Regional Surficial Geochemistry of the Northern Great Basin

Ludington, Steve; Folger, Helen W.; Kotlyar, Boris B.; Mossotti, Victor G.; Coombs, Mary Jane; Hildenbrand, Thomas G.

doi:10.2113/gsecongeo.101.1.33

Cited by 10 publications

(2 citation statements)

References 51 publications

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“…Another recommended, broader-scale method would be conventional stream sediment sampling (e.g., Ludington et al, 2006). In addition to sampling the sediment in the active channel, the authors found that sampling of vegetation within drainages and sampling stream drainage soils within the drainage depression but outside the active channel are potentially effective broader scale methods.…”

Section: Key Findings and Recommendationsmentioning

confidence: 99%

Geochemical Exploration for Gold Through Transported Alluvial Cover in Nevada: Examples from the Cortez Mine

Muntean¹,

Taufen²

2011

Economic Geology

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Geochemical orientation surveys were completed over covered Carlin-type gold deposits in the Cortez mine area with the expressed aim of identifying and evaluating exploration methods to discover Au ore under transported alluvial cover in Nevada. Orientation tests were designed to assess the utility of geochemical applications at various scales of exploration, both drill targets at the deposit scale and "footprints" associated with deposits at the district scale. Detailed surveys were completed over the covered Gap deposit, located adjacent to the giant Pipeline deposit. Both Carlin-type gold mineralization and earlier, spatially associated, base metal skarn mineralization at Gap were located by soils, soil gas, and vegetation. Loam soils at 6-to 12-cm depth provided a consistent and uniformly available sample medium. Gold ore under 10 m of cover in the northern portion of the Gap deposit was readily detected by analysis of Au by fire assay and ultra trace aqua regia methods in the-80 mesh fraction of these loam soils. Arsenic anomalies occur over the northern end and over the main ore zone at Gap, where there is 25 to 50 m of alluvial cover. Zinc concentrations in soil show the most coherent spatial relationship with underlying Au ore. Tests of MMI-B and Enzyme Leach selective leaches did not result in significant enhancement of the anomalies relative to aqua regia. CO2 and O2 in soil gas indicate faults and underlying mineralized carbonates at Gap, where weathering reactions likely generated CO2 from acid reaction with carbonate. Elevated Au and As in mixed sagebrush and shadscale occur over most ore zones, with the highest Au concentrations over the main ore zone rather than the shallowly buried northern zone. Like soils, elevated Zn in vegetation shows the most coherent spatial relationship with underlying ore. Assays from 1,859 drill holes show a 4-to 5-km 2 "footprint" at the basin gravel-bedrock unconformity centered on the Pipeline Carlin-type gold deposit, where samples of basal alluvium provide a large, coherent >50 ppb Au anomaly. Enriched As, Tl, K, and F in alkaline groundwater sampled from monitoring wells surrounding the Pipeline open pit provide a ≥5-km 2 hydrogeochemical footprint. Higher As and Tl concentrations occur down gradient from Pipeline indicating Carlin-type Au mineralization is the source of the enrichment. The surface metal anomalies are consistent with upward migration of metals through fractured alluvial cover. Likely metal transport mechanisms include barometric pumping of gases or seismic pumping of groundwater. Upward diffusion of metals through the thick vadose zones in northern Nevada is not a viable process. Surface anomalies over Gap and other deposits appear to be mature and may have developed over millions of years. In such mature anomalies, much of the metal that migrated from underlying bedrock is probably hosted in resistant secondary minerals, which are more readily dissolved by aqua regia than by various selective leaches. Sampling of soil gas and soils is appropriate ...

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Section: Key Findings and Recommendationsmentioning

confidence: 99%

Geochemical Exploration for Gold Through Transported Alluvial Cover in Nevada: Examples from the Cortez Mine

Muntean¹,

Taufen²

2011

Economic Geology

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“…Numerous geochemical studies have been conducted at a regional level, among them Ludington et al (2006) in the U.S. northern Great Basin, Zumlot, Goodell, and Howari (2009) in New Mexico, and Lapworth et al (2012) in Nigeria. Other studies have concentrated instead in a smaller area; for example, the characterization of mineralized areas in northeast Algeria (Bounessah & Atkin, 2003) and Catorce-Matehuala in northern Mexico (Chiprés et al, 2009a).…”

Section: Introductionmentioning

confidence: 99%

Exploratory Analysis of Sediment Geochemistry to Determine the Source and Dispersion of Ba, Fe, Mn, Pb and Cu and in Chihuahua, Northern Mexico

Gutiérrez¹,

Gómez²,

Herrera³

et al. 2012

JGG

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Exploratory Data Analysis (EDA) was applied to a sediment geochemistry data set (N = 2,584) within the Chihuahuan Desert in northern Mexico. Each data point contained information on the location, concentration of 19 elements, and lithology. A Box Plot analysis was applied to the data to determine mild and extreme anomaly thresholds. Anomaly maps revealed areas of concentration of anomalies as well as dispersion patterns for each element; Ba was the most mobile of the five elements and Pb the least. Specific potential sources of contamination were identified visually after superimposing anomalies with map layers of mines, urban centers and/or hydrology. The patterns revealed that mining was an important source of Pb, Fe, Mn and Ba contamination, while copper instead was associated to the presence of Tertiary volcanic rocks that abound in the western edge of the study area. Multi-element exploratory techniques yielded four principal components that accounted for 74% of total variance, exposing a strong association among Fe, Mn, P and Mg in PC1, Ca and Sr in PC2, Co, Cu, Cr, and Ni in PC3 and Pb in PC4. By identifying potential contaminant sources, EDA shed some light into the nature of the contamination, if natural or anthropogenic, a critical piece of information to impact assessment studies and best management plans.

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2011

Economic Geology Principles and Practice

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Regional Surficial Geochemistry of the Northern Great Basin

Cited by 10 publications

References 51 publications

Geochemical Exploration for Gold Through Transported Alluvial Cover in Nevada: Examples from the Cortez Mine

Geochemical Exploration for Gold Through Transported Alluvial Cover in Nevada: Examples from the Cortez Mine

Exploratory Analysis of Sediment Geochemistry to Determine the Source and Dispersion of Ba, Fe, Mn, Pb and Cu and in Chihuahua, Northern Mexico

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