Relation Between Natural Radioactivity in Sediment and Potential Heavy Mineral Enrichment on the Washington Continental Shelf

AN ABSTRACT OF THE THESIS OF

RONALD CARL SCHEIDT for the degree MASTER OF SCIENCE (Name) (Degree) in OCEANOGRAPHY presented on August 30, 1974 (Major department) (Date) Title: RELATION BETWEEN NATURAL RADIOACTIVITY IN

SEDIMENT AND POTENTIAL HEAVY MINERAL ENRICH-

MENT ON THE WASHINGTON CONTINENTAL SHELF Redacted for Privacy Abstract Approved:72 Norman H. Cutshall

Natural radionuclides may be indicators for dense mineral placers along marine shorelines.Relict beach and river deposits occur in continental shelf sediments. These deposits result from the reworking of beach sands by wave action during the Holocene Trans- gression. Some dense, resistant minerals associated with placer deposits are known to contain238Uand232Thactivities.Shelf sediments, enriched in heavy minerals, might be expected to be high in these natural radioactivities.The usefulness of natural radioactivity to locate and to map dense mineral deposits was therefore explored and relations between natural radioactivity in marine sediments and dense mineral content were established.

High40Kactivity in sediments was positively correlated significantly with high mud content. High230Thand232Thactivities were associated with fine, well-sorted sands and correlated very highly with the weight percent total heavy mineral sands in the sediment. These relations distinguish depositional environments as high in content and erosional environments as high in230Thand232Th content. Two areas of enrichment were found by radiometric mapping and by mineral analyses.Off Destruction Island, Washington, maximum 232 230Th and Th activities were found in 30 m water depth.Activity distribution and mineral enrichment were consistent with general northward transport of nearshore sediment. In 33 m water depth off Clatsop Spit, Oregon, the second enrichment area was found.The 232Th/230Th activity ratios. are different for these two areas. Probably the heavy minerals in these two areas are from different sources. Relation between Natural Radioactivity in Sediment and Potential Heavy Mineral Enrichment on the Washington Continental Shelf

by Ronald Carl Scheidt

A THESIS submitted to Oregon State University

in partial fulfillment of the requirements for the degree of Master of Science

June 1975 APPROVED:

Redacted for Privacy Research Associate in Oceanography in charge of major

Redacted for Privacy

of School of Oceanography

Redacted for Privacy

Dean of Graduate School

Date thesis is presentedAugust 30, 1974 Typed by Suelynn Williams for Ronald Carl Scheidt ACKNOWLEDGEMENTS

I would like to thank Dr. Norman Cutshall for his sponsorship and for his suggesting a major part of this investigation. I also wish to thank the Environmental Protection Agency, National Science Foundation and the Veterans Administration for their financial assistance while pursuing this work. Sample collection and instrumental analyses were accomplished under U. S. Atomic Energy Commission Contract AT(45-l)2227, Task Agreement 12.(RLO-2227-Tl2-52). I am grateful to the officers and crews of the R/V YAQUINA and R/V THOMPSON for their assistance in obtaining the marine sediments. I thank my colleague Vernon Johnson for his hours of discussion and for his many suggestions and observations. Finally, I thank my wife, Patricia, for unstinting support and encouragement, and my children for their patience, during the years of my graduate study and research. TABLE OF CONTENTS

IN TR ODUC TION 1 BACKGROUND 2 Holocene Stilistands and Relict Beaches 2 Geochemistry and Geochemical Balance of238U and 232Th Series 3 Uranium and Thorium Bearing Minerals 5 Minerals in Placer Deposits 9 Geology Adjacent to the Study Area 11 Oceanographic Conditions and Bathymetry of the Study Area 12 Previous Work 15 SAMPLING AND ANALYTICAL PROCEDURES 17 Collection of Samples 17 Sediment Analyses 17 General Treatment 17 Preparation of 238U and 232Th Standards 17 Radioanalysis of Shell Sediments 20 Sampling and Resolution Errors 20 Mineral Analysis 21 Texture Analysis 22 Magnetic Susceptibility and Mineralogy of a Selected Station 22 RESULTS AND DISCUSSION 24 Relations between Natural Radioactivity and Mineral Facies 24 232Th Activity and Total Heavy Mineral Sands 24 23OTh Activity and Total Heavy Mineral Sands 27 40K, Mud and Light Mineral Sands 30 230Th/40K Activity Ratio and Total Heavy Mineral Sands 32 23OTh and 232Th, and the 230Th/40K Activity Ratio and 232Th 35 Distribution of Natural Radioactivity and Total Heavy Mineral Sands and Sediment Textures on the Washington Continental Shell 38 Iistribution of 232Th Activity and Total Heavy Mineral Sands 38 Distribution of 40K Activity and Sediment Textures 40 Mineralogy of Heavy Detrital Sands at 45 m off Destruction Island (T711OEE12) 42 TABLE OF CONTENTS (Continued)

CONCLUSIONS 46 BIBLIOGRAPHY 48 APPENDIX I Station Numbers, Sample Locations and Water Depths 52 APPENDIX U Thorium- 232, Thorium- 230 and Potas sium- 40 Content in Sediment on the Washington and Northern Oregon Continental Shelf 54 APPENDIX IllWeight Percent Mud, Light Mineral Sands, Heavy Magnetic Mineral Sands, and Heavy Mineral Sands in Sediment on the Washington and Northern Oregon Continental Shelf 59 APPENDIX IVSize Analyses of Sediment from Cape Alava to Tillarnook Head 61 APPENDIX V Procedure for Cleaning Marine Sediments 62 APPENDIX VIMagnetic Susceptibility Fractions, and Quantitative and Qualitative Mineralogy of Each Fraction of the Heavy Mineral Sands from T711OEE12 63 APPENDIX VU Correlation Coefficients at the 5% and 1% Level of Significance 64 LIST OF TABLES

Table Page

1 Concentration of some natural radionuclides in the sea. 6

2 Uranium and thorium in minerals in igneous rocks. 8

3 Stability of minerals under weathering conditions. 7

4 Resistant minerals commonly found in placer deposits. 10

5 Statistical evaluation of counting, fitting and sampling errors. 21 LIST OF FIGURES

Figure Page

1 Geochemistry and geochemical balance of 8U and 232Th, and some of their daughters. 4

2 Diagrammatic representation of hydraulic equivalence of the commoner accessory heavy minerals. 11

3 Relationship of volcanic rocks to associated drainage patterns of the Pacific Northwest. 13

4 Sampling stations on the Washington and northern Oregon continental shelf. 18

5 Relation between232Thactivity and total heavy mineral sands. 25

6 Relation between232Thactivity and mud. 28

7 Relation between230Thactivity and total heavy mineral sands. 29

8 Relation between230Thactivity and mud. 31

9 Relations between40Kactivity and mud and light mineral sands. 33

10 Relation between230Th/40Kactivity ratio and total heavy mineral sands. 34 230 232 ha Relation between Th activity and Th activity. 36 llb Relation between230Th/40 K activity ratio and 232Th activity. 37 232 12 Distribution of Th activity in marine sediments on the Washington and northern Oregon continental shelf. 39 LIST OF FIGURES (Continued)

Figure Page

13 Distribution of total heavy mineral sands in marine sediments on the Washington and northern Oregon continental shelf. 41

14 Distribution of activity in marine sediments on the Washington and northern Oregon continental shelf. 43

15 Mean particle diameters on the Washington and northern Oregon continental shelf. 44 RELATION BETWEEN NATURAL RADIOACTIVITY IN SEDIMENT AND POTENTIAL HEAVY MINERAL ENRICHMENT ON THE WASHINGTON CONTINENTAL SHELF

INTRODUCTION

The coastal zone is a unique mineral province.Perhaps the most accessible mineral deposits in this province are the dense mineral placer deposits found on exposed beaches and accumulations associated with submerged relict beaches.Both types of placers are accumulated by winnowing of light (low density) minerals away from heavy (higher density) metal-bearing minerals by waves and currents. Terrestrial geochemical and geophysical prospecting techniques, such as seismic profiling, magnetometer survey profiling and gravity survey profiling, have been adapted to mineral resource assessment on the continental shelf.Radiometric techniques have proven successful in locating terrestrial placer deposits and uranium-bearing sedimentary rocks (Heinrich, 1958; Seigel, 1968). The present work explores the usefulness of natural radioactivity for locating and mapping submerged dense mineral deposits on the Washington continental shelf and investigates the relation between natural radioactivity and dense mineral content in marine sediments. 2

BACKGR OU ND

Holocene Stilistands and Relict Beaches

Sea level fluctuations during the Quaternary have had a marked effect on geomorphology and sediments of the continental shelves. Sufficiently reliable data are available to determine times and magni- tudes of these fluctuations from the last 20, 000 years. The stilistand of sea level that occurred between 20, 000 and 17, 000 years before the present was at a present water depth of 120 m (Curray,. 1965). Between 17, 000 and 7, 000 years before the present there appears to have been a rapid transgression (Holocene Transgression) of the sea. It has also been postulated that minor regressions occurred during the Holocene Transgression and several submerged shorelines might be present between 120 m and the present-day shoreline. Beaches may have formed during these minor regressions. At each sea level lowering, coastal streams cut channels across the continental shelf to the new shoreline.Beach and stream deposits were submerged during the final stage of the Holocene Transgression. Should proper concentrating conditions have existed off-shore and there have been an adjacent source of dense minerals, relict beach and stream placer deposits might be expected. 3 Geochemistry and Geochemical Balance of238Uand232ThSeries

There are several sources of natural radioactivity.Rivers transport dissolved and mineral-borne radionuclides. Geochemical balances for uranium(238U)and thorium(232Th),and some of their daughter radionuclides, are shown in Figure 1 (Koczy, 1956; Koczy etal., 1957).The values in the figure represent fluxes, expressed as g/cm2 /yr. The uranyl ion(UO2++)is very soluble, whereas the uranous ion(13+4)is easily precipitated in seawater. Carbonate ions in seawater strongly complex uranyl ions and prevent precipitation. A dissociation constant of 10-10has been proposed for the uranyl carbonate complex (UO2)(CO3)2 (Rogers and Adams, 1969b). Uranium is known to be adsorbed on clays, the amount adsorbed being proportional to the base exchange capacity of the clay (Rogers and Adams, 1969b). Thorium presents a different situation.It occurs in nature only as the tetravalent ion and is closely associated with potassium in a wide variety of rocks (Rogers and Adams, 1969a).Slightly basic solutions hydrolyze thorium to an oxide or hydroxide precipitate. For this reason thorium is insoluble in seawater; the solubility product of Th(OH)4 is approximatelyio.42. Radium daughters of238U and232Th are relatively soluble in seawater. The solubility product for RaSO4is 4.25 x10_li(Kirby and Salutsky, 1964).Reported concentrations in seawater are so low 230Th 222Rn \\ \\8x/o9 238u "N 230Th 1.6 x/O' 7u10"r226R0 Iz/O 222Rn - ... : SEAWATER p206Pb \ 2U \. 2U+230Th 20°Th ,226Raizz6R'J t::::::::::;:::::::::::::::::;:::::::::::: ,222Ri -...222Rn - +206Pb 232Th /01' \\ \\8t . . 232Th 228Ra 1228Th ,224Ra . SEAWATER ii, "\\232Th 232Th.....+228J p228Th228Th ,224Ro,224Ro - ... 208Pb t GainLoss bythrough toprecipitation. surface river sedimentinput. 4 Loss by radioactive decay. fromGain surfaceto seawater sediment. by dissolution Gainanddiffusion to subsurface seawater from bysurface Figure 1. Gainsubsurface by diffusion sediment. fromGeochemistry(modified from and Koczy,geochemical 1956; balanceKoczy etal.,of 1957). ' : fromGain seawater.to atmosphere by diffusion 238 U and 232 Th, and some of their daughters sediments. 5 that the solubility product is not exceeded.It has been proposed that fifty percent of soluble r dium-228 (228Ra) is due to river input and the remaining fifty percent is due to diffusion fromnearshore and continental shelf and rise sediments (Moore, 1969a, 1969b). Decay modes for238U and232Th, their daughters, and potas- siurn-40(40K)and their estimated concentrations in seawater and surface sediment are given in Table 1. Uranium-235 is also included in the table even though its contribution to total radioactivity is insignificant.

Uranium and Thorium Bearing Minerals

Uranium and thorium occur in a variety of minerals in igneous rocks, but generally are concentrated in a few species of minor abundance. Where uranium is present in major minerals such as quartz and the feldspars and where thorium occurs in epidote or potassium feldapars, their mode of occurrence is uncertain, but the following possibilities might be considered:(1) isomorphous sub- stitution in the lattice,(2) concentration in lattice defects, (3) adsorp- tion along crystal imperfections and grain boundaries, and (4) inclusion as microcrystals (Rogers and Adams, [969a, 1969b).In accessory minerals uranium(U+4)and thorium(Th+4)are isomorphous with zirconium (Zr), rare-earth elements, calcium (Ca) and ferrous iron(Fe+Z)(Heinrich, 1958).Various major and accessory Table 1.Concentration of some natural radionudlides in the sea (Joseph etal. , 1971).

Mode Estimated concentration Radio- of I seawater surface sediment Nuclide element - Half-life decay I fe/U (PCiIg)

Thorium Series (4n)

232Th Th l.42x10'°y a l.0x1040 5.0z106 0.54 228 Ra MeTh1 6.7y 1.4 x 2.3 x l0 0.54 228 -20 Ac MaTh2 6.13 h 1.5 x10 2.4 xio.19 0.54 228 -17 -16 Th RdTh 1 91y <4OxlO 7 OxIO 0.58 224 -20 -18 Ra ThX 3.64 d a 2.1 xlO 3.4x10 0.54 220 -24 -22 Rn Tn 51.5s a 3,3x10 5.4x10 216 . -26 -24 Po ThA 0.158s a 1.OxlO 1.7x10 212Pb ThB 10.6h 2.4x102' 3.9x10'9 0.54 -22 -24 212B1 1-ThC 60.5 m ,a 2.2 x10 3.7 x 10 0.54 212 -32 -2 Po33.7% ThC'-13 04x10 5 a 1 2x10 2.4x10 208,. -24 -22 L___...ThC,I100% 3. 10 m 4. 1 x10 6.7 x 10 0. 19 208Pb W Stable

Uranium Series (4n + 2)

238U UI 4.49x109y a 3.0x106 1.OxlO6 0.33 234 UX1 24.1 d 4.3x1017 1.4x1017 0.32 234Pa UX2 1.14m 1.4x10'9 4.3x1022 0.30 UU 2.48 x 105y a 1.9 x10° 6.2 x10' 0.38 23°Th lo 7.52x104y a <3.OxlO'3 2.OxlO'° 4.14 226Ra Ra l.622x103y a 1.0x1013 4.OxlO'2 3.91 222Rn Rn 3.823 d a 6.3 x 2.5 x 3.85 2l8, RaA 3.OSna a 3.4x1022 1.4x102° 3.95 RaB 26.8 m 2.9 xlO21 1.2x1O9 3.92 214Bi RaC 19.7 m 2.1 x1021 8.8 x10° 392 214Po RaC' 1.64x104a a 3.0x1028 1.1 x1027 210Pb RaD 19.4y 1.1 xlO15 4.5x1044 3.93 210Bi RaE 5.01 d 7.8x109 3.1 x1047 210Po RaF 138.4d a 2.2x1047 8.8x1016 3.95 206Pb RaG Stable

Actinium Series (4n+3)

AcU 7.13 x108y a 2.1 xio8 7.1 x l0 0.02

40K 1.25x109y E.C.4.7x105 (0.8-4.5)x106 5.73-32 7 minerals in igneous rocks, reported to contain uranium and thorium, and the concentration ranges in these minerals are shown in Table 2. Although uranium and thorium begin their geochemical life together in lithospheric rocks, they soon are separated. Thorium remains with its original minerals which are resistates. Uranium, as the uranyl ion, becomes soluble and can combine with other ions to form authigenic minerals (Heinrich, 1958). During weathering not all resistant minerals will persist. Stability of some accessory minerals has been investigated and the results are given in Table 3.The stability is somehow related to the mineral hardness (Pettijohn, 1949).The stability index shows

Table 3.Stability of minerals under weathering conditions (Dryden and Dryden,1946). b b Stability Density Hardness Mineral Indexa (g/cc) (Moh) Zircon 100 4.6-4.7 7 TourmalineC 80(?) 3.0-3.2 7 Sillimanite 40 3. 2 7 Monazite 40 4.6-5.4 5-5k Chloritoidsc 20(?) 3.5-3.6 6 Kyanite 7 3.6 4-7 Hornblende 5 3.0-3.4 6 Staurolite 3 3.7-3.8 7 Garnet 1 3.6-4.3 7-7f Hypersthene l(?) 3.4-3.5 5-6 aG taken as 1. 0. bData from Berry and Mason, 1959. CEstimatesonly, no data available. 8

Table 2.Uranium and thorium in minerals in igneous rocks (Adams et al.,1959; Clark et al.,1966; Rogers and Adams, 1969a,1969b).

Th U Mineral (ppm) (ppm) Th/U Major minerals Biotite 0.5-50 1-60 0.5-3.0 Hornblende 5-50 0.2-60 2-4 Potassium Feldspar 3-7 0.2-3. 0 2-6 Muscovite 2-8 Olivine (from dunite) 0.02 0.05 Plagioclase 0.5-3.0 0.2-50 1-5 Pyroxene 2-25 0.1-50 4-5 Quartz 0.5-10 0.1-10 2-5 (in beach sands) 2. 0 0.7 3 Accessory minerals Allanite(average) 500-5000 30-700 5-10 (in pegmatites) 1000-20,000 ?-100 high Apatite(average) 20-150 5-150 1 (in coarse aggregates) 50-250 (?) 10-50 (?) 10-25 Epidote 50-500 20-50 2-6 Garnet 6-30 Huttonite nearly pu1eThSiO4 Ilimenite 1-50 Magnetite 0.3-20 1-30 variable Mona zi t e 25,000-200,000 500-3000 25-50 Sphene (Titanite) 100-600 100-700 1-2 Thorianite and varies from Th02 to UO2 U raninite Thorite and varies from ThSiO4 to USiO4 U ranotho rite Xenotime low 500-35, 000 low Zircon(average) 100-2500 300-3000 0.2-1 (in pegmatites) 50-4000 100-6000 1 zircon and monazite to be very resistant.These two accessory minerals are of moderately high density and might be expected in marine placer deposits if adjacent continental rocks contain them.

Minerals in Placer Deposits

A wide variety of minerals are found in placer deposits.Table 4 lists the resistant minerals commonly found.It should not be con- strued that all placer deposits will contain these minerals as a suite nor that all placer deposits are highly radioactive.Again, source rock and mineral stability play an important role in determining which minerals will form a suite.Deposits that contain appreciable magnetite, chromite and/or ilmenite are often termed "black sands". Hydraulic equivalence also plays an important role in selective sorting and determines what minerals will remain to form placer deposits in erosional environments. Features which determine hydraulic equivalence of minerals are effective density, size and habit.Heavier minerals will generally be smaller than lighter minerals. For example, if zircon, quartz and muscovite are compared in terms of hydraulic equivalence, zircon will be smallest, quartz will be intermediate and muscovite will be largest. Should changes occur in current velocity in a transporting medium or in wave energy, there will be changes in average size and shape and a change in ranges of size and shape. A pair of minerals with the same density and habit should react 10

Table 4.Resistant minerals commonly found in placer deposit. (data tabulated from Berry and Mason, 1959).

Mineral Composition Density Comment Thorium and Uranium Bearing Minerals Apatite Ca5(PO4)3(F, Cl,OH) 3.1-3.2 U impurity common. Epidote Ca2(A1,Fe)3Si3O12(OH) 3.3-3.6 Th and U impurities common. Monazite (Ce,La,Y,Th)PO4 4.6-5.4 Major source of Ce and Tb. Sphene CaTiSiO5 3. 5 U and Th impurities common. Thorite ThS104 6. 7 Potential source of Tb for reactors. Zircon ZrSIO4 4. 6-4.7 Source of Zr and Hf. Other Dense Minerals of Economic Importance

Andalusite Al2SiO5 3. 2 Used in rnullite refractorie s. Cassiterite SnO2 6. 9 Source of Sn, Chromite (Mg.Fe)Cr204 5.1 Source of Cr. Columbite (Fe,Mn)Nb206 5. 2 Source of Nb. Corumdum A1203 4. 0-4. 1 Used as abrasive. Diamond 3. 5 Found in Africa. Garnet (Ca,Mg,Fe,Mn)3(A1,Fe, Cr)(SiO4)3 3.6-4.3 Used as abrasive. Gold Au 19. 3 Found in Alaska, Calif.Ore.and Wash, sands. Ilmenite FeTIO3 4.7 Source of Ti. Magnetite Fe304 5. 2 Source of Fe. Platinum Pt 14-19 Found in Alaska, Calif., Ore. , and Wash, sands. Rutile Ti02 4. 3 Source of Ti. Tantalite (Fe,Mn)Ta2O6 7.9 Source of Ta. Topaz Al2S1O4(OH, F)2 3. 5-3.6 Gemstone. Major Minerals Biotite K(Mg,Fe)2(A1S13010)(OH)2 2.8-3.4 Feldspars (Na,K, Ca)(Al,Si)A151208 2.6-2.8 Used in ceramics. Ferromagne sium minerals Fe,Mg Silicates 3.0-3.5 Olivine used in refractory bricks. Muscovite KAl2(A1Si3O10)(OH)2 2.8-2.9 Used for electrical insulation and capacitors. Quartz SiO 2. 66 Most common in 2 sands. 11 similarly under the same hydraulic conditions.If they differ in either density or habit, they should react differently.The commoner accessory heavy minerals in sediments are classified on the basis of density and habit (Figure 2).

Habit Aciculor

Gypsum lllSuhimonhte Apotte Rutule11111 IllllIZircon Tourmaline Prismatic Cordierite LIIIIIIIUIJAmphibole IIIIuuIuIIuIuuuuIIIIuIjlmenite Titonite Pyrosene Feldspar Monoztite Staurolite 1111111111111 , Epido;edllfi I Leucoxene11111.uuuuuuuuI1uuul1111u111n11111111 Caicutei Titanite Quortz WLimonite Mognetite Equant = FIuor IIIIiiiIIiiiiliIHhlHlI ,uuuuuuIIIuuu inn. urn.Gornet . Pyrite Glouconite Spinel Feldspar 11111Anotose

Tabular Borite Kyonite Andalusitem Brookite Hematite 1W 11111 -..- Chlorite 0 Topaz Platy Biotite . = Chloritoid mu Muscovite wlMontmorullonte Diaspore 11kaolinite

Density 2.0 25 3.0 3.5 4,0 45 50 5.5

Figure 2.Diagrammatic presentation of hydraulic equivalence of the commoner accessory heavy minerals (from Griffiths, 1967).

Geology Adjacent to the Study Area

Physiographic divisions adjacent to the study area have been termed the Pacific Border Province (Fenneman, 1931).This province consists of north-south tending valleys bounded to the east and west by mountain chains.The valleys form the Puget Trough (Fenneman, 1931) which contains the Puget Basin to the north and the Willamette 12 Valley to the south. The Puget Trough is bounded on the east by the Cascade Mountains and on the west by the Coast Ranges. The Coast Ranges consist of the Olympic Mountains in Washington, the Oregon Coast Range in northern Oregon and the Klamath Mountains in southern Oregon. The Coast Ranges are characterized by cliffs which show evidence of an eroding coastline (Campbell, 1962).Terraces are also common on the coast.These terraces suggest that the coastline has risen in recent geologic time (Dickens, 1961). Basaltic rocks of the Pacific Border Province have been investigated and basaltic types differentiated by mineral suites (Waters, 1962). The relation between volcanic rocks and associated drainage patterns is shown in Figure 3.

Oceanographic Conditions and Bathymetry of the Study Area

Well seaward of the Washington-Oregon coast is the south setting, slow moving California Current. During winter months the north-setting Davidson Countercurrent develops and runs north to about 48° N latitude.This countercurrent is found at all depths on the coastal side of the California Current.In spring and summer, when upwelling takes place, it disappears in the surface layer (Sverdrup etal., 1942). 124° 22° I 120° I 118° 116° r -, 'I Lrj' . ) W4SIJ1Ør COLUMBIA ? .r V J LP ,ø4) / > ' "N. ( i QUATERNARY COPAUS HEAD Y/'SEATTLE). \ç-\ \\ -2m /// SPOKANE l PLIOCENELarqe Andesite TO RECENTCones TILLACOLUMBIA NOOK 8W/rt77//,Ø :A' Olivins Basalt ( 7i!'///1Y// MIOCENE JII Columbia River Basalt i huh 2 ______AndesiteUPPER EOCENE Comples TO LONER PtJOCENE 4 GENETZ I EOCENE TO LOWER OLIGOCENE LJ 10 fr lI1IIl!iiIIhiII 110 _ir)' .... BURNS - - - .. "-t- OREGON 0 STATUTE 50 MILES 00 Figure 3. 1240 I northwestRelationshipCALIFORNIA (Waters, of volcanic 1962, rocks modified to associated by-&n Ballard, drainage 1964). patterns of the122° PacificI . 20°I 0 118° KILOMETERS 80 60 1160 14 Winds off the Washington-Oregon coast are seasonal. Wind direction is from the north and northwest in the summer and from the southwest and southeast in the winter (Cooper, 1958).Waves generated by these winds move in the same general direction which results in seasonal reversal of the littoral drift. Littoral drift is a most important process acting to transport sand in the nearshore region. Seaward of the drift, where muds are deposited, ocean currents are the dominant forces transporting suspended sediment. There is a persistent northward-setting near-bottom current on the central continental shelf off Washington during the winter (Gross etal., 1969)with the result that net movement of sediment discharging from rivers, especially the Columbia River, is to the north (Gross, 1966; Gross and Nelson, 1966). The continental shelf is narrow and steep with a seaward limit of 144 m north of Astoria Canyon. South of the canyon the limit is between 162 m and 180 m (Byrne, 1963).South of the Columbia River (450 55' N to 46° 15' N) the shelf slope is steepest between 18 m and 90 m, Between 90 m and 180 m the slope is less steep, but general bathymetry is variable, with bank-like shoals, depressions and small submarine canyons. North of the Columbia River to the Straits of Juan de Fuca the shelf is uniform and only a few features such as shoals and depressions are found, but several canyons do intrude into the shelf. 15 Previous Work

Several workers have investigated heavy mineral concentrations on beaches and in continental shelf sediments. South of CapeFlattery, at Shi Shi beach, wave-cut terraces containing black sands yielded $15, 000 in gold in 1904 (Pardee, 1927),Heavy mineral content in beach sands from Tillamook head to the north spit of Grays Harbor has been studied (Ballard, 1964). Maximum enrichments of non-opaque heavy minerals occur immediately north of Grays Harbor, Willapa Bay and the Columbia River. These enrichments probably reflect local sources which have been winnowed by winter storm waves approaching the shoreline from the southwest. Mineral and size analyses of shelf sediments from the Columbia River to Cape Blanco suggest that much of the inner-shelf sand (water depths 100 m or less) is probably relict sand deposited during the last transgression. Modern sands are probably confined to water depths no greater than 18 m (Runge, 1966), White (1967) investigated shelf sediments from the north head of Willapa Bay to Tillamook Head, examining the mineralogy, geochemistry, distribution and occurrence of total heavy minerals (opaque and non-opaque minerals) and general petrology.The object was to delineate relict marine environments around the Columbia River and to map formation areas of authigenic glauconite. Continental shelf sediments are suspected to contain relict beach and river placer deposits.The shelf sands were reworked during several sea level stilistands and regressions in the Holocene Transgression. Wave action winnowed light minerals from heavy minerals, concentrating fine-grained heavy resistates. Some of these resistant minerals are known to bear andZ3ZTh.Investigations of shelf sediments and modern beach sands indicate that several of these radioactive minerals are present, but no efforts have been made to measure the natural radioactivity in these sediments and sands. This work explores the proposal that natural radioactivity can be used to locate and map submerged potential heavy mineral deposits on the Washington continental shelf. 17

SAMPLING AND ANALYTICAL PROCEDURES

Collection of Samples

Surface sediment samples were collected on cruises of the R/V YAQUINA (Oregon State University) and the R/V THOMAS G. THOMPSON (University of Washington) using a Smith-McIntyre grab sampler (Smith and McIntyre, 1954).Fifty-five samples were collected from. Cape Alava to Tillamook Head in water depths ranging from 20 m to 200 m. Sample locations are shown in Figure 4 and cruise and station numbers, latitude, longitude and water depths, are listed in Appendix I.

Sediment Analyses

General Treatment

Sediment samples were air dried in aluminum trays.Clayey samples were broken up by rolling a soft wooden dowel over them. All dried sediments were placed in plastic bags, homogenized and subsampled for radioanalysis, for heavy mineral content and for texture analysis.

Preparation of238Uand232ThGamma-ray Standards

A232Thstandard was prepared by dispersing monazite sand ii Cape Alova

48°N .. .

Destruction Is. * W4 SHING TO/V

Raft River : .

Grays Harbor S I' .. 470

Willapa Bay 5, $

.Columbio Cape Disappointment River Clatsop Spit

46° Tillamook Head ' .. OREGON

126°W 125° 124° 123°

Figure 4.Sampling stations on the Washington and northern Oregon continental shelf. 19 within sugar in a capped polypropylene counting tube.The tube was 17 mm x 95 mm and the sugar and monazite occupied 12 cc.This insured that the standard counting geometry was the same as the counting geometry of the sediments to be analyzed. A standard for

238Uplus daughters, was prepared by dispersing powdered high- grade uranium ore in sugar. Each standard was counted for 10 mm in a 5-in x 5-in Naj(Tl) crystal well detector.The detector was interfaced to a Nuclear Data multichannel analyzers in which 256 channels were used to collect and store the y -ray spectrum. Measurements of short-lived daughter activity levels were used to calculate concentrations of long-lived parents. Concentrations were calculated by determining the area under the appropriatephoto- peaks (Covell, 1959), by using available nuclear data (Lederer etal., 1967) and by using the intrinsic efficiency curve for the detector (Heath, 1964).Thorium-232 was determined by using the 0.239 Mev 212Pbphotopeak and the 0.3385 Mev228Acphotopeak.The 0.187 Mev 226Ra photopeak was used to determine238U.This photopeak is complicated by the presence of235U with the238U. As a result, 230 238 values measured for Th ( U) may not be quantitative.However, this does not affect the precision of the data nor the correlations derived from the data. 20

Radioanalysis of Shelf Sediments

Sufficient sediment from each station was packed in counting tubes to give a 12 cc occupied volume. Net sediment weights were obtained and the samples counted for 400 mm in the well detector.

The' -ray spectra were carefully examined toinsure that no gain shifts or base-line shifts occurred during the counting interval. The spectra were plotted by an X-Y plotter and the digital data punched on paper tapes. 238 232 40 Sediment spectra were resolved for U, Th and K by least- squares analyses, using' the Gamma Program (Frederick, 230 232 40 1967).Results for Th, Th andK analyses, at lo counting and fitting level, are given in Appendix U. Concentrations reported are picocuries per gram of dry sediment(pCi/g).Note that230Th, rather than238U,is reported in Appendix II.Thorium-230 may or may not be in equilibrium with its predecessor,238U.

Sampling and Resolution Errors

Counting and spectrum-fitting errors and sampling method errors were determined by analyzing eight subsamples from one station (Y7208B27). The statistical results are given in Table 5. Pooled deviations were c1culated from the icr counting and fitting errors. The F-test shows that no significant errors are being 21 introduced by sampling techniques.

Table 5.Statistical evaluation of counting, fitting and sampling errors.

230Th 232Th

Mean (x) 1.26 1 . 74 6.94 Standard Deviation (a-) 0.05 0.06 0.49 Standard Error (a-) 0.02 0.02 0.17 Pooled Deviations'(o- ) 0.09 0.08 1 . 03 F-test (cr/a- ) 3.29 1 . 79 4.24 F-test (5% level) 3. 79 F-test (1% level) 7.00

Mineral Analysis

Thirty-five stations were subsampled for mineral analyses. Each station was wet-sieved on a 6 1iJ sieve and the difference between original sample weight and the weight dry mineral sands retained by the sieve was considered mud (<6lii).The sand fractions (>6lFi) were transferred to 125 ml separatory funnels containing 1, 1,2, 2, -tetra- bromoethane (Sp. Gr. = 2.96 g/cc).The mineral sands were allowed to separate into light and heavy mineral fractions.Both fractions were filtered, thoroughly washed with acetone, driedand weighed. The heavy mineral fractions were further processed by passing a hand magnet, held at 10 mm, over the minerals.This procedure removed the opaque magnetic minerals. Weight percents of the four fractions (mud, light mineral sands, magnetic heavy mineral sands 22 and non-opaque heavy-mineral sands) for each station analyzed are given in Appendix III.

Texture Analysis

Twenty-four stations were subsampled for texture analyses. The analyses were done by hand-sieving dried sediment through a tier of 8-in Tyler standard sieves.The retained sediment on each sieve was weighed and mean-O, median-O, sorting and skewness parameters were calculated (Shepard, 1963).Sieve sizes used in the analyses were 2.362mm (-1.250),0.991 mm (0.000),0.495mm

(1.030) 0.246mm (2.050)'0. 124 mm (3.000) 0.061mm (4.100) and Pan (<4. 1 00). Size analysis data are tabulated in Appendix IV.

Magnetic Susceptibility and Mineralogy of a Selected Station

Station T711OEE12, on the Destruction Islandtransect, was analyzed in further detail. A subsample was wet-sieved on a 6lii. sieve. The dry mineral sands were separated into a light and heavy fraction by density difference.The heavy mineral sands were treated to remove organic material, carbonates, hydrous oxide coatings and aluminum oxide coatings.Details on this cleaning procedure are given in Appendix V. The cleaned, heavy mineral sands were passed through a 23 Frantz Isodynamic Magnetic Separator and separated into eleven susceptibility groups (Bowen, 1972).Grain mounts of ten susceptibility groups were prepared for quantitative and qualitative identifi- cation with a petrographic microscope. The mounting medium was Aroclor 4465 (refractive index = 1. 66), manufactured by Monsanto. The results of magnetic separation, qualitative mineralogy on ten susceptibility groups and quantitative non-opaque mineralogy on four susceptibility groups are in Appendix VI. 24

RESULTS AND DISCUSSION

Analytical results were statistically reduced by regression analysis.To compare the significance of the correlation coefficients (r) for the data, for a given sample size (ii), expected correlation coefficients at the 5% and 1% significance levels are given in

Appendix VU.

R elations betwe en Natural Radioactivity and Mineral Facies

232ThActivity and Total Heavy Mineral Sands

The relation between232Thand percent of total heavy mineral sands is shown in Figure 5.Total heavy mineral sands are the combined percents heavy magnetic and non-opaque heavy sand fractions.The rationale is that both mineral fractions are232Th-bearers (see Table 2).Two regression lines are shown.One line shows the results from Cape Alava to Cape Disappointment off the Columbia River. The other line includes all data from Cape Alava to Tillamook Head. Regression lines were calculated by regressing232Thactivity on weight percent total heavy mineral sands. The correlation coefficient between232Thand total heavy mineral content in the sediment is statistically significant for stations to Cape Disappointment (r0. 72, n = 31), as well as, for stations to K Figure 5. Relationn=35.Cape Alava between to Cape Disappointment, r = 0.72, n = 31. Curve (b): 0 232Th TOTAL HEAVY MINERAL SNVDS(T. H. M5), percent by weightactivity and total heavy mineral sands. CurvetO (a): 20 30 40 all stations, r = 0.86, stations50 from 26

Tjllamook Head (r = 0. 86, n = 35).However, the slopes for the two curves are different. One possible explanation for the slope difference is source rock provenance. North of the Columbia River shelf sediments are derived from Columbia River basalt in the Columbia Plateau, olivine basalt and andesite complexes in the Cascade Range and Eocene basalt (tholeiitic pillow basalt) in the Olympic Mountains (Waters, 1962). The Cordilleran Glacier also rafted vast quantities of material from British Columbia into the area.One tongue of the glacier moved through the Puget Basin. The other tongue passed through the Straits of Juan de Fuca, moved southward and deposited material on the shelf and on Mount Olympus (Campbell, 1962).Glacially rafted material is particularly evident in sediment in 190 m off Destruction Island.The sediment is unsorted and consists of sand and striated cobble.South of the Columbia River the shelf sediments are princi- pally derived from Eocene basalt in the Oregon Coast Range (Waters, 1962 and Figure 3). Besides source rock differences, mineral stability is another factor to consider.Minerals transported by the Willamette and Columbia Rivers are subject to longer abrasive action than are minerals derived from adjacent coastal sources.This could lead to variations in mineralogy and mineral sizes.Finally, hydraulic sorting by wave action would further change the character of the 27 original mineral suite deposited. The intercepts or the two curves can be interpreted as232Tb in resistant minerals less than 6land/or adsorbed on clays. A plot of232Thactivity against the percent of mud results in a bimodal distribution.Thorium-232 concentration is essentially constant for samples with greater than 10% mud (Figure 6).It would then appear that the intercepts are due to232Thactivity in fine resistant minerals.

230ThActivity and Total Heavy Mineral Sands

The relation between230Thactivity and total heavy mineral sands is graphically presented in Figure 7.The correlation coefficients for data from Cape Alava to Cape Disappointment (r = 0. 56, n = 31) and for data from Cape Maya to Tillamook Head (r 0. 75, n = 35) are statistically significant.However, the degree of significance is not as great as for the relation between232Thactivity and total heavy mineral sands.The intercept and slope for Cape Alava to Cape Disappointment are not significantly (90% confidence level) different from the intercept and slope for Cape Alava to Tillamook Head. The lack of variation in the slopes and intercepts might possibly be explained by238U-seriesgeochemistry and by mud distribution on the continental shelf.Many uranium-bearing minerals are easily weathered, with the result that uranium is oxidized to the uranyl ion. Uranium is soluble in seawater as the uranyl carbonate complex. S 3. 232Th Act. 0.37 + 0.0005 (wf. % MUD) c3 K 2. S 1.01- I. 2' S S S S S S S S S. 5 S S S S 0 Figure 6. Relation20 between MUD, percent by weight 40 232 Th activity and mud, r = 0. 17, n = 18. 60 80 100 I I I (a) 230Th(b) 230Th Act. Act. = 0.37 + 0.0197 (wt. % T.H.M.S.) 0.42 + 0.0l58(wt. % T.H.M.S.) (b) .0- S K (a) S S $ S . .5- S S . . I . S . Figure 7. r0.75,fromRelation Cape n35. Alavatobetween Cape Disappointment, r = 0.56, n = 31. Curve (b): To TA L HEAVY MINERAL S4NDS( T H.I M 5), percent by 230Thweight I activity and total heavy mineral sands. CurveI (a): all stations, stations 30 234 230 When U in seawater decays to Th, the daughter does not remain in seawater. Thorium has a high ionic potential and, as a result, 230Th forms highly insoluble hydroxides in seawater. Suspended clays readily adsorb the230Th.These suspensoids eventually settle in low energy regimes to form muddy sediments. Muds might then be expected to be high in230Th activity.This. possibility was explored further by plotting230Thactivity against the weight percent of mud. The230Th activity is. bimodal in distribution.The correlation coefft- dent for sediments with greater than 10% mud is significant (r0. 76, n = 18) and the graph is given in Figure 8.Sediments with less than 10% mud vary widely in230Thactivity; whereas, above 10% mud,

230Thactivity increases with increasing percent of mud. From these results, it is proposed that the intercepts are due to both mud adsorbed 230Th and very fine238U-bearing resistant,. detrital minerals.The presence of mud probably "damps out" variations in supported230Th activity in heavy mineral sands and would explain why the slopes are the same.

Mud and Light Mineral Sands

Many major minerals in igneous rock contain40Kand some supported230Th.Potassium feldspar and micas are usually high in The feldspars are easily weathered to other minerals with a resultant loss of potassium. Weathering of igneous rock produces 18. n 0.76, r mud, and activity Th 230 between Relation 8. Figure too 80 weight 00 by percent MUD, o. ('J cl. Kc) 32 clay minerals which have40Kadsorbed on their surfaces, bound in interstitial sites or bound chemically. Authigenic glauconite is particularly high in40Kactivity and is an example of chemically bound potassium. The correlation between40K and percent mud is more significant (r = 0.76, n = 35) than the relation between40Kand light mineral sands (r = 0,61, n = 35) (Figure 9).Since increase in mud content is accompanied by increase in40Kactivity, sediments with high40K activities may represent depositional environments, and sediments with low40Kactivities may reflect erosional conditions. Erosional environments also have high230Thand232Thactivities.

230Th/40KActivity Ratio and Total Heavy Mineral Sands

As the mud content increases in sediments,230Thand activities increase (Figures 8 and 9).If the230Thactivity is normalized to40Kactivity, this should diminish the influence of the230Th adsorbed component on the regression.Then,230Th/40 K activity ratios, plotted against the total heavy mineral sands should more accurately represent detrital mineral-radioactivity relationships (Figure 10). Normalization significantly improved the correlation forstations from Cape Alava to Cape Disappointment (r = 0.82, n = 31).Correlation between the230Th/40Kactivity ratios and total heavy mineral sands for stations from Cape ) LIGHT MINERAL SANDS (L.MS.), percent by weight20 40 60 80 100 (a) S 0 . 0 .1 S 0 - I I.- S 0 a:' 0 -I 0 H I ,b) 0 . .5. . 0 0 00 00 0 I 0 0 .1 (b)(a)40K °I< Act.Act. = 15.29 - 0.0869 (wt. % L.M.S.) 7.92 + 0.0869(wt: 0/ MUD) 20 MUD, percent by weight 40 60 80 100 Figure 9. nstations,Relations = 35. rbetween = 0.76, n = 35. Curve (b): 40 K activity and mud and light mineral sands. Curve .(a): mud, all light mineral sands, all stations, r 0.61, c3c3 O. - CS.j 0 10 20 30 40 50 Figure 10. TOTALRelationstations,stations HEAVY between from r MINERAL Cape 230Th/40K Alava SANDS to activityCape Disappointment,(T ratio H andM. total S.), heavy r = 0.82,percent mineral n = 31. sands. by Curveweight (a): 0.87, n = 35. Curve (b): all 35 Alava to Tillamook Head was also improved (r = 0.87, n = 35), but the improvement was not dramatic. No significant difference was found for the slopes or intercepts of the two lines.The intercept represents230Thactivity in very fine grained resistates.

230Thand232Th,and the230Th/40K Activity Ratio and 232Th

Data analyses show that230Th and232Th activities are highly correlated with the total heavy mineral sands in sediments. In resistant minerals230This supported by238Uand is associated with 232 232Th. Abundances of238U and Th in accessory resistant minerals are affected by such factors as variation in concentration in the original magma and in the magmatic crystallization history.

The association of230Thand232Thactivities in marine sediments is shown in Figure ha, b.The curves were determined by a method described by Imbrie (1956); the method makes no assumption 232 of independence. The relation between230Th activity and Th activity (Figure 1 la) is highly correlated for stations from Cape Alava to Cape Disappointment (r = 0.90, n47) and for stations from Cape

Alava to Tillamook Head (r = 0.90, n55).The difference in the slopes for the two curves can be explained by difference in source rock south of the Columbia River. At Clatsop Spit the232Th/230Th ratio for sediment containing 50% total heavy mineral sands is 2. 23. 36

I I I 1/

(a)°Th Act.' 0.17 + 0.6879e32Th Act.) (b) 230Th Act.' 0.25 0.4855( 232Th Act.) 5. / (a) (b)

.0- .

(.)

S I . S S S [I.:.5- .. . : S

'S. S

I I I I 0 1.0 2.0 3.0 232p ACTIVITY, pC//q

Figure ha. Relation between230Thactivity and232Thactivity. Curve (a):stations from Cape Alava to Cape Disappoint- ment, r = 0.90, n = 47.Curve (b):all stations, r = 0.90, n = 55.

L 37

I I I

30 Th Act. a) = -0.003 + 0.12l4(232Th Act.) 40K Act.

230Th Act. (b) 0.010 + 0.0876 ( 232Th Act.) K Act.

20 c3I (a) (b)

S S S

S I 4.. . . .5 .5

I I I I

0 1.0 2.0 3.0 232 ACT/V/TV, pC//g

230 40 232 Figure 1 lb.Relation between Th/ K activity ratio and Th activity.Curve (a):stations from Cape Alava to Cape Disappointment, r = O87, n = 47,Curve (b):all stations, r0.89, n = 55, The same ratio for sediments off Destruction Island, which contain 21.2% total heavy mineral sands, is 1.38.

In Figure 1 lb the230Thhas been normalized to40Kand the activity ratios plotted against232Th.The two curves tend to pass through the origin since the fine detrital component and adsorbed component are normalized. These curves describe the trends of natural radioactivity, as related to mineral facies, in marine sediments. As the230Th/40Kactivity ratio increases, the total heavy mineral sands increases (See Figure 10), the232Thactivity increases

(See Figure 5), the40Kactivity decreases and the weight percent light mineral sands increases (See Figure 9).High230Th/40 K activity ratios would imply erosional environments and low ratios would imply depositional environments.

Distribution of Natural Radioactivity and Total Heavy Mineral Sands and Sediment Textures on the Washington Continental Shelf

Distribution of232Th Activity and Total Heavy Mineral Sands

Spatial distribution of232Thactivity in shelf sediments from Cape Alava to Tillamook Head is shown in Figure 12.On each transect the general tendency is for232Thactivity to decrease with water depth. Maximum activity is found in water depths around 30 m, except at Cape Alava where the maximum is at 50 m and at Willapa Bay where /25° /24°

IVITY, pCi/g I.00 Figure 12. continentalDistribution shelf. of 232Th activity in marine sediments on the Washington and northern Oregon '0 40 it is at 60 m. At any given depth, north of Willapa Bay,232Th activity generally increases with latitude. Maximum activity occurs off Destruction Island. The activity is lower at 48° N and again increases at Cape Alava. Several lines of evidence suggest Holocene stilistands at water depths of 18, 29, 47, 102 and 150 m, with an accuracy of 5 m (Chambers, 1968).The highly radioactive sediments around 30 m and 50 m are probably exposed relict beach sands. 232 The distribution of230Th activity is similar to the Th distribution and is not shown. The relation between230Thand232Th can be found in Figure ha, b. Heavy mineral sand distribution on the continental shelf is shown in Figure 13.The sands have the same general trends in distribution as the232Th activities. Where232Th activity is high, the total heavy mineral sands are high.There is an exception on the Grays Harbor transect where the232Thactivity is low, but where heavy mineral sand content is high at 32 m water depth. Seaward at 54 m is rounded pea gravel, low in heavy mineral sands. The roundness of the gravel strongly suggests that they were river transported, possibly by the Chehalis River.

Distribution. . of40K Activity and Sediment Textures

Distribution of40Kactivity shows tendencies opposite to /25° /24° S,percent HEAVYby weight MtNERAL L0Ho120 Figure 13. northernDistribution Oregon of total continental heavy mineral shell. sands in marine sediments on the Washington and /25° 42 distribution of232Thactivity and heavy mineral sands. These trends are seen in Figure 14.Generally, high40K activity (over 10 pCilg) is found in areas high in mud content and low in heavy mineral sands. Activities between 5 pCi/g and 10 pCi/g are associated with sandy sediments. Sandy sediments, particularly those high in heavy minerals, are high in232Th. Sediment texture is closely related to40Kand232Thactivities. The mean-ø diameters of some shelf sediments are shown in Figure 15. From Cape Alava to Raft River, sediments are well-sorted, fine-grained sands out to 60 m water depth.The mean diameters are around 3.00and dispersions (sorting) <0.75. These sands are low 232 in40K activity and high in Th activity.The sediment on Grays Harbor transect is fine sand at 30 m, pea gravel at 54 m and fine sand at 100 m. Off Willapa Bay the sediment is fine, well-sorted sand at 27 m and poorly sorted mud at 54 m. Sediment off Cape Disappoint- ment is mud at 20 m and well-sorted fine sand at 79 m. These muds probably represent the beginning of the central dispersion line of Columbia River suspensoids. Sediments from Clatsop Spit to Tilla- mook Head are very well-sorted, fine sand to depths of 95 m.

Mineralogy of Heavy Detrital Sands at 45 m off Destruction Island (T711OEE12)

The Washington continental shelf off Destruction Island .s unique /25° /24° ITY, pCi/g 120L0 Figure 14. continentalDistribution shelf. of 40K activity in marine sediments on the Washington and northern Oregon /25° /25° /24° AMETER,PARTICLE M0 Figure 15. Mean particle diameters on the Washington and northern Oregon continental shelf. /25° 45 in its natural radioactivity and heavy mineralenrichment. Separation of heavy mineral sands by magnetic susceptibility showsthat 72%, by weight, of the minerals are in the range of 8 to129 xio6cgs units and that 6. 7% of the minerals are magnetite.Maximum non-opaque minerals are in the 32 to 41 x106cgs unit fraction and arecomprised of nearly equal quantities of amphiboles, garnets and pyroxenesand a trace of epidote. The non-magnetic fraction (0 to 1.55 x1O6cgs units) is particularly interesting.This fraction comprises 5. 1 %, by weight, of the heavy mineral sands and consists of 24% non-opaqueminerals. How- ever, th nbn-bkau minrals are 70. 3% ircon,which represents

3.9% ofallnon-opaque minerals,It wbuld appear that apatité, epidote and zircOn are the main accessory mineralsrésponsitile fOr 232 high230Th and Th activities at this station, and possibly at all stations in the vicinity of Destruction Island. 46

CONG LUSIONS

1.Natural radioactivity in surface sediments on the Washington continental shelf reflects the mineralogy of the sediment. Sediment high in40Kactivity is consistently high in mud. Fine, well-.sorted 232 40 sands have high230Th and Th activities and relatively low K activity.The mean particle diameter of these sands is around 3.00 232 (0.125 mm). Relations between230Th activity, Th activity and total heavy mineral sands in sediment have been established and are significantly correlated.The230Threlation is complicated by230Th adsorbed on clay particles, but the problem can be resolved by normalizing230Thactivity to40Kactivity.

2.Radiometric analysis of shelf sediment can be applied to identify shelf regions with similar energy regimes. For example, 230 232 high40K activity and low Th and Th activities are characteris- tic of depositional environments; wereas, low40Kactivity and high 230Th and232Th activities are consistently associated with erosional environments. 230 232 3.High Th and Th activities are observed in water depths out to 60 m. Generally, the maximum activity, on a transect, occurs around 30 m. It is postulated that Holocene stillstandsexist at 18 ± 5, 29 ± 5, and 50 ± 5 m (Chambers, 1968).It is proposed that the high activity, near these depths, reflects exposed relict beach 47 sands.

4.Radiometric mapping of continental shelf sediments, applied to heavy mineral enrichments, appears feasible.The tech- nique has proven successful on the Washington and northern Oregon continental shelf, where two areas of enrichment have been found. One enrichment area is off Destruction Island, Washington. Maxi- mum enrichment occurs in 30 m of water and the enrichment tends to be skewed northward towards Cape Alava.The other enrichment area is in 33 m of water at Clatsop Spit, Oregon. The232Th/230Th activity ratios for these two locations are quite dissimilar, strongly indicating that the heavy minerals are from different sources. Heavy mineral analyses have substantiated the radiometric analyses.

5.Petrographic examination of heavy detrital grains in the vicinity of Destruction Island reveals that the non-opaque mineral 232 fraction contains 3.9% zircon.The high230Th and Th activities observed at Destruction Island are mostly due to this resistant mineral and due, to some extent, to apatite and epidote.Minor contributors to activity in this area are amphiboles (mostly hornblendes), garnet, pyroxene and olivine. 48

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APPENDIX I.Station numbers, sample locations and water depths. Cruise and Latitude Longitude Depth Station (North) (West) (Meters)

T711OEE4 48°07.3' 124°45.6' 33 T711OEE5 48°06.0' 124°50.5' 50 T711OEE6 48°03.8' 125°02.0' 135 T711OEE7 48°01.9' 125°14.9' 150 Y7208B44 48°00.0' 124°49.5' 50 Y7208B43 48°00.0' 124°58.0' 98 Y7208B42 48°00.0' 125°10.5' 150 Y7001A15 47°53.0' 124°44.0' 40 Y7001A14 47°42.0' 125°00.0' 140 T711OEE9 47°40.5' 124°54.1' 100 T711OEE12 47°40.0' 124°37.2' 45 Y7106A16 47°39.0' 124°40.0' 60 Y7106A17 47039.0' 124°50.0' 100 Y7106A18 47°39.0' 125°00.0' 150 Y7106A19 47°39.0' 125°05.0' 200 T711OEE13 47°38.7' 124°29.7' 20 Y7208B27 47038.0' 124°32.0' 30 Y7208B28 47°38.0' 124°39.0' 56 Y7208B29 47°38.0' 124°50.0' 105 Y7208B30 47°38.1' 124°57.0' 137 Y7208B31 47°38.1' 125°05.0' 190 Y7001A13 47°35.0' 124°35.0' 48 T711OEE14 47°28.2' 124°27.3' 20 T711OEE15 47°28.0' 124°32.9' 43 T711OEE16 47°28.1' 124°42.1' 91 T7J1OEE17 47°28.0' 124°47.8' 150 Y7208B26 47°27.0' 124°29.9' 32 Y7208B35 47°27.0' 124°32.0' 42 Y7208B34 47°27.0' 124°40.0' 80 T7110EE22 47°08.7' 124°25.1' 50 Y7208B25 47°08.0' 124°17.2' 32 Y7208B24 47°08.0' 124°25.0' 51 T711OEE2O 47°08.0' 124°39.0' 95 Y7208B23 47°08.0' 124°40.0' 100 Y7208B22 47°08.0' 124°52.0' 140 T71JOEE18 47°07.7' 124°56.3' 165 Y7208B21 47°08.2' 124°58.7' 200 T7110EE28 46°39.3' 124°35.3' 131 Y7208B18 46°38.0' 124°10.0' 27 Y7208B17 46°38.1' 124°15.0' 54 53

Cruise and Latitude Longitude Depth Station (North) (West) (Meters)

Y7208B16 46°22.0' 124022.0' 74 T711OEEZ9 46026.9' 124°26.9' 85 Y7208B14 46°38.0' 124°41.0' 166 T71]OEE31 46°37.8' 124°09.8' 31 T7110E24 46°37.7' 124038.6' 165 Y7208B11 46°16.0' 124°09.5' 20 Y7208B12 46°16.0' 124°16.2' 79 Y7208B7 46°09.P 124°05.0' 33 Y7208B8 46°09.1' 124°12.0' 73 T7110EE35 45°56.0' 124°01.5' 51 Y7208B6 45°56.0' 124°02.0' 51 Y7208B5 45056.0' 124°11.6' 95 T7110EE34 45°56.0' 124°13.7' 99 T7110EE32 45°56.0' 124°40.5' 198 T7110EE33 45°55.4' 124°27.7' 150

Note: T - R/V THOMAS G. THOMPSON, University of Washington. Y R/V YAQUINA, Oregon State University. APPENDIX II. andThorium-232, northern Oregon thorium-230 continental and potassium-40 shelf (± values content indicate in sediment lo- fitting of error). the Washington CruiseT711OEE4 and Station 0.24±0.01(pCi/g)232Th 0.28±0.02(pCi/g)230Th 8.18±0.28(pCi/g) 232Th 0.03 230Th 0.03 0.86 Y7208B44T711OEE7T711OEE6T711OEE5 0.36±0.050.73±0.020.64±0.030.22±0.03 0.60±0.050.46±0.030.27±0.030.57±0.03 13.78±0.956.49±0.495.01±0.457.75±0.38 0.130.030.09 0.090.040.07 0.810.601.281.39 Y7001A14Y7001A15Y7208B42Y7208B43 0.42±0.070.87±0.030.39±0.040.33±0.02 0.61±0.070.67±0.030.49±0.050.38±0.02 14.53±1.2812.96±0.8310.50±0.428.55±0.47 0.030.10 0.040.08 0.870.691.300.80 T711OEE12T711OEE9 0.49±0.050.41±0.030.56±0.061.21±0.051.04±0.04 0.88±0.051.04±0.050.56±0.060.51±0.060.60±0.06 13.39±0.8114.12±0.6412.66±1.007.55±0.617. 52±0.61 0.040.030.160.14 0.140.040.050.12 0.930.880.801.161.18 Y7106A18Y7106A17Y7106A16 0.41±0.060.43±0.040.60±0.031.13±0.05 0.48±0.040.64±0.070.46±0.030.96±0.05 14.08±1.2112.43±0.748.50±0.447.54±0.61 0.030.070.15 0.050.040.13 0.640.901.301.17 Cruise and 232 Th 230 Th 40 K 232Th 40 K 230Th 40 K 232Th230 Th Y7208B27T711OEE13Y7106A19 Station 0.74±0.120.16±0.021.73±0.09 (pCi/g) 0.67±0.130.28±0.021.23±0.09 (pCi/g) 10.67±0.46(pCi/g)6.45±1.125.98±1.69 0.120.010.27 0.110.030.19 0.571.101.41 1.74±0.091.76±0.081.71±0.081.67±0.071.66±0.071.86±0.09 1.22±0.081.19±0.081.27±0.101.31±0.101.31±0.091.21±0.08 6.93±0.966.76±0.936.78±1.137.44±1.027.20±0.907.62±1.14 0.230.250.240.260.240.25 0.170.180.190.18 1.411.371.391.461.331.34 Y7208B29Y7208B28 0.32±0.030.90±0.051.75±0.081.74±0.08 0.39±0.030.79±0.061.26±0.091.30±0.08 10.56±0.564.99±0.756.94±1.036.14±0.97 0.290.030.180.25 0.160.180.210.04 0.821.141.381.35 T711OEE14Y7001A13Y7208B31Y7208B30 0.73±0.030.26±0.040.18±0.020.37±0.05 0.39±0.050.29±0.020.55±0.060.71±0.03 14.14±1.088.20±0.449.17±0.799.14±0.42 0.030.020.09 0.090.040.03 0.670.621.03 T711OEE15 0.64±0.030.66±0.030.59±0.030.53±0.030.70±0.03 0.67±0.030.64±0.030.69±0.0.66±0.030.60±0.03 03 6.85±0.416.82±0.416.87±0.407.90±0.457.60±0.45 0.080.090.09 0.090.100.08 0.880.830.931.061.10 CruiseT711OEE16 and Station 0.33±0.020.31±0.03(pCi/g)232Th 0.40±0.020.43±0.03(pCi/g)230Th 10.93±0.5010.04±0.42(pCi/g) 40K 232Th0.0340K 230Th 0.040.04 230Th 0.830.72 Y7208B26T711OEE17 0.71±0.030.62±0.030.32±0.050.32±0.03 0.66±0.030.58±0.030.61±0.050.42±0.03 13.91±0.9610.49±0.467.56±0.487.52±0.50 0.090.080.020.03 0.040.080.090.04 0.761.081.070.52 Y7208B34Y7208B35 0.51±0.030.67±0.030.39±0.02 0.56±0.030.62±0.030.45±0.030.54±0.030.52±0.03 6.29±0.416.81±0.427.54±0.498.97±4.705.76±0.40 0.040.080.090.07 0.050.090.100.08 0.940.910.980.87 T711T7110EE22 0EE22 (sand) 0.26±0.010.38±0.020.37±0.020.21±0.01 0.28±0.010.21±0.010.42±0.030.38±0.02 8.37±3.337.79±0.266.87±0.247.77±0.39 0.050.040.03 0.050.040.03 0.970.931.000.90 Y7208B24Y7208B25 (pebbles) 0.25±0.020.42±0.020.41±0.020.43±0.02 0.31±0.020.40±0.020.41±0.020.41±0.02 6.52±0.347.48±0.297.14±0.367.00±0.32 0.040.06 0.040.060.05 0.811.021.031.05 Y7208B23T711OEE2O 0.33±0.020.33±0.03 0.42±0.030.46±0.03 9.34±0.459.02±0.54 0.04 0.050.04 0.720.79 0'U.' CruiseY7208B22 and Station - 0.43±0.04(pCi/g)232 Th 0. 53±0.05(pCi/g)230 Th 13.95±0.79(pCi/g) 40 K 232Th 400.03 K 230Th 0,04 40 K 230232Th 0.81 Th T711OEEZ8Y7208B21T711OEE18Y7208B18 0.22±0.020,27±0.020.34±0.020.45±0.04 0.46O.040.25±0.020.34±0,020.37±0.03 15.13±0.788.25±0.338.72±0.439.83±0.45 0.030.03 0.030,040.04 0.920.980.880.79 Y7208B16Y7208B17 0,54±0.040.60±0,030.32±0.020.30±0.02 0.35±0.030.32±0,020.57±0.050.52±0,03 14.70±0.7912.32±0,509,40±0.398.96±0.32 0.050.030.04 0.040.04 0.910.940.951,15 T711OEE31Y7208B14T7110EE24T711OEEZ9 0.64±0.040.35±0.030.32±0.020.29±0.03 0.25±0,030.41±0,030.65±0.030.34±0.03 10.76±0.7013.34±0.5713.97±0.595.96±0.45 0.050.020.060.03 0.060,030.040.03 0.710.981.031.28 Y7208B8Y7208B7Y7208B12Y7208B11 0.52±0.030.56±0.030.26±0.023.39±0.23 0.26±0.020.45±0.030.46±0.041.52±0.24 14.45±0.6115.52±0.648.74±0.356.17±2.50 0.040.030.550.04 0.030.030.250,03 2.231.001,161.22 T7110EE35 0.71O.02 0.40±0.03 8.10±0.39 0.04 0.04 1.78 -,Ui 232Th 230Th 232Th CruiseY7208B6 and Station 0.43±0.040.44±0.040.45±0.04(pCi/g)232Th 0.41±0.040.42±0.040.39±0.04(pCi/g)230Th 10.50±0.6710.54±0.6710.57±0.66(pCi/g) 0.040.0440K 0.0440K 230Th 1.071.101.07 T7110EE33T7110EE32T7110EE34Y7208B5 0.46±0.040.35±0.030.41±0.050.23±0.04 0.0.57±0.060.32±0.040.47±0.04 39±0.03 13.56±1.0023.46±0.9712.11±0.6614.23±0.52 0.030.010.040.02 0.040.030.040.01 0.980.900.720.82

u-I 59

APPENDIX III.Weight percent mud, light mineral sands, magnetic heavy mineral sands and heavy mineral sands on the Washington and northern Oregon continental shelf. Heavy Minerals Light Magnetic Non-magnetic Cruise and Mud Minerals Minerals Minerals Station (wt.%) (wt.%) (wt.%) (wt. %) T71JOEE4 2.8 95.3 0.2 1.7 T711OEE5 1.9 89.2 0.8 8.1 T711OEE6 81.2 18.8 0.0 0.0 Y7208B44 4.2 81.9 1.4 12.5 Y7208B43 17.6 76.8 0.8 4.8 Y7208B42 92.6 7.4 0.0 0.0 T711OEE9 74.9 25.1 0.0 0.0 T7J1OEEI2 4.1 75.8 1.7 18.4 4.5 76.8 1.7 17.9 4.3 76.3 1.7 18.2 T711OEE13 1.9 87.1 0.4 10.6 1.8 86.8 0.6 10.8 1.9 87.0 0.5 10.7 Y7208B27 4.0 72.1 2.7 21.2 Y7208B28 3.6 70,1 3.5 22.8 Y7208B29 33.9 62.1 0.8 3.2 Y7208B30 86.8 13.2 0.0 0.0 Y7208B31 Too unsorted for analysis T711OEE14 4.5 82.5 1.1 11.9 3.7 82.5 1.1 12.7 4.1 82.5 1.1 12.3 T711OEE15 3.0 82.7 1.2 13.1 T711OEE16 28.7 65.4 0.7 5.2 T7I1OEE17 83.7 16.3 0.0 0.0 Y7208B26 2.6 88.6 1.0 7.8 Y7208B35 1.7 87.8 1.0 9.5 Y7208B34 16.0 73.3 0.9 9.3 Y7208B25 3.6 78.2 1.4 16.8 Y7208B24 3.2 95.3 0.0 1.5 Y7208B23 27.9 64.3 0.8 7.0 Y7208B22 43.8 52.1 0.4 3.4 Y7208B21 6.4 80.5 1.4 11.7 Y7208B18 3.7 88.2 1.1 6.9 Y7208B17 30.4 63.9 1.8 3.9 Y7208B16 54.6 42.2 0.4 2.5 't7208B14 26.0 71.2 0.5 2.2 Y7208B11 46.6 48.7 0.9 3.7 Heavy Minerals Light Magnetic Nonmagnetic Cruise and Mud Minerals Minerals Minerals Station (wt.%) (wt.%) (wt.%) (wt. %)

Y7208B12 24.6 71.0 1.1 3.3 Y7208B7 5.8 44.4 16.3 33.5 Y7208B8 16.1 78.6 0.9 4.4 Y7208B6 8.2 75.4 1.2 15.1 Y7208B5 10.5 84.6 0.7 4.1 61

APPENDIX IV.Size analyses of sediment from Cape Alava to Tillamook Head. Inman Indices M Md a C rui s e and Depth 0 0 Station (meters) (Mean) (Median) (Sorting) (Skewness) Y7208B44 50 3.14 3.14 0.71 +0.01 Y7208B43 98 3.17 3.09 0.81 +0.10 Y7208B42 150 5.18 5.16 0.99 +0.02 Y7208B27 30 3.08 3.19 0.76 -0.14 T711OEE12 45 2.96 2.92 0.71 +0.06 Y7208B28 56 2.90 2.84 0.61 +0.09 Y7208B29 105 3.49 3.48 1.89 +0.01 Y7208B30 137 5.00 5.12 1.16 -0.10 Y7208B26 32 2.62 2,63 0.44 -0.02 Y,7208B35 42 2.51 2.49 0.47 +0.43 Y7208B34 80 2.79 2.65 0.59 +0.24 T711OEE17 150 3.94 3.82 0.74 +0.16 Y7208B25 32 2.75 2.69 0.53 +0.11 Y7208B24 54 0.23 0.29 0.99 -1.29 Y7208B23 100 3.25 2.92 0.99 +0.33 Y7208B18 27 2.82 2.79 0.57 +0.05 Y7208B17 54 5.04 5.06 1.08 -0.02 Y7208B11 20 4.02 4.01 1.36 +0.01 Y7208B1 2 79 2.97 2.72 0.75 +0.33 Y7208B7 33 2.82 2.85 0.56 -0.05 Y7208B8 73 2.63 2.64 0.43 -0.02 Y7208B6 51 2.74 2.67 0.54 +0.13 Y7208B5 95 2.77 2.69 0.59 +0.14 62

APPENDIX V.Procedure for cleaning marine sediments. I Removal of Organic Matter

1.Cover sand with 30% neutral H202. 2.Heat until frothing ceases. 3,Allow sand to settle, decant supernate and wash three times with distilled water. Removal of Carbonates

1.Cover sand with buffered acetic acid (glacial acetic acid buffered to pH 5 with iN sodium acetate). 2.Heat until no further emination of CO. 3.Allow sand to settle, decant acetic acid solution and wash sand three times with distilled water. Removal of Hydrous Oxide Coatings

1.Add 40 ml 0. 3N sodium citrate and 5 ml 1M sodium bicarbonate. 2.Heat to 80°C. 3. Add 1 g dithionite (Na2S2O4) and stir vigorously for i mm, then occasionally for 5 mm. 4.For heavy oxide coatings, add 1 g dithionite after 2 mm and stir occasionally for 5 mm. 5.Allow sand to settle, decant liquid and wash twice with 0. 3N sodium citrate and three times with distilled water. Removal of Aluminum and Silica Oxide Coatings

1.Add 50 ml 0.4M sodium carbonate and boil for 20 mm. 2.Allow sand to settle, decant liquid and wash sand three times with distilled water. 3.Dry sands at 110°C for 24 hrs. APPENDIX VI. Magneticeach fraction susceptibility of the heavy fractions, mineral and sands quantitative from T711OEE1Z. and qualitative mineralogy of SusceptibilityMagnetic%(x b-6 cgs units) (wt.) separated 6.7 8300 0.9 - 8300- 5175.2 129517- 5.2 13.7129- 41 41-32 8.4 2032-18.8 20-17.414.4 13.414.4- 8.0 8.0-1.55 5.1 01.55- 5.1 QuantitativeMineralogy (% count) WeatheredNon-opaqueOpaque 100.0 0.0 33.323.643.0 51.027.321.6 31.057.012.0 51.023.026.0 81.017.0 2.0 80.315.0 4.6 59.340.0 0.6 54.345.3 0.3 69.629.3 1.0 75.624.0 0.3 MineralogyQualitative Non-opaque(% count) ApatiteAmphibolesEpidote 19.3 33.3 1.2 54.413.2 10.1 4.4 ZirconTopazRutileOlivineGarnetPyroxene 69.0 4.10.8 31.533.9 11.814.7 4.41.5 10.3 7.07.60.6 0' 64

APPENDIX VII.Correlation coefficients at the 5% and 1% level of significance (Snedecor and Cochran, 1967). Degrees of Freedoma 5%-Level 1%-Level

16 0.468 0.606

29 0.355 0.456

33 0.335 0.430

45 0.288 0.372

53 0.266 0.345

aDegreesof Freedom = Sample Size - 2.