Metal Absorption by 

Equisetum (Horsetail)

GEOLOGICAL SURVEY BULLETIN 1278-A

Metal Absorption by 

Equisetum (Horsetail)

By HELEN L. CANNON, HANSFORD T. SHACKLETTE, and HARRY BASTRON

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

GEOLOGICAL SURVEY BULLETIN 1278-A

A study of the metal content of 

horsetail plants as related to 

the amounts of metals in the 

soil on which they grew

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract__ _________________----_______--_-__--_-_-_--__--_------ Al

Introduction._____________________________________________________ 1

Previous work___________________________________________________ 4

Objectives and methods_____________________________-_-___--____-__ 8

Uptake and concentration of metals by Equisetum____________---__-__- 8

Normal concentrations of metals in Equisetum_________________________ 8

Anomalous metal contents in Equisetum from mineralized areas ______ 9

Ore Hill mine._________________________________________________ 9

Lead-zinc district of southwestern Wisconsin._____________________ 13

Various parts of Alaska______________________________________ 15

Summary of the concentration of trace elements in Equisetum-.-------.- 16

____-_____---________ --__________--___--__-_-_---_-_--- 16

__________-_____.__________-__-_---_-__-____-----_----- 17

Copper_ _________________--___---____--____-_-__--_-----_--_ 18

Gold and silver___-_______-.-_-_______--____-___-_----------- 19

Other trace elements_________-____-______---______-----_-_----_ 19

Conclusions_ _________--_____-_.___________-____-___-_-----_----- 19

References cited___________-__-..____-_-_-___________------------- 20

ILLUSTRATION

Page 

FIGURE 1. Equisetum arvense L., field horsetail..________--_-______- A3

TABLES

TABLE 1. Some analyses of Equisetum ash reported in the literature_____ A6

2. Accumulation of elements by Equisetum in the conterminous

United States__.______________________ 10

3. Average and maximum trace element contents in ash of Equisetum compared with the average for all types of vegetation.. 12

4. Copper, lead, and zinc in plants growing in acidic sulfide environment of Ore Hill mine, New Hampshire____________ 12

5. Amounts of certain elements in the ash of Equisetum and in 

soils and evaporite at selected mineralized and unmineralized 

sites in southwestern Wisconsin______________________-__ 14

6. Accumulation of elements by Equisetum species from Alaska. _ 16

7. Zinc and lead absorption by Equisetum growing on drained and

undrained bogs near Manning, N.Y____________________ 17

in

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

METAL ABSORPTION BY EQUISETUM (HORSETAIL)

By HELEN L. CANNON, HANSFORD T. SHACKLETTE, and HARRY BASTRON

ABSTRACT

Samples of Equisetum (horsetail) have been collected from a variety of mineralized and unmineralized areas throughout the conterminous United States 

and Alaska and analyzed for 28 elements to determine whether this primitive 

plant is an accumulator of metals.

The metal content of Equisetum collected from 15 mineralized areas was generally lower than that of other plants growing there. Gold contents in the ash of 

Equisetum averaged only 0.17 part per million in the conterminous United States 

and 0.54 part per million in Alaska. Early reports of large amounts of gold in 

Equisetum may be erroneous; a study of the analytical procedures that were used 

suggests that other metals, in addition to gold, were measured and reported as 

amounts of gold.

Equisetum consistently accumulates zinc in amounts greater than are in the 

substrate; commonly these amounts are also greater than those in other plants 

that grow in the same soil. Equisetum is, therefore, an accumulator of zinc but, 

contrary to earlier reports, is not an accumulator of gold.

INTRODUCTION

The purpose of this study was to determine whether species of Equisetum are accumulators of metals, as suggested by the high gold values 

reported in these plants (Nemec and others, 1936). Samples of 

Equisetum (horsetail, scouring rush) for this study were collected 

throughout the conterminous United States and Alaska, largely from 

mineralized areas, and analyzed for 28 elements. The samples were 

collected and analyzed at intervals over a long period of time, but only 

recently have sensitive analytical methods for gold in plants been 

available.

The genus Equisetum includes about 25 species and is found throughout the world except in Australia and New Zealand (Core, 1955, p. 

222). Some species grow in ponds and marshes, some in damp shady 

places, and some in relatively dry sites (Smith, 1938, p. 235). They are 

commonly abundant around tailings ponds in mining districts. The

Al
A2 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

plant is made up of annual or perennial aerial stems 10-20 cm high 

that arise from a deep-seated perennial rhizome. The stems are cylindrical and jointed, and the minute leaves unite to form a sheath at each 

node. Reproduction is by means of spores that are borne in conelike 

structures produced at the tips of the stems (fig. 1). The root system 

commonly is extensive; Equisetum sylvaticum growing on the tundra 

was found by Malyuga (1964, p. 72) to have roots at a depth of 150 

cm where permafrost occurred at a depth of 60 cm.

Some species of horsetails were used as scouring rush in pioneer 

days, and all species have a high content of silica and are rough to the 

touch. Equisetum a/rvense has been found to have a poisonous effect on 

grazing stock when it occurs in any quantity in hay or pasturage, according to Benedict (1937, p. 1126) and others. Both aconitic acid and 

the alkaloid equisetin, which is a nerve poison, have been identified in 

this plant (Tehon and others, 1946). However, Porsild (1951, p. 67) 

wrote, "The species is of considerable importance to wildlife; the 

green, sterile plant and also the starch-filled root-tubers furnish an 

important food supply for a large number of herbivorous mammals 

and birds." Some Eskimos and other native people of Alaska refer 

to this and other species of Equisetum as "goose grass" because the 

young shoots are avidly eaten by large flocks of wild geese in early 

spring.

The scientific and common names of the species of Equisetum 

that are discussed in this report are (Fernald, 1950) :

Equisetum arvense L., common or field horsetail

E. fkwiattte L.,1 water horsetail

E. hyemale L., scouring rush

E. Jiyetnale var. robustum (A. Br.) A. A. Eat., scouring rush

E. Jeansanum Schaffn., Kansas horsetail

E. Umosumlu.^ water horsetail

E. litorale Kohlewein, shore horsetail

E. pcHustre L., marsh horsetail

E. pratense Ehrh., meadow horsetail

E. sylvaticum L., woodland horsetail

E. telmateia Ehrh., giant horsetail

E. variegatum Schleich., variegated horsetail

Samples were collected in as many types of mineral districts 

as possible and also in unmineralized areas for comparison. Plants

1 The synonomy of E. fluviatile and E. limosum, two closely related species, is confused; 

each is considered to be a form or variety of the other by different writers.
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A3

FIGURE l. Equisetum arvense L., field horsetail. A, Fertile stems bearing sporeproducing cones (strobili). B, Sterile stem with part of rhizome, young stems, 

and roots. C, Node of sterile stem with cylindrical toothed sheath and whorl of 

branches.
A4 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

were collected, therefore, from areas mineralized with antimony, 

copper, gold, iron, lead, mercury, molybdenum, silver, tungsten, 

uranium, vanadium, and zinc.

PREVIOUS WORK

The chemical composition of the siliceous scouring rush has interested many workers since 1870, but actual analyses of samples of 

the genus are relatively rare. (See table 1.) Wolff (1871, 1880) and 

Mariani (1888) published analyses for major constituents in the ash 

of Equisetum arvense and E. telmateia. The results are not unusual 

except for the large percentages of silica, in which respect horsetails 

resemble grasses. The high iron values reported by Mariani were 

probably due to contamination from iron vessels. Dieulafait (1885) 

found a mean of 12.0 percent potassium sulfate and 14.3 percent 

calcium sulfate in 168 samples of Equisetum ash. Thus, as these primitive plants use sulfates rather than carbonates in their metabolic 

processes, he proposed that the sulfur in the Coal Measures was derived from Equisetum.

Bateman and Wells (1917) studied the tolerance of various species 

of plants to the tailings ponds of the Anaconda smelter. Equisetum 

variegatum was one of the more tolerant plants to grow there and 

contained 296 ppm (parts per million) copper in the ash, although 

other species more restricted in distribution contained as much as 6,210 

ppm. Vogt, Braadlie, and Bergh (1943) analyzed E. arvense growing 

on a sulfide copper deposit and found 43 ppm copper, 16 ppm lead, 

4,800 ppm zinc, 140 ppm manganese, and 380 ppm iron. These values, 

except that for zinc, are considerably below average for plants. Robinson, Lakin, and Reichen (1947) found Equisetum to accumulate more 

zinc than any other genus growing on the zinc slime ponds at Friedensville, Pa. A maximum value of 7,000 ppm dry weight (approximately 

3.2 percent in the ash) was reported for 14 unwashed samples; the 

average was 4,000 ppm. A sample collected close to the one having 

the maximum value and brushed very carefully contained 3,200 ppm, 

but a washed sample contained only 1,900 ppm. Apparently two-thirds 

of the metal in ash of unwashed plants from highly contaminated 

areas can be discounted as dust clinging to the plant.

Lovering and Engel (1968) have recently conducted greenhouse 

experiments with Equisetum and three grasses. Plants were grown in 

pots of basalt and rhyolite and fed a nutrient solution. Silicon and other 

elements were absorbed from the ground rock by both grasses and 

Equisetum although not in normal quantities. The silicon was shown to 

be translocated to the above-ground parts of the Equisetum as an
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A5

organic complex, aromatic in nature, and to be precipitated in the cell 

walls as plant opal.

Equisetwn has attracted much attention as a reported plant accumulator of gold since 1936 when Nemec, Babicka, and Oborsky obtained 

610 ppm gold in the ash of E. palustre that had grown in soil containing only 0.2 ppm. Other plants collected from the same area also had 

exceptionally large amounts of gold. These values have been quoted by 

several other workers (Benedict, 1941; Lundberg, 1941; Thyssen, 

1942; Malyuga, 1964).

In view of the values that have been reported from other areas since 

1936, it might be well to review in detail the collection and analytical 

data of these particular samples. Babicka (1943) gave, in his report 

"Gold in living organisms," a full account of the investigation begun 

by Nemec and Babicka in 1935.

Near the village of Oslany in old Slovakia, andesite and rhyolite 

containing 0.1 gram gold per ton are weathered to gravels and clays 

enriched to 0.2 gram gold per ton. The gold is believed to occur as 

colloidal gold because it has never been observed in the metallic state; 

this fact is considered by Babicka to be significant to the phenomenon 

of unusual gold accumulation by plants. The gold was originally found 

in 1934 in corn being grown in the area, and a long investigation was 

commenced. Research on analytical methods resulted in an original 

colloid-pectin method. In 1935, samples of Equisetum palustre, the 

swamp horsetail, and E. arvense, the field horsetail, were collected, and 

control samples were collected from the nearby village of Hornia Ves. 

The samples were air dried and then ashed at very low temperatures in 

porcelain dishes. The ash was dissolved in aqua regia, and the solution 

was then evaporated. The residue was treated with hydrochloric acid, 

and the solution was boiled to precipitate silicic acid and then was 

filtered. The dilute hydrochloric acid filtrate was treated with hydrogen sulfide to precipitate the acid-insoluble sulfides, apparently considered by the authors to be solely gold sulfide. If the amount of precipitate was large, it was then weighed directly; if small, the residue was 

put into solution and the gold was precipitated, using pectin as a 

protective colloid, and measured colorimetrically against standards. 

It should be pointed out that a group of metals would be precipitated 

by this method, and direct weighing of the residue would include the 

sulfides of copper and several other metals. Thus the high values of 611 

ppm gold in E. pahistre and 63 ppm in E. arvense may be erroneous.

The Equisetum samples from Oslany and Hornia Ves, which were 

analyzed for major constituents as well as for gold, contained large 

amounts of aluminum and silica. The silica content varied consider-
A6 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

TABLE 1. Some analyses of Equisetum

[Converted from oxide and from dry weight to approximate ash values where necessary. Number in

Leaders (_) indicate

Year

1871

1888

1917

1936

1943

1943

1945

1947

1950

1963

Author

Wolfl »-. ...

Wells.

BabiCka, and 

Oborsky.2

BabiCka. ........

and Bergh;

Edgington. 

Robinson,

Lakin, and 

Reichen.

Delavault.

Roshkov.

Sample localities

Montana.

Slovakia.

ia, on andesite clays.

Insel on 

Danube 

alluvium.

deposit in 

Rjirosfeltet.

Friedensville,

Pa., slime 

ponds containing anomalous amounts 

of Zn, Pb. 

Background.. _

British 

Columbia 

(Au).

 .do... . 

 do.. ...

Aldan Shield,

U.S.S.R.

Species

 .do ~

 .do 

 .do 

 do ...

 do ....

 .. .do 

Ash 

content (percent)

18.7

26.7

17.39

6.05

21.65(*)

23. §5(*)

25.0

31.1(2) 

16.70

17.20

18.00

22.75

Al (percent)

0.51

 99(*)

2. 30(* j

2.K*)

Ca (percent)

12.15

6.14

9.65

14.16

5.76C)

5.53(*)

3.60(*)

01 (percent)

6.12

5.49

5. 42(*)

5. 30(*)

Mg (percent)

1.69

1.09

1.32

4.16

1.23(*)

1. 63(*)

1.76(*)

P

(percent)

1.22

.62

.55

1.26

.70(*)

1.01(*)

1 The values have been converted from the oxides.

2 Quoted by McMurtrey and Robinson (1938), Lundberg (1941), Thyssen (1942), and BabiCka (1943).

ably; a maximum content of 83.5 percent SiO2 was found1 in older 

plants. Individual species had consistently high contents of A12O3 .

Several species of plants were then studied from a second area at 

Grossen Schutt Insel, on the Danube River. The alluvial deposits on 

which these plants grew were also derived from andesite and contained more than 0.2 gram gold per ton. The gold, which occurred 

both as colloidal gold and as coarser particles, diminished with depth. 

Equisetum arvense was sampled several times during the year to determine its average composition. The samples contained an average of 

only 16 ppm gold in the ash of aerial parts. Babicka believed that the 

value was lower at this locality than at Hornia Yes because the gold is 

coarser and, thus, is not as readily absorbed by plants. On the other 

hand, the gold analyses were made by J. Splidhal in a laboratory set
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A7

ash reported in the literature

parentheses Is number of samples averaged; asterisk (*) signifies average of many samples. 

no data available]

K (percent)

15.90

6.64

7.69

3.53

12.46(*)

16.35 (*)

21.58(*)

Si 

(percent)

41.7

32.97

14.51

2.89

28.58(*)

33.1(*)

23.45(*)

37.22(*)

32. 7(*)

Na 

(percent)

0.37

.44

1.05

5.73

,56(*)

.59(*)

1.07(*)

S 

(percent)

4.00

1.12

3.58

2.71

1. 06(*)

1 Ad (*}

Cu 

(ppm)

296

snf*~\

43

Au

(ppm)

»610(*)

»63(*)

8 16(*)

.34

.17

.34

.33

.4(8)

Fe 

(ppm)

4,900

9,800

163,500

261,000

ft ^nnf'1^

21, 000 (*)

f)t QftfH*'*

380

Pb 

(ppm)

16

Mn 

(ppm)

150-10, 000(*)

14ft

As 

(ppm)

1.0

Ti 

(ppm)

 tonnnw

Zn 

(ppm)

o 7nnf*\

4,800

18, 440(14)

522(2)

' Soil contained 0.2 ppm gold.

up in the Kolozs-Nema area, in the plant-physiology institute of the 

Karls University in Czechoslovakia and in the Geological Institute in 

Prague. These analyses presumably were made by orthodox methods, 

so that the separation of gold from the associated metals may have 

been more nearly complete. In the samples of Eqidsetum that have 

been analyzed more recently and reported by other workers, no such 

high values have been obtained; in fact, no sample has contained more 

than 1 ppm gold in the ash. Four samples collected by Warren and 

Delavault (1950) in the Clinton district of British Columbia contained from 0.17 to 0.34 ppm gold in the ash. Eight samples from the 

Aldan shield, U.S.S.R., analyzed by Razin and Rozhkov (1963), contained an average of 0.4 ppm gold.
A8 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS 

OBJECTIVES AND METHODS

The collection of Equisetum in various types of mineralized environments and the spectrographic analyses of the material were 

proposed for two reasons. First, the information available in the 

literature suggested that this primitive plant might be a remarkable 

accumulator of metals; second, analysts of the U.S. Geological Survey 

spectrographic laboratories believed that the ashed plant material 

would be especially amenable to analysis by their spectrographic techniques for rocks, minerals, and other materials (Bastron and others, 

1960; Myers and others, 1961) because of the high silicon content.

The data presented here were not collected at a single time as a 

part of an organized project but as the opportunity permitted over a 

period of nearly 20 years. The samples, collected largely by Helen 

Cannon and Hansford Shacklette, were all taken from above-ground 

parts but were not washed. The samples were ashed at temperatures 

not exceeding 450 °C. Most of the minor-element analyses were performed by Harry Bastron using emission spectrography; a few major 

elements were analyzed chemically, and the gold values, which are 

below the usual limits of spectrographic detectability, were obtained 

by Thelma Harms using an atomic-absorption method developed by 

Thompson, Nakagawa, and YanSickle (1968) for geologic materials.

UPTAKE AND CONCENTRATION OF METALS 

BY EQUISETUM

Concentrations of 21 elements in the ash of Equisetum, collected 

from unmineralized and mineralized ground throughout conterminous 

United States, were obtained by spectrographic and chemical analyses 

as shown in table 2. Contents of tin, lanthanum, beryllium, scandium, 

yttrium, and ytterbium were below the sensitivity of the method. Contents of copper, molybdenum, lead, zinc, and manganese were greater 

in samples from mineralized ground than in background samples.

NORMAL CONCENTRATIONS OF METALS IN EQUISETUM

Equisetum growing in unmineralized ground generally has a lower 

percentage of metals than the average for all types of vegetation as 

shown in table 3.
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A9

A plant such as Equisetum that accumulates silicon in its tissues 

will yield more ash per unit of dry weight than will a plant with a 

lower silicon content. For this reason, the percentage of a metal that 

is reported in Equisetum ash may be lower than that in the ash of 

average vegetation, although the actual amounts in dry weight of 

Equisetum may be average.

ANOMALOUS METAL. CONTENTS IN EQUISETUM FROM 

MINERALIZED AREAS

The metal content of Equisetum collected from 15 mineralized areas 

was surprisingly low and in many samples did not equal that of 

other plants growing in the same environment (table 3).

The highest lead, zinc, and molybdenum contents occurred in Equisetum collected from districts where these respective metals were 

mined commercially. The highest chromium, titanium, and zirconium 

contents occurred in plants collected as background material at Kenwood Beach, Va., and Jones Wharf, Md.

Many of the other metals in Equisetum showed little correlation 

with the major economic metal of the area. The uptake of these metals 

by Equisetum may depend upon the solubility of the metal and the pH 

of the soil rather than on the total amount of metal that occurs 

there.

QBE HILL MINE

A comparison between the uptake of copper, lead, and zinc by 

Equisetum, from a sulfide-ore environment and that by other types 

of plants was made at the Ore Hill mine, Warren, N.H. The mine lies 

at an elevation of 1,600 feet, in the White Mountain National Forest, 

about 3~y2 miles west of Warren. It was originally opened for copper 

in 1840, but zinc was found to predominate at a depth of 150 feet, and 

the mine was worked intermittently until about 1922 for zinc and 

the byproducts copper, lead, and iron. The ore contained black sphalerite mixed with copper, lead, and iron sulfides and occurred in heavily 

sheared schist near the base of the Ammonoosuc Volcanics.

The top few inches of surface soil and tailings that were sampled 

contained more lead than either copper or zinc, but a comparison with 

fresh samples of the tailings collected at a depth of 4 feet by the U.S. 

Bureau of Mines (C. L. Rogers, 1943, unpub. data) showed that all 

three metals are largely leached from the surface soils, and that zinc 

predominates at depth. The two Equisetum collections contained small 

amounts of copper but large amounts of lead and very large amounts 

of zinc (table 4). The chlorotic Equisetitm sample contained more 

zinc than the sample of birch or the algae that grew in a highly mineralized stream. Undoubtedly Equisetum is an accumulator of zinc.

291-025 68 2
TABLE 2. Accumulation of elements by Equisetum in the conterminous Un

[Analysts: Harry Bastron, C. 8. Papp, G. H. VanSickle, and J. G. Watterson. Leader

Sample 

No. Locality

150342 Ely, Orange County, Vt.. ................

150343 do.....

150344 Warren, Grafton County, N.H. ...........

150345 ... do

150346 Franklin, Sussex County, N .J ... .........

 do . 

150351 Manning, Orleans County, N.Y. .........

150352 ....do....... .. .

150353 ....do-... . ..

150356 Friedensville, Lehigh County, Pa 

150357 Nederland, Boulder County, Colo.. ......

150358 Climax, Lake County, Colo... ............

150361 Black Hawk, Gilpin County, Colo........

150364 ....do ...............

150365 Slick Rock, San Mlguel County, Colo - 

150366 Santa Fe Creek, Santa Fe County, N. 

Mex. 

150362 Black Canyon Spring, Jerome, Yavapai 

County, Ariz. 

150363 Kokomo, Summit County, Colo. .........

150359 Arapaho Basin, Summit County, Colo.... 

150355 Falls Church, Fairfax County, Va~ ....

150354 Kenwood Beach, Hanover County, Va 

150349 Jones Wharf, Worcester County, Md...

150347 Blanding, Grafton County, N .H. .........

Collection data

Outcrop of acid schist..... __ ............ .....

Undrained North Oak Orchard bog, mineralized- .

Eleme

sub

ex

bac

v

Cu_. . .

Cu 

Cu, Zn

An

Cu -

r1 !!

Cu 

Zn,P

Zn, Pb

Zn 

W. ---

Mo, W

An

A 11

V,U. 

Cu, Fe

Cu... 

. ...do

.-..do

...-d

.... do 

.... do 

-...d

....do
Sample

No.

150342

150343

150344

150345

150346

150348

150350

150351

150352

150353

150356

150357

150358

150361

150364

150365

150366

150362

150363

150360

150359

150355

150354

150349

150347

58-375

Ag

0.6

.4

1.2

1.6

.4

1.0 15111

(01

(»)

(')

.6

.8

.7

(')

0)

(')1

0) (l)

.4

0

Al

1,300

860

3,400

5,000

1,300

9,000

4,800

34, 000

7,700

820

640

640

1,300

7,500

6,200

400

1,500

900

9,000

540

600

470

4,600

1,200

4,700

2,200

1,900

1,000

Au

0.1

.2

.1

< !

.1

.1

0)

(1)

(*)

(})

(')

(0

.1

.1

.2

.2

.1

.2

.2

(i)

.1

0)

(1)

.1

.4

B

130

.160

270

210

190

80

190

1,300

300

180

260

100

140

340

610

350

420

460

360

280

410

1,100

620

1,600

140

250

250

140

Ba

270

540

680

900

400

360

230

380

240

300

230

200

640

800

680

480

390

640

580

150

420

350

800

570

140

70

360

950

Co

6200060

37403003

120024306300000

Cr

01123

128

140

204238

137071

1012032 to 

lo

1132

Cu Fe Mg

100 300 14,000

36 370 16, 000

140 1,800 11,000

120 2,600 14,000

50 1,200 22,000

72 6,200 50,000

400 4,200 18,000

1,900 95,000 32,000

550 13,000 19,000

40 410 50,000

42 500 40,000

10 320 26,000

94 1,000 35,000

160 5,100 21,000

240 4,300 27,000

140 120 19, 000

160 1, 400 5, 800

300 500 10,000

270 5, 900 7, 500

600 320 11, 000

36 230 13,000

55 150 11,000

95 1,800 22,000

65 740 19,000

11 2 800 4 500

27 2,' 200 9^200

19 1,000 11,000

62 590 6, 000

Mil

460

40

170

90

1,000

1,400

110

2,200

320

180

1,000

60

50

800

29, 000

140

1,100

100

1,000

140

190

430

750

320

i "in JLoU

80

80

65

Mo Na

0 300

12 1, 800

5 1, 200

6 2, 200

65 800

7 10, 000

7 7, 200

5 11,000

7 7, 600

5 1, 700

11 3, 400

0 500

5 900

8 10, 000

150 6, 400

0 400

0 1,600

5 4,400

0 2, 800

0 4,500

0 500

0 700

6 2, 200

5 1,100

0 2 300

5 i 400

0 1, 500

0 1, 000

1 Insufficient quantity of sample for analysis.

3 Species was not determined.
A12 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

Food and Drug Administration personnel rechecked the Vaccinium 

canadense sample and found 86 ppm lead in the dry weight using a 

gravimetric method.

TABLE 3. Average and maximum trace element contents in ash of Equisetum, in 

parts per million, compared with the average for all types of vegetation

Element

Barium __ _________

Chromium. _

Cobalt

Iron _ _

Molybdenum. _ _ _ _ .

Nickel ____ ______..

Silver.

Strontium. _

Titanium. _ _____ _ .

Vanadium. _

Zirconium __

Average content expected 

in all types of 

vegetation l

1,100

580

13

_ ft

7,000

70

3,300

13

65

1,730

460

20

1,220

20

Average content of eight 

samples of 

Eguisetum from 

unmineralized 

ground

430

570

<5

= 2

1, 180

0.2

12

250

7

300

280

<200

<50

Maximum content in all 

samples of 

Eguisetum that 

were analyzed

4,500

1,600

18

30

15, 000

0.5

420

29, 000

150

280

2

1,500

1,200

50

9,000

230

Metal produced 

in district 

where maximum content 

was found

Hg

None

None 2

Pb, Zn

Pb, Zn

Hg

Zn, Pb

Mo

Mo

Mo

Au

None

None 2

Mo

Zn

None 2

> Calculated from published analyses and from data in U.S. Geol. Survey files. 

2 Beach sands.

TABLE 4. Copper, lead, and zinc in plants growing in acidic sulfide environment of 

Ore Hill mine, New Hampshire, in parts per million

[Analysts: H. W. Lakin and L. E. Reichen]

Copper Lead Zinc

Location and kinds of sample In dried In ash of In dried In ash of 

plant or plant plant or plant 

soil soil

Rusty stream flowing past tailings 

dump, total heavy metal, 16 

ppm, pH 3.5:

Edge of ore dump:

Pinus strubus, white pine.. ... 

Above dam:

Vaccinium canadense, blueberry (stunted, red coloraOutcrop of schistose hanging wall: 

Equisetum arvense, horsetail

Old pile of tailings: 

Equisetum arvense, horsetail 

(healthy)-..... . 

Composite sample of tailings at 

depth of 4 ft i.... .... ......

920 

120 ...

13

12

100 ...

26 

19 

20

38 

2,000 ...

1, 300 6, 600 

.......... 660 ...

37 23 

25. 5 23

... . 660 ...

74.2 9 

55. 9 81 

80 90

152 86 

. ....... 21,000 ...

9,420

65.7 

48.9

25.7 

238 

360 

344

In dried In ash of 

plant or plant 

soil

2,900 

390 ...

540 

100

190 ...

650 

120 

1,400

460 

27,000 ...

4,140

1,540 

210

1,850 

350 

5,600 

1,840

i Analyzed by U.S. Bur. of Mines.
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A13 

LEAD-ZINC DISTRICT OF SOUTHWESTERN WISCONSIN

A study of the element content of Equisetum arvense and E. kansanum that grew on substrates ranging from unmineralized to heavily 

mineralized was made in the lead-zinc mineral district of southwestern 

Wisconsin. Analyses of samples of the plants and of the soil or of 

evaporite from water in which the plants grew are given in table 5.

The amounts of the macronutrient elements calcium and magnesium 

are less variable in the plants than in the soil and evaporite (table 5). 

This fact may indicate that absorption of these elements by Equisetum 

is related to metabolic requirements of the plant. The amount of the 

micronutrient zinc that is absorbed is directly related to the amount 

in the soil, but only on soils having a low zinc content does the amount 

of zinc in plant ash exceed the amount in the soil. The range in 

amounts of this element in the plants, 100-8,000 ppm, indicates that 

absorption of zinc (at least in large amounts) is not controlled by 

metabolic requirements of the plant, and that Equisetum can be considered a zinc accumulator.

In contrast to the concentrations of zinc, the amounts of the micronutrient copper are the same in all Equisetum samples, in spite of the 

fourfold difference between the low and high values in the soils. The 

absorption of the micronutrient manganese is similar to that of copper, and a relation of the absorption of both elements to metabolic 

requirements is suggested.

The micronutrient iron appears to be absorbed in amounts greater 

than are required for metabolism, and these amounts are dependent in 

part on the amount in the soil. The greatest amount of iron in Equisetum reported in table 5,15,000 ppm, was found in the ash of plants 

that grew on soil having 50,000 ppm iron.

The remaining elements listed in table 5 commonly are considered 

to be nonnutritive (Sutcliffe, 1962, p. 6) and in general are not concentrated in the plants in amounts greater than are in soils unless the 

soils contain a greater than normal concentration of the elements. This 

tendency in concentration is illustrated by the amounts of cobalt, lead, 

nickel, and titanium in both soil and plant samples at the heavily 

contaminated New Diggings site; however, chromium, vanadium, and 

zirconium do not have this relationship in the two kinds of samples.

Although Equisetum may accumulate large amounts of zinc and 

lead if growing in metal-rich soils, some other plants at the New Diggings site contained even larger amounts of these elements. For example, ragweed (Ambrosia artemisiifolia L.) contained 12,000 ppm 

zinc and 500 ppm lead in its ash. Redcedar (Juniperus virginiana L.) 

stems and leaves contained 80 ppm copper in the ash an amount four
A14 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

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METAL ABSORPTION BY EQUISETUM (HORSETAIL) A15

times greater than the maximum copper content of Equisetum at this 

location.

Both gold and silver were looked for by means of semiquantitative 

spectrographic analysis, but neither element was found in these Equisetum samples.

VARIOUS PARTS OF ALASKA

Samples of four species of Equisetum were collected in Alaska from 

three mining districts and one area where there are no known ore 

deposits (table 6). The McGrath sites are in deposits of sandy alluvium adjacent to the Kuskokwim River. There are no known ore deposits in the vicinity of these sites; however, the Kuskokwim River 

and its tributaries drain areas of known mineral deposits. The metal 

values for Equisetum from McGrath, therefore, may not represent 

background values for this plant.

The Red Devil sites were in areas where quicksilver ore (cinnabar) 

was being, or had been, mined. The minerals associated with the cinnabar deposits are stibnite, realgar, orpiment, and native mercury (Cady 

and others, 1955, p. 105-106). Mining operations or placer ore presumably had contaminated the sites, although the substrate of Equisetum was largely loess.

One Latouche Island site was near a copper mine and mill (now 

inoperative) and was heavily contaminated by teachings from a tailings pile and dust from the ore mill. Another site on this island was 

on the workings of a small prospect pit, and two sites were on the undisturbed muskeg; one was above a large pyrite body that was said 

by Stejer (1956, p. 114) to contain copper, lead, and zinc minerals, and 

the other was above graywacke that contained no known mineral 

deposits.

The Kantishna site, in the Alaska Range a few miles outside Mount 

McKinley National Park, is in a small drain from tailings of a gold 

mine (now inoperative) at a lode deposit. Gold, silver, lead, and antimony are the chief metals of economic value in this area, but pyrite 

and arsenopyrite are also common (Wells, 1933).

Analyses of the samples from McGrath suggest that the values are 

somewhat higher than those in the background samples, and the metals 

in the alluvium may have come from mineral deposits upstream. Both 

gold and silver were found in all samples. Because the three Equisetum 

species at this location grew in different types of habitat, these data 

do not conclusively demonstrate a difference in metal absorption between species the differences that are shown may be due to variation 

in metal content of soils at the sites. The samples from Latouche Island and Kantishna were analyzed before the currently used sensitive 

method for gold determination was available, and the semiquantita-
A16 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

TABLE 6. Accumulation of elements by Equisetum

[Collector: Hansford T. Shacklette. Analysts: Harry Bastron, E. F. Cooley, Thelma Harms, D. Marx, C. S.

Locality

McGrath: 

In muskeg over alluvial sand- .... 

Do...........................

T>o...... .....................

Eed Devil: 

In ravine by mercury smelter _ ... 

In lake fed by drain from abandoned mercury mine. 

On loess near active mercury mine _ 

Latouche Island:

In drain from Beat son copper 

mine tailings. 

Slate dump by prospect pit near 

Duke mine. 

Kantishna: In drain from tailings, 

Eed Top mine.

Element in 

the substrate 

in excess of 

background 

values

None known 

None known 

None known

Hg, Sb, As 

Hg, Sb, As

Hg, Sb, As

Fe, S, Cu 

None known 

Cu, S

Fe, S 

Au

Sample 

No.

58-369 

-370 -371

-372 

373

-374

57-2982 

-2997 

-3128

-3135 

-3784

Species of 

Equisetum

limosum..... 

sylvaticum...

.....do......

limosum..... 

sylvaticum...

.... .do......

----do-._..-

.--do._.___

sylvaticum...

Ashcontent 

(percent)

15.1 

13.2 

14.8

24.6 

14.1

14.5

12 

21 

15

18 

32

Element J

Ag

1 

1 

1

nd 

nd

1

<2 

<2 

Tr.

<2 

2

Al

1,000 

1,000 

2,000

1,000 

2,000

1,000

Au

0.4 

.2 

.4

.1

.5

.4

i Looked for but not found: As, Be, Bi, Cd, Ce, Ga, Ge, Hf, Hg, In, Ir, La, Li, Nb, Pd, Ft, Re, Ru, Sb,

tive spectrographic method did not detect gold in these samples, although silver was found in two of them.

The values presented in table 6 show that analyses of Equisetum 

tend to correspond with the presence of large amounts of certain metals 

in the substrate. This tendency is illustrated by the relatively large 

amounts of copper, lead, nickel, and zinc in ash of the plants from the 

prospect pit at Latouche Island and from the mine tailings on this 

island and at the Kantishna site. Other kinds of plants, however, are 

equally useful for biogeochemical prospecting at similar sites.

SUMMARY OF THE CONCENTRATION OF TRACE 

ELEMENTS IN EQUISETUM

ZINC

The zinc content of the ash of Equisetum growing on unmineralized 

ground is less than 200 ppm, which is considerably lower than that in 

average vegetation. The plant can, however, accumulate large amounts 

of zinc when the zinc is in a soluble form. The maximum amount accumulated was 9,000 ppm from the Friedensville slime ponds.

The collections from the drained and undrained mucks near Manning, N.Y., which receive lead and zinc from the mineralized Lockport 

Dolomite, illustrate differences in uptake. The largest amounts of 

copper, lead, zinc, manganese, iron, strontium, and barium were absorbed from the drained oxidized muck. The least amounts, regardless 

of soil contents, were absorbed from the bogs in which the metal has 

remained in a reduced state (table 7).
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A17

species from Alaska, in parts per million of ash

Papp, and G. H. VanSickle. nd, not detected; <, less than the amount stated; Tr, trace;.., no data availablel

Element ' Continued

B

20 

30 

40

30 

30

60

100 

100 

200

100 

100

Ba

800 

1,100 

750

380 

600

4,500

500 

300 

500

200 

30

Co

2 

nd 

nd

nd 

3

14

<10 

<10 

10

20 

<10

Cr

4

2 

9

5 

9

2

<20 

<20 

<20

<20 

<20

Cu

80 

39 

62

35 

62

48

80 

40 

150

100 

80

Fe

590 

340 

840

330 

1,100

320

2,100 

300 

500

200 

3,000

M«

4,000 

8, 000 

20, 000

30, 000 

40, 000

30, 000

20, 000 

15, 000 

20, 000

20, 000 

20,000

Mo

25 

7 

14

nd 

15

nd

<10 

<10 

<10

<10 

<10

Mn

630 

230 

110

45 

650

700

3,000 

150 

500

1,000 

200

Na

3,000 

1,000 

3,000

2,000 

7,000

3,000

Ni

6 

5 

6

nd 

3

21 

10

50

50

5

P

6,000 

5,000 

6,000

4,000 

20,000

6,000

Pb

nd 

nd 

nd

nd 

nd

nd

100 

100 

200

200 

100

Sn

nd 

nd 

nd

nd 

nd

nd

<10 

<10 

<10

<10 

<10

Ti

100 

84 

260

64 

210

64

10 

<10 

10

10 

50

V

10 

nd 

20

10 

10

10

<10 

<10 

<10

<10 

<10

Zn

200 

250 

200

100 

150

250

400 

200 

2,000

1,000 

4,000

Zr

10 

nd 

10

nd 

20

nd

<10 

<10 

<10

<10 

<10

Sc, Ta, Th, Tl, U, W, Y, and Yb.

After the mucks in an area south of Manning were drained, the 

availability of zinc in the peat increased and toxic areas developed 

where no crops could be grown (Cannon, 1955).

Large concentrations of zinc were also found in Equisetum growing 

in the Black Hawk gold district, Colorado, the Ore Hill lead-zinc mine 

in Warren, N.H. (table 4), the zinc mine at Franklin, N.J., the Wisconsin lead-zinc district (table 5), and Kantishna, Alaska (table 6).

LEAD

The amounts of lead absorbed by Equisetum in unmineralized areas 

averaged only 13 ppm in the ash. The extremely high values of 350 

and 420 ppm found in E. arvense at the Ore Hill mine were not caused 

by traffic contamination and are valid, for the mine has been inactive 

for 25 years, and the collection sites are not near the highway.

TABLE 7. Zinc and lead absorption by Equisetum growing on drained and undrained bogs near Manning, N.Y., in parts per million of ash

[Analyst: L. E. Reichen]

Location of sample site

Undrained area near north edge of 

Oak Orchard bog _

Drained and oxidized muck in

Undrained bog south of Albion____

Zinc

Plant

1,000

1,300

100

Soil

6,700

2, 100

8,400

Lead

Plant

16

83

7

Soil

26

12

100
A18 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

The absorption of lead, copper, and zinc by Equisetum as compared 

with other plants growing at Ore Hill, N.H., is shown in table 4. These 

primitive plants appear to accumulate more lead than trees or shrubs 

but not nearly as much as the algae growing in the stream that drained 

the tailings.

Fairly high values were obtained at the New Diggings site in Wisconsin, below the tailings of the Climax Molybdenum mill in Colorado, 

in drainage from the Black Cat gold mine at Black Hawk, Colo., and 

in the mineralized peat bogs near Manning, N. Y. All lead values were 

high in samples collected on Latouche Island and at Kantishna in 

Alaska.

COPPER

The average background copper content in different classes of 

vegetation ranged from 120 to 250 ppm in the ash. Background copper 

in samples of the ash of Equisetum averaged only 48 ppm.

Two samples of Equisetum qrvense were collected at a copper mine 

in altered volcanic schists at Ely, Vt. One grew on tailings and contained 100 ppm copper; the other grew on natural soil near the mine 

shaft and contained 36 ppm. More copper was absorbed by Equisetum 

growing near a sulfide (copper-iron-uranium) ore body in a limfoergite 

dike on Santa Fe Creek, N.Mex., than by that growing at Ely. High 

copper values were obtained in several samples collected near copper 

mines on Latouche Island, Alaska. The largest amount, 600 ppm in the 

ash, was found in E. variegatum growing in Black Canyon spring in 

the Gaddes Basalt near Jerome, Ariz. This basalt was not suspected to 

be an anomalous source of copper. Values of more than 100 ppm copper 

were found in Equisetum growing in mineralized areas that were economically valuable as sources of some other metal for example, the 

Ore Hill lead-zinc mine at Warren, N.H.; the tailings of the Climax 

molybdenum mill, Colorado; the dump of a tungsten mine north of 

Nederland, Colo.; alluvium below the Black Cat gold mine at Black 

Hawk, Colo.; and the dump and stream alluvium below the Slick Rock 

uranium-vanadium mill in Colorado. The increased uptake of copper 

in some mineralized areas may be caused by the decrease in pH rather 

than by the total copper present in the soil. The Equisetum, sample 

collected at the Kearsarge mine in Houghton, Mien., was found to be 

contaminated with mineral matter. This contaminant was separated 

from the ash 'and analyzed separately. Table 2 gives the results of 

analyses of the purified ash, the mineral contaminant, and an unrefined 

sample. The mineral matter contained nearly 2,000 ppm of copper, and 

the purified plant ash only 400 ppm.
METAL ABSORPTION BY EQUISETUM (HORSETAIL) A19 

GOLD AND SILVER

Gold in Equisetum throughout the conterminous United States 

ranged from less than 0.1 ppm in the ash to 0.4; the latter amount was 

in a sample collected as background material from Utley, Henderson 

County, Ky. Of the samples from mineralized areas, those collected in 

gold-producing districts averaged 0.17 ppm compared with 0.12 ppm in 

non-gold-producing areas. The samples collected in Alaska averaged 

0.34 ppm; this value corresponds closely with those obtained by Warren and Delavault (1950) for Canadian samples. The difference in 

average content in plants growing on mineralized and unmineralized 

ground however, is not significant and suggests that Equisetum would 

not be useful in prospecting for gold.

Silver is absorbed by Equisetum more readily than gold, and the 

amount of silver absorbed seems to be related to the amount of silver 

present in the soil. Samples collected at the silver-producing Ore Hill 

mine, New Hampshire, averaged 1.4 ppm; those from other mineral 

districts averaged 0.7 ppm.

OTHER, TRACE ELEMENTS

An anomalous amount of molybdenum was found in Equisetum from 

Climax, Colo., and also in that growing on mineralized limestone at 

Franklin, N. J. The uptake of molybdenum, unlike that of most metals, 

is favored by an alkaline environment.

Manganese, cobalt, nickel, chromium, vanadium, strontium, and 

boron contents were highest in the Equisetum collected at Climax. The 

titanium and zirconium contents suggest the possibility of dust contamination of the samples, although it is unlikely that the large 

amounts of other elements that were found can be attributed entirely 

to dust. The amounts of nickel found in Equisetum collected below the 

gold mine at Black Hawk, Colo., were high compared to those found 

at other sampling localities.

The concentrations of titanium, zirconium, and chromium in Equisetum samples that were collected as background material from beach 

sands along the eastern shore of Maryland may be significant for 

prospecting buried black-sand deposits. The concentration of these 

elements by the plants seems to be real and is not, as commonly suggested in the literature, purely a sign of dust contamination.

CONCLUSIONS

Twenty-two metals have been found in varying amounts in samples 

of Equisetum collected from areas mineralized with copper, lead, zinc, 

gold, tungsten, molybdenum, vanadium, uranium, and silver and also
A20 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

from unmineralized ground. Contents of all metals are lower in the 

ash of background Equisetum than in a,verage vegetation. The total 

metal content of Equisetum was generally lower than that of the ash 

of other plants growing in mineralized ground. Contents of lead, zinc, 

molybdenum, and silver were higher in Equisetum in districts where 

these metals were mined, but the contents of other metals were more 

closely related to availability than to total metal present. The accumulation of zinc in Equisetum from mineralized ground is greater than 

that of any other metal and is also large in comparison to the uptake of 

zinc by other plants. Equisetum can therefore be considered an accumulator of zinc.

No amounts of gold greater than 0.5 ppm were found in the ash of 

any sample. The samples collected from mineralized areas in Alaska 

had slightly higher gold contents than the samples collected in the 

conterminous United States. The high values reported in the early 

literature and since quoted by many writers may have been erroneous.

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METAL ABSORPTION BY EQUISETUM (HORSETAIL) A21

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