GOLD, SILVER AND PLATINUM - . This blog is prepared to provide information on some important metallic minerals as mentioned consisting their Introduction, properties , origin, occurrence ,uses and Distribution
This blog will help you to know about metallic minerals in easy ways and will increase your interest in this topic.
There are many types of metallic minerals found in earth with its own properties and advantages . This blog will help you to know about these minerals.
Minerals to be studied:
- Gold
- Silver
- Platinum
1.Gold :
Introduction:
Gold was the earliest metal to be mined by mankind. The references of gold mining are seen in holy scriptures like the Rigveda.
Mineralogy:
Physical Properties:
Gold is bright yellow in colour with resplendent metallic lustre, quite soft, resistant to tarnish , highly malleable and ductile.
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Hardness- 3, Specific gravity -19.32 , Melting point -1063 ℃.
Chemical properties - It dissolves in aqua Regia and fuming HCL.
Nature: In native state gold is found in nature of irregular masses, stringers ,scales . It crystallizes in isometric system , the common crystal forms being octahedron ,dodecahedron and cube.
Uses:
- Most of the gold goes into monetary reserve and forms a monetary base for currency.
- It is used in making jewelry.
- In textile industry it is used for Zari work.
- It is used in preparation of glass bangles , lettering, interior decorations and plating.
Mode of occurrence and origin:
Gold occurs in 2 forms:
- Lodes
- Placers
1. Lodes deposits:
Lodes 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 associated with : Sulphides of non- ferrous and related metals like chalcopyrite, sphalerite, galena, pyrite and antimonite.
Lodes deposits are mostly formed through igneous emanations during last stages of cooling magma that came up along openings like fissure, faults fractures, shear zones .
Example: Kolar gold field.
2. Placer deposits :
Gold occurs as placers , deposited together with alluvium, sands ,gravels and conglomerates. In placers deposits ,natural agencies play important role in breaking the rock containing gold, its transport and concentration.
Gold is associated with: Minerals like magnetite, ilmenite, cassiterite, garnet and monazite.
Type of deposits |
Category |
Locality and geological details |
A. Lode deposits |
1. Principal Deposits(Active mines) |
(a) Kolar (Karnataka): Gold is associated with champion quartz-lodes and sulphide-bearing reefs, especially oriental lode within schist-belt, belonging to hypothermal class. |
(b)Hutti (Karnataka): Gold is associated with quartz-reefs within meta basalts, represented by greenstones passing into chlorite-schist. |
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2.Potential Deposits(Abandoned Mines) |
(a)Ramgiri,Anantpur distt,Andhra Pradesh. The auriferous belt,150-200m wide and comprising quartz-vein zone, is spread over a strike length of about 15km within schistose rock. |
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(b) Gadag, Karnataka: The gold is associated with vein-quartz, occurring in en-echelon fashion mainly within greenstone for about 50 km. |
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(c)Wynad, Tamil Nādu: The gold is associated with quartz-reefs within biotite-gneiss and interbanded hornblende_ granulite, and at places within magnetite- quartzite. |
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(d)Kundrakocha, Bihar: The gold mineralisation is associated with quart-veins within cherty phyllite of iron-ore formation. |
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3.Minor occurrences | These include numerous occurrences and small old prospects' few may be named as : Gooty(Anantapur dist.),Bisa Natham (Chittoor) and Gavanikonda (Kurnool) of Andhra Pradesh, Sithaura (Nalanda) |
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Placer deposits |
Gold washing has been carried out in the alluvial and gravel beds of many rivers in parts of Assam, Bihar and H.P. The rivers Subansiri, Lohit, Dihang,Buri Dihing and Janglu. |
2.Silver:
Introduction: Silver is precious metal next to gold .The world mine reserves of silver is estimated around 420 million kg out of which over 85% reserves are from eight principal countries - USA, Canada, Mexico ,Russia, Africa, Japan and Australia.
Mineralogy:
Physical properties;
Silver is white lustrous metal, highly malleable and ductile .It is unaltered by dry or moist air.
Specific gravity- 10.5, Melting point-1000. It is a good conductor of heat and electricity.
Silver minerals and their characters:
Minerals |
Chemical Composition |
Chief Characters |
Native silver |
Ag associated with small amounts of Cu, Au, Pt, Hg, Pb, Zn etc |
Usually Filiform arborescent or massive, colour and streak silver white, metallic ,malleable and ductile, H=2.5-3,Sp.gr-10.1-11.1. |
Argentite |
Ag2S |
Blackish grey in colour and streak, Metallic lustre H=2-2.5,Sp.gr-7.19-7.36 |
Stephanite |
Ag5SbS4 |
Iron black in colour and streak, brittle, H=2-2.5,Sp.gr-6.26. |
Prousite |
Ag3AsS3 |
Commonly granular and massive, conchoidal, red in colour and streak=2-2.5,Sp.gr=5.55-5.64. |
Hessite |
Ag2Te |
Lead grey, metallic, ductile, H-2.5,Sp.gr-8.4. |
Uses:
- Silver are used in coinage, plate and jewelry.
- Some amounts are employed in electroplating, soldering and bearing.
- Silver salts are used in medicine, photography for colouring glass and for various subordinate purpose.
- The addition of a small amount of a copper produces an alloy having lower melting point, a great hardness and affording a sharper casting then pure silver.
Origin and occurrence:
1.Silver ore occur in veins, Stringers and disseminations as replacement deposits, contact metamorphic deposits or as alluvial.
2.The upper parts of silver deposits are weathered in several cases.
3.Below this haloid zone, a zone of secondary enrichment with native silver and rich secondary sulphides.
Primary deposits with poor ore exists below secondary sulphide enrichment zone.
Distribution:
In India there is no silver deposits .It is found associated with mainly with lead and zinc and to some extent with copper and gold.
3.Platinum:
Introduction:
Platinum was first found in alluvial deposits of river pinto in Colombia, S.america from where it was taken to Europe by Spanish mathematician Antonio de Ulloa. Here it first received its name from" platina" as platinum.
Mineralogy:
Platinum belongs to group of metals, consisting of palladium, osmium, iridium, rhodium and ruthenium.
It occurs in nature in fine scales and minute grains in following forms:
1. Native state- Element platinum (Pt).
2.Arsenide- Sperrylite (PtAs2)
3.Arseno-sulphide - Cooperite (Pt (As, S)2)
Physical properties:
Platinum is a greyish white lustrous metal, with white steel-grey streak
Hardness- 4-4.5 , Sp.gr- 21.46 (pure) , Melting point- 1760℃, Boiling point - 4300℃
Chemical properties:
It is malleable and ductile with high tensile strength and resistant to acids and other chemicals. It displays hackly fracture like gold.
Uses:
- Platinum is not only precious , but also used as catalyst in production of higher grade petrol.
- Demand for Pt is increasing with re-emergence of oil industry.
- It is considered as a good industrial catalyst used in the contact process for manufacture of sulphuric acid and oxidation of ammonia to nitric acid.
- It is used in laboratory apparartus and in electro-chemistry.
- In alloys it is used in dentistry and jewelry as for diamond settings in U.S.A.
- It is used in resistance thermometer which gives accurate results up to 1000℃.
Mode of occurrence and origin:
The platinum metal occurs genetically in the following 5 modes:
1.Early magmatic concentrations:
(i) Disseminations: Sparse disseminations with chromite in dunite. e.g.- Urals, Alaska.
(ii) Segregations by fractional crystallisation: e.g. Rustenburg, S.Africa .
2.Late magmatic concentrations:
(i) Immiscible liquid segregations:- e.g. Vlackfontein,S.africa.
(ii)Immiscible liquid injections-e.g. Sudbury, Canada.
