RC 04 - NOV 12

According to a recent theory, Archean-age gold-quartz
vein systems were formed over two billion years ago from
magmatic fluids that originated from molten granitelike
bodies deep beneath the surface of the Earth. This theory is
(5) 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.
he recently developed theory has considerable practical
importance. Most of the gold deposits discovered during
(10)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
(15) 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
(20) 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
(25) envelop mineralization. However, none of these hightechnology
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
(30) likely to be mineralized. Such ground selection relies to
varying degrees on conceptual models, which take into
account theoretical studies of relevant factors.
These models are constructed primarily from empirical
observations of known mineral deposits and from theories
35) 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.


198. The author is primarily concerned with
(A) advocating a return to an older methodology
(B) explaining the importance of a recent theory
(C) enumerating differences between two widely used methods
(D) describing events leading to a discovery
E) challenging the assumptions on which a theory is based


199. According to the passage, the widely held view of Archean- age
gold-quartz vein systems is that such systems

(A) were formed from metamorphic fluids
(B) originated in molten granitelike bodies
(C) were formed from alluvial deposits
(D) generally have surface expression
(E) are not discoverable through chemical tests

200. The passage implies that which of the following steps would be
the first performed by explorers who wish to
maximize their chances of discovering gold?
(A) Surveying several sites known to have been formed more than two
billion years ago
(B) Limiting exploration to sites known to have been formed from
metamorphic fluid.
(C) Using an appropriate conceptual model to select a site for further
exploration
(D) Using geophysical methods to analyze rocks over a broad area
(E) Limiting exploration to sites where alluvial gold has previously been found

202. It can be inferred from the passage that which of the following
is easiest to detect?
(A) A gold-quartz vein system originating in magmatic fluids
(B) A gold-quartz vein system originating in meamorphic fluids
(C) A gold deposit that is mixed with granite
(D) A gold deposit that has shed alluvial gold
(E) A gold deposit that exhibits chemical halos


203. The theory mentioned in line 1 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 models.
(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.

204. According to the passage, methods of exploring for gold that are
widely used today are based on which of the
following facts?
(A) Most of the Earth's remaining gold deposits are still molten.
(B) Most of the Earth's remaining gold deposits are exposed at the surface.
(C) Most of the Earth's remaining gold deposits are buried and have no
surface expression.
(D) Only one type of gold deposit warrants exploration, since the
other types of gold deposits are found in
regions difficult to reach.
(E) Only one type of gold deposit warrants exploration, since the
other types of gold deposits are unlikely to yield
concentrated quantities of gold.


205. It can be inferred from the passage that the efficiency of
model-based gold exploration depends on which of the
following?
I. The closeness of the match between the geological features
identified by the model as critical and the actual
geological features of a given area
II. The degree to which the model chosen relies on empirical
observation of known mineral deposits rather than on
theories of ore-forming processes
III. The degree to which the model chosen is based on an accurate
description of the events leading to
mineralization
(A) I only
(B) II only
(C) I and II only
(D) I and III only
(E) I, II and III