Ci a ion: Yesa es, L.;
González-Jiménez, J.M.;
Jiménez-Can izano, F.A.;
González-Pé ez, I.; Ca o-Mo eno, D.;
Sánchez, I.M. Un eiling High-Tech
Me als in Roas ed Py i e Was es om
he Ibe ian Py i e Bel , SW Spain.
Sus ainabili y 2023,15, 12081.
h ps://doi.o g/10.3390/
su151512081
Academic Edi o s: Alessand o
Ca allo and Micol Bussolesi
Recei ed: 26 June 2023
Re ised: 17 July 2023
Accep ed: 31 July 2023
Published: 7 Augus 2023
Copy igh : © 2023 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
sus ainabili y
A icle
Un eiling High-Tech Me als in Roas ed Py i e Was es om he
Ibe ian Py i e Bel , SW Spain
Lola Yesa es 1,*, JoséMa ía González-Jiménez 2, F ancisco Abel Jiménez-Can izano 3,4, Igo González-Pé ez 5,
Da id Ca o-Mo eno 3and Isabel Ma ía Sánchez 6
1Depa amen o de Mine alogía y Pe ología, Facul ad de Ciencias Geológicas, Uni e sidad Complu ense de
Mad id, C/JoséAn onio No áis 12, 28040 Mad id, Spain
2Ins i u o Andaluz de Ciencias de la Tie a (CSIC-UGR), A da. Palme as 4, 18100 A milla, Spain;
jmgonzj@ug .es
3Agencia de Medio Ambien e y Agua, Jun a de Andalucía, C/Johan G. Gu enbe g, 41092 Se illa, Spain
4Depa amen o de Ciencias Analí icas, Facul ad de Ciencias, Uni e sidad Nacional de Educación a
Dis ancia (UNED), Senda del Rey 9, 20840 Mad id, Spain
5Depa amen o de Mine alogía y Pe ología, Facul ad de Ciencias, Uni e sidad de G anada,
A da. Fuen enue a s/n, 18001 G anada, Spain
6Cen o de Ins umen ación Cien í ica, Uni e sidad de G anada, Paseo P o eso Juan Oso io, s/n,
18071 G anada, Spain
*Co espondence: myesa [email p o ec ed]
Abs ac :
The Ibe ian Py i e Bel (IPB), in he sou hwes e n Ibe ian Peninsula, is a la ge me allogenic
p o ince exploi ed since ancien imes. As a esul o his o ical and cu en mining ac i i y, a as
olume o me allic mine al was e, mainly de i ed om he p ocessing o py i e, is s ill in si u and
pollu ing he en i onmen . A speci ic mine was e esiduum locally known in he a ea as “mo ongos”,
which was p oduced du ing py i e oas ing mainly in he 19 h cen u y, is e alua ed he e in o de o
un a el un apped esou ces o high- ech me als commonly used in high- ech de ices. Applying a
combina ion o whole- ock geochemical (ICP-AES, ICPMS, FA-AAS) and single-g ain mine alogical
echniques (EPMA, LA-ICP-MS, FESEM, and FIB-HRTEM) on he “mo ongos”, we unhide he s ill-
p esen ema kable concen a ions o Au, Ag, Pb, Zn, and Cu in hem. The mine alogical exp essions
o hese economic me als include oxides (hema i e, magne i e, and he cyni e), a sena es, sul a es o
he ja osi e g oup, na i e me als, and, o a lesse ex en , elic ic sul ides. This i s -e e es ima ion
o hese economic me als in his ype o esidue allows hei e alo iza ion, highligh ing hem as
sui able sou ces o he exploi a ion and eco e y o me als necessa y o he clean ene gy ansi ion.
Keywo ds:
mine was e; oas ed py i e; Ibe ian Py i e Bel ; high- ech me als; un apped esou ces;
ci cula economy; mine alogical was e cha ac e iza ion
1. In oduc ion
These days, ou daily li es in a connec ed and en i onmen ally sus ainable wo ld
boos he de elopmen o new high- ech and g een- ech echnologies, which a e p og es-
si ely equi ing new me als in signi ican economic and s a egic sec o s. Fo example,
manu ac u ing ba e ies, cons uc ion ools, senso s, elec onic de ices, medical de ices,
me als, au omo i e, de ense, o enewable ene gy sec o s. Wi h a ising global popula-
ion, he demand o me als necessa y o hese echnological applica ions will g ow e e
g ea e [
1
,
2
]. Howe e , he na u al esou ces o many o he me als necessa y o his
echnological p og ess a e limi ed o a e y ew coun ies, which means ha in he nea
u u e, many de eloped coun ies will no be able o each he sel -supply o ce ain me als.
Thus, some me als a e acqui ing he ca ego y o “c i ical” o “s a egic” o many de eloped
coun ies [
3
], commonly including he pla inum-g oup elemen s (PGE: Os, I , Ru, Rh, P ,
Pd), a e ea hs o he hea y (HREE: Eu, Gd, Tb, Dy, Ho, E , Tm, Yb, Lu) and ligh (LREE:
La, Ce, P , Nd, Pm, Sm) subg oups, as well as Cu, Ni, Co, Li, Sb, Bi, Nb, Ta, W, Ge, Ti, and
Sus ainabili y 2023,15, 12081. h ps://doi.o g/10.3390/su151512081 h ps://www.mdpi.com/jou nal/sus ainabili y
Sus ainabili y 2023,15, 12081 2 o 23
Ga. O he me als, iden i ied as non-c i ical bu ha a e also essen ial o he unc ioning
and in eg i y o a wide ange o indus ial ecosys ems, include he e ous (C , Fe, W) and
non- e ous (Al, Pb, Sn, S , Zn, Mo, Ag, Au) me als, which collec i ely wi h he c i ical ones
a e named as high- ech me als [4].
As no ed, high- ech me als a e concen a ed in speci ic egions o he Ea h’s c us .
Fo ins ance, 90% o PGE p oduc ion is in he Republic o Sou h A ica [
5
], whe e he PGE
a e concen a ed in magma ic deposi s o Ni-Cu sul ides and C oxides, esul ing om
he injec ion o man le-de i ed ul abasic magmas in o he con inen al c us . Almos 70%
o globally a ailable Co esou ces a e wi hin he Democ a ic Republic o he Congo [
6
]
in hyd o he mal- ela ed sedimen a y-hos ed deposi s. The global ma ke o REE a ge s
he ex ac ion and manu ac u ing o o es ela ed o alkaline-ca bona i e igneous ocks [
7
]
and g ani ic pegma i es [
8
]. In addi ion, he ex ac ion, concen a ion, and me allu gy o
mine als usually endowed wi h se e al high- ech me als in p ima y deposi s a e becoming
mo e di icul and expensi e.
Facing his conce n o e high- ech me al supply eliabili y and i s u he implica ions,
di e si ying supplies o high- ech me als is pe haps he only solu ion o many coun ies.
Fo ins ance, in Eu ope, he Ci cula Economy Ac ion Plan [
9
] is an ambi ious bu conc e e
p og am ha s imula es Eu ope’s ansi ion owa ds a Ci cula Economy by con ibu ing
o ‘closing he loop’ o p oduc li e cycles. The measu es in he ac ion plan co e he whole
li e cycle o p oduc s, om p oduc ion and consump ion o was e managemen , as well as
he ma ke o seconda y aw ma e ials (SRM). Inno a ion and in es men in he ield ha e
been p omo ed h ough he H2020 p og am in Eu ope. Mo eo e , simila en i onmen al,
social, and go e nance ac ions a e being implemen ed in many o he de eloped coun ies
in o de o u he s eng hen bo h euse and ecycling as well as he eco e y o SRMs,
e.g., [
10
–
12
]. A seconda y ma ke o high- ech me als is now p omised by incoming
policies. Hence, SRMs would p o ide a s a egic esou ce o high- ech me als o many
coun ies. Aiming o achie e a scena io o maximum euse and ecycling o high- ech
c i ical me als, many s a e- unded agencies, o en in collabo a ion wi h p i a e companies,
a e seeking al e na i es in he g een ield o u ban and mining was es, e.g., [
13
]. U ban
was e has been sugges ed as a wo hy a ge o o e come he nea u u e demand o
me als [
14
]. Howe e , global ecycling a es o many o he high- ech me als in u ban
was e a e low (<5% o Ge, Li, o REE as an example [
15
,
16
]), while hei euse is o en
hinde ed by ab ica ion ba ie s (i.e., minia u iza ion). The e o e, hese al e na i es a e s ill
subs an ially insu icien o mee he incoming demand o high- ech me als.
In he scena io exposed abo e, mine was es a e seen as a mo e a ac i e sou ce o
me al eco e y [
17
–
20
]. In pa icula , py i ic- ich mining-was e ocks, ep esen ing a global
isk o en i onmen al pollu ion due o hei eno mous po en ial o p oduce acid d ainage
mine (ADM), seem o s ill con ain p o i able amoun s o many ech me als [
21
–
23
]. On
his line, he applica ion o mine alogical cha ac e iza ion o hese ypes o mine was es
has he po en ial o educe he en i onmen al isk due o he eco e y o he mine als,
guide app op ia e mine planning o ac i e mines, op imize emedia ion design a closed
o abandoned mines, and e alo ize un apped esou ces o me als o cu en economic
alue [24].
The Ibe ian Py i e Bel (IPB), in he sou hwes e n Ibe ian Peninsula, is one o he
Ea h’s la ges olcanogenic massi e sul ide (VMS) me allogenic p o inces [
25
]. I s long-
e m and la ge-scale ex ac ion and p ocessing o me als, since p ehis o ic imes (i.e., he
chalcoli hic pe iod, ca. 4500 yea s ago un il oday [
26
,
27
], has le behind a legacy o
abandoned mines and on-si e py i e- ich was e ma e ial. In ha sense, he IPB has been
ecognized as one o he mos pollu ed places on Ea h because o acid mine d ainage
discha ges [
28
–
31
]. A speci ic esidue known in he a ea as “mo ongos” was mainly
p oduced du ing he 19 h cen u y when 40–50 M o py i ic o e wi h a low Cu g ade
(< 3%)
was p ocessed o sul u emo al and subsequen Cu ex ac ion by oas ing o py i e
ollowed by a i icial cemen a ion [
32
]. Cu en ly, he “mo ongos” mine was e s ill emains
on si e in many old and cu en mines and is being exposed o wea he ing. As a esul , i
Sus ainabili y 2023,15, 12081 3 o 23
is unde going a mosphe ic oxida ion while eleasing emana ions ha acidi y wa e s wi h
a high isk o con amina ing he su ace and sub-su ace wa e s connec ed o he i e
d ainage ne wo k. Mos o hese py i ic esidues a e no ea ed, posing a se ious h ea o
he en i onmen and, consequen ly, o public heal h and sa e y. P e ious aluable s udies
in he a ea ha e ocused mainly on he oxic na u e o he “mo ongos” esidues [
33
,
34
],
whe eas hei economic po en ial o ech me als has been unexplo ed.
He e, we a ge he geochemical and mine alogical cha ac e iza ion o a wide sui e o
me als in hese mine was es by means o a combina ion o analy ical echniques o whole
ock analysis (Induc i ely Coupled Plasma A omic Emission Spec oscopy (ICP-AES),
Induc i ely Coupled Plasma Mass Spec ome y (ICP-MS), Fi e Assay A omic Abso p-
ion Spec opho ome y (FA-AAS), and mine al nano- o-mic on scale analysis (Elec on
Mic op obe (EPMA), Lase Abla ion Induc i ely Coupled Plasma Mass Spec ome y (LA-
ICP-MS), Field Emission Scanning Elec on Mic oscopy (FE-SEM), and Focused Ion Beam
High Resolu ion T ansmission Elec on Mic oscopy (FIB-HRTEM). The p esen s udy con-
ibu es o a sus ainable supply o me als o he ecological ansi ion by means o he
i s e e es ima ion o he e alo iza ion and eclassi ica ion o hese mining esidues as
possible new esou ces o ech me als.
2. Con ex ualiza ion o he Roas ed Py i ic Was es “Mo ongos”
2.1. The Massi e Sul ide Deposi s o he Ibe ian Py i e Bel
The Ibe ian Py i e Bel is loca ed in he sou hwes e n po ion o he Ibe ian Peninsula
(Figu e 1). Ex ending abou 250 km om Se illa p o ince, in SW Spain, o sou h o
Lisbon, Po ugal, i g oups, wi hin a bel o 40–60 km wide, abou 90 olcanogenic massi e
sul ide (VMS) deposi s o polyme allic na u e (Cu, Pb, and Zn; [
35
–
37
]). Byp oduc s and
ace me als (Au, Ag, Co, Ni, Mn, Cd, In, Sn, Se, Bi, Te, Ga, Ge, Sb, and Ba) a e also
epo ed in concen a ions anging om ens o hund eds o ppm [
37
–
42
]. The VMS
o es mainly consis o py i e [FeS
2
] (>90 ol.%) wi h a iable amoun s o o he sul ides,
including (chalcopy i e [CuFeS
2
], galena [PbS], sphale i e [(Zn,Fe)S], ennan i e- e ahed i e
[(Cu,Fe)
12
As
4
S
13-
(Cu,Fe)
12
Sb
4
S
13
], and a senopy i e [FeAsS]). Mino mine alogy includes
Bi- and Pb-sul osal s, cassi e i e [SnO
2
], magne i e [Fe
3
O
4
], s anni e [Cu
2
FeSnS
4
], elec um
[AuAg], and cobal i e [CoAsS]. O e bodies a e mainly hos ed by black shales o he sou h
and elsic olcanic and olcaniclas ic ocks o he no he n pa (Figu e 1; [
36
,
42
]). The
economic alue o he IPB is mainly concen a ed in abou 2000 M o massi e sul ide
o e, wi h se e al majo deposi s, including Tha sis (>110 M ), Massa Val e de (~100 M ),
Aznalcólla -Los F ailes (~160 M ), Rio ion o (~500 M ), Ne es Co o (>210 M ), Aguas
Teñidas (>50 M ), So iel-Migollas (~130 M ), and La Za za (~170 M ) [43].
2.2. The Roas ed Py i ic Was es “Mo ongos”
As no ed in Sec ion 1, “mo ongos” is a speci ic mining was e p oduced in he IPB du -
ing he 19 h cen u y as a esul o S emo al and Cu ex ac ion by py i e oas ing ollowed
by a i icial cemen a ion. This py i e p ocessing usually ook place in he icini y o he
mine al ex ac ion a eas, when py i e o e was oas ed in special open-ai heaps o
100–800 ,
known as “ ele as”. The i ing o he py i e heaps (bo h conical and p isma ic) usually las s
be ween six and se en mon hs, eleasing sul u dioxide in o he a mosphe e while lea ing
behind he so-called “mo ongos”. These “mo ongos” we e washed wi h wa e in o de
o lixi ia e Cu-sul a e. Then, Cu-sul a e was accumula ed in decan a ion ponds o emo e
suspension loads and, inally, in o “cemen a ion” anks, om whe e i ci cula ed h ough
channels (i.e., “canaleos”) illed wi h s eel sc ap ha allowed p ecipi a ion o Cu by ionic
eplacemen o he Fe. Cemen Cu, named “cásca a”, eached g ades o 60% o 90% Cu.
The consump ion o Fe o acili a e Cu p ecipi a ion anged om 1.5 o 3.0 kg pe kg o Cu.
The loca ion si es chosen o his s udy co e di e en po ions o he Odiel i e
d ainage ne wo k, which s eams no h- o-sou h o 128 km h ough sou he n Spain o
join he Tin o Ri e and o m a common es ua y a he own o Huel a (Figu e 2). The
a ea has a mean annual ain all o 630 mm wi h an e ec i e ain all o close o 396 mm
Sus ainabili y 2023,15, 12081 4 o 23
(in e ed om da a eco ded du ing he pe iod 1940–2022). The d y pe iod las s om
Ap il o Oc obe . The was e dumps loca ed in he uppe pa o he d ainage ne wo k a e
he sep en ional ones a San Telmo (ST), Valdelamusa (V), and Cue a de la Mo a (CM),
whe eas hose down sou h co espond o Tin o San a Rosa (TSR), So iel (S), and Tha sis
(TH), espec i ely (Figu es 2and 3).
Sus ainabili y 2023, 15, x FOR PEER REVIEW 4 o 24
Figu e 1. Geog aphical loca ion o he Ibe ian Py i e Bel (IPB) in he geologic ame o sou h-wes -
e n Eu ope (modi ied om [44]) showing he loca ion o he main VMS exploi ed in he a ea.
2.2. The Roas ed Py i ic Was es “Mo ongos”
As no ed in Sec ion 1, “mo ongos” is a speci ic mining was e p oduced in he IPB
du ing he 19 h cen u y as a esul o S emo al and Cu ex ac ion by py i e oas ing ol-
lowed by a i icial cemen a ion. This py i e p ocessing usually ook place in he icini y
o he mine al ex ac ion a eas, when py i e o e was oas ed in special open-ai heaps o
100–800 , known as “ ele as”. The i ing o he py i e heaps (bo h conical and p isma ic)
usually las s be ween six and se en mon hs, eleasing sul u dioxide in o he a mosphe e
while lea ing behind he so-called “mo ongos”. These “mo ongos” we e washed wi h
wa e in o de o lixi ia e Cu-sul a e. Then, Cu-sul a e was accumula ed in decan a ion
ponds o emo e suspension loads and, inally, in o “cemen a ion” anks, om whe e i
ci cula ed h ough channels (i.e., “canaleos”) illed wi h s eel sc ap ha allowed p ecipi-
a ion o Cu by ionic eplacemen o he Fe. Cemen Cu, named “cásca a”, eached g ades
o 60% o 90% Cu. The consump ion o Fe o acili a e Cu p ecipi a ion anged om 1.5 o
3.0 kg pe kg o Cu.
The loca ion si es chosen o his s udy co e diffe en po ions o he Odiel i e
d ainage ne wo k, which s eams no h- o-sou h o 128 km h ough sou he n Spain o
join he Tin o Ri e and o m a common es ua y a he own o Huel a (Figu e 2). The a ea
has a mean annual ain all o 630 mm wi h an effec i e ain all o close o 396 mm (in e ed
om da a eco ded du ing he pe iod 1940–2022). The d y pe iod las s om Ap il o Oc-
obe . The was e dumps loca ed in he uppe pa o he d ainage ne wo k a e he sep en-
ional ones a San Telmo (ST), Valdelamusa (V), and Cue a de la Mo a (CM), whe eas
hose down sou h co espond o Tin o San a Rosa (TSR), So iel (S), and Tha sis (TH), e-
spec i ely (Figu es 2 and 3).
Figu e 1.
Geog aphical loca ion o he Ibe ian Py i e Bel (IPB) in he geologic ame o sou h-wes e n
Eu ope (modi ied om [44]) showing he loca ion o he main VMS exploi ed in he a ea.
The was e pile o “mo ongos” c opping ou nea he San Telmo open pi (also known
as San a Bá ba a) co e s a su ace a ea o 11,578 m
2
and has a maximum hickness o
6 m
(Figu e 2a). In his s ockpile, he e a e en chimneys o oas ing py i e, sugges ing
ha his was e dump is s ill in si u (Figu e 3a,b). An unknown po ion o he o iginal
mo ongo s ockpile p oduced du ing he second hal o he 19 h cen u y is missing due o
he expo a ion o Cu-deple ed “mo ongos” as Fe o e in he 1960s [45].
A Valdelamusa, wo “mo ongos” dumps c op ou in he p oximi ies o he homonym
locali y, co e ing a o al a ea o 17,525 m
2
wi h a maximum hickness o 3 m (Figu e 2b).
These py i ic was es a e no in si u, bu hey co espond o mixed ma e ial coming om
he nea by mines o Lome o-Poya os, San Telmo, Cue a de la Mo a, El Ca pio, and/o
Con esiona ios (Figu e 3c). This is due o he ac ha Valdelamusa was a main ailway
s a ion whe e py i es and mine was es we e s ockpiled o be la e anspo ed by ain o
he Po o Huel a (a dis ance o 67 km) o expo a ion.
The Cue a de la Mo a “mo ongos” a e loca ed on he i e bank o he Oli a gas
C eek (Odiel i e basin), placed o e a sla e deb is dump (Figu e 2c). This was e acili y
ha co e s an a ea o 179,695 m
2
wi h a maximum hickness o 10 m was iden i ied by
he code 1038-1-0004 in he Spanish na ional in en o y o mine and me allu gical was e
de elopmen by he IGME; his documen ema ks ha hose “mo ongos” could be
alo ized [
46
]. This ma e ial comes om a mining ope a ion ac i e since 1875, in ol ing
(1) open-ai calcina ions in “ ele as”, and (2) a mix u e o c ushed ich Cu-g ade o e wi h
“mo ongos” (in he p opo ion o 1 o 3). This has esul ed in places o mixed ma e ial
made up o “mo ongos” wi h sla es and py i e (Figu e 3d,e).
Sus ainabili y 2023,15, 12081 5 o 23
Sus ainabili y 2023, 15, x FOR PEER REVIEW 5 o 24
Figu e 2. D ainage ne wo k o he Odiel i e in he geological amewo k o he IPB in sou hwes -
e n Spain showing he loca ions and a eal dis ibu ion o he oas ed py i ic was e “mo ongos”
a ge ed in his s udy (a– ).
Figu e 2.
D ainage ne wo k o he Odiel i e in he geological amewo k o he IPB in sou hwes e n
Spain showing he loca ions and a eal dis ibu ion o he oas ed py i ic was e “mo ongos” a ge ed
in his s udy (a– ).

Sus ainabili y 2023,15, 12081 6 o 23
Sus ainabili y 2023, 15, x FOR PEER REVIEW 6 o 24
The was e pile o “mo ongos” c opping ou nea he San Telmo open pi (also known
as San a Bá ba a) co e s a su ace a ea o 11,578 m2 and has a maximum hickness o 6 m
(Figu e 2a). In his s ockpile, he e a e en chimneys o oas ing py i e, sugges ing ha
his was e dump is s ill in si u (Figu e 3a,b). An unknown po ion o he o iginal mo ongo
s ockpile p oduced du ing he second hal o he 19 h cen u y is missing due o he expo -
a ion o Cu-deple ed “mo ongos” as Fe o e in he 1960s [45].
Figu e 3. Pic u es o open-ai py i e oas ing esidues (“mo ongos”) dumps om he 19 h cen u y
a San Telmo (a,b), Valdelamusa (c), Cue a de la Mo a (d,e), So iel ( ,g), and Tha sis (h).
A Valdelamusa, wo “mo ongos” dumps c op ou in he p oximi ies o he homo-
nym locali y, co e ing a o al a ea o 17,525 m2 wi h a maximum hickness o 3 m (Figu e
2b). These py i ic was es a e no in si u, bu hey co espond o mixed ma e ial coming
om he nea by mines o Lome o-Poya os, San Telmo, Cue a de la Mo a, El Ca pio,
and/o Con esiona ios (Figu e 3c). This is due o he ac ha Valdelamusa was a main
ailway s a ion whe e py i es and mine was es we e s ockpiled o be la e anspo ed by
ain o he Po o Huel a (a dis ance o 67 km) o expo a ion.
The Cue a de la Mo a “mo ongos” a e loca ed on he i e bank o he Oli a gas
C eek (Odiel i e basin), placed o e a sla e deb is dump (Figu e 2c). This was e acili y
ha co e s an a ea o 179,695 m2 wi h a maximum hickness o 10 m was iden i ied by he
code 1038-1-0004 in he Spanish na ional in en o y o mine and me allu gical was e de-
elopmen by he IGME; his documen ema ks ha hose “mo ongos” could be alo -
ized [46]. This ma e ial comes om a mining ope a ion ac i e since 1875, in ol ing (1)
open-ai calcina ions in “ ele as”, and (2) a mix u e o c ushed ich Cu-g ade o e wi h
“mo ongos” (in he p opo ion o 1 o 3). This has esul ed in places o mixed ma e ial
made up o “mo ongos” wi h sla es and py i e (Figu e 3d,e).
The Tin o-San a Rosa oas ed py i e heap has a su ace a ea o 3123 m2 and a maxi-
mum hickness o 10 m (Figu e 2d). These “mo ongos” a e cu en ly placed nex o he
Tin o-San a Rosa open pi mine, we e ac i e du ing he second hal o he 19 h cen u y
due o an a emp o back ill hem du ing he ehabili a ion measu es ha we e ca ied
ou in he 1990s. He e he “mo ongos” may be, in places, also mixed up wi h o he ypes
o mining was e.
The was e dump a ge ed in So iel is unique o his s udy and was p oduced by py i e
oas ing du ing he 20 h cen u y. I is loca ed nea he i e banks o he Odiel Ri e , and
is in i s looding a ea, co e ing an a ea o app oxima ely 4364 m2 wi h up o 10 m hickness
(Figu e 2e). He e, he “mo ongos” may also be locally mixed wi h o he ypes o mining
was e (Figu e 3 ,g). Ne e heless, hey a e in si u and a es o he iden i ica ion o some
abandoned mining acili ies, such as an open-ai py i e oas ing heap known as “ ele a”,
Figu e 3.
Pic u es o open-ai py i e oas ing esidues (“mo ongos”) dumps om he 19 h cen u y a
San Telmo (a,b), Valdelamusa (c), Cue a de la Mo a (d,e), So iel ( ,g), and Tha sis (h).
The Tin o-San a Rosa oas ed py i e heap has a su ace a ea o 3123 m
2
and a maximum
hickness o 10 m (Figu e 2d). These “mo ongos” a e cu en ly placed nex o he Tin o-
San a Rosa open pi mine, we e ac i e du ing he second hal o he 19 h cen u y due o
an a emp o back ill hem du ing he ehabili a ion measu es ha we e ca ied ou in
he 1990s. He e he “mo ongos” may be, in places, also mixed up wi h o he ypes o
mining was e.
The was e dump a ge ed in So iel is unique o his s udy and was p oduced by py i e
oas ing du ing he 20 h cen u y. I is loca ed nea he i e banks o he Odiel Ri e , and is
in i s looding a ea, co e ing an a ea o app oxima ely 4364 m
2
wi h up o 10 m hickness
(Figu e 2e). He e, he “mo ongos” may also be locally mixed wi h o he ypes o mining
was e (Figu e 3 ,g). Ne e heless, hey a e in si u and a es o he iden i ica ion o some
abandoned mining acili ies, such as an open-ai py i e oas ing heap known as “ ele a”, a
“cemen a ion” pond, and channels called “canaleos” whe e coppe was p ecipi a ed upon
sc ap Fe.
The wo mine was e dumps s udied in he Tha sis mining complex a e o me “ ele a”
si es (Figu e 2 ). A signi ican po ion o he “mo ongos” p oduced du ing he 19 h cen u y
was leached du ing he end o he 20 h cen u y, a emp ing o eco e p ecious me als
(i.e., Au
and Ag) [
47
,
48
], hus lea ing a s ockpile co e ing an a ea o 16,317 m
2
wi h a
maximum hickness o 2 m. The o iginal “mo ongo” s ill p ese ed in si u co e s an a ea
o 11,991 m2wi h a maximum hickness o 10 m (Figu e 3h).
3. Ma e ials and Me hods
3.1. Sampling and Sample P epa a ion
A sampling ne wo k was designed in se e al p o iles pa allel o and pe pendicula
o he was e dumps. The posi ion o he samples was loca ed on he upda ed o he yea
2020 egional o hopho og aphy—0.25 m esolu ion— om he Andalusian En i onmen al
In o ma ion Ne wo k [
49
]. Samples we e collec ed using a polyp opylene sho el and
subsequen ly ans e ed o clean p opylene bags and anspo ed o he labo a o y. Each
one o he samples weighed 1.5–3 kg and was he composi e o a leas h ee ex ac ions
pe o med andomly (bu sepa a ed by a leas 1 m) ac oss he e ical o he s ock pile.
The ex ac ion si es we e selec ed on he basis o changes in he mac oscopic appea ance
o he was e ma e ial, aking in o accoun colo , ex u e, and he deg ee o agg ega ion.
In he labo a o y, each o he samples was d ied a 60
◦
C o 48 h, hen b oken in o solid
clods and subsequen ly mixed o homogeniza ion. A e his p ocess, 10 g ounded sub-
samples o iginally collec ed in he ield om he same locali y we e educed o a inal subse
Sus ainabili y 2023,15, 12081 7 o 23
o 15 samples, which we e subsequen ly employed o geochemical and mine alogical
cha ac e iza ion. Aliquo s we e also employed o ob ain se e al hin sec ions, polished hin
sec ions, and cylind ical polished Epoxy®moun s.
3.2. Bulk-Rock Analysis o Majo , Mino , and T ace Elemen s
Majo , mino , and ace elemen s o he selec ed samples we e de e mined a he
MSALABS labo a o ies (Langley, BC, Canada) using a 4-acid diges ion (hyd ochlo ic, ni ic,
pe chlo ic, and hyd o luo ic acids), ICP-AES, and ICP-MS. The composi ions o e e ence
ma e ials OREAS-601, MP-1b, and CDN-ME-1407 we e analyzed as unknowns du ing he
analy ical uns and show good ag eemen wi h he wo king alues o hese in e na ional
s anda ds. Au con en s we e ob ained om aliquo s o he samples by Fi e Assay A omic
Abso p ion Spec oscopy (FA-AAS). The analyses o he CDN-GS-P8H-ce i ied e e ence
ma e ial compa ed well wi h he published alues o hese s anda ds. Resul s and de ec ion
limi s a e gi en in Table S1.
3.3. FE-SEM and EPMA
Polished hin sec ions and moun s we e s udied i s ly unde ansmi ed and e lec ed
ligh o e mic oscopy in an e o o p elimina y iden i y mine als and hei ex u al ela ion-
ships. Mine als o in e es we e imaged and iden i ied quali a i ely by hei cha ac e is ic
Ene gy Dispe si e Spec a (EDS) using wo di e en ins umen s: a QEMSCAN 650F
Field Emission Gun En i onmen al Scanning Elec on Mic oscope (FEG-ESEM) and a Leo
Gemini Field Emission FE-SEM belonging o he Cen o de Ins umen ación Cien í ica o
he Uni e sidad de G anada, Spain. These ins umen s a e equipped wi h SE, BSE, and
EDS de ec o s. The accele a ing ol age was 20 kV, and he beam cu en was op imized
o a su icien numbe o coun s o each EDS analysis and mapping.
Once iden i ied in he polished hin sec ions, he majo and mino -elemen compo-
si ions o mine als, including silica es, sul ides, oxides, and sul a es, we e ob ained by
wa eleng h-dispe si e spec ome y (WDS) EPMA using a JEOL JXA-8230 a he Cen es
Cien í ics i Tecnològics o he Uni e si y o Ba celona (CCiTUB, Ba celona, Spain). An
accele a ing ol age o 15 keV and a beam cu en o 20 nA we e used. All elemen s we e
measu ed wi h a coun ing ime o 15 s o he peak. Da a a e p o ided in Table S2 o each o
he h ee speci ic ou ines designed o he analyses o silica e, oxides, sul a es, and sul ides.
Calib a ion o silica e analyses was pe o med using na u al diopside o SiO
2
, kyani e o
Al
2
O
3
, luo i e o F, pe iclase o MgO, wollas oni e o CaO, o hoclase o K
2
O, hodoni e
o Mn, u ile o TiO
2
, and syn he ic albi e o Na
2
O, AgCl o Cl, and Fe
2
O
3
o FeO;
he X- ay lines employed we e K
α
o all he analyzed elemen s. The s anda ds used o
he analyses o oxides and sul a es included na u al kyani e o Al2O3, pe iclase o MgO,
albi e o Na
2
O, u ile o TiO
2
, o hoclase o K
2
O, ba i e o SO
3
, hodoni e o MnO,
chalcopy i e o CuO, and sphale i e o ZnO, syn he ic GaAs o As
2
O
5
, Fe
2
O
3
o Fe, PbS
o PbO, and HgS o HgO, and me allic Sb o Sb
2
O
5
, Ag o Ag
2
O, and Au o Au
2
O.
The X- ay lines employed K
α
o Al, Mg, Na, Ti, K, Fe, Mn, Cu, Zn, and S, L
α
o Sb, Au,
and Ag, and L
β
o As, M
α
o Pb, and M
β
o Pb. Fo sul ide analyses, we employed he
ollowing calib a ion na u al s anda ds: FeS
2
o S and Fe, PbS o Pb, chalcopy i e o Cu,
sphale i e o Zn, and he syn he ic HgS o Hg, In
2
Se o In and Se, GaAs o As, CdS o
Cd, me allic Co o Co, me allic Ni o Ni, Au o Au, Ag o Ag, Sb o Sb, and Bi o Bi.
The X- ay lines employed we e K
α
o S, Se, Fe, Co, Ni, Cu, and Zn, K
β
o As, M
α
o
Pb, Hg, and Bi, and L
α
o Ag, In, Cd, Sb, and Au. The esul s o EPMA a e p o ided in
Table S2.
3.4. FIB-HRTEM
Thin- oil samples om oxide-silica e, amenable o examina ion unde ansmission
elec on mic oscopy (TEM), we e p epa ed using a Dual Beam FEI The mo-Fishe Scien i ic
Helios 650 belonging o he Labo a o io de Mic oscopías A anzadas a he Ins i u o de
Nanociencia de A agón (INA)—Uni e si y o Za agoza, Spain. The chosen loca ions o
Sus ainabili y 2023,15, 12081 8 o 23
in e es we e in a i s s age co e ed by p o ec i e hin s ips o C o ~300 nm hickness
and P o ~1
µ
m hickness. Soon a e , he bulk ma e ial was i s emo ed on bo h
sides o he lamella by ough Ga ion milling wi h a 30 kV cu en a 2.5 nA and was
subsequen ly polished wi h a 30 kV cu en a 0.23 nA. The inal polishing s ep was
pe o med on hin oil in o de o achie e elec on anspa ency. This was comple ed by
subsequen ly milling he hin oil wi h a 5 kV cu en a 68 pA. The elec on anspa ency
was moni o ed wi h an E e ha -Tho nley SE de ec o using a 5 kV elec on beam. A e
achie ing elec on anspa ency, he hin oil was apidly polished using a low-ene gy
5 kV
cu en a
10 pA
o educe he amo phiza ion un il a inal hin oil hickness o ~90 nm was
a ained. Subsequen ly, he hin oil was unde cu wi h a 30 kV a 2.5 nA cu en , li ed
ou , and ans e ed om he sample o a TEM g id using an OmniP obe nanomanipula o
wi h a ungs en ip. Ion beam-assis ed P deposi ion was used o weld he hin oil o he
ungs en ip and he TEM g id.
The hin oils we e subsequen ly analyzed by means o a FEI Ti an G2 TEM equipped
wi h a ield emission gun (XFEG) belonging o he Cen o de Ins umen a ion Cien í ica o
he Uni e si y o G anada, Spain. This mic oscope is co ec ed o sphe ical abe ance in
he objec i e lens and is also equipped wi h ou ene gy dispe si e X- ay (EDX) de ec o s
(FEI mic oanalysis Supe X) and a high-angle annula da k ield de ec o (HAADF). The
hin oils we e inspec ed in his ins umen a 300 kV while a Ga an CCD Came a was
employed o acqui e high magni ica ion elec on mic oscopy images (HMEM) and HRTEM.
Selec ed mine al a eas o in e es sampled wi hin he hin oil we e hen imaged and
chemically cha ac e ized using a combina ion o EDX elemen al maps, HAADF ( o ob ain
Z high con as images), HMEM ( o cha ac e ize he ex u e o he g ains), and HRTEM
( o p ope ly de ine he o de ing o he mine al agg ega es). All hese images we e ea ed
using Digi al Mic og aph so wa e ( e sion 1.71.38), while he maps we e p ocessed wi h
he INCA Mic oanalysis Sui e ( e sion 4.09) so wa e package.
3.5. In Si u Analysis o Mino and T ace Elemen s in Mine als by LA-ICP-MS
In si u analyses o mino and ace elemen s in oxides (i.e., magne i e and hema i e)
and silica es we e ob ained by means o LA-ICP-MS on polished moun s a LabMaTe ,
Uni e si édu Québec àChicou imi (UQAC) (Table S3). The LA-ICP-MS ins umen used
was a The mo X7 ICP-MS wi h a high-pe o mance in e ace coupled wi h a New Wa e
Resea ch 213 nm Nd: YAG UV lase abla ion mic op obe. Abla ed ma e ial was ca ied by a
He–A gas mix u e and analyzed using he The mo X7 ICP-MS ope a ing in ime- esol ed
mode using peak jumping. The analyses we e conduc ed using a 10-
µ
m spo diame e , a
25-Hz equency, a 7 J/cm
2
luence o oxides, a 15-Hz equency, and a 6 J/cm
2
o silica es
du ing a 60-s analysis (~30 s o he gas blank and ~30 s o he signal). All da a we e
educed using Ioli e 4 so wa e and by sub ac ing he gas blank om each o he iso opes
analyzed. The ins umen was calib a ed agains he ce i ied e e ence ma e ial GSE-1g o
all elemen s. Fe and Si alues ob ained by EPMA we e used as in e nal s anda ds o he
calib a ion o oxides and silica es, espec i ely.
The analyses o oxides we e ocused on he iso opes
24
Mg,
27
Al,
51
V,
29
Si,
45
Sc,
49
Ti,
51
V,
55
Mn,
59
Co,
60
Ni,
63
Cu,
66
Zn,
71
Ga,
73
Ge,
75
As,
107
Ag,
111
Cd,
118
Sn,
121
Sb,
125
Te,
197
Au,
208
Pb, and
209
Bi. Si, K, Au, Sn, Ag, and Pb we e moni o ed o check o he p esence o solid
mine al inclusions. The ce i ied e e ence ma e ials NIST610, GP obe15, and MASS1, as
well as he in-house M1A we e analyzed as unknowns du ing each analy ical un o check
he accu acy and p ecision o he analyses. The analysis o e e ence ma e ial (NIST610
and GP obe-15) shows ha he accu acy and p ecision a e <15% RD and RSD, espec i ely,
o mos elemen s excep o some ace elemen s, which a e he e ogeneously dis ibu ed
wi hin he sample. The in-house M1A and he e e ence ma e ial MASS-1 exhibi highe
a ia ions in RD bu main ain good RSD o mos elemen s (Table S3). The analyses o
silica es moni o ed
24
Mg,
27
Al,
45
Sc,
49
Ti,
51
V,
55
Mn,
59
Co,
66
Zn,
69
Ga,
75
As,
85
Rb,
88
S ,
208
Pb, and
209
Bi. The accu acy and p ecision o he ce i ied e e ence ma e ials NIST610,
Sus ainabili y 2023,15, 12081 9 o 23
NIST612, MASS-1, and GP obe-6 a e <15% o mos elemen s excep o some ace elemen s
(Table S3).
4. Resul s
4.1. Whole-Rock Dis ibu ion o Majo , Mino , and T ace Elemen s
I on is he majo cons i uen o he oas ed py i e was es (37 o 50%), ollowed by
sul u (<5%), and o he less abundan li hophile elemen s such as Al (<4%), K (2%), Ti
(<1%), Mg (<0.2%), Na (<0.2%), and Ca (<0.1%) (Figu e 4a and Table S1). The wo mixed
samples om So iel (S-2) and Tin o-San a Rosa (TSR-2) show signi ican ly lowe Fe alues
(13%), bu highe sul u alues (up o 10%) (Figu e 4a and Table S1).
Sus ainabili y 2023, 15, x FOR PEER REVIEW 9 o 24
3.5. In Si u Analysis o Mino and T ace Elemen s in Mine als by LA-ICP-MS
In si u analyses o mino and ace elemen s in oxides (i.e., magne i e and hema i e)
and silica es we e ob ained by means o LA-ICP-MS on polished moun s a LabMaTe ,
Uni e si é du Québec à Chicou imi (UQAC) (Table S3). The LA-ICP-MS ins umen used
was a The mo X7 ICP-MS wi h a high-pe o mance in e ace coupled wi h a New Wa e
Resea ch 213 nm Nd: YAG UV lase abla ion mic op obe. Abla ed ma e ial was ca ied by
a He–A gas mix u e and analyzed using he The mo X7 ICP-MS ope a ing in ime- e-
sol ed mode using peak jumping. The analyses we e conduc ed using a 10-µm spo di-
ame e , a 25-Hz equency, a 7 J/cm2 luence o oxides, a 15-Hz equency, and a 6 J/cm2
o silica es du ing a 60-s analysis (~30 s o he gas blank and ~30 s o he signal). All da a
we e educed using Ioli e 4 so wa e and by sub ac ing he gas blank om each o he
iso opes analyzed. The ins umen was calib a ed agains he ce i ied e e ence ma e ial
GSE-1g o all elemen s. Fe and Si alues ob ained by EPMA we e used as in e nal s and-
a ds o he calib a ion o oxides and silica es, espec i ely.
The analyses o oxides we e ocused on he iso opes 24Mg, 27Al, 51V, 29Si, 45Sc, 49Ti, 51V,
55Mn, 59Co, 60Ni, 63Cu, 66Zn, 71Ga, 73Ge, 75As, 107Ag, 111Cd, 118Sn, 121Sb, 125Te, 197Au, 208Pb, and
209Bi. Si, K, Au, Sn, Ag, and Pb we e moni o ed o check o he p esence o solid mine al
inclusions. The ce i ied e e ence ma e ials NIST610, GP obe15, and MASS1, as well as
he in-house M1A we e analyzed as unknowns du ing each analy ical un o check he
accu acy and p ecision o he analyses. The analysis o e e ence ma e ial (NIST610 and
GP obe-15) shows ha he accu acy and p ecision a e < 15% RD and RSD, espec i ely,
o mos elemen s excep o some ace elemen s, which a e he e ogeneously dis ibu ed
wi hin he sample. The in-house M1A and he e e ence ma e ial MASS-1 exhibi highe
a ia ions in RD bu main ain good RSD o mos elemen s (Table S3). The analyses o
silica es moni o ed 24Mg, 27Al, 45Sc, 49Ti, 51V, 55Mn, 59Co, 66Zn, 69Ga, 75As, 85Rb, 88S , 208Pb, and
209Bi. The accu acy and p ecision o he ce i ied e e ence ma e ials NIST610, NIST612,
MASS-1, and GP obe-6 a e <15% o mos elemen s excep o some ace elemen s (Table
S3).
4. Resul s
4.1. Whole-Rock Dis ibu ion o Majo , Mino , and T ace Elemen s
I on is he majo cons i uen o he oas ed py i e was es (37 o 50%), ollowed by
sul u (<5%), and o he less abundan li hophile elemen s such as Al (<4%), K (2%), Ti
(<1%), Mg (<0.2%), Na (<0.2%), and Ca (<0.1%) (Figu e 4a and Table S1). The wo mixed
samples om So iel (S-2) and Tin o-San a Rosa (TSR-2) show signi ican ly lowe Fe alues
(13%), bu highe sul u alues (up o 10%) (Figu e 4a and Table S1).
Me als o economic in e es a e, in o de o abundance, Pb, As, Cu, and, o a lesse
ex en , Zn, Sb, Ba,Bi, P, and Mn (Figu e 4b and Table S1). Pb, As, Cu, and Zn a e de ec ed
in he a e age ange o housands o ppm, whe eas Sb, Ba, Bi, P, and Mn a e below 300
ppm.
Figu e 4. Bulk- ock dis ibu ion o majo (a) and mino (b) elemen s in he analyzed samples.
Me als o economic in e es a e, in o de o abundance, Pb, As, Cu, and, o a lesse
ex en , Zn, Sb, Ba,Bi, P, and Mn (Figu e 4b and Table S1). Pb, As, Cu, and Zn a e de ec ed in
he a e age ange o housands o ppm, whe eas Sb, Ba, Bi, P, and Mn a e below 300 ppm.
T ace elemen s de ec ed in he ange o 10 ppm include, in o de o abundance, Se, S ,
Sn, Z , Tl, Mo, V, Ce, Co, Rb, La, and C (Figu e 5a and Table S1). In con as , ul a ace
elemen s de ec ed in p opo ions below 10 ppm include, in o de o abundance, In, Ni, Ga,
Y, Th, W, Nb, U, Li, Sc, Te, Cd, H , Cs, Ta, and Be (Figu e 5a and Table S1).
Sus ainabili y 2023, 15, x FOR PEER REVIEW 10 o 24
Figu e 4. Bulk- ock dis ibu ion o majo (a) and mino (b) elemen s in he analyzed samples.
T ace elemen s de ec ed in he ange o 10 ppm include, in o de o abundance, Se,
S , Sn, Z , Tl, Mo, V, Ce, Co, Rb, La, and C (Figu e 5a and Table S1). In con as , ul a ace
elemen s de ec ed in p opo ions below 10 ppm include, in o de o abundance, In, Ni,
Ga, Y, Th, W, Nb, U, Li, Sc, Te, Cd, H , Cs, Ta, and Be (Figu e 5a and Table S1).
All analyzed samples bu one (i.e., Tin o-San a Rosa-1 (TSR1)) ha e app eciable con-
en s o Ag (35–100 ppm) and Au (2 ppm on a e age). I is wo h no ing ha he highes
Au con en s (up o 5 ppm) we e de ec ed in he Tha sis-1 (TH-1) sample (Figu e 5b and
Table S1).
Figu e 5. Bulk- ock dis ibu ion o ace and ul a- ace elemen s (a) and p ecious me als (b) in he
analyzed samples.
4.2. Mine alogy
Oxides o he spinel g oup, including magne i e (Fe3O4), hema i e (Fe2O3), and he -
cyni e (FeAl2O4), a e he mos abundan mine als in all he samples (Figu es 6 and 7).
O he less abundan mine als (Figu e 7) a e sul a es [ja osi e, KFe3(SO4)2(OH)6; plumboja -
osi e, PbFe6(SO4)4(OH)12; anglesi e (PbSO4) and ba i e (BaSO4)], a sena es [beudandi e
PbFe3(AsO4)(SO4)(OH)6], sul ides [galena (PbS), py i e (FeS2) and e ahed i e
(Cu,Fe)12Sb4S13], and na i e me als [Pb0, Cu0, Bi0 and Au0]. Qua z is also ela i ely abun-
dan , in addi ion o ace amoun s.
The Fe-oxides o he spinel g oup equen ly o m composi e agg ega es wi h/wi h-
ou Si-(Al)- ich glass (he ea e pelle s) (Figu e 6a–l). These pelle s, which may be up o
0.5 mm ac oss, exhibi a ange o mo phologies om pu ely sphe oidal o d ople -like o
holly-lea , wi h cha ac e is ic he e ome ic in e nal po osi y (Figu es 6a–l and 7a–e). Some
o he pelle s consis ing o po ous he cyni e o magne i e a e usually eplaced by hema i e
along hei ims (Figu e 7a–c).
Figu e 5.
Bulk- ock dis ibu ion o ace and ul a- ace elemen s (
a
) and p ecious me als (
b
) in he
analyzed samples.
All analyzed samples bu one (i.e., Tin o-San a Rosa-1 (TSR1)) ha e app eciable con-
en s o Ag (35–100 ppm) and Au (2 ppm on a e age). I is wo h no ing ha he highes
Au con en s (up o 5 ppm) we e de ec ed in he Tha sis-1 (TH-1) sample (Figu e 5b and
Table S1).
Sus ainabili y 2023,15, 12081 16 o 23
4.3.2. Silica es
The silica e glass o ming he pelle s is cha ac e ized by an a e age high o SiO
2
(88.4 w .%),
Al
2
O
3
(32 w .%), and K
2
O (9.86 w .%), bu low MgO (2.88 w .%), TiO
2
(2 w .%),
CaO (4.07 w .%), and Na
2
O (3.78 w .%) (Figu e 12a). O he me als o economic in e es
de ec ed by means o LA-ICP-MS include Z (151 ppm on a e age), S (30 ppm on a e age),
and Pb (145 ppm on a e age) (Figu e 12b).
Qua z shows a homogenous composi ion in e ms o majo elemen s (Figu e 13a and
Table S2), being cha ac e ized by i s deple ion in mos o he analyzed elemen s excep Ti
(30,291 ppm on a e age), Pb (1025 on a e age), and Mg (614 on a e age) (Figu e 13b and
Table S3).
4.3.3. Sul ides
The EPMA analyses on selec ed py i e g ains show ela i ely low concen a ions in
mos me als o economic in e es (<0.1 w .%), bu As (up o 0.84 w .%) and Pb (0.27 w .%)
(Figu e 14a and Table S2).
4.3.4. Sul a es
Plumboja osi e has a e y homogenous composi ion, al hough some g ains con ain
de ec able amoun s o Al
2
O
3
(up o 3.69 w .%), As
2
O
5
(2.5 w .%), Na
2
O (2 w .%), K
2
O
(2.4 w .%), Ag
2
O (1 w .%), HgO (0.43 w .%), and CuO (1.16 w .%), e y likely due o
he p esence o inclusions (Figu e 14b). Likewise, anglesi e shows a composi ion nea ly
s oichiome ic (Table S2).
5. Discussion
5.1. Genesis o he “Mo ongos” du ing Py i e Roas ing and La e E olu ion
The mine alogy, mo phology, and in e nal mic os uc u es o he pelle s iden i ied in
he s udied “mo ongos” (Figu es 6a–l, 7a–e, 8and 9) a e simila o hose esul ing om he
oas ing and/o calcina ion p ocesses o py i e as documen ed in bo h na u al se ings and
expe imen al uns [
50
–
52
]. The nano- o-mic on-sized s uc u es consis ing o mix u es o
he cyni e, magne i e, and/o hema i e and silica e glass shown by ou pelle s a e consis en
wi h (1) cooling om a mel ed mass; and (2) decomposi ion, upon cooling, o a p ecu so
high- empe a u e spinel phase.
Expe imen s conduc ed a a high empe a u e (1200
◦
C) indica e ha he Fe-Al end-
membe spinel he cyni e may dissol e up o 16.5 w .% o he magne i e componen in
i s s uc u e while eleasing i upon dec easing empe a u e and/o inc easing oxygen
con en [
53
,
54
]. Fu he mo e, he eplacemen ex u es o he cyni e and magne i e by
hema i e (Figu e 7a–c) a e consis en wi h he p og essi e oxida ion sequence o py i e
→
he cyni e/magne i e
→
hema i e ha is ypically p oduced du ing combus ion o py i e in
oxygen-con aining a mosphe es, pa icula ly when Al-bea ing silica es a e p esen in he
gangue o he py i e o e subjec ed o combus ion [51].
The p oposed sequence o decomposi ion o py i e o he cyni e, and hen mag-
ne i e and/o hema i e, usually le behind by he la e oxides en iched in Al (i.e., up
o
12.13 mol.% o Al2O3),
has been de ec ed in hese ypes o oxides syn he ized a
1200 ◦C.
This is consis en wi h he ac ha he newly o med Fe-oxides analyzed he e show el-
a i ely high Al
2
O
3
con en s (up o ~52 w .% in he cyni e, ~2.5 w .% in magne i e, and
~1.8 w .% in hema i e; Figu es 10 and 11 and Table S2), e idencing he con ibu ion o
Al- ich phases du ing py i e combus ion. I is wo h no ing ha phyllosilica es such as
chlo i e and se ici e we e he main gangue mine als o he py i ic o es employed o he
oas ing p ocess [
36
,
55
], hus p o iding a po en ial sou ce o Al in he newly o med
mine als. The he mal s abili y o hese hyd a e-mine als is <600
◦
C [
56
], which is a
below he empe a u es eached du ing he i ing o py i e in he s udy a ea. Fo ins ance,
Re . [
32
] expe imen ally es ed ha mine alogical decomposi ion o py i e du ing oas ing
in he nea by Rio in o “Tele as”, whe e he “mo ongos” esidues we e p oduced, could

Sus ainabili y 2023,15, 12081 17 o 23
ha e eached up o 600
◦
C du ing i ing wi h oxida ion and phase ansi ion o py i e in o
Fe-oxides a >900 ◦C, consis en wi h es ima ions made he e.
Addi ionally, we ha e also obse ed he eplacemen magne i e
→
hema i e, bo h
lacking Al (Figu e 7c). This aises ano he possible pa hway du ing i ing, whe e py i e
decomposes o hose Fe-oxides wi hou he necessi y o a he cyni e p ecu so . A possibili y
is he wo-s age p ocesses obse ed by [
52
] in hei expe imen s conduc ed a 500–700
◦
C,
whe e py i e is i s ly oxidized o magne i e and he la e o hema i e upon inc easing
oxygen ugaci y, acco ding o he ollowing eac ions:
3FeS2+ 16O2→Fe3O4+ 6SO2(1)
2Fe3O4+ 1/2O2→+ 3Fe2O3(2)
Fu he mo e, he obse a ion o single g ains o hema i e wi h po ous and/o onion-
shape mo phology and ou e ou lines esembling pseudomo phs o o me py i e c ys als,
as obse ed in Figu e 7d,e. These ex u es could be explained by he di ec oxida ion o
p ecu so py i e wi hou in e media ies as ollows:
FeS2+ O2→Fe2O3+ SO2(3)
Expe imen al da a indica e ha his eac ion [
3
] may p oceed wi hin a wide ange o
empe a u es (500–700
◦
C) bu in a mosphe es e y en iched in oxygen (>5%). Ne e heless,
di ec ans o ma ion o py i e
→
magne i e is also possible, bu a highe empe a u es and
lowe oxygen condi ions [
51
–
55
], hus explaining some single po ous-like Al- ee magne i e
g ains documen ed he e.
I is wo h no ing ha e lec ed ligh mic oscopy and FESEM cha ac e iza ion e eal
submic oscopic pa icles o na i e Au and elec um (Au-Ag) in he “mo ongos”. Mos o
hese pa icles a e associa ed wi h highly po ous hema i e, while some o hem a e ound
as isola ed g ains (Figu e 7k,l). P e ious wo ks [
42
,
55
–
61
] ha e ecognized Au pa icles
hos ed in py i e as bo h “ isible” pa icles and “ e ac o y”—i.e., bounded in o he py i e
s uc u e o as nanopa icles “in isible” o con en ional op ical mic oscopy. Indeed, some
o he Au g ains now obse ed as bo h isola ed c ys als o associa ed wi h he oxides
could co espond o hose p ecu so isible Au pa icles ha would ha e su i ed he
oas ing p ocesses. Complemen a ily, hese could be byp oduc s o py i e i ing. Re . [
52
]
ha e ecen ly demons a ed in hei expe imen s ha du ing py i e oas ing, Au o iginally
ound o be “ e ac o y” may be eleased o o m disc e e pa icles. These au ho s s essed
ha compa ed o he o iginal py i e used in hei expe imen s, he su ace a ea and po e
olume o he oas ed p oduc s, especially he meso- and mic o-po osi y, inc eased by one
o de o magni ude when oas ing was ca ied ou a 500–600
◦
C. Bu he su ace a ea and
po osi y signi ican ly dec eased when he empe a u e inc eased up o 700
◦
C, meaning ha
pa icle sin e ing occu ed du ing oas ing. Na u al obse a ions and hea ing expe imen s
o py i e- ype ma ices sugges ha such sin e ing o p ecious me al pa icles may be he
esul o bo h solid-s a e di usion and Au-bea ing nanomel mig a ion and accumula ion
when high-po osi y channels a e p oduced du ing desul u iza ion-oxida ion o sul ides
expe iencing he mal inpu [
62
–
65
]. In he case o Au, mig a ion and coa sening aided by
nanomel o ma ion should be a o ed by he lowe mel ing poin o me al nanopa icles
han hei bulk coun e pa s (e.g., Au pa icles o <4 nm mel a 370
◦
C ins ead o 1064
◦
C o
he bulk; Re . [
63
]). A simila in e p e a ion can be assumed o explain he minu e bleb-like
pa icles o uniden i ied compounds o Pb
±
Bi
±
Cu encased in hema i e pseudomo ph we
obse ed in he sample TH-3 om Tha sis (Figu e 7 ). A ailable empi ical and expe imen al
wo ks [
66
–
68
] suppo he exis ence o mel s wi h a a iable p opo ion o Pb
±
Bi
±
Cu
wi hin he qua e na y Bi-Pb-Cu-S sys em a empe a u es depa ing om 271
◦
C upwa ds.
On he o he hand, many o he oxide-silica e pelle s display ims o Fe- ich sul a es
and/o ja osi e wi h a ying con en s o Pb (e.g., Figu e 6c,l). In his ype o py i e was e,
hese ims we e in e p e ed as he combina ion o oas ing and wea he ing [
33
]. The
Sus ainabili y 2023,15, 12081 18 o 23
expe imen al esul s by [
50
,
52
] indica e ha di ec oxida ion o py i e akes place wi h a
sh inking un eac ed co e likely con olled by he chemical eac ion o he inwa d di usion
o oxide due o he po e-blocking e ec o he o ma ion o e ic/ e ous sul a e. These
Fe-sul a es a e able o inhe i signi ican amoun s o ace elemen s ini ially p esen in he
py i e la ice o hei mine al inclusions (e.g., Pb). Subsequen exposi ion o a mosphe ic
condi ions may cause hyd oxyla ion and hyd a ion du ing wea he ing, gi ing ise o
pa ial ans o ma ion in o mine als o he ja osi e g oup ha ing a iable amoun s o Pb.
I is wo h no ing ha his mechanism o py i e oas ing and i s esul ing p oduc s ha e
p e iously been desc ibed by [52].
O he sul a es like anglesi e (PbSO
4
), ba i e (BaSO
4
), and minium can be asc ibed o
his la e-s age wea he ing- ela ed oxida ion-hyd a ed mechanism o p e-exis ing sul ides.
Upon exposu e o he ai and wa e , galena may unde go aqueous and a mosphe ic oxida-
ion and hen be ans o med in o seconda y sul a es, and/o a sena es, and/o oxides, as
hose obse ed in Figu e 7i,j.
Finally, qua z is also obse ed, indica ing ha i is he mos s able phase du ing
combus ion, al hough i shows eac ion edges, which sugges s ha i is pa ially des a-
bilized due o he high empe a u es (Figu e 7e), bu s ill esis an o low- empe a u e
su icial al e a ion.
5.2. Mine alogical Si ing o Economic Me als in he Roas ed Py i ic Was e: Economic Po en ial
The bulk- ock da a show ha Fe is he majo cons i uen o he oas ed py i e was e
analyzed he e, wi h concen a ions a ying om 37 o 50% (Figu e 4a and Table S1). The
mine alogical exp ession o his Fe en ichmen is he abundance o Fe oxides and sul a es
(Figu es 6,7a–h, 8and 9). Howe e , o he majo elemen s de ec ed in he samples, such as
Al (~4%) and Ti (1%), ha e hei mine alogical exp ession in he ela i ely high abundance
o Al and Ti in oxides like he cyni e (up o 52 and 0.3 w .%, espec i ely) and silica e glass
(up o 32 and 2 w .%, espec i ely) as de ec ed by EPMA
(Figu es 10–12 and Table S2).
As
no ed abo e, he wo mixed samples om So iel (S-2) and Tin o-San a Rosa (TSR-2) show
signi ican ly lowe Fe alues (13%), which a e co ela ed wi h highe S (up o 10%) and
Al (up o 4.34%) (Figu e 4a and Table S1). The highe S in hese samples is consis en
wi h abundan py i e (hos ing inclusions o e ahed i e;
e.g., Figu e 7i)
and galena g ains
ound as isola ed b oken agmen s wi h euhed al mo phology (Figu e 7h). These la e
ea u es sugges incomple e oas ing, o mo e likely, he abo e-a gued na u e o some o
he collec ed samples consis ing o mixing o he “mo ongos” wi h o he ypes o mining
was es made up o p ima y o es.
As no ed abo e, he main me als o economic in e es a e Pb, As, Cu, and, o a
lesse ex en , Zn. These a e de ec ed in a e ages o >8500, ~4000, ~1235 and ~785 ppm,
espec i ely (Tables S2 and S3). The EPMA analysis shows ha Pb is mainly concen a ed
in he newly- o med anglesi e (up o ~75 w .%) and plumboja osi e (up o ~20 w .%), as
well as in galena elic s (ideally ~86 w .%) and py i e (up o ~0.3 w .%) (Table S2). A senic
is a undamen al componen o he seconda y a sena e beudan i e (~15 w .% As
2
O
5
) and
he sul a es plumboja osi e (up o 2.5 w .% As
2
O
5
) and anglesi e (up o 0.6 w .% As
2
O
5
).
I is also a main cons i uen o he accesso y inclusions o e ahed i e- ennan i e wi hin
elic ic py i e (wi h up o 0.6 w .% As) in he samples (Table S2). Cu and Zn a e essen ially
e ained in e ahed i e. In si u LA-ICP-MS also e eals no iceable amoun s o Pb (~1800 on
a e age), As (~1200 ppm on a e age), Cu (~800 ppm), and Zn (1600 ppm) in he Fe-oxides
(magne i e and hema i e) also esul ing om he oxida ion o py i e (Table S3), whe eas
hey a e ex emely low in he silica e glass and coexis ing elic ic qua z (As ~90 ppm, Zn
~85 ppm, Pb ~15 ppm, and Cu ~5 ppm; Table S3).
O he me als o economic impo ance include Sb, Ba, Bi, Mn, and P, which a e p esen
in he s udied py i e was es in concen a ions below 300 ppm. These a e ound as ace
elemen s in all he epo ed mine als, as hey a e de ec ed by bo h EPMA and LA-ICP-MS
(Supplemen a y Tables S2 and S3).
Sus ainabili y 2023,15, 12081 19 o 23
On he o he hand, he ela i ely high bulk- ock concen a ion o Ag (up o 100 ppm)
can be ela ed o he p e e en ial pa i ion o his elemen in o sul a es and sul ide elic s
(i.e., ja osi e, galena, and e ahed i e) and, o a lesse ex en , oxides (mainly hema i e;
Figu e 11b). In con as , high bulk- ock con en s o Au (up o 5 ppm) a e associa ed wi h
g ains o na i e gold, o en hos ed in hema i e (Figu e 7k,l).
Summa izing he obse a ions abo e, he analyzed “mo ongos” ha e po en ial o
Fe as well as o he me als like Pb, Cu, Zn, Ag, and Au, whose abundances (up o 10,000,
4446, 1908, 100, and 5 ppm, espec i ely) a e simila o e en highe han he me als mean
g ades in mos cu en ac i e mines in he a ea. Fo example, Ce o Colo ado-Rio in o has
a g ade o 0.03% Pb, 0.3% Cu, and 0.1% Zn, and Masa Val e de has a g ade o 0.6% Pb,
0.6% Cu, 1.3% Zn, 29 g/ Ag, and 0.6 g/ Au [
69
]. No ewo hy, he analyzed “mo ongos”
om he IPB yield a a he homogenous esidue, highligh ing ha he py i e oas ing
p ocess p oduced mo e consis en esidues i compa ed wi h o he economically in e es ing
mine was es. Tailings, o example, al hough also economically in e es ing, o en show
subs an ial spa ial geochemical changes, g ain-size g a i y-d i en seg ega ions, as well
as some en iched o deple ed pseudo-ho izon al al e a ion on s [
70
–
73
]. Mo eo e , he
mine alogical and ex u al ea u es o he “mo ongos” make hem a ma e ial sui able o
me al eco e y by means o a wide ange o possible mine al p ocessing me hods, including
lo a ion, g a i y sepa a ion, elec os a ic sepa a ion, and/o magne ic p ocesses [
74
–
76
].
Owing o he low abundance o e ac o y phases, such as sul ides, oge he wi h he
high abundance o leachable mine als, including oxides, sul a es, and na i e me als, we
sugges ha he mos p omising me allu gical p ocess could be hyd ome allu gical me al
ex ac ion [
77
,
78
]. Me al eco e y om oas ed py i e by means o en i onmen ally iendly
hyd ome allu gical p ocesses is cu en ly being es ed (e.g., Re . [
22
] epo ed up o 84.6%
Cu and 68.7% Co eco e y by phospho ic acid leaching, and [
79
] epo ed up o 90% Au
and 41.1% Ag eco e y by elec ochlo ina ion).
6. Conclusions
This wo k is he i s -e e s udy a emp ing o e alua e he po en iali y o high- ech
me als o a speci ic ype o en i onmen ally isky mining was e p oduced in he Ibe ian
Py i e Bel du ing he 19–20 h cen u ies. Locally known as “mo ongos”, he esidue was
he esul o py i ic o e me allu gical p ocessing by open-ai oas ing a ela i ely high
empe a u es (>500 ◦C), as illus a ed by he nano- o-mic on scale mine alogical s udy.
O e all, “mo ongos” om he IPB show a homogeneous geochemical and mine alog-
ical composi ion. In addi ion o he high Fe concen a ion, he economically in e es ing
elemen s a e Pb, Cu, Zn, Ag, and Au.
The co ela ion be ween bulk ock geochemis y, mine alogy, and mine al chemis y
da a is e y high. Majo elemen s (e.g., Fe, S, Al, K, Ti, Mg, Na, and Ca) co ela e wi h
hema i e, magne i e, he cyni e, glass, and silica es. Ce ain me als and me alloids o
economic in e es , such as Pb, Cu, Zn, Ag, and Au, a e undamen ally associa ed wi h
oxides, a sena es, sul a es, na i e me als, and, o a lesse ex en , wi h sul ide emains.
The e o e, “mo ongos” om he IPB ha e he po en ial o become an asse , hus
con ibu ing ou new da a o a mo e ci cula economy o ecycling and ep ocessing
was e ma e ials.
Supplemen a y Ma e ials:
The ollowing suppo ing in o ma ion can be downloaded a : h ps:
//www.mdpi.com/a icle/10.3390/su151512081/s1, Table S1: Whole ock analyses; Table S2: EPMA
analyses; Table S3: LA-ICP-MS analyses. Re e ence [80] is ci ed in he supplemen a y ma e ials.
Au ho Con ibu ions:
Concep ualiza ion, L.Y. and J.M.G.-J.; ieldwo k, L.Y., J.M.G.-J., F.A.J.-C. and
D.C.-M.; me hodology, L.Y., J.M.G.-J., F.A.J.-C. and D.C.-M.; o mal analysis, J.M.G.-J., L.Y., I.M.S. and
I.G.-P.; in es iga ion, all he au ho s; esou ces, F.A.J.-C., D.C.-M., L.Y. and J.M.G.-J.; w i ing—o iginal d a
p epa a ion, L.Y. and J.M.G.-J.; w i ing— e iew and edi ing, all he au ho s; p ojec adminis a ion,
L.Y.; unding acquisi ion, L.Y. and J.M.G.-J. All au ho s ha e ead and ag eed o he published e sion
o he manusc ip .
Sus ainabili y 2023,15, 12081 20 o 23
Funding:
This esea ch was ully unded by he MECRAS P ojec A-RNM-356-UGR20 “P oyec os
de I+D+i en el ma co del P og ama Ope a i o FEDER Andalucía 2014–2020” o he Conseje ía de
Economía, Conocimien o, Emp esas y Uni e sidad de la Jun a de Andalucía (Spain).
Ins i u ional Re iew Boa d S a emen : No applicable.
In o med Consen S a emen : No applicable.
Da a A ailabili y S a emen : No applicable.
Acknowledgmen s:
The au ho s would like o acknowledge Xa ie Llo e om UB o assis ing in
elec on mic op obe analyses.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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