Ore formation Flashcards
2 types of ore formation
- endogenous (forms at same time as rock)
- exogenous (form on the surface)
ore
natural occurring
metal mineral in high concentration
looks metallic
ore processes
magmatic processes (cumulates) Hydrothermal processes:
hydrothermal processes
hot hydrothermal, transport and despot mineral, precipitate out via hydrothermal, mineral rich water, cools, cracks, fissures, evaporates leaving mineral (vien)
black smoker
is hydrothermal leaving ground, metals and minerals still inside
trap site
point at which high concentration builds up: ore high concentration through processes
Magmatic Processes
- fractional crystallisation, ores form in the magma (what point it crystallises out)
- liquid immiscibility
- different minerals crystallise at different levels
liquid immiscibility
2 liquids cant mix
- magma and water
- sulphide liquids
In magma sulphide immiscibility occurs when magma is saturated in sulphur
Sulphide immiscibility
elements like nickle, copper, platinum group and coblat are, strongly found in sulphur melt
cannot mix with magma
all dense, high specific gravity
Economics of element (platinum)
platinum, 75% comes from S.Africa, used in electronics, catalytic convertors
melting of upper mantle
ultra mafic, ultra basic, low viscosity magma
Ore Formation processes
- source for the metal (magma)
- transport
- crystal settling in a magma chamber
- hydrothermal activity
- erosion and deposition in sediments
- trap to concentrate the ore
- to levels that are economic to extract
Endogenous
ores that form at the same time as the host rock
Exogenous
processes that concentrate ores near the surface
- weathering, erosion, deposition (placer deposits)
hydrothermal circulation
- cold sea-water penetrates into cracks and fissures in the ocean crust
- waters heated at depth by magmatic processes and minerals from host rock become dissolved
- hot mineral-rich waters are buoyant and rise back to se floor
- white and black smokers
