Download Mineral resources 2

Mineral resources 2
Gold
Read pages 80-82
to find out more
about gold
Gold
• Your handouts on gold would come in really
handy right now
• You must know the following:
– How gold is formed and the geological setting
– Where it is mined from in WA
– https://www.youtube.com/watch?v=bAKu2YuE
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Gold
• Hydrothermal process for gold formation
• Hot saline fluids passing through country rock
• Gold picked up in fluids which pass through cracks, fractures and
soluble rocks
• As the fluids move away from heat source, fluids crystalise (mostly
silica -> quartz, therefore quartz veins) and gold forms
• First miners chased quartz veins – now mining last of veins and
soluble rocks like the Golden Mile Dolerite
• Geological setting is an area of rock that has been hydrothermally
altered and a likely host of disseminated gold
Hydrothermal processes
• Most hydrothermal solutions are hot aqueous
brines, containing salts including those derived
from circulating sea water
• Metals e.g. gold, copper, lead, iron, zinc, arsenic
and molybdenum leached out of rocks and
solutions circulate and travel within the brines
• As solutions cool, individual metals precipitate
out at different temperatures, forming zoned
deposits
Hydrothermal alteration
• Hot and contain variety of metals and other elements
• Hot fluids head rock walls to temp of solution reaction causes change in mineral composition
• Elements added or redistributed
• Mineralogy of rock changed – hydrothermal alteration
• Hydrothermal alteration forms zone known as
alteration halo around intruded fluid
Hydrothermal alteration
• Hydrothermal solutions lose heat as energy is
passed to surrounding rock
• Varying temperatures result in zonation in the
alteration mineralisation assemblages
• Alteration halo can be used as a guide in the
field to find smaller orebodies (large mass of
ore)
Hydrothermal ore deposits
• Formed by hot aqueous solutions
• Hydrothermal gold vein deposits are a good
example
• Task: read page 82 and make notes on case
study 2 – important for exam!
Superpit, Kalgoorlie
High tonnage, low grade, 2-3ppm!
Price of gold makes it worth it ;)
Exam practice
• Some ore deposits are formed by the redistribution of
metals associated with hydrothermal activity, while
others are associated with magmatic processes, such
as fractional crystallisation, gravitational settling or
immiscible liquid separation.
• Choose one of the above processes of ore formation
and then use a labeled diagram or flow chart, to
explain clearly how the minerals are concentrated.
Include the source of metals and fluids in the system
you illustrate and the physical conditions or properties
that are required for the ore deposit to form. (6 marks)