Abstract: The Ajjanahalli gold deposit is a remobilized stratabound as well as stratiform type deposit where gold concentration is found within sulphidic BIF along several epigenetic quartz and quartz-carbonate veins. The sulphide minerals associated with the deposit are dominantly pyrite, pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, Bi-sulphide, PGE minerals along with native phases of gold, bismuth and gold alloys such as auricupride, electrum and allopalladium. Almost all the sulphides occurring in the area have undergone deformation. There are two generations of sulphides, the primary sulphides along with sulfosalts occur as relicts and skeletal crystals, corresponding to the peak metamorphic assemblage of the area. The 2 nd generation sulphides are observed as idioblastic crystals and porphyries around which the silicate and ductile sulphides have swirled. The remobilization and concentration of sulphides and gold in the Ajjanahalli gold deposit has been assisted by hydrothermal fluids as well as melting. Various studies have constrained the temperature of metamorphism at Ajjanahalli between 450 to 550 ° C. Studies have shown that pyrite and arsenopyrite can react to form pyrrhotite + melt at temperatures as low as 251 ° C. In the current study, an attempt has been made to study the evidences of sulphide melting from field, petrographic and ore microscopic studies as well as mineral chemistry. The recognition of features in sulphides which show indications of melting at the time of peak metamorphism provides a possible explanation for the erratic pattern of distribution of gold in the deposit.

Abstract: All the known lode gold prospects and deposits in Chitradurga schist belt (CSB) are spatially associated with two transcrustal shear zones, Chitradurga Eastern Shear Zone (CESZ) and Chitradurga Central Shear Zone (CCSZ), though they have varied geological setting with regards to lithology and host structure. Along its entire stretch, the CCSZ is characterized by a wide zone of intense carbonatisation, however no such regionally extensive carbonatisation is associated with CESZ. Auriferous quartz carbonate lodes are localized along zones of dialatation like second order structures and/or contacts of litho units of contrasting competency. Overpinting of the structural fabric of second deformational phase (D 2) on the quartz lodes in prospects associated with CCSZ clearly constrain the event as D 1 . However, lodes localized along second order structure related to CESZ ought to be syn-to late D 2 which is the event of CESZ development. In the lower sequence of Dharwar Supergroup, gold mineralisation in quartzite of Bababudan Group is recorded in Halekallu outlier; BIF hosted gold mineralization in Kalinganahalli, Yediyur-Karigatta belt, and vein type mineralization associated with mafic-ultramafic sequence in Kenchanahalli and Honnabetta prospects, Nagamangala belt, which constitutes the southern continuation of CSB. The lone occurrence of gold related to Vanivilas Formation where mineralization is hosted in Fe-Mn phyllite is recorded near Bodimardi in the northern closure area of the Sirankatte dome. The varied nature of gold mineralization in terms of host rock characteristics and structural controls and its continuum over time from the base of Dharwar Supergroup sedimentation, volcanism, deformation and metamorphism indicates recycling and localization of gold from the volcano-sedimentary sequence over a protracted period of time.

Abstract: About 100kg of tailing sample containing 0.72g/t of gold was collected from the Kolar Gold Fields, Karnataka and passed the entire quantity through three processes conducted on Lab scale. The first process is Hyper accumulation of Gold from Tailing (HAGT). This process involved the aquatic plant Eichhornia crassipes commonly known as Water Hyacinth which was cultivated and harvested in ponds loaded with the 100kg of gold-bearing tailing sample. In the 2 nd process, the harvested Water Hyacinth was introduced into Microbe Incubated Bio Reactor (MIBR) where in the Hydrogen, Carbon, Lignin, Hemicellulose, Cellulose and Glucose contained in Water Hyacinth were converted to natural gas by methane-producing bacteria using a proprietary process called Microbe Incubated Bio-Reaction . In the 3 rd stage, which is the final stage, the gold Nuggetization process namely Microbial Enzymatic Gold Nuggetization (MEGN) was introduced to treat the product outcome from MIBR process. The MEGN process was very effective in extraction and concentration of gold. The MEGN process employed certain harmless non-pathogen microorganisms such as Cupriavidus metallidurans and Delftiaacidovorans which were cultivated by the authors in their laboratory. These microorganisms produced an enzyme called Cup A and Cop A which have the ability to convert gold compounds into their non-absorbable forms and accumulate or concentrate them in their exterior. The size of such accumulated gold compounds varied from a few microns to a few millimetres, hence are termed nuggets and the process is named nuggetization. The weight of such accumulated nuggets was a few micrograms to milligram. The net weight of the processed and dried Water Hyacinth from the first process (HAGT) was about 3.2 kg. A 100-gram sample of this was analysed for its efficacy. The concentration of metals especially gold and silver showed significant concentrations in all tissues of the plants. The analysis revealed higher contents of heavy metals such as Cadmium (Cd), Chromium (Cr) in the roots of Water Hyacinth, whereas significant concentration of Nickel (Ni), Lead (Pb), Cobalt (Co), Gold (Au), Silver (Ag), Silicon (Si) and Iron (Fe) were observed in shoots. Interestingly the content of Nickel was the highest. The gold concentration was 78mg/kg. The product of the 2 nd process (MIBR) was designated as the Super-Ore which weighed about 2 to 3 % of the net weight of the pre-processed water hyacinth. The Super-Ore was subjected to Nuggetization process (MEGN) when the concentration of gold increased from 78mg/kg to 120mg/kg as analysed by fire assay, whilst the quantity of super-ore got reduced. Thus, the gold present in the 100 kg of tailing was accumulated through water hyacinth, converted to a “super-ore” and nuggetized.