Everest jumps back in Revere saddle with new gold model
Everest Metals says it has identified evidence that the gold system at its Revere project in Western Australia’s Mid West comprises a series of stacked saddle reefs – a style that commonly favours repetitive, high-grade gold mineralisation.
The revelation comes on the back of the company’s bulk sampling program at its Revere project, which kicked off in early April and has important implications for its mineralisation modelling ahead of future exploration and development. The project sits within WA’s Murchison region, 900km north of Perth.
At the start of the year, Everest described Revere’s reef architecture as a complex mineralised shear zone composed of geologically-distinct, structurally-variable high-grade veins running at grades between about 5 grams per tonne to 50g/t gold. It also notes that Sandfire Resources’ famed DeGrussa deposit nearby was discovered though follow-up drilling across a zone of oxide gold mineralisation similar to that observed at Revere.
That description was a good opener, but by the end of June, the company’s bulk sampling program had further clarified the story by exposing a shear zone characterised by high-grade gold veins and stockworks surrounded by an extensive halo of low-grade mineralisation
At the bulk sampling site, 96 blast holes for a total of 1152m were drilled by an air blast rig and sampled at 1m intervals to support its categorised mine-style grade control. Bulk samples were taken from confirmed gold-endowed reefs and stockpiled into estimated high and low-grade mineralised material.
By that time, excavation had also moved 8000 tonnes of mineralised material to a stockpile to await treatment by an ore processing plant and sampling revealed grades of up to 35g/t gold. Analyses and visual inspections of bulk sample trench excavation provided evidence of an extensive saddle reef gold mineralisation system consisting of stacked folded quartz and saddle reefs along an anticlinal axis.
The current bulk sampling program continues to unlock our understanding of the geological mineralised system which demonstrates the existence of repeatable high-grade gold reef systems and associated mineralisation. The system has a strong geological correlation to the high-grade, nuggety Bendigo gold fields deposits of central Victoria.
Further work completed by Everest has opened the show up a bit more and confirms that the Revere system features a well-developed saddle reef structure along the anticlinal axis. Mineralisation appears to be concentrated along south-west, shallow-plunging anticlinal fold crests and is continuous along the north and south dipping legs of the saddle reefs.
Management says the width and depth of the gold distribution along the anticlinal axis and bedding planes are yet to be established. And while the stacked quartz reefs are relatively thin, they appear generally consistent along strike and are associated with a mineralised halo with a distinct arsenic geochemical signature.
Gold mineralisation in the halo around the quartz reefs ranges from 0.1g/t to 0.9g/t gold, while historical bulk sampling of the quartz reefs is reported to have yielded wild grades of up to about 325g/t gold.
This type of saddle-reef formation is analogous to those found in central Victoria’s famous Bendigo goldfields, which history shows had a cumulative output of more than 60 million ounces of gold.
Bendigo was a major contributor to the nation’s total gold production during the Victorian gold rush between about 1851 and the late 1860s, prompting the Victorian Gold Discovery Committee to write in 1854: “The discovery of the Victorian Goldfields has converted a remote dependency into a country of worldwide fame; it has attracted a population, extraordinary in number, with unprecedented rapidity; it has enhanced the value of property to an enormous extent; it has made this the richest country in the world; and, in less than three years, it has done for this colony the work of an age, and made its impulses felt in the most distant regions of the earth.”
Everest says it has begun primary and secondary crushing of the bulk sample material and expects to see its 5500m gold exploration drilling program kick off at the end of the month and its Gekko gold processing plant to now be mobilised to site in September. It says the significance of the Revere structure is highlighted by the existence of shallow gold mineralisation to surface and by its mostly free-milling coarse gold that can be liberated from the ore by crushing to no finer than 1mm.
Free-milling is more desirable than refractory gold, which means the gold is tied up with other mineralisation such as arsenic or other sulphides and often requires additional processing to liberate the gold.
The combination of free milling and coarse gold means that the precious yellow metal can be concentrated by a relatively simple gravity plant, instead of requiring chemical leaching via carbon-in-pulp or similar systems that entail more complex infrastructure to meet the milling and leaching demands, along with typically finer grind and more reagents.
Additionally, if any gold resides in fine tails off the gravity separation plant, it can be stockpiled and leached in small tanks, retention ponds or dumps, subject to the sophistication of the preceding gravity recovery circuit.
Everest sees further great potential in the Revere structural system, which extends through 7km of strike along a zone up to 300m in width, suggesting a large mineralisation system with multiple gold deposits in the ground where it holds title for the entire target area. Management says it believes its initial sampling to date does not do justice to the potential of the project as it has only targeted a small part of the 7km-long system.
The company says it will continue with its accelerated, systematic approach to its exploration and resource drilling and sampling program, while progressing its mine permitting.
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