GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Ben Pang

Sarra Hayes

Eastern Australia Ground Control Group

13th March 2014

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Introduction

Ground Control Strategy

Mining method Interpretation & Analysis

Data Collection

Long-term monitoring

data

Simplified Ground Control Process

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Borehole logs

Rock joint mapping data

Field testing result

Laboratory testing report

Monitoring reading

Common Geotechnical Data

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

What about the unsampled location?

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Interpolate the collected data using Block Model

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

The Dargues Reef project site was located within the Lachlan Fold Belt underlain by Devonian-aged Granodiorite

Dargues Reef

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

This block model aimed to assist in determining interlode pillar stability and dilution estimates during the feasibility study

The software SurpacTM was used to develop a mine-wide block model to carry out spatial interpolation for all available RQD drillhole data

Block modelling

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Size of block

Interpolation method

Search ellipsoid

Maximum search radius and vertical search distance

Block modelling parameters

The selection of above parameters depends on the geological and geotechnical conditions and the purpose of the modelling

The following set of parameters are required for each block model

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Depends on the amount of data available and the purpose of the block model

For the Dargues Reef block model, we used a 10m block size

Size of block

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Inverse Distance method is adopted

The Inverse Distance interpolation method assumes that the variance between values is solely based on the distance between data points

Interpolation method

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

The RQD values often trend along geological structures or lithology

For this case, the orientation of the ellipsoid search is assumed to be the dip and dip direction of the ore body to address the anisotropic condition of data

Search ellipsoid

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

The selection of maximum search radius and the maximum vertical search distance depends on the geotechnical and geological variability

If the search radius and vertical search distance are too small, literally no interpolation would be implemented

For Dargues Reef example, a 25 m maximum search radius was adopted

Search radius & vertical distance

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Gold mineralization at Dargues Reef is structurally controlled and is hosted within east‐west trending steeply dipping lenses.

An approximately 10 to 15m thick diorite dyke is located sub-parallel to the mineralisation.

Numerous drill holes had been logged for RQD

Mineralisation

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Plan view showing diorite dyke and numerous mineralised lenses

Mineralisation

N

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

10m blocks showing interpolated RQD values for each block

Model can be sliced so that area of interest can be seen

Example shows horizontal slice through the model

Model Results

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Model Results

Few data values

Areas of low RQD

N

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

The diorite dyke runs sub parallel to the mineralisation

Expect that geotechnical characteristics in the dyke may be different from country rock

Look at how removing values from within the dyke effects the results

Model Result

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Model Result

Area of low RQD – outside dyke

Low RQD within dyke - removed

N

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

What if a 20m block and a wider search radius were used?

Model Result

Area of high RQD to the North

Very generalised results

Low RQD areas not clear

N

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Block model not split it into domains Quantity and Quality of Data

Co

mp

lexi

ty o

f R

ock

mas

s (a

re t

he

pro

per

ties

dif

fere

nt

for

dif

fere

nt

do

ma

ins?

)

•Good coverage based on data available

•Smoothing of data values across domains

•Good coverage based on data available

•Smoothing of data values across domain boundaries

•Significant errors

•Need to carefully consider search radius

•Excellent coverage

•Need to carefully consider search radius

•May highlight change in rock properties

•Some smoothing of data values across domain boundaries

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Block model split it into domains Quantity and Quality of Data

Co

mp

lexi

ty o

f R

ock

mas

s (a

re t

he

pro

per

ties

dif

fere

nt

for

dif

fere

nt

do

ma

ins?

)

•Smoothing of data values

•May be large gaps in coverage

•Consider DTM accuracy

•Smoothing of data values

•Significant errors

•May be large gaps in coverage

•Consider search radius

•Excellent coverage

•Reliable results

•Consider search radius

•May highlight change in rock properties

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

The mine-wide block modelling aims to indicates the quality of rock mass in general.

The block model also highlighted the areas with potential low RQD and their spatial characteristics, i.e. location, depth, extent and orientation.

This assists in the understanding of the spatial relationships of the geotechnical conditions within the rock mass.

The block model may need to be further subdivided if there is evidence to suggest distinct geotechnical domain boundaries exist and there is sufficient data

Discussion

GEOHART CONSULTANTS

Geotechnical (Mining & Civil)

Always remember that every model is a simplified reality no matter how complicated

The “unknown” addressed by a model gives the direction of the next step for ground investigation

Understanding of site geology and judgement are essential to determine the extent of block model and the associated input parameters

Conclusions