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Groundwater Sampling

NGE’s Groundwater Chemistry Exploration Program
 

The analyses retrieved from the public datasets are of varying quality.  The data were collected over many years, by unrelated organizations using different collection and analytical techniques.  While the combined dataset works well for examining regional groundwater chemistry, in order to evaluate Nevada’s valleys, and identify and justify investing resources on specific exploration targets, NGE requires more precise and accurate groundwater chemistry data, collected using standardized procedures and analyzed using modern laboratory technology.

In 2004, NGE began a reconnaissance groundwater chemistry exploration program across Nevada to identify new exploration targets.  Because there were no established procedures for collecting and analyzing groundwater samples for mineral exploration, nor existing software for spatial groundwater chemistry data collection and analysis, NGE developed new sampling procedures and custom software.

NGE has now collected more than 3,000 samples from springs, wells, windmills, and other available sources of groundwater.  To prioritize sampling in areas of geologic interest, NGE’s field teams use an extensive exploration database interest.  NGE uses a standardized sampling protocol to collect samples, ultra-low detection mass-spectrometry to analyze the samples, and adheres to rigorous Quality Assurance and Quality Control procedures to monitor data quality.  The resulting proprietary dataset is the product of the most accurate and comprehensive survey of Nevada’s groundwater ever completed.


Map of groundwater samples collected in Central Nevada during 2004 and 2005. (Scale: approximately 10km grid [6mi])

To orient the results of the survey, and most importantly the gold values, NGE has collected new groundwater samples at 31 known gold deposits. The average gold in groundwater concentration at the 31 deposits is three orders of magnitude (~1,000 times) greater than the observed median value of the reconnaissance samples, and the gold in groundwater concentrations at 27 of the 31 deposits fall within the top 10% (90th percentile) of all observed values. Once again, the data prove that Nevada’s gold deposits are surrounded by recognizable and measurable groundwater chemistry signatures. With this data, NGE has improved its proprietary groundwater chemistry models and fine-tuned its exploration thresholds for gold and other elements.


Gold values in groundwater samples. The high gold in groundwater values at 33 new exploration targets, shown in red, are in the top 5% of all samples collected.

With well defined, objective metrics, based on the groundwater chemistry of known mineralization, NGE has evaluated the reconnaissance dataset to look for new exploration targets with elevated gold and trace metal groundwater chemistry suggestive of nearby gold mineralization. Focussing on the top 5 percent of all gold in groundwater values (95th Percentile), and on areas with high sample density, NGE successfully identified 33 targets with groundwater chemistry similar to that at known gold deposits (Figure 6). Each target: (1) exhibits gold in groundwater at least 15 times greater than the survey median, (2) exhibits supporting trace element groundwater chemistry analogous to known gold deposits, and (3) is located in a prospective area based on geological characteristics in addition to groundwater chemistry.

Taking the Next Step
 

While existing sources of groundwater provide cost-effective access to groundwater samples, their spatial distribution is not generally sufficient to make exploration decisions at an individual project-scale.  For instance, while a handful of wells and windmills spaced over several square miles may identify a prospective groundwater chemistry target, more densely spaced groundwater chemistry data is required to delineate and justify the expense of an actual exploration program.  To collect groundwater samples at intervals appropriate for defining project-scale groundwater chemistry, NGE has adopted sampling technology developed by the environmental industry.

Modeling groundwater contamination is important to the environmental industry, and directly analogous to NGE’s groundwater chemistry exploration program.  The need to collect groundwater samples at discrete, regularized intervals has prompted the development of specialized sampling equipment; specifically, the environmental industry has supported the development of direct-push sampling equipment (“Hydroprobes”) that are able to push hollow, steel rods up to several hundred feet into the ground and retrieve groundwater samples with minimal environmental impact.  After visiting a manufacturer and testing the equipment, NGE confirmed that direct-push equipment was well suited to groundwater chemistry exploration and purchased a Hydroprobe (Figure 7).  NGE’s Hydroprobe was the first in Nevada and the first in the gold exploration industry.  NGE is using its Hydroprobe to: (1) advance its exploration targets, (2) direct the next stages of development at its properties, and (3) locate additional prospective targets in areas that lack existing sources of groundwater.

Direct-Push Groundwater Sampling Equipment - hollow rods are pushed down to the groundwater table and used to retrieve a representative groundwater sample.

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