Mode of Occurrence and Mineralogy of Northern Khetri Copper Deposits, Jhunjhunu District, Rajasthan

Copper deposits in Khetri copper belt are hosted in the proterozoic sequence of rocks belonging to Ajabgarh group of Delhi supergroup situated in foot hill zone of Aravalli mountain range North-West, India. Khetri copper belt is about 100 km long NE-SW trending metallogenic province, starting from Singhana in the north to Sangarava in the south. The study area is the northern Khetri copper belt 190 km SW of Delhi, the capital city of India. In the present work an attempt has been made to determine the mode of occurrence and nature of mineralization with special emphasis on mineragraphic study of copper ores. The ore bodies are found in the form of multiple lodes regionally but locally in the forms of veins, stringers, dissemination, sporadic, cavity filling and replacement. Enriched mineralized zones are localized along the contact of Alwar and Ajabgarh group. Copper, the main entity in the belt occurs dominantly as sulphides, oxides, carbonates and sulphosalts mineral hosted in pelitic and psammitic rocks. Pyrrhotite, pyrite, magnetite and sphalerite are the other ore mineral associated with the copper ore in a considerable amount. From the textural, structural and multigenerational minerals, mineral assemblage studies, it is assumed that deposit has undergone metamorphism and multi-stage mineralization. Replacement has a profound influence on mineralization in the northern Khetri copper deposits.


Introduction
Copper is most important base metal used in various industries due to its high 75˚44'), Chandamari (27˚56': 75˚46') and many other described by [1].The present study is pertained to these deposits.At present Kholian and Madhan-kudhan (Khetri Mine) are the only two underground productive mines in the study area.The principal sulfide ore minerals in the northern Khetri copper deposits are chalcopyrite, pyrrhotite, and pyrite [2]- [9] and [10].Copper minerals in subordinate amount include cubanite, tetrahedrite, azurite, malachite and chalcocite etc.Other associated ore minerals are magnetite, sphalerite, ilmenite, arsenopyrite, molybdenite, cobaltite, pentlandite, marcasite, zircon, mackinawite and sulphosalts.Though the area is under intensive investigations from a long time, the complete mineralogical appraisal of copper in these deposits and a comparative description are lacking.In the present work an attempt has been made to lay emphasis on the mode of occurrence and mineralogy of Mudan-Kudan (Khetri), Kolihan and Chandmari copper deposits.

Geology and Structure of the Study Area
Regionally, the study area is a part of Delhi Supergroup.[11] divided this Supergroup into South Delhi Fold Belt (SDFB) and North Delhi Fold Belt (NDFB).
The division based on the purported diachronous nature of sedimentation and granite magmatism in the two belts.According to [12] and [13]  eastern part of the NKCB are inferred to have been deposited under shallow marine conditions inferred from the preserved sedimentary and syn-sedimentary deformation structures like ripple marks current bedding mud cracks, load cast and convolute laminations etc. while those in the western side are of relatively deep marine origin [7] and [21].The rocks of the NKCB are multiply deformed and polymetamorphosed [14] [16] [22] [23] [24].Three generations of folds, F1, F2 and F3 are identified, of which F1 and F2 are co-axial in many places, and the axial trace of F3 is at high angle with the former [2] and [24].Three different phases of deformation have been recognised.The temperature and pressure conditions during M1 and M2 have been inferred to be 550˚C ± 50˚C and 550˚C -650˚C with pressure range of 3 -5 Kb during the M1 and M2 phases, respectively [7] [22] [23].The M 3 retrograde event marked by chloritization, biotization and sericitization at the garnet, amphibole, carderite and andalusite [1].The last metamorphic event has been dated at 950 -910 Ma through chemical dating of monazite [19] and [25].

Methodology
About 50 samples of ore were collected from Mudhan-Kudhan (Khetri), Kolihan and Chandmari mine.The collected samples were megascopically examined and from each collected sample polished block was prepared in accordance of [27] in the Department of Geology AMU., Aligarh.The final polished blocks studied in reflected light under the ore microscope in the Department of Geological Sciences, Jadavpur University.Six selected samples of ores from different locations were powdered to 200 mash size.An X-ray diffraction study was carried out in the Department of Mechanical Engineering AMU, Aligarh.The peaks were observed from 5˚ to 90˚ with step size of 0.05/Second.Raw data is interpreted in X-pert High Score Plus and finally plotted in Origin 8.5.

Madhan-Kudhan (Khetri) Deposit
Madhan-Kudhan mine is the largest underground metal mine in the country.Mine workings extend over a strike length of about 3.6 km.The ore bodies occur as series of discontinuous layers sub-parallel lodes (Figure 1(aa') cross section).

Kolihan Deposit
The total mine development work has been carried out in mine is 1, 03, 123.20 meters and the mine has produced 189, 53,441 tonnes @1.37% Cu. till 31.03.2013[28].The economic concentration of ore at Kolihan-Chandmari mine is around 40 million tons @1.12% -1.71% Cu, 0.2 -0.6 g/t Au and 2 -8 g/t Ag [26].This is the first mine in India which was developed on trackless and ramp system of mining.The Kolihan Copper Mine has been developed over a strike length of 700 metres and has eight levels at vertical interval of 60 metres.Ore bodies occur similar to Madhan-Kudhan (Khetri) mine in the form of lodes (Figure 1

Chandmari Deposit
Chandmari area (Latitude 26.000N; Longitude 75.046E) is located 1 km north west of Khetri town.The rock formations of the area belong to the Alwar and Ajabgarh groups of the Delhi Supergroup.The main rock types outcropping in the area are andalusite-biotite-quartz schist, phyllite, amphibole quartzite, talc-magnetite-amphibole-schist and felspathic quartzite [29].Quartz veins and Natural Resources

Mode of Occurrences
Geologically copper mineralization is reported in the Alwar and Ajabgarh series of rocks of Delhi supergroup [1] [15] and [7] the extent of mineralization is relatively wide in the ajabgarhseries.The Copper ore deposits of Khetri have been Natural Resources reported to occur all along the belt with highest potential in the khetri town in the northern part of the belt.In most places their presence was indicated at the surface by the occurrence of gossans consisting of oxidized ores of copper and iron having stains of malachite and azurite, boxwork of lenticular limonitic or red ochre bands [1] and [30].Major copper ores, association and mode of oc- The mineralization, however, is not confined to any particular rock type of either of the two series.Local as well as regional shift in mineralization is common in this belt.Passing further south, the occurrence of copper has also been reported from the biotite-schist, phyllites and amphibolites [32].

Chalcocite
Chalcocite is opaque and dark-gray to black with a metallic lustre and shiny black to lead gray lustre.It has a hardness of 2.5 -3 and specific gravity around 5.5 -5.8.Chalcocite is found in the samples collected from the deeper levels of the underground madhan-Kudhan (Khetri) and Kolihan mines and did not traced in samples collected from Chandmari area.Chalcocite is reported as secondary mineral formed from the alteration of other minerals like chalcopyrite, pyrite, covellite and bornite.It occurs as bluish white colour, fine grain aggregate, most commonly along the boundry of chalcopyrite grains (Figures 3(a)-(c)).

Bornite
Bornite is brown to black with a typical purplish to bluish tarnish, a reddish bronze colour on freshly broken surfaces.It is opaque with metalliclustre and greyish black streak.Its striking iridescence gives it the nickname peacock copper or peacock ore.Hardness is around 3 and specific gravity is approximately 4.9 to 5.3.Good crystals are rare and thus bornite is commonly known as simply a massive ore mineral.Bornite has pinkish brown to orange colour, weak anisotropism and slight bireflectence which is visible on grain boundaries.It shows a common association with chalcopyrite (Figure 3(a)).

Cubanite
Cubanite is bronze to brass yellow colour in appearance.It has metallic lustre with black colour streak.Its hardness varies from 3.5 -4 while specific gravity is 4.0 -4.2.It commonly occurs as elongated to thick tabular crystals.[5] described three types of cubanite in the Kolihan mine as isometric, tetragonal, and orthorhombic cubaniteon the basis of optical properties.Isotropic cubanite is similar to cubanite II of [33].The first two varities are similar to chalcopyrite.The exsolution lamellae of cubanite are commonly found in chalcopyrite.One or two set of cubanite lamellae (Figure 3(f)) exsolve along (III) planes is well known [34] [35] and [36].

Tetrahedrite
Tetrahedrite is a copper antimony sulfosalt mineral which is isotropic and ligh-grey in colour.It is the antimony end member of the continuous solid solution series with arsenic-bearing tennantite.High peaks of tetrahedrite are observed in the X-ray diffraction studies of copper ores.Fe-and Zn-bearing tetrahedrite-tennantite solid solutions are common constituents of polymetallic base metal sulfide deposits [37] [38] [39] (Wu and Petersen, 1977;Einaudi, 1977;Knight, 1977).Tetrahedrite is found to be associated with chalcopyrite in replacement relationship and generally found along the boundaries of chalcopyrite and pyrrhotite (Figure 3

Azurite
Azurite is transparent to translucent, azure blue coloured, soft copper ore.It has pale blue Streak and vitreous to sub-adamantine lustre.Hardness ranges from 3.5 -4 with specific gravity around 3.70 to 3.90.It was reported by [40].It is a secondary mineral produced by weathering of primary sulphides and found in the oxidized zone of copper ore deposits.It occurs in association with chalcopyrite and pyrrhotite (Figure 2(d)).Its individual specimen is not found but can be visualise in hand specimens in association with chalcopyrite, chalcocite and pyrrhotite.

Malachite
Malachite is a green copper carbonate hydroxide mineral with a chemical composition of Cu 2 (CO 3 )(OH) 2 [41].Malachite is rarely found as a crystal.
Non-crystalline specimens are opaque, are bright green in colour, usually with a dull to earthy lustre.Malachite has high specific gravity that ranges from 3.6 to 4.0 and hardness ranges from 3.5 to 4.0. it generally occur as botryoidal coatings and as a secondary mineral transformed from other sulphides (Figure 2(f) and

Cuprite
Cuprite is a minor ore of copper occurring as secondary mineral in the oxidized zone of copper sulfide deposits.It frequently occurs in association with native copper, azurite, chrysocolla, malachite and a variety of iron oxide [42].It has distinctive red colour, sub-metallic to brilliant adamantine lustre, about 3.5 to 4 hardness and a relatively high specific gravity of about 6.1.It is found associated with chalcopyrite and chalcocite in garnetiferous quartz chlorite schist (Figure 2(b)).

Results and Discussion
Mineralization in the khetri copper deposits occurs as multiple lodes of varying shapes and dimensions are localized in medium grade metamorphosed pelitic and psamitic rock units [2] and [7].A polymetallic type of mineralization has been found in the study area and IOCG type of mineralization is ascertained due to its characters analogous to IOCG-type deposits of the world (Knight et al.,

Paragenesis
The main ore minerals are chalcopyrite, pyrrhotite and pyrite.The textural relations observed andearlier study [5] it appears that there are two principle generations of sulfide minerals and are referred here as hydrothermal phase I and II.
The dominant sulfide minerals in both the phases of mineralization are chalcopyrite and pyrrhotite.In addition to these two minerals there are other minerals formed by exsolution.
The two phases of mineralization are separated by an interval manifested by invasion of carbonate-bearing solutions, during which pyrrhotite of the first generation has been converted into pyrite and marcasite [5].Due to the complex deformational history, multiphase mineralization, missing of certain phases locally as well as regionally variable controls on mineral localization and diverse nature of mineralization, complete paragenetic sequence cannot be developed for the northern Khetri copper deposits.However the different assamblages observed are tabulated in Table 1.
Table 1.Mineral assemblage of ore minerals in Mudhan-Kudhan (Khetri), Kolihan and Chandmari mine and various associations observed in the polished blocks and X-ray diffraction studies.

Conclusion
In the Khetri deposits mineragraphic and XRD study of ores reveals a diverse nature of mineralization.Ore bodies occur as multiple lodes of varying size and How to cite this paper: Ahmed, M., Shaif, M., Siddiquie, F.N. and Khan, R. (2018) Mode of Occurrence and Mineralogy of Northern Khetri Copper Deposits, Jhun-M.Ahmed et al.DOI: 10.4236/nr.2018.912024390 Natural Resources conductivity, strength and durability.Its crustal abundance is 60 ppm.It occurs in native form but mostly in association with sulphur, oxygen, carbonates and other transition metals as sulphosalts.Khetri copper belt is a 100 km long NE-SW trending located in NDFB of Aravalli Mountains.This belt is named after Khetri town where most enriched mineralization is traced.Khetri copper belt is the largest copper ore repository in India.This study is constrained to the northern part of Khetri copper belt.The important localities in the northern part of the area are Madhan-Kudhan (Khetri) (28˚4'15": 75˚47'25"), Kolihan (28˚:

Figure 1 .
Figure 1.(a) Location of Khetri copper belt in Aravalli mountain range in the map of India.(b) Geological map of study area showing the sample collection sites (modified after [9].a-a', b-b'and c-c' are the cross sections of Mudhan-Kudhan (Khetri), Kolihan and Chandmari Ore bodies (after [26]).
(bb')    Cross section) constrained to garnetiferous-quartz-chlorite schist and amphibole bearing feldspathic quartzite (Figure2(b) & Figure2(d)).The rock exposures around the Kolihan mine shows traces of malachite and azurite.The surface area of Kolihan mine is subsiding due to the presence of highly sheared phyllite bed along the lodes of ore bodies.

Figure 2 .
Figure 2. Photographs showing mode of occurrences and mineral associations from northern khetri copper deposits Jhunjhunu dist.Rajasthan.(a) shows sharp contact of chalcopyrite with host rock, (b) shows chalcopyrite and cuprite in garnetiferous quartz chlorite schist, (c) showing sporadic occurrences of chalcopyrite in amphibole quartzite, (d) showing the association of chalcopyrite with pyrrhotite and azurite, (e) shows vein of chalcopyrite in feldspathic quartzite, (f) shows the alteration of chalcopyrite into malachite.
(c) & Figure 3(e)) as fine aggregate or crystal intergrowth.In on sample it is documented as replacing arsenopyrite and infillings M. Ahmed et al.DOI: 10.4236/nr.2018.912024397 Natural Resources along the fractures in arsenopyrite.

Figure 3 (
Figure 3(b)).It occurs in association with chalcopyrite, pyrite, and azurite in the samples collected from Kolihan and Chandmari copper mine.
2002).According to[43] the Cu-(Au) mineralization is contemporary with regional Ca-Na metasomatism in the Khetri Copper Belt, which was accompanied by significant mobilization of certain metals and may facilitate the formation of Cu-(Au) ore.Khetri area has the highest potential for copper ores and slag heaps at different location representing the traces of ancient copper mining in the area.Ore body in the study area occurs regionally as lodes, hand specimens and cross M. Ahmed et al.DOI: 10.4236/nr.2018.912024398 Natural Resources sections as veins, stringers, disseminations and sporadic.Khetri copper deposits are sulphide deposits with minor proportion oxides, carbonates and silicates ore minerals.The general features of ore minerals in hand specimens and mineral assemblage, nature of mineralization and mode of occurrence documented shows a multistage of mineralization.The complete mineral assemblage observed in hand specimens, polished blocks and X-ray diffraction studies (Figures 4(a)-(f)) of the ore samples is tabulated in (Table1).
shape.Mineralization is not constrained to any single litho-unit.The structures like joints, faults and fractures have dominant control over mineralization.Ore minerals occur as veins, stringers, disseminations, stock works and fracture fillings.Chalcopyrite is the main copper ore in the Khetri copper deposits.Cubanite, chalcocite, covalite, azurite, tetrahedrite, malachite and numerous Copper sulphosalts are also found associated with chalcopyrite.The mode of occurrence of ore and various textures and structures in the NKCB reveals that the deposit is formed as a result of hydrothermal solution and later on altered by metamorphism.Copper deposits in the northern part of the belt are associated with number of other metal ores of Co, Zn, Ni, Ag, Au etc.