The evolution of sulfide wastes promotes acid mine drainage and
phenomena of supergenic neoformation. These contribute to a
secondary paragenesis, often dominated by salt efflorescences.
These can be used as mineralogical indicators of reactivity
conditions and of AMD potential. The present study shows the
salt efflorescences that develop in the Spanish sector of the
Iberian Pyrite Belt, as a result of the strong acid mine drainage
observed in this region. The obtained results showed dominance
of metallic sulfates. Depending on the proximity to the sulfide
sources, there are different types of assemblages. Iron and
cooper minerals dominate inside the mining areas, whereas
magnesium sulfates occur more abundantly in the receiving river
networkFinancial support was provided by the Andalusian Autonomous
Government Excellence Project, code P06-RNM-02167. This work
was also co-funded by the European Union through the European
Regional Development Fund, based on COMPETE 2020 (Programa
Operacional da Competitividade e Internacionalização), project
ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-
007690 and national funds provided by Fundação para a Ciência
e Tecnologia.info:eu-repo/semantics/publishedVersio

de la Torre, Maria Luísa

Grande, Jose Antonio

Valente, Teresa Maria Fernandes

Universidade do Minho: RepositoriUM

SESIÓN 3.MÉTODOS MATEMÁTICOSY ANALÍTICOSXII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICAInvestigar los recursos cuidando el ambienteLinares (Jaén), 26 a 28 septiembre 201772SALT EFFLORESCENCES IN THE IBERIAN PYRITE BELT:OCCURRENCE AND DISTRIBUTIONValente, Teresaa, Grande, Jose Antoniob, de la Torre, Maria Luísaca Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, Professor, email: teresav@dct.uminho.pt;b University of Huelva & Escuela Técnica Superior de Ingeniería, Spain, Professor, email: grangil@uhu.es;c University of Huelva & Escuela Técnica Superior de Ingeniería, Spain, Professor, email: mltorre@uhu.esABSTRACTThe evolution of sulfide wastes promotes acid mine drainage andphenomena of supergenic neoformation. These contribute to asecondary paragenesis, often dominated by salt efflorescences.These can be used as mineralogical indicators of reactivityconditions and of AMD potential. The present study shows thesalt efflorescences that develop in the Spanish sector of theIberian Pyrite Belt, as a result of the strong acid mine drainageobserved in this region. The obtained results showed dominanceof metallic sulfates. Depending on the proximity to the sulfidesources, there are different types of assemblages. Iron andcooper minerals dominate inside the mining areas, whereasmagnesium sulfates occur more abundantly in the receiving rivernetwork. Keywords: Acid mine drainage, AMD-precipitates, Sulfates,Iberian Pyrite Belt, Spain1. INTRODUCTIONThe overall process of acid mine drainage production is accom-panied by the development of newly-formed solid phases thatresult from processes such as evaporation, oxidation, hydrolysisand neutralization (Hammarstrom et al., 2005; Jerz and Rimstidt,2003). Thus, these phases are generically called AMD-precipita-tes. They are mainly represented by efflorescent salts and byochre products composed of iron oxyhydroxides and iron oxyhy-droxysulfates. The current study presents data about the AMD-precipitates that compose typical mineralogical assemblages ofthe Spanish sector of the Iberian Pyrite Belt (IPB).The study comprises the entire fluvial network of this metalloge-netic province, including the main river basins that are receivingAMD discharges (Guadiana–Chanza, Tinto, Odiel and Guadiamar(Figure 1). The Iberian Pyrite Belt assumes as a paradigmatic region for suchtype of study, taken in consideration features, such as antiquity(more than 5000 years of metals exploitation), and environ-mental contamination related to the mining legacy. The region isknown as one of the largest accumulations of pyritic wastes inthe World (e.g., Davis et al., 2000; Sanchéz-España et al., 2005)with an estimation of AMD- affected land of about 4,847 ha.Taking into account this figure and combining it with the annualaverage precipitation it gives about 31,504,000 m3/year of dis-charging water affected by the presence of sulfides (Grande etal., 2013). The Figure 2 illustrates the typical aspect of the con-taminated rivers in the IPB, while table 1 presents average dataof Tinto River, which is well-known by its AMD contamination.The region has a Mediterranean climate, which can be classified assemi-arid, due to low precipitation rates. Annual precipitation isabout 630 mm/year, being mostly concentrated in the wet sea-son from October to May. Monthly precipitation ranges from 3 to121 mm, corresponding to June and December, respectively.Average annual temperature is 17.1ºC, January being the coldestmonth with a mean of 9.8ºC, while in the summer, July and Augusthave the highest temperatures (mean 25.7 ºC) (Instituto Nacionalde Meteorología; unpublished data). It should be noted that sam-pling for this study was performed in July, with temperature and re-lative humidity readings consistent with the typical mean annualvalues (temperature up 25ºC and relative humidity around 50%).Taken into account the mining, environmental and climate con-texts described below, AMD-precipitates assume critical rele-vance as indicators of the reactivity of the AMD solutions and ofthe contamination magnitude in the IPB. Therefore, the main ob-jectives of the present study are: i) to present an inventory ofAMD-precipitates in the IPB; ii) to know local temperature andhumidity conditions that control stability of secondary phases; iii)to present the main characteristics of the efflorescent minerals,such as chemical composition, morphology, typical assemblages,and iv) to evaluate their role controlling retention/mobilizationcycles of acidity, sulfate and metal(oids) in the river network.2. METHODOLOGYThe sampling campaign was performed under strong evapora-tion and low flow hydrological conditions (July 2015). The sam-pling network comprised two distinctive environments. Onerefers to waste-dumps, seepages and leachates inside the mi-ning complexes, representing the main sources of AMD. Theother environment corresponds to the watercourses, which re-present the global receiving system. For this last, eight samplingareas were established, in order to represent the affected sub-ba-sins defined in the IPB by Perez-Ostalé (2014). At each samplingSESIÓN 3. MÉTODOS MATEMÁTICOS Y ANALÍTICOSSalt efflorescences in the Iberian Pyrite Belt: occurrence and distributionwww.congresodegeoquimica.org 73Figure 1 – Location map of the Iberian Pyrite Belt, including the main watersheds (Grande et al., 2013).Figure 2 – Deposition of ochre products and filamentous algae that give typical aspects to the AMD-affected river network. Images fromTinto River (left) and Odiel River (right).Sampling station pH CE (µS/cm) SO4 (mg/l) As (mg/l) Cd(mg/l) Cu(mg/l) Fe (mg/l) Zn (mg/l) Mn (mg/l)Naya 2.50 12,760 8,257 0.640 2.00 329.8 2,353 494.6 141.6Niebla 2.53 2,239 371.0 0.042 0.094 23.84 316.4 20.26 10.36TABLE 1 – AVERAGE WATER PROPERTIES OF THE TINTO RIVER NEAR THE MINE (UPSTREAM-NAYA) AND DOWNSTREAM -NIEBLA).DATA FROM DE LA TORRE ET AL. (2011)area, the AMD-precipitates were collected in order to representthe field variability, given rise to approximately 200 complexsamples, mainly composed by efflorescent salts. Inside each sam-pling area there were a variable number of samples, which weremeant to cover the diversity observed in the field on the basis ofmacroscopic properties. Occurrence modes, color, and texturewere used to define this diversity.Efflorescent salts and crusts were examined for morphology, pho-tographed and sorted by binocular microscopy. Then, samples werelightly ground and analyzed by X-ray powder diffraction (XRD) witha Philips X’pert Pro-MPD difractometer, using Cu Ka radiation.Morphological and compositional features were analyzed byscanning electron microscopy (on gold or platinum-coated sam-ples) with a LEICA S360 microscope, combined with an energydispersive system (SEM–EDS, 15 keV). 3. RESULTS AND DISCUSSIONIn the present work, the inventory of AMD-precipitates is mainlyfocused on the minerals that occur as efflorescences, resultingfrom evaporative processes in the semi-arid condition of the te-rritory under study.Figure 3 are field images, showing occurrence modes of salt ef-florescences from different mines in the IPB.Most of the identified minerals are sulfates or oxyhydroxisulfates.Sulfates usually occur as efflorescences of varied colors (white orgrayish, yellowish, green, orange, and blue) and habit (rosaceous,botryoidal, or very fine powders).The inventory of AMD-precipitates put in evidence the distributionof the identified phases, allowing differentiating the samplingconditions:- One relates to the mineralogical phases occurring in the rivernetwork, corresponding to samples taken in each of the eightbasins. Here, in the river network, some of the most abun-XII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICAInvestigar los recursos cuidando el ambienteLinares (Jaén), 26 a 28 septiembre 201774Figure 3 - Field images of typical sulfate efflorescences. a) yellow-reddishcrustified efflorescences of copiapite and coquimbite from Tharsis mine; b)globular green efflorescences of melanterite from Riotinto mine; c) Bluepowder efflorescences of chalcantite from Herrerias mine; d)  white glo-bular cotton-like bunches of epsomite from San Telmo mine.dant minerals are: Epsomite, gypsum, hexahydrite, alpersite,pickeringite, alunogen, tamarugite and jarosite. - A second one comprises the AMD-precipitates occurring in re-presentative abandoned mining complexes of the IberianPyrite Belt. Among the dominant minerals are: melanterite,chalcantite rozenite, gypsum, epsomite, hexahydrite, copia-pite, magnesiocopiapite, aluminocopiapite, ferricopiapite, pic-keringite, halotrichite, apjohnite (?), rhomboclase,szomolnokite, coquimbite, paracoquimbite, starkeyite, butle-rite, fibroferrite, jarosite, and schwertmannite.To exemplify the properties of the salt efflorescences, Figure 4shows the morphologies of one of the most typical assemblagesfound in the river systems, which is dominated by magnesiumand aluminum sulfates as demonstrated by the respective XRD.Although XRD allowed identifying only epsomite and tamarugite,the SEM analysis showed the growth of acicular aggregates ofpickeringite over the magnesium sulfate.The other scenario, correspondent to the efflorescences that occurnear the sulfide sources, is exemplified by the SEM results of twominerals occurring in the the Riotinto Mines: butlerite and fibro-ferrite (Figure 5).Figure 4 – SEM-ES image of a sample collected in the Meca River(a) and respective XRD (b). The mineralogical assemblage is do-minated by epsomite (Eps; MgSO4 7H2O; mass aggregates), ac-companied by tamarugite (Tam; NaAl(SO4)2 6H2O; plate habit)and pickeringite (Pick; MgAl2(SO4)4 22H2O) acicular aggregates).SESIÓN 3. MÉTODOS MATEMÁTICOS Y ANALÍTICOSSalt efflorescences in the Iberian Pyrite Belt: occurrence and distributionwww.congresodegeoquimica.orgThe above results show that in distal conditions (in the receivingwatersheds), the mineralogical assemblages are dominated bymagnesium and aluminum sulfates. Usually jarosite (and or go-ethite) are the only iron minerals. Meanwhile, near the sulfidesources, in the mining complexes, there is higher mineralogicaldiversity. In such proximal conditions, in addition to magnesiumsulfates, iron and cooper sulfates assemblages are very common.Often, the iron sulfates put in evidence specific paragenetic rela-tionships, namely controlled by hydration/dehydration cycles. Forexample, the sequence melanterite (FeSO4 7H2O – rozenite(FeSO4 4H2O) – szomolnokite (FeSO4 H2O) was observed in dis-tinctive environments, with melanterite always near the water,then, for the most humid conditions, while rozenite and szomol-nokite appear usually in more dry conditions, forming associationwith other iron minerals.4. CONCLUSIONSThe present paper presents the salt efflorescences that occur inthe entire Spanish sector of the Iberian Pyrite Belt. The obtainedinventory stressed the distribution of sulfate efflorescences. Inproximal conditions, iron and cooper sulfates are very common.In more distal conditions, the depletion of iron is accompanied bythe dominance of magnesium and aluminum sulfates. Here, ironoccurs mainly in the oxyhydroxisulfates and/or oxyhydroxides.However the aluminum sulfate pickeringite is ubiquitous, occu-rring generally as a late phase. Paragenetic relationships are con-trolled by hydration/dehydration and oxidation cycles. Differences in ore paragenesis appear reflected in the secondarysulfate assemblages. Hence, paradigmatic mines, such as riotintomines, shows great abundance of iron sulfates, with the threevalence states of iron: such as melanterite (Fe(II)) and copiapite(Fe(II,III)) and coquimbite (Fe(III)). Moreover, copper sulfates,mainly alpersite and chalcantite are highly present in the miningenvironments, like in San Telmo and Herrerías mines. Copiapiteis ubiquitous near the sulfide wastes, being detected in all thestudied mining sites.5. ACKNOWLEDGEMENTFinancial support was provided by the Andalusian AutonomousGovernment Excellence Project, code P06-RNM-02167. This workwas also co-funded by the European Union through the EuropeanRegional Development Fund, based on COMPETE 2020 (ProgramaOperacional da Competitividade e Internacionalização), projectICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by Fundação para a Ciênciae Tecnologia. 6. REFERENCES- Davis Jr., R.A. Welty A.T., Borrego J., Morales J.A., Pendon J.G.,Ryan J.G.. Rio Tinto estuary (Spain): 5000 years of pollution(2000). Environ. Geol. 39: 1107-1116.- De la Torre, M.L., Grande, J.A., Graiño, J., Gómez, T., Cerón, J.C..Characterization of AMD pollution in the River Tinto (SWSpain). Geochemical comparison between generating sourceand receiving environment (2011). Water Air Soil Pollut:216:3–19.- Grande J.A., Valente T., de la Torre M.L., Santisteban M., CerónJ.C., Pérez-Ostalé E.. Characterization of acid mine drainagesources in the Iberian Pyrite Belt: base methodology for quan-tifying affected areas and for environmental management(2013). Environ Earth Sci: 71:2729–2738.- Hammarstrom, J.M., Seal II, R.R., Meier, A.L., Kornfeld, J.M.(2005). Secondary sulfate minerals associated with acid drai-nage in the eastern US: recycling of metals and acidity in sur-ficial environments. Chem. Geol. 215: 407–431.- Jerz, J.K., Rimstidt, J.D. (2003). Efflorescent iron sulfate mine-rals: paragenesis, relative stability, and environmental impact.Am. Mineral. 88: 1919–1932.- Pérez-Ostalé, E. (2014). Caracterización ambiental de estruc-turas mineras en la Faja Pirítica Ibérica como soporte meto-dológico de gestión territorial. PhD. Thesis, Universidad deHuelva. - Sanchéz-España, J., López Pamo, E., Santofimia, E., Aduvire, O.,Reyes, J., Barettino, D. (2005). Acid mine drainage in theIberian Pyrite Belt (Odiel river watershed, Huelva, SW Spain):geochemistry, mineralogy and environmental implications.Appl. Geochem. 20, 1320–1356.- Valente T., Grande J.A., de la Torre M.L., Santisteban M., CerónJ.C.. (2013). Mineralogy and environmental relevance of AMD-precipitates from the Tharsis mines, Iberian Pyrite Belt (SW,Spain). Appl Geochem 39: 11-25. 75Figure 5 – Typical morphology and chemical composition of fibroferrite(above) and butlerite (below) (SEM-EDS results).

Salt efflorescences in the iberian pyrite belt: occurrence and distribution

http://repositorium.sdum.uminho.pt/bitstream/1822/49204/1/Valente.pdf

Salt efflorescences in the iberian pyrite belt: occurrence and distribution

Abstract

Similar works

Full text

Available Versions

Universidade do Minho: RepositoriUM