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Chapter 24
Sulfides and related minerals
Hydrothermal processes
Introduction
500 sulfide minerals: most metal or semi-metal:
pyrite, chalcopyrite, sphalerite
– Simple sulfides, salts of HS: ZnS
– Salts of thioacids, such as H3SbS3: Ag3SbS3
– Salts of polysulfuric acid, H2S2: FeS2
NB economic minerals: major ores for Cu, Zn,
Pb, Hg, Bi, Co, Ni, As, Sb
NB mineral properties in Table 24.1
Crystal chemistry
Bonding between metal and sulfur
– Sulfur has large ionic radius relative to small radius of
most metals
– Sulfides mostly NOT in simple close packing
Exceptions are: ZnS, PbS, HgS, FeS, CuFeS2
– Sulfur ions are usually polarized to form large
diversity of crystal structures
– Most sulfides have combination of metallic, covalent
and also ionic bonding
ZnS
Crystal chemistry
Stibnite
Pyrite
Molybenite
Important sulfide minerals
Chalcosite
Galena
Sphalerite
Cinnabar
Pyrrhotite
Pentlandite
Nickeline
Cu2S
PbS
(Zn,Fe)S
HgS
Fe0.83S to FeS
(Ni,Fe,Co,Ag)9S8
NiS
Important sulfide minerals
Realgar
Orpiment
Stibnite
Molybdenite
Chalcopyrite
Bornite
As4S4
As2S3
Sb2S3
MoS2
CuFeS2
Cu3FeS4
Important sulfide minerals
Tetrahedrite
Pyrite
Cobaltite
Marcasite
Arsenopyrite
Cu12(SbS3)4S
FeS2 (isometric)
Co(AsS)
FeS2 (lighter yellow; orthorhombic)
Fe(AsS)
Sulphide genesis:
•Magmatic ore forming processes
•Hydrothermal ore forming
processes and deposits
Magmatic ore-forming processes
Layered complexes, e.g.: Bushveld
Complex
Immiscible liquids, e.g.: sulfide
deposits: Ni-Cu at Sudbury
Hydrothermal ore-forming processes
Hypothermal
Mesothermal
Epithermal
(500 – 300ºC)
(300 – 200ºC)
(200 – 50 ºC)
Hypogene:
– Deposits formed during the upward migration
of mineralising solutions
Supergene
– Deposits formed by descending solutions
Hydrothermal ore-forming processes
Most common sulfide deposits are hydrothermal
Precipitation from aqueous or carbonaceousaqueous fluids and liquid solutions
Porosity or fracturing required to have sulfidebearing solutions mobilised through rocks
Alter composition of rocks
– E.g.: Greisens: enriched in tin (cassiterite), tungsten
(scheelite, wolframite) and gemstones (beryl, topaz,
tourmaline)
Hydrothermal ore-forming processes
Plutonic hydrothermal deposits
– Solution from crystallizing granitic magma, enriched in heavy metals:
forms pegmatites (veins) surrounding granite
Pneunomatolitic deposits
– Fractured zone adjacent to granitic intrusion; quartz, cassiterite and
scheelite precipitate from supercritical water in fractures – Sn and W
Skarns
– At contacts of granitic intrusions and limestone/marble; calcsilicate
minerals form; altered by hot supercritical liquid; W, Sn, Zn, Cu, Pb, Be
Porphyry copper deposits
– Shallow granitic intrusion underlying stratovolcanoes; alteration zone
and vein network with metal ores; Cu and Mo deposits
Volcanogenic massive sulfides
– Hydrothermal systems vent on seafloor depositing sediments with Fe,
Cu, Zn, Pb sulfides – Black smokers
Hydrothermal sedimentary deposits
– During deposition and diagenesis metal rich water replace pore water;
sulfides precipitate during compaction; Cu, Pb-Zn-Fe, Fe-Mn deposits
Stratiform deposits
– Sedimentary & volcanoclastic rocks; brine precipitate Cu-Pb-Zn sulfides
in intergranular spaces of shales, sandstones, carbonate rocks
Hydrothermal ore-forming processes:
Plutonic hydrothermal deposit
Hydrothermal ore-forming processes:
Porphyry copper
Hydrothermal ore-forming processes:
Volcanogenic massive sulfides
Black smokers
Riftia pachyptila
(Tube worms)
Calyptogena magnifica
(Mollusks)
Alvinella pompejana
Crabs
GLG 214
Mineral Project
Available on Blackboard
You have been assigned a mineral to investigate. Describe this mineral optically, physically,
crystal chemically and chemically and describe the formation process(es) whereby this mineral is
formed. Give the typical minerals that occur associated with your mineral and give the rock types
in which it occurs. Give the most important uses for this mineral and state at least two locations in
Southern Africa where this can be found. If the mineral does not occur in Southern Africa, give two
international locations for it.
NB: Use at least three different non-internet references for this study and use scientific referencing
of all the information. Websites can also be used as extra references, make sure to add this
referencing in the correct format. Remember to include ‘in-text’ referencing.
1000-1500 words
Due: Tuesday 26 April 2011
Typed report
Evaluation criteria in your study guide.
THERE IS ALSO AN ASSIGNMENT FOR GLG212 ON
BLACKBOARD.