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8/18/2019 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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