Design and implementation improvements for wall control blasting in an anisotropic rock mass at the Phu Kham Copper-Gold Operation

E.J. Sellers, L.D. Kennelly, B Withers, K Monro, D Reid

PanAust Limited

PanAust Limited is an Australian-headquartered copper and gold producer in Laos, with pre-development and exploration assets in Laos, Papua New Guinea and Chile.

In Laos, PanAust owns a 90 per cent interest in the Lao-registered company, Phu Bia Mining. The Government of Laos owns the remaining 10 per cent.

Operations

PanAust’s producing assets in Laos are the Phu Kham Copper-Gold Operation and the Ban Houayxai Gold-Silver Operation; both operated by Phu Bia Mining.

Phu Kham and Ban Houayxai are located in the Company’s 2,600 square-kilometre Phu Bia Contract Area.

Phu Kham Copper-Gold Operation

Ban Houayxai Gold-Silver Operation

Phu Bia Contract Area

The Phu Kham deposit

• The deposit at the Phu Kham Operation is a classical stock work disseminated porphyry copper-gold system

• The figure on the left shows its complex geology

• The excavation of basement red beds is required to access deeper parts of the orebody

Bennett et al, 2014

Red beds

The red beds are a stratified siltstone

Three projects

• Mine-to-mill

– Increase drill productivity and mill throughput

• Waste cut back

– Fragmentation of non-acid forming material for the tailings dam

• Wall control

– Steepen the walls and reduce damage from high-energy production and waste blasts

The Wall Control Project was one of three blasting-focussed initiatives to improve productivity and reduce risk at the Phu Kham Operation

Blasting challenges

• The dip of the strata was controlling the breakage and leading to underbreak at the toes and overbreakat the crest

• Some larger fragments were noticeable where the layers slid back into the muckpile causing digging issues

Underbroken toe Overbreak in crest

Anisotropy

The main challenges were associated with the anisotropy of the red beds

Blast design and implementation

Anisotropy

Trim blast Waste production blast

Blast design and implementation

No damage at toe if decoupled 4 metre damage when coupled

Without clear design approaches for this type of rock, a series of blasts were monitored to define the rock – explosive interactions

Decoupled holes created no breakage at the toe and couples holes created extensive back break

Decoupled

Coupled

The Wall Control Project

• Requirement to increase overall wall angle

• One of six design options selected:

– 20 metre bench (mined as 2 metres x 10 metres), a batter angle of 80o, pre-split over 20 metres if possible

– This provided a berm width of 16 metres

• Trials

• Change of Design

• Trial

• Implementation

Presplit trialsAngledVertical

New design with trim or trim/productionOld design New design

Flattened timing contours near wall

Old timing New timing + 100 metre delay on stab row

Success

Value added by good wall control

Larger blasts improved drill usage and reduced the risk

Trim + production blasts increased the mining rate

Improved fragmentation for the ‘green’ waste in the tailings dam

Back damage reduced by 75 per cent reduction; underbreakreduced by 66 per cent; no secondary blasting

Stable walls without loose rock allowing the waste cutback to proceed safely

High energy ore blasting improved plant throughput 14 per cent to 54 per cent

Access to ore that was planned for the final pit design

Conclusions

• High-energy blasting to improve productivity does not need to adversely affect open-pit walls

• The anisotropy of the rock mass challenged the conventional understanding of blast damage and wall control blast design approaches

• Further research is required (ongoing) to develop better quantification of the effect of anisotropy on rock – explosive interactions

Acknowledgements

• Phu Bia Mining

• JKTech

• Mining3

• The efforts of Dwayne Symonds, Arthur Pacuana, Bounyod Munxayaphom, Chanol Yim Yam and the drill and blast team at Phu Kham are highly appreciated

Important notices

This presentation has been prepared solely for informational purposes and not as specific advice to any particular party or person. The information is based on publicly available information, internally developed data and other sources. No independent verification of those sources has been undertaken and where any opinion is expressed in this presentation it is based on the assumptions and limitations mentioned herein and is an expression of present opinion only. No warranties or representations can be made as to the origin, validity, accuracy, completeness, currency or reliability of the information. PanAust Limited (Company) disclaims and excludes all liability (to the extent permitted by law), for losses, claims, damages, demands, costs and expenses of whatever nature arising in any way out of or in connection with the information, its accuracy, completeness or by reason of reliance by any person on any of it. The Company does not have any obligation to advise any person if it becomes aware of any inaccuracy in, or omission from, the information contained in this presentation.