El Soldado Research Articles

Development of self-efficacy in high school students through soil analysis in the protected natural area "Estero El Soldado"

Teaching various scientific disciplines involves both hands-on and theoretical methods aimed at sparking students' curiosity in learning concepts. Students enhance their comprehension by actively engaging in direct activities rather than solely relying on explanations provided by teachers. The development of a research project carried out by 12th grade students during the semester allowed them to develop scientific or technological research to understand nature and act on it. The research project involved taking soil samples of natural protected area “Estero El Soldado” and analyzing it using a microscope, increasing student’s self-efficacy using the microscope. Self-efficacy was measured before and after the proposed research project using the General Self-Efficacy Scale instrument (Baessler and Schwarzer, 1996), which consists of 10 items and measures a person's perception when facing a variety of stressful situations. The participation of 43 12th grade students was analyzed. After the completion of the research project students, the results from the pre-test (M = 66.89, SD = 19.52) and post-test (M = 80.34, SD = 19.84) self-efficacy evaluation indicate that carrying out the research project resulted in an improvement in self-efficacy, t(84) = 2.01, p = 0.0008. We can conclude that integrating hands-on research projects like soil analysis using different laboratory equipment boosts 12th-grade students' scientific self-efficacy, as evidenced by improved scores on the General Self-Efficacy Scale. These findings underscore the value of experiential learning in nurturing both scientific skills and confidence in students.

Observing changes of fish community in a semi-arid subtropical coastal lagoon subject to ecological conservation

El Soldado is a semi-arid subtropical coastal lagoon subject to ecological conservation in the Gulf of California, where we reviewed the changes in the fish community structure before (1972; 1978–79; 1990–92) and after (cycle 1, 2018–2019; cycle 2, 2019–2020) the decree as a protected area, and we determined spatio-temporal changes between two consecutive annual cycles. We conducted monthly fish sampling cycles 1 and 2 with a small trawl net at three sites, where water and sediment variables were recorded, and drift macroalgae biomass was estimated. Results showed 99 fish species have been recorded in previous studies, and our study added 11 species. The fish assemblage (2018–2020) comprised 34 marine species and nine of them were dominant in both cycles. In general, higher fish abundance, richness, and diversity were observed in the cycle 1. Spatial changes, in both cycles, showed higher fish abundance, richness, and diversity in the innermost area of the lagoon, characterized by silty sediment and higher drift macroalgae biomass. Temporal changes showed higher fish abundance, richness, and diversity in summer-autumn during cycle 1, while during cycle 2, the higher values were in winter-autumn, mainly associated with seasonal variations in water temperature and the biogeographic affinity of fish species, but were also attributed to changes in the density of species classified as dominant. There was notable a drastic decrease of fish richness, diversity, and density during summer in cycle 2, which was attributed to be a warmer year. El Soldado fish community showed changes before and after the decree as a protected area, but also in the contiguous cycles. These changes include the addition of species, the prevalence of common species over 48 years, and the current dominant species that belong to indicator groups, which exhibit effectiveness in the conservation of this ecosystem.

Comparing the biogeochemical functioning of two arid subtropical coastal lagoons: the effect of wastewater discharges

ABSTRACT Nutrient flux, net metabolism, and N2 fixation and denitrification processes were estimated and compared in two semi-arid subtropical coastal lagoons in the Gulf of California: El Soldado (ES), where no wastewater is discharged, and El Rancho (ER), where shrimp farm effluents are regularly discharged. Biogeochemical processes were evaluated with the LOICZ model. Flushing time was <2 days in both systems. Nutrient fluxes were higher in ER than in ES and both systems acted as nutrient sinks for most of the year. ER showed a larger nutrient flow rate in the summer and autumn due to the input of shrimp-farm effluents. Nitrogen fluxes increased in both ER and ES in the winter in response to the increased nutrient supply from coastal upwellings. ER and ES both showed autotrophic metabolism and N2 fixation in the spring, autumn, and winter, but heterotrophic metabolism and denitrification in the summer. Denitrification dominated in ER (−2.21 mmol m2 day−1) and values were higher than those estimated in ES (−0.45 mmol m2 day−1). The comparative analysis between ES and ER evidenced the significant changes in its biogeochemical performance caused by the input of anthropogenic nutrients, and can orient the environmental management of coastal lagoons.

En torno a la corte de la Monarquía Hispánica en una novela recientemente descubierta: El Soldado Quexoso de João Franco Barreto

En este trabajo damos a conocer una novela inédita escrita en castellano por el portugués João Franco Barreto en 1628. Se trata de una obra manuscrita que contaba con todas las licencias para ser impresa por Paulo Craasbeeck, pero que nunca llegó a imprimirse. El Soldado Quexoso muestra una visión muy interesante sobre los usos y costumbres de la corte tanto en Lisboa como en Madrid.

The Vietnam War and Chicana/o Environmentalism in El Grito del Norte (1968–73)

The Vietnam War and Chicana/o Environmentalism in El Grito del Norte (1968–73) Emily Cheng (bio) This essay addresses El Grito del Norte (EGDN), a Chicana/o nationalist newspaper published in Española, a small working-class town in northern New Mexico, from 1968 to 1973. The paper was originally formed to support the politics of La Alianza Federal de Mercedes (Federal Alliance of Land Grants), the organization led by Reies López Tijerina that in the 1960s and 1970s sought the restoration of land grants established under the Spanish and Mexican governments. Written and run by women, the paper was founded and edited by Elizabeth "Betita" Martínez (known previously as Elizabeth Sutherland), whose socialist and third-world feminist politics shaped the paper's concern with the connections between rural Chicana women of New Mexico and other women of color in the US and abroad.1 Though the paper was committed to Chicana/o issues grounded in New Mexico, it soon moved away from its original role as a mouthpiece for the Alianza to include reports on indigenous issues in Latin America, Africa, and Asia. EGDN was, in Martínez's words, the "only one" of "about twenty Chicano newspapers … that was completely international."2 Of particular importance was the newspaper's reporting on Vietnam, which made it exceptional among a Chicano press in the 1960s that, George Mariscal notes, "was largely silent on the topic of the war in Southeast Asia."3 The paper's coverage included a special issue on North Vietnam by Martínez, a five-part series by Valentina Valdez explaining Vietnam and the war to readers, articles addressing Chicanos serving in the military by Enriqueta Vasquez that appeared in "El Soldado Razo Today" and her column, "Despierten! Hermanos," reports on the military events of the war, poetry by Ho Chi Minh, and a report on the Chicano Viêt Nam Project, a solidarity organization.4 While other scholars have written about the newspaper's concerns with land in New Mexico and, to a lesser extent, its third-world feminist politics, I examine how these aspects of the paper come together with its internationalism [End Page 55] to represent a distinctive and radical "environmental" politics. I do not mean to argue that the writers and activists who contributed to EGDN identified themselves as environmentalists or to attach this label to them. What I do want to argue is that, in contrast to the mainstream environmental movement that emerged in this period, these women writers possessed an environmental understanding that fundamentally engaged social justice, particularly around issues of race, gender, and imperialism. The environmental epistemology in EGDN was shaped by, but moved beyond, the long-standing relationship between Mexican-origin people, land, and nature in the US Southwest that was central to Chicana/o nationalist politics, as I discuss through Vasquez's article "La Santa Tierra." In considering Vietnam as another site in which to explore and understand the violence the US empire inflicts on land and colonized people, EGDN made connections between the US Southwest and Vietnam that developed its alternative environmental lens. Approaching the North Vietnamese as fellow peasants, or "campesinos," whose harmonious relationship to the land was being attacked by US imperialism, the newspaper made womanhood central to forging this relationship between Chicana/o and North Vietnamese anticolonialism. The feminist politics of "global sisterhood" facilitated the writers' interest in Vietnam, and their access to direct encounters with Vietnamese women through the international women's peace movement. The women writers of the paper also deployed a gendered lens that highlighted the role of women in environmental resistance to masculine military violence and symbolically established similarities between the two communities through idealized portrayals of rural, domestic life. With its attention to the lived human relationship to land, EGDN offered an alternative to notions of land that were central to mainstream American environmental thinking, which generally assumed the "separability of the human and natural realms … expressed through a melancholic attitude linking natural plenitude with human absence."5 In this mainstream tradition, land has been considered through the ideal of wilderness, and the human realm predominantly characterized by the individual relationship to the land through possession...

Libros como trincheras. El Servicio de Lecturas del Soldado de la Biblioteca de la Universidad de Zaragoza durante la Guerra Civil (1936-1939)

The Servicio de Lecturas para el Soldado was an organization promoted by Miguel Artigas from the University Library of Zaragoza during the Civil War (1936-1939) as one more instrument that contributed to the military triumph of the rebel forces. The objective of this work is to analyze its fundamental aspects: the difficult cohabitation with the ordinary activity of the university library; the evolution of its operation and scope; the role of librarians; and the results obtained, framed within a context in which war emergencies coexist and a peculiar symbiosis between the concepts of therapeutic and guided reading.

CALIDAD DE SEDIMENTOS ASOCIADA A ACTIVIDADES ANTRÓPICAS EN LAGUNAS COSTERAS SEMIÁRIDAS SUBTROPICALES DE LA COSTA CENTRAL ESTE DEL GOLFO DE CALIFORNIA

The quality of the superficial sediments of the coastal lagoons of Lobos and Tobari, both in the central-east zone of the Gulf of California, Mexico, and receptors of sewage effluents from the Yaqui Valley, was evaluated. The comparison was carried using the coastal lagoon of el Soldado, as a reference site, on account of being a natural protected area, which does not receive anthropogenic unloads. The levels of nickel, zinc, copper, cadmium, manganese, lead and iron were determined. The enrichment factor (EF), the metallic pollution index (MPI) and the index of geoaccumulation (I geo ) were calculated. Besides the guidelines of sediment quality (SQV) were used to assess the concentrations of metals that can cause a potential risk to the marine biota health. Lagoon Lobos obtained significantly higher levels of zinc (70.1 μg/g) and copper (16.3 μg/g), Tobari had the highest mean of manganese (747 μg/g). El Soldado had the lowest mean of iron (1.05 %) and the lowest value of MPI. In Lobos and Tobari, manganese was the only metal with an EF, which indicates anthropogenic influence, and it also had an I geo index of moderate. The sites most affected in both lagoons were the nearest to the agricultural zones. The SQV suggests that there must be a track of nickel levels > 51.6μg/g (registered once in Lobos) and of manganese levels > 260μg/g (Lobos and Tobari). Concentrations over those levels can cause adverse effects on the marine environment such as the deterioration of the natural conditions that support the reproduction, breeding, and protection of the species that live there.

Deep Translation and Subversive Formalism

Although better known in world of Spanish letters, Salomon de la Selva is shadowy figure in history of U.S. poetry. He was born on March 20, 1893, to be eldest of ten siblings, in Leon, Nicaragua--a rare fact in dearth of information we have about his early life. (1) According to Edgardo Buitrago and Carlos Tunerman, de la Selva lived in Nicaragua until age of eleven, when he left his family and took scholarship to live and study in Northeastern U.S. We don't know for sure where he lived in U.S. from age of eleven to twenty-one, when, in 1914, he served as Ruben Dario's translator in New York, and record becomes clearer. In 1915, de la Selva collaborated, with American poet Thomas Walsh, to publish translation of Eleven Poems of Ruben Dario, and henceforth his reputation grew. He was mentored by his compatriot Dario and Dominican poet Pedro Enriquez Urena, and in 1916 de la Selva was appointed to faculty of Williams College, to teach Spanish and French. He soon befriended Edna St. Vincent Millay, at time senior at Vassar, and sowed seed of profound, if short-lived, relationship between two poets. (2) Like Millay, de la Selva preferred formal verse in English (3)--especially sonnet, iambic meter, and rhyme--which explains in part why contemporary Anglophone critics now place him as marginal figure. By measure of experimentation, his English poems seem flaccid compared to those of avant-garde contemporaries like Pound, Williams, or Cummings. Today poets and scholars find it easy to regard formal verse from early twentieth century as intellectually and stylistically retrograde, but to truly understand de la Selva's work we need to reconsider norms of artistic radicalism, and for two related reasons: he was far more aesthetically challenging when writing poems in Spanish, and English verse forms were alien to him. When dealing with poet who endeavors to escape restraints of the Tradition--and here nationality does play part in implicit sense of entitlement--we see deconstruction of forms, and thus beauty fails new aesthetic, replaced with what Eliot famously described as intensity. (4) But when that poet is entering the Tradition, he swims against wave of avant-garde to do something quite different: to dialogue for sake of establishing legitimacy. De la Selva, as native Nicaraguan living and writing in U.S., entered not only an alien literary tradition, but also an alien language, and given all cultural spheres this process generates, de la Selva's achievement should be regarded with these political implications in mind. Steven White, writing on de la Selva's work in both English and Spanish, considers de la Selva as a Nicaraguan poet who wrote his first book, Tropical Town & Other Poems, in very traditional English verse forms, then rejected English language entirely to produce, in Spanish, El soldado desconocido, an experimental, testimonial work that combines variety of genres (the chronicle, diary, letter, and ballad) to produce multi-faceted description of microcosmic experience of history that, ultimately, becomes universal. (5) In fact, Tropical Town (1918) is both de la Selva's first book of verse and his first book in English. Although it is rumored that he published second book of English verse, A Soldier Sings (1919), in England, no extant copy of book is known to exist. (6) Of A Soldier Sings, White has noted that its alleged existence is result of Nicaraguan poet Ernesto Mejia Sanchez sending bibliographical information (London: The Bodley Head, 1919) to [Nicaraguan critic] Jorge Eduardo Arellano, who at time was compiling an extensive bibliography of books and articles by and about de la Selva for fundamental publication Homenaje Salomon de la Selva: 1959-1969 and that Arellano himself believed A Soldier Sings is a legend, one more myth in our literature rich in myths. …

Key issues on the post-Mesozoic Southern Caribbean Plate boundary

Abstract A lithospheric-scale, geodynamic model of the Caribbean southern boundary takes into account tectonic and stratigraphic elements previously unconsidered or not well constrained. The Falcón, Bonaire, Blanquilla and Grenada basins are parts of a former single back-arc basin associated with the migrating Mesozoic Caribbean Arc in Late Eocene–Oligocene times. Spreading of the crescent-shaped basin was triggered by declining Caribbean eastward motion in response to increased convergence between the two Americas at around 38–33 Ma. Dextral wrenching along the southern boundary started in western Venezuela at 17–15 Ma and progressed eastward to the El Pilar Fault by 12 Ma. Eastward motion of the Caribbean relative to South America was earlier accommodated by east-progressing, non-partitioned oblique subduction and collision, as illustrated today in eastern Venezuela around the Los Bajos–El Soldado fault system. Extrusion of the Maracaibo and Bonaire blocks towards the NNE started around 5 Ma, thus the dextral Boconó fault is a young feature. Total plate boundary Cenozoic dextral wrenching recorded onshore Venezuela does not exceed 100 km and is more likely to be in the order of 55 km.

Reproduction, condition and mortality of the Pacific oysterCrassostrea gigas(Thunberg) in Sonora, México

Starting in 1997, mortality outbreaks in cultured oysters Crassostrea gigas have been reported in northwestern México. Previous studies have shown that massive die-offs result from multi-factor processes related to reproduction of the species. We studied the reproductive cycle and the condition index of cultured oysters in the coastal lagoon of El Soldado, Sonora, as well as the relationship of the life cycle with environmental parameters. We used oocyte diameter to determine reproductive stages and the condition index to describe the physiological state of oysters. Additionally, the temperature, salinity, seston and chlorophyll a were recorded at the study site. The results showed that C. gigas began accelerated reproductive activity in March under the influence of high temperature and increased concentrations of food. No spawning events were recorded and gametes were reabsorbed within the gonad in September and October. The results showed a period of nutrient storage during autumn–winter and another period of gamete production in spring–summer. A mortality event occurred at the end of winter, tied to significant increases in temperature and availability of food and in accelerated reproductive activity and high condition index. These conditions were very similar to those reported in other countries during summer die-offs of C. gigas.

The role of bitumen in strata-bound copper deposit formation in the Copiapo area, Northern Chile

In northern Chile, between 27 and 33°S, there are numerous deposits where residual petroleum is associated with Cu-(Ag) mineralisation (the most famous being El Soldado). All of these deposits are hosted by Lower Cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin. This close relationship suggests that the generation, migration and emplacement of hydrocarbons in the Cretaceous volcanic units is a regional process, associated with the evolution of the Cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar Cu–(Ag) deposits. The present work analyses four small strata-bound copper deposits located along a north–south belt approximately 10 km east of Copiapo in northern Chile. These deposits are typically hosted by pyrobitumen-rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate Pabellon Formation, the youngest formation within the Chanarcillo Group. The strong genetic and spatial relationships between the pyrobitumen-rich lavas and the mineral deposits allow us to define this volcanic belt as the Ocoita-Pabellon Metallotect. Two hydrothermal events can be distinguished based on the mineralogical, textural, fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum. During the early event, petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by Fe-rich hydrothermal fluids, which precipitated pyrite as an early sulphide phase. The second event is characterised by Cu-rich hydrothermal fluids, which induced three successive sub-stages of Cu-sulphide precipitation. The hydrothermal fluids chemically and thermally altered the first-stage bitumen, transforming it into pyrobitumen. The present work documents similarities between the Ocoita-Pabellon Metallotect and the El Soldado ore deposit and emphasises important differences. In the El Soldado host rocks, a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids, the framboidal pyrite was formed by assistance of bacteria, the S of the Cu sulphides was inherited from the pyrite, and the fluid source was basin connate-metamorphic brine. In the Ocoita-Pabellon Metallotect, the hydrocarbons were mobilised into the host rocks by hydrothermal fluids; the pyrite is epigenetic, the δ34S values of pyrite and copper sulphides are very different, with distinctive light δ34S signature of Cu sulphides (δ34S between −44.7 and −17.9‰), and the calculated δ18O of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system.

Fluid history of andesite-hosted CuS-bitumen mineralization, Copiapó district, North Central Chile

Copper sulphide mineralization is intimately associated with solid bitumen (migrated hydrocarbon) within a 70-m-thick porphyritic lava horizon in a Neocomian back-arc basin near Copiapó, North Central Chile. Bitumen occurs as veins and vesicle-fill and exhibits well-developed anisotropic textures. Fluid flow paragenesis is divided into three principal stages, essentially pre-, syn- and post-metallic mineralization. Ore deposition occurred via the reduction of hot (>300 °C) mineralizing fluids by in situ labile bitumens. Comparative study between the Copiapó porphyry-hosted mineralization and the El Soldado massive Cu deposit (150 Mt Cu reserves), located further to the south, reveal striking geologic and genetic similarities.

A SULFUR, CARBON, OXYGEN, AND STRONTIUM ISOTOPE STUDY OF THEVOLCANIC-HOSTED EL SOLDADO MANTO-TYPE COPPER DEPOSIT, CHILE: THE ESSENTIAL ROLEOF BACTERIA AND PETROLEUM

Strata-bound, manto-type copper deposits of Chile are a major source of copper, and some deposits (e.g., Mantos Blancos, El Soldado) contain as much metal as do large porphyry copper deposits elsewhere. El Soldado (200 Mt @ 1.35% Cu), the largest manto-type copper deposit in the Coastal Cordillera of central Chile, is hosted by the rhyodacite-basalt upper member of the marine Lower Cretaceous Lo Prado Formation. Paragenetic studies indicate that the deposit formed in two stages. The first was a low-temperature stage (stage 1; 130–125 Ma) in which liquid petroleum migrated from underlying carbonaceous shales into the overlying host volcanic rocks and abundant framboidal pyrite developed in a paleopetroleum reservoir. A later hydrothermal stage (stage 2; ca. 103 Ma) introduced copper and replaced earlier pyrite to form chalcopyrite, bornite, and chalcocite ores. This study presents isotopic data that support bacterial sulfur reduction as the process that formed the essential precursor stage 1 pyrite, and the participation of basinal fluids in the hydrothermal second stage. A wide range of δ 34S values for early stage 1 pyrite (–11.1 to +28.0‰) supports the hypothesis that low-temperature, incomplete sulfate reduction from connate seawater sulfate and Fe-enriched oil-field brines took place in a compartmentalized petroleum reservoir by bacterial sulfate reduction. With the exception of a small proportion of Cu-Fe sulfides with δ 34S values between –2.0 and +2.0 per mil, the bulk of stage 2 Cu-Fe sulfides replaced earlier pyrite and mimic the broad range in δ 34Svalues (–12.7 and +19.0‰) of stage 1 pyrite. Sulfur from early pyrite was recycled with no significant homogenization, fractionation, or addition of new sulfur, and indicates the essential role of hydrocarbons and bacteria in the formation of the deposit. The δ 13C values of gangue calcite vary between –4.2 and –20.2 per mil and reflect a mixing of various proportions of oxidized, pyrobitumen-derived organic and inorganic carbon from the mineralizing fluid. Pyrobitumen in the ores has δ 13C values of –30 to –26 per mil, consistent with it being a residue of the original liquid petroleum. δ 18O values of K-feldspar in both ore and barren samples are similar (12.0–12.7‰) and are compatible with the fluids being of metamorphic, rather than magmatic, origin. The similar δ 18O ranges of calcite (2.7‰) and K-feldspar (0.7‰) suggest that they formed from the same hydrothermal fluid and that the fluid was in equilibrium with the host rocks. The 87Sr/86Sr ratios in calcite of 0.7041 to 0.7051 reflect isotopic ratios inherited from the subaerial andesitic rocks that overlay the deposit where the ore-forming fluids are thought to have originated.

Age of mineralization by basinal fluids at the El Soldado manto-type copper deposit, Chile: 40Ar/ 39Ar geochronology of K-feldspar

Manto-type copper deposits of the southern Central Andes are strata-bound, epigenetic mineral concentrations hosted by bimodal volcanic and volcaniclastic rock suites. They are economically important, but since they are not obviously related to intrusions, their genesis has been controversial, to some extent, because it has proven difficult to date the ore-forming event and distinguish it from the age of low-grade regional metamorphism. El Soldado, the largest manto-type copper deposit in central Chile, is hosted by marine volcanic and subvolcanic intrusive rocks of the Lower Cretaceous extensional arc. To discriminate between regional metamorphism and mineralization, we dated 11 samples of K-feldspar by the stepwise-heating 40Ar/ 39Ar method. Hydrothermally precipitated K-feldspar associated with copper sulfides precipitated at temperatures of >300 °C and range in age from 100.5±1.5 to 106.1±1.1 Ma (mean 103±1.6 Ma; n=8). Syn-mineralization K-feldspar gave an age of 102.5±2.0, which is interpreted to be the age of mineralization. K-feldspar unrelated to ore yields older ages between 109.4±1.1 and 112±2 Ma (mean=110.3±1.4 Ma; n=3) is variably reset by the younger ca. 103 Ma mineralization episode. The above ages are interpreted to represent the age of alkali redistribution and crystallization due to burial metamorphism of the host sequence. Fission track dating of apatite in the host rocks yields an age of ca. 90 Ma, indicating fast cooling of the system to less than ca. 100 °C after mineralization. Time–temperature modeling of fission track length data are compatible with initial fast exhumation, followed by slow exhumation and cooling to surface temperatures. High levels of atmospheric Ar were detected in all K-feldspar samples and are tentatively attributed to connate meteoric fluids incorporated into the basinal metamorphic mineralizing fluids.

Organic petrology, chemical composition, and reflectance of pyrobitumen from the El Soldado Cu deposit, Chile

Solid pyrobitumen (residual petroleum) is found intimately associated with sulfides in several manto-type (strata-bound) Cu deposits of central Chile. El Soldado (lat 32°38.8′S, long 71°06.7′W) is one of the largest deposits of this type (>130 Mt @ 1.5% Cu) and is hosted by volcanic and subvolcanic rocks of the Cretaceous Lo Prado Fm. Detailed organic petrology of authigenic sulfide inclusions, degassing vesicles, and anisotropic pyrobitumen and graphitic carbon allowed the elucidation of a complex diagenetic history of a biodegraded reservoir in faulted volcanic and subvolcanic rocks. Due to the overmaturity of the host sequence, biomarker techniques (aliphatic and aromatic) were unsuitable to investigate the composition of the pyrobitumen. However, microprobe and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analyses, Rock-Eval pyrolysis, and 13 C NMR techniques were used to ascertain the composition of the pyrobitumen. Spatial variations in the maturity of the pyrobitumen were assessed using both random reflectance ( R o) and rotational reflectance ( R omax and R omin). The data are consistent with the following evolution for El Soldado: As a result of burial in the Cretaceous back-arc basin, petroleum was generated from organic-rich shales in the underlying lower Lo Prado Fm. and migrated into primary and structural porosity in the host rocks, the predominantly volcanic upper Lo Prado Fm. Low-temperature (<90°C) biodegradation of petroleum developed an early assemblage (Stage I assemblage) of pyrite (±sphalerite±chalcopyrite). Geopetal structures related to pressure degassing of semisolid petroleum suggest that migration occurred while the strata were horizontal, at ca. 130 Ma. Continued basinal burial led to thermal degassing, increased maturation and contraction of the petroleum into pyrobitumen. Around 20 Ma later an influx of high-temperature (ca. 250–350°C) Cu-rich fluids induced by regional granitoid intrusion (Stage II assemblage) replaced preexisting pyrite and pyrobitumen. The mineralizing fluids altered the pyrobitumen physically and chemically: (a) increasing R o to greater than ca. 5% in the core of the orebodies against a background level of ca. 3%; (b) developing anisotropy (nongranular, fine to coarse mosaic, and coarse flow mosaic) within the pyrobitumen and locally graphitized the pyrobitumen, developing graphitic carbon; and (c) incorporating Cl (±Cu±Fe) into the pyrobitumen during the development of anisotropy.

The role of organic matter in the genesis of the El Soldado volcanic-hosted manto-type Cu deposit, Chile

Solid bitumen (residual petroleum) occurs intimately associated with sulfides in several manto-type Cu deposits of central Chile. El Soldado (32 degrees 38'S; 71 degrees 04'W) is one of the largest manto-type deposits (>130 million metric tons1.5% Cu) and is hosted by rhyolites and andesites of the Lower Cretaceous Lo Prado Formation.As a result of basinal burial in the Early Cretaceous back-arc basin, petroleum was generated from organic-rich shales in the underlying lower Lo Prado Formation and migrated into primary and structural porosity in the upper Lo Prado Formation. Migration was controlled by extensional basinal faults. Low-temperature (<90 degrees C) biodegradation of petroleum developed an early stage I assemblage of (mostly framboidal) pyrite (+ or - sphalerite + or - chalcopyrite). Geopetal structures related to pressure degassing of semi-solid petroleum suggest that migration occurred while the strata were horizontal, at ca. 130 Ma. Continued basinal burial led to thermal degassing, increased maturation, and solidification of the petroleum.Low-grade regional (pumpellyite-prehnite) metamorphism of the sequence was followed, at ca. 110 to 103 Ma, by the influx of high-temperature (ca. 300 degrees C), Cu-rich fluids concurrently with emplacement of the Cretaceous batholith into the basin. Basinal fluids were focused into a now tilted sequence by a brittle shear (north-south to north-northwest) fault system. Copper sulfides (stage II assemblage) replaced preexisting pyrite and bitumen, forming zoned orebodies with a central chalcocite-hematite zone, followed outward by bornite-chalcocite, chalcopyrite-bornite, and pyrite-chalcopyrite zones. The mineralizing fluids altered the bitumen thermally and chemically as follows: (1) reflectance (R o ) increased up to ca. 5 percent in the core of the orebodies against a background of ca. 3 percent; (2) anisotropy (nongranular, microscale, and domain) developed and the bitumen was locally graphitized; (3) chlorine (+ or - Cu + or - Fe) was incorporated into the bitumen affecting its reflectance. The source of Cu was most likely the overlying oxidized volcanic pile; the Cu was transported as chloride (CuCl) complexes, precipitating where the CuCl-rich solutions reacted with bitumen (adsorption/reduction) and pyrite from the stage I assemblage.The study demonstrates that in the Lower Cretaceous basin of Chile, degraded petroleum reservoirs can be important controls for metallic mineralization derived from hydrothermal solutions of different sources, particularly if biodegradation generated pyrite.

Re-Os-Isotope Systematics of Sulfides from Base-Metal Porphyry and Manto-Type Mineralization in Chile

Chile is a major world producer of copper, most of which occurs in base-metal porphyry and in manto deposits. A fundamental difference between these two types of deposits is the relative importance of intrusions spatially associated with the mineralization. The porphyry deposits are set within Mesozoic to Tertiary intrusive complexes. The manto-type deposits are restricted to volcanic and volcano-sedimentary sequences of Middle-Late Jurassic, Early Cretaceous, Late Cretaceous, and Early Tertiary times. Large intrusive centers are not spatially associated with these deposits, although minor intrusions are common. A central question in the metallogenesis of these deposits is the source of ore-forming components, in particular the ore metals. Initial 187Os/188Os isotopic data from sulfides from the El Teniente, La Disputada, and Andacollo base-metal porphyry deposits range from 0.19 to 1. These data indicate that the Os (and, by inference, Cu) is mostly crustally derived, since it is more radiogenic than that of the mantle, which has a 187Os/186Os ratio of ∼0.12. The isotopie data for El Soldado, which is an important example of manto-type mineralization, are significantly more radiogenic, with 187Os/188Os ratios greater than 3. These radiogenic values require that the Os come from a crustal reservoir with a high Re/Os ratio, such as black shales. The Os-isotopic data indicate that the source for these two types of base-metal deposits is different, but that both Os reservoirs reside in the crust.

Hydrocarbon Involvement in the Genesis of Ore Deposits: An Example in Cretaceous Stratabound (Manto-Type) Copper Deposits of Central Chile

The analysis of the empirical association of organic carbon in its various forms (e.g., oil, gas, coal) with a variety of ore-deposit types can be a rewarding exercise in the formulation of genetic models and exploration. In many ore provinces, organic matter, residing in its source rocks, migrating in the form of hydrocarbons, or in transient, permanent, leaking, or degrading reservoirs, is likely to have interacted with ground waters, with hydrothermal solutions of diverse origin, or with magmas. After a brief review of these associations, we describe the ubiquitous occurrence of remnant petroleum in two representative “manto-type” stratabound copper deposits in Chile and suggest its possible genetic role and exploration significance. Overmature petroleum (solid bitumen, pyrobitumen) is found in association with copper ores in the southern orebodies of the El Soldado copper deposit in central Chile. Textures indicate that petroleum occupied the host-rock porosity before copper mineralization. Isotopic data for C and O in total organic carbon and carbonate confirm the affiliation with organic carbon and suggest that gangue carbonates are in part the result of the oxidation of hydrocarbons. Reflectance of the solid bitumen is highest near ore (BR o ∼ 4%), and its geochemistry (Rock-Eval) indicates that the residual hydrogen (i.e., hydrocarbon) content is very low. It is proposed that mineralizing solutions interacted with a pre-existing degraded hydrocarbon reservoir. The hydrocarbons physically prevented low-grade metamorphic minerals from sealing the porosity, were oxidized to form carbonate gangue and alteration, and possibly acted as a reductant at the site of sulfide precipitation. Copper sulfides (bornite, chalcocite, chalcopyrite) filled spaces among bitumen, carbonate, and pre-existing sulfides (arsenopyrite, pyrite) only after significant burial and faulting of the host volcanic strata and trachytic subvolcanic intrusives had occurred, after migration of liquid petroleum into the porosity and during or after its solidification there; this makes syngenetic and early diagenetic models previously proposed for the deposit untenable. Similar occurrences of bitumen in the ores of the Talcuna copper/manganese district and in several other stratabound copper deposits in central and north-central Chile suggest that organic matter may have been involved in the genesis of many Andean manto-type deposits. The identification of source-trap systems that could have generated oil or gas reservoirs, which in turn could have interacted later with hydrothermal solutions from various sources, may be a useful exploration model for metallic ore deposits in the back-arc basins of the Andes.

Contribution to the knowledge of the malacological fauna of four costal lagoons in the state of Sonora, Mexico

A study was conducted on the malacological fauna of four coastal lagoons in Sonora, Mexico: El Sargento, Santa Rosa, La Cruz and El Soldado. The study covers aspects of species composition and diversity in the four lagoons, as well as qualitative observations of eight commercially important species: Chione gnidia, Chione fluctifraga, Chione californiensis, Chione subrugosa, Anudara grandis, Megapitaria squalida, Megapitaria aurantiaca and Glycimeris gigantea. A total of 102 species of 75 genera were identified, 60 of which were gastropods, 37 pelecypods, 4 polyplacophores, 1 scaphopod and 1 aplacophore. The greatest diversity was found in El Soldado Lagoon and the lowest in La Cruz Lagoon.

Results of extrapolating metallogenetic controls of the El Soldado mine to strategic prospecting in the Aconcagua region, Chile

Results of extrapolating metallogenetic controls of the El Soldado mine to strategic prospecting in the Aconcagua region, Chile