GENESIS OF HIGH GRADE IRON ORE FROM BIF IN DALLI-RAJHARA, CHHATTISGARH, INDIA

Abstract

Iron is one of the most important metal used in the world mainly for iron and steel industry to meet the requirement in infrastructural development. For the purpose it requires the high grade iron ore more suitably lumpy ore without any other deleterious elements like silica, alumina and phosphorous which is readily get attached to iron ore from its protolith in the nature. The iron ore occurs in varied geological environment such as sedimentary, hydrothermal and magmatic origin. However, World’s most high-grade iron ore deposits are associated with Banded Iron Formation (BIF). Unlike other protore rocks for metallic minerals deposits BIF itself consist of 30-35 wt percentage of iron (Klein 2005). BIF then upgraded to high grade iron ore (>64 wt. % Fe) through complex geological processes. This process of upgradation may take place geologically rapid < 5million years as established for many hydrothermal systems (Chiaradia et. al., 2014) or it may be as long as 100 million years. In case iron ore is further upgrade by weathering/supergene processes, which is mostly took in last 20 million years (Angerer et. at., 2014). India is also one of the leading producer of iron ore. Nearly all major deposits of high-grade iron of India occurs in association with BIF of all four major Cratonic areas. The Banded Iron Formation is popularly known as BHQ/BMQ/BHJ/ BMJ in India. The iron ore distribution in India has been classified in following five zones (designated as Zone-A to Zone- E) The study area for this work is Dalli-Rajhara, which lies in the zone-B. Several major iron mines occur in the Dalli –Rajhara Iron ore belt, which is the northern extension of Bailadila iron ore group of Bastar Craton in Chhattisgarh, where metamorphosed and heterogeneously deformed Banded Iron Formation (BIF) is regionally called Banded Hematite Quartzite (BHQ), was transformed into high-grade (Fe >64%) hematite ores. The area has been chosen because of the suitability of development of diverse kind of high-grade iron ore at one place and it also been academically less studied The objective of the present study mainly focus on the systematic change in mineralogy and geochemistry while enrichment from least BIF into high-grade iron ore. The characteristic and source of fluid responsible for this selective leaching. In addition, response of Au, Ag, PGEs during the process of high-grade iron ore formation. Based on hardness, two distinct type of high-grade iron ore are occurred in mines; hard and soft ore. Both the ore type having the laminated and massive textures. All the mine are mainly ii dominated by laminated ore from very hard to soft nature. Despite of various hardness and textural variation, mineralogically the ore are monomineralic i.e. hematite and martite (a low temperature pseudomorph of magnetite). Hematite grains are having several habits such as granular, tabular to anhedral. Gangue minerals are rarely present in hard ore, in soft are there may be presence of some Mn-oxide and ferrihydrites such as goethite and lepidorocite in micropores. Chemically high-grade iron ore either hard or soft entirely composed of Fe2O3 with a minimal presence of SiO2 but Al2O3 and phosphorous is seldom present in soft ore. Both the ore types are depleted in trace elements. The high-grade iron ore of Dalli-Rajhara show dual phenomenon of ore genesis; hypogene as well as supergene processes. The occurrence of hard massive iron ore within unaltered BHQ is the signature of hypogene process and presence of core stones (undigested BHQ) within soft ore marks the incomplete leaching of silica by meteoric water, as the silica is easily removed/leached in comparison to hematite. EPMA studies confirms the presence of precious metals such as Silver and Gold especially in pore spaces created while water circulation. These metals are present in BHQ as well as in ores; they are supposed to be more enriched in ores that are modified by supergene processes as they are resistant to chemical weathering. Trace elements concentration signifies that whole ore body is affected by supergene alteration. BHQ generally showing near to flat REE pattern having significant negative Eu anomaly but all the enriched iron ore showing some increase in LREE and positive Ce anomaly. There is two population of V concentration in massive as well as laminated ore signifies V concentration enriched in ores that are oxidized during meteoric alteration. Co and Cu remain in positive correlation with the Fe2O3. The fluid inclusion studies were carried out in some of the selected quartz vein samples collected from the ore zone. These veins are supposed to be precipitated during the mineralization/ enrichment. Based on petrography primary secondary and some of the pseudo-secondary inclusions are identified. Most of these inclusions are biphase aquous (Type I) another is liquid rich carbonic biphase inclusion (Type II). Only primary inclusion are taken into consideration in this study. The homogenization temperature of Type I inclusion is varies between 122-344˚C and salinity of Type I varies from 0.18- 35.41 wt. % NaCl equiv. XPS analysis of samples give some exciting result as it give good concentration of PGEs in BHQ and getting enriched in iron ores. The main PGE that is consistently present are Ru, Os iii and Pt. The presence of PGE in this deposit is being reported here at the first time. This requires an extensive study for scientific and economic purpose to be use the deposit for the future resource for the extraction of the PGE especially Platinum and Osmium. The iron ore deposits of the study area may also be defined as supergene modified hydrothermal iron ore deposit. The mineralization is normally found northern flank of the hills and the area has undergone atleast two phases of deformation, which created numerous easy passage for the circulation of meteoric water, causing an effective leaching of silica. Thus, a structural/ physiographic control is there for the localization of ore. Apart from the high-grade iron ore, the study area can be good a prospect for the economic resource of PGE in future.