Marine gold placers along the Gulf of Alaska margin

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Publication type: Report

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Title: Marine gold placers along the Gulf of Alaska margin

Series title: Bulletin

Series number: 1415

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Year Published: 1976

Language: ENGLISH

Publisher: U.S. Govt. Print. Off.,

Description: 16 p. :maps (1 fold. col. in pocket) ;24 cm.

Marine gold placers along the Gulf of Alaska margin

Bulletin 1415

Erk Reimnitz and George Plafker

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iCIl SURVEY

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Marine Gold Placers Along the 

Gulf of Alaska Margin

GEOLOGICAL SURVEY BULLETIN 1415

Or

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Marine Gold Placers Along the 

Gulf of Alaska Margin

By ERK REIMNITZ and GEORGE PLAFKER

GEOLOGICAL SURVEY BULLETIN 1415

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 76-608199

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington, D. C. 20402

Stock Number 024-001-02850-6
CONTENTS

Page

Abstract ___________________________________.._____ 1

Introduction _____________________________________ 1

Geologic setting ___________ __ ____ 4

Bedrock _________________________________ ._____. 4

Unconsolidated surficial deposits ______-________ ____ 5

Placer gold sources ____________________________ 6

Marine environment ____________________________________ 7

Methods of investigation ________ ___ ____ ______ _. 8

Results and their interpretation _____________ __ 9

Offshore heavy-metal potential _._. ____ --_-__ 10

A new look at modern beach placers _-__ __-_ 12 

Conclusions ___________________ _____________ _. 13

References cited _______________________________ ___ 14

ILLUSTRATIONS

Page 

PLATE 1. Generalized geology and placer gold sampling localities,

Gulf of Alaska ___ ____________________ In pocket 

FIGURE 1. Location map_______ ________________________ 2

III

MARINE GOLD PLACERS ALONG THE 

GULF OF ALASKA MARGIN

By ERK REIMNITZ and GEORGE PLAFKER

ABSTRACT

Fifty-five beach samples, collected along the Gulf of Alaska between Dry Bay and 

Prince William Sound, were analyzed for their gold content in order (1) to gather 

information on gold placers in areas that have not been mined, such as the Copper 

River Delta, (2) to gather information needed in the search for placers on the adjacent 

continental shelf, and (3) to learn more about the occurrence and behavior of modern 

beach placers with a view toward enhancing their economic potential.

In general, the beaches contain very little gold, but certain areas along the Copper 

River Delta contain as much as other areas to the east that have been productive, and 

on a unit-length basis one of the barrier islands appears to contain more dark sand 

than most other areas. More detailed study of the heavy-mineral distribution on the 

Copper River Delta seems warranted.

Much of the gold on the beaches appears to have been concentrated from the 

Yakataga Formation. This formation also underlies much of the adjacent continental 

shelf where it has been truncated. The potential for finding auriferous submarine 

beach or relict nearshore deposits therefore is great.

Available evidence suggests that gold is being lost from the beaches to the offshore 

area. Therefore, gold may be concentrated in favorable nearshore locations at present 

and may also have formed in such areas in the past. Thus, the search for economic 

placer deposits on continental shelves should not be restricted to relict beach and 

residual deposits.

Heavy-mineral concentrates with associated gold on the beaches of the Gulf of 

Alaska generally are small in volume and are short-lived owing to high rates of reworking, redistribution, and longshore transport. For these reasons, the possibility 

should be investigated of enhancing the economic potential of future placer mining 

operations by using fixed engineering structures that modify the surf-zone environment, thereby concentrating gold and other valuable heavy constituents.

INTRODUCTION

In the summer of 1969 a five-day reconnaissance survey by helicopter covered about 400 km of coastline along the Gulf of Alaska Coast 

between Hinchinbrook Island and Dry Bay (fig. 1). Fifty-five samples 

of beach material were collected during this survey and later were 

analyzed for gold. The purpose of the investigation is severalfold: (1) 

to compare the gold content of black-sand-bearing beaches in the 

Copper River Delta area with those in the Yakataga, Yakutat, and 

other areas where beach placers have been mined; (2) to apply this 

information to the adjacent continental shelf region, with a yiew to
152° 148°

144

*.' 

Hinchinbrookf!: 

Island

Controller

0 100 200 

FIGURE 1. Location map of the sampled a
INTRODUCTION 3

outlining offshore areas in which future exploration might be profitable; and (3) to obtain data that might be useful for the development of 

better beach-mining methods.

The beaches in the Lituya Bay area were mined sporadically for 

gold by the Russians before 1867 and since 1894 by the Americans. In 

1896, 150-200 men were engaged in these operations (Thomas and 

Berryhill, 1962). In the Yakutat area, gold was first noted in beaches 

in 1886 or 1887 (Tarr and Butler, 1909) and was mined on a small 

scale continuously for several decades and intermittently since. In 

the Yakataga district, gold was first found in 1897 or 1898, and about 

40 men worked primarily along a 6-km (3.8 miles) stretch of beach 

east of Cape Yakataga in 1903 (Maddren, 1914). Intermittent smallscale placer mining has continued in this area to the present day. 

Small-scale placer mining has also been conducted on the southwest 

tip of Middleton Island (Brooks, 1913, p. 43) and on certain stretches 

of beaches on Kodiak Island around the turn of the century (Maddren, 

1919). Overall production estimates are highest for the Yakataga 

district.

Beach-placer gold production from the Gulf of Alaska

[From Cobb, 1972]

Production 

Area (in ounces)

Lituya and Yakutat districts ___-____-__________________Up to 3,700

Yakataga district _______________________________ 15,000-16,000 

Middleton Island ______________________________ a few hundred

Kodiak Island (west coast) __________________-____ a few thousand

Homer district (mainly from Anchorage Point) __________________ unspecified

During the last 15 years, private companies have investigated certain beach areas within the Lituya district and near Yakataga for 

gold and heavy minerals, but no production has resulted to date. The 

U.S. Geological Survey made a reconnaissance study of radioactive 

materials in the Yakataga beach placers in 1947-49 (Moxham, 1952), 

and in 1957 and 1958 the U.S. Bureau of Mines carried out extensive 

auger drilling to outline heavy-mineral concentrations in the area 

between Cape Suckling and Icy Point in southeastern Alaska 

(Thomas and Berryhill, 1962). Unfortunately these data are unsuitable for compilation of gold values for comparison. In 1967, the University of Alaska and the U.S. Geological Survey, carried out 

seismic-reflection surveys and bottom-sampling in an unsuccessful 

search for gold concentrations in Yakutat Bay (Wright, 1969) and on 

the continental shelf between Bering Glacier and the Dangerous 

River (R. von Huene, oral commun., 1969). Bottom samples generally 

contained less than a few parts per billion .gold. In addition, a number 

of stream-sediment samples and one beach sample in the report area
4 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA

were analyzed for gold (MacKevett and Plafker, 1970). The beach 

sample, from a black-sand concentrate near the mouth of Situk River, 

contained 0.5 ppm gold. Fifty-two samples, both from modern and 

ancient beaches in the Cape Yakataga region, were analyzed for gold 

and other minerals by Cook (1969).

Along much of the coast of the Gulf of Alaska, sand concentrates of 

heavy minerals (often referred to as "ruby sand" because of their 

reddish color) occur in patches as relatively thin layers on the modern 

beach near the high-tide line and behind storm berms near the base 

of the sand dunes or sea cliffs. They commonly have a high garnet, 

magnetite, and ilmenite content and generally contain trace amounts 

of rutile, zircon, chromite, and also fine gold. Minor amounts of 

platinum have been recovered from beach placers in the Yakutat and 

Lituya districts and on southwestern Kodiak Island. The highest concentrations of gold occur along a stretch of beach west of Cape 

Yakataga, along short beaches at the west side of Yakutat Bay, and 

along the open coast in the Yakutat area. None of these areas, however, can support continuous, profitable mining operations at present. 

The gold grains are so small that many are lost with the traditional 

methods of concentration.

The volume of beach material with higher concentrations of heavy 

minerals generally is small, and the accumulations are transient. 

The concentrations occur in the upper, active parts of beaches, principally after winter storms, and often the heavy minerals are reworked 

or covered with fresh deposits as the beach changes. At least one 

example of the short-lived nature of economic concentrations has 

been described by Maddren (1919); he reported that deposits formed 

by one storm often could not be recovered before the next storm arrived. In this respect, conditions in the report area are very similar. 

Moreover, the rate of supply of fresh materials and winnowing within 

the marine environment in the report area is such that small-scale 

mining operations would deplete a particular beach in a few years.

Techniques used in the past in the offshore exploration for gold did 

not serve to delineate the most likely ancient or modern settings for 

economic concentrations. Widely spaced surface samples show only 

very low gold values associated with relict gravel or nearshore sand. 

In this report we will consider some new concepts and areas for future 

exploration.

GEOLOGIC SETTING

BEDROCK

The rocks exposed in and adjacent to the report area may be 

broadly divided into three major sequences that are separated by 

unconformities and that differ considerably in age, lithology, degree
GEOLOGIC SETTING 5

of deformation, and topographic expression (Miller, 1961a-e; Plafker, 

1967, 1971). From oldest to youngest, these sequences are as follows:

(1) A crystalline complex consisting of a diverse assemblage of late 

Paleozoic(?) and Mesozoic mica schist, volcanic rocks and marble 

metamorphosed to the high-grade greenschist to amphibolite facies.

(2) A slightly metamorphosed, eugeosynclinal sequence of late 

Mesozoic age (Yakutat and Valdez Groups) that is metamorphosed to 

zeolite or epidote amphibolite facies and is characterized by abundant 

volcaniclastic detritus, intense deformation, and tectonically intermixed rock fragments and blocks of widely diverse origin and age 

(melange). (3) Mildly to strongly deformed continental and marine 

sedimentary rocks at least 12,000 m (40,000 ft) thick that range in 

age from Paleocene through Pleistocene. The Cenozoic sequence is 

further broadly divisible into (a) a lower unit of well-indurated, 

strongly deformed marine and continental coal-bearing rocks of 

Paleocene through early Oligocene age; (b) an overlying unit of lessdeformed and less-indurated marine clastic and volcanic rocks of 

Oligocene and early Miocene age, and (c) a thick upper unit of 

slightly to moderately deformed marine clastic rocks characterized by 

abundant glacial detritus (Yakataga Formation) that ranges in age 

from middle Miocene through early Pleistocene.

The two older bedded sequences are intruded by numerous quartz 

diorite, granodiorite, and adamellite plutons that range in age from 

middle Jurassic to middle Tertiary. In addition, three late Mesozoic 

plutons of distinctive layered mafic and ultramafic rocks occur within 

the crystalline sequence in the Fairweather Range (Plafker and 

MacKevett, 1970). Numerous small aplite and pegmatite dikes are 

associated with some of the granitic plutons, and the plutons locally 

have extensive aureoles of migmatite or hornfels. In addition, widely 

scattered smaller intrusive bodies of Tertiary age cut both the preTertiary and Tertiary sequences. These include lamprophyric to 

diabasic mafic dikes and plugs and rare stocks, plugs, and dikes of 

quartz porphyry.

The Chugach-Saint Elias and Fairweather fault systems, which 

strike roughly parallel to the Gulf of Alaska coast, form important 

structural boundaries between geologically and physiographically 

distinctive terranes. In general, the rugged mountainous terrane 

north of these faults is underlain by crystalline igneous and 

metamorphic rocks, whereas the adjacent foothills and coastal-plain 

belt to the south is underlain largely by Cretaceous and Cenozoic 

bedded rocks with associated small igneous intrusive bodies.

UNCONSOLIDATED SURFICIAL DEPOSITS

The Tertiary and older bedrock formations around the Gulf of
6 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA

Alaska are overlain unconformably, at most places with marked angular discordance, by flat-lying unconsolidated surficial deposits that 

are largely, if not entirely, of Holocene age. These deposits were 

formed in both marine and terrestrial environments and are thickest 

and most extensive on the coastal lowland and on some elevated 

marine terraces (fig. 2). They have been subdivided and described by 

Miller (1961a-e) and other geologists. In the coastal region, the major 

types, classified according to lithologic character and origin, are (1) 

well-sorted sand and gravel formed at or near the present beach and 

on former beaches, including strand lines elevated by Holocene tectonic uplift; (2) well-sorted dune sand on or near the present or former 

beaches; (3) interbedded mud and sand containing much organic debris, which were formed on tidal flats, in bays or lagoons, and in clear 

lakes and swamps; (4) interbedded mud and poorly sorted to moderately well-sorted sand and gravel, which were formed on the flood 

plains or fans of streams on the outwash aprons of glaciers and in 

glacial lakes; and (5) till formed at or near the margins of glaciers, 

including terminal and ground moraine and ice-rafted deposits.

The thickness of the unconsolidated deposits on the coastal lowland 

and along the raised beach ridges is not well known. Data from oilcompany exploratory wells and seismic profiling indicate that the 

unconsolidated deposits are commonly up to a few hundred metres 

(several hundred feet) thick. Marine deposits on the highest terrace 

(elevation up to 230 m (750 ft)) in the Lituya district, between Lituya 

Bay and Sea Otter Creek, are estimated to be 15-30 m thick (50-100 

ft), and the deposits on an elevated terrace at the northwestern margin of the La Perouse Glacier are 3 m (10 ft) thick. In the Yakataga 

district, surficial deposits on elevated marine terraces between Icy 

Bay and Cape Yakataga range in thickness from less than a meter (a 

few feet) to 10 m (30 ft). Marine sand and gravel on the elevated 

terraces in the Katalla district are of an uncertain thickness; where 

exposed in coastal cliffs, these deposits are generally less than 3 m (10 

ft) thick. Offshore Holocene deltaic deposits on the Copper River 

Delta are up to 180 m (600 ft) thick (Reimnitz, 1966). Stratified 

marine terrace deposits on Middleton Island range in thickness from 

less than a metre to at least 6 m (20 ft) (Miller, 1953).

PLACER GOLD SOURCES

The original source of placer gold and other valuable heavy minerals in the beaches around the Gulf of Alaska is undoubtedly the 

igneous rocks and related alteration zones in the coastal (and possibly 

interior) mountains. There are no operative lode-gold mines in this 

region. Numerous gold lodes occur throughout the Chugach and 

Kenai Mountains. Gold was produced from mines along the north
MARINE ENVIRONMENT 7

flank of the Chugach Mountains, in northern Prince William Sound, 

and in the area east of Cordova between about 1910 and 1940. It 

generally occurs associated with quartz veins cutting graywacke, argillite, and greenstone of the late Mesozoic Valdez Group and early 

Tertiary Orca Group (Moffit, 1954, p. 302-307).

A geochemical reconnaissance of parts of the Yakutat and Malaspina districts showed small amounts of gold in a few bedrock samples 

(MacKevett and Plafker, 1970, p. 17). The richest of these contained 

0.08 parts per million gold and were from narrow quartz veins that 

cut metamorphic rocks near the Fairweather fault and from an altered zone in quartz diorite. In the Lituya district the ultramafic and 

mafic plutons of the Fairweather Range, which locally contain significant amounts of ilmenite, magnetite, platinum, and other heavy 

minerals, are probably the source of much of the placer beach deposits 

in the Lituya and Yakutat districts (Plafker and MacKevett, 1970).

Some of the placer gold and other valuable minerals on the present 

beaches and in the subparallel emergent shorelines have apparently 

been derived directly from mineralized bedrock in the mountains and 

transported to the coast by glaciers and (or) streams. Gold of the 

Copper River Delta is in this category; some of the heavy minerals in 

beach placers along the southern margins of the Malaspina Glacier 

and on the Yakutat Foreland may also have been similarly derived. 

Much of the placer gold, however, was involved in one or more cycles 

of deposition in the clastic Cenozoic formations of the region before 

being reworked and concentrated in the beach deposits. Gold is probably distributed generally at random in the marine-glacial deposits of 

the late Cenozoic Yakataga Formation and, possibly, in other parts of 

the thick sequence of Cenozoic strata exposed along the Gulf of 

Alaska margin. The prevailing fine size of the placer gold and its 

occurrence on beaches at Middleton Island, near Lituya Bay, and at 

Cape Yakataga in outcrop areas of the Yakataga Formation suggest 

that in these localities it is being reworked from that formation. 

Significantly, the only possible source for the placer gold found on 

the beaches at Middleton Island is the Yakataga Formation, which 

underlies the entire island and much of the shelf. A detailed 

geochemical sampling program of the different types of sedimentary 

rock in the Yakataga Formation would be required to determine how 

and where the gold occurs in the Cenozoic sequence.

MARINE ENVIRONMENT

The beaches that were sampled during this investigation for the 

most part are exposed to the full force of storm waves generated over 

the Gulf of Alaska. The storms, most common and severe from October through February, blow from a southeasterly to easterly direc-
8 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA

tion (Reimnitz, 1966). Longshore transport therefore is northwesterly 

to westerly, and this trend is reflected in the configuration of barrier 

islands and sand spits. The tidal range is great, reaching extremes of 

over 6 m (20 ft), causing strong currents around tidal inlets, river 

mouths, and bay entrances. For these reasons, the rate of reworking 

of material supplied to the sea is fast, and delta fronts are straight, 

blending into the general shoreline.

The beaches in most areas consist of well-sorted medium-grained 

sand. At the Copper River Delta, where rates of sediment supply are 

high, the modern sand extends offshore to a depth of 50 m (165 ft) 

(Reimnitz, 1966). This great depth range of sand probably is common 

around the Gulf of Alaska and is related to reworking of material by 

storm waves and currents.

Pebbles, cobbles, or boulders within the beach prism occur only on 

short stretches of coast bordered by cliffs exposing Quaternary or 

older rocks, in areas where morainal material is reworked by the sea, 

and in the Sitkagi Bluffs region at the foot of the Malaspina Glacier. 

Elsewhere, material coarser than sand size is uncommon.

METHODS OF INVESTIGATION

The beaches from Hinchinbrook Island at the west to Dry Bay at 

the east, were sampled at 55 locations (pi. 1) within a period of 5 days, 

using a helicopter for transportation. Most samples were collected 

from the beach surface, either near the high-tide line, on the berm, or 

just landward of the berm, where concentrations are highest. Conspicuous layers of dark minerals were sampled preferentially. Sample locations in any particular area were chosen to avoid relatively 

unwinnowed areas of accretion, as for example on the downdrift end 

of barrier spits where low heavy-mineral contents are expected. Only 

a few samples are exceptions to the general sampling approach used. 

Thus, sample 22 at Cape Suckling, was collected from a small pocket 

of sand on a bedrock surface exposed at low tide seaward of the beach. 

Sample 20 near the above station was collected from the top of a 

stream-dissected soil horizon forming the base of a beach that became 

inactive after the 1964 uplift associated with the Alaska earthquake. 

Sample 40 consists of a noticeable concentration of dark minerals 40 

cm (1.3 ft) below the beach surface; sample 41 is from a thin, highly 

concentrated surface layer at the same location on Black Sand Spit. 

Sample 30 represents dune sand from Cape Yakataga, which is gold 

bearing according to Charlie Bilderback (oral commun., 1969), a 

prospector of Yakataga.

Sample locations are closely spaced in the Yakataga and Yakutat 

areas, which have been productive, and along the beaches of the 

Copper River Delta where the senior author noted dark-mineral con-
RESULTS AND THEIR INTERPRETATION 9

centrations during a study of the delta (Reimnitz, 1966). Pete Dahl 

Bar is notable among the barrier islands of the Copper River Delta. 

The distribution of dark sand, as observed from the air, was widespread along the upper beach and also on the flat part of this barrier 

island behind the beach where it is not covered by sand dunes. Digging at various places near the three sample localities on this island 

revealed that the relatively high concentration of dark minerals was 

not restricted to a thin surface layer but extended to a depth of at 

least a metre (3 ft) in some areas. A semiquantitative spectrographic 

analysis of a beach sample collected in previous work near the east 

end of this island showed high concentrations of Fe, Ti, Mn, Cr, Ni, V, 

and Zr; this heavy-mineral assemblage is similar to that of other 

beaches studied previously along the Gulf of Alaska coast.

Between 2 and 8 kg (4.4 and 17.6 pounds) of material from each 

station was submitted for analysis. The analyses, by atomicabsorption techniques, were done by Kam Leong, U.S. Geological 

Survey, Menlo Park, Calif. In view of the small particle size of the 

gold in this area, the sample sizes probably were sufficient to fulfill 

the requirements for obtaining representative results, dictated by the 

particle sparsity effect (Clifton and others, 1969). For analysis, bulk 

samples were split into about six portions of about 700 g (1.5 pounds) 

each, small enough to be handled by the methods used. Five samples 

were sized before analysis; the gold in these was found primarily in 

the smaller thanl25/xmifractions.This fact and the comparable gold 

values obtained for the different splits of each sample indicate that 

the gold values shown are fairly representative for the samples submitted.

RESULTS AND THEIR INTERPRETATION

The analytical results are shown on plate 1. Generally gold values 

are very low. The highest values east of the Copper River with a 

maximum of 1.87 ppm are from thin layers of "ruby sand" with limited areal extent at Situk (42), east of Sitkagi Bluffs (33), and east of 

the mouth of the White River (51). A small "ruby sand" sample collected in 1967 at Situk contained 0.5 ppm gold (Plafker and MacKevett, 1970, p. L7), and another sample (69 Apr 108C) collected by 

Plafker in 1969 from near locality 33 contained 16 ppm. A sample 

with a pronounced concentration of "ruby sand" (41) from Black Sand 

Spit, however, contained very little gold. On the Copper River Delta, 

samples from two of the barrier islands were relatively high in gold. 

Sample 12, with 0.24 ppm gold, is from the east end of Grass Island on 

the upper beach face, where no obvious concentrations of heavy minerals were noted.

Sample 16, with 0.25 ppm gold, is from a 5-cm-thick surface layer
10 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA

with a notable concentration of dark minerals at the west end of Pete 

Dahl Bar. The other two samples from this barrier island contained 

only a trace of gold.

The potentially richest sand was sampled at each location throughout the area investigated, yet all the samples contained only small 

quantities of gold. The generally low gold-content probably relates in 

part to physical conditions; there were no large storms just prior to 

the fieldwork, and the ocean was calm during the period of sampling. 

Thus the beaches had steep foreshores and were well nourished with 

light-mineral constituents, and heavy minerals were sparsely disseminated. The uniformity of conditions that prevailed all along the 

coast during the fieldwork allows a comparison to be made between 

regions in which much prior work has been done and the barrier 

islands of the Copper River Delta which had not previously been 

sampled for their dark sand content.

In two localities, the beaches of the Copper River Delta have as 

much gold as beaches that have been mined. Furthermore, Pete Dahl 

Bar appears to contain other heavy minerals in concentrations similar to those reported for the Yakataga area, and these in the future 

might also be of economic interest. Most important, however, is that 

the volume of material containing heavy minerals on this island appears to be much larger than that of a similar stretch of beach in the 

Yakataga area.

The low gold values in samples taken east of the delta indicate that 

the heavy minerals of Pete Dahl Bar are not supplied by littoral drift 

from the east but rather from the Copper River drainage basin. Prior 

to the shift in dominant river discharge to a more easterly position, as 

a result of uplift associated with the great earthquake of 1964, Pete 

Dahl Bar bordered the tidal inlet that carried the principal Copper 

River discharge (Reimnitz, 1966). If a causative relationship exists 

between position of river discharge and the location where heavy 

minerals concentrate, Grass Island Bar, where samples No. 12 and 13 

were collected, may presently be the area of maximum heavy mineral 

accumulation. It is likely that earlier, similar deposits have been 

incorporated into the wedge of delta sediments that accumulated during the last 6,000 years (Reimnitz, 1966).

OFFSHORE HEAVY-METAL POTENTIAL

Shelf areas that are bordered by beaches containing heavy-metal 

accumulations are of interest for their future economic potential, 

even though they might not be profitably mined at present. Exploration has identified areas of interest on the continental shelf bordering 

Nome (Nelson and Hopkins, 1969). Similarly, possible heavy-metal
OFFSHORE HEAVY-METAL POTENTIAL 11

accumulations have been identified on the shelf of northern California and Oregon (Kulm and others, 1968; Clifton, 1968; Moore and 

Silver, 1968). In the Gulf of Alaska, fjords and other embayments are 

unlikely sites for economic concentrations of heavy minerals because 

their sediment accumulated rapidly and with virtually no sorting 

(Reimnitz and others, 1970; Wright, 1969). In contrast, much of the 

open shelf in this part of the Gulf of Alaska is an erosional surface 

with little or no Holocene sediment cover and might well warrant 

future studies. R. von Huene (oral commun., 1969), in his reconnaissance of the shelf seaward of Yakataga and Yakutat, did not locate 

any areas of economic interest; but he did discover lag gravel in the 

Fairweather Ground area that contained trace amounts of gold and 

nearshore sand with considerable heavy mineral concentrations and 

traces of gold.

Wherever lag deposits unconformably overlie the Yakataga Formation, the probably source of much of the placer gold along the 

coast, the likelihood of finding heavy-metal concentrations should be 

good. One such area is Tarr Bank, a broad topographic high between 

Middleton Island and the Copper River Delta. Deformed strata of the 

Yakataga Formation lithologically similar to those constituting Middleton Island, although probably younger, are truncated by the bank 

top, and a thick layer of sediment has been removed by erosion 

(Reimnitz, 1966). High-resolution seismic records showed that the 

surface of the bank may be very similar to the flat top of Middleton 

Island; individual strata crop out in small-scale relief on the sea floor, 

and the erosional products have been transported northward and deposited in foreset beds that dip landward away from the bank (Reimnitz, 1966). Small lenses of Holocene sediment occur locally on the 

bank. Tarr Bank apparently has been affected by currents, waves, 

and possibly also by drifting ice in the recent past when the water 

depth was shallower than today (Reimnitz, 1966). The nature of the 

Holocene material found in shallow depressions on the bank top and 

above the northern flank is poorly known. But the possibility of finding lag deposits and relict beach and nearshore-sand deposits on the 

bank, or coarse granular erosional debris north of the bank, is good. 

Since the source for such deposits is probably the Yakataga Formation, the chances of finding concentrations of heavy minerals and of 

gold in them should be investigated.

Tarr Bank apparently is not the only area in this part of the Gulf of 

Alaska in which a topographic and structural high exposing the 

Yakataga Formation has been subjected to shallow-water reworking. 

Future exploratory work in these regions might well be fruitful. 

High-resolution seismic profiling and magnetometer surveys should 

be used to delineate regions with highest mineral potential.
12 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA 

A NEW LOOK AT MODERN BEACH PLACERS

A number of factors, which have been described earlier, and which 

probably are not unique to the beaches of the Gulf of Alaska, have 

made small-scale placer mining operations in the area difficult if not 

uneconomical. The transient nature and small volume of beach sand 

with high gold concentrations would also hinder any future largescale mining operations, using standard methods such as dredging. 

The feasibility of taking advantage of active processes in the surfzone environment should be investigated to guide in the design of 

better mining methods.

Beach material is constantly being shifted by combined surf action 

and littoral drift, which in the area of investigation is predominantly 

to the west. The movement and winnowing of sediment take place 

primarily inside the surf zone along the beach foreshore but also in 

the offshore zone possibly to considerable depth in this high-energy 

environment. For example, very well-sorted sand extends to a depth 

of about 50 m (165 ft) off the Copper River Delta (Reimnitz, 1966).

The winnowing and sorting of light- and heavy-mineral fractions 

are affected by the interplay of such factors as wave regime, shoreline 

configuration, and bottom topography in a complex manner which 

still is not well understood. Local obstruction to littoral drift may 

block the movement of fine gold, causing it to accumulate in places 

(Nelson and Hopkins, 1969), but this does not appear to be a general 

rule. Previous detailed sampling in the Yakataga region showed that 

gold contents of beach deposits are high for many kilometres east of 

Cape Yakataga but become low immediately west of the cape 

(Thomas and Berryhill, 1962). Here the rocky promontory and shallow reef extending for some distance offshore may stop the movement 

of most of the gold, which is very fine. The gold content in the material moved westward by littoral drift, however, may also become 

masked by sediment influx from sources west of the cape. There is a 

third possiblity, namely that Cape Yakataga and its submerged seaward extension deflect the littoral transport, including gold and other 

valuable minerals, offshore to such depth or location with respect to 

the wave pattern that it is lost to the littoral drift system. 1 Along 

retreating coasts with narrow beaches there probably is a slow net 

loss of beach material by shoreface erosion. This appears to be true for 

the Yakataga area. Superimposed on this slow transfer of beach 

material is the temporary loss of all beach material during storms. 

Commonly gold and other heavy minerals are moved out along with 

the general beach material during these events (Charlie Bilderback,

 This view is contradictory to results from some studies dealing specifically with transport of sediment in the 

littoral zone. Such studies, however, have been done only during periods of relatively calm weather when heavy 

minerals are retained in the nearshore zone.
CONCLUSIONS 13

oral commun., 1969). Whether heavy minerals and gold, in time, 

again are returned to the beach cycle, and whether any sorting of 

heavy- and light-mineral fractions takes place in the offshore region 

under ideal conditions is not known. However, the pattern of beach 

mining operations along the Gulf of Alaska, where the first activity 

in one particular area was not more profitable than the last one, 

indicates that the amount of gold that can be retained in the beach 

reaches a peak within several decades, and that thereafter gold is lost 

to the offshore.

The shelf-sampling program carried out in this area by von Huene 

(oral commun., 1969), shows that in the nearshore sandy-sediment 

zone, and notably off the areas where modern beaches contain the 

highest amounts of gold and heavy minerals, heavy-mineral concentrations were up to 47 percent. Samples from this zone also contain 

small amounts of gold, confirming that gold and heavy minerals are 

transported offshore today. The shelf-sampling program did not extend into shallow water and did not investigate specific topographically favorable locations where concentrations of heavy minerals 

might be still greater.

Available evidence from the beaches of the Gulf of Alaska indicates 

that trace-size gold and heavy-mineral sand are highly mobile in the 

beach environment, and some part of these may continuously be lost 

to the beach cycle. In small-scale mining operations, the practice has 

been to recover gold from local, small, impermanent patches. These 

operations therefore had to be mobile. Any future large-scale mining 

operations working the entire beach prism also would have to be 

mobile, as the beach volume generally is small.

In areas of rapid reworking and sediment transport by marine 

agencies, as along the Gulf of Alaska coast, it should be possible to set 

up stationary placer operations. This might be achieved by designing 

engineering structures to intercept longshore transport. Groins 

might be used to accumulate and separate sediment in transit along 

the foreshore or to deflect this material to favorable locations 

offshore, from which it could be recovered for processing. Studies of 

existing shore-protection structures in regions where beaches are 

rich in heavy minerals might indicate types which preferentially 

bypass or retain light- or heavy-mineral fractions. The harnessing of 

marine processes to concentrate valuable minerals and gold from 

materials moving alongshore might enhance the economic potential 

of some beach placers. Furthermore, the fixed nature of such an operation should reduce its operating cost.

CONCLUSIONS

Reconnaissance sampling of Gulf of Alaska beaches showed that, in
14 MARINE GOLD PLACERS ALONG THE GULF OF ALASKA

general, these beaches have low gold content. Where values are comparatively high, the volume of beach material containing gold is 

small. Beach placers of the Copper River Delta compare favorably in 

gold value and heavy-mineral constituents with other areas that 

have been mined in the past, and there appears to be more dark sand 

per length of beach in one of the barrier islands than in most other 

areas. A more detailed study of the Copper River Delta seems to be 

warranted.

A review of high- and low-resolution seismic profiles from Tarr 

Bank, on the open continental shelf between Middleton Island and 

the Copper River Delta, suggests this as a favorable area for future 

gold exploration. The Yakataga Formation, probable source of much 

of the placer gold along the shore of the Gulf of Alaska, has been 

truncated on Tarr Bank and reworked by shallow-water processes. 

Similar favorable regions may lie on the shelf to the east and west.

Many of the beaches in the area investigated have not accreted 

over a period of years while the coast retreated; therefore, they are in 

a state of equilibrium, with supply balanced by loss to offshore areas. 

Available evidence suggests that gold also is lost to the offshore region. This specific aspect of the dispersal mechanism for fine gold 

apparently has been little investigated. The difficulty in taking large 

research vessels nearshore partly accounts for the lack of knowledge 

concerning gold and heavy-mineral concentrations of modern 

offshore deposits, especially in high-energy environments. On the 

other hand, where shelf areas have been explored for heavy-mineral 

concentrations, such work generally has been limited to the collection 

of surface samples. Because relict offshore deposits are in deeper 

water than beaches corresponding in age and therefore commonly are 

covered by Holocene shelf sediments, they have been neglected in 

past investigations. These gaps in our knowledge should be filled by 

suitable studies of possible heavy-mineral concentrations in areas 

close to, but outside of, the surf zone.

Future studies should also test the feasibility of using fixed engineering structures to concentrate gold or other valuable heavy constituents by the natural forces of the surf-zone environment. Basic 

background information on this problem could best be obtained in 

areas more accessible than the Gulf of Alaska.

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