- A revised Inferred Mineral Resource of 75.9 Mt at 4.6% Pb, 2.3% Zn, 0.25% Cu and 119 g/t Ag has been estimated for the Bawdwin project based on a cut-off grade of 0.5% Pb above the 750m RL and a cut-off grade of 2% Pb below the 750m RL.
- The revised estimate was increased to include 34 million tonnes of low-grade material within the block model that was not classified in the previous Mineral Resource estimate (ASX release 17 October 2017) as it fell below a 2% Pb cut-off grade.
- Revised estimate includes 66.5 Mt at 4.2% Pb, 2.2% Zn, 0.25% Cu and 112 g/t Ag above the 750m RL (0.5% Pb cut-off) and 9.4 Mt at 7.9% Pb, 3.4% Zn, 0.2% Cu and 165 g/t Ag below the 750m RL (2% Pb cut-off).
- A recently completed open pit optimisation study by CSA Global as part of the current Scoping Study indicates that a reduced cut-off grade of 0.5% Pb above 750m RL is appropriate to reflect potential economic extraction.
- The pit optimisation suggests that most of the resource above the 750m RL will fall within the final pit shell, and there is potential to increase this proportion through extending shallow resources by drilling.
- The remaining resource below the 750m RL supports the potential for a future underground mine at Bawdwin.
- The revised Mineral Resource estimate is underpinned by more than 56 kilometres of historical underground sampling and geological mapping of exploration drives, supported by almost 3000 metres of diamond drilling undertaken in 2016-17; geological mapping of mineralisation in the dormant open pit; and 669 metres of channel sampling
- The Inferred classification despite high data density reflects the absence of QAQC information for historical data.
- 92% of the Mineral Resource is in the preferred Fresh sulphide zone with 8% in Transitional and Oxide zones.
- Much of the original in-situ resource remains un-mined – the reported estimate reflects 15% depletion, based on modelled void volumes, from the total estimated pre-mining resource.
- Highly likely that old stopes contain mineralised backfill (low-grade mineralisation and sand fill from tailings) – upside for open pit production beyond the estimated mineral resource.
- Drilling is planned to commence in January 2018 leading to an updated Mineral Resource estimate in the second quarter.
- Bawdwin Scoping Study to be released shortly.
Myanmar Metals Limited (ASX: MYL) (“MYL” or “the Company”) is pleased to report a revised Mineral Resource estimate completed by CSA Global and reported under the guidelines of the JORC Code 2012 Edition. The maiden Mineral Resource estimate for Bawdwin was reported under the JORC Code and announced in the Company’s release to the ASX on 17th October 2017. The revised estimate is based on the same block model and estimation parameters but applies different cut-off grades.
The Mineral Resource estimate is based on extensive historic channel sampling of underground exploration cross cuts supported by new diamond drilling and channel sampling data collected in 2017. The Mineral Resource estimate highlights the potential of the Bawdwin Project to be redeveloped as a large-scale mining operation.
As previously reported, MYL holds an option over the Bawdwin project with Win Myint Mo Industries Co. (“WMM”), the Myanmar company that holds the 38 km2 Mining Concession at Bawdwin under a production sharing agreement with Myanmar state mining company, Mining Enterprise No. 1.
Myanmar Metals Limited’s Chairman, John Lamb, commented:
“This revised Resource estimate is further evidence of the significant unlocked value of the Bawdwin deposit. The mining study undertaken by CSA Global as part of the current Scoping Study demonstrates significant potential for a very low cost open pit operation which in turn supports a lower cut-off grade for that portion of the resource, allowing more material to be classified in the Inferred Mineral Resource category.
While the previously published estimate of 41 million tonnes grading 7.5% Pb, 3.5% Zn, 0.33% Cu and 178g/t Ag quoted at a 2% Pb cut-off remains a valid and conservative view of the deposit, the opportunity to recover additional low-grade material from within the pit shell is compelling as it adds a substantial amount of contained metal into the total resource.
Based on these revised estimates, we expect to publish the Scoping Study on Bawdwin in the coming week.
As well, MYL’s in-country partner, Win Myint Mo Industries, is now planning for a second drilling program in January which will lead to this revised Mineral Resource estimate being updated again.
We are very encouraged by the progress we are making at Bawdwin and will continue to update shareholders on our progress.”
Bawdwin Mine Background
The Bawdwin Mine in the northern Shan State in Myanmar was a globally significant lead, zinc and silver mine in the 1920’s and 30’s. Large-scale production ceased during World War 2 and the mine never returned to pre-war production levels. It was nationalised in the 1960’s and no modern exploration has been conducted on the site up until the present time.
Figure 1. Location map for the Bawdwin Project
Geology and Mineral Resource Estimate
The revised Mineral Resource estimate is provided in Table 1. This estimate is an update of the estimate reported to the ASX on 17th October 2017. The updated estimate is based on the same block model and all of the input data and interpolation parameters and methodology are unchanged from those reported previously. The new estimate is based on a lower 0.5% Pb cut-off grade applied to the block model above the 750m RL. The reduced cut-off grade is based on the results of a pit optimisation study that forms part of the Scoping Study on an open-pit development at Bawdwin that is nearing completion.
Table 1: Bawdwin Inferred Mineral Resource Estimate
The Mineral Resource has been classified as Inferred in accordance with guidelines contained in the JORC Code 2012 Edition. The Mineral Resource is contained in three separate zones, termed the Shan Lode, China Lode, and Meingtha Lode. Each includes high-grade massive sulphide zones that were mined historically underground (‘lode’ mineralisation) and lower-grade disseminated and stockwork mineralisation (‘halo’ mineralisation) that has been exploited in the open pit on the China Lode.
Figure 2. Plan view of the Bawdwin block model for Pb on a detailed DTM from a 2017 drone survey. The surrounding low-resolution DTM is derived from SRTM data.
The topography over the deposit is constrained by a high-resolution DTM captured with drone survey in 2017. This survey covers the main mineralised corridor but not the full extent of a likely open pit. A more extensive survey will be undertaken as part of the next work programme at Bawdwin.
Weathering and oxidation is deep on the ridges (20-50 metres), but much thinner in the valleys. The existing open pit at Bawdwin has largely removed the weathered zone and fresh sulphides observed at surface in the pit highlight underlying massive sulphide lodes. Only eight percent of the estimated Mineral Resource is in the transitional and oxidised zones. The oxidation surface is not well constrained by the limited drilling to date and will be more accurately defined by the next phase of planned drilling.
The Inferred Mineral Resource estimate is based on drill-hole sampling, open pit channel and historical underground channel sampling. The Mineral Resource is classified as Inferred because existing data is sufficient to imply but not verify geological and grade continuity due to the absence of QAQC information for the historical underground data. The Inferred classification has considered all available geological and sampling information and the classification level is considered appropriate. Key criteria that have been considered when classifying the Mineral Resource are detailed in JORC Table 1 which is contained in Appendix 1.
Figure 3. Oblique view of the Bawdwin Pb block-model from the southwest. Note that the ‘cliffs’ are artefacts between the high- and low-resolution DTMs.
Figure 4. Bawdwin block-model long section showing the 750m RL boundary for reporting at 0.5% Pb or 2% Pb cut-off grade
Historical Underground Exploration at Bawdwin – Basis of the Mineral Resource
The Inferred Mineral Resource estimate is largely underpinned by historical underground exploration and grade-control data from the Bawdwin Mine, including over 56,000 metres of underground drive sampling.
Exploration by mapping and sampling cross-cuts was the main exploration method at Bawdwin and continued until the 1980s. Cross cuts were developed on each of the mine levels at intervals of 20 to 60 metres and extending from 20 to 100 metres from the main lodes, with some drives extending up to 200 metres. Most exploration drives were developed on the eastern footwall side of the main lodes, especially in the relay zone of the China Lode where the open pit was developed in the 1980s.
Most underground exploration occurred above the No. 6 level (approx. 850m RL), underground exploration was less extensive from the No. 7 to 12 levels.
The exploration cross cuts were geologically mapped in detail and channel sampled for assaying at the mine laboratory. Geology and sample intervals were recorded on level plans. The assay level plans show the drives on the level along with the sampling traverse locations and Ag, Pb, Zn and Cu values. Sampling and mining between the levels is recorded on multiple floor plans at seven-foot (2.13 m) intervals.
The sampling data dates largely from the 1930s until the 1980s and utilised consistent sampling and analytical protocols through the mine history. Sampling consisted of 2-inch (5 cm) continuous channels cut with hammer and chisel at waist-height along both walls of across-strike drives and across the backs of strike drives. The sample interval was 5 feet (1.5m) and weights were around 5 pounds (2.3 kg).
Samples were prepared in the mine laboratory. Samples were crushed in a jaw crusher, mixed, and coned and quartered. Two 100-gram samples were then dried and pulverised in a ring mill to approximately 100 mesh. Two 0.5-gram homogenised samples were taken for lead and zinc titration using Aqua Regia (Pb) and Nitric acid (Zn). Results were recorded in ledgers. Averaged results from each wall of the exploration cross-cuts were recorded on the level plans.
The mine laboratory is still operational and employs the same analytical methods. It is operated by trained chemists and is kept in very good condition.
Data Capture and Validation
The mapping, sampling and analytical data represent a very valuable historical record that has been meticulously maintained until the present, with plans and ledgers stored in a fire-proof safe room at the Bawdwin Mine office. Most of this valuable dataset was digitally captured during 2017. The assay level plans were systematically scanned together with a subset of intervening floor plans. Levels were digitised and assay intervals and Ag, Pb, Zn and Cu assay values were entered from the plans into spreadsheets and imported into an Access database. Mined stopes were also digitised from level and floor plans and built into 3D wireframes. These were ultimately used to deplete the Mineral Resource Estimate.
Validation of the historical data by resampling is not possible as access is no longer possible. Confidence in the general validity of the data can be derived from the maintenance of consistent sampling and analytical techniques for sampling and grade control throughout the active mine history. The 2017 drilling also validates the historic records by confirming similar location and tenor of
mineralisation. However, in the absence of validation sampling or QAQC, the historical data can only support an Inferred classification for the Mineral Resource.
Depletion of the Mineral Resource
The Mineral Resource estimate was first completed on a pre-mining (un-depleted) basis with the inclusion of sampled underground development that was later mined out. This approach is true to the data and allows data in mined areas to inform the estimate in unmined areas. It requires depletion or subtraction of the mined volume and tonnages after the estimate is complete. The resource was depleted using wireframes of mined stopes that were constructed from scanned level plans and some of the intervening floor plans that document all the square-set stopes. These records were kept meticulously up until underground mining ceased.
The pre-depletion Mineral Resource estimate at the same 0.5% Pb and 2% Pb cut-off grade criteria totals 89.5 Mt at 6.3% Pb, 3.3% Zn, 0.29% Cu and 163 g/t Ag. The difference in tonnage with the depleted resource of 13.6 Mt compares well with estimate of historical mine production. The depletion represents 15% of the block model tonnage at the applied 0.5% and 2% Pb cut-off grades, though a higher proportion of the contained metal due to the high grade of historically-mined material.
The stopes at Bawdwin are reported to have been largely backfilled with mine waste. Considering the high cut-off grade used in historic mining, it is likely that significantly mineralised backfill exists within these back-filled stopes.
After the flotation plant was constructed at the Bawdwin site in the early 1980s, tailings were separated into coarse (sand) and fine fractions and the coarse tailings were also used as backfill. Given the poor recoveries from the flotation plant, it is considered likely that this material may also carry significant metal grades.
Bawdwin Block Model and Grade Distribution
The high-grade mineralised zones or ‘lodes’ were wireframed separately and estimated as separate domains with hard boundaries to prevent the smearing of high grades into the lower-grade envelope, and vice-versa. However, some high-grade zones are too narrow or discontinuous to be modelled separately.
The block model shows remnant high-grade zones close to mined stopes. These zones may not have been mined because of the constraints of the square-set stoping method, however, there may also be discrepancies between surveys of sampled drives and mined stopes affecting the accuracy of the depletion of the resource. This is reflected in the Inferred classification.
Resource Model Sections
Figures 4, 5 and 6 show a cross-section through the deposit highlighting lead, silver and zinc block- model grades respectively.
These figures show:
• The relatively high grade of the entire resource, noting that lead, silver and zinc metal is co- located within the same rocks (i.e. true polymetallic mineralisation);
- The relatively small proportion that has been previously mined;
- The historical mining of the oxidised material near surface;
- The topography (i.e. a valley and historical open cut), which assists development of an open pit mine on this deposit by reducing strip ratio; and
- The shallow nature of the deposit with the overwhelming majority of the resource located within 300-350 metres of the current natural surface (being the valley floor, current road and 1980’s pit floor).
Figure 5. Cross Section through the Pb block model at the China Lode. Mined stopes are in black. Note the 750m RL approximating to Level 9
Figure 6. Cross section through the Zn block model at the China Lode. Mined stopes are in black. Note the 750m RL approximating to Level 9.
Figure 7. Cross section through the Ag block model at the China Lode. Mined stopes are in black. Note the 750m RL approximating to Level 9.
Figure 8. Long section through the Pb block model for the Shan, China and Meingtha lodes. Mined stopes are in black.
Figure 8 shows the resource (silver) block model and topography on a section line along the strike of the deposit. The high-grade, relative lack of historical depletion and amenability of the topography to open pit mining are clearly apparent and the long-section also clearly identifies areas with potential for resource extension through near-mine exploration. These areas appear as white space in the model signifying the absence of data.
Exploration and Resource Extension Potential
Previous exploration at Bawdwin has been minimal outside the areas where exploration cross-cuts were developed. The underground exploration was quite limited at the deeper levels of the mine where additional peripheral lodes may exist.
The Company considers that there is high potential for extensions of mineralisation with significant grade below the very high cut-off grades used in historical mining. There is also potential for offset extensions to the high-grade lodes to north and south and at depth, related to the en-echelon relay geometry of the lodes or later fault offsets.
Initial structural mapping has been completed at Bawdwin and has improved the understanding of the structural controls on mineralisation. Additional future structural mapping and drill-core logging will provide a robust framework for the targeting of structurally controlled high-grade lodes.
Furthermore, systematic mapping of alteration and zonation is expected to provide additional vectors towards identifying high-grade mineralisation, further enhancing targeting effectiveness. This will be facilitated by using multi-element analysis of existing core samples, alteration mapping and logging using a Terraspec Halo SWIR for determining clay and mica mineralogy, and petrological studies.
Preliminary petrophysical testwork indicates that mineralisation at Bawdwin has a strong geophysical response. The high-grade lodes are conductive and amenable to detection and the lower- grade mineralisation is chargeable and amenable to detection by induced polarisation (IP) methods.
It is expected that the combination of electro-magnetic (EM) and IP surveys will provide a strong basis for direct targeting of mineralisation at Bawdwin, noting that geophysical exploration has never been conducted previously.
Bawdwin – Next Steps
The Scoping Study by CSA Global into the development of an open pit mine and supporting infrastructure at Bawdwin and Namtu is nearing completion and the results of this study will be promptly reported to the ASX. Results from the study will underpin detailed discussions with the Myanmar government in the coming weeks and months.
At the same time, work will commence on supplementary technical studies including metallurgy and environmental assessments as well as a drilling programme. Drilling is planned to commence in January 2018 and will initially target the ‘starter pit’, with the aim of establishing and reporting an Indicated Mineral Resource Estimate in the second quarter of 2018.
This work will underpin the exercise of the Bawdwin option on or before 21 May 2018; thereafter a bankable feasibility study will be undertaken.
Forward Looking Statements
The announcement contains certain statements, which may constitute “forward –looking statements”. Such statements are only predictions and are subject to inherent risks and uncertainties, which could cause actual values, results, performance achievements to differ materially from those expressed, implied or projected in any forward-looking statements.
Competent Person Statements
The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (the ‘JORC Code’) sets out minimum standards, recommendations and guidelines for Public Reporting in Australasia of Exploration Results, Mineral Resources and Ore Reserves. The Information contained in this announcement has been presented in accordance with the JORC Code.
The information in this report that relates to Geology and Exploration Results is based, and fairly reflects, information compiled by Dr Neal Reynolds, who is a Fellow of the Australasian Institute of Mining and Metallurgy and a Member of the Australian Institute of Geoscientists. Dr Reynolds is employed by CSA Global Pty Ltd, independent resource industry consultants. Dr Reynolds has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he is undertaking to qualify as a Competent Person as defined in the 2012 Edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’. Dr Reynolds consents to the inclusion in the report of the matters based on his information in the form and context in which it appears.
The information in this report that relates to Mineral Resources is based, and fairly reflects, information compiled by Serikjan Urbisinov, who is a Member of the Australian Institute of Geoscientists. Mr Urbisinov is employed by CSA Global Pty Ltd, independent resource industry consultants. Mr Urbisinov has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he is undertaking to qualify as a Competent Person as defined in the 2012 Edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’. Mr Urbisinov consents to the inclusion in the report of the matters based on his information in the form and context in which it appears.