Electrochemical reactions driving Mn-enrichment in Fe-Mn supergene ores: a mineralogical perspective

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.