EXPLORATION SCENARIO FOR COPPER LEAD AND ZINC IN INDIA

Overview of Copper, Lead and Zinc Exploration in India

India holds substantial reserves of copper, lead and zinc, which are primarily located in the regions of Rajasthan, Jharkhand, and Madhya Pradesh. Despite having significant reserves, the exploration intensity, measured by exploration expenditure per square kilometer, is relatively low compared to global standards. This indicates substantial growth potential in exploration activities.

India's relatively low expenditure per square kilometer can be attributed to several factors including less intensive exploration activities, regulatory challenges, and sometimes the focus on expanding known deposits rather than greenfield exploration.

Exploration Efforts

India is deficient in its resources for base metal and has a poor resource-cum reserve base despite having the geological potential for large resources. The scarce resource base for base metals needs special attention for their exploration as they consume a lot of foreign exchange for their imports.

A strategy has to be evolved for an integrated approach towards exploration of these minerals. Data generated in course of geological mapping activities has helped GSI in identifying favorable geological domain (OGP) for base metal mineralisation over an area of 192606.49 sq. km area in India. GSI has renewed its efforts for systematic exploration for base metals throughout the country by focussing on the OGP areas in various states.

An area of 1.926 lakh sq. km (0.19 million sq. km) area has been delineated in the year 2020 to be potential for base metal occurrence in the country based on distribution of more than 200 prospects, nearly 920 occurrences of base metals, genetic association, geological set-up etc. The base metal potential areas are distributed in the States of Rajasthan, Karnataka, Gujarat, Madhya Pradesh, Jharkhand, Chhattisgarh, Odisha, Arunachal Pradesh, Andhra Pradesh, Maharashtra, West Bengal, Uttar Pradesh, Goa, Haryana, Kerala, Tamil Nadu, Manipur, Telangana, Himachal Pradesh, Sikkim, Meghalaya, Nagaland, Jammu & Kashmir, Bihar, Assam and Uttarakhand in the order of extent of geologically potential areas.

Copper, Lead and Zinc exploration projects by GSI since 2012
Year	No. of Projects
2012-13	22
2013-14	41
2014-15	67
2015-16	92
2016-17	117
2017-18	150
2018-19	187
2019-20	244

Resources:

Copper

The total resources of copper ore as on 1.4.2015 (as per IMYB 2018) is estimated at 1.51 billion tonnes as per UNFC system. Of these, 207.77 million tonnes (13.74%) fall under 'reserves'. Of the total ore resources, 8.28 million tonnes (0.55%) comprise ore containing 1.85% Cu or more and 657.92 million tonnes (43.53%) 1% to below 1.85% Cu grade. With regard to reserves, there were no reserves above 1.85% Cu grade. However, 203.83 million tonnes fall under 1.0% to below 1.85% Cu grade.

The total copper metal content in the resources is 12.16 million tonnes of which 2.73 million tonnes constitute reserves. Largest resources of copper ore to a tune of 813 million tonnes (53.81%) are in the state of Rajasthan followed by Jharkhand with 295 million tonnes (19.54%) and Madhya Pradesh with 283 million tonnes (18.75%). Copper resources in Andhra Pradesh, Gujarat, Haryana, Karnataka, Maharashtra, Meghalaya, Nagaland, Odisha, Sikkim, Tamil Nadu, Telangana, Uttarakhand and West Bengal accounted for remaining 7.9% of the total all India resources.

Lead-Zinc

The total resources of lead and zinc ores as on 1.4.2015 as per UNFC system, are estimated at 749.46 million tonnes. Of these, 106.12 million tonnes (14.16%) fall under 'reserves' category while balance 643.34 million tonnes (85.84%) are classified as 'remaining resources. The resources of ore containing + 10% Pb & Zn were estimated at 124.23 million tonnes, ore containing 5 to 10% Pb & Zn were 329.88 million tonnes and ore containing less than 5% Pb& Zn were 295.35 million tonnes.

The total metal content in resources of lead is 13 million tonnes Lead and that of zinc is 36.36 million tonnes and for lead zinc metal is 0.14million tonnes. In terms of reserves, 2.48 million tonnes of lead metal and 9.99 million tonnes of zinc metal have been estimated. Rajasthan is endowed with the largest resources of lead-zinc ore amounting to 670.34 million tonnes (89.44%), followed by Andhra Pradesh 22.69 million tonnes (3.03%), Madhya Pradesh, 14.84 million tonnes (1.98%), Bihar 11.43 million tonnes (1.52%) and Maharashtra 9.27 million tonnes (1.24%). Resources are also established in Gujarat, Meghalaya, Odisha, Sikkim, Tamil Nadu, Uttarakhand and West Bengal (IBM YB 2019).

Planning for the next five years should involve exploration strategy to

1. Discover deeper extensions (>500m) of known deposits and prospects and also to identify potential mineralization under cover. Application of 3D seismic and magneto-telluric surveys which are increasingly used to discover base metal mineralization >300m from the surface.

2. For regional-scale, an integrated approach involving geology, geochemistry, remote sensing and aero geophysical data, with focus on volcano-sedimentary sequences of Archean and Proterozoic age can help delineate zones for more detailed exploration. A first order empirical guide will be to prioritize areas with altered submarine volcanic rocks for VMS deposits and carbonate-associated sedimentary sequences for SEDEX and MVT-type deposits. For vein-type and intrusion-related Cu-mineralization younger granites of calc-alkaline affinity should be seen as source rocks.

3. Focus on large greenstone belts and volcano-sedimentary belts for VMS, SEDEX and intrusion related base metal deposits. For example, Central Indian Tectonic Zone is important with several volcanic and sedimentary sequences such as Betul Belt, Sausar Belt and Mahakoshal Belt.

4. Emphasis on Archean Dharwar greenstone belts for Cu-Au VMS deposits and younger calc-alkaline granitoids for porphyry-type Cu ± Au ± Mo deposits.

5. Search for base metal deposits in the Archaean cratonic part of Jharkhand - Odisha region and Singhbhum shear zone.

6. Margins of Archean Cratons like Bastar, Dharwar and Bundelkhand to search for IOCG-type mineralization

7. The Aravalli-Delhi belt still remains one of the most prospective terrain for discovering large VMS, SEDEX and IOCG-type deposits. The exploration strategies for these areas should involve targeting concealed mineralization through potentially covered unconsolidated sediments of a general thickness of 80m to 150m.

8. New exploration strategies are to be applied to the covered terrains (greenfield areas) for the entire concealed part of Rajasthan State to expand mineral search space for base metal mineralization by carrying out techniques being evolved in UNCOVER (India), a northern transect.

9. The selective greenfield targeting projects for the covered terrains of the Western Region should involve the creation of buried topography, predictive geological maps, distal foot printing of mineralization, application of integrated geoscience and mineral systems in the covered terrains of the Western Region and later to other areas.

Exploration Opportunities

Augmentation of copper ore resources in the country can be achieved through further inputs for intensive exploration with an aim of firming up and upgradation of reserve figures in known prospects and in the extension areas of the known or established deposits. The three prominent belts, where copper deposits are located include Singhbhum Copper Belt (SCB), Khetri Copper Belt and Malanjkhand Copper Belt. In Rajasthan, copper mineralisation is mainly associated with Delhi Supergroup. Many occurrences of copper have been recorded in the basement rocks as well. Some copper prospects are located in the lead-zinc belts associated with the Aravalli rocks. In central India, search for granite host rocks similar to Malanjkhand with Mesoproterozoic age and calc-alkaline signatures can be a potential tool.

Obvious Geological Potential Areas for Copper, Lead and Zinc
States	OGP Areas (in sq. km)
Rajasthan	67995.71
Karnataka	35572.67
Gujarat	12948.79
Madhya Pradesh	12144.29
Jharkhand	10227.95
Chhattisgarh	8781.29
Odisha	6574.91
Arunachal Pradesh	6354.49
Andhra Pradesh	6336.41
Maharashtra	5174.21
West Bengal	3010.54
Uttar Pradesh	2795.89
Goa	2361.73
Haryana	2346.9
Kerala	1440.42
Tamil Nadu	1302.37
Manipur	1135.36
Telangana	1093.11
Himachal Pradesh	1033.86
Sikkim	992.04
Meghalaya	852.86
Nagaland	712.98
Jammu & Kashmir	454.42
Bihar	288.44
Assam	224.27
Uttarakhand	90.83
All India OGP-2020 for Base metals	192606.49

 

Keeping in view the prospects, future targets of exploration for copper and associated metals may be identified in Dariba-Bethumbi Belt, Jahazpur Belt, Pur-Banera Belt for copper-lead-zinc-gold, Jasma-Akola-Bhinder Belt, parts of South Delhi Fold belt, South Khetri Belt, Ajmer metallogenic district and Salumber-Dhariwad belt in Rajasthan and in extension areas of South Delhi Fold Belt in Gujarat. The South Khetri Copper Belt is relatively less explored.

Most of the lead zinc mines of the country occur in the Proterozoic fold belts in the western Indian shield. In the Precambrian shield of the western India as well as in the other shield areas, several smaller and medium grade lead-zinc deposits have been identified and explored. A number of occurrences of leadzinc have been recorded from the Himalayan region, particularly in the Lesser Himalayan Zone, comprising Precambrian rocks, tectonically disturbed and deformed during the younger mountain building movements. The application of modern exploration techniques with emphasis on airborne and deep – probing geophysical methods may help in identifying new deposits in the above area. There are several occurrences associated with greenstone sequences in Dharwar Craton (Kalyadi, Ingaldhal etc). Base metal deposits are also known in the Cuddapah sedimentary rocks (Agnigundala, Zangamrajapalli, Markapur etc). Fault-related copper-mineralization is known to occur in the granitic terrain of eastern Dharwar Craton (Tintini, Kalluretc). Extension of these areas has to be studied in detail.

Potentially covered large terrains of Western India over the North Delhi Fold belt, Aravalli Region is essentially a key Region giving the opportunity for the next generation of base metal mineral deposits in the country. In these areas the targeted Geoscience Goals should include,

1. Basement surface elevation or buried topography.
2. Exploring effectively and efficiently through cover.
3. Managing drill hole data and magnetic data for mapping through the cover.
4. Preparation of predictive geological maps and tracing concealed structures.
5. Groundwater and Calcrete studies for distal foot printing of mineral deposits.
6. Subsurface movement of groundwater and its possible linkages with mineral belts, host lithology, delineating buried rock type, etc.
7. Understanding mineral dispersion through cover.
8. Designing and progressing efficacy of geochemical sampling techniques in buried terrains.
9. Establishing links to magnetic/ gravity anomaly in the subsurface with secondary dispersion record in calcrete, groundwater, lithology etc. and deriving metallogenic implications.
10. Exploratory drilling and characterizing geophysical domains and updating the predictive geological and buried topography map of the area in the second year of the project.

With an objective to deliver,

a.     First hand buried topographic map.

b.     First hand predictive geological map of buried terrain.

c.     Making of structural interpretive map by integration geoscience.

d.    Distal foot-printing of geochemical anomalous zones in buried terrain.

e.  Declineation of areas for furthering dense geophysical and geochemical data acquisition by integrating geoscience.

f.   The exploratory drilling is expected to lead in bringing out new buried belts, extension of known mineral belts below cover etc.

g.  These works will result in exploratory drilling to decipher the areas for characterizing geochemical, geophysical signatures to increase the chance of concealed mineral deposits.

Challenges

Exploration:

The discovery of new deposits based on surface indications will be extremely remote considering that most known areas have already been explored. The challenge is to find base metal deposits in new areas/ concealed terrain within volcano-sedimentary sequences and those associated with intrusive rocks. This will require the acquisition of high-resolution aeromagnetic data and its integration with other geological and ground-geophysical data. Also, modern concepts of mineral systems and their understanding is crucial in identifying potential terrains. Researching and mineral targeting in green field regions is vital in the country. Discovering new deposits/area is essential requirement to keep continuous supply of minerals to fulfill country’s needs. Selecting the most suitable area, geological field and terrain will assist in making the exploration easy, cheap and quick. Geophysical study plays a vital role in exploration of buried ore deposit.

Geophysical exploration may be used with advantage to locate boundaries between different elements of the subsoil as these procedures are based on the fact that the gravitational, magnetic, electrical, radioactive or elastic properties of the different elements of the subsoil may be different.

A large part of basement areas of Rajasthan, Gujarat, Haryana, Uttar Pradesh etc., are covered with unclassified sediments posing challenges to the mineral exploration geoscientists. Geological basement favorable for mineralization in parts Rajasthan are mostly covered with windblown sand having variable thickness. Generally, the thickness of cover sediments is thinner near outcropping areas and the depth of cover range from 80m to 150m in parts of Churu, Jhunjhunu, Sikar, Alwar districts of Rajasthan. The basement geology of major parts of Gujarat, Uttar Pradesh, Haryana, Bihar is masked with unclassified sediments.

Processing and Analysis

Since base metals are associated with a wide-range of associated ore metals it is important to have high-quality analytical support for analyzing the entire spectrum of associated trace elements. These trace elements form important by-products and add value-addition to the primary ore assemblages. High precision ICP-AES analyses is essential for low concentration (ppm) levels.

Beneficiation:

As per SOP, the mineralized cores are sent for beneficiation studies to the Mineral Processing Laboratory like IBM for beneficiation study to understand the metal recovery from a particular ore type. About 50-100 kg of each mineralized core samples having assay above cut off values is to be collected for bench scale beneficiation study with an objective to assess the feasibility of Cu, Pb or Zn up- gradation suitable for smelter. Bond’s ball mill work index of the host rocks is to be determined at the ground product -150# (-105 microns), which is the product size as per BWI standard procedure (DID base metal2012).

Beneficiation of base metals face several constraints including 1. Complex nature of ores, 2. intergrowth of silicate and ore, 3. Presence of deleterious elements like graphite etc. In this scenario, the beneficiation is more or less custom-made for individual mines and plants taking into account the nature of ore and associated gangue minerals.

Copper ore from the mine is processed to yield copper cathodes which are basically 99.99% pure copper. Common type of copper ore is copper oxide and copper sulphide, which undergo different processes. Copper oxide is processed through hydrometallurgy whereas, copper sulphide is processed through pyrometallurgy. Lead and zinc ores are pre concentrated by gravity methods, employing heavy mineral separation, jigging and tabling depending on liberation size and ultimately concentrated by xanthate flotation. Usually lead sulphides are selectively floated from the ore followed by activation and separation of zinc in case of complex lead-zinc ores. Bulk flotation followed by separation of lead and zinc differential flotation is not uncommon.

Mineralogical characterization:

A complete and comprehensive analyses and characterization of the associated ore minerals and alteration assemblages are vital to develop exploration strategies in existing prospects/mines as well as regionally to select areas for more detailed exploration. Petrographic studies of the host rocks and the ore mineral assemblage bears significant role in understanding the nature and control of mineralization in a particular mineral system. Besides these, the paragenetic sequence, textural relationship and ore mineral assemblages tell a lot about the deposit type and genesis of the ore deposit. Ore mineral assemblages of a deposit and their geochemistry have great significance in describing the type of depositional environment. SEM/EPMA studies of ore assemblage will help in identifying trace elements, for example, to identify presence of Au, Ag, Re, Pt, Pd in Cu-rich porphyry systems. It is well-known that several alkaline porphyry copper deposits are sometimes also enriched in Pt-Pd, which can be recovered as valuable by-products. LA-ICP-MS analyses of sulphides are increasingly used to understand ore-genesis, thereby facilitating the fingerprinting of depositional processes and mineral system type. This can be effectively used as a rapid assessment tool in base metal exploration to distinguishing economically important prospects/zones from those of relatively lesser significance.

Future Research & Development

The mineral system concepts and models can be translated into effective exploration targeting criteria and serve as the basis of forceful, testable exploration models. Base metal deposits are predominantly hydrothermal in nature and mineral system concepts of source, driver, pathway and depositional gradients are particularly pertinent. In this scenario, emphasis should be laid on mineral-system wise targeting. In Indian scenario, mineral system classification is having not gained much importance and application. Initially, all known deposits and prospects should be re-assessed from the point of modern basis of classification schemes. A mineral-system scheme provides important clues and proxies for extending exploration regionally (district-scale) as well as locally (deposit-scale).

 

References:

1.       A Brief on Exploration for Base metal Mission in India – 2020 – GSI Publication

2.       Mineral Exploration in India at a Glance -2020 – GSI Publication