6 Year Integrated M. Tech. Geotechnology and Geoinformatics
e-Learning Material
PAPER CODE: MTIGT0601
ECONOMIC GEOLOGY
Dr. J. SARAVANAVEL Assistant Professor Centre for Remote Sensing Bharathidasan University Tiruchirappalli- 620023 Email: [email protected]
e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. [email protected]
1 MTIGT0601- ECONOMIC GEOLOGY
1. Economic ore mineral deposits: Ore and gangue minerals – Hypogene (Primary) and Supergene (Secondary) deposits – concentration of elements in the crustal rocks - Classification of ore mineral deposits (Lindgren’s, Bateman’s and recent classifications). Metallogenic provinces and epochs – Distribution pattern of ore resources in the world – review of crustal evolution and metallogeny and evidences from Indian shield- Geologic Thermometry – Non isotopic methods – Direct and indirect methods – Isotopic methods – Principles of ore microscopy – microtextures of ore minerals and their significance.
2. Processes and environment of ore formation: Magmatic Deposits – Contact metasomatic deposit – Hydrothermal deposits- Sedimentary and residual deposits – Metamorphic deposits – Oxidation and supergene enrichment – Paragenesis of mineral deposits.
3. Physical properties, Chemical composition, mode of occurrences and Indian distributions of native elements and metals (Gold, Silver, Platinum), semi metals (Arsenic, Antimony) and non metals (Diamonds, Graphites) – Sulphides (Sphene, Molybdenite, Cinnabar, Aresenicpyrite, Stibnite, etc.) – Halites (halites, fluorite) – Oxides (Rutile, Corundum, Iluminite, Cassiterite, Columbite, Tantalite, Spinel, Franklinite, Chrysoberyl, Beryl) – Tungstates (Wolframite, Scheelite) – Talc, Steatite, Asbestos, Tourmaline.
4. Metaliferous deposits: Mineralogy, mode of occurrence and distribution of Iron, Manganese, Aluminium, Lead and Zinc, chromium and Gold in India.
5. Industrial Minerals: Mineralogy, mode of occurrence and distribution of minerals used for Abrasives, Fertiliser, Paint, Refractory, Glass, Ceramic and Cement.
e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. [email protected]
2 Text Books:
1. Bateman, AM and Jonsen, M.L., Economic mineral Deposits, John Wiley 2. Gokhale & Roa, Ore Deposits of India, Thomson press, 1972, 3. Krishnaswamy,S., Indian Mineral Resources, Oxford IBH, 1980,
References: 1. Alkinson, Ore Deposit Geology Chapman & Hall,1985 2. Craig, 1985, Ore Petrology and Petrography, Wiley, 1981. 3. Desppande M.L., Gemstones and Semiprecious stones. Indian Minerals, Vol-32 No.1 Geol. Survey of India Pub. 1978. 4. Iyengar, N.K.N. Mineral wealth of Tamilnadu, Madras Govt. 5. Karanth, K.V., Gems and Gem Industry in India, Geol. Soc., 2000. 6. Krishnan, M.S. Mineral Resources of Madras, Geology Society of India Pub. 7. Laford,S.J., Industrial minerals and Rocks, AIME Pub., 1975. 8. Lindgren, W, Mineral Deposits, McGraw Hill, 1942. 9. Nancy, & Ron Perry, Practical Gem Cutting, David & Charles, 1982. 10. Prasad, V., Economic Geology, CBS Pub., 1994. 11. Ram Dohr, P., Ore Deposits and their Relationship, Springer Verlaz, 1960. 12. Stanter, R.L. Ore Petrology, McGraw Hill, 1972. 13. Sinha RK & Sharma, N.L., Treatise on Industrial Minerals of India, Pub, 1967. 14. Subramanyan, K.S. Geology of Tamilnadu and Pondicherry, Geol Soc. India, Pub., 2001. 15. GSI, Geology and Mineral Resources of Tamilnadu, Geol. Survey of India Pub.
e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. [email protected]
3 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ECONOMIC GEOLOGY
e – Learning Material: Unit-1
ORE AND GANGUE MINERALS
4 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Economic Geology is an important branch of Geology which deals with different aspects of economic minerals being utilized by mankind to fulfill his various needs Economic Minerals are those which can be extracted profitably This subject deals with • Minerals and their origin •Processes of mineral formation • control of localization •Metalogenic epoch and provinces, etc.
What is a mineral?
A solid naturally-occurring compound having a definite chemical composition Examples:
quartz - SiO2 (an oxide)
hematite - Fe2O3 (another oxide) chalcopyrite - CuFeS (a sulphide)
5 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MINERAL DEPOSITS
The term Mineral Deposit refers to any accumulation of useful minerals of the mineral kingdom. Such deposit may be classified as metalliferous (Copper, lead) or non-metallic (Bauxite) The elements that enter into the constituents of the mineral deposits are derived either from the rocks of the earth crust or from the molten bodies (magma) Metallic Mineral Deposit: The concentration of metals in the deposit is called Metallic Mineral Deposit. These metals generally associated with other elements such compounds are said to be ore minerals
Non-Metallic Deposits: The non-metallic deposits consist of solids, liquids and gases. The term ‘ore’ is not generally used to refer such deposits. They called by the name of the substance itself such as Mica, Petroleum, Coal, Asbestos The unwanted material is simply called as ‘Waste’ and not as gangue The price is generally low compare to metallic deposit, they are common substances Except Gemstones, most of the non-metallic deposits are free of waste or little waste Feldspar, Barite, etc. have a considerable waste
6 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
What is an ore?
An occurrence of minerals or metals in sufficiently high concentration to be profitable to mine and process using current technology and under current economic conditions.
A high grade lead deposit in Antarctica may not considered as ore at present, since it can not be commercially utilized To be an Ore, there are two factors 1) The cost of production and 2) the market value Single ores contain a single metal and complex ore (ore minerals) consist of more than one metal Molybdenum – single metal in Molybdenite Chalcopyrite – Copper association with Iron and Sulphur
7 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Most ore minerals are combinations of metals with sulphur, oxygen and other non-metals Some metals like gold, plattinam, copper are occur in native form
Single metals may form many ore minerals or single metal can be extracted from the number of ore minerals. For example:- Copper as a native metal – Cuprite as a Silicate – Chrysocolla as a Sulphides – Chalcopyrite, bornite, covellite, chalcocite as a Carbonates – Malachite, azurite
Gangue: The ore minerals are usually associated with non-metallic materials or rock forming silicates which are not desired . These unwanted materials are called as Gangue Gangue is mainly composed of rock forming minerals like Quartz, feldspar, Calcite However, certain gangue minerals are collected as byproducts and utilized. For example: rock Gangue may be utilized as road metal, fluorspar and limestone as flux, quartz as abrasive, pyrite for manufacturing sulphuric acid
8 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The tenor of ore is the metal content of the ore. Which is required to give profit The tenor is usually expressed as • Weight percentage (base metals)
• Grams/tonne (precious metals) The tenor varies with the Price of the metal , cost of production, ores of different metals, different ores of same metals The Higher price of the metal, the lower the metal content is required to make it profitable Most of the iron ore is profitable – tenor of 35 – 50% The tenor of copper is 0.8% Gold 1/1000 of 1 %
Economically Important Metal Concentrations in Earth’s Crust
Concentration Metal (% by weight) Aluminum 8.0 Note for comparison: Iron 5.8 Silicon 28% Copper 0.0058 Oxygen 46% Nickel 0.0072 Zinc 0.0082 Uranium 0.00016 Lead 0.001 Silver 0.000008 Gold 0.0000002
9 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral Resources 'Mineral Resource' is a concentration or occurrence of material of intrinsic economic interest in or on the Earth's crust in such form and quantity that there are reasonable prospects for eventual economic extraction.
The location, quantity, grade, geological characteristics and continuity of a Mineral Resource are known, estimated or interpreted from specific geological evidence and knowledge. Mineral Resources are sub-divided, in order of increasing geological confidence, into Inferred, Indicated and Measured categories.
• Inferred: That part of a Mineral Resource for which tonnage, grade and mineral content can be estimated with a low level of confidence. • Indicated: That part of a Mineral Resource for which tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a reasonable level of confidence • Measured: That part of a Mineral Resource for which tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a high level of confidence.
10 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral Resources and Ore Reserves
An 'Ore Reserve' is the economically mineable part of a Measured or Indicated Mineral Resource. It includes diluting materials and allowances for losses which may occur when the material is mined.
Appropriate assessments, which may include feasibility studies, have been carried out, and include consideration of metallurgical, economic, marketing, legal, environmental, social and governmental factors.
These assessments demonstrate at the time of reporting that extraction could reasonably be justified. Ore Reserves are sub-divided in order of increasing confidence into Probable Ore Reserves and Proved Ore Reserves .
Mineral Resources and Ore Reserves A 'Probable Ore Reserve' is the economically mineable part of an Indicated, and in some circumstances Measured Mineral Resource.
A Probable Ore Reserve has a lower level of confidence than a Proved Ore Reserve.
A 'Proved Ore Reserve' is the economically mineable part of a Measured Mineral Resource. It includes diluting materials and allowances for losses which may occur when the material is mined. Appropriate assessments, which may include feasibility studies, have been carried out, and include consideration of and modification by realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors. These assessments demonstrate at the time of reporting that extraction could reasonably be justified.
11 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
RESERVES
• Probable: The economically mineable part of an Indicated and, in some circumstances, Measured Mineral Resource.
• Proven: The economically mineable part of a Measured Mineral Resource.
Mineral Resources and Ore Reserves
12 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
SOME OF THE IMPORTANT ORES AND OREMINERALS
13 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
14 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
15 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Formation of Mineral Deposits
16 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
PRIMARY OR HYPOGENE AND SECONDARY OR SUPERGENE
Ore minerals may be divided into primary or hypogene and secondary or supergene minerals Primary or hypogene minerals are those which form during the original periods of metallisation The supergene or secondary minerals are formed by the alteration of the former by weathering or by other surficial processes resulting from descending surface water Hypogene minerals are formed by ascending fluids
Formation of Mineral Deposits
Endogenous Processes (Primary or Hypogene) • Magmatic concentration • Metamorphism/Metasomatism • Hydrothermal process
Exogenous Processes (Secondary or supergene) • Weathering & Supergene enrichment • Chemical deposition • Mechanical concentration
17 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Endogenous Processes of Ore Formation
18 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Exogenous Processes of Ore Formation
• Weathering/Supergene Enrichment
• Chemical Deposition
• Mechanical Concentration
Laterite
Bauxite
Weathering
19 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chemical Deposition
Mechanical Concentration
20 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
THE FORMATION OF MINERALS AND MINERAL DEPOSITS
To have a better understanding of mineral deposits, it is important that how mineral deposits are formed The formation of a mineral generally involves a change from a mobile to solid state Since most of the mineral deposit from solutions, the temperature and pressure play important roles In general decrease of temperature and pressure promote precipitation from aqueous solutions and magmas The mineral deposits formed in several ways, the important of which are discussed
Crystallization from Magmas Magma is a molten fluid which form igneous rocks on cooling It is composed of mutual solutions of silicates, silica, metallic oxides, sulphides and volatile substances The temperature of magma varies from 6000 C to 12500C When magma cools the saturation point of certain minerals may be reached and if the temperature of the magma is below the fusion point of these minerals tend to crystallise For example: Apatite, Magnetite, Chromite, diamond, platinum, etc. have formed from by crystallization
21 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Sublimation Certain substances like sulphur are readily volatilised by the heat of igneous activity These substances may be deposited when the vapour is cooled around the vents of volcanoes, fumaroles without passing into liquid state. This is called Sublimation
Distillation It is believed that petroleum and natural gas are formed by the slow distillation of organic matter buried with sediments at the considerable depth
Evaporation and Supersaturation
Salts in solution are deposited when evaporation brings about supersaturation. Ex. Salt deposition from brines and the deposition of sulphate of copper, iron, zinc, calcium, etc.
Reaction of gases with other gases Igneous activity is accompanied by large quantities of gaseous emanations that contain the elements and compounds of mineral deposits. Reaction between different gases and vapours result in the precipitation of metals and other substances contained in them For example: native sulphur and hematite formation
2H2S +SO2 = 3S + H20
Fe2CL6 + 3H20 = Fe2O3 + 6HCL
22 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Salt mine from Sal Island
Reaction Between Gases and Solids The magmatic gases react with the intruded rocks particularly carbonate rocks and produce complex mineral assemblages and same way reaction between gases and liquids at high and normal temperatures Example: Precipitation of Copper sulphides from Cupric sulphate Reaction of Liquids with Liquids and solids Consolidating magmas may give off enormous quantities of magmatic fluids which are rich in minerals. These solution are liquids and responsible for formation of many deposits During their ascent journey they may meet surface waters of different composition or other magmatic fluids and wall rock of varying composition and react with them and result in the precipitation of minerals These reaction took place through various processes such as Metasomatism, Solubility, Reduction and Oxidation
23 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
a) Metasomatic Replacement It is a process by which a substance is removed in solution and simultaneously a new substance is deposited in its place. It is also known as replacement Replacement is the most important process in the formation of epigenetic deposits example: Copper sulphate in solution may replace limestone to form copper carbonate or pyrite to chalcocite b) Relative solubility of solid and solute Determines the precipitation of many minerals from solution. For example: if copper sulphate solution comes into contact with sphalerite (ZnS) which is more soluble, copper sulphide will be precipitated at the expense of sphalerite. But the reverse is not possible
c) Reduction and Oxidation Reduction and Oxidation may also cause precipitation of minerals when a solution contacts a solid For example: Gold is reduced from cupriferous solutions by pyrite or organic matter. Native copper is deposited when cupriferous solutions are oxidised by ferric iron Oxidation of pyrite yields limestone
24 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Deposition In Open Spaces
When a solution comes into contact with a solid the materials contained in it may be simply deposited in the open space by changes in temperature and pressure without any replacement Certain types of wall rocks also favor precipitation by reaction Catalytic Action There are certain mineral substances which cause the precipitation of mineral matter from solutions without themselves entering into the solution Base Exchange Occurs between solids and liquids whereby cations of similar size are exchanged producing new minerals
Precipitation by Bacteria It has been established that many iron ore deposits have precipitated by soil bacteria Unmixing of Solid Solutions: The term solid solution refers to the existence of more than one solid in a single homogenous phase Among minerals many solid solutions are known such as solid solutions of gold and silver, magnetite and ilmentite, chalcocite and covelite, etc Some solid solutions are stable at low temperature and others stable at high temperature When temperature falls down at certain points such solid solutions are unstable and separate into their original constituents. This is known as exsolution or unmixing Thus ilmenite separate from magnetite, covelite laths from chalcocite
25 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Colloidal Deposition: Colloids are matter in a particular state. The colloidal solutions are two phase systems one is the continuous medium and generally liquid The other is the discontinuous medium may be solid, liquid or gas and is disseminated in the other in minute particles but not in true molecular solutions. Such systems are generally referred to as sols. If the dispersed phase is a solid, the sols are called suspensoid, if liquid is called emulsoids The particles in sols are of submicroscopic size and in the same sol they carry similar electrical charges Deposition of these particles is therefore brought by the addition of electrolytes carrying opposite charges
Colloidal Deposition…. Colloids are readily precipitated from natural solutions as floculent or gelatinous masses These floculent or gelatinous masses may harden to rounded or other colloform masses such as botryoidal, reniform, mamillary, nodular or pisolitic forms The solidified colloids may persist in an amorphous state such as opal or they may acquire crystallinity such as marcasite, malachite or psilomelane Thus many minerals are formed by colloidal precipitation
26 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Weathering and Mechanical Concentration Process Weathering processes are very important in the formation of economic mineral deposits Mechanical weathering does not create any new mineral but chemical weathering produces new minerals by acting upon the preexisting mineral deposits Placers, mineral in alluvium, etc are the Mechanical concentration
Metamorphism Many economic minerals are produced by recrystallisation and recombination of the ingredients of the rocks during metamorphism. Example: Garnet, Graphite and Sillimanite
Melting glaciers: sand and gravel
Abundance of Elements in the Earth Crust
27 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
CLASSIFICATION OF MINERAL DEPOSIT
Classification of mineral deposits has been attempted by many authors, but none of them have been unanimously accepted. The genetic classification is considered to be valuable for the working geologist, since it can be applied directly to the field
The earlier classification by Beck (1904), Bergsat and Steizner (1904) and Irving (1908) on the basis of origin.
Classifications Based on Geological Processes
Hydrothermal/Pegmatitic mineral deposits form in association with hot water- or gas-rich fluids Magmatic mineral deposits concentrated in igneous rocks; Metamoprhogenic mineral deposits concentrated by metamorhism / metasomatism Sedimentary mineral deposits are precipitated from a solution, typically sea water;
28 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Classifications Based on Host Lithology
• Unconsolidated Deposits • Sedimentary Rocks • Volcanic Rocks • Intrusive Rocks • Regionally Metamorphosed Rocks
I. Protogene (Primary) A. Syngenetic 1. With eruptive rocks For example: Bergsat 2. With sedimentary rock and Steizner (1904) B. Epigenetic classification 1. Cavity filling 2. Replacement II. Secondary A. Residual B. Placers
29 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Lindgren (1911) Classification
Lindgren (1911) classified mineral deposits in two main sub-divisions
1)Those formed by mechanical concentration and 2)Those formed by chemical reaction in solutions
The basis of this classification is the temperature and pressure of formation
A. In surface water 0 – 70 o C medium (pressure) 1. By reactions 2. By Evaporation Lindgren (1911) B. In bodies of rocks Classification 1. Concentration of substances contained within rocks a) By weathering 0 – 100 o C Medium (Pressure) b) By groundwater 0 – 100 o C Medium c) By metamorphism 0 – 400 o C High 2. By Introduced substances a) with out igneous activity 0 – 100 o C Medium b) related to igneous activity 1. Epithermal deposits 50 – 200 o C Medium 2. Mesothermal deposits 200 – 500+ o C High 3. Hypothermal deposits 500 – 600+ o C High c) By direct igneous emanation 1. Pyrometasomatic deposits 500 – 800 o C High 2. Sublimates 100 – 600 o C Low to Medium C. In magmas by differentiation 1. Magmatic deposits 700 – 1500 o C High 2. Pegmatites 575+ o C High
30 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Lindgren classification is most accepted genetic classification, but does not have the frame work for all kind of deposits. For example: deposit of native copper, regionally metamorphosed deposits, oxidation, supergene deposits, etc. It consider mostly on temperature and pressure, but this is not in all cases
Bateman’s (1942) genetic classification based on the various processes of formation of mineral deposits
Processes Deposits a) Early magmatic – disseminated 1. Magmatic Concentration crystallization, segregation, injection b) Late magmatic – Residual liquid segregation, residual liquid injection. Immiscible liquid segregation and immiscible liquid injection
2. Sublimation Sublimate 3. Contact metasomatism Contact metasomatic 4. Hydrothermal processes a) Cavity filling b) Replacement 5. Sedimentation a) Sedimentary
31 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Bateman’s (1942) genetic classification based on the various processes of formation of mineral deposits….
Processes Deposits 6. Evaporation a) Evaporites
7. Residual and Mechanical a) Residual deposits concentration b) Placers
8. Surfacial oxidation and Oxidised, supergene sulphide supergene enrichment
9. Metamorphism Metamorphosed and metamorphic deposit
On the basis of the analysis of several mineral deposit, Mitchell and Garson (1976) identified certain environment related to lithosphereic plates, conducive for the formation of mineral deposit
1. Ocean floor spreading 2. Subduction zones related 3. Collision related 4. Transform fault
32 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The classification based on genesis is meant only for technocrats and is not of any commercial importance Classification based on the nature and most prevalent use of minerals
A. Metallic Mineral Deposits
1. Precious metals, e.g. gold, silver, platinum 2. Ferrous and Ferro-alloy metals e.g. iron, manganese 3. Non-ferrous and allied metals, e.g. copper, lead, etc. 4. Light metals, e.g. lithium, magnesium, etc. 5. Radio-active metals, e.g. uranium, thorium 6. Rare metals, e.g. palladium, selenium, etc.
33 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
B. Non-Metallic Mineral Deposits
1. Mineral fuel, e.g. Coal, petroleum 2. Gemstones, e.g. diamond, ruby, etc. 3. Abrasive minerals, e.g. corundum, garnet, etc. 4. Building materials and the dimension stones e.g. marble, granite, etc. 5. Industrial Minerals, e.g. mica, asbestos, etc. 6. Refractory Minerals e.g. Fireclay, graphite, etc. 7. Glass manufacturing materials, e.g. quartz, silica, etc. 8. Ceramic minerals, e.g. clay, felspar,etc. 9. Fertilizer minerals, e.g. phosphorite, sulphur, etc. 10.Chemical minerals, e.g. rock salt, borax, etc. 11.Mineral pigments, e.g. ochre, umber, etc. 12.Mineral water and groundwater
Ore Genesis Ore genesis deals with various attributes that provide direct or indirect evidence related to formation of ore deposits.
It is outcome of detailed studies involving geological, geochemical, petrological, isotopic and time-space relationship between ores and their repository set up.
The following attributes are important in understanding genesis of ore deposits:
34 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
35 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral Paragenesis and zoning, metallogenic epochs and provinces are the important factors of controls of mineral localization
Mineral Paragenesis: The term mineral paragenesis defines the mutual relationships and time sequence of minerals The individual minerals in mineral deposit of magmatic affiliations are formed in an orderly sequence and this sequential arrangement is termed paragenesis The mineral paragenesis is identified by the field evidences and microscopic studies
36 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral Zoning Mineral zoning is the tendency for certain minerals or ores to be deposited at varying distances from a related focus of igneous activity
The higher temperature and least soluble minerals are found nearest the source The low temperature and most soluble minerals are found farthest from source
Zoning in hydrothermal aureoles can also be classified according to direction. Zoning along the direction of flow of the ore-forming fluids is termed axial. Zoning outward from ore into wallrock, in a direction normal to the hydrothermal flow direction, is termed transverse.
Based on studies of a large number of deposits of different types, shows the following average sequence of metals
At specific deposits, deviations from this sequence are found but generally do not involve discrepancies of more than one or two positions in the series
37 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Enclosing a steeply dipping body of polymetallic ores, the prinicple ore elements (Pb, Zn, Cu, Au) give rise to primary halo that roughly matches ore body shape Lower temperature path elements (Ag, As, Hg) form primary halos shifted along the rise of the ore body
Halos from readily volatile elements (Cl, Br, I) are formed in top lying over the ore body
The halos from elements of higher temperatures association (W, Mo, Co) are shifted in the direction of dip (downward) from the centre of the ore body From the above, the ore element is lead, low temperature pathfinder element is mercury, high temperature element is cobalt and readily volatile elements is iodine
Metallogenic Epochs
Metallogenetic epochs are specific periods characterized by formation of large number of mineral deposits within 10-20 million years or much less
In India, the important metallogenentic epochs are 1. Precambrian 2. Late Palaeozoic 3. Late Mesozoic to Early Tertiary
38 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metallogenic Epochs …… Precambrian Epochs The Precambrian epochs is the most important world over because of great length of time and presence of large and varied mineral deposits The huge sequence of Precambrian metasediments and associated granitoids, gneisses, etc. are supposed to have a different metallogenic history The endogenic deposits have been broadly correlated to ultrabasic, basic, acid-intermediate and post- orogenic acidic phases of magmatism. The exogenic deposits like iron and manganese are related to sedimentary, metamorphic and other processes
Metallogenic Epochs …… The iron ore deposits of Precambrian epoch in southern singhbhum (Bihar), Keonjhar, Mayurbhanj and Sundargarh (Orissa), Baster and Durg (Madhya Pradesh), Chanda and Ratnagir (Maharashtra), Dharwar, Bellary, Sendur, Shimoga and Chikmagalur (Karnataka) and Goa The Chromite deposit in Singhbhum (Bihar), Dhenkanal, Cuttack and Keonjhar (Orissa), Mysore and Hassan (Karnataka) Bhandara and Ratnagiri (Maharashtra)
The Gold deposits in Kolar, Hutti and Gadag (Karnataka) Ramagiri and Anantpur (Andhra Pradesh) Wynad (Tamil Nadu) and Kondrakocha (Bihar)
39 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metallogenic Epochs ……
Copper deposit in Singhbhum (Bihar), Khetri (Rajasthan), Malanjkhand (Madhya Pradesh) Mailaram, Gani and Agnigundala (Andhra Pradesh), Ingaldalur and Kalvadi (Karnataka) Lead and Zing in Zawar, Deri, etc (Rajasthan) Sargipalli, Kesarour, Karmali (Orissa), Vadodara (Gujarat) Many more examples are available for Precambrian epoch
Metallogenic Epochs ……
Permo-Carboniferous (Late Palaeozoic) Epoch
Towards the upper Carboniferous (Late Palaeozoic), the Hercynian movements introduced a great changes on the surface of the globe and this movement is marked by mountain building and initiation of sedimentary era In India, the epoch is known by rich coal deposits of Lower Gondwana for example: Jharia, Bokaro, Karanpura, Giridih, Ramgarh, Auranga, Hutar, Daltonganj, Deoghar and Rajmahal of Bihar Raniganj, Barjora and Darjeeling of West Bengal Singrauli, Korba, Chirimiri, Sohagpur, of Madhyapradesh A large number of hypabyssal basic intrusive-dolerites and basalt and mica-rich ultrabasic traverse these coal fields Other important mineral deposits of this epoch are fireclay, iron stone and ochure which occur within Gondwana formation
40 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metallogenic Epochs and Provinces……
Late Mesozoic to Early Tertiary Epoch
This epoch is dominated by fissure eruption of basaltic lave flow (Deccan trap) which is cover 50,000 sq km in western and central India with semi-precious stones like rock crystal, amethyst, agate, onyx chalcedony Rare copper mineralisation is noted in the trap rock Igneous activities of this epoch marked by granites, granodiorites, basic and ultrabasic rocks of extra Peninsular India (Main Himalaya, Manipur-Meghalaya and Andaman. These are associated with occurrence of fluorite, copper, lead, zinc, chromaite, magnesite, clay asbestos, magnesite and talc.
Nickel and chromaite in Andaman-Nicobar areas
METALLOGENIC PROVINCES The metallogenic province is known by the name of dominant and specific mineral such as Gold province, Copper province, Iron-ore Province, etc. It may comprise the mineralisation of more than one epoch, each superimposed upon the other In India, many examples for metallogenic provinces, a few of them are 1. Gold provinces of Karnataka (Hutti-Kolar) – Andhra Pradesh (Anantpur-Godag) – Tamil Nadu (Wynad) 2. Copper province of Singhbhum (Bihar) 3. Copper province of Khetri-Pur, Banera-Bhinder (Rajasthan) 4. Lead-Zinc province of Hesatu-Belbathan (Jharkhand) 5. Iron-ore province of Southern Singhbhum-Keonjhar-Sundergarh- Mayurbhanj 6. Iron ore province of Drug-Baster-Chanda-Ratnagiri 7. Iron ore province of Karnataka-Goa 8. Manganese Province if Balaghat-Bhandara-Nagpur
41 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
GEOLOGICAL THERMOMETERS Minerals which yield information regarding the temperatures of their formation and of the enclosing deposits are said to be geologic thermometers They are very useful in understanding the origin of minerals
These thermometers that record fairly accurately the specific temperature condition of formation of deposits The thermometers that provide an upper or a lower temperature above or below which the deposits do not form The thermometers that provide a range of temperature within which the deposit form The presence of two or more precise geological thermometers in a deposit narrows the range of temperature of formation for the deposits
GEOLOGICAL THERMOMETERS….
Methods for preparation of Geologic thermometry
1. Direct Measurement
This includes direct measurement of temperatures of lavas, fumaroles, hotspring, etc. where the formation of minerals take place. A maximum temperature of 12500 C has been recorded for basic lavas Fumeroles have a maximum temperature of about 7000 C According to Bowen, earliest minerals of basic rocks, in general form between 8700 C – 6000C decreasing with increase of silica content – Chromite which is high temperature mineral form within the above temperature The surface temperature of Puga hot springs, ladakh is measured up to 850C. Sulphur, Borax and Potash which occur there may formed at or above the temperature 850C.
42 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Methods for preparation of Geologic thermometry 2. Determination of Melting points and Inversion points of Minerals The melting points of minerals indicate the maximum temperature at which they can crystallise The melting point of galena is known to be 11200C. The galena of Hesatu-Belbathan belt, Bihar have formed at the temperature below 11200C The presence of other substances generally reduce the melting point of the minerals melting point of some Inversion point of some minerals minerals Tridymite invert to Cristobalite - 14700C Olivine - 18900C Sphalerite to Wurzite - 10200C Anorthite - 15500C Kyanite to Mullite - 10000C Antimony - 6300C High Quartz (Beta) to Tridymite - 8700C Stibnite - 5460C Low Quartz (Alba) to High Quartz - 5730C Bismuth - 2710C Sulphur - 1190C
Methods for preparation of Geologic thermometry 3. Study of Dissociation, (ii) Exsolution, (iii) Recrystallisation and (iv) Liquid inclusion in minerals
Dissociation
Minerals that dissociate water content or other volatile constituents or any other mineral at certain temperatures may form good geological thermometers For example: Zeolite, when heated, lose water content and thus form geological thermometer indicate low temperatures of their formations
• Tremolite yields diopside at 9000C • Calcite disscoiates at 9000C • Pyrite into Pyrrhotite and sulphur vapour at 6850C
43 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Methods for preparation of Geologic thermometry 3. Study of Dissociation, (ii) Exsolution, (iii) Recrystallisation and (iv) Liquid inclusion in minerals
Exsolution
Exsolution is separation of one mineral from another at particular temperatures • Magnetite to ilmentite at 7000C • Chalcopyrite to Pyrrhotite at 6000C • Stannite to Chalcopyrite at 5000C • Bornite – Tetrahedrite at 2750C Recrystallisation This method is adopted principally for native minerals • Copper - 4500C • Gold - 3600C • Silver - 2000C
Methods for preparation of Geologic thermometry 3. Study of Dissociation, (ii) Exsolution, (iii) Recrystallisation and (iv) Liquid inclusion in minerals
Liquid Inclusion
It is possible to find out the temperature of formation of the crystals approximately by noting the amount of contraction of the liquid inclusion which filled completely the cavities initially To determine the temperature of formation by this method the mineral may be heated till the cavity is completely filled by the inclusion and the temperature at this point may be read The temperature of certain sphalerite was found to be 115 to 1350C
44 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Methods for preparation of Geologic thermometry 4. Changes in the Physical Properties of some minerals Some minerals undergo distinct changes in their physical properties at certain temperatures • Limestone – Pigment expelled - 6050C • Mica - Pleochroic haloes destroyed - 4800C • Smoky quartz – Colour disappears - 3000C • Amethyst – Loses colour - 240-2600C • Fluorite - Loses colour - Around 1750C 5. Associated Minerals The associated low, intermediate and high temperature minerals give information about their temperature of formation High Intermediate Low Temperature Magnetite Chalcopyrite Marcasite Pyrrhotite Arsenopyrite Adularia Cassiterite Galena Chalcedony Garnet Sphalerite Rhodochrosite Pyroxene Tetrahedrite Siderite
Element Wt % Oxide Atom % O 60.8 Si 59.3 21.2 Abundance of the elements Al 15.3 6.4 Fe 7.5 2.2 in the Earth’s crust Ca 6.9 2.6 Mg 4.5 2.4 Na 2.8 1.9
Major elements: usually greater than 1%
SiO2 Al2O3 FeO* MgO CaO Na2O K2O H2O Minor elements: usually 0.1 - 1%
TiO2 MnO P2O5 CO2 Trace elements: usually < 0.1% everything else
45 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
A typical rock analysis
Wt. % Oxides to Atom % Conversion Oxide Wt. % Mol Wt. Atom prop Atom %
SiO2 49.20 60.09 0.82 12.25
TiO2 1.84 95.90 0.02 0.29
Al2O3 15.74 101.96 0.31 4.62
Fe2O3 3.79 159.70 0.05 0.71 FeO 7.13 71.85 0.10 1.48 MnO 0.20 70.94 0.00 0.04 MgO 6.73 40.31 0.17 2.50 CaO 9.47 56.08 0.17 2.53
Na2O 2.91 61.98 0.09 1.40
K2O 1.10 94.20 0.02 0.35 + H2O 0.95 18.02 0.11 1.58 (O) 4.83 72.26 Total 99.06 6.69 100.00 Must multiply by # of cations in oxide
Table 8-3. Chemical analyses of some representative igneous rocks Peridotite Basalt Andesite Rhyolite Phonolite SiO2 42.26 49.20 57.94 72.82 56.19 TiO2 0.63 1.84 0.87 0.28 0.62 Al2O3 4.23 15.74 17.02 13.27 19.04 Fe2O3 3.61 3.79 3.27 1.48 2.79 FeO 6.58 7.13 4.04 1.11 2.03 MnO 0.41 0.20 0.14 0.06 0.17 MgO 31.24 6.73 3.33 0.39 1.07 CaO 5.05 9.47 6.79 1.14 2.72 Na2O 0.49 2.91 3.48 3.55 7.79 K2O 0.34 1.10 1.62 4.30 5.24 H2O+ 3.91 0.95 0.83 1.10 1.57
Total 98.75 99.06 99.3 99.50 99.23
46 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
GLOBAL METALLOGENY (in Relation to Crustal Evolution) The continents are widely believed to have developed by accretion
Each continent has developed from a volcanic nucleus or nuclei, being joined and added to by peripheral volcanic nuclei.
The process is aided by the accumulation of volcanic matter (pyroclastic material) and products of erosion.
The pattern is complicated by later fractures and relative movement, perhaps drift, of various crustal segments. This evolutionary pattern seems to form a plausible framework for the succession of geologic environments and evolution of ore types.
The process of crustal evolution is considered in six successive stages. STAGE I: THE EARLY VOLCANIC STAGE
The beginning of crustal evolution is marked by the formation of broad swells on the basaltic ocean floor.
These represent the early stages in the development of volcanic islands.
Development of these swells leads to block faulting, extrusion of lavas, and their protrusion above the sea level to form volcanic islands (Eg Solomon Is in SW Pacific)
MINERAL DEPOSITS: Native copper and associated sulfides as orthomagmatic disseminations and vesicular fillings Eg Solomon Islands. Nickel and associated sulfides in volcanic sills Eg Kambalda, W Australia, Manitoba. Precious metals viz. tellurides Eg Fiji.
Minor chemical sedimentation viz. manganese and iron with jasper.
47 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
STAGE II: EARLY ALPINE TYPE ULTRAMAFIC STAGE
Vulcanism continues, but changes to basaltic andesite, gradually progressing to andesites, dacites and rhyolites.
Pyroclastic activity becomes prominant with the onset of the andesitic stage and increases with the increase in the felsic nature of vulcanism.
The older swells are undergoing extensive erosion and much sedimentation. The sediments become folded, faulted and deformed due to near vertical block faulting and gravity collapse.
MINERAL DEPOSITS: Alpine type chromite deposits in intrusives Eg Paleozoic to Tertiary "Serpentine Belts" everywhere.
Nickel sulfide concentrations and Nickel also occurs as Ni-rich olivine which may be concentrated to ore by later weathering.
STAGE III: DEVELOPING EUGEOSYNCLINAL STAGE The volcanic islands are by now well established and are enlarged by bodily uplift, volcanic accretion and sedimentation. Volcanic products are becoming more felsic and pyroclastic material is becoming prominent. Earliest plutonic rocks of granitoid texture and dioritic- granodioritic composition appear (in pipe or stock form). These are of shallow subvolcanic nature. These may be products of magmatic differentiation or transformation of the deeply buried pyroclastic rocks.
MINERAL DEPOSITS: Banded Iron Formations developed as volcanic chemical sediments as a result of sea- floor exhalative activity. Deposition of these took place in troughs (eugeosynclines) in inter-island regions of arcs. Considerable jasper and some manganese Eg Guyana. Stratiforn Sulfide Deposits of marine and marine-volcanic affiliation. All these are essentially sea floor volcanic accumulations. A few of these are associated with basaltic and more mafic lavas Eg Cyprus and Japan, whereas a vast majority are associated with andesitic and dacitic rocks. Eg Base metals of Ontario, Mount Isa and McArthur River (Precambrian); Bathurst, New Brunswick and E. Australia (Paleozoic) and Japan (Tertiary). Some Banded Iron Formations and minor manganese concentrations and barite are associated with the Stratiform Sulfide Deposits. Most of these deposits are formed near the continental margins and biological activity (2500 y ago) is always indicated.
48 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
STAGE IV: ADVANCED EUGEOSYNCLINAL & MIOGEOSYNCLINAL STAGE The oldest swells have become quite large (Java & Sumatra) with smaller intervening swells beginning to coalesce (Aleutian-Malaysian).
There is a mixing of volcanic material with products of continental erosion around volcanic festoons bordering continents. There is, therefore, a hybrid sedimentation on the continental side of the arc (the miogeosyncline) while volcanic sedimentation progresses in the outward seaward trough (the eugeosyncline). Vulcanism at this stage becomes more felsic.
MINERAL DEPOSITS Stratiform or non-stratiform marine volcanic sulfide ores. Banded Iron Formations in the eugeosynclines (for some reason major iron formations are not associated with basemetal sulfide deposits). Volcanic basemetals are contributed to the reef and off-reef environments on both sides of the arc (particularly on the miogeosynclinal side). These are eventually concentrated by sedimentary, diagenetic and later processes to form Limestone-Lead-Zinc Deposits. Some manganese deposits (Usinsk Type) also develop in the eugeosynclines and miogeosynclines.
STAGE V: EARLY CONTINENTAL AND INTRUSIVE STAGE
The volcanic islands are by now welded to each other and also to the continental margins. Intense fault movement, compressional folding, more felsic plutonic intrusions, waning of vulcanism and rapid erosion are characteristic of this stage of crustal evolution. Plutonic rocks are granitic and pegmatitic in composition.
MINERAL DEPOSITS: Cassiterite deposits as disseminations in granites, contact metamorphic deposits and pegmatitic deposits. Quartz-cassiterite veins. Quartz-wolframite veins. Quartz-scheelite veins. Quartz-gold veins. Stibnite and stibnite-scheelite-gold veins. Basemetal sulfide veins with arsenopyrite and increasing proportions of Pb & Zn as compared to Cu. Plutonic type anorthositic iron-titanium oxides. In the more mafic parts of these intrusions chromite is segregated. Eg Bushveld Complex. Sometimes ilmenite, magnetite and minor Fe-Ti-O. Major nickel-copper sulfides (Eg Sudbury) are also identified with this stage Chromite deposits formed in ultramafic rocks during the Alpine Type Ultramafic Stage (II) are well serpentinized by this time and move along large fault systems (along which they formed) and take up new lithological and structural positions in the evolving crust.
49 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
STAGE VI: SHELF AND SHIELD STAGE
Continuing folding, faulting and varying degrees of metamorphism leads to the formation of a "Continental Shield". This stage is marked by outpouring of flood basalts and stabilization of the crustal segment.
Erosion and peneplanation lead to the development of broad flat areas susceptible to inundation during sea-level rises resulting in extensive deposits of detrital sediments, reefs (carbonate), evaporites and chemical sediments.
Movement of the shoreline in response to sea-level fluctuations leads to the interfingering of shallow water marine and fluviatile sediments, particularly in the lower reaches of braided streams, deltas and outwash fans.
Mineral deposits forming at this stage include a variety of igneous and sedimentary ores, and deposits formed during the earlier stages undergo substantial metamorphism.
MINERAL DEPOSITS: There are few mineral deposits associated with flood basalts. Exceptions are the copper bearing lavas of the eweenaw Peninsula, Lake Superior. Limestone-lead-zinc deposits often associated with oil bearing strata and evaporites, Eg Pine Point, Canada. Non-volcanic sedimentary manganese deposits (orthoquartzite- glauconite-clay association), Eg Nikopol, USSR, and Morocco. Ironstones of the Clinton, Lorraine and English type associated with near-shore, estuarine or lagoonal sedimentation. "Sandstone Type" Cu-U-V ores formed in coarse sediments of outwash fans, near-shore braided streams and deltas, Eg Colorado. Gold-uranium deposits of Witwatersrand-Bhind River- Jacobina Type in coarse conglomerates and grits of braided stream channels. Basemetal sulfide deposits of non-volcanic association occurring with evaporites, Eg Kupferschiefer Marl Slate of Europe and England and the Copperbelt of Zambia.
50 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MAJOR ORE TYPES OF INDIA AND THEIR TECTONIC SETTING
51 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ECONOMIC GEOLOGY
e – Learning Material: Unit-2
Process of formation of mineral deposits
52 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Process of formation of mineral deposits
Mineral deposits are classified on the basis of their genesis or the processes that operates to form them.
1. Magmatic concentration 2. Sedimentation inclusive of evaporation 3. Metamorphism 4. Contact metasomatism 5. Hydrothermal processes 6. Oxidation and supergene enrichment 7. Sublimation 8. Residual and mechanical concentration
Type The mechanism of ore deposition Example 1- Early magmatic Disseminated crystallization Diamond pipes, A- Dissemination without concentration some corundum deposits,chromite Crystallization differentiation Bushveld chromite, B- Segregation and accumulation Stillwater, chromite 2-Late magmatic A- Gravitative liquid accumulation 1- Residual liquid Crystallization differentiation Titanomagnetite segregation and residual magma deposits and 2. Residual Liquid accumulation. Platinum deposits in Injection Bushveld Complex B- Immiscible liquid 1- Immiscible liquid Immiscible liquid separation Sulfide deposits segregation. and accumulation. Same, with injection 2-Immiscible liquid injection
53 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MAGMATIC CONCENTRATION or Ore Deposits Related to Magmatic Activity
Certain accessory or uncommon constituents of magmas become enriched into bodies of sufficient size and richness to constitute valuable mineral deposits eg. Chromite and platinum.
Magmatic ore deposits are characterized by their close relationship with intermediate or deep seated intrusive igneous rocks
They constitute either the whole igneous mass or a part of it
Magmatic Deposits result from
1. Simple crystallization
2. Concentration by differentiation of intrusive igneous masses.
There are several modes of formation of magmatic deposits.
They originate during different periods of magma crystallization – in some the ore minerals crystallize early, in others late, and in still others they remained as immiscible liquids until after crystallization of the host rock
54 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Classification of Magmatic Deposits I. Early Magmatic Deposits: Those which resulted from straight magmatic processes (orthotectic and orthomagmatic). These deposits have formed by: a. Simple crystallization without concentration b. Segregation of early formed crystals c. Injection of material concentrated elsewhere by differentiation.
A. Dissemination Deep seated crystallization will yield a granular rock in which the early formed crystals are disseminated. If such crystals are valuable and abundant, the whole rock or a part of them becomes the orebody. The individual crystals may be phenocrysts
B. Segregation Concentration of early formed crystals in-situ. These are early concentrates of valuable constituents of the magma that have taken place as a result of gravitative crystallization differentiation, eg. Chromite. These orebodies are generally lenticular and small in size, commonly disconnected pod shaped lenses, stringers
55 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Early Magmatic Deposits – Indian Examples
a.) Disseminated in the enclosing rock e.g. diamond in kimberlite of Majhagawan pipe, MP and Wajrakarur pipe, AP. The diamonds might have crystallised early and were transported with the enclosing magma, and perhaps, even continued to grow before final consolidation took place in the present pipes.
b.) Segregated due to gravitational crystallization differentiation e.g. stratiform and banded graded deposits of chromite in Nausahi- Sukinda area, Orissa and other places. The early magmatic segregation may be due to sinking of heavy early formed crystals to the lower part of the magma chamber or by marginal accumulation.
56 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Early Magmatic Deposits – Indian Examples
c.) Injected into the host rocks or the surrounding rocks e.g. vanadiferous magmatic deposits of Dublabera, Singhbhum district in Bihar. It occurs as veins and lenses within ultrabasics and gabbro.
The early formed ore mineral, magnetite, did not remain at the site of original accumulation but have been injected into ultrabasic rocks of Iron-Ore Formation. Due to sinking of heavy early formed crystals to the lower part of the magma chamber or by marginal accumulation.
d.) Injected into the host rocks or the surrounding rocks e.g. vanadiferous magmatic deposits of Dublabera, Singhbhum district in Bihar. It occurs as veins and lenses within ultrabasics and gabbro.
The early formed ore mineral, magnetite, did not remain at the site of original accumulation but have been injected into ultrabasic rocks of Iron-Ore Formation.
57 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Schematic model of a fully grown kimberlite pipe
Stratiform chromite deposit, Bushveld Complex, South Africa
58 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
II. Late Magmatic Deposits: Those which consist of minerals crystallizing from a magma towards the close of magmatic period.
The ore minerals are later than the rock silicates and cut across them, embay them, and yield reaction rims around earlier minerals. They are always associated with mafic igneous rocks.
The late magmatic deposits have resulted from:
a. Variations of crystallization differentiation.
b. Gravitative accumulation of heavy residual liquids.
c. Liquid separation of sulfide droplets.
A. Residual Liquid Segregation In certain mafic magmas, the residual liquid becomes enriched in iron, titanium and volatiles. This liquid settles to the bottom of the magma chamber, or crystallizes in the interstices of early formed crystals. Examples: Titaniferous magnetite layers of the Bushveld Igneous Complex, S. Africa.
B. Residual Liquid Injection The iron-rich residual liquid accumulated in the above manner may be subjected to movement because of:
a. Gentle tilting (causing lateral movement). b. Pressure and be squirted out to places of lesser pressure.
In both cases it may be injected into adjacent rocks and even in the earlier consolidated parent silicate mass. Examples: Titanomagnetite Deposits, Adirondack Region, New York; Allard Lake Deposits; Magnetite Deposits of Kiruna, Sweden.
59 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
C. Immiscible Liquid Segregation Immiscible liquid - Typical example is oil and water. In ore deposits we deal with silicate and sulfide magmas. As a magma cools, sulfides coalesce as droplets and due to higher density settle out. Most common sulfides are iron sulfides, but nickel, copper and platinum also occur.
Sulfide-rich magmas are immiscible in silicate rich magmas. This gives rise to separation even before crystallization. The accumulated sulfide may not necessarily be pure – in fact it quite often is an enrichment of sulfides in the lower parts of the magma.
Deposits formed in this manner are pyrrhotite-chalcopyrite- pentlandite nickel-copper ores confined to rocks of the gabbro family. Examples: Ni-Cu Deposits of Insizwa, S. Africa; Nickeliferous Sulfide Deposits of Bushveld, S. Africa & Norway; Nickel Sulfide Deposits of Sudbury, Ontario.
D. Immiscible Liquid Injection
Examples: Vlackfontein Mine of S. Africa; Nickel Deposits of Norway.
60 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
. As magmas cool, they can split into two liquids of different composition and density.
. One of these liquids is the silica- rich melt. It has the most volume
. The other, typically much smaller in volume, can be rich in metal oxides, sulfides or carbonates.
Late Magmatic Deposits – Indian Example
a.) Residual liquid segregation wherein the residual magma with crystallization becomes progressively richer in silica, alkali and water. It sometimes contains titanium and iron which on crystallization segregated to form titaniferous magmatic deposit e.g. titaniferous magmatite of Hassan District, Karnataka, which occurs as comformable bands in amphibolites and basic schists. Vanadiferous magnetite deposits of Mayurbhanj, Orissa is another example. Here, it occurs associated with gabbro-anorthosite suite of rocks.
b.) Residual liquid injection which takes place due to earth’s disturbance like igneous intrusion. E.g. on dated 23 August, 2007, Igneous intrusions took place in 8km from Kimin, in Arunachal Pradesh; the residual liquid rich in iron when injected crystallised to form magnetite deposits, e.g. magnetite dyke rock of Kasipatanam, Visakhapatanam district, AP, where it occurs as cutting across the NE- SW foliation of charnockite-gneiss and also metamorphoses the wall rocks.
61 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Late Magmatic Deposits – Indian Example
c.) Immiscible liquid segregation in which certain salts in magma under certain conditions separate out an unmixed solutions like oil and water, and segregate to form important mineral deposits. It has been observed that sulphur and silica form two hot immiscible liquids wherein a molten mass consists of various metals. The examples of this category are lead-zinc-copper-sulphide deposits of Hesatu- Belbathan Belt, Bihar where they occurs associated with altered basic- schists in disconnected bodies.
d.) Immiscible liquid injection when the unmixed sulphide rich fraction accumulated in the magma chamber, as described above, is squirted out before consolidation towards the places of less pressure, such as shear zones. They intrude the older rocks and enclose brecciated fragments of host and foreign rocks. The nickeliferous chalcopyrite pockets associated with altered basic-schists (chlorite-biotite schist) of Singhbhum Copper Belt may be cited as an example. This type of deposits shows transition to hydrothermal type with enrichment of volatile matters.
Pegmatitic Deposits: Pegmatites are very coarse grained igneous rocks. Commonly form dike-like masses a few meters to occasionally 1-2 km in length. Economic ore deposits are associated with granitic pegmatites since felsic magmas carry more water. Residual elements such as Li, Be Nb, Ta, Sn and U that are not readily accommodated in crystallizing silicate phases end up in the volatile fraction. When this fraction is injected into the country rock a pegmatite is formed. Temperatures of deposition vary from 250-750°C. Pegmatites are divided into simple and complex. Simple pegmatites consist of plagioclase, quartz and mica and are not zoned.
Complex have a more varied mineralogy and are strongly zoned. Crystals in pegmatites can be large, exceeding several meters. Three hypotheses to explain their formation:
• fractional crystallization • deposition along open channels from fluids of changing composition • crystallization of a simple pegmatite and partial to complete hydrothermal replacement
62 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Pegmatite dyke in a granodiorite body
Association of Rocks and Mineral Products:
Definite associations exist between specific magmatic ores and certain kinds of rocks:
1. Platinum occurs only with mafic to ultramafic rocks such as varieties of norite, peridotite or their alteration products. 2. Chromite (with rare exceptions) is formed only in peridotites, anorthosites and similar mafic rocks. 3. Titaniferous magnetite and ilmenite are found with gabbros and anorthosites. 4. Magnetite deposits occur with syenites. 5. Ni-Cu deposits are associated with norite. 6. Corundum occurs with nepheline syenite. 7. Diamond occurs only in kimberlite, a variety of peridotite. 8. Pegmatite minerals, such as beryl, cassiterite, lepidolite, scheelite, and niobium-bearing minerals occur chiefly with granitic rocks.
J.Saravanavel Economic eology Unit-563 12 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Characteristics of different rock types: Peridotite: A coarse grained mafic igneous rock composed of olivine with small amounts of pyroxene and amphibole.
Anorthosite: A plutonic rock composed mainly of Ca-rich plagioclase feldspars. Gabbro: A black, coarse grained intrusive igneous rock, composed of calcic plagioclases and pyroxenes. The intrusive equivalent of basalt.
Syenite: A group of plutonic rocks containing alkali feldspars, a small amount of plagioclase, one or more mafic minerals, and quartz only as an accessory, if at all. The intrusive equivalent of trachyte.
Kimberlite: A peridotite that contains garnet and olivine and is found in volcanic pipes.
Pegmatite: An igneous rock with extremely large grains (> 1 cm in dia). It may be of any composition, but is most frequently granitic.
HYDROTHERMAL DEPOSITS
64 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Hydrothermal mineral deposits are those in which hot, mineral laden water (hydrothermal solution) serves as a concentrating, transporting, and depositing agent. They are the most numerous of all classes of deposit.
The term hydrothermal means hot water with possible temperature of 5000 to 500C. The fluid resulting as an end product of magmatic differentiation, constitutes hydrothermal solution which carries metals originally present in the magma to the site of deposition.
The process is responsible for formation of epigenetic mineral deposits i.e. those formed later than the rocks that enclose them. The hydrothermal solution in its journey through the rocks loses heat and metal contents with increased distance.
The deposition may have taken place at high temperature (hypothermal deposit), intermediate temperature (mesothermal deposit) or low temperature (epithermal deposit).
Origins of the Solutions
The water in a hydrothermal solution can come from any of several sources.
It may be released by a crystallizing magma;
it can be expelled from a mass of rock undergoing metamorphism; or
it may originate at the Earth's surface as rainwater or seawater and then trickle down to great depths through fractures and porous rocks, where it will be heated, react with adjacent rocks, and become a hydrothermal solution.
Connate waters, when set into motion by tectonic activity, may also constitute hydrothermal fluids.
65 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
66 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Composition of the Solutions
The principle ingredient of hydrothermal solutions is water. Pure water, however, can not dissolve metals.
Hydrothermal solutions are always brines, containing dissolved salts
such as NaCl, KCl, CaSO4 and CaCl2.
The range in salinity varies from that of seawater (around 3.5 wt %) to about ten times the salinity of seawater.
Such brines are capable of dissolving small amounts of elements such as Au, Ag, Cu, Pb and Zn. High temperatures increase the effectiveness of the brines to dissolve metals
67 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Conditions necessary for the formation of hydrothermal ore deposits
Presence of hot water to dissolve and transport minerals
Presence of interconnected openings in the rock to allow the solutions to move
Availability of sites for the deposits, and
Chemical reaction that will result in deposition
68 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Openings
Pore spaces, crystal lattices, bedding planes, vesicles, cooling cracks, breccias, fissures, shear zones, folding and warping, volcanic pipes, solution and rock alteration etc. are the various types of openings in the rocks permitting movement of solution or deposition of ore-minerals.
For large deposits vast quantities of solution and fairly large confined channel ways are needed. The flow of solution must be confined to avoid dispersal of mineral matter.
Fissures, shears and permeable beds may provide confined channel-ways. Volcanic breccias, on the other hand, exhibit widespread permeability and the mineralizing solution is spread over a large area which results in dispersed ore. Crystal lattices permit diffusion which is a slow process and may not generate large deposits.
The deposition from hydrothermal solutions is influenced due to chemical changes in solution, reactions between solution and wall rocks or veins matter and changes in temperature and pressure. The loses temperature and pressure which decreases solubility and promotes precipitation.
The heat loss is also influenced by nature of openings. Open fissures with straight wall would cause less heat loss than the intricate openings of breccia with large exposed area.
Although hydrothermal ore deposits may form in any host rock, deposition is influenced or localized by certain kinds of rock.
For example, lead-zinc-silver ores in some parts of Mexico occur in dolomitic rather than pure limestone
69 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Wall rock alteration
The wall-rock alteration is quite common in case of hydrothermal deposits.
The nature of mineralizing solution like its chemical character, temperature and pressure as well as character and kind of wall rock decide about the nature and intensity of alteration. Sericitization, kaolinisation and silicification are the common forms of alteration in the wall rock.
High temperature minerals like tourmaline, topaz and amphibole may develop. Basic and ultrabasic igneous rocks are serpentinized accompanied by the production of epidote and chlorite.
Advanced argillic - characterized by the clays dickite, kaolinite and pyrophyllite (all hydrated aluminum silicates) and quartz. Sericite may be present as well as alunite and tourmaline. Alteration involves the extreme leaching of cations, especially the difficult to leach alkalis and calcium, and the concentration of H+. This type of alteration is characteristic of many epithermal precious metal deposits and a smaller number of mesothermal deposits such as Butte, Montana.
Potassic alteration - characterized by secondary kspar + biotite. Anhydrite may be present, but its susceptibility to solution generally results in its dissolution in near surface environments. Because it is characterized by common silicates, potassic alteration is often difficult to detect. Pyrite and minor chalcopyrite and molybdenite are the only ore minerals associated with this alteration.
Sericitization (Phyllic) - characterized by the assemblage quartz + sericite + pyrite. Generally the most common form of alteration. Sulfides present, in addition to pyrite, include chalcopyrite, bomite and a variety of less common copper sulfides. rock. Generally the result of oxidation of Fe.
70 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Argillic - characterized by kaolinite + montmorillonite. Somewhat similar to advanced argillic alteration, but with a lesser degree of leaching of cations. Also unlike advanced argillic alteration which is associated with vein type deposits, argillic alteration is more closely associated with disseminated deposits, porphyry coppers in particular. Sulfides are less common in association with this alteration type.
Propylitic - characterized by the assemblage chlorite + epidote + calcite. Albite as well as other carbonates may be present. Due to presence of the green minerals chlorite and epidote this zone is usually easily recognizable by its color. Associated sulfides include pyrite, copper sulfides, galena, sphalerite and a host of complex arsenides. Often this zone can be quite large and is useful during mineral exploration. Unlike the previous types above which are characterized by leaching of cations this zone seems to represent the addition of cations.
Silicification - characterized by quartz or chert. Can be added by solutions as is the case in many low temperature deposits or the result of complete leaching of all cations plus aluminum.
Dolomitization - addition of magnesium to limestone to form dolomite. Common in Mississippi Valley type deposits.
Other alteration types:
Feldspathization - kspar + albite, forms in the deep zones of some porphyry copper deposits.
Greisenization - tourmaline + topaz + cassiterite + various tungsten- bearing minerals. Common form of alteration on association with porphyry tin deposits.
Fenitization - characterized by nepheline, alkali feldspar and Na-bearing amphiboles. Hematization - characterized by secondary hematite.
Bleaching - not characterized by any specific mineral assemblage, but rather a color change between altered and unaltered rock. Generally the result of oxidation of Fe.
71 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Types of Deposits
The hydrothermal deposits are formed within a temperature range of 500 to 50°C.
The modes of formation are replacement and cavity filling.
Lindgren divided this class into three subclasses viz. (a) hypothermal, (b) mesothermal and (c) epithermal, according to the temperature of formation of the minerals
The replacement deposits are formed at the higher end of the temperature range and close to the intrusive. Most deposits of gold, silver, copper, lead and zinc, mercury, antimony and molybdenum come under this class.
Most deposits of minor metals and many non-metallic minerals are formed by this process. Cr, Ti, V, Zr, U, Ce, Ta and Pt are absent in deposits of this class.
The replacement deposits have always an alteration zone surrounding the ore-bodies. The nature of the alteration varies with the kind of enclosing rocks. The different types of wall rock alteration characteristic of different sub-classes of hydrothermal deposits may be summarised as follows :
1. Hypothermal : Greisenization, Serpentinization
2. Mesothermal : Sericitization, silioification. and argillic alteration
3. Epithermal : Silicification, argillic alteration & alunitization.
The wall rock alterations have often been used as a guide to ore- finding for where weathering has removed the top of the ore-body, these alteration haloes serve as indicator of hidden ore-bodies.
72 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Hydrothermal Deposits Forming Today 1.Imperial Valley, southern California In 1962, oil/gas drilling struck a 350°C brine at 1.5 km depth. As the brine flowed upwards and cooled, it deposited a siliceous scale. Over a period of 3 months, some 8 tons were precipitated, containing 20 wt % Cu and 8 wt % Ag. This was the first unambiguous evidence that mineral deposits can be formed from hydrothermal fluids. 2.Red Sea In 1964, oceanographers discovered a sries of hot, dense brines at the bottom of the Red Sea. The higher density of the brines (i.e. increased sanility) means that they remain at the bottom of the sea, despite being hot. The sediments at the bottom of these pools contain ore minerals such as chalcopyrite, sphalerite and galena. The Red Sea is a stratabound mineral deposit in the making. 3.East Pacific Rise In 1978, deep-sea submarines on the East Pacific Rise, at 21°N, found 300°C hot springs emerging in plumes along the oceanic ridge, 2500 m below sea level. Minerals precipitated out of the solution as soon as it emerged, and around the vents was a blanket of sulphide minerals. This is the modern analogue of volcanogenic massive sulphide (VMS) deposits.
Control of ore localisation The ore localisation is controlled by the following factors:
Chemical and physical characters of host rock: this determines the location, shape and size of opening. For example, carbonate rocks permits solution openings and brittle rocks shatter more readily to localize fractures or breccia. Permeability which is necessary in rock for passage of solution and ore localisation is caused due to pore spaces, fissibility, cleavage planes, brecciation, joints, fractures etc.
Structural features: structural features like fissures, shears, folds, faults, bedding planes, lamination and unconformity serve important localisers of hydrothermal deposits.
Intrusives: intrusive being source of ore-bearing fluid, constitute ore loci on a regional scale.
73 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
74 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Submarine hydrothermal vent or “Black Smoker”
Cavity filling and replacements are the two types of deposits formed due to hydrothermal processes.
Cavity filing is due to deposition of minerals in various types of openings
Metasomatic replacement or replacement deposit the earlier formed minerals is replaced by the new mineral.
In general, replacement deposits are formed at higher temperature and pressure, and cavity filling deposits at lower temperature and pressures.
However, both types of deposits may also form at the same time and at all temperature.
75 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
(a) CAVITY FILLING
The precipitation of minerals forms mineralizing solution in the cavities or the open spaces in rock forms cavity filling deposits.
The walls of the cavity are lined first by the first mineral to be deposited. The minerals usually grow inward with development of crystal faces pointed towards the supplying solution in the form of comb structure.
Successive crust of different minerals may be precipitation and if the cavity is a fissure, a crustified vein is formed.
Symmetrical crust may result with similar precipitation on both the walls of the vein, and asymmetrical with unlike crustification on each side. In case of breccia, the crusts surround the breccia and cockade ore is formed.
The cavity filling may also give rise to ribbon structure with narrow layers of quartz separated by thin dark seams of altered wall rock. The following types of deposits may result due to cavity filling -
Fissure vein:
It is a tabular type of deposit, involving formation of fissure itself by stresses operating within earth’s crust, and ore forming processes, e.g. fissure filling deposit of magnesite in Salal area, Jammu.
These fissure veins may be massive or crustified. They may be simple, composite, linked, sheeted, dilated and chambered.
They may be vertical or inclined. Pinches and swells produced by movement along irregular fissures may occur. Several minerals, both ore and gangue, may fill in the fissure.
Fissures may occur in groups, and may have formed at the same time or may be different ages. The depth of fissure vein is quite variable. Some of them continue to depth of several thousand metres like those at Kolar Gold Mine.
76 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Segregated Veins of Auriferous Quartz in Gneiss
Fig. 1. - Gash Viens filled with Lead Ore Galena Lime stone. a.Crevie opening.b, c. Crevices with pocket openings.
Fig. 2. - Horizontal Gash Veins or Floors of Lead in Galena Limestone, a. Crvice with pocket opening, b. Crevice opening. Fig. 6. - Fissure Vein with Cavity of "Tug" at Centre. aa Country rock, bb. Heavy spar, c c. Calc spar. dd. Blende, e e. Coinby quartz. f. Vug.
77 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Crustiform banding
78 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Shear zone deposits: a shear zone with sheet like connected openings, and large exposed surfaces serves as excellent channel ways for mineralizing solutions and precipitation takes places as thin plates of minerals or in the form of fine grains, e.g. Singhbhum shear zone deposits.
Stockwork: it signifies a network of small ore bearing veinlets and stringers traversing a mass of rock. The veinlets show crustification, comb-structure and druses, and represent open space fillings. For example, in Zawar area, Rajasthan, veins and stringers of galena and sphelerite traverse dolomite mass and form lenticular bodies. Stockworks of asbestos occur in the Archeaen terrain of Barabana area, Singhbhum, Bihar.
Saddle reef: it results when alternating competent and incompetent rocks are closely folded. This gives rise to openings in the crest part of the arch, which latter on filled with ore minerals. The quartz reefs of Hutti gold deposit, Karnataka, and those of Wynad gold deposit, Tamil Nadu are the best illustrations.
Anticlinal fold in sandstones and shales, United Kingdom. The white material in the hinge of the fold at the center of the photograph is quartz, and fills a void that opened up during folding. Such filled-in features are called saddle reefs.
79 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Gold-bearing quartz vein of an orogenic gold deposit, which has been sheared several times. Fluids migrated along the shear bands (dashed) and mineralized the quartz with sulfides and gold.
80 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Ladder veins: this type of deposit forms due to transverse veins or fracture, e.g. magnesite deposit of Mysore, Karnataka, and asbestos deposits of Cuddapah district, AP.
Pitches and flats: these are formed due to folding of brittle sedimentary beds which gives rise to a series of disconnected deposits. Iron-ore deposits of Bailadila and Chotadongar, Baster district, MP, lead – zinc deposits of Baghmari (Katuria), Banka district, Bihar, and talc deposits of Cannore and Kalicut district, Kerela are the several examples.
Breccia filling deposits: the breccias offer openings spaces in between the angular fragments for deposition by the mineralizing solutions traversing through them. These may be volcanic breccia, tectonic breccia or collapse breccia deposits. Wajrakarur kimberlite pipe, AP, and fault breccia in Singhbhum Shear Zone, Bihar with copper, lead, uranium and apatite mineralization may be cited as examples.
Solution cavity filling: certain solution forming rocks like limestone, gives rise to this type of deposit e.g. barytes deposits in Krol limestone of Sirmur district, Himachal Pradesh.
Pore cavity filling: many mineral deposits occur as pore space fillings, say in sandstone. Oil, gas and water are the most important among all. Disseminated lead-zinc deposit in gritty conglomerate dolomite and quartzite of Zawar, Rajasthan is an example of pore space filling.
Vesicular filling: the vesicular lava flows being permeable form channel ways for mineralizing solution and sites of mineral deposits. Copper occurrence is Dras volcanics, Kargil area, Jammu and Kashmir and in Deccan trap of Maharastra and Gujarat, and agate, chalcedony, amethyst and opal occurrences in the Deccan trap is the examples of vesicular fillings.
81 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Solution cavity filling: certain solution forming rocks like limestone, gives rise to this type of deposit e.g. barytes deposits in Krol limestone of Sirmur district, Himachal Pradesh.
Pore cavity filling: many mineral deposits occur as pore space fillings, say in sandstone. Oil, gas and water are the most important among all. Disseminated lead-zinc deposit in gritty conglomerate dolomite and quartzite of Zawar, Rajasthan is an example of pore space filling.
Vesicular filling: the vesicular lava flows being permeable form channel ways for mineralizing solution and sites of mineral deposits. Copper occurrence is Dras volcanics, Kargil area, Jammu and Kashmir and in Deccan trap of Maharastra and Gujarat, and agate, chalcedony, amethyst and opal occurrences in the Deccan trap is the examples of vesicular fillings.
Archaen Gold – Structural Settings
82 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Quartz veins formed in this rock.
When minerals are deposited in open spaces, large crystals form
83 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Amygdules (mineral deposits filling extrusive vesicles) in the Neoproterozoic- aged Catoctin Formation meta-basalt, Shenandoah National Park, Virginia.
84 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metasomatic replacement is defined as a process of simultaneous solution and deposition by which earlier formed mineral is replaced by a new one
Metasomatic replacement deposits form, when the hydro- thermal solutions react with some mineral or substances in the crust, dissolving one substance and replacing it with the ore condition Mostly these deposits are formed under hypothermal condition
The chemical composition and physical characteristics of the host rocks or minerals and the composition, temperature and pressure of the invading mineralising solutions determine the Metasomatic replacement deposits are characterised by:
(a) Presence of remnants of the country-rock.
(b)Presence of pseudomorphs of replacing minerals after the replaced ones.
(c) Absence of crustification etc.
Volcanogenic Massive Sulphide (VMS) Deposits At divergent boundaries, water from the ocean floor flows through fractures in the oceanic crust. The waters are heated by the nearby magma source, producing a seawater convection cell which reacts with neighbouring rocks to leach out metals.
These dissolved metals are transported to the ocean floor where they mix with cold bottom waters. The sudden decrease in temperature causes the minerals to precipitate from solution and they are incorporated into sediments deposited along the ocean ridge system.
Circulation of fluids and precipitation of mineral deposits at divergent boundaries
85 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Ore Deposits Formed by Metamorphism
86 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metamorphic processes profoundly alter pre-existing mineral deposits and form new ones. The chief agencies involved are heat, pressure, time, and various solutions. The materials acted upon are either earlier formed mineral deposits or rocks. Valuable nonmetallic mineral deposits are formed from rocks chiefly by the crystallization and the combination of rock making minerals.
Role of Temperature and Pressure
Metamorphic processes occur to make adjustments between the chemical potential of any system and the changes in temperature and pressure.
A particular chemical reaction that cannot occur in one environment may readily do so under different temperature and pressure conditions.
An increase in pressure will cause a reaction to move in a direction in which the total volume of the system decreases, for example increasing pressure results in the following changes with a reduction in the total molar volume:
87 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Olivine + anorthite garnet augite +anorthite garnet + quartz ilmenite + anorthite sphene + hornblende nephelene + albite glaucophane or jadeite anorthite + gehlenite + wollastonite grossularite andalusite sillimanite kyanite An increase in temperature normally results in endothermic reactions. A possible example is the conversion of pyroxene to hornblende during the metamorphism of diabase to amphibolite.
In short, metamorphic reactions result from the tendency of mineral systems to adjust to their physicochemical environment of high temperatures and pressures in contrast to the low temperatures of weathering processes, both of which processes generally occur in the presence of water.
Metamorphism of Earlier Deposits When rocks are metamorphosed, enclosed mineral deposits may also be metamorphosed. Unlike rocks that undergo both textual and mineralogical changes, Ores undergo less mineral re-combinations. Textual changes, however, are pronounced. Schistose or gneissic textures are induced, particularly with sectile minerals, and flow structure is not uncommon. Galena, for example, becomes gneissic. It may also be rendered so fine grained that individual cleavage surfaces cannot be discerned with a hand lens. It "flows" around hard minerals, such as pyrite. Other minerals, such as chalcopyrite, bornite, covellite, or stibnite, behave similarly. The result is that ores may exhibit streaked, banded, smeared appearances with indistinct boundaries between minerals of different color. The original textures and structures may be so obscured that it is difficult to determine to which class the originally deposits belonged. Such deposits are then classified as "metamorphosed".
88 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Formation of Mineral Deposits by Metamorphism Several kinds of nonmetallic mineral deposits are formed as a result of regional metamorphism. The source materials are rock constitutions that have undergone recrystallization or re-combination, or both. Rarely, water or carbon dioxide has been added, but other new constitutions are not introduced as they are in contact metasomatism deposits. The enclosing rocks are wholly or in part metamorphosed; it is the rock metamorphism that has given rise to the deposits. The chief deposits thus formed are asbestos, graphite, talc, soapstone, andalusite-kyanite-sillimanite, dumortieritea, garnet, and possibly some emery.
Asbestos forms by the metamorphism (hydration) of ultrabasic igneous rocks – peridotites and dunites. Graphite forms by regional metamorphism of organic matter, crystallization from igneous rocks, contact metamorphism and hydrothermal solutions. Talc, soapstone and pyrophyllite form by a mild hydrothermal metamorphism of magnesian minerals eg tremolite, actinolite, olivine, epidote and mica. Talc also occurs in regionally metamorphosed limestones, altered ultrabasic igneous rocks, and contact metamorphic zones. Andalusite-kyanite-sillimanite – these minerals are high grade refractories. Kyanite is formed by the dynamothermal metamorphism of aluminous silicate minerals. Andalusite is formed by the pneumatolytic action on aluminous silicates. Sillimanite results from high temperature metamorphism of aluminous crystalline rocks. Garnet forms during the regional and contact metamorphism and is consequently found in schists and gneisses. It is also found as a constituent of igneous rocks. Emery is a mixture of corundum and magnetite with hematite or spinel and is a product of contact metamorphism.
89 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Bedded manganese deposits in parts of Madhya Pradesh and Maharashtra, primarily of sedimentary origin, have been subsequently effected by metamorphism. Braunite, a manganese silicate, is the important ore mineral besides several other oxide minerals.
Ore Deposits Formed by Sedimentation
The process of sedimentation results in the formation of some important mineral deposits viz., iron, manganese, copper, phosphate, coal, oil shale, carbonates, cement rock, diatomaceous earths, bentonite, fuller’s earth magnesite, sulfur and uranium-vanadium deposits.
The essential conditions for the formation of sedimentary deposits are:
1) an adequate source of material
2) gathering of the solution by solution or other processes
3) transportation of the material to the site of deposition, and
4) deposition of material in sedimentary basins.
5) Compaction, alteration or other chemical changes may follow deposition.
90 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Source of Material: Materials of sedimentary deposits have been derived chiefly from:
1) weathering of rocks 2) weathering and oxidation of former mineral deposits viz., iron, manganese, copper.
The earth’s crust contains on average 5.6% Fe. This means that beneath the surface, upto a depth of 30 km, the earth’s crust contains about 30 million tons/km2 of iron. Of this, only 0.0001% is concentrated in commercial deposits. Iron in sedimentary rocks comes from the iron bearing minerals of igneous rocks such as hornblende, pyroxene and mica, from the iron-bearing minerals of sedimentary and metamorphic rocks, and from the red coloring matter of sedimentary rocks. Manganese of sedimentary deposits hs been derived from the weathering of Mn-bearing minerals in rocks, former sedimentary concentrations and lode deposits of manganese. Mn makes up about 0.095% of the earth’s crust, there being 50 times as much iron as manganese. There are over 200 minerals containing manganese as an essential constituent.
The source of sedimentary phosphate is phosphorous bearing minerals , among which apatite is the most common. Some phosphorous is also derives from the weathering of collophanite and dahllite in sedimentary rocks. Constituents of sedimentary carbonates viz., industrial limestone, dolomite and magnesite are derived from the sea or saline waters to which they are largely supplied by rock weathering. Constituents of clay deposits, bentonite and fuller’s earth originate in rock weathering. Solution & Transportation: Solution of material constituting sedimentary deposits goes on during weathering. This is true of Fe, Mg, P, CO3, Cu, and some rare metals, but not of clays. The chief solvents are carbonated waters, humic and other organic acids and sulfate solutions.
91 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Carbonated Waters:
These are very effective solvents of limestones, iron, Manganese and phosphorous. Vast quantities of metals are transported as carbonates by carbonated waters. Ferrous iron is soluble whereas ferric iron offers resistance.
To undergo solution, ferric iron must first b converted to the ferrous state. Organic matter aids such a conversion. The Precambrian iron ores were probably transported as ferrous bicarbonate solutions or in the colloidal state.
Humic and other Organic Acids:
These are the decomposition products of vegetation and are considered excellent solvents. Weak organic acids dissolve large quantities and are the most effective of all solvents. It has been noticed that iron is not carried as bicarbonate in surface waters rich in organic matter.
Sulfate Solutions: These are excellent solvents of Fe and Mn but rarely abundant enough to effect large scale solution and transportation.
FeS2 + 7O + H2OFeSO4 + H2SO4
Most of the materials (except coal) are transported by rivers and subsurface waters.
Most often these substances reach the sea, but some are arrested en route and are deposited in inland water bodies or basins. The dissolved substance remain in solution so long as the solution does not undergo any appreciable physical or chemical change. Some or all of the iron and manganese may be lost if the solution traverses limestone country.
If Fe and Mn escape these hazards, they may be transported to bogs, lakes, playas or the sea, where their concentration and deposition takes place.
92 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Five important processes are associated with the sedimentary mineralisation, viz.
1.Residual concentration.
2. Mechanical concentration.
3. Oxidation and Supergene Enrichment.
4. Remobilisation by meteoric circulating water.
5. Sedimentation.
The manner of deposition depends upon:
a) The nature of solvent b) The place of deposition c) The pH and Eh (redox) conditions, eg. in the sea or swampy basins.
Deposition from solutions depends upon the environmental relations of chemical sediments in normal sea water.
Depositional Separation of Manganese & Iron:
Depositional Separation of Manganese & Iron:
Separation of manganese and iron occurs if precipitation is taking place from carbonate solutions. This happens because manganese carbonate is more stable in carbonate solutions than iron carbonates, and is hence carried further than the latter.
The separation of iron and manganese in an oxidizing environment takes place because the iron oxides precipitate at a lower oxidation potential than the comparable manganese compounds at any given pH.
Similarly under fixed Eh, iron starts precipitating as an oxide at a lower pH than manganese. In a neutral environment both iron and manganese may precipitate together as carbonates.
93 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Residual concentration: The term 'residual concentration indicates the concentration of ores as residue. Residue left as insitu after weathering, followed by transportation sometimes give rise to valuable ore deposits.
These are the insoluble products of rock weathering, the process which removes the undesired constituents of rocks or minerals. The residue may continue to accumulate until their purity and volume make them commercially important.
Of the three modes of weathering, the chemical mode of weathering is of paramount significance for the formation of residual deposits The effects of weathering usually do not extend deeper than a couple of meters but occasionally reach 30 to 60 meters. It is most active in tropical and sub-tropical climates.
In such climates, rock decay is carried further; leaching is more complete; the silicates are thoroughly broken down and surface water readily removes the silica, thus bringing about the concentration of the residual material which, when useful, forms valuable mineral deposits.
Process of Formation of Residual Deposits: The first condition is the availability of rocks or lodes containing valuable minerals, of which the undesired substances are soluble and the desired ones insoluble under surface conditions. The climatic conditions should favour chemical decay. Tropical & sub-tropical climatic conditions are most favourable. The relief must not be too great, or the valuable minerals will be washed away as soon as they are in the least concentrated. Long continued crustal stability is essential for residues to accumulate in quantity, and the deposits may not be destroyed by erosion. Important deposits include: Iron ores, manganese, bauxite, clays, nickel, phosphate, kyanite, barite, ochers, tin, gold, etc. Given these conditions, a limestone formation with minor iron oxides will slowly be dissolved leaving the insoluble iron oxides as a residue. As bed after bed of limestone disappears, an overlying mantle of iron ores of sufficient thickness, and grade accumulates to make a workable deposit.
94 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Residual deposits therefore form in two ways:
1) the residue is simply an accumulation of a mineral that has not changed during the process e.g. iron oxides in banded iron formations, and
2) the valuable mineral first comes into existence as a result of weathering processes, and then persists and accumulates e.g. the feldspars of a syenite decomposes upon weathering to form bauxite, which persists at the surface while other constituents are removed in solution.
Valuable deposits of iron ore, manganese, bauxite, clays, nickel, phosphate, kyanite, barite, ochre, tin, gold and other substances occur as residual concentrations.
Residual Deposits and their Source Materials:
Iron Concentrations:
1) Lode deposits of siderite or iron sulfides - these residues are rarely used as iron ores.
2) Disseminated iron minerals in non-aluminous limestones.
3) Limestones that have been partly replaced by iron minerals, either before or during the period of weathering.
4) Basic igneous rocks.
5) Ferruginous siliceous sediments.
95 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Lateritic Residuum (a-c) and Ferricrete (d-f)
Manganese Concentrations:
1) Limestones or dolomites low in alumina but containing disseminated syngenetic manganese carbonates and oxides.
2) Limestones containing disseminated introduced manganese. Carbonate rocks precipitate manganese under certain conditions.
3) Manganiferous silicate rocks such as crystalline schists or altered igneous rocks.
4) Lode deposits of manganese minerals or ores high in manganese e.g. veins, replacement deposits or contact metasomatic deposits (containing rhodochrosite, rhodonite, manganiferous siderite and calcite, spessartite, tephroite, alleghenite, piedmontite, hausmannite, manganosite, etc.).
96 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Bauxite Formation: Rocks relatively high in aluminum silicates and low in iron and free quartz e.g. 1) nephline syenite. 2) Limestones or clays in limestones 3) Clastic sediments derived from Archaean rocks 4) Basalts 5) Clay alluvium 6) Feldspathic sandstones
Clay Formation: The source rocks are crystalline rocks and silicic granular rocks rich in feldspars and low in iron minerals such as: 1) Granites and gneisses 2) Basic ignous rocks 3) Feldspar rich pegmatites 4) Syenites 5) Limestones 6) Shales 7) Sericitized igneous rocks
Formation of Mineral Deposit by Mechanical Concentration:
When mineral grains of different density are moved by flowing water, the less dense grains will be most rapidly moved, and a separation of high-density and low-density grains can be effected. Mineral deposits formed as a result of gravity separation based on density are called placer deposits.
For effective concentration, placer minerals must not only have a high density (greater than about 3.3 grams per cubic centimetre), they must also possess a high degree of chemical resistance to dissolution or reaction with surface water and be mechanically durable.
The common sulfide ore minerals do not form placers, because they rapidly oxidize and break down.
Ore minerals having suitable properties for forming placers are the oxides cassiterite (tin), chromite (chromium), columbite (niobium), ilmenite and rutile (titanium), magnetite (iron), monazite and xenotime (rare-earth metals), and zircon (zirconium). In addition, native gold and platinum have been mined from placers, and several gemstone minerals--in particular, diamond, ruby, and sapphire--also concentrate in placers.
97 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Requirements for mechanical concentration: (a) The valuable minerals should be of high specific gravity. (b) They should be chemically resistant to weathering. (c) They should be of adequate durability. (d) There should be a continuous supply of placer minerals for concentration.
Factors Affecting Formation of Placer Deposits: (i) Specific gravity of minerals. (ii) Specific surface of the particles. (iii) Shape of the particles. (iv) The ability of a body of flowing water to transport the particles and the viscosity of the transporting medium.
These are essentially four factors which have much significance in the formation of placer deposits, they are:
(i) Geomorphological factors. (ii) Climatic factors. (iii) Hydrographic factors which is associated with the river action and the deposits at the meandering of the river and the junction between the tributaries. (iv) Tectonic factors, which is associated with the rejuvenation of the base level of local and general erosion, creating conditions for recurrent cycles of erosional activity for development of alluvial placers.
98 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Types of placer deposits: (a) Eluvial placers: Placer deposits along hill slopes are formed due to weathering and erosion of the country rocks containing low-grade deposits of the desired materials and are known as eluvial placers. (b) Deluvial placers: When the weathered and disintegrated material is shifted down hills deluvial (scree or talus) placers are formed. (c) Proluvial (colluvial) placers: Accumulation of the material at the foot of a slope can lead to the development of proluvial placers. (d) Alluvial placers: Running water is the most important agency in the formation of alluvial placers. Irregularities on the floor of the channel in the form of natural barriers or riffles encourage deposition of placer deposits. Besides, at the meander¬ing of the river and at the confluence of tributaries, alluvial placers are formed. (e) Aeolian placers: These are because of wind action, by which the lighter sand particles are blown away leaving behind a mass of coarser detritus containing valuable minerals. (f) Beach placers: These are formed along the shores of lakes seas and oceans, mainly by the wave action.
99 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Elluvial and Residual Deposits
Alluvial Deposits
100 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Placer deposits occur in any area where current velocity is low, such as;
2) behind rock bars 1) between ripple marks
Placer Stream Direction Placer Stream Direction Deposit Deposit
3) on the inside of 4) in holes on the . meandering bottom . of a stream streams
Placer Placer Stream Direction Deposit Deposit
Alluvial Deposits
101 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Alluvial Deposits
Beach Placers
102 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Ore Deposits Formed by Oxidation and Supergene Enrichment
The portion of the ore-body lying above the water-table is described as the zone of oxidation, since within this zone the ore- minerals forming the deposit may be oxidised readily in presence of air and water.
By the reaction of the surface water containing free oxygen with the ore a solvent is formed. This solvent is very reactive and is helpful to oxidise the whole of the rock up to the water-table.
An orebody thus becomes oxidized and generally leached of many of its valuable materials down to the groundwater table, or to depth where oxidation cannot take place.
This process is called as 'Infiltration' deposits also. This involves weathering and leaching of the upper parts of a mineral deposit (zone of oxidation) and re-deposition of the ore-minerals at lower levels (zone of secondary or supergene enrichment).
As the cold, dilute, leaching solutions trickle downwards, they may lose a part or all of their metallic content within the zone of oxidation to give rise to oxidized ore deposits
The oxidized or near-surface part of an orebody is made colorful due to the oxidation of sulfides to oxides and sulfates.
As the down trickling solutions penetrate the water table, their metallic content may be precipitated in the form of secondary sulfides to give rise to a zone of secondary or supergene sulfide enrichment.
The lower, unaffected part of the orebody is called the hypogene zone.
103 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Secondary enrichment An especially important class of residual deposit is formed by both the removal of valueless material in solution and and redeposition of valuable ore minerals.
Because solution and redeposition can produce highly enriched deposits, the process is known as a secondary enrichment.
Different circumstance of Secondary enrichment 1) The first circumstance arises when gold-bearing rocks--even rocks containing only traces of gold--are subjected to lateritic weathering. Under such circumstances, the gold can be secondarily enriched into nuggets near the base of the laterite.
The importance of secondary enrichment of gold in lateritic regions was realized only during the gold boom of the 1980s, especially in Australia.
104 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
2.) The second circumstance involves mineral deposits containing sulfide minerals, especially copper sulfides, that are subjected to weathering under desert or tropical conditions.
Sulfide minerals are oxidized at the surface and produce sulfuric acid, and acidified rainwater then carries the copper, as copper sulfate, down to the water table.
Below the water table, where sulfide minerals remain unoxidized, any iron sulfide grains present will react with the copper sulfate solution, putting iron into solution and precipitating a copper mineral.
The net result is that copper is transferred from the oxidizing upper portion of the deposit to that portion at and just below the water table.
Secondary enrichment of porphyry copper deposits in the southwestern United States, Mexico, Peru, and Chile is an important factor in making those deposits ores. Lead, zinc, and silver deposits are also subject to secondary enrichment under conditions of desert weathering.
3.) The third circumstance in which secondary enrichment is important involves Banded Iron Formations and sedimentary manganese deposits.
A primary BIF may contain only 25 to 30 percent iron by weight, but, when subjected to intense weathering and secondary enrichment, portions of the deposit can be enriched to as high as 65 percent iron.
Sedimentary manganese deposits, especially those formed as a result of submarine volcanism, must also be secondarily enriched before they become ores.
105 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chemical Changes:
There are two main chemical changes within the zone of oxidation:
a) Oxidation, solution and removal of the valuable material. b) Transformation, in situ, of metallic minerals into oxidized compounds.
Most metallic minerals contain pyrite, which rapidly yields sulfur to form iron sulfate and sulfuric acid:
FeS2 + 7O + H2O →FeSO4 + H2SO4 2FeSO4 + H2SO4 + O → Fe2(SO4)3 + H2O
The ferrous sulfate readily oxidizes to ferric sulfate and ferric hydroxide:
6FeSO4 + 3O + 3H2O → Fe2(SO4)3 + 2Fe(OH)3 The ferric sulfate hydrolizes to ferric hydroxide and sulfuric acid: Fe2(SO4)3 + 6H2O → 2Fe(OH)3 + 3H2SO4
Ferric sulfate is also a strong oxidizing agent and attacks pyrite and other sulfides to yield more ferrous sulfate: Fe2(SO4)3 + FeS2 →3FeSO4 + 2S The ferric hydroxide changes over to hematite and goethite and forms the ever present “limonite” that characterizes all oxidized zones; The part played by ferric sulfate as a solvent can be seen by the following reactions: Pyrite FeS2 + Fe2(SO4)3 → 3FeSO4 + 2S Chalcopyrite CuFeS2 + 2Fe2(SO4)3 → CuSO4 + 5FeSO4 + 2S Chalcocite Cu2S + Fe2(SO4)3 →CuSO4 + 2FeSO4 + CuS Covellite CuS + Fe2(SO4)3 →2FeSO4 + S Sphalerite ZnS + 4Fe2(SO4)3 + H2O →ZnSO4 + 8FeSO4 + 4H2SO4 Galena PbS + Fe2(SO4)3 + H2O + 3O →PbSO4 + 2FeSO4 + H2SO4 Silver 2Ag + Fe2(SO4)3 → Ag2SO4 + 2FeSO4
Most of the sulfates formed are readily soluble, and these cold dilute solutions slowly trickle downwards through the deposit till the proper Eh-pH conditions are met to cause deposition of their metallic content. If pyrite is absent in deposits undergoing oxidation, only minor mounts of solvents are formed, and the effects are mild. This is illustrated in the New Cornelia Mine, Ajo, Arizona.
106 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Gossan:
Oxidation, solution and consequent downward move¬ment of the valuable minerals lead to the concentration of useless residual materials and some of the desiccated products of oxidation upon the surface, where the ore-body had its outcrop and these together form a hard mantle known as gossan or cap-rock.
The gossan is made up principally of limonite, gangue minerals and some of the oxidised products of the ore minerals. Sometimes, false gossans are, however, produced as a result of precipitation of extraneous ferruginous solutions upon the exposed surfaces of the country-rocks.
But in the majority of cases, gossans supply many decipherable inferences as to the size, character and mineral contents, of the hidden ore deposits. Therefore gossans are considered as sign boards of oxidised as well as enriched zones beneath the surface.
107 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Ore Deposits Formed by Evaporation
Evaporation is an important mineral forming process, which supplies valuable materials used by the housewife, farmer, builder, chemist, engineer, manufacturer and even birds, beasts and plants.
Great sections of the oceans may be cut off during slow oscillations of land and sea and be gradually evaporated to yield deposits of gypsum, common salt and potash.
Ground waters reaching arid surfaces leave behind valuable minerals upon evaporation.
Lakes may disappear under arid conditions to form playas
Conditions of Formation: Evaporation proceeds most rapidly in warm humid climates. Evaporation o bodies of saline water leads to concentration of soluble salts, and when supersaturation is reached, the salts are precipitated. Deposition of minerals by evaporation depends on supersaturation, which in turn depends upon other factors, chief of which are: a) temperature b) pressure c) depositional environment, and d) seasonal & climatic changes Sea water is the prime source of minerals formed by evaporation. About 3.45% of which consists of dissolved salts of which 99.7% by wt. Is made up of only seven ions: Na+ (30.61), Mg2+ (3.69), Ca2+ (1.16), K+ (1.10), Cl- (55.04), SO42- (7.68) and HCO3- (0.41). About 45 other elements whose concentration is known in sea water occur as trace minerals in evaporites. Few carbonates occur in marine evaporites as compared to terrestrial evaporites. Calcite, dolomite and magnesite are the chief carbonates of marine evaporites.
108 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Deposition from Oceanic Waters:
The salts of oceanic waters are mainly obtained from the weathering of terrestrial rocks. Rain water carries soluble salts from continental areas to the oceans, evaporates, leaving behind the salts, to return to the continents as more rain. Small mounts are contributed by submarine volcanism, and by solution from oceanic rocks. The total amount of salts in the ocean is estimated to be 21.8 million km3, enough to form 60 m thick layer over the ocean bottom. Of this common salt would constitute 47.5 m, MgCl2 5.8 m, MgSO4 3.9 m, CaSO4 2.3 m and the remaining salts 0.6 m. The rivers of the world are estimated to contribute 4 billion tons of salt to the ocean annually. Ocean water also contains gold, silver, base metals, manganese, aluminum, vanadium, nickel, cobalt as well as iodine, fluorine, phosphorous, uranium, arsenic, lithium, rubidium, cesium, barium and strontium.
Of these, iodine concentrates in sea weeds, copper in shellfish, manganese, copper, nickel and other metals in nodules which alone have become concentrated into potentially commercial deposits. To attain the necessary conditions to induce precipitation, bodies of sea water must become isolated from the ocean in places where evaporation exceeds inflow. Such isolation may be effected by: a) formation of barrier reefs b) cutoffs near coasts where sills or reefs isolate sinking inland basins c) formation of sand bars If the original body of water contained 100 km3 of water and this were to be concentrated to 50 km3, the iron oxide and calcium carbonate present would be precipitated. The water would still contain 3500 million tons of salt of which 2700 million tons would be common salt. If evaporated to 20 km3, gypsum would be precipitated. When the volume reaches about 10 km3, common salt would be deposited. Subsequent evaporation would bring about deposition of magnesium sulfate and chloride followed by the bittern salts.
109 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Deposition from Salt Lakes:
The deposits formed from the evaporation of salt lakes are similar to those obtained from ocean water because salt lakes contain the same salts as the ocean, but generally in greater proportions. The relatively small size of lakes makes them more responsive to climatic changes resulting in greater fluctuations of deposition. Evaporites formed during periods of dessication may be redissolved during periods of subsequent expansion. Since lakes constantly receive new supplies of fresh water, salts and sediments, their deposits are generally thin bedded alternations of impure salts and clays. On salt playas, desert winds distribute sands and silt upon which later salts may be deposited during subsequent lake periods.
Deposition from Groundwater:
Evaporation of groundwater is universal and in arid regions the evaporites may accumulate as long as the climate remains dry. Groundwater contains salts similar to those of the ocean and salt lakes but their concentration is low and the proportion of individual salts may vary according to the character of the soil, bedrock, topography and climate. Calcium carbonate is almost always present; magnesium, sodium, potassium, iron and manganese compounds are common. Silica, phosphorous and locally boron and iodine are relatively abundant. Deposition ensues when evaporation occurs at or near the surface, or in caves. If the site of evaporation is fed by fresh supplies of groundwater, extensive deposits may eventually result. Evaporation of groundwater will proceed most rapidly where it is supplied relatively close to the surface viz., valley bottoms, slopes where hills and valleys merge, and long hill slopes interrupted by gentler or reverse grades.
110 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Deposits of economic importance are:
a) nitrate salts with iodine b) boron c) calcium and sodium carbonate d) common salt e) Gauber’s salt f) soda g) epsom salts h) borax
111 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ECONOMIC GEOLOGY e – Learning Material: Unit-3
Metallic Mineral Deposits
112 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Precious Metals - GOLD
Gold was the earliest metal mined by the mankind The references of gold mining are seen in holy scriptures like the Rid Veda, the Puranas, the shastras, the Hebrew, creek and Roman literatures, etc.
INDIA • Between 1967 and 1998 about 19 tons of gold has been mined from the KGF, 2 tons from Ramagiri & about 20 tons from Hutti Gold Mines – a total of about 41 tons
• India’s current production is only3 tons/annum from its only producing mine at Hutti and about 6 tons as a by product of copper mining
• The South Africa is the leading producer with 40 % of total world production, Russia – 17%, USA 7%, Canada 6.6 %, Australia 5%, India – 0.1 %
Gold potential of the Indian terrain • There were over a hundred gold mining centres in the early part of the last century & these were mostly operated by the Britishers. The mines were located in parts of Kolar, Hutti, Gadag, Chitradurga & Shimoga in Karnataka; Wynad & Nilambur in Kerala; Kotagiri & Dharmapuri in Tamil Nadu, Ramagiri & Jonnagiri in AP State; Kunderkocha, Lawa, Mayisara & Sonapet in Jharkand; Sonadehi in Chhattisgarh; Parsori & Pular in Maharashtra. Gold panning by local people is a prominent activity in many parts of India. • From a total of 127,242 tons of gold metal produced in the world, 76,500 tons came from precambrian terrains (Archaen & proterzoic). A major portion of India, barring the Indogangetic alluvial tract & Deccan lavas, is composed of precambrian rocks – yet our contribution to the precambrian gold resource is a meagre 1.17% (900 tons of which has come from a single precambrian belt ie Kolar) • Gold-bearing potentiality of a geological terrain can be expressed in terms of kilograms of gold per sqkm area comprising gold metal already produced + gold reserve in the ground identified by exploration & available for mining in the future. For Western Australia this index works out 50kg/sqkm, for Canada 55kg/sqkm and for S. Africa it is 80kg/sqkm. In comparison the index for India is a mere 1.6kg/sqkm (excluding Kolar) inspite of the fact that India has been known for wide spread gold mining in the past. Surely there is much scope for finding new mineable gold resources in the country.
113 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineralogy of Gold
Chemical Au Formula Composition Gold, with small amounts of silver; sometimes also copper and iron Variable (Au,Ag) ; Formula (Au,Ag,Cu,Fe) Color Golden yellow to brass yellow Streak Golden yellow Hardness 2½ - 3 Crystal Forms (Isometric) Dendrites, wires, nuggets, encrustations, and small flakes are the and Aggregates common forms. Octahedral, dodecahedral, and cubic crystals also occur, but they are uncommon and are often distorted. Crystals usually have some level of hopper growth. Transparency Opaque Specific Gravity 15.5 - 19.3 Luster Metallic Cleavage None Fracture Hackly Tenacity Ductile and malleable Other ID Marks Excellent conductor of electricity
114 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Distinguishing Pyrite and Marcasite (also known as "Fools" Gold - different Similar Minerals streak (black), less dense (4.8 - 5.2), harder (6 - 6½) Chalcopyrite - different streak (black), less dense (4.1 - 4.3), harder (3½ - 4) Commonly Quartz, Pyrite, Arsenopyrite, Silver, Limonite Occurs With
Complex Soluble only in aqua regia and fuming HCL Tests (Aqua regia - (HCl),(HNO3) Mixture of hydrochloric and nitric acids. It is an extremely destructive mixture and can dissolve gold and platinum, as well as many other minerals
Note: Aggregate composed of skeletal or tree-like formations (Dendrites) Aggregate composed of long, slender, curvy, interwoven wires. Nugget - Compact, waterworn, amorphous mass, found in placer deposits. Encrustations: A disorganized, crusty, mineral coating that can be thin or thick.
The Breckenridge District of Colorado is well known for fine wire crystal gold specimens. The area was very rich in the early days and many fine specimens like this one were melted down for their bullion.
115 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Gold Comments: Well crystallized bright metallic gold specimen.
Location: Red Ledge mine, Nevada Co., California. Scale: 3.5 x 6 cm in size.
Gold, Silver
Mineral: Gold: Au Silver: Ag Comments: Very well crystallized Electrum (Silver rich gold) on quartz. The analysis gave 31.47% silver. Location: Verespatak (now Rosia Montana), Transylvania, Romania. Scale: 2.8 x 3.4 cm.
116 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Arsenopalladinite: Pd8(As,Sb)3 Isomertieite: Pd11Sb2As2 Gold: Au Bornite: Cu5FeS4 Comments: Light grayish grain of intimately intergrown isomertieite and arsenopalladinite (in the center of the picture), with pale yellow gold and brownish to violet bornite. Polished section (from microprobe analysis) in reflected light. Location: Noril'sk, Putoran Mts, Taymyrskiy Autonomous Okrug, Eastern-Siberian Region, Russia. Scale: Picture size 0.1 mm.
Mineral: Gold: Au Petzite: Ag3AuTe2 Comments: Dark, stubby petzite crystals with native gold on quartz. Location: Rosia Montana (Verespatak), Transylvania, Romania.
117 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Gold: Au Comments: Two skeletal octahedral crystals of gold. Stereo pair images.. Location: Berezovsk Mine, Russia. Scale: Crystal size 1.1 cm.
Mineral: Gold: Au Rucklidgeite: (Bi,Pb)3Te4 Comments: Polished section (PPL) image of sphalerite(sph)-chalcopyrite ore associated with hessite (he), rucklidgeite (rk), pyrite (py) and native gold (Au). Location: Level 1070 m., Massive sulphide deposits of the Hanson-Flin Flon-Snow Lake, Manitoba, Saskatchewan, Canada. Scale: Picture Size 0,12 mm.
118 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
119 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
USES of GOLD Gold has been used as a precious metal throughout the history of mankind. Most of the gold produced goes into the monetary reserve and forms a monetary base for currency.
This is due to its resistance, beauty, rareness, and the fact that it is very easy to work with. Many exotic gold ornaments from the past have been found. In India it is used in the textile Zari work.
Especially noteworthy are the golden ornaments from the tombs of the Pharaohs in Egypt, where gold masks, statues, coins, and much jewelry was archeologically excavated. Gold has been used for coinage throughout the centuries, and is currently accepted internationally as a standard value. Nowadays, the main use of gold is for jewelry.
As pure gold is easily bent and dented, it is always alloyed with other metals when used in jewelry. This makes it more durable and practical for ornamental use. The purity of the gold based on the alloyed metal is measured in karat weight. The karat measurement determines the percentage of gold to other metals on a scale of 1 to 24 , with 24 karats being pure gold.
Due to gold's distinctive properties as a metal, it has several industrial uses. It is used in photography, dentistry, coloring, and is currently being studied for cancer treatments.
Varieties of Gold
The color of pure gold is bright golden yellow. Besides for strengthening the gold, other metals may be alloyed with gold to give the gold distinct color tinges. The different types of gold are based on the particular color tinge:
Rose Gold - Gold with a slightly reddish hue, caused by copper
White Gold - Pale, almost silver-colored gold, caused by nickel (and sometimes zinc or platinum)
Green Gold - Gold with a slightly greenish hue, caused by copper and silver
Blue Gold - Gold with a slightly bluish hue, caused by iron
120 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mode of Occurrence and Origin
Gold occurs mainly in tw forms 1) Lodes and 2) placers
(i) Lodes Deposits
The lode deposits are primary in nature. The Primary gold deposits occur in intrusive rocks (dyke rocks) having composition of diorites, quartz – diorites and granites and their metamorphic equivalents Gold is found commonly associated with sulphides of non-ferrous and related metal like chalcopyrite, sphalerite, galena, arsenopyrite, pyrite and antimonite Quartz and limonite are the main gangue associates The iron hats (gossan) or limonites at times contain appreciable quantities of gold. Gold mostly occurs in quartz-vein (where yellow brown or blue quartz has been found to be favourable carrier for example: Kundrakocha, Singhbhum district, Bihar)
These quartz veins also known as lodes or reefs, which contain either native gold or gold sulfides and tellurides.
Mode of Occurrence and Origin… (i) Lodes Deposits….
The lode deposits are mostly formed through igneous emanations during the last stages of chilling of magma which came up along some opening like fissures, faults, fractures, shear zone and folds to upper layers of earth crust During cooling of magma gold crystallises in native state or in combination with other elements like Ag, Cu, Hg, Sb, Bi, Se, Te, As and S depending upon their physical and chemical conditions prevailing there The Bulk deposits are formed at the end stages of differentiation they are hydrothermal in origin with accumulation of gases and water which act as carrier e.g. Kolar gold field. A few lode deposits are formed at various stage of processes e.g. Magmatic segregation deposits (Utah Gold hill, Gold curry, etc.) and Contact metasomatic deposits (Montana Cable Mine, British Columbia) Narainswamy et al (1960) state Kolar gold deposit formed by the high temperature hydro-thermal mineralization
121 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Gold load deposits with Quarz reef
Small bits of gold are scattered through this piece of mesothermal vein quartz from the mother lode region of California. The gold is mostly concentrated around the edges of dark colored spots of iron oxide that were likely originally clots of pyrite. This is very rich gold ore.
122 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
These are crystals of Calaverite - a gold, silver and tellurium mineral. This is very high grade gold ore from the Cripple Creek district in Colorado. Many old time miners mistook this type of mineral for low grade sulfides, but this silvery metallic material probably is 40 percent gold by weight. Tellurides are often associated with rich ore - and that was true at Cripple Creek as it was elsewhere.
Gold does not commonly combine with other elements, but there are exceptions. These are the telluride minerals such as Calaverite. This very rich gold ore specimen came from the El Paso gold mine in the Cripple Creek district in Colorado.
123 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
(ii) Placer Deposits Placer deposits are sourced from pre-existing gold deposits and are secondary deposits.
Placer deposits are formed by alluvial processes within rivers, streams and on beaches.
Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as bends in rivers and behind boulders.
Often placer deposits are found within sedimentary rocks and can be billions of years old, for instance the Witwatersrand deposits in South Africa.
Sedimentary placer deposits are known as 'leads' or 'deep leads'.
Placer deposits are often worked by fossicking, and panning for gold is a popular pastime.
Laterite gold deposits are formed from pre-existing gold deposits (including some placer deposits) during prolonged weathering of the bedrock. Gold is deposited within iron oxides in the weathered rock or regolith, and may be further enriched by reworking by erosion. Some laterite deposits are formed by wind erosion of the bedrock leaving a residuum of native gold metal at surface
This very large nugget gold specimen contains significant quartz and is from Alaska. It's rounded shape shows the signs of wear and tumbling in a river environment.
124 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Montana Bob Dansie assembled this fantastic collection placer of gold using various Minelab metal detectors. He dug each flake, one nugget at a time. Most if this placer material is from Arizona, but it also includes some gold from other locations. The upside down jar with the small gold contains several pounds of small flakes and pieces placer gold.
These angular pieces of gold have not been shaped by the flows of a stream. They were mined on the hilltop near the rocks in which they were formed. They are from California and were also recovered by the author.
125 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
This is a piece of gold ore from the famous Witwatersrand gold deposits of South Africa. The ore consists of conglomerate pebbles mostly of quartz, in a sandy matrix, with abundant pyrite in the cement. The gold, which occurs in the cement but not in the pebbles, is closely connected with the pyrite and is not visible to the naked eye. It is generally agreed that this auriferous conglomerate represents an ancient placer, although the gold and pyrite have been re-disolved and moved around or recrystalized after emplacement. Most geologists see these ores as fossilized placer deposits altered by heat and water flows.
The vast majority of gold mined in Nevada is tiny - microscopic in size. However a small percentage is large and here is an example of a pan full of gold taken from the Round Mountain Mine in Nye County. Only about 3% of their total production is coarse like this, but even 3 % of all their gold is a large quantity. The round Mountain Mine is operated by Kinross and is located North of Tonopah in Nye county. Check out this web page if you want to learn more about Nevada's Rich Micron Gold deposits.
126 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Gold Distribution in India
127 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Distribution of Gold in India
All gold productions of India have come from the vein deposits (lode deposit) and very little from placers. The vein deposits may be further classified into
1) Principal deposits (active mine) which are at the moment producing gold. E.g. the Kolar and the Hutti gold fields 2) Potential deposits which at one time or other have produced gold and may hold promise of turning out to be commercially important. e.g. Anantour gold field (Andhra), Gadag gold field (Karnataka) and Wynad gold field (Tamil Nadu) 3) Minor occurrences which have not been fully assessed or have been explored to some extent and found to be importants
Age Types of Category Locality and geological details deposits Dharwars A. Lode 1.Principal (a) Kolar (Karnataka): Gold is associated with Deposits deposits champion quartz-lodes and sulphide bearing (Active reefs, especially oriental lode with schist belt, mines) belonging to hypothermal class (b) Hutti (Karnataka): Gold is associated with quartz-reefs within metabasalts, represented by greenstones passing into chlorite-schist
2.Potential a) Ramgiri, Anantpur dist (A.P). The auriferous deposits belt, 150-200m wide and comprising quartz- (abandoned vein zone is spread over a strike length 15km mine) within schistose rock b) Gadag (karnataka): associated with Qz vein with greenstone for 50 km c) Wynad, TN: associated with quartz reefs within biotite gneiss and hornblende-granulite d) Kundrakocha, Bihar: quartz vein with cherty phylite
128 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Age Types of Category Locality and geological details deposits Dharwars A. Lode 3.Minor Gooty (Anantpur dist), Bisanatham (Chittoor) and Deposits Occurrences Gavanikonda (Kurnool) of A.P. Sithaura (Nalanda), Sonapet (Ranchi) and Pahariha, lowa and Mysara (Singhbhum) of Bihar Alech hills (Jamnagar) of Gujarat Kojhikoda and Cannore (Kerala)
Pleistocene B.Placer Gold washing carried out in the alluvial and gravel & Recent Deposits beds of many rivers in parts of Assam, Bihar andH.P. The rivers subansiri, lohit, Dihang, Buri, Dihang, Buri and Janglu of Assam-Arunachal Sona, Subernarekha and South keol of Singhbhum
Several streams different part of India
State
Proved Probable Possible Total Remarks
Andhra Pradesh (i)Ore (million tonnes) 1.396 1.583 3.861 6.840 Primary Gold (ii) Metal (tonnes) 6.0 7.4 18.3 31.7 Reserve Bihar (Kundrakocha) Primary Gold (i) Ore - - 0.008 0.008 Reserve (ii) Metal - - 0.1 0.1 Reserves of Gold Karnataka in India (i) Ore 6.855 6.063 0.695 13.613 Primary Gold (Recoverable (ii) Metal 32.6 29.4 2.9 64.9 Reserve Reserves as on Kerala 1.4.1990) (i) Ore - 2.552 22.198 24.750 Both primary (ii) Metal - 2.3 2 4.4 and placer gold reserve
Madhya Pradesh Ore - - 1.7 1.7 Primary Gold Reserve
India Total Reserve Ore 8.251 10.198 26.162 45.211 Metal 38.6 39.2 23.3 101.1
129 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
as on 01.04.2005
World Distribution: Many localities for fine specimens. In Russia, in Siberia, along the eastern slope of the Ural Mountains; important localities near Yekaterinburg (Sverdlovsk), as at Beresovsk; in the Miass district; large crystal groups from along the Lena River, Sakha. Sharply crystallized from Romania, at Ro¸sia Montan˘a (Verespatak) and S˘ac˘arˆımb (Nagy´ag).
In Australia, many occurrences, as at Bendigo, Ballarat, and Matlock, Victoria; along the Palmer River and at Gympie, Queensland; from Kalgoorlie, Western Australia, with gold telluride ores, also very large alluvial nuggets. At the Porgera mine, Mt. Kare, Papua New Guinea.
The world’s most important gold district is the Witwatersrand, Transvaal, South Africa, which, however, only rarely produces crystalline material. In Canada, especially in Ontario, in the Porcupine and Hemlo districts.
In the USA, in California, in the Mother Lode belt of the Sierra Nevada, with fine examples from both lode and placer deposits. In South Dakota, from the Homestake mine at Lead, Lawrence Co.; in Colorado, wire and leaf gold from Breckenridge, Summit Co.; in Lake Co., at Leadville; in Alaska, in lode mines in the Juneau district and placers along the Yukon River. Near Santa Elena, in the Grand Savannah River region, Venezuela, a placer producing exceptional skeletal crystals.
A bonanza gold rush occurred at Serra Pelada, Par´a, Brazil.
130 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
PROSPECTING GUIDES 1.Host Rock and Associated Minerals
Intrusive rocks of composition diorites, quartz-diorites and granites are found to be suitable host rocks of primary gold The associated minerals are sulphides of non-ferrous and the related metals such as chalcopyrite, sphalerite, galena, arsenopyrite, pyrite and stibnite besides quartz and limonite In vein deposits yellowish brown or blue quartz has been found to be favourable carriers of gold The limonite or iron hat (gossan) is also of great interest 2.Rock Examination The outcrops of quartz veins, silicified rock and quartz boulders should be examined carefully for visible gold specks or sulphide minerals Free gold is often found confined to fine cracks 3. Soil-Cover Areas In soil cover areas, the soil under uprooted trees, animal burrows, rain-rill, etc may be examined for mineralised fragments of quartz or other rocks The gravels of river channel are looked for mineralised fragments
PROSPECTING GUIDES 4. Pebble and Boulder Tracinhg
Find out the primary gold lode by tracing the mineralised quartz fragments pebble or any other rock in the river gravel upstream
5. Panning
Panning is the principal prospecting method in case of placer gold The samples should be taken from the lowest layers of gravels (near bed rock)
6. Specimen Collection A specimen/sample for chemical analyses should be one to two kg with small fragments of rock taken from different perts of ore body
7. Soil-Cover Areas The gold values of 2 g/tonne and above are suggestive of the area for detailed exploration The value 4 g/t are indicative of economic deposit worth mining
131 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Precious Metals - SILVER
Silver is a precious metal next to gold Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a by-product of copper, gold, lead, and zinc refining. Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils (hence the term silverware), and currency coins. Today, silver metal is also used in electrical contacts and conductors, in mirrors and in catalysis of chemical reactions. Its compounds are used in photographic film and dilute silver nitrate solutions and other silver compounds are used as disinfectants and microbiocides. While many medical antimicrobial uses of silver have been supplanted by antibiotics, further research into clinical potential continues.
The world mine reserve of silver is estimated at around 420 million kg 85% of above from USA, Canada, Mexico, Peru, Russia, Africa, Japan and Australia. Amongst Mexico is the topest Silver mining through open pit and underground operation Physical Properties of Silver Cleavage: None Color: Silver white, Gray white, Gray, Specific gravity: 10 - 11, Average = 10.5 Diaphaneity: Opaque Fracture: Hackly - Jagged, torn surfaces, (e.g. fractured metals). Habit: Arborescent - "Tree like" growths of branched systems (e.g. silver). Habit: Dendritic - Branching "tree-like" growths of great complexity (e.g. pyrolusite). Habit: Massive - Uniformly indistinguishable crystals forming large masses. Hardness: 2.5-3 - Finger Nail-Calcite Luminescence: Non-fluorescent. Luster: Metallic, Magnetism: Nonmagnetic, Streak: silver white Melting point: 10000C Metallic conductor: Heat and electricity
132 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Atomic Mass 107.8682 Atomic Number 47 Name Origins Anglo Saxon, siolfur = "silver": Latin, argentum Year Discovered Prehistoric Discovery Credits Known to ancient civilizations. Soft, malleable metal with characteristic silver sheen. Stable to water and oxygen but attacked by sulfur compounds in air to form black sulfide layer. Dissolves in sulfuric and nitric acid. Used in photography, silverware, jewelry, electrical industry, and glass (mirrors). Remarks Diagnostic tests: Easily reduced on charcoal using a blowpipe or propane torch after roasting the sample forming a malleable silvery bead. Silver, along with lead and mercury form white, insoluble chlorides from aqueous solutions.
Silver Minerals and their Characters Minerals Chemical Comp Chief Characters
Native silver Ag (usually associated Usually filiform, arborecsent or massive with small amounts of other metals – Cu, Au, Pt, Hg, Pb, Zn, Bi, etc. Argentite (Silver Ag2S Blackish gray in colour and streak, metallic glance) lustre
Stephanite (Brittle Ag5SbS4 Iron black in colour and streak, brittle, H= 2- Silver Ore) 2.5, sp.g = 6.26 Prousite (Light red Ag3AsS3 Commonly granular and massive, red in silver Ore) colour and streak, H = 2-2.5, Sp.g. = 5.55- 5.64 Pyragyrite (Dark Ag3SbS3 Commonly massive, black to cochineal red red silver ore) in colour and streak H= 2-3, sp.g. 5.7-5.9 Ceragyrite (Horn AgCl Usually massive and wax like and also in Silver) encrustations, pale shades of grey. Some times greenish or bluish streak, shining, H = 2-3, sp.gr = 5.8 Hessite Ag2Te Lead grey, metallic, sectile, H = 2.5, sp.gr = 8.4
133 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Native Silver
Native Silver
Arborescent habit silver crystals etched out of calcite Origin: Kongsberg, Norway Sample size: 3 x 3 x 1 cm
134 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Native Silver with Lead
Rich lead - silver ore from the famous mines of Wallace, Idaho. These mines have been mined to very deep levels below the surface.
Native Silver with sulphur
This sulfide rich silver ore from Nevada is dark gray and colored by a heavy content of metallic sulfides. The rich silver minerals pyrargyrite and stephanite boost the silver content of this bonanza grade ore.
135 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Silver on galena Origin: Comstock Lode, Storey County, Nevada, U.S.A. ex. John Sinkankas Collection Sample size: 2 x 1.75 x 0.5 cm
Mineral: Silver: Ag Comments: Numerous fine, silver wires to 4 mm in diameter attached to a matrix of massive white calcite and minor sulfides. Location: Himmelsfahrt mine, near Freiberg, Saxony, Germany. Scale: 4 x 4.5 x 6 cm.
136 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Silver with copper Origin: Keweenaw Peninsula, Houghton Co., Michigan, U.S.A. Sample size: 2.7 x 2.1 x 1.5 cm Photo courtesy of:
Chemical Formula: Ag2S Argentite Composition: Molecular Weight = 247.80 gm Silver 87.06 % Ag Sulfur 12.94 % S Empirical Formula: Ag2S Environment: Low temperature ore veins. IMA Status: Not Approved IMA Locality: Mexico, Saxony, Great Britain and Kongsberg, Norway are notable localities. Link to MinDat.org Location Data. Name Origin: After the Latin, argentum, meaning "silver". From the Greek, akanta, Mineral: Acanthite: Ag2S meaning "arrow." Argentite is stable above 179 Argentite: Ag2S C. Acanthite is stable below 179 C. Comments: Dark metallic acanthite crystals up to 3 mm. Most of the crystals are a cubic habit, so the acanthite is pseudomorphing the original argentite. Location: San Juan de Rayas Mine (Rayas Mine), Guanajuato, Mun. de Guanajuato, Guanajuato, Mexico. Scale: 18x12x12 mm.
137 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Physical Properties of Argentite Cleavage: {001} Poor, {110} Poor Color: Black, Lead gray. Density: 7.2 - 7.4, Average = 7.3 Diaphaneity: Opaque Fracture: Sectile - Curved shavings or scrapings produced by a knife blade, (e.g. graphite). Habit: Arborescent - "Tree like" growths of branched systems (e.g. silver). Habit: Blocky - Crystal shape tends to be equant (e.g. feldspars). Habit: Skeletal - Crystals form crude outlines with missing faces. Hardness: 2-2.5 - Gypsum-Finger Nail Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Nonmagnetic Streak: black
Chemical Formula: Ag5SbS4 Stephanite is 68.5% Silver by weight. Colors: Dark Gray to black. Its streak is black. Hardness: 2 Density: 6.2 to 6.3 Cleavage: The cleavage is perfect parallel to (010) and the fracture uneven. Crystallography: Orthorhombic Stephanite crystallizes in hemimorphic orthorhombic crystals. The crystals are highly modified, 125 forms having been identified upon them. They have usually the habit of hexagonal prisms, their predominant planes. Crystals are usually small. Also twinned in Stephanite Ag5SbS4 pseudohexagonal crystals. Luster:. Sub-metallic to metallic Optics: (Refractive Index) Opaque
138 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Stephanite Ag5SbS4…
Composition, Structure and Associated Minerals: Stephanite, though a comparatively rare mineral, is an important ore of silver in some mining camps. It is found associated with other sulphantimonites of silver, etc. Crystals usually short prismatic and tabular parallel to the base. It occurs massive, in disseminated grains and as aggregates of small crystals. Analyses indicate a composition very close to the requirements of the formula Ag5SbS4.
Occurrence, Localities and Origins: The mineral is associated with other silver ores in the primary ores and the secondary zone of enrichment of veins at Freiberg, Saxony; Joachimsthal and Pribram, Bohemia; at Guanajuato and Arizona, Sonora, etc., at many points in Mexico, Peru and Chile and other mines in the Rocky Mountain region and at many points in Mexico and Peru. It is particularly abundant in the ores of the Comstock Lode, and other silver deposits in Nevada, and of the Las Chispas Mine, Sonora, Mex. It is formed at low to moderate temperatures.
Proustite
Chemical Formula: AgAsS3 (Light Ruby Silver)Sulfo-arsenite of silver, silver is 64.5 % by weight. May contain a small amount of antimony substituting for arsenic. Colors: Ruby Red to Brownish red Its streak is deep red to brownish black. Hardness: 2.0 Density: 5.5 Cleavage: Imperfect, but it is easily sectile, and can be cut with a knife like lead. Crystallography: Rhombohedral Found in pointed crystals, but more commonly occurs as granular and massive forms. Luster:. Adamantine luster. Transparent to translucent. High refractive index.
139 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Composition, Structure and Associated Minerals:
Proustite, or light ruby silver, is isomorphous with pyrargyrite. It differs from the latter mineral in containing arsenic in place of antimony. It occurs both massive and in crystals, and like pyrargyrite is an important silver ore. The mineral occurs in veins associated with other compounds of silver such as native silver, acanthite (argentite), stephanite, and sometimes with galena and arsenopyrite. It is most commonly found in the zone of secondary enrichment of silver veins, but also is formed as a primary ore mineral in some near surface epithermal systems rich in silver.
Occurrence, Localities and Origins: Overall, proustite is a fairly rare mineral, occurring in silver veins associated with various other sulpharsenites and sulphantimonites. It is generally less abundant than pyrargyrite. Found in the silver mines of Saxony; Bohemia; at Chaftarcillo, Chile, in fine crystals; common in the silver mines of Peru and Mexico. Found in Colorado in the silver mines of the San Juan Mountains and elsewhere; in various epithermal silver districts in Nevada, etc. Handsome crystal specimens of proustite occur at Freiberg and other places in Saxony, at Wolfach in Baden, at Markirchen in Alsace and at Chanarcillo in Chile. It is associated with pyrargyrite and with other ores of silver. In parts of the western United States it is quite abundant, more particularly in the Ruby district, Colorado, at Poorman lode in Idaho, and in all other localities where pyrargyrite occurs. In some locations it is an important silver ore
Pyrargyrite Chemical Formula: Ag3SbS3 Pyrargyrite is 59.7% Silver by weight. Also known as Dark Ruby Silver. Colors: Dark Gray to black. The mineral is apparently opaque and its color is grayish black in reflected light, but is transparent or translucent and deep ruby red in transmitted light. streak is purplish red. Hardness: 2 to 2.5
Density: 5.85 Cleavage: The cleavage of pyrargyrite is distinct parallel to R(1011). Its fracture is conchoidal or uneven. Crystallography: Orthorhombic Crystals are usually distorted and often with complex development, and frequently twinned. Luster:. Adamantine, transparent to translucent. Optics: (Refractive Index) 2.9 (very high index of refraction)
140 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The Comstock lode district was perhaps the largest single silver ore find ever made in the USA. The Comstock lode is famous for its ore bodies of bonanza grade silver ore rich in sooty silver sulfide minerals like acanthite (formerly known as argentite). The ore also contains considerable other sulfide minerals and some free gold as well. The Comstock is famous for great bonanzas of crushed, mineralized quartz, in part exceedingly rich in silver minerals, were found at intervals along the lode, especially in chambers or vertical fissures probably produced by normal faulting of the hanging wall. The ores consist of quartz and some calcite, in places banded with pyrite, galena, chalcopyrite, sphalerite, and finely distributed rich silver minerals. The valuable minerals are mainly native gold, acanthite (argentite), stephanite, and polybasite.
Origin: Elura Mine (Endeavor Mine), Booroondarra, Cobar, Robinson Co., New South Wales, Australia Sample size: 5 x 4 x 75 mm Dendritic crystallized native silver on a small amount of matrix with minor calcite. Origin: New Nevada Mine, Batopilas, Andres del Rio District, Mun. de Batopilas, Chihuahua, Mexico Sample size: 20 x 5 x 35 mm
141 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Iron black in colour and streak, brittle, H= 2-2.5, sp.g = 6.26
Ag5SbS4
Silver 68.33 % Ag
Antimony 15.42 % Sb
Sulfur 16.25 % S
Mineral: Silver: Ag Stephanite: Ag5SbS4
Comments: Thick, ropy, native silver wires with blocky, well-crystallized stephanite on white and tan calcite matrix. Location: Freiberg, Erzgebirge, Saxony, Alemania, Germay. Scale: Picture size 3 cm.
The sooty black colored material in this specimen is cerargyrite, an important ore of silver. In many deposits located in desert regions, silver sulfide minerals like acanthite (argentite), stephanite, and polybasite or oxidized by exposure to air and water into a silver chloride, also known as cerargyrite. as a result, this type of silver ore is only found near the surface. Once miners get down below the water table, this type of mineral and ore will disappear and only sulfides will be found in its place. This rich specimen was taken from the Tonopah Divide mine, in the Divide district of Nye County, Nevada.
142 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Telluride minerals such as calaverite, are also important silver ores in some mining districts. This sample of rich gold and silver ore comes from the Cripple Creek district in Colorado. The mossy metallic colored mineral on this specimen is calaverite, a mineral rich in both gold and silver.
In the Calico District, deposits of silver chloride in fissure veins, and in small fractures and pockets in volcanic tuffs and sandstones, probably of the Pliocene series. Below the oxidation zone, rich chlorides give way to silver bearing sulfides as shown in this specimen. They occur in Southwestern California, in that portion of the State belonging to the Great Basin geologic province. The ore was thought by Lindgren to have come in heated solution from below and to have filled the fissures and overflowed, forming the surface deposits in the tuffs. They are considered epithermal in origin.
143 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Rhodochrosite and silver ore, Peru: This beautiful specimen of silver ore comes from the country of Peru in South America. The dark colored minerals are the ones which are silver bearing, while the red and pink colored crystals are Rhodochrosite, a common manganese mineral that is found in a number of silver ores.
Mode of occurrence and Origin
Silver ores occur in a variety of ways such as Veins, stringers and disseminations, replacement deposits, contact metamorphic deposits or alluvial The upper part of the silver deposits like Ceragrgyrite (AgCl), Bromyrite (AgBr) and Iodyrite (Agl) are weathered and form the gossan in the surface Hydrothermal solutions might be responsible in bringing about the replacement or cavity filling deposits Massive or load replacement of silver-lead ores are numerous The most of the world’s silver is from the fissure veins of mesothermal and epithermal types
144 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Hydrothermal deposits
Silver grains to 2-3 mm in granitic matrix Origin: Sophia mine, Wittichen, Schwarzwald, Germany Sample size: 5 x 6 x 2 cm
Silver occur in veins
Vein and leaf silver in two large fractures 4 and 3.5 cm long. The exposed silver is aver 1 cm in length. Origin: O'Brien mine, Cobalt, Ontario, Canada Sample size: 6.5 x 4 x 2 cm
145 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Distribution
In India there is no silver deposit at present Silver is found associated with lead, zinc, copper and gold The Galena of Rajasthan, Andhra Pradesh, Uttar Pradesh and Bihar are argentiferous Lead-zinc samle from Zawarmala mine, udaipur Rajasthan have 18ppm silver The lead occurrences in Heasatu-Belhathan belt, Bihar and Birgana, UP are found to be argentiferous galena Production
In India silver is recovered as a by-product from the smelting od lead, zinc, gold and copper The production of silver during 1990-91, 91-92, 92-93 respectively 35, 38 and 47 thousand kg
Precious Metal - Platinam Platinum was first found in the alluvial deposits of river Pinto in Colombia, S America from where it was taken to Europe in 1735 by Spanish Mathematician Antonio de Ulloa No workable platinum deposits in India. The Ural mountains of Russia where platinum was discovered in 1819 Canada, Africa, Australia, S America and Alaska are the other main producing countries
Platinum Nugget, California Natural Platinum Crystals
146 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineralogy - Platinam Chemical Formula: Pt Colors: Steel-gray with a bright metallic shine. The color of platinum is a little more gray than that of silver. Its streak is also gray. Hardness: 4 to 4.5 Hardness unusually high for a metal. Density: 14 to 19 depending on impurities Cleavage: None Crystallography: Isometric Usually found in small grains or scales. Sometimes in irregular masses and nuggets of larger size. Crystals very rare and commonly distorted. Luster:. Bright metallic luster. Optics: (Refractive Index): Opaque • It is malleable and ductile, a good conductor of electricity, and it is infusible before the blowpipe except in very fine wire.
• Its melting temperature is 1755.
• Platinum is unattacked by any single acid, though soluble, like gold, in a mixture of hydrochloric and nitric acids (aqua regia).
Platinum is a rare metal which occurs almost exclusively native and in fine scale and minute grains
Platinum is usually alloyed with several percent of iron and with smaller amounts of iridium, osmium, etc.
The amount of metallic platinum present seldom exceeds 80 per cent.
Though the metal occurs usually in grains and plates, nevertheless its crystals are sometimes found. On them cubic faces are the most prominent ones, though the octahedrons, the dodecahedrons and tetrahexahedrons have also been identified. Like the crystals of silver and gold, those of platinum are frequently distorted.
147 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Platinum is a rare metal which occurs almost exclusively native and in fine scale and minute grains in the following forms
1. Native state – Element Platinum 2. Arsenide – Sperrylite (PtAs2) 3. Aresen-sulphide – Cooperite (Pt (As,S)2) 4. Alloyed with other metals of its group
Sperrylite Formula: PtAs2 Sperrylite in chalcopyrite
148 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Crystal system: cubic
Crystal class: 2/m -3 Sperrylite - PtAs2 Colour: tin-white
Diaphaneity: opaque
Luster: bright metallic
Habit: crystals cubic or cubo-octahedral, may be highly modified
Hardness: 6 to 7
Specific gravity: 10.46 to 10.6
Cleavage: 1; {001} distinct
Tenacity: conchoidal, brittle
Streak: black
Sperrylite
Origin: Oktyabr'sk mine, Norl'sk, Krasnoyark ray, Yaymyrskiy Nats. Okrug, Siberia, Russia Sample size: 2 x 5 x 4.5 cm
149 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Cooperite Formula: (Pt,Pd,Ni)S Cleavage: None Color: Steel gray. Density: 9.5 Diaphaneity: Opaque Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz). Hardness: 4-5 - Fluorite-Apatite Luster: Metallic
Cooperite Formula: (Pt,Pd,Ni)S
Creamy-grayish fractured grains of cherepanovite with gray granular cooperite, white massive grains of iridian ruthenian platinum and white crystals of iridian ruthenian osmium. Polished section in reflected light
Origin: Placer Deposit, Northern Pekul'nei River, Pekul'nei Range, Chukotka (Tchukotka) Okrug, Chukot Peninsula, Far-Eastern Region, Russia Picture size: 0.12 mm
150 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MODE OF OCCURRENCE AND ORIGIN The platinum may occur in five modes 1. Early Magmatic Concentrations Disseminations: Sparse dissemination with chromite in dunite. E.g. Urals, Alaska, Colombia Segregations by fractional crystallization – e.g. Rustern burg, S.Africa 2. Late Magmatic concentrations Immiscible liquid segregations – e.g. Vlackffontein, S.Africa Immiscible liquid injections – e.g. Sudbury, Canada 3. Contact Metasomatic Deposits – e.g. Potgietersmast, S.Africa 4. Hydrothermal – e.g. Waterburgs, S.Africa & Sudbury, Canada 5. Placers – e.g. Urals, Colombia, Alaska
Platinum are primarily found in ultrabasic rocks, usually associated with chromite and nickel ores In Ural mountains it occurs sparse disseminations with chromite in dunites The erosion of the platinum rich ultrabasic rocks has yielded placer deposits in Urals, Alaska, Colombia In South Africa, the platinum associated with dunite pipes of the differentiated Bushveld igneous complex, chromite and nickel- sulphides of the complex The platinum associated with the nickel-copper sulphide deposits - Immiscible liquid segregations – e.g. Vlackffontein, S.Africa
151 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Metallogenic Epochs
Late mesozoic to Early Tertiary: Occurs in Zambales, Phillipines as the ‘Alpine’ type. The minor occurrence in Dhangawan Bauxite, M.P., India Late Palaeozoic: Occurs in Alpine type of ultramafic intrusion related Hercynical folding movement in Ural mountains, Russia and dunitic rocks of New Zealand Precambrian: Occurs in stratiform type of Bushveld Igneous complex, Transvaal, South Africa. Late magmatic injection in frood Breecia, Sudbury, Ontario, Canada. The placer occurrence reported in Assam, West Bengal and Bengal
Distribution: No workable deposits has so far been located in India. But some small occurrences reported
1. Assam: Platinum associated with gold was reported by Dalton & Hanny in the sands of the Noa Dihing River observed by Mallet (1882). The source for this platinum is ultrabasic suite Patkoi range 2. Bihar: Dunn (1937) recorded the occurrence of platinum associated with gold in the sands along the Gurma river near Dhadka. The origin of such platinum may possibly be connected with basic intrusive rocks 3. Karnataka: The gold washings of the Kolar mines have shown traces of platinum 4. Madhya Pradesh: H.L. Chibber found traces of platinum in a sample collected from the bauxite deposit of Dhangawan on Jabalpur – Katni road 5. Tamil Nadu: The stratiform magnesio-chromites laminated with ultramafics of Sittampundi complex have indicated presence of platinum and palladium. 6. West Bengal: A sample of alluvial gold from Guram river have the minute grains of platinum (Chatterji, 1937)
152 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
153 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ECONOMIC GEOLOGY e – Learning Material: Unit-4
FEROUS AND ALLIED METALS
154 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
IRON Iron is the second most abundant metallic element in the Earth’s crust and accounts for 5.6% of the lithosphere.
The principal minerals of iron are the oxides (haematite and magnetite), hydroxide (limonite and goethite), carbonate (siderite) and sulphide (pyrite).
Iron, like most metals, is found in the Earth's crust only in the form of an ore, i.e., combined with other elements such as oxygen or sulfur.
Haematite and magnetite are the two important iron ores from which iron is extracted. Of these, haematite is considered to be superior owing to its high grade. It is rarely found in native state except in meteorites and some eruptive rock The mineral containing iron must be mineable at profit is called iron ore. The total world iron production in 1990 is 1,008 million tonnes and India is 55.5 million tonnes and nearly 5.5%
The chief ores of iron are its oxides and carbonates
Mineral Formul Crystal Opaci Hard Color Lustre Streak SG Fracture Name a System ty ness Blackish brown, Adam reddish or antine- Orange to 3.3 Orthorh Opaqu 5 to Uneven; Goethite FeO(OH) yellowish metalli brownish to ombic e 5.5 brittle brown, c to yellow 4.3 brownish dull yellow
Steel-gray Metalli Deep red Subconc Trigonal to iron- c, - black, thin Opaqu or 5 to hoidal to Hematite Fe2O3 subme 5.26 Hexago fragments e brownish 6 uneven; tallic, nal deep blood red brittle red dull Yellow, Amorph brown, ous/ Non 2.7 Uneven, FeO.OH. brownish- Opaqu Yellowish- 4 to Limonite Cryptoc metalli to subconch nH2O black, e brown 5.5 rystallin orange- c 4.3 oidal e brown Splen Subconc Iron-black, dent 5.5 Opaqu hoidal to Magnetite Fe3O4 Cubic grayish metalli Black to 5.17 e uneven; black c to 6.5 brittle dull
155 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The chief ores of iron are its oxides and carbonates
Mineral Crystal Hardne Formula Color Opacity Lustre Streak SG Fracture Name System ss Low Pale brass- yellow to Orthorhombi Greenis Uneven; Marcasite FeS2 tin-white, Opaque Metallic 6-6.5 4.92 c h black brittle darkens on exposure Conchoida Brass- l to Pyrite FeS2 Cubic Opaque Metallic Empty 6-6.5 5.01 yellow uneven; brittle Bronze- Subconch Monoclinic yellow to grayish oidal to Pyrrhotite Fe1-xS and bronze-red; Opaque Metallic 3.5-4.5 4.53 black uneven; hexagonal tarnishes brittle dark brown Pale yellowish, pale green, Transluc Conchoida yellowish Vitreous, ent to l to Siderite FeCO3 Trigonal brown, pearly or White 4 3.96 subtransl uneven; brown, silky ucent brittle reddish brown, white
Chemical Formula: Fe Composition: Molecular Weight = 55.85 gm Iron 100.00 % Fe Empirical Formula: Fe0+ Environment: In meteorites and rarely basalts that have intruded carbon-rich sediments. Cleavage: {001} Perfect, {010} Perfect, [100} Perfect Color: Iron black, Dark gray, Steel gray. Density: 7.3 - 7.9, Average = 7.6 Diaphaneity: Opaque Fracture: Hackly - Jagged, torn surfaces, (e.g. fractured metals). Habit: Disseminated - Occurs in small, distinct particles dispersed in matrix. Habit: Granular - Generally occurs as anhedral to subhedral crystals in matrix. Habit: Massive - Uniformly indistinguishable crystals forming large masses. Hardness: 4-5 - Fluorite-Apatite Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Naturally strong NATIVE IRON Streak: gray
156 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Iron
Gray metallic native iron in basalt. Cut (but not polished) section. Origin: B?eimar, Kassel, Hesse, Germany Picture size: 7 mm Owner: Thomas Witzke
Mineral: Iron: Fe Comments: Specimen of volcanic rock containing dark gray grains of native Iron. This locality is one of the very few known localities for terrestrial native iron. Location: Disko Island, Greenland. Scale: Picture size 1 cm.
157 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Defernite: Ca6(CO3)2-x(SiO4)x(OH)7(Cl,OH)1-2x (x=0,5) Hematite: Fe2O3 Comments: Specular hematite rich with crystalline grains of reddish brown defernite. Location: Kombat Mine, Kombat, Grootfontein District, Otjozondjupa Region, Namibia. Scale: 3.9 x 2.5 cm.
Hematite Chemical Formula: Fe2O3 Composition: Molecular Weight = 159.69 gm Iron 69.94 % Fe, Oxygen 30.06 % O, 100.00 % Fe2O3 Environment: Magmatic, hydrothermal, metamorphic and sedimentary.
Color: Reddish gray, Black, Blackish red. Density: 5.3 Diaphaneity: Subtranslucent to opaque Fracture: Conchoidal Habit: Blocky - Crystal shape tends to be equant (e.g. feldspars). Habit: Earthy - Dull, clay-like texture with no visible crystalline affinities, (e.g. howlite). Habit: Tabular - Form dimensions are thin in one direction. Hardness: 6.5, Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Magnetic after heating Streak: reddish brown
158 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Hematite: Fe2O3 Comments: Black, platy hematite and minor white magnesite. Location: Brumado, Bahia, Brazil. Scale: 9 x 4.5 cm.
Mineral: Hematite: Fe2O3 Rutile: TiO2 Comments: Acicular, golden yellow crystals of rutile epitaxially overgrown on black crystals of hematite. The overgrowths are perpendicular to the trigonal crystallography of the hematite. Location: Novo Horizonte, Bahia Brazil. Scale: 4 x 3.5 x 3 cm.
159 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Magnetite Composition: Fe3 04 Iron 72.36 % Oxygen 27.64 % O Environment: Common accessory mineral in igneous and metamorphic rocks. Can be biogenically produced by a wide variety of organisms. Cleavage: None Color: Grayish black, Iron black. Density: 5.1 - 5.2, Average = 5.15 Diaphaneity: Opaque Fracture: Sub Conchoidal - Fractures developed in brittle materials characterized by semi-curving surfaces. Habit: Crystalline - Fine - Occurs as well-formed fine sized crystals. Habit: Massive - Granular - Common texture observed in granite and other igneous rock. Magnetite Habit: Massive - Uniformly indistinguishable crystals forming large masses. Magnetite octahedrons on albite Hardness: 5.5-6 - Knife Blade-Orthoclase Origin: Hinter-Kohlergraben, Binntal, Luminescence: Non-fluorescent. Switzerland Luster: Metallic Picture height: 18 mm Magnetism: Naturally strong Streak: black
Large, well-formed magnetite crystals to 2.5cm associated with 6 cm frosted quartz crystals and unusual yellow calcite crystals to 2cm. Origin: Dashkesan, Azerbaijan
160 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Marcasite with Quartzite
Marcasite (FeS2) with Calcite
Marcasite (FeS2)
Cleavage: {010} Indistinct Color: Bronze, Light brass yellow, Tin white. Density: 4.89 Diaphaneity: Opaque Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Globular - Spherical, or nearly so, rounded forms (e.g. wavellite). Habit: Stalactitic - Shaped like pendant columns as stalactites or stalagmites (e.g. calcite). Habit: Tabular - Form dimensions are thin in one direction. Hardness: 6-6.5 - Orthoclase-Pyrite Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Magnetic after heating Streak: gray brownish black
161 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Goethite FeO(OH) Cleavage: {010} Perfect, {100} Distinct Color: Brown, Reddish brown, Yellowish brown, Brownish yellow, Ocher yellow. Density: 3.3 - 4.3, Average = 3.8 Diaphaneity: Subtranslucent to opaque Fracture: Hackly - Jagged, torn surfaces, (e.g. fractured metals). Habit: Acicular - Occurs as needle-like crystals. Habit: Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite) Habit: Reniform - "Kidney like" in shape (e.g.. hematite). Hardness: 5-5.5 - Apatite-Knife Blade Luminescence: Non-fluorescent. Luster: Adamantine - Silky Streak: yellowish brown
Occurrence: A common weathering product derived from numerous iron-bearing minerals in oxygenated environments; an important component of ore in weathered iron deposits. Also a primary precipitate in hydrothermal, marine, and bog environments upon oxidation of reduced iron-bearing waters.
Goethite with quartz Origin: Bottalack, Cornwall, England Sample size: 6 x 5 x 4 cm
162 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Origin: Nandan, Guangxi Province, China Sample size: 18 x 10 x 9 cm
163 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Goethite Origin: Mesabi Range, Minnesota, U.S.A. Sample size: 10.5 x 8 x 6 cm
Mineral: Goethite: Fe+++O(OH) Comments: Stellate crystalline aggregates of acicular goethite crystals. Location: Pribram, Bohemia, Czech Republic.
164 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Siderite Iron 62.01 % FeO Carbon 37.99 % CO FeCO3 2 Cleavage: {1011} Perfect, Color: Yellowish brown, Brown, Gray, Yellowish gray, Greenish gray. Density: 3.96 Diaphaneity: Translucent to subtranslucent Fracture: Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments. Habit: Botryoidal - "Grape-like" rounded forms (e.g.. malachite). Habit: Massive - Uniformly indistinguishable crystals forming large masses. Habit: Tabular - Form dimensions are thin in one direction. Hardness: 3.5 - Copper Penny Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: white Environment: Primarily bedded, biosedimentary deposits, also in metamorphic and igneous rocks
Siderite FeCO3
Iron 62.01 % FeO
Carbon 37.99 % CO2
Mineral: Arsenopyrite: FeAsS Siderite: Fe++CO3 Comments: White, metallic arsenopyrite and tan siderite crystals. Location: Panasqueira (2000, 3rd level), in the region of Beira Baixa, Portugal. Scale: 11 x 7 cm.
165 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Siderite: Fe++CO3 Comments: Bladed siderite crystal groups on crystallized quartz matrix. Location: Peyrebrune, Tarn, France. Scale: 8.7 x 6.5 x 4.7 cm.
Classification of Iron-ore Deposits Metamorphic banded deposits: The major iron ore deposits of India fall within this group. They are typically sedimentary or volcano-sedimentary and metamorphosed rocks consisting of rich iron-ore and siliceous (chert) bands The banded magnetite quartzite are typical example The Indian iron ore deposits of Bihar-Orissa belt, Bailadila (M.P) and Karnataka are Indian example Continental sedimentary deposits: These are assumed to have formed in fresh water (Fluvial or lagoonal) or under brakish swamp (Lacustrine) conditions. Ironstone of Raniganj and Auranga coalfields are typical examples of this type of deposits Marine sedimentary deposits such as oolites, detrital, placer and mixed type: The type area is in lorrain, france. The Indian example is magnetite deposits of coastal regions such as at Travancore associated with ilmenite and heavy mineral sand Volcano-sedimentary: These related to volcanic group of initial geosynclinal magmatism. Insignificant minor pockets of iron ore in Dras-Thasgam area, Ladakh are the Indian Example
166 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Classification of Iron-ore Deposits Liquid magmatic deposits: They are during the early crystallizaion of Plutonic rocks, mainly by gravitational differentiation. Tirano-vanadium bearing iron ore deposits of Mayurbhanj district, Orissa Intrusive magmatic deposits: They are related to alkaline rocks of the Precambrian shields. Apatite – Magnetire rocks of Singhbhum represent this type Contact metasomatic deposits: The granitoid intrusions within the limestone and are widely distributed. Main ore mineral is magnetite
Polymetallic skarn ore deposits: These occur associated with sedimentary deposits which are latter affected by regional metamorphism. No Indian example for this type. Deposit at Utah is best example
(a) Coarse fragments of goethite– kaolinite-rich mottled saprolite with yellowish-brown cutans characteristic of broad ridge crests. Hammer for scale
(b) Hematite-rich ferruginous pisoliths and nodules with yellowish- to reddish- brown cutans on upper backslopes
167 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
(c) Fine, black hematite–maghemite-rich ferruginous pisoliths
Fe-saprolite, lithic fragments and quartz.
(e) Coarse fragments of ferruginous saprolite
(f) Goethite-rich iron segregations after sulfide-rich rocks
168 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The Indian Iron ore deposits can be classified into six basic type
Banded ferruginous formation of Precambrian age: The ores can be classified into massive ore, laminated ore and blue dust. This is major type in the country Sedimentary iron-ores of sideritic or limonitic composition e.g found in coal fields of Bihar and West Bengal and Tertiary formation of Assam Lateritic iron ore: Associated with Deccan trap, also widespread in the country Apatite magnetite rocks of Singhbhum Copper belt Titaniferous and vanadiferous magnetites: S.E Singhbhum of Bihar, Mayurbhanj of Orissa, Tumkur of Karnataka Fault and fissure fillings of hematite of Valdurthi and Ramalkota in Kurnool and in Cuddapah districts
Geological and Geographical Distribution of Iron ore in India Formation Types of Deposit Occurrences/Deposits Precambrian Basic & Ultrabasic Titaniferous and SE Singhbhum (Bihar), Mayurbhanj Vanadiferous (Orissa), Tumkur (Karnataka) magnetite Granodiorite Apatite-Magnetite Singhbhum Copper belt and Granite rock (Residual) Mayurbhanj,Assam Jantia Hills Banded iron ore Hematites (Massive, Singhbhum; Bonai, Keonjihar & formation Shaly, Powdery) Mayurbhanj (Orissa); Poonch (J&K); Baster, Durg and Jabalpur (MP), Chanda and Ratnagiri (Maharashtra); Dharwar, Bellary, Sundar, Shimoga and Chikmagalur (Karnataka) Banded iron ore Magnetite-Quartzite Guntur (AP), Salem (Tamil Nadu), Shimoga formation (Karnataka), Mandi (HP) (Metamorphosed) Bijawar/Gwalier Hematite & Bijawar, Gwalier, Indore, Rewa (MP); Ferruginous Mohindargarh (Haryana), Jhun-Jhunu, Quartzite Sikar, Jaipur (Rajasthan); Cuddapah
169 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Geological and Geographical Distribution of Iron ore in India Formation Types of Deposit Occurrences/Deposits Gondwana Barakar - Ironstone Birbhum(W Bengal) and Auranga coal field Mahadeva (Bihar) Ironstone-shale Ironstone and Raniganj coal field (W Bengal) siderite Triassic Sirban Limestone Hematite & Siderite Udhampur (J&K)
Jurassic Rajmahal trap Ironstone Rajmahal (Bihar), Birbhum (West Bengal) (inter-trappean beds) Eocene and Ironstone NE districts of Assam, Kumaon (UP), Miocene Travancore and Malabar (Kerala) Quaternary Laterite Several states of India. Derived from different formations including Deccan trap
170 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
171 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
172 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
173 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MANGANESE
The metallic manganese on earth is rated as the 12th most abundant element in the lithosphere, estimated around 28.46x1018 tonnes or so i.e., 0.1087% by proportion of weight. Thus it almost becomes a scarce one, so far as its deposits are concerned. Industrially manganese metal is a vital component of steel and its major use is for metallurgical purpose. The 96% of global production of manganese today is from barely 7 countries viz. CIS,RSA, Brazil, Gabon, Australia, China and India in decreasing order of tonnages raised annually. The global resource base is close to 12 billion tonnes including Indian reserve of about 240 million tonnes. Indian manganese ores are preferred by many as they are generally hard, lumpy and amenable to easy reduction. The deposition of manganese in varying geological processes but the sedimentary mode of formation far outweighed other methods such as supergene enrichment etc.
174 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
In nature, manganese does not occur in the native state The following are the common Manganese minerals Mineral Name Formula 1. Oxides Pyrolusite MnO2 Hydrated oxide of Mn Psilomelane (Ba,H2O)2Mn5O10 Manganite MnO(OH) Brownite Mn2O3 Hausmanite Mn3O4 2. Carbonate Rhodocrosite MnCO3 3.Silicate Rhodonite MnSiO3 Pyrolusite and Psilomelane are two important ores of Manganese
Pyrolusite (MnO2) Manganese 63.19 % Oxygen 36.81 %
A mass of silvery-metallic pyrolusite composed of many smaller crystals with some open specimen with larger crystals up to 3mm or so.
Mineral: Pyrolusite: MnO2 Comments: Steel-gray metallic prismatic pyrolusite crystals. Location: Hori Blatna, Czech Republic.
175 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Pyrolusite (MnO2) Cleavage: {110} Perfect Color: Steel gray, Iron gray, Bluish gray. Density: 4.4 - 5.06, Average = 4.73 Diaphaneity: Opaque Fracture: Brittle - Generally displayed by glasses and most non-metallic minerals. Habit: Dendritic - Branching "tree-like" growths of great complexity (e.g. pyrolusite). Earthy - Dull, clay-like texture with no visible crystalline affinities, (e.g. howlite). Reniform - "Kidney like" in shape (e.g.. hematite). Hardness: 6-6.5 - Orthoclase-Pyrite Luminescence: Non-fluorescent. Luster: Sub Metallic Magnetism: Nonmagnetic Streak: black Formed in low-temperature hydrothermal or hot-spring manganese deposits. OCCURRENCES: As a weathering product, typically as botryoidal masses, in unconsolidated deposits -- e.g., residual clays.
Hydrated oxide of Mn Psilomelane (Ba,H2O)2Mn5O10 Cleavage: None Color: Iron black, Dark steel gray. Density: 4.4 - 4.7, Average = 4.55 Diaphaneity: Opaque Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Botryoidal - "Grape-like" rounded forms (e.g.. malachite). Reniform - "Kidney like" in shape (e.g.. hematite). Hardness: 5-6 - Between Apatite and Orthoclase Luminescence: Non-fluorescent. Luster: Sub Metallic
Magnetism: Nonmagnetic Mineral: Psilomelane: (Ba,H2O)2Mn5O10 Streak: brownish black Comments: Banded massive psilomelane. Location: Compton, Virginia, USA.
176 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Botryoidal form - Psilomelane
Psilomelane on massive barite.
Manganite MnO(OH) Cleavage: {010} Perfect Color: Black, Gray, Grayish black. Density: 4.3 - 4.4, Average = 4.34 Diaphaneity: Opaque Fracture: Brittle - Generally displayed by glasses and most non-metallic minerals. Habit: Massive - Fibrous - Distinctly fibrous fine- grained forms. Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline). Pseudo Orthorhombic - Crystals show an orthorhombic shape. Hardness: 4 - Fluorite Mineral: Manganite: MnO(OH) Luminescence: Non-fluorescent. Comments: Lustrous feathery crystals of manganite to 0.75 cm. Luster: Sub Metallic Location: N'Chwaning Mine, Kalahari Manganese Magnetism: Nonmagnetic Field, Northern Cape Province, South Africa. Streak: dark brown Environment: Formed in low-temperature hydrothermal or hot-spring manganese deposits.
177 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Manganite: MnO(OH) Sudoite: Mg2(Al,Fe+++)3Si3AlO10(OH) 8 Manganite - Ilfeld, Germany Comments: Pinkish to nearly white earthy sudoite with dark manganite. Location: Ilfeld, Nordhausen, Erfurt district, Harz Mts, Thuringia, Germany.
Mangenite Shiny, black prismatic needles in vugs & veins of reddish brown host rock. Crystals sparkle, tips could be semi- opaque.
178 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Rhodocrosite MnCO3
Cleavage: Perfect Color: Pinkish red, Red, Rose red, Yellowish gray, Brown. Density: 3.69 Diaphaneity: Translucent to subtranslucent Fracture: Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments. Habit: Botryoidal - "Grape-like" rounded forms (e.g.. malachite), Columnar, Massive - Granular - Hardness: 3 -Calcite Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: white
Rhodochrosite - Wolf Mine, Herdorf, Germany Rhodochrosite replacing barite Origin: Huaron, Pasco, Peru Sample size: 13 x 6 x 6 cm
Rhodochrosite with quartz
179 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Rhodonite MnSiO3
Cleavage: {110} Perfect, {110} Perfect Color: Pink, Rose red, Brownish red, Black, Yellow. Density: 3.5 - 3.7, Average = 3.6 Diaphaneity: Transparent to translucent Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Massive - Granular - Massive - Uniformly indistinguishable crystals forming large masses. Tabular - Form dimensions are thin in one direction. Hardness: 6 - Orthoclase Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: white
Mineral: Rhodonite: (Mn++,Fe++,Mg,Ca)SiO3 Comments: Light red rhodonite and minor quartz.
180 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mineral: Rhodonite: (Mn++,Fe++,Mg,Ca)SiO3 Comments: Deep red blocky prismatic crystals of rhodonite to 3cm. Location: Broken Hill mine, New South Wales, Australia.
Uses
Manganese ore are important raw materials in iron and steel industry and as ferro-manganese alloy It improve strength, toughness, hardness and workability of steel The 90 % of world Mn is used for iron and steel metallurgy Mn used for dry cell batteries It is used in cotton industry as dye Also used in medical, glass industries, etc.
181 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Based upon the utilisation in the user industries, an Expert Group of the Dept. of Minesr ecommended the following specification for the manganese ore
Annual consumption in India
182 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Mode of Occurrence
The greenstone hosted manganese deposits are older in age and have general close association of Banded Iron Formation such as in the Dharwarian rocks of Karnataka, Goa as also the Iron Ore Supergroup of Orissa, namely in Benai-Keonjhar tracts of North Orissa.
The time sequence changes over from Archaeau to Protuozoic, both the Khoudalit-hozted as well as the Adilabed beds of ore with the Penganga sequence have no association of iron or BIF, indicate progressive separation of iron from manganese.
Tertiary-Quaternary lateritisation processes with alternates wet and dry spells of climate, had affected the manganiferous sequences of the subtrata. Thus the ‘lateritoid’ ores are situated over some gondites and the Khondalite hosted material as also on the BIF- associated greenstone hosted ore material.
The manganese ore deposits of M.P.-Maharashtra belt, Visakhapatnam-Srikakulam belts of Andhra Pradesh, Gangpur Manganese belt of Orissa and a part of North Kanara deposits are bedded type.
The deposits of Singhbhum-Keonjhar-Bonai belt, Bellary- Hospet and North Kanara belt of Karnataka are mainly of lateritoid type.
Manganese ores of Bonai-Keonjhar belt are known for their low phosphorous content.
More than 50% of the manganese ore deposits of M.P and Maharashtra are of high grade.
183 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The state-wise ore reserves of recoverable material as per National Mineral Inventory (NMI) compiled by Indian Bureau of Mines (IBM) as on 01-04-1990 are as under:
Additional ore reserve of Karnataka and Goa worked out by GSI but not included in the NMI of IBM. The total resources of Indian manganese ore, as on data, may hence be deemed to be around 240 million tonnes.
INDIAN OCCURANCES of Mn ore Adilabad district, Andhrapradesh The Mn ore occur as this lenses with chert and jaspar within limestone. Deposits are minor nature with low phosphorous content Srikakulam district, Andhrapradesh The Mn ore associated with Kodurite rock (Garnet Granulite) forming a part of Khondalite formation and ore formed due to supergene enrichment. The ore is low grade due to high phosphorous content Visakhapatnam district, Andhrapradesh The Mn ore associated with Kodurite and Khondalite formation Singhbhum district, Bihar Associated with rocks of Iron ore and Kojham formation as lenticles parallel to bedding and as lateritic materials at places Goa The deposits are of Lateritoid type found at surface or near Panch Mahal, Vadodara district, Bihar The ore are partly lateritid and partly primary associated with less metamorphosed Dharwars
184 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
INDIAN OCCURANCES of Mn ore Bellary, Chitradurga, Uttarkannad, Dharwad, shimoga, Tumkur districts, Karnataka The deposits are of varying dimensions, associated with limestones, schistose grits and ochery-schists of the Shimoga-Chitradurga schist of Dharwar group. The ore are of lateritoid type and the indvidual deposits are lenticular and impersistent Balaghat district, Madhya Pradesh They represent gondite type of deposits associated with metamorphosed Dharwar rocks Bhandara, Nagpur districts, Maharashtra The ore bodies are banded braunite-quartzite and grade on to quartz spessartite – rhodonite bearing gondite. Waethering has given rise to residual enrichment deposits Ratnagiri district, Maharashtra They represnet secondary enrichment deposits associated with lateritised Dharwarian metasediments, composed of quartzite, banded hematite- quartzite and phylite. The ore generally more ferruginous
INDIAN OCCURANCES of Mn ore Sundargarh & Keonjhar (Bonai-Keonjhar area) districts, Orissa The ore bodies occur as lenses or in irregular shape in shales, brecciated cherts and laterites capping them belonging to Iron-ore group of rocks. Bonai-Keonjhar belt of north Orissa contributes 90% of the production of manganese ore of the State whose share comes to 36% of the country’s total production. This belt is one of the most important manganese ore producing region of India because of its low phosphorus content in the ore.
Bonai-Keonjhar iron ore manganese belt forms a 60 km long & 25 km wide synclinorium. The banded iron formations; which broadly define the outline of the synclinorium. Manganese ore bearing shales occur within the core region of the fold Koraput, Kalahandi, & Bolangir and Patua districts, Orissa The ore bodies associated with Khondalite suite of Eastern Ghats group Sambalpur District, Orissa: The deposits are associated with laterites on the meta sediments Banswara district, Orissa The deposits are associated with laterites on the meta sediments
185 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ECONOMIC GEOLOGY e – Learning Material: Unit-5
CHROMIUM
186 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chromite is the only economic source of Chromium. It has a wide range of uses in metallurgical, chemical, refractory industries.
The properties of chromium that makes it most versatile and indispensable are its resistance to corrosion, oxidation, wear and galling and enhancement of hardenability.
In metallurgical industry, chromite is used for manufacturing low- carbon and high carbon ferro-chrome and charge chrome which in turn are used as additives in making stainless steels and special alloy steel.
Hard lumpy chromite is used for producing high carbon ferrochrome while friable ore and fines briquettes are used for low carbon ferrochrome. Both briquette fines and lumpy ores are used in production of charge chrome.
In chemical industry, chromite is used for production of sodium bichromate which is the source material for making various chromium-based chemicals. These chrome-chemicals are used in chromium plating, leather tanning, furniture and fixtures, vehicles, safety matches, as dyes in clothings, drilling muds and as catalysts and pigments. The most objectionable impurities are silica and lime. In refractory industry, chromite is used as a refractory material because of its high melting point (1,700o to 1,900o C). Generally, refractories are made using magnesite and chromite together and depending on the chromite to dead-burnt magnesite (DBM) ratio, bricks are called chrome-mag bricks (50 to 55% chromite) and mag-chrome bricks (45 to 50% chromite). Dense chrome bricks containing 100% chromite are also manufactured. Chromite refractories used for lining of open hearth steel furnaces serve as neutral refractories. The refractory industry prefers hard lumpy ore containing low silica and low lime. Chromite is also used in ceramic industry and electrode making industry
187 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chromium 46.46 % Chromite (FeCr2O4) Iron 24.95 % Cleavage: None Oxygen 28.59 % Color: Black, Brownish black. 100.00 % Density: 4.5 - 5.09, Average = 4.79 Diaphaneity: Opaque Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Granular - Generally occurs as anhedral to subhedral crystals in matrix. Massive – Granular, Nuggets - Irregular lumps produced by stream transport Hardness: 5.5 - Knife Blade Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Naturally weak Streak: brown Environment: Cummulate mineral found in ultramafic portions of layered mafic intrusions. Common in meteorites. an accessory mineral in alpine- type peridotites except carbonaceous chondrites, and in lunar mare basalts
Locality: Campo Formoso ultramafic complex, Bahia, Brazil Chromite in octahedral crystals
188 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Origin: Onverwacht, Eastern Bushvel, RSA Sample size: 3 x 5 cm
Massive black chromite in serpentine matrix Origin: Psonas, Euboea Island, Greece Sample size: 4.5 x 6.5 cm
Origin: Clear Creek area, New Idria District, San Benito Co., California, U.S.A. Sample size: 5.7 x 4.9 x 4.1 cm
189 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Massive black chromite in serpentine matrix Origin: Psonas, Euboea Island, Greece Sample size: 4.5 x 6.5 cm
ChromferideFe3Cr Chromium 11.04 % Cr Iron 88.96 % Fe ______100.00 %
190 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Ferchromide Cr3Fe Chromium 87.47 % Cr
Iron 12.53 % Fe ______100.00 %
191 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
WORLD RESOURCES AND PRODUCTION
The huge deposits of South Africa, constituting more than 75% of known world resources, are now the major sources of chromite ore globally.
The important countries where considerable reserves of chromite ore are known and mined for production of ferro-chrome and charge-chrome etc. are Brazil, Republic of South Africa, Kazakhstan, India, Russia and Finland. Internationally,
79% consumption of chromite made in metallurgical industry, 13% in chemical industry and 8% in refractory industry, on an average. In the metallurgical industry, 60% is consumed for stainless steel productions
192 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
GEOLOGY AND DISTRIBUTION OF INDIAN CHROMITE DEPOSITS
Archaean Greenstone Association: Sukinda and Baula- Nausahi in Orissa, Sinduvalli and Byrapur in Karnataka, Bhandara – Napur belt, Sindhudurg belt and Chandrapur belt in Maharashtra, Roro and Jojohatu in Jharkhand , Ponda- Dudsagar area in Goa.
Proterozoic Granulite Association: Kondapalli in Andhra Pradesh, Sitampundi complex of Tamil Nadu.
Mesozoic Ophiolite Association: Chromite occurrences in Manipur, Nagaland, Andaman & Nicobar Islands and Jammu & Kashmir.
Major share (98.6%) of chromite resources in the country is located in Orissa. The chromite deposits occur in number of localities along NE-SW belt associated with ultramafic complexes of Sukinda, Baula-Nausahi and similar occurrences of ultramafic rocks at Bhalukasoni and Ramgiri.
Chromite deposits of Sukinda and Katpal ultramafic belt of Cuttack and Dhenkanal districts, Orissa constitutes 95% of the country’s chromite resources. Here chromite with nickel ore occurs as concentration and disseminations in the ultramafic rocks, in the form of lenses, pockets, thin seams and stringers. Chromite deposits of Nausahi in Keonjhar district, Orissa occur in band and lenses within serpendine, peridotite, pyroxenite, gabbro, Vanadiferous magnetite and anorthosite resembling well known stratiform of world Other states contributing to the country’s resources of chromite are Manipur, Karnataka, Jharkhand, Maharashtra, Tamil Nadu and Andhra Pradesh. In Manipur, chromite is associated with serpentine. In Karnataka, the ultramafic rocks bearing chromite occur in two belts; viz Nuggehalli, Arsikhera and Nanjangud in Mysore district. In Maharashtra, it occurs in altered ultramafic rocks. In Andhra Pradesh, it occurs in Eastern Ghat group of rocks in Khammam and Krishna district. In Tamil Nadu, chromite associated with amphibolites bands are found in Sitampundi complex of anorthosites. In Nagaland, nickeliferrous chromite has been located in ultramafic belt. The major chromite resources are from Sukinda followed by Baula-Nausahi area of Orissa. Small resources have been established in Karnataka, Maharashtra and Jharkhand
193 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
194 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
1. Massive chrome ore included in the gabbro of the brecciated zone collected from sub surface Bangur mine of Orissa Mining Corporation. 2. Granular chromite ore from Roro-Jojohatu 3. Banded chrome ore showing crude layering of chromite and altered peridotite collected from a quarry in Nuasahi mines of IMFA. 4. Field photograph of well preserved mm scale rhythmic banding displayed by Rangapura ultramafic body, Karnataka. Dark bands correspond to chromitite and the light bands to serpentinised dunite- peridotite.
5. Small scale slump structure in rhythmically layered chromitite of TISCO mines, Grade-1 quarry. 6. Disseminated chrome ore from a bore hole in Kalarangi chromite mine of Orissa Mining Corporation (OMC).
195 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Igneous breccia containing chromite clasts (view approximately 16 m high) (Boula, Orissa, India).
MINING & PRODUCTION The production of chromite at 4799 thousand tonnes during 2007-08 is decreased by 9 % as compared to that in the previous year owing to decrease in market demand. The number of reporting mines was 21 in both the years. Six principal producers operating 12 mines together accounted for 90% of the total production during the year. The contribution of 13 mines, each producing more than 10000 tonnes per annum was 99.70 % of the total production. The share of public sector in total production was 30% in 2007-08 as compared to that of 31% in the previous year. About 30% of the total production was reported from captive mines in current year as compared to that 26% in the previous year.
196 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Locality: Kraubath, Leoben, Styria, Austria Chromite in partly serpentinized dunite, upper left some chromian clinochlore. Polished slab,
Locality: Augraben, Kraubath, Leoben, Styria, Austria Black chromite grains in serpentinite matrix. Width of the picture:15mm
197 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Locality: Caledonia Mine, Holguín Province, Cuba Black nodular chromite in matrix.
Locality: Finero Ultramafic Complex, Different Municipalities, Verbano-Cusio- Ossola Province, Piedmont, Italy Cromite crystals in peridotite.
198 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
MINING & PRODUCTION Chromite is mined mostly by opencast method in the country. M/S TISCO is operating open cast mine at Sukinda. M/s OMC has open cast chromite mines at South Kaliapani, Kaliapani, Sukrangi, Kalarangi,Kathpal and Bangur in Orissa. Other open cast mines are Ostopal of M/s FACOR, Suruabil of M/s Mishrilal Jain, Kamarda of M/s B. C. Mohanty, Chingudipal and Sukinda of M/s IMFA, Tailangi of M/s IDCOL and Bangur of M/s ICCL. OMC is also developing underground mine near Bangur, in Baula-Nausahi chromite belt. Underground mines are confined to Byrapur of M/s MML in Karnataka and Boula and Kathpal mines (both underground and open cast) of M/s FACOR and Nuasahi of M/s IMFA (underground development was going on) in Orissa. In Sukinda area, deposits of chromite lying below 100 m depth may have to be exploited by highly specialized underground mining techniques. M/s Mysore Mineral Ltd. is mining chromite ore in Hassan District, Karnataka. Out of the existing six leases, two are underground mines (Byrapur chromite mines) and the rest four leases namely, Thagdur, Jambur, Bhakhtahalli, Aldahalli, opencast method in working is practiced.
199 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Great intrusive body with 530km length, The Great Dyke, Zimbabwe The image shows Archeozonic mafic dyke in Zimbabwe (approx. 2.46billion years). The great dyke is 3-12km wide and stretches out 530km from north-northeast to south- southwest, crossing the whole southern Zimbabwe region. The image focuses on 80km at the southern edge. In the image, a few faults can be observed across the great dyke, of which the most peculiar right lateral fault at the upper part from northwest to southeast direction, causing the dyke to slide by a few kilometers. A river runs along the fault. Valuable metal deposits including platinum and chrome are distributed all over the great dyke, providing an important source of income for the country's economy.
NON-FEROUS AND ALLIED METALS
200 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
COPPER Copper, the pinkish coloured and comparatively softer metal, is well known to all of us. It is one of the few metals to occur in native metal form as nuggets and masses in nature and is being used prior to iron by mankind since ancient past. Hence, it is the metal that has high cultural significance.
On record this metal was known to some of the oldest civilizations and has a history of use that is at least 10,000 years old. A copper pendant was found in what is now northern Iraq that dates to 8700 BC. Evidence of regular use of copper artifacts also came from Mehrgarh in Baluchistan (earlier part of India) datable to 6500 BC.
Use of copper compounds also dates back to before 4000 BC. In the past it was also used in making mirror.
The archaeological studies made on the basis of excavations at Ganeshwar, an old mining town located east of Khetri in north Rajasthan (India), ascribe the earliest Indian copper mining to Indus valley civilization (3000-1500 BC). Large number of the ancient copper mining and metallurgical sites (slag heaps) present in almost all States of the country bear testimony to it. In Kumaun (central Himalaya) copper smithy is considered an old traditional technology.
Mention of copper mining and metallurgy in country exists in several ancient works e.g. Kautilya's Arthsastra (3rd Century BC) to Ain-i-Akbari in 1590 AD.
The Faynan district of Jordan is known for its rich copper ore deposits. A three thousand-year-old industrial scale metal production operation in the region is now being touted as "King Solomon's mines." Photograph by Kenneth Garrett.
201 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
During the ancient period ‘native copper’ was the initial source of this metal until it was possible to extract copper from its ores, which are far more abundant in nature and, therefore, form the main source of copper today.
Copper possesses some of very special characters such as excellent ductility, high conductivity of heat and electricity, resistance to corrosion, ability to form alloys with other metals and beauty. It is completely soluble with gold. Its length can be increased as much as 5,000 times. Hence, it is an ideal metal for making wire.
Copper has 29 distinct isotopes ranging in atomic mass from 52 to 80. Two of these, 63Cu and 65Cu, are stable and occur naturally, with 63Cu comprising approximately 69% of naturally occurring copper. The other 27 isotopes are radioactive and do not occur naturally. The most stable of these is 67Cu with a half-life of 61.83 hours
When found in free metallic state it is called ‘native copper’ forming polycrystalline mass, wire, distorted crystals, grains etc. In nature it occurs in mineral form. It forms a primary mineral in basalts, the volcanic rocks.
It’s most common mineral forms are sulphides, carbonates and oxides. Copper constitutes 70 parts per million of the Earth's crust and is present to the extent of 0.020-0.001 parts per million in seawater.
NATIVE COPPER
Copper in calcite
202 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Crystallized loose grouping of native copper partly encrusted by tiny red cuprite crystals
Copper altering to malachite
203 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
COPPER SULPHIDE ORE
Hardness / Opacity/ Lustre/ Cleavage / Copper Ore Color SG Low/ SG Habit streak Fracture High Crystals sphenoidal, Chalcopyrite Brass-yellow, Opaque 3.5-4 {011} sometimes resemble tetrahedrons; CuFeS2 tarnishes Metallic 4.35 distinct massive, compact; reniform, Tetragonal iridescent Greenish black 4.35 Uneven; brittle botryoidal Opaque Bornite 3.3 {111} in traces Crystals cubic, octahedral or Copper-red or Metallic Cu5FeS4 5.079 Conchoidal to dodecahedral, rare; massive, bronze, Light grayish Cubic 5.079 uneven granular black {110} indistinct Crystals pseudohexagonal Chalcocite Opaque 2.5-3 Blackish gray Conchoidal; prisms formed by twinning; Cu2S Metallic 5.5 to black brittle, somewhat short prismatic or thick Monoclinic Blackish gray 5.8 sectile tabular; massive Opaque {0001} perfect Covellite Submetallic to 1.5-2 Crystals thin tabular Light to dark Uneven; brittle, CuS dull 4.681 hexagonal plates; massive, indigo-blue thin laminae Hexagonal Shining gray- 4.681 foliated flexible black {110} perfect, Enargite Opaque 3 {100} and {010} Crystals prismatic or tabular; Grayish black Cu3AsS4 Metallic 4.45 distinct, {001} massive, granular or to iron-black Orthorhombic Grayish black 4.45 indistinct prismatic Uneven; brittle Tetrahedrite Crystals tetrahedral, Opaque, 3-4.5 Empty (Cu,Fe)12Sb4S Steel-gray to modified, contact penetration Metallic, Black to 4.6 Subconchoidal to 13 iron-black twins; massive, coarse brown to dark red 5.1 uneven; brittle Cubic granular to compact
COPPER OXIDE ORE
Hardness / Opacity/ Copper Ore Color SG Low/ Cleavage / Fracture Habit Lustre/ streak SG High Transparent to Crystals cubic, translucent octahedral or Red, brownish Cuprite Adamantine or 3.5-4 dodecahedral; hair-like red, purplish {111} interrupted, {001} rare Cu2O submetallic to 6.14 forming wads or mats red to almost Conchoidal to uneven; brittle Cubic earthy 6.14 (chalcotrichite); black Brownish red, massive, compact, shining granular Crystals acicular or Translucent to {201} perfect, {010} fair short to long prismatic, Malachite Bright green to opaque 3.5-4 Subconchoidal to uneven; wedge-shaped Cu2(CO3)(OH)2 dark or Vitreous to 4.05 crystals brittle; massive terminations, small; Monoclinic blackish green adamantine 4.05 material tough massive; compact Pale green crusts; botryoidal Crystals varied in habit and often Transparent to Azurite Light blue to modified; tabular or nearly opaque 3.5-4 {011} slightly imperfect; {100} Cu3(CO3)2(OH) very dark blue, short prismatic, equant Vitreous 3.77 fair; {110} in traces 2 usually azure or rhombohedral; Blue, lighter than 3.77 Conchoidal; brittle Monoclinic blue massive, stalactitic, color earthy, nodular concretions
204 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
COPPER silicate and native ORE
Hardness / Color Opacity/ Cleavage / Fracture Habit Copper Ore SG Low/ Lustre/ streak SG High Transluscent Chrysocolla Green, Vitreous, greasy, 2-4 None Reniform, botryoidal Cu2H2Si2O5(OH)4 bluish dull 2 Uneven to conchoidal masses Monoclinic green, blue White to pale blue 2.2 or green Copper- Crystals cubic, red, octahedral, Copper, Cu brown; Opaque 2.5-3 Empty dodecahedral, Cubic pale rose Metallic 8.94 Hackly; malleable and ductile tetrahexahedral; Native when Pale red 8.94 arborescent, wirelike, fresh, pale massive, powdery pink
Chalcopyrite Well-formed crystals of chalcopyrite and Chemical Formula: CuFeS2 quartz. Iron 30.43 % Fe, Copper 34.63 % Cu, Sulfur 34.94 % S Common in sulfide veins and disseminated in igneous rocks.
Cleavage: {112} Indistinct Color: Brass yellow, Honey yellow. Density: 4.1 - 4.3, Average = 4.19 Diaphaneity: Opaque Fracture: Brittle - Generally displayed by glasses and most non-metallic minerals. Hardness: 3.5 Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Magnetic after heating Streak: greenish black
205 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Bornite (Cu5FeS4) Iron 11.13 % Fe,Copper 63.31 % Cu, Sulfur 25.56 % S Disseminated in igneous intrusions and a primary and secondary mineral in copper ore veins Cleavage: {111} Imperfect Color: Copper red, Bronze brown, Purple. Density: 4.9 - 5.3, Average = 5.09 Diaphaneity: Opaque Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz). Habit: Granular - Generally occurs as anhedral to subhedral crystals in matrix. Massive - Granular - Common texture observed in granite and other igneous rock. Reniform - "Kidney like" in shape (e.g.. hematite). Hardness: 3 -Calcite Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Magnetic after heating Streak: grayish black
206 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Bornite (Cu5FeS4)
Chalcocite (CU2S) Copper 79.85 % Cu, Sulfur 20.15 % S
Cleavage: {110} Indistinct Color: Blue black, Gray, Black, Black gray, Steel gray. Density: 5.5 - 5.8, Average = 5.65 Diaphaneity: Opaque Fracture:Conchoidal Habit: Euhedral Crystals - Occurs as well-formed crystals showing good external form. Granular - Generally occurs as anhedral to subhedral crystals in matrix. Massive - Uniformly indistinguishable crystals forming large masses. Hardness: 2.5-3 - Finger Nail-Calcite Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Nonmagnetic Streak: grayish black
207 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Cuprite Cu2O Copper 88.82 %, Oxygen 11.18 % Cleavage: {111} Imperfect Color: Brown red, Purple red, Red, Black. Density: 6.1 Diaphaneity:Transparent to translucent Fracture: Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments. Habit: Capillary - Very slender and long, like a thread or hair (e.g. millerite). Habit: Massive - Granular - Common texture observed in granite and other igneous rock. Hardness: 3.5-4 - Copper Penny-Fluorite Luminescence: Non-fluorescent. Luster: Adamantine Magnetism:Nonmagnetic Streak: brownish red
Dark red ball or sphere of cuprite crystals set on a pearly white dolomite crystal matrix.
208 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Malachite Cu2(CO3)(OH)2 Secondary mineral in the oxidized zones of copper ore deposits
Cleavage:{201} Perfect, {010} Fair Color: Green, Dark green, Blackish green. Density: 3.6 - 4, Average = 3.8 Diaphaneity:Translucent to subtranslucent to opaque Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Botryoidal - "Grape-like" rounded forms (e.g.. malachite). Massive - Fibrous - Distinctly fibrous fine-grained forms. Stalactitic - Shaped like pendant columns as stalactites or stalagmites Hardness: 3.5-4 Luminescence: Non-fluorescent. Luster: Vitreous - Silky Streak: light green
Dark blue stubby pyramidal azurite crystals and green botryoidal-shaped radial aggregates of malachite.
Botryoidal malachite
209 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Azurite Cu3(CO3)2(OH)2 Cleavage: {011} Perfect, {100} Fair Color: Azure blue, Blue, Light blue, Dark blue. Density: 3.77 - 3.89, Average = 3.83 Diaphaneity: Transparent to subtranslucent Fracture: Brittle - Conchoidal Habit: Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline). Stalactitic - Shaped like pendant columns as stalactites or stalagmites. Tabular - Blue, hairy crystals of cyanotrichite Form dimensions are thin in one direction. with dark-blue, blocky azurite on a green, malachite matrix Hardness: 3.5-4 - Copper Penny- Fluorite Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: light blue
Azurite with malachite
210 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Copper-bearing ores fall into three main classes i.e. oxide, carbonate and the sulfide. There are more than 150 ore minerals of copper.
The important oxide ores include cuprite (Cu2O) and tenorite (CuO). The carbonate ores are malachite (Cu2CO3(OH)2) and azurite (Cu3(CO3)2(OH)2).
The common sulfides of copper include chalcopyrite (CuFeS2), covellite (CuS), chalcocite (Cu2S) and bornite (Cu5FeS4).
Fresh copper sulphides form deeper parts of the ore zones or lodes, which are not exposed to weathering. Near the surface, these get altered by oxidation and other chemical actions to native metal, oxides and carbonates.
These secondary copper minerals also form rich ore and owing to characteristic green or blue colour, even small amounts of copper ore is identified easily in the rocks.
Cuprite is a secondary mineral, which forms in the oxidized zone of copper sulfide deposits. It has a relatively high specific gravity of 6.1; and is also known as ‘ruby copper’ due to its distinctive red color. The tenorite is dull grey-black colored mineral of copper.
The malachite is a green-colored copper mineral, which crystallizes in the monoclinic system, and most often forms botryoidal, fibrous or stalagmitic masses.
Azurite is a soft, deep blue copper mineral produced by weathering of copper ores. It occurs as massive to nodular, and often stalactitic in form. It tends to lighten in color over time due to weathering into malachite. Both the minerals were used as mineral pigment for centuries.
The chalcopyrite is brassy yellow in colour, shows metallic lustre and tarnishes to iridescent blue, green, yellow and purple. Its hardness is 3.5 to 4 on the Mohs scale and specific gravity 4.2. It breaks with conchoidal fracture and becomes magnetic on heating. When exposed to air, it oxidizes to a variety of oxides, hydroxides and sulfates. Chalcopyrite occurs in a variety of ore types such as huge masses, irregular veins and disseminations. Its streak is diagnostic as green tinged black. Half of the world's copper deposits are in the form of chalcopyrite ore.
The covellite is a rare copper sulfide mineral of indigo blue colour and was the first discovered natural superconductor. It is commonly found as secondary mineral, rarely as a primary mineral, and very rare as volcanic sublimate.
211 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chalcocite is opaque, dark-gray to black in colour with a metallic lustre. It has a hardness of 2½ - 3 with an orthorhombic crystal system. It is a secondary mineral that forms from the alteration of other minerals; it has been known to form pseudomorphs of different minerals.
Bornite is brown to copper-red in colour on fresh surfaces that tarnishes to various shades of blue to purple. Its striking iridescence gives it nickname ‘peacock ore’. It crystallizes in orthorhombic system and occurs mostly as granular masses and disseminations in different rocks. It has of grayish black streak. It is also magnetic after heating.
Copper ores occur in varied forms viz. in native form as wire, grains, crystals etc., in mineral form as disseminations, veins, stock work etc. in variety of rocks.
Mode of Occurrence and Origin of Copper
Copper occurs in a variety of ways Magmatic Segregations – Dissiminated forms, veins and lodes Contact metamorphic deposits – bedded deposits Porphyry copper deposits – Stocks, chonoliths intrusions of monzonite or diorite porphyry of early Tertiary age In India, Copper lodes occur mostly in veins, stringers, patches, dissiminated forms, fracture and cleavage fillings, etc. and associated with different types of rocks mostly Dharwar and Cuddapah age Copper associated with lead, zinc, silver, gold, etc. Copper deposits mostly originated by hydrothermal solutions
212 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Copper is extracted from its ores by two principal methods i.e. pyrometallurgical and the hydrometallurgical method.
In the first method ore is crushed into powder. Minerals are concentrated into slurry. Copper minerals are separated by flotation. Smelting of concentrate and extraction of metal follow it; by heat, flux and addition of oxygen. Sulfur, iron and other undesirable elements are removed and product is called ‘blister copper’. It is further refined by fire and electro-refining methods.
The second method i.e. ‘solvent extraction’ and ‘electro-winning’ is most dominant leaching process in use today in recovering copper by chemical solutions. It involves two major stages: solvent extraction - the process by which copper ions are leached or extracted from the ore using chemical agents; and electro-winning - electrolysis of Cu ions plated onto the cathode and thereafter removed in elemental form.
The most common copper-base alloys are the ‘bronze’ made of copper and tin, and the ‘brass’ made of copper and zinc. Bronze was the first to be produced by man during ancient period and is of two kinds i.e. wrought bronze and the cast bronze. Alloying it with other elements such as aluminum, silicon, manganese, beryllium, lead etc different types of bronzes are produced, which have different usage. The bronze figure of a dancing girl recovered from Mohenjodaro is a testimony of the knowledge of copper alloying of the Indians during Harappan (Sindhu-Sarasvati) civilization.
Brass is comparatively stronger than bronze; its colour changes with zinc content. German brass looking like gold contains 20 parts zinc in hundred, and is used in making cheaper ornaments by rolling it into thin foils. The naval brass is made of tin, copper and zinc and it strongly resists corrosion in seawater
Copper is one of the oldest metals ever used and has been one of the important materials in the development of civilization. Today it has become a major industrial metal, ranking third after iron and aluminum in terms of quantities consumed.
Copper has been fashioned into ornamental objects and cooking utensils. Coins have been made of copper throughout history. Copper is also used in pigments, insecticides, and fungicides. Electrical uses of copper, including power transmission and generation, building wiring, telecommunication, electrical and electronic products account for about three quarters of total copper usage.
Copper is the third most abundant trace mineral in the body. The human body contains approximately 100-500 mg of copper but it's role is important as it serves as a cofactor for enzymes involved in hemoglobin and collagen formation and is involved in incorporating iron into the structure of hemoglobin. It strengthens blood vessels, bones and nerves.
213 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Copper producing localities in the world are too numerous to mention here. Worldwide famous localities are Broken Hill (Australia); Daye, Hubei Chengmenshan, Jiurui, Jiangxi Province (China); Ogonja (Namibia); and Callington District, Cornwall (England). In addition, Bolivia, Kazakhstan also produce significant amount of copper.
In India, Hindustan Copper Limited (HCL) under Ministry of Mines carries out mining and production of copper. The Company’s mines and plants are spread across four operating Units, one each in the States of Rajasthan, Madhya Pradesh, Jharkhand and Maharashtra i.e. Khetri Copper Complex (KCC) at Khetri Nagar, Rajasthan; Indian Copper Complex (ICC) at Ghatsila, Jharkhand; Malanjkhand Copper Project (MCP) at Malanjkhand, Madhya Pradesh; and Taloja Copper Project (TCP) at Taloja, Maharashtra.
The Khetri Copper Belt, situated in Aravalli Range in Jhunjhunu and Sikar districts, Rajasthan, hosts several copper deposits. The area comprises of tightly folded Proterozoic metasediments that rest over basement gneisses. The prominent copper deposits in the belt are Khetri, Kolihan, Banwas, Chandmari, Dholamala, Akwali and Muradpur-Pacheri. KCC was established in 1967. It has two mechanized underground mines namely 'Khetri' and 'Kolihan' with capacity of 1.0 million tonnes of ore per annum.
It’s ore resources include 26 million tonnes @ 1.13 % Cu at Khetri Mine; 20.64 million tonnes @ 1.35 % Cu at Kolihan Mine; 25.02 million tonnes @ 1.69 % Cu at Banwas Block and 12.10 million tonnes @ 1.03 % Cu at Intervening block.
The Malanjkhand copper belt comprises of a large body of copper ore in granitic rocks. Its prominent deposits include Malanjkhand, Shitalpani, Gidhri Dhorli, Jatta and Garhi Dongri. GSI had initiated systematic explorations for this deposit in 1969. MCP was established in 1982. It has an open pit mine, and concentrator plant. It has 221.00 million tonnes @ 1.31% copper resources at Malanjkhand Mine.
The Singhbhum copper belt of Jharkhand comprises of Proterozoic volcano- sedimentary sequence with a prominent shear zone called Singhbhum shear zone. Copper mineralisation is localized along this shear zone.
Prominent deposits are at Chapri, Rakha, Surda, Kendadih, Pathargora and Dhobani. A British company established the ICC LTD in 1930 at Ghatsila. It was merged with HCL in 1972. It has a cluster of underground copper mines, concentrator plant and smelter. Its operating mine is Surda having 26 MT of ore @ 1.20% Cu. Additional reserves include 47.19 million tonnes @ 0.97% copper at Rakha mine; 12.85 million tonnes @1.73% copper at Kendadih Mine; 63.50 million tonnes @1.14% copper at Chapri Block. The Taloja copper project, set up in 1990, has a plant to produce mainly copper rods (CCR) with ore input from HCL mines. The capacity for the production of primary copper in India has risen from a mere 47,500 t/pa till 1997 to 9,47,000 tonne in 2008-09, with the result that India is now a net exporter of refined copper.
214 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
COPPER ORE IN INDIA Bihar SInghbhum Copper Belt – It is localised in a shear zone moulded along the northern and northeastern margin of singhbhum granite massif Precambrian Archaean quartz-chlorite-biotite schist, metamorphosed basic rock and soda granite Hesatu-Belbathan belt – The mineralised rocks occur as lenses or pockets within chotanagpur granite-gneiss Precambrian - Tremolite-Actinolite-Schist, Calc-granulite and amphibolite
215 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chalcopyrite and pyrite are the principal sulphides in the mineralised zone. Chalcopyrite is dominant and comprises about 70 to 80% by volume of the total sulphides.
Pyrrhotite is locally developed and is more common in the deeper levels (generally at depths greater than 300 m).
The other sulphides present in the mineralised zone consist pentlandite, molybdenite, marcasite, tetradymite, tetrahedrite, cubanite and arsenopyrite, violarite, millerite etc. The principal gangue minerals are quartz, chlorite, biotite, magnetite, apatite felspar and tourmaline.
RAJASTHAN Copper mineralisation is mostly confined to the rocks of the Delhi Supergroup in northern Rajasthan and is mostly distributed in three distinct belts: namely : Khetri copper belt and a parallel eastern zone in Jhunjhunu and Sikar districts on the west.
Nim-Ka-Thana copper belt in Sikar district in the middle and
Alwar-Jaipur belt in Alwar and Jaipur districts on the east
216 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
KHETRI COPPER BELT, JHUNJHUNU DISTRICT Khetri copper belt extends over a strike length of 80 m from Singhana (28°06' : 76°54') in the NNE of Raghunathgarh (27°39' : 75°21') in the SW.
It trends NNE-SSW in the northern part while to the south of Kantli river, there is a swing towards ENE-WSW. The Kantli river probably flows along a fault trending NNW-SSE with the mineralised belt to the south of the river shifted further westwards.
The Khetri copper belt is located in a semi-desert tract. It is reported that copper was mined at Khetri even during the Mauryan period. The first recorded mention of copper mining activity, during the Mughal period is in ‘Ain-e-Akbari’ (1590 AD).
The Khetri copper belt is made up of the Alwar and Ajabgarh Groups of rocks of the Delhi Supergroup (Precambrian).
The older Alwar Group predominantly comprises felspar and amphibole bearing quartzites with lenticular intercalations of phyllites, amphibolites, amphibole-magnetite rock, amphibolite etc.
The Ajabgarh Group is dominantly made up of meta-pelitic rocks, viz., phyllites with andalusite, chiastolite/staurolite; carbonaceous phyllites; biotite-schist ± garnet ± andalusite; and quartz-chlorite schist ± garnet with intercalations of banded amphibole (anthophyllite / cummingtonite) quartzite, felspathic quartzite with lenses of magnetite amphibole rock and amphibole marble ± magnetite.
217 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Sulphide mineralisation occurs in a variety of rock types, viz., garnetiferous chlorite-quartz schist/quartzite, chlorite-biotite and amphibole bearing schist, amphibole biotite-chlorite-quartz schist, carbon phyllites, garnetiferous chlorite quartzite, felspathic quartzite, amphibole quartzite, amphibolite, amphibolemagnetite schist, andalusite bearing phyllite etc.
The bulk of the mineralisation occurs close to the contact of the Alwar quartzites with the meta-pelites of the Ajabgarh Group.
MADHYA PRADESH
Malanjkhand copper deposit:The Malanjkhand (22°02' : 80°43' - 54 B/12) copper deposit located in the Balaghat district is presently under exploitation by open cast mining by M/s. Hindustan Copper Limited.
The zone of copper mineralisation is located in the approximately 2.6 km. long arcuate Malanjkhand hill (elevation about 600 m. above m.s.l.).
The rocks of the basement complex (Malanjkhand granitoid) comprise granites and quartz reefs intruded by rnetabasics. The basement rocks are overlain by the upper Precambrian metasediments of Chilpi Ghat Series with an erosional unconformity. The granitic rocks range in composition from a biotite granite to quartz diorite and are highly kaolinised,seriticised and saussuritised in the mineralised zone. The metasediments comprise conglomerates, grits, phyllites and shales.
copper mineralisation is localised in the quartz reefs, associated with the granites.
218 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
TAMIL NADU In Tamil Nadu, only one basemetal deposit, Viz., the multimetal copper-lead-zinc deposit at Mamandur is so far known.
This deposit lies in the Peninsular Archaean complex in the transition zone between charnockites on the west and migmatites on the east. The Mamandur area is made up of migmatites and charnockites with bands of garnetiferous biotite sillimanite gneiss, magnetite quartzite and a suite of ultrabasic rocks comprising pyroxenite, gabbro, norite and anorthosite. The general trend of foliation is NNE-SSW to NE-SW with dips of 60 to 65° towards SE. Galena from the mineralised zone has given an Isotope age of 2581 to 2600 M.Y.
Arumanullur (8°19'15'' : 77°24'35'' - 57 H/7) and adjacent areas, Kanyakumari District
In this area, sulphide mineralisation is found in meta-norite bands which occur interbanded with charnockites and garnetiferous biotite sillimanite ― graphite gneisses, Incidence of pyrite - pyrrhotite - chalcopyrite have been recorded from a number of meta-norite bands occurring in the Arumanullur area and in the areas lying about 3 to 10 km to the north and north-east of Arumanullur.
KARNATAKA
Only a few small low grade deposits of basemetal are so far known from Karnataka. But a large number of occurrences of basemetal mineralisation, particularly copper mineralisation have been recorded from a variety of geological settings from different parts of the State. The deposits / occurrences can be broadly grouped into the following 4 categories 1. Those associated with the metavolcanic - metasedimentary greenstone belts of the Dharwar Supergroup. 2. Those associated with sheared quartz veins and metabasic rocks traversing the granitoids of the Peninsular Gneissic Complex. 3. Those associated with ultramafic complexes. 4. Those occurring in the schist belts occurring as enclaves within thePeninsular Gneissic Complex. At present, two small deposits, one at Ingaldhalu located in the Chitradurga schist belt and the other at Kalyadi located in Dharwar schist enclave within the Peninsular Gneissic Complex are being worked on a scale of about 200 tonnes per day by the Chitradurga Copper Company which is a subsidiary of the Hutti Gold Mines Co., Ltd.
219 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
ANDHRAPRADESH
Several small basemetal deposits and a large number of occurrences are known from Andhra Pradesh. These deposits and occurrences are mostly hosted in rocks of the Cuddapah Supergroup and to a lesser extent in rocks of the Kurnool Group, Pakhal Supergroup, Dharwar and Sargur Supergroups and Peninsular Gneissic Complex.
The copper deposit at Mailaram in the Sargur Supergroup are being worked on a small scale respectively by M/s. Hindustan Zinc Limited and the Andhra Pradesh Mining Corporation Limited.
LEAD
220 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
This metal was probably one of the first metals to be produced by man because it is highly malleable, easy to smelt and work with. The earliest lead beads are reported from Catal Hüyük (Turkey) dated as 6400 BC.
Chemical symbol of lead ‘Pb’ is derived from Latin ‘plumbum’ for soft metal (originally ‘plumbum nigrum’ for ‘black plumbum’).
Lead metal is bright bluish-white in color when freshly cut, tarnishes to dull grey when exposed and shows a silvery lustre when melts.
It is very soft, ductile and highly malleable metal and poor in electrical conductivity. It breaks with hackly fracture and shows isometric crystal system.
It is highly resistant to corrosion, hence, is used for storage of acids. It becomes stronger by adding small amount of other metals. Earth crust shows lead concentration of 13 ppb.
Lead is poisonous, hence, is dangerous to human health. It is also the end product of radioactive decay. Lead has several isotopes but four (204Pb, 206Pb, 207Pb, 208Pb) are stable ones, and its common radiogenic isotope of 202Pb has a half-life period of about 53,000 years
Occurrence of metallic or native lead is very rare. It occurs as ore minerals mostly associated with zinc-cadmium-silver, and some copper ores in varied geological environments and different rock formations.
A total of 59 ore minerals of lead are known but the most common are galena (PbS), cerussite (PbCO3), anglesite (PbSO4) and minium (Pb3O4).
In Ancient Egypt galena was used as ‘kohl’ to be applied around the eyes, to reduce desert glare and repelling insects.
Within the zone of weathering or oxidation, galena alters to anglesite or cerussite.
221 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
GALENA (PbS), Galena is the most important lead mineral and contains about 86.6% lead. Sometimes it contains silver upto 1%, hence, is known as leading silver ore.
It shows silver grey colour with a bluish tinge, metallic lustre, 2.5 to 2.75 hardness on Mohs scale,
7.2 to 7.6 specific gravity,
sub-conchoidal fracture and
lead-grey streak.
It occurs in isometric crystal system; often showing octahedral forms
Cerussite (PbCO3), Cerussite, also known as white lead ore or lead-spar, contains about 77.5% lead.
It crystallizes in orthorhombic system, and frequently occurs as twinned crystals, granular mass and sometimes in fibrous form.
It is colourless, white or with grey/ greenish tinge and
adamantine and resinous lustre
conchoidal fracture.
Its hardness is 3.0 to 3.5,
specific gravity of 6.5. Mineral: Cerussite: PbCO3 Hydrocerussite: Pb3(CO3)2(OH)2 Initially it was used in paints and cosmetics. Comments:Platy crystals of milky white hydrocerussite covering cerussite.
222 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Anglesite (PbSO4)
Anglesite is an oxidation product of galena shades of various colours.
It occurs as prismatic (orthorhombic-dipyramidal) crystals and earthy masses.
hardness of 2.5 to 3.0
6.3 specific gravity
brittle to conchoidal fracture and adamantine (in crystals) and Anglesite: PbSO4 Crystalline anglesite with minor earthy lustre. duftite. The crystal at the top of the specimen is partially doubly Secondary, weathered deposits of terminated. lead ore
The important lead-zinc deposits of India include Rampura-Agucha (Bhilwara district), Rajpura-Dariba and Sindesar (Rajsamand district), Zawar (Udaipur), Sawar and Kayar-Ghugra (Ajmer district), Basantgarh and Deri (Sirohi district) in Rajasthan; Amba Mata (Banaskantha district) in Gujarat; Buniyar (Baramula district) in Jammu and Kashmir; Rangpo and Pachekhani (East district) in Sikkim; Rupa-Shergaon (West Kameng district) in Arunachal Pradesh; Sargipalli (Sundargarh district) in Orissa; Mamandur (South Arcot district) in Tamil Nadu; Bandalamottu, Dhukonda (Guntur district) and Zangamrajupalle (Cuddapah district) in Andhra Pradesh; Imalia (Jabalpur district) in Madhya Pradesh; Askot (Pithoragarh district) in Uttar Pradesh; and Gorubathan (Darjeeling district) in West Bengal. Currently lead is produced by HZL alongwith zinc at Zawar (located in Aravalli rocks), Rampura-Agucha, Rajpura-Dariba and Sindesar (located within cover sequences in BGC) mines in Rajasthan; Sargipalli mine in Orissa and Agnigundala mine in Andhra Pradesh.
223 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Lead is the main constituent of lead-acid batteries and is widely used as a coloring agent in stained glasses for reducing the radiation transmission. Because of its high specific gravity it is used as fishing sinkers and in balancing wheels of vehicles. It is also used in polyvinyl chloride (PVC) plastic for coating the electrical metal wires, and for shielding from radiation in x-ray laboratories. In electronics its use as soldering agent is well known. Molten lead is used as a coolant in lead-cooled fast reactors. It is the traditional base metal of organ pipes, mixed with varying proportions of tin to control the tones. Sheet-lead is used for sound proofing system. Lead has many applications in building constructions e.g. sheets as architectural metals in roofing, cladding, flashings, gutters and joints, etc. It is well-known that lead was used as water proofing media (17th century) in Rajsmand Reservoir located in Udaipur district, Rajasthan.
ZINC Chemical symbol: Zn Atomic number: 30 Atomic mass: 65.409(4) g/mol Melting point: 419.53°C Boiling point: 907°C Density: 7.14 g.cm-3 Crystal structure: hexagonal Hardness: 2.5 Moh’s scale Lustre: metallic Magnetic ordering: diamagnetic ID marks: bluish white silvery colour
224 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Centuries before zinc was recognized as a distinct element, zinc ores were used for making brass. A prehistoric statuette containing 87.5% zinc was found in a Dacian archaeological site in Transylvania (modern Romania).
Palestinian brass from the 14th to 10th centuries BC contains 23% zinc.
The primitive alloys with less than 28 per cent zinc were prevalent in many parts of the world before India.
Brass in Taxashila has been dated from third century BC to fifth century AD.
Recently two brass bangles belonging to the Kushana period are discovered from Senuwar (U.P.), which also shows 35 percent zinc.
Zinc was rediscovered in Europe by Marggraf in 1746.
It got its name after German word ‘zinke’ for this metal.
In English and French it became ‘zinc’, in German and Dutch ‘zink’, in Spanish ‘cinc’ and in Welsh ‘sinc’ (pronounced "shink").
The Greek word for zinc is ‘pseudargyros’, literally meaning "pseudo- silver" for its silvery lustre. In Russian, it is ‘tsink’.
In India it is known as ‘Yashad’, Jasta, Jast, Naag in Hindi/ Sanskrit, Tunga in Tamil and Naagam in Malyalam.
225 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Zinc is a bluish-white, lustrous, diamagnetic metal
Zinc makes up about 75 ppm (0.007%) of the Earth's crust. It is the 24th most abundant element in the Earth's crust. Soil contains 5 to 770 ppm of zinc with an average of 64 ppm. Seawater has only 30 ppb zinc.
After iron, aluminum and copper, zinc is the fourth-most used metal, competing with lead. A sheet of zinc looks like an aluminum sheet but it is more than twice as heavy.
The hardness of zinc at Mohs scale is 2.5. Zinc is brittle at ordinary temperatures but malleable at 100 to 150°C. Above 210°C, it becomes brittle again and can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has relatively low melting (419.53°C) and boiling points (907°C). Zinc is not very ductile or malleable, especially when pure.
It is relatively resistant to corrosion in air or water, and therefore, is widely used as a protective layer on iron products to protect from rusting.
Zinc is recovered from a number of different zinc ores.
The types of zinc ores include sulfide, carbonate, silicate and oxide.
Most significant of these ores are
zinc sulphide or sphalerite i.e. (Zn,Fe)S,
zinc carbonate or smithsonite (ZnCO3),
zinc silicate or willemite (Zn2SiO4) and
zinc oxide or zincite (ZnO).
Ores of lead, zinc, cadmium and silver often occur together.
226 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Sphalerite (Zn,Fe)S is the most important zinc ore as it contains 64.06% zinc. It occurs mostly as veins. It shows brown, yellow, red, green and black colour, uneven fracture and occur as colloform (Forming from a gel or colloidal mass)17 , euhedral crystals and granular masses. It has 3.5 to 4 hardness, brownish white streak, 3.9 to 4.2 density and adamantine lustre. It is fluorescent and triboluminescent. It occurs in isometric-hextetrahedral crystal system, which is analogous to diamond. Sphalerite: (Zn,Fe)S
Sphalerite is a polymorph (many shapes Highly lustrous, black, complex but same chemistry) and has two sphalerite crystals to 15 mm in size minerals i.e. wurtzite and matraite. It is completely covering the top of a sometimes difficult to identify sphalerite sulfide matrix. due to its variable colour, lustre and crystal habit.
Sphalerite on quartz
Sphalerite on quartz
Yellow sphalerite Sphalerite on calcite crystal with small pyrite crystals on top
Sphalerite on quartz
227 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The smithsonite (ZnCO3), commonly shows various shades of green and purple;
has a silky to pearly lustre; and occurs in trigonal crystal system and botryoidal form.
It shows white streak, hardness of 4 to 4.5 and specific gravity of 4.4.
Fraipontite: (Zn,Al)3(Si,Al)2O5(OH)4 Zinalsite: Zn2AlSi2O5(OH)4·2(H2O) (?) Smithsonite: ZnCO3 Pearly white, sub-mm fraipontite (zinalsite) crystals associated with green smithsonite.
Creedite: Ca3Al2(SO4)(F,OH)10·2(H2O) Smithsonite: ZnCO3 Purple transparent crystals of creedite to 6 mm on matrix of creamy botryoidal crystalline smithsonite.
The willemite(Zn2SiO4) is somewhat rare zinc mineral. It has vitreous to resinous lustre, hardness of 5.5; specific gravity from 3.9 to 4.2, trigonal crystal system, conchoidal to uneven fracture and white streak. It fluoresces a bright green colour under ultra-violet light. Sky blue botryoidal willemite Some willemite specimens with dark to white dolomite. even show phosphorescence. Phosphorescence is the ability of a mineral to glow after the initial light is removed. Pinkish gray crystalline glaucochroite intermixed with pale green willemite, with dark red zincite and white calcite.
228 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The zincite (Zn2SiO4) is also rare zinc mineral, which is orange-yellow to deep brown or red in colour. It shows orange- yellow streak, conchoidal fracture, hardness of 4 and specific gravity between 5.4 and 5.7. It occurs in hexagonal crystal system forming small crystals and masses
Zincite: (Zn,Mn)O Orange Zincite hexagonal pyramid.
Zinc ores occur in a variety of geological environment Principal lead- zinc deposit types include carbonate-hosted ores, sandstone-hosted ores, shale-hosted deposits and volcanogenic deposits.
Zinc mines are throughout the world with the largest producers being Australia, Canada, China, Peru and United States. Most zinc mines are underground (80%) but some are of the open pit type (8%). China produced 2,600,000 tonnes i.e. one-fourth of the global zinc output in 2006 while India produced 420,000 tonnes.
Important zinc-lead deposits, mostly localized within Precambrian peninsular shield, include Zangamrajupalle and Gollapalle in A.P.; Amjhore within Vindhyan rocks in Bihar; Amba Mata in Delhi Supergroup of rocks in Gujarat; Kolari within Sakoli Group of rocks in Maharashtra; Agucha within Banded Gneissic Complex; Deri and Kayar-Ghugra within Delhi Supergroup; Rajpura-Dariba, Devpura, Samodi, Sindesar and Tiranga within Pur-Banera belt of Pre-Aravalli; and Paduna and Zawar within Aravalli Supergroup of rocks in Rajasthan; Mamandur within Peninsular Archaean Complex of rocks in Tamil Nadu; and Gorubathan within Extra-peninsular Daling Formation (Pre-Cambrian - Cambrian) in West Bengal.
229 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Important zinc-lead deposits, mostly localized within Precambrian peninsular shield, include Zangamrajupalle and Gollapalle in A.P.;
Amjhore within Vindhyan rocks in Bihar;
Amba Mata in Delhi Supergroup of rocks in Gujarat;
Kolari within Sakoli Group of rocks in Maharashtra;
Agucha within Banded Gneissic Complex;
Deri and Kayar-Ghugra within Delhi Supergroup;
Rajpura-Dariba, Devpura, Samodi, Sindesar and Tiranga within Pur-Banera belt of Pre-Aravalli; and Paduna and Zawar within Aravalli Supergroup of rocks in Rajasthan;
Mamandur within Peninsular Archaean Complex of rocks in Tamil Nadu; and
Gorubathan within Extra-peninsular Daling Formation (Pre-Cambrian - Cambrian) in West Bengal.
Zinc production in India initially was done by government through a public sector company i.e. Hindustan Zinc Limited. It was the biggest company in India, which took care of mining to extraction of zinc.
In April 2002, HZL was privatized. Vedanta Group (still named HZL) is now conducting mining and production zinc and associated metals in the country. Reserves and resources of 232.3 Mt of ore containing 27.5 Mt of zinc-lead metal are present as on 31.3.08.
HZL’s operations include three lead-zinc mines (Agucha in Bhilwara district, Zawar in Udaipur district and Rajpura-Dariba in Rajsamand district in Rajasthan), three zinc smelters (Debari and Chanderiya in Rajasthan; Vizag in A.P.).
HZL’s zinc production increased from 283,698 tonnes in 2006 to 426,323 tonnes in 2008. The expansions at the Sindesar Khurd and Kayar mines will be completed in phases by early 2012. A zinc smelter of Binani is located at Alwaye in Kerala.
230 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Molybdenum
Molybdenum is a refractory metal used principally as an alloying agent in steels, cast irons and super alloys to enhance hardness, strength, toughness and wear and corrosionresistance.
Primarily added in the form of molybdic oxide or ferromolybdenum, it is frequently used in combination with chromium, columbium, manganese, nickel, tungsten or other alloy metals to achieve desired metallurgical properties.
The versatility of molybdenum has ensured it a significant role in contemporary technology and industry, which increasingly require materials that are serviceable under higher stresses, greater temperature ranges and more corrosive environments.
Moreover, molybdenum finds significant usage as a refractory metal in numerous chemical applications including catalysts, lubricants and pigments.
The variety of molybdenum materials, few of which afford acceptable substitutions has resulted in a demand that is expected to grow at a greater rate than most other ferrous metals.
231 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
From the period of the Greek and Roman civilizations to the late 18th century, terms such as ‘molybdaena’ were applied to minerals that were soft and ‘lead like’ in character, probably including minerals now known as galena, graphite and molybdenite.
This confusion was resolved in 1778 when the Swedish chemist, Karl Scheele, demonstrated that molybdenite, the principal molybdenum mineral was a discrete mineral sulphide.
World War I generated the first appreciation of utilisation of molybdenum, when it was substituted for tungsten in high speed steels and used as an alloying element in certain steels for military armament.
The Climax deposit in Colorado and the Questa deposit in New Mexico were initially exploited from 1917 to 1919. Development of the Climax deposit being the world’s largest, proved the viability of high tonnage extraction of relatively low grade ore and established United States as the leading producer of molybdenum.
Molybdenum is a silver-white metallic element with an atomic number of 42, atomic weight of 95.95 and a density of 10.2 grams per cubic centimetre. Molybdenum is a strong carbide forming element and much of its alloying effect in steel is imparted through the formation of carbides. It has a melting point of about 2,610°C. significant physical properties of molybdenum metal are good thermal conductivity (about one half that of copper), the lowest coefficient of thermal expansion of the pure metals, high strength at elevated temperatures and resistance to corrosion in a variety of mediums. Molybdenum metal is stable in air or water at moderate temperatures but above 500°C, it oxidises readily.
Molybdenum does not occur in nature in its free or native state, but is found only in chemical combination with other elements. Small deposits of molybdenum bearing minerals occur throughout the world, but the only molybdenum mineral of commercial importance is molybdenite. Wulfenite, powellite and ferrimolybdite are common but have provided very little molybdenum.
232 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Chemical Formula: MoS2 Help on Composition: Composition: Molybdenum 59.94 % Mo Sulfur 40.06 % S
Cleavage:{0001} Perfect Color: Black, Lead gray, Gray. Density: 5.5 Diaphaneity: Opaque Fracture:Sectile - Curved shavings or scrapings produced by a knife blade, (e.g. graphite). Molybdenite: MoS2 Habit:Disseminated - Occurs in small, Sharp metallic molybdenite crystal on matrix. distinct particles dispersed in matrix. Foliated. Massive Hardness: 1 -Talc Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Nonmagnetic Streak: greenish gray
Molybdenite (MoS2) is a lead-grey metallic mineral that characteristically occurs in thin, tabular, commonly hexagonal plates and also disseminated as fine specks. It has a specific gravity of 4.6 to 4.7, a hardness of 1 to 1.5, a greasy feel and it soils the fingers.
Superficially, it resembles graphite, for which it is commonly mistaken. However, molybdenite differs from graphite by bluish tinge.
233 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Molybdenite concentrate is converted to technical grade molybdic oxide.
Molybdic oxide is the major form of molybdenum used by industry and the base material for production of ferromolybdenum, chemicals and molybdenum metal powder.
WORLD RESOURCES
234 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
INDIAN OCCURENCE There is no known occurrence of primary molybdenite, which is presently being mined in India. The annual requirement of molybdenum is met by imports.
There is a meagre contribution to India’s requirement of molybdenum from Uranium Corporation of India (UCIL) which is producing molybdenite concentrate as a by-product of its uranium mill at Jaduguda, Bihar.
However, incidence of primary molybdenite is known from different parts of India Geological Setting and Resources The geological setting and mode of occurrence of the molybdenum mineralisations vary widely.
It occurs in granite plutons or their associated aplites, pegmatites or quartz veins as is known in the Ambalavayal granite in Kerala of Southern Granulite Terrain, younger granitoids of Bundelkhand and Baster cratons in parts of Madhya Pradesh and Chattisgarh respectively and in the Myliam granite in the Meghalaya craton.
Molybdenite is also known from the metasediments of the Delhi Super Group of Rajasthan and the Sausar Group of Maharashtra.
The molybdenite prospects of Dharmapuri district of Tamil Nadu are referable to the late phase hydrothermal activity related to the Alkaline Carbonatite intrusives in the rift valley setting.
The incidence is also known in the amphibolites of Kolar Schist belt in the Kudithinapalli area and in the adjoining gneiss in Andhra Pradesh.
In Rajasthan, molybdenite occurs as an associated mineral with copper in the Khetri Copper Belt while in Jharkhand it occurs in small quantities along with copper and uranium in the Singhbhum shear zone. In the Kolar Schist belt, it is associated with gold and galena. However, it may be generalised that molybdenite always occurs in association with other sulphides.
235 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
The controls of mineralisation also show considerable variation.
Shear zone forms the major control for the prospects in northern Tamil Nadu, Kudithinapalli in Andhra Pradesh and Singhbhum shear zone in Jharkhand.
The occurrence in Rajasthan is controlled by fold hinges.
The Contact of the meta sedimentary of the Sausar Group and the intrusive constitute the control in Maharashtra.
The occurrence in Meghalaya and Kerala are controlled by fracture systems in and around the granite plutons.
Molybdenite occurrences of Southern Granulite Terrain viz., Harur- Uttangarai,Alangayam-Rasimalai, Danishepet, Toppur, Pakkanadu, Kurichi (all these locations fall within Dharmapuri Suture Rift Zone (DSRZ) of Northern Tamil Nadu),
Ambalavayal (Northern Kerala, along Bhavali – Moyar Shear Belt), Karadikuttam - Palayam (Madurai Terrain of South Central Tamil Nadu) and Putteti (Nagarkoil Terrain of Southern Tamil Nadu)
The fracture filing/stock work type of molybdenite mineralisation occurs in alkali granite (595 ± 20 Ma) of Ambalavayal area, in the late pink syenite body east of Elagiri Complex (720 Ma) and in Pakkanadu Syenite Complex (610 Ma).
In Putteti area molybdenite is seen disseminated within the coarse grained syenite dykes which cut through the layered syenite intrusives (580 Ma).
The quartz vein type molybdenite mineralisation is exposed in different parts within the DSRZ. These quartz (± barite ± carbonates) veins of DSRZ are considered the end phase of the alkali – carbonatite magmatism (620 to 800 Ma) of northern Tamil Nadu.
In Karadikuttam area molybdenite mineralisation is seen in association with the pegmatite and aplite veins. In Palayam, molybdenite is observed at the contact zone between crystalline limestone and pegmatite.
As per the UNFC (as on 1.4.2000), the total resources of molybdenum ore in the country are estimated at about 16.29 million tones containing about 10,500 tonnes MoS2.
236 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
DIAMOND
The ancient Indians were the first in the world to take notice of the mineral diamond for its beauty and hardness. Diamond was discovered by the Indians in the eighth century B.C.
They used to collect diamonds from its secondary sources i.e., the quaternary gravel beds and gravelbars in the sediments.
Despite this ancient tradition, the primary sources of diamonds (kimberlite, lamproite, and other kimberlite clan rocks) have been found in India only after its Independence (except the Majhgawan pipe, Panna Madhya Pradesh ).
The diamondiferous Majhgawan pipe has operated as India's only significant primary diamond mine with a grade of about 10 carats per hundred tonnes.
237 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Diamond occurrences in India are quite widespread. Information on the ancient diamond mines and geology of the diamond bearing strata is available from the writings of the medieval period European travellers traders and Portuguese and British officials and geologists of the Geological Survey of India (GSI).
Systematic geological details are obtained from the investigations carried out for diamonds since, 1950's, mostly by the GSI, which were at peak in 1980s with implementation of National Diamond Project, aimed at assessing the diamond potentials of different known host rocks.
Subsequent works were oriented towards locating primary host rock for diamond and many kimberlite bodies in the already known areas and new kimberlite/lamproite fields in virgin areas were discovered
The known areas of occurrences of diamond source rocks are broadly grouped into three diamond provinces, namely the South Indian Diamond Province (SIDP), the Central Indian Diamond Province (CIDP) and the East Indian Diamond Province (EIDP).
Each of these Provinces extends approximately over an area of 100,000 sq. km and includes both primary (Kimberlites/Lamproites) and secondary source rocks (conglomerates and gravels) for diamond.
The SIDP is confined to the Dharwar Craton in the states of Andhra Pradesh, Karnataka and Maharastra, the CIDP to the Aravalli Craton in the states of Madhya Pradesh, Rajasthan and Uttar Pradesh and the EIDP to the Bastar and Singhbhum Cratons in the states of Maharastra,Chhattishgarh, Orissa, Jharkhand and Madhya Pradesh.
238 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Considering the Cratons and presence of diamonds and the source rocks, areas have been prognosticated for kimberlite search in India.They are:
(1) South Indian Diamond Province (SIDP) including East Dharwar Craton and adjoining Dharwar Mobile Belt; (2) West Dharwar Province; (3) East Bastar Craton including parts of Eastern Ghat Mobile Belt (EGMB); (4) West Bastar Craton; (5) Southern part of Bundelkhand – Aravalli Craton ; (6) North of Central Indian Suture (CIS); (7) Southern part of Singhbhum Craton including Singhbhum Mobile Belt; (8) Raigarh Mobile Belt; (9) Structural Corridor of Son – Narmada rift zone; (10) Structural Corridor of Tapti Lineament Zone; (11) Mahanadi Gondwana Graben and (12) Godavari Gondwana Graben.
The SIDP consists of both primary and secondary source rocks of diamond. The kimberlites localised within the Eastern block of the Dharwar Craton are grouped into three fields, namely Wajrakarur Kimberlite field, (WKF), Narayanpet kimberlite Field (NKF) and Raichur Kimberlite Field (RKF).
The major lamproite dykes occurring along the eastern margin of the Craton i.e. within the Nallamalai Fold Belt (NFB) and close to the north eastern margin of the Cuddapah basin are included in the Chelima Lamproite Field (CLF) and Jaggayyapeta Lamproite Field (JLF) respectively.
The CIDP also consists of primary and secondary source rocks. The NE- SW trending Panna Diamond belt with established ancient mining activity is located within this province.
This is the only belt where active mining for diamond is presently carried out in the country. The National Mineral Development Corporation Ltd is exploiting Majhgawan kimberlite/lamproite, the only diamond producing mine.A little amount of diamond is being recovered from placer occurrences.
Diamond has been the most priced among the gems since more than 2000years.The price of diamond depends upon its weight, quality, shape and flawlessness. Diamond has a high refractive index and strong dispersion which gives it that exciting brilliance when cut as facetted stone.
Gem diamonds are transparent and colourless or show faint shades of different colours. The transparent water clear diamonds are known as " of first water" or "blue white". When yellowish tinge is present, they are termed as off-colour stones. Diamonds with green, blue or red shades are rare but are most valuable gems.
239 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
PRODUCTION & STOCKS Production of diamond at 57,406 carats in 2000-2001 registered an increase of 40% over the previous year. There are two reporting mines both in public sector located in Panna district of Madhya Pradesh.
Of these, one mine, owned by National Mineral Development Corporation Ltd (NMDC) contributed as much as 99% to the total output of diamond and the remaining 1% was by the Department of Geology & Mining, Govt of Madhya Pradesh.
CHEMISTRY C Carbon CRYSTALLOGRAPHY Isometric (Cubic) CRYSTAL GROWTH AND HABITS Most crystals of Diamond are modified octahedrons but they are also found as dodecahedral, tetrahedral or cubic crystals. Diamond crystals are commonly flattened or elongated and are also found as crude spheres with a radial structure. COLOR AND OTHER OPTICAL PROPERTIES Diamonds are colorless, pale yellow to deep yellow, brown or bluish. Other colors of diamond are also known. Diamond is transparent to translucent and even opaque, depending on the amount of impurities (commonly graphite). HARDNESS 10 SPECIFIC GRAVITY 3.5 LUSTER Adamantine to greasy STREAK White Elongated, flattened crystal of BREAKABILITY Diamond has a very good octahedral cleavage (4 directions) and also has conchoidal fracture Diamond in a matrix of Kimberlite, and is brittle. from South Africa. OCCURRENCE Diamonds are formed in high temperature, high pressure environments as in igneous kimberlite pipes or dikes. Diamonds are also found as placer deposits. ASSOCIATED MINERALS Olivine, Phlogopite, Pyrope, Diopside, Ilmenite
240 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
Origin: South Africa Sample size: each approx. 1 cm on edge (17.4 carats total weight)
Mineral: Diamond: C Comme Photomicrographs (PPL) of numerous microdiamonds in Kumdy- nts: Kol caboniferous dolomite marble (Elements v1, no 2). Locatio Kokchetav Massif, Kumdy-Kol ultra high pressure facies area, n: northern Kazakhstan.
241 e-learning Material – Economic Geology Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
There are five varieties of kimberlite: 3. Kimberlite breccia with phlogopite. 1. Basaltic kimberlite with phlogopite. 4. Kimberlite breccia without phlogopite and 2. Basaltic kimberlite without phlogopite. 5. Kimberlite breccia with abundant phlogopite
KIMBERLITE PIPE IN AUSTRALIA
242 Materials used for construction (Building Stones & Cement)
The term 'construction minerals' is used to describe all minerals and rocks used by the construction industry, for example in road making, in house construction and as railway ballast. The largest component of construction minerals and the most voluminous materials extracted in India are 'aggregates' - a term used to describe granular or particulate material which is suitable for use, on its own or with a binder such as cement, lime or bitumen, in construction as concrete. The two principal types of aggregate are crushed rock (limestone, igneous rock and sandstone) and sand and gravel.
Dimension stone was for centuries the principal load-bearing material of buildings, bridges, harbour works and so on, a function now largely taken over by concrete and steel. The common building stones are granites and massive sandstones and limestones, which can be quarried in sizeable rectangular blocks free from internal fractures, without yielding an undue proportion of waste fragments. High compressive and shear strengths are required for load-bearing structures. A wider variety of porphyritic igneous rocks, marbles, tuffs, fossiliferous limestones and travertine are used as decorative stone for facings, pavings and interior walls. Slate, characterised by a closely spaced cleavage developed by crustal stresses, which facilitates the separation of thin layers, is a traditional roofing material. The bulk and weight of dimension stone required for major building works demand ease of transport from quarry to construction site.
The most durable building stones used both as aggregate and dimension stone are granites and similar plutonic rocks with massive texture, low porosity and stable minerals. Sandstones, especially those with calcareous cement, are subject to the effects of permeation by water, and limestones to solution and reaction on a larger scale. Despite these disadvantages, limestones have provided some of the most beautiful building materials.
Other minerals used in the construction industry are clay, chalk and limestone for cement making, brick clay, gypsum, and slate.
Table 1 - Non-metallic construction materials. Product Sources Desirable properties
dimension stone limestone, sandstone, granite, regular, widely spaced partings other igneous rocks. (bedding, joints), high compressive Ornamental stone includes strength, resistance to weathering, limestone, marble, tufa, granite, especially in industrial regions syenite etc. slate strongly cleaved fine-grained regular, closely spaced cleavage, metamorphic rocks, usually of resistance to weathering pelitic composition, locally pyroclastic roadstone crushed basalt, dolerite, fine resistance to abrasion (massive, fine to granite, greywacke, quartzite, medium grain Size), low porosity, e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
243 hornfels, flint etc., industrial binds well with bitumen, non-slip waste in combination with surface, does not acquire polish bitumen aggregate (for sand and gravel (fluvial, glacial, appropriate range of particle sizes, low concrete and as marine), crushed rock as for contents of impurities, especially fill for road and roadstone, industrial waste sulphides, organic matter, coal, building micaceous rocks, opal, chalcedony foundations, dams) bricks, tiles clay, marine, alluvial, glacial or no excess water, low iron, sulphides, in deep weathering zones: raw sulphates CaCo3>5% minimizes materials fired at high shrinkage, carbonaceous matter (≥S%) temperatures assists firing cement limestone, argillaceous constant composition, correct ratios limestone, often mixed with CaO, Al203, SiO2, Fe2O3, low S, MgO, clay: limestone converted to P, alkalies lime by calcining in kiln, product ground to powder glass quartz sand, quartzite absence of impurities, low iron plaster, gypsum, anhydrite from --- plasterboard evaporates insulating fibrous and flaky metamorphic not injurious to health materials minerals, asbestos, mica, vermiculite: diatomite bitumen residue from distillation of oil: Appropriate melting temperature for natural residues of oil seepages conditions of use e.g. in road making
Availability of Construction Material in India
In India, rocks are quarried largely for use as building stones. Not all rocks are, however, suitable for this purpose, since several indespensible qualities are required in a building-stone which are satisfied by but a few of the rocks from among the geological formations of a country. Rocks that can stand the ravages of time and weather, those that possess the requisite strength, an attractive colour and appearance, and those that can receive dressing whether ordinary or ornamental-without much cost or labour, are the most valuable. Resistance to weather is an important factor.
With this in view the architects of New Delhi, who required a most extensive range of materials for a variety of purposes, building as well as ornamental, invited the opinion of the Geological Survey of India in regard to the suitability of the various building and ornamental stones quarried in the neighbouring areas of Rajasthan and Central India. A special officer of the Survey was deputed to advise on the matter after an examination of the various quarries in the vicinity. e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
244 In northern India, the ready accessibility of brick-making materials in unlimited quantities has rendered the use of stone in private as well as public buildings subordinate. Excellent material exists in large quantities in a number of the rock- systems of the country.
Granites: Granites and coarsely foliated gneisses form very desirable and durable building- stones. These rocks, by reason of their massive nature and homogeneous grain, are suitable for monumental and architectural work as well as for massive masonries. Their wide range in appearance and colour - white, pink, red, grey, black, etc. - renders the stones highly ornamental and effective for a variety of decorative uses. The charnockites of Tamil Nadu, the Arcot gneiss, Bangalore gneiss, the porphyries of Seringapatam, and many other varieties of granite obtained from the various districts of the Peninsula are very attractive examples. Its durability is such that the numerous ancient temples and monuments of South India built of granite stand today almost intact after centuries of wear, and to all appearance are yet good for centuries to come. From their wide prevalence, forming nearly three-fourths of the surface of the Peninsula, the Archaean gneisses form an inexhaustible source of good material for building and omamental uses.
Limestones: Limestones occur in many formations, some of which are entirely composed of them. Not all of them, however, are fit for building purposes, though many of them are burnt for lime. In the Cuddapah, Bijawar, Khondalite and Aravalli Groups limestones attain considerable development; some of them are of great beauty and strength. They have been largely drawn upon in the construction of many of the noted monuments of the past in all parts of India. Vindhyan limestones are extensively quarried, as already referred to, in Madhya Pradesh, Rajasthan and elsewhere, and form a valued source for lime and cement, as well as for building stone. The Gondwanas are barren of calcareous rocks, but the small exposures of the Bagh and Trichinopoly Cretaceous include excellent limestones. The Nummulitic limestones of the extra-Peninsular districts, viz. Sind, Hazara, the Salt-Range, Punjab and Assam, are an enormous repository of pure limestone, and when accessible are in very large demand for burning, building, as well as road-making purposes.
Limestones suitable for the manufacture of both lime and cement occur in enormous quantities in the Vindhyan and older Formations. Cement grade limestone is quarried from Shahbad and Singhbhum districts of Bihar, Jabalpur (Katni and Jukheri areas) and Satna districts of Madhya Pradesh, Sundergarh district of Orissa, Narji limestone from the Guntur and Kurnool districts of Andhra Pradesh, Ambala and Mahendragarh districts of Punjab, Kangra district of Himachal Pradesh, and the Carboniferous e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
245 limestone from the Raisi tahsil of J & K. The Vindhyan limestone in the Son Valley of Uttar Pradesh is also used for the manufacture of cement.
In the plains of India, the only available source of line is ‘kankar’, which occurs plentifully as irregular concretionary disseminations in clays. The clay admixture in kankar is often in sufficient proportion to produce a hydraulic lime on burning.
Marbles: Coarse-grained marbles are more suitable for architectural and monumental uses; it is the coarseness of the grain, which is the cause of the great durability of marble against meteoric weathering. The fine-grained, purest white marbles are reserved for statuary use, for which no other varieties can be of service.
The marble deposits of India are fairly widespread and of large extent. The principal source of the marbles of India is the crystalline formation of Rajasthan -- the Aravalli series. Marble quarries are worked at Mekrana (Jodhpur), Kharwa (Ajmer), Maundla and Bhainslana (Jaipur), Dadikar (Alwar), and some other places, from which marbles of many varieties of colour and grain, including the beautiful white variety of which the Taj Mahal is built, are obtained. It was the accessibility of this store of material of unsurpassed beauty which, no doubt, gave such a stimulus to the Mogul taste for architecture in the seventeenth century.
Good quality marble also occurs in a large outcrop near Jabalpur, Jaisalmer in Rajasthan, Motipura in Baroda, Narsingpur in Madhya Pradesh, Kharwa in Ajmer. Some quarries in and around Jaipur furnish a dense black marble, capable of taking an exquisite polish, largely employed in the ancient buildings of Delhi, Agra and Kashmir.
Serpentine: Serpentine forms large outcrops in the Arakan range of Burma and also in Baluchistan. It occurs as an alteration-product of the basic and ultra-basic intrusions of Cretaceous and Miocene ages. From its softness and liability to weather on exposure it is of no use for outdoor architectural purposes, but serpentines of attractive colour are employed in internal decorations of buildings and the manufacture of vases, statuary, etc. Serpentinous marble (Verde antique) is rare in India.
Sandstones: Vindhyan sandstones - The Vindhyan and, to a lesser extent, the Gondwana formations afford sandstones admirably suited for building works. The most preeminent among them are the white, cream, buff and pink Upper Vindhyan sandstones, which have been put to a variety of uses. It is the most widely quarried stone in India, and being both a freestone as well as a flagstone it can yield, according to the portion selected, e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
246 both gigantic blocks for pillars from one part and thin, slate-like slabs for paving and roofing from another part. The superb edifices, modern and medieval, of Delhi, Rajasthan and Agra are built of red and white Vindhyan sandstone quarried from a number of sites in the vicinity.
Some of the Vindhyan sandstones are so homogeneous and soft that they are capable of receiving a most elaborate carving and filigree work. Centuries of exposure to the weather have tested their durability.
Upper Gondwana sandstones - Another formation possessing resources in building- stones of good quality is the Upper Gondwana, which has contributed a great store of building-stone to Orissa and Chanda. The famous temples of Puri and the other richly ornamented buildings of these districts are constructed of Upper Gondwana sandstones.
The Mesozoic (Umia) sandstone of Dhrangadhra and the Cretaceous sandstone underlying the Bagh beds of Gujarat (Songir sandstones) furnish Gujarat with a very beautiful and durable stone for its important public and private buildings.
Among the Tertiary sandstones, a few possess the qualities requisite in a building- stone, e.g. the Murree and Kamlial (Tarki) sandstones; but the younger Siwalik sandstones are too unconsolidated and incoherent to be fit for employment in building work.
Quartzites:
Quartzites are too hard to work and have a fracture and grain unsuitable for dressing into blocks.
Laterite:
Laterites of South India are put to use in building works, due to the ease with which they are cut into bricks or blocks when freshly quarried and their property of hardening with exposure to air. Its wide distribution from Assam to Comorin makes laterite a widely used material for road-metal. This stone is not capable of receiving dressing for any architectural or ornamental use.
Slates:
Slates for paving and roofing are not of common occurrence in India, except in some mountainous areas, e.g. at Kangra and Pir Panjal in the Himalayas and Rewari in the Aravallis. When the cleavage is finely developed and regular, thus enabling them to e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
247 be split into thin even plates, the slates are used for roofing; when the cleavage is not so fine, the slates are used for paving. True cleavage-slates are rare in India; what generally are called slates are either phyllites or compacted shales in which the planes of splitting are not cleavage-planes.
The chief slate-quarries of India are those of Kangra, in the Kangra district; Rewari, in the Gurgaon district; and Kharakpur hills in the Monghyr district.
Traps:
Besides the foregoing examples of the building-stones of India, a few other varieties are also employed as such when readily available and where a sufficient quantity exists. Of these the most important are the basalts of the Deccan, which, from their prevalence over a wide region of Western India, are used by the Railways and Public Works Department for their buildings, bridges, the permanent way, etc. The traps furnish an easily workable and durable stone of great strength, but its dull and subdued colour does not recommend it to popular favour. Recently, some trachytic and other acidic lavas of light buff and cream colours have found use in buildings.
Gypsum:
Gypsum forms large bedded masses or aggregates occurring in association with rocks of a number of different geological formations. Large deposits of pure gypsum occur in the Tertiary clays and shales of Rajasthan, Gujarat (Kutch) and Tamil Nadu (Madras), though in less pure state. In Jodhpur, Nagour and Bikaner, beds of gypsum are found among the silts of old lacustrine deposits and are of considerable economic interest. Millions of tons of gypsum, the alteration-product of pyritous limestone of Salkhala age, are laid bare in the mountains of the Uri and Baramula area of Kashmir in a stretch of about 40 km along the strike. In Spiti, Sirmur, Kumaon and other Himalayan areas, the gypsum occurs in large masses replacing Carboniferous or other limestones. In some cases gypsum occurs as transparent crystals (selenite) associated with clays.
Clays:
Ordinary alluvial clay, mixed with sand and containing a little proportion of iron is used for brick-making. Fine grained clay, nixed with fine sand, is used in tile making. Clays suitable for brick-making should have a fusion point around 950 to 1000oC so as to render strength to the fired brick. Such clays occur in considerable quantities in Uttar Pradesh, Bihar, Madhya Pradesh and West Bengal.
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
248
Minerals for the Ceramic Industry
The Principal mineral raw materials for the manufacture of ceramic products are the silica in different forms and the alumino-silicates. These minerals, in appropriate combinations, are fused at high temperatures to obtain the required product. While silica minerals include quartz and other forms like silica sand, the alumino-silicates comprise of the feldspars (orthoclase, microcline and albite) and clays. In addition, limestone and also minor amounts of a large number of other minerals find use to certain extent in ceramics. Feldspar and pegmatite, suitable for ceramic industry, should contain less than 9.5 per cent of Fe203; no less than 11 and 8 per cent of K2O + Na20 (in feldspar and pegmatite respecdvely); less than 1-2 per cent of CaO; and less than 10 and 30 percent of SiO2 in feldspar and pegmetite respectively.
Silica:
For ceramic products, the quartz should be of good quality. Iron staining and iron oxide minerals are considered as objectionable. The important geological sources for silica suitable for the ceramic industry are the pegmatites (with well developed crystals of quartz), vein quartz, sandstones of high siliceous nature, high silica sands and orthoquartzites.
In India, the major producing centres of silica are in the Sankargarh, Lohargarh and Bargarh regions (Uttar Pradesh), Bundi and Dausa in Jaipur and Adalpur in Sawai Madhopur (Rajasthan), Shimoga district (Karnataka), Burdwan district (West Bengal), Singbhum and Dhanbad districts (Bihar) and Guntur district (Andhra Pradesh). Extensive deposits of quartzite suitable for glass manufacture occur in Mayurbhunj district of Orissa. Some of the sandstones from Himmatnagar, Padharanali and Sankhera in Gujarat are suitable for the ceramic industry.
Beneficiation: The common impurities are clay, slime, iron stains and iron silicate minerals such as garnets. Feldspar and mica are objectionable. The raw material is ground in conventional manner and deslimed to remove the clayey fraction. If iron is present as surface coating, this can be removed either by scrubbing or by chemical treatment (like heating in a dilute solution of titanous sulphate with some hydrofluoric acid). Tabling can be adopted for the removal of clayey minerals and the heavy minerals like ilmenite and rutile.
The associated impurities such as mica and iron minerals can be removed by adopting flotation techniques. The process is carried out in acid circuits (with pH between 2 e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
249 and 3). Mica is floated by using a combination of fuel of oil and some amine acetate. Then the pulp is treated with one of the petroleum sulphonates and iron is removed in the subsequent stage of operation. In the final stage, feldspar is floated by using hydrofluoric acid and amine acetate.
Feldspars:
Feldspars are used as fluxing material in the preparation of ceramic bodies, enamels and glazes. Commonly potash feldspars (orthoclase and microcline) are used for this purpose and soda feldspar is chiefly used for glazing purposes. Feldspars for use in ceramic industry should contain a minimum of 65-72% SiO2 and not less than 4% Na2O.
Feldspar is one of the dominant ingredients in acid igneous rocks, particularly of granitic and pegmatitic nature. Pegmatites are often zoned into distinct bands of quartz and feldspar. In India, the pegmatites of the famous mica belts in Rajasthan, Bihar and Andhra Pradesh are the major sources ceramic grade feldspars. The other producing areas are in Salem and Tiruchirapalli districts of Tamil Nadu, Burdwan and Purulia districts of West Bengal and Hassan district of Karnataka. Indian feldspars are exported to the U.K., France, W. Germany, Italy and Japan.
Beneficiation: The common impurities to be eliminated are the iron-bearing minerals such as garnet and mica. The quarried material is broken and feldspar is removed easily by handpicking. The picked feldspar is reduced in size by crushing in conventional crushers and by subsequent grinding in pulverizers. For glazing purposes and for the manufacture of ceramic ware, iron contamination during size reduction is avoided by carrying out the grinding in pebble mills using flint pebbles as the grinding media. The flotation techniques, similar to silica beneficiation, are also adopted for feldspar concentration.
Clays:
Clays have been classified on the basis of their physical properties and the industrial usage. Of the various clays, ball and china clay are extensively used in ceramic industry. China clay and ball clay belong to the kaolin group. Although the primary constituent is kaolinite in both these clays, ball clay has greater plasticity and lesser refractoriness owing to the presence of montmorillonite in considerable amounts. It is normally added to china clay to achieve greater strength and the required plasticity. These clays are a product of weathering processes of feldspathic rocks. During weathering, the silica and iron oxides are partially leached with the residue (essentially of an aluminium silicate in composition) forming the in-situ deposits. Depending upon the efficiency of the weathering process, impurities like e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
250 grit (siliceous particles) and iron oxide minerals exist in different percentages in various clay deposits.
Ball Clay: Ball Clays with high plasticity ranges have been reported from Khajwana, Indawar, jodhpur and Sheo areas in Rajasthan, Rampurda, Vagedia, Bagagela and Thoangadh areas in Gujarat, Kundra in Kerala, parts of Chingleput district in Tamil Nadu and Dwarka-Tirumala in Andhra Pradesh.
China clay: Usage of china clay for ceramic industry depends on factors such as plasticity, shrinkage (after drying and on firing), colour on firing and refractori- ness. The grit content should normally be less than 1% and should never exceed 2%.
India has extensive deposits of china clays distributed in almost all the states. However, good deposits are in Bhagalpur, Ranchi, Singbhum and Monghyr districts in Bihar; Mayurbhunj district in Orissa; Bankura and Birbhum districts in West Bengal; Banda district in Uttar Pradesh; Barmer, Pali, Bikaner and Ajmer districts in Rajasthan; Chingleput, North and South Arcot and Salem districts in Tamil Nadu; Adilabad, Anantapur, Nellore and Guntur districts of Andhra Pradesh; Chanda and Ratnagiri districts in Maharashtra; Shimoga and Hassan districts in Karnataka; Sabarkantha district in Gujarat and Udhampur in Jammu and Kashmir.
Beneficiation: Major impurities in china clay are quartz, mica, felaspar and iron oxide minerals. Methods such as sieving, washing, elutriation and levigation may be employed. Normally the washing is done by 'levigation' process, which involves passing the clay slurry through a series of troughs or channels with different slopes. This process aids in the settling of grit and other heavy mineral and floating of light fractions like mica. Settling of finest quality clay takes place in the final tank. Decolourising of the clay is also attempted for certain clays, which are coloured due to the presence of iron and titanium oxides. However, no elaborate beneficiation techniques are employed in India and even the raw material that is marketed is not properly graded and specified. This has been creating special problems to industries, particularly to those of smaller sizes.
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
251
Minerals used in Refractories and Fillers Materials that retain their shape and chemical identity without marked expansion at high temperatures are required for lining kilns and furnaces and for many purposes in the electrical and chemical industries. These are classed as refractories and technical ceramics which require a range of specialized properties and are derived from both natural and synthetic sources. The more important natural sources are listed in the table below. Raw Material Source Product and Use Fireclay Fireclays are of sedimentary origin Refractory bricks for and occur as horizons below the domestic fireplaces, coal seams furnaces Quartz sandstone, Pegmatites, sands and quartzites Silica bricks for furnaces quartzite Dolomite rock Basic refractories stable Magnesite in the presence of slags, Serpentine, olivine for iron and steel rock & Chromite furnaces. Mullite Sparking plugs, other electrical equipment Alumina Kyanite and Sillimanite Technical ceramics Talc, steatite Insulators in radio industry Graphite Crucibles used for steel manufacture
Fillers are used to add bulk or weight to paper, rubber, paints and other synthetic products. They are derived mainly from inert clay minerals and from barite (BaSO4). They are also used as a component of oilfield drilling muds. Barite is a common gangue mineral in hydrothermal and exhalative sulfide deposits and it occasionally forms larger concentrations.
Fire-clay: Fireclays are of sedimentary origin and occur as horizons below the coal seams. In India fire clays from Raniganj and Jharia coalfields are very important. The fireclays e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
252 from Raniganj are excellent in quality. The super-refractories are manufactured by blending them with certain proportions of bauxite from Lohardaga. In general, the fireclays from both these coal fields occur within Barakars. Important deposits are around Kumardhubi, Mugma, Garphalbari-Dahibari region, Damagpria, Radhabhallabhpur, Pohargora Garb Dhamo, Churulia and Pathardi. The Rajhara and Daltonganj coalfields are also important suppliers of plastic fireclay. In Orissa, workable deposits of fireclay occur in Sambalpur, Cuttack, Sunde garh, Puri and Dhenkanal districts. Fireclays from Belpahar are extensively used in steel plants. In Madhya Pradesh, highly plastic and refractory clays are reported injabalpur, Betul, Bilaspur, Drug, Hoshangabad and Satna districts. In Karnataka, good occurrences are reported in Shimoga, Bangalore and Kolar districts. Good refractory fireclays also occur in Nizamabad, Asifabad, East Godavari and Cuddapah districts (Andhra Pradesh) and North and South Arcot districts (Tamil Nadu). In Rajasthan, the fireclays are distributed in jaisalmer, Sawai Madhopur and Bikaner areas.
Quartz, Sandstone & Quartzite: The main sources of silica are the sands and quartzites. Important occurrences in India are as follows: Bihar: Between Rakha Mines and Kendadih (Singbhum district), Rajagoan Hills (Gaya district), Ratanpur (Monghyr district) and Bihar Shariff (Patna district). Orissa: Khajuria-Pravasoni (Bamra district), jhargati and Garpati (Sambalpur district). Karnataka: Dodguni area (Tumkur district). Sands from Jabalpur (Madhya Pradesh) are also often used as refractory lining for the furnaces. In recent years good sands have been obtained from the crushing of pure quartzose Vindhyan sandstones at several localities in Uttar Pradesh, from Gondwana (Damuda) sandstone of the Raj Mahal hills, and from Cretaceous sandstones and Archaean and other pure quartzites of some parts of Tamil Nadu and Maharashtra. For silica brick manufacture, the raw material should contain at least 96 to 98% SiO2. While magnesia and alkalies are objectionable, iron oxide in limited quantities helps in acting as a binder. Firing is done around 1,480oC in periodic kilns with 2% lime as binding material. The silica bricks have spalling with temperature fluctuations but strength is retained below the temperature of their fusion because of high thermal conductivity.
Dolomite:
For refractory usage, dolomite should have an equimolecular proportion of CaCO3, and MgCO3. It must be low in SiO2, Fe2O3 and Al2O3 (together less than 3%). For calcined dolomite, the specifications are very rigid and SiO2 and Al2O3 should not
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
253 exceed 1% each. Calcined dolomite is distinctly preferred over the raw dolomite for maintaining the open-hearth steel furnaces. Dolomite and dolomitic limestone are used extensively for the steel furnaces owing to the low cost and easy availability in contrast to magnesite. Workable deposits of dolomite used in refractories are reported in Orissa around Birmitrapur and Purnapani areas of Sundergarh district. These are generally high in silica and are used in furnace operations at TISCO, Rourkela and Durgapur. The dolomite occurs in a band of 300 metres width over a length of 7,000 metres and depth up to 50 metres. The estimated reserves are 252 million tonnes. In Madhya Pradesh, the marbles of Narmadaghat (Jabalpur district) are dolomitic. Dolomite from Bilaspur and Satna districts is used in open-hearth furnaces of Rourkela and Bhilai steel plants. In Karnataka, refractory grade dolomite is worked around Sankargudda in Shimoga district and is the principal source of refractories for use in the steel plant at Bhadravati. The total reserves of blast furnace and steel melting shop grades of dolomite in India are estimated at 720 and 428 million tonnes respectively. The dolomite bricks are made on conversion to di-calcium or tri-calcium silicates. In the case of di-calcium silicate, the dusting encountered during cooling can be avoided by adding minor amounts of Fe2O3 within limits. The tri-calcium silicate is obtained by adding 15% serpentine to powdered dolomite and calcining the mixture at 1,600oC in a rotary kiln.
Magnesite: Large deposits of magnesite (MgCO3) occur in the district of Salem as veins associated with other magnesian rocks such as dolomite, serpentines, etc. The magnesite is believed to be an alteration-product of the dunites (peridotite) and other basic magnesian rocks of Salem. When freshly broken it is of a dazzling white colour and hence the magnesite-veins traversing the country have been named the Chalk hills of Salem. The magnesite of Salem is of a high degree of purity (MgO 46.4 %), is easily obtained and, when calcined at a high temperature, yields a material of great refractoriness. Other places in India also contain magnesite-veins traversing basic rocks, viz. Coorg, Coimbatore, Mysore, Almora and parts of Eastern Himalayas.
Serpentine, Olivine Rock and Chromite: Dunites (rocks rich in olivine) occur as a product of magmatic differentiation in the form of layered masses and veins associated with ultra-basic, intrusive rocks, like chromites, peridotites, serpentines, etc. Serpentinites (rocks rich in serpentine) occur as products of weathering and alteration of olivine rich rocks. These occur in Karnataka, in several districts of Orissa (chiefly Keonjbar), and in Singhbhum. The e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
254 Orissa reserves are the largest computed at over 3.5 million tons. Less important deposits have been found in parts of Tamil Nadu and in Ratnagiri in Maharashtra. Some chromite occurs in the " Chalk hills " (magnesite-veins) near Salem, but it is not worked. Large deposits of chromite occurring in dunite intrusions forming mountain-masses have been discovered in the Cretaceous volcanics of Burzil and Dras valley of Ladakh, Kashmir.
Kyanite and Sillimanite: Kyanite and sillimanite are similar in chemical composition (Al2O3) . However, they differ in their crystal structure and physical behaviour. They occur in metamorphic altiminous rocks. India has the richest deposits of kyanite and sillimanite in the world.
Kyanite In India, the chief occurrence of kyanite is the Lapsa Buru deposit (in Kharswan, Bihar). This is the largest deposit of kyanite in the world. Kyanite, in massive acicular, coarse and fine-grained forms, occurs in association with quartz rocks within a zone of 100 kms. length and the reserves are estimated to be around 0.7 million tonnes. Large deposits of kyanite are also mined in Bhandara district of Maharashtra. The total reserves are estimated at 143 min. tonnes from all sources.
Sillimanite The most important occurrence of sillimanite is in the Khasi Hills (Assam) in Nongstoin area (around the villages of Sonapahar, Nongpur and Nangbain) in Meghalaya. The host rocks are cordierite-biotite-quartz-muscovite-gueiss or a sillimanite-quartz-schist with intrusions of granite. Sillimanite occurs as massive sillimanite boulders. Reserves are estimated around 255,000 tonnes of sillimanite up to 7 metres depth. Besides the Assam sillimanite, the only other important occurrence is around Pipra (Madhya Pradesh) popularly known as Rewa sillimanite. The reserves are estimated around 110,000 tonnes up to 10 metres depth. The only disadvantage of Rewa sillimanite is that it is slightly sensitive to thermal shocks. Indian sillimanite can be used as a refractory without calcination since it exhibits very little expansion. Sillimanite bricks, in general, have a low running cost, smaller load on furnace-supporting structure and a longer life.
Talc and Steatite: e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
255 Talc and steatite occur widely in India, forming large masses in the Archaean and Dharwar rocks of the Peninsula. Workable deposits occur in Bihar, Jabalpur, Salem, Idar and Jaipur. The Rajasthan, the deposits occur as thick lenticular beds of wide extent in the schists. Some of these beds persist for miles. At most of these places steatite is quarried in considerable quantities for commercial purposes. In its geological relations, steatite is often associated with dolomite (as in Jabalpur) and other magnesian rocks, and it is probable that it is derived from these rocks by metamorphic processes resulting in the conversion of the magnesium carbonate into the hydrated silicate. In other cases it is the final product of the alteration of ultra- basic and basic eruptive rocks.
Graphite: Graphite deposits in India are associated with metamorphic rocks. in Orissa, the deposits are in Sambaipur district (in Nawapara, Sargipalli and Bargarh regions). Bolangir district (in Titlagarh, Bolangirpatna and Laha regions), Dhenkanal district (Dandatapa, ]3amur and Athmallik regions), Koraput district (Marijkelam, Arugali and Karriguda areas), Phulbani district (Tumdibandh region) and also in Kalahandi district. These deposits occur in the form of veins, lenses and pockets in the khondalite series of rocks. The khondalites are paraschists which include garnetiferous-quartz-sillimanite rocks, garnetiferous qartzites, calciphyres and graphite schists. These are typically developed in Eastern Ghats and often contain local concentrations of graphite veins of varying thickness and extent. Two varieties (the flaky and amorphous) of graphite are reported. The graphite from Orissa has a fixed carbon content between 55 and 60%. In Andhra Pradesh, the well known deposits are, around Peddanakonda in Bhadrachalam taluk, occurring in khondalite series. The crude material contains 40-65% fixed carbon which is processed to yield flaky graphite of 92% carbon. The graphite deposits of Bihar are distributed around Sokra, Khandih and Rajhara. These occur in schists, gneisses and limestones and the fixed carbon content is around 50%. In Karnataka, graphite of fine grained amorphous variety is in Kolar schist belt in Bangarpet taluk and the flaky variety is near Mavinhalli and Tonvalli (Mysore district) in crystalline schists. Bond clay, sand and kaolin, besides grog, are used with graphite for crucibles. Graphite crucibles used for steel are approximately of 50% graphite, 30% bond clay, 10% sand and 10% kaolin while those used for brass have 45% graphite, 35% bond clay, 10% grog and 10% kaolin. The graphite for crucibles should contain 80% fixed carbon. Mica, carbonates and sulphur (in the form of pyrite) are the undesirable impurities. While mica fuses causing holes in the crucibles, carbonates and pryite dissociate resulting in volume changes. Graphite is also used as a foundry facing material. e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
256 Barite: Barytes occurs in sufficient quantities at many places in India in the form of veins and as beds in shales. The chief localities for barytes are Cuddapah and Kurnool districts; Alwar; Salem; and Sleemanabad (in the Jabalpur district). Barytes is used as a pig- ment for mixing with white lead, as a flux in the smelting of iron and manganese, in paper-manufacture, in pottery-glazes, etc. The whiter and better-quality barytes is used in the local manufacture of paints (lithophone); the coloured variety is used in making heavy drilling mud by the oil companies. Minerals used in Refractories and Fillers Materials that retain their shape and chemical identity without marked expansion at high temperatures are required for lining kilns and furnaces and for many purposes in the electrical and chemical industries. These are classed as refractories and technical ceramics which require a range of specialized properties and are derived from both natural and synthetic sources. The more important natural sources are listed in the table below. Raw Material Source Product and Use Fireclay Fireclays are of sedimentary origin Refractory bricks for and occur as horizons below the domestic fireplaces, coal seams furnaces Quartz sandstone, Pegmatites, sands and quartzites Silica bricks for furnaces quartzite Dolomite rock Basic refractories stable Magnesite in the presence of slags, Serpentine, olivine for iron and steel rock & Chromite furnaces. Mullite Sparking plugs, other electrical equipment Alumina Kyanite and Sillimanite Technical ceramics Talc, steatite Insulators in radio industry Graphite Crucibles used for steel manufacture
Fillers are used to add bulk or weight to paper, rubber, paints and other synthetic products. They are derived mainly from inert clay minerals and from barite (BaSO4). They are also used as a component of oilfield drilling muds. Barite is a e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
257 common gangue mineral in hydrothermal and exhalative sulfide deposits and it occasionally forms larger concentrations.
Fire-clay: Fireclays are of sedimentary origin and occur as horizons below the coal seams. In India fire clays from Raniganj and Jharia coalfields are very important. The fireclays from Raniganj are excellent in quality. The super-refractories are manufactured by blending them with certain proportions of bauxite from Lohardaga. In general, the fireclays from both these coal fields occur within Barakars. Important deposits are around Kumardhubi, Mugma, Garphalbari-Dahibari region, Damagpria, Radhabhallabhpur, Pohargora Garb Dhamo, Churulia and Pathardi. The Rajhara and Daltonganj coalfields are also important suppliers of plastic fireclay. In Orissa, workable deposits of fireclay occur in Sambalpur, Cuttack, Sunde garh, Puri and Dhenkanal districts. Fireclays from Belpahar are extensively used in steel plants. In Madhya Pradesh, highly plastic and refractory clays are reported injabalpur, Betul, Bilaspur, Drug, Hoshangabad and Satna districts. In Karnataka, good occurrences are reported in Shimoga, Bangalore and Kolar districts. Good refractory fireclays also occur in Nizamabad, Asifabad, East Godavari and Cuddapah districts (Andhra Pradesh) and North and South Arcot districts (Tamil Nadu). In Rajasthan, the fireclays are distributed in jaisalmer, Sawai Madhopur and Bikaner areas.
Quartz, Sandstone & Quartzite: The main sources of silica are the sands and quartzites. Important occurrences in India are as follows: Bihar: Between Rakha Mines and Kendadih (Singbhum district), Rajagoan Hills (Gaya district), Ratanpur (Monghyr district) and Bihar Shariff (Patna district). Orissa: Khajuria-Pravasoni (Bamra district), jhargati and Garpati (Sambalpur district). Karnataka: Dodguni area (Tumkur district). Sands from Jabalpur (Madhya Pradesh) are also often used as refractory lining for the furnaces. In recent years good sands have been obtained from the crushing of pure quartzose Vindhyan sandstones at several localities in Uttar Pradesh, from Gondwana (Damuda) sandstone of the Raj Mahal hills, and from Cretaceous sandstones and Archaean and other pure quartzites of some parts of Tamil Nadu and Maharashtra. For silica brick manufacture, the raw material should contain at least 96 to 98% SiO2. While magnesia and alkalies are objectionable, iron oxide in limited quantities helps in
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
258 acting as a binder. Firing is done around 1,480oC in periodic kilns with 2% lime as binding material. The silica bricks have spalling with temperature fluctuations but strength is retained below the temperature of their fusion because of high thermal conductivity.
Dolomite:
For refractory usage, dolomite should have an equimolecular proportion of CaCO3, and MgCO3. It must be low in SiO2, Fe2O3 and Al2O3 (together less than 3%). For calcined dolomite, the specifications are very rigid and SiO2 and Al2O3 should not exceed 1% each. Calcined dolomite is distinctly preferred over the raw dolomite for maintaining the open-hearth steel furnaces. Dolomite and dolomitic limestone are used extensively for the steel furnaces owing to the low cost and easy availability in contrast to magnesite. Workable deposits of dolomite used in refractories are reported in Orissa around Birmitrapur and Purnapani areas of Sundergarh district. These are generally high in silica and are used in furnace operations at TISCO, Rourkela and Durgapur. The dolomite occurs in a band of 300 metres width over a length of 7,000 metres and depth up to 50 metres. The estimated reserves are 252 million tonnes. In Madhya Pradesh, the marbles of Narmadaghat (Jabalpur district) are dolomitic. Dolomite from Bilaspur and Satna districts is used in open-hearth furnaces of Rourkela and Bhilai steel plants. In Karnataka, refractory grade dolomite is worked around Sankargudda in Shimoga district and is the principal source of refractories for use in the steel plant at Bhadravati. The total reserves of blast furnace and steel melting shop grades of dolomite in India are estimated at 720 and 428 million tonnes respectively. The dolomite bricks are made on conversion to di-calcium or tri-calcium silicates. In the case of di-calcium silicate, the dusting encountered during cooling can be avoided by adding minor amounts of Fe2O3 within limits. The tri-calcium silicate is obtained by adding 15% serpentine to powdered dolomite and calcining the mixture at 1,600oC in a rotary kiln.
Magnesite: Large deposits of magnesite (MgCO3) occur in the district of Salem as veins associated with other magnesian rocks such as dolomite, serpentines, etc. The magnesite is believed to be an alteration-product of the dunites (peridotite) and other basic magnesian rocks of Salem. When freshly broken it is of a dazzling white colour and hence the magnesite-veins traversing the country have been named the Chalk hills e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
259 of Salem. The magnesite of Salem is of a high degree of purity (MgO 46.4 %), is easily obtained and, when calcined at a high temperature, yields a material of great refractoriness. Other places in India also contain magnesite-veins traversing basic rocks, viz. Coorg, Coimbatore, Mysore, Almora and parts of Eastern Himalayas.
Serpentine, Olivine Rock and Chromite: Dunites (rocks rich in olivine) occur as a product of magmatic differentiation in the form of layered masses and veins associated with ultra-basic, intrusive rocks, like chromites, peridotites, serpentines, etc. Serpentinites (rocks rich in serpentine) occur as products of weathering and alteration of olivine rich rocks. These occur in Karnataka, in several districts of Orissa (chiefly Keonjbar), and in Singhbhum. The Orissa reserves are the largest computed at over 3.5 million tons. Less important deposits have been found in parts of Tamil Nadu and in Ratnagiri in Maharashtra. Some chromite occurs in the " Chalk hills " (magnesite-veins) near Salem, but it is not worked. Large deposits of chromite occurring in dunite intrusions forming mountain-masses have been discovered in the Cretaceous volcanics of Burzil and Dras valley of Ladakh, Kashmir.
Kyanite and Sillimanite: Kyanite and sillimanite are similar in chemical composition (Al2O3) . However, they differ in their crystal structure and physical behaviour. They occur in metamorphic altiminous rocks. India has the richest deposits of kyanite and sillimanite in the world.
Kyanite In India, the chief occurrence of kyanite is the Lapsa Buru deposit (in Kharswan, Bihar). This is the largest deposit of kyanite in the world. Kyanite, in massive acicular, coarse and fine-grained forms, occurs in association with quartz rocks within a zone of 100 kms. length and the reserves are estimated to be around 0.7 million tonnes. Large deposits of kyanite are also mined in Bhandara district of Maharashtra. The total reserves are estimated at 143 min. tonnes from all sources.
Sillimanite The most important occurrence of sillimanite is in the Khasi Hills (Assam) in Nongstoin area (around the villages of Sonapahar, Nongpur and Nangbain) in e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
260 Meghalaya. The host rocks are cordierite-biotite-quartz-muscovite-gueiss or a sillimanite-quartz-schist with intrusions of granite. Sillimanite occurs as massive sillimanite boulders. Reserves are estimated around 255,000 tonnes of sillimanite up to 7 metres depth. Besides the Assam sillimanite, the only other important occurrence is around Pipra (Madhya Pradesh) popularly known as Rewa sillimanite. The reserves are estimated around 110,000 tonnes up to 10 metres depth. The only disadvantage of Rewa sillimanite is that it is slightly sensitive to thermal shocks. Indian sillimanite can be used as a refractory without calcination since it exhibits very little expansion. Sillimanite bricks, in general, have a low running cost, smaller load on furnace-supporting structure and a longer life.
Talc and Steatite: Talc and steatite occur widely in India, forming large masses in the Archaean and Dharwar rocks of the Peninsula. Workable deposits occur in Bihar, Jabalpur, Salem, Idar and Jaipur. The Rajasthan, the deposits occur as thick lenticular beds of wide extent in the schists. Some of these beds persist for miles. At most of these places steatite is quarried in considerable quantities for commercial purposes. In its geological relations, steatite is often associated with dolomite (as in Jabalpur) and other magnesian rocks, and it is probable that it is derived from these rocks by metamorphic processes resulting in the conversion of the magnesium carbonate into the hydrated silicate. In other cases it is the final product of the alteration of ultra- basic and basic eruptive rocks.
Graphite: Graphite deposits in India are associated with metamorphic rocks. in Orissa, the deposits are in Sambaipur district (in Nawapara, Sargipalli and Bargarh regions). Bolangir district (in Titlagarh, Bolangirpatna and Laha regions), Dhenkanal district (Dandatapa, ]3amur and Athmallik regions), Koraput district (Marijkelam, Arugali and Karriguda areas), Phulbani district (Tumdibandh region) and also in Kalahandi district. These deposits occur in the form of veins, lenses and pockets in the khondalite series of rocks. The khondalites are paraschists which include garnetiferous-quartz-sillimanite rocks, garnetiferous qartzites, calciphyres and graphite schists. These are typically developed in Eastern Ghats and often contain local concentrations of graphite veins of varying thickness and extent. Two varieties (the flaky and amorphous) of graphite are reported. The graphite from Orissa has a fixed carbon content between 55 and 60%. In Andhra Pradesh, the well known deposits are, around Peddanakonda in Bhadrachalam taluk, occurring in khondalite series. The crude material contains 40-65% fixed carbon which is processed to yield flaky graphite of 92% carbon. e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
261 The graphite deposits of Bihar are distributed around Sokra, Khandih and Rajhara. These occur in schists, gneisses and limestones and the fixed carbon content is around 50%. In Karnataka, graphite of fine grained amorphous variety is in Kolar schist belt in Bangarpet taluk and the flaky variety is near Mavinhalli and Tonvalli (Mysore district) in crystalline schists. Bond clay, sand and kaolin, besides grog, are used with graphite for crucibles. Graphite crucibles used for steel are approximately of 50% graphite, 30% bond clay, 10% sand and 10% kaolin while those used for brass have 45% graphite, 35% bond clay, 10% grog and 10% kaolin. The graphite for crucibles should contain 80% fixed carbon. Mica, carbonates and sulphur (in the form of pyrite) are the undesirable impurities. While mica fuses causing holes in the crucibles, carbonates and pryite dissociate resulting in volume changes. Graphite is also used as a foundry facing material.
Barite: Barytes occurs in sufficient quantities at many places in India in the form of veins and as beds in shales. The chief localities for barytes are Cuddapah and Kurnool districts; Alwar; Salem; and Sleemanabad (in the Jabalpur district). Barytes is used as a pig- ment for mixing with white lead, as a flux in the smelting of iron and manganese, in paper-manufacture, in pottery-glazes, etc. The whiter and better-quality barytes is used in the local manufacture of paints (lithophone); the coloured variety is used in making heavy drilling mud by the oil companies.
Minerals used in Organic chemicals and Synthetics Until little more than fifty years ago, all but a minute proportion of the oil, gas and coal extracted from the Earth was used as a fuel. Today, a substantial fraction of world production (mostly of hydrocarbons) goes to provide feedstock for the production of organic synthetics (see list below). The petrochemical industry produces relatively cheap alternatives to many natural organic and inorganic materials. The technology involved in the manufacture of these substances is complex and only the principal processes employed are mentioned here. The lower unsaturated olefins such as ethylene, C2H4, provide the starting points from which many synthetic molecules are made. These olefins are obtained largely from the paraffins in crude oil by high-temperature cracking procedures which rupture long carbon chains and remove excess hydrogen; they can be subsequently combined e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
262 with molecules containing oxygen or chlorine in addition to carbon and hydrogen. Once formed, these varied compounds provide building blocks for the synthesis of high polymers in which thousands or tens of thousands of atoms are linked. Polymerisation gives analogues of molecules in wood, silk, cotton, rubber and other natural substances for which the synthetic materials can substitute. A selective list of products is given in the table below:
Derivatives of hydrocarbons and coal (other than fuels).
Refinery products Extracted from crude oils and their derivatives:
lubricating oils bitumens waxes (used mainly for waterproofing) detergents (refinery products mixed with other chemicals)
Breakdown products ammonia and ammonium salts made from hydrogen in combination with atmospheric nitrogen, starting point for synthesis of nitrogenous fertilisers carbon made by high-temperature dissociation, used to strengthen synthetic rubberand forcarbon fibre
Polymers of hydrocarbon derivatives plastics, e.g. polyethylene, PVC, polystyrene silicones synthetic fibres, e.g. nylon, terylene, acrylic fibre dyes and paints pharmaceuticals insecticides aerosol propellants explosives
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
263
Minerals used in the Fertilizer Industry During the last four decades, with the emphasis on agricultural production in India, increased attention was given to the manufacture of chemical fertilizers. The fertilizer plants use the raw materials both from natural sources and from the chemical materials. Gypsum, pyrite and rock phosphates form the principal mineral sources. While the first two find extensive use in the manufacture of sulfate fertilizers, the rock phosphates are mainly utilized in the production of phosphate fertilizer.
Source of various constituents in Fertilizers Principal nutrient Source organic fertilizers including animal manure, plant waste, seaweed, fishmeal, dried blood etc, give exchangable nitrogen nitrogen fixing bacteria in soil or in symbiotic relationship with Nitrogen (N) legumes nitrates, non-marine evaporates of Chile ammonia and its derivatives from petrochemical plants organic fertilisers, especially manure Potash (K) bittern salts of marine evaporites shells and bone Lime (Ca) carbonate rocks including limestone, tufa, calcrete bone meal, manure guano (consolidated droppings of sea birds, from oceanic islands, Phosphates (P) now largely worked out) superphosphate derived from phosphorite basic slag byproduct of steel production salt domes (reduction of gypsum) Sulfur (S) iron sulphides
GYPSUM DEPOSITS
Gypsum is a hydrated calcium sulfate (CaSO4.2H20 ) and its anhydrous form
(CaSO4) is known as anhydrite. Deposits of gypsum are either of sedimentary origin (bedded type) or of marine evaporate nature. Gypsum finds extensive use in the cement, paper, textile and paint industries. The mineral, calcined around 200oC e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
264 loses 75% of its water and the product, known by its trade name as 'plaster of paris', is widely used in building industry as a good finishing material. It can be moulded into any shape with the addition of water and sets to a hard mass.
In India, gypsum is produced in Rajasthan. Tamil Nadu, Uttar Pradesh, Gujarat and Maharashtra. Of these, the first three are the important producers with Rajasthan possessing around 95% of the total Indian reserves (estimated to be around 1,000 m tonnes). The deposits in Rajasthan are situated mainly in Bikaner, jodhpur, Nagaur and jaisalmer districts. The Rajasthan occurrences are associated with the Vindhyan limestones.
In Tamil Nadu the deposits are situated in Tiruchirapalli, Coimbatore and Ramanathapuram districts and are associated with the shales in Cretaceous sequence. The gypsum from these sources is chiefly utilized in the cement and pottery industry. In Uttar Pradesh, deposits are reported in Dehradun, Garhwal and Nanital districts. The Majhara deposit in Dehradun district and Lakshmanjhula in Garhwal district are exploited at present.
For use in fertilizer industry, gypsum with a minimum of 87% CaSO4.2H2O is preferred. The Sindri fertilizer plant gets its main supply from the Bikaner deposits.
PYRITE DEPOSITS
Sulfur and pyrite (FeS2) are the principal raw materials in the manufacture of sulfuric acid which forms the back-bone of many modern industries such as fertilizers, chemicals, paints and textiles. Pyrite is either mined as a principal mineral or is recovered from the sulfide assemblages of copper, lead-zinc, gold and other metallic ore deposits.
In India, pyrite deposits occur in Bihar, Karnataka, Rajasthan and Tamil Nadu. However, the largest deposits are from Amjhore region in Shahabad district of Bihar where pyrite occurs as a uniform bed of about one metre thickness in the Bijaigarh black shales of Kaimur series (Vindhyan system). The deposit (located at nine places within the Amjhore region) has a remarkable conformity with the overlying and underlying Vindhyan formations and is confined to a single e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
265 stratigraphic horizon. Two types of pyrite occurrences have been reported: the massive cryptocrystalline variety, which forms the bulk of the deposit and the fine pyrite grains, disseminated within the black shale. About 390 million tonnes of pyrite (with 48% S) are estimated to be available within an area of 120 sq. km in Amjhore region.
In Karnataka, pyrite deposits occur around Ingaldahl in Chitaldrug district. The mineralization is localized in the ferruginous chert bands interbanded with Dharwarian greenstones in the eastern flank of an anticlinal structure. It may be noted that copper mineralization in this region is on the western flank of this structure. The Ingaldahl pyrite reserves are estimated to be around 2.0 million. tonnes (of 20-30% S). The deposits in Rajasthan occur at Saladipura and the inferred reserves are of the order of85 million tonnes (with 22% S). In Tamil Nadu, the deposits are located around Polur in the Thaniyar reserve forest.
Besides the above occurrences, pyrite is also associated with gold, copper, lead and zinc deposits as also in Tertiary coals. In the metallic ores, after the recovery of primary minerals the tailings containing pyrite are discarded in India. Plans are underway to recover and utilize pyrite from such tailings, Sizeable deposits of sulphur have been reported from Puga valley in Ladakh.
In India, the requirements of sulphur are of the order of 3,00,000 tonnes per year. At present the mining activity is at Amjhore by the state-owned Pyrites, Phophates and Chemicals Ltd. A sulphuric acid plant of 400 tonnes per day capacity has been set up at Sindri in Bihar.
ROCK PHOSPHATE DEPOSTS
Phosphate deposits of sedimentary origin and of economic importance are known as phosphorites or rock phosphates. The formation of these is restricted to marine environments and is a result of deposition under specific pH conditions from the phosphorus-bearing solutions derived from the weathering of phosphate minerals like apatite of igneous source. It is thought that redox potential does not play any role in their formation. In all the phosphate minerals, phosphorus exists in its highest valent state, e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
266 In India, with the development of superphosphate fertilizer industry, the exploration for rock phosphate deposits has been accelerated. Deposits of economic significance are reported from Rajasthan and Uttar Pradesh. In Rajasthan, they are located in Udaipur and jaisalmer districts. The Udaipur deposits occur around Jhamar Kotra area, Kanpur region (Kanpur, Karbaria Ka Gurha and Maton blocks) and Dakan Kotra area. The phosphorites are confined to limestone or cherty quartzite and are in the form of lenticular masses of variable thickness with the P2O5 content between 15 and 25%. However, the published analyses for Maton deposits indicate P2O5 as high as 36%. The Jaisalmer deposits are mainly located in the Fatehgarh area where the phosphorite horizon was associated with the Mesozoic sandstones. The
P2O5 content varies from 5 to 15%. Two types of mineral associations are reported from Rajasthan deposits: pellets of collaphane and black chert in calcareous shaly sandstones and the banded phosphorites (of alternate collophane with quartz on calcite bands) with limestone bands. The basic characteristic feature of these phosphorites is their association with limestones, which distinguishes the same from those of Uttar Pradesh. Around 80 million tonnes are estimated to be available in Rajasthan.
In Uttar Pradesh, the deposits occur mainly at Mussoorie and Meldeota, although in all about 10 deposits are located. The phosphate-bearing zones, thickness varying from a few centimetres to about 15 metres at places, are mainly restricted to chert and carbonaceous shale formations of Lower Tals or at the contact of the underlying argillaceous limestones of Upper Krols. Three varieties of phosphorite -- granular, pelletal and nodular -- have been reported. The P2O5content of these deposits varies between 15 and 35%. The deposits from Uttar Pradesh contain the collophane species of phosphates together with quartz, calcite, chert, muscovite and clay minerals. The development of the Mussoorie deposits is beset with several difficulties such as their complex mineralogy, lack of precise estimates as regards the quantity and quality of ore available, remoteness of the deposits and the need for underground mining. In India, the major share of the requirements for rock phosphates is met from the imports of the order of 5,75,000 tonnes per year while the production is around 6,44,000 tonnes. A beneficiation plant is being set up at Matas near Udaipur by Hindustan Zinc Limited to upgrade the phosphorite from 25% e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
267 P2O5 to >32% P2O5 with consequent reduction of silica. It is planned to send these concentrates to the superphosphate unit at Debari smelting plant.
e-learning Material – Economic Geology. Dr.J.Saravanavel, Assistant Professor, Centre for Remote Sensing, Bharathidasan University. Email: [email protected]
268