Utilization of Mull (Forest 

Humus Layer) in Geochemical 

Exploration in the Empire 

District, Clear Creek County, 

Colorado

GEOLOGICAL SURVEY BULLETIN 1278-B

Utilization of Mull (Forest 

Humus Layer) in Geochemical 

Exploration in the Empire 

District, Clear Creek County, 

Colorado

By GARY C. CURTIN, HUBERT W. LAKIN, ARTHUR E. HUBERT, E. L. MOSIER 

and K. C. WATTS

CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

GEOLOGICAL SURVEY BULLETIN 1278-B

Sampling of the forest humus layer may 

be an effective geochemical tool in 

areas where the bedrock is covered 

by colluvium or glacial drift

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

(Library of Coagwas <*tatog-4»id No. 75-170292)

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

Washington, D.C. MM2 - Price 30* (paper cover)
CONTENTS

Page

Abstract.____________________________________________________________ Bl

Introduction_ ________________________________________________________ 1

Acknowledgments--_______________________________________________ 3

Geologic setting ______________________________________________________ 4

Geochemical investigations _______-___-__--_--__________-_----__-----__ 7

Materials sampled_-_____________________________________________ 7

Contamination of mull samples..------------------------------- 8

Analytical procedures..____________________________________________ 8

Distribution of geochemical anomalies----__--_--___-_--------------- 8

Gold-copper-bismuth anomalies.____.___-_________-__-__-__-__._ 9

Silver-lead-zinc-molybdenum anomalies __________________________ 10

Tungsten-tin anomalies ________________________________________ 10

Manganese anomalies._________________________________________ 10

Tellurium-mercury anomalies______-_______-_._____----_-_-_---- 10

Metal enrichment in mull ash_ - ___________________________________ 10

Metal content of ash of pine and aspen trees in the Empire district. _ _ _ _ _ 12

Correlation analysis._______-_-___.____-_____________-_-_-_-_-_---_ 13

Summary ____________________________________________________________ 15

References cited_____________________________________________________ 16

ILLUSTRATIONS

Page 

FIGURE 1. Index maps showing location of Clear Creek County and

Empire district________----__---.___--__-__-___--___. B2

2. Geologic map of the north half of the Empire district.________ 4

3. Map of the north half of the Empire district showing sample

localities. _____________________________________________ 6

4-21. Geochemical maps and histograms of 

4. Gold in mull ash_______________________________ 18

5. Goldinsoil__-__---_-------______--__________ 19

6. Copperin mull ash----__---_-_.____--_-_-___-____ 20

7. Copperin soil__--_--_-__.____--_-_-_-__---_____ 21

8. Bismuth in mull ash-__-___-_-____-.--__--_-__.___ 22

9. Bismuth insoil-___-_------_--_---_-----__------- 23

10. Silver in mull ash__--_-_-__--___-_--__---_---_-_- 24

11. Silverinsoil_-------__-------__-____---______ 25

12. Lead in mull ash__------___________________ 26

13. Leadinsoil______.____________^_______________ 27

14. Zinc in mull ash___-__---__-____._-._______-_-__ 28

15. ZmcinsoiL_---_---------_-------_-------__-__-_ 29

16. Molybdenum in mull ash_________.____--._-_____ 30

III
IV CONTENTS

	Page 

FIGURES 4-21. Geochemical maps and histograms of Continued

17. Molybdenum in soil...__-__-----_-_--_-----------_----- B31

18. Tin in mullash_____________________-___-____--_--_---

19. Tininsoil..._________________-----_________.-_

20. Tungsten in mull ash..________-___._.__-__-___----_--_

21. Tungsten in soil...____-__________----____--_----------

22. Geochemical map of manganese in mull ash.________---__

23. Histograms of manganese in mull ash and soiL___________

24. Geochemical map of tellurium in soil _____________________

25. Geochemical map of mercury in soil._______-____-__---__

32

33

34

35

36

37

38

39

TABLES

Page

TABLE 1. Metal content in the ash of pine and aspen trees that grow in 

the Empire district compared with that of various plants 

that grow elsewhere.._________________________________ B12

2. Matrix showing correlation of selected metals in mull ash with

each other and with percent ash________________________ 14

3. Matrix showing correlation of selected metals in soil with each

other. __-_-_--__-__._----__---__--_--_---------_-.--_- 14
CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING 

FOR MINERALS

UTILIZATION OF MULL (FOREST 

HUMUS LAYER) IN GEOCHEMICAL

EXPLORATION IN THE EMPIRE

DISTRICT, CLEAR CREEK COUNTY,

COLORADO

By GABY C. CURTIN, HUBERT W. LAKIN, ARTHUR E. HUBERT, 

E. L. MOSIER, and K. C. WATTS

ABSTRACT

Results of geochemical studies in the Empire district, Clear Creek County, Colo., 

show that the distribution of anomalously high amounts of gold, copper, and bismuth 

in mull reflects the known distribution of these metals in bedrock beneath an extensive 

cover of colluvium and glacial drift; but their distribution in the transported soil that 

underlies the mull poorly delineates the distribution of the known metal deposits.

High anomalies of silver, lead, zinc, and molybdenum in the mull encircle the principal anomalies of gold, copper, and bismuth and may reflect enrichment of silver, 

lead, zinc, and molybdenum in the bedrock beneath the colluvial and morainal cover.

The high anomalous concentrations of gold, copper, bismuth, silver, lead, zinc, 

molybdenum, tin, and tungsten detected in the mull ash and the detection of these 

metals (except tungsten) in the ash of pine and aspen trees may reflect a geochemical 

cycle in which these metals are leached from the bedrock, are absorbed by the trees, 

and then in part deposited in the leaves and needles; they are finally concentrated in 

the mull as the leaves and needles decay.

Some areas anomalously high in certain metals in mull are not related to known 

mineralization and merit further investigation.

INTRODUCTION

The Empire district, which has an area of approximately 6 square miles, 

is located in the southern part of the Empire 7^-minute quadrangle, 

Clear Creek County, Colo., about 37 miles west of Denver in the Front 

Range of the Rocky Mountains (fig. 1). Altitudes in the district range 

from 9,000 to 11,000 feet. The U.S. Geological Survey has made geochemical investigations of the north half of the district as part of its 

investigation of the geochemistry of gold in the zone of weathering.

Bl
B2 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

CLEAR CREEK COUNTY

_J

40' 106°

39'

Breckenridge

_J

10 20 30 MILES

APPROXIMATE SCALE

DENVER

COLORADO

FIGURE 1. Index maps showing location of Clear Creek County and Empire district.

Mining began in the district in 1862 (Spurr and Garrey, 1908, p. 401) 

with the discovery of gold in the oxidized and decomposed rock of the 

Silver Mountain ore zone (fig. 2). This rock was washed in sluices and 

yielded approximately $2 million in gold during 1862-65 (Harrison, 1964,
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B3

p. 93). These placer operations decreased in economic importance in the 

1870's, but they continued on a small scale for many years.

Lode mining was conducted intermittently from the 1860's to 1943. 

Some of the more important mines in the north half of the district are the 

Minnesota, the Silver Mountain, and the Conqueror (fig. 3). During 

1933-43 more than 90,000 ounces of gold was produced from lode deposits 

in the district, mostly from the Minnesota. Small amounts of copper and 

silver have been produced from time to time.

The geology of the Empire district has been described by S. H. Ball (in 

Spurr and Garrey, 1908), Lovering and Goddard (1950), and Braddock 

(1969). The ore deposits have been described by Spurr and Garrey (1908) 

and Lovering and Goddard (1950).

This investigation includes a study of the distribution and association 

of gold, silver, copper, bismuth, lead, zinc, molybdenum, tin, tungsten, 

and manganese in mull (forest humus layer) and in the underlying soil 

(6- to 12-inch depth), and of tellurium and mercury in the soil. Mull is 

defined by the U.S. Department of Agriculture (1951, p. 245) as "a humusrich layer consisting of mixed organic and mineral matter, generally with a 

gradational boundary to the underlying mineral horizon." Results of the 

geochemical studies show that the distribution of anomalously high 

amounts of gold, copper, and bismuth in mull reflects the known distribution of these metals in the bedrock beneath a cover of colluvium and 

glacial drift; but their distribution in the transported soil that underlies 

the mull poorly delineates the known metal deposits. The distribution of 

anomalously high amounts of silver, lead, zinc, molybdenum, tungsten, 

and tin in mull may also reflect enrichment of these metals in bedrock 

beneath a cover of glacial drift. In general the geochemical data on mull 

ash (figs. 4-17) show that a central zone containing the principal high 

anomalies of gold, copper, and bismuth is encircled by a peripheral zone 

containing the principal high anomalies of silver, lead, zinc, and 

molybdenum.

ACKNOWLEDGMENTS

We thank Mr. H. C. Nelson, Mr. C. P. Clifford of the Minnesota 

Mines, Inc., Mrs. H. M. Stoner, Mr. Harrison Bristol, and Mr. E. J. 

Woodriff for permission to publish data on samples collected on their 

properties. Mr. Nelson was especially helpful in aiding us in the proper 

identification of abandoned mines and mill sites and in supplying other 

relevant information not available in published reports. The following 

members of the U.S. Geological Survey assisted us in both the field 

investigations and the analytical work: M. A. Chaffee, H. D. King, 

C. W. Gale, J. G. Frisken, K. E. Espelie, R. C. Humphrey, K. R. Murphy, 

and O. J. Roman.
B4 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

GEOLOGIC SETTING

The Empire district is underlain by igneous and metamorphic rocks of 

Precambrian age which have been intruded by porphyries of Tertiary age 

(fig. 2). The Precambrian rocks are biotite gneiss and microcline gneiss 

that have been intruded by large, partly concordant bodies of Boulder 

Creek Granite and relatively small bodies of Silver Plume Granite. A 

small stoc'k of hornblende granodiorite porphyry, a small stock of leucocratic monzonite, and dikes of granodiorite porphyry, hornblende 

granodiorite porphyry, biotite granodiorite porphyry, biotite quartz 

monzonite porphyry, and bostonite porphyry, all of Tertiary age, intrude 

the Precambrian rocks. Bedrock in most of the area is covered either by

105-40'30"

FIGURE 2. Geologic map of the north half of the Empire
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B5

Quaternary colluvium or by Quaternary glacial drift which ranges in 

total thickness from about 3 feet to 40 feet. The Quaternary deposits 

shown in figure 2, which were not subdivided during mapping (Braddock, 

1969, p. 45), consist only of glacial drift and solifluction debris (watersaturated colluvium).

The ore deposits of the north half of the Empire district are fissure 

fillings, placers, and disseminated deposits of auriferous pyrite (Levering 

and Goddard, 1950, p. 156, 158). Principal vein minerals are pyrite, 

chalcopyrite, and quartz. Gold content increases with chalcopyrite content, and silver content of the ore generally is only a few ounces to the ton 

(Levering and Goddard, 1950, p. 158). A small quantity of native bismuth 

was reported from the Silver Mountain ore zone (S. H. Ball, in Spurr and 

Garrey, 1908, p. 399).

The veins of the Minnesota mine and the Silver Mountain ore zone are 

the two principal vein systems in the area studied (fig. 2). The Minnesota 

mine is composed of one primary vein and several discrete secondary 

veins which either coalesce into or are parallel to the primary vein, 

whereas the Silver Mountain ore zone is a strong zone of fracturing and 

alteration as much as several hundred feet wide in places. Individual ore 

bodies occur as irregular shoots along the veins and range from a few feet 

to 100 feet in height, and from less than 1 foot to 20 feet in width, and 

from a few feet to 1,800 feet in length. The vein system shown on the 

geologic map and the geochemical maps (figs. 2, 4-25) was compiled in 

part from field mapping during the summer of 1967 and in part from

EXPLANATION

Solifluction debris and morainal deposits J ^

Biotite quartz monzonite porphyry

Granodiorite group

Tg, granodwrite porphyry undivided 

Thg. hornblende granodiffrite porphyry 

Tbg, triotite granodwrite porphyry

Silver Plume Granite

Boulder Creek Granite

Biotite gnei

Contact

Dashed where approximately located

Vein or mineralized fault 

Dashed where approximately located

Inclined Vertical 

Strike and dip of foliation

district. Geology modified from Braddock (1969).
B6 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGUEE 3. Map of the north half of the Empire district showing sample localities 

(small dots). Contour interval, 200 feet.

previous maps by Braddock (1969), Lovering and Goddard (1950, fig. 59, 

p. 157, pi. 13), and Spurr and Garrey (1908, pi. 81).

A small stock of hornblende granodiorite porphyry is located in the 

area between the Minnesota mine and the Silver Mountain ore zone. 

Lovering and Goddard (1950, p. 156) suggested that the vein systems 

were formed by the stresses related to the intrusion of the stock and subsequent collapse of the roof when some of the underlying magma was 

withdrawn after late-stage consolidation of the stock.

Although argillic alteration is relatively widespread in the Precambrian 

rocks surrounding the hornblende granodiorite porphyry stock, it is 

confined to narrow zones in the wallrocks of veins in the peripheral zone
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B7

of the area. Both iron and manganese oxide stains were observed on the 

fracture surfaces of the altered rock.

GEOCHEMICAL INVESTIGATIONS

The purpose of this study was to determine if the distribution of gold 

and associated ore metals in vegetation, forest humus, and soil reflects 

the distribution of these metals in the underlying bedrock. The Empire 

district was chosen for the study after G. J. Neuerburg (unpub. data) in 

1965 and 1966 showed the presence of anomalously high amounts of gold 

and other metals in the soil of the north half of the district.

The present study showed that gold and associated ore metals generally 

are enriched in the forest humus layer relative to the underlying soil.

Results of the geochemical investigations are summarized in the geochemical maps of the distribution in mull ash and soil of gold, copper, 

bismuth, silver, lead, zinc, molybdenum, tin, tungsten (figs. 4-21), the 

distribution of manganese in mull ash (figs. 22, 23), and the distribution 

of tellurium and mercury in soil (figs. 24, 25). Analytical data from the 

mull ash and soil samples were treated statistically in the U.S. Geological 

Survey IBM 360/65 computer with card input using the STATPAC 

statistical evaluation library. The output included histograms (figs. 4-23) 

and the linear correlation coefficients between pairs of logarithms of 

variables (tables 2 and 3).

MATERIAL SAMPLED

Samples of mull and soil that were used in this study were collected at 

894 localities (fig. 3). Mull only was collected at 35 localities, soil only was 

collected at 78 localities, and both soil and mull were collected at 781 

localities.

The forest cover of the Empire district is chiefly lodgepole pine (Pinus 

contorta), but limber pine (Pinus flexilis) and groves of aspen (Populus 

tremuloides) are present locally. Samples of roots, trunks, branches, 

needles, and leaves of pine and aspen trees were collected at nine localities 

where the mull contained gold.

Pine mull is present as pads, 1-3 inches thick, beneath individual trees. 

The burrowing of rodents and the action of downslope wash have resulted 

in the addition of varying quantities of mineral matter to these pads. 

Aspen mull is present as a diffuse layer rarely more than 1 inch thick. 

Mull samples were collected beneath pine trees where possible, but about 

100 samples of aspen mull were collected at localities where pine trees 

were absent.

A layer of gray, ash-textured material (2-4 in. thick) that contains 

abundant small roots is present beneath the mull layer. Below this layer 

is a mixture of weathered cobbles and yellow to yellow-brown coarse to 

fine sand, of colluvial or morainal origin, that does not visibly change in
B8 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

mineralogic composition or texture downward to bedrock. Soil samples 

were collected at a depth of 6-12 inches.

CONTAMINATION OF MULL SAMPLES

Locally the mull is contaminated. Detrital pyrite was observed in the 

heavy-mineral fractions (that fraction composed of minerals having a 

specific gravity of 3 or more) of six mull samples collected near mine 

dumps. As much as 52 percent of the total gold was in the heavy-mineral 

fractions of nine samples collected near large dumps. The gold in the 

heavy-mineral fractions of these samples could have been contributed 

principally by windblown auriferous pyrite. Even in these contaminated 

samples the organic fractions contained as much as 26 percent of the 

total gold.

Most of the samples that contain high contents of gold and other metals 

were collected at localities relatively remote from sources of contamination, however, and one of these samples that was studied in detail contained no observable pyrite or other contamination. The organic fractions 

of this sample contained 72 percent of the total gold. The presence of 

appreciable gold in the interior wood of pine and aspen trees (table 1) and 

in the organic fractions of the mull substantiates the biogeochemical 

origin of most of the high gold anomalies found in the area studied.

ANALYTICAL PROCEDURES

Samples were analyzed by several procedures. Gold was determined by 

atomic absorption (Thompson and others, 1968), tellurium by a wet 

chemical method (Lakin and Thompson, 1963), and mercury by an atomic 

absorption method (Vaughn and McCarthy, 1964); and the other metals 

were determined by a semiquantitative spectrographic field method 

(Grimes and Marranzino, 1968). Most of the analyses were made in 

mobile field laboratories. Soil samples were sieved and the minus 2-millimeter fraction was ground and pulverized before it was analyzed. Mull 

samples were sieved and the minus 2-millimeter fraction was ashed and 

analyzed. The ash of the mull, as used in this report, is the sum of the 

admixed mineral matter and the ash of the organic matter. The metal 

content of the mull samples is reported on an ash-weight basis.

Vegetation samples were air dried, weighed, and ashed at 450°C in a 

thermostatically controlled furnace and the metal content was reported 

on an ash-weight basis. The bark and outer wood layer were shaved from 

the trunks and large roots of the pine and aspen trees. The interior wood, 

free from contamination, was analyzed.

DISTRIBUTION OF GEOCHEMICAL ANOMALIES

The areas of anomalous concentrations of metals in mull ash and soil are 

shown in figures 4-25. An area rich in gold, copper, and bismuth is shown
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B9

in figures 4, 6, and 8, and an area rich in silver, lead, zinc, and molybdenum 

is shown in figures 10, 12, 14, and 16. The geographic distribution of tin 

and tungsten in mull ash (figs. 18, 20), does not correspond well with 

either of the above-mentioned two groups, but tin and tungsten roughly 

correspond with each other.

The central part of the mapped area that area bounded on the west by 

Lion Creek and on the east by North Empire Creek contains most of the 

high gold, bismuth, and copper anomalies in mull ash (figs. 4, 6, 8). Areas 

of anomalously high silver, lead, zinc, and molybdenum in mull ash (figs. 

10, 12, 14, 16) form an encircling zone more prominent on the west than 

on the east around the gold, bismuth, copper area.

This zoning pattern is similar to the zoning pattern in the Central City 

district (Sims and others, 1963, p. 38-41; Lovering and Goddard, 1950, 

p. 170, 173, pi. 9).

GOLD-COPPER-BISMUTH ANOMALIES

In mull ash the geographic distribution of gold is so pervasive at a 

minimum concentration level of 0.2 ppm (parts per million) (fig. 4) that 

the known vein systems are not delineated. This pattern of distribution 

suggests that gold is dispersed in the zone of weathering, possibly by 

inclusion of vein material in colluvium, by the biogeochemical cycle 

(described on p. 11) or by windblown material from mine dumps. The 

geographic distribution of gold in mull ash at a minimum concentration 

level of 0.6 ppm (fig. 4), however, appears to delineate the known gold 

deposits as well as additional areas that merit further investigation.

Copper distribution in mull ash at a minimum concentration of 150 ppm 

(fig. 6) generally corresponds with the distribution of gold in mull ash at a 

minimum concentration of 0.6 ppm (fig. 4). The association of gold and 

copper in the ash of the mull layer reflects the increase in tenor of gold 

with chalcopyrite in the veins (Lovering and Goddard, 1950, p. 158; 

S. H. Ball, in Spurr and Garrey, 1908, p. 399).

Bismuth distribution in mull ash at a minimum concentration of 15 

ppm (fig. 8) roughly corresponds with high gold and copper anomalies 

(figs. 4, 6). However, bismuth is also associated to a lesser extent with the 

silver-lead-zinc-molybdenum group. Anomalously high bismuth in mull 

ash generally ranges from 10 to 30 ppm, and increases to 200 ppm in 

places on the eastern periphery of the district. Three samples of mull ash 

collected at localities on the first ridge east of North Empire Creek contain 

70, 150, and 200 ppm bismuth. The mull ash sample that contains 200 

ppm bismuth was collected over a gold-bismuth-silver vein. The gossan 

of this vein contains 1.5 percent bismuth.

In soil, in contrast to mull ash, the distribution of metals (figs. 5, 7, 9) is 

erratic High metal values in many of the soil samples in areas without 

known gold deposits may be due chiefly to the inclusion of vein material
BIO CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

in otherwise barren colluvial or morainal cover. However, some areas of 

high gold, copper, and bismuth (figs. 5, 7, 9) in soil coincide with known 

gold deposits in bedrock, and these may reflect metal enrichment in the 

soil by the biogeochemical cycle.

SILVER-LEAD-ZINC-MOLYBDENUM ANOMALIES

The prominent high silver-lead-zinc-molybdenum anomaly in the ash 

of the mull layer west of Lion Creek and near the south edge of the 

mapped area (figs. 10, 12, 14, 16) is in an area where the bedrock is hidden 

by a cover of glacial drift (fig. 2). This anomalous area, which is remote 

from a source of contamination, may reflect mineralized bedrock and, 

therefore, it merits further investigation. The widespread lead anomaly 

in mull ash and scattered isolated anomalies of silver and zinc in the 

northwest corner of the mapped area also warrant further exploration.

TUNGSTEN-TIN ANOMALIES

The distribution patterns of tungsten and tin roughly correspond with 

each other and in part with several of the extensive high gold, copper, and 

bismuth anomalies (figs. 4, 6, 8). The most significant high tungsten 

anomaly in mull ash is on Lion Creek near the west edge of the Silver 

Mountain ore zone (fig. 20) where tungsten values of 100-500 ppm 

correspond to a widespread high gold anomaly (fig. 4). This tungsten 

anomaly may reflect mineralized rock at depth and should be investigated 

further.

MANGANESE ANOMALIES

The distribution of manganese in mull ash at concentrations of 5,000 

ppm or more (fig. 22) forms anomalies that partly encircle the extensive 

area of high gold-copper-bismuth anomalies. These manganese anomalies 

correspond rather well with the silver-lead-zinc-molybdenum group of 

high anomalies.

Most of the low manganese values in mull ash (1,500 ppm or less) are in 

the central part of the area (fig. 22). They partly correspond with the 

gold-copper-bismuth group of high anomalies and the principal high 

tungsten anomaly.

TELLURIUM-MERCURY ANOMALIES

Owing to lack of adequate methods for the analysis of tellurium and 

mercury in mull ash, data on these elements in mull ash are not available. 

However, the scattered high tellurium-mercury anomalies in soil (figs. 

24, 25) are within the general area occupied by the high gold-copperbismuth anomalies in mull ash and soil.

METAL ENRICHMENT IN MULL ASH

The distribution and abundance of metals shown on the geochemical 

maps (figs. 4-25) demonstrate the enrichment of metals in mull ash
MULL IN GEOCHEMICAL EXPLORATION, COLORADO Bll

relative to soil. Enrichment of certain elements in humus (a major constituent of mull) has been reported by Goldschmidt (1937), Cox and 

Hollister (1955), and Boyle and Dass (1967). Goldschmidt (p. 670) found 

that the uppermost humus layer of a very old forest of beech and oak in 

central Germany was enriched in gold, thallium, beryllium, cobalt, nickel, 

zinc, germanium, arsenic, cadmium, tin, lead, and silver. Goldschmidt 

(1954, p. 204), in a discussion of the geochemistry of gold, concluded that 

the enrichment of gold in humus was convincing evidence for the circulation of gold in living plants; he stated "It is possible that this observation 

may be used as an indication of the occurrence of gold in the lower levels 

of the soil." Cox and Hollister (p. 939) reported zinc enrichment in humusrich soil over a zinc deposit covered by glacial till in Stevens County, 

Wash. Boyle and Dass (p. 274) found that in areas of deciduous tree 

cover near Cobalt, Ontario, the A horizon (organic-rich) of the soil was 

enriched in lead, zinc, copper, arsenic, antimony, molybdenum, silver, 

cobalt, manganese, and mercury relative to the B horizon (organic-poor); 

and they suggested that the A horizon becomes enriched in metals as the 

leaves decay.

The anomalously high concentrations of gold, bismuth, silver, lead, 

zinc, molybdenum, and tin detected in mull ash (see histograms, figs. 

4-23) probably are caused by a geochemical cycle in which these metals are 

leached from bedrock, are absorbed by the pine and aspen trees, and then 

are deposited in the leaves, needles, cones, woody material, and bark. 

The metals are finally concentrated in the mull as the leaves, needles, and 

other parts of the trees decay. Tree roots have been observed in the 

Empire district in fractures in bedrock at mine workings, sample pits, 

and trenches. In one of the mine workings tree roots were observed 50 

feet below the surface.

The histograms (percent frequency distributions) of metal content in 

mull ash and soil (figs. 4-21, 23) show that in the Empire district mull ash 

is significantly enriched in lead (sixfold), manganese (fourfold), gold, 

silver, bismuth, zinc, molybdenum, and tin relative to the soil. The 

amount of enrichment of gold, bismuth, silver, zinc, molybdenum, and 

tin in mull ash relative to soil cannot be determined because the histograms (figs. 4, 8, 10, 14, 16, 18) are truncated at the concentration determined by the lower limits of analytical detection. The enrichment of 

these metals in mull ash relative to the underyling soil, however, is shown.

Mull ash is only slightly enriched in copper and tungsten. The enrichment of mull ash in metals such as gold, bismuth, silver, zinc, and lead 

relative to soil suggests that mull may be a useful sample medium in 

delineating the distribution of these metals in the bedrock beneath a 

transported overburden.
B12 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

METAL CONTENT OF ASH OF PINE AND ASPEN TREES 

IN THE EMPIRE DISTRICT

The anomalously high metal content of the mull ash suggests that the 

pine and aspen trees from which the mull is formed should also contain 

high amounts of metal. Samples of roots, trunks, branches, needles, and 

leaves of pine and aspen trees were collected and analyzed in order to test 

this possibility. The samples were collected at nine localities where the 

mull ash contains high amounts of gold and bismuth or gold, silver, and 

bismuth and only moderate to minor amounts of molybdenum, lead, 

zinc, tin, and tungsten. In table 1 the maximum and minimum metal 

contents (in ppm) in the ash of pine and aspen trees that grow in the 

studied area are compared with the average metal content in the ash of 

more than 1,000 species of plants that grow in unmineralized ground 

(Cannon, 1960, p. 596), with the ash of conifer needles from trees growing 

on silicic rocks in Finland (Lounamaa, 1967, p. 310), and with the ash of 

1,501 samples of vascular plants (Shacklette, 1965, p. D14).

The gold, silver, and lead content of the ash of pine and aspen trees 

collected in the Empire district generally is anomalously high relative to 

the gold, silver, and lead content of the ash of vegetation reported in the 

literature cited in table 1. The presence of bismuth in the ash of pine trees 

collected in the Empire district (table 1) and the presence of tin in both 

pine and aspen trees in the district (table 1) may be anomalous because 

bismuth and tin were detected in only 2.8 and 1.9 percent, respectively, 

of the 1,501 vascular plant samples (table 1) reported in the literature.

The copper, molybdenum, and zinc content in the pine and aspen trees, 

however, ranges from slightly less to slightly more than the average 

copper, molybdenum, and zinc content of the ash of vegetation reported 

in the literature cited in table 1.

TABLE 1. Metal content, in parts per million, in the ash of pine and aspen trees that

[N, not detected at values shown in parentheses. _ ...., no data given in published source. Empire

no tungsten

Empire district

Root Trunk 

interior interior 

(1 sample) (4 samples)

Metal

Au.._ 

Cu...

Mo'." 

Pb.._

Ag~-~"

Sn ....

3 

200 

10 

10 

700 

1,000 

30 

10

Min

0.5 

150 

N(10) 

5 

300 

300 

1.5 

N(10)

Max

1 

500 

10 

10 

2,000 

1,000 

100 

15

Pine

Branch 

interior 

(5 samples)

Min

0.2 

100

<5 

150 

700

N(0.5)

Max

2 

500 

50 

10 

1,000 

2,000 

100 

N(10)

Needles 

(12 samples)

Min

0.04 

100

<5 

100 

500

.5

Max

0.7 

200 

10 

15 

1,000 

1,500 

3 

N(10)

Aspen

Root Trunk 

interior interior 

(1 sample) (7 samples)

0.2 

200 

N(10) 

20 

300 

300 

7 

N(10)

Min

0.7 

100 

N(10) 

N(5) 

50 

500 

N(0.5) 

N(10)

Max

1.6 

1,000

15 

700 

1,000 

20 

10

1 Values from Lounamaa (1967).

2 Values from Cannon (1960).

3 Values from Shacklette (1965), based on 1,501 plant samples.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B13

The relatively high content of gold, silver, bismuth, and lead and the 

average content of copper, molybdenum, and zinc in the ash of pine and 

aspen trees collected in the Empire district is congruent with the metal 

content of both the ash of the underlying mull and the oxidized zone of 

the underlying mineralized bedrock. The presence of metals in the pine 

and aspen trees substantiates the biogeochernical origin of the metal 

content of the mull.

CORRELATION ANALYSIS

The product moment coefficient of correlation was calculated for every 

pair of elements in soils and mull ash in order to indicate the degrees of 

association among the elements in these media. Arbitrary constants were 

assigned to values reported as not detected, to values less than the lower 

limit of detection, and to volumes greater than the upper limit of detection. The analytical data were transformed to logarithms for correlation 

analysis because the correlation coefficients of the logarithms of the metal 

content are less subject to the effects of extremely high or low values than 

are the correlation coefficients of the untransformed metal content. 

Correlation matrices of the logarithmic concentrations of elements in 

soils and mull ash are shown in tables 2 and 3. Elemental components of 

the soil sample correlation matrix are gold, copper, bismuth, silver, lead, 

zinc, molybdenum, tin, tungsten, iron, manganese, tellurium, and 

mercury. Elemental components of the mull ash correlation matrix are 

gold, copper, bismuth, silver, lead, zinc, molybdenum, tin, tungsten, iron, 

manganese, and percent ash of the mull. A correlation coefficient of 0.3 

or greater is classified as significant, a correlation coefficient of 0.2 to 0.3 

is classified as slight (noticeable linear relationship, but not significant), 

and a correlation coefficient of less than 0.2 is classified as insignificant.

grow in the Empire district compared with that of various plants that grow elsewhere

district samples: gold analyses by A. E. Hubert; all other analyses by E. L. Hosier and K. C. Watts; 

detected]

Empire district Continued Areas other than Empire district

Aspen Continued

Branch 

interior 

(5 samples)

Min Max

<0.04 1. 

300 500 

N(10) <10 

N(5) 5 

70 500 

1,000 2,000 

2 15 

N(10)

Leaves 

(9 samples)

Min Max

0 0. 

50 

N(10) 

N(5) 

30 

700 

N(0.

06 0.1 

150

5 

300 

1,000 

5) 2 

N(10)

Average metal content of 

Deciduous 

trees and 

shrubs '

150

5 

16 

2,100

Conifer 

needles 1

240

2

38 

1,500

1,000 + 

species of 

plants 2

<0.007 

183

13 

70 

1,400

Vascular 

plants 3

112 

30 

25 

111 

1,010 

5 

68

Percent 

vascular 

plants in 

which metal 

found

99.9 

2.8 

4.7 

88 

99.9 

1.5 

1.9
B14 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

TABLE 2. Matrix showing correlation of selected metals in mull ash with each other and

with percent ash

[Numbers are linear correlation coefficients calculated after logarithmic transformation. Boldface figures 

indicate significant positive correlation; italic figures indicate slight positive correlation; roman figures 

indicate insignificant correlation; and boldface italic figures indicate slight to significant negative 

correlation]

Cu

Bi

Ag

Pb

Zn

Mo

Sn

W

Fe

Mn

Percent 

ash

.45

.00

-.02

-.17

-.06

-.08

.26

.25

.07

-.26

.17

Au

.37

.07

.19

.18

.13

.37

.21

.42

.00

-.03

Cu

.0*

.18

.08

.05

.33

.15

.02

.31

-.08

Bi

.55

.48

.35

.28

.03

.09

.33

-.32

Ag

.46

.31

.31

-.11

.10

.58

-.37

Pb

.29

.19

-.01

.14

.34

-.27

Zn

.25

.04

.04

.21

-.19

Mo

.07

.13

.11

-.06

Sn

.12

-.12

.15

W

.08

.04 -.30

Fe Mn

TABLE 3. Matrix showing correlation of selected metals in soil with each other

[Numbers are linear correlation coefficients calculated after logarithmic transformation. Boldface figures 

indicate significant positive correlation; italic figures indicate slight positive correlation; and roman 

figures indicate insignificant correlation]

Cu

Bi

Ag 

Pb

Zn

Mo

Sn

W

Fe

Mn

Te 

Hg

.07

.34

.12

-.03

-.02

-.02

.20

.25

.15

.02

.18

.23

Au

.31

.12

.19

.10

.14

.26

.19

.46

.34

.03

.32

Cu

.16

.09

-.09

.04

.25

.22

.00

.02

.05

.17

Bi

.17

.17

.13

.13

.17

-.08

-.06

.03

.16

Ag

.03

.07

.09

.10

.14

.30

-.03

.11

Pb

.007

.002

-.03

.11

.26

.05

.15

Zn

.11

.13

.04

.09

.01

-.001

Mo

.37

.12

-.03

.06

.10

Sn

.12

-.04

.17

.14

W

.52

-.06 -.11

.29 .25 .09

Fe Mn Te

Gold, copper, and bismuth show either significant or slight positive 

correlations with each other in both the mull ash and the underlying soil.

Silver, lead, zinc, molybdenum, and manganese show significant positive 

correlations with each other in mull ash with the exception of the zincmolybdenum pair (slight positive correlation), but all these metals show 

only slight to insignificant correlations with each other in the underlying 

soil. The significant positive correlations among silver, lead, zinc, molybdenum, and manganese in mull ash and the absence of significant correlations among these metals in the transported soil suggest that the metals in 

the mull reflect mineralized bedrock, particularly in the absence of any 

known source of contamination. The percentage of mull ash is an inverse 

function of the amount of organic matter in the mull (see definition, 

p. 3). The inverse relation of silver and lead with percentage of mull ash 

indicates a direct relation of silver and lead with the organic matter in the
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B15

mull. Therefore, the biogeochemical origin of silver and lead in the mull is 

demonstrated by the significant negative correlation that percentage of 

mull ash shows with the silver and lead.

Although tin values are relatively low (fig. 18), the widespread distribution of tin in mull ash is suggested by the significant to slight positive 

correlation that tin shows with copper, bismuth, lead, silver, tungsten, 

gold, and molybdenum in mull ash. Tin shows a significant positive 

correlation with tungsten and a slight positive correlation with gold, 

copper, and bismuth in soil.

SUMMARY

In the Empire district, gold deposits in bedrock beneath the colluvial 

and glacial cover are best delineated by the gold and, to a lesser extent, by 

the copper and bismuth content of the mull ash. The distribution of 

anomalously high amounts of these metals in the soil below the mull 

corresponds to the gold deposits in bedrock only in places, and many of 

the high anomalies in soil probably reflect the inclusion of vein material 

in otherwise barren colluvial or morainal cover.

Zoning of the metals into two principal groups (gold-copper-bismuth 

and silver-lead-zinc-molybdenum-manganese) is shown in the geochemical 

maps and is substantiated by the correlation analysis. In general, the 

central part of the mapped area that area bounded on the west by Lion 

Creek and on the east by North Empire Creek contains the principal 

high gold-copper-bismuth anomalies. High silver-lead-zinc-molybdenummanganese anomalies encircle more prominently on the west than on the 

east the central zone. Tungsten and tin correspond with each other and 

in part with the high gold-copper-bismuth anomalies to form a rather 

extensive high anomaly on Lion Creek at the west end of the Silver 

Mountain ore zone.

The histograms show that the mull ash is appreciably enriched in gold, 

silver, bismuth, lead, zinc, molybdenum, and tin relative to soil, whereas 

the mull ash is moderately enriched in copper and is only slightly enriched 

in tungsten relative to soil.

The accumulation of gold, silver, and other metals by trees is demonstrated by the presence of these metals in the interior of roots, trunks, 

and branches and in pine needles and aspen leaves. This accumulation 

probably accounts for most of the metal content of the mull.

The results obtained in the Empire district suggest that mull may be an 

effective geochemical sampling medium for gold, silver, bismuth, lead, and 

zinc in forested areas blanketed by colluvium or glacial drift where the 

transported material offers no clue to the nature of the underlying 

bedrock.
B16 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

REFERENCES CITED

Boyle, R. W., and Dass, A. S., 1967, Geochemical prospecting Use of the A horizon 

in soil surveys: Econ. Geology, v. 62, no. 2, p. 274-276.

Braddock, W. A., 1969, Geology of the Empire quadrangle, Grand, Gilpin, and Clear 

Creek Counties, Colorado: U.S. Geol. Survey Prof. Paper 616, 56 p.

Cannon, H. L., 1960, Botanical prospecting for ore deposits: Science, v. 132, no. 3427, 

p. 591-598.

Cox, M. W., and Hollister, V. F., 1955, The Chollet project, Stevens County, Washington: Mining Eng., v. 7, no. 10, p. 937-940.

Goldschmidt, V. M., 1937, The principles of distribution of chemical elements in 

minerals and rocks: Chem. Soc. [London] Jour., January-June, p. 655-673.

 1954, Geochemistry: Oxford, Clarendon Press, 730 p.

Grimes, D. J., and Marranzino, A. P., 1968, Direct-current arc and alternatingcurrent spark emission spectrographic field methods for the semiquantitative 

analysis of geologic materials: U.S. Geol. Survey Circ. 591, 6 p.

Harrison, L. C., 1964, Empire and the Berthoud Pass: Denver, Big Mountain Press, 

482 p.

Kvalheim, Aslak, ed., 1967, Geochemical prospecting in Fennoscandia: New York, 

Interscience Publishers, 350 p.

Lakin, H. W., and Thompson, C. E., 1963, Tellurium A new sensitive test: Science, 

v. 141, no. 3575, p. 42-43.

Lovering, T. S., and Goddard, E. N., 1950, Geology and ore deposits of the Front 

Range, Colorado: U.S. Geol. Survey Prof. Paper 223, 319 p. [1951].

Lounamaa, J., 1967, Trace elements in trees and shrubs growing on different rocks in 

Finland, in Kvalheim, Aslak, ed., Geochemical prospecting in Fennoscandia: New 

York, Interscience Publishers, p. 287-317.

Shacklette, H. T., 1965, Element content of bryophytes: U.S. Geol. Survey Bull. 

1198-D, 21 p.

Sims, P. K., Drake, A. A., Jr., and Tooker, E. W., 1963, Economic geology of the 

Central City district, Gilpin County, Colorado: U.S. Geol. Survey Prof. Paper 

359, 231 p.

Spurr, J. E., and Garrey, G. H., 1908, Economic geology of the Georgetown quadrangle (together with the Empire district), Colorado, with General geology, by 

S. H. Ball: U.S. Geol. Survey Prof. Paper 63, 422 p.

Thompson, C. E., Nakagawa, H. M., and VanSickle, G. H., 1968, Rapid analysis for 

gold in geologic materials, in Geological Survey research 1968: U.S. Geol. Survey 

Prof. Paper 600-B, p. B130-B132.

U.S. Department of Agriculture, 1951, Soil survey manual: U.S. Dept. Agriculture 

Handbook 18, 503 p.

Vaughn, W. W., and McCarthy, J. H., Jr., 1964, An instrumental technique for the 

determination of submicrogram concentrations of mercury in soils, rocks, and gas, 

in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501-D, 

p. D123-D127.
FIGURES 4-25
B18 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 4. Gold distribution in mull ash. Light stipple, ash contains 0.2-0.59 ppm 

gold; heavy stipple, ash contains at least 0.6 ppm gold. Heavy lines are veins. 

Analyses by A. E. Hubert.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B19

FIGURE 5. Gold distribution in soil (6- to 12-inch depth). Light stipple, soil contains 

0.2-0.59 ppm gold; heavy stipple, soil contains at least 0.6 ppm gold. Heavy lines are 

veins. Analyses by A. E. Hubert.
B20 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

1000 2000 3000 FEET

 1___________1___________I

FIGURE 6. Copper distribution in mull ash. Light stipple, ash contains 150-299 ppm 

copper; heavy stipple, ash contains at least 300 ppm copper. Heavy lines are veins. 

Analyses by E. L. Hosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B21

PARTS PER MILLION

2000 3000 FEET

FIGURE 7. Copper distribution in soil (6- to 12-inch depth). Light stipple, soil contains 150-299 ppm copper; heavy stipple, soil contains at least 300 ppm copper. 

Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
B22 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 8. Bismuth distribution in mull ash. Light stipple, ash contains 10-19 ppm 

bismuth; heavy stipple, ash contains at least 20 ppm bismuth. Heavy lines are veins. 

Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B23

3 «-

2 23RSS

PARTS PER MILLION

FIGTJKE 9. Bismuth distribution in soil (6- to 12-inch depth). Light stipple, soil contains 10-19 ppm bismuth; heavy stipple, soil contains at least 20 ppm bismuth. 

Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
B24 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 10. Silver distribution in mull ash (6- to 12-inch depth). Light stipple, ash 

contains 1-1.9 ppm silver; heavy stipple, ash contains at least 2 ppm silver. Heavy 

lines are veins. Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B25

FIGURE 11. Silver distribution in soil (6- to 12-inch depth). Light stipple, soil contains 1-1.9 ppm silver; heavy stipple, soil contains at least 2 ppm silver. Heavy lines 

are veins. Analyses by E. L. Mosier and K. C. Watts.
B26 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 12. Lead distribution in mull ash. Light stipple, ash contains 500-999 ppm 

lead; heavy stipple, ash contains at least 1,000 ppm lead. Heavy lines are veins. 

Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B27

FIOUBE 13. Lead distribution in soil (6- to 12-inch depth). Light stipple, soil contains 500-999 ppm lead; heavy stipple, soil contains at least 1,000 ppm lead. Heavy 

lines are veins. Analyses by E. L. Hosier and K. C. Watts.
B28 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

-___ ^ /

1OOO 2OOC 3000 FEET

FIGURE 14. Zinc distribution in mull ash. Light stipple, ash contains 700-1,499 ppm 

zinc; heavy stipple, ash contains at least 1,500 ppm zinc. Heavy lines are veins. 

Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B29

1000 2000 3000 FEET

FIGURE 15. Zinc distribution in soil (6- to 12-inch depth). Stipple area, soil contains 

700-999 ppm zinc. Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
B30 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 16. Molybdenum distribution in mull ash. Light stipple, ash contains 15-49 

ppm molybdenum; heavy stipple, ash contains at least 50 ppm molybdenum. Heavy 

lines are veins. Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B31

FIGURE 17. Molybdenum distribution in soil (6- to 12-inch depth). Light stipple, soil 

contains 15-49 ppm molybdenum; heavy stipple, soil contains at least 50 ppm 

molybdenum. Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
B32 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 18. Tin distribution in mull ash. Light stipple, ash contains 20-69 ppm tin; 

heavy stipple, ash contains at least 70 ppm tin. Heavy lines are veins. Analyses by 

E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B33

FIGUBE 19. Tin distribution in soil (6- to 12-inch depth). Light stipple, soil contains 

20-69 ppm tin; heavy stipple, soil contains at least 70 ppm tin. Heavy lines are veins. 

Analyses by E. L. Hosier and K. C. Watts.
B34 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 20. Tungsten distribution in mull ash. Light stipple, ash contans 50-99 ppm 

tungsten; heavy stipple, ash contains at least 100 ppm tungsten. Heavy lines are 

veins. Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B35

FIGURE 21. Tungsten distribution in soil (6- to 12-inch depth). Light stipple, soil 

contains 50-99 ppm tungsten: heavy stipple, soil contains at least 100 ppm tungsten. 

Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
B36 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 22. Manganese distribution in mull ash. Light stipple indicates that ash 

contains 1,500 ppm or less manganese; heavy stipple, ash contains 5,000 ppm or 

more manganese. Heavy lines are veins. Analyses by E. L. Mosier and K. C. Watts.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B37

30 

O

Z

LU

LU

tr

u.

iu 10-

o

ct

LU

CL

o .

-HT-T-T

S|§8

_

i-i

30 

>

CJ

Z

LU

D ?n 

LU

cc

IJL

1 

n LU 10 

o

tr

u

CL

l_

_^_rr

 i

_

M-n

^H ~* CM n m m » < ^H CM co m

A

PARTS PER MILLION 

A.

PARTS PER MILLION 

B.

FIGURE 23. Manganese distribution in mull ash (.A) and in soil (B).
B38 CONTRIBUTIONS TO GEOCHEMICAL PROSPECTING FOR MINERALS

FIGURE 24. Tellurium distribution in soil (6- to 12-inch depth). Stippled areas, soil 

contains at least 0.5 ppm tellurium. Heavy lines are veins. Analyses by R. L. Turner 

and J. R. Watterson.
MULL IN GEOCHEMICAL EXPLORATION, COLORADO B39

FIGUEE 25. Mercury distribution in soil (6- to 12-inch depth). Stippled areas, soil 

contains at least 0.1 ppm mercury. Heavy lines are veins. Analyses by W. W. Janes.

 &U.S. GOVERNMENT PRINTING OFFICE: 1971 0 4U-S60