Nevada Exploration Inc. (“NGE” or the “Company”) (TSX-V:NGE) (OTCQB:NVDEF) is pleased to report that its ongoing work at South Grass Valley has established further evidence for a Carlin-type mineral system at the Project. Specifically, based on the latest research on the size and nature of the isotope and geochemical footprints surrounding large Carlin-type gold deposits (“CTGDs”) in Nevada, NGE believes that the bedrock exposed in outcrop at Goodwin Butte, approximately 800 metres northwest from the northern end of the covered exploration target at South Grass Valley, exhibits characteristic hallmarks of the geochemical and alteration footprint seen at Cortez Hills, located 48 km to the north.
Researchers from the Mineral Deposit Research Unit at the University of British Columbia (“MDRU”) have examined thousands of rock samples from in and around large CTGDs in the Carlin and Cortez (Battle Mountain- Eureka) Trends to establish the background concentrations and anomalous thresholds for geochemical and isotope pathfinders associated with CTGDs, as well as the size of the resulting footprints and halos in the surrounding bedrock for each pathfinder defined by these thresholds. The importance of this research is that it establishes the characteristics of the hydrothermal fluid flow pathways, which are critical building blocks of these large systems, as well as the relative relationships of pathfinders to a deposit over distance. Together this provides the information required for vectoring in bedrock during early-stage drilling at a project, especially during the first few drill holes, prior to encountering significant concentrations of gold.
At Barrick Gold Corp.’s Cortez Hills deposit, MDRU analysed approximately 2,200 bedrock samples for carbon and oxygen isotopes, and integrated these results with a large geochemistry drill hole database. Based on this large sample set, the MDRU research shows that at Cortez Hills (the nearest large CTGD to NGE’s South Grass Valley Project) the isotopes and pathfinder elements travelled outboard of the economic mineralization in the following order by distance (nearest to farthest, analogous to a bullseye): Au < 13C & Tl < Sb < Hg < As < 18O. Where the mineralized hydrothermal fluids encountered zones of increased permeability (layers of more permeable rocks within less permeable bedrock), the isotopes and pathfinder elements travelled further outboard of the mineralization, travelling 100s to 1,000s of metres along these higher-flow fluid pathways, while generally only travelling 10s of metres into the adjacent less permeable, lower-flow bedrock units. This research from Cortez Hills provides the context for identifying zones of hydrothermal fluid flow and for following the fluid flow along these pathways back towards their source during exploration. Importantly, this research also provides the actual concentrations used to define the pathfinder thresholds at Cortez Hills.
At South Grass Valley, there is a 700-metre-thick sequence of exposed, favorably iron rich, permeable, and chemically reactive “lower-plate” carbonate host rocks that dips under the cover at the Project towards the exploration target, which NGE defined based on a focused north-south zone of enriched gold in groundwater above shallow, oxidized, silicified, and decalcified limestone, siltstone, and sandstone. NGE has completed bedrock mapping and sampling of the exposed bedrock surrounding the Project. With the latest Cortez Hills research from MDRU, NGE is now able to compare the pathfinder element concentrations seen in the exposed favourable host units dipping under its target with those seen surrounding the Cortez Hills deposit.
Most of the exposed bedrock south of the target is within the contact metamorphic aureole of a Jurassic age granitic stock (intrusive) where its primary permeability has been reduced. The nearest exposed outcrop north of the target is Goodwin Butte, which is located 0.8 km to the northwest, outside the area that has been affected by the intrusive activity. The results of NGE’s sampling of a small carbonate breccia pipe at Goodwin Butte noted high concentrations of CTGD pathfinder elements in only moderately permeable and reactive Goodwin Limestone. Based on the MDRU research, most of the important pathfinder concentrations seen in the carbonate breccia at Goodwin Butte are well above the thresholds that define the footprint surrounding the Cortez Hills deposit:
- Arsenic: the MDRU “Highly Anomalous Threshold” for arsenic at Cortez Hills (used to define the extent of the alteration halo at the deposit) is 98 ppm, which defines an alteration halo extending 1.5 to 2 km from the Cortez Hills deposit – the 306 ppm arsenic seen at Goodwin Butte significantly exceeds this threshold;
- Mercury: the Goodwin Butte samples did not contain anomalous mercury; however, samples from the exposed bedrock located 3 km south of the target did contain mercury values up to 0.75 ppm, which are well above the MDRU “Background Threshold” (used to define the extent of the geochemistry footprint) at Cortez Hills of 0.11 ppm, and are approaching the MDRU “Highly Anomalous Threshold” of 1.2 ppm;
- Antimony: the 46.7 ppm antimony seen at Goodwin Butte exceeds the 20 ppm MDRU “Highly Anomalous Threshold” for antimony at Cortez Hills, and so is also consistent with the Cortez Hills halo; furthermore, at these threshold levels, because antimony defines a smaller footprint at Cortez Hills relative to arsenic, extending a shorter distance into the surrounding bedrock, the high antimony at Goodwin Butte suggests the potential for a relatively closer source, consistent with Goodwin Butte being located only a short distance from the target; and
- Thallium: the 0.5 ppm thallium seen at Goodwin Butte exceeds the 0.35 ppm MDRU “Background Threshold” for thallium at Cortez Hills, and approaches the 1.2 ppm MDRU “Highly Anomalous Threshold”, which at Cortez Hills is constrained to an area immediately adjacent to the gold mineralization, providing a final piece of supporting evidence that the exposed bedrock at Goodwin Butte, adjacent to the covered South Grass Valley target, is within what would be considered the geochemical and alteration halo at Cortez Hills.
Discussing the importance of the results, NGE’s CEO, Wade Hodges: “As we transition from exploring in near-surface to covered search spaces, we must always be looking for better tools to vector in blind settings. While brownfields exploration is largely tasked with following known mineralization outwards into adjacent areas, when conducting greenfields exploration, we need to rely on different clues prior to encountering gold in bedrock. Our hydrogeochemistry program has allowed us to follow measurable gold and related pathfinder elements in groundwater to vector into a shallow, favourable bedrock target at South Grass Valley, and as we transition to deeper bedrock drilling, we must switch gears and now begin to vector with these same pathfinder elements in bedrock.
“The MDRU research is powerful for explorers tasked with finding new CTGDs in Nevada. While these concentrations of pathfinder elements on their own are not diagnostic, the fact that at South Grass Valley they are contained within a visually unremarkable carbonate breccia unit suggests that the CTGD pathfinder elements were transported by hydrothermal fluids that travelled along fluid flow pathways that passed through nearby favourable limestone host rocks. Importantly, these concentrations also tell us that the hydrothermal fluids active in the system had a budget of gold-related trace elements consistent with that seen at Cortez Hills. Furthermore, based on the MDRU research, we know that these high concentrations of pathfinder elements define relatively tight footprints surrounding the deposit at Cortez Hills, which suggests that by vectoring with gold in groundwater, our detailed hydrogeochemistry borehole program has brought us close to the source.
“As we prepare to complete our first drilling program, based on this research we already know we’re on the game board. Geochemically, we’re already in what at Cortez Hills would be considered the deposit’s geochemical and alteration halo, and we’re not yet even into what are considered the more permeable or reactive units present higher in the sequence, which based on historic drilling we expect to encounter at shallow depths. It is important to remember that the actual size of the gold mineralization is often relatively small, even at a major deposit like Cortez Hills. To maximize our odds of discovery, we need to maximize the information we can extract from our early drill holes. The MDRU research improves our ability to vector using a full suite of CTGD pathfinder elements and isotopes, as well as to respond to the full geologic picture by identifying and following fluid flow pathways, all of which are based on the known characteristics of Nevada’s large CTGDs. With this information we believe we have established that South Grass Valley possesses the required critical components to host a large CTGD. This is going to be an exciting drilling program.”
For more information about the Company’s South Grass Valley Project, including the most recent technical presentation, readers are encouraged to visit: http://nevadaexploration.com/projects/south_grass/.