Summary:
All the deposits at Zawar are hosted by epizonal metamorphosed dolomites of the Tiri Formation, Aravalli Supergroup (1.7 – 1.8 Ma), either in north-south structures (Post-Aravalli orogeny) or in W-E structures (Delhi orogeny). The mineralisation comprises sphalerite and galena as disseminations or veinlets in bodies defined by grade contacts only. Silver mineralisation has been concentrated in the upper levels of the mines which have been depleted either by historical mining of earlier modern mining. The deposits are either tabular, steeply northeast-dipping and west-plunging (Mochia and Balaria), or complex-shaped lenses following the Northern plunge of a fold-axis (Zawarmala). At Baroi, mineralisation is largely disseminated and organised in poorly constrained Northwest dipping bodies.
The deposits are considered to be syn-metamorphic stratabound carbonate-hosted (dolomite) lead-zinc deposits (Mississippi Valley Type in the wider sense). There are minor cross cutting post-mineralisation intrusives of Precambrian and Cretaceous age. The deposits have the following general geometry:
• Mochia Central: strike: 1,050m E – W, consisting of 8 lenses; lenses strike 60 - 200m; Dip 80-85º towards the S; Width 2-45m; dominant plunge of 50-60º towards the SW.
• Mochia West: strike: 1,800m E – W, consisting of 32 lenses; lenses strike 60 – 150m; Dip 80-85º towards the S; Width 2 – 20m; dominant plunge of 50-60º towards the SW.
• Balaria Central: strike: 1,050m NW – SE, consisting of 21 lenses; lenses strike 60 – 200m; Dip 70º towards the SW; Width 2 – 40m; dominant plunge of 50-60º towards the SW.
• Balaria West: strike: 1,800m WNW – ESE, consisting of 15 lenses; lenses strike 60 – 200m; Dip 70º towards the NW; Width 2 – 10m; dominant plunge of 50-60º towards the SW.
• Zawarmala: strike: 550m NW – SE, consisting of four lenses; lenses strike 60 – 200m; Dip 70º towards the SW; Width 2 – 40m; dominant plunge of 30-60º towards the NW.
• Baroi Central: strike: 1,200m NW – SE, consisting of 12 lenses; lenses strike 60 – 250m; Dip 70º towards the NW; Width 2 – 20m; dominant plunge of 50-60º towards the NW.
• Baroi North: strike: 1,300m NW – SE, consisting of 9 lenses; lenses strike 100 – 120m; Dip 50-60º towards the NW; Width 2 – 15m; dominant plunge of 50-60º towards the NW.
Deposit Types
The mineralization in the lease hold area is in the form of echelon & fracture filled structures due to which the orebody shows pinching and swelling in both dip and strike directions. The initial delineation of the orebodies by surface drilling and underground exploratory drilling, usually differs from the later stage (After definition Drilling) delineation which also includes underground mapping and correlation. By virtue of exploiting the deposit during the last few decades, the general trend of variation found to be positive. The reserves of the delineated orebodies after the definition drilling, usually from the developmental drives, is always found to be larger than the resource of the orebody when it was delineated from surface exploration.
Mineralization
Base metal sulphide deposits occur throughout Zawar, solely within the dolomitic horizon of the Baroi Magra formation. Most of these occurrences are manifested at the surface by ancient workings in the form of long-abandoned trench mines, circular shafts and inclines. These usually penetrate for a few tens of metres in depth but some of the early workings in Zawar Mala, Balaria and Mochia do extend for more than 100 m vertical depth. The ancient mines systems give much information to the mining geologist concerning the shape, size and attitude of the exploited or explored ore lenses and of the deposits below the surface, but they give little data on the grade of the ore mined in the past or of the depth extension of mineralization.
Salient aspects of four deposits of Zawar Lease Block 1 are:
• Host Rock. Carbonate sequence (dolomites & its facies variants) belonging to Mochia member overlying a rhythmic succession of greywacke, phyllite & quartzite.
• Genesis & Control of Mineralization. Stratiform & strata bound, has undergone transformation & re-mobilization under low temperature conditions.
• Mochia & Balaria. Galena (Pb ore) & sphalerite (Zn ore) veins and veinlets concentrate into E-W to NW-SE trending, steeply dipping & westerly plunging tabular ore bodies with a width ranging from 2 m to 45 m.
• Zawar Mala. Mineralization is concentrated at the core of the anticline and follows the axial plane of the fold plunging 40° due North.
• Baroi. Disseminated Pb & Zn mineralization is in the form of NE-SW trending tabular ore bodies dipping NW and plunging to the West.
The main ore minerals at Zawar are, in order of abundance: sphalerite, pyrite and galena, although at Baroi, galena is the predominant base metal sulphide mineral. All Zawar ore is indicated to be “clean” and easy to liberate with minimal level of metal impurities or other contaminants reporting into the concentrates. The base metal sulphides are indicated to be mainly associated with the gangue minerals and can be liberated at relatively coarse size with little intergrowth of the lead and zinc minerals. Cadmium is reported to occur with sphalerite while silver occurs predominantly in solid solution with galena.