Transcript Integrated Analysis of Landsat TM,Aeromagnetic and Mineral

H. Asadi Haroni & Martin Hale
International Institute For Aerospace Survey
and Earth Sciences (ITC), Netherlands
Overview of presentation
Introduction
Objectives
Study area
Deposit recognition criteria
Data inputs to the GIS
Weights of evidence method
Predictive GIS exploration model
Conclusion and recommendations
Introduction
Takab area (NW Iran); a region of high potential for gold and base metals,
but difficult access, for which an innovative exploration approach is required
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Geology
Mineral Occurrences
Aeromagnetic
Landsat TM
Objectives
• Using weights of evidence analysis, to quantify the spatial correlations between
the features representing deposit recognition criteria and known mineral deposits
• To identify areas of most interest for follow up exploration
Map A: Zagros orogenic belt of Iran. Map B: the spatial distribution of
mineral occurrences with the Tertiary volcano-plutonic rocks of NW Iran
B
A
Caspian sea
B
39º N
N
Iran
36º N
Persian gulf
Study area
Takab
Thrust
Fault
Ophiolites
Tertiary volcano-plutonic
rocks of Zagros
orogenic belt
Large Au deposit
Small Au deposit
As/Sb deposit
Large Cu deposit
Large Pb/Zn deposit
33º N
ZSFB = Zagros Simply
folded belt
0
100 km
ZSFB = Sanandaj-Sirjan Zone
50000
3600000
46º E
Esfahan
50º E
54º E
Cu
Quaternary Sediment

Au/As
Tertiary Sediment
Tertiary VolcanoPlutonic Rocks
Pb/Zn
Sb
Pb/Zn
Au
5 km
Upper PaleozoicMetamorphosed Ophiolitic
rocks
Precambrian Marble
Precambrian Mica-schist,
Amphibolite and gneiss
Geological and Mineral Occurrence Map of Takab Area
Takab area
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
Epithermal origin of known Au, As, Sb and base metal mineralization
Zarshuran is a Carlin type gold deposit:
•Highly fractured black shale, jasperoids and carbonate host rocks
•Silicification, Sericitization and kaolinitization
•Occurrence of invisible gold in arsenian pyrite and sphalerite
•Structural controls
•Association of high gold concentrations with As, Sb, Hg and Zn
•High tellurium concentration
•Intrusion of a highly altered granitoid rocks
•Proximity to volcanic rocks
•Abundance of gas-rich fluid inclusions
•Presence of very high magnetic-suscceptibility intrusive rocks
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

Agh-Darreh: the richest mineralization occurs in Tertiary ferruginous carbonates
Occurrence of copper and gold in faulted zones of altered Tertiary volcanics
Presence of several active mines and ancient mining activities for As, Sb, and
base metals, which commonly contain considerable amount of gold
Deposit recognition criteria
1) Host rock lithology: a) Precambrian balck shale and carbonates,
b) Highly fractured Oligo-Miocene calcareous shale,
karsted limestone and ferruginous carbonates
2) Associated Oligo-Miocene igneous rocks (surface and subsurface)
3) Hydrothermal alteration (argellic and iron oxides)
4) Structures (faults, anticlines)
Data Inputs to the GIS of Takab Area
Data name
Data type
Bedrock geology
Polygons
Mineral occurrences Points
Landsat TM
Raster
Aeromagnetics
Raster
Digital Capture
Table digitized
ASCII file, UTM coordinates
Computer-compatible CD
Table digitized, gridded
Attributes
Rock types
Commodity types
Reflectance bands (6)
Total magnetic field
Weights of evidence method
N t = 5000, 100%
Mt = 20, 100%
Nd = 500 or 10 %
Md= 10, 50%
Nt - Nd = 4500 or 90%
Baysian Weights of Evidence Probability Analysis
Positive Spatial
Association if
% min. occurrences in Dm
>
% of total area occupied by Dm
1
Dm
Negative Spatial
Association if
No Spatial
Association if
% min. occurrences in Dm
<
% of total area occupied by Dm
% min. occurrences in Dm
=
% of total area occupied by Dm
1
1
0 . 50 / 0 . 10 =
5
C
=
W+ - W-
0 . 50 / 0 . 90 =
0 . 55
Cs
=
S2 (W+) + S2(W-)
W+ = ln 5
=
+ 1.6
C/Cs = 4. 04,
W+ = ln 0 . 55
=
-0.6
=
2.2
4 . 22, 3.5
Iron Oxide Mapping
Eigenvector covariance matrix for Iron Oxide mapping
PCs TM1
TM3
TM4
TM5
Variance %
PC1
PC2
PC3
PC4
0.41
0.44
-0.23
-0.77
0.37
0.10
-0.79
0.48
0.79
-0.52
0.33
0.03
92.80
5.20
1.45
0.55
0.27
0.73
0.47
0.42
PCs
PC1
PC2
PC3
PC4
Variance %
0.752
-0.655
0.655
0.752
72.64
29.36
Cu
N
K
Pb/Zn
K
Sb
Pb/Zn
Sb
Au/As
Sb
Pb/Zn
Au
5 km
47º15’E
Iron Oxide Image
Cu
N
K
Pb/Zn
K
36º45’N
Sb
Pb/Zn
Sb
Au/As
Sb
Au
Pb/Zn
5 km
47º15’E
Hydroxyl Image
B
Cu
N
K
Pb/Zn
K
Sb
Sb
Pb/Zn
Au/As
Sb
Au
Pb/Zn
5 km
Shaded Relief Total Field Magnetic Image
Cu
N
Cu
K
K
Pb/Zn
Pb/Zn
K
Au/As
Sb
36º45’N
Sb
Sb
Pb/Zn
K
Pb/Zn
Sb
Au/As
Sb
Sb
Au
Au
Pb/Zn
Pb/Zn
5 km
5 km
47º15’E
Total magnetic field reduced to pole
Analytical signal of total magnetic field
Steps of weights of evidence method applied to the 4 deposit recognition criteria in Takab area
1. Creating a series of
binary domains with 6 influence zones (0, 100, 200, 300, 400, 500 m)
away from each deposit recognition criteria.
2. Crossing the raster map of mineral occurrence points with each of the raster maps of
binary domains.
3. Calculating the weights (W+ and W-) for each of the binary domains
4. Determining the spatial correlations between the mineral occurrence points and
each of the domains.
5. Assigning weights (W+ and W-) to the binary map domains which have the best
spatial correlations with the known mineral deposits
7. Combining these domains to generate a predictive map indicating the
potential areas for gold and base metal exploration
Weights of evidence analysis of hydrothermal alteration domain
Dis. Min.
Dis.m)
(m) Occ.
Points
100
200
300
400
500
%
No. of %
Ratio W+ W- C
Occ. pixels in Domain
domain
6
9
12
12
13
31.58
47.37
63.16
63.16
84.21
19369
27944
36699
43424
45313
10.85
15.66
20.56
24.33
25.39
2.91
3.03
3.07
2.60
3.32
1.07
1.11
1.12
0.39
1.20
-0.26
-0.47
-0.77
-0.72
-1.55
1.33
1.58
1.89
1.11
2.75
S2(W+) S2(W-) S (C) C/S(C)
0.17
0.11
0.08
0.08
0.08
0.08
0.10
0.14
0.14
0.33
0.49
0.46
0.48
0.48
0.63
2.70
3.44
3.97
2.34
3.55
N
W+ = 1.15
W- = -0.77
5 km
Mineral occurrence
Host lithology domain (black) with 300 m buffer zone (green)
N
W+ = 0.78
W- = -0.77
Mineral occurrence
5 km
Igneous heat source domain (black) with 200
m buffer zone (green)
N
W+ = 1.12
W- = -0.77
5 km
Mineral occurrence
Hydrothermal alteration domain (black) with 300 m buffer zone (green)
W+ = 1.05
W- = -0.75
Structural domain with 500 m buffer zone, The
optimum buffer is 200 m.
Weights of evidence for deposit recognition criteria binary maps
Recognition Criteria
Favorable host lithology
Igneous heat sources
Hydrothermal alteration domain
Favorable structural domain
Cumulative total
W+
1.15
0.78
1.12
1.05
W-0.77
-0.77
-0.77
-0.75
4.10 (maximum) -3.06 (minimum)
Predictive model map outlining prospective zones in Takab area
Conclusions
• PC Transformation Technique is an effective tool for mapping outcropping
hydrothermal alteration zones
•High resolution aeromagnetic data can be used for mapping igneous heat source
and zones of demagnetization which are spatially associated with epithermal
mineralization
• Deposit recognition criteria can be quantified using weights of evidence probability
analysis
• GIS and remote sensing can provide a reliable, fast and economic
selection of target areas for further mineral exploration.
Recommendations
• Follow up investigations of identified target areas
• Applying this approach for epithermal gold exploration to the remainder of the
boundary between UDMA and SSZ (2000 km) of Iran