Development of kimberlite exploration Geographic Information System
Fig.3 IRS 1D image view of the area of investigation.
Exploration guides for Kimberlite
General: Area comes under Bastar craton with abnormally cool keel of lithosphere, Eastern Ghat Orogenic Mobile Belt borders Bastar craton; Archaean rocks of Bastar craton are in contact with the Proterozoic intracratonic Khariar basin; a zone of high magnetic permeability as defined by repeated intrusion of various types of igneous rocks; Morphological depressions are recognised.
Geochronology: Eastern Ghat Mobile Belt (EGMB) is thermo-tectonically reactivated in 1500±2000 Ma and 800±100 Ma; 1000 Ma event in EGMB coincides with the kimberlite orogeny; the Khariar Proterozoic platformal sediments indicate two cycle of sedimentation i.e. 1100-900 Ma and 700-450 Ma. The maximum thickness of sedimentary cover rock is about 1000m.
Tectonic: Area is bordered by the Mahanadi, Pranhita and Godaveri linear grabens / aulacogens rifts that have history of frequent reactivation; lineament study indicates that the area is under crustal tension with mantle reaching deep seated fault i.e. Sondur lineament etc; splay of secondary faults and intersection of linear fractures /fault corridors are common in the area; indicates an intersection of high permeability zone; dome shaped uplifts is displayed in fairly plastic sedimentary cover i.e.Khariar sediments, while block shaped uplifts occur in more rigid cover rocks or within outcrops of basement on craton (Bastar craton).
Lithologic: Most of the craton part in the Mainpur-Deobhog Area (MDA) is represented by Archon and Proton; Presence of Khariar platform cover rock on the Bastar craton; the kimberlites always occur in cluster and four pipe rocks are already discovered; MDA is included in alkaline rock province.
Geophysical: Geophysical (aeromagnetic) survey is in progress; high magnetic anomaly is reported; represents high boundary velocity (vp) and high gravity anomaly; area absolutely comes under low geothermal gradient.
Geochemical: Streams sediments show dispersion halos of diamond indicator; Local diggers recover placer diamonds.
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The lithologic, tectonic, drainage maps and geochemical data of the selected window are digitized and used as database for KEGIS. The software used for development of KEGIS is ILWIS-2.1, developed by ITC, The Netherlands. The software gives highest flexibility and combines raster and vector based GIS, as some analytical technique can be best performed in vector mode while others in raster mode. The information is extracted from prepared thematic maps and finally six important 'attribute input data' are identified for further operation. The attribute input data are subjected to Fuzzy Logic Operation that is based on membership values given as attribute value, ranging
between 0 & 1. The contact between Proterozoics and Archaeans and, the area occupied by coarse-grained granite are selected from the geological map and buffered to produce a proximity map. Similarly proximity map is derived from the structural map indicating distance of influence zone from the normal fault, which is used as an evidence for proximity to heat source. Based on distance from the center, the coarse grained granite is separated into 10 different zones and each zone is buffered. The geochemical data for elements Ni, Co and Cr, supposed to be important indicators for rocks of the kimerlite clan, is classified on
a scale designed to accentuate and enhance those areas with anomalous high value of Ni (650 to 2000 ppm), Cr (400 to >1000 ppm), Co (40 to 200 ppm). Choosing anomalous drainage patterns enhances the drainage map and allows preparing the derivative map. The attribute data and the assumptions are combined together in the base buffer zone to be used in KEGIS.