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According to a recent theory, Archean-age gold-quartz vein

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Joined: 30 Jun 2011
Posts: 267

Kudos [?]: 87 [0], given: 20

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According to a recent theory, Archean-age gold-quartz vein [#permalink]

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New post 24 Dec 2011, 05:40
Discussed in detail at the below mentioned link

According to a recent theory, Archean-age
gold-quartz vein systems were formed more than
two billion years ago from magmatic fluids that
originated from molten granite-like bodies deep
beneath the surface of the Earth. This theory is
contrary to the widely held view that the systems
were deposited from metamorphic fluids, that is,
from fluids that formed during the dehydration of
wet sedimentary rocks.
The recently developed theory has considerable
practical importance. Most of the gold deposits
discovered during the original gold rushes were
exposed at the Earth’s surface and were found
because they had shed trails of alluvial gold
that were easily traced by simple prospecting
methods. Although these same methods still lead
to an occasional discovery, most deposits not yet
discovered have gone undetected because they are
buried and have no surface expression.
The challenge in exploration is therefore to
unravel the subsurface geology of an area and
pinpoint the position of buried minerals. Methods
widely used today include analysis of aerial images
that yield a broad geological overview; geophysical
techniques that provide data on the magnetic,
electrical, and mineralogical properties of the
rocks being investigated; and sensitive chemical
tests that are able to detect the subtle chemical
halos that often envelop mineralization. However,
none of these high-technology methods are of any
value if the sites to which they are applied have
never mineralized, and to maximize the chances of
discovery the explorer must therefore pay particular
attention to selecting the ground formations most
likely to be mineralized. Such ground selection relies
to varying degrees on conceptual models, which
take into account theoretical studies of relevant
These models are constructed primarily from
empirical observations of known mineral deposits
and from theories of ore-forming processes.
The explorer uses the models to identify those
geological features that are critical to the formation
of the mineralization being modeled, and then tries
to select areas for exploration that exhibit as many
of the critical features as possible.

The theory mentioned in lines 1–5 relates to the
conceptual models discussed in the passage in which
of the following ways?
(A) It may furnish a valid account of ore-forming
processes, and, hence, can support conceptual
models that have great practical significance.
(B) It suggests that certain geological formations,
long believed to be mineralized, are in fact
mineralized, thus confirming current conceptual
(C) It suggests that there may not be enough
similarity across Archean-age gold-quartz vein
systems to warrant the formulation of
conceptual models.
(D) It corrects existing theories about the chemical
halos of gold deposits, and thus provides a basis
for correcting current conceptual models.
(E) It suggests that simple prospecting methods still
have a higher success rate in the discovery of
gold deposits than do more modern methods.

Kudos [?]: 87 [0], given: 20

According to a recent theory, Archean-age gold-quartz vein   [#permalink] 24 Dec 2011, 05:40
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According to a recent theory, Archean-age gold-quartz vein

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