2 targeted ni-cu-pge exploration in large igneous provinces: 0 · 2015-07-16 · large igneous...
TRANSCRIPT
Depth
Depth\
Depth
Introduction
STUDY AREA
Blanchard JA 1, Ernst RE 1, Samson C 1, King A 2
1 Dept. of Earth Sciences, Carleton University, Ottawa, Ontario; 2 Geoscience North, Sudbury, Ontario
Targeted Ni-Cu-PGE exploration in Large Igneous Provinces:
a) Mackenzie dyke swarm and plume center (star), Victoria Island.
b) Model for Mackenzie magmatism.
Methods
Results: 2D Subsurface Models of Geophysical Anomalies Near 3 Plume Centers
Study Area
Large Igneous Provinces (LIPs) are large volume,
short duration, intraplate magmatic events that
show great potential for mineral exploration.
This study focuses on layered (ultra)mafic
intrusions, where Ni-Cu-PGEs tend to be hosted.
Our goal is to improve the current understanding
of the distribution of layered intrusions within
plume center regions by modeling geophysical
data.
We present preliminary 2D models near 3 mantle
plume centers: the 1270 Ma Mackenzie LIP, the
130-80 Ma HALIP, and the 66 Ma Deccan Traps.
13
0-8
0 M
a H
igh
Arc
tic
LI
P (
HA
LIP
) 1
.27
Ga
Mac
ken
zie
LIP
6
6 M
a D
ecca
n T
rap
s
Proposed Model
Modeling potential field data can be ambiguous
since no unique solution exists. However, with
sufficient geological and geophysical controls,
models can be produced that are realistic
representations of the subsurface geology.
Several geophysical controls were applied in this
study including magnetic, gravity and seismic
constraints, as well as known local geology.
The geophysical data is reproduced by a layered intrusive body at an average depth of ̴8 km, beneath ̴2km of volcanics exposed at the surface.
Half-Maximum Techniques
Deccan Traps region and plume center (star).
Vanderkluysen et al. 2011
Modeling layered intrusions in plume center regions using potential field data
Potential Field Data
Bouguer anomaly map with magnetic contour lines near the +80 mgal Mumbai anomaly previously modeled as a layered (ultra)mafic intrusion (Battacharji et al., 2004). Profile E-F intersects three +70 mgal anomalies directly adjacent to the plume center (star).
Bouguer Anomaly (mgal)
-100 -40 -20 0 65 10 -10
A map of the HALIP region with a plume center near Ellesmere Island, Nunavut.
The depth to the center of a sphere is roughly equal to the half-width of the corresponding gravity anomaly.
As causative bodies are located deeper, the corresponding gravity anomalies are broader and less pronounced (curve B). This gives a 1st O approximation of the depth to the intrusion.
Summary
Layered intrusions are important for the mining industry, especially those near plume centers as these tend to be the most prospective for Ni-Cu-PGE mineralization. The models presented in this study demonstrate that the geophysical anomalies observed can be reproduced by layered intrusions and provide insight into their depth, composition and volume. Future work will include constraining these models and extending this work to additional centers.
90°
18
0°
Plume center
Dyke swarms
HALIP
Jowitt et al. (2014)
LIPs – SUPERCONTINENT RECONSTRUCTION PROJECT
WWW.SUPERCONTINENT.ORG
A +600 nT and +60 mgal anomaly is located on Ellesmere Island (Nunavut) at ̴100 km from the plume center. Profile A-B intersects the anomaly in an East-West direction.
Several ̴50 mgal anomalies circumscribe the plume center at an average distance of 200kkm, one of which is likely linked with the Muskox intrusion to the south. Profile C-D intersects a 55 mgal gravity anomaly to the East.
Bouguer Anomaly (mgal)
-50 -10 0 10 90
Magnetic Anomaly (nT)
-80 900 0 -120 -460
82°
Dep
th (
km
) G
rav
ity
(mg
al)
Mag
neti
cs
(n
T)
Dep
th (
km
) G
rav
ity
(mg
al)
Mag
neti
cs
(n
T)
Cross-section
Top View
500 km
Buchan et al. 2010 Baragar et al. 1996
a
b
-90° -86° -82°
81°
82°
-94°
81°
82°
-90° -86° -82° -94°
Upper Crust
C D
Distance (km) Magnetic Anomaly (nT)
750 100 50 -10 -60 -260
100000 0 100000 200000
(meters)
WGS 84 / UTM zone 11N
Gravity
-257.36 743.56-130.17 -94.57 -68.03 -47.40 -31.82 -19.34 -6.70 0.09 6.29 12.89 25.96 38.16 51.04 64.04 76.87 91.97 110.03 131.54 157.77 193.58
Mag AnomalynT
65
°6
6°
67
°6
8°
69
°7
0°
71
°7
2°
73
°
65
°6
6°
67
°6
8°
69
°7
0°
71
°7
2°
73
°
-136° -134° -132° -130° -128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104° -102° -100° -98°
-128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104°
2
0
2 0
20
80
100000 0 100000 200000
(meters)
WGS 84 / UTM zone 11N
Gravity
-257.36 743.56-130.17 -94.57 -68.03 -47.40 -31.82 -19.34 -6.70 0.09 6.29 12.89 25.96 38.16 51.04 64.04 76.87 91.97 110.03 131.54 157.77 193.58
Mag AnomalynT
65°
66°
67°
68°
69°
70°
71°
72°
73°
65°
66°
67°
68°
69°
70°
71°
72°
73°
-136° -134° -132° -130° -128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104° -102° -100° -98°
-128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104°
- 150
-1
50
-1
50
- 1 5 0
- 1 50
- 1 5 0
0
0
0
0
0 0
0
0
0
0
0
0
0
0
0
0
0
0
0 0
0
0
0
0
0
15
0
15
0
15
0
15
0
150
15
0
1 5 0
150
15 0
15
0
150
1 50 15
0
15
0
1 50
150
15
0
30
0
45
069°
70°
71°
68°
-124° -120° -116° -112° -108° -128°
67°
72°
Distance (km)
A B
Below is an example of a type of constraint that can be obtained from potential field data. Similar constraints exist for more complex density distributions, which were applied in this study.
19°
20°
21°
22°
Bouguer Anomaly Map
Mumbai-92.7
-89.2
-85.5
-80.2
-74.7
-69.6
-62.9
-53.6
-45.5
-39.7
-35.8
-33.1
-30.7
-28.5
-26.8
-25.1
-23.4
-21.9
-20.2
-18.7
-17.2
-15.3
-13.6
-11.7
-9.6
-7.3
-5.4
-3.3
-1.1
1.7
4.3
6.7
8.9
11.4
14.5
18.3
22.5
29.0
Bouguer Anomaly(mgal)
18°
19°
20°
21°
22°
71° 72° 73° 74°
003-
- 2 0 0
- 2 0 0
- 2 0 0
00
1-
- 1 0 0
- 1 0 0
001-
0
00
0
0
0
0
02
2 0
2 0
20
02
20
40
4 0
40
4 0
04
1 0 0
001
1 0 0
00
2
002
100 km
72° 73° 71°
Remanent magnetization is reported in the area (eg. Vandamme et al. 1991). The majority of samples from the Deccan Traps show reversed magnetic field orientations.
A layered intrusive body is modeled at a depth of 20 km with two secondary mafic chambers at the base of the upper crust. The presence of magmatic underplating, sills and a sedimentary basin are additionally supported by the model.
Supporting Data • Gravity • Magnetics • Surface Geology
• Crustal layer models from
seismic data
Supporting Data • Gravity • Magnetics • Surface Geology • Seismic data supporting the
presence of mafic underplating at the base of the lower crust.
• Crustal layer models from seismic data
Victoria Island
Ellesmere Island
50 km Axel Heiberg Island
Dep
th (
km
)
E F
Distance (km)
Three shallow intrusive bodies sit at the base of the upper crust, underlain by the Deccan flood basalts and sediments.
Supporting Data
• Gravity
• Magnetics
• Surface Geology
• Seismic data supports:
• mafic underplating at the base of the lower crust
• Deccan flood basalt thicknesses
• Crustal layers
• Paleomagnetic Data
• Previous modeling in nearby areas
Sphere A
Sphere B
A
B
d = 500 m
d = 1000 m
Ultramafic zone D=3.4, S=0.032
Bouguer Anomaly (mgal)
-60 -40 -20 115 -85
100000 0 100000 200000
(meters)
WGS 84 / UTM zone 11N
-86.24 114.38-60.00 -40.00 -20.00 0.00
Bouguer Anomaly(mgal)
Gravity
65
°6
6°
67
°6
8°
69
°7
0°
71
°7
2°
73
°
65
°6
6°
67
°6
8°
69
°7
0°
71
°7
2°
73
°
-136° -134° -132° -130° -128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104° -102° -100° -98°
-128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104°
2
0
20
20
80
69°
70°
71°
68°
-124° -120° -116° -112°
100000 0 100000 200000
(meters)
WGS 84 / UTM zone 11N
-60.00 -40.00 -20.00 0.00
Bouguer Anomaly(mgal)
-86.24 114.38-60.00 -40.00 -20.00 0.00
Bouguer Anomaly(mgal)
Gravity
65
°66
°67
°68
°69
°70
°71
°72
°73
°
65
°6
6°
67
°6
8°
69
°7
0°
71
°72
°73
°
-136° -134° -132° -130° -128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104° -102° -100° -98°
-128° -126° -124° -122° -120° -118° -116° -114° -112° -110° -108° -106° -104°
20
2 0
20
80
-108° -128°
67°
72°
100 km
Gra
vit
y
(mg
al)
Mag
neti
cs
(n
T)
Radius = 200 m Δρ = 0.4 g/cm3