Metals Flashcards
pg 188-198
Resource
A useful and valuable natural resource
Reserve
The amount of a resource which can be extracted at a profit using existing technology
Ore
A mineral containing valuable metals
Gangue mineral
Low value waste material
Average crystal abundance
The amount of metal in ‘average’ continental crust
Cut off grade
Minimum grade that is economic to mine
Concentration factor
The amount by which the medal is concentrated to make an ore deposit
Why are reserves difficult to estimate accurate?
Unexpected faulting, demand fluctuations, improvement in technology
How do placer deposits form?
Mechanical and chemical weathering breaks down exposed mineral veins and minerals are then transported, sorted and concentrated when deposited
Name 4 properties of placer deposits
Dense
Hard
Little or no cleavage
chemically resistant
How are placer deposits mined?
Dredging
Hydraulic mining
How do gravity gravity survey indicate metal mineral deposits?
Dense rock (ore/mafic)=positive anomaly Less dense rocks(silicic)= negative anomaly
How do magnetic surveys indicate metal mineral deposits?
Minerals rich in iron produce positive magnetic anomalies
How do electrical resistivity surveys indicate metal mineral deposits?
Metal ores=low resistivity
Galena
Lead ore
Casserite
Tin ore
Magnetite
Iron ore
Spalerite
Zinc ore
Bauxite
Aluminium ore
Chalcopyrite
Carbon ore
Secondary enrichment
Oxidising conditions above water table convert copper sulphides into soluble copper sulphates.
Copper sulphates leached out and move down towards water table.
On meeting reducing conditions at water table copper sulphates react and are precipitated out as copper sulphides
Concentration factor equation
Concentration of metal ore/ average crystal abundance
Dredging
Material is scraped or sucked from a river or sea bed
Hydraulic mining
The use of high power water jets to dislodge material
Gravity settling
magma cools, minerals with high melting points crystallise out first. minerals with high density sink towards base of intrusion, forming a cumulate layer enriched with metals
where do placer deposits form? x5
fast flowing stream joins a river plunge pool in river bed projections in stream bed inside of meander bends on a beach
what are the pros and cons to dredging and hydraulic mining?
pros- less waste produces cons-scars landscape noise and dust stirred up silt=surface water pollution quickly exhausted
what are the aims of exploration drilling? x4
what ores are present
grade
amount of gangue
depth and extent of ore body
open cast mining
if ore is relatively close to the surface it is more economical to remove the overburden by quarrying
pros of open cast mining x6
low cost efficient small workforce less expensive machinery no ventilation needed thinner ore bodies can be mined at a profit
underground mining- stope
shafts drilled vertically downwards, then drive horizontal levels through to the orebody.
longwall retreat
2 horizontal roadways driven out to furthest point to be mined. Roadways connected with a ‘longwall’. Shearer cuts seam by moving to and fro along face, removing slices of coal onto a conveyor belt up to the surface. Hydraulic supports hold up roof.
geochemical anomaly
a concentration of a metal above its normal background value
how can metal be found in a stream survey?
downstream= anomalous values
upstream of source= normal values
size of anomaly decreases downstream due to dilution
how can metal be found in a soil survey?
soil samples on top and downslope of source will have anomalous metal values.
soil sample upslope of source will have normal metal values
