Lithogeochemistry and fluid flow in the epithermal Veta Rublo base metal-silver deposit, Chonta Mine (Huancavelica, Perú)

The Chonta Mine (75º00’30” W & 13º04’30”S, 4495 to 5000 m absl), owned by Compañía Minera Caudalosa, operates a polymetallic Zn-Pb-Cu-Ag vein system of the low sulphidation epithermal type, hosted by cenozoic volcanics of dacitic to andesitic composition (Domos de Lava Formation). Veta Rublo, one of the main veins of the system, is worked underground to nearly 300 m. It strikes 60-80º NE and dips 60-70º SE; its width varies between 0.30 and 2.20m, and it crops out along 1 km, but is continued along strike by other veins, as Veta Caudalosa, for some 5 km. Typical metal contents are 7% Zn, 5% Pb, 0.4% Cu and 3 oz/t Ag, with quartz, sericite, sphalerite, galena, pyrite, chalcopyrite, fahlore as main minerals, and minor carbonate and sulphosalts.

Extensive boiling as a precipitation mechanism for precious and base metal ores, Bienaventurada Mine, Huancavelica, Perú

The Bienaventurada mine operates a polymetallic Ag-Pb-Zn (Cu, Au) vein system of the low sulphidation epithermal type. Fluid inclusions, FI, are abundant in quartz, sphalerite and adularia. FI petrography demonstrates typical primary growth zoning which occurs frequently in crystalline quartz, and defines the most common primary FI. These are usually very small, but several types of primary, P, and secondary, S, FI Assemblages (FIAs) comprising FI of measurable size (3 to > 100 μm) can also be identified through careful petrographic work. The fluids are aqueous and undersaturated, and no evidence of CO2 was found; the degree of fill is usually high (~70-80 %) in the L-rich inclusions, but extremely low in V-rich inclusions. The measured microthermometric values are very consistent in the FIAs selected; they are for the most part roughly similar in the P and S assemblages: the median is typically ~258ºC for total homogenization temperatures, Th, and -1.5 ºC for ice melting temperatures, Tm (corresponding to 2.57 wt% NaCl eq). The widespread occurrence of L-rich and V-rich FI in the same FIA and the consistent Th values point to an extensive boiling system along the vein. In these conditions, Th equals T of trapping, and the ores are assumed to have been precipitated from an aqueous low salinity boiling fluid, of likely meteoric origin, at some 250-280º C, under ~500 m hydrostatic head.

Real Options: A Tool for Managing Technical Risk in a Mine Plan

NPV is a static measure of project value which does not discriminate between levels of internal and external risk in project valuation. Due to current investment project?s characteristics, a much more complex model is needed: one that includes the value of flexibility and the different risk levels associated with variables subject to uncertainty (price, costs, exchange rates, grade and tonnage of the deposits, cut off grade, among many others). Few of these variables present any correlation or can be treated uniformly. In this context, Real Option Valuation (ROV) arose more than a decade ago, as a mainly theoretical model with the potential for simultaneous calculation of the risk associated with such variables. This paper reviews the literature regarding the application of Real Options Valuation in mining, noting the prior focus on external risks, and presents a case study where ROV is applied to quantify risk associated to mine planning.

Comparative study of the pathogenicity of seabed isolates of Fusarium equiseti and the effect of the composition of the mineral salt medium and temperature on mycelia growth

The pathogenicity of seven strains of Fusarium equiseti isolated from seabed soil was evaluated on different host plants showing pre and post emergence damage. Radial growth of 27 strains was measured on culture media previously adjusted to different osmotic potentials with either KCl or NaCl (-1.50 to - 144.54 bars) at 15º, 25º and 35º C. Significant differences and interactive effects were observed in the response of mycelia to osmotic potential and temperature.

The lead salt quantum dot intermediate band solar cell

We propose a new kind of quantum dot (QD) materials for the implementation of the intermediate band solar cell (IBSC) [1]. The materials are formed by lead salt QDs of the family IV-VI (PbTe, PbSe or PbS) embedded in a semiconductor of the family II-VI (Cd1-xMgxTe, CdxZn1-xTe, and CdS1-xSex or ZnSe1-xTex, respectively). These QDs are not nucleated due to lattice mismatch, as it is the case of the InAs/GaAs QD material system grown by the Stranski-Krastanov (S-K) mode. In these materials, the QDs precipitate due to the difference in lattice type: the QD lead salt material crystallizes in the rocksalt structure, while the II-VI host material has the zincblende structure [2]. Therefore, it is possible to use lattice-matched QD/host combinations, avoiding all the strain-related problems found in previous QD-IBSC developments. In this paper we discuss the properties of the lead salt QD materials and propose that they are appropriate to overcome the fundamental drawbacks of present III-V-based QD-IBSC prototypes. We also calculate the band diagram for some examples of IV-VI/II-VI QD materials. The detailed balance efficiency limit of QD-IBSCs based on the studied materials is found to be over 60% under maximum concentration.

Replacing bare fallow with cover crops in an irrigated cropping system: soil salinity and salt leaching

In irrigated areas where cover crop establishment can be assured, consequent soil or nutrient conservation could increase sustainability of cropping systems. Replacing bare fallow with cover crops may increase sustainability by enhancing soil aggregate stability, water retention capacity or controlling nitrate leaching. Nevertheless, adoption of cover crops increase evapotranspiration and reduce water percolation beyond the root systems; therefore, it could lead to salt accumulation in the upper soil layers. This study was conducted during four years to determine the effect of replacing bare fallow by a cover crop on soil salt accumulation and salt leaching in an irrigated maize production system.

HKT2;2/1, a K+-permeable transporter identified in a salt tolerant rice cultivar through surveys of natural genetic polymorphism

We have investigated OsHKT2;1 natural variation in a collection of 49 cultivars with different levels of salt tolerance and geographical origins. The effect of identified polymorphism on OsHKT2;1 activity was analysed through heterologous expression of variants in Xenopus oocytes. OsHKT2;1 appeared to be a highly conserved protein with only five possible amino acid substitutions that have no substantial effect on functional properties. Our study, however, also identified a new HKT isoform, No-OsHKT2;2/1 in Nona Bokra, a highly salt-tolerant cultivar. No-OsHKT2;2/1 probably originated from a deletion in chromosome 6, producing a chimeric gene. Its 5¢ region corresponds to that of OsHKT2;2, whose full-length sequence is not present in Nipponbare but has been identified in Pokkali, a salt-tolerant rice cultivar. Its 3¢ region corresponds to that of OsHKT2;1. No-OsHKT2;2/1 is essentially expressed in roots and displays a significant level of expression at high Na+ concentrations, in contrast to OsHKT2;1. Expressed in Xenopus oocytes or in Saccharomyces cerevisiae, No-OsHKT2;2/1 exhibited a strong permeability to Na+ and K+, even at high external Na+ concentrations, like OsHKT2;2, and in contrast to OsHKT2;1. Our results suggest that No-OsHKT2;2/1 can contribute to Nona Bokra salt tolerance by enabling root K+ uptake under saline conditions.

Phytoextraction of heavy metals from mine soils using hyperaccumulator plants.

Phytoextraction is an environmental-friendly and cost-effective technology that uses metal hyperaccumulator plants to remove heavy metals from soils. The metals are absorbed by the roots, transported and accumulated in the aerial parts of the plants, which can be harvested and eliminated. The aim of this work was to study some hyperaccumulator species that could be useful to decontaminate mine soils and also to investigate the bioavailability and uptake of these metals by plants with the addition of organic amendments. Pot experiments were performed with soil samples collected from two mining areas in the north of Madrid, where there was an intense mining activity more than 50 years ago. Three species (Thlaspi arvense, Brassica juncea and Atriplex halimus) were grown under controlled conditions in pots filled with contaminated soils mixed with 0 Mg, 30 Mg and 60 Mg per hectare of two different organic amendments: a commercial compost made of pine bark, peat and wood fiber and other made of horse and sheep manure and wood fiber. Plants were harvested at the end of their crop cycle and were digested in order to measure metal concentration (Zn, Cu and Cd) in roots and shoots. Highest plant metal concentration was observed in pots treated with pine bark amendment and with pure soil due to an increase in metal bioavailability with decreasing pH. Also in those treatments the total plant biomass was lower, even some plants could not germinate. On the contrary, there was a lower metal concentration in plant tissues of pots with manure because its higher pH whereas plant growth was significantly larger so there was an incresing amount of metals removed from soil by plants. Comparing the three species results indicate a higher total metal uptake in A. halimus than B. juncea and T. arvense. In conclusion, results show that pH affects metal bioavailability and uptake by hyperaccumulator plants. Addition of organic amendments could be a successful technique for stabilization of metals in contaminated soils.

Chemical speciation and mobilization of copper and zinc in naturally contaminated mine soils with citric and tartaric acids

A one-step extraction procedure and a leaching column experiment were performed to assess the effects of citric and tartaric acids on Cu and Zn mobilization in naturally contaminated mine soils to facilitate assisted phytoextraction. A speciation modeling of the soil solution and the metal fractionation of soils were performed to elucidate the chemical processes that affected metal desorption by organic acids. Different extracting solutions were prepared, all of which contained 0.01 M KNO3 and different concentrations of organic acids: control without organic acids, 0.5 mM citric, 0.5 mM tartaric, 10 mM citric, 10 mM tartaric, and 5 mM citric +5 mM tartaric. The results of the extraction procedure showed that higher concentrations of organic acids increased metal desorption, and citric acid was more effective at facilitating metal desorption than tartaric acid. Metal desorption was mainly influenced by the decreasing pH and the dissolution of Fe and Mn oxides, not by the formation of soluble metal–organic complexes as was predicted by the speciation modeling. The results of the column study reported that low concentrations of organic acids did not significantly increase metal mobilization and that higher doses were also not able to mobilize Zn. However, 5–10 mM citric acid significantly promoted Cu mobilization (from 1 mg kg−1 in the control to 42 mg kg−1 with 10 mM citric acid) and reduced the exchangeable (from 21 to 3 mg kg−1) and the Fe and Mn oxides (from 443 to 277 mg kg−1) fractions. Citric acid could efficiently facilitate assisted phytoextraction techniques.

The role of cover crops in irrigated systems: Soil salinity and salt leaching

Soil salinity and salt leaching are a risk for sustainable agricultural production in many irrigated areas. This study was conducted over 3.5 years to determine how replacing the usual winter fallow with a cover crop (CC) affects soil salt accumulation and salt leaching in irrigated systems. Treatments studied during the period between summer crops were: barley (Hordeum vulgare L.), vetch (Vicia villosa L.) and fallow. Soil water content was monitored daily to a depth of 1.3 m and used with the numerical model WAVE to calculate drainage. Electrical conductivity (EC) was measured in soil solutions periodically, and in the soil saturated paste extracts before sowing CC and maize. Salt leaching was calculated multiplying drainage by total dissolved salts in the soil solution, and use to obtain a salt balance. Total salt leaching over the four winter fallow periods was 26 Mg ha−1, whereas less than 18 Mg ha−1 in the presence of a CC. Periods of salt gain occurred more often in the CC than in the fallow. By the end of the experiment, net salt losses occurred in all treatments, owing to occasional periods of heavy rainfall. The CC were more prone than the fallow to reduce soil salt accumulation during the early growth stages of the subsequent cash crop.

CO2 Emission from two old mine drillings (Mt. Amiata, Central Italy) as a possible example of storage and leakage of deep-seated CO2

CO2 Emission from two old mine drillings (Mt. Amiata, Central Italy) as a possible example of storage and leakage of deep-seated CO2

Stresses and stability of a mine paste fill

Se describe el comportamiento de los rellenos de pasta de las cámaras primarias de la mina de Aguas Teñidas y se calcula la resistencia que deben tener dichos rellenos para que no se desmoronen las paredes de los mismos que quedan expuestas al extraer las cámaras secundarias.Abstract:This article presents the study carried out at an underground mine to understand the stress distribution in the paste fills and to calculate the stability of the paste walls. The mine is operated using sublevel stopes. Three-dimensional numerical models designed with the FLAC 3D software are used to study the distribution of the vertical stresses in the paste. The numerical models have demonstrated that an arc-like effect is produced in the paste fills of the primary stopes. This effect relieves the vertical stresses and increases the stability of the exposed paste wall fill. Based on the results of the numerical models, in the 30m high secondary stopes, the arc effect starts to be evident only in paste walls with a width/height ratio lower than 0.8. 3-D calculations show that the use of Mitchell, R. J. et al. (1982) formula may be risky when estimating the fill stability in secondary stopes.

Molecular basis of salt tolerance in Physcomitrella Patens model plant: potassium homeostasis and physiological roles of chx transporters

El suelo salino impone un estrés abiótico importante que causa graves problemas en la agricultura ya que la mayoría de los cultivos se ven afectados por la salinidad debido a efectos osmóticos y tóxicos. Por ello, la contaminación y la escasez de agua dulce, la salinización progresiva de tierras y el aumento exponencial de la población humana representan un grave problema que amenaza la seguridad alimentaria mundial para las generaciones futuras. Por lo tanto, aumentar la tolerancia a la salinidad de los cultivos es un objetivo estratégico e ineludible para garantizar el suministro de alimentos en el futuro. Mantener una óptima homeostasis de K+ en plantas que sufren estrés salino es un objetivo importante en el proceso de obtención de plantas tolerantes a la salinidad. Aunque el modelo de la homeostasis de K+ en las plantas está razonablemente bien descrito en términos de entrada de K+, muy poco se sabe acerca de los genes implicados en la salida de K+ o de su liberación desde la vacuola. En este trabajo se pretende aclarar algunos de los mecanismos implicados en la homeostasis de K+ en plantas. Para ello se eligió la briofita Physcomitrella patens, una planta no vascular de estructura simple y de fase haploide dominante que, entre muchas otras cualidades, hacen que sea un modelo ideal. Lo más importante es que no sólo P. patens es muy tolerante a altas concentraciones de Na+, sino que también su posición filogenética en la evolución de las plantas abre la posibilidad de estudiar los cambios claves que, durante el curso de la evolución, se produjeron en las diversas familias de los transportadores de K+. Se han propuesto varios transportadores de cationes como candidatos que podrían tener un papel en la salida de K+ o su liberación desde la vacuola, especialmente miembros de la familia CPA2 que contienen las familias de transportadores KEA y CHX. En este estudio se intenta aumentar nuestra comprensión de las funciones de los transportadores de CHX en las células de las plantas usando P. patens, como ya se ha dicho. En esta especie, se han identificado cuatro genes CHX, PpCHX1-4. Dos de estos genes, PpCHX1 y PpCHX2, se expresan aproximadamente al mismo nivel que el gen PpACT5, y los otros dos genes muestran una expresión muy baja. La expresión de PpCHX1 y PpCHX2 en mutantes de Escherichia coli defectivos en el transporte de K+ restauraron el crecimiento de esta cepa en medios con bajo contenido de K+, lo que viii sugiere que la entrada de K+ es energizada por un mecanismo de simporte con H+. Por otra parte, estos transportadores suprimieron el defecto asociado a la mutación kha1 en Saccharomyces cerevisiae, lo que sugiere que podrían mediar un antiporte en K+/H+. La proteína PpCHX1-GFP expresada transitoriamente en protoplastos de P. patens co-localizó con un marcador de Golgi. En experimentos similares, la proteína PpCHX2-GFP localizó aparentemente en la membrana plasmática y tonoplasto. Se construyeron las líneas mutantes simples de P. patens ΔPpchx1 y ΔPpchx2, y también el mutante doble ΔPpchx2 ΔPphak1. Los mutantes simples crecieron normalmente en todas las condiciones ensayadas y mostraron flujos de entrada normales de K+ y Rb+; la mutación ΔPpchx2 no aumentó el defecto de las plantas ΔPphak1. En experimentos a largo plazo, las plantas ΔPpchx2 mostraron una retención de Rb+ ligeramente superior que las plantas silvestres, lo que sugiere que PpCHX2 promueve la transferencia de Rb+ desde la vacuola al citosol o desde el citosol al medio externo, actuando en paralelo con otros transportadores. Sugerimos que transportadores de K+ de varias familias están involucrados en la homeostasis de pH de orgánulos ya sea mediante antiporte K+/H+ o simporte K+-H+.ix ABSTRACT Soil salinity is a major abiotic stress causing serious problems in agriculture as most crops are affected by it. Moreover, the contamination and shortage of freshwater, progressive land salinization and exponential increase of human population aggravates the problem implying that world food security may not be ensured for the next generations. Thus, a strategic and an unavoidable goal would be increasing salinity tolerance of plant crops to secure future food supply. Maintaining an optimum K+ homeostasis in plants under salinity stress is an important trait to pursue in the process of engineering salt tolerant plants. Although the model of K+ homeostasis in plants is reasonably well described in terms of K+ influx, very little is known about the genes implicated in K+ efflux or release from the vacuole. In this work, we aim to clarify some of the mechanisms involved in K+ homeostasis in plants. For this purpose, we chose the bryophyte plant Physcomitrella patens, a nonvascular plant of simple structure and dominant haploid phase that, among many other characteristics, makes it an ideal model. Most importantly, not only P. patens is very tolerant to high concentrations of Na+, but also its phylogenetic position in land plant evolution opens the possibility to study the key changes that occurred in K+ transporter families during the course of evolution. Several cation transporter candidates have been proposed to have a role in K+ efflux or release from the vacuole especially members of the CPA2 family which contains the KEA and CHX transporter families. We intended in this study to increase our understanding of the functions of CHX transporters in plant cells using P. patens, in which four CHX genes have been identified, PpCHX1-4. Two of these genes, PpCHX1 and PpCHX2, are expressed at approximately the same level as the PpACT5 gene, but the other two genes show an extremely low expression. PpCHX1 and PpCHX2 restored growth of Escherichia coli mutants on low K+-containing media, suggesting they mediated K+ uptake that may be energized by symport with H+. In contrast, these genes suppressed the defect associated to the kha1 mutation in Saccharomyces cerevisiae, which suggest that they might mediate K+/H+ antiport. PpCHX1-GFP protein transiently expressed in P. patens protoplasts co-localized with a Golgi marker. In similar experiments, the PpCHX2-GFP protein appeared to localize to tonoplast and plasma x membrane. We constructed the ΔPpchx1 and ΔPpchx2 single mutant lines, and the ΔPpchx2 ΔPphak1 double mutant. Single mutant plants grew normally under all the conditions tested and exhibited normal K+ and Rb+ influxes; the ΔPpchx2 mutation did not increase the defect of ΔPphak1 plants. In long-term experiments, ΔPpchx2 plants showed a slightly higher Rb+ retention than wild type plants, which suggests that PpCHX2 mediates the transfer of Rb+ from either the vacuole to the cytosol or from the cytosol to the external medium in parallel with other transporters. We suggest that K+ transporters of several families are involved in the pH homeostasis of organelles by mediating either K+/H+ antiport or K+-H+ symport.

Phytoextraction of heavy metals from mine soils using hyperaccumulator plants

The aim of this work was to study some hyperaccumulator species that could be useful to decontaminate mine soils and also to investigate the bioavailability and uptake of these metals by plants with the addition of organic amendments. Pot experiments were performed with soil samples collected from two mining areas in the north of Madrid, where there was an intense mining activity more than 50 years ago. Three species (Thlaspi arvense, Brassica juncea and Atriplex halimus) were grown under controlled conditions in pots filled with contaminated soils mixed with 0 Mg, 30 Mg and 60 Mg per hectare of two different organic amendments: a commercial compost made of pine bark, peat and wood fiber and other made of horse and sheep manure and wood fiber. Plants were harvested at the end of their crop cycle and were digested in order to measure metal concentration (Zn, Cu and Cd) in roots and shoots. Highest plant metal concentration was observed in pots treated with pine bark amendment and with pure soil due to an increase in metal bioavailability with decreasing pH. Also in those treatments the total plant biomass was lower, even some plants could not germinate. On the contrary, there was a lower metal concentration in plant tissues of pots with manure because its higher pH whereas plant growth was significantly larger so there was an incresing amount of metals removed from soil by plants. Comparing the three species results indicate a higher total metal uptake in A. halimus than B. juncea and T. arvense. In conclusion, results show that pH affects metal bioavailability and uptake by hyperaccumulator plants. Addition of organic amendments could be a successful technique for stabilization of metals in contaminated soils.

Effects of sheep and horse manure and pine bark amendments on metal distribution and chemical properties of contaminated mine soils.

Mine soils usually contain large levels of heavy metals and poor fertility conditions which limit their reclamation and the application of phyto-remediation technologies. Two organic waste materials (pine bark compost and sheep and horse manure compost), with different pHs and varying degrees of humification and nutrient contents, were applied as amendments to assess their effects on copper (Cu) and zinc (Zn) bioavailability and on fertility conditions of mine soils. Soil samples collected from two abandoned mining areas near Madrid (Spain) were mixed with 0, 30 and 60 t ha?1 of the organic amendments. The concentrations of metals among the different mineral and organic fractions of soil were determined by several extraction procedures to study the metal distribution in the solid phase of the soil affected by the organic amendments. The results showed that the manure amendment increased the soil pH and the cation exchange capacity and enhanced the nutrient levels of these soils. The pine bark amendment decreased the soil pH and did not significantly change the nutrient status of soil. Soil pH, organic matter content and its degree of humification, which were altered by the amendments, were the main factors affecting Cu fractionation. Zn fractionation was mainly affected by soil pH. The addition of manure not only improved soil fertility, but also decreased metal bioavailability resulting in a reduction of metal toxicity. Conversely, pine bark amendment increased metal ioavailability. The use of sheep and horse manure could be a cost-effective practice for the restoration of contaminated mine soils.