UNITED STATES DEPARTMENT OF THE INTERIOR 
GEOLOGICAL SURVEY
Geochemical Evidence for Metallization on 
St. Thomas and St. John, U.S. Virgin Islands
by
R. E. Tucker, H. V. Alminas, 
and R. T. Hopkins
Open-File Report 85-297 
1985
This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards and stratigraphic nomenclature. 
Any use 
of trade names is for descriptive purposes only and does not imply endorsement 
by the USGS.
CONTENTS
Page 
Introduction.............................................................. 
1
Geologic Settlng.......................................................... 
1
Sample collection, preparation, and analysis.............................. 
6
Geochemi cal data..................................................... 
7
Rock geochemical data........................................... 
7
Nonmagnetic fraction of the panned concentrate.................. 20
Minus-80-mesh fraction of the soil samples...................... 25
Oxalic acid leach analysis...................................... 25
Magnetic fraction of the panned concentrates.................... 36
Minus-80-mesh fraction of the stream sediments.................. 36
Discussion................................................................ 36
Conclusions............................................................... 44
References ci ted.......................................................... 45
ILLUSTRATIONS 
Figure 
1. 
Index map of the Virgin Islands and vicinity.................. 2
Figure 2. 
Geologic map of St. Thomas, U.S. Virgin Islands............... 
3
Figure 
3. 
Geologic map of St. John, U.S. Virgin Islands................. 4
Figure 4. 
Sample locality map of St. Thomas, U.S. Virgin Islands........ 8
Figure 5. 
Sample locality map of St. John, U.S. Virgin Islands.......... 
9
Figure 6. 
Distribution of anomalous Ba concentrations from rocks
on St. Thomas, U.S. Virgin Islands................................... 11
Figure 7. 
Distribution of anomalous Ba concentrations from rocks
on St. John, U.S. Virgin Islands..................................... 12
Figure 8. 
Distribution of anomalous Cu concentrations from rocks
on St. Thomas, U.S. Virgin Islands................................... 13
Figure 9. Distribution of anomalous Cu concentrations from rocks
on St. John, U.S. Virgin Islands..................................... 14
ILLUSTRATIONS (continued)
Figure 10. 
Distribution of anomalous Mo concentrations from rocks
on St. Thomas, U.S. Virgin Islands................................... 15
Figure 11. 
Distribution of anomalous Mo concentrations from rocks
on St. John, U.S. Virgin Islands..................................... 16
Figure 12. 
Distribution of anomalous Ag concentrations from rocks
on St. Thomas, U.S. Virgin Islands................................... 17
Figure 13. 
Distribution of anomalous Au and Ag concentrations from rocks
on St. John, U.S. Virgin Islands..................................... 18
Figure 14. 
Distribution of anomalous Ag, Bi, and Sb concentrations in 
the nonmagnetic fraction of the stream sediments from St. John, 
U.S. Virgin Islands.................................................. 21
Figure 15. 
Distribution of anomalous Ba concentrations in the 
nonmagnetic fraction of the stream sediments from St. John, 
U.S. Virgin Islands.................................................. 22
Figure 16. Distribution of anomalous Cu concentrations in the 
nonmagnetic fraction of the stream sediments from St. John, 
U.S. Virgin Islands.................................................. 23
Figure 17. Distribution of anomalous Pb concentrations in the 
nonmagnetic fraction of the stream sediments from St. John, 
U.S. Virgin Islands.................................................. 24
Figure 18. 
Distribution of anomalous Pb and Cu concentrations in the 
nonmagnetic fraction of the stream sediments from St. Thomas, 
U.S. Virgin Islands.................................................. 26
Figure 19. Distribution of anomalous Ba concentrations in the
nonmagnetic fraction of the stream sediments from St. Thomas,
U.S. Virgin Islands.................................................. 27
Figure 20. 
Distribution of anomalous Ag, Bi, and Sb concentrations
in the nonmagnetic fraction of the stream sediments from St. Thomas, 
U.S. Virgin Islands.................................................. 28
Figure 21. 
Distribution of anomalous Ba concentrations from 
the minus-80-mesh fraction of soil samples from St. John, 
U.S. Virgin Islands.................................................. 29
Figure 22. 
Distribution of anomalous Pb and Cu concentrations from 
the minus-80-mesh fraction of soil samples from St. John, 
U.S. Virgin Islands.................................................. 30
Figure 23. 
Distribution of anomalous Ba and Cu concentrations from 
the minus-80-mesh fraction of soil samples from St. Thomas, 
U.S. Virgin Islands.................................................. 31
ILLUSTRATIONS (continued)
Figure 24. 
Distribution of anomalous Pb and Ag concentrations from 
the minus-80-mesh fraction of soil samples from St. Thomas, 
U.S. Virgin Islands.................................................. 32
Figure 25. 
Distribution of oxalic acid soluble Pb and Cu
concentrations in coarse, light sediments from St. John,
U.S. Virgin Islands.................................................. 33
Figure 26. 
Distribution of oxalic acid soluble Pb and Cu
concentrations in coarse, light sediments from St. Thomas,
U.S. Virgin Islands.................................................. 34
Figure 27. 
Distribution of oxalic acid soluble Mo
concentrations in coarse, light sediments from St. Thomas,
U.S. Virgin Islands.................................................. 35
Figure 28. 
Distribution of oxalic acid soluble Ag
concentrations in coarse, light sediments from St. John,
U.S. Virgin Islands.................................................. 37
Figure 29. Distribution of oxalic acid soluble Ag
concentrations in coarse, light sediments St. Thomas,
U.S. Virgin Islands.................................................. 38
Figure 30. 
Distribution of anomalous Ba and Pb concentrations from
the magnetic fraction of the panned concentrate samples, St. John,
U.S. Virgin Islands.................................................. 39
Figure 31. 
Distribution of anomalous Pb, Ag, and Mo concentrations from 
the magnetic fraction of the panned concentrate samples, St. Thomas, 
U.S. Virgin Islands.................................................. 40
Figure 32. 
Distribution of anomalous Cu and Ba concentrations from
the magnetic fraction of the panned concentrate samples, St. Thomas, 
U.S. Virgin Islands.................................................. 41
TABLES
Table 1. 
Summarized stratigraphic relationships of the rocks on
St. Thomas and St. John, U.S. Virgin Islands......................... 
5
Table 2. 
Silver, gold, and tellurium analyses of a quartz vein cropping
out within the Muhlenfels anomaly, St. Thomas, U.S. Virgin Islands... 19
Table 3. 
Silver, gold, and tellurium analyses from rock samples from
the White Cliffs, St. John, U.S. Virgin Islands...................... 20
INTRODUCTION
The U.S. Geological Survey began multidisciplinary studies of the U.S. 
Virgin Islands in 1983 to assist the government of the Islands by providing 
necessary information for future planning and resource appraisal. 
The initial 
objective of the geochemical phase of the study was to examine the regional 
geochemical characteristics of the Islands including the identification of the 
foci of mineralization. Sampling of St. Thomas and St. John was conducted in 
June of 1983 and January of 1984, respectively.
The U.S. Virgin Islands are located in the Greater Antilles island arc 
some 64 km east of Puerto Rico (fig. 1). 
The major islands include 
St. Thomas, St. John, and St. Croix. There are about 50 smaller islands in 
the study area, most of which are located near St. Thomas and St. John.
St. Thomas is 19 km long by approximately 5 km wide with a surface area 
of some 91 km. St. John is 11 km long, on the average is 5 km wide, and has 
an area of approximately 54 km2 . 
The topography of both islands is 
mountainous. 
The highest elevation on St. Thomas is about 474 meters (Crown 
Mountain) and 390 meters on St. John (Bordeaux Mountain). The islands have 
irregular coastlines with many bays and offshore islets. There are only a few 
free-flowing streams, and these are intermittent. The climate is tropical, 
but annual rainfall is generally less than 130 cm. Many of the small outer 
islands are considered arid. 
Second-growth forests, which were formerly 
cultivated fields or plantations, now cover much of both islands.
GEOLOGIC SETTING
St. Thomas and St. John are part of the eastern portion of the Greater 
Antilles island arc chain, which extends to Cuba. The Puerto Rico Trench lies 
to the north of St. Thomas and St. John. 
The Annageda trough lies to the east 
and the Muertas trough lies to the southeast.
The geology of St. Thomas and St. John has been studied by many authors 
including Cleve (1882), Earle (1924), Meyerhoff (1926), and more recently by 
Donnelly (1959, 1966). 
The rocks in the study area are island-arc related 
Cretaceous to Tertiary volcanic and volcaniclastic sediments, near surface 
intrusions, and layered carbonates. 
In this paper the rock unit descriptions 
and structural relationships of the rocks have been taken from Donnelly (1959, 
1966). Geologic maps of St. Thomas and St. John are given in figures 2 and 3. 
The stratigraphic units are listed on Table 1.
The oldest rocks in the study area occur along the southern coasts of 
both islands. These rocks consist of keratophyres, spilites, and 
radio!arites, collectively called the Water Island Formation. 
The 
keratophyres are felsic extrusive or shallow intrusive rocks of submarine 
origin and contain predominantly albite and quartz. Spilite is a mafic rock 
of submarine origin. 
In the Water Island Formation, spilite is slightly 
greenish with chlorite and albite. 
Remnant phenocrysts of diopside and augite 
are common in the spilite. Amygdules are abundant within the spilite and 
generally contain epidote, calcite, or prehnite.
The Louisenhoj Formation unconformably overlies the Water Island 
Formation. 
This unit is a sequence of pyroclastic to epiclastic augite 
andesites believed to be derived from a nearby vent. The distribution of 
these rocks is shown in figures 2 and 3.
Overlying the Louisenhoj Formation is the Outer Brass Limestone which 
consists of thinly bedded siliceous limestones.
60
66
DOMINICAN 
REPUBLIC
GREATER ANTILLES
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VIRGIN ISLANDS 
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MDA
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KILOMETERS
Figure 1.--Index map of the Virgin Islands and vicinity,
05
65° 00'
55'
50'
BUCK 
ISLAND
MILES 
1234
5 
6
KILOMETERS
Figure 2.--Geologic map of St. Thomas, U.S. Virgin Islands. 
(Donnelly,1966)
64* SO'
45
40'
22'3O'
O
CONGO
MINGO
(7
1
H M H H
MILES 
234
IUUUUU"
KILOMETERS
Figure 3.--Geologic map of St. John, U.S. Virgin Islands. 
(Donnelly, 1966)
TABLE 1.--Summarized stratigraphic relationships of the rocks on St. Thomas 
and St. John, U.S. Virgin Islands (Donnelly, 1966)
Age
Stratified rocks
Intrusive rocks
present
Lower Tertiary 
to Upper 
Cretaceous
Alluvium- gravels and sands 
of recent origin
Hans Lollik Formation 
augite andesite volcanic 
breccia and tuff
Tutu Formation: 
volcanic wacke. Includes 
the Congo Cay Limestone 
Member
Outer Brass Limestone: 
thin-bedded, silicious 
1imestone
Louisenhoj Formation: 
augite andesite volcanic 
breccia and tuff, with 
minor conglomerate
UNCONFORMITY
Dikes and plugs: 
quartz-andesine 
porphyry; andesine- 
hornblende porphyry
Dioritic rocks
Quartz keratophyre 
dikes and plugs
Water Island Formation: 
keratophyre flows, flow 
breccias and tuff: 
radio!arian cherts; 
spilite flows
The Tutu Formation overlies the Outer Brass Limestone. This unit 
consists of interbedded sequences of fine- to coarse-grained volcanic wackes 
that appear to be reworked Louisenhoj andesites. Sedimentary textures in the 
Tutu Formation suggest a high energy environment of deposition (Donnelly, 
1966).
The Congo Cay Limestone is a light gray coarsely crystalline limestone 
found only on Congo Cay in the American Virgin Islands and on the southern 
coast of Tortola in the British Virgin Islands (fig. 3).
The Hans Lollik Formation outcrops over the entire island of Hans Lollik 
(fig. 2). 
This rock consists of augite-andesite, pyroclastic to epiclastic in 
origin and is very similar in texture and composition to the Louisenhoj 
Formation.
Upper Cretaceous to lower Tertiary rocks are also observed. 
Intrusive 
dioritic rocks, dikes and small plugs of quartz andesine porphyry, and 
andesine-hornblende porphyry are found locally (figs. 2 and 3).
Hydrothermal alteration is widespread along the southern shore of both 
St. Thomas and St. John and on many of the small islands in the study area. 
Two prominent areas of argillic alteration, silicification, and iron 
enrichment were observed on St. Thomas, at Red Point near the airport and in 
the vicinity of Jersey Bay. 
At Red Point, a pyritized-silicic breccia pipe 
and copper minerals are exposed in recent excavations. Near Jersey Bay, at 
site 14, veins of iron oxides up to 1.5 m in width cut the intensely 
argillized country rock. 
Epidote is common in small veinlets along the 
southern coast. Quartz veins, commonly containing pyrite, also occur at 
several localities. One series of quartz veins near Muhlenfels Point, St. 
Thomas, contains precious metals.
In the vicinity of Bordeaux Mountain, St. John, intense argillic 
alteration, silicification and iron enrichment occurs over a broad region. 
Gossan boulders are present near the crest of the mountain. The White Cliffs 
area contains highly altered rocks with alunite, turquoise, sulfur, and 
paratacamite.
The hydrothermal alteration has been interpreted as cogenetic with the 
cooling of the keratophyre magma because alteration only affected the Water 
Island Formation (Donnelly, 1966). 
Interpretation of the geochemical data 
suggests that most of the hydrothermal alteration post-dates much of the Water 
Island Formation. Broad metal halos appear to have been superimposed on the 
original chemical compositions of the Water Island Formation, extending into 
the Louisenhoj Formation and to a lesser degree, into the overlying 
sedimentary formations. 
Propylitic-1ike alteration occurs throughout much of 
the Louisenhoj Formation.
A continuous skarn zone occurs on Mingo Cay, Lovengo Cay, and Mary Point, 
St. John. 
The skarn consists of marble with epidote and garnet. 
Pyrite 
occurs locally within the skarn zone, particularly on Mingo Cay. 
Small pods 
of copper minerals occur within the skarn zone on Mingo Cay.
SAMPLE COLLECTION, PREPARATION AND ANALYSIS
Rock, soil, minus-80-mesh stream sediment, and panned-concentrate stream- 
sediment samples were collected from St. Thomas and St. John. Drainage basins 
with an area! extent generally less than 0.6 km were sampled. 
At each 
drainage site four different samples were collected. 
A 4.5 to 7 kg composite 
sample of the sediment was collected for panning. A 0.2 kg composite sample 
of the sediment was collected and later sieved to recover the minus-80-mesh 
fraction. 
A 0.2 to 0.5 kg soil sample was collected near the stream-sediment
site and, when possible, approximately 0.5 kg of rock chips were collected 
from a representative outcrop of the local bedrock. 
Veins, dikes, and altered 
areas were also sampled. 
At various locations a 4.5 to 7 kg soil sample was 
collected and panned. 
The sample localities and the geochemical anomalies 
discussed in the text are shown in figures 4 and 5 for St. Thomas and 
St. John.
All the samples were oven dried at 120°C for approximately six hours, 
except the panned concentrates, which were air dried. 
The soil samples and 
one portion of the stream sediment samples were disaggregated and sieved to 
minus-80-mesh prior to analysis. 
The rocks were crushed and then pulverized 
using ceramic plates. 
The panned concentrate samples were sieved to recover 
the minus-20-mesh fraction and then placed in bromoform (density 2.86) to 
separate two mineral fractions according to their density. 
The low density 
fraction contains minerals such as feldspars, quartz, and calcite. 
The 
heavy-mineral fraction contains: 
various rock-forming minerals (biotite, 
amphiboles, pyroxenes); accessory minerals (magnetite, ilmenite, sphene, 
zircon, and monazite); and primary or secondary base-metal minerals (sulfides, 
sulfates, carbonates, and oxides).
The magnetite and other very magnetic minerals were removed using a hand 
magnet. 
A Frantz Isodynamic Separator was used to separate the remainder of 
each sample. 
A forward slope of 25° and a side slope of 15° was used. 
Very 
magnetic minerals were separated at a setting of 0.2 amperes and added to the 
minerals already removed with the hand magnet. 
A magnetic fraction and a 
nonmagnetic fraction were separated at a setting of 1.0 ampere.
All samples were analyzed by the six-step D.C.-arc semiquantitative 
emission-spectrographic method (Grimes and Marranzino, 1968) for 31 elements.
Mineral grains less dense than bromoform from the panned-concentrate 
fraction were leached with oxalic acid. 
The oxalic acid selectively dissolves 
the Fe-Mn oxide coatings on the mineral grains (Alminas and Mosier, 1975). 
The size fraction was minus-20-mesh to approximately plus-80-mesh. 
The leach 
was performed using 25 ml of a 5% oxalic acid solution (weight/volume) added 
to 5 g of sample and boiled for 10 minutes. 
The hot leachate was filtered, 
evaporated to dryness, then heated for 4 hours at 250°C to roast off the 
oxalate. 
The resulting oxide powder was analyzed by the six-step D.C.-arc 
emission spectrographic method.
The upper 10-20 percent of the concentration range within a particular 
media for each element is considered to be anomalous. 
Natural breaks in the 
frequency distribution were also used in subjectively defining the limits of 
the anomalous concentrations. 
Data results for all media are in Hopkins and 
others (1984).
Geochemical data 
A. Rock geochemical data
The use of geochemical data is a valuable approach toward understanding 
geologic events that have occurred within an area and in evaluating an area's 
mineral potential. 
Examination of the rock data within the study area 
suggests that in many instances the concentrations of several elements are 
changed relative to fresh rock. 
These changes appear to be related to 
processes such as hydrothermal alteration. 
Large portions of both islands 
appear to have been affected by hydrothermal alteration.
00
s^
"I-
y
Red Po'.nt 
Qeochemical Anomaly
19 "f
Jersey Bay 
Qeochemical Anomaly
Figure 4 --Sampling sites on St. Thomas, U.S. Virgin Islands.
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The data from rocks was used to identify areas of potential mineral 
deposits based on the changes in the amounts of certain elements. Variations 
in barium concentrations in rock samples may be useful in identifying certain 
alteration types. 
The felsic rocks of the unaltered Water Island Formation 
generally have lower concentrations of Ba than the rocks of the Louisenhoj 
Formation. 
However, the highest Ba concentrations occur in rocks mapped as 
Water Island Formation (Donnelly, 1959 and 1966), from samples collected at 
Redhook Bay, St. Thomas, and Mary Point and Bordeaux Mountain, St. John (figs. 
6 and 7). 
These rocks have been intensely altered, which suggests that Ba has 
been enriched in the felsic rocks, possibly derived from circulating 
hydrothermal fluids. Anomalous concentrations of Ba are found at many sites 
near Bordeaux Mountain, also mapped as being within the Water Island 
Formation. 
The distribution of samples with anomalous Ba concentrations on 
St. John is shown in figure 7.
The distribution of samples containing anomalous Cu is shown in figures 8 
and 9 for St. Thomas and St. John, respectively. 
The felsic rocks generally 
have the lowest copper concentrations with the notable exception of samples 
from Bordeaux Mountain and Mary Point, St. John (fig. 9). 
Anomalous copper 
concentrations are not restricted to the Louisenhoj Formation but extend into 
the overlying sedimentary rock units on both islands.
The distribution of samples containing anomalous Mo concentrations is 
given in figures 10 and 11. 
Areas of intense argillic alteration and iron 
enrichment occur near Jersey Bay on the eastern end of St. Thomas and Bordeaux 
Mountain, St. John, and have the greatest concentration of anomalous Mo 
values.
Only a few rock samples have detectable concentrations of precious metals 
(figs. 12 and 13). 
The highest concentrations of Au and Ag are from iron-rich 
veinlets collected on or near Bordeaux Mountain, St. John, and a quartz vein 
on St. Thomas. 
The quartz veins crop out between the main dock at Charlotte 
Amalie and Muhlenfels Point, north of sample site 50, St. Thomas (figure 12). 
The largest quartz vein is approximately 1 m wide. 
Samples from the largest 
vein were taken at approximately 15-m intervals over a strike length of 135 m. 
Table 2 lists the Ag, Au, and Te concentrations of these samples. 
Secondary 
copper minerals were observed in veins in the adjacent country rock. 
This 
area is referred to as the Muhlenfels geochemical anomaly (fig. 4).
A large geochemical anomaly occurs in the vicinity of the Harry S. Truman 
airport, on St. Thomas and is referred to as the Red Point geochemical anomaly 
(fig. 4). 
Secondary copper minerals, a pyritic-quartz breccia pipe, argillic 
alteration and iron enriched veins are exposed in recent excavations. 
The 
small cays or islands south of Red Point (sites 20 and 21) have been intensely 
silicified. 
Samples from the islands do not contain anomalous metal 
concentrations but the presence of silica flooding is a possible geologic 
indicator of hydrothermal activity. 
Propylitic-1ike alteration extends into 
the Louisenhoj Formation to the north.
The rocks along the coast on the west side of Jersey Bay, St. Thomas, and 
nearby islands have been intensely altered to clays with iron introduced. 
There are nearly vertical veins (up to 1.5 m in width) of iron oxide minerals 
that cut the very altered country rock near site 14. 
There are also a series 
of 2-8 cm veinlets of iron oxides that form a boxwork-like texture in the 
cliffs. 
This area is referred to in the text as the Jersey Bay geochemical 
anomaly (fig. 4).
10
Figure 6.--Distribution of anomalous Ba concentrations from rocks on St. Thomas, U.S. Virgin Islands.
£=>
Barium (ppm) 
Q>1000 
0 = 500-700 
A< 20
1 
.5 
O
Figure 7.--Distribution of anomalous Ba concentrations from rocks on St. John, U.S. Virgin Islands
Figure 8.--Distribution of anomalous Cu concentrations from rocks on St. Thomas, U.S. Virgin Islands.
Copper (ppm)
> 500
O= 150-300 
A< 5
1 
.5 
0
Figure 9.--Distribution of anomalous Cu concentrations from rocks on St. John, U.S. Virgin Islands
.
/"*: 
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ST. THOMAS 
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Molybdenum (ppm)
0=5-20
^'-c?
Figure 10.--Distribution of anomalous Mo concnetrations from rocks on St. Thomas, U.S. Virgin Islands.
Molybdenum (ppm) 
0 
= 200 
0=5-20
1 
.5 
0
Figure 11.--Distribution of anomalous Mo concentrations from rocks on St. John, U.S. Virgin Islands
Figure 12.--Distribution of anomalous Ag concentrations from rocks on St. Thomas, U.S. Virgin Islands.
40'
CO
21'JO"
Silver (ppm) 
= 200 
0,5-3
Gold (ppm) 
/Vo.05-0.6
Figure 13.--Distribution of anomalous Au and Ag concentrations from rocks on St. John, U.S. Virgin Islands
TABLE 2. Silver, gold, and tellurium analyses of a quartz vein cropping out 
within the Muhlenfels anomaly, St. Thomas, U.S. Virgin Islands
[Ag analysis by six-step D.C.-arc emission spectrograph; Au and Te analyses by
atomic absorption]
Sample 
Ag 
Au 
Te
(concentration in ppm)
01
03
04
05
06
07
08
09
10
0.5
30
5
100
200
15
150
100
70
1.1
2.1
0.35
1.3
5.5
0.45
16
0.90
0.65
6.7
24
3.7
81
35
3.9
240
42
31
A skarn is exposed on Mingo Cay, Lovango Cay, and Mary Point (fig. 3). 
A small pod and veinlets of copper and iron minerals occur on the east end of 
Mingo Cay along with massive garnet and epidote. 
A four-foot wide vein of 
magnetite bordered by barite veins crosscuts the uplifted limestones on the 
north side of the Cay. 
The limestone has been recrystallized to marble and 
contains pyrite and garnet. This area is referred to as the Mingo Cay 
geochemical anomaly (figs. 4 and 5). 
Similar skarn-type deposits are 
indicated on Great Thatch Island, Tortola, and other islands immediately to 
the north and northeast in the British Virgin Islands group (Shomburgk, 1837). 
It is speculated that the heat source (stock) that formed the skarns could be 
large enough to cause the recrystallization of the Congo Cay Limestone 
observed on Congo Cay and in the British Virgin Islands.
Gossan was observed at site 52R, St. John (fig. 5), and an unweathered 
and highly siliceous intrusive rock containing pyrite was also observed in an 
excavation pit. 
The gossan sample contains anomalous concentrations of Ag, 
Mo, Au, and Te. 
This area is referred to as the Shore geochemical anomaly
(fig. 5).
Bordeaux Mountain, St. John, contains large boulders of gossan, intensely 
argillized areas, and nearly vertical iron oxide-rich veins. 
Anomalous Ag, 
Au, and Te values are found in many of the rock samples collected from one 
traverse along the crest of the mountain (fig. 13). 
The argillic and 
hematitic alterations extend from the crest of Bordeaux Mountain to the sea 
coast and can be identified in road cuts inland as well. 
This area is 
referred to as the Bordeaux Mountain geochemical anomaly (fig. 5).
The White Cliffs on St. John contain intensely altered rocks with 
alunite, jarosite, and fine-grained silica. 
There are turquoise veinlets, 
native sulfur pods and crusts, and greenish crusts of paratacamite 
(Cuo^hOgCl). 
Thirteen rock samples were collected in this area. 
The Au, Ag, 
and Te values are given in table 3. 
This area is considered to be within the 
Bordeaux Mountain anomaly.
19
TABLE 3. Silver, gold, and tellurium analyses from rock samples from the 
White Cliffs, St. John, U.S. Virgin Islands
[Ag analysis by six-step D. C.-arc emission spectrograph; Au and Te analyses 
by atomic absorption Detection limits for each element are given in 
parentheses. 
An "L" indicates the elemental concentration was slightly 
lower than the lower detection limit, an "N" indicates the element was not 
detected]
Sample 
Ag (0.5) 
Au (0.05) 
Te (0.1
(concentration in ppm)
111
111R1
111R2
111R4
111R5
111R6
111R7
111R8
111R9
111R10
111R11
111R12
111R13
N
1
L(0.5)
N
N
N
N
N
N
0.7
1.5
N
1.5
N
N
N
L(0.05)
0.60
0.05
0.05
N
L(0.05)
L(0.05)
L(0.05)
N
L(0.05)
0.1
5.9
9.4
0.8
5.2
N
0.9
N
3.8
0.2
1.2
N
0.4
B. Nonmagnetic fraction of the panned concentrate
The nonmagnetic fraction of the panned concentrate samples is the most 
effective medium for identifying areas of high metal potential. Many of the 
minerals found in the nonmagnetic fraction are associated elsewhere with 
mineral deposits and hydrothermal alteration. The concentration of these 
minerals in this medium greatly enhances detection. 
Lead concentrations from 
most drainage basins sampled are below 100 ppm, but values greater than 10,000 
ppm (1%) are found at sites 24 and 32 which are in drainages on the east side 
of Bordeaux Mountain. 
Lead concentrations in the minus-80-mesh fraction for 
the same samples from Bordeaux Mountain were only 70 and 20 ppm, respectively.
The Bordeaux Mountain geochemical anomaly is the most pronounced and 
extensive anomaly identified to date on both islands. 
The distribution of Ag, 
Bi, and Sb (fig. 14), Ba (fig. 15), Cu (fig. 16), and Pb (fig. 17) clearly 
show that many stream drainages from Bordeaux Mountain contain anomalous 
concentrations of most of the above elements.
The data from the study suggest that silver, and to a lesser degree, Bi 
and Sb, are possible pathfinder elements in locating basins in which 
precious-metal-bearing veins may be located. 
Anomalous concentrations of 
these three elements were found in samples from streams draining Bordeaux 
Mountain (sites 24 and 32), near Mary Point (sites 11 and 13), and in Fish 
Creek (sites 53 and 54). 
The highest silver concentration (700 ppm) occurs at 
site 53. 
Anomalous concentrations of Ag, Ba, Cu, Pb, Sb, Bi, and Sn are found 
in samples from sites 53, 54, 72, and 203, derived from a small area. This 
area is referred to as the Fish Creek geochemical anomaly (fig. 5).
20
Silver (ppm)
Antimony (ppm)
' 
3 
O
O^ 1.5-10
Bismuth (ppm)
X =30-300
Figure 14. --Distribution of anomalous Ag, Bi, and Sb concentrations in the nonmagnetic fraction of the stream 
sediments from St. John, U.S. Virgin Islands.
ro 
ro
Barium (ppm) 
Q>10,000 
= 2000-7000
1 
.5 
0
Figure 15.--Distribution of anomalous Ba concentrations in the nonmagnetic fraction of the stream sediments 
from St. John, U.S. Virgin Islands.
1 
.5 
0
Copper
> 3000 
O = 500-2000 
A < 10
Figure 16.--Distribution of anomalous Cu concentrations in the nonmagnetic fraction of the stream sediments 
from St. John, U.S. Virgin Islands.
ro
1H*>710*
Lead (ppm) 
Q> 10000 
O = 700-7000 
A < 20
1 
.5 
0
Figure 17.--Distribution of anomalous Pb concentrations in the nonmagnetic fraction of the stream sediments 
from St. John, U.S. Virgin Islands.
There are two drainage basins near the Shore geochemical anomaly. 
Anomalous concentrations of Pb, Ba, and Sn occur in these drainages.
The Red Point geochemical anomaly (St. Thomas) was delineated on the 
basis of anomalous concentrations of Pb and Cu (fig. 18), Ba (fig. 19), 
Ag, Bi , and Sb (fig. 20).
The Muhlenfels Point geochemical anomaly (St. Thomas) is detected by 
anomalous concentrations of Cu, Ba, Ag, Pb, and Sn at site 50.
A small nugget of Au was observed in the concentrate from site 2. 
This 
site also contains elevated concentrations of Ag, Cu, Pb, Mo, and Ba. 
Gold 
was also observed in the concentrate from site 106 (Grass Cay) and from sites 
10 and 92 (St. John).
Anomalous metal concentrations occur in samples from Thatch, Grass, 
Mingo, Lovango, and Congo Cays (figs. 14, 15, and 17). 
This data coincides 
with the rock data.
C.--Minus-80-mesh fraction of the soil samples
The geochemical interpretation of the minus-80-mesh fraction of the soil 
samples generally coincides with the previously discussed sample media.
Soil samples collected near the crest of Bordeaux Mountain contain 
anomalous Ba (fig. 21), Pb, and Cu (fig. 22) concentrations. Slightly lower 
metal concentrations generally occur in soil samples from sites near the 
stream drainage sites. Anomalous Cu concentrations occur in the Fish Creek 
and Shore geochemical anomalies (fig. 22).
The soil samples do not contain anomalous metal concentrations within the 
Red Point and Muhlenfels Point anomalies on St. Thomas. 
However, anomalous Cu 
concentrations (fig. 23) and Pb and Ag concentrations (fig. 24) occur on the 
small islands between Red Point and Muhlenfels Point.
Anomalous metal concentrations occur on the east end of St. Thomas 
(Jersey Bay anomaly). 
The Ag concentrations at sites 13, 49, 67, 70, and 74 
(fig. 24) are not reflected in the other media sampled. 
The Ag values in the 
soils at sites 62 and 63 coincide with rock and nonmagnetic fraction data 
(fig. 24).
D.--Oxalic acid leach analysis
The oxalic acid leach selectively dissolves Fe-Mn hydroxides and releases 
any metal ions that have been adsorbed (Alminas and Mosier, 1975). 
The metals 
observed in the leachate can give an indication of the relative importance of 
hydromorphic transport in the redistribution of metals released from the rocks 
within a basin. 
The results from these analyses indicate that many metals 
that are often relatively immobile, such as Pb and Ag, are apparently very 
mobile in this environment.
The distribution of anomalous Pb and Cu concentrations is given in 
figure 25. 
Anomalous Pb concentrations occur in the Bordeaux Mountain, Fish 
Creek, and Shore anomalies. Anomalous Pb and Cu concentrations on St. Thomas 
indicate the Red Point anomaly (fig. 26). 
Anomalous lead concentrations are 
also found at sites from the east end of St. Thomas, within the Jersey Bay 
anomaly (fig. 26).
The distribution of samples with anomalous Mo concentrations on St. 
Thomas appears to be more localized than the other elements discussed 
(fig. 27). 
Anomalous Mo concentrations occur at sites 21S and 54 within the 
Red Point anomaly (St. Thomas). 
Several samples from the Jersey Bay anomaly 
(St. Thomas) contain anomalous Mo concentrations (fig. 27).
25
Lead (ppm) 
/\> 10000 
A =2000-7000
Copper (ppm) 
>2000 
O = 700-1500
Figure 18.--Distribution of anomalous Pb and Cu concentrations in the nonmagnetic fraction of the stream sediments 
from St. Thomas, U.S. Virgin Islands.
ro
Barium (ppm) 
Q>10000 
O =1000-7000
Figure 19. --Distribution of anomalous Ba concentrations in the nonmagnetic fraction of the stream sediments 
from St. Thomas, U.S. Virgin Islands.
ro
CO
Antimony (ppm) 
/\>200
Bismuth (ppm) 
x > 30
Figure 20.--Distribution of anomalous Ag, Bi, and Sb concentrations in the nonmagnetic fraction of the stream 
sediments from St, Thomas, U.S. Virgin Islands.
22" 3 f
ro
Barium (ppm) 
> 2000 
O = 500-1000
1 
.5 
O
Figure 21.--Distribution of anomalous Ba concentrations from the minus-80-mesh fraction of soil samples from 
St. John, U.S. Virgin Islands.
22'30*
Lead (ppm)
Copper (ppm) 
Q>500 
O =200-300
1 
.5 
O
Figure 22.--Distribution of anomalous Pb and Cu concentrations from the minus-80-mesh fraction of soil 
samples from St. John, U.S. Virgin Islands.
Barium (ppm) 
/\>500
= 200-300
Figure 23.--Distribution of anomalous Ba and Cu concentrations from the minus-80-mesh fraction of soil samples 
from St. Thomas, U.S. Vifgin Islands.
OJ
no
Lead (ppm)
O->5°
Silver (ppm)
Figure 24.--Distribution of anomalous Pb ,and Ag concentrations from the minus-80-mesh fraction of soil samples 
from St. Thomas, U.S. Virgin Islands.
22' So"
GO 
CO
no-i"
Lead (ppm) 
A £300
Copper (ppm)
1 
.5 
0
Figure 25. --Distribution of oxalic acid soluble Pb and Cu concentrations in coarse, light sediments from 
St. John, U.S. Virgin Islands.
Lead (ppm) 
* 300
Copper (ppm)
Figure 26. --Distribution of oxalic acid soluble Pb and Cu concentrations in coarse, light sediments from 
St. Thomas, U.S. Virgin Islands.
r/i vj&
  ' Y2 c 
i.~/^
Molybdenum (ppm)
= 10-50
Figure 27.--Distribution of oxalic acid soluble Mo concentrations in coarse, light sediments from St. Thomas, 
U.S. Virgin Islands.
Anomalous silver concentrations occur throughout both islands (figs. 28 
and 29). 
The distribution of anomalous values cannot be characterized by 
locality or by association with any specific rock type.
E. Magnetic fraction of the panned concentrates
The interpretation of analyses of the magnetic fraction of the panned 
concentrates can often be complicated because of certain geochemical 
characteristics of the minerals selectively isolated in this medium. The 
magnetic fraction may contain minerals such as hornblende, ilmenite, garnet, 
and sphene. These minerals may contain high concentrations of elements such 
as Pb, Sn, Nb, Zn, and Cu (Hurlbut, 1971; Parker and Fleischer, 1968). The 
abundance of these minerals must be taken into consideration when defining 
geochemical anomalies.
The magnetic fraction can be very useful in detecting potential 
metallization that may occur at depth (Alminas and VanTrump, 1978; Miller and 
others, 1982; Tucker and others, 1982). The magnetic fraction amplifies the 
effect of the magnetic minerals or coatings precipitated from hydrothermal 
fluids emenating from a metalized stock. These minerals may selectively 
incorporate many metals from the hydrothermal solutions.
The distribution of anomalous Ba and Pb concentrations from St. John is 
given in figure 30. 
These metals delineate the Bordeaux Mountain anomaly. 
Anomalous copper concentrations are found in samples surrounding Coral Bay and 
on the cays west of Mary Point. 
The Fish Creek and Shore geochemical 
anomalies are not well represented by this fraction. Samples in the Mingo Cay 
anomaly have anomalous concentrations of Pb and Ba (fig. 30).
Anomalous concentrations of Pb, Ag, and Mo on St. Thomas are shown in 
figure 31 and Cu and Ba are shown in figure 32. Many of these elements occur 
from samples in the Red Point and Muhlenfels Point geochemical anomalies. The 
Jersey Bay geochemical anomaly contains anomalous concentrations of Pb, Ag, 
and Mo which coincides with the oxalic acid leach data and the rock data from 
this area.
F.--Minus-80-mesh fraction of the stream sediments
The minus-80-mesh fraction of the stream sediments is a composite sample 
representing the major rock-forming minerals, Fe-Mn hydroxide coatings, and 
heavy minerals. 
It is difficult to determine the relative contributions of 
each component to the overall content of the stream sediment. The 
predominance of barren rock fragments and minerals cause a dilution and thus a 
dampening of the anomaly to background contrast. This fraction was not 
utilized in mineral appraisal; however, the data may be useful in other 
applications.
DISCUSSION
The Bordeaux Mountain anomaly is the most intense and continuous geochem- 
ical anomaly identified in the study area and is represented by all the media 
discussed. 
The anomaly is characterized by Fe, Ag, Ba, Bi, Cu, Pb, Sn, and Zn 
in many of the drainage samples (for elements not previously discussed see 
Hopkins and others, 1984). 
The anomaly is particularly well delineated by the 
magnetic and nonmagnetic stream-sediment-concentrate fractions. 
Rock and soil 
samples collected on a single traverse along the crest of Bordeaux Mountain
36
Silver (ppm) 
0^200 
O =15-150
Figure 28.--Distribution of oxalic acid soluble Ag concentrations in coarse, light sediments from St. John, 
U.S. Virgin Islands.
CO
O3
Silver (ppm) 
Q>200 
O =15-150
Figure 29.   Distribution of oxalic acid soluble Ag concentrations in coarse, light sediments St. Thomas, 
U.S. Virgin Islands.
CO
to
Barium (ppm) 
^ 300
Lead (ppm)
i 
.5 
o
Figure 30.--Distribution of anomalous Ba and Pb concentrations from the magnetic fraction of the panned 
concentrate samples, St. John, U.S. Virgin Islands.
Lead (ppm)
Silver (ppm)
Molybdenum (ppm)
*tr*0
Figure 31.--Distribution of anomalous Pb, Ag, and Mo concentrations from the magnetic fraction of the panned 
concentrate samples, St. Thomas, U.S. Virgin Islands.
Copper (ppm) 
O £ 300
Barium (ppm) 
/\>700
Figure 32.--Distribution of anomalous Cu and Ba concentrations from the magnetic fraction of the panned concentrate 
samples, St. Thomas, U.S. Virgin Islands.
contain anomalous concentrations of Ba, Ag, Au, Pb, Cu, Zn, and Mo. 
Soil and 
rock samples from the surrounding area generally contain slightly lower metal 
concentrations than those from the crest. The elements observed in the 
various sample media and the distribution of these elements suggests that a 
metallizing event occurred in the vicinity of Bordeaux Mountain. The focus of 
the metallization possibly occurred near the crest and metal-rich fluids 
migrated through the surrounding rocks. The large gossan boulders on the 
crest indicate that abundant sulfide minerals were once present. 
The geo- 
chemical halos and metal associations around Bordeaux Mountain are similar to 
those that occur in the vicinity of known metal deposits such as Red Mountain, 
Colorado (Westra and Keith, 1981; Wallace and others, 1978), Pine Grove, Utah 
(Westra and Keith, 1981), and Marysvale, Utah (Cunningham and others, 1984). 
The Red Mountain and Pine Grove deposits are porphyry-type molybdenum deposits 
with associated vein-type base-metals occurring in the upper levels of the 
deposits. These deposits occur in a rhyolitic to granitic terrain.
The White Cliffs area (St. John) appears to be an ancient hot springs, 
which, owing to its proximity to Bordeaux Mountain, may be genetically related 
to a metallizing event that apparently occurred in the Bordeaux Mountain 
region. 
Al unite, silica, and iron oxides occur in the vicinity. A similar 
occurrence of ancient hot springs with alunite, iron minerals and other 
minerals also occur near Marysvale, Utah. The alunite rich areas near 
Marysvale have been interpreted as hot springs genetically related to the 
emplacement of a metallized intrusive in the central mining district 
(Cunningham and others, 1984). 
The alunite on Alunite Ridge, west of 
Marysvale, Utah, has been interpreted as reflecting outgassing of thermal 
fluids genetically related to the emplacement of a postulated porphyry-type 
deposit (Cunningham and others, 1984). 
Studies of outcrop samples (Tucker and 
others, 1981) and stream-sediment-concentrate samples (Tucker and others, 
1982) in the Mount Belknap-Marysvale area identified geochemical suites and 
characteristics related to the emplacement of the postulated metallized 
intrusive. Many of the same geochemical suites are present in samples from 
the Bordeaux Mountain anomaly.
The presence of rhyolitic rocks, extensive argil lie alteration, iron 
enrichment, copper minerals, alunite, and gossan all indicate that the 
metallization in the Bordeaux Mountain anomaly is related to the emplacement 
of an intrusive body that was pregnant with metals. 
The postulated metallized 
intrusive under Bordeaux Mountain may contain porphyry-type metallization.
There are known metallized areas within the region extending from Puerto 
Rico (Learned and others, 1980; 1981; Miller and others, 1982). 
The abandoned 
mine on Virgin Gorda contained supergene and primary copper minerals, precious 
metals, and molybdenite (Martin-Kaye, 1955).
The high concentration of many metals in the oxalic acid leach may 
reflect hydromorphic transport. Many of the basins around Coral Bay have 
anomalous concentrations of Ag, Pb, and V. 
It would be interesting to examine 
areas of quiescence in Coral Bay for chemical precipitates of these metals.
The Fish Creek and Shore anomalies have similar geochemical signatures to 
that of the Bordeaux Mountain anomaly. These two areas are near Bordeaux 
Mountain and may also be related to the Bordeaux Mountain metallizing event. 
The Fish Creek anomaly is a small, possibly fault controlled, metallized zone 
or zones that are best represented in the nonmagnetic fraction, suggesting 
that the metallization may be near the surface within the basins of sites 53, 
54, 72, and 203. 
The geochemical data further suggest that the metallized 
zones may contain precious metals. Detailed rock and soil samples could 
further define the source and extent of this anomaly.
42
The Shore anomaly is best represented in the rock data. 
However, 
anomalous metal concentrations are found in the sediments from nearby basins 
which give subtle indications of the metallized zone. 
Detailed rock and soil 
sampling would be useful in delineating the halos around the anomaly, and 
possible mineral potential.
The skarn-type metallization observed in the Mingo Cay anomaly contains 
anomalous concentrations of Pb, Ba, Cu, Sn, Ag, and Au. 
A dioritic intrusive 
is exposed on Mary Point and on Tortola, which may have been the heat source 
to form the skarn. 
The geochemical data suggest that hydrothermal fluids may 
have introduced many metals into the original skarn.
The Congo Cay Limestone has been mapped as a distinct rock unit within 
the Tutu Formation (Donnelly, 1959 and 1966). 
Anomalous metal concentrations 
are found in samples from all the cays which suggests that a similar 
metalizing event has affected the whole area. 
The rocks on Tortola south of 
the Congo Cay Limestone member are mapped as limestone, however, descriptions 
of these rocks by Schomburgk (1837) indicate the presence of marble and garnet 
in these rocks. 
These observations are very similar to those noted on Mingo 
Cay and suggests that the originally uniform sediment has been thermally and 
chemically altered to varying degrees. 
The limestone near the thermal source 
was recrystallized to marble and contains garnet, epidote, and pyrite. The 
Congo Cay Limestone does not contain the above minerals but has a very coarse 
crystalline texture and anomalous metal concentrations. 
On Tortola, the 
limestone north of the Congo Cay Limestone member is apparently unaltered 
(Donnelly, 1966).
The geochemical characteristics of the data from St. Thomas are more 
difficult to interpret than those from St. John. 
The Jersey Bay and Red Point 
anomalies appear to represent two centers of anomalous metal concentrations 
with overlapping boundaries.
The Jersey Bay anomaly contains anomalous concentrations of Ba, Cu, Pb, 
Mo, and Ag in all of the sample media. 
This anomaly can be characterized in 
the rock data by Ba halos extending some 2 km inland from the area of intense 
argillic alteration and iron-rich dikes near sites 13, 14, and 15. 
Anomalous 
Ag and Mo concentrations in the rocks are restricted to a somewhat smaller 
area. 
Anomalous Pb and Cu concentrations in the nonmagnetic fraction tend to 
form extended halos around the altered zone. Anomalous Cu concentrations are 
found in soil samples in the altered zone and anomalous Ba, Pb, and Ag 
concentrations in the soils are more widespread. 
The distribution of Mo in 
the oxalic acid leach is very localized in the altered zone and Ag seems to 
form a broad halo around the Mo. 
Anomalous Pb, Ag, Mo, Cu, and Ba 
concentrations in the magnetic fraction extend from Jersey Bay to the northern 
coast. 
The magnetic minerals precipitated from hydrothermal solutions may 
trap other metals from the parent solution, thus giving an indication as to 
the metal potential and the depth of the parent stock (Alminas and VanTrump, 
1978). 
There are a number of faults in the area which could have allowed the 
hydrothermal fluids to migrate through the rocks from the postulated intrusion 
at Jersey Bay. 
The interpretation of the geochemical data suggests that a 
metal-rich, possibly porphyry-type intrusive was responsible for the 
alteration and metal overprints within the area. 
The high number of metals in 
the magnetic fraction also suggests that the metal-rich intrusive may be at 
greater depth than the Bordeaux Mountain intrusive.
The Red Point anomaly (St. Thomas) can be identified in all the sample 
media but is not as distinct as the Bordeaux Mountain or Jersey Bay anomalies. 
The geologic features observed in the Red Point area are possibly the best 
indicators of a metallizing event. 
The small cays south of Red Point exhibit