Magmatic
rock which formed large porphyry deposit in Chile.
A geologist at the University of
Exeter has developed a new and relatively inexpensive way to establish whether
certain types of magmatic rocks are more likely to contain valuable metal
deposits.
In a study published in Nature
Geoscience, Dr Ben Williamson, of the University’s Camborne School of Mines,
together with Dr Richard Herrington from the Natural History Museum, London,
have proposed a new method to explore for porphyry-type copper deposits. These
deposits provide around 75 per cent of the world’s copper and a significant
amount of molybdenum and gold which makes them extremely important to the world
economy. The deposits, which originally form at several kilometres depth below
the Earth’s surface, above large magma chambers, are relatively rare,
particularly the largest deposits which are most economic to mine. In addition,
most near-surface deposits have already been discovered. Any new method to
locate deeper deposits is therefore of great interest to the mining industry.
The project, funded by Anglo
American, a major global mining company, compared the chemical compositions of
minerals from magmatic rocks that host porphyry deposits against those which
are barren. A case study was then undertaken of a major new porphyry discovery
in Chile, to test their theory. Minerals from magmatic rocks which host
porphyry deposits have distinctive chemical characteristics which can be used
as one of a suite of indicators to home-in on porphyry deposits. Unravelling
the causes of the distinctive chemical signatures has also brought new insights
into the formation of porphyry copper deposits, and more generally the
generation of the magmatic rocks from which they form, which are an important
component of the Earth’s crust. The main finding in this regard is that the
magma chamber below the porphyry undergoes discrete injections of water-rich
melts or watery fluids which enhance the magma’s ability to transfer copper and
other metals upwards to form a porphyry copper deposit.
Dr Ben Williamson, of the
University of Exeter’s Camborne School of Mines, said: “This new method will
add to the range of tools available to exploration companies to discover new
porphyry copper deposits. Our findings also provide important insights into why
some magmas are more likely to produce porphyry copper deposits than others,
and add to our understanding of how their parent magmatic rocks evolve.”
Source: University of Exeter
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