Resources and Reserves

Aeris Resources Limited has updated its Mineral Resource and Ore Reserves estimates for its Tritton Copper Operations as at 30 June 2019. Total reported Measured and Indicated Mineral Resource estimate, after mining depletion, is 12.9 million tonnes at 1.5 per cent copper for 200,000 tonnes of contained copper metal. Inferred Mineral Resource is 6.9 million tonnes at 1.3 per cent copper for 89,000 tonnes of contained copper.

This represents a 6 per cent net decrease in contained copper compared with the 30 June 2018 estimate. Total reported Proved and Probable Ore Reserves, after mining depletion, are estimated at 6.7 million tonnes at 1.5 per cent copper for 100,000 tonnes of contained copper metal. The Ore Reserve has been reduced by 30 thousand tonnes of copper since the last estimate at 30 June 2018, a 23 per cent net decrease in contained copper.

Actual copper production was 27 thousand tonnes in concentrate with processing recoveries estimated at 94.7 per cent, equivalent to 28 thousand tonnes of copper in ore. Ore Reserve depletion in excess of production is due to change in; cut-off grade; Mineral Resource models; and change in mining designs.

Aeris’ Statement of Mineral Resources and Ore Reserves as at 30 June 2019 for the significant projects at the Tritton Copper Operations, has been reported in accordance with the guidelines in the 2012 Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code 2012). Full documentation of the estimates can be found on the Company website.

The estimates for the Company’s other projects that are not considered to be significant and where there was no change since last reporting are documented in accordance with the JORC Code 2004. These estimates were prepared and first disclosed under the JORC Code 2004. They have not been updated since to comply with the JORC Code 2012 on the basis that the information has not materially changed since it was last reported. The following projects continue to be reported in accordance with the JORC Code 2004.

  • Budgery Mineral Resource; and
  • Yandan Mineral Resource.

Mineral Resource

Aeris’ copper Mineral Resource inventory is focused at the Tritton Copper Operations. The only gold Mineral Resource is located in the Drummond Basin (Yandan gold project) in Queensland. This project is not considered significant to the Company. The Tritton Copper Operations area is host to a cluster of deposits. Mineralisation across the Tritton Copper Operations’ deposits are hosted within Ordovician turbidite sequences within the Lachlan fold belt. The deposits are characterised by massive to semi-massive pyrite and chalcopyrite sulphide deposits. Deposit geometries are characterised as tabular systems. Dimensions range between 15 metres to 250 metres (strike), 90 metres to >2,000 metres (down dip) and 2 metres to 300 metres (width). Mineralised assemblages are dominated by pyrite with lesser chalcopyrite, gold and silver concentrations. Primary copper mineralisation occurs as banded and stringer chalcopyrite within pyritic rich units. The Tritton Copper Operations area deposits’ Mineral Resource estimates are defined by diamond drilling and some reverse circulation percussion drilling. Holes are geologically logged and assayed. Mineral Resource volumes are developed from geology interpretation of the drill hole data at nominal copper cut-off grades between 0.4% to 0.5% copper and varies with the deposit. Quality assurance and control procedures are in place for the assay information used in the Resource estimation. The deposits are all located on a granted Mining Lease or Exploration Lease. Resource modelling and grade interpolation within the interpreted mineralised volumes uses Ordinary Kriging with careful domain control to limit the influence of high-grade data. Reconciliation of Mineral Resource estimates against mined and processed ore for the Tritton and Murrawombie deposits mined during the year shows a slight increase in grade and tonnes after allowance for dilution and ore loss. Details of the Mineral Resource estimates can be found in the Investor Centre.

Tritton Deposit Changes

Since 30 June 2018, the Tritton deposit Measured and Indicated Mineral Resource has been reduced by an estimated 17,000 tonnes of contained copper metal. Changes to the Mineral Resource include depletion associated with mining and sterilisation of the Mineral Resource surrounding mined stopes and along the margins of the orebody as mineralised thicknesses thin and pinch out.

Measured Mineral Resource additions have occurred from grade control drilling targeting the conversion of Indicated Mineral Resource below the mining front. Measured Mineral Resource was extended a further 80 metres vertically to the 4,030mRL level. A limited amount of grade control drilling down to the 3,970mRL level enabled the Indicated Mineral Resource to be extended an additional 30 metres vertically.

Tritton Upper Level Remnant Pillars

The Tritton upper level remnant pillars are a small portion of the Tritton deposit Indicated Mineral Resource estimate, (170,000 tonnes). They are the remnant blocks of mineralisation left between mined out stopes that have not been filled with cemented paste backfill. Due to the higher risk nature of pillar mining these blocks of mineralisation are critically reviewed to ensure they have a reasonable likelihood of successful extraction to qualify for inclusion in the Mineral Resource estimate.

Mining of the pillars continued in FY2019 depleting the Indicated Mineral Resource by an estimated 2,000 tonnes of contained copper metal. A further 5,000 tonnes of contained copper metal was depleted via sterilisation. This material is currently not viable for economic extraction.

Murrawombie Deposit Changes

Since 30 June 2018, the Murrawombie deposit Indicated Mineral Resource has been reduced by an estimated 1,000 tonnes of contained copper metal. During the year grade control drilling has added to the Indicated Mineral Resource Inventory. Grade control drilling intersected mineralisation outside the previous Mineral Resource footprint. The strike extensions occur toward the base of the previous Indicated Mineral Resource extents. Previous drilling in this area had not adequately closed off mineralisation along strike. The additions to the Mineral Resource offset the mined depletion of the Mineral Resource during the year.

Budgerygar Deposit Changes

The Budgerygar deposit was subject to an internal geological review which included an updated geological interpretation and Mineral Resource estimate based on key learnings from Tritton and Murrawombie. The updated Mineral Resource included revised geology models. No additional drill hole data has been collected at Budgerygar since the completion of the previous Mineral Resource estimate in 2009. The updated Mineral Resource reports an additional 9,000 tonnes of contained copper metal. The increase in contained copper metal is primarily associated with the manner in which density estimates were determined.

June 2019

Tonnes (kt)Cu (%)Cu (kt)Au (g/t)Au (koz)Ag (g/t)Ag (koz)
TRITTON UNDERGROUND
Measured4,7001.5680.10154.6690
Indicated9801.3120.0622.374
Total M + I5,6001.4800.09174.2770
Inferred3,4001.2410.13143.9430
TOTAL9,0001.31200.11314.11,190
TRITTON PILLARS (RECOVERABLE)
Measured
Indicated1702.240.26110.958
Total M + I1702.240.26110.958
Inferred
TOTAL1702.240.26110.958
MURRAWOMBIE
Measured
Indicated4,6001.6730.31465.3780
Total M + I4,6001.6730.31465.3780
Inferred8301.3100.2775.4140
TOTAL5,4001.5830.30535.3930
AVOCA TANK
Measured
Indicated7702.9230.862115.6390
Total M + I7702.9230.862115.6390
Inferred1301.010.2313.213
TOTAL9002.6240.772213.8402
BUDGERYGAR
Measured
Indicated
Total M + I
Inferred2,3001.5340.20155.2380
TOTAL2,3001.5340.20155.2380
BUDGERY
Measured
Indicated1,7001.1190.137
Total M + I1,7001.1190.137
Inferred3000.930.071
TOTAL2,0001.1220.128
Tonnes (kt)Cu (%)Cu (kt)Au (g/t)Au (koz)Ag (g/t)Ag (koz)
STOCKPILES
Measured401.61
Indicated
Total M + I401.61
Inferred
TOTAL401.61
TOTAL
Measured4,7001.5680.10154.6690
Indicated8,3001.61300.29774.91,310
Total M + I12,9001.52000.22924.82,000
Inferred6,9001.3890.17374.4970
TOTAL19,8001.52900.201304.72,960

June 2018

Tonnes (kt)Cu (%)Cu (kt)Au (g/t)Au (koz)Ag (g/t)Ag (koz)
TRITTON UNDERGROUND
Measured3,8001.7640.13165.9720
Indicated2,7001.2330.0863.4290
Total M + I6,5001.5970.11234.91,020
Inferred3,8001.3500.12144.0490
TOTAL10,3001.41500.11374.51,510
TRITTON PILLARS (RECOVERABLE)
Measured
Indicated4202.6110.2239.6130
Total M + I4202.6110.2239.6130
Inferred
TOTAL4202.6110.2239.6130
MURRAWOMBIE
Measured
Indicated4,6001.6740.29436.0900
Total M + I4,6001.6740.29436.0900
Inferred8301.3100.2775.4140
TOTAL5,4001.5840.29505.91,040
AVOCA TANK
Measured
Indicated7702.9230.862115.6390
Total M + I7702.9230.862115.6390
Inferred1301.010.2313.213
TOTAL9002.6240.772213.8400
BUDGERYGAR
Measured
Indicated
Total M + I
Inferred1,6001.5240.116
TOTAL1,6001.5240.116
BUDGERY
Measured
Indicated1,7001.1190.137
Total M + I1,7001.1190.137
Inferred3000.930.071
TOTAL2,0001.1220.128
STOCKPILES
Measured302.11
Indicated
Total M + I302.11
Inferred
TOTAL302.11
TOTAL
Measured3,9001.7640.1165.8720
Indicated10,2001.61600.2815.21,710
Total M + I14,1001.62200.2985.42,430
Inferred6,7001.3890.1283.0650
TOTAL20,7001.53100.21304.63,080

 

Ore Reserves

The 30 June 2019 Ore Reserves estimate is a revision of the 30 June 2018 estimate that accounts for changes in the Mineral Resource, depletion due to mining; changes to cut-off grades; and mine design changes. The mining method assumed in the Ore Reserve estimate varies with the deposit. At the Tritton deposit, the method is sub-level open stoping with cemented paste fill. At the Murrawombie deposit, the ore is currently extracted using underground bench stopes and small open stopes with cemented rockfill. Future mining of the Murrawombie deposit will be by open pit, as the final extraction stage. The yet to be developed Avoca Tank deposit project is planned to use up-hole benching with dry rock fill.

The Tritton deposit Ore Reserve estimate has decreased from depletion due to mining. There has been no change in the Ore Reserve cut-off grade at Tritton during 2019. It remains at 1.2% copper. The Mineral Resource is reported using a lower cut-off grade of 0.6% copper. The significant difference in cut-off grade between Ore Reserve and Mineral Resource, combining with change in the character of the deposit at depth, means that a large portion of the available Mineral Resource has not converted to Ore Reserve due to economic constraints.

The residual Mineral Resource remains available for future mining review. The Tritton deposit has changed with depth from a deposit with one to two lenses of massive to stringer ore with a small halo of lower grade disseminated mineralisation, into multiple smaller lenses of massive to stringer ore within a much larger volume of disseminated mineralisation. This change in deposit character makes the estimate of Mineral Resource and Ore Reserves sensitive to cut-off grade selection, where it has not been historically.

The Murrawombie deposit Ore Reserve has decreased from a combination of depletion due to mining and an increase in the cut-off grade. Diamond drilling and geological modelling has added to the available Mineral Resource to partially offset depletion. The Murrawombie deposit contains several discrete lenses, with the 101, 102, 105 and 108 lodes being included in the underground mine Ore Reserve estimate. A cut-off grade of 1.2% copper is used to estimate Ore Reserve in the higher-grade lodes 102 and 108. A cutoff grade of 0.9% copper is used for the lower grade 101 and 105 lodes that are to be mined in retreat at end of mine life.

The Murrawombie deposit has separate Ore Reserve estimates for underground mining; and open pit mining. The open pit Ore Reserve is estimated for a small final push back on the existing open pit to extract mineralisation in the pit wall, and remnant areas above the underground mine where underground stoping is not viable. The Avoca Tank Ore Reserve estimates have not changed since last reported. At the Avoca Tank deposit, the Ore Reserve cut-off grade is 1.2 per cent copper. This deposit is high grade and not sensitive to cut-off grade.

The cut-off grade criteria applied at all deposits is copper grade, (per cent copper). The cut-off grade is applied as a whole of stope average grade after dilution factors are applied. There are no significant deleterious elements in the ore and the by-product value of gold and silver is of modest economic importance.

Where considered appropriate, the precious metal value is managed by applying a small copper equivalent credit to the cut-off grade. All Ore Reserve estimates for the underground mines are entirely sulphide mineralisation. This ore will be treated in the Tritton processing plant by flotation techniques. An average recovery of copper to concentrate of 93 to 95 per cent is assumed, consistent with historical plant performance.

Ore Reserves are estimated following the application of modifying factors that account for dilution and ore loss. The factors applied vary with the deposit, detailed design of the stopes, fill exposures and planned extraction sequence. In this report, the Ore Reserve estimates for the Tritton and Murrawombie deposits include gold and silver and gold only for Avoca Tank. There is no silver reported for the Avoca Tank deposit Ore Reserve, as at the time the estimate was prepared in 2013, it was not our practice to report silver in Ore Reserves.

No gold and silver is reported for the end of year stockpiles and so it is not reported in the total figures. Details of the Ore Reserve estimates can be found in the Mineral Resource and Ore Reserve reports on the Aeris website. All estimates are reported according to the 2012 Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves.

 

June 2019

Tonnes (kt)Cu (%)Cu (kt)Au (g/t)Au (koz)Ag (g/t)Ag (koz)
TRITTON UNDERGROUND
Proved2,4001.5370.185.2400
Probable6001.480.1574.481
TOTAL3,0001.5450.1655.1480
MURRAWOMBIE UNDERGROUND
Proved
Probable1,4001.8240.3158.2262
TOTAL1,4001.8240.3158.2262
MURRAWOMBIE OPEN PIT
Proved
Probable1,6000.9140.12302.8150
TOTAL1,6000.9140.12302.8150
AVOCA TANK
Proved
Probable7002.5180.818
TOTAL7002.5180.818
STOCKPILES
Proved401.60.6
Probable
TOTAL401.60.6
TOTAL
Proved2,4001.537
Probable4,3001.565
TOTAL6,7001.5100

June 2018

Tonnes (kt)Cu (%)Cu (kt)Au (g/t)Au (koz)Ag (g/t)Ag (koz)
TRITTON UNDERGROUND
Proved3,4001.5510.1135.1560
Probable3001.750.1345.450
TOTAL3,7001.5560.1475.2610
MURRAWOMBIE UNDERGROUND
Proved
Probable2,3001.6380.3236.6500
TOTAL2,3001.6380.3236.6500
MURRAWOMBIE OPEN PIT
Proved
Probable1,6000.9140.182.8150
TOTAL1,6000.9140.182.8150
AVOCA TANK
Proved
Probable7002.518
TOTAL7002.518
STOCKPILES
Proved302.10.7
Probable
TOTAL302.10.7
TOTAL
Proved3,4001.552
Probable5,0001.575
TOTAL8,4001.5130