metamorphic ore deposits , economic geology and metamorphic ore

1. Topic
Ore of metamorphic affiliation
Submitted by - Submitted to -
Vishesh Gupta Prof Ajay Mishra
M.Sc 2nd semester University of Lucknow

2. Ore of metamorphic affiliation
Metamorphic ore deposits
Metamorphic ore deposits are those which are
form as a result of metamorphic processes and are
hosted in metamorphic rocks.
This group does not include previously existing ore
deposits which are later altered or deformed
during a metamorphic events .
It is not always clear cut whether a deposits is
of the former or the later category .

3. Metamorphic deposits are formed in
different types of metamorphic conditions
,ranging from low to high temperature and
low to high pressure.
Metamorphic ore deposits is a class that
owes its economic interest to largely
isochemical equilibrium and
recrystallization of pre-existing rock.

4. Example – transformation of alumina rich
claystones to kyanite/sillimanite deposits or
graphite flakes formed formed from dispersed
between contact metamorphism of ore in the
heated zone around magmatic bodies is usually
static.

5. Sulphur release [e.g. from pyrite ] may induce
formation of metamorphic pyrrhotite or even
magnetite iron oxides ore at contact may
recrystallize to a different oxidation states
[e.g. hematite to magnetite ] controlled by
the oxygen activity imposed by magma or by
heated country rocks .

6. Oxidation and sulphidation reaction during
metamorphism
Hematite Magnetite + Oxygen
Hydrogen +pyrite Pyrrhotite + fluid

7. Skarn and contact metasomatic ore deposits
skarn and metasomatic ore deposits are intimately
related to the thermal aureoles of magmatics intrusion .
They may be said to be product of contact
metasomatism but the causal agents is the interaction
with magmatic fluids and not simple change by
heating ,therefore it was discussed in the magmatic
domain.

8. Fig: skarns and contact metasomatic ore
deposits

9. Orogenic (regional) metamorphism
Orogenic metamorphism of ore deposits is
common. Temprature may reach 1100 degree
celcius and pressure 30 kb . Under these
condition volatiles are partly of wholly(at very
high metamorphic grade )
removed from the system.

10. Metamorphic rocks exhibits coarsening preferred
orientation of minerals and a penetrative fabric
(e.g. schistosity , foliation)
under regional metamorphic conditions oxides
react readily with carbonate and silicate minerals .
This caused , for example formation of the
digenetic metamorphic skarn rock in Sweden.

11. Fig: orogenic metamorphism

12. Ore could also be formed from metamorphic
fluid
The metamorphic fluids can also be considered as
solution that are in equilibrium with host rocks
and although they are dilute, their sheer mass
allows significant transfer of dissolved matte.
 metamorphic fluid originate primirally by
chemical releases (volatization) increasing
metamorphism from subgreenschist facies to
anatexis produces a steady flow of volatiles in the
respective metamorphic rocks.

13. Shale contain 4wt% water in contrast to mica schist
with 2wt%. By exothermic reaction basalt assimilate
water during the formation of greenschist to a
maximum of 13% siliceous carbonates lose
carbondioxides due to generation of metamorphic
calcsilicate minerals.

14. Example of dehydration reaction at the transition
from greenschist to amphibole
4 Chlorite + 18 Zeolite + 12 quartz
5 Tschermakite – amphibole + 26 Anorthite

15. Water in metamorphic rocks occurs mainly in OH-
groups of hydrous minerals and in fluid inclusion
grain boundries also host tiny inclusion. Some
fluid open fissures and the pore spaces.
Fluids liberated from rock undergoing prograde
metamorphism acquire economically interesting
trace metals or other elements either together
within the volatile water , fluorine and calcium
from the lattice of transforming minerals.

17. Some metamorphic equivalents of primary rock types
accompying volcanic-associated massive sulphide
deposits
Primary rock type Medium grade High grade
metamorphism metamorphism
 Chert Quartzite
 Pyrite pyrite- pyrohotite-
mica schist
 Rhyolite Muscovite
 Rhyolite-tuff feldspar
 Rhyolite-breccia
 Rhyolite-agglomerate
 Quartzite
 Pyrite- pyrrhotite-mica gniess
 Granitic- gniess

18. Three general type of metamorphic deposits
are known
I. Copper rich type
II. Gold rich type
III.Lead- zinc- silver rich type

19. Copper – Rich Type
These metamorphic deposits are characteristclly
associated with very low grade to low grade
metamorphism.
Most often they are form in terrains where mafic and
ultramafic basement rocks are overlain upsection by
organic- rich sedimentary rocks.
Background copper values of the mafic rocks are low,
nevertheless they are belived to provide the source of
copper by liberation during a leaching process caused
by passing to low temperature hydrothermal fluids.

20. The fluid move upward above local hotspot, and
especially along fault or other structure where fluid
migrates.
When the fluid encounter the rock layer containing
the orogenic matter, precipitation results .

21. Example
I. Kennicott,Alaska : Ore = Chalcocite +Bornite
average grade 6% Copper 140pt silver
II. White pine Michigan :Ore =chalcocite + bornite
+chalcopyrite + minor sphalerite Proterozoic subareal
basaltoverlain by sandstone –shale sequence.

22. Gold-Rich Type
Gold rich metamorphic deposits are of two type –
a) Archean iron formation types
b) Quartz carbonate veins types

23. Archean- iron formation type
Archean – iron formation types mostly occurs in
Precambrian shield areas vein morphology but most
veins apparently concentrated in peculiar iron rich
shales and sandstone
Which are upgraded by at least one and usually
several metamorphic events .
Iron bearing minerals from a minerals zonations down
down –trip from oxides to silicates to carbonates to
sulphides .

24. The zonation is thought to result from
diagenesis gold occurs in quartz veins in the
silicates or sulphates facies host rocks.
Example :
Precambrian of wyoming
Jardine, Montana

25. Quartz- Carbonate Type
 Quartz – carbonate types often associated with
greenstone belts in shield areas . Serious deformation
of host rocks ore formed in structural zones/shear
zones which are regional I scales
The districts usually contain large scale folding as well
typically dismembered associated with greenschist
facies rocks namely greenstone .

26. Also hosted in deformed metaigneous rocks,
particularly where they intrude shaley rock.
Moderately high temperature fluids with
significant carbondai oxides content mechanism in
the precipitation of gold.
Typical mineral is quartz + carbonate +sericite
or chlorite + pyrite + native gold

27. Example :
Valdez creek district,Alaska
Conn Mine, Eastern district
AJ mine southeast Alaska

28. Lead- Silver Rich Type
Lead –silver rich types of metamorphic deposits
typically contain galena sphalerite and locally
tetrahedrite and chalcopyrite as are minerals.
The group is typically quartz and siderite mineral
zoning in from galena + sphalerite in the lower
portion of the veins to galena + siderite in the upper
portion of the veins.

29. Example
Coer da lane district ldaha.

30. Reference :
Economic geology –Umeshwar prashad
www.sciencedirect.com
www.slideshare.com
Wikipedia

31. Thank you