Rex Minerals Ltd (ASX: RXM) announced that the ongoing field work and research by at its Hog Ranch Property in Nevada USA, has shown potential for gold mineralisation on a much larger scale than originally anticipated.
The company reported that the geological features that are common to the style of gold mineralisation found at Hog Ranch are interpreted to extend over an area that is more than five times the size of the combined historically mined area (0.3Mozs) and current Mineral Resource area (1.4Mozs).
Rex said that it interprets these features to be related to a series of repeating structures that exist along a broad gold trend which appear to be controlling the gold deposition at Hog Ranch.
The company said that within this gold trend, it is exploring for two economically significant target types; shallow, large-scale gold mineralisation amenable to low-cost (open cut) mining and heap leach processing; and high-grade vein hosted gold mineralisation, underneath the shallow gold positions.
This was evidenced by many high-grade historical drill intercepts including drill hole 95-031 with 6.1m @ 61.8g/t gold (~3m true width) and drill hole 89-042 with 9.1m @ 19.7g/t gold (~3m true width).
Rex reported that it has followed up this work by more than doubling its land position at Hog Ranch.
The company said that it is now mobilising to commence drilling in Q3 2020 with a focus on both the shallow disseminated gold and the underlying high-grade gold targets.
Hog Ranch project
The Hog Ranch Property is located in Washoe County in north-west Nevada, approximately 45km from the California border and 91km from the Oregon border in the USA.
The Property comprises 347 unpatented mining claims on Federal Land for a total area of approximately 2,800 hectares.
Hog Ranch has a Gold Mineral Resource of 1.4Mozs. The Maiden Hog Ranch Mineral Resource includes Bells Project to the south and the Krista Project area to the north.
Regional gold potential
The company reported that the geological features that are linked to the historical mining area and the current Mineral Resource at Hog Ranch are found to exist over a broad area beyond the current limits of the Mineral Resource.
Series of repeating structures
RXM said that these features support the interpretation that there are multiple epithermal deposit types that could host significant gold mineralisation and which appear to occur along a defined corridor or trend.
This includes hydrothermal silica with surrounding clay minerals or alteration features in the surface rocks, overlapping geochemical anomalies, and the coincidence of favourably-oriented fault intersection points.
The company said that at this stage, Rex has limited the scope of its regional exploration work to the local host rocks which are part of a large volcanic caldera known as the Cottonwood Creek Volcanic Center (CCVC).
Two target types
Rex said that as part of the gold mineralisation at Hog Ranch, there exist two distinct target types which are common for this type of deposit in Nevada.
They are, shallow, large-scale gold mineralisation; and high-grade vein hosted gold mineralisation.
The target types are vastly different from each other in terms of their location, size, grade and subsequent mining and processing options.
Shallow, large-scale gold mineralisation
The company said that the historical mining area at Hog Ranch and current Mineral Resource along with a larger series of well-supported exploration targets near the surface (less than 200m deep) are all based on flat-lying disseminated gold mineralisation.
Because of the weathered gold mineralisation, the gold particles within the permeable host rocks are easily recovered using heap leach processing methods. In addition, the near-to-surface and flat-lying nature of the gold mineralisation at Hog Ranch means that open pit mining with low strip ratios can be employed.
The company said that the recently completed Bells Scoping Study has highlighted that even as a small-scale gold operation, the economics of mining shallow disseminated gold mineralisation at Hog Ranch appear very attractive.
Targets in Krista project area
Rex had conducted a detailed review of the structures that host the earlier mined area and current Mineral Resource area at the Krista Project, to understand the larger-scale potential at Hog Ranch.
The company said that the information from this research has highlighted the importance of the gold mineralisation relative to key fault intersections, with the higher-grade sections of the gold mineralisation spreading into lower grades away from these intersection points.
In the Krista area, it has been identified that the combined historical mining area and current Mineral Resource contains just under 0.8Mozs gold over a total of nine defined structure intersection points within the Krista Tuff rock unit.
This geological understanding at Krista subsequently led Rex to complete a larger geological interpretation to identify extensions to the known structures which extend into the favourable Krista Tuff at shallow levels.
The company said that the results from the updated geological interpretation have identified 30 structural intersection points which relate to gold-bearing structures that pass through the Krista Tuff and which remain untested.
Additional locations
Rex said that there are additional locations throughout the host volcanic rocks at Hog Ranch which have similar features to what is observed at both the Krista and Bells Projects, located further outside of the Krista Project area.
The company said that the area defined by Rex which has evidence for epithermal mineralisation now exceeds 10km2.
High grade vein hosted gold mineralisation
Rex reported that in addition to the large-scale shallow gold potential at Hog Ranch, there exists evidence for the presence of high-grade lode gold (or vein-hosted gold) mineralisation.
The high-grade gold mineralisation is interpreted to be most prominent in a favourable position known as the “boiling zone.” Rex interprets that the structures in the “boiling zone” have not yet been effectively tested at Hog Ranch
Significant drilling results from the Hog Ranch drill hole database for all intersections that are interpreted to exist in quartz vein-hosted vertical structures and which also exist outside of the historical open pits include the following.
What’s next?
Rex reported that it is in the final stages of planning the Nevada summer drilling program which is aimed at testing a number of shallow disseminated gold and deeper high-grade gold targets.
The company said that this drilling program, which will be completed over the 3rd quarter of this year, will provide important evidence to support the current interpretations for both target types.
Management comments
Rex’s Managing Director, Richard Laufmann, said: “Our outlook and options for Hog Ranch have evolved and grown substantially. It all started with the initial review of a small-scale start-up project at Bells, and now we see a much larger suite of targets following a very large trend.
Beyond the shallow heap leach gold potential at Hog Ranch, there are quite a number of tasty historical high-grade gold hits that are screaming out to be followed up. If the scale of shallow gold at Hog Ranch is anything to go by, the potential for high-grade vein-hosted gold at depth could deliver equally, if not more exciting, prospects for Rex.”