Exploration in Shazand –Aligudarz zone of Iran


A. Mohebi
Geological Survey of Iran
Tehran-Iran
a-mohebi@gsi-iran.org

M. Sadeghi
Geological Survey of Iran
Tehran-Iran
msadeghi52@gsi-iran.org

S.T. Delavar
Geological Survey of Iran
Tehran-Iran
stdelavar@gsi-iran.org


ABSTRACT
Mineral exploration strategy plan was revised in Geological Survey of Iran (GSI) in 1998 and about 20 high potential zones for Cu, Au, Pb, Zn, and Fe has been defined. One of these zones is Shazand- Aligudarz zone which has been located in west of Iran. The investigated area is covered by Golpaygan and Khoram abad geological map (scale 1:250,000) and is located in 51 00 - 49 00 longitude and 33 00 -43 00 latitude.

From the structural point of view in the area there are 4 major structural Zone: Zagros, Bistune, Central Iran and metamorphic rocks and intruded granitoides.

The eldest rocks in the area is metamorphic rocks of archean. Other rocks include Permian and Cretaceous carbonate rocks. One of the important points for mineral exploration in this zone is the existence of important mine and mineral occurences such as iron, lead, zinc and gold in different rock types.

In this research based on the GIS modeling for mineral exploration we used five data sources including: geological map (1: 100000 scale), geochemistry data, remote sensing, airborn geophysics and mines and mineral occurences data.
According to the database in this zone It's applyed different types of modeling such as index-overlay, fuzzy-logic and weights-of-evidence in GIS environment.

After all processes and preparing the mineral potential maps , the best area controlled in the field, then the good one's are offered for further studies.

INTRODUCTION
The Geological Survey of Iran (GSI) - Geomatics Group have initiated a program to develop mineral exploration in Iran. The initial phase of this program consists of airborne geophysical surveys, the acquisition and processing of remote sensing (RS) data, the development of mineral prediction models for the Esfandagheh areas and initial field programs to test the predictive capability of the GIS and RS models. The area which have been defenited via GIS modelling in not an exact ore, but they can have potential for ore mineralization and have to be checked in field study and sampling for introducing for future and detail work.

The area of this zone covered by Golpaygan and Khoram abad geological map (scale 1:250,000) and located in 51 00 - 49 00 longitude and 33 00 -43 00 latitude.

Geology:
The eldest rocks and volcanism in Shazand – Aligudarz Zone are related to Precambrian. Mooteh Granite and its Au mineralization have the same age. Sedimentary rocks covered the metamorphic complex in this area. Mila dolomites has been located in the north part of this zone. In some area the base of volcanic rocks some cretaceous units that have relationship to mineralization can be observed.

Three phase of erosion are knowing in Shazand- Aligudarz zone:
  1. Metamorphic complex (with structure trend north west-south east)
  2. Folded structures of Permian
  3. Alpian phase
There are 7 sheets of geological map with 1:100,000 scale (Delijan, Mahalat,Varche, Aligudarz, Shazand, Aligudarz, Golpaygan, Kuh dahagh) and 2 sheets of geological map with 1:250,000 scale (Golpaygan, Khoram abad).





Structural geology: based on structural zonation map(Sahandi 2004) shzand –Aligudarz zone are located in central Iran and Sanandaj –Sirjan Zone



Economic Geology and metalogeny:
Based on the strategy plan of mine in Iran which has been accomplished last year there are several good potential of Au(Carlin, epithermal and shear zone modeling) Pb-Zn(Carbonate hosted and Skarn modeling)and Fe(Skarn and Algoma modeling) mineralization in this zone.This can be also emphases with existence of several mine and indication of Au, Pb-Zn, Fe, Cu, W, Mn and Ba (figure 3).

According to metalogenic map of iran (B.Samani) there are three zone :
  1. Neotethes are complex Triassic Jurassic Submarine Volcanogenic Series late Cimmerian basement.
  2. Late Cimmerian Alpin mobile belt (Zone)
Pan – African Gondwana type platform.
There are three major work for exploration modelling in GIS environment:
Gathering existing data and imput them to system,Proceccing data,Modelling.

Gathering, imput and processing data:
Geology layer: All the geology map of these area and also topography map, were dijitized and GIS ready. And rock unit which have related to mineraliztion have been selected.

Geochemical layer: Gathering, dijitizing. processing of geochemical data and finally anomalous area forAu, Pb-Zn, Fe, Mn, Cu,…. have been distinct.

Remote sensing layer: Study and processing remote sensing data and identifying alterationarea
( argillaceous and Fe-oxides), and major structures.

Geophysical layer
After processing geophysical data, shallow body intrusions and major geophysical structures have been distinct. Mine data layer
Gathering all the mine data in the study area such as active and abandoned mine and indication, and distinguishimg their relationsheep with ore mineralization in study area.

Modelling
Shazand-Aligudarz zone based on strategical map for exploration inable to have Au(Carlin, epithermal and shear zone modeling) Pb-Zn(Carbonate hosted and Skarn modeling)and Fe(Skarn and Algoma modeling) mineralization. As the accuracy of data in this project was in 1:250,000 scale, we can't use the method which depending on data (data driven method) such as fuzzy logic and weight of evidence. Hence after field checking we got the best results in our modelling with index overlay method.In this modeling one take score to all layer and to all feature of a layer. Moderate score for a feature of final map come from this equation:



Au modeling
Au Carlin modeling :
For Carlin modeling we used geology, geochemistry, Alteration and structures layer.
  1. geology: Volcanic and carbonate rocks were selected and were merged. Volcanic rocks that younger than next carbonate are selected, Permian carbonate get more score. Final layer convert to grid and reclass between 0-10.
  2. Geochemistry:Anomal area of Au, Ag, As, Hg, W, Sb and Ba are important for Au Carlin modeling, we get this score to them.


  3. Alteration: Alteration layer is generated on remote sensing base in two type: Iron oxide and clay.
  4. Structure:The structures based on geological map and remote sensing merge together and buffered until 100 meter. Then entropy map of structure generated.
  5. Modeling: All layer in index overlay method are integrated in this score:


Au Epithermal modeling :
For Au Epithermal modeling we used geology, geochemistry, Alteration and structures layer.
Geology: the volcanic rocks of Cenozoic are selected and covert to a grid map in score between 0-10.
Geochemistry:Anomal area of Au, Ag, As, Hg, Sb, Pb and Zn are important for Au epithermal modeling, we get this score to them.



Structure and alteration layer is such as Carlin model.
Modeling: All layer in index overlay method are integrated in this score:



Au Shear zone modeling :
For Shear zone modeling we used geology, geochemistry, and structures layer.
Geology: the green schist facies rocks are selected and covert to a grid map in score between 0-10.
Geochemistry: Anomal area of Au, Ag, As, Pb and Zn are important for Au shear zone modeling, we get this score to them.



Structure layer is such as Carlin model.
Modeling: All layer in index overlay method are integrated in this score:



Pb-Zn modeling:
Pb-Zn carbonate hosted modeling:
For Pb-Zn Carbonate hosted modeling we used geology, geochemistry, and structures layer.
Geology: Dolomite unit, dolomitic limestone , limestone of precambrean to cretaceous rocks
are selected and covert to a grid map in score between 0-10.
Geochemistry:Anomal area of Pb, Zn, Mg, Cu, Ag, Cd,Sb,As and Ba are important for Pb-Zn Carbonate hosted modeling, we get this score to them.



Structure and alteration layer is such as Carlin model.
Modeling: All layer in index overlay method are integrated in this score:



Pb-Zn Skarn modeling:
For Pb-Zn Skarn modeling we used geology, geochemistry, and shallow depth of airborn geophyzics layer.
Geology layer:The carbonate rocks that located next to acidic to intermediate igneous rocks and are older than them were selected and covert to a grid map in score between 0-10.
Geochemistry:Anomal area of Pb, Zn, Mn, Cu, Ag, As,Au,W,Sn and Be are important for Pb-Zn Carbonate hosted modeling, and use this score for them.



Modeling: finally all layers with the following score are integrated with index overlay method:



Fe modeling:
Fe Algoma modeling:
For Fe Algoma modeling we used geology, geochemistry, and shallow depth of airborn geophyzics layer
Geology layer: Felsic to mafic volcanics, detrital sediments, volcanoclastic sediment and green schist facies rocks of Precambrian to Silurian were separated and converted to grid map in score between 0-10.
Geochemistry:Anomal area of Fe and Mn are important for Fe Algoma modeling, we get this score to them.



Modeling: All layer in index overlay method are integrated in this score



Fe Skarn modeling:
For Fe Sarn modeling we used geology, geochemistry, and shallow depth of airborn geophyzics layer.
Geology layer:The carbonate rocks that located next to igneous rocks and are older than them were selected and igneous rocks merged and covert to a grid map in score between 0-10.
Geochemistry:Anomal area of Fe, Zn, Au, Sn,Cu and Be are important for Fe Skarn modeling, we get this score to them.



Modeling: All layer in index overlay method are integrated in this score:



After evaluation of different layers we used different methods for integeration of layers such as Index Overlay ,Weight of Evidence and Fuzzyloggic, which the best results obtained from Index overlay.

After modelling promicing area for different mineral according to their priority were introduced. During a field checking all of the first priority target area have been checked and sampling and according to analysis of samples some good results distinct and introduce for detaile and future worcks

ACKNOWLEDGMENTS
The author of this report wishes to thank all the members of the GSI spatially GIs group who provided assistance and support during the field program.

DISCUSSION AND CONCLUSIONS
During the field program, 39 areas were examined at the reconnaissance level. Several target area were identified during the course of the field work as warranting further investigation or as having mineral potential. The area will require follow-up work (mapping, prospecting, sampling and analyses and geophysical surveys) in order to evaluate their mineral potential or, diamond drilling and underground exploration work to assess their potential.

several of the targets that could not be examined during the field program should be examined and sampled on a reconnaissance basis in order to evaluate their economic potential.







REFERENCES

  1. Bonham-Carter, G.F., 1994. Geographic Information Systems for Geoscientists: Modeling with GIS
  2. Eexploration reports in golpaygan area, 250,000 scale, Geological suvey of Iran.
  3. Geochemical exploration reports in 100,000 scale.
  4. Hammer exploration reports in 100,000 scale.
  5. Copper Deposits in Iran, Geological Survey of Iran, Report No.13, 1969.