Chemical Geology 630 (2023) 121488
A ailable online 23 Ap il 2023
0009-2541/© 2023 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-
nc-nd/4.0/).
Elec ochemical eac ions d i ing Mn-en ichmen in Fe
–
Mn supe gene
o es: A mine alogical pe spec i e
And ´
e Jo ge Pin o
a
,
*
, Nu ia Sanchez-Pas o
b
, Raul San os Jo ge
c
a
Depa amen o Geology, Facul y o Sciences, Uni e si y o O iedo, C/ Jesús A ias de Velasco, s/n, 33009 O iedo, Spain
b
Depa men o Mine alogy and Pe ology, Facul y o Geological Sciences, Uni e si y Complu ense o Mad id, C/ Jos´
e An onio No ais, 12, Mad id 28040, Spain
c
Uni e si y o Lisbon, Facul y o Sciences, Dom Luiz Ins i u e (IDL), Campo G ande, Ed. C6, 1749-016 Lisbon, Po ugal
ARTICLE INFO
Edi o : Ma co Fio en ini
Keywo ds:
Manganese oxides
i on oxides
Supe gene en ichmen
Elec ochemical eac ion
ABSTRACT
I on and manganese oxides embody a geochemical sys em o g ea en i onmen al, biological, and economical
ele ance. Chemical equilib ia and he s abili y o Fe
–
Mn phases unde su ace o nea -su ace condi ions can
in luence he a e o con aminan s in he en i onmen , impac biological me abolic p ocesses, o Fe and Mn
phase dis ibu ion in wea he ed o es. In he p esen wo k, we ocus on he ex u al, mine alogical, and chemical
s udy o Fe
–
Mn o es om he wea he ed zone o a ein-hos ed deposi ou c opping in he Ibe ian Py i e Bel , SW
Po ugal, by means o mic o-Raman spec oscopy coupled wi h elec on mic op obe mic oanalysis. The aims o
ou in es iga ion a e i) iden i ying he se e al Fe and Mn phases occu ing in di e en ly en iched o es samples,
ii) ela ing hei chemical composi ion wi h possible mine aliza ion mechanisms, and iii) de ining he mine al
pa agene ic pa hway ela ed o he obse ed ex u al ea u es. Ou app oach enabled bo h he iden i ica ion o
he coexis ing Fe and Mn phases, and un a elling pa agene ic pa hways leading o supe gene en ichmen min-
e aliza ions. Collec ed e idence demons a es ha changes in Eh/pH can lead o goe hi e dissolu ion unde
educ i e condi ions, p omo ing he elease o Fe
2+
in o solu ion, whose elec ochemical in e ac ion wi h Mn
4+
esul s in he o ma ion o se e al ypes o Mn oxides, and seconda y goe hi e. Ou da a shows a clea ela-
ionship be ween he ype o Mn oxide c ys allized and he a io o aqueous Mn
3+
/Mn
4+
, alongside o he
p e alen ca ions, inco po a ed in o unnel o in e laye s uc u al si es, which may be also deso bed/solubilized
om p ima y goe hi e.
1. In oduc ion
I on and manganese a e wo elemen s o high indus ial ele ance,
since hey a e essen ial o manu ac u e s eel, a undamen al ma e ial o
he de elopmen and sus enance o a mode n indus ialized socie y
(Gu zme and Beukes, 2009). Fu he mo e, manganese oxides o e
applica ions in he manu ac u e o p oduc s such as ba e ies, insula o s
o ce amics (e.g. McB een, 1975; Singh and Meenaloshini, 2008; Mali-
nenko e al., 2013). Bo h elemen s may occu oge he in na u e, due o
hei simila geochemical cha ac e is ics (Luo e al., 2018), commonly
associa ed wi h he hyd o he mal al e a ion and supe gene en ichmen
p ocesses, while mino deposi s o magma ic and con ac me amo phic
o igin also exis . Gu zme and Beukes (2009) p o ide an ex ensi e e-
iew o he mos ele an mine alogical, geochemical, and economic
aspec s o i on and manganese o e deposi s wo ldwide.
I on and manganese oxides play an impo an ole in he
en i onmen al a e and mobili y o oxic me als and pollu an s, due o
hei small pa icle size and high eac i e su ace, coupled wi h an Eh/
pH-dependen high eac i i y (e.g. Hochella e al., 2008; Zhao e al.,
2012, e c.). Fo ins ance, he wo k o Rou e al. (2014), whose indings
poin owa ds a majo e ec o Mn inco po a ion o e he adso p ion
capaci y o goe hi e ega ding me als such as Pb
2+
, o Cd
2+
, unde lines
he en i onmen al ele ance o he Fe and Mn sys em. The e ec i eness
o such adso p ion eac ions is ela ed o oxide su ace p ope ies, whose
a ia ion can in luence he solubili y, oxici y and bioa ailabili y o
con aminan s in soils and aqui e s (e.g. Huang and Zhang, 2020; Taujale
e al., 2016). Huang and Zhang (2020) analyzed he s a e-o - he a
esea ch conce ning edox Fe and Mn oxide eac ions in complex sys-
ems, wi h a special ocus on a ising en i onmen al implica ions. The e
is also a link be ween manganese oxides and he biosphe e, since many
na u ally occu ing Mn oxides o m h ough biologically media ed
p ocesses (Tebo e al., 2004; San elli e al., 2011).
* Co esponding au ho .
E-mail add esses: [email p o ec ed] (A.J. Pin o), [email p o ec ed] (N. Sanchez-Pas o ), [email p o ec ed] (R.S. Jo ge).
Con en s lis s a ailable a ScienceDi ec
Chemical Geology
jou nal homepage: www.else ie .com/loca e/chemgeo
h ps://doi.o g/10.1016/j.chemgeo.2023.121488
Recei ed 6 Feb ua y 2023; Recei ed in e ised o m 17 Ma ch 2023; Accep ed 13 Ap il 2023
Chemical Geology 630 (2023) 121488
2
The c ys al chemis y o Mn oxides is pa icula ly complex, s em-
ming om he la ge a ie y o s uc u al ypes and he non-
s oichiome ic ea u es a ec ing na u al mine aliza ions, when
compa ed o ideal composi ions. Mo eo e , na u al manganese oxides
equen ly o m masses o poo ly c ys alline ma e ials, ha d o dis in-
guish bo h in he ield and in hand specimens. Following on he oo s eps
o Be na dini e al. (2019), Pos e al. (2020, 2021) p o ide a comp e-
hensi e Raman spec al analysis o unnel and laye -s uc u e manga-
nese oxides, using bo h syn he ic and na u al specimens. Bo h
in es iga ions include insigh s on manganese oxida ion s a es, s uc u al
and c ys allog aphic peculia i ies o Mn oxides, alongside hei chemical
composi ions. This body o wo k p o ides a me hodological pa hway o
in e p e mine al pa agene ic sequences when di e en ypes o Mn
oxides and hyd oxides a e inely in e g own, enabling a mo e ealis ic
app oach when i comes o deciphe ing he physical-chemical go e ning
ac o s o mine al e olu ion in hese sys ems.
P e ious esea ches on Fe
–
Mn o e mine aliza ions ha e ocused
especially on he cha ac e iza ion o oxide phases owa ds he es ab-
lishmen o b oad me allogene ic models o i on and manganese depo-
si ion (e.g. Roy, 1981; P acejus e al., 1988; Michailidis e al., 1997),
lea ing aside he chemical equilib ia in icacies es ablished among
oxide phases, as e lec ed by ex u al ea u es, commonly a he mic o-
scopic scale. In he p esen wo k, by means o mic o-Raman spec os-
copy coupled wi h elec on mic op obe mic oanalysis, we ocus on he
ex u al, mine alogical, and chemical s udy o Fe
–
Mn ma e ials
sampled om he wea he ed zone o a ein-hos ed deposi (Se a da
Mina, Ibe ian Py i e Bel , SW Po ugal). The aims o ou in es iga ion
a e i) iden i ying he se e al Fe and Mn phases occu ing in di e en ly
en iched samples, ii) ela ing hei chemical composi ion wi h possible
mine aliza ion mechanisms, and iii) de ining he mine al pa agene ic
pa hway ela ed o he obse ed ex u al ea u es.
2. Sample p o enance and con ex
The p esen s udy ocuses on he mine al pa agene ic associa ions
occu ing in he wea he ed/en iched zone o he ein-hos ed Fe
–
Mn
deposi o Se a da Mina, SW Po ugal. These mine aliza ions a e
included in he wes e n po ion o he Ibe ian Py i e Bel , mos speci -
ically in he Ce cal-Odemi a sec o , whe e a se ies o di e en ypes o
Fe
–
Mn deposi s occu . Despi e i s onnage ele ance (Ca alho e al.,
1971), he mine aliza ion p ocesses ela ed o Se a da Mina deposi a e
s ill poo ly unde s ood, wi h ew ecen li e a y e e ences. Almeida
(1945) p oposes a p ima y mine aliza ion o Fe and Mn ca bona es,
subsequen ly eplaced by oxides o he same me als, by nea su ace,
low- empe a u e p ocesses. Fo he pu poses o his esea ch, he
wea he ed/en iched zone o Se a da Mina deposi o e s excellen ex-
amples o a la ge a ie y o Fe
–
Mn oxide mine aliza ions; a window
opened owa ds he physical-chemical ac o s go e ning mine al
nuclea ion and g ow h. The p ima y, ein-hos ed mine aliza ions o his
deposi consis o associa ions o hema i e and goe hi e, wi h mino
amoun s o py olusi e, qua z, and galena. Tec onic emobiliza ion
e en s, unde pinning he polyphasic ein mine aliza ion, lead o a sec-
onda y mine al pa agenesis o goe hi e, hema i e, py olusi e, c yp o-
melane, manganomelane, and qua z. Con inuous supe gene
en ichmen o e he la e o es yielded associa ions o goe hi e, py o-
lusi e, c yp omelane, co onadi e, amsdelli e, manganomelane, qua z,
and ba i e. The samples p esen ly discussed o igina ed om he la e
o e zone, and a ecen in dep h cha ac e iza ion o Se a da Mina deposi
is included in San os (2020).
Fig. 1 displays images o hand-specimens o he wo en iched ma-
e ials sampled in his in es iga ion, cha ac e is ic o he wea he ed
sec ion o he Se a da Mina deposi p o ile, including he geog aphical
coo dina es o sampling si es (Wo ld Geode ic Sys em). Fig. 1a depic s
sample CO-102, ela i e o a zone whe e a po ous goe hi e and hema i e
hick laye is unde lain by a ac u ed ba i e and qua z ein. Be ween
hese wo laye s, a da ke , pu plish s a um o Fe and Mn oxides occu s,
also ex ending downwa ds, illing c acks and ac u es wi hin he ein.
Fig. 1b co esponds o sample CO-79, also qui e po ous, comp ising
mos ly acicula Fe oxides (goe hi e and hema i e), inely in e g own
wi h Mn-oxides, which also exis as geodes in ca i ies. The mine al g ain
size o sample CO-79 makes i impossible o iden i y he Mn phases
p esen wi hou he aid o a mic oscope.
3. Ma e ials and me hods
Selec ed samples o he wo mine alogically dis inc Mn-en iched
zones, CO-102 and CO-79, collec ed a Se a da Mina si e, we e
embedded in esin, polished, and s udied wi h a pe og aphic mic o-
scope, unde bo h ansmi ed and e lec ed ligh obse a ion modes.
The Raman spec a o a ge ed phases we e collec ed using a
Fig. 1. Ma e ials om he wea he ed-en iched zone o he Se a da Mina deposi , Ibe ian Py i e Bel , SW Po ugal; a) Sample CO-102, co esponding o less en iched
ma e ials, and b) sample CO-79, collec ed om he zone iche in Fe
–
Mn oxides. Geog aphical coo dina es co espond o WGS84 sys em (Wo ld Geode ic Sys em).
Hem =Hema i e, G h =Goe hi e, Qz =Qua z, B =Ba i e, MnOx =Manganese oxides, Diss =dissemina ed.
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
3
con ocal The mo Fische DXR Rama Mic oscope, wi h poin -and-shoo
capabili y and one mic on o spa ial esolu ion. A 10×magni ica ion
objec i e was employed alongside a 532 nm lase sou ce o 10 mW a
100% powe , bu lowe lase po ency (<10 mW) was used o hyd a ed
phases. The a e age spec al esolu ion o he Raman shi anging om
70 o 3400 cm
−1
was o 2–4 cm
−1
, i.e. g a ing 900 lines/mm and a spo
size o 2
μ
m. The sys em was ope a ed unde OMNIC 1.0 so wa e, i ing
wo king condi ions such as pinhole ape u e o 25
μ
m and bleaching
ime o 1–2 s; ou exposu es a e aged in ime o 12 s each.
Band componen analysis was ca ied ou using he so wa e package
“Fi yk” (Wojdy , 2010), which enables he analysis o Raman spec a by
employing di e en i ing unc ions. Fu he mo e, he so wa e allows
he manipula ion o speci ic pa ame e s, such as band heigh , cen e ,
and hal wid h a hal maximum (hwhm).
A e ma king a ge zones o analysis, he polished hin sec ions
we e ca bon coa ed p io o Elec on Mic op obe (EMP) de e mina ions.
The employed EMP was a JEOL Supe p obe JXA-8900 M equipped wi h
i e WDS spec ome e s, an EDS spec ome e , and a backsca e ed
elec on de ec o (BSE), enabling an on-session selec ion o he su aces
o be analyzed. S anda d analyses applied 5
μ
m o beam diame e a a
beam ime cu en o 10 nA a 20 kV. Coun ing imes on peaks and
backg ound anged om 15 o 60s and 5 o 30s, espec i ely. The
calcula ed de ec ion limi s we e 208 ppm o Si and 108 ppm o Na
(albi e s anda d), 278 o Fe ppm and 312 ppm o Mn (almandine
s anda d), 225 ppm o Ti, 153 ppm o Ca, and 133 ppm o Mg
(kae su i e s anda d), 570 ppm o Zn (gahni e s anda d), 143 ppm o
Al (sillimani e s anda ds), 452 ppm o Ba (ba i e s anda d), 114 ppm
o S and 165 o Pb (galena s anda d), 255 ppm o Sn ( in me al
s anda d), 115 ppm o K (mic ocline s anda d), 293 ppm o S
(s on iani e s anda d) and 334 ppm o Ge (syn he ic glass s anda d).
4. Resul s
4.1. Sample pe og aphy
Fig. 2 displays e lec ed-ligh op ical mic og aphs o he sampled
mine aliza ions o Fe
–
Mn belonging o he en iched zone o he Se a
da Mina deposi . Sample CO-102 (Fig. 2a) is cha ac e ized by he
occu ence o goe hi e included in a pe asi e mass o co onadi e.
F equen ly, he la e exis s in con ac wi h ine-g ained abula goe hi e
o a la e gene a ion wi h espec o he massi e one, as e lec ed by he
ex u e displayed in Fig. 2b. He e, ex u al ela ionships be ween bo h
ypes o goe hi e can be obse ed, depic ing an anhed al g ain o
goe hi e wi h a im o ine-g ained abula goe hi e, along a ough
con ac . Anhed al hema i e also occu s sca e ed h oughou he
goe hi e ma e ials, as well as anhed al o subhed al qua z g ains. These
mine alogical associa ions co espond o he Fe and Mn-en iched laye
in sample CO-102, ma ked wi h a whi e ci cle in he hin-sec ion image
included in Fig. 2a, unde lain by he ba i e and qua z ein wi h
dissemina ed Mn-oxides, as depic ed in Fig. 1a. Fig. 2c and d a e e e en
o he mine alogical con en s o sample CO-79, domina ed by he
pa agene ic associa ion o in e g own goe hi e and mangani e, he la e
occu ing bo h as ose es o p isma ic c ys als and anhed al masses
(Fig. 2c). Fig. 2c and d a e e e en o he mine alogical con en s o
sample CO-79, domina ed by he pa agene ic associa ion o in e g own
goe hi e and mangani e, he la e occu ing bo h as ose es o p isma ic
c ys als and anhed al masses (Fig. 2c).
The po ous na u e o sample CO-79 is depic ed in Fig. 2d, ela ed o
he abula habi o indi iduals in he goe hi e ma ix, wi hin which
la ge ca i ies appea lined wi h d usy g ow hs o a hollandi e- ype
phase, and illed wi h geodes o andomly o ien ed, p isma ic chalco-
phani e c ys als.
Deciphe ing he c ys alliza ion sequences mi o ed by he ex u es
encoun e ed in bo h samples, as well as he physical-chemical go e ning
mechanisms unde pinning he implied en ichmen p ocess, en ails
Fig. 2. Op ical e lec ed-ligh mic og aphs unde plane-pola ized ligh o samples CO-102 (a, b), and CO-79 (c, d). Fig. 2b displays he ex u al ela ionship be ween
wo gene a ions o goe hi e. Hem =Hema i e, Co =Co onadi e, G h =Goe hi e, Mnn =Mangani e, Cph =Chalcophani e, Holl =Hollandi e, Qz =Qua z.
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
4
in es iga ing he s uc u al and chemical sub le ies o all obse ed
phases; he objec o he nex sec ions.
4.2. Raman spec oscopy
Fig. 3 displays ep esen a i e expe imen al Raman spec a, ela i e
o Fe oxyhyd oxide phases p esen in bo h CO-102 and 79 samples,
ocusing on he 150–750 cm
−1
ange, he mos sui able shi in e al o
cha ac e ize such phases (Oh e al., 1998). No ele an di e ences we e
encoun e ed be ween he Raman spec a o abula indi iduals and hei
massi e coun e pa s, i.e. he same se o bands we e ob ained, in spi e
o some shi s a ibu able o impu i ies and sligh a ia ions in chemical
composi ion. The la e will be add essed in Sec ion 4.3.
The spec um o Fig. 3a, e e en o he sample CO-102, e eals a se
o 8 peaks in he icini ies o 161, 201, 241, 295, 392, 476, 545, and 681
cm
−1
shi s. Wi h he excep ion o he band a 161 cm
−1
, all peaks can be
asc ibed o ib a ional modes o he goe hi e (
α
-FeOOH) s uc u e
e e enced in he scien i ic li e a u e (i.e. Hanesch, 2009, Oh e al.,
1998, De Fa ia e al., 1997, e c.), wi h he ypical mos in ense peak a
392 cm
−1
( his s udy) and a b oad peak a 681 cm
−1
. The peak a 161
cm
−1
could be ela ed o he inco po a ion o impu i ies in o he
s uc u e o hese phases, o as su ace adso ba es. The spec a ob ained
o Fe oxyhyd oxides in sample CO-79, exempli ied in Fig. 3b, e eals a
simila se o peaks (a cm
−1
167, 207, 301, 389, e c.), indica i e o he
p esence o goe hi e. Howe e , a second se a ound shi s o 227, 483,
512 and 613 cm
−1
is also displayed, which can’ be asc ibed o such i on
oxyhyd oxide. The peak in he icini ies o 389 cm
−1
e eals wo bulges
owa ds highe shi alues, whose decon olu ion displays a good le el
o i ing wi h he combina ion o bands a 403 and 416 cm
−1
. These las ,
aken oge he wi h he a o emen ioned second se o peaks, a e in good
ag eemen wi h e e ence da a ega ding hema i e (Fe
2
O
3
) (Hanesch,
2009, Oh e al., 1998, De Fa ia e al., 1997, e c.). Since a lowe lase
powe was employed in measu ing hese phases, i is unlikely ha he-
ma i e is he p oduc o goe hi e dehyd a ion du ing analy ical
p ocedu es.
Figs. 4 and 5 display ep esen a i e Raman spec a o unnel-
s uc u e Mn oxides, ocusing in he 200–800 cm
−1
Raman shi ange.
Fig. 4a, ela i e o sample CO-79, e eals a complex spec um wi h a
se o peaks a 270, 342376, 577, 629, and 747 cm
−1
consis en wi h
e e ence in o ma ion ega ding amsdelli e, MnO
2
, (Pos e al., 2020).
Since his phase is isos uc u al wi h diaspo e, c ys allizing wi h space
g oup Pnma, he esul ing symme y implies 18 Raman modes (Fa eley
e al., 1972), he e o e explaining such spec al complexi y. Fu he -
mo e, a second se o peaks a 398, 509, and 675 cm
−1
is asc ibable o
he ib a ional modes o a hollandi e-g oup phase (Pos e al., 2020). In
such case, he peak a 629 cm
−1
, could co espond o a composi e band
o Mn
4+/3+
-O ib a ional modes o bo h phases in ha spec al egion.
Ramsdelli e and hollandi e-g oup mine als sha e impo an s uc u al
simila i ies (i.e. double chains o MnO
6
oc ahed a, o ming s uc u al
unnels), and he e o e hei opo ac ic in e g ow h is a common
ea u e. Fig. 4b, also ela i e o sample CO-79, depic s a Raman spec-
um whose peaks a 264, 292, 383, 491, 530, 616 cm
−1
a e consis en
wi h published da a (Pos e al., 2020) ega ding mangani e, MnOOH,
wi h he excep ion o he band a ound 715 cm
−1
. In ac , bo h spec a
consis en ly display a band in he 710 cm
−1
egion, which allows
specula ing ha ano he phase is esponsible o i . The bes candida e is
e ihyd i e, Fe
10
O
14
(OH)
2
, whose s ong band in he men ioned egion
is s ill isible a mode a e lase powe (Hanesch, 2009). A ins ances,
mangani e spec a include a band a ound he 763 cm
−1
egion, which,
gi en he common na u al in e g ow h o mangani e wi h py olusi e,
MnO
2
, could be mos likely ela ed o he la e phase. Since py olusi e is
isomo phic wi h u ile (TiO
2
), and c ys allizes wi h space g oup P4
2
/
mnm, h ee ou o he a ising ou Raman-ac i e phonon modes in he
icini ies o 120, 535 and 665 cm
−1
a e la gely o e lapped by mangani e
bands in he same egions, esul ing in a di icul spec al iden i ica ion
when he wo phases a e in e g own.
Fig. 5 shows ep esen a i e Raman spec a ela i e o Hollandi e-
g oup phases in samples CO-102 and CO-79 (Fig. 5a and b, espec-
i ely). In each case, an inse depic ing esul s in he 150–1300 cm
−1
ange is included, alongside he main spec al analysis ocused in he
150/250–750 cm
−1
in e al. Bo h spec a show band associa ions,
which a e dis inc i e o hollandi e-g oup mine als (Pos e al., 2020),
such as he MnO
6
oc ahed a ib a ional modes a 505, 579 and 665
cm
−1
, and 513, 576 and 635 cm
−1
, o samples CO-102 and 79 espec-
i ely. O he bands e eal a good le el o ag eemen wi h he e e ence
in o ma ion published by Pos e al. (2020), such as he mode a ely
in ense band a 177 cm
−1
(sample CO-102), and peaks a 399 and 382
cm
−1
(samples CO-102 and 79, espec i ely). The unde e mined band in
he egion o 715 cm
−1
may be ela ed o he p esence o e ihyd a e, as
p e iously desc ibed, and he bands in he 1320 cm
−1
zone o ei he OH
ib a ional bending modes, ela ed o OH
−
g oups wi h mo ion in he
unnel di ec ion (Pos e al., 2020), o a poo ly c ys alline hema i e
phase (Hanesch, 2009).
Peaks a 216 and 529 cm
−1
in sample CO-102 could no be ela ed o
a speci ic phase. Hollandi e g oup mine als a e de ined by he ca ion and
wa e con en included in unnel posi ions and he co esponding elec-
os a ic compensa ion by lowe alence ca ions in he oc ahed al si e,
o ming a complex solid solu ion sys em among mul iple endmembe s.
Pos e al. (2020) de ised a co ela ion be ween he Mn
–
O s e ching
band in he 631 cm
−1
egion and he ac ion o Mn
3+
in he oc ahed al
amewo k, associa ed wi h he Jahn-Telle dis o ion o he Mn-
cen e ed coo dina ion polyhed a, gi en by he exp ession:
Fig. 3. Rep esen a i e Raman spec a o a) goe hi e (sample CO-102) and b) in e g own goe hi e and hema i e (sample CO-79). The inse mic og aphs depic he
poin s o spec a acquisi ion. ** Non-asc ibed peak, *Peaks asc ibed o hema i e ib a ional modes.
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
5
Mn3+/Mn o al = − 0.0090499
ν
max +5.9021 (1)
whe e
ν
max
co esponds o he Raman shi in cm
−1
o he Mn
–
O highes
equency mode. The applica ion o his ela ionship o he ob ained
esul s e eals a ios o Mn
3+
/Mn
o al
o 0.35 and 0.16 o samples CO-
102 and CO-79, espec i ely. The o me is close o alues ypical o
co onadi e, Pb(Mn
4+
, Mn
3+
)
8
O
16
.
nH
2
O, and hollandi e, Ba(Mn
4+
,
Mn
3+
)
8
O
16
.
nH
2
O, while he la e esembles he a ios ound in c yp o-
melane, K(Mn
4+
, Mn
3+
)
8
O
16
.
nH
2
O, and manji oi e, (K, Na)(Mn
4+
,
Mn
3+
)
8
O
16
.
nH
2
O. Fu he chemical de ini ion o hollandi e phases will
be pu sued in Sec ion 4.3.
Fig. 6 displays an expe imen al Raman spec um o p isma ic, acic-
ula c ys als occu ing as geodes in sample CO-79, op ically iden i ied as
chalcophani e, ZnMn
3
O
7
⋅3H
2
O, ocused in he 250–750 cm
−1
spec al
ange. The ob ained se o bands a 299, 378, 485, 512, 570, and 672
cm
−1
a e consis en wi h e e ence in o ma ion ega ding such phase
(Pos e al., 2021). The mode a 697 cm
−1
co esponds o a bulge o-
wa ds highe equencies in he peak a 672 cm
−1
, and could be he
esul o an adso bed impu i y. Simila ly o hollandi e g oup mine als,
Pos e al. (2021) ound a co ela ion be ween he Raman equencies o
ce ain MnO
6
ib a ional modes and he Mn
3+
/Mn
o al
a io o phyllo-
mangana es. I nea ly all Mn is e a alen , he highes equency modes
ela ed o in e nal MnO
6
oc ahed al ib a ions should occu a highe
wa enumbe s in compa ison o s uc u es wi h some p e alence o
Mn
3+
in hei composi ion. The co ela ion be ween he wo pa ame e s,
de ined by Pos e al. (2021), is gi en by:
Mn3+/Mn o al = − 0.012034 max +8.0561 (2)
In he p esen case, he calcula ed alue (Mn
3+
/Mn
o al
~ −0.03) is
close o ze o, poin ing owa ds ei he chalcophani e o anciei e,
Fig. 4. Rep esen a i e Raman spec a o a) amsdelli e and a hollandi e-g oup phase, and b) mangani e, bo h occu ing in sample CO-79. The inse mic og aphs
depic he poin s o spec a acquisi ion. ** Possible e ihyd i e, *Peaks asc ibed o he ib a ional modes o a hollandi e- ype s uc u e.
Fig. 5. Rep esen a i e Raman spec a o a) hollandi e-g oup phase in sample CO-102 wi h es ima ed Mn
3+
/Mn
o al
=0.35, and b) hollandi e-g oup phase occu ing
in sample CO-79 wi h es ima ed Mn
3+
/Mn
o al
=0.16. The inse mic og aphs depic he poin s o spec a acquisi ion. * Non-asc ibed bands.
A.J. Pin o e al.

Chemical Geology 630 (2023) 121488
6
CaMn
3
O
7
⋅3H
2
O. Ne e heless, he occu ence o well-de ined spec al
bands, uncha ac e is ic o anciei e (Pos e al., 2021), seem o con i m
he iden i y o chalcophani e. Chemical analysis included in he
ollowing sec ion will con ibu e in se ling his ma e .
4.3. Chemical cha ac e iza ion Fe and Mn phases
Table 1 displays ep esen a i e analysis o he di e en kinds o
goe hi e encoun e ed in samples CO-102 (1–3) and CO-79 (4 and 5),
wi h a omic ac ions based in wo oxygen a oms pe uni o mula.
Resul s ob ained o goe hi es in sample CO-102 all yield o mulas
close o (Fe
3+
, Al
3+
Mn
4+
, Zn
2+
, Pb
2+
)
Σ=0.8–0.9
O
1+x
OH
1–2x
, whose s oi-
chiome ic de ia ions om an ideal o mula can be asc ibed o adjus -
men s in he O
−2
/OH
−
a io o compensa e he inco po a ion o ca ions
wi h di e en alence. A simila c ys al-chemical ea u e has been
in oked o explain he chemical composi ion o yellow och e by Cla k
and Cu i (1998), la e ela ed by Hanesch (2009) wi h he deg ee o
c ys allini y o goe hi e. Goe hi es o sample CO-79 also e eal such
sligh de ia ion om an ideal s oichiome y, wi h o mula Fe
1.3
OOH.
Goe hi e in sample CO-102 occu s as mino amoun s o massi e
anhed al mine aliza ions (analysis 1) and mo e equen ly as la e
gene a ion ine-g ained agg ega es o abula indi iduals (analyses 2
and 3). Despi e sha ing simila s uc u al o mulas, no iceable a ia ions
exis ega ding he concen a ion o Zn, which in abula goe hi es is
nea ly wo- old as concen a ed as in massi e ones. Tabula goe hi es
occu ing in co onadi e- ich zones (3) ha e lowe Pb concen a ions ha
hose o med in a eas wi h less co onadi e (2). All goe hi e in sample CO-
79 o ms a ine-g ained ma ix o abula c ys als, o which high and low
Zn a ie ies occu (analyses 4 and 5, espec i ely). The o e all compo-
si ions o goe hi es in samples CO-102 and CO-79 e eal highe con en s
o bo h Pb and Zn in he o me , showing app oxima ely he double
concen a ion o Zn ega ding CO-79, which me ely con ains ace
amoun s o Pb.
Table 2 illus a es ep esen a i e analysis o he pe asi e
hollandi e-g oup phase p esen in sample CO-102, whose op ical cha -
ac e is ic and Raman spec al ea u es poin ed owa ds co onadi e.
He e, he highes concen a ed di alen ca ion is Pb
2+
, which u he
con i ms such iden i ica ion, and he e o e he calcula ed a omic ac-
ions a e based on 16 oxygen pe uni o mula. Analyses (1) and (2) a e
e e en o co onadi e in he goe hi e-bea ing ma ix, and spa sely
dissemina ed in ba i e eins, espec i ely. The de e mined o mulas a e
e y simila o bo h ins ances, con o ming o (Pb
2+
, Zn
2+
, Ba
+
, Na
+
,
K
+
)
Σ=1.08–1.11
(Mn
4+
, Mn
3+
Al
3+
, Fe
3+
)
Σ=6.88–7.29
(O, OH)
16
.
nH
2
O. De-
ia ions om he ideal s oichiome y can be ela ed o he eplacemen
o oc ahed al O
2−
o OH
−
, o compensa e he exis ence o bo h mono
and di alen ca ions in he unnel si es (Pos e al., 2020). Finally, only
sligh chemical di e ences exis be ween he wo modes o occu ence,
namely a sligh ly highe con en in Pb and lowe Mn in co onadi e
associa ed wi h Fe oxyhyd oxides.
Table 3 e e s o ep esen a i e chemical analyses o Mn oxides
occu ing in sample CO-79, namely amsdelli e (1), chalcophani e (2),
and c yp omelane (3). Analysis (1) e lec s a hyd a ed amdselli e
composi ion, wi h o mula (Mn
4+
, Fe
3+
, Al
3+
)
Σ=0.82
(O
,
OH)
2
. The esul s
lis ed in analysis (2) a e ela i e o p isma ic c ys als o chalcophani e
occu ing in geodes, he e o e wi h a omic ac ions based in 10 oxygen
pe uni o mula. Acco ding o Pos and Appleman (1988), Mn
2+
may
occu in he in e laye si e o chalcophani e, which in he p esen case,
a e illing he oc ahed al MnO
6
posi ion, yields a o mula (Zn
2+
, Fe
2+
,
Mn
2+
)
Σ=1.12
Mn
3
4+
O
7
.
2.82H
2
O. The occu ence o simila ly peculia
s oichiome ies and hei ela ionships wi h s uc u al de ia ions om
an ideal chalcophani e is discussed in Michailidis e al. (1997).
Fig. 6. Rep esen a i e Raman spec a o chalcophani e occu ing in geodes in
sample CO-79. The inse mic og aphs depic he poin o spec a acquisi ion.
Table 1
Chemical analysis o goe hi es om Se a da Mina deposi : (1)–(3) sample CO-
102 and (4)–(5) sample CO-79. The a omic ac ions we e de e mined acco ding
o 2 oxygen pe uni o mula. *Exp essed as o al i on, **Calcula ed by di e -
ence o weigh pe cen , b.d. =below de ec ion.
(1) (2) (3) (4) (5)
Al
2
O
3
0.3 0.5 0.7 0.1 0.2
Na
2
O 0.2 0.2 0.2 0.1 <0.1
MnO 1.5 2.6 1.1 0.2 0.6
MgO <0.1 <0.1 <0.1 <0.1 <0.1
Fe
2
O
3
O* 79.0 74.1 76.3 79.5 80.4
PbO 1.8 1.3 0.6 <0.1 <0.1
ZnO 1.7 3.2 3.2 1.4 0.7
SO
3
0.6 b.d. 0.3 0.1 0.1
SiO
2
b.d. b.d. b.d. 1.7 1.4
H
2
O** 15.2 18.0 17.6 16.9 16.6
To al 84.8 82.0 82.4 83.1 83.4
Al <0.1 <0.1 <0.1 <0.01 <0,01
Na <0.01 <0.01 <0.1 <0.01 <0.01
Mn <0.1 <0.1 <0.1 <0.01 0.01
Mg <0.001 <0.001 <0.001 <0.001 <0.01
Fe
3+
0.8 0.7 0.8 1.3 1.3
Pb <0.1 <0.01 <0.01 <0.001 <0.001
Zn <0.1 <0.1 <0.01 0.02 0.01
S <0.1 – <0.01 <0.01 <0.01
Si – – – <0.1 <0.1
Table 2
Chemical analysis o co onadi e om Se a da Mina deposi occu ing in
sample CO-102. The a omic ac ions we e de e mined acco ding o 16
oxygen pe uni o mula. *Exp essed as o al i on, **Calcula ed by di e -
ence o weigh pe cen , b.d. =below de ec ion.
(1) (2)
Al
2
O
3
0.7 0.1
BaO 0.2 0.5
K
2
O <0.1 0.1
Na
2
O <0.1 0.5
MnO 53.3 58.6
TiO
2
b.d. –
Fe
2
O
3
* 4.4 0.3
CaO <0.1 –
PbO 26.1 21.6
ZnO 0.3 0.4
H
2
O** 14.8 17.8
To al 85.2 82.3
Al 0.1 <0.1
Ba <0.1 <0.1
K <0.1 <0.1
Na <0.1 0.1
Mn 6.7 6.8
Fe
3+
0.5 <0.1
Ca <0.01 <0.01
Pb 1.0 0.8
Zn <0.1 <0.1
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
7
Analysis (3) is ela i e o he hollandi e-g oup phase ound lining he
inne walls o chalcophani e-bea ing ca i ies, whose o mula based in
16 oxygen e eals a non-s oichiome ic solid, close o he c yp omelane
(i.e. K- ich) endmembe . Such o mula co esponds o (K
+
, Na
+
, Ba
2+
,
Ca
2+
, Mg
2+
, Zn
2+
)
Σ=0.70
(Mn
4+
, Mn
3+
Al
3+
, Fe
3+
)
Σ=7.05
(O, OH)
16
.
nH
2
O.
The inely in e g own cha ac e o mangani e and py olusi e made i
impossible o ob ain eliable analysis o each phase, especially consid-
e ing hei e y simila chemical con en s.
Table 4 includes he de ailed s uc u al o mulas o all analyzed
phases o each sample, alongside wi h he mine al mode o occu ence.
5. Discussion
5.1. Goe hi e dissolu ion and a ia ions in ca ion con en
The ex u es o goe hi e mine aliza ions obse ed in sample CO-102
s ongly sugges he occu ence o wo sepa a e nuclea ion e en s
yielding he o ma ion o Fe-oxyhyd oxide. The ea lies one in ol ed he
o ma ion o massi e, anhed al goe hi e – olume ically less p e alen
in he sample – ollowed by he o ma ion o abula , ine-g ained
goe hi e, su ounding, and eplacing ea lie goe hi e. Sample CO-79
only e eals goe hi e c ys allized in he la e mode o occu ence.
These pa agene ic ela ionships poin owa ds changes in he physical-
chemical en i onmen (i.e. lowe pH, educing condi ions), leading o
he des abiliza ion o ea lie goe hi e and i s dissolu ion, wi h he
consequen elease o i s chemical con en s o he aqueous phase.
Fa o able physical-chemical ci cums ances, o be discussed in Sec ion
5.2, esul ed in he c ys alliza ion o a second-gene a ion goe hi e
alongside Mn oxides. A clea co ela ion exis s be ween he ca ionic
con en s o second-gene a ion goe hi es and he ype o co-c ys alized
Mn oxide. Fo ins ance, in sample CO-102, abundan in co onadi e (a
Pb-bea ing Mn oxide), abula goe hi es exhibi lowe Pb con en s han
hei ea lie - o med massi e coun e pa s. Fig. 7a) and b) display he
a ia ions o Zn and Pb, espec i ely, as a unc ion o Mn in all analyzed
goe hi es o samples CO-102 and CO-79, exp essed as weigh pe cen o
ca ion oxide. Sample CO-79 comp ises exclusi ely second-gene a ion
abula goe hi es, whose composi ions in Zn
2+
and Pb
2+
a e s ikingly
lowe han goe hi es in sample CO-102, ega dless o occu ence mode.
Fu he mo e, a close inspec ion shows ha sample CO-79 is also iche
in Mn oxides, bo h olume ically and in s uc u al a ie y (i.e. laye ed
and unnel-s uc u e Mn oxides). I is possible, hen, o conclude in a o
o a solu ion-media ed concen a ion and ans e o ca ionic con en
om p ima y, massi e goe hi es o a coho o Mn oxides, o which
sample CO-79 ep esen s a mo e ad anced s age, accompanied by he
o ma ion o seconda y goe hi e.
Such p ocess o p og essi e dissolu ion o i on oxide coupled wi h e-
p ecipi a ion o solu e con en s in seconda y Fe
–
Mn o es amoun s o
supe gene en ichmen , a mechanism mi o ed by he highes dispe sion
o Zn and Pb concen a ions in goe hi es occu ing in sample CO-102,
when compa ed o CO-79.
5.2. Mn oxide pa agene ic sequence
The pa agene ic sequence ela ing he o ma ion o a second gene -
a ion o goe hi e and manganese oxides is necessa ily con olled by
edox eac ions aking place be ween aqueous Fe and Mn. An acidic and
low O
2
aqueous solu ion could lead o dissolu ion o p ima y goe hi e,
and he elease o i s chemical con en in o he luid (Michailidis e al.,
1997). Unde such condi ions, he p esence o aqueous Fe
2+
is a o ed. I
he e is also Mn
4+
p esen in he sys em ( o ins ance in he o m o an
oxide), a 25 ◦C and oom p essu e, he elec ochemical exchange
es ablished be ween he wo ions esul s in he oxida ion o i on o Fe
3+
and educ ion o manganese o Mn
3+
, in esponse o he mo e posi i e
s anda d edox po en ial (E
0
) o he Mn
4+
in MnO
2
, acco ding o he
hal -equa ions:
Fe3+(aq)+e−↔ Fe2+(aq),E0=0.77 (3)
Table 3
Chemical analysis o (1) amsdelli e, (2) chalcophani e and (3) c yp omelane
om Se a da Mina deposi occu ing in sample CO-79. The a omic ac ions
we e de e mined acco ding o 2, 10 and 16 oxygen pe uni o mula o analysis
(1), (2) and (3), espec i ely. *Exp essed as o al i on, **Calcula ed by di e -
ence o weigh pe cen , b.d. =below de ec ion.
(1) (2) (3)
Al
2
O
3
0.7 0.2 0.4
BaO 0.3 0.2 0.6
K
2
O 0.3 1.9 3.0
Na
2
O 0.2 0.9 0.6
MnO 71.9 58.5 70.4
TiO
2
<0,1 b.d. –
MgO <0,1 0.2 0.0
Fe
2
O
3
* 1.8 – –
FeO* – 1.2 2.0
CaO <0.1 <0.1 0.2
PbO b.d. b.d. <0.1
ZnO 0.5 12.0 0.8
SO
3
<0.1 <0.1 <0.1
SiO
2
0.2 0.2 0.1
H
2
O** 24.0 24.5 22.0
To al 76.2 75.5 78.0
Al <0.01 <0.1 <0.1
Ba <0.01 <0.1 <0.1
K <0.01 <0.1 0.4
Na <0.01 <0.1 0.1
Mn 0.8 3.4 6.8
Ti <0.001 – –
Mg <0.001 <0.1 <0.001
Fe
3+
<0.001 – –
Fe
2+
– 0.1 0.2
Ca <0.1 <0.1 <0.1
Pb – – <0.01
Zn <0.01 0.6 <0.1
S <0.001 <0.1 <0.01
Si <0.01 <0.1 <0.1
Table 4
Summa y o phase o mulas de e mined om EMP analyses. The ac onym n.s.
e e s o ‘non-s oichiome ic’.
Sample Phase Mode o
occu ence
Fo mula
102
Goe hi e
Massi e,
anhed al
(Fe
3+
0.82
, Al
3+
0.01
, Mn
4+
0.02
, Zn
2+
0.02
,
Pb
2+
0.01
)
Σ=0.88
O
1+x
OH
1–2x
Tabula ,
co onadi e- ich
zone
(Fe
3+
0.70
, Al
3+
0.01
, Mn
4+
0.03
, Zn
2+
0.03
,
Pb
2+
0.005
)
Σ=0.78
O
1+x
OH
1–2x
Tabula ,
co onadi e-
poo zone
(Fe
3+
0.80
, Al
3+
0.01
, Mn
4+
0.01
, Zn
2+
0.03
,
Pb
2+
0.002
)
Σ=0.85
O
1+x
OH
1–2x
Co onadi e
Fe
oxyhyd oxide
ma ix
(Pb
2+
1.04
, Zn
2+
0.03
, Ba
+
0.01
, Na
+
0.01
,
K
+
0.01
)
Σ=1.1
(Mn
o al
6.69
, Al
3+
0.12
, Fe
3+
0.49
)
Σ=7.3
(O, OH)
16
.
nH
2
O
Dissemina ed in
ba i e einle s
(Pb
2+
0.80
, Zn
2+
0.04
, Ba
+
0.03
, Na
+
0.14
,
K
+
0.02
)
Σ=1.03
(Mn
o al
6.82
, Al
3+
0.02
, Fe
3+
0.03
)
Σ=6.87
(O, OH)
16
.
nH
2
O
79
Goe hi e
Tabula , highe
Zn (Fe
3+
1.30
, Zn
2+
0.02
)
Σ=1.32
O
1+x
OH
1–2x
Tabula , lowe
Zn (Fe
3+
1.30
, Zn
2+
0.01
)
Σ=1.31
O
1+x
OH
1–2x
Ramsdelli e Anhed al, d usy (Mn
4+
0.80
, Fe
3+
0.009
, Al
3+
0.006
)
Σ=0.82
(O
,
OH)
2
C yp omelane,
n.s. Anhed al, d usy
(K
+
0.44
, Na
+
0.14
, Ba
2+
0.03
, Ca
2+
0.02
,
Mg
2+
0.006
, Zn
2+
0.06
)
Σ=0.70
(Mn
o al
6.84
,
Al
3+
0.05
, Fe
3+
0.17
)
Σ=7.06
(O,
OH)
16
.
nH
2
O.
Chalcophani e
P isma ic,
geodes in
ca i ies
(Zn
2+
0.6
, Fe
2+
0.1
,
Mn
2+
0.4
)
Σ=1.11
Mn
3
4+
O
7
.
2.82H
2
O
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
8
MnO2(s)+4H+(aq)+e−↔ Mn3+(aq)+2H2O(l),E0=0.95 (4)
whe e all E
0
alues we e aken om Ba d e al. (1985). F om he
obse a ion o bo h hal - eac ions, i becomes ob ious ha oxida ion o
Fe and educ ion o Mn is p omo ed a acidic pH condi ions. While i is
di icul o specula e on he p esence o Mn
2+
in solu ion a such s age,
Luo e al. (2018) demons a ed ha aqueous Mn
2+
does no a ec he
o med i on oxide species bu inc eases he oxida ion a e o Fe
2+
. Since
Mn
3+
is he mos ele an species o he nuclea ion o bo h laye ed and
unnel‑manganese oxides, such species is a he cen e o ou discussion.
In his amewo k, i is possible o pos ula e ha he ex ension o
goe hi e dissolu ion is a majo con olling ac o behind he a io o
Mn
3+/
Mn
4+
in solu ion, which in u n in luences he sa u a ion s a e
wi h espec o di e en ypes o Mn oxides. Fo ins ance, as deduced
om he p esen da a alongside wi h he de e mina ions o Pos e al.
(2020), hollandi e-g oup solid solu ion membe s comp ise manganese
in bo h oxida ion s a es wi h a ying p opo ions, o neu alize ca ionic
con en s o s uc u al unnel si es. In sample CO-79, co esponding o a
highe en ichmen in Mn oxides, mos o he mine alogical con en e-
la es o in e g own acicula goe hi e and mangani e (MnOOH), whe e
all manganese is in 3+oxida ion s a e. Such ex u al ela ionship a ises
om he ollowing eac ion:
MnO2(s)+Fe2+(aq)+2H2O(l)↔ Mn(OH)3(s)+Fe(OH)3(s)+2H2O(l)+2H +(aq)
(5)
Since bo h Fe(OH)
3
and Mn(OH)
3
a e uns able, hey eadily o m
goe hi e and mangani e by dehyd a ion (Be ech in, 1971). A s iking
ea u e om he desc ibed eac ions is he inc ease in acidi y as a by-
p oduc o he p ecipi a ion o Mn(OH)
3
, which will necessa y back-
eed u he dissolu ion o goe hi e, and he o ma ion o mo e manga-
ni e ollowing he acidic educ ion exp essed by hal - eac ion (4). The
occu ence o bo h massi e and acicula mangani e seems o suppo
such mechanism o con inuous mine alogical ans o ma ion. In ac , a
simila p ocess o mobilizing and e-p ecipi a ing as amoun s o bo h
manganese and i on was p oposed by P acejus e al. (1988), in i s
seminal wo k abou he Mn sedimen a y o es o G oo e Eyland . I is
wo h no ing ha lowe alence Mn mine als a e passi e unde he
educing condi ions and become concen a ed as highe alence oxides
a e leached away (P acejus e al., 1988). The absence o mangani e in
sample CO-102, whe e he p edominan Mn-phase is co onadi e, may be
explained by a concen a ion o aqueous Mn
3+
insu icien o each
sa u a ion wi h espec o mangani e. Such also equa es o he
occu ence o less educ i e condi ions leading o he o ma ion o
co onadi e (Mn
3+
/Mn
4+
=0.35) in sample CO-102.
In sample CO-79, he occu ence o amsdelli e (MnO
2
) lining he
walls o ac u es and ca i ies sugges s he p ecipi a ion o Mn oxide
unde oxida i e condi ions, a e he o ma ion o mangani e. Fig. 8
displays a mic og aph o a ca i y in sample CO-79, connec ed o a
complex ne wo k o ac u es, which enabled he eac i e ci cula ion o
luids. The shown chemical p o ile ac oss he ca i y-bea ing ein,
ega ding con en s in Mn, Ba, Zn and K, oge he wi h he acqui ed
Raman spec a, enabled iden i ying he se e al Mn oxide phases p esen
in a sequence o laye s. The d usy g ow hs om ac u e walls clea ly
indica es ha he c ys alliza ion sequence p og essed inwa ds, owa ds
he ca i y, ollowing he o de amsdelli e, c yp omelane, and chalco-
phani e, his las in geodes. Focusing on he oxida ion s a e o manga-
nese in he s uc u e o each phase, he ini ial condi ions clea ly
p og essed om oxida i e, p omo ing he p ecipi a ion o Mn
4+
O
2
, o
mo e educing condi ions, yielding he p ecipi a ion o c yp omelane,
whe e Mn
3+/
Mn
4+
co esponds o app oxima ely 0.16. Fu he mo e,
aqueous ca ionic con en supplied he necessa y species o unnel
s uc u al si es. G ow h o chalcophani e as geodes o p isma ic c ys als
in ca i ies indica es nuclea ion and g ow h om an isola ed, s a ic luid.
The ea lie p ecipi a ion o Mn in o he phases and he isola ion o
he aqueous phase om he su ounding media, a o ed he c ys alli-
za ion o a s uc u ally laye ed manganese oxide wi h lowe a ios o Mn
wi h espec o o he ca ions in unnel o in e laye s uc u al si es (7:1
in hollandi e g oup mine als, 3:1 in laye ed Mn oxides). Howe e , he
ex u e seems o sugges a pa adoxical combina ion o an acidic luid
wi h low O
2
coexis ing wi h a manganese oxide phase whe e all oc a-
hed al Mn is in +4 oxida ion s a e. I is wo h no ing ha chalcophani e
is a Zn
2+
- ich mine al and Mai h eepala and Doong (2004) ound ha
such ca ion displayed an inhibi o y e ec o e he educ i e eac i i y o
Fe
2+
- ea ed goe hi e owa ds Mn. Fu he mo e, he lack o a con inuous
supply o aqueous elec on dono s in a s a ic, isola ed luid may ha e
a o ed he nuclea ion o a phase whe e all manganese in oc ahed al
si es is in 4+oxida ion s a e. In he p esen wo k, howe e , we ound
ha a small excess o Mn may be p esen in in e laye si es as Mn
2+
.
Fig. 9 depic s a sequen ial schema ic ep esen a ion o he eac i e
pa hway leading o he pa agene ic associa ions p ese ed in bo h
samples CO-102 and 79.
6. Conclusions
The p esen esea ch in ended o apply Raman spec oscopy and
Fig. 7. a) ZnO and, b) PbO s. MnO con en s in weigh pe cen (%) o he analyzed goe hi es in samples CO-102 and CO-79. The da a ega ding sample CO-79 e e s
exclusi ely o acicula goe hi es.
A.J. Pin o e al.
Chemical Geology 630 (2023) 121488
9
EMPA analysis, o bo h he cha ac e iza ion and ex u al in es iga ion o
co-gene ic, na u ally occu ing Mn oxides. F om ou esea ch, ocusing
on samples om wo di e en sec ions o he en iched zone o Se a da
Mina Manganese Deposi , Po ugal, i is possible o no only iden i y he
se e al coexis ing Fe and Mn phases, bu also un a el he eac i e
pa hways leading o supe gene en ichmen mine aliza ions. Namely,
Fig. 8. Composi ional p o ile (w % MnO, ZnO, BaO and K
2
O) ac oss a ca i y-bea ing Mn-oxide ein in sample CO-79. Rmd =Ramsdelli e, Cml =C yp omelane, Cph
=Chalcophani e, Hem =Hema i e, G h =Goe hi e.
Fig. 9. De elopmen o he pa agene ic associa ions p ese ed in sample a) CO-102, and b) CO-79. The ull explana ion o he mine aliza ion sequence is included in
he ex o Sec ion 5.2. G h =Goe hi e, Mnn =Mangani e, Rmd =Ramsdelli e, Cph =Chalcophani e.
A.J. Pin o e al.