The use of dempster-shafer model and GIS in integration of geoscientific data for porphyry copper potential mapping, north of Shahr-e-Babak, Iran Eigenvector loadings for some visible and infrared bands of TM, (bands 1, 3, 4, 5 and 7), showed that in each case of analysis the first principal component is an indication for albedo, and the third for vegetation. Features with lower importance such as iron oxides or hydroxyls are concentrated in subsequent principal components. PC4 of unstretched data transformation on bands 1, 4, 5, and 7 indicate the hydroxyl bearing areas around the porphyry intrusives. Some enhanced areas coincide with present porphyry deposits, and some indicate new exploration targets. PC4 of unstretched data transformation on bands 1, 3, 4, and 5 indicate that iron oxide stained areas coincide with sedimentary terrains and are not suitable for exploration. The results of principal component transformation on stretched TM bands were relatively similar using the unstretched bands but the images were brighter and the distinction between lithological units was easiear. The enhanced areas for hydroxyls were then digitized and input into GIS as an important binary predictor.  Fig. 3: Plausibility map for the porphyry copper deposits to the north of Shahr-e-Babak, Iran. The ordered legend is on the basis of increasing plausibility. A Helicopter Magnetic / Electromagnetic / Radiometric (HMER) survey was flown by Geonex Aerodat Incorporated over an area of 7000 Km2, in the Kerman province, south central part of Iran. The aim of the project was mainly exploration of porphyry and vein-type mineralization in the Kerman region. Reford and Paterson (1994) have worked on a part of HMER data and concluded that the porphyry copper deposits in the Kerman region are associated with a distinct low magnetic, relative to the host rock, a high potassium and low resistivity. The pre-processing of aeromagnetic raster data was done previously in the GIS department of Geological Survey of Iran. The magnetic anomaly districts were classified in 4 magnetic intensity groups. The magnetic anomaly map, available as hard copy, was digitized and input into the model.  Fig. 4: Uncertainty map for the porphyry copper deposits at the north of Shahr-e-Babak. The ordered legend is on the basis of increasing uncertainty. Assigning belief function values The assignment of Belief function values for input layers can be performed by a statistical method if an exploration area is well surveyed and there are sufficient target occurrences. The assignments using a statistical method is based on traditional probability theory. When an exploration area is not well-studied, the assignments must rely mainly on the knowledge and expertise of exploration geologists (Wright and Bonham-Carter 1996). For the study area the assignment of the belief function values was made subjectively for the input maps listed in the Table 1. In practice, two problems are encountered at this stage. The first difficulty is the conceptualization of belief and disbelief. There is a tendency to think of disbelief as one minus the belief. It is often difficult to quantify an opinion indicating the difference between disbelief and uncertainty. For dealing with this problem, it is suggested to evaluate the support and plausibility for the proposition, which could readily be quantified, and to calculate the disbelief and uncertainty, using the mentioned equations (Wright and Bonham-Carter 1996). The second problem is that if both two maps considered for integration have large support values, the combined support becomes close to 1. Further combination with other maps with high support values results in values even closer to 1 (and disbelief and uncertainty approaching zero), making the results difficult to interpret. Assigning the low values for support as listed in Table 1 can be suggested for dealing with this problem. The target proposition for the north of Shahr-e-Babak area is: “ there is a porphyry copper deposit”. The propositions for porphyry copper from the input maps, indicated by Di (i = 1, 2, ..., 11), are: Sptci = “ a porphyry copper deposit exists from Di “ Disci= “ a porphyry copper deposit does not exsits from Di “ Uncci = 1- Spt ci - Disci The values of Sptci, Disci, Uncci, and Plusci assigned to the attributes of Di, using a knowledge-based evaluation, are listed in Table 1. |