Dissertation: Chemical evolution of acidic, high-sulfidation
state hydrothermal fluids in carbonate rocks – a
case study of the Superior porphyry-type deposit, Pinal county, Arizona
My current research integrates extensive field mapping data (both on the
surface and underground )and petrographic work
with thermodynamic modelling to evaluate chemicial reaction paths
taken by acidic, high-sulfidation state hydrothermal
fluids in carbonate rocks. These aqueous solutions
are analogous to those recorded in some active geothermal
systems in the circumpacific (e.g. Pinatubo Philippines
and White Island New Zealand). The exposures
created by the mine at Superior Arizona provide remarkable
access to the paleogeothermal system there,
allowing detailed study of 1) the chemical mechanisms of
replacement of carbonate by metaliferous solutions,
2) the stratigraphic/lithological control on the distribution
of fracture aquifers adjacent to faults, and 3) the
evaluation of stable isotopic tracers in determining fluid
flow paths in carbonate rocks.
Or, for those of you who aren't professional geologists:
Deep underground in areas of active volcanic activity lie bodies of
hot lava that haven't made it to the surface of the earth.
Technically, lava that hasn't made it to the surface is called magma.
That magma just sits down there, slowly cooling off and solidifying into
There's more than just hot magma down there, though. There
are also many cracks deep in the rock through which water flows. Where does
the water come from? Well, some of it is rain water that seeps down from
the surface. That's called meteoric water. That's usually a good
portion of all the water. The water you may have seen spouting out of
the ground as geysers at Yellowstone is meteoric water.
In some cases, however, the cooling magma itself
separates into magma with lots of little bubbles of water, sort of like
how oil and vinegar salad dressing separates after it has been shaken up.
The bubbles of water separate out of the magma just like the salad dressing,
with the light water floating to the top. This "new" water is called
magmatic water (because it comes from the magma). When it
separates from the magma, it carries with it a lot of dissolved copper,
iron, sulfur, gold, and all the other goodies.
This metal-rich magmatic water flows out into the many cracks in the
rock, and deposit the dissolved metals in the form of minerals. If you've
read the rest of my web pages, you've learned that a crack in the rock
filled with minerals is called a vein. Well, sometimes the water
all flows through one or two really big cracks and you get a few really
big veins. More commonly, though, the magmatic water flows out into
a ga-zillion little cracks less than a tenth of an inch wide. We call
the resulting ore deposit a porphyry copper deposit (pronounced
poor-furry copper deposit).
(I'll finish this later -- please come back again to hear how the story
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