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Geochemical Framework - Southwest Alaska

Regional Geologic, Geochemical, Geophysical, and Mineral Deposit Data for Economic Development in Alaska in the 21st Century

Photo of stream in Taylor Mountains quadrangle

Geochemistry, in the broadest sense, is concerned with the chemistry of the earth and the processes leading to elemental distribution or dispersion. Elements are dispersed under earth surface conditions through physical and chemical weathering and biogeochemical cycling. The systematic study of elemental dispersion is fundamental to both environmental and exploration geochemistry. This task will focus on improving both the availability of basic geochemical data and the understanding of the distribution processes important in southwest Alaska. Researchers will (i) acquire basic geochemical data in order to determine geochemical baselines and variability; (ii) characterize the geochemical dispersion signature relative to the lithologic units and geologic terranes; (iii) define the relative contribution of environmentally important metals to the landscape from various natural sources (mineralized vs. non-mineralized terrains); and (iv) define the source, mobility, transport, speciation, and bioavailability of selected environmentally important metals on a regional basis for central southwestern Alaska.

Exploration Geochemistry

Implicit in exploration geochemistry is the recognition that mineralized areas and ore deposits impart a measurable chemical signature in the surrounding environment. Geochemical data is used to define elemental background values, elemental anomalies, and deposit type fingerprints, in order to elucidate the geochemical cycling of elements in an environment, and to help in identifying geologic processes. In central southwest Alaska, exisiting geochemical data is limited, particularly for the Taylor Mountains area. In addition, there has not been a systematic synthesis of the existing geochemical data relative to the known geology and mineral occurrences. Exploration research will focus on improving the availability of basic geochemical data, determining element distributions and baselines, determining the factors that affect the mobility and transport of metals, and understanding the effects of ore deposits on the regional environment of central southwest Alaska.

To accomplish this, stream-sediment, heavy-mineral concentrate, and stream-water geochemical data will be collected to determine trace element distributions, baselines, and variability, and to aid in the geologic mapping of the study area. To aid in developing predictive models to evaluate the potential for undiscovered mineral resources, data analysis will characterize the geochemical signatures and dispersion patterns of some of the known mineral occurrences. Using geochemical and mineralogical data field and laboratory studies will be designed that may aid in understanding the anomalous occurrence of unusual (and unexpected) elements and minerals, particularly unusual forms of some of the rare-earth elements (REE).

Environmental Geochemistry

Geochemical distributions of potentially toxic and non-toxic elements are reflections of the weathering of rocks and primary minerals, as well as elemental mobility in the geochemical/biogeochemical cycles. Understanding distribution on both a spatial and chemical level (i.e. chemical speciation) is important to evaluating the current mobility and potential toxicity of mineral-deposit metals. For example, physical weathering may make an element more geoavailable, but not necessarily bioavailable. Chemical weathering and biogeochemical cycling redistribute elements into secondary minerals, partitions them into adsorbed or dissolved phases, changes their chemical species, and may alter their bioavailability and/or toxicity.

Geoenvironmental research will aim to define the relative contribution of environmentally important metals to the landscape from various natural sources (i.e., mineralized vs. non-mineralized terrains). It will also define, on a regional basis, the source, mobility, transport, speciation, and bioavailability of selected environmentally important metals in central southwestern Alaska.

Collecting samples in the Taylor Mountains quadrangle

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Last Modified: 21 April 2017