Asadi, Hooshang 
  
USING 2D GIS TO ASSIST 3D MODELLING OF THE ZARSHURAN GOLD DEPOSIT, IRAN 
* Hooshang ASADI HARONI, Edmund SIDES, Kiiza NGONZI 
International Institute for Aerospace Survey and Earth Sciences (ITC), The Netherlands 
* Ministry of Higher Education, Tehran, Iran 
harouni @itc.nl 
sides@itc.nl 
Technical Commission Session Themes TC VII-8 
KEY WORDS: Spatial data, Integration, Geology, Geophysics, GIS, Data mining, Information extraction 
ABSTRACT 
The Zarshuran gold deposit in NW Iran is an area of historic mining for gold and arsenic with considerable potential for 
discovery of economic gold mineralisation. Geological, geochemical and geophysical data, collected by the Ministry of 
Mines and Metals were compiled and analysed in a 2-dimensional (2D) GIS. This resulted in the definition of major 
structural features, and lithological units, that control the gold mineralisation. Spatial modelling and interpretation of 
the geochemical and geophysical data showed that the mineralization is mainly controlled by chemically-reactive 
Precambrian carbonates and black shales, extending in a NW-SE direction, and also by NE-SW high angle faults and 
their intersections with NW-SE structures. The results obtained, from the 2D GIS analysis, were used in the initial phase 
of the construction and validation of the 3-dimensional (3D) models used for resource estimation. Comparison of the 
statistical analyses of geochemical data in soils and in drillcore indicated enhanced concentrations of gold in soils at 
surface, due to residual enrichment. An enrichment relationship was established based on interpretation of the 
cumulative frequency plots for gold in soil and drillcore samples. Based on this relationship the gold anomalies 
interpreted from the soil geochemical data were used to infer a resource potential, to a depth of 200m below surface, of 
10Mt at an average grade of 0.2 g/t gold. The combined interpretation of results from the geochemical and geophysical 
data highlight several features which warrant follow-up with further drilling. 
1 INTRODUCTION 
The Zarshuran gold deposit is located north of Takab town in northwestern Iran (Figure 1). It is a well-known area of 
ancient arsenic and gold mining. In modern times orpiment and realgar have been mined for several decades on a small 
scale. In 1989, the Ministry of Mines and Metals of Iran undertook a gold exploration project to define and locate gold 
mineralisation in the Zarshuran mining district. This project resulted in identifying the district as having the highest 
mineral potential in Iran particularly for the occurrence of deposits of Au, Ag, Sb, Hg and As. An area of about 
0.65km" around an arsenic mine has been the target for gold exploration during the last ten years. Results obtained from 
geological mapping, geophysics, soil geochemistry and drilling have been used to define a possible resource tonnage of 
2.5 million tonnes of ore with an average grade of 10g/t of gold (Samimi, 1992). 
The study presented here shows how an analysis of deposit scale surface geo-information, in a 2-dimensional (2D) GIS, 
can be used to provide valuable information for use in the initial phases of construction and validation of the 3- 
dimensional (3D) models used for resource estimation. The development of a 2D spatial model, which highlights 
features characteristically associated with gold mineralisation, is illustrated. The use of 3-dimensional sub-surface 
geological structures, inferred from an interpretation of this 2D spatial model, in the evaluation of the location, size and 
morphology of the potential orebody is also discussed. 
2 GEOLOGY AND MINERALIZATION 
The Zarshuran area is underlain mainly by rocks of Precambrian age. The oldest unit, the Iman Khan unit, forms the 
core of the Iman Khan anticline, symmetrically-plunging NW-SE over some 7 km. The Iman Khan unit mainly consists 
of chlorite-amphibole-schist and locally serpentinite. The Iman Khan schist is followed upwards by the Chaldagh 
limestone, the Zarshuran black shale with silica and carbonate intercalations and the Qaradash shale, tuff and sandstone. 
An Oligo-Miocene granitoid, intruded into the mineralised Precambrian formations, is highly altered, mylonitised and 
  
82 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.