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Tracers of Surficial Processes Affecting Mineral Deposits in Humid Environnmets

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This project is summarized in this pubication:
Seal, R.R., and Ayuso, R.A., 2011, Understanding processes affecting mineral deposits in humid environments: U.S. Geological Survey Fact Sheet 2010–3105, 6 p., available online, http://pubs.usgs.gov/fs/2010/3105/.

Project Tasks:

1. Geochemistry of Aluminum in Surficial Environments

2. Geoenvironmental Studies of Mineral Deposits in Humid Coastal Settings

3. Geochemistry of Cadmium in Surficial Environments

4. Science in support of Mitigation and Remediation

5. Geoenvironmental Studies of Mineral Deposits in Tropical Settings

6. Tracking geologic sources of trace elements in mineral deposits formed in sedimentary basins


1. Geochemistry of Aluminum in Surficial Environments:
The objective of this task is to develop new approaches for tracing and modeling near-surface processes that affect mineral deposits in humid enveronments through the study of minerals, mineral surfaces, and related substrate material. Atomic force microscopy and multi-gas BET surface area analysis will be used to complement existing techniques. The stoichiometries and pathways of weathering reactions and reaction mechanisms for aluminous minerals will be studied to provide needed quantification to rate-controlled processes that result in elemental mobility in silicate-dominated rocks in humid environments. Solid solutions in processes will be studied to develop an understanding of (solid and liquid) solution effects on thermodynamic parameters for these systems. The task will integrate field and laboratory studies of previously well-characterized surficial environments to identify selected minerals that can be used to effectively track reaction pathways for metals and other pollutants in low temperature environments.

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2. Geoenvironmental Studies of Mineral Deposits in Humid Coastal Settings:
The main objectives of interest include the discovery of metal sources and establishing an inventory of metal distribution:

The work will focus on selected base metal mines (Pb-Zn) that produced intermittently since the 1800s and into the early 1980s in Penobscot Bay, in an area where urban coastal development has placed exceptional pressure on availability of natural resources, water quality, and organic systems.
Two major mineralized systems will be studied:
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3. Geochemistry of Cadmium in Surficial Environments:
The investigation of geochemical processes governing the behavior of cadmium associated with the weathering of mineral deposits and their wastes. The research will be conducted through integrated state-of-the-art field, analytical, experimental, and geochemical investigations. The task will emphasize the use of a variety of geochemical tracers such as stable and radiogenic isotopes and metal ratios in various solid, liquid, and biologic media. Field-based studies will emphasize distinctions between acidic and alkaline settings, including how these distinctions relate to biologic uptake. Experimental studies will investigate compounds for which fundamental properties are lacking or questionable.
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4. Science in Support of Mitigation and Remediation:
The sustainable development of mineral resources and the remediation of the environmental legacy of historic mining requires a thorough and predictive understanding of the physical and geochemical processes that affect mineral deposits and their waste products under a variety of climatic settings. The behavior of contaminants is is dictated by complex combinations of these processes. The interplay among these processes forms the basis of natural attenuation of contamination nd of remediation of mine sites, but is poorly understood. This task aims to better understand the geochemical details of processes such as:

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5. Geoenvironmental Studies of Mineral Deposits in Tropical Settings:
The objectives of this task center around investigating geochemical processes associated with the weathering of mineral deposits and their wastes in humid tropical climatic settings, which are characteristic of the eastern United States. The research will be conducted as in Task 4 above. Likely deposit types to be studied include porphyry copper deposits and high-sulfidation epithermal deposits.

6. Tracking geologic sources of trace elements in mineral deposits formed in sedimentary basins:
In this task we will study, at various scales, the interaction of fluids, metal sources, and processes that lead to the generation of metalliferous organic environments in selected sedimentary basins representing a transect across metamorphic grade, and including an examination of pristine modern sedimentary environments. Studies will focus on the effects of metamorphism and the changing mineralogical framework hosting the toxic metals, and on the effects of prograde and retrograde metamorphic and surficial weathering processes on felsic schistose rocks that result in mobilization of toxic metals and their availability in the near-surface environment.

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