4500-year-old mining pollution in Southwestern Spain: Long-Term implications for modern mining pollution

Abstract

The Tinto river drains the Rio Tinto mining district, which comprises the world's largest known massive sulfide deposits; these orebodies have been mined from the third millenium BC to the present. The Tinto river is strongly acidic (pH, 1.5-2.5); during flood events, it transports a sandy material, including abundant detrital pyrite grains. A core drilled in the Holocene sediments of the Tinto estuary allows for investigation of recent and historical mining pollution. Two anomalous horizons have been recognized (0-1.3 m; 3-4 m). Both are characterized by very high metal content (100 times over the background) and by the presence of abundant clastic pyrite grains. The metal association (Pb, Ba, As, Cu, Zn, Sn, Tl, Cd, Ag, Hg, Au) is typical of that of the Rio Tinto pyritic ore. The upper horizon corresponds to the modern mining activity; the lower horizon has been dated at 2530 BC ( 14C AMS calibrated age). We show here that active mining occurred early (Copper Age) in the Rio Tinto area, resulting in a water-shed-scale metal contamination. We also show that anthropogenic input of metals may be accumulated and immobilized during thousands of years in estuarine sediments.

Full text

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Introduction
Mining activity is a major source of metal contamina-
tion by toxic metals released into surface waters. Re-
newed interest in the impact of mining followed the re-
cent accident at Aznalcollar, Spain. On April 25, 1998, a
tailings spill from the mine of Aznacollar, in the southern
Iberian pyrite belt, released about 7 ×106 m3of sulfide
sludge in a tributary of the Guadalquivir river (Van Geen
and Chase, 1998), which drains the Donana national
park, the most important wildlife reserve of UNESCO in
Europa (Fig. 1). The sulfide sludge contained a mixture
of acidic waters (pH, 2–3.5) and very fine sulfide mater-
ial (<30 µm) dominated by pyrite, with about 2 percent
Zn, 0.9 percent Pb, 0.6 percent As, 0.2 percent Cu (dry
material) and abundant traces of other toxic metals such
as Tl, Hg and Cd (Table 1). The flood wave was toxic for
plankton, benthos, fish, and crab populations in the
river. One week after the spill, extremely elevated Zn
concentrations (0.6–1.2%) were found in the river sedi-
ments downstream from the mine over a distance of 40
km (Van Geen and Chase, 1998).
There is much archeological evidence of ancient min-
ing in the Iberian pyrite belt; it is well known, for exam-
ple, that the Rio Tinto orebodies have been mined at
various times since the third millennium BC (Briard,
1976; Rothenberg and Blanco Freijero, 1980). The aim
of this study was to investigate the impact of ancient
mining, at a watershed-scale, and to compare ancient
mining contamination with modern mining release. This
should allow predictions of the long-term behavior of
modern metal-contaminated sediments in this area.
The Rio Tinto Watershed
The southern Iberian pyrite belt, which belongs to the
southern part of the Iberian Variscan orogenic belt, is
the largest repository of volcanogenic massive sulfide de-
posits in the world. The pyrite belt includes more than
80 known deposits that are hosted in a Late Visean vol-
cano-sedimentary sequence. These massive pyrite de-
posits contain (mined and reserves) about 32 Mt Zn, 13
Mt Cu and 11 Mt Pb (metal tonnages, Leistel et al.,
1994).
The Rio Tinto massive sulfide district is the biggest in
its class. The Rio Tinto district comprises more than 109
t of massive pyrite ore. These super-giant deposits have
abundant base metal sulfides (Zn, Cu, Pb) and associ-
ated trace metals (Cd, As, Tl, Sn, Hg, Ag and Au; Table
1). The deposits have also had an extensive mining his-
tory. The Rio Tinto deposit has been mined since the
Copper Age, then during Tartessian and Phoenician
times (1200–500 BC), with greatest amount of activity
taking place during the Roman period (Flores, 1981).
Mining started again in the last part of the nineteenth
century and has continued to the present. These succes-
sive mining activities, from the Copper Age until the
present day, have exploited outcropping and near-sur-
face pyritic orebodies, leaving wide volumes of pyrite-
rich waste rocks and mining wastes.
Acid mine drainage resulting from the oxidation of
pyrite is especially important in the Rio Tinto mining
district. The headwaters of the Tinto river are in the area
of intense mining, which includes wide stockpiles of
pyrite-rich wastes and retention ponds of acid mine
4,500-YEAR-OLD MINING POLLUTION IN SOUTHWESTERN SPAIN:
LONG-TERM IMPLICATIONS FOR MODERN MINING POLLUTION
M. LEBLANC,†
Hydrosciences, UMR CNRS-Université Montpellier 2, 34095, Montpellier, France
J. A. MORALES, J. BORREGO,
GIGC, Departamiento de Geología, Universidad Huelva, 21819 Huelva, Spain
AND F. ELBAZ-POULICHET
Hydrosciences, UMR CNRS-Université Montpellier 2, 34095, Montpellier, France
Abstract
The Tinto river drains the Rio Tinto mining district, which comprises the world’s largest known massive sul-
fide deposits; these orebodies have been mined from the third millenium BC to the present. The Tinto river is
strongly acidic (pH, 1.5–2.5); during flood events, it transports a sandy material, including abundant detrital
pyrite grains. A core drilled in the Holocene sediments of the Tinto estuary allows for investigation of recent
and historical mining pollution. Two anomalous horizons have been recognized (0–1.3 m; 3–4 m). Both are
characterized by very high metal content (100 times over the background) and by the presence of abundant
clastic pyrite grains. The metal association (Pb, Ba, As, Cu, Zn, Sn, Tl, Cd, Ag, Hg, Au) is typical of that of the
Rio Tinto pyritic ore. The upper horizon corresponds to the modern mining activity; the lower horizon has been
dated at 2530 BC (14C AMS calibrated age).
We show here that active mining occurred early (Copper Age) in the Rio Tinto area, resulting in a water-
shed-scale metal contamination. We also show that anthropogenic input of metals may be accumulated and im-
mobilized during thousands of years in estuarine sediments.
Economic Geology
Vol. 95, 2000, pp. 655–662
† Corresponding author: e-mail, leblanc@dstu.univ-montp2.fr

drainage waters. The name of the Tinto river (“tinto ” means
“red wine” in Spanish) clearly refers to the uncommon
brown-red color of its waters.
The Tinto river, which is 90 km long, remains strongly
acidic (pH, 1.5–2.5) from its source zone, about 400 m elev,
down to its estuary in the Ria of Huelva (Fig. 1). Its red-col-
ored waters contain high sulfate and dissolved metal contents
(Nelson and Lamothe, 1993; Elbaz-Poulichet et al., 1999).
The mean discharge is relatively small—about 15 m3/s, rang-
ing from 1 to 100 m3/s depending on seasonal variations, in-
cluding dry periods and rainy periods with floods. The Tinto
river sediments are gray sands, including quartz and slate el-
ements and abundant detrital pyrite grains that are weakly
weathered and slightly rounded.
Methods and Materials
A core was drilled (lat. 37°18'16", long. 6°48'10"), down to
the bedrock, through the Holocene sediments of the upper
part of the Rio Tinto estuary (Fig. 1). This zone corresponds
today to a flood plain that is usually dry, being 1.15 m above
the mean high-water level. The core, 7 cm diameter, is about
15 m in length. Core recovery was relatively good (92%) and
the core material was only moderately disturbed and frag-
mented; consequently, there is no uncertainty in depth con-
trol. Core material was protected in a PVC sheath. It was
sawed longitudinally in four parts for lithological, geochemi-
cal, and dating studies, and the last part was kept as reference.
Lithology was studied both using optical microscopy and
scanning electronic microscopy to investigate the sulfide
phases. Twenty samples of core material (30–50 g dry mater-
ial) were selected for major and trace elements analysis (Fig.
2).
Present sediments from the Tinto river were collected ran-
domly within the uppermost 5 cm. They were dried before
examination by SEM, then analyzed (30–50 g) for major and
trace elements. The sulfide sludge from Aznalcollar was col-
lected along the banks of the Guadiamar river one day after
the spill.
The geochemical analyses for major (including S, CO2,and
organic C) and trace elements (including Cl and Hg) were
done by X-RAL laboratories (Don Mills, Ontario, Canada)
and at the Montpellier University, using XRF (X-ray fluores-
cence), NAA (neutron activation analysis), ICP-MS (induc-
tively coupled plasma-mass spectrometry) and AA (Atomic
Absorption) spectrophotometry.
The SEM investigations were performed with a Hitachi S-
4500 instrument coupled with an energy-dispersive X-ray
spectrometer (EDS); detection limits were about 0,1 percent,
with a precision within 20 percent.
Activation mass spectrometry (AMS) radiocarbon dating
was performed by Beta Analytic, Inc. (Miami). The analyzed
sediment samples (35–75 g) contained enough organic carbon
(0.5–1%) to ensure accurate analysis and all analytical steps
went normally (graphitization and AMS radiocarbon count-
ing); a charcoal fragment (4.3 g) was picked for complemen-
tary analysis. The conventional 14C ages were calibrated to
calendar years using the Pretoria Calibration Procedure
based on tree-ring data as calibration curves (dendrocalibra-
tion); the calibrated ages are given BC ages with 95 percent
probability.
The 210Pb determinations were done on the uppermost 30
cm of the core in order to determine the chronology of pollu-
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Mining areas
drill hole
Rio Tinto
Mine Aznalcollar
Mine
SEVILLA
HUELVA
GULF OF
CADIZ
Guadiamar river
Tinto river
Odiel river
Guadalquivir river
6° 206° 40
37° 20
37° 00
Donana
park
30 km
Fig. 1. Sketch map (southwest Spain) showing the location of the Rio
Tinto and of the Aznalcollar mining areas and the location of the core drilled
in the upper estuary of the Tinto river (Huelva ria).
TABLE 1. Metal Contents of the Two Anomalous Horizons of the Core and Comparizon with the Normal Estuarian Sediments of the Core
Zn Cu Pb As Cd Sn Ag Tl Hg Au Ba
Rio Tinto massive sulfide ore (avg)120,000 7,000 7,000 2,000 150 350 45 35 40 0.8 Unknown
Pyritic tailings of Aznalcollar (spill) 21,200 2,120 8,500 6,100 31 22 50 103 Unknown 0.06 70
Pyrite-rich sand from the Tinto river 3,200 950 1,200 3,900 57 20 14 24 12 0.07 2,900
Upper pyrite-rich sand horizon (core) 300 760 5,300 1,400 9 100 17 18 5.1 0.2 3,400
Lower pyrite-rich sand horizon (core) 240 400 2,500 900 6 45 10 12 3.0 0.1 1.600
Normal estuarian black mud (core) 67 24 7 12 <1 2 0.9 0.4 0.04 0.003 230
All values given in ppm
Metals concentrations in the sands from the upper part of the Tinto river, in Rio Tinto massive pyrite ore, and in pyrite sludge released from the Aznal-
collar spill are given for comparizon with the anomalous horizons of the core
1 Leistel et al, 1993

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Pb
Pb
Cu
Cu
As
As
As
Tl
Tl
Tl Cu
Hg
Hg
Au
ppm (g/t)
110 100 1000
0.1
0.01
110 100 1000
0.1
0.01
ppm (g/t)
Hg
m
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Surface
Calibrated
radiocarbon age
(BC)
1930+/-55
2530+/-70
3600+/-100
6000+/-140
FLUVIAL CHANNEL ESTUARINE ACCRETION BODIES ESTUARINE CHANNEL CHANNEL MARGIN FLOOD PLAIN
Erosion
Au
Cu
shells
plant fragments
authigenic pyrite (pyritospheres)
detrital pyrite grains
Pb
data
210
samples
1 ppm
1000 ppm = 0.1 %
UPPER
HORIZON
LOWER
HORIZON
conglomerate
FIG. 2. Description, age dates and metal concentrations of the core. The lithostratigraphic sequence corresponds to an
estuarine evolution, ending with an erosional hiatus (flood plain). The 14C AMS radiocarbon dates (given as calibrated BC
ages) agree with an Holocene transgressive cycle; the 210Pb data from the uppermost part indicate present sediments. Two
horizons show metal concentrations (ppm) that are two orders of magnitude over background. Both metal-contaminated
horizons include abundant clastic pyrite grains.

tion associated with modern mining (Davis et al., in press);
analyses were conducted at Florida State University by W.
Burnett and associates.
Results
Lithostratigraphy
From bottom to top, the following materials are present in
the core (Fig. 2): (1) coarse detrital sediments (fluvial channel
and fluvial bar); (2) shelly and sandy black muds, including
shell-rich horizons with authigenic pyritic nodules (estuarine
accretion bodies); (3) muddy sands with shell fragments (es-
tuarine channel); (4) alternating yellow sands and dark green
muds (channel margins); and (5) yellow sands of the flood
plain at the top of the core. This uppermost horizon results
from flood deposits that may be strongly erosional, as sug-
gested by the lithologic break and the sharp discontinuity
with the underlying muddy horizon. Almost every year there
is a major flood from the Tinto river, eroding and/or deposit-
ing up to 50 cm of sandy material on the flood plain.
Presence of metal-rich horizons
The trace metal contents in the Holocene estuarine sedi-
ments (Fig. 2, Table 1) are similar to averaged continental
sediments (Taylor and McLennan, 1985). The highest con-
tents are in organic carbon-rich sediments containing diage-
netic pyrite (Fig. 3D) overgrowing plant debris or shell frag-
ments. Against this normal geochemical background two
remarkable horizons (0–1.3 m and 3–4 m) are characterized
by metal concentrations that are two orders of magnitude
higher than those of the other layers (Fig. 2). These horizons
contain 2,500 to 5,300 ppm Pb and 900 to 1,400 ppm As, re-
spectively. In both cases the same metal association is present,
composed of high Pb, Ba, As-Cu, Zn-Sn, Tl-Cd, Ag, Hg-Au,
in decreasing order of importance.
SEM observations (Fig. 3)
The two anomalous horizons are also remarkable for their
mineralogic composition. They consist mainly of light yellow
sands and silts, including abundant clastic pyrite grains (2–12
wt %). The pyrite grains are small and well sorted (20–50
µm); they correspond to angular fragments of subhedral
pyrite grains (Fig. 3A2) that have been only slightly rounded,
and which exhibit only rare dissolution pits and cracks. The
only oxidized material consists of ochre fragments in the silt
layers. EDS-SEM investigations suggest that galena is pre-
sent as small accessory grains (1–5 µm), partly included in
pyrite; rare gold inclusions (0.5 µm) are also present in pyrite.
The high barium content is clearly explained by the presence
of lamellar fragments of barite in the pyrite-rich sands. Cassi-
terite is present as small, perfectly euhedral crystals (10 µm),
explaining the high Sn contents (40–100 ppm Sn).
The lower horizon (0.5–1.2% organic carbon) contains
black plant fragments that often display woody cellular tex-
tures (Fig. 3C). These charcoal fragments are very small and
well sorted (0.1–1.2 mm). A few small globules (30–500 µm)
of vesicular glass, with smooth surfaces, are also present in
this horizon (Fig. 3B). EDS-SEM analysis suggests they con-
sist either of a Fe-Si glass, with traces of sulfur, or of a carbon-
iron material with small contents of copper and sulfur
(0.1–1%). These compositions, which differ from those of
natural vesicular glasses, such as lavas, are similar to those of
scorias and slags from metallurgical furnaces.
Dating results
The four 14C calibrated ages (BC) obtained are consistent
with the relative stratigraphic position of the analyzed sam-
ples (Fig. 2) : 6,000 ±140 yr for the base of the estuarine ac-
cretion bodies (12.5 m); 3,600 ±100 yr for the base of the es-
tuarine channel (7.5 m); 2,530 ±70 yr for the lower
metal-contaminated horizon (4 m) and 1,930 ±–55 yr for the
floor of the uppermost metal-contaminated horizon (1.3 m).
The 210Pb concentrations along the uppermost 30 cm of the
core (Davis et al., in press) are strikingly constant and rela-
tively high (8 ± –2 Bq/kg).
Discussion
Evolution of the Holocene depositional environment
The lithostratigraphic sequence and the 14C ages corre-
spond fairly well to the Holocene transgression that started in
the Huelva area about 8,000 BC, filled up the estuary, and
ended with a stabilization of the sea level about 3,000 BC
(Borrego et al., 1999). The transgression is connected with a
deglacial sea-level rise (Mannion, 1997). From 14C radiodat-
ing, it appears the sedimentation rates of the estuarine sedi-
ments were between 1 and 7 mm/yr.
The two metal-contaminated horizons correspond to well-
sorted sandy flood deposits. The lower horizon results from
input of fluvial sands during a progradation stage in the estuar-
ine system; the overlying muddy and shelly horizon corresponds
to tidal sediments along channel margins. The upper horizon re-
sults from discontinuous input of fluvial sands over the surface of
the flood plain—which is usually dry—during seasonal floods.
Geochemical and mineralogical evidence for
metal contaminations from the Rio Tinto mineralization
The metals present in these two anomalous horizons reflect
fairly well those of the Rio Tinto sulfide ore, including base
and trace metals (Table 1). For example, the relatively high
Au content of the pyritic horizons (0.1–0.2 ppm) is in agree-
ment with the presence of gold in the Rio Tinto mineraliza-
tion (0.5–1.5 ppm); SEM observations reveal that gold inclu-
sions are present in the detrital pyrite grains. The abundance
of barium, and the presence of barite detrital grains, may be
explained by the fact that barite is a common gangue mineral
of the sulfide ores. The relatively high Sn concentrations and
the presence of cassiterite grains are in agreement with the
presence of cassiterite in the Rio Tinto ore. The arsenic con-
centrations in detrital pyrite grains, which have been picked
up from the core, range from 1 to 2 percent As, explaining the
high arsenic contents of the pyrite-rich horizons.
However, the order of abundance is not exactly the same.
For example, Zn and Cd concentrations are low compared to
the other base metals (Pb, Cu) in the pyrite-rich sands. This
may be explained either by the fact that Zn and Cd are rela-
tively more easily soluble in surface waters or that sphalerite
was not abundant in the transported pyritic material.
The pyrite grains from the two metal-contaminated hori-
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20 µm
20 µm
20 µm
20 µm
20 µm
20 µm
50 µm
shell
20 µm
BaSO4
py
py
py
py
20 µm
py
py
A1 A2
B1 B2
CD
A- Clastic pyrite
B- Slags
C- Wood fragment D- Authigenic pyrite
actual 4,500 yr old
FIG. 3. Scanning electronic microscopic (SEM) images. A. (A1) Clastic pyrite grains, displaying subhedral to angular
shapes, from the present sands of the Tinto river. (A2) Pyrite grains from the lower metal-contaminated horizon of the core
(dated at 2530 ±70 BC) are similar in shape and size to the clastic pyrite grains from the present sands of the Tinto river (A1);
note the presence of a barite fragment. B. (B1) Slag droplet from the lower metal-contaminated horizon; its composition is
that of a Si-Fe glass with minor contents of sulfur (0.1–1% S). (B2) Vesiculated slag fragment, from the lower metal-conta-
minated horizon, showing a C-Fe-O composition with minor contents of copper, sulfur and silica (0.1–1%). The analytical
data were performed using an energy-dispersive X-ray spectrometer (EDS). C. Wood fragments (charcoal) are relatively
abundant (1%) in the lower metal-contaminated horizon (dated at 2530 ±70 BC) D. Authigenic pyrite crystallizing as agre-
gates of pyritospheres in shell or plant fragments from the lower part of the core (black muddy estuarine sediments); note
the difference in shape and size compared to the detrital pyrites (A1, A2).
actual A - Clastic pyrite 4,500 yr old
B - Slags
C - Wood fragment D - Authigenic pyrite

zons are angular clastic pyrite grains (Fig. 3A2) that may be
slightly rounded and corroded. They are clearly different in
shape and size from the authigenic pyrite crystals and the
spherulitic agregates of pyrite (Fig. 3D) that are present in
the shelly black mud horizons of the core (Fig. 2). The only
obvious source of pyrite in the catchment zone of the Tinto
river is the Rio Tinto mining area. There are outcropping
massive pyrite orebodies, with subhedral pyrite grains similar
in shape and size to those of the anomalous horizons of the
core, and huge stockpiles of pyrite-rich tailings and wastes
from modern mining activity. The pyrite grains are very abun-
dant in the present surface sands collected along the bed and
the banks of of the Tinto river: in the immediate vicinity of
the mine area, there are pyritic sands containing up to 60 wt
percent pyrite, and downstream from the coring location, the
estuarian sediments still contain 1 to 10 wt percent pyrite.
The pyrite-rich sediments of the Tinto river display very high
concentrations of toxic metals (0.5% As, 0.5% Pb, 0.3% Zn,
0.2% Cu; Table 1). These high metal contents can be ascribed
to pyrite (this is the case for As) or to discrete Pb-Zn-Cu sul-
fide phases associated with or included in pyrite. The clastic
pyrite grains from the surface sands along the Tinto river are
similar in shape and size (Fig. 3A1) to those from the metal-
contaminated horizons at depth in the core, providing evi-
dence that pyrite grains may be transported by the Tinto river
from the Rio Tinto mining zone to the estuarine zone. Con-
sidering the hydric flow during seasonal flood events and the
average geometry of the Tinto river, the rate of sediment
transport can be roughly calculated: the time for the trans-
portation of the pyrite grains—from the source zone to the
estuary—may be from 15 to 45 hours. Consequently, the
pyrite grains may be deposited very quickly in the estuarine
sediments without having suffered any weathering during
their transportation. The same shape and size of pyrite grains
characterize the pyritic sludge released within a few hours by
the Aznalcollar tailings spill in the Donana national park, 40
km downsream (Fig. 1).
These geochemical and mineralogical observations are the
first indication that the two anomalous horizons correspond
to input of pyrite-bearing and metal-rich sands resulting from
mining activity in the Rio Tinto source region.
Age of the upper metal-contaminated horizon
The impact of intensive modern mining activity that started
130 yr ago has been clearly recorded in shelf surface sedi-
ments of the Gulf of Cadiz (Van Geen et al., 1997). The upper
metal-contaminated horizon of the core may correspond to
this modern mining. The uppermost 30 cm of the core have
high and constant 210Pb concentrations; this means that the
upper part of the upper contaminated horizon was deposited
a short time ago, probably during recent flood events. How-
ever, considering the discontinuous sedimentary and/or ero-
sional history of the flood plain of the upper estuary, we are
not sure that this 1.3-m-thick pyrite-rich horizon corresponds
in its entirety to the modern mining period. A 14C AMS ra-
diocarbon dating was performed on an ochre layer, just below
the upper horizon (Fig. 2). The ochre has an age of 1930 ±50
BC (calibrated age). This is consistent with the chronostratig-
raphy of the core but indicates that the upper part of the
Holocene sequence has been eroded before or during the de-
position of the upper, metal-contaminated horizon.
Age of the lower metal-contaminated horizon
The lower horizon has been dated at 2530 ±70 BC (AMS
14C calibrated age). The analyzed sample (pyrite-rich sand)
contains 1 percent organic carbon. Tiny black fragments of
charcoal are the only possible organic carbon source; there
are no shell fragments or carbonate (<0.1%). Dating of a sin-
gle charcoal material, picked up 10 cm below the first dated
sample, has given a 500-yr older age (3015 ±70 yr BC), which
could indicate derivation from a 500-yr-old tree (“old wood
effect”) or material derived from an older layer. Although the
ancients may have been burning old wood in their furnaces,
this is unlikely to have significantly affected the observed 14C
stratigraphy of the core. The logical progression of 14C dates
down the core suggests that resedimentation processes in the
estuary have not resulted in major disturbances in in the
chronostrtigraphy.
These ages correspond to the Copper Age in the western
Mediterranean area and confirm that active mining started
early in the Rio Tinto district.
The presence of small droplets and fragments of likely slags
(vesicular glasses with Fe-Si or C-Fe compositions and up to
0.5% copper and sulfur) in the lower horizon (Fig. 3B), is
compelling evidence for contemporaneous metallurgical ac-
tivity. In the same way, the presence of tiny and well-sorted
charcoal fragments may reflect the common use of small
charcoal fragments during metallurgical treatments.
Copper Age mining and metallurgy in the Rio Tinto area
The oldest findings indicate that metallurgical activities in
the region date from 2700 BC (Rothenberg and Blanco Frei-
jero, 1980). Except for a few metal tools in some graves and
scarce traces of mining excavations and ovens, there has been
little evidence of important Copper Age mining activity in the
Rio Tinto district. However, the Almerian Copper Age civi-
lization (3000–2200 BC) is well known in eastern Andalusia,
Spain, for the important development of copper mining and
metallurgy (i.e., in the fortified site of Los Millares, Almeria).
Similar activity was likely taking place in western Andalusia,
notably in the Rio Tinto area (Briard, 1976). Unfortunately,
the subsequent mining periods probably erased most of the
Chalcolitic mining and metallurgical works. The Romans
started their mining activity from the Tartessian-Phoenician
works, and active mining today recovers gold (1–1.5 ppm)
from the Roman mining wastes.
Conclusions
1. We show here a new record of watershed-scale impact of
early mining, over a distance of about 100 km. A 4,500-yr-old
(2530 BC) metal contamination, caused by Copper Age min-
ing, has existed in southern Spain. Notwithstanding the re-
cent accident at Aznalcollar, it is possible that long-term re-
lease of metals from ancient mining operations that have not
received the benefit of modern remediation may be a more
serious problem than the impact of much larger, modern-day
operations.
2. Anthropogenic input of metals may remain immobilized
for millennia in estuarine sediments. Most metals can be
locked as sulfides in estuarine sediments where anoxic condi-
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tions (organic matter, fast sedimentation rates) can enhance
the formation of authigenic sulfides and/or prevent the oxida-
tion of detrital sulfides. Considering the recent spill of pyrite
tailings at Aznalcollar, these findings may have implications
for modern mining. Part of the sulfide-rich material recently
discharged into the Guadiamar river (Fig. 1) might remain
stored in the Guadalquivir estuarine sediments for millenia.
Precautions must be taken to prevent any change in the estu-
arine system, particularly oxidation (by draining, dredging, or
erosion) of these potentially highly toxic or deleterious mate-
rials.
3. Sulfide grains can be quickly transported far away from
their source zone, during flood events, without having suf-
fered weathering. This kind of metal transportation in surface
waters, often neglected, can be of great importance, locally.
Acknowledgments
This work was funded by the European Commission
(DGXII) under contract TOROS (Tinto Odiel Ocean River
System), Environment and Climate Programme (ELOISE);
for more information see the website <http://carpanta.ugr.es/
toros/>.
We are grateful to Lex van Geen and to an anonymous
member of the Editorial Board, who helped us considerably
to improve this manuscript.
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