brisbane isatisseminar gdavies

Application of EDA to Domaining and
Use of the Variogram for DHSA
Isatis Seminar Brisbane - 28th August 2006
Presenter: J. G. Davies
Senior Resource Evaluation Geologist
BHP Mitsubishi Alliance Coal Pty Ltd
Aims of the Study
•
Demonstrate the value of geostatistics to BMA as an
input to mine planning and operations.
•
Integrate geostatistics into the resource modelling
procedures through improved domaining and use of
variography.
•
Effect integration of processes through the use of
Isatis.
Why South Walker Creek?
•
South Walker Pit: problematic quality parameters – in
particular Phosphorous.
•
Phosphorous shown to have both lateral and vertical
variability.
•
Misallocation of mined coal as a result of unclear
understanding of the phosphorous variability.
•
In-pit sampling data used to control coal stockpiles.
Location and Geological Setting
•
South Walker is located ~ 25km west of Nebo and
140km from Hay Point.
•
Resources located on the eastern limb of Northern
Bowen Basin.
•
Deposit situated on the Western Margin of the Nebo
Synclinorium, characterised by large and small scale
folding with thrust and normal faulting throughout.
•
South Walker is relatively free of compressional
features.
Cross Section Through Mulgrave Pit
Phosphorus within South Walker Creek
•
•
•
•
•
Affects mine development strategy.
Selective mining of various splits required to manage
phosphorous levels to meet market specifications.
Phosphorous is highly variable both laterally and
vertically.
Require adequate modelling of these ‘plies’ to allow
selective mining.
High and low phosphorous can then be stockpiled with
subsequent increased ability to meet specifications for
product coal.
EDA: reminder
7
EDA
MB2 Seam THICKNESS
10
7596500
Y (m)
7596000
7595500
7595000
7594500
7594000
9
8
7
6
643000 644000 645000 646000 647000 648000
X (m)
5
643000 644000 645000 646000 647000 648000
XG
Isatis
•
Use of linked windows to investigate the spatial
distribution of variables
8
EDA
9
EDA
0.25
0.25
EAST
0.15
0.10
0.05
0.00
WEST
0.20
Frequencies
Frequencies
0.20
0.15
0.10
0.05
5
6
7
MB2 Seam THICKNESS
0.00
7
8
9
10
MB2 Seam THICKNESS
Isatis
10
EDA
•
Evaluation of variables is quite rapid.
•
Visual analysis of the spatial distribution.
•
Creation of selections is instantaneous.
•
Impact on geostatistical characteristics can be
assessed immediately.
11
EDA
Distance (m)
Distance (m)
500
1000
13
0.50
36
1500
N205
25
40
19
111 88
71
64
N125
112
46
99
0.25
65
0
2000
EAST
5
Variogram : MB2 Seam THICKNESS
Variogram : MB2 Seam THICKNESS
0
500
1000
1500
405
N205
81
400
314
N125
0.50
451 443
129
181
219 420
458
0.25
153 341
202
WEST
12
17
3
0.00
0
500
1000
Distance (m)
1500
2000
0.00
0
500
1000
1500
Distance (m)
Isatis
12
EDA
•
•
•
•
Use of EDA to produce preliminary domains.
Incorporation of geological knowledge to improve
definition.
Validation of domaining through investigation of
sliced statistical profiles.
Feedback process.
13
South Walker Creek - EDA Analysis
South Walker Creek - EDA Analysis
Slice Statistics
West – Phos ~0.037%
‘Transition’ zone
0.088%
0.079%
East – Phos ~0.057%
SWC Domains
Effect of Domaining on Variography
•
Impact of domaining is marked.
•
East/West distinction produces better structured, lower
silled variograms.
South Walker Creek, Mulgrave Pit –
Domain Conclusions
Summary of Domaining Strategy
• East-West distinction mandatory;
• Phos Plies geostatistically sensible;
• B1H also a ‘High Ash-Low Yield’ ply;
• B2L-B3H-B4L ‘Low Ash-High Yield’ ply.
The Variogram - Uses
Variogram: Adjunct to Geological Study
•
Validity of East/West distinction confirmed for Phos
B2L.
•
Poor spatial continuity: ~70% Nugget. Indicator that a
high degree of smoothing will be required for
estimation. ID2 or ID3 simply not adapted.
•
Re-focus investigation on Transitional Zone (WestEast).
Nugget Effect
Nugget Interpretation
•
Overall ~ 0.0002 => nugget stdev (0.0141).
•
Find nearby pairs (quality-quality;
resource-resource; quality-resource).
•
Assess if nearby samples can vary by as much as
0.015% Phos.
Nugget Effect - what does it mean?
0.059 & 0.040
0.039 & 0.047
0.040 & 0.029
DHSA
•
Application (reminder OB’s demo).
•
Batch processing allows rapid production of
DHSA results.
•
Use for classification purposes.
DHSA
PHOS - MB2 Seam over a Nominal 1, 2, 5 & 8 years based on 4.0Mt per
annum - MULGRAVE PIT WEST
1 year
2 years
5 years
8 years
80%
60%
50%
40%
30%
20%
10%
Drill Hole Spacing (m)
1250x1250
1000x1000
750x750
625x625
500x500
375x375
250x250
125x125
0%
50x50
Global Estimation Precision
70%