The geological formations in the Hutti area consists of the pre-cambrian metavolcanic rocks of the Dharwar system (consisting of metabasalts with acid volcanic rock and chlorite biotite schists). Chlorite-biotite schist generally form the host rocks for gold mineralisation and occur as parallel to sub-parallel lode zones.
The main auriferous zone of the Hutti Gold Mines consists of nine known reefs namely, Main, Oakley's, Middle, Zone-I, village, Strike, Foot-wall & Hanging wall of Strike & New East Reefs. The general trend of the lodes is N200W-S200E and dip steeply due west at 60-700, usually occur in an en-echelon to mylonitised pattern along with shear fractures. Theses lodes abruptly stop at the schist-granite contact in the southern part of the area, whereas in the North they continue beyond the major dolerite dyke of about 70.00 m. The gold quartz mineralisation is confined to the chlorite-biotite schist zones traversed by quartz veins which are considered as the alteration products of metabasalts along the parallel to sub-parallel shear zones and structures such as minor cross-folds, shear fractures and other dilatant structures appear to have controlled localisation of mineralisation. Branching of the lodes both along the strike and dip is another important structural feature. Quartz is the main filling, in the form of veins, numerous lenses and irregular pods occupying the shear fractures and shear cavities in the delation zones.
The total ore reserves estimated as on 31.03.2015 is 9.39 million tonnes at 5.34 g/t, upto 26th Level (842 m). Based on the detailed survey with ultra-violet lamps for demarcating the scheelite rich zones and re-sampling of the mineralised zones, a total of 1,64,771 tonnes of scheelite ore with a grade & 0.08 to 0.10% WO3 over 2.29mts widths, was proved so far. The indicated reserves for scheelite ore are put at 9,12,666 tonnes. The major thrust in this mine is to establish the depth extension of the ore zones within the existing lease. To attain the targeted production, 2nd phase Mining has started below 20th L. presently, development works in 24th L, 26th L, 27th L & excavation of ore pass system, 28th L plat cutting and further deepening of Mallappa Shaft are going on as per schedule. Circular Shaft of 6m dia sinking upto a depth of 940 m has been started with initial preparation work from 25.01.2015 to increase the intake quantity of fresh Air, to lower & hoist the persons, large machineries & equipments to improve the production & ventilation of the mine. In the Hutti South area, the recent surface diamond drilling and exploratory mining has established the potential mineralized zones. The evaluation of this exploration data has indicated that, further exploration inputs are required for mining feasibility studies. For this, it is planned to take up exploratory mining works at Grey shaft & South Hutti area. A mega surface diamond drilling programme of 7000.00 m is started to explore the lateral extension of different parallel reef's and their depth persistence. A total of 6345.00 m of underground diamond drilling is started to explore the strike & depth continuity of existing & un-correlated lodes.