Issuu

www.runge.com,

Chairman Vice-Chairman Honorary Secretary Honorary Treasurer Committee

Honorary Editor

Wes Nichols Bill Hayes Mark Biggs Peter Crosdale Brian Coxhead Lloyd Hamilton Ken O'Reilly Ken Preston Warwick Smyth Jim Beeston

Address for editorial matters: Honorary Editor Australian Coal Geology 8 Lana Street Tarragindi, Qld 4121 j im.beeston@gmail.com

II I

I I l I

! 1, Address for other matters: Mark Biggs Honorary Secretary Coal Geology Group PO Box 433 Banyo, Qld 4014 mark.biggs@moultrie.com.au Published by the Coal Geology Group, © Geological Society of Australia Inc. ISSN 0725-4938 Issued February, 2011 Price to non-members - $10.00 per issue

f I

CONTENTS DSM - A tool for exploration land access management in BMA (W. Lin, N. Pranoto, D. Dunn & T. Fouet) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 1

Challenges in fault modelling for coal deposits ( M. Biggs)

Closure landform design: an integrated approach (M. van Zyl).

Bowen Basin Symposium 2010 Workshop Presentations 6th October 2010 (on CD) PRESENTATION 1: Challenges in the reconciliation and reporting of coal recovery in situ to sales. Presented by Andrew Scott, Scott Mine Consulting Services Pty Ltd, andrew@scottmining.com.au PRESENTATION 2: Bore core coal quality process mapping 'innovation driving progress' Coal Quality Data Handling - Constructing an Efficient Process. Presented by Christopher McMahon, McMahon Coal Quality Resources, mcmahon@gil.com.au PRESENTATION 3: Geotechnical strata characterisation from geophysical borehole logs. Presented by Peter Hatherly - Coalbed Geoscience, geophys@bigpond.net.au and Terry Medhurst - PDR Engineers tmedhurst@pdrengineers.com.au PRESENTATION 4: Coal Seam Gas Reservoirs. Presented by Ray Williams, currently at Runge Mining, formerly at GeoGAS Pty. Ltd, www.runge.com, www.geogas.com.au.

EDITORIAL This issue of Australian Coal Geology contains contributions to the Bowen Basin Symposium 2010 that missed the deadline production date. Also from popular request w.e enclose a CD containing some of the workshop presentations that enthralled those that attended on the first day. The 2010 symposium was touted as being the sixth in a series. In fact it could be argued that it was the eighth. In 1967, officers from Broken Hill Propriety Limited made a request to the Geological Survey of Queensland (GSQ) and the Bureau of Mineral Resources (BMR) for 'discussions on aspects of the Upper Permian coal measures'. What was initally proposed as a 'conference room' meeting was quickly upgraded to a semi-formal seminar due to the amount of interest attracted from other sources. The GSQ approached the University of Queensland who offered their premises in the old Masonic Temple in Alice Street, Brisbane. For three days 73 representatives of government universities and industry discussed matters including coal deposition, coal quality and stratigraphy. The proceedings were published in

Australian Coal Geology

GSQ Record 1967/01 as ' The Bowen Basin Coal Measures Symposium', edited by WL (Bill) Hawthorne and GW (Gus) Tweedale. In 1970 a second conference was held by the GSQ entitled the 'Second Bowen Basin Symposium' . Altogether 105 delegates met in the Queensland Main Roads Department auditorium in Spring Hill. The proceedings were published as GSQ Report 62, edited by A (Alan) Davis. The Geological Society of Australia Coal Geology Group was born in 1978, and proceeded to run a Symposium on the Surat Basin, in 1979, in Toowoomba (see Coal Geology 1(3,4)). By 1985 it was decided that the Bowen Basin was again in need of review. The Coal Geology Group, in conjunction with the GSQ, organised the 'Bowen Basin Coal Symposium' , this time in Rockhampton, on lst-3rd November, 1985. Abstracts were published in the Geological Society of Australia Abstracts series (Number 17). In 1990 the newly formed Bowen Basin Geologists Group (BBGG) convinced the Geological Society of Australia - Queensland Division (GSA-Qld), the CGG, and the GSQ, that periodic reviews of the Bowen Basin could be the order of the day. The GSQ was committed to a major drilling program instigated by the Queensland Government, and had just produced a new 1:500 000 scale geological map of the Bowen Basin. Company exploration was also on the rise. The symposium, this time organised by the BBGG, was held in Mackay in September 1990, with the proceedings published as 'Bowen Basin Symposium 1990' by GSA (Qld). By 1995 a pattern was emerging. The Symposium was to run every 5 years, organised by a dedicated committee from the BBGG, and the proceedings published by the CGG. This resulted in the ' Bowen Basin Symposium 1995' in Mackay 1-2 October 1995, the 'Bowen Basin Symposium 2000 -The New Millennium - Geology' in Rockhampton 22-24 October, 2000, the 'Bowen Basin Symposium 2005 - the Future for Coal - Fuel for Thought' in Yeppoon 12-14 October 2005, and the 'Bowen Basin Symposium 2010 - Back in (the) Black' in Mackay 6-8 October 2010. With a record attendance in 2010, the Bowen Basin Symposia phenomenon has expanded into a premiere event for updating on all coal science and technology issues around Australia, and indeed from other parts of the globe. Bring on 2015 .

Dr Jim Beeston Honorary Editor Australian Coal Geology

Australian Coal Geology

DSM -A TOOL FOR EXPLORATION LAND ACCESS MANAGEMENT IN BMA W. Lin, N. Pranoto, D. Dunn & T. Fouet Lin, W., Pranato, N. , Dunn, D. & Fouet, T., 2011: DSM- a tool for exploration land access management in BMA. Australian Coal Geology, 12, 1-13. BMA Geological Services carries out exploration activities for BHP Billiton Mitsubishi Alliance and BHP Mitsui Coal, drilling in excess of 3,500 holes and conducting 285km of seismic surveys every year on both mine and exploration sites. To ensure that exploration activities comply with BMA and BHP Billiton Standards and legislation (Cultural Heritage Act, Environmental Protection Act, Mineral Resources Act, Coal Mining Safety & Health Act); Geological Services commissioned Snowden Technology to develop a system to manage BMA's exploration land access processes. The Drill Site Management (DSM) System was developed to manage process flow of BMA exploration activities through the planning, permitting, survey/clearance, site preparation, drilling/recording, and rehabilitation/closure stages. The DSM incorporates the One BMA Permit to Disturb and Permit to Dig/Penetrate processes and is a key component ofBMA Geological Services 1SO14001 accredited environmental management system. The system has two interfaces: a web services based portal, called the BMA Geology Portal, where geologists handle process flow and, input required documents, coupled with a Personal Digital Assistant (PDA) which is used by field technicians to survey and record field data. The system implemented has successfully managed complex environmental, cultural and heritage risks and minimised compliance costs.

Wenjing Lin, Noel Pranoto and Doug Dunn, BMA Coal Tracy Fouet, Snowden Technology

Introduction

Goonyella Riverside, Broadmeadow, Peak Downs, Saraji, Norwich Park, Gregory, Crinum and Blackwater - and the Hay Point BHP Billiton Mitsubishi Alliance (BMA) is coal export terminal near Mackay. BMA also Australia's largest coal miner and exporter, manages the operations of BHP Mitsui Coal, and the world's largest supplier to the which is owned by BHP Billiton (80%) and seaborne coking coal market. BMA is a 50/50 Mitsui and Co (20%). These include South alliance between the world's largest Walker Creek Mine and Poitrel Mine. We diversified resources company BHP Billiton produce over 50Mtpa and will double and the world's largest general trading production by 2020. company Mitsubishi Development Pty Ltd. The companies share equal ownership of eight Central Queensland coal mines -

BMA Geological Services are increasing exploration activities to ensure the growth

Australian Coal Geology

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Australian Coal Geology

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• Optimised resource. To fulfil these requirements, we have implemented a system that: • Integrates exploration processes and improves end-to-end data management • Makes use of the CAN, the Wireless LAN, PDA and future IT infrastructure directions • Allows seamless control of exploration process • Integrates with centralised drill hole database systems • Supports BMA and BHPB industry leadership position through Innovation & Best Practice with the Business Process improvement gains as a result. Figure 4: Personal Digital Assistant

pipeline is kept filled. Geologists need to ensure exploration activities comply with legislation.

This DSM system expands BMA's Field Data Capture System (FDCS) to include the capture and processing of the drill site and geophysical survey line planning, permitting, clearance, preparation, grouting and site rehabilitation as shown in Figure 1.

It is a challenge for geologists and field technicians to remember all the requirements for permits and clearances without a system to aid them. Any steps omitted could mean a breach of legislation.

The system assists BMA staff to follow the BMA procedures for conducting drilling and geophysical programs and to assist in tracking the status of these programs throughout the process described in Figure 2.

In developing a system to address these issues we needed to be cognisant of BMA IT architecture requirements. These include:

The system includes the tools to easily track the status of drilling and geophysical survey programs for each project and to ensure all BMA policy requirements are met throughout the process. Figure 3 shows an example of this report.

• Supply chain optimisation • Leverage embedded technology • Manage information • Rationalise and integrate systems

Data collection is carried out with the use of mobile computing devices Personal Digital Assistant (PDAs) (Figure 4) that synchronise with BMA's central SQL Server database.

• Optimal communication networks • World Class IT service delivery effective training & support

Throughout the DSM System tollgates have been put in place, that require the project geologist to perform a task before the site /

Australian Coal Geology

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Project geologist impor1S data into GBIS and assigns a cost code

A11tlbutes automatically assigned by the system: - Tenement number • Surface rights (YIN} • Encroach ERE 500m (YIN) - Encro11ch N11tional Park 1000m (YIN} - Gas lease number -Site Senior Executive (SSE ) area • Cadastral Information • Lot number - Site Preparabon requirements (for boreholes)

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Australian Coal Geology

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Australian Coal Geology

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line can progress to the next stage. Email notifications have been incorporated into the DSM system that will inform the project geologist if permits are nearing expiration or have expired, or if new survey data has been uploaded from a PDA and is awaiting approval.

Drill site and geophysical survey management process

mining tenure type, environmental/cultural heritage areas and landholder information. After the planned site is imported into the system, project geologists are required to review it to ensure all user and system defined attributes have been assigned correctly. If a site requires changes (e.g. it is relocated) the planning information can be updated and attributes will be automatically updated to reflect the changes. These attributes are listed in Figure 5.

Site Planning Process Site Permitting Process The site planning process is the starting point for the DSM System. Project geologists prepare drill planning data. The data can include downhole predictions from modelling.

The permitting process starts with the geologist selecting a series of planned boreholes or seismic lines which will define a specific drilling or seismic program.

During the import process the project geologist assigns values to a number of additional attributes which will be associated with the borehole or seismic line and be used throughout subsequent processes.

Once the program has been defined the permitting requirements are dependent on the attributes which were associated with the sites during the planning stage.

The DSM system will assign additional attributes based on polygonal data such as

Figure 6 outlines the process involved in determining what permitting is required.

Australian Coal Geology

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If at any point in the process a permit expires, the system will not allow the site to progress and will alert any users attempting to use the data of the need to update the expired permit. Additionally, the system will email notifications informing the project geologist that a permit is about to expire. The warning period will be user configurable for each permit type, allowing for longer lead times to re-acquire particular permits. Figure 7 shows how permitting process history can be viewed anytime for audit.

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The initial site survey is carried out once all of the required permits have been obtained for a drilling or seismic program. At the start of this process (Figure 8) the field technicians will transfer data to a GPS enabled PDA. The PDA is used in the field to locate and record the proposed site in the field and photograph site conditions. The field data uploads to the server for approval by the Project Geologist.

Clearances may be obtained at any stage before; during or after the initial site survey is completed. Once the initial site survey has Figure 8: Initial Site Survey and Clearance Process been completed the Clearance Received column will be highlighted orange to warn the project geologist to review that the Before a site can progress to the next stage all clearances are still valid at the new location of the permits need to be acquired and (Figure 9). New clearances may be required if registered in the system. the pegged location is outside the area of the previously obtained clearances. For each compulsory permit, users will be required to provide the following details: Clearance requirements are based on the • The application date tenement type with the number of sites awaiting either the ML Clearances or • The permit approval date EPC/MDL Clearances. Figure 10 shows the clearance process. • The expiration date (if one exists) • Required documentation (e.g. Notice of Where drill sites are located on an operating tenure, a 'One BMA Permit to Disturb' and a Entry, Environmental Authority Amendment etc.). This will need to be 'Permit to Dig' are issued and registered loaded into BMA's document against the associated sites. Upon completion management system with a link to this of Initial Site Survey and after obtaining document registered through the BMA these permits, the site will progress to the Site Preparation stage. Geology Portal.

Australian Coal Geology

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Drill sites located on undeveloped tenures will require both environmental survey and cultural heritage clearances. A data pack and associated sign off form is generated from the DSM Survey and Clearances Summary page in the BMA Geology Portal. These inspection forms are automatically populated with the selected site numbers and coordinates.

Once approval has been obtained, the clearance sign off form is registered against the relevant sites (Figure 11 ). This can be done for more than one site at a time.

Once the initial site survey field data has been uploaded to the server and clearances have been completed, a user notification will be displayed in the Geology Portal and an email notification sent to the project geologist indicating that survey data is awaiting approval. After approval of survey and clearances, the site preparation can commence.

Site Preparation The site preparation process (Figure 12) is initiated once the initial site survey and clearances have been obtained. Planned sites, cleared and available for site preparation, are transferred to the PDA. _ Figure 13 shows ERE buffer zones and drill sites on PDA. A data pack for the site preparation operator is accessible from the Preparation Process page in the DSM Geology Portal. ~en the sites have been ' Prepared' the user will then record information such as: • Updated coordinates ifrequired • Date the site preparation was completed • Photos of prepared sites • Additional comments.

Australian Coal Geology

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A list of site preparation checks is displayed on the PDA. Affirmation that the site preparation has been completed adequately is done by saving the confirmation of the site preparation check list. The PDA data will be uploaded to the server. The current status of all boreholes with

completed site preparation would then be available to the project geologist through the Geology Portal. An email reminder will be sent to both the field technician and project geologist to check any prepared sites that are older than three months and which have not been used.

Australian Coal Geology

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~ ht:t:p ://bmabn•-w~b01/ cyb~,rJoa/ •tc... f or• sp•d f ic fil~ v~rsWn

or a docum,,nt numb•r t o •lw•ys pojnt to th• /•test versWn jr, Hummjngbird.

Figure 11: Exploration Clearance Page

In this case the site will either need to be checked in the field to ensure it is still available to be used or flagged as "not to be drilled" in which case it will immediately be set as available for rehabilitation.

Site Grouting Process

The cementation requirements for a borehole are set at the hole planning stage. However these can be modified by the project geologist at any time throughout the process. A hole Site Drilling will automatically be set to cementation stage (if required) once its full completion has been Sites that have been approved through the site confirmed. These requirements can, however be modified by the user at any time preparation process will be available for throughout the DSM process. Holes can be transfer onto a toughbook for drilling and manually made available for cementation data capture. The data collection process for once the hole status has been set to logged boreholes is currently managed through the and LAS data has been loaded. FDCS.

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Before a borehole can be grouted the project geologist is able to check that all required data has been collected including lithology, core photos and geophysical data through the portal. Once these checks have been completed the borehole can be flagged as available for grouting.

Produce map, lis! of boreholes

and site preparation requirements

Download available borehole data toPOA

Supply lnformataon lO bactchoe operator

Clear site & dig pots (d required)

Site Rehabilitation and Program Completion Process Figure 14 outlines the process for the rehabilitation of both boreholes and seismic lines. The sites available for rehabilitation are downloaded to the PDA device along with any additional information required (e.g. rehabilitation type).

Check hole and record data (GPS ooordina:es, date completed & any remarks)

Si:e Preparaoon Complete

Se! rernnder lO check holes al'.er 3 monihs Yes

No Sites will automatically be available for •to ""Not Ontlec' rehabilitation once the site has been • hofe for confirmed and the site either didn't require cementation or cementation has been Figure 12: Site Preparation completed and has not already been manually set to rehabilitation stage. The user can manually make a site available for rehabilitation if all required data is stored in the system and did not require cementation. -.:i3:.1~ .at'ld ftaq

t&hdb

For each rehabilitated site the field technician will need to: • Record the site ID and GPS coordinates • Complete the rehabilitation checklist on the PDA • Take a photo of rehabilitated site. This rehabilitation data is then uploaded from the PDA to the server. The project geologist can access the Geology Portal Rehabilitation Process page to approve each site' s rehabilitation as completed and progress the site to the finalisation status. The 'Final Rehabilitation Report ' can also be Figure 13: ERE Buffer Zones and Drill Sites on generated from this page, for completed PDA programs on a tenement without surface rights.

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Download oorrl)lete<l boreholes (cemented & approved) to PDA for rehabilitatio

Field assis1an dlecks off required rel\abilita1ion list i PDA as boreholes are rehabilitated

Weekly err.a I notlflcatlor, to Pro,ect Geologist o borehole nished more than 5 months ago

Weet-ly emai notificalio of holes within one week of the 6 rno, l deadllr'e ent to Goologlcal Services superintendent

For EPL, MDL and M without SR complete Final rel\abilita1ion report once clnll program complete

Environmental report compl ed as neces ary (predominantly on groond rel1nq ulshments)

Sl:e mar ..gen- n: process complete

Figure 14: Site Rehabilitation Process

The report is registered against the associated program as part of the final inspection process. Sites remain at the finalisation status until rehabilitation requirements for the entire program have been approved.

are met throughout the process in compliance with Sarbanes Oxley requirements of tracking and auditing of records, • Reduced time spent by site and project geologist in managing process flow from planning to rehabilitation and closure,

RESULTS The system has proved to be time and cost effective, as follows: • Fundamental to the success of BMA' s Mining operations - to ensure the availability of accurate, timely and completed primary drill hole data, • Seamless controlled process to track the status of drilling and geophysical survey programs for each project and to ensure all BMA policy requirements

• Reduction in relocation and standby costs for drill rigs through standardised planning and scheduling, • DSM process enables standards to be defined which in turn facilitates improved data quality, results and responsibilities, • Increased probability of grouting boreholes without requiring a cleanout ng,

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• Paperless field work as DSM PDA replaces paper-based field information capture process,

additional value from the system in regards to tracking processes and accessing sites.

The DSM has been in use at BMA for over a • Improved documentation management, year. While the system continues to evolve it has already demonstrated its value to the • The system provides the tools to company in ensuring there are no breaches of communicate and monitor the drilling tenure, environment or cultural heritage on and seismic programs leading to BMA' s exploration drilling sites. The DSM is increased operational efficiency, a key component on BMA Geological Services ISO 14001 accredited environmental • Ensures compliance of relevant mining management system. acts and legislation and reduced risk of breach of any legislation, and • Manage environmental, cultural heritage risk and minimise compliance costs.

Acknowledgements

The BMA Geological Services team, BMA site customers, and staff of Snowden are In FY 2010 BMA introduced the 'One BMA' acknowledged for their hard work, enthusiasm and professionalism in Permit to Disturb as part of One BMA developing and supporting the system. initiatives. The permit is now embedded in DSM survey/clearance stage and captures

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CHALLENGES IN FAULT MODELLING FOR COAL DEPOSITS M. Biggs Biggs, M., 2011 : Challenges in fault modelling for coal deposits. Australian Coal Geology, 12, 15- 26.

Fault modelling in coal has evolved in recent times from thought processes in 2D to those in 3D. However, many practitioners modelling faults and coal seams have become mesmerised by the software. Faults are not just green lines on the plan. The geometry of fault styles and their distribution leads to a predictive regional structural framework that can be used for hazard identification and exploration targeting. Successful modelling requires a return to geological first principles, and this starts with an understanding of the regional structural setting of the study area. Examination of all reports, plans, and field mapping notes by government geologists and University Honours students can provide important clues into fault styles, frequency, and spatial distribution. There are many sources for fault characterisation at a mine or local level, such as pit exposures or borehole intersections. Transferring known information about coal measure faulting into mine planning packages requires transformation into dislocating and often intersecting planes. There are many characteristics that define the fault planes such as strike, dip, sense, height datum, era, influence extent, and segments. Each is examined in the paper with several examples of modelled faults and their field counterparts compared. Modelling faults in this way is an iterative process. Structure contour plots and perpendicular-to-strike cross-sections are frequently used to satisfy the commonly asked modelling questions, like: • What is the strike length of the fault? • What coal seams are affected? • What are the fault' s throws? and • At what is the height datum of the fault? Successful modelling of faults has far-reaching influence on mine planning and design, as there are always adverse implications for mining. Tools now exist to better achieve this objective, but their application needs to be more systematic than current industry practice. Mark Biggs, Principal Geologist, Moultrie Database and Modelling Pty Ltd

Introduction Fault uncertainty and risk have widely recognized adverse impacts on the exploration and mining of underground coal

deposits, especially longwall mining. Geological uncertainties may cause significant delays in production schedules, impose substantial changes to mine plans, reduce expected recoverable coal quantities,

Australian Coal Geology

2o·s 0

100

200

kilometres

(\ ·Grantleigh Trough ·

{

;

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~ Normal fault

-..- Reverse fault -.- Normal fault, later reversed

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Figure 1: Regional Structural Setting of the Bowen Basin.

adversely affect safety, and heavily influence the financial viability of a mine.

individuals and in clusters, and can prove difficult to model (Figure 1 and 2).

Fault and joint swarms commonly found in the Bowen and Sydney Basin coalfields often consist of high intensity, closely-spaced joint clusters together with faults distributed as

As Australia' s coal mining industry is becoming increasingly reliant upon longwall mining, there is a need to implement a more effective, quantitative and yet practical

Australian Coal Geology

CL( A\I AOI ,._O NT

Regional c ross-section NE- W through Moura Mine (after Hammond & Mallett, 1988). NE

200 metres

Representative detailed croH-section through Moura Mine (after Hammond & Sullivan, 1988).

Figure 2: An example of a local structural setting

approach to geological fault risk modelling, • Statistical prediction of the fault pattern in the unmined area of interest. uncertainty assessment and integration of risk management so that mining companies can better plan both underground exploration By contrast, Homby (1993) pointed out that activities and longwall operations. commonly-used standard contouring methods are not entirely satisfactory, and require considerable skill to interpret. By studying Many past studies have attempted to outline residuals and cross-validation estimates methods of quantifying fault modelling and obtained from trend surfaces, it is possible to prediction. Shepherd & others (1981) used highlight areas where in which seam simple statistics to calculate joint and fault disruptions are likely, and to give a statistical spacing intensity measured along scan-lines basis to the estimation of the seam disruption. using a nearest neighbour technique. He found a substantial increase in the intensity of Techniques such as image filtering, Fourier occurrence of discontinuities has been found analysis and Radon transformation can significantly enhance the ability of the seam in the vicinity of fault zones. level data to resolve faults. In another study, Fischer & Shepherd (1993) specifically addressed: • Estimation of key parameters such as average spacing between fault clusters, preferred orientation of clusters, the total amount of clean coal likely to be found, and in what size blocks, etc; • Stochastic modelling of fault patterns consistent with these parameters;

Finally, in order to deal with the quantification of fault uncertainty in coal seams, Dimitrakopoulos & others (2001) developed a new fault simulation algorithm based on a fractal (power-law) model for fault size distributions and length versus maximum throw relationships. The project's review of the technical literature on fractal models for modelling fault systems did also document the then current technological understanding and demonstrated wide support

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of fractal relations for characterising fault systems as used in this project. The algorithm developed has three distinct characteristics worth stressing: 1.

• Digitising perturbations in structure floor plans • Missing seams in stratigraphic sections • Photogeological interpretation

It uses underlying spatial patterns to

place faults within a study area;

• Probabilistic modelling/extrapolation

It integrates 'soft' geological

• Cross-section displays showing crossing correlation lines

information that serves as background in the simulation process; and 3.

It extrapolates the fault placement

• Increased water flows recorded whilst drilling

based on available information and underlying fault spatial patterns.

• Seam splitting and splay diagrams.

This study takes a different approach and will attempt to show that successful fault modelling is dependent upon fully characterising each fault that will influence the mine or deposit structural model.

Fault Sources and Interpretation

Often a keen eye is required when examining historical records and all comments should be documented (Figure 3). A standard structural study of coal deposit areas often highlights how borehole data can contribute in several ways to the structural model: 1.

faulting, such as the presence of fault gouge or drilling difficulties;

There are many sources for fault characterisation at a mine or local level, such as:

• Open cut highwall exposures • Borehole dislocation (fault intersected)

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Large faults may be interpreted from discrepancies in gridded elevation models of the seams floor or roof.

Figure 4 is an example from the Bowen Basin of a downhole geophysical log showing natural gamma and density responses for a fault-repeated coal seam.

• Rapid change of level between closely-spaced boreholes

It may contain indirect evidence for

faulting, such as duplicated or missing stratigraphic intervals, and

• Underground exposures

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Figure 3: An example of recording faulting evidence from Borehole records

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.. 100

105

1 10

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120

Figure 4: Downhole Geophysical traces illustrating a seam repeat due to faulting.

During the search for geological controls on the regional fault patterns, it is often necessary to build a single modelled surface to represent the shape of a marker horizon as it dips down into the basin. Such surfaces can then be used to analyse the fault locations

and characteristics with respect to their location on the horizon map. One conclusion from the use of borehole data during any detailed study is that the confidence of interpretation is strongly

Australian Coal Geology

l'lan Vim, La.:, t

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Figure 5: Common Faulting Conventions for Modelling.

dependent on borehole spacing and seam correlation; such that even very large faults can be hidden amongst sparse exploration drilling data and smaller faults may be missed in even the densest drilling.

a fault, especially one factor not often contemplated, which is the range of target seams affected (MINCOM, 2008). Other characteristics such as those listed below are also of importance as each contributes to understanding seam dislocations:

Fault Characterisation • Type One of the requirements of successful fault modelling is to attribute all known features to

• Confidence

FAULT TYPES AND THROWS BARREN OR 11 OVERTHRUST SORT 1 2 1 2 1 2 232 1 2 3 4

ID I N001 19A 5 L22_N_A_2 19C N 2 16DON_2 N1D16 SEIS 2 24DU_R_5 NIB11 49C1 NIB8

Easting I 400887.93 401255.83 399723.65 401565.28 402379.37 400611 .83 387679.92 400564.61 400398.24 400624.96 400450.98

Northing I 7256041 .74 7262066.48 7270269.77 7260580.21 7264861.93 7257243.24 7303249.20 7258095.95 7259406.73 7258089.09 7259946.26

RL I MINCOM DIP I 2050.00 0 2087.00 0 1989.29 120 2142.00 105 2074.51 30 2124.82 70 1150.00 60 2133.50 90 2112.58 90 2137.00 90 2086.50 90

I MAX THROW I ZONE WIDTH

DIP

Figure 6: A Typical Fault Characterisation

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0 0 60 75 30 70 60

90 90 90 90

0.0 0.0 1.5 2.0 0.5 0.5 200.0 1.0 3.0 5.0 12.0

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TYPE HORIZONTAL HORIZONTAL NORMAL

NORMAL REVERSE REVERSE REVERSE VERTICAL VERTICAL VERTICAL VERTICAL

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Figure 7: Fault Throw Characterisation, with length along the fault plotted against throw.

An example of this type of data from an operating coal mine survey has been tabulated and illustrated in Figure 6.

• Strike • Dip • Sense (for example see Figure 5)

Fault throws attributed to any fault warrant special mention, as many mine planning software packages require each fault to begin and end with a zero throw. This has the effect of turning each fault into a hemispherical object, as illustrated by Figure 6, which plots fault throw on the vertical axis against distance along the fault as digitised in the

• Height datum • Era • Extent • Segments

Table 1: CSIRO Fault Confidence Classification Scheme (modified after Sliwa, 2006) DATA

HIGH

MODERATE Reliable on sections, correlation between sections reasonably

LOW Reliable on sections, correlation between sections based on regional constraints

2D seismic

Reliably identified on multiple closely spaced sections

Underground mapping

Structures mapped in detail, relays and fault zones resolved in detail

n/a

Open cut seam surveys

Fault position and throw well established

n/a

Boreholes

Suggested by sections, may resolve High data density. Reliable position, clearly seen on slope maps, as rolls rather than faults, normal

confident

evidence of thrust duplications

Low data density, geological inference only 'The fault must be faults mapped on one seam inferred here somewhere' to pass through other seams

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Figure 8: Contours of Fault throws (in metres) overlying fault position, used to detect anomalies (Note: the insert highlights an incorrectly modelled segment of the fault).

"u u

_., _,.

...

modelling software. The data is a small sample from a mainly normal fault dominated terrain, however as evidenced by the graph, there is considerable variation in fault character. Fault throws can also be contoured to identified anomalies or trends in the geologist's interpretation as evidenced by Figure 8. This type of simple analysis CSIRO Fault Confidence (Esterle & Sliwa, highlighted anomalous fault throws in the 2002; Sliwa, 2006) and is demonstrated in south-western comer of the coal deposit, where the model had a scissor fault in it when Table 1. there was no such evidence in the surrounding borehole data.

Field examples

The success of any coal structural model also depends upon the confidence that the modeller attributes to each individual fault, as they can be classified so that they may be omitted from, or returned to, modelling if desired. One such classification scheme is the

Fault modelling is greatly enhanced if field examples, especially from open-cut pit or strip exposures can be observed to confirm a particular modelling characterisation (Mallett & others, 1988). Figure 9 illustrates such an

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Figure 9: An example of ground truthing a modelled fault

exposure from the Bowen Basin mine, where the modeller had originally only inserted one fault plane into the mine planning model, where clearly two are required to fully accommodate the seam dislocation. Seismic interpretation of faulting is becoming more commonplace, with the results, often with associated confidence levels, routinely fed back into the coal deposit structural models iteratively as surveys progress. All fault styles can be observed from the seismic data, including back thrusts. As the proliferation of especially 3D seismic surveys continues, the dilemma for the modeller will also increase. This is due to the complexity of the faulting currently being observed and interpreted in the 3D seismic volume. This complexity far exceeds the capability of any of the current coal mine planning software packages available in Australia to accurately replicate

them in the model. Some salient examples are shown in Figure 10.

Modelling Questions It is the author' s assertion that successful structural modelling of coal deposits can be achieved if a series of questions about the faulting component can be answered by the modeller, namely: • What is the fault ' s strike length? • What seams are affected? • What are the fault's throws? • What is the confidence that this fault exists and that its throw and location are accurately known?

Australian Coal Geology

1(ll)

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Figure 10: Various Fault Interpretations from reprocessed 2D seismic lines, Bowen Basin. Modified after Sliwa (2006)

Australian Coal Geology

Figure 11: Complex Faulting illustrated by cross-section.

• What is the zone of influence, which is the width of affected strata away from the fault plane? • At what height datum should the fault be set at? • Can it be validated graphically, i.e. can the fault be drawn simply on a cross-section by hand? • Does it match the borehole data?

minimise the current incidence of coal structural models not being up to the rigours of modem mine planning requirements. The challenge is for software houses operating in Australia to improve the modelling tools (or adapt them from other industries such as the Petroleum exploration industry) so as to enable features such as varying the dip and throw down-the-dip of a fault and not just along the strike.

• Does it match the geophysics e.g. dipmeter?

Hence fault planes in modelling need to have more flexibility, including the ability to • What are the implications for mining? respond to a coal basin' s tectonic history, whereby allowing simpler fault dislocation mechanisms in the software. The handling of When most of these questions can be answered and are incorporated into the model fault repeats is still problematical in many mine planning packages, and further often quite complex dislocations can be alternatives are sought. modelled, as illustrated by Figure 11.

Conclusions Field confirmation of modelled fault data is not always possible. The asking and answering of a series of questions about faults being modelled will hopefully

Finally, faults are often best displayed in a cross-sectional view and the author cannot stress enough that often the only answer is to draw many more cross-sections, or even to hand draw the suspected faulting sequence so that the full implications of a fault sequence on a stack of coal seams may be appreciated.

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References

Geological Society of Australia, Brisbane, p33-43.

DIMITRAKOPOULOS, R., LI SHUXING., SCOTT, J. & MACKIE, S., 2001: Quantification offault uncertainty and risk management in underground longwa/1 coal mining, A CARP Project C7025, WH Bryan Mining Geology Research Centre, The University of Queensland, Brisbane. ESTERLE, J. & SLIWA, R., 2002 Bowen Basin Supermodel 2000, End-of-Grant Report, Australian Coal Association Research Program (ACARP) Project C9021.

HAMMOND, R.L. & SULLIVAN, T.D., 1988: Geological structure of coal mining areas in the Bowen Basin - I: Moura. CSIRO Geomechanics of Coal Mining Report No 67. MALLETT, C.W., HAMMOND, R.L., LEACH, J.H.J., ENEVER, J.R. & MENGEL, C., 1988 Bowen Basin stress, structure and mining conditions assessment for mine planning. NERDDC Project No. 901, 233pp. MINCOM, 2008. Introductory Stratmodel Training, Chapter 8 - Faults, unpublished manual, Mincom Pty Ltd, Brisbane.

FISHER, . & SHEPHERD, J., 1993: SHEPHERD, J., CREASEY, J.W. & Counting EMU's: using fault patterns to forecast recoverable coal. In Beeston, FISHER, N.I., 1981: Statistical analysis J.W., (Editor): Proceedings of the New of spacings between geological Developments in Coal Geology discontinuities in coal mines, with Symposium, Coal Geology Group of the applications to short-range forecasting of mining conditions, Australian Coal Geological Society of Australia, Brisbane, 55. Geology, 3 (2), 71-80. SLIWA, R., 2006: Regional Structural HORNBY, P., 1993: Fault location using statistical and image processing methods. Analysis of the Baralaba Coal Measures, eastern Bowen Basin, unpublished In Beeston, J.W., (Editor): Proceedings of the New Developments in Coal Geology confidential report CSIRO Exploration Symposium, Coal Geology Group of the and Mining, P2006/738, September 2006.

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CLOSURE LANDFORM DESIGN: AN INTEGRATED APPROACH M. van Zyl Van Zyl, M., 2011: Closure landform design: an integrated approach. Australian Coal Geology, 12, 27-42. Deriving a closure landform design is an iterative process, requiring the integration of aspects such as operational material handling, land use, landform and cover design. The overarching objectives in terms of closure landform design are the protection of Human Health and the Environment. This paper provides an environmental focus on mining related rehabilitation and aims to provide an overview of some of the aspects that should be considered when deriving a landform design for a mining disturbed area. Integrated closure landform design infers the integration of mining lifecycles with whole-site water balances and water quality predictions. Understanding these aspects assists in defining operational material handling strategies that are cost effective in the long term. In terms of closure landform design, operational material management requires, amongst other aspects, segregation and selective material placement. Appropriate cover design forms an important part of the closure landform design process. Various cover types exist that can be applied depending on site specific conditions and mitigation requirements. The specification of revegetation parameters is a key constituent of a landform design process. Hand-in-hand with revegetation efforts are the assessment of aftercare measures as part of the completion of the landform design. The re-establishment of a vegetative cover on rehabilitated mining disturbed areas is important in terms of providing erosion protection and slope stability of the landform. In this way the landform can be returned to an environmental setting similar to what existed prior to the disturbance of the area. Successful closure landform design is defined as the achievement of a self-sustaining system that is eventually integrated into the larger community structure. Morne van Zyl, Senior Environmental Scientist, Klohn Crippen Berger Ltd, Level 5 - 43 Peel Street, South Brisbane Qld, Australia 4101

Introduction This paper focuses on mining related rehabilitation and aims to provide an overview of some of the aspects that should be considered when deriving a landform design for a mining disturbed area. Most of the topics covered in this paper have been extensively researched by others and are only

covered here in a synoptic manner. Relevant case studies are discussed at the end of each methodology subsection to illustrate results and provide concepts for consideration. The title of the paper highlights the concepts of Closure and Integration. Closure in this instance does not only refer to entire mine closure, but is also related to the

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closure of a component of the mining business, such as facility closures (e.g. Pit, Waste Rock, Slurry Impoundment etc).

landform is safe and poses an acceptable impact as far as the safety of downstream communities and the environment are concerned (van Zyl, 2003).

Integration in this instance refers to: • The integration of mining lifecycles, i.e. closure requirements are considered and acted upon during the Feasibility, Construction and Operational phases of the mine. This implies that closure landform designs are derived during commissioning (even if only at a conceptual level) and that rehabilitation is performed progressively and in line with appropriate post-mining land uses during the operational phase (Department of Industry, Tourism and Resources, 2006a); and, • The integration of hydrogeological, hydrochemical and water balance predictions into rehabilitation design. Closure landform design, therefore, requires a sound understanding of whole site hydrogeology and geochemistry in order to define material handling strategies during the operational mine phases in order to support intended long term landforms and land uses at facility and, eventually, mine closure (Department oflndustry, Tourism and Resources, 2006b ).

Further to this, closure landform designs should attempt to support the principles of sustainability and inter-generational equity, i.e. ensuring that the health, diversity and productivity of the environment are protected for the use of future generations. Design objectives can be summarised as follows: • Protection of human health 0

Ensure no spontaneous combustion is taking place

Ensure no dangerous/steep slopes remain as part of the final landforrn

Rehabilitation Objectives o

The overarching objectives in terms of closure landform design are the protection of Human Health and the Environment. As such, when decommissioning and rehabilitating a facility, one should strive to ensure geotechnical stability, so that the final

Ensure, as far as possible, that all run-off from the final landform is clean

• Protection of th_e Environment 0

Deriving a closure landform design is an iterative process, continuously requiring the integration of the aspects outlined above with the understanding that no single aspect can dominate the ultimate design.

Ensure stability/safety of the final landform

Ensure no spontaneous combustion is taking place, to prevent releases of these gases to the environment Minimise, as far as possible, any seepage to prevent the contamination of groundwater resources in the area Ensure, as far as possible, that all run-off from the final landform is clean, to prevent the contamination of surface water resources in the area

• Secure sustainability of the final landform

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Ensure, as far as possible, that the final rehabilitated landform can be utilised in the long term.

Methods

In terms of closure landform design, operational material management requires segregation and selective material placement in order to: • Limit spatial exposure across the site,

Operational Material Handling for Closure Optimising operational material handling strategies is a complex process that requires integration of various aspects, inclusive of: • Landform and land use requirements,

• Conserve certain materials (such as soil horizons) that may be required for rehabilitation at mine or facility closure, and • Support closure landform and land use requirements (further discussed under Land Use and Landform Design (page 31).

• Characterisation of the geohydrological Hydrogeological and Hydrochemical System and geochemical environment, Characterisation provides an overview of the determination of hydro geological and • Water balance requirements, hydrochemical parameters, whilst Material Management Strategies (page 30) discusses • Mining layout and life of mine the consequent material management requirements, and strategies that can be developed based on this information. • Rehabilitation designs (even if just at the conceptual level). Topsoil management strategies have been Management (page 36). Based on this, suitable material management addressed in Topsoil strategies can be developed and refined over the life of the mining operation. Hydrogeological and Hydrochemical In order to derive closure designs at an early stage of the mining lifecycle quantitative scientific data is required for planning and design purposes. In fact, current environmental management policies advocate a risk averse approach. This approach requires that detailed site investigations are carried out in order to negate scientific uncertainty. Integrated closure landform design infers the integration of mining lifecycles with whole-site water balances and water quality predictions. Understanding these aspects assists in defining operational material handling strategies that are cost effective in the long term.

System Characterisation There is an inherent interaction/integration that occurs between the derivation of a rehabilitation design and the understanding of the hydrogeological and hydrochemistry of a mine site. Understanding site groundwater parameters and waste geochemistry provides a basis from where site conceptualisation and whole site water balance modelling can be performed. This forms the basis from where rehabilitation design concepts can be derived and long term effects predicted so that closure designs can be compiled through an iterative process.

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Material Management Strategies Material management strategies are compiled to manage the way in which mined materials (e.g. ore, waste rock, tailings, cover materials and soils) are segregated and stored. These management strategies should support closure landform design, taking hydrogeological and hydrochemical site specific factors into account. For example, closure landform design may dictate that soils are selectively stripped and stored in areas where it will be available during facility closure phases.Benign and reactive waste rock may be indentified during the geohydrological and geochemical phases and govern the selection of cover materials and reactive materials that require encapsulation.

Results and Discussion: Case Study Material Management

• Maintaining riparian and operational water volume requirements (operational, closure and post closure), • Flood water management, • Potential dam/dump failure due to geohazards, • Tailings and waste rock geochemistry creating acidic conditions, • Ground and surface water quality, and • Dust. In order to appropriately manage these issues a material management strategy was developed. The key drivers in the development of the material management strategy for the project were geotechnical stability, waste geochemistry and the management of water quality and volume effects, including floods.

KCB were commissioned to develop a Mine Waste Management Report for a Copper - Gold project in south-east Asia.

The majority of waste that will be generated through mining is considered to be either potentially acid forming (P AF) or cannot be practically separated from the PAF material. Geochemical characteristics of the tailings High risk PAF waste rock is to be isolated and waste rock were assessed and predictions and stored to reduce the impacts of extensive were made of likely water quality and water oxidation and subsequent generation of acid volumes over life of mine and post closure. and release of metals. Tailings will be stored in saturated conditions in the tailings storage Further to this a water balance analysis was facility (TSF). Saturation of waste is the completed for the proposed mine operations industry best practice for control of acid rock using GoldSim simulation software. The drainage. A riparian release facility was model used in the analysis contained site designed to maintain downstream water components related to water management. quality and quantity related aspects. The purpose of the model was to determine appropriate water storage requirements in order to meet the concentrator and riparian release requirements, whilst minimising the size of the embankments and requirements for the water treatment facilities. During the design process the following key environmental issues were identified:

Further to this, conceptual closure strategies were developed for the project. The objective of the closure strategies was to ensure that the waste storage facilities are geotechnically and geochemically stable and do not give rise to unacceptable environmental impacts; specifically, the management of waste geochemistry to protect downstream water quality.

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Land use and Landform Design area is compatible with the surrounding land The key to deriving land use and landform requirements is the consideration of sustainability and intergenerational equity. This process is usually driven by stakeholder/landowner, regulator and safety requirements. Appropriate community consultation processes need to be followed throughout the commissioning, operational and closure phases of the mining operation to determine rehabilitation criteria that can be utilised to determine a suitable land use and assist in the landform design process (Department of Industry, Tourism and Resources, 2006b).

Land Use

and useable by the next land user. The final landform should therefore be accessible and have slope gradients that support the selected post-mining land use. In order to satisfy the overall objectives as described above the following general guidelines should be followed: • The area should be shaped to visually blend in with the surrounding landscape, • All slopes should have angles that ensure easy access for humans and animals (in general long slopes should not be steeper that 1:5, and short slopes, such as contour berms, should not be steeper than 1:3),

• Where these slopes cannot be achieved, The final land use should, as far as possible, straight ridges and sharp changes of any be compatible with community needs, angle should be avoided, and regulatory requirements, climate, soils, local • The geometry of the final landform topography, and the degree of management should, as far as possible, be made to available after rehabilitation. It can therefore be free draining. an at taken be be seen that a decision needs to early stage as to the desired final land use for a site. Examples of desired final land uses Erosion Control that may be considered are high production pasture grazing, low production pasture Erosion can be described as the loss of soil grazing, natural pasture (natural ecosystem) particles from the rehabilitated surface. The or combinations of the above. main driver of erosion will be via the movement of water across the rehabilitated Landform surface. This involves the breaking of soil aggregates into finer particles that are then down slope when the energy of transported very is landform The geometry of the final the moving water exceeds the forces binding important as it should not only ensure the the soil particles together. On disturbed areas, protection of human health and the this type of erosion can be controlled by environment but should also be sustainable slowing the water flow velocity across the and aesthetically pleasing. As stated surface and reducing the impact of raindrops previously, landform and land uses are the soil surface. on The closely inter-related (van Zyl, 2003). final landform must therefore be safe, non-erosive and be rehabilitated to have those Depending on slope length, slope gradient and the applied soil cover, erosion protection environmental characteristics that will it berms/contours can be constructed on side support the final land use. Further to this should be kept in mind that the final landform slopes to reduce the quantity of water flowing down the slopes. It should be noted that even design should ensure that the rehabilitated

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on relatively flat slopes (< 15°), should the slope length be very long, severe erosion could occur and therefore long slopes should be broken by erosion protection berms/contours. Further to this, accumulated water along the slope of contours berms/drains have the potential to cause catastrophic failures at the exit points of these structures. As such, adequate erosion protection measures should also be constructed in these areas to prevent large erosion gullies from forming and to ensure that the run-off from rehabilitated areas is adequately catered for. Designs should always consider that aftercare and maintenance activities should ideally be performed by mechanical means (i.e. vehicles and tractors should be able to move safely on these structures).

Surface Water Surface run-off occurs whenever rainfall reaches the ground faster than it can infiltrate the underlying soil. Surface runoff is a major cause of soil loss by erosion on rehabilitated surfaces. The deeper and faster the surface runoff flow, the greater its capacity to remove and carry sediment particles. As such, surface water management structures have to be designed and constructed to remove run-off in a controlled manner that minimises erosion as far as possible. Groundwater

Once water has infiltrated into the rehabilitated surface, its movement is largely determined by the hydraulic head of the groundwater system, and the aquifer characteristics. As groundwater moves Vegetal covers minimise erosion in three through the rehabilitated profile, potential ways; firstly by binding the soil via a network pollutants may be leached. Groundwater of roots, secondly by sheltering the seepage points/zones may form if horizontal rehabilitated surface and thirdly by trapping layers are present in the rehabilitated profile already eroded material. The use of a vegetal that have very low permeability (relative to cover and how it can assist in the slowing of the overlying strata), such as along the side erosion is discussed in greater detail under slopes and toe-ends of a Waste Rock Facility. Revegetation (page 37). The seepage results from the continued accumulation of infiltrated water on these low The following general guidelines should be permeability layers and ultimately discharge considered: along the side-slopes. In order to manage these types of impacts, the polluted water • Reduce the volume of water flowing should be controlled, captured and prevented down a slope, from discharging to the environment. In general, the use of sub-surface drains and toe • Slopes should be designed so as to dams should be considered in landform reduce the velocity of run-off as the designs. catchment slope increases, and • Establish the vegetation cover as early as possible in-as-much as the newly formed surface is exposed and very susceptible to erosion.

Water Management

Results and Discussion: Case Study Landform Design KCB were commissioned to design a post closure landform of a waste rock dump and tailings storage facility for a mining project located in Western Australia.

The management of water related environmental impacts also have an influence The site is located in an arid region with on rehabilitation designs. evaporation exceeding precipitation by nine

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times during an average year. The natural groundwater table is approximately six metres below the ground surface in the vicinity of the tailings storage facility and has a very low hydraulic gradient. Landform evolution modeling (LEM) was undertaken as part of the assessment. The results of the modelling indicate how a landform will evolve over time and can be used as a tool to identify problematic areas of the landform and re-design the landform to minimise those problems. KCB used SIBERIA to complete the LEM. SIBERIA is a physically based mathematical model that simulates geomorphic evolution of landforms subjected to fluvial and diffusive erosion and mass transport practices. The program links widely accepted hydrology and erosion models under the action of runoff and erosion over long timescales (Hancock, 2004). Figures 1 to 8, model how a landform may evolve over time given various erosion protection scenarios. Model outputs were interpreted and re-gridded to evaluate the changing landform. Results from the LEM indicated that the final landform would not be stable unless areas where water drains from the landform were reinforced. With reinforcement in these areas of the landform, erosion from the top surface of the land form and from the side slopes is limited. Erosion protection is also required to reduce erosion of the natural ground surface at the three areas where flows are directed off the constructed landform. The LEM further indicated that the concave batters of the waste rock dump and tailings storage facility when used in conjunction with the crest bunds were stable in the long term. Similarly, the gently sloping top surfaces of the landform were found to be stable if the critical points where water exits the landform remain stable at their design elevation. If the points where water exits the

landform were allowed to erode, the gullies extend back into the landform and the grade of the drainage lines on the top surface increase, leading to more erosion.

Cover Design Appropriate cover design forms an important part of closure landform design. Design parameters should consider the following aspects: • Climate, • Revegetation (as described in Revegetation, page 37), • Land use, and • Residue geochemistry (as described in Hydrogeological and Hydrochemical System Characterisation, page 29). Based on an understanding of these aspects a cover system can be designed. Various cover types exist that can be applied depending on site specific conditions (such as local climatic factors) and mitigation requirements.

Types Dry Cover Dry covers are designed to shed excess water during high rainfall events, although the cover will probably remain wet during periods of prolonged rainfall. This type of cover provides a growth medium for vegetation establishment, long term stability and protection from direct access to the underlying residue.

Wet Cover The overall aim of a wet cover is to keep residue below the water level thus reducing the potential to oxidise elements that may be detrimental to humans, animals and the

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·~

Figure 1: Landform without Erosion Protection: Short Term

l Figure 2: Landform without Erosion Protection: Medium Term

•>

",.

l Figure 3: Landform without Erosion Protection: Long Term

Figure 4: Landform without Erosion Protection: Very Long Term

. •

. #

·I

Figure 5: Landform with Erosion Protection: Short Figure 6: Landform with Erosion Protection: Term Medium Term

Figure 7: Landform with Erosion Protection: Long Term

Figure 8: Landform with Erosion Protection: Very Long Term

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environment. The main purpose of the wet cover is to: • Establish a water column over the residue surface and limit contact with atmospheric oxygen, • Prevent dispersion of contaminated material by wind and water erosion, and • Isolate residue from human contact.

Option 3 - Soil cover with rock mulch, compacted low permeability zone and underlying reducing layer

Option 4 - Simple soil cover with rock mulch with underlying capillary break

Option 5 - Soil cover with rock mulch, compacted low permeability zone with underlying capillary break

Dry/Wet Store/Release Cover

These options were evaluated to select the preferred alternative (Table 1).

Store/release covers can be utilised in seasonal, arid or semi-arid climates. These covers are designed to store water during periods of high rainfall (without causing erosion) and then to release moisture through evapotranspiration during the dry season.

Based on the key considerations of human and animal contact with water and/or residue; berm engineering; vegetation establishment; and compliance with conceptual closure plan, the Dry Cover was selected as the preferred option.

Results and Discussion: Case Study Cover Design

Revegetation and Aftercare

The assessment of revegetation parameters is an important component of a landform design KCB were commissioned to develop an In-Pit process. Hand-in-hand with revegetation Residue Storage Facility for a nickel project, efforts is the development of aftercare located in the South Pacific. In order to measures as part of the completion of the develop an effective closure strategy, closure landform design (van Zyl, 2003). objectives were established. These objectives guided the engineering designs and The re-establishment of a vegetative cover on rehabilitation works and the closure plan in rehabilitated mining disturbed areas is general. important in terms of providing: As part of the Closure Plan various conceptual cover designs were proposed for dry, wet and combined scenarios:

• Erosion protection and slope stability of the landform. • End land use guarantee

• Base Case - Simple soil cover with rock mulch, o

Option 1 - Simple soil cover with rock mulch and reducing layer Option 2 - Soil cover with rock mulch and compacted low permeability zone

• Aesthetic quality of the landform • Overall sustainability of the area • Improvement of biodiversity • Improvement of soil nutrient status • Improvement of soil structure

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Table 1: Cover Option Comparison CONSIDERATION

DRY COVER

WET AND DRY

WET COVER

OPTIMUM

Dewatering/drying of residue prior to placement of cover

Required

Not required

Wet Cover

Dust generation from residue

Potential dust generation while dewatering occurring

Potential dust generation while dewatering and during times of low rainfall

Yes, ifleak in liner and during dry periods.

Wet Cover - if seepage into bedrock is mitigated to perpetuity. Dry Cover - if seepage to bedrock is expected

Oxidation of residue

Potential for residue oxidation, pending adopted cover design.

Permanently oxidised layer and partially oxidised layer (increased potential of flushing oxidised residue)

No oxidation of residue prolonged dry season (beyond design criteria) taken into account.

Wet Cover

Uptake of minerals into vegetation

Potential to occur

Vegetation unlikely

Wet Cover

Vegetation Establishment

Yes

Yes, both wet and dry but depends on range of water levels

Unlikely due to fluctuation in water level

Dry Cover

Water balance

Not dependent on water balance

Dependent on water balance

Dry Cover

Residue storage volume potential

Highest

Medium

Lowest

Dry Cover

Channels to divert upstream flows

Required during operation / progressive closure

Nil

Materials needed for closure

Yes - growth medium

Yes - growth medium of some of cell

Yes - some soil to form inert boundary layer

Wet Cover

Human and animal contact with water and/or residue

None

Yes, at the dry/wet interface and along the edge of the cells.

Yes, along the edge of the cells and limited due to no vegetation

Dry Cover

Berm Engineering

Design based on residue retaining structure.

Design based on water retaining structure.

Dry Cover

Compliance with conceptual closure plan

Yes

No. Revegetation not proposed for entire disturbance area and "contact water" expected.

No. Revegetation not proposed for entire disturbance area.

Dry Cover

• Control (limited) over surface and sub-surface water quality.

An overview of sub-components related to revegetation and aftercare activities are provided under Topsoil Management (this page), Revegetation (page 37) and Aftercare and Maintenance Programs (page 38).

Topsoil Management The selective stripping and storage of topsoil may be paramount to the success of any rehabilitation effort. This is especially the case in situations where the desired closure land use cannot be supported by mine overburden or tailings. Sound topsoil management practices should be employed

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Compaction during the commissioning and operational phases of a mine to ensure that associated closure design objectives can be met, such as: The soil cover placed on rehabilitated areas often becomes compacted by earthmoving equipment after its placement (also during the • Sufficient volume is available to construction of contours, berms and other achieve the desired cover thickness, erosion control structures). Compaction of the soil cover leads to a decrease in the • Topsoil is stored to conserve, as far as macropores and hydraulic conductivity. This possible, soil fertility and biota. This reduces the effective rooting volume of plants may also involve specifying topsoil and inhibits the development of a good stockpile storage heights and storage vegetation cover. In order to mitigate against times (ideally placing should closely this the soil cover should, where possible, be follow stripping), and deep ripped/scarified prior to seeding. • Topsoil storage locations are optimised Soil pH and Fertilization to cater for fmal void positions and also to optimise haulage distances. The pH of the soil cover (if the soil is acidic) should be corrected. This, together with the fertilizer requirements, should be determined Revegetation via soil testing at a soil testing laboratory. Based on these results the liming One of the main aims of rehabilitation is the requirements and fertilizer requirements must establishment of an adequate vegetation be determined. cover to stabilise the new landform and control erosion. Establishment of a vegetation Soil Nutrient Status cover is governed by seasonal rainfall variability; with the most appropriate time for Low organic matter content in soils results in seedbed preparation prior to the wet season poor plant nutrition and poor physical when temperature and rainfall are most suited properties of the soil. Organic matter is to seed germination. required to fix nitrogen in soil and make it available for plants to utilise. Organic matter requirements can also be determined via soil Species selection will depend largely on the conditions soil area, the for testing at a soil testing laboratory. selected land use and climate. Combinations of native species can be sown to good effect in the Seed Bed Preparation establishment of high or low production grazing pastures. The supply of seed is an Provision of sufficient moisture and aeration important factor to consider. In this regard to seeds is paramount in the early stages of seed may either be purchased or collected and plant growth. The seed must be in contact propagated. The planning of any native seed with the soil in order to take up the soil collection and propagation program should moisture. Furthermore, the soil around the commence well in advance of the actual seed must be loose enough, allowing for the seeding effort to ensure that sufficient seedling to grow through the soil and amounts are available. establish a rooting system. The following aspects, synoptically summarised hereunder, should be considered during the design of a revegetation effort:

Finally, the seed bed should be free of weeds, which may limit the growth of the selected revegetation species. This can only be

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achieved through proper tillage operations that should involve the following: • Ripping/scarifying, in order to reduce soil compaction, • Ploughing, in order to turn the sod and allow for better infiltration, and • Disking, in order to mix the lime, fertilizer and organic ameliorants into the soil and to break up large soil clasts.

Aftercare and Maintenance Programs The success of any revegetation effort in providing stability to a newly rehabilitated landform will be dependent on an ongoing dedicated aftercare program. These programs are put in place because acceptable soil nutrient status and structure are rarely achieved after revegetation has taken place. In order to achieve landform stability an active program of soil amelioration and defoliation is required to promote the progressive build up of soil organic carbon and prevent the forming of bare patches and consequent erosion.

Seeding Seeding should take place immediately prior to the onset of reliable rains; preceding the wet season. There are various methods of broadcasting seeds. The method selected will ultimately be dictated by terrain conditions such as slope angle and seed size and shape. The seeding of steep angle slopes and short slopes (such as contours and berms) may require manual handling. It is advisable to roll the surface subsequent to seeding in order to ensure the seeds are adequately buried and in contact with the soil. Mulch may be applied to aid with temperature control, moisture control and protection against wind and raindrop erosion. Typically the mulch bales should consist of grass cuttings of the same species of grass as those included in the seed mix already sown.

It is advisable that a formal aftercare and maintenance program be compiled. The type of aftercare program will depend mostly on the selected final land use. A typical aftercare program should contain at least the following: • Rehabilitation aims and objectives, such as the selected final land use, for example high production pasture grazing, low production pasture grazing, or combinations of the above, • Based on this land use a period of aftercare needs to be specified, after which and pending appropriate rehabilitation, the area should be self sustaining, • A description of the surface ownership of the rehabilitated area upon closure,

Weed Control It is important to control the introduction of weeds to the newly rehabilitated area. Care must be taken that weeds are not introduced via the application of organic ameliorants or mulches. Further to this cutting of the area during the initial vegetation establishment phase could be considered to control weed growth and encourage a vigorous plant cover.

• A definition of the managerial roles and responsibilities of the aftercare program, • Methods and frequencies of soil fertility testing, • Methods and frequencies of fertilizer application,

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• Methods and frequencies of defoliation Rehabilitation construction of the VOP commenced during 2008. Revegetation (i.e. cutting and baling, grazing or efforts were seriously constrained by the burning), quality of the growth medium available for • Methods and frequencies for aftercare seeding. The following is noteworthy: rehabilitation processes (e.g. repair of erosion damage, re-seeding of • All the soil samples analysed were developed bare ground etc), typified by a dominant sand fraction (with specific amelioration • Methods and frequencies for the requirements), installation of frre breaks, a A particle size distribution • Methods and frequencies for weed dominated by a sand fraction can be control, and very good from a rehabilitation perspective as it decreases the • Fence maintenance measures. chances of salinisation of the top soil. However, the soil requires a Study Case Discussion: and Results significant amount of organic material to increase the water and Revegetation nutrient holding capacity; Xstrata Coal South Africa (Pty) Ltd Voorslag Open Cut Spitzkop Colliery (SC) is located in the Mpumalanga province of South Africa and is owned and operated by Xstrata Coal South Africa (XCSA). Rehabilitation designs were requested for the decommissioned Voorslag Open Pit (VOP) operation that formed part of the SC operation. The VOP consists of a number of sections that covers approximately 250ha. Rehabilitation designs were compiled to support long term sustainability aims for the area, focussing on: • The provision, as far as possible, of flat slopes, a

Bearing in mind that the overall material balance calculated for the area indicated that there was not enough material to fill the open pit void spaces that remained

• Low clay content of the samples rendered the media very prone to leaching, • The pH of most of the soil samples were below 5.5 indicating a significant lime requirement whilst at the same time precluding the use of any Ammonium CNH1) based fertilizers as a source of Nitrogen (N), • The exchangeable cation ratios deviated significantly from the expected percentages and confumed a dolomitic lime requirement for the area, and • All of the soil samples clearly indicated deficient Potassium (K) concentrations that are exacerbated by elevated Sodium (Na) concentrations.

In order to address these issues soil amelioration and aftercare efforts were • Revegetation efforts that would support focussed on systematically improving soil a low production pasture land use (van organic carbon levels and improving soil structure. Further to this, nitrate-based Zyl, 2006). inorganic fertilizers were utilised as opposed Figure 9 indicates a 'before' photo record for to ammonium-based products. In order to minimise early season erosion, the applied a selection of the VOP area.

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,.,...----4--~---+-----'/ ~

Figure 9: Voorslag photo record before construction

seed mix was adjusted to contain higher application rates for the fast perennial grass species so as to stabilise the planted areas quickly (these would be succeeded naturally by non-perennial species that would also be palatable and support the objective of creating a low production pasture).

In addition a dedicated aftercare program was implemented focussing on soil sampling, soil amelioration, erosion control and defoliation. The overarching objective in respect of the aftercare efforts was to systematically improve the nutrient status and soils structure of the area in order to improve slope stability

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. ... ...

...

'-<.

Figure 10: Voorslag photo record after construction and revegetation

and ultimately support the intended land use for the area.

sustainable and stable slopes for the sections that have been rehabilitated to date.

Whilst construction efforts are currently ongoing for the VOP at SC, Xstrata Coal South Africa have managed to achieve

Figure 10 provides a photographic record of a selection of areas that have been shaped and revegetated to date.

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Conclusions

References

The sustainability of mining is largely based on the successful rehabilitation of all disturbed areas. Closure landform design is an iterative process that requires the integration of various aspects throughout the mining lifecycle. Successful rehabilitation can be defmed as the achievement of self-sustaining systems that are eventually integrated into the larger community structure, for example, the rehabilitation of a waste rock facility or open pit area to a low production grazing area that can be utilised by a local landowner.

Acknowledgements

DEPARTMENT OF INDUSTRY TOURISM AND RESOURCES, 2006a: Mine Closure and Completion. Leading Practise Sustainable Development Program for the Mining Industry Handbook, Australian Government. DEPARTMENT OF INDUSTRY TOURISM AND RESOURCES, 2006b: Mine Rehabilitation. Leading Practice Sustainable Development Program for the Mining Industry Handbook, Australian Government. HANCOCK, G.R., 2004: Modelling soil erosion on the catchment and landscape scale using landscape evolution models a probabilistic approach using digital evolution model error, Paper presented at the 3rd Australian and New Zealand Soils Conference, 5-9 December 2004.

VAN ZYL, M, 2003 : Guideline for the rehabilitation of the Tweefontein Discard Dump, prepared for Xstrata Coal South The compilation of this paper and symposium Africa, JMA Consulting (Pty) Ltd. participation has been sponsored by Klohn Crippen Berger Limited. Xstrata Coal South VAN ZYL, M, 2006: Rehabilitation Plan Africa (Pty) Ltd is acknowledged for making Report V oorslag Opencast Area, prepared case study material available for inclusion for Xstrata Coal South Africa, Ibubesi into this paper. Consulting CC.

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NOTES

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