The Quantitative Inversion of Iron Ore under Strong Constrain in
Panzhihua-Baima Districts in Sichuan Province Based on the High-
Precision Aeromagnetic Survey
Tengfei Ge
1,2*
, Jingzi He
1,2
, Xue Yang
2
and Xuzhao Huang
2
1
China University of Geosciences(Beijing);
2
China Aero Geophysical Survey&Remote Sensing Center of land and resources.
Email:564465031@qq.com
Keywords: Magmatic iron ore, inversion, Panzhihua layered intrusion, South-West China
Abstract: The PanXi region in Sichuan province, Sounthwest China is famous for magmatic Fe-Ti-V oxide deposits in
the country. The metallogenesis of the Panzhihua type V-Ti magnetite deposits remains controversial. Here
we apply an interactive inversion technique on profiles of magnetic anomalies to study the deep geological
structure of the Baima area. Combined with previous petrological and sedimentological studies on these
rocks, the inversion results indicate that Baima iron deposits consist of several layered iron ore bodies.
Different characteristics in the geometric forms of Panzhihua rock body and Baima rock body show
different mineralization characters when forming magnetite ore layers under the gravity variation, resulting
in different ore structures. Although the large aeromagnetic anomaly could be the signal of the buried huge
iron ore bodies at depth in Panxi area, this has not been confirmed by deep drilling exploration. In order to
solve this puzzle, we computed the aeromagnetic anomalies along profiles in the proven iron deposits of the
Baima districts. The results reveal marked contrast between the calculated and observed anomalies. Based
on these results and previous studies on the metallogenic features, we predict the presence of large iron ore
bodies at depth beneath the Baima districts.
1 INTRODUCTION
The PanXi region has several large mafic-layered
intrusions that host world-class Fe–Ti–V oxide
deposits, such as the Panzhihua Fe-Ti-V deposit and
Baima Fe-Ti-V deposit that form part of the ~260
Ma Emeishan Large Igneous Province. This region
have attracted interest over the last decade because
of their association with ore deposits(
Zhou et al 2008)
(Shellnutt et al., 2010) and the Panzhihua Fe–Ti–V
oxide mine makes China a major producer of V and
Ti, accounting for 6.7% and 35.2% of the total
world production of V and Ti, respectively (Zhou et
al., 2005).
Several models have been proposed for the
formation of the Panzhihua deposit that are related
to the Emeishan large igneous province (LIP): (1)
the Panzhihua ore bodies developed concentrations
of Fe and Ti through the fractional crystallization of
ferrobasaltic or ferropicritic magmas, followed by
separation into silicate magma and Fe-rich oxide ore
melt (Zhou et al., 2005); (2) early crystallization of
Fe–Ti oxides from a parent magma with 1.5 wt.%
H
2
O and oxide accumulated through crystal setting
at the base of the intrusion (Pang et al., 2008; Zhou
et al., 2008); and (3) an increase in magma fO
2
related to the CO
2
-degassing of the footwall
carbonates resulted in the accumulation of Fe–Ti
oxides (Ganino et al., 2008) .The Fe–Ti oxides had
crystallized at an early stage of the solidification of
the Panzhihua intrusion, in consideration of an
effective accumulation of titanomagnetite in the
Panzhihua intrusion (Ganino et al., 2008).
Although the depth of exploration conducted so
far is shallow, there are some clues to indicate the
presence of greatly potential iron ores at depth in the
Panzhihua-Xichang area. He have suggested that the
known deposits may not have appeared in their
overlapping anomaly regions of 1:50,000 ΔT
reduced-to-pole upwards vertical second derivative
and ΔT reduced-to-pole downwards continuation
,the 3D model of Hongge Fe–Ti–V deposit was also
built under the constrain of the drilling profiles and
high- precision aeromagnetic data(Ganino and Arndt,
Ge, T., He, J., Yang, X. and Huang, X.
The Quantitative Inversion of Iron Ore under Strong Constrain in Panzhihua-Baima Districts in Sichuan Province Based on the High-Precision Aeromagnetic Survey.
In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 369-379
ISBN: 978-989-758-342-1
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
369
2009). Ge suggested that the deep levels beneath the
Daheishan and Minzhengxiang districts are benefit
space for future prospecting (Ge et al. 2015).
The interactive inversion technique on profile of
magnetic anomalies is a new method that can be
used to infer the depth and attitude of deeply buried
ore bodies through geophysical data inversion, and
has been successfully applied for the prediction of
several iron ore bodies (Fan et al., 2010, 2012; Yu et
al., 2007). To evaluate the possibility of deep iron
ore bodies in these areas, we conducted 15 magnetic
inversion lines across both Panzhihua area and
Baima area, among them 10 magnetic inversion
lines in Panzhihua area and 6 magnetic inversion
lines in Baima area proved to be of obvious ore
prospecting potential. The results from the inversion
aid in evaluating the possibility of the presence of
deep iron ore bodies and understanding the
distribution of iron ore bodies in the Panzhihua-
Baima area.
2 GEOLOGICAL SETTING
Numerous papers have described the geological
setting of the ~260 Ma Emeishan Large Igneous
Provinceand the large mafic-ultramafic intrusions
that are considered to be part of the plumbing
system of the Emeishan flood basalt (Zhou et al.,
2008). The Emeishan magmas intruded sedimentary
rocks of the Sichuan basin. In the Panxi region,
uplift and erosion has exposed large
mafic~ultramafic intrusions that are considered to
be part of the plumbing system of the Emeishan
flood basalts (Figure 1).
The Panzhihua gabbroic intrusion dips 50~60°
NW and extends about 19 km along strike. The
majority of the wall rocks are Neoproterozoic
(Sinian) dolostones (Figure 2a). These rocks are
almost pure and most contain very low contents of
clay and silica minerals, but they are interbedded
with siliceous limestones, marlstones and shales
(Pêcher et al. 2013).
From stable isotope analyses, Ganino estimated
that the Panzhihua gabbro assimilated 8~13.7 wt.%
of carbonate wallrock (Ganino et al., 2013),and
provided preliminary descriptions of the marbles
and skarns and explained how carbon dioxide
released during the metamorphism may have
triggered both the ore formation and global climate
change (Ganino et al., 2008). Magnetite-rich
melanogabbro at the base grades through normal
gabbro to leucogabbro near the top. The large Fe-Ti-
V oxide ore deposits occur as magnetite-rich
cumulate layers or discordant lenses along the
southeast margin of the intrusion. The contact
aureole is >300 m thick and is mostly composed of
brucite marble that formed from the thermal
metamorphism of dolostones, and various calc-
silicate rocks (olivine, diopside or garnet bearing
marbles) that formed from marly layers. Banded
carbonate-serpentinite reaction rims, “zebra-rocks”,
surround small dolerite dykes that were probably the
early intrusions associated with the emplacement of
Panzhihua magma.
The Baima mafic layered intrusion is located in
the central part of the Panxi area, SW China (Figure
1). The N–S striking intrusion is 24 km long and 2
km wide, dips to the west in 50–70°, and is
emplaced into the Sinian metamorphic sandstone,
phyllite, slate and marble (Figure 3). After
emplacement, the Baima intrusion was surrounded
and cut by ~259 Ma syenitic intrusions and dykes
(Zhang, et al., 2012). In addition, several NW–SE-
trending faults separate the Baima intrusion into five
segments, including Xiajiaping, Jijiping,Tianjiacun,
Qinggangping and Mabinglang (Figure 3). Along
the strike, the Baima intrusion shows a thickness
gradation from a more primitive facies in the north
to a more evolved thinner facies in the south. The
magnetite ore reserve of Baima intrusion is 1497 Mt
(millionton) with mean grades of ~26% total Fe,
~7% TiO
2
and ~0.21% V
2
O
5
(Zhang, et al., 2012).
Figure 1: Simplified regional geology of the Panxi area,
Emeishan large igneous province, SW China, showing the
distribution of Panzhihua, Hongge and Baima mafic-
ultramafic intrusions
that host Fe-Ti-(V) oxide ore.
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370
Figure 2: (a) Geological map of the Panzhihua area.; (b)
aeromagnetic anomalies in the Panzhihua area;1 –
Quaternary~Neogene; 2 - Lower Jurassic; 3 - Upper
Triassic; 4 - Middle Permian (Emeishan basalt); 5 - Lower
Triassic; 6 - Middle Triassic phonolite; 7 - Sinian
limestone and marble; 8 - Kangding complex
Pianjiangtian unit; 9 - Kangding complex Huatan unit; 10
- Kangding complex Bude unit; 11 - Early Triassic
granite; 12 – Permian Syenite; 13 - Middle Permian
gabbro (containing seam); 14 - Middle Permian gabbro
and dioritic; 15 - Middle Permian pyroxenite; 16 - Faults;
17 - Inversion profiles(5 low potential profiles in the
northern part are not mentioned).
Figure 3. (a) Geological map of the Baima area.; (b)
aeromagnetic anomalies in the Baima area; 1 –
Quaternary; 2 - Middle Permian (Emeishan basalt); 3 -
Upper Cambrian; 4 - Lower Cambrian; 5 - Sinian
Dengying Formation; 6 - Sinian Guanyinya formation; 7 –
Lower Proterozoic; 8 – Granite; 9 - Granite porphyry; 10 -
Plagiogranite; 11 – Huangcao Syenite; 12 - Quartz
syenite; 13 – Baima Syenite; 14 - Gabbro; 15- Dolerite; 16
- Diorite; 17- Faults;18- Inversion profiles(9 low potential
profiles in the sorthern part of this area are not mentioned).
3 GEOPHYSICAL SETTING
3.1 Characteristics of Magnetic
Anomalies
On the 1:50,000 contour map of the aeromagnetic
ΔT in Baima area (Figure 3b), several anomalies
with an intensity 775~ 1200 nT is identified in the
Baima area ,known iron ore belts is located along
the S-N high magnetic anomaly zone. According to
the contour map of the aeromagnetic ΔT, the area of
the high magnetic anomalies is much larger than the
iron ore belts. From Laocunpingzi to Womalin
where iron deposits have not been found, the
intensity of the aeromagnetic anomalies is more than
1000nT.
3.2 Physical Properties of Rocks and
Ores
We measured the physical properties of selected iron
ores, the ore bearing layers and cover strata, and the
statistical results are listed in Table 1. The
susceptibilities of the metamorphic rocks,
sedimentary rocks and are in the range of (0~10) ×
10
−5
SI, which can be generally regarded as non-
magnetic. Gabbro (the ore bearing layer) shows a
much higher susceptibility of (11,768.79~116.99) ×
10
−5
SI. The susceptibilities of the iron ore are in the
range of (129,000–20,499) × 10
−5
SI, which is a
geological body that could cause a strong magnetic
anomaly in this area, with densities in the range of
3.1–4.2 g/cm
3
.
Removing errors in measurement ,the
relationship between Susceptibility and Ore grade is
positive correlation (Sun et al,1991; Tian et
al,2013).We conducted magnetic susceptibility
measurement and optical film identification upon 30
magnetite samples (Figure 4) from Panzhihua
deposit and Baima deposit , and the results indicated
that the magnetic susceptibility can be used as the
basis for the division of rich iron ores.
Figure 4. The relationship between susceptibility and ore
grade in Panxi area.
The Quantitative Inversion of Iron Ore under Strong Constrain in Panzhihua-Baima Districts in Sichuan Province Based on the
High-Precision Aeromagnetic Survey
371
Table 1: Physical properties of geological bodies.
Name
Number of
measured
points
Susce
p
tibilit
y
(10
-5
SI)
area
Maximal
value
Minimum
value
Average
value
medium-grade ore 32 116000 38090 76541 Panzhihua area
high-grade ore 31 129000 55741 111521 Panzhihua area
Low-
g
rade ore 34 113000 20063 61041 Panzhihua area
Submar
g
inal ore 30 46062 20499 33618 Panzhihua area
Gabbro 38 6539 2865 4564 Panzhihua area
Gabbro 35 11768 116 6406 Panzhihua area(drill core)
Gabbro(ore
b
earin
g)
30 19014 3483 11286 Panzhihua area
Gra
y
marble 33 10 0.2 0.7 Panzhihua area
S
y
enite 32 3357 1508 2243 Panzhihua area
Phonolite 32 4916 1815 3364 Panzhihua area
Basalt 30 5556 807 4186 Panzhihua area
Sandstone 31 12 0.4 5 Panzhihua area
g
ranite
g
neiss 30 1244 98 560 Panzhihua area
g
ranite 34 2011 104 1121 Panzhihua area
P
y
roxenite 30 15905 6428 11075 Panzhihua area
Low-
g
rade ore 31 89903 30004 59442 Baima area
hi
g
h-
g
rade ore 31 127000 20163 98134 Baima area
Gabbro(ore
b
earin
g)
32 26486 1063 9846 Baima area
Gabbro 36 10497 142 4983 Baima area
Gra
y
marble 32 14 1.2 5.5 Baima area
S
y
enite 30 5669 2305 4323 Baima area
Basalt 30 5556 807 4057 Baima area
Granite 37 34 1 9 Baima area
dolomite 30 10.9 0.2 3.3 Baima area
Sandstone 31 11 1 3 Baima area
g
ranite
g
neiss 32 53 2 14 Baima area
4 INTERACTIVE INVERSION
TECHNIQUE OF MAGNETIC
ANOMALIES ALONG THE
UNDULATING TERRAIN
PROFILE
Along undulating terrain profiles can be expressed
in 2.5-D. The magnetic anomalies are calculated
above the initial model with polygonal sections of
level prism 2.5-D that are created on the basis of the
known geological structures, the property data and
semi-quantitative interpretation. Thereafter the
model parameters continue to be adjusted until the
calculated gravity and magnetic anomalies are
consistent with measured gravity and magnetic
anomalies. Finally, based on these, we can
understand some important information such as the
depth, shape and volume of iron ore bodies (Fan et
al., 2012).
Deep ore deposit prediction has been achieved
by utilizing this technology (Cong et al., 2012; Fan
et al., 2010, 2012; Yu et al., 2007). Yu noted that
two iron ore bodies dipping to the south occur at
230–480 m and 630–880 m, with a horizontal
distance of 200 m through the aeromagnetic
anomaly inversion of Xiangbishan profile across
Daye iron deposit in Hubei province, China. The
borehole ZK21-8 exploration has successfully
confirmed the inversion result (Fan et al., 2012) ,
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372
several layered ore bodies with a total thickness of
14.6m at 40–45% Fe were found at a depth interval
of 740–840 m, consistent with the above prediction.
4.1 Calculation Method for Magnetic
Anomalies
The three-components of magnetic field for any
point P (x, y, z) on the section of the level prism 2.5-
D could be calculated by the formula (Fan et al.,
2010):
H
(
)
=−
∑
sinφ
(J
I
+J
I
+J
I
)①
H
(
)
=−
∑
(J
sinφ
−J
cosφ
)I
−
J
((sinφ
I
− cosφ
I
)②
Z
(
)
=−
∑
cosφ
J
I
+J
I
+J
I
③
which can be further calculated as:
I
=P
(
Y
)
−P
(
Y
)
,j = 1,3④
(
)
= cosφ
ln
−sinφ
arctan
−
arctan
⑤
=ln
⑥
(
)
= cosφ
ln
− cosφ
arctan
−
arctan
⑦
The magnetic anomaly of the total field is:
△T
(
P
)
=H
(
)
cosI
cosD
+H
(
)
cosI
sinD
+Z
(
)
sinI
⑧
which can be further calculated as:
u
=x
cosφ
+Z
sinφ
,u
=x
cosφ
+Z
sinφ
⑨
=(
+
+
)
/
,
=(
+
+
)
/
⑩
=
=−
+
⑪
= ,
= ,
=
where, Io: geomagnetic inclination and
Do:geomagnetic declination; i: prism corner
number; N:prism side number; J: prism
magnetization; I: prism magnetic inclination and D:
prism magnetic declination. Because the formula
applies to arbitrary points on the section, we infer
that it may be applied to almost all undulated
terrains.
4.2 The Interactive Inversion Software
The interactive inversion software used in this study
is called GMVPS (Sui et al., 2004). It simulates the
underground geological conditions at deep level by
creating a model or multiple models that consist of
finite horizontal prisms with a section of arbitrary
polygons. The corner number of the polygons may
be added, reduced or moved based on the known
geological structures and anomaly characteristics. In
addition to inductive susceptibility, inductive
magnetic inclination, inductive magnetic
declination, residual magnetization, residual
inclination, horizontal ext ension of the model and
pattern of the polygonal section,some other relevant
parameters, including geomagnetic field
strength,geomagnetic inclination, geomagnetic
declination, profile azimuth, are also entered and
corrected in the dialog box. The computational curve
above the model is updated in real time as the
change of the model parameters (Fan et al., 2010).
The shape of the model is terminated at the least
difference between the calculated and measured
anomalies. Thus,we can get the final model by an
inversion result(Figure 5 as a example).The physical
properties used in the software is given according to
the physical properties measured (table 2).
Figure 5: Aeromagnetic anomaly caused by the proven
Panzhihua iron deposit along Panzhihua 4-4 'profile
(Figure legend refer to figure 7).
The Quantitative Inversion of Iron Ore under Strong Constrain in Panzhihua-Baima Districts in Sichuan Province Based on the
High-Precision Aeromagnetic Survey
373
Table 2: Physical properties used in software.
Area Name Susceptibility
κ(10
-5
SI)
Effective
magnetization
Js(10
-3
A/m)
direction of
magnetization;(°)
Density
(10
3
g/cm
3
)
Baima
area
Gabbro
(
ore bearin
g)
9840 3761.79 41.7
Gabbro 4983 1927.45 41.7
Gray marble and
dolomite
5.5 2.2 41.7
Syenite(mixed with
g
abbro
)
4320 1698.26 41.7
S
y
enite 1850 727 41.7
Basalt 4050 1552.81 41.7
Sandstone and siltstone 3 1.2 41.7
Archean and Proterozoic
metamor
p
hic rocks
14 5.6 41.7
Granite 9 3.6 41.7
High grade ore (more
than 45%
)
98100 37778.5 47 4.0
Low grade ore (<45%) 59442 23367.6 47 3.2
Panzhihua
area
Gabbro
(
ore bearin
g)
11200 4288.99 40.9
Gabbro 5600 2144.5 40.9
P
y
roxenite 11075 4270 40.9
Gray marble and
dolomite
0.7 0.3 40.9
S
y
enite 2243 857.79 40.9
Phonolite 3364 1286.7 40.9
Basalt 4486 1715.6 40.9
Sandstone and siltstone 5 2 40.9
Archean and Proterozoic
metamor
p
hic rocks
560 214.449 40.9
Granite 1121 428.99 40.9
g
rade I ore
(
TFe≥45%
)
111060 42890 53.0 4.2
grade II ore
(
44.9%≥TFe≥30%
)
76500 30022 53.0 3.7
grade III
ore
(
29.9%≥TFe≥20%
)
61000 23503.6 53.0 3.4
Submarginal
ore
(
19.99%≥TFe≥15%
)
33600 12867 53.0 3.1
5 RESULTS
The parameters of the normal maetic field of the
Panxi area used in the interactive inversion are the
following: geomagnetic field strength = 48,202 nT,
geomagnetic inclination = 40.9°, geomagnetic
declination =−1.4°, and profile azimuth=
125°(Panzhihua)/90°(Baima). The initial model is
built on the basis of cross sections (Figure 6 and
Figure 7 for example).
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374
Figure 6: Aeromagnetic anomaly caused by the proven
Panzhihua iron deposit along Panzhihua 4-4 'profile
(Figure legend refer to figure 8).
Figure 7: Aeromagnetic anomaly caused by the
proven Baima iron deposit along Baima 2-2 'profile
(Figure legend refer to figure 9)
5.1 Aeromagnetic Anomaly Caused by
the Proven Panzhihua Iron Deposit
The salient features of the Panzhihua iron deposit
(Figure 6 and Figure 8) are summarized as follows.
The exploration depth is ~600 m. The ore body is
~200m thick, ~5000m long, and dips to the
northwest at dipping angle of 50°. The wall rocks
around the ore body are mainly Permian gabrro
which intruded into Simian limestone and Archean
gneiss.(Figure 6 and Figure 8).
Figure 8: Inversion profiles 1~10 in Panzhihua area.
1- Quaternary; 2 - Permian phonolite; 3 - Permian basalt;
4 - Triassic sandstone; 5 - Sinian limestone; 6 - Archean,
Proterozoic metamorphic rocks; 7 - Gabbro; 8 - Syenite; 9
-Pyroxenite; 10 - Granite; 11 - Grade I ore (TFe≥45%); 12
- Grade II ore (TFe 30~44.9%); 13 - Grade III ore
(TFe20~29.9%); 14 - Submarginal ore (TFe15~19.9%);
15 - faults; 16 - Flight trajectory; 17 - Drilling controlled
part.
On the basis of physical properties and
aeromagnetic anomaly features, the aeromagnetic
anomaly can be accomplished by running GMVPS,
and is shown on the geological section of the proven
Panzhihua iron deposit (Figure 6 and Figure 8). The
physical properties of the rock and the ore data for
modeling are listed in Table1 and shown in Figure 7.
5.2 Aeromagnetic Anomaly Caused by
the Proven Baima Iron Deposit
The salient features of Baima iron deposit (Figure 7
and Figure 9) are summarized below. The
exploration depth is ~430 m. The ore body is ~200
m thick, ~13000 m long(cut and translated by faults
The Quantitative Inversion of Iron Ore under Strong Constrain in Panzhihua-Baima Districts in Sichuan Province Based on the
High-Precision Aeromagnetic Survey
375
into more than 5 ore blocks), and dips to the west at
a dipping angle of 70°. The wall rocks around the
ore body are mainly Permian gabrro(Figure 7 and
Figure 9). We calculate the aeromagnetic anomaly
of the Baima iron deposit via the abovementioned
method (Figure 7 and Figure 9).The physical
parameters of the rocks and ores for modeling are
listed in Table 1 and shown in Figure 9.
Figure 9: Inversion profiles 1~6 in Baima area(Cross
sections were showed in the enlarged views)
1- Quaternary; 2 - Sinian limestone; 3 - Proterozoic; 4 -
Granite; 5 - Gabbro; 6 – Syenite;7 - Rich ore(TFE≥45%);
8 - Lean ore(TFE<45%).
5.3 Results of Interactive Inversion on
Magnetic Anomalies along
Panzhihua and Baima Profiles
Based on the range of physical properties for rocks
and ores in the Panzhihua and Baima area, we can
get these physical parameters for modeling (Table
1). The parameters listed in Table 2 indicate
magnetite ores are the strongest magnetic, and the
ore-bearing layers(mainly gabbro) display the
transition between non-magnetic or weakly
magnetic limestone and syenite. However, the
strength and the center position of magnetic
anomalies significantly depend on the shapes of iron
bodies. To obtain the best results, we corrected the
models of the iron ore bodies constantly, until the
residual anomaly between aeromagnetic fitting
curve and the measured curve is the minimum.
Consequently, when the aeromagnetic residual
anomalies are the least, we can obtain the final
model for Panzhihua and Baima profiles (Figure 8
and Figure 9).
6 DISCUSSION
6.1 Deep Mineral Exploration in the
Panzhihua and Baima Area
Several magmatic Fe-Ti-V oxide deposits in the
Panxi region, SW China, are hosted in layered
mafic-ultramafic intrusions of the Emeishan Large
Igneous Province(ELIP) (Figure 1) (Zhong et al.,
2002; Zhou et al., 2005). Examples are the giant
deposits of Panzhihua, Hongge and Baima. The
Hongge deposit alone contains 4572 Mt of ore
reserves with 1830 Mt of Fe, 196 Mt of Ti and 14.7
Mt of V (Ganino et al., 2013). In addition to these
three giant deposits, other deposits currently being
mined include the Taihe deposit to the north of the
Baima deposit. In recent years, With the continuous
development of the prospecting work ,several
deposits, including Anyi , Mianhuadi and Wuben,
were discovered.
Our investigation suggests that there are
potential targets for iron ore exploration in the
Baima area. As shown in Figure 6 and 7, the
calculated aeromagnetic anomalies are much lower
than the observed anomalies in Baima deposit. The
similar scenario can also be seen in the other
inversion lines in Panzhihua and Baima area (Figure
8 and Figure 9,curves were omitted). It suggests that
there might be buried large-scale iron ore bodies
both in Panzhihua and Baima, because such large
measured anomalies cannot be produced by the
proven iron ore bodies or the gabbro surrounded
them. The Panzhihua and Baima iron ore bodies
extend to larger depth level and as shown in Figure
7 and 8. On the whole, the Panzhihua and Baima
iron deposit consists of a several layered iron bodies.
The proven iron ore bodies of Panzhihua iron
deposit are situated on the southeast part of the iron
ore layers and the volume only accounts for ~50%
of the volume predicted by the inversion result.
Therefore, we believe that there is a great potential
to discover large iron ore bodies beneath the
Panzhihua and Baima area. The exact results of the
prospecting targets of Panzhihua and Baima area
were confirmed according to the top projection of
the inferred iron ore layers and the vertical first
derivative of the magnetic field(Figure 10).
According to the study, profiles 1-1’, 2-2’, 3-3’ , 4-
4’and 5-5’ in Panzhihua have little potential in
finding new iron ore deposits near-surface, only
deep ores delow the known deposits are
expectable.Profiles 6-6’, 7-7’, 8-8’ and 9-9’ proved
to be most potential for the iron ore in Panzhihua
area for the large volume according the study.
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376
Similarly, profiles 2-2’, 3-3’, 4-4’, 5-5’and 6-6’
proved to be most potential for the iron ore in Baima
area.
Figure 10: Prospecting targets in Panzhihua and Baima
area.
1- Prospecting area; 2 - Prospecting targets(Rich ore); 3 -
Prospecting targets(Lean ore); 4 - Locations; 5 - Inversion
profiles.
6.2 Shape of Rock Bodies and Its
Relationship with Ore Grade in the
Panzhihua and Baima Area
Comparing the similarity and diversity between
Panzhihua and Baima iron deposit, we concluded
that the controlling factors of mineralization are
similar：(1)the crystallization of Fe-Ti oxides from
iron rich mafic magma in the earlier stage is the
prerequisite of mineralization; (2)Gravity separation
is the physical mechanism of the formation of Fe Ti
oxide ore of vanadium titanium magnetite.
After the parent magma separated into silicate
magma and Fe-Ti rich oxide ore melt (Zhou et al.,
2005), the Fe-Ti rich magma migrated into
Panzhihua and Baima rock body, Olivine,
plagioclase and Fe-Ti oxides become liquidus
minerals, forming magnetite ore layer under the
gravity variation.
According to the inversion results(Figure 8 and
Figure 9),the shapes of Panzhihua rock body and
Baima rock body show different characteristics in
geometrical forms .In Panzhihua area , as a result of
the obvious concave section at the bottom of the
magma chamber and the smaller horizontal area of
single rock body, the gravity separation of magnetite
is more abundant in the process of magmatic flow,
leading to the formation of thick massive ore(richer
ore) in Zhujiabaobao area. Relatively speaking,in
Baima area the bottom of the magma chamber is
relatively gentle, and the horizontal area of single
rock body is larger , gravity separation is not
abundant ,thus formed dense disseminated
ore(leaner ore).
6.3 Genesis of Panzhihua Type V-Ti
Magnetite Deposits
Different explanations were given for the ore
forming proce ss including immiscibility (Zhou et
al., 2005), fractionation (Pang et al., 2008) and
assimilation (Ganino et al.,2008). Large contact
aureoles, mostly composed of brucite marbles and
calc-silicate rocks, developed at the contact of the
intrusions (Zhou et al., 2008).
Based on the inversions we conducted, we
measured the length of the contact aureole on each
inversion profiles to make some conservative
estimates of the dimensions of the part of the aureole
that underwent partial decarbonatization, the
thickness was estimated as 300 m. The volume of
the aureole between two profiles can be calculated
as prismoid or frustum of a pyramid, giving a total
volume of 13.6 km
3
. If the rock density is 2,750
kg/m
3
, the mass of the dolostone was 37.5Gt. If we
assume that 80% of dolomite is transformed into
brucite, then 190 g of CO
2
is released for each
kilogram of rock (Ganino et al., 2008).The total
amount of CO
2
is calculated as 5.7 Gt, which is
similar to result Ganino obtained. However,90% of
the aureole on the inversion profiles were located
near Hualaipa area, 6.2 kilometers northwest of the
panzhihua deposit. Although large volume of
blinded gabbro were inferred in Hualaipa area, based
on the inversions, the metallogenic potential is low.
How CO
2
-rich fluids Interacted with the magma is
hard to estimate, and the inversions above does not
support the view that assimilation with carbonate
rocks is vital condition in the formation of
Panzhihua type V-Ti magnetite deposits.
The Quantitative Inversion of Iron Ore under Strong Constrain in Panzhihua-Baima Districts in Sichuan Province Based on the
High-Precision Aeromagnetic Survey
377
7 CONCLUSIONS
Computation through forward and inverse methods
of the magnetic anomalies of Panzhihua and Baima
profiles have been conducted through interactive
inversion technique. Our study leads to the
following three major conclusions.
There is a potential to find large-sized iron ore
bodies buried at depth in the Panzhihua and Baima
area that remain to be discovered, the inversions we
conducted provides prospecting targets for mineral
exploration. According to the study, profiles 6-6’, 7-
7’, 8-8’ and 9-9’ in Panzhihua area and Profiles 2-2’,
3-3’, 4-4’, 5-5’and 6-6’ in Baima area proved to be
most potential for the iron ore.
The Panzhihua iron deposit is composed of thick
massive ore and disseminated ore, while in Baima
deposit only disseminated ore was found. The
inversions indicated that such phenomenon could be
explained by the different shapes of different magma
chamber which related to the process of gravity
separation of magnetite.
Based on the inversions, the quality of CO
2
released from dolomite that underwent partial
decarbonatization is ~37.5Gt.Most of the aureole is
located beneath Hualaipa area where the
metallogenic potential is low, which probably mean
that assimilation with carbonate rocks is not the vital
condition in the formation of Panzhihua type V-Ti
magnetite deposits.
ACKNOWLEDGEMENTS
Financial support for this work was provided by the
The national key research
projects(2017YFC0602206), 973 Program(Grant
No. 2012CB416805) and Projects of the China
Geological Survey Bureau Program
(DD20160066,DD2016006637).
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