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1.
Christopher A. Thoms   《Geoforum》2008,39(3):1452-1465
Community forestry in Nepal vests rights of access, use, exclusion, and management of national forestland to local user groups. There is strong potential for community forests to serve as the basis for improving the quality of life and the status of livelihoods in rural Nepal while conserving forest resources. Frequently, community forest user groups are dominated by local elites who choose to close access to community forestland for several years. As a result, forest conditions are improving, but the poorest households bear the cost of strict protection. In this paper I argue that community forestry is thus having rather limited success at improving rural livelihoods. Although community forestry is fairly successful at conservation, there remain huge wealth disparities between community forest member households, limited access to vital forest products, and significant power disparities within community forest user groups. Such conditions of inequity, reinforced by current community forestry policy and practice, severely challenge the development potential of community-controlled natural resources. In Nepal, overcoming these challenges may require a change in policy that mandates more inclusive local decision-making.  相似文献   

2.
Hutton  David  Haque  C. Emdad 《Natural Hazards》2003,29(3):405-421
The purpose of this research was to identify social, culturaland psychological aspects of riverbank erosion-induced displacement in the flood plainsof Bangladesh. Although considerable research has examined the social and economicimpacts of riverine hazards in Bangladesh, there has been a general neglect of associatedpsychosocial implications. The specific objectives of the study were to: (1) assess hazardawareness in relation to riverbank erosion, (2) determine the magnitude of psychologicaldistress associated with displacement, and (3) identify patterns of psychosocial copingand adaptation common to displaced persons in Bangladesh. Although displacees were foundto have a significantly higher level of distress than non-displacees, this was relatedprimarily to socioeconomic deprivation rather than to displacement per se. The findingsof this study showed that the constant threat of riverbank erosion has contributed to asubstantial disaster subculture in the riverine zones of Bangladesh. The commonly hypothesized factorssuch as loss of land and frequency and duration of displacement were notsignificantly associated with distress levels.The need to integrate into hazard analysis and mitigation studiesa social, cultural and psychological context is recommended. In Bangladesh, the poor copewith hardship and problems by relying on religion, which in turn significantlyinfluences how they perceive and interpret natural calamities. It is argued that the capacityof people to respond to environmental threats is a function of not only the physicalforces which affect them, but of indigenous social and cultural belief systems which influencehow people interpret and organize their activities. Hazard analysis and mitigation wouldbe most effective when it takes into account psychological and socio-cultural aspects ofdisasters, due to the fact that psychological distress impacts the capacity of people toachieve livelihoods, but also important social and psychological processes determine the waypeople perceive and adapt to natural hazards.  相似文献   

3.
This study investigated the relationship between near-surface lithology and the spatial variability of As concentrations using sediment grain-size analysis and electromagnetic induction survey in the southeast Bangladesh. It has been observed that the aquifers overlain by finer sediments have higher concentrations of As in groundwater, whereas As concentrations are remarkably low in aquifers having permeable sandy materials or thinner silt/clay layer at the surface. The near-surface lithology acts as a controlling factor for spatial distributions of groundwater As within the very shallow depths (<15 m). Shallow alluvial aquifers can provide low-As drinking water in many areas of the country when tube wells are properly installed after investigation of the overlying near-surface sediment attributes and hydraulic properties.  相似文献   

4.
The extremely heterogeneous distribution of As in Bangladesh groundwater has hampered efforts to identify with certainty the mechanisms that lead to extensive mobilization of this metalloid in reducing aquifers. We show here on the basis of a high-resolution transect of soil and aquifer properties collected in Araihazar, Bangladesh, that revealing tractable associations between As concentrations in shallow (< 20 m) groundwater with other geological, hydrological, and geochemical features requires a lateral sampling resolution of 10–100 m. Variations in the electromagnetic conductivity of surface soils (5–40 mS/m) within a 500 m × 200 m area are documented with 560 EM31 measurements. The results are compared with a detailed section of groundwater As concentrations (5–150 μg/L) and other aquifer properties obtained with a simple sampling device, “the needle-sampler”, that builds on the local drilling technology. By invoking complementary observations obtained in the same area and in other regions of Bangladesh, we postulate that local groundwater recharge throughout permeable sandy soils plays a major role in regulating the As content of shallow aquifers by diluting the flux of As released from reducing sediments.  相似文献   

5.
Harold A. Perkins 《Geoforum》2011,42(5):558-566
The US Department of Agriculture Forest Service and the Wisconsin Department of Natural Resources coordinate the distribution of urban forestry grants to nonprofits and citizen groups. These granting agencies increased state funding during a period of neoliberal, fiscal austerity in order to channel ecosystem services provided by urban forests. Increased funding is an instance of rollout neoliberalism whereby the fiscally austere state builds market capacity to harness these services as part of an ecologically modernist agenda. A Gramscian perspective and data gathered from 20 in-depth interviews with foresters are used in this paper to theorize how rollout policy is deployed through urban forestry to extend market hegemony to new geographies. This is anything but a smooth process because the public’s perception of urban trees is highly varied. State bureaucracies must build civil sector capacity to educate people about the ecosystem services trees provide as market commodities. In doing so the state’s market-oriented regulatory legitimacy is consolidated through the apparently benign act of promoting urban forestry. This dialectical process limits participation in urban forestry because markets are inherently selective. Yet it potentially gives rise to an alternative political ecology of praxis beyond market ideology when grant recipients participate in the production of urban ecology and recognize their relationship with nature.  相似文献   

6.
Arsenic contaminates groundwater across much of southern, central and eastern Bangladesh. Groundwater from the Holocene alluvium of the Ganges, Brahmaputra and Meghna Rivers locally exceeds 200 times the World Health Organisation (WHO) guideline value for drinking water of 10 µg/l of arsenic. Approximately 25% of wells in Bangladesh exceed the national standard of 50 µg/l, affecting at least 25 million people. Arsenic has entered the groundwater by reductive dissolution of ferric oxyhydroxides, to which arsenic was adsorbed during fluvial transport. Depth profiles of arsenic in pumped groundwater, porewater, and aquifer sediments show consistent trends. Elevated concentrations are associated with fine-sands and organic-rich sediments. Concentrations are low near the water table, rise to a maximum typically 20–40 m below ground, and fall to very low levels between about 100 and 200 m. Arsenic occurs mainly in groundwater of the valley-fill sequence deposited during the Holocene marine transgression. Groundwater from Pleistocene and older aquifers is largely free of arsenic. Arsenic concentrations in many shallow hand-tube wells are likely to increase over a period of years, and regular monitoring will be essential. Aquifers at more than 200 m below the floodplains offer good prospects for long-term arsenic-free water supplies, but may be limited by the threats of saline intrusion and downward leakage of arsenic.
Resumen El arsénico ha contaminado gran parte de las aguas subterráneas en el Sur, centro y Este de Bangla Desh. Su concentración en las aguas subterráneas del aluvial Holoceno de los ríos Ganges, Brahmaputra y Meghna supera localmente en un factor 200 el valor guía del arsénico en el agua potable, establecido por la Organización Mundial de la Salud (OMS) en 10 µg/L. Aproximadamente, el 25% de los pozos de Bangla Desh superan el estándar nacional de 50 µg/L, afectando al menos a 25 millones de personas. El arsénico ha llegado a las aguas subterráneas por la disolución reductora de hidróxidos férricos a los que se adsorbe durante el transporte fluvial. Los perfiles del arsénico en las aguas subterráneas bombeadas, agua de poro y sedimentos del acuífero muestran tendencias coherentes. Las concentraciones elevadas están asociadas a arenas finas y sedimentos ricos en materia orgánica. Las concentraciones de arsénico son bajas cerca del nivel freático, se incrementan hasta un máximo que se localiza generalmente a entre 20 y 40 m bajo la cota del terreno, y disminuyen a valores muy pequeños entre alrededor de 100 y 200 m. El arsénico se encuentra sobretodo en las aguas subterráneas existentes en la secuencia de sedimentación que tuvo lugar en el valle durante la transgresión marina del Holoceno. Las aguas subterráneas del Pleistoceno y acuíferos más antiguos están mayoritariamente libres de arsénico. Es probable que las concentraciones de arsénico aumenten en los próximos años en muchos pozos de tipo tubo perforados manualmente, por lo que será esencial efectuar un muestreo regular. Los acuíferos ubicados a más de 200 m bajo las llanuras de inundación ofrecen buenas perspectivas de abastecimiento a largo plazo sin problemas de arsénico, pero pueden estar limitados por las amenazas de la intrusión salina y de la precolación de arsénico desde niveles superiores.

Résumé Larsenic contamine les eaux souterraines dans la plus grande partie du sud, du centre et de lest du Bangladesh. Les eaux des nappes alluviales holocènes du Gange, du Brahmapoutre et de la Meghna dépassent localement 200 fois la valeur guide donnée par lOMS pour leau de boisson, fixée à 10 µg/l darsenic. Environ 25% des puits du Bangladesh dépassent la valeur standard nationale de 50 µg/l, affectant au moins 25 millions de personnes. Larsenic a été introduit dans les nappes par la dissolution par réduction doxy-hydroxydes ferriques sur lesquels larsenic était adsorbé au cours du transport fluvial. Des profils verticaux darsenic dans leau souterraine pompée, dans leau porale et dans les sédiments des aquifères montrent des tendances convergentes. Les concentrations élevées sont associées à des sédiments à sable fin et riches en matières organiques. Les concentrations sont faibles au voisinage de la surface de la nappe, atteignent un maximum typiquement entre 20 et 40 m sous le sol, puis tombent à des niveaux très bas entre 100 et 200 m. Larsenic est surtout présent dans les eaux souterraines de la séquence de remplissage de vallée déposée au cours de la transgression marine holocène. Les eaux souterraines des aquifères pléistocènes et plus anciens sont très largement dépourvus darsenic. Les concentrations en arsenic dans de nombreux puits creusés à la main doivent probablement augmenter au cours des prochaines années ; aussi un suivi régulier est essentiel. Les aquifères à plus de 200 m sous les plaines alluviales offrent de bonnes perspectives pour des alimentations en eau sans arsenic à long terme, mais ils peuvent être limités par les risques dintrusion saline et la drainance descendante de larsenic.
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7.
Dominique Moran 《GeoJournal》2001,55(2-4):541-547
This paper explores the relationship between the forestry enterprises (leskhozi) and the inhabitants of forestry villages in the northern rayony of Perm oblast, Russian Federation in the context of the `new regional geography'. These relationships are compared with those identified between peasant farmers and collective and state farms post-1991, and a theory of the cultivation of these relationships as a coping mechanism for both households and enterprises facing difficult economic circumstances is advanced. The situation in the northern rayony is contextualised through discussion of the settlement and development history of the region, which was a recipient of forced and voluntary labour migration during the Soviet period. The paper concludes that in accordance with recent theories of post-communist regional development, the experience of transition in the northern rayony of Perm oblast is determined at least in part by its social and economic context. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
This paper examines the nature and causes of September 2004 hazardous flood that affected the dry and drought prone southwestern region of Bangladesh. It also examines human perception of this new hazard and their methods of adjustments to its negative impacts. Field research for this study includes personal interviews of 453 victim families living in four thanas (lowest administrative units) in Jessore and Satkhira districts of southwestern Bangladesh. Findings of the study suggest that all victim respondents viewed this flood event as a natural hazard, which has caused severe damage to standing crops, fish ponds, permanent trees and homesteads, and deteriorated human health and sanitation conditions. Its long-term impacts on fish farming, soil quality degradation, as well as changing land use/land coverage are also noteworthy but yet to be adequately explored. Both perceived and scientific causes of this flood event include high rainfall for a week before the flood, unusual movement of low pressure system into the affected area, cloudy weather and low evaporation, siltation of the regional riverbeds, and rolling back of the Ganges River water through the Ichamati and Bhagirati rivers. These factors also caused hazardous flooding at the same time in the Ichamati and Bhagirati Rivers and their floodplains in the West Bengal province of India. To release the overflow of flood water inside India, the Indian border patrol breached the Ichamati river embankment in several places along Satkhira and Jessore international border which had aggravated the flood situation in the study area.  相似文献   

9.
Application of hornblende thermobarometry and fluid inclusion studies to the Palaeoproterozoic (1.7 Ga) basement rocks from Maddhapara, NW Bangladesh, provide information on the pressure and temperature (P–T) conditions of crystallization, the emplacement depth and composition of magmatic fluid. The basement rocks are predominantly diorite or quartz diorite with a mineral assemblage of plagioclase, hornblende, biotite, quartz, K-feldspar, titanite, and secondary epidote and chlorite. The calculated P–T conditions of the dioritic rocks are 680–725 °C and 4.9–6.4 kbar, which probably correspond to crystallization conditions. Fluid inclusion studies suggest that low- to medium-salinity (0–6.4 wt.% NaCleq) H2O-rich fluids are trapped during the crystallization of quartz and plagioclase. The isochore range calculated for primary aqueous inclusions is consistent with the P–T condition obtained by geothermobarometry. The basement rocks likely crystallized at a depth of 17–22 km, with a minimum average exhumation rate of 12–15 m/Ma during Palaeoproterozoic to Lopingian time. Such slow exhumation indicates low relief continental shield surface during this period.  相似文献   

10.
 Arsenic toxicity in groundwater in the Ganges delta and some low-lying areas in the Bengal basin is confined to middle Holocene sediments. Dissected terraces and highlands of Pleistocene and early Holocene deposits are free of such problems. Arsenic-rich pyrite or other arsenic minerals are rare or absent in the affected sediments. Arsenic appears to occur adsorbed on iron hydroxide-coated sand grains and clay minerals and is transported in soluble form and co-precipitated with, or is scavenged by, Fe(III) and Mn(IV) in the sediments. It became preferentially entrapped in fine-grained and organic-rich sediments during mid-Holocene sea-level rises in deltaic and some low-lying areas of the Bengal basin. It was liberated subsequently under reducing conditions and mediated further by microbial action. Intensive extraction of groundwater for irrigation and application of phosphate fertilizer possibly triggered the recent release of arsenic to groundwater. This practice has induced groundwater flow, mobilizing phosphate derived from fertilizer, as well as from decayed organic matter, which has promoted the growth of sediment biota and aided the further release of arsenic. However, the environment is not sufficiently reducing to mobilize iron and arsenic in groundwater in the Ganges floodplains upstream of Rajmahal. Thus, arsenic toxicity in the groundwater of the Bengal basin is caused by its natural setting, but also appears to be triggered by recent anthropogenic activities. Received: 23 August 1999 · Accepted: 16 November 1999  相似文献   

11.
Emdad Haque  C. 《Natural Hazards》1997,16(2-3):181-202
In probabilistic terms, Bangladesh is prone, to at least one major 'tropical cyclone' every year. This situation is primarily due to the geographical location of Bangladesh in tropical Asia, and to its concave coastline and shallow continental shelf. The devastating impact of such cyclones on humans stems from a combination of intense human occupation of the area, predominance of traditional sociocultural values and religion, the precarious socioeconomic conditions of the majority of the coastal inhabitants, and the lack of a coordinated institutional disaster planning and management strategy. Bangladesh has experienced several catastrophic environmental disasters during the last decade; among these events, the 1991 April cyclone was the most catastrophic in terms of both physical and human dimensions.An initial study was carried out in the coastal regions of Bangladesh less than two weeks after they were hit by the severe cyclone of 29 April 1991. This research examined the process through which warning of the impending disastrous cyclone was received by the local communities and disseminated throughout the coastal regions of Bangladesh. It was found that the identification of the threatening condition due to atmospheric disturbance, the monitoring of the hazard event, and the dissemination of the cyclone warning were each very successful. The present study followed up on the initial research by surveying 267 respondents with an elaborate survey instrument, focusing on the most crucial academic and planning issues identified in the 1991 study. In particular, the nature and characteristics of the cyclone preparedness of the coastal inhabitants were assessed by the study; other factors considered included rural-urban variations, mainland-island differences, the nature and role of previous knowledge, and the disaster experience.The survey results show the variety of indigenous adjustment mechanisms that help to rehabilitate the survivors; also visible are the profound roles played by the social inequality variables and the magnitude of physical vulnerability in influencing the disaster loss and recovery process. The study recommends that hazard mitigation policies should be integrated with national economic development plans and programs. Specifically, it is suggested that the cyclone warning system should incorporate the human response to warnings as its constituent part, and in this way accommodating human dimensions in its operational design.  相似文献   

12.
Samantha Jones 《Geoforum》2007,38(3):558-575
In the buffer zone of the Royal Chitwan National Park (RCNP), community forests represent a key land use to meet the objectives of the buffer zone concept. This article examines three diverse community forests surrounding the national park and explores how national policy has been mediated by emerging community forestry institutions to create different levels of resource access and benefit distribution both within and between local user groups. Mindful of recent critiques of community-based conservation, the analysis gives considerable attention to the dynamics of power relations and inequality. The extent to which property rights have been transferred to the local level is evaluated and to whom power has been devolved in the process is assessed. The distribution of benefits arising from community forestry is critically examined. It seems that the current system for community forestry creates sufficient incentives for local cooperation due to the potential for increased access to important resources and a high perception of ownership of community forests among the communities. However, emerging institutions vary in the extent to which they reproduce favourable resource access conditions for elites and benefit distribution does seem to be skewed in favour of the wealthy and higher castes, even where management practices on the surface appear fair. National policy creates sufficient but not necessary conditions for achieving downward accountability, transparency and fairness. Greater attention to these issues is needed for buffer zone community forestry to better serve the poor and marginalised populations within user groups.  相似文献   

13.
Using a three-dimensional finite element model, this study characterizes groundwater flow in a costal plain of the Seto Inland Sea, Japan. The model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow. Geological geometry and the number of aquifers have been analyzed based on a large amount of geological, hydrogeological and topographical data. Results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer. For calibrating the numerical groundwater model, the groundwater flow was simulated in steady state. In addition, the groundwater level and trend in the transient state has also been elucidated. The numerical result provides excellent visual representations of groundwater flow, presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways. Results build a base for further analysis under different future scenarios.  相似文献   

14.
This paper explores the logic driving the evolving geography of business service provider/suppler relationships in Norway. It explores the ways in which Norwegian SMEs access external knowledge provided by management consultants through three case studies that have been developed using a matched pairs methodology (clients and consultants). The paper highlights the relationships between geography and client sourcing of external knowledge and expertise in three kinds of client/consultant relationship: local (clustered) knowledge; dislocated or distantiated knowledge, and; knowledge that is relatively distance insensitive. The concept of dislocated expertise or knowledge adds an additional dimension to literatures that highlight the importance of localised knowledge and strategies to reduce transaction costs, as well as providing insights into the complex relationships that occur between suppliers and consumers of knowledge and expertise. The importance of local business cultures and patriotic purchasing are also identified as playing important roles in influencing the behaviour of Norwegian firms.  相似文献   

15.
Encouraged by government policies to promote city centre living and to increase residential land use on brownfield sites, there has been considerable repopulation of the city centre. Through detailed small-area census analysis of Birmingham, Bristol, Cardiff and Swansea, supplemented by household surveys and key informant interviews, the research points to a range of population characteristics and changes occurring in the British city centre. Certain characteristics such as a high proportion of lone person households, fewer children and low car ownership remain fairly consistent. However, substantial population expansion affirms that a large part of the population is “new”. Between 1991 and 2001, men came to outnumber women, and each of the city centres saw a relative expansion of its young adult population. The new residents have a higher appreciation than longer term residents of proximity to work and leisure facilities, and of the stylishness of city centre living. Most of the new residents rent their accommodation, generally in flats, and the predominance of renting is associated with a transient attitude to city centre residence among the new population. Socio-economic evidence indicates a striking rise in social status or gentrification in all the city centres investigated, especially where high status private housing developments encourage the trend. With policies promoting residential development, the city centre is becoming increasingly socially exclusive.  相似文献   

16.
Social movement organizations (SMOs) play an important role in movement building, however, the particular context and structure of a SMO has a direct impact on its ability to foster and sustain collaboration. In this paper I investigate the unique positioning of provincial networking organizations (PNOs) in Canadian food movements and document their efforts to support alternative food initiatives (AFIs) to interact and act collaboratively for food system change. The research draws on a network survey, over 35 in-depth interviews, site visits, and background information collected in three Canadian provinces to explore the ongoing work necessary for linking together heterogeneous elements without central coordinating mechanisms. I describe the ways that PNOs have established a series of common networking strategies to bring AFIs together across sectors, scales and places: (1) the creation of physical spaces that involve direct contact in particular places; (2) the development of virtual spaces where connections are mediated through digital technologies; and (3) the use of scalar strategies that scale-up local projects to address provincial level policy. I conclude by identifying key areas of contention that arise within the networks, and show that the different structures of the PNOs impact their ability to establish and implement networking strategies. I argue that addressing these challenges must be a preemptive focus in order to sustain networking activity. My contention that contemporary structures of social mobilization require novel strategies and support from networking organizations provides insight for studies of SMOs and movement building more broadly.  相似文献   

17.
Frame analysis has been widely employed to understand environmental conflicts. Such studies emphasize the internal dynamics of conflict and focus on how actors discursively struggle with each other in order to gain hegemony over the dominant discourse on the issue. In this paper, we argue that the explanatory power of framing theory could be enhanced by relating issue specific frames to the broader cultural context in which framing efforts are situated. In order to investigate the link between the success of framing strategies and the cultural background of such strategies, we suggest rethinking the concept of cultural resonance. We propose social representations theory as a novel way of understanding this cultural resonance of spatial and environmental frames. Based on a dispute over the management of a national park in the Netherlands, we empirically illustrate how contending stakeholders refer to different social representations of nature in the framing of local conflicts. A local protest group proves to be much more in touch with the views of the local community and is thus more successful in its framing of the dispute than the nature conservation agency involved. While the protest group uses a wide range of locally embedded representations of nature to enhance the currency of its framing efforts, the nature conservation agency responsible for the management of the forest refers to a much more limited range of representations. By making references only to the wilderness representation of nature, the cultural resonance of the agency’s framing efforts remains limited to those residents who adhere to this specific representation of nature. Consequently, this framing is not very successful among groups that adhere to other representations of nature, such as aesthetic or inclusive representations. Our analysis shows that combining framing theory with social representations theory enables one to disentangle the framing of environmental disputes from the more constant cultural values and opinions on which this framing is based.  相似文献   

18.
To avoid dominant positivist explanations of links between climate change and security, I use alternative, human security approaches to study how climate security is managed in one of Spain’s most endangered coastal ecosystems, the Ebro Delta. I find that increasing the downstream flow of sediments retained in upstream dams is a crucial measure for dealing with climate change threats (sea-level rise) in the Delta. Yet, state policies do not increase sediment flow, but instead implement incremental adaptation at the site of climate impact (coast), which, at times, requires executing small-scale land expropriations. Refraining from improving human security via increasing sediment flow benefits corporate interests upstream. At the same time, expropriation silences mild farmer protest downstream and adds insult to injury by conveying to farmers a sense of blame for their vulnerability to climate change. Meanwhile, using expropriation at the service of incremental adaptation goes against the very rationale of expropriation established by Spanish legislation and creates a fundamental contradiction between what the practice is meant to deliver, namely security and the social contract from the part of the state, and what it actually does, i.e. permit the state to evade providing human security. I conclude that, under climate change, achieving human security, the delivery of the social contract, and corporate rent-seeking at the same time may not be possible. Moreover, rather than the social contract been threatened by state incapacity to respond to the effects of climate change and breached social contract expectations of vulnerable communities, it is the actual mobilisation of the contract in order to respond to climate change that diminishes human security.  相似文献   

19.
Commercial afforestation in South Africa dates back to the 1870s and started as an alternative to the fast disappearing indigenous timber resource. It involves the planting of exotic timber species and has impacts on water resources, soil biodiversity, landscapes, etc. Commercial afforestation of land has been subjected to regulation through the Afforestation Permit System (APS) since 1972, primarily to protect the national water resource. Since the APS no longer adequately dealt with afforestation regulation, it was replaced in 1999 with a procedure that was supposed to integrate the requirements of relevant legislation and general environmental management principles. This paper is a theoretical review of the background and development of the new South African Streamflow Reduction Activities licensing procedure, as well as whether it complies with the requirements of an environmental management system such as ISO 14001. The main conclusion is that the new procedure, although an improvement on the previous procedure, still has shortcomings especially with regard to the operational and decommissioning phases of forestry in South Africa. It is recommended that these aspects be addressed in order to mitigate the impact of forestry on water sustainability in South Africa. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
The Lince–Estefanía stratabound copper deposit in the Michilla district is one of the most important deposits in the Coastal Cordillera of northern Chile and is one of the most representative of this type of deposit. Chalcocite and bornite characterize the main stage of hypogene copper sulfide mineralization. Rhenium and osmium isotopes are used here to constrain the age of hypogene mineralization and the source of osmium contained in these ore minerals. A Re–Os isochron yielded an age of 160±16 Ma (2σ), with an associated initial 187Os/188Os ratio of 1.06±0.09 (mean square of weighted deviates=1.8). This age is consistent with available geochronological data from volcanic rocks that host the mineralization and associated alteration phases. The high initial 187Os/188Os ratio indicates a lower crustal component for the source of Os and, by inference, the Cu sulfides that contain this Os. Late hematite occurs as an isolated phase or, more commonly, is associated with the chalcocite–bornite and supergene chalcocite–covellite associations. Analyses performed on pure hematite indicate a disturbance of the Re–Os system, and hence, this mineral phase is not useful as a Re–Os geochronometer.  相似文献   

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