Predictive targeting outcomes:

August 2007

pmdCRCb003-07

More information:

Jamie Robinson: Structural Geologist, CSIRO, @csiro.aujamie.robinson

Warren Potma: Modelling Project Leader, CSIRO, warren.potma@csiro.au

CSIRO report P2007/586Authors: Jamie Robinson and Warren Potma, CSIRO Exploration and Mininng/pmd*CRC

The predictive targeting outcomes presented in this report result from numerical modeling/simulation of complex mechanical/fluid flow/chemical/thermal systems. The modeling process utilizes both empirical data and geological interpretations as a basis for

model construction and some intrinsic assumptions are required by the process. Every effort has been made to simulate these processes as accurately as possible based on the available geological interpretation and data, however, it must be noted that changes to

numerical inputs following further data acquisition or variations in geological interpretation may result in different modeling outcomes.

Kink bands containing the

mineralised tension veins may dip

to the southeast, or east-southeast

and control with the plunge

direction of the ore shoots within

area 223.

https://pmd-twiki.arrc.csiro.au/twiki/bin/view/PIRSA2MinotaurAu/WebHome

The most likely location of tension

veins associated with high gold

grades is within dilational sites

related to the kinking of the

pre-existing foliation. Greater

dilation will be produced with

greater angles between the

northeast and southwest-dipping

sections of the fabric. However,

significant dilation (in the form of

steep-dipping tension veins) is also

found where the fabric is near

vertical or steeply-dipping

suggesting that while the greater

angle is optimal, dilation is

produced when the change in

fabric dip is as little as 10 to 20

degrees.

Proximity to the major faults will

always be advantageous as the

faults act as major fluid pathways

through the area. Dilational sites,

such as within the kink zones,

draw fluid from the faults but it is

the downstream terminations that

trap fluids. Results suggest that

dilational sites in proximity to the

footwall will be the best focus for

mineralising fluid, consistent with

the know distribution of gold in

area 223.

Aim of the fluid-flow modelling:

To examine how subtle variations in the dip and strike of the pre-existing shear fabric may influence the localisation of strain and dilation.

To identify what fabric orientations are best for producing dilation with stress fields known to be associated with mineralisation and, therefore, determine the best targets for high-grade mineralisation.

Model design and setup:

The basic geometry consists of a steep west-dipping unit 100m in width representing the Central Alteration Zone (CAZ). Thin planar zones representing faults have been placed on the eastern & western margins of the CAZ around which is a matrix representing Tunkillia Augen Gneiss (TAG).

The CAZ is divided into a number of individual regions in the Z (vertical) and Y (north-south) direction so as to allow different oriented planes of weakness to be applied to the different regions of the CAZ using the ubiquitous joint constitutive model (Figure 1).

The ubiquitous joint model allows an anisotropy, or fabric/plane of weakness with its own strength properties and orientation, to be applied throughout particular zones.

Changing the thickness of the kink bands influences the amount of dilation and shear strain. Having thicker kink bands produces lower but more widespread dilation and lower shear strain in the regions of southwest-dipping fabric. When the kinks are thin, localised regions of high dilation are produced while higher, more evenly distributed shear strain is produced in the regions of southwest-dipping fabric.

Plots of integrated fluid flux, for the best of the model results, show that most fluid over the life of the model passes up the footwall fault AND flows into the dilational sites within the kinks adjacent to the faults. The results of this plot are consistent with the distribution of mineralisation within area 223 (Figure 4).

Tunkillia Deposit Scale Modelling: Predictive Targeting Outcomes

Mineralised tension veins are likely

to be upright to steeply dipping

and roughly north-south striking.

The strength of the fabric was calibrated to be slightly weaker than the host rock. The orientation of the fabric is the main variable of these models.

Dip of the dominant shear fabric tested: o o

- 70, 80 or 90 northwest/ 70, 80 southwest.

Strike of the dominant shear fabric tested: - 320, 330, 340 or 350 degrees.

N

Fault

Central Alteration Zone

Ubiquitous joint region A

Ubiquitous joint region B (Kink)

100 m

Mafic Dyke (MAD)

Dacite Dyke (DAD)

Central Alteration Zone (CAZ)

Drill hole

Au intercept 1 to 2 g/t

Au intercept 2 to 5 g/t

Au intercept 5 g/t +

Kink Band ?

BOPO

BOCO

Concentration of higher Au grades towards footwall

Increased fluid flux towards footwall

Figure 4.

predictive mineral discovery CRC - Update #2

PIRSA 2 - Minotaur Numerical Modelling Project

Figure 1.

Results:

The results indicate that variations in both strike and dip of the fabric within the Central Alteration Zone can potentially produce localised dilation and high shear strain (Figure 2).

Figure 2.

oA change in strike or dip of the fabric of 10 or less is sufficient to affect shear strain and dilation. Variations in the orientation of the planar fabric within the Central Alteration Zone are important!

o oIn the transpression stress field, with 140 compression direction, a fabric strike of 130 produced the best localisation

oof dilation, while 140 strikes produce the highest shear strain within the CAZ.

o oIn the transpression stress field, with 160 compression direction, a fabric strike of 140 produced the best localisation of dilation and high shear strain within the CAZ.

o oDips of 80 southwest produced an even distribution of shear strain while dips of 70 produced more localised zones of high shear strain.

The greater the angle between the southwest-dipping fabric and the northeast-dipping fabric the greater the potential for dilation in the kink (Figure 3). However, minor changes in the dip and strike of the fabric also produces some dilation.

Figure 3.

N

High shear strain

High shear strain

High shear strain

High shear & volume strain

High shear strain

Highvolumestrain

1

23

1

23

Schistosity Shear veinsTension veins

Kink and vein plungeKink and vein plunge

oStrike 130

Dip A = 80SW

Dip B = 70NE(Kink)

Dip A = 80SW

Dip B = 80NE(Kink)

Dip A = 80SW

N

(a)

(b)

(c)

Dip B = 90NE(Kink)

predictive mineral discovery CRC - Update #2

PIRSA 2 - Minotaur Numerical Modelling Project

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