From this we suddenly understand why specific hot spots or magma
chambers are copper sources while others are not. Deep 3D seismic could prove very useful in
determining the best hot spots, although surface indications usually do that
for you anyway.
This also tells me that the ancient continental margin that passes
through Saskatchewan needs to scouted better on its Eastern side for hot spots
and flanking mineral zones. The same structure strikes south into outcrops in
Wyoming which led to uranium occurrences.
This is also a reminder that mining prospects are numerous in the
western USA and Mexico and are presently constrained by a mishmash of State and
Federal mining law dating even from the nineteenth century.
Were all jurisdictions to merely adopt the present system established
in BC, an investment boom in mining would be unleashed that would soon employ
millions directly and indirectly.
Instead human perfidy rules supreme.
What the US needs to do is to
download all land management to the State
Level in exchange for adopting a suitable version of the aforementioned
regime now used in BC. There you can
acquire a property for small change, but very quickly you perform or you go
home. Otherwise speculators hold
properties off the market in the hope that it will rain
Copper Chains: Earth's
Deep-Seated Hold On Copper Revealed
ScienceDaily (Apr. 5,
2012) — Earth is clingy when it comes to copper. A new Rice University
study recently published in the journal Science finds that nature
conspires at scales both large and small -- from the realms of tectonic plates
down to molecular bonds -- to keep most of Earth's copper buried dozens of
miles below ground.
"Everything throughout
history shows us that Earth does not want to give up its copper to the
continental crust," said Rice geochemist Cin-Ty Lee, the lead author of
the study. "Both the building blocks for continents and the continental
crust itself, dating back as much as 3 billion years, are highly depleted in
copper."
Finding copper is more than an
academic exercise. With global demand for electronics growing rapidly, some
studies have estimated the world's demand for copper could exceed supply in as
little as six years. The new study could help, because it suggests where
undiscovered caches of copper might lie.
But the copper clues were just
a happy accident.
"We didn't go into this
looking for copper," Lee said. "We were originally interested in how
continents form and more specifically in the oxidation state of
volcanoes."
Earth scientists have long
debated whether an oxygen-rich atmosphere might be required for continent
formation. The idea stems from the fact that Earth may not have had many
continents for at least the first billion years of its existence and that
Earth's continents may have begun forming around the time that oxygen became a
significant component of the atmosphere.
In their search for answers,
Lee and colleagues set out to examine Earth's arc magmas -- the molten building
blocks for continents. Arc magmas get their start deep in the planet in areas
called subduction zones, where one of Earth's tectonic plates slides beneath another.
When plates subduct, two things happen. First, they bring oxidized crust and
sediments from Earth's surface into the mantle. Second, the subducting plate
drives a return flow of hot mantle upwards from Earth's deep interior. During
this return flow, the hot mantle not only melts itself but may also cause
melting of the recycled sediments. Arc magmas are thought to form under these
conditions, so if oxygen were required for continental crust formation, it
would mostly likely come from these recycled segments.
"If oxidized materials
are necessary for generating such melts, we should see evidence of it all the
way from where the arc magmas form to the point where the new
continent-building material is released from arc volcanoes," Lee said.
Lee and colleagues examined
xenoliths, rocks that formed deep inside Earth and were carried up to the
surface in volcanic eruptions. Specifically, they studied garnet pyroxenite
xenoliths thought to represent the first crystallized products of arc magmas
from the deep roots of an arc some 50 kilometers below Earth's surface. Rather
than finding evidence of oxidation, they found sulfides -- minerals that
contain reduced forms of sulfur bonded to metals like copper, nickel and iron.
If conditions were highly oxidizing, Lee said, these sulfide minerals would be
destabilized and allow these elements, particularly copper, to bond with
oxygen.
Because sulfides are also
heavy and dense, they tend to sink and get left behind in the deep parts of arc
systems, like a blob of dense material that stays at the bottom of a lava lamp
while less dense material rises to the top.
"This explains why
copper deposits, in general, are so rare," Lee said. "The Earth wants
to hold it deep and not give it up."
Lee said deciding where to
look for undiscovered copper deposits requires an understanding of the
conditions needed to overcome the forces that conspire to keep it deep inside
the planet.
"As a continental arc
matures, the copper-rich sulfides are trapped deep and accumulate," he
said. "But if the continental arc grows thicker over time, the
accumulated copper-bearing sulfides are driven to deeper depths where the
higher temperatures can re-melt these copper-rich dregs, releasing them to
rejoin arc magmas."
These conditions were met in
the Andes Mountains and in western North America. He said other potential
sources of undiscovered copper include Siberia, northern China, Mongolia and
parts of Australia.
Lee noted that a high school
intern played a role in the research paper. Daphne Jin, now a freshman at the
University of Chicago, made her contribution to the research as a high school
intern from Clements High School in the Houston suburb of Sugarland.
"The paper really
wouldn't have been as broad without Daphne's contribution," Lee said.
"I originally struggled with an assignment for her because I didn't and
still don't have large projects where a student can just fit in. I try to make
sure every student has a chance to do something new, but often I just run out
of ideas."
Lee eventually asked Jin to
compile information from published studies about the average concentration of
all the first-row of transition elements in the periodic table in various
samples of continental crust and mantle collected the world over.
"She came back and showed
me the results, and we could see that the average continental crust itself,
which has been built over 3 billion years of Earth's history in Africa,
Siberia, North America, South America, etc., was all depleted in copper,"
Lee said. "Up to that point we'd been looking at the building blocks
of continents, but this showed us that the continents themselves followed the
same pattern. It was all internally consistent."
In addition to Jin, Lee's
co-authors on the report include Rajdeep Dasgupta, assistant professor of Earth
science at Rice; Rice postdoctoral researchers Peter Luffi and Veronique Roux;
Rice graduate student Emily Chin; visiting graduate student Romain Bouchet of
the École Normale Supérieure in Lyon, France; Douglas Morton, professor of geology
at the University of California, Riverside; and Qing-zhu Yin, professor of
geology at the University of California, Davis.
The research was funded by the
National Science Foundation.
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