ORIGINAL ARTICLE

Further evidence for magnetic susceptibility as a proxyfor the evaluation of heavy metals in mining wastes: case studyof Tlalpujahua and El Oro Mining Districts

Juan Morales1 • Marıa del Sol Hernandez-Bernal2 • Pedro Corona-Chavez3 •

Avto Gogichaishvili1 • Francisco Bautista4

Received: 18 May 2015 / Accepted: 22 October 2015

� Springer-Verlag Berlin Heidelberg 2016

Abstract Magnetic susceptibility is nowadays used in

most areas of environmental research as a proxy for heavy

metal pollution in industrial and urban areas. Although the

relationship between magnetic susceptibility and concen-

tration of toxic elements in different environments has been

pointed out in several studies, mining wastes (tailings) have

hardly been investigated by magnetic methods. We report

the relationships between magnetic susceptibility and

potentially toxic elements monitored at 12 vertical ground

profiles of the Tlalpujahua and El Oro mining districts,

western Mexico. Specific bulk magnetic susceptibility

(k) measurements, percentage frequency-dependent sus-

ceptibility (%XFD) determinations as well as the identifi-

cation of the magnetic carriers within the samples were

accomplished using standard rock-magnetic techniques on

geochemically well characterized sister samples. Magnetite

and/or Ti-poor titanomagnetite seem to be the main mag-

netic carriers in the samples. Tight correspondence

between k and Fe concentrations, as well as Pb and As with

the iron content were found. This association seems to hold

also for pH variations.

Keywords Mining tailings � Magnetic susceptibility �Potentially toxic elements � Proxy

Introduction

Industrial mining in Mexico has been developed since 1550

and consequently there are abundant mining districts

associated with several billion tons of waste mining (tail-

ings) scattered around the country (Corona et al. 2010).

Nowadays, the study of the distribution and concentra-

tion of potentially toxic elements (PTE) contained in the

mining tailings acquires great relevance since it has been

recognized that such elements may cause serious environ-

mental and health problems to populations established in

their vicinity (Monroy et al. 2002; Armienta et al. 2003;

Talavera et al. 2005; Ramos-Arroyo et al. 2004; Canet

et al. 2008 and references therein). Moreover, due to social

and demographic aspects, among other reasons, tailings of

abandoned mining districts in Mexico are now occupied

and serve as settlements for various inhabitant groups.

These studies are carried out traditionally by means of

geochemical analysis, which are expensive, laborious and

time-consuming. The need for fast and inexpensive moni-

toring tools of heavy metal pollution has led to the search

of other methods of determination (Morton-Bermea et al.

2009). The correlation between magnetic susceptibility and

heavy metal content has been reported in numerous works

(Petrovsky et al. 1998, 2001; Durza 1999; Shu et al. 2001).

This correlation could be due to the fact that heavy metal

elements are incorporated into the lattice structure of the

ferrimagnetics during combustion process or are adsorbed

onto the surface of ferrimagnetics already present in the

environments (Petrovsky et al. 1998; El Baghdadi et al.

2012).

& Juan Morales

jjulio1962@yahoo.com.mx; jmorales@geofisica.unam.mx

1 Laboratorio Universitario de Geofısica Ambiental (LUGA),

Unidad Michoacan del Instituto de Geofısica, UNAM

Campus Morelia, Mich, Mexico

2 Escuela Nacional de Estudios Superiores (ENES), Unidad

Morelia, UNAM Campus Morelia, Mich, Mexico

3 Instituto de Investigaciones en Ciencias de la Tierra,

UMSNH, Morelia, Mich, Mexico

4 Laboratorio Universitario de Geofısica Ambiental (LUGA),

Centro de Investigaciones en Geografıa Ambiental, UNAM

Campus Morelia, Mich, Mexico

123

Environ Earth Sci (2016) 75:309

DOI 10.1007/s12665-015-5187-8

However, except by the study by Matasova et al. (2005)

carried out in wastes of the mining industry in Western

Siberia, Russia and very recently that of Perez et al. (2014)

accomplished in a metallurgical area in the San Luis Potosi

State, Mexico; magnetic methods have not been applied

systematically to the study of tailings in spite of the fact

that magnetic measurements are sufficiently sensible to

detect the magnetic signal of the minor fraction of ferro-

magnetic materials, in most of the cases with concentra-

tions less than 1 % (Chaparro 2006). Their results remain

scarce.

Because of the more than 60 years of abandon, the

Tlalpuhajua and El Oro mining districts, western Mexico

(see below for details), represent a potentially pollution

problem due to the more than 60 tons of wastes dispersed

on the area estimated by Uribe Salas (2008).

Aimed to overcome this situation, we focused on eval-

uating the potentiality of magnetic methods to reliably

determine PTE concentrations in tailings in a faster and an

economical way; magnetic susceptibility determinations

(the key magnetic parameter used in this study) are low-

cost, easy and fast to obtain.

We report the relationships between magnetic suscep-

tibility and pH with PTEs, monitored at 12 different ver-

tical ground profiles in tailings of the Tlalpujahua and El

Oro mining districts, western Mexico.

Study area

Historical background

It is widely recognized that the extraction of metals in

Mexico began since pre-Hispanic times (e.g. Horcasitas de

Barros 1981; Maldonado 2005; Martınez-Medina 2009),

while the formal mining activity until the XVI century,

during the colonial era. In this time, a series of exposed

silver and gold veins were located and exploited for more

than five centuries in the heart of the modern cities of

Tlalpujahua and El Oro (hereafter referred to as TOMD);

which was known as the ‘‘Real de Minas of Tlalpujahua’’

(Corona et al. 2010) and where more than 60 tons of wastes

were generated and disposed of, as estimated by Uribe

Salas (2008).

The TOMD is located at the boundaries of the

Michoacan and Estado de Mexico states (Fig. 1) and is part

of the hydrological basin ‘‘Lerma Santiago River’’ (Corona

et al. 2010). Although the TOMD is recognized essentially

as a gold-deposit, the mineralization in this district is

considered as a part of the big-silver metallogenic province

(Ostrooumov and Corona Chavez 1999; Albinson et al.

2001). The TOMD is located within the Miocene-Pliocene

Trans-Mexican Volcanic Belt (Morales-Gamez and

Corona-Chavez 2006 and references therein) and is

emplaced over a Jurassic-Early Cretaceous rock basement

(Centeno-Garcıa et al. 2003), Fig. 2. The surface covered

by the tailings dams was estimated by Martınez-Medina

(2009) in approximately 62 ha.

Samples

Samples were taken from tailings belonging to two mining

localities: Tlalpuhajua and El Oro, Michoacan and Estado

de Mexico states, respectively.

Tlalpujahua

At the Tlalpujahua District thickness of tailings varies from

2 up to 48 m (Fig. 3a). According to Martınez-Medina

(2009) textures are diverse, but using soil texture triangle

recognizable horizons are classified as silty loam, sandy

loam, loam sand, silty clay loam, silt, silty clay, medium

loam and sand.

El Oro

Thickness of tailings at El Oro District varies from 1 up to

20 m (Fig. 3b). Textures of the tails correspond to loamy

sand, silt, silty loam, clay loam and silty clay loam. In both

cases, the textures are different and there is no predomi-

nance of any, except in the profile of El Carmen (Tlalpu-

jahua), where certain homogeneity is observed,

predominantly silty loam, because the deposit is the result

of the overflow of the dam tailings Los Cedros in 1937.

At both mining localities, samples of 1.5–2 kg in

weight were taken within each profile every 20 cm,

Fig. 1 Location map of the Tlapujahua-El Oro Mining District

(TOMD)

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packed into plastic bags and identified sequentially

accordingly to the corresponding profile (S) and horizon

(H). Particular attention of sampling was taken when

clear evidence of different horizons was evident. Some

isolated samples, when profile excavation was not

possible, were also taken. In total, 12 profiles were

sampled (Fig. 4); eight from Tlalpujahua and four from

El Oro, yielding 57 samples. Samples were dried by

placing them in an oven at a temperature \40 �C for a

period of 12 h, and were then homogenized by

quartering. Finally, they were stored in hermetic

cylindrical PVC containers.

Methodology

Background

Based on the results of a geochemical and mineralogical

study on the variations within Au-tailings from

Fig. 2 Simplified geological

map of TOMD. Modified from

‘El Oro de Hidalgo E14-A16’

chart of ‘Servicio Geologico

Mexicano 2000’

Fig. 3 Current view of Cedros tailings dam at Tlalpujahua (a) and Tiro Mexico at El Oro (b)

Environ Earth Sci (2016) 75:309 Page 3 of 10 309

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Tlalpujahua-El Oro mining district, Corona et al. (in

preparation) noted certain linear variation between some

mayor element (ME) oxides (CaO, MgO, Al2O3, Fetot)

when plotted against the corresponding SiO2 and pH val-

ues. Worth of noting for the aim of the present study is the

inverse linear relationship between SiO2 (the oxide nor-

mally used in geochemical studies as an evolution param-

eter, depending on the mineral phases that crystallize) and

Fetot (Fig. 5). Based on this observation, it seems natural to

follow a symmetrical approach to that employed in geo-

chemical analysis but using the Fe concentration (or

alternatively magnetic susceptibility, which is the key

parameter used as a proxy in magnetic studies) as the basis

for an alternatively magnetic methodology for the study of

PTEs, see below.

XRF methodology

The procedure for pressed-pellet sample-preparation and

XRF analysis are widely described elsewhere (e.g. Lozano

and Bernal 2005). Chemical composition of samples was

determined by X-ray fluorescence using a Xenemetrix

energy dispersion spectrometer (EDXRF X-Calibur, with

Rh tube and a Beryllium detector) at Laboratorio Univer-

sitario de Geofısica Ambiental (LUGA) facilities.

Magnetic methodology

Magnetic susceptibility is directly proportional to the

quantity and grain size of the ferromagnetic or ferrimag-

netic materials in a sample (Verosub and Roberts 1995).

Therefore, among other information, magnetic suscepti-

bility measurements provide a straightforward and rapid

estimation of the iron content (Fe concentration) in a

sample. Powdered samples were packed into standard

10 cc cubic plastic containers for the magnetic analysis.

These specific bulk magnetic susceptibility (k) and per-

centage frequency-dependent susceptibility (%XFD) mea-

surements were carried out using a Bartington MS2

susceptibility meter at LUGA facilities. Alternatively, the

identification of the magnetic carriers within the samples

was accomplished by means of continuous low-field high-

temperature susceptibility (k–T) curves or saturation-mag-

netization curves (thermomagnetic curves) using standard

techniques at LUGA.

Fig. 4 Location of sampled

sites

Fig. 5 SiO2 vs Fe2O3tot plot from the mining district Tlalpujahua-El

Oro

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Physical–chemical analysis

Electric conductivity and pH measurements were done at

the chemistry lab of the ENES facilities using a multi-

parametric kit HI 2020.

Results

Most samples present null and/or very low frequency

dependence of k (%XFD % 0), except those situated at the

very upper part of the profiles (10 % B %XFD B 15 %).

This fact reflects a considerable amount of superparamag-

netic particles (SP) within the particulate matter (PM)

\0.03 lm. In most of the cases, magnetite or Ti-poor

titanomagnetite seem to be the main magnetic minerals

within the samples, with variable proportions of other

weaker phases (Fig. 6).

Magnetic susceptibility values of tailing samples were

plotted against their corresponding XRF-determined Fe

concentrations (FeXRF) values. The results of such corre-

lation are presented in Fig. 7. Note the tight correspon-

dence between k and Fe concentrations variations. This

correspondence seems to hold also for pH variations

(Fig. 8). It is also worth noting the predominantly alkaline

character of most of the tailings (7.5\ pH\ 8.5), asso-

ciated to very low conductivity values (EC\80 lS/cm),

which suggests an active leaching processes within the

tailings.

Following this approach, the plots of different trace

elements (TE) present in the tailing samples make evident

the correlation between these elements and the iron content

(Fe concentration) (Fig. 9). Figure 10 shows the individual

regression that best represents the correlation between

some TE concentrations with the corresponding FeXRFwithin the samples.

In order to verify the above presented correlations, TE

concentrations of tailing samples were plotted against

corresponding volume susceptibility j. Figure 11 shows

the obtained correlations.

Discussion and concluding remarks

In a study carried out in lake sediments of lake Nechranice,

the captive area being typical for intensive industrial and

mining activity from Northern Bohemia, Petrovsky et al.

(1998) found no positive correlation with magnetic sus-

ceptibility of toxic elements present in the samples, except

for Mn; arguing that the practically random observation of

magnetic susceptibility data could be caused by complex

effects of various pollution sources.

On the contrary, Matasova et al. (2005) found an inverse

correlation between Pb and Zn content in the upper ground

layer and magnetic susceptibility in an environmental study

of areas polluted with wastes of the mining industry in

Western Siberia. The authors concluded that the mecha-

nisms responsible for the relationships between magnetic

characteristics of the deposit and the degree and charac-

teristic of its pollution should be quite different from those

in industrial and urban areas.

Fig. 6 Representative

thermomagnetic curves. Both

curves show similar single

ferrimagnetic phases (Ti-poor

titanomagnetite). Curie

temperatures (Tc) of the

ferrimagnetic phases are quite

similar

Fig. 7 k values of tailing samples vs their corresponding XRF-

determined Fe concentrations (FeXRF). Tight correspondence between

k and Fe concentrations variations is observed

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Sarris et al. (2009) also confirm that magnetic suscep-

tibility measurements provide the basis for an environ-

mental study in polluted areas with the results they

obtained in an environmental study for pollution in the area

of Megalopolis power plant (Peloponnesos, Greece) where

a very high correlation among magnetic properties; spe-

cially between v and Fe was observed.

Likewise the former study, some other recent investi-

gation (e.g. Zhang et al. 2012; Perez et al. 2014) relates the

enhancement of magnetic susceptibility values with

increased concentration of PTEs based on the high positive

correlation coefficients between these elements and mag-

netic susceptibility. It is worth noting, however, that the

outcomes and conclusions of these studies are the result of

investigations carried out mainly on surface soils collected

in the vicinity of the tailings and on farmland soil irrigated

with polluted river water in the vicinity of a steel plant,

respectively.

As properly pointed out by Matasova et al. (2005),

mining wastes seems to belong to a special class of objects

that has not been sufficiently investigated by magnetic

methods, in which an inverse correlation between PTE and

magnetic susceptibility exists.

Such an inverse correlation could be explained in terms

of the combined results of the active leaching processes

and significant differences in atomic weight between Fe

(*55.8) and some PTEs (e.g. As: *74.9; Pb: *207.2).

Samples at the bottom show low (high) Fe(Pb) concen-

trations. This relationship varies inversely through the

profile so that at the upper part of the tailings higher Fe

concentrations and lower Pb concentrations are observed

(Fig. 12). In the case of elements with similar atomic

weights to that of Fe (Cr: *52.0; V *51.0), direct linear

correlations between them are observed (Fig. 13).

On the other hand, recent environmental investigations

include a series of rock-magnetic measurements (e.g.

NRM, IRM, SIRM ARM, etc.), and the calculation of

different ratios (e.g. S, XLF/SIRM, FD/ARM, etc.) as

indicators of pollution in addition to magnetic suscepti-

bility determinations. Their use is widely employed and

represents a comprehensive way to fully characterize the

magnetic mineralogy. However, their inclusion in any

environmental study protocol would make magnetic

investigations lose some of their distinctive characteristics

which make them nowadays an alternative to traditional

techniques as a proxy for heavy metal pollution investi-

gations; namely, speediness, easiness and economy.

Furthermore, pH measurements seem to be also an

indirect and complementary sign of variation in Fe con-

centration and, consequently, of potentially polluted areas.

Among the analyzed elements, Pb and As versus j plots

show the highest correlation coefficients. Magnetic sus-

ceptibility, along with k–T curves, can be used as a pre-

liminary fast and inexpensive method in the evaluation of

PTE content in mining wastes.

Fig. 8 pH vs k within the

tailing samples. A close

correspondence variation is also

observed. Abbreviations on the

horizontal axis are as follows:

S stands for profile while H for

horizon, so that S5H1

corresponds to sample taken

from horizon 1 at profile 5

Fig. 9 Overview of trends followed by different trace elements (TE)

with the iron content (Fe concentration)

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Fig. 10 Trends followed by different trace elements (TE) plotted against SiO2 content (left part) and against the iron content (Fe concentration,

right part). Note the higher R2 value for plots on the right side, compared to the corresponding value for plots on the left part

Environ Earth Sci (2016) 75:309 Page 7 of 10 309

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Fig. 11 a, b Trends followed by different trace elements (TE) with magnetic susceptibility (k)

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A detailed and quantitative identification of polluted

areas should be based on a comprehensive study, focused

on those areas highlighted by the magnetic results as the

most probable contaminated areas.

Acknowledgments The authors are grateful to Doris A. Dıaz and

Julio C. Gomez, undergraduate students who actively participated in

this project. Neftali Razo is acknowledged for the supervision of

physical–chemical analysis. Gabriela Solis-Pichardo is greatly

acknowledged for her careful review of the manuscript for an

appropriate grammatical style. This study was supported by UNAM-

PAPIIT project IA102413.

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