Taknar polymetal massive sulfide (Cu, Zn, Au, Ag and Pb) is located 28
km to the Northwest of Bardaskan in Khorasan Razavi province (Northeast
Iran). It is structurally part of the Taknar zone which is situated between
Doroune fault (great Kavir fault) to the south and taknar (Rivash) fault
to the north (Fig. 1).
Taknar deposit is a syngenetic type mineralization formed at specific
horizon within Taknar formation (Paleozoic?). Both volcanic and sub-volcanic
rocks were formed during the sedimentation and they have wide range of
composition covering from acid to mafic (Karimpour and Malekzadeh Shafaroodi,
||Location map of the study area
(a) Geological and Mineralization map of Tak 1 with
ground magnetic profiles, (b) Geological and Mineralization map of
Tak 4 with ground magnetic profiles and (c) Geological and Mineralization
map of the outside of Tak 1 with ground magnetic profiles
Low grade regional metamorphism (Green Schist facies) was effected
Taknar zone late in Paleozoic (Karimpour et al., 2004). Geology
and the magnetic survey profiles are shown in Fig. 2a-c.
Three style of mineralization such as layered, massive and stockwork
have been recognized. Major minerals are: pyrite±magnetite±chalcopyrite±sphalerite±galena,
chlorite ±quartz±sericite±calcite. Magnetite increases
toward the massive part (up to 80%) which is situated in the upper section.
Sphalerite and galena are found mainly within the upper layered and massive
Situated within a window of active tectonic setting, the original position
and dimension of the deposit had been changed and the present deposits which
are called Tak-1, 2, 3 and 4, originally were part of a big deposit and due
to faulting, they have been cut and moved at least 3 km from each other (Karimpour
and Malekzadeh Shafaroodi, 2005).
All Known volcanogenic massive sulfide are associated with phyrrhotite
or phyrrhotite and magnetite. Taknar deposit is a new type having only
magnetite (Karimpour and Malekzadeh Shafaroodi, 2005). VMS massive lenses
normally have high conductivity, density and susceptibility (Ford et
al., 2006). EM and gravity have not been applied at taknar mineral
deposit. However IP results had no success for the discovery of new deposit
(Sarafzadeh, 2001). Due to the presence of high amount of magnetite in
Taknar deposit and lack of magnetic minerals in the country rocks magnetic
method is ideal for identification of new covered deposits (Haidarian
Shahri et al., 2004). The aim of this work was to use ground magnetic
survey for exploration of new deposit.
MATERIALS AND METHODS
||Geological mapping at scale of 1:1000 in Tak 1, 4 and outside of
||Collecting 57 rock chip samples from surface and tunnel of Tak 1
and analyzed for Cu, Zn, Pb, Au, Ag, Bi and Mo in both Ferdowsi University
of Mashhad and Sarcheshmeh copper mine laboratories by Atomic Absorption
|| Measurement of Total Magnetic Intensity (TMI) on 716 points over
Tak 1, 4 and to the east of Tak 1 on 36 lines. Line spacing was 25,
20 and 10 m, respectively. Station spacing was 10 meter and reduced
to 5 m where the gradient of TMI was high. The magnetometer was proton
ENVI model of Sintrex having accuracy of 0.1 gamma
|| Measurement of magnetic susceptibility over 536 rock outcrops along
survey profiles. Magnetic susceptibility meter was GMS2 Sintrex having
accuracy of 1x10-5 SI
|| Plotting all magnetic and susceptibility profiles
|| Applying diurnal variation correction to magnetic data
|| Producing contour maps and images of TMI
|| Producing images of RTP, first vertical gradient and continued
maps using ER Mapper
||Interpreting the magnetic anomalies using known geology, mineralogy
and magnetic susceptibility
RESULTS AND DISCUSSION
The position of the survey lines are shown in Fig. 2a-c.
TMI varied from 48149 to 49580 gamma on Tak 1, 47988 to 50227 on Tak 4
and 48724 to 49231 on the outside of Tak 1. Main magnetic field of the
earth in the survey area was 48000 gamma. Diurnal variation was corrected
using Tie Line collecting data due to steep topography and lack of recording
base station magnetometer. Atmospheric variation of the magnetic field
was reported to be quite during the survey (inquired from Iranian Geophysical
Susceptibility varies from 1x10-5 to 5068x10-5
SI on Tak 1, 1x10-5 to 950x10-5 SI on Tak 4 and
2x10-5 to 1428x10-5 SI on the outside of Tak 1.
All TMI profiles were investigated in terms of magnitude and width and
compared with their corresponding susceptibility profiles. Profiles 200
S on Tak 1, 100 N on Tak 4 and 40 N on the outside of Tak 1 are shown
here for comparison (Fig. 3-5).
||(a) Susceptibility and (b) TMI in Tak 1
||(a) Susceptibility and (b) TMI in Tak 4
||(a) Susceptibility and (b) TMI in outside of Tak 1
This comparison provides an estimation of the relative depth of the magnetic
anomalies (i.e., where, both susceptibilities and TMI are high the source
of the magnetic anomaly is near surface and where susceptibility is low
and magnetic anomaly is high the source of the magnetic anomaly is deep).
Canadian VMS deposits often associated with pyrrhotite resulting in ideal
magnetic anomaly (Ford et al., 2006). The magnetic responses of
an idealized volcanogenic massive sulfide model associated with various
mineral assemblages are given by Gunn and Dentith (1997). Magnetic responses
of Taknar VMS deposit neither comparable with the Canadian VMS deposit
nor with the idealized models of Gunn and Dentith (1997) due to having
high amount of magnetite and displaced tectonically from its original
location (Karimpour and Malekzadeh Shafaroodi, 2005). Having no magnetic
minerals in the country rocks of Taknar deposit magnetic anomaly should
be related to magnetite along with mineralization provided that the magnetic
data collected accurately and interpreted properly. The information available
in magnetic data is generally underutilized and this is in part due to
poor display of the data. Magnetic data either airborne or ground measurements
cannot be interpreted until is displayed. To maximize the amount of information
extracted from the data set and overcome the limitation imposed by using
only one kind of display format, several display should be used to provide
different perspectives. A wide range of presentation and enhancements
are possible for magnetic data. Many Examples can be found in the literature
particularity in ASEG, SEG and CSEG publications. Broom (1990), Isles
et al. (1991), Teskey and Hood (1993), Milligan and Gunn (1997)
and Liu and Mackay (1998) have all discussed the presentation and interpretation
of magnetic data.
Data display along profiles and also using contour maps are both needed
to have a preliminary idea about the amplitude of the anomalies and the
magnetic trend. Images show the general pattern of the anomalies but not
the gradient and it should be used together with more conventional presentations,
such as contour map. Unenhanced color image of TMI with profiles path
superimposed on the contour map are presented here for Tak 1, 4 and outside
of Tak 1 (Fig. 6a-c).
Two separate anomalies on the western side of Tak 1 (Fig.
6a) strike N, NE-S, SW and correspond to the trend of the western
abandoned tunnel. The length and width of the northern anomaly are 120
and 100 m and the southern one are 60 and 70 m, respectively. Several
separate anomalies are present on the eastern side of Tak 1 (Fig.
6a) which overly the eastern old tunnel. The largest of these anomalies
has 100 m length and 60 m width and strikes N-S. The source of all the
anomalies on Tak 1 is magnetite along with mineralization which is remained
between the surface and the roof of the tunnels and not mined.
A NW-SE anomaly with the surface dimension of 150x100 m is present on
Tak 4 (Fig. 6b), which has surface mineralization
on the trenches. The source of this anomaly is also magnetite associated
with mineralization. A triangle shape anomaly which its apex is directed
towards the Southwest and its base trends towards the Northeast is identified
outside of Tak 1 (Fig. 6c).
||TMI color image and profile path superimposed on the
contour map. (a) Tak 1, (b) Tak 4 and (c) outside of Tak 1
Neither surface mineralization
nor mining old tunnel coincides with this newly found anomaly. In terms
of amplitude and width this anomaly is similar to the anomalies on Tak
1 which overlie the old mining tunnel.
||TMI-RTP Images of (a) Tak 1, (b) Tak 4 and (c) outside
of Tak 1
By analogy the source of the new
anomaly outside of Tak 1 (Fig. 6c) is interpreted as
magnetite along with mineralization which has been displaced from Tak
1 by active normal fault. The proper position of this new anomaly is presented
on the Reduction to the Pole (RTP) map.
Magnetic anomalies should be reduced to the pole to remove the asymmetry
due to the inclination of the magnetic field. This function puts the anomaly
above it source (Clark, 1997). The RTP maps for Tak 1, 4 and outside of
Tak 1 (Fig. 7a-c) were produced. They indicate a small
displacement of the anomalies towards the Northwest relative to the TMI
maps but the shape and general pattern remained unchanged.
Potential field data commonly presented as vertical gradient which enhances
high frequency shallow features at the expense of the deep ones and sharpening
the edges (Gunn, 1996).
First vertical derivative maps were produced from the RTP maps for Tak
1, 4 and outside of Tak 1 (Fig. 8a-c).
|| First vertical derivative maps of (a) Tak 1, (b) Tak
4 and (c) outside of Tak 1
||Upward continued maps of: (a) Tak 1, (b) Tak 4 and (c)
outside of Tak 1
The shallow expression of the anomalies on Tak 1 and 4 (Fig. 8a,b) are consistent with surface mineralization. The new anomaly outside of Tak 1 (Fig. 8c) shows also shallow sources indicating that the anomaly sources is not deep. First vertical derivative map of the outside of Tak 1(Fig. 8c) gives an indication of the relative depth of the anomaly. This is important because this anomaly is not associated with surface mineralization.
Another common presentation of potential field data is the upward continued
map. This function enhances deep and low frequency sources while diminishing
the shallow features (Gunn, 1996). RTP maps of Tak 1 and 4 continued up
to 50 m (Fig. 9a, b). The shallow
features disappeared on these maps and a deep source is evident. The RTP
map of outside of Tak 1 continued up to 90 m. A deep feature is apparent
on this map. The continued map of Tak 1, 4 and outside of Tak 1 indicates
that all anomalies are shallow.
The RTP map of Tak 1 revealed two anomalies on the western part of Tak
1 trending N, NE-S, SW. These anomalies coincide with the trend of the
surface mineralization and the western old tunnel on Tak 1. Therefore
magnetite along with mineralization confirms the source of these anomalies.
Several anomalies were identified on the RTP map on the eastern part of
Tak 1. The major one trend N-S and occurs over the eastern old tunnel
of Tak 1. Consequently the source of all the anomalies on the eastern
side of Tak 1 are also magnetite associated with mineralization. A single
NW-SE anomaly is identified on the RTP map of Tak 4 which coincides with
the surface mineralization on the trenches. The source of this anomaly
is also magnetite along with mineralization. A triangle shape anomaly
outside of Tak 1 was found on the RTP map. It is similar in magnitude
to the anomalies on Tak 1 and 4 but associated with neither surface mineralization
nor old tunnel. By analogy, the source of this anomaly is also magnetite
along with mineralization. Since there is evidence of active fault on
the eastern side of Tak 1 we believe that the source of this anomaly is
also magnetite and it is part of the mineralization on Tak 1 which has
been displaced from it by faulting.
Vertical gradient maps of Tak 1 and 4 reveal shallow features which correlate
with surface mineralization. Vertical gradient map of the outside of Tak
1 also shows shallow sources but there is no surface mineralization. This
means that the source of the anomaly is shallow.
Upward continued map of Tak 1 indicated that the shallow sources of the
western anomalies disappeared at 50 m while the eastern ones persist to
90 m. The upward continued map of Tak 4 indicates the expression of the
anomaly up to 100 m. Both vertical gradient and continued maps of the
outside of Tak 1 reveal that the source of the anomaly extends from near
surface to 100 m. The position of the anomaly of the outside of Tak 1
on the RTP map has priority order and proposed for drilling.