Summary:
The Rajpura Dariba Mine is located at the southern extremity of the belt. The ore bodies are designated as Main Lode and East Lode. Main lode with a N-S strike is further divided into two, viz àviz the North lode (900m in length and dipping at 70°-75°E) and the South lode (500m in length and dipping 60°-70°E). The East lode is located about 150 to 200m away from the hanging wall side of the South lode and has a length of 600m. The area between the South and North Lodes is traversed by 2-10 m wide meta-basic dykes. Four sets of joints are developed due to deformation. Shears are represented by narrow zones of crushing, brecciation and gouging, mostly 0.1-2.0 m wide. These are highly persistent along strike and dip and occur at the contacts and within the ore bodies for South and North Lodes. However, they are not found in East Lode. Faults are of reverse type with low southeasterly dipping planes striking N40°-60°E.
The 17 km long Dariba-Bethumni Mineral Belt comprises medium to high-grade metamorphosed metasediments belonging to the early Proterozoic Bhilwara Supergroup. The sequence forms an isoclinal fold and is surrounded by gneisses and migmatites of the Mangalwar complex. The main ore minerals are galena and sphalerite and minor silver-bearing fahlore, while pyrite and pyrrhotite are the main sulphide gangue minerals.
The Rajpura Dariba deposit comprises several mineralised lodes: on the west flank of the syncline, the North and South Lodes, which incorporate the Main Lode, and on the east flank of the syncline, the East Lode, comprising E0, E-1, E-10 and E-11. The North, South and East Lodes are 15 to 50 m thick, dip east with the stratigraphy at 65º and have strike lengths of >900 m, 500 m and 600 m respectively. The lodes have been mapped from surface, where a thick robust gossan has been mapped.
Deposit Types
Mineralisation exhibits lithological, stratigraphic and structural controls and occurs in the form of fracture-filling veins, stringers and disseminations forming tabular to lenticular ore bodies. The mineralization is of probable SEDEX-origin and concentrated in calcsilicate bearing dolomites and in graphite mica schists. The deposit forms part of a larger, regional-scale mineralised belt.
There remain areas with excellent potential to add resource that require further delineation drilling. These areas are located close to existing underground infrastructure and development, and therefore, should be prioritised over exploration of deeper currently inaccessible areas. In the North Lode, ground stability is affected by a shear zone along the hanging-wall, as well as by dissolution of dolomite by acidic water from adjacent oxidised zones. This area presents a challenge both metallurgically and geotechnically. Shearing is evident throughout the mineralised lenses and causes stability issues and mining difficulties, however, does not appear to affect the grade or geological continuity to any great degree. The extension of the North deposit at depth comprises a large proportion of heavily oxidised material with limited geological knowledge and test work results.
Mineralization
A spectacular zone of in situ gossan is found capping the ridge between Dariba (24°57’: 74°08’) and Rajpura (24°58’: 74°08’) villages in Udaipur district over a strike length of 4.5 km with width ranging from 2 m to 40 m.
The nature of mineralisation is synsedimentary, later remobilised and recrystallised during subsequent polyphase deformation and metamorphism. The principal ore forming minerals are sphalerite (ZnS) and galena (PbS). Pyrrhotite is most abundant and ubiquitous gangue while pyrite (FeS) and arsenopyrite (FeAsS) are rare. The rock forming minerals are calcite, dolomite, quartz, mica, garnet, tremolite, argillaceous and carbonaceous materials.
The mineralization in calc-silicate bearing dolomite is mostly confined to structural openings. Ore minerals occur as bands, stringers, disseminations, fracture-filling veins etc. and are recrystallised in places. The mineralization in graphite mica schist is in the form of laminae parallel to schistosity, stringers, blebs and recrystallised massive patches.
The economic ore is hosted in two different types of mineralised environments: calc-silicate dolomites and graphite mica schists. The mineralogy of the RDM material is indicated to be relatively complex with zinc and lead minerals occurring as intergrowths and fine disseminations among other sulphide and gangue minerals. Gangue minerals include dolomite, muscovite, quartz and feldspar.