Incorporating hydrogeochemistry to systematically explore Nevada’s covered search spaces

As detailed in Seeing Through Cover, hydrogeochemistry (groundwater chemistry) is an important new exploration tool that can provide valuable geological information in covered settings.  With more than half of Nevada’s prolific gold endowment potentially remaining to be found in the bedrock beneath its covered valleys (see Opportunity in Nevada), Nevada’s covered valleys are an obvious new search space to incorporate hydrogeochemistry into systematic, regional-scale, generative exploration programs.

While government and industry have begun working together to develop and apply hydrogeochemistry exploration methodologies in other parts of the world, most notably in Australia (see Technical Resources for more information), Nevada Exploration is the first group to capitalize on the opportunity to apply hydrogeochemistry to discover large new Carlin-type gold deposits (CTGDs) in Nevada’s covered valleys.  To date, Nevada Exploration has;

  • Combined approximately 50,000 historic groundwater samples to build the largest hydrogeochemistry database in Nevada;
  • Established industry-first hydrogeochemistry sampling protocols to leverage the part-per-trillion level analyses now available in commercial laboratories;
  • Sampled the hydrogeochemistry surrounding many of Nevada’s largest gold mines;
  • Completed the first regional-scale groundwater sampling program for gold in Nevada’s history; and
  • Built a portfolio of new gold projects in Nevada all directly defined by enriched concentrations of gold in groundwater.

Nevada Exploration is a part of a growing group of explorers leveraging modern hydrogeochemistry to explore in covered terranes, and the Company is systematically incorporating it to evaluate prospective valley basins in Nevada.  As an early entrant using hydrogeochemistry in Nevada, Nevada Exploration is well positioned to focus on the largest targets that offer the best chances for discovering large new CTGDs.

Aggregating and leveraging existing hydrogeochemistry data

With tens of thousands of wells across the State, Nevada’s water management agencies have collected decades of water quality data.  This data represent a vast store of information about Nevada’s groundwater; however, the data have not been easily accessible nor readily usable, and have been widely-scattered across local, State, and Federal agencies, mostly in hardcopy, non-digital formats.  Recognizing that hydrogeochemistry is going to be a cornerstone of future gold exploration in Nevada, Nevada Exploration has invested considerable resources to locate, copy, collate, organize, integrate, digitize, and spatially reference publicly available datasets to create the largest hydrogeochemistry database of its kind in Nevada, with approximately 50,000 historic samples from approximately 20,000 unique locations collected from 28 different agencies.

Historical samples of Nevada

While these historical sample records predominantly only include analyses for elements important for drinking water standards, and do not contain gold analyses, they do contain analyses for many important pathfinder elements associated with gold.  To further validate the exploration premise that gold deposits create distinct, recognizable hydrogeochemistry, Nevada Exploration combined its hydrogeochemistry database with a comprehensive geologic dataset and examined the hydrogeochemistry around Nevada’s known gold mines.  The results demonstrate that Nevada gold deposits produce distinct and measurable hydrogeochemistry signatures defined by important pathfinder elements, such as antimony, arsenic, copper, lead, and zinc, supporting the earlier findings of David Grimes at the U.S. Geological Survey, who completed hydrogeochemistry characterization studies around several large CTGDs in Nevada during the 1990’s, including Twin Creeks and Lone Tree (to review Grimes’s research, see Technical Resources).

By compiling and leveraging existing public datasets, Nevada Exploration has established unique context and understanding of the background hydrogeochemistry across Nevada, as well as the hydrogeochemistry associated with CTGDs.  Nevada Exploration is now leveraging its database to support its regional-scale reconnaissance groundwater sampling program, where it is now sampling groundwater and analyzing its directly for gold and other pathfinder elements across prospective covered terrains in Nevada.

Regional-scale hydrogeochemistry sampling program

Building from the regional context provided by its State-wide hydrogeochemistry database, Nevada Exploration uses its proprietary sampling protocols (specially developed to take advantage of the latest ultra-trace detection limit laboratory analytical tools) and used specialized boring equipment (to collect groundwater samples where there are no existing sampling bores) to complete the most comprehensive sampling program of Nevada’s groundwater ever completed.

As discussed in more detail in Seeing Through Cover, to overcome the compounding challenges of gold’s relatively low solubility and the limited and erratic distribution of existing sampling bores, Nevada Exploration uses purpose-drilled boreholes to control sample spacing, essentially “drilling for water”, in order to respond directly to gold in groundwater as a primary pathfinder.  Nevada Exploration’s ability to control sample distribution and spacing differentiates its efforts from others using hydrogeochemistry, most importantly in that this allows Nevada Exploration to systematically incorporate hydrogeochemistry with other geologic tools to provide an otherwise missing scale of geochemistry data across prospective search spaces supported by other lines of evidence, such as projections of favourable geology and geophysics.
With this integrated approach and its specialized sampling protocols and equipment, Nevada Exploration has collected approximately 6,000 groundwater samples, predominantly focused on covered valley basins in north-central Nevada that were prioritized based on conventional geologic tools, as well as the Company’s database of historic groundwater samples.  To orient the results of its sampling program, Nevada Exploration has also collected samples from the groundwater surrounding 31 known gold deposits in the State.

Nevada Exploration samples in Nevada

In terms of the distribution of gold in groundwater seen across Nevada, not surprisingly, the results of Nevada Exploration’s sampling program show widespread low background concentrations, with about 80 percent of samples clustering within three times the median value, which is only slightly higher than the detection limit.  Against this low background, the sampling program identified high-contrast (multi-order-of-magnitude) anomalies in the upper few percentiles of the dataset, with the top 2% of samples showing gold in groundwater 100 times greater than background.  In terms of the groundwater samples collected near the known deposits, the groundwater surrounding 27 of the 31 deposits contained significantly enriched gold concentrations (>90th percentile), with an average concentration approximately three orders of magnitude (1,000 times) greater than background, providing further examples of Nevada gold deposits creating distinct hydrogeochemistry footprints defined by measurable gold concentrations.  For regional-scale exploration, once we see gold-in-groundwater concentrations one order-of-magnitude (10x) greater than background, we consider them anomalous.  Generally, our projects are initially defined by gold-in-groundwater concentrations one to two orders of magnitude (10x-100x) greater than background, and at these levels, we respond to only the top 5% percent of samples collected.

For additional context on gold-in-groundwater concentrations, including deposit-scale characterization studies from known deposits, as well as the results of other large groundwater sampling programs, see Parts per trillion gold in groundwater – can we believe it and what’s anomalous available on the Technical Resources page.

Using well-defined, objective metrics, based on the hydrogeochemistry of known mineralization and supported by the largest hydrogeochemistry database in the State, Nevada Exploration is demonstrating that hydrogeochemistry can be a robust and cost-effective sampling tool to explore for gold in covered terranes.  With easy-to-interpret, high contrast, low frequency anomalies, the Company’s hydrogeochemistry program is reducing Nevada’s large covered search spaces down to focused targets exhibiting significant gold-in-groundwater enrichment.  For a comparatively small investment, the Company is using hydrogeochemistry to evaluate prospective areas and focus resources on targets with the highest probability of success, based on direct indications of gold, prior to acquiring ground or applying more expensive conventional exploration tools.

With its integrated, generative exploration program, Nevada Exploration is lowering the risks and costs of exploring under cover.  As the first exploration group to capitalize on this opportunity, Nevada Exploration is advancing an industry-leading portfolio of new gold exploration targets in Nevada’s highly-prospective, yet underexplored, covered basins.