Northparkes Mines’ Current Air Blast Risk Assessment Practices for Block Caving Operations

9 May 2016 Claudia Vejrazka

Outline

• CMOC

• Background

• Modelling Assumptions & Parameters

• Volume Flow Modelling

• Ventsim Visual™ Modelling

• Nomogram Creation

• Conclusions & Future Work

CMOC Overview

High quality and diversified asset portfolio with strong leverage to China and emerging economies

(1) Actual 2015 First Half

Beijing

Sydney

Sandaozhuang (100%)

Molybdenum /

Tungsten

Shangfanggou (55%)

Molybdenum / Iron

East Gobi Project (65%)

Molybdenum

Northparkes (80%)

Copper / gold

Henan Province

Xinjiang

CHINA Moly Roaster & FeMo

plants

Phoenix, AZ, USA

Overseas HQ

Shanghai Regional

Office

Sydney Regional Office

Luoyang City HQ

BRAZIL

AUSTRALIA

Nióbio Brasil Limitada

& Fosfatos Brasil

Limitada (100%)

Niobium and

Phosphates –

Transaction to be

completed in 2nd half

2016

CMOC’s vision and strategy

5

Our objective is to become a leading globally diversified mining and industrial company with international base, specialty and precious

metals production, the building blocks of society

1. Continue to be a leader in health safety &

environment

2. Build on our world class position in

molybdenum, tungsten, copper, gold

3. Improve production technologies and

operational efficiency

4. Acquire & diversify - infrastructure assets as well as base, specialty and precious metals

5. Leverage relationships to maximize asset values

Objectives

Our place in Central West New South Wales

Great Australian Basin

Murray Basin

South Australia

Victoria

New South Wales

Elura

CSA

Peak

Woodlawn

Wonominta Block

Lake Cowal

Gidginbung

Ballarat

Bendigo

Broken Hill

Sydney

Melbourne

Canberra

OrdovicianVolcanics

200 km0

LachlanOrogen

Cadia

Peak Hill

Mt Boppy

Hill EndNorthparkes

Captain's Flat

Currawong

Background – Lift 1 Air Blast

• On 24th November 1999 5.5Mm3 of rock displaced 4.1Mm3 killing four of our colleagues – Colin Lloyd-Jones, Stuart Osman, Ross Bodkin and Michael House

• Ross and van As prepared a detailed background paper on the event for the 9th Underground Operators Conference in 2005

(van As and Jeffrey, 2000)

Background (cont.)

• Air blast is a principal mining hazard of block caving

• Mechanics are not very well understood

• Published literature generally sparse

• Quantitative approaches often very labour intensive

• Limitations of models not always communicated well to operations

So what are we after?

Modelling Assumptions

𝑝𝑉𝑘 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡

𝑇𝐸𝑛𝑑 = 𝑇𝑆𝑡𝑎𝑟𝑡(𝑝𝐸𝑛𝑑

𝑝𝑆𝑡𝑎𝑟𝑡)

𝑘−1𝑘

(Fowler, Hebblewhite & Sharma, 2003)

Where p is pressure V is volume of air

κ is adiabatic index (1.4) T is temperature

(Derrington, 2004)

(Derrington, 2004)

(Derrington, 2004)

Modelling Parameters – porosity

• Varies widely

• E26 Lift1 back analysis 25%

• E26 Lift2N estimate 17%

• E48 at breakthrough 4%

• E48 March 2016 24%

𝑄 ~ 𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦

𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦 ~1

𝑅

• Best estimate at

feasibility study stage

• Triggers for a review

process required

(Vejrazka, 2008)

Modelling Parameters – muckpile resistance

• E26 Lift 1 back analysis: 0.0018Ns2m-7 per metre muckpile height

𝑃 = 𝑅 ∗ 𝑄2 = 𝑅 ∗ 𝐴2 ∗ 𝑣2

𝑅~1

𝐴2

• Normalised to 10,000m2 undercut area: 0.0203Ns2m-7 per metre muckpile height

• Normalised measurements from other mine: 0.0299Ns2m-7 per m per 10,000m2

Volume Flow Modelling

• Constrained to cave exits being on similar level

• Muckpile has to be relatively even

Ventsim Visual™ Modelling – Model Creation

Ventsim Visual Modelling – Monitoring Stations

Ventsim Visual Modelling – Model Simulation

Conversion of ventilation model

Model case creation Model simulation

Modelling Results

Nomogram Creation

Caving event Max. volume flows Location of

highest air speeds

small < 900m3/s CV10

medium 900m3/s -1500m3/s AD

large > 1500m3/s TOB

Conclusion & Future Work

• Principal mining hazard that needs to be managed

• Results in conservative estimates

• Transparent & automated process

o time savings of 39% compared to previously used methods

o Repeatable/auditable results

• Very little empirical knowledge

• Basic cave geometries

• Limits to importing/exporting of data

to and from Ventsim

ALWAYS use engineering judgement when employing results in an operational context!

Investment in fundamental research

Include air blast modelling

into ventilation package

such as Ventsim

Bibliography • Derrington, A, 2004. Northparkes Mines - Airflow through muckpile from potential cave

collapse, AMC Report 303095.

• Fowler, JCW, Hebblewhite, BK, Sharma, P, 2003. Managing the hazard of wind blast/ air blasts in caving operations in underground mines, in ISRM 2003 – Technology roadmap for rock mechanics, SAIMM 2003.

• Ross, I, van As, A, 2005. Northparkes Mines – Design, Sudden Failure, Air-Blast and Hazard Management at the E26 Block Cave, in Proceedings Ninth Underground Operators’ Conference, pp 7 – 18 (The Australasian Institute of Mining and Metallurgy: Melbourne).

• Van As, A, Jeffrey, RG, 2000. Hydraulic Fracturing as a Cave inducement Technique at Northparkes Mines, in Proceedings Third International Conference and Exhibition on Mass Mining (MassMin 2000) (ed: G Chitombo), pp 165–172 (The Australasian Institute of Mining and Metallurgy: Melbourne).

• Vejrazka, C. 2008, Optimisation of block caving operations, master thesis submitted at the TU Bergakademie Freiberg in fulfilment of the requirements for the degree of Diplom - Ingenieur für Bergbau.

Questions?