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Gregory K. Lee

Publications and source records attributed to Gregory K. Lee.

13 recordsLinked to original sources
USGS2016

The geochemical atlas of Alaska, 2016

A rich legacy of geochemical data produced since the early 1960s covers the great expanse of Alaska; careful treatment of such data may provide significant and revealing geochemical maps that may be used for landscape geochemistry, mineral resource exploration, and geoenvironmental investigations over large areas. To maximize the spatial density and extent of data coverage for statewide mapping of element distributions, we compiled and integrated analyses of more than 175,000 sediment and soil samples from three major, separate sources: the U.S. Geological Survey, the National Uranium Resource Evaluation program, and the Alaska Division of Geological & Geophysical Surveys geochemical databases. Various types of heterogeneity and deficiencies in these data presented major challenges to our development of coherently integrated datasets for modeling and mapping of element distributions. Researchers from many different organizations and disparate scientific studies collected samples that were analyzed using highly variable methods throughout a time period of more than 50 years, during which many changes in analytical techniques were developed and applied. Despite these challenges, the U.S. Geological Survey has produced a new systematically integrated compilation of sediment and soil geochemical data with an average sample site density of approximately 1 locality per 10 square kilometers (km 2 ) for the entire State of Alaska, although density varies considerably among different areas. From that compilation, we have modeled and mapped the distributions of 68 elements, thus creating an updated geochemical atlas for the State.

Alaska↗
USGS2015

Targeting Cu–Au and Mo resources using multi-media exploration geochemistry: An example from Tyonek Quadrangle, Alaska Range, Alaska

Regional stream and pond sediment, panned concentrate, and water sampling at and around known mineral occurrences in the Tyonek quadrangle, Alaska Range, Alaska were undertaken to determine geochemical signatures in the different media. For sediment samples, two different size fractions (− 80 mesh and − 230 mesh) were analyzed. Elevated concentrations (mostly ~ 2 × median) of elements such as As, Au, Cd, Cu, Mo, Pb, and/or Zn were measured in both size fractions in streams draining known occurrences as well as from several other locations. Gold, molybdenite, arsenopyrite, and/or Cu minerals identified in panned concentrates explain some of these elevated values. Water samples from most stream, pond and seep sediment sample sites were analyzed by high-resolution ICP-MS methodology. Relative high concentrations of constituents (including Mo, Re, As, Tl, and/or Cu and/or SO 4 ) were commonly measured in waters where high metal concentrations were also measured in corresponding sediments and/or heavy mineral concentrates. However, water chemistry yielded higher contrast of upper quartile and anomalous groups relative to median values than observed in sediments. Elevated As, Mo and/or Re probably relate both to deposit mineralogy and the higher solubility of these metals (compared to that of Cu, Pb, Zn) under the predominantly oxidized and near-neutral pH conditions. Our pilot study indicates that, despite large input of snowmelt and very low absolute concentrations (μg/L), water chemistry can be useful for delineating sulfide-bearing mineral occurrences in this region.

Alaska↗
USGS2013

Effect of ultramafic intrusions and associated mineralized rocks on the aqueous geochemistry of the Tangle Lakes Area, Alaska

Stream water was collected at 30 sites within the Tangle Lakes area of the Delta mineral belt in Alaska. Sampling focused on streams near the ultramafic rocks of the Fish Lake intrusive complex south of Eureka Creek and the Tangle Complex area east of Fourteen Mile Lake, as well as on those within the deformed metasedimentary, metavolcanic, and intrusive rocks of the Specimen Creek drainage and drainages east of Eureka Glacier. Major, minor, and trace elements were analyzed in aqueous samples for this reconnaissance aqueous geochemistry effort. The lithologic differences within the study area are reflected in the major-ion chemistry of the water. The dominant major cation in streams draining mafic and ultramafic rocks is Mg 2+ ; abundant Mg and low Ca in these streams reflect the abundance of Mg-rich minerals in these intrusions. Nickel and Cu are detected in 84 percent and 87 percent of the filtered samples, respectively. Nickel and Cu concentrations ranged from Ni <0.4 to 10.1 micrograms per liter (mg/L), with a median of 4.2 mg/L, and Cu <0.5 to 27 mg/L, with a median of 1.2 mg/L. Trace-element concentrations in water are generally low relative to U.S. Environmental Protection Agency freshwater aquatic-life criteria; however, Cu concentrations exceed the hardness-based criteria for both chronic and acute exposure at some sites. The entire rare earth element (REE) suite is found in samples from the Specimen Creek sites MH5, MH4, and MH6 and, with the exception of Tb and Tm, at site MH14. These samples were all collected within drainages containing or downstream from Tertiary gabbro, diabase, and metagabbro (Trgb) exposures. Chondrite and source rock fractionation profiles for the aqueous samples were light rare earth element depleted, with negative Ce and Eu anomalies, indicating fractionation of the REE during weathering. Fractionation patterns indicate that the REE are primarily in the dissolved, as opposed to colloidal, phase.

Alaska↗
USGS2007

Major and Trace-Element Data from Stream-Sediment and Rock Samples Collected in the Taylor Mountains 1:250,000-Scale Quadrangle, Alaska

In the summers of 2004, 2005, and 2006, the U.S. Geological Survey conducted a reconnaissance geochemical survey of the drainage basins throughout most of the Taylor Mountains 1:250,000-scale quadrangle, in southwestern Alaska. The purpose of the study was to locate areas of potential interest for ore minerals, provide data that may be used to determine regional-scale element baselines, and provide data for the concurrent U.S. Geological Survey geologic mapping and mineral resource assessment effort. This report provides the stream-sediment sample data for the study.

Open-File Report↗
USGS2007

Landscape geochemistry near mineralized areas of eastern Alaska: Chapter H in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

The Pogo lode gold deposit was discovered in eastern Alaska in the early 1990s and provided the opportunity to study elemental distribution and mobility in the natural environment prior to mine development. Studying mineralized systems prior to mining allows us to compare the natural biogeochemical signature in mineralized versus nonmineralized areas. The resultant data and interpretation also provide a baseline for evaluating what, if any, changes in elemental distribution result from development. This report investigates the chemistry of stream water, streambed sediment, and soil in the context of regional bedrock geology. The major-ion chemistry of the waters reflects a rock-dominated aqueous system, and the waters are classified as Ca 2+ and Mg 2+ - HCO 3 - to Ca 2+ and Mg 2+ - SO 4 -2 waters. Creeks draining the gneissic lithologies tend to be more sulfate dominated than those draining the intrusive units. Sulfate also dominated creeks draining mineralized areas; however, the underlying paragneiss unit could be contributing substantially to the sulfate concentration, and the sulfate concentration in these creeks may reflect a complex baltholith-paragneiss boundary rather than mineralization. Arsenic concentrations in bed sediments were elevated in mineralized areas relative to nonmineralized areas. Elevated concentrations of nickel, chromium, iron, manganese, and cobalt appear to reflect the presence of ultramafic rocks in the drainage. In general, aqueous metal concentrations were below the State of Alaska’s Aquatic Life Criteria and Drinking Water Standards, with the exception of arsenic in stream water, which ranged in concentration from less than 1 to 14 micrograms per liter (&mu;g/L) and exceeded the drinking water standard at one site. The arsenic and antimony concentration in the A, B, and C soil horizons ranged from 3 to 410 milligrams per kilogram (mg/kg), 6.1 to 440 mg/kg, and 2 to 300 mg/kg, respectively, for arsenic and 0.4 to 24 mg/kg, 0.6 to 25 mg/kg, and 0.2 to 16 mg/kg, respectively, for antimony. The arsenic and antimony concentrations in stream waters correlate well with the concentrations in soils. However, significantly less arsenic and antimony was extracted from C horizon soils in water leaching experiments, indicating that the arsenic and antimony in the C horizon is present in a less available form than in the A or B horizons. Arsenic and antimony uptake by grayleaf willow (Salix glauca L.) appears minimal, with arsenic concentrations ranging from less than 0.01 to 0.14 mg/kg and antimony concentrations ranging from less than 0.003 to 0.23 mg/kg in willow leaves. In general, the highest concentrations of both arsenic and antimony in water and soils were found near mineralized areas. Elevated arsenic concentrations were also found in bed sediments from mineralized areas. In these sample matrices, the presence of arsenic and (or) antimony was a good indicator of contact with mineralized rock units.

Alaska;Yukon↗
USGS1995

Map showing potential metal-mine drainage hazards in Colorado, based on mineral-deposit geology

This map, compiled by the U.S. Geological Survey (USGS) in cooperation with the Colorado Geological Survey (CGS) and the U. S. Bureau of Land Management (BLM), shows potential mine-drainage hazards that may exist in Colorado metal-mining districts, as indicated by the geologic characteristics of the mineral deposits that occur in the respective districts. It was designed to demonstrate how geologic and geochemical information can be used on a regional scale to help assess the potential for mining-related and natural drainage problems in mining districts, unmined mineralized areas, and surrounding watersheds. The map also provides information on the distribution of different mineral deposit types across Colorado. A GIS (Geographic Information System) format was used to integrate geologic, geochemical, water-quality, climate, landuse, and ecological data from diverse sources. Likely mine-drainage signatures were defined for each mining district based on: (1) a review of the geologic characteristics of the mining district, including mineralogy, trace-element content, host-rock lithology, and wallrock alteration, and; (2) results of site specific studies on the geologic controls on mine-drainage composition.

Colorado↗