Pre-mining Conditions Research Articles

Geochemical Baseline and Pre-Mining Environmental Assessment of Heavy Metals at Iron Exploration Area, Northeastern Aswan, Egypt

Wadi Abu Subeira area contains many farms and houses and is one of the promising areas for iron mining. Therefore, 21 surface soil samples were collected and investigated for toxic heavy metals (Pb, Cr, Ni, Cu, Zn, Co, and As) using inductively coupled plasma (ICP) to establish a geochemical baseline for these metals during pre-mining conditions. To decipher the sources of these metals and their interrelationships, multivariate statistical analysis was applied, while to evaluate the degree of pollution and potential environmental risks the environmental indices were used. Abundances of Pb, Cr, Ni, Cu, Zn, Co, and As fluctuated from 17.72 to 0.06, 47.12 to 10.86, 47.88 to 9.25, 45.04 to 6.23, 51.93 to 17.82, 10.55 to 1.24, and 7.04 to 1.66 mg/kg, respectively, displaying a declining trend of Zn > Cr > Ni > Cu > As > Co > Pb. Additionally, the mean concentrations of all studied metals were found to be significantly lower than the selected international reference standards. Pearson correlation coefficient, principal component analysis, and cluster analysis revealed two geogenic geochemical associations for the studied toxic elements: (1) Zn-As-Ni-Cr-Cu-Co; and (2) Pb. Negative Igeo values were observed for all metals, which showed that the samples were uncontaminated and can be considered a geochemical baseline for the study area. Moreover, all CF values were lower than or close to 1, suggesting low contamination levels from all studied metals and supporting the association with natural geological processes. Similarly, Er and RI values of all metals were below 40 and 150, respectively, indicating a low-risk environment. Ultimately, the obtained levels of the studied metals can be used as a geochemical baseline for tracking the future changes in their accumulations in soil sediments considering the current assessment of the area as an environmentally safe area.

Cinnamon Gulch revisited: Another look at separating natural and mining-impacted contributions to instream metal load

Baseline, premining data for streams draining abandoned mine lands is virtually non existent, and indirect methods for estimating premining conditions are needed to establish realistic, cost effective cleanup goals. One such indirect method is the proximal analog approach, in which premining conditions are estimated using data from nearby mineralized areas that are unaffected by mining. In this paper, we combine the proximal analog approach with a quantitative mass balance framework using data from a spatially-detailed synoptic sampling campaign. The combined approach is applied to Cinnamon Gulch, a headwater stream with numerous draining adits. Synoptic sampling results indicate that three of the top five metal sources are affected by mining activities, and stream segments draining these sources account for a large percentage of overall metal loading within the study reach. These initial calculations overestimate the effects of mining, as the affected stream segments were likely acidic and metal rich prior to mining. Premining loads and concentrations were therefore determined through a replacement approach in which the chemistry of each mining-affected stream segment is revised based on proximal analog concentrations. The revised loading profiles indicate that 15–17% of the Al, Cd, Cu, Mn, Ni, and Zn loads are attributable to mining, whereas the mining contribution for Pb is 40%. Premining concentrations of Al, Cd, Cu, Mn, and Zn are estimated to be in excess of aquatic life standards over the length of the study reach.

Surface coal mine permit application for successful reclamation, semi-arid shortgrass prairie (Wyoming, USA)

Approximately 40% of USA coal originates in an ecologically sensitive area of semi-arid shortgrass prairie in Wyoming. Before a surface coal mine can begin operation in the USA, it must secure a mining permit and comply with regulations and performance standards under the USA Surface Mining Control and Reclamation Act (SMCRA), other federal environmental acts, and state programs. The Wyoming Department of Environmental Quality (WDEQ)/Land Quality Division (LQD) administers Wyoming’s coal regulatory program. The permit application and bonding process for the largest surface coal mine permit in the USA, North Antelope Rochelle Mine (NARM) located in short grassland prairie in the northeast Wyoming, is discussed. The permit application process begins with the collection of baseline environmental data that characterizes premining conditions of the permit area. The permit application includes adjudication information, baseline information, mine and operation plans, and reclamation plans. Fulfillment of permit commitments and requirements of rules and regulations are inspected monthly by the LQD’s representative in the field. Before a mine permit is issued, the mine operator must submit a reclamation bond to secure the performance of reclamation obligations that is later revised annually. In Wyoming, four reclamation bond release phases indicate the completion of various stages of the reclamatikon process. NARM’s specific bond release verification cirteria, performance standards, and field verificatoins of bond release phases are discussed. The Bond Release Geodatabase (a GIS/GPS approach) was developed for this mine to monitor progress in meeting criteria and performance standards for incremental bond release. The Bond Release Geodatabase significantly reduces the time needed to track bond release progress, reach agreement between operator and regulator, and improve the state inspector’s ability to assess reclamation adequacy and progress.

Factors influencing colonisation processes in two contrasting mine sites in the Namib Desert

I investigated vegetation recovery in a uranium mine in the central Namib and a diamond mine in the southern Namib to better understand natural recovery processes in arid areas. Environmental variables influencing colonisation processes were investigated using multivariate analyses to examine the relative importance of environmental variables on vegetation recovery at the two mines. Disturbance level was the most important variable influencing colonisation processes in the central Namib whereas distance to seed source was the most important in the southern Namib. At both mines, the proximity of a species pool to the disturbed areas (reference species pool) was more important than the pool of available species in the broader ecological community in which the mines were located (ecological species pool). The study indicates that merely relying on spontaneous, natural recovery is insufficient in the Namib if (1) pre-mining conditions are the restoration goal and (2) presently undisturbed or well recovered areas in the mine cannot be preserved as a suitable seed sources in the southern Namib. Appropriate completion criteria need to be developed that consider local conditions in order to ensure that restoration of mines in arid areas is realistic.

Dendrochronology in mineral exploration: developing tools to see through anthropogenic impacts

The Sudbury Igneous Complex (SIC) and its associated mining camp is one of the largest Cu, Ni, PGE ore systems in the world. Due to a long history of mining (>100 years), the SIC has been extensively explored making the discovery of new surface deposits difficult. This study explored the use of dendrochemical analysis as an economic means to locate deposits concealed by overburden. Tree cores combined with soil samples were collected and analyzed from two sites to provide a comparison between a known deposit (Broken Hammer) and a known contamination location (downwind site). Samples were collected from both White Pine (Pinus Strobus) and Scots Pine (Pinus Sylvestris) species, however White Pine proved to have a stronger affinity for the uptake of ore-associated metals (i.e., Cu, Ni, Fe, Co, Hg, Cd, Pb, Sb, S). Analyses of tree-core intervals revealed clear anthropogenic effects in the samples from both sites; however, due to the age of the trees the magnitude of these effects compared to pre-mining conditions could not be determined. The concentrations of S, Cu, Ni, Fe, Al, Pb and As in the downwind samples increased over time. On average, S increased from 6.37 to 8.98 ppm, Cu from 0.503 to 0.908 ppm, Ni from 0.605 to 1.18 ppm, Fe from 124 to 273 ppm, Al from 4.38 to 6.60 ppm and As from 0.008 to 0.012 ppm. Conversely, the concentrations of Cu, Fe, Ni, Al, S and As in the samples from Broken Hammer decreased over time. Copper decreased from 0.84 to 0.55 ppm, Fe from 2.45 to 1.19 ppm, Ni from 1.02 to 1.18 ppm, Al from 6.81 to 4.96 ppm, S from 7.62 to 7.57 ppm and As from 0.014 to 0.002 ppm. The total Pb concentration decreased over time in all samples from both sites. There were no trends in the Pb isotopic ratios with the exception of the 207 Pb/ 206 Pb. A comparison of the samples from each location revealed unique trends in the distribution of the data, which could suggest two sources. Soil (Ah and B horizon) collected proximal to the sampled trees near Broken Hammer showed the metal concentration increasing with depth. Copper averaged 33.6 – 187.9 ppm, whereas Ni had an even steeper trend, increasing from an average of 22.4 ppm–234.5. Sulphur and Hg also displayed a similar trend, however the difference was not as substantial. The highs and lows in concentration levels in the tree cores correspond to various historical events. During WWII (1939 – 1945), the Korean War (1950 – 1953) and the Vietnam war (1964 – 1973), the demand for Ni increased resulting in increased smelting activities and a spike in contamination levels. Conversely, the recession in the late 1970s early 1980s and the INCO strike in the late 1990s resulted in a decrease in Ni production and a drop in contamination levels. The distribution of metal concentrations at Broken Hammer indicates a lack of surface contamination and therefore a non-contaminated B-horizon. The higher concentrations in the B-horizon are anomalous to other studies in the Sudbury area suggesting a possible subsurface source. This is encouraging and the potential remains to develop a method for mineral exploration applications utilizing tree core samples, even in heavily mining impacted areas like the Sudbury.

Empty Promises and the Myth of Mining: Does Mining Lead to Pro-Poor Development?

AbstractMining operations in the Global South often worsen conditions for affected communities after the conclusion of the operations as compared to pre-mining conditions. This is regression, not progress, which is contrary to the narrative surrounding mining’s promise of economic growth. While mining certainly brings profit, this profit does not result in social and economic development of affected communities and people living in poverty. This is the ‘myth of mining’ and the objective of this article is to expose this myth, identify its failings and propose a notion of ‘equitable mining’ that could ensure a pro-poor mining industry.

Simulating the hydrologic response when streams are incorporated in valley-fill design

The geomorphic landform design (GLD) approach has the potential to incorporate stream networks into valley-fill reclamation. This work modelled the potential hydrologic response of GLD by evaluating storm response as well as flooding of the receiving reach of one West Virginia valley fill in several construction phases (i.e. pre-mining, conventional design and GLD). The GLD during construction condition resulted in peak flowrates that were more than twice the undisturbed pre-mining condition, but peak flowrates reduce to pre-mining conditions over time. A GLD that included surface ponds was presented to offer on-site streamflow. A retrofit example was presented to improve bond failing sites.

Development of ecosystem structure and function on reforested surface-mined lands in the Central Appalachian Coal Basin of the United States

Surface mining in the Appalachian Coal Basin drastically disturbs the landscape. Post-mining reforestation efforts have reached reliable tree survivability and growth; however, it is unclear whether these reforestation efforts also restore the ecological functions associated with the native forest ecosystem. The objectives of this study were to quantify the rate at which certain key ecosystem functions return to the landscape, and to relate the development of those functions to structural attributes of the ecosystem. A chronosequence of four reclaimed and reforested stands (ages 5, 11, 21 and 30 years) and unmined reference stands representing pre-mining conditions, were identified on the Appalachian Plateau in southwestern Virginia. Total soil nitrogen (N) and component (mineral soil, forest floor, root, and aboveground biomass) ecosystem carbon (C) pools were quantified. Throughout the growing season, monthly samples for soil gas fluxes [i.e., carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)], available inorganic-N [nitrate (NO3 −) and ammonium (NH4 +)], and total and active microbial biomass were measured. As expected, soil organic C (SOC) and total ecosystem C returned to the mined landscape, although at levels still less than half of the unmined reference after 30 years. Ecosystem C accumulation was significantly correlated with soil N (r = 0.80; p = 0.0003) as well as total and active microbial biomass (r = 0.92; p = <0.0001 and r = 0.86; p = <0.0001, respectively). Surprisingly, available inorganic-N and gas fluxes of CO2 and N2O showed no significant differences among any of the mined and unmined stands; however, the reforested mined soils showed a significantly diminished capacity for CH4 uptake, where upland soils typically represent the largest global biogenic sink of atmospheric CH4. Thus, although many ecosystem components (e.g., forest and microbial biomass) and functions (e.g., N cycling), rapidly returned to the reclaimed landscape, some critical ecosystem functions (e.g., methanotrophy) exhibited a fundamentally different rate of return, if present at all. Our results indicate that reforestation of native hardwoods on reclaimed surface mined lands is largely successful at restoring many ecosystem functions, but that certain functional attributes are decoupled from the observed redevelopment of ecosystem structure. Thus, reforestation and forest ecosystem restoration are not necessarily the same thing, and a better understanding of potential disconnects between the two concepts can be critical in guiding both the science and the practice into the future.

Reconstructing a sediment pulse: Modeling the effect of placer mining on Fraser River, Canada

AbstractGold mining along 525 km of the Fraser River between 1858 and 1909 added an estimated 1.1 × 108 t of tailings, half gravel and the rest finer, to the river's natural sediment load. We simulate the response using a 1‐D multigrain size morphodynamic model. Since premining conditions are unknown and modern data are insufficient for tuning the process representation, we devised a novel modeling strategy which may be useful in other data‐poor applications. We start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization. Simulations with an appropriate choice of natural supply rate closely match the best available test data, which consist of a detailed 1952–1999 gravel budget for the distal part of the model domain. The simulations suggest that the main response to mining was rapid bed fining, which allowed a major increase in bed load transport rate with only slight (~0.1 m) mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward. We compare this pattern of response by a large, powerful river with previous case studies of river adjustment to sediment supply change.

Pre-mining acid rock drainage in the Talvivaara Ni–Cu–Zn–Co deposit (Finland): Natural peat layers as a natural analog to constructed wetlands

Altogether 62 peat, 411 bedrock, and 1163 glacial till samples were selected in pre-mining conditions around the present Talvivaara Ni–Cu–Zn–Co mine in Finland. The samples were collected from different lithological areas representing mineralized (>0.07% Ni) and non-mineralized bedrock. The influence of bedrock and till composition, and subsequent groundwater and surface water quality, on the metal and sulfur concentrations in the peat deposits was evaluated. The peat samples at the non-mineralized mica schist study site M1 showed moderate increase in element concentrations (Cu, Ni, S) and decreasing electric conductivity (EC) as a function of depth, whereas at the mineralized black schist study sites M2 and M3 the heavy metal (Fe, Ni, Zn) and sulfur concentrations and EC exhibited a significant increase towards the Carex-dominated bottom layers. Besides anomalous metal (up to 12.0wt.% Fe, 758mg/kg Ni, 5270mg/kg Zn) and S (13.6wt.%) concentrations, the site M2 presented anomalously high ash content (median 35%) and low pH (3.4), which were attributed to the acid rock drainage derived from an adjacent mineralized black schist outcrop. Samples from site M2 were subjected to sequential extractions to study elemental distribution. The studied peatland is a natural analog to constructed wetlands in passive treatment of acid mine drainage waters, though the retention capacity is lower due to low pH and decreased buffering capacity.

Long-term lake sediment records and factors affecting the evolution of metal(loid) drainage from two mine sites (SW Finland)

Geochemical profiles were analyzed from 137Cs-dated lake sediment cores near two sulfide mines (Ylöjärvi and Haveri) in SW Finland to obtain long-term records of elemental discharge to surface waters from the mine sites before, during and after mining. The results showed that both the intensity and chemical composition of mine water loading changed over time, and that pre-mining land uses (e.g. agriculture) also mobilized mining-associated elements in an area with mine potential. At Ylöjärvi the sulfide-derived metal concentrations peaked during mining, but the lack of post-closure peaks probably resulted from the diffuse nature of the loading from the tailings facility. Major post-mining acid mine drainage (AMD) impact was detected at Haveri, where the relative amounts of metals accumulated in sediments corresponded to the amounts of metals leached from the oxidized layer of the tailings. However, the temporal sequence of metal loading (Ni>Cu, S>Ag, As, Cd, Fe, Zn, V>Co, Mo) did not follow the classical sequence of sulfide weathering due to geochemical processes acting along the pathway to the receiving lake. The metal concentrations gradually decreased in recent sediments because of the progressive depletion of sulfides in the oxidized surface tailings, attenuating mechanisms such as adsorption by secondary Fe(III) minerals and increasing percolation of the contaminant plume into the groundwater. Nevertheless, the recent recorded values remain above the pre-anthropogenic levels, especially for copper. The examination of lake sediment cores allows assessment of the long-term evolution of metal and metalloid drainage from mining areas including pre-mining conditions.

Evaluation of geochemical background levels around sulfide mines – A new statistical procedure with beanplots

Abstract Geochemical background levels and pre-mining conditions can be defined and quantified in several ways with different outcomes. Numerous authors have attacked the background assessment problem by generating various statistical procedures for estimating the level or threshold for concentrations assumed to represent the background. None of the methods have been generally accepted as a de facto standard. Some methods assume a normal distribution, leading to trimming or normalization procedures and some are based on more generally applicable non-parametric methods. The uncertainties always present in geochemical data are rarely reported with background levels. In this study the geochemical background is considered as the range of levels anchored at the time of sampling under pre-mining conditions. A statistical description of a distribution assumed to represent such a background is suggested including the non-parametric median, confidence interval of the median and a modified beanplot, which illustrate the variation and uncertainty of the data. The procedure is demonstrated on data from the vicinity of the Talvivaara black shale -hosted Ni–Cu–Co–Zn–Mn mine in eastern Finland, and the differences in levels between the mineralized and non-mineralized subareas in stream sediments and stream water are presented. The sampled materials are well-decomposed organic stream sediments (259 samples), poorly decomposed organic stream sediments (285 samples), minerogenic stream sediments (102 samples), and stream water (149 samples). The median values for Cu, Fe, Ni, Pb and Zn are significantly higher in mineralized subareas than in non-mineralized subareas in organic stream sediments and minerogenic stream sediments. In stream waters Cu, Ni and Zn behave similarly showing a significant difference. The results show that the average geochemical background in stream sediments and stream water can vary significantly across lithologies, and that medians with confidence intervals together with diagrams depicting the distributions in detail, such as beanplots, are useful tools for assessing and illustrating the background levels.

English

Reforestation of the Appalachian coalfields with native hardwoods is becoming increasing popular. However, establishing some hardwood species has been difficult due to the poor quality of many mine soils. The purpose of this study was to contrast after 15 years the growth, survival, and overall performance of seven hardwood species planted on three mine sites in Southwestern Virginia. The seven hardwood species were divided into species groups of a non-native fuelwood species, upland hardwoods, riparian species, and a valuable but off-site hardwood species. Overall tree performance was examined as a function of mine soil chemistry and fertility. Eastern cottonwood grew fastest, and black walnut grew slowest. By age 15, the native hardwoods, white and northern red oaks and yellow poplar, grew better than the American sycamore and white ash riparian species. They also responded to a mine soil fertility gradient while the others did not. The overall forest capability of the post-mined condition of these sites was far less than the pre-mined capability. The average weighted site indices (by extent of all soil series) of 10,000 acres in the vicinity of the mined sites are 82 and 77 for yellow poplar and northern red oak, respectively. Reduction in yellow poplar site index between the preand post-mined capability was 26 feet, and the difference for red oak was 15 feet. Northern red oak, white oak, and yellow poplar, all upland native commercial hardwood species, would be better choices for general reforestation than riparian species; however, better reclamation procedures then those used when this study was established (compacted mix of overburden materials with heavy herbaceous ground cover) are needed to restore forest land capability to pre-mining conditions. Additional

Reactive solute-transport simulation of pre-mining metal concentrations in mine-impacted catchments: Redwell Basin, Colorado, USA

With the increased importance of water resources in the western United States and many areas worldwide, the remediation of impacts from historical mining becomes ever more important. A possible process of making decisions about remediation for a catchment might include identification of principal sources of metals in the catchment, classification of the sources as natural or anthropogenic, and simulations to evaluate different options for removal of anthropogenic sources. The application of this process is based on understanding the pre-mining conditions in the catchment, so that remediation goals appropriately correct for the impacts of mining. A field experiment in Redwell Basin, Colorado, provided a setting to demonstrate this process and to evaluate pre-mining concentrations through reactive solute-transport modeling. The field experiment provided spatially detailed stream and inflow samples that were the basis for model calibration. Only two inflows along the study reach were affected by mining or mine exploration. To simulate pre-mining conditions, these inflows were removed from the model calibration; the result was a simulation of the stream with all the non-mining inputs. At a point downstream from the two mining inflows, the simulated pre-mining pH would have been 5.1, up from the measured 3.8. At the higher pH, the streambed likely would have been coated with Al precipitate. Simulated pre-mining Zn and Cu would have been 1300 µg/L and 18 µg/L, lower than the measured concentrations of 3340 and 93 µg/L. Despite these changes, the pre-mining conditions would not have met aquatic-life standards.

What was the groundwater quality before mining in a mineralized region? Lessons from the Questa project

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department and supported by Molycorp, Inc (currently Chevron Minerals), has completed a 5-year investigation (2001–2006) to determine the pre-mining groundwater quality at Molycorp’s Questa molybdenum mine in northern New Mexico. Current mine-site ground waters are often contaminated with mine-waste leachates and no data exists on pre-mining ground-water quality so that pre-mining conditions must be inferred. Ground-water quality undisturbed by mining is often worse than New Mexico standards and data are needed to help establish closure requirements. The key to determining pre-mining conditions was to study the hydrogeochemistry of a proximal natural analog site, the Straight Creek catchment. Main rock types exposed to weathering include a Tertiary andesite and the Tertiary Amalia tuff (rhyolitic composition), both hydrothermally altered to various degrees. Two types of ground water are common in mineralized areas, acidic ground waters in alluvial debris fans with pH 3–4 and bedrock ground waters with pH 6–8. Siderite, ferrihydrite, rhodochrosite, amorphous to microcrystalline Al(OH)3, calcite, gypsum, barite, and amorphous silica mineral solubilities control concentrations of Fe(II), Fe(III), Mn(II), Al, Ca, Ba, and SiO2, depending on pH and solution composition. Concentrations at low pH are governed by element abundance and mineral weathering rates. Concentrations of Zn and Cd range from detection up to about 10 and 0.05 mg/L, respectively, and are derived primarily from sphalerite dissolution. Concentrations of Ni and Co range from detection up to 1 and 0.4 mg/L, respectively, and are derived primarily from pyrite dissolution. Concentrations of Ca and SO4 are derived from secondary gypsum dissolution and weathering of calcite and pyrite. Metal:sulfate concentration ratios are relatively constant for acidic waters, suggesting consistent weathering rates, independent of catchment. These trends, combined with lithology, mineralogy, and mineral solubility controls, provide useful constraints on pre-mining ground-water quality for the mine site where the lithology is known.

English

California’s Surface Mining and Reclamation Act of 1975 (SMARA) was amended in 1991 to require that the State Mining and Geology Board (Board) adopt regulations specifying minimum, verifiable statewide reclamation standards. The state legislature directed the Board to adopt standards to include, but not be limited to, (1) wildlife habitat; (2) backfilling, regrading, slope stability, and recontouring; (3) revegetation; (4) drainage, diversion structures, waterways, and erosion control; (5) prime and other agricultural land reclamation; (6) building, structure, and equipment removal; (7) stream protection; (8) topsoil salvage, maintenance, and redistribution; (9) tailing and mine waste management. Each mine reclamation plan approved in California must include site specific performance criteria for measuring reclamation success. While site specific performance criteria may be based on pre-mining conditions, reclamation to a beneficial end use it the goal, not restoration. Reclamation standards are set to be achievable in a reasonable timeframe. Where best management practices focus on reclamation methodology, performance standards focus on results. Performance standards provide mine operators with clear expectations for reclamation, and regulators with a clear trigger for determining reclamation success and return of financial assurances. Additional

A simulation-based approach for estimating premining water quality: Red Mountain Creek, Colorado

Regulatory agencies are often charged with the task of setting site-specific numeric water quality standards for impaired streams. This task is particularly difficult for streams draining highly mineralized watersheds with past mining activity. Baseline water quality data obtained prior to mining are often non-existent and application of generic water quality standards developed for unmineralized watersheds is suspect given the geology of most watersheds affected by mining. Various approaches have been used to estimate premining conditions, but none of the existing approaches rigorously consider the physical and geochemical processes that ultimately determine instream water quality. An approach based on simulation modeling is therefore proposed herein. The approach utilizes synoptic data that provide spatially-detailed profiles of concentration, streamflow, and constituent load along the study reach. This field data set is used to calibrate a reactive stream transport model that considers the suite of physical and geochemical processes that affect constituent concentrations during instream transport. A key input to the model is the quality and quantity of waters entering the study reach. This input is based on chemical analyses available from synoptic sampling and observed increases in streamflow along the study reach. Given the calibrated model, additional simulations are conducted to estimate premining conditions. In these simulations, the chemistry of mining-affected sources is replaced with the chemistry of waters that are thought to be unaffected by mining (proximal, premining analogues). The resultant simulations provide estimates of premining water quality that reflect both the reduced loads that were present prior to mining and the processes that affect these loads as they are transported downstream. This simulation-based approach is demonstrated using data from Red Mountain Creek, Colorado, a small stream draining a heavily-mined watershed. Model application to the premining problem for Red Mountain Creek is based on limited field reconnaissance and chemical analyses; additional field work and analyses may be needed to develop definitive, quantitative estimates of premining water quality.

English

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, has completed a 4-year investigation (2001-2005) to determine the pre-mining ground-water quality at Molycorp's Questa molybdenum mine in northern New Mexico. Current mine-site ground waters are often contaminated with mine-waste leachates and no data exists on pre-minng ground-water quality so that pre-mining conditions must be inferred. Ground- water quality undisturbed by mining is often worse than New Mexico standards and data are needed to help establish closure requirements. The key to determining pre-mining conditions was to study the hydrogeochemistry of a proximal natural analog. Main rock types exposed to weathering include a Tertiary andesite and the Tertiary Amalia tuff (rhyolitic composition), both hydrothermally altered to various degrees. Two types of ground water are common in mineralized areas, acidic ground waters in alluvial debris fans with pH 3-4 and bedrock ground waters with pH 6-8. Siderite, ferrihydrite, rhodochrosite, amorphous to microcrystalline Al(OH)3, calcite, gypsum, barite, and amorphous silica mineral solubilities control concentrations of Fe(II), Fe(III), Mn(II), Al, Ca, Ba, and SiO2, depending on pH and solution composition. Concentrations at low pH are governed by element abundance and mineral weathering rates. Concentrations of Zn and Cd range from detection up to about 10 and 0.05 mg/L, respectively, and are derived primarily from sphalerite dissolution. Concentrations of Ni and Co range from detection up to 1 and 0.4 mg/L, respectively, and are derived primarily from pyrite dissolution. Concentrations of Ca and SO4 -2 are derived from secondary gypsum dissolution and weathering of calcite and pyrite. Metal:sulfate concentration ratios are relatively constant for acidic waters, suggesting consistent weathering rates. These trends, combined with lithology, mineralogy, and mineral solubility controls, provide useful constraints on pre-mining ground-water quality for the mine site where the lithology is known.

Rapid natural acid weathering, physical erosion, and debris-flow hazards in scar areas developed on hydrothermally-altered rocks along the Red River Valley near Questa, New Mexico, USA

In southern Rocky Mountains, catchments characterized by acidic, metalliferous waters that are relatively unaffected by human activity usually occur within areas that have active or historical mining activity. The US Geological Survey has utilized these mineralized but unmined catchments to constrain geochemical processes that control the surfaceand ground-water chemistry associated with near surface acid weathering as well as to estimate premining conditions. Study areas include the upper Animas River watershed, Lake City, Mt. Emmons, and Montezuma in Colorado and Questa in New Mexico. Although host-rock lithologies range from Precambrian gneisses to Cretaceous sedimentary units to Tertiary volcanic complexes, mineralization is Tertiary in age and associated with intermediate to felsic composition, porphyritic plutons. Pyrite is ubiquitous. Variability of metal concentrations in water is caused by two main factors: mineralogy and hydrology. Parameters that potentially affect water chemistry include: host-rock lithology, intensity of hydrothermal alteration, sulfide mineralogy and chemistry, gangue mineralogy, length of flow path, precipitation, evaporation, and redox conditions. Springs and headwater streams have pH values as low as 2.5, sulfate up to 3700 mg/L and high dissolved metal concentrations (for example: A1 up to 170 rag/L; Fe up to 250 mg/L; Cu up to 3.5 mg/L and Zn up to 14 mg/L). With the exception of evaporative waters, the lowest pH values and highest Fe and A1 concentrations occur in water draining the most intense hydrothermally altered areas consisting of the mineral assemblage quartz-sericite-pyrite. Stream beds tend to be coated with iron floc, and some reaches are underlain by ferricrete. When iron-rich ground water interacts with oxygenated waters in the stream or hyporheic zone, ferrous iron is oxidized to ferric iron, which is less soluble, leading to the precipitation of iron oxyhydroxides. Ground-water wells have been drilled and sampled in two unmined, alpine catchments to characterize constituent concentrations, to identify hydrogeochemical processes controlling constituent concentrations, to determine rock hydraulic properties, and to delineate flow paths. By using an integrated approach to investigating surface and ground waters in these acidic catchments a more complete understanding of the hydrogeologic framework is gained.

Environmental Impact of Uranium Mining and Ore Processing in the Lagoa Real District, Bahia, Brazil

Uranium mining and processing at Lagoa Real (Bahia, Brazil) started in 2000. Hydrogeochemical monitoring carried out from 1999 to 2001 revealed generally good quality of the water resources outside and inside the mineralized area. No chemical contamination in waters for domestic uses was observed. Hydrochemical characteristics did not vary significantly after 1 year of U exploitation, as compared to premining conditions. Due to the short time of mining, the results cannot exclude future variations in water quality. Leaching experiments helped to describe processes of ore and waste degradation. Sulfate was identified as an indicator for different types of contamination. Potential hazards related to local climate (hot rainy season) were identified. They indicate that tailings derived from the ore processing, destabilized by sulfuric acid attack, may induce acidification and salinization in the surrounding environment. Another potential source of environmental impact could be linked to local radium-rich mineralization, originating radon emission.