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Science of The Total Environment 04/2013; 454-455C:245-249. · 3.29 Impact Factor
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ABSTRACT: This paper presents Cu–Zn–As geochemical data from stream sediment surveys carried out in the three main watersheds of the
Coquimbo Region of Chile. This mountainous semiarid realm occupies an area of 40,656km2 between 29° and 32°S. Given that the area has a long historical record of mining activities, important environmental disturbances
were expected. However, despite the detection of three major geochemical anomalies for Cu, Zn, or As, only one can be unmistakably
linked to the development of mining–metal recovery procedures (Andacollo–Panulcillo). An investigation of the other two anomalies
(Elqui and Hurtado) reveals three major causes that fully or partially account for them: (1) the type of ore deposit and associated
hydrothermal alteration; (2) the regional structural setting (intensity of fracturing); and (3) climate–landscape. Cu–Au–As
epithermal deposits/prospects along the so-called El Indio belt are here regarded as the sources of both the Elqui and Hurtado
anomalies. The strong advanced argillic alteration present in some of the epithermal deposits/prospects of the El Indio belt
may have induced the loss of the buffering capacity of rocks, and therefore favoured metal dispersion during later oxidation–leaching
of sulphides. This applies to the Elqui and Hurtado anomalies. Conversely, given that the potassic, propylitic and phyllic
alterations do not affect the buffering capacity of rocks, only minor metal dispersion is observed in relation to the Los
Pelambres porphyry copper deposit. Besides, the epithermal belt is located within a highly fractured Andean domain (3,000–4,000m
of altitude), which may have conditioned the fast unroofing of ore deposits, contributed to enhanced circulation of meteoric
waters, and eventually, to strong oxidation, and leaching of metals. Metal dispersion is aggravated during rainy years in
response to strong El Niño episodes.
Environmental Geology 04/2012; 53(2):283-294. · 1.13 Impact Factor
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Journal of Geochemical Exploration 01/2011; · 1.44 Impact Factor
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ABSTRACT: The MERSADE Project (LIFE--European Union) tested the Las Cuevas decommissioned mining complex (Almadén mercury district, Spain) as a potential site for the installation of a future European prototype safe deposit of surplus mercury from industrial activities. We here present the results of a baseline study on the distribution of mercury in soils and air in the Las Cuevas complex and surrounding areas, and show the results of a plume contamination model using the ISC-AERMOD software. Despite restoration works carried out in 2004, the Las Cuevas complex can still be regarded as hotspot of mercury contamination, with large anomalies above 800 microg g(-1) Hg (soils) and 300 ng Hg m(-3) (air). In the case of soils, high, and persistent concentrations above 26 microg g(-1) Hg extend well beyond the complex perimeter for more than 2 km. These concentrations are about three orders of magnitude above world baselines. The same applies to mercury in air, with high concentrations above 300 ng Hg m(-3) inside the perimeter, which nonetheless fade away in a few hundred meters. Air contamination modelling (Hg gas) predicts formation of a NW-SE oriented narrow plume extending for a few hundred meters from the complex perimeter. The geographic isolation of Las Cuevas and its mining past make the complex an ideal site for mercury stocking. The only potential environmental hazards are the raising of livestock only a few hundred meters away from the complex and flash floods.
Science of The Total Environment 09/2010; 408(20):4901-5. · 3.29 Impact Factor
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ABSTRACT: Almadenejos is a small town located some 14 km to the East of
Almadén, and has been the site of mining and metallurgical
activity, linked to the world-class Almadén mercury mining
district: the now-abandoned cinnabar (HgS) mines of Vieja
Concepción (active in 1699-1800), Nueva Concepción (active
in 1794-1861, 1943-1945 and 1960-1967) and El Entredicho (active in
Arabs times, and 1981-1997) are located on its neighbourhood, as well as
the Almadenejos decommissioned metallurgical precinct (active
1794-1861),what makes the area one of the most contaminated ones of the
district. We present here results and maps of a survey including soils
sampling with mercury analysis and other pedological parameters, as well
as determinations of mercury inmission in the atmosphere, using a common
sampling grid. Analysis of soils samples has been carried out using a
LUMEX RA-915+ mercury analyser, with RA-91 pyrolysis chamber, and air
determinations, using the same RA-915+ device in air analysis mode. The
maps have been obtained by means of SURFER 8 software, as well as by
ArcGIS software, and puts forward contaminated areas centred inside the
metallurgical precinct, with up to 1.5% Hg in soils and up to 20.000 ng
Hg•m-3 in the atmosphere.
03/2009; 11:10044.
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Science of The Total Environment 03/2009; 407(11):3605-8. · 3.29 Impact Factor
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ABSTRACT: We present data from a study of mercury concentrations in air and plant specimens from the MAF Herbarium in Madrid (Spain). Hg (gas) emissions from old plant collections treated with mercuric chloride (HgCl(2)) in herbaria may pose a health risk for staff working in installations of this type. This is an issue not yet properly addressed. Plants that underwent insecticide treatment with HgCl(2) at the MAF Herbarium until the mid 1970s have persistent high concentrations of Hg in the range 1093-11,967 microg g(-1), whereas untreated specimens are in the range of 1.2-4.3 microg g(-1). The first group induces high concentrations of Hg (gas) in the main herbarium room, with seasonal variations of 404-727 ng m(-3) (late winter) and 748-7797 ng m(-3) (early summer) (baseline for Hg: 8 ng m(-3)). A test survey at another herbarium in Madrid showed even higher concentrations of Hg (gas) above 40,000 ng m(-3). The World Health Organization guidelines for chronic exposure to Hg (gas) are estimated at a maximum of 1000 ng m(-3). While staff was aware of the existence of HgCl(2) treated plants (the plant specimen sheets are labelled as 'poisoned'), they had no knowledge of the presence of high Hg (gas) concentrations in the buildings, a situation that may be relatively common in herbaria.
Science of The Total Environment 12/2007; 387(1-3):346-52. · 3.29 Impact Factor
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ABSTRACT: The Elqui watershed (northern Chile) constitutes a highly contaminated river system, with arsenic exceeding by up to three orders of magnitude the average for river waters. There are three main reasons that explain this contamination: (1) the regional geology and hydrothermal (mineralizing) processes that developed in this realm during Miocene time; (2) the later unroofing-erosion-oxidation-leaching of As-Cu rich sulfide ores, a process that have been taking place for at least 10,000 years; and last but not least (3) mining activities at the high-altitude (>4000 m above sea level) Au-Cu-As El Indio mine, from the late 1970s onwards. The El Indio mineral deposit hosted large veins of massive sulfides, including the important presence of enargite (Cu(3)AsS(4)). The continuous natural erosion of these veins and their host rocks (also rich in As and Cu) during Holocene time, led to important and widespread metal dispersion along the river system. During the studied pre mining period (1975-1977), the high altitude river Toro waters already showed very large As concentrations (0.36-0.52 mg l(-1)). The initiation of full scale mining at El Indio (1980 onwards) led to an increase of these values, reaching a concentration of 1.51 mg l(-1) As in 1995. During the same year other rivers of the watershed reached peak As concentrations of 0.33 (Turbio) and 0.11 mg l(-1) (Elqui). These figures largely exceed the USEPA regulations for drinking water (0.01 mg l(-1) As), and about 10% of the total As data from the river Elqui (and 70% from the river Turbio) are above the maximum level allowed by the Chilean law for irrigation water (0.1 mg l(-1) As).
Environmental Geochemistry and Health 10/2006; 28(5):431-43. · 1.62 Impact Factor
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ABSTRACT: We present data from an early reconnaissance survey (stream sediments, soil, and water Hg chemistry; plants and water crustaceans Hg intake) of the Almadén district (central Spain), that was carried out to establish the potential environmental hazards derived from the anomalous mercury concentrations measured in this realm. The Almadén mercury district (∼300 km2) can be regarded as the largest geochemical anomaly of mercury on Earth. The district includes a series of mercury mineral deposits, having in common a simple mineralogy (dominant cinnabar: HgS, and minor pyrite: FeS2). The ore deposits have been mined for more than 2000 years, and the main mine of the district (Almadén), has been active from Roman times to present day with almost no interruptions. The mercury distribution in soils of the district reveals the existence of high, and extremely high mercury values (up to 8889 μg g− 1), whereas concentrations in stream sediments and waters reach exceptional values of up to 16,000 μg g− 1 and 11,200 ng l− 1 respectively. On the other hand, very high concentrations of methylmercury (MeHg) have been detected in calcines (up to 3100 ng g− 1), sediments (0.32–82 ng g− 1), and waters (0.040–30 ng l− 1). Mercury gets incorporated to edible river crustaceans and plants. The red swamp crayfish Procambarus clarkii, has Hg concentrations of up to 9060 ng g− 1 (muscle) and 26,150 ng g− 1 (hepatopancreas). Regarding plants, the local wild asparagus (Asparagus acutifolius) yields values of up to 298 μg g− 1 Hg. Mercury also escapes to the atmosphere, and mineral deposits, together with metallurgical activities, generate strong anomalies of atmospheric Hg. The most important concentrations relate to the emissions from the Almadén metallurgical roaster, in the order of 14,000 ng Hg m− 3. Additionally, large open pit operations also contribute to the district atmospheric pool of mercury, with high concentrations above 1000 ng Hg m− 3. Thus, no system (rocks, soils, sediments, waters, atmosphere, biota) in the Almadén district is free from strong Hg contamination.
Science of The Total Environment 04/2006; · 3.29 Impact Factor
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V Congreso Ibérico de Geoquímica y IX Congreso de Geoquímica de España, Soria (Esapña); 01/2005
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VII Congreso Nacional del Medio Ambiente (CONAMA), Madrid (España); 01/2004
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ABSTRACT: Almost no environmental data on mercury distribution and speciation in soils have been published so far for the Almadén mining district (central Spain), despite its huge size and historic importance. The mercury distribution in soils of the district reveals the existence of high and extremely high mercury values (up to ∼9000 ppm Hg). The Hg-thermodesorption curves for soils from a decommissioned metallurgical precinct (Almadenejos) and a phytoremediation site show that mercury occurs in the forms of cinnabar and as mercury bound to organic matter. The TEM-EDX study of the highly contaminated anthrosols from Almadenejos (samples with Hg >5000 ppm) shows the existence of cinnabar particles adsorbed to the surface of chlorite grains. Given the generally pyrite-poor character of the ores, and the presence of carbonates in the host rocks, cinnabar solubilization is limited, which in turn mitigates environmental hazards in the district. The only by-product of cinnabar leaching in the mineral dumps is schuetteite (Hg3SO4O2). Preliminary results on local plants (Asparagus acutifolius, Dittrichia graveolens, Marrubium vulgare) show that mercury gets incorporated to roots, stems and leaves, with values of up to about 300 ppm Hg.
Journal of Geochemical Exploration 01/2003; · 1.44 Impact Factor
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Applied Earth Science IMM Transactions section B 07/2002; 111(2):119-122.
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ABSTRACT: The Hercynian mercury mineralization of Las Cuevas is hosted by a highly folded and sheared sequence of basalts, intrusive
breccias, slates, psamitic rocks and quartzites. The mineral paragenesis is simple and consists of cinnabar, native mercury
and pyrite. Hydrothermal alteration can be divided into `proximal' and `distal' with respect to the mineralized bodies. The
proximal alteration (≤1.3 m wide) consists of quartz-pyrophyllite-kaolinite, quartz-pyrophyllite-(kaolinite)-(illite), and
quartz-illite-(pyrophyllite)-(kaolinite). The distal alteration (∼100 m wide) consists of (quartz)-illite-chlorite-(pyrophyllite),
or rectorite-(chlorite). These assemblages overprint an earlier, regional alteration consisting of quartz-chlorite-albite-carbonates
(±ankerite, ±siderite, ±magnesite, ±calcite). The mercury deposit of Las Cuevas can be regarded as an unusual combination
of mercury deposition and advanced argillic alteration within a relatively deep environment (≥1.8 km).
Mineralium Deposita 12/1998; 34(2):211-214. · 1.68 Impact Factor
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ABSTRACT: The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper"Abs1"> The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper
deposits of Lower Cretaceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic deposits of Lower Cretaceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic
units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese
mineralization (Mn1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the mineralization (Mn1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the
second one (Mn2) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting second one (Mn2) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting
during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros
Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag) Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag)
and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar
in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bornite, with variable amounts in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bornite, with variable amounts
of galena, tetrahedrite (vein-related), chalcocite, sphalerite, pyrite, hematite, digenite and covellite. Alteration processesnd covellite. Alteration processes
at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of
Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native
silver, polybasite, cerargyrite and pyrargyrite-proustite; associated alteration includes strong chloritization of the country silver, polybasite, cerargyrite and pyrargyrite-proustite; associated alteration includes strong chloritization of the country
rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between
120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with 120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with
salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result
of the complex interplay of two different processes: boiling and fluid mixing; the former is considered to control the major of the complex interplay of two different processes: boiling and fluid mixing; the former is considered to control the major
mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization
(manto-type stage) developed in response to widespread hydrothermal activity (geothermal field-type) involving basinal brines.ctivity (geothermal field-type) involving basinal brines.
Mineralium Deposita 09/1998; 33(6):547-559. · 1.68 Impact Factor
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ABSTRACT: The Central Iberian Zone of the Hesperian Massif hosts a series of late Hercynian veintype Sb deposits. One of them is the Mari Rosa mineralization, hosted by metagreywackes and slates belonging to the so-called Schist-Greywacke Complex (Upper Precambrian). The mineralization is characterized by a complex paragenesis comprising arsenopyrite-(pyrite), stibnite-gold and pyrite-pyrrhotite-galena-sphalerite-chalcopyrite-tetrahedrite-boulangeritestibnite. Of these only the second episode was of importance and gave rise to the main mineralized bodies of the deposito Two types of veins can be defined in Mari Rosa: Vp, showing pinch and swell structures parallel to the main foliation planes (S<sub>2</sub>), and Vo, massive lensoid-shaped bodies of gold bearing stibnite postdating the Vp veins and cross-cutting S<sub>2</sub>. Hydrothermal alteration consists oí a mild sericitization, chloritization and carbonatization oí the metasedimentary rocks around the veins. Due to the mineralogy oí the hostrocks (muscovite, chlorite, quartz), these alteration facies are not easily recognizable. However, the study of chemical changes around the veins allow a clear characterization of the hydrotermal processes. !hus, a remarkable increase in the ratio K<sub>2</sub>O/Na<sub>2</sub>O (from 1.2 in the regional rocks to 5.1 lfi the Vp contact rocks) and a decrease in the ratio SiO<sub>2</sub>/volatiles (írom 27.4 in the regional rocks to 13.5 in the Vp contact rocks) can be used as clear-cut indicators of the extension and magnitude of the hydrothermal alteration. Other changes included increases lfi. Sb (between 5,000 and 10,000 times the regional background), Mo (up to 60 times the regional background) and Au (values oí up to 32 ppm) around the veins. Besides, a high positive correlation between Sb and Mo is observed (R = 1 in the veins and R = 0.9 in the host rocks). The isotopic signature of stibnite and pyrite (average δ<sup>34</sup>S of 0.3â° and -3.9â°, respectively) is close to the typical values of magmatic sulphur. This, together with the high correlations between Sb and Mo strongly suggest a genetic relationship between the Mari Rosa mineralization and the intrusion of the Alburquerque batholith.
La zona Centro Ibérica del Macizo Hespérico contiene una serie de depósitos filonianos de antimonio de edad tardihercínica. Uno de ellos es la mineralización de Mari Rosa, encajada en metagrauvacas y pizarras pertenecientes al Complejo Esquisto Grauváquico (Precámbrico Superior) y situada en las proximidades del batolito de Alburquerque (Westfaliense/ Estefaniense). La mineralización está caracterizada por una paragénesis compleja que incluye arsenopirita-(pirita), estibina-oro y pirita-pirrotina-galena-esfalerita-calcopirita-tetraedrita- boulangerita-estibina. De éstos, sólo el segundo episodio fue importante y dio lugar a los principales cuerpos mineralizados del depósito. Dos tipos de venas pueden definirse en Mari Rosa: Vp, mostrando estructuras abudinadas paralelas a la esquistosidad principal (S<sub>2</sub>/), y Yo, bolsadas lenticulares de estibina masiva aurífera posteriores a Vp y cortando a S<sub>2</sub>/. La alteración hidrotermal consiste en una débil sericitización, cloritización y carbonatización de las rocas metasedimentarias en torno a las venas. Debido a la mineralogía de estas rocas (moscovita, clorita, cuarzo), estas facies de alteración no se reconocen fácilmente. Sin embargo, el estudio de los cambios químicos alrededor de las venas permite una caracterización adecuada de los procesos hidrotermales. Así, un notable incremento en la razón K<sub>2</sub>O/Na<sub>2</sub>O (desde 1,2 en las rocas regionales a 5,1 en la proximidad de las venas Vp) y un descenso en SiO<sub>2</sub>/volátiles (desde 27,4 en las rocas regionales a 13,5 en la proximidad de las venas Vp) pueden ser utilizados como marcadores de la magnitud y extensión de la alteración hidrotermal. Otros cambios incluyen importantes incrementos en Sb (valores entre 5.000 y 10.000 veces la media regional), Mo (hasta 60 veces su concentración regional) y Au (con valores máximos de hasta 32 ppm) en torno a las venas. Por otra parte, se observa una elevada correlación positiva entre Sb y Mo (R = 1 en las venas mineralizadas, R = 0,9 en las rocas encajantes). La composición isotópica media de estibina y pirita δ<sup>34</sup>S = 0,3 â° y-3,9 â°, respectivamente) presenta valores próximos a los de azufre de origen magmático. Esto, junto con las significativas correlaciones entre Sb y Mo permiten sugerir una relación genética entre la mineralización de Mari Rosa y la intrusión del batolito de Alburquerque.
Estudios Geologicos. 01/1994;
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ABSTRACT: We welcome the discussion of our paper by Tornos et al. The epithermal character of the Hiendelaencina veins might have been an assumption in the early to mid 1980s, however, this early idea has been reaffirmed after many years of research involving fieldwork and mineralogical, sulphur isotopes, and fluid inclusions studies. The same applies to the alleged extensional frame, a tectonic episode now well documented not only in central Spain (Spanish Central System: Doblas 1987; Doblas et al. 1988; Doblas 1991) but in France (French Central Massif: Mnard and Molnar 1988; Malavieille et al. 1990; Munoz et al. 1992).The deposits are hosted by metamorphic rocks and the nearest volcanic outcrops to Hiendelaencina are those of Atienza (andesites; some 12 km northward). This is the reason why the relationships between the Atienza volcanics and the Hiendelaencina veins were initially regarded as obscure. These Stephanian-Permian volcanic outcrops are only local evidence of the late Variscan magmatism, which in the case of Hiendelaencina remained concealed. It is evident that the geologic environments of Hiendelaencina and Atienza are very different (see Discussion, p. 88 of the paper). As a direct consequence of this, the local structural conditions led to contrasted expressions of the late Variscan magmatism i.e. subaereal at Atienza and hypabyssal at Hiendelaencina.
Mineralium Deposita 05/1993; 28(3):219-221. · 1.68 Impact Factor
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ABSTRACT: The northeastern sector of the Spanish Central System hosts important Stephanian-Permian silver-base metal epithermal mineralizations defining the so-called Hiendelaencina District. The overall geotectonic evolution of this region indicates a major late Variscan extensional period involving the unroofing of dome-shaped metamorphic core complexes, which ultimately led to the radial brittle disruption of these bodies allowing the ascent of andesitic magmas and high-level hydrothermal activity. The deposits are hosted by high-grade metaphorphic rocks belonging to these complexes. Mineralogical and fluid inclusion studies reveal that the mineralizations were formed during two to four hydrothermal stages. These are the result of complex interactions between fluids of contrasted temperatures and salinities. Data on sulphur isotopes suggest that two sources of sulphur existed: magmatic (andesitic derived, with 34S + 6) and metasediment-derived (with initial 34S probably + 25).
Mineralium Deposita 02/1992; 27(2):83-89. · 1.68 Impact Factor
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ABSTRACT: Fluid inclusion studies on quartz and barite samples from the Hiendelaencina Ag-base metals epithermal deposit (late Hercynian) suggest that this mineralization was formed during four hydrothermal stages. Ore stage I was characterized by aqueous-carbonic fluids from which pyrite and arsenopyrite were precipitated. The interaction between probably magmatic-derived fluids (aqueous solutions; Th = 320 â 200º C, 12 eq. wt. % NaCl) and meteoric waters (of lower temperature and salinity) caused a generalized decrease in both, T and salinity (from 12 eq. wt. % NaCl to 3 eq. wt. % NaCl), thus probably inducing the precipitation of Cu and Zn minerals (ore stage 11). Ore stage 111 (silver stage) was characterized by the interaction between fluids of low temperature and contrasted salinities (Th = 100 â 150º C; 3 eq. wt. % NaCl to 18-22 eq. wt. % NaCl). A final and «barren stage » (stage IV) resulted in the precipitation of a late generation of quartz and barite.
Estudios de inclusiones fluidas en muestras de cuarzo y baritina del yacimiento epitermal argentífero de Hiendelaencina sugieren que esta mineralización se formó a lo largo de cuatro episodios hidrotermales. El estadio mineral I estuvo caracterizado por la presencia de fluidos acuoso-carbónicos que precipitaron pirita y arsenopirita. La interacción entre fluidos de probable origen magmático (soluciones acuosas; Th = 320 â 200º C, 12 % eq. NaCl) y fluidos de origen meteórico (de menor temperatura y salinidad) causó un decrecimiento generalizado en T y salinidad (desde 12 % eq. NaCl a 3 % eq. NaCl), lo cual probablemente indujo la precipitación de minerales de Cu y Zn (estadio mineral 11). El estadio mineral 111 (estadio argentífero) se caracterizó por la interacción entre fluidos de baja temperatura pero de salinidades contrastadas (Th = 100 â 150º C; 3 % eq. NaCl a 18-22 % eq. NaCl). Un estadio final y estéril (estadio mineral IV) originó la precipitación de una generación tardía de cuarzo y baritina.
Estudios Geologicos. 01/1991;
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ABSTRACT: Sediments from the Elqui watershed river system (9800 km2; northern Chile) are highly enriched in arsenic. The river system initiates in the high altitude domain of the Andes (3500–4000 m) and drains important hydrothermal alteration zones and epithermal deposits, including the copper-, and arsenic-rich gold veins of the well-known El Indio–Tambo district. In order to study the extent, source, and age of contamination, we carried out a geochemical survey of stream sediments and older, Early Holocene lacustrine sediments. The results reveal very high contents of arsenic in both, the stream (55–485 ppm As) and lacustrine sediments (119–2344 ppm As). As shown by the ESEM-EDX study, arsenic is associated with the iron oxide mineral phase. Given that arsenic is enriched in both the stream sediments and the Early Holocene sequence, we suggest that contamination is not only industrial derived (mining operations), but also a major geological process, related to long-lived erosion of the As-rich epithermal ores and alteration zones. Erosion in this realm is particularly important during El Niño years, when increased activity of the Westerly winds brings intense rains, with catastrophic consequences in the Elqui watershed, including the massive removal of sediments in the form of large debris flows.
Journal of Geochemical Exploration.
