Gold mineralization in the Hutti Mining Area, Karnataka, India. A reply

A polemic in reply to A. Roy (ibid., 450)​. The paper was intended to be a broad-​based summary of Au ore mineralization at the Hutti Mine (Karnataka, India)​. The main structural-​tectonic framework was earlier described by K. K. Raju (1978)​

Minerographic study of some of the sulfide ore from Ingaldhal, Chitaldurg district, Mysore state

Mineragraphic study of the ore samples collected from Ingaldhal Cu mines shows that the ore are largely massive, banded, and disseminated in structure. The primary minerals are pyrite, arsenopyrite, cobaltite, sphalerite, pyrrhotite, galena, and chalcopyrite and the secondary pyrrhotite, chalcopyrite, stromeyerite, bornite, chalcocite, and tennantite as secondary minerals are present. The ore exhibit inclusion, panidiomorphism, mutual boundary, exsoln., and replacement textures. From the mineralogical assemblage and the textures it is inferred that the ore deposits were formed at 350-​500°. The entire sulfide ore mineralization in the Ingaldhal area was brought about by hydrothermal processes, the pyrite ore exhibiting the sedimentary features being diplogenic

Minerographic study of some of the sulphide ores from ingaldhal, chitaldurg district, mysore state

Minerographic study of the ore samples collected from Ingaldhal copper mines shows that the ores are largely massive, banded and disseminated in structure. Pyrite, arsenopyrite, cobaltite, sphalerite, pyrrhotite, galena and chalcopyrite as primary minerals and pyrrhotite, chalcopyrite, stromyerite, bornite, chalcocite and tennantite as secondary minerals are present. The ores exhibit inclusion, panidiomorphic, mutual boundary, exsolution and replacement textures. From the mineralogical assemblage and the textures it is inferred that the ore deposits were formed inthe temperature range of 350°–500° C

Study of the nickel silicates associated with the ultrabasic rocks of Nuggihalli schist belt, mysore state

The occurrence of some nickel silicate minerals as encrustations along joint planes and shear zones of the chromite bearing ultrabasic rocks of Nuggihalli schist belt is described. Chemical and X-ray study shows besides amorphous nickel silicate, the presence of granierite, nepouite or nickel antigorite. The nickel minerals are secondary developed by the action of circulating waters. The source of nickel is olivine, in the structure of which Ni is known to be present, either as camouflaged or captured ion

Occurrence of cubanite and pyrargyrite in the sulphide ores of Ingaldhal, Chitradurga district, Mysore state

Cubanite occurs as small veinlets in chalcopyrite and as anhedral aggregates of small grains. Individual grains or aggregates are not common. Pyrargyrite occurs as unoriented grains in chalcopyrite. Cubanite was reported from liq. magmatic, pegmatitic, pneumatolytic, and hydrothermal veins. The presence of Cubanite in the S ores shows that the complex ore deposition is formed by hydrothermal process at temps. >250°. Pyrargyrite is an earlier mineral formed through the hydrothermal process

Water and nitrate exchange between a managed river and a peri-urban floodplain aquifer: quantification and management implications

The management of rivers for navigation, hydropower and flood risk reduction involves the installation of in‐channel structures. These influence river levels and can affect groundwater flow within hydraulically‐connected riparian floodplain aquifers. A comprehensively monitored, peri‐urban, lowland river floodplain in the southern United Kingdom was used to explore these dependencies and to examine the implications for the flux exchange of water and nitrate between the river and the floodplain alluvial aquifer. The study demonstrated that rivers maintained at high levels by management structures, result in raised groundwater levels in the adjacent aquifer and complex groundwater flow patterns. Engineered river management structures were shown to promote flow from river to aquifer through the river bed but the majority of the associated nitrate was removed in the hyporheic zone. High‐ nitrate groundwater recharge to the alluvial aquifer also occurred through overbank flood flows. Across the floodplain, substantial denitrification occurred due to anaerobic conditions resulting from carbon‐rich sediments and the shallow water table, the latter linked to the river management structures. An upper limit on the total annual mass of nitrate removed from river water entering the floodplain aquifer was estimated for the study site (2.9 x 104 kg), which was three orders of magnitude lower than the estimate of annual in‐channel nitrate flux (1.8 x 107 kg). However, this capacity of lowland floodplains to reduce groundwater nitrate concentrations has local benefits, for example for private and public water supplies sourced from alluvial aquifers. The insights from the study also have relevance for those considering schemes that include the installation, removal or redesign of river management structures, as the resultant change in groundwater levels may have consequences for floodplain meadows and the nutrient status of the aquatic system

Gold mineralization in the hutti mining area, Karnatake, India - A reply

Economic deposits of gold associated with sulfides occur in the Precambrian (Dharwar) rocks of the Hutti-Muski schist near Hutti village (16 degrees 12' N, 70 degrees 39' E) in the northern part of Karnataka State and have been exploited since 1904. The principal mine has produced about 22,500 kg of gold. The average yield, which was 19.49 g per ton of ore in 1920 has now decreased to an average of about 6.3 g per ton. The auriferous lodes, confined to the schist belt composed of metabasalts and massive chert bands, comprise vein quartz with parallel to subparallel, narrow, linear layers of chlorite-biotite schist. The entire schist belt has been intruded by granite and aplite in its western and northern parts. Of nine essentially parallel gold-quartz-sulfide lodes only six are being mined. The lodes are localized along narrow zones of highly sheared chlorite-biotite schist. Structurally the schist belt appears to represent an original isoclinal fold, with its axis striking north-northwest-south-southwest, which has suffered later cross folding. There is evidence of at least three periods of folding. The area is also traversed by a major postmineralization fault trending N 70 degrees W-S 70 degrees E. On a regional scale ore mineralization exhibits stratigraphic, lithologic, and predominantly structural controls. Mineralogically, the ores are composed of gold, sulfides, and oxides. The gangue minerals are quartz, chlorite, biotite, sericite, actinolite, hornblende, tourmaline, calcite, siderite, and ankerite. Textural studies indicate that in the first stage, rutile, pyrite containing inclusions of gold, arsenopyrite, specularite, quartz, and carbonates were formed. During the second stage, pyrrhotite, chalcopyrite, sphalerite, galena, and gold were deposited. During the last stage, pyrite, calcite, and quartz were formed. Further, the studies also suggest that gold deposition occurred mainly during the second stage. The gold occurs in the native state and contains silver up to a maximum of 9 percent, copper up to 0.05 percent, and traces of iron, nickel, and cobalt. Genetically, the gold lodes appear to have been formed by remobilization of the metals present in the mafic volcanic rocks during late periods of tectonic disturbance