5.MIN GEOL. GL 318 Metamorphism

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Part III

METAMORPHIC DEPOSITS Metamorphism – Miera! Deposits

Hoste" #$ Metamorphi% Ro%&s

S&ar Deposits

Greise Deposits


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METAMORPHISM Metamorphism is the mineralogical, chemical, and structural

adjustment of solid rocks to physical and chemistry conditions

which have generally been imposed at depth below the surface

zones of weathering and cementation, and which dier from the

conditions under which the rocks in question originated.

D$ami% metamorphism is the total processes and eects of

orogenic movements and dierential stresses in producing new

rocks from old, with market structural and mineralogical changes

due to crushing and shearing at low temperatures extending to

higher temperatures.

Dynamically metamorphosed rocks are typically developed innarrow zones, such as major faults, and thrusts, where particularly

strong deformation has occurred.

Epi'eeti% ores developed in dilatant zones along faults, oftenshow signs of dynamic eects brecciation, plastic !oage etc."


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Metamorphism

Cota%t metamorphi% ro%&s crop out at or near the contacts of

igneous intrusions and in some cases the degree of metamorphic

change can be seen to increase as the contact is approached.

#n contact metamorphism or thermal metamorphism the main agent

of metamorphism in these rocks is the heat supplied by the intrusion.

Re'ioa! Metamorphism

• $egionally metamorphosed rocks occur over large tracts of the earth%s

surface. &hey are not necessarily associated with either igneous

intrusions or thrust belts, but these characteristics may be present.

• $egionally metamorphosed rocks suered metamorphism about the

time they were intensely deformed. 'onsequently they contain

structures as

%!ea(a'es) s%histosit$) *o!iatio or !ieatio) which can be seen

in macroscopic and microscopic scales.


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Metamorphism

• Metamorphism is in principle isochemical, but temperature and

pressure changes may result in the production of gaseous phases

'()* '+* -* +)(*" which are liable to move out the area in whichthey are formed, and hence, change the overall composition.

• etassomatism where the transport of material is essential.

Re%o'itio o* metamorphose" ores

• #n contact and regionally metamorphosed areas these rocks

generally show/

0 &he development of metamorphic textures

0 1 change of grain size 2 usually an increase

0 &he progressive development of new minerals.


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METAMORPHIC +ACIES


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METAMORPHIC +ACIES


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Miera! Deposits Hoste" #$ Metamorphi% Ro%&s

#t can be distinguished three main sub0groups/

• Metamorphi% Deposits

etamorphic deposits are formed prior to metamorphism and

without signi3cant metamorphic changes.

• Mi,e" Metamorphose"-Metamorpho'ei% Deposits

&he mixed metamorphosed0metamorphogenic deposits are

marginal to sub0economic deposits formed prior to metamorphism

which have become upgraded and economic due to

metamorphism.

• Metamorpho'ei% Deposits

&he metamorphogenic deposits formed by metamorphic processes

generally involving metamorphic mineralising !uids and structuralor tectonic traps.


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• &his 3gure shows how a 4halo5 of new minerals can form aroundan igneous intrusion due to the high temperatures.

• &his is an example of a %ota%t metamorphi% "eposit.


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S.ARN DEPOSITS

S&ars are coarsely2crystalline metamorphic rocks composed of

calcium0iron0magnesium0manganese0aluminium silicate minerals

commonly refers to as 4calc0silicate5 minerals" that form byreplacement mainly of carbonate 2 bearing rocks during contact

or regional metamorphism and metassomatism.

S&ar "eposits have been termed hydrotermal metamorphic,

igneous metamorphic, but the most common term used waspyrometassomatic.

&he deposits form when magmatic0hydrotermal !uids expelled

from cooling magmas react chemically with carbonate0richsedimentary rocks

S&ars generally form where a granitoid pluton has intruded

sedimentary strata that include limestone and other carbonate

rocks.


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S.ARN DEPOSITS

&he orebodies are characterized by the development of calc0

silicate minerals such as diopside, wollastonite, andradite, garnet

and actinolite.

&he skarn deposits are relatively small and extremely irregular in

shape. &ongues of ore may project along any available planar

structure 2 bedding, joints, faults, etc.

&he principal materials produced from skarns deposits are/

0 iron, copper, tungsten,

0 graphite, zinc, lead, molybdenium, tin,

0 uranium, garnet, talc and wollastonite.

9xoskarn and endoskarn may contain ore


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S.ARN DEPOSITS


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CLASSI+ICATION O+ S.ARN DEPOSITS

• A /m#er o* "i0eret meta!s are mie" *rom s&ar "eposits

i" agnetite skarn deposits

agnetite and hematite, some pyrite and chalcopyrite, and the usual:e0rich contact minerals auch as olivine, hedenbergite, andradite andilvaite.

Deposits occur in ural ountains $ussia", the island of 9lba #taly", etc.

• ii" 'assiterite skarn deposits

'assiterite with wolframite, scheelite, ;i, b, well known from'anada* =evada and 'alifornia ?-1"* =9 ;rasil* @ing #sland, 1ustralia*and 1zegour, orroco.

• iv" olibdenite skarn deposits

olibdenite with the sulphids of :e, 'u,


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CLASSI+ICATION O+ S.ARN DEPOSITS

• v" 'halcopyrite skarn deposits

'halcopyrite with other 'u sulphide and the sulphides of :e,


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S&ar


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• &his 3gure shows how a 4halo5 of new minerals can form aroundan igneous intrusion due to the high temperatures.

• &his is an example of a %ota%t metamorphi% "eposit.


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GREISEN AND S.ARN DEPOSITS

GREISEN DEPOSITS


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GREISEN DEPOSITS

&he term 'reise is Berman and comes from greissen, 4to

split5. #t was originally used by miners in -axony with reference

to relatively coarse0grained aggregates of quarz and muscovitefound on the borders of tin veins in granites of the 9rzgebirg,

Bermany and the 'zech $epublique.

Greise can be de3ned as a granoblastic aggregate of quartzand muscovite or lepidolite" with accessory amounts of topaz,

tourmaline and !uorite formed by the post0magmatic

metassomatic alteration of granite ;est, EF) and -temprok,

EFG".

Greises are formed by endoskarn alteration of granite during

the cooling stages of emplacement. Breisens !uids are formed

by granites as the last highly gas0 and water0rich phases of

complete crystallization of granite melts. &his !uid is forced into


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GREISEN DEPOSITS

• Greise are usually developed at the upper contacts of granite

intrusions and are sometimes accompanied by stockwork development.

• Greise are important mainly for their production of tin and tungsten.

?sually one element is predominant but there may be by product

output of the other

• (re minerals may include cassiterite, wolframite, scheelite,

molybdenite, bismuth, and bismuthinite, accompanied in some deposits

by pyrrhotite and sphalerite, in additiion to chalcopyrite and other

sul3des.

• T$pi%a! 'reise "eposits i%!/"e

9rzgebirge 2 'zech $epublic tin greisen"

&in deposits of 'ornwall

1rdlethan, Cachlan :old ;elt, 1ustralia tin0antimony greisen deposit"

&imbarra, Cachlan :old ;elt, 1ustralia gold greisen deposit"


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Topa2 a" /art2) S%he%&estei %!i0) .ie!#er'

Mo/tai) .!i'etha!) 4o't!a") Sa,o$) Germa$5

Stepha 6o!*srie" photo

Cassiterite 7 H H 3 %m Hori S!a(&o( mie


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Cassiterite) 7 H H 3 %m) Hori S!a(&o( mie

9S%h!a''e:a!";) C2e%h Rep/#!i%5 Photo %o/rtes$ o*

httpemiera!s5%om5

Apatite mai %r$sta! 1 ? %m a%ross Sa/#er'


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Apatite) mai %r$sta! 15? %m a%ross) Sa/#er'mie)

Ehre*rie"ers"or*) Er2'e#ir'e) Sa,o$)

Germa$

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5.MIN GEOL. GL 318 Metamorphism

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