A brief idea of different process of formation of mineral deposits; Igneous , Sedimentary and Metamorphic

By:- UMESH BEDIA(08),RAJESH MEENA(13), AKSHAY ABHIJEET(21)

DEPT: METALLURGICAL AND MATERIALS ENGINEERING

N I T JAMSHEDPUR

Igneous Deposits

Definition of Igneous Deposits• Formed by crystallisation of hot molten material

called magma or lava or sometimes magmatic melt by the process of cooling.

• Important condition: 1.High temperature 2.Molten state

Principal types of Igneous Deposits

A.Magmatic Deposits

B.Hydrothermal Deposits

Magmatic Deposits During crystallisation of a magmatic melt, many minerals of economic value also get

formed depending on the original composition of the melt.

Minerals may get concentrated towards the bottom or margins or other places within the cooling body of magma because of some factors operating at the time of crystallisation.

Major source of some important metal like gold, chromium, titanium and uranium.

OCCURANCE OF MAGMATIC DEPOSITS

Segregation Dissemination Magmatic Injection

Segregation In the earlier stages of crystallisation, when most of the magma is still in molten state,

minerals that happened to form sink to and settle at the bottom due to gravity, is called gravitative settling.

In the late stage when most of magma has crystallized into solid rock, some left over melt containing economic mineral crystallises along with margins of the solidified magma called residual magmatic segregation.

Examples: 1. Early- Chromium 2. Late- Titanium

Dissemination Economic minerals are dispersed at random in a cooled igneous rock

Dispersion may be in a limited space from which valuable minerals are obtained by mining and extraction or over a large volume when the concentration is not economically exploitable.

Examples: Diamond dissemination obtained from rock kimberlites.

MAGMATIC INJECTIONS Thin, lenticular or slightly tabular bodies of magmatic minerals that appear as

having been intruded or injected into host rocks.

Magma rises up with sufficient hydrostatic force, it may intrude into available fissures and fractures in the surrounding rocks when eventually cool down.

Result both as early and late stages of crystallization

Hydrothermal DepositsThis is another distinct group of economic minerals which has been

formed from cooling of gaseous and liquid solution in cavities ,fissures or pore spaces of the rocks.

The solvent in such cases is vey often, superheated steam emanating from magmas towards the final stages of crystallisation.

The three essential conditions for the formation of hydrothermal deposits are:-

Highly active and enrichment fluids

Suitable pathways(cracks , fissures etc.) for their migration through the rocks.

Suitable physico - chemical environment for their deposition to take place.

Deposition may take place due to :

a) a change in temperature or pressure ( or both, of the ascending solutions.

b) ensuing chemical reactions between various components present within these liquid gas solutions.

c) chemical reactions between the components of the solutions and those of the country rock.

i. Fissure-veins :- These may be defined as mineral bodies of elongated or tabular shape

deposited in pre- existing fissures.

ii. Ladder-veins :- these are commonly found in igneous rocks such as dikes and similar bodies and consist of transverse, roughly regularly spaced fractures.

iii. Gash vein :- these are narrow, sloping and thick-bodies in solution fissures or cracks of the host rock.

iv. Stock works :- It occurs in veins or fissures of exceptionally small size, but in good number within limited space, traversing the body of rock profusely.

Forms of Hydrothermal Deposits:A. Veins:- These are narrow, elongated or tabular bodies of economic minerals

occurring within a host rock of entirely different composition and origin. These are further distinguished into following types:

B. Cavity Fillings:-these are such ore bodies that get deposited from the hydrothermal fluids in well defined open space available in rock host

SEDIMENTARY DEPOSIT

Some very important deposits of ores of iron , copper , gold , phosphate and coal are of Sedimentary Origin . Their accumulation takes place due to one or more of the following processes.

WeatheringSedimentary genesisPlacer deposit

Weathering• Atmospheric gases and water vapour reacts with surface of rock and

decomposed product is called mantle of waste.

• Loosed mantle is leached away by water

• Some residual material left behind(Residual Deposit)

• Example : Aluminum- Bauxite Iron- Limonite , Hematite

• Soluble component of molten waste taken into Solution

• By Percolating waters and redeposited at lower levels duringthe process of Infiltration .

• Forms infiltration types of deposits

• Example :ore of Uranium , Silicate- Carbonate group of Iron native Sulphur and Hydrous calcium sulphate(Gypsum)

Sedimentary genesis • Such deposits originates due to set of natural processes in almost an orderly

fashion which involves

• The deposit of pure sedimentary origin occur in the form of layered formation of extensive areal extent and considerable depth.

• In economic value they range from Non-Metallic deposit like sandstone and limestone, salts of sodium, potassium to those of metals like iron , manganese , copper , uranium and vanadium etc.

• Coals also form a distinct group of sedimentary deposit in which biochemical changes have also taken place during the process of deposition and diagenesis.

Physical and Chemical disintegration of Rocks by weathering and erosion into sediments .

Transport of these sediments by wind ,water andice to the suitable environment of deposition .

Deposition, followed by diagenesis of these sediments sedimentary formation

Placer Deposit• Described as special group of weathering that have been accumulated in varied environment by

virtue of some particular qualities of the materials involved.

• Among such qualities are high density , chemical stability , good strength and hardness etc.

• These economic mineral or substances once released from the original rock masses due to processes of physical and chemical weathering are transported to places of deposition by wind , water , glacier and ice etc.

• Placer deposits are the source of such minerals and metals as (1) gold (4) tungsten (7) garnet (2) diamond (5) titanium (8) magnetite (3) platinum (6) tin (9) zircon

• The coastal deposit of Australia and beach placer of South India are rich source of many heavy and rare minerals.

• The coastal tract of Kerala , Tamil Nadu , Andhra Pradesh and Orissa contains deposit of monazite associated with reserves of ilmenite and rutile

Types of Placer Deposit:1) Deluvial placer : when gravity as agency

involved, found along foot hills.

2) Aeolian placer : when sorting is carried out by the wind.

3) Alluvial placer : where running water such as of streams and rivers is involved in their transport.

4) Beach placer : deposit of economic value accumulated by waves along waterbodies like seas , lake and oceans.

METAMORPHIC DEPOSITS

DEFINATION OF METAMORPHISM

• It is a natural process of change brought out in rocks of all type subjected to change condition of temperature, pressure and chemically active fluids.

In this process, pre-existing rocks and minerals of economic value may undergo metamorphic changes.

Result of metamorphic change

New materials or rock of some economic value are formed.

EXAMPLES: Marble deposits formed from limestone Slate deposits formed from shale's Many refractory minerals like kyanite , silliminite and andalusite form as a result of metamorphism

ConclusionFrom the above paper we concluded that Igneous rock forms from magma that cools and solidifies in a process called crystallization. Sedimentary rock forms from the lithification of sediment. Metamorphic rock forms from rock that has been subjected to great pressure and heat in a process called metamorphism. Some of the most important accumulations of metallic mineral resources are produced by igneous and metamorphic processes. Vein deposits (deposits in fractures or bedding planes) and disseminated deposits (deposits distributed throughout the entire rock mass) are produced from hydrothermal solutions—hot metal-rich fluids associated with cooling magma bodies

Reference www.wikipedia.org

Engineering and general geology by parbin singh.

www.geology.com

THANK YOU