Exploration of minerals Flashcards
Concentration factor equation
Grade (%) ÷ average crystal abundance (%)
What is the main ore mineral for copper??
Chalcopyrite CuFes2
what is secondary enrichment??
when metal ore is leeched from within surface rocks and precipitate just below WT
Formation of chalcopyrite
hydrothermal fluids dissolve copper from I rocks
precipitate in surrounding contact met sed rocks
often found in hydrothermal veins
Why don’t we exploit copper from chalcopyrite
Conc factor not high enough
not at cut off grade
part of resource not reserve
inaccessible
Flow diagram for secondary enrichment
(of chalcopyrite)
Chalcopyrite
In forms of sulphides - insoluble in H20
Chalcopyrite exposed and chem weathering /oxidation
produces copper sulphate
this is soluble in H20
percolates down in ground
reaches WT = saturated and anaerobic
reduced + dep as Cu just below WT
now much more conc and econ viable to mine
What is gossan?
an insoluble cap of iron oxide at the surface of a mineral vein
why are gossans useful
marker for Cu below surface left over from secondary enrichment of chalcopyrite
porphyry def
a large igneous intrusion with a porphyritic texture (2 stage cooling)
formation of porphyry cooper dep
flow diagram
form as a result of hydrothermal processes associated with granite intrusions at convergent plate margins
C plate boundary
melting
granite intrusion (S and wet) high H20
M chamber cools and common S minerals form e.g. quartz and feldspar
Leftover= H2O and incompetent metals e.g. Au Cu U Mo called at top of M chamber
some crystals take up more space as solid rather than liquid
less space pressure builds
surrounding C rock fractures
hydrothermal fluid moves away from porphyry and cools
metals are dep /come out of solution along fractures as come out of solution at diff temps
form mineral veins
What is a Placer deposit
surface deposits formed by sed processes of weathering and erosion, transport and dep
why are Placer dep important
Dense physically and chem resistant mineral e.g. cassiterite , gold and diamond can be converted by these processes until small but high grade ore dep
How do Placer deps form?
during weathering ore is broken up by mech weathering or left as insoluble metals by chem weathering, ore and gangue sep into individual grains
weather metals transported pla
