Bulk Sampling Program
- Bulk sample mining of 36,000 tonnes of Revere Reef Gold system high grade ore
- Modular Gekko low-cost mobile crushing-grinding-primary gravity concentration gold processing plant secured
- Metallurgical results confirm a coarse liberated gold, amenable to concentration processing with recoveries of 88%
Revere Reef Gold System
- 7km’s of reef system with gold mineralisation from surface to depth of 130m
- The Revere Reef is a shear zone structure, high-grade vein and stock work occurrence, set within a large halo of low-grade mineralisation
- Reconciled grade of quartz lodes by historical processing reported 17 to 325 g/t Au
- 8,845m of historical drilling undertaken to establish exploration target
“Latest Metallurgical studies continue to confirm excellent recoveries of 88% of the high-grade ore gold at the Revere Gold and Base Metal Project. The very high gold recoveries through a primary gravity concentrate at a coarse grind size for the gold bearing quartz vein is especially pleasing as this facilitates processing via a simple gravity circuit. The combination of such high-grade gold occurrences from surface, access to a processing plant and a near AUD 3,000 per ounce gold price places EMC in an excellent position as it works towards potential income generation from the Revere Project. Our updated exploration target further substantiates the potential of the project”Chief Operating Officer, Simon Phillips commented on the Revere Gold and Base metal project:
Everest Metals Corporation Limited (ASX: EMC) (“EMC” or “the Company”)is pleased to announce planning has commenced for a bulk sampling and gold extraction program utilising the results from previously undertaken metallurgical test work of mineralised rock material from the Revere Gold and Base Metal Project (“Revere” or “RGP”) and an Exploration Target has been generated. Results of the previous metallurgical test work emphasised the high nugget distribution of gold at the Revere Project and achieved high recoveries of 87.7% to a primary gravity concentrate from the quartz vein sample. Given a test feed grade of 60.5 g/t Au, the corresponding concentrate grade equated to 275.7 g/t Au.
The Revere Project is 82km2 and includes granted tenements E51/1766, E51/1770, P51/3240, P51/3241 and pending applications M51/905, E51/2119, E51/2088 and E51/2145. EMC has the right to earn up to a 100% interest in the tenements. The project is located just off the Great Northern Highway approximately 90km to the northeast of Meekatharra in the Murchison Region of Western Australia and sits proximal along the interpreted northern extension of the Andy Well greenstone shear system in proximity to the prospective northeast trending Goodin fault zone (Figure 1). This fault zone is being actively explored for high grade volcanic massive sulphide copper mineralisation similar in style to the DeGrussa and Monty Mines, located 55km to the northeast of the Revere project. This metallogenic zone has numerous mesothermal-style gold stockwork systems and has produced numerous coarse gold nuggets from quartz reefs over the past 100 years (Figure 2).
Figure 1: Location map of the Revere Gold Project tenements; granted exploration tenements (red), pending exploration tenements (blue) and pending mining tenement (black).
Figure 2: Visible gold in the Revere Reef system (coasten location: 701112.71, N7126828)
The area continues to deliver a prolific amount of alluvial gold from the extensive mineralised reef systems. Bulk samples of the quartz reefs designed to investigate the potential of a high nugget gold distribution, generally produced gold grades between 18 – 65 g/t Au. The Revere Reef is essentially a complex mineralised shear zone structure, composed of geologically distinct, structurally variable, high-grade vein (5-50 g/t Au), lens and stockwork occurrences, set within a large halo of background containing low-grade mineralisation (~0.2 g/t Au).
In March 2023, the Company reported successful results of Gravity Recoverable Gold (“GRG”) test work, which comprised two distinct samples: one from the main quartz vein and one from its siltstone host rock. The quartz vein sample showed excellent gravity gold recovery of 97% to a very high-grade primary concentrate (~50kg/t) with the Knelson Concentrator fed with a coarse feed (P90 of 0.85mm). Substantially finer grinding (to ~75 microns) prior to secondary and tertiary gravity separation increased the gold recovery by 1.8%. The siltstone host sample also resulted in high recovery to the primary concentrate (92.8%) although the concentrate was lower grade.
The Revere Quartz Reef mineralised zones could host a potential resource up to 334,000 ounces of gold (4.1 million tonnes of quartz lodes at SG of 2.5). Historical drilling at Revere has found gold in numerous holes as indicated by the red stars in Figure 3 and the anomalous grades in Figure 4. Intersected grades were between 0.1 to 28g/t Au in the RC drill holes but went over 1000g/t Au in larger samples (1195g/t Au from 80kg taken in 2007 and when two bulk samples of more than 200kg were taken (258kg and 293kg) in 2018 the grades of the same reefs were producing 18g/t and 357g/t Au. These are undiluted grades from the mineralised quartz reefs.
The potential quantity and grade of the Exploration Target is conceptual in nature and as such there has been insufficient exploration drilling conducted to estimate a Mineral Resource. At this stage it is uncertain if further exploration will result in the estimation of a Mineral Resource. The Exploration Target has been prepared in accordance with the JORC Code (2012).
An accurate and/or JORC compliant resource cannot therefore be produced using the current drilling grades as they under report due to the nugget effect. The future bulk sampling grades will be applied to the known mineralised quartz reefs (known geological continuity) to determine an inferred JORC compliant resource as is the accepted method and industry standard for nuggety gold deposits.
Figure 3: Exploration Target resource area at Revere Project
The resource evaluation and classification problems associated with mineral resources with high nugget effects are well known and documented. Due to the nugget effect the only way to confirm resource grade is through a representative bulk sample of the quartz reefs. The process is well known in the Bendigo gold fields in central Victoria, producing on average 130,000 ounces of gold per km per quartz reef depth along anticline axial surface – stacked saddle reefs. Work done on the nuggety Bendigo gold fields and the Revere Reef system has clearly demonstrated the gross geological continuity of the gold reefs. On the local scale, the gold-rich veins are generally narrow and discontinuous with high-grade patches of coarse visible gold. These findings qualify the current approach to resource estimation based upon close-spaced drilling, on-reef development, and bulk sampling.
There is currently an Exploration Target over the drill and bulk sample area of approximately:
2.5 – 4.1 million tonnes grading at 1 – 2.5g/t of gold determined as follows:
- The target area is ~800m long and ~150m wide. The saddle reefs or fault reefs appear to be at least 20-50m wide and are found to repeat or occur at least 7 times from surface to a currently defined depth of at least 130m (Figure 4). This information is based on 194 RC holes drilled in 2018 by MRC for a total of 8,845m and 1997 samples analysed for gold (Appendices C and D).
- There is a defined mineralised envelope of 1.8 million m3 (>0.2g/t Au; Leapfrog Model 2019, AEMCO). This correlates very well with the estimated volume of quartz lodes that have been defined by drilling over the same area. On average 4 quarts lodes (10-20cm thick) are intersected every 50m in cross section. Over the defined mineralised with of 200m along strike of 800m and down to a depth of 130m there is a potential resource of at least 1.6 million m3 of quartz lodes.
- This target resource can have a potential grade of ~2.5g/t Au based on a determined average mineralised grade of 2.5g/t Au Bottle Roll Cyanide analysis from 80kg of drill sample material (DRC047:33-37m). The mineralised zones can therefore host a potential resource up to 334,000 ounces of gold (4.1 million tonnes of quartz lodes at SG of 2.5).
Figure 4: RC drill sample with interpreted mineralised zones along quartz reefs (Top), Mineralised envelope (isosurface) section (Bottom), looking east
The current Exploration Target grade will be determined by the results of a very large bulk sample programme of 36,000 tonnes which will be taken over the three areas as indicated in Figure 7. Trenching over these areas have already confirmed the presence of saddle reefs that will now be excavated and processed on site to determine the final recovery grade of the material.
A summary of important assessment and reporting criteria used for this Exploration Target announcement is provided in JORC Table 1 (Appendix B) in accordance with the checklist in the Australian Code for the Reporting of Exploration Results, Mineral Resources, and Ore Reserves (the JORC Code, 2012).
Metallurgical Test Work
A 61kg bulk sample collected from the Revere Reef system (located in tenement E51/1766 and pending mining application M51/905) was submitted to an independent laboratory, Gekko Metallurgical Laboratories (“Gekko Systems”) in Perth, WA for test work to determine amenability of ore samples to gold concentration via a Gekko InLine Pressure Jig and batch centrifugal concentration. The outcomes from the test work will be as part of the process flow design and will provide plant-scale recovery estimates.
To optimise the application of this cycle using continuous gravity in the separating step, Gekko developed the Continuous Gravity Recovery (“CGR”) laboratory test work protocol. CGR protocols are an alternative to the standard batch Gravity Recoverable Gold test work program offered by many independent laboratories that were previously used for the metallurgical test work for the Revere Project in March 2023. CGR test work provides an improved and more accurate understanding of an ore’s response to gravity separation devices by plotting the recovery against mass yield. CGR test work programs are designed to simulate single pass or recirculating load circuit designs.
The sample was jaw crushed to 100% passing 11.2 mm and the sample was roll crushed to P100 1.00 mm. The ore was homogenised and approximately 28kg split for single stage CGR test work. Approximately 30kg of P100 1.00 mm composite sample remains. Various table concentrate samples remain, as well as approximately 12kg of table tails. The average head grade of sample from the reconciled grades from the various assays, sizings and tests carried out, equated to 70.7g/t Au (Table 1). The average head grade is considered to be an accurate method of determining the head grade as it is based on the largest sample mass, and largest number of assays.
Table 1: Samples of Reconciled Head Grades Assay
|Test||Au Grate (g/t)|
|LeachWELL Head Assay (1 kg)||64.0|
|P100 1.18 mm Table Feed Size Assay (1 kg)||87.7|
|Single Stage CGR Testwork (30 kg)||60.5|
Approximately 30kg of sample at 100% passing 1 mm, were tabled individually using a laboratory sized Wilfley table (Figure 5). During operation of the Wilfley table, a thin film of water was applied to the table surface to help separate the lighter particles from the heavier ones. The heavier material was collected in a series of concentrate ports at the end of the table, while the lighter material was collected in a port on the side of the table. The products were collected into individual tubs and decanted, with the solids filtered and dried. Five concentrate products were produced aiming for a cumulative 1%, 5%, 15%, 30% and 50% of the original sample mass, with the concentrate and tails samples assayed.
The single stage CGR test results indicated the composite sample tested was amenable to gravity concentration via a Gekko InLine Pressure Jig. Approximately 87.7% of the gold was able to be recovered into 19.2% of the feed mass. Given a test head grade of 60.5 g/t Au, the corresponding concentrate grade equated to 275.7 g/t Au. The recoveries and mass yields achieved in the tabling test are comparable to those expected from a rougher stage InLine Pressure Jig (Table 2). Yield-Grade curve is also presented in Figure 6.
Table 2: Single Stage CGR Results Summary
|Sample||Mass Yield Cumulative (%)||Au|
|Assay (g/t)||Cumulative Distribution (%)||Cumulative grade (g/t)|
Figure 5: Laboratory Size Wilfley Table (View from Discharge End)
Overall, these results indicate the composite sample tested contains coarse liberated gold, amenable to concentration via a Gekko InLine Pressure Jig. Based on the sample tested, and due to the coarse distribution of the gold, the CGR test work yielded comparative recovery results of GRG test work and a smaller mass yield.
Figure 6: Single Stage CGR Recovery-Yield and Grade-Yield Curves
A summary of important assessment and reporting criteria used for this Metallurgical Results announcement is provided in JORC Table 1 (Appendix A) in accordance with the checklist in the Australian Code for the Reporting of Exploration Results, Mineral Resources, and Ore Reserves (the JORC Code, 2012).
Bulk Sampling Program
The Company intends to commence a 36,000 tonne bulk sampling program of the Revere Reef system in the December quarter, 2023 to delineate the extent of the high-grade gold mineralisation contained in the reefs. Bulk sampling and any additional drilling to confirm the Exploration Target will be completed within a period of 18 months (Figure 7).
Figure 7: Location of bulk sampling areas, processing, and turkey’s nest water storage at Revere
Significant high grade surface gold has been processed by prospectors over many years through visual and detector identification. Visual observations of the lode material from the Revere Reefs indicated that coarse visible gold is contained within iron oxide (gossan mineralisation) which forms the matrix of the quartz breccias. Mapping and drilling of the quartz-carbonate gold reef system indicate a complex stockwork of gold lodes that are hosted within a broad, at least 300m wide, greenschist facies alteration system that is at least 7km long. Gold mineralisation has been intersected from surface to at least 130m below surface. The alteration system appears to represent a classic precious metal ductile shear system – the Revere Reef System – that is associated with the Capricorn orogenic event. The west-northwest striking breccia shear zone is interpreted to be related to deep-seated structures and to represent part of a plumbing system for metalliferous fluids that migrated upwards into suitable trap horizons – the quartz breccia or any other suitable structural traps. This Bulk Sampling program will assist the Company in identifying the extent of the mineralisation in just a small section of the 7km’s of identified “Revere Reef”.
The Company expects meaningful gold recoveries from the program as well as generating a substantial JORC resource through the conversion of historical high-grade mineralisation (17g/t to 325g/t Au) into an inferred/indicated mineral resource. The program is expected to take approximately 6 months to complete. Following the bulk sampling program, EMC will progress an air core drilling campaign to establish additional JORC compliant resources with near surface gold potential. Additional metallurgical test work is planned from the bulk samples to further evaluate gold production using a simple gravity gold circuit for processing Revere ore. Furthermore, a Program of Work (“POW”) for turkey’s nest water storage (170 x 50m) and general surface disturbance has already been approved by DMIRS. The Company is planning to set up a gravity gold processing plant with minimal project capital and operating costs which has the potential to generate income from the projected gold recoveries.
Figure 8: Gekko Mobile Gravity processing plant layout
EMC is evaluating options to purchase or lease a Gekko 10 TPH Mobile Gravity processing plant for the processing of Revere ore (Figure 8). The Gekko system is designed to produce a concentrate that could be directly sold to the Perth Mint.
- Bulk sampling and additional metallurgical test work to commence in Q4-2023
 ASX:EMC announcement; EXCEPTIONAL GOLD RECOVERIES FROM METALLURGICAL TESTWORK AT REVERE GOLD PROJECT, WA, dated 14 March 2023.
 ASX: ENT announcement; Annual Report 30 June 2007
 ASX:MRC announcement, HIGH GRADE GOLD MINERALISATION RESULTS FROM DOOLGUNNA PROJECT, WA, dated 5 September 2018
 Dominy, S., Platten, I.M., Raine, M.D., 2003, Grade and geological continuity in high-nugget effect gold-quartz reefs: Implications for resource estimation and reporting.
 Johansen, G.F., Raine, M.D., Dominy, S. C., Bartlett, J. K., 2003, Challenges of sampling extreme nugget-effect gold-quartz reefs at the New Bendigo Project, Central Victoria, Australia
 Annual Mineral Exploration Report (A120658), 2019
 ASX:EMC announcement; EXCEPTIONAL GOLD RECOVERIES FROM METALLURGICAL TESTWORK AT REVERE GOLD PROJECT, WA, dated 14 March 2023