began to 

behave like an enormous water-saturated debris flow.

Mapping the upper limits (inundation limit) of the 

Osceola Mudflow along the steep-sided White River Valley 

between Mount Rainier and Mud Mountain, 75 km downstream, reveals that the peak-stage height of the mudflow 

attenuated sharply near the volcano then reached an equilibrium height downstream. In the Inter Fork Valley, deposits of 

the mudflow are present 400 m above the valley bottom. Five 

kilometers downstream, the inundation limit is 200 m; farther 

downstream, it stabilizes, varies between 85 m and 140 m, and 

averages about 100 m. The decrease of the maximum inundation depth downstream by longitudinal spreading and by 

deposition was counteracted by the additional discharge from 

the West Fork 45 km downstream and by bulking of the flow 

through the incorporation of eroded sediment. 

Mud and debris of the Osceola Mudflow that ran up onto 

Goat Island Mountain, about 10 km from Mount Rainier, and 

onto a ridge dividing the White and Greenwater Rivers, about 

45 km downstream of Mount Rainier, allow the maximum 

velocity and peak discharge of the flow to be estimated at 

these two places (fig. 49). Clay-rich Osceola debris is present 

to an altitude of 2,054 m on Goat Island Mountain but not 

just up valley at an altitude of 1,944 m at the top of a low 

divide between Emmons Glacier and Fryingpan Creek. The 

debris on Goat Island Mountain suggests that the Osceola 

Mudflow ran up 110 m. Using v = (2gh)1/2, the velocity of the 

flow must have been at least 46 m/s. Taking a typical nearby 

cross-sectional area in the Main Fork valley of about 190,000 

m2 suggests a discharge of approximately 8,000,000 m3/s. 

If the velocity was the same about 10 km downstream in 

the West Fork valley, a typical cross-sectional area of about 

80,000 m2 suggests a discharge of approximately 4,000,000 

m3/s there and a simultaneous discharge of about 12,000,000 

m3

. Similarly, at the confluence of the West and Main Forks 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

12

of the White River, mud and debris of the West Fork flow 

that ran up about 18 m onto a ridge dividing the White and 

Greenwater Rivers (fig. 49) allow a maximum velocity of 19 

m/s to be estimated. Taking a typical nearby cross-sectional 

area in the West Fork valley of at least 70,000 m2 suggests a 

discharge of approximately 1,300,000 m3/s. If the simultaneous discharge along the Main Fork was as large, then the 

total discharge of the Osceola Mudflow near the confluence 

of the two forks of the White River would have been about 

2,600,000 m3/s.

When it encountered a narrow gorge of the White River 

at Mud Mountain that is only 300 m wide, the Osceola Mudflow spread out over glaciofluvial terraces of Vashon age that 

are as much as 110 m above the White River. As it continued 

westward, the mudflow poured over terrace scarps to form a 

spectacular pair of falls. The upper fall would have formed an 

arc more than 6 km wide and over 80 m high, and the second 

would have been more than 3 km wide and over 110 m high.

In the lowland, the Osceola Mudflow completely choked 

the channel of the White River, which in pre-Osceola time 

followed the relatively confined valley of South Prairie Creek 

southwestward to join the Puyallup River at Orting, then 

flowed northwestward across the drift plain into the Green 

River drainage (Crandell, 1963). When the White River 

reestablished normal flow, it flowed northwestward toward 

Auburn along the radically different course near the axis of 

the lahar lobe.

The Osceola entered the Duwamish and Puyallup 

embayments of Puget Sound via deltas at the mouths of the 

Green and Puyallup Rivers (fig. 49). Low gradients on the 

deltas caused the debris flow to pile as much as thicknesses of 

more than 20 m near Auburn and Sumner (Dragovich and others, 1994). Deposits are generally present only in the subsurface in the Duwamish and Puyallup Valleys. Wood-bearing, 

clayey, gravel-rich deposits at depths of 20 to 100 m northwest of Puyallup and north of Auburn show that the Osceola 

Mudflow retained its coherence and flowed more than 20 km 

under water.

Osceola Mudflow deposits comprise three facies. The 

axial facies forms normally graded deposits 1.5 to 25 m thick 

in lowlands and valley bottoms and thinner ungraded deposits 

in lowlands; the valley-side facies forms ungraded deposits 

0.3 to 2 m thick that drape valley slopes; and the hummocky 

facies, interpreted before as a separate (Greenwater) lahar, 

forms 2-to-10-m-thick deposits dotted with numerous hummocks as much as 20 m high and 60 m in plan.

The Osceola Mudflow transformed completely from 

debris avalanche to clay-rich lahar within 2 km of its source 

because of the presence of large volumes of pore water and 

abundant weak hydrothermally altered rock within the preavalanche mass. A survey of clay-rich lahars suggests that the 

amount of hydrothermally altered rock in the pre-avalanche 

mass determines whether a debris avalanche will transform 

into a lahar or remain a largely unsaturated debris avalanche. 

The potential for transformation has important implications 

for hazard assessments because lahars are more mobile than 

debris avalanches, and therefore spread more widely and travel 

much greater distances down valley.

Hydrothermal Alteration in the Osceola Mudflow

Preliminary study of the Osceola Mudflow and other 

Holocene debris flows from Mount Rainier indicates that 

three major types of hydrothermal alteration were present 

on Mount Rainier prior to volcano collapse and formation of 

the debris flows (John and others, 2003)—(1) an intermediate argillic assemblage consisting of smectite-group clay 

minerals + pyrite ± silica ± barite ± anhydrite/gypsum; (2) 

advanced argillic alteration consisting of kaolinite + opal/

chalcedony + pyrite/marcasite ± alunite ± pyrophyllite; and 

(3) jarositic alteration (jarosite + alunite + opal). Study of the 

matrix of the Osceola Mudflow where unaffected by postflow surficial weathering indicates that it contains abundant 

fine-grained pyrite (fig. 50), in addition to the high clay contents previously documented by Crandell (1971) and Vallance 

and Scott (1997). X–ray diffraction studies of the matrix of 

the Osceola Mudflow also indicate the presence of finegrained pyrophyllite and quartz. Alteration types 1 and 2 are 

common in the Osceola Mudflow and have been recognized 

in exposures of the mudflow along the White River near 

Greenwater (fig. 51). Alteration type 3 has not been found in 

the Osceola Mudflow.

Assemblage 1 alteration (smectite-pyrite) is present in 

large numbers of clasts in the Osceola Mudflow and in other 

Holocene debris flows from Mount Rainier (fig. 52). Clay 

minerals replace mafic phenocrysts and groundmass and fill 

vesicles (fig. 53 and 54). Plagioclase phenocrysts commonly 

are fresh or only weakly altered, mostly along microfractures. 

Preliminary x–ray diffraction and SEM–EDA studies suggest 

a range of smectite compositions. Pyrite is present as disseminated crystals, lining vesicles, and filling narrow veins and 

microfractures. Pyrite abundance commonly reaches 5 to 10 

volume percent. Barite inclusions in vein-filling pyrite crystals 

are present locally.

Assemblage 2 alteration (kaolinite-opal-pyrite ± alunite 

± pyrophyllite) is less abundant than assemblage 1 in debris 

flows, probably because this alteration results in softer and 

more readily abraded rocks. It has been found in clasts in the 

Osceola Mudflow as far as 50 km down valley from Mount 

Rainier. This alteration is much more intense and pervasive 

than assemblage 1, resulting in complete replacement of igneous minerals and groundmass (figs. 55 and 56). Some clasts 

of this alteration in the Osceola Mudflow are hydrothermal(?) 

breccias that are cemented by opal, alunite, kaolinite, and 

pyrite. Alunite mostly forms fine-grained (<5 μm) lath-like 

crystals locally intergrown with kaolinite (fig. 57). Coarsergrained alunite (as much as 30 μm long) locally fills vugs 

(fig. 58). Pyrite and (or) marcasite content locally reaches 20 

percent. Vug-filling anhydrite/gypsum, native sulfur, cinnabar, 

barite, and fluorite are present locally (fig. 59).

Most alunite crystals from Mount Rainier are Na-rich with 

molar K/(K+Na) ≈ 0.00 to 0.30. Compositional zoning is evident 

in some well-formed crystals with cores generally having more 

K–rich compositions than most of the outer parts of the crystals; 

some crystals also have very narrow (<1 μm) K–rich rims. Some 

alunites contain P–rich domains with as much as several weight 

percent P2

O5 (fig. 58). We have not detected phosphate minerals, 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

13

such as woodhouseite (CaAl3

(PO4)SO4(OH)6) or crandallite 

(CaAl3

(PO4)

2

(OH)5•H2O), in our samples, although Zimbelman (1996) reported them from outcrops near the summit. 

Chemical analyses of 10 samples of altered rocks from 

the Osceola Mudflow (mostly pyrite-rich smectite alteration) 

and nine lahar matrix samples indicate strong enrichment of 

sulfur, but little or no enrichment in most elements characteristic of base- or precious-metal mineral deposits (Au, Ag, As, 

Sb, Hg, Tl, Cu, Pb, Zn, Bi). Previous geochemical studies of 

altered rocks by Zimbelman (1996) and Bruce (1998) showed 

similar results, although most of their samples were oxidized 

surface samples.

Stop 4: Osceola Mudflow along White River 

near Greenwater, Washington

Many features of the Osceola Mudflow, a clay-rich lahar 

derived from edifice collapse of Mount Rainier’s hydrothermal system 5,600 calendar years B.P. (4,800 14C years B.P.), 

are exposed in outcrops along the right (northeast) bank of 

the White River near Greenwater. Note that, whereas axialfacies deposits like this one range from a few to 20 m thick, 

the Osceola Mudflow filled the valley in this area to the much 

greater depth of 100 m.

Erosion by the White River has exposed 8 m of Osceola 

Mudflow deposit at this location (fig. 51). Underlying the 

Osceola are runout facies of clay-poor lahars derived from an 

eruptive episode of Mount Rainier dated between 6,800 and 

7,200 calendar years B.P. (6,000 to 6,400 14C years B.P.).

The exposure here provides excellent views of the 

sedimentologic characteristics of a clay-rich lahar deposit. 

The outcrop is normally graded, not only with respect to the 

coarse gravel-size fraction, but also with respect to the fraction of sand within the matrix (sand versus sand + silt + clay). 

Conversely, clay (chiefly of hydrothermal origin in the precollapse edifice) and other particles affected by hydrothermal 

alteration increase up-section within the outcrop.

Deposits show a progressive downstream improvement 

in sorting, increase in sand and gravel, and decrease in clay. 

These downstream progressions are caused by incorporation 

(bulking) of well-sorted gravel and sand. Normally graded 

axial deposits, like those in this outcrop show similar trends 

from top to bottom because of bulking. The coarse-grained 

basal deposits in valley bottoms are similar to deposits near 

inundation limits. Normal grading in deposits is best explained 

by incremental aggradation of a flow wave, coarser grained at 

its front than at its tail (fig. 60).

A wide variety of hydrothermally altered rocks and 

hydrothermal minerals from Mount Rainier are present as 

clasts and matrix in the mudflow here. The larger clasts, as 

much as 1 m in wide, are mostly fresh or weakly altered to 

a smectite-pyrite assemblage. More strongly altered clasts, 

notably advanced argillic assemblages (kaolinite-pyriteopal±alunite), tend to form much smaller, well-rounded clasts. 

Much of the mudflow matrix here is clay rich. The clay size 

fraction of the matrix contains smectite, kaolinite, alunite, 

hydrothermal quartz, and minor pyrophyllite. Unoxidized parts 

of the clay matrix are dark gray due to the presence of abundant fine-grained pyrite (fig. 50) 

Stop 5: Osceola Mudflow in the Corliss Gravel 

Quarry, Enumclaw, Washington

The Corliss quarry produces sand from fluvial gravels 

and glacial kame terraces that banked along the west side of 

the Cascades Range during late Pleistocene continental glaciation that covered the Puget Sound lowlands. The Osceola 

Mudflow is exposed locally in the quarry as a 4- to 5-m–thick 

deposit overlying the fluvial-glacial deposits (fig. 61). In this 

stop, we will compare characteristics of the Osceola exposed 

here to the Osceola exposed near Greenwater (stop 4), about 

25 km farther up the White River Valley and closer to the 

source of the mudflow on Mount Rainier. 

The Osceola Mudflow in the Corliss quarry consists mostly 

of rounded cobbles and small boulders as much as about 50 cm 

wide (fig. 62). Quaternary andesites from Mount Rainier are the 

most common clasts, but clasts of Tertiary andesites, welded 

tuffs and granites also are common. The ratio of rocks from 

Quaternary Mount Rainier to older rocks is much lower here 

than at the Greenwater locality, an indication of “bulking” of 

the mudflow by incorporation of surface materials that it passes 

over. Hydrothermally-altered clasts are much less common than 

at Greenwater, probably indicating both dilution by incorporation of surface materials (bulking) and mechanical abrasion of 

the softer, hydrothermally-altered rocks during transport. The 

Osceola here also contains small trees and tree branches that 

were incorporated during flowage (figs. 61 and 62).

The matrix of the Osceola Mudflow in the Corliss quarry 

is a gray sand that is noticeably more clay rich than the 

underlying fluvial and glacial deposits, but much less clay rich 

than the matrix of the Osceola at the Greenwater stop. A 1 to 2 

cm thick, Fe-rich hardpan is present locally at the base of the 

Osceola (fig. 63).

References

Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, 

J.B., 1965, Late Pleistocene stratigraphy and chronology in 

southwestern British Columbia and northwestern Washington: Geological Society of America Bulletin, v. 76, no. 3, p. 

321-330.

Arribas, Antonio, Jr., 1995, Characteristics of high-sulfidation 

epithermal deposits, and their relation to magmatic fluid, in

Thompson, J.F.H., ed., Magmas, fluids, and ore deposits: 

Mineralogical Association of Canada Short Course Series, 

v. 23, p. 419-454.

Ashley, R.P., Rytuba, J.J., John, D.A., Blakely, R.J., Box, S.E., 

and Newport, G., 2003, The White River silica deposits, 

Washington: Upper parts of an early Miocene porphyry CuAu system? [abs.]: Geological Society of America Abstracts 

with Programs, v. 35, n. 6, p. 232-233.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

14

Blakely, R.J., 1995, Potential theory in gravity and magnetic 

applications: New York, Cambridge University Press, 441 p.

Blakely, R.J., and Simpson, R.W., 1986, Approximating edges 

of source bodies from magnetic or gravity anomalies: Geophysics, v. 51, p. 1494-1498.

Blakely, R.J., Wells, R.E., and Weaver, C.S., 1999, Puget 

Sound aeromagnetic maps and data: U.S. Geological Survey 

Open-File Report 99–514, http://geopubs.wr.usgs.gov/openfile/of99-514.

Breit, G.N., Rye, R.O., John, D.A., Kester, C.L., and Berry, 

C.J., 2003, Isotopic studies of sulfur-bearing minerals in 

the clasts and matrix of Holocene debris flows from Mount 

Rainier, Washington [abs.]: Geological Society of America 

Abstracts with Programs, v. 35, n. 6, p. 553.

Bruce, V.L., 1998, Geochemistry of hydrothermal alteration 

along a radial transect from the summit of Mount Rainier, 

Washington: Riverside, University of California, M.S. 

thesis, 120 p.

Callaghan, Eugene, 1940, Alunite deposits near Enumclaw, 

King and Pierce Counties, Washington: unpub. U.S. Geological Survey report, 12 p. plus table.

Christiansen, R.L., and Yeats, R.S., 1992, Post-Laramide 

geology of the U.S. Cordilleran region, in Burchfiel, B.C., 

Lipman, P.W., and Zoback, M.L., eds., The Cordilleran 

Orogen; Conterminous U.S.: Boulder, CO, Geological 

Society of America, the Geology of North America, v. G-3, 

p. 261-406.

Crandell, D.R., 1963, Surficial geology and geomorphology 

of the Lake Tapps quadrangle, Washington: U.S. Geological 

Survey Professional Paper 388-A, 84 p.

Crandell, D.R., 1971, Postglacial lahars from Mount Rainier 

National Park, Washington: U.S. Geological Survey Professional Paper 677, 75 p.

Dragovich, J., Pringle, P.T., and Walsh, T.J., 1994, Extent and 

geometry of the mid-Holocene Osceola Mudflow in the 

Puget Sound Lowland—Implications for Holocene sedimentation and paleogeography: Washington Geology, v. 22, 

no. 3, p. 3–26.

Glover, S.L., 1936, Nonmetallic mineral resources of Washington: Washington Division of Geology Bulletin 33, 135 p.

Gustafson, L.B., and Hunt, J.P., 1975, The porphyry copper 

deposit at El Salvador, Chile: Economic Geology, v. 70, p. 

857-912.

Heald, P., Foley, N.K., and Hayba, D.O., 1987, Comparative 

anatomy of volcanic-hosted epithermal deposits: Acid sulfate 

and adularia-sericite types: Economic Geology, v. 82, p. 1-26.

Hedenquist, J.W., 1990, The thermal and geochemical signature structure of the Broadlands-Ohaaki geothermal system: 

Geothermics, v. 19, p. 151-185.

Hedenquist, J.W., Arribas, Antonio, Jr., and Gonzalez-Urien, 

Eliseo, 2000, Exploration for epithermal gold deposits, 

in Hagemann, S.G., and Brown, P.E., eds., Gold in 2000: 

Reviews in Economic Geology, v. 13, p. 245-277.

Huntting, M.T., 1955, Gold in Washington: Washington Division of Mines and Geology, Bulletin 42, 158 p.

John, D.A., Breit, G.N., Rye, R.O., Sisson, T.W., and Vallance, 

J.W., 2003, Hypogene hydrothermal alteration of Quaternary volcanic rocks from Mount Rainier, Washington [abs.]: 

Geological Society of America Abstracts with Programs, v. 

35, n. 6, p. 553.

Kelly, H.J., Strandberg, K.G., and Mueller, J.I., 1956, Ceramic 

industry development and raw-material resources of 

Oregon, Washington, Idaho, and Montana: U.S. Bureau of 

Mines Information Circular 7752, 77 p.

Livingston, V.E., Jr., 1971, Geology and mineral resources of 

King County, Washington: Washington State Division of 

Mines and Geology Bulletin, n. 63, 200 p.

Mattinson, J.M., 1977, Emplacement history of the Tatoosh 

volcanic-plutonic complex, Washington; ages of zircons: 

Geological Society of America Bulletin, v. 88, p. 1509-

1514.

McCulla, M.S., 1986, Geology and metallization of the White 

River area, King and Pierce Counties, Washington: Corvallis, Oregon State University, Ph.D. dissertation, 213 p.

Mullineaux, D. R., 1974, Pumice and other pyroclastic 

deposits in Mount Rainier National Park, Washington: U.S. 

Geological Survey Bulletin 1326, 83 p.

Plumlee, G.S., Rye, R.O., Breit, G.N., and John, D.A., 2003, 

Chemical modeling of volcanic gas interactions with 

ground water and andesite: Insights into hydrothermal 

alteration at Mount Rainier, Washington [abs.]: Geological 

Society of America Abstracts with Programs, v. 35, n. 6., 

p. 553.

Ransome, F.L., 1909, The geology and ore deposits of Goldfield, Nevada: U.S. Geological Survey Professional Paper 

66, 258 p.

Rye, R.O., Bethke, P.M., and Wasserman, M.D., 1992, The 

stable isotope geochemistry of acid-sulfate alteration: Economic Geology, v. 87, p. 225-262.

Rytuba, J.J., John, D.A., Foster, Andrea,, Ludington, S.D., and 

Kotylar, Boris, in press, Hydrothermal enrichment of gallium in zones of advanced argillic alteration; examples from 

the Paradise Peak and McDermitt ore deposits, Nevada, in

Bliss, J.D., Moyle, P.R., and Long, K.R., eds., Contributions 

to Industrial-Minerals Research: U.S. Geological Survey 

Bulletin 2209, Chapter C, 34 p.

Schoen, R., White, D.E., and Hemley, J.J., 1974, Argillization 

by descending acid at Steamboat Springs, Nevada: Clays 

and Clay Minerals, v. 22, p. 1-22.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

15

Sillitoe, R.H., 1999, Styles of high-sulphidation gold, silver, 

and copper mineralization in the porphyry and epithermal 

environments: PacRim ’99, Bali, Indonesia, 10-13 October, 

Proceedings, p. 29-44.

Sillitoe, R.H., 2000, Gold-rich porphyry deposits: Descriptive and genetic models and their role in exploration and 

discovery, in Hagemann, S.G., and Brown, P.E., eds., Gold 

in 2000: Reviews in Economic Geology, v. 13, p. 315-345.

Sisson, T.W., Lanphere, M.A., and Calvert, A.T., 2003, Alteration and the magmatic history of Mt. Rainier, Washington 

[abs.]: Geological Society of America Abstracts with Programs, v. 35, n. 6, p. 552.

Sisson, T.W., Vallance, J.W., and Pringle, P.P., 2001, Progress made in understanding Mount Rainier’s hazards: Eos 

(Transactions, American Geophysical Union), v. 82, p.113-

120.

Steven, T.A., and Ratte, J.C., 1960, Geology of ore deposits 

of the Summitville district, San Juan Mountains, Colorado: 

U.S. Geological Survey Professional Paper 343, 70 p.

Stoffregen, R.E., 1987, Genesis of acid-sulfate alteration and 

Au-Cu-Ag mineralization at Summitville, Colorado: Economic Geology, v. 82, p. 1575-1591.

Tabor, R.W., Frizzell, V.A., Jr., Booth, D.B., and Waitt, R.B., 

2000, Geologic map of the Snoqualmie Pass 30 x 60 minute 

quadrangle, Washington: U.S. Geological Survey Geologic 

Investigations Series Map I-2538, scale 1:100,000.

Valentine, G. M., 1960, Inventory of Washington minerals-Part 

I, Nonmetallic minerals, 2nd ed., revised by M.T. Huntting: 

Washington Division of Mines and Geology Bulletin 37, v. 

1, 175 p.

Vallance, J.W., and Scott, K.M., 1997, The Osceola Mudflow 

from Mount Rainier: Sedimentology and hazard implications of a huge clay-rich debris flow: Geological Society of 

America Bulletin, v. 109, p. 143-163.

Vallance, J.W., Breit, G.N., and John, D.A., 2003, Involvement 

of a hydrothermal system in the catastrophic 5600 BP eruption of Mount Rainier [abs.]: Geological Society of America 

Abstracts with Programs, v. 35, n. 6, p. 552-553.

Weyerhaeuser Company, 1996, Summary Report, Weyerhaeuser Exploration Package, White River Properties, King 

County, Washington, unpublished internal report, 50 p.

Zimbelman, D.R., 1996, Hydrothermal alteration and its influence on volcanic hazards—Mount Rainier, Washington, a 

case history: Boulder, University of Colorado, Ph.D. dissertation, 384 p.

Zotov, Alexandre, Mukhamet-Galeev, Alexandre, and Schott, 

Jacques, 1998, An experimental study of kaolinite and 

dickite relative stability at 150-300°C and the thermodynamic properties of dickite: American Mineralogist, v. 83, 

p. 515-524.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

16

Figure 1. Map showing location of the Western Cascades and High Cascades arcs and mineral deposits in the northwestern United 

States. Also shown is location of the White River altered area. Mineral deposits from U.S. Geological Survey Mineral Resources Data 

System database.

Columbia

Mount Rainier

Goat Rocks volcano

Mount Adams

Mount

St. Helens

Glacier Peak

Mount Baker

47°

48°

46°

49°N

44°

45°

43°

41°

42°

40°

X

127°W 126° 125° 124° 123° 122° 121° 120° 119° 118° 117°

CANADA

UNITED STATES

WASH.

OREG River

Columbia River

WASH.

IDAHO

Seattle

Portland

P

acific Ocean

ORE.

NEVADA

NEVADA

CALIF.

CALIF.

Lassen Peak

Mount Shasta

Medicine Lake

Mount Hood

Newberry

caldera

Mount

Jefferson

Three

Sisters

Crater

Lake

0 500 KILOMETERS

Western

Cascades

High

Cascades

Porphyry Cu

Cu breccia pipe

Polymetallic vein

Silica-alunite

Simple Sb

Low-sulfidation epithermal Au-Ag

Hot-spring Hg

Silica-carbonate Hg

Volcanogenic U

Epithermal Mn

Deposit Types

Major faults

Quaternary High Cascades

volcanic rocks

Late Eocene to Pliocene

Western Cascades arc rocks

Late Eocene to middle

Miocene granitic rocks

Major Quaternary volcanoes

White

River
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

17

25 km

Electron Orting

Mount

Rainier

Puyallup

Kent

Tacoma

Seattle

Enumclaw

Buckley

?

Puget

Sound

ELECTRON/

ROUND PASS

COLLAPSES

OSCEOLA

COLLAPSE

PARADISE

COLLAPSE

Figure 2. Map showing areas inundated by 

Holocene debris flows from Mount Rainier. The 

Osceola and Electron Mudflows and the Paradise and Round Pass lahars all have clay-rich 

matrixes and contain abundant clasts of hydrothermally altered rocks. Modified from Sisson 

and others (2001).

Figure 3. Photograph of vuggy silica alteration in the Scatter Creek (James Hardie) 

silica quarry, White River altered area. Snow-covered Mount Rainier is in the background.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

18

1

1

1

1

1

6

3

0

0 10 KILOMETERS

5 MILES

CONTOUR INTERVAL 50 METERS

47°00'

122°30' 123°00'W

47°15'N

122°45'

1

5

2

3

4

Figure 4. Geologic map of the SW quarter of the Snoqualmie Pass 30 x 60 

minute quadrangle, showing field trip stops. Geology from Tabor and others (2000). Red box shows White River altered area and outline of figure 8.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

19

20

20

20

40

30

30

LIST OF MAP UNITS

Man-Modified land (Holocene)

Alluvium (Holocene and Pleistocene)

Bog deposits (Holocene and Pleistocene)

Landslide deposits (Holocene and Pleistocene)

Mass-wastage deposits (Holocene and Pleistocene)

Talus deposits (Holocene and Pleistocene)

Lahar deposits (Holocene and Pleistocene)

Surficial deposits, undivided (Holocene and Pleistocene)

Alpine glacial deposits (Pleistocene)

Deposits of Vashon stade of Fraser glaciation of Armstrong

and others (1965) of Cordilleran ice sheet (Pleistocene)

Recessional outwash deposits

Ice-contact deposits

Till

Advance outwash deposits

Vashon Drift, undivided

Glacial and nonglacial deposits of pre-Fraser glaciation age (Pleistocene)

Alpine glacial drift of pre-Fraser glaciation age (Pleistocene)

Andesite of Mount Rainier (Pleistocene)

Basalt of Canyon Creek (Pleistocene)

Basaltic tuff and breccia

Basalt of Dalles Ridge (Pliocene)

Howson Andesite (Miocene)

Volcaniclastic rocks of Cooper Pass (Miocene)

Carbon River stock (Miocene)

Intrusive rocks (Miocene and Oligocene)

Pyroxene andesite porphyry

Tonalite

Altered porphyry

Dacite porphyry

Fifes Peak Formation (Miocene)

Volcaniclastic rocks

Andesite and basalt megabreccia

Crystal-lithic tuff

Rhyolite unit of Clear West Peak

Intracaldera rhyolite

Extracaldera rhyolite tuff

Rhyodacite tuff

Sun Top unit

Chenuis Ridge unit

Volcanic rocks of Eagle Gorge (Miocene and Oligocene)

Ohanapecosh Formation (Oligocene)

Tuff member of Lake Keechelus

Volcanic rocks (Oligocene)

Diabase, gabbro, and basalt (Oligocene? and Eocene)

Contact

High-angle Fault

Major Folds

Anticline

Syncline

Overturned Syncline

Strike and dip of bedding

Inclined

Inclined, top known

Overturned

Overturned, top known

Vertical

Vertical, top towards ball

Horizontal

Strike and dip of foliation

Inclined

Vertical

Lineation

Zone of sheared rock

Zone of silicified rhyolite

Crest of moraine

Spillway

Landslide arrow

5 Field trip stops

Figure 4. Geologic map of the SW quarter of the Snoqualmie Pass 30 x 60 minute quadrangle, showing field trip stops. Geology from 

Tabor and others (2000). Red box shows White River altered area and outline of figure 8—Continued.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

20

Figure 5. Heterolithic breccia (lahar) in the 

Fifes Peak Formation. Rock consists of unaltered 

clasts of several types of andesite in a propylitically or argillically altered matrix.

Figure 6. Subhorizontal, finely bedded tuffs 

from small outcrop about 0.5 km north of the 

Superior quarry. Tuff is variably silicified or 

altered to alunite.

Figure 7. Silicified flow-banded dacite showing large 

flow fold open to the left side of photo. Cliffs above WA 

SR 410 south of the Superior quarry. 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

21

ContactFault, dotted where concealedIP survey (fig. 14)

Qvl

Qa

Qg

Qg

Tfpr

Qls

Qvl

Tfpa

Qls

Tfpa

Qg

Qa

Qa

Qg

Tfpa

Tfpa

Tfpr

Tfpa

Qls

Qad

Tfpa

Tfpr

Qa

Tfpa

Tfpa

Taugow

Cady Hill

Bridge Camp

alunite

Scatter Creek

quarry

Superior

quarry

Denny-Renton

quarry

Quarry

Hill

Mapped Alteration Alteration Types (PIMA)—see table 1

AluniteDickite

HalloysiteMontmorillinite

± Dickite

Illite

Kaolinite

Montmorillinite

Pyrophyllite

Silica

Z

121°53'W 121°52' 121°51' 121°50' 121°49' 121°48' 121°47'

47°09'47°10'

47°11'N

1,000 0 1,000 meters 500

Silicification and alunitePervasive argillic alteration

Figure 8. Map showing distribution of hydrothermal alteration, Portable Infrared Mineral Analyzer (PIMA) alteration mineralogy, and locations of silica quarries and other geographic 

features in the White River area. Areas of hydrothermal alteration modified from unpublished mapping by Weyerhauser Co. (1996). Z, zunyite locality. Geologic map modified from Tabor and others (2000). Qa, alluvium; Qls, landslide deposits; Qvl, lahar deposits; Qg, glacial deposits, undivided; Tfpr, Fifes Peak Formation rhyolite; Tfpa, Fifes Peak Formation andesite.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

22

Figure 9. Voids developed from leaching of plagioclase and pyroxene phenocrysts 

in a porphyritic andesite flow in the Fifes Peak Formation by acidic hydrothermal 

fluids during vuggy silica alteration. Late, white chalcedonic silica locally replaces 

and infills the gray vuggy silica. Scatter Creek quarry.

Figure 10. Sharp contact shown by pen between vuggy silica alteration (VS) and 

alunitic alteration (AA) exposed in narrow northeast-trending rib in the Scatter 

Creek quarry (also see figs. 38 and 42). 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

23

KAOLINITE

MUSCOVITE

K-FELDSPAR

ALUNITE

KAOLINITE

HEMATITE

PYRITE

CHLORITE

COVELLITE

DIGENITE

ENARGITE

TENNANTITE

PYRITE+BORNITE

CHALCOPYRITE

250°C

2 4 6 8

-38

-36

-34

-32

-30

pH

LOG

ƒ

O

2

H2S

HSHSO4

-

(Na,K)SO4

-

+Quartz

V

V

X

+

X X

V

X

+

X

X X

V V V

V

X X

X

X

V V

XX X

V V V

V V

V

X

+

+

X XX

X X X

X XX

V

X

X

X

V V V

500m

500m

Dome

Porphyry stock

Ignimbrite

Chalcopyrite in K-silicate alteration

Steam-heated acid-leached zone

Au-tennantite in vuggy quartz

Au-enargite/luzonite in vuggy quartz

Quartz-alunite

Quartz-dickite/kaolinite

Disseminated Au-Ag in vuggy quartz

Illite out to

illite/smectite

Barren Intermediate argillic alteration

(sericite up to pyrophyllite)

(modified from Sillitoe, 1999)

Schematic reconstruction of a high-sulfidation deposit

White River

Figure 11. Schematic model for high-sulfidation gold deposits, showing zoning of hydrothermal alteration assemblages and ore types. Most 

of the White River altered area is inferred to have formed in the uppermost part of this type of hydrothermal system where vuggy silica alteration is extensively developed in permeable horizons (green box). Figure courtesy of Antonio Arribas, Jr., and based on Sillitoe (1999).

Figure 12. Log ƒO2

-pH diagram at 250°C, total sulfur=0.02 molal, salinity=1 molal with Na/K=9, 

and quartz saturation, modified from Heald and others (1987). Magmatic-hydrothermal fluids 

forming vuggy silica alteration (star) likely had pH<2 where Al solubility dramatically increases 

(Stoffregen, 1987). Progressive reaction of this acidic fluid with relatively reduced, plagioclase 

feldspar-rich wall rocks increased the pH and lowered the oxygen fugacity of the fluid resulting in zones of quartz-alunite, quartz-kaolinite, and quartz-muscovite (illite) alteration outward 

from fluid conduits as indicated by arrow. At higher temperatures (>270°C), pyrophyllite will 

replace kaolinite. Stability relations between kaolinite and dickite are uncertain and may 

reflect higher temperature stability of dickite and/or kinetics (Zotov and others, 1998).
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

24

5'

Zone of silicified Rhyolite

47o05'

47o15'

0 2 4 6 8 10 KILOMETERS

Qa

Ql

Qlh

Qag

Qvr

Qvi

Qvu

Qpfa

Qcc

Tf

Tfci

Tfce

Tfrt

Tfst

Tfcr

Teg

To

Tdg

Tp

Alluvium (Holocene and Pleistocene)

Landslide deposits (Holocene and Pleistocene)

Lahar deposits (Holocene and Pleistocene)

Recessional outwash deposits

Ice-contact deposits

Vashon Drift, undivided

Alpine glacial deposits (Pleistocene)

Fifes Peak Formation (Miocene)

Ohanapecosh Formation (Oligocene)

Diabase, gabbro, and basalt

(Oligocene? and Eocene)

Puget Group

Alpine glacial drift (Pleistocene)

Basalt of Canyon Creek (Pleistocene)

Intracaldera rhyolite

Extracaldera rhyolite tuff

Rhyodacite tuff

Chenuis Ridge unit

Sun Top unit

Volcanic rocks of Eagle Gorge

(Miocene and Oligocene)

122o 121o50' 121o40'

47o05'

47o15'

B

Magnetization boundaries

Magnetic anomaly low

A

B

White River

Fault Zone

White River fault zone

A

Figure 13. A, Aeromagnetic anomalies of the White River altered area and surrounding regions. White 

dots represent magnetic contacts calculated automatically using the method of Blakely and Simpson 

(1986). Magenta stars indicate location of Superior (Ash Grove) and Scatter Creek (James Hardie) quarries. Labels A and B indicate negative and positive anomalies discussed in text. B, Geologic map of the 

White River altered area, modified from Tabor and others (2000). The bold, dotted polygon shows the 

location of the aeromagnetic low, determined from the magnetic-contact analysis. Red line shows induced 

polarization (IP) profile shown in figure 14.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

25

Figure 14. Inversion modeling completed by Gradient Geophysics, Inc., using University of British Columbia program, DCIP2D. High resistivity anomalies represent near-surface 

silicification and high chargeability anomalies indicate the presence of sulfide minerals. Profile line shown on figures 8 and 16

B.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

26

122o 121o50' 121o40'

47o05'

47o15'

47o05'

47o15'

A

B

Gravity station

Magnetic anomaly low

0 2 4 6 8 10 KILOMETERS

B A

Figure 15. A, Observed aeromagnetic anomalies transformed to pseudogravity. B, Observed isostatic residual gravity anomalies. Yellow triangles are gravity 

stations. See figure 13 for other symbols.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

27

2500 0 2500 5000 Meters

47°7 3' 0" 47°12 3' 0" 47°7 3' 0" 47°12 3' 0"

-121°55' -121°50'

>1

0.5-1

0.2 - 0.5

0.1 - 0.2

0.05 - 0.1

< 0.05

Magnetic Susceptibility (SIU X 1000)

259.1

179.7

128.1

92.6

60.8

33.6

6.9

-17.3

-42.4

-64.4

-84.3

-103.4

-129.2

-163.7

-212.6

nT

A

B

A

B

X

IP line A (fig. 14)

Figure 16. Ground-magnetic studies. A, Map showing the location of all susceptibility measurements (dots) 

with respect to aeromagnetic anomalies. Susceptibility color coded by value. Stipple pattern, is zone of silicified rhyolite (Tabor and others, 2000). Labels A and B indicate anomalies discussed in text. X indicates susceptibility measurement of laterally restricted area of unaltered basalt. B, Representative ground-magnetic 

profile plotted along route and in map projection. Black and white fill indicates positive and negative anomaly, 

respectively, relative to base station at Taugow.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

28

Profile 6-5-4

-122.94 -122.92 -122.90 -122.88 -122.86 -122.84 -122.82 -122.80 -122.78

1000.00

-500.00

0.00

500.00

1000.00

Individual Measurements

500-point filter

Relative Magnetic Intensity, nT

Figure 17. Ground-magnetic profile across White River altered zone. See figure 16 for profile location. Values along profile have been 

projected onto an east-west line and are shown relative to base-station measurements at Taugow. Green dots are individual measurements; red line is low-pass version of individual measurements. Arrow indicates magnetic gradient discussed in text.

Figure 18. View of the Superior (Ash Grove) quarry from Taugow.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

29

TREES

TREES

TREES

TREES

TREES

TREES

TREES

1450

1460

1480

1500

1520

1540

1560

1580

1600

1620

1610

1590

1570

1550

1490

1510

1530

1550

1570

1590 1590

1580

1570

1560

1550

1610

1580

1570

1560

1550

1540

1530

1550

1550

1560

1570

51 08

51 07

1560

1550

1560

1570

1560

1550

1550

1570

158

1570

0

1560

1560

1550

1

1630

620

1610

1600

1590

1580

1570

1560

1590

1600

1600

1580

1600

1590

1580

1580

1570

1530

1550

151

1500

0

1480

1580

1550

1580

1570

1560

1550

1570

1560

1540

1520

1500

1

1

480

460

1450

1550

1560

1570

1560

15

15

40

20

1500

148

1

0

460

1450

1550

1540

1530

1520

1510

1500

1490

1480

1490

1500

1640

1630

1610

1590

1570

1550

1560

1540

1550

1560

1570

61 02

061 0

851 0

1570

1560

1550

1540

1530

1520

1510

1560

1550

1550

1560

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

2250 E 130

2500 E 130

2750 E 130

3000 E 130

3250 E 130

3500 E 130

3750 E 130

N 668500N 668250N 668000N 667750N 667500

?

?

? ? ? ?

?

?

?

?

?

?

0 50' 100' 200'

Scale in Feet

300' N

Felsite Porphyry Dike --trending north-south across Ashgrove Hill.Buff-white to tan, fine-grained dike with occasional quartz phenocrysts

cuts most of the hydrothermal breccia events. Dike margins exhibit a

faint flow banding accentuated by limonite staining. The felsite is cut

by irregular, milky quartz veins and fine hairline veinlets. In at least

one location, a late hydrothermal breccia dike cuts the dike.

Hydrothermal Breccia Masses --complex, multi-staged breccias of a

hydrothermal origin. Breccias vary from massive, coarse heterolithologicintrusions to fine grain "shatter" brecciation consisting of host rock fragments

with a rock flour matrix. Various breccia stages often crosscut one another.

Breccia massed commonly attenuate into narrow breccia dikes and veins.

Bedded, Vent Facies Micro-Pyroclastics --hydrothermally derived,

"pool accumulates" consisting of dark gray to black, horizontally

bedded, fine grained, volcanic ash containing fragments of ash andpumice. High volumes (+7 vol. percent) of bedded sulfides (pyrite)

are commingled with the fine volcanic ash.

Dacite Flow Dome --local dacitic flow dome centered in the Ashgrove Hill area.

Flow dome rocks consist of nearly horizontal, composite layers of flows, tuffs,

ignimbrites, and possible local accumulations of vent facies pyroclastics with

widely varying textures and sub-horizontal flow layering. Flow dome rocks in thewestern portion of the Superior Quarry display numerous flattened pumice

fragments and welded eutaxitic textures. In the northwestern portion of the

Superior Quarry, flow dome rocks consist of tuffs with only rare indications of

flow foliation. The dacite flow dome is host to the extensive hydrothermal breccia

masses in the Superior quarry.

GENERALIZED GEOLOGY

ASHGROVE - SUPERIOR QUARRY

(G. Heinemeyer, 2003)

Lithology

Ash Grove Superior Quarry (8.5 x11).dwg [Ash Grove Superior Quarry (8.5 x11).mcl] 10/10/2003

Figure 19. Generalized geologic map of the Superior quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

30

Figure 20. Gray vuggy silica rock with abundant voids after plagioclase and pyroxene phenocrysts in andesite flow. From Superior quarry.

A B

Figure 21. A, Enargite crystals in vug and 

groundmass (gray areas) of vuggy silica rock. 

Largest crystal is about 5 mm wide. B, Backscattered SEM image of enargite and pyrite 

crystals in vuggy silica alteration. Samples from 

Superior quarry.

Figure 22. Small dark gray enargite crystals filling 

funnel-shaped feature (hydrothermal vent?) in white 

chalcedonic silica, Superior quarry. Cluster of enargite 

crystals is about 8 mm wide.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

31

Figure 23. Tan chalcedony replacing relict 

flow and devitrification layers in dacite flow. 

Gray areas are hematite after pyrite. Sample 

is about 15 cm wide. From the Superior quarry.

Figure 24. Massive tan chalcedony cut by 

hydrothermal breccias with sulfide minerals in 

gray areas. From the Superior quarry.

Figure 25. Steeply dipping, quartz-bearing felsic dike 

cutting dacite in the southwest highwall of the Superior 

quarry. Dike forms light-colored rocks in the center of 

the photo (between red lines).
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

32

Figure 27. Sulfide mineral-bearing hydrothermal breccia developed in massive tan silicified 

rock in the Superior quarry.

Figure 26. Hydrothermal breccia with clasts 

of early stage white chalcedony in tan to gray 

chalcedony with sulfide minerals in gray areas. 

From the Superior quarry.

Figure 28. Massive tan silicified dacite tuff(?) 

cut by stockwork of sulfide mineral-bearing 

gray chalcedony in the Superior quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

33

Figure 31. North-striking fault with red clay 

gouge developed in massive vuggy silica rock in 

the Superior quarry.

Figure 29. Brecciated, finely laminated, siliceous hydrothermal sedimentary rocks in the southwest part of the 

Superior quarry (see fig. 19).

Figure 30. Fault breccia with clay-supported 

fragments that contains the highest gold content 

(1.7 ppm) in the Superior quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

34

Figure 34 Knob of alunitic alteration on 

Taugow. Rocks are probably tuff and tuff 

breccia now replaced by pale pink alunite and 

fine-grained white silica. White River Valley in 

distance.

Figure 32. Red to brown smectite clay zone 

developed from alteration of bedded tuff. Note 

faults on left and right sides that terminate bedding. From the Superior quarry.

Figure 33. Taugow from the Superior quarry. 

Outcrops near top of Taugow consist of alunitically-altered tuff breccia. High ridge in background is north of the White River Fault Zone 

and is underlain by the Oligocene Ohanapecosh 

Formation.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

35

Figure 37. Blocks of vuggy silica alteration in 

hydrothermal breccia near top of Taugow. Largest block shows relict flow banding or bedded 

tuffaceous texture. Breccia matrix consists of 

fine-grained silica and hematite.

Figure 35. Leached silicified tuff breccia with 

relict pyroclastic textures exposed in roadcut 

near top of Taugow.

Figure 36. Narrow fine-grained silicic dike cutting silicified tuff breccia near top of Taugow.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

36

TREES

TREES

1950

1960

1980

1990

2000

2010

2020

2030

2040

2050

2060

2070

2080

04 20

1970

2020

2020

2010

2000

1990

2030

2020

2050

2020

2030

2040

1970

1980

1990

2000

2010

2000

2010

2000

1990

1980

1970

2040

2030

2020

1990

2020

2010

1990

2010

2020

2020

2020

2030

2040

2050 2030

2040

2050

20 04

2030

2020

2010

2010

2010

2000

1990

1980

1970

1960

1950

2040

BRUSH

BRUSH

BRUSH

BRUSH

101

N 14000N 14250N 14500N 14750

17250 E

17000 E

16750 E

?

?

?

?

?

?

?

?

?

?

?

?

?

?

42∞

U

D

U D

U

D

U

D

0 50' 100' 200'

Scale in Feet

300'

N

Felsite Porphyry Dikes? --felsitic, dike-like masses which cut outcrops of

massive, hydrothermal breccia. Strongly silicified, tan to buff, cherty textured

(no recognizable phenocrysts), irregular dikes containing varying amounts of

rounded hydrothermal breccia fragments. Lateral tendrils of the dike attenuate

into, and intrude darker, massive hydrothermal breccia and often transforminto anastomosing, milky quartz veins before terminating.

Hydrothermal Breccia Masses --complex, multi-staged, silicified breccias of

a hydrothermal origin. Breccias vary from massive, coarse heterolithologic

intrusions to fine grain "shatter" brecciation consisting of host rock fragments

with a rock flour matrix. Fragments consist of Fifes Peak andesite, vent facies

pyroclastics and previous breccia stages. Various breccia stages often crosscut

one another indicating coeval formation.

Vent Facies Pyroclastics --local, vent related pyroclastics derived from a possible

volcanic center to the west and south of the Hardie pit. These pyroclastics are

comprised of fragments of Fifes Peak andesite, dacitic flow dome material and

undefined ignimbritic material, ash and pumice. Pyroclastics are predominantly

altered to clays or silica depending on location in relation to hydrothermal vent zones.

Fifes Peak Andesite Flows --primary host to massive hydrothermal breccias

exposed in the Hardie pit. Although commonly strongly silicified, the Fifes Peak

is discerned by its uniform fine-grained porphyritic texture where original plagioclasephenocrysts have been leached leaving equally dispersed cavities.

Unconformity

GENERALIZED GEOLOGY

SCATTER CREEK QUARRY - PIT "A" (G. Heinemeyer, 2002)

Lithology

Major Faults U

D Pit Outline

Scatter Creek_Hardie Silica (8.5 x11).dwg [Scatter Creek_Hardie Silica (8.5 x11).mcl] 10/9/2003

"Clay

Hole" FIGURE 48

white outcrop of

leached rock

FIGURE 10

Figure 38. Generalized geologic map of the Scatter Creek quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

37

Figure 41. Voids developed in porphyritic 

andesite after leached plagioclase and pyroxene 

phenocrysts by acid hydrothermal fluids leaving 

a residual ground mass of silica. Tan chalcedonic 

veins cut the vuggy silica. Label is about 4 cm 

wide. From the Scatter Creek quarry.

Figure 39. Stockpile of sized silica at Scatter 

Creek quarry being loaded for shipment to James 

Hardie Building Products, Inc., for use in producing fiber cement-based building products.

Figure 40. Gray vuggy silica replacing porphyritic andesite cut by white quartz and chalcedony 

veins and hydrothermal breccias. From the Scatter Creek quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

38

Figure 43. “Clay Hole” (fig. 38). South side of northeasttrending rib of vuggy silica alteration (fig. 42) consisting of 

reddish colored illitic alteration and pale green chloritemontmorillonite-rich propylitic alteration that forms floor of 

the Scatter Creek quarry.

Figure 42. Northeast-trending rib of orangish-brown vuggy silica alteration (VS) bordered by light-colored alunitic (AA) and illitic 

(I) alteration localized along fault zone in 

Scatter Creek quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

39

Figure 45. Vuggy silica cut by early stage of white chalcedonic hydrothermal 

breccia and veins. From the Scatter Creek quarry.

Figure 44. Oxidation in the Scatter Creek quarry. Leaching of hematite from vuggy 

silica in the near surface forms a white vuggy silica rock that is underlain by gray 

to brown vuggy silica with abundant hematite. Relict pods of pyrite-rich alteration 

indicate that hematite is replacing pyrite.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

40

Figure 47. Fracture in vuggy silica filled with 

late-stage hydrothermal red clay composed of 

hematite, smectite, and dickite and commonly having elevated concentrations of Au, As, Sb, and Hg. 

From the Scatter Creek quarry.

Figure 46. Vuggy silica in andesite cut by hydrothermal breccias with tan chalcedony matrix and 

hematite after pyrite and associated chalcedony 

and quartz veins. From the Scatter Creek quarry.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

41

Figure 49. Map showing 

distribution of Osceola 

Mudflow and Paradise 

lahar (modified from 

Crandell, 1971, plate 3). 

Distribution of Osceola 

Mudflow in subsurface 

from Dragovich and others (1994). Distributions 

of tephra layers F and S 

(Mullineaux,1974) shown 

near Mount Rainier. Figure 

reproduced from Vallance 

and Scott (1997, fig. 1).

Figure 48. White outcrops of leached rock 

that formed in the near-surface steam-heated 

zone. Altered rocks in background are densely 

silicified and formed below the paleo ground 

water table in the upper part of the hydrothermal 

system. See figure 38 for outcrop location.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

42

Figure 52. Typical smectite-pyrite alteration of 

andesite clast in the Osceola Mudflow near Greenwater. Clast has a narrow oxidation (weathering) rind surrounding rock with unoxidized 

disseminated and vesicle filling pyrite.

Figure 50. Dark-gray clay-pyrite rich matrix of 

the Osceola Mudflow near Greenwater. Orange 

color due to surface oxidation of pyrite that 

extends a few cm or less below the outcrop 

surface. Small white clasts are advanced argillic 

alteration. 

Figure 51. Typical outcrop of the Osceola 

Mudflow along the White River near Greenwater. Osceola Mudflow is about 8 m thick. 

The characteristic pale yellow color is due to 

surficial weathering of pyrite in clay-rich matrix. 

The Osceola Mudflow here overlies about 1 m 

of gray compact silt, sand and angular pebbles 

and sparse cobbles, which is a runout facies of 

lahars (LRO) that were associated with eruptions at Mount Rainier between 6,000 and 6,400 

radiocarbon years ago (6,700 and 7,400 calendar 

years B.P.). The gray LRO, in turn, overlies stream 

gravel (reddish-brown unit right at river level).
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

43

Figure 55. Back-scattered SEM image of alunite, opaline 

silica (SiO2), and pyrite in advanced argillic altered clast in 

the Osceola Mudflow.

Figure 53. Back-scattered SEM image of smectite alteration of andesite clast in the Osceola Mudflow. Plagioclase 

phenocrysts are relatively unaltered.

Figure 54. Back-scattered SEM image of smectite-pyrite 

alteration of andesite clast in the Osceola Mudflow. Plagioclase phenocrysts are relatively unaltered.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

44

Figure 58. Back-scattered SEM image of intergrown alunite 

and kaolinite in advanced argillic altered clast in the Osceola 

Mudflow.

Figure 56. Back-scattered SEM image of alunite, anhydrite/

gypsum, and pyrite in advanced argillic altered clast in the 

Osceola Mudflow.

Figure 57. Back-scattered SEM image of alunite containing P-rich domains in advanced argillic altered clast in the 

Osceola Mudflow.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

45

Figure 60. Schematic diagram of stage height versus time (hydrograph) for mass flow at point in bottom 

of valley, and depositional sequence of flow illustrating incremental deposition model for explaining normal grading. Deposition illustrated for two stations 1 and 2 at heights h1 and h2 above valley bottom and 

with ultimate thicknesses t1 and t2. Short dashed lines through hydrograph indicate uniform incremental 

deposition. Sense of motion of mass flow is to left. See text for explanation. Figure reproduced from Vallance and Scott (1997, fig. 13).

Figure 59. Back-scattered 

SEM image of vug-filling 

anhydrite/gypsum and fluorite 

in advanced argillic altered 

clast in the Osceola Mudflow. 
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

46

Figure 63. Base of the Osceola Mudflow in 

the Corliss quarry. Note dark orange, iron rich 

hard pan forming beneath the Osceola and well 

rounded clasts in the Osceola.

Figure 61. Exposure of Osceola Mudflow overlying well bedded late Pleistocene glacial-fluvial 

deposits in the Corliss quarry. Note dark gray 

trees protruding from the center of the Osceola 

Mudflow. Figure 62. Partly charred trees protruding from the Osceola Mudflow in the Corliss 

quarry. Note generally rounded cobbles up to 50 

cm in the Osceola.

Figure 62. Partly charred trees protruding from 

the Osceola Mudflow in the Corliss quarry. Note 

generally rounded cobbles up to 50 cm in the 

Osceola.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

47

Alteration type 

(fig. 8)

Mineral assemblage1 Occurrence

Silica Quartz, cristobalite, and (or) 

chalcedony ± pyrite

Silicified zones (fig. 8), including vuggy 

silica

Alunite Quartz + alunite ± pyrite Silicified zones and fringing silicified 

zones (fig. 8)

Dickite Quartz + dickite ± pyrite Fringing silicification

Illite Quartz + illite + pyrite Fringing silicification and transitional to 

propylitic alteration

Kaolinite Quartz + kaolinite ± pyrite ± alunite Fringing silicification

Pyrophyllite Quartz + pyrophyllite + pyrite ± alunite Vug-filling and fringing silicification

Montmorillonite Montmorillonite/smectite + pyrite ± 

chlorite ± calcite

Recessively weathering, argillic and 

propylitic alteration

Halloysite Halloysite ± pyrite Late fault zone; hydrothermal breccia 

matrix

Montmorillonite ± 

dickite

Montmorillonite/smectite ± dickite + 

hematite

Late Fe-rich clay-filled fracture and fault 

zones cutting vuggy silica 1

Mineral assemblages defined on the basis of hand specimen identification, PIMA analyses, and limited petrographic study. 

Nearly all samples probably had pyrite, but pyrite is oxidized in most samples.

Table 1. Hydrothermal alteration assemblages in the White River altered area defined by Portable Infrared Mineral Analyzer (PIMA) 

analyses.
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

48

Type Formation Where? Significance Metals LS or HS White River

Sinter From near-neutral pH 

hot springs

Only at surface Paleosurface, topographic 

(hydrologic) depression, focus of upflow

Var. As, Sb, 

Hg, Tl, (Au, Ag if flared vent)

LS only Not present

Residual silica 

(opaline)

Moderate leaching, 

pH ~2-3, 80-90 percent SiO2

In vadose zone Steam-heated origin, above 

paleowater table

Hg, unless 

overprint

LS or HS Scatter Creek 

quarry

Chalcedony horizon Silica remobilized 

from steam-heated zone; deep fluid may contribute to outflow

At water table, up 

to 1-2+ km from source

Paleowater table, may be 

distal from source

Hg if only 

steamheated, As, Sb, Au Ag, if deep fluid

LS or HS Superior quarry

Chalcedony veins, 

colloform bands; cryptocrystalline veins

From low-T 

fluid, colloids; 

recrystallized from gel

Shallow depth, <150 

m

<200°Cm rapidly cooling 

fluid, boiling at depth; 

cryptocrystalline at ~200°C

As, Sb, Se, Au, 

Ag

LS or late HS Widespread 

chalcedony veins and breccias

Quartz veins, vugs From cooling 

solution

>150 m >200°C Au, Ag, base 

metals

LS, late HS Superior quarry and 

in drill holes

Residual silica 

(vuggy quartz)

Extreme leaching at 

pH<2, >95 percent SiO2

Core of volcanichydrothermal 

system

Permeable core, principal host 

to high-sulfidation ores

Barren, or Cu, 

As, Au, Ag

HS only Widespread

Silicification From cooling water Surface to 500 m, 

massive <150 m depth

Shallow portion of system, 

pervasive flow

Trace Au, Ag LS, mid to late 

HS

Widespread

Abbreviations: LS, low sulfidation; HS, high sulfidation.

Table 2.

Types of silicic alteration in the White River altered area (modified from Hedenquist and others, 2000, table 4).
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

49
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

50
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

51
Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

52