'entral 
DOSits. 
sis in 
sodata 
aphic, 
| class 
e used 
ebraic 
served 
roduct 
using 
on the 
e with 
lineral 
ration, 
lential 
ta into 
rmally 
Zy set 
mann, 
sed on 
sing a 
being 
)genic 
; work 
N and 
many 
>ycles, 
cheme 
gen et 
phism 
Porwal, Alok 
  
  
Conformable, stratabound, sediment-hosted 
basemetal deposits in the area are hosted by Lower to 
Middle Proterozoic supracrustal rocks of the Aravalli 
supergroup, and by Pre-Aravalli(?) metasediments of 
the Bhilwara area. These deposits exhibit a marked 
preference for non-clastic carbonates and graphitic 
rocks (Deb, 1982). Major concentrations of 
mineralisation in the Bhilwara area occur in the 
Rampura-Agucha deposit and in the Pur-Banera- 
Rajpura-Dariba belt. Rampura-Agucha is a Zn-Pb- 
(Ag) deposit with the highest combined metal grade 
(about 15%) of all basemetal deposits in India. In the 
Rajpura-Dariba area, the Zn-Pb-Cu-(Ag-Sb-Cd-As- 
Au) mineralisation is located in a 17 km long belt 
running from Bethumni in north through Rajpura to 
Dariba in the south, with a lean pyrite zone to the 
Fig. 1 Location map of the test area south of Dariba. There is another lean polymetallic 
zone to the northeast, known as the Pur-Banera zone. 
Copper, gold and uranium mineralisation occurs in the 
basal sequences of lower supracrustals (Lower Aravalli group) between Udaipur and Banswara. The Upper Aravalli 
group hosts the Zn-Pb mineralisation of the Zawar belt, which comprises the deposits of Mochia Magra-Balaria, 
Zawarmala and Baroi Magra. 
Z 
  
  
  
  
1.2 Overview of the approach 
Recognition criteria for basemetal mineralisation in the study area were identified on the basis of published work on 
metallogenesis in Aravalli province. A regional GIS was then established using several public-domain geodata sets for 
this area. These were reviewed, reclassified and gridded to generate a series of multi-class evidential theme maps. 
Fuzzy membership values for each evidential map were derived using weights assigned subjectively. Finally, the fuzzy 
membership values of the evidential maps were combined using the fuzzy gamma operator to generate favourability 
maps. 
2 RECOGNITION CRITERIA AND EVIDENTIAL MAPS 
The mineral deposits in the area have been interpreted as exhalative-sedimentary deposits. Deb and Sarkar (1990), in a 
review of these deposits based on detailed field, fluid inclusion, stable isotope and other geochemical data, have 
explained metallogenesis in Aravalli province in a framework of extensional tectonism. According to these authors, the 
Zn-Pb(-Cu) sulphide deposits at Rampura-Agucha and in the Rajpura-Dariba and Pur-Banera belts were formed by 
convective sea water circulation in zones of crustal extension. The metal content of the exhalative brines was 
precipitated in troughs with high biological activity. The Zn-Pb deposits of the Zawar belt were formed close to a 
basement inlier, in second order basins with biological activity, by hydrothermal fluids convecting through a 
heterogeneous source. 
On the basis of the published studies on metallogenesis in the Aravalli province, lithology, stratigraphic position, 
proximity to major fold axes and evidence of deformation were identified as key recognition criteria for the basemetal 
deposits. The first two criteria were based on the syngenetic nature of mineralisation, while the last two were selected 
on the basis of the extensive remobilisation of mineralisation by subsequent deformation, especially in the Zawar belt. 
An extensive regional scale GIS was compiled in ArcView GIS software by digitising lithostratigraphical map (Heron, 
1953), structural map (Gupta et al., 1980), total intensity aeromagnetic map (GSI, 1981), magnetic zones (GSI, 1981), 
gravity map (Reddi and Ramakrishna, 1987) and lineament density map. The mineral locations were compiled from 
various sources and digitised as point features in the GIS. Based on a consideration of the genetic model, we selected 
five thematic maps, which were deemed most likely to provide useful evidence for the presence of recognition criteria 
for basemetal deposits in the study area. The evidence maps selected were the lithological, stratigraphic, structural, 
magnetic zones and lineament density maps. 
The lithostratigraphic map was reclassified into two independent maps, viz., lithological map and stratigraphic map. 
The structural map of the Aravalli region was classified according to the fold type and deformation phase. The fold axes 
were buffered to a distance of 1 km on the basis of visual inspection of spatial association between fold axes and the 
known mineral occurrences 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1179