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Unformatted text preview: ch is sometimes
added during smelting to remove waste material from the
ore, could add quantities of elements to the final product.
An elemental property that is unchanged through these
chemical processes is the isotopic composition of each
metallic element in the ore. Isotopic composition, the
percentages of the different isotopes of an element in a given
sample of the element, is therefore particularly suitable as an
25 indicator of the sources of the ore. Of course, for this purpose
it is necessary to find an element whose isotopic composition
is more or less constant throughout a given ore body, but
varies from one copper ore body to another or, at least, from
one geographic region to another.
The ideal choice, when isotopic composition is used to
investigate the source of copper ore, would seem to be copper
itself. It has been shown that small but measurable variations
occur naturally in the isotopic composition of copper.
However, the variations are large enou gh only in rare
35 ores; between samples of the common ore minerals of copper,
isotopic variations greater than the measurement error have
not been found. An alternative choice is lead, which occurs
in most copper and bronze artifacts of the Bronze Age in
amounts consistent with the lead being derived from the
40 copper ores and possibly from the fluxes. The isotopic
composition of lead often varies from one source of
common copper ore to another, with variations exceeding
the measurement error; and preliminary studies indicate
virtually uniform isotopic composition of the lead from a
45 single copper-ore source. While some of the lead found in
an artifact may have been introduced from flux or when
other metals were added to the copper ore, lead so added in
Bronze Age processing would usually have the same isotopic 50 66 composition as the lead in the copper ore. Lead isotope
studies may thus prove useful for interpreting the
archaeological record of the Bronze Age.
(473 words) 4. The author first mentions the addition of flux during
smelting in the last sentence in the last paragraph in
(A) give a reason for the failure of elemental
composition studies to determine ore sources
(B) illustrate differences bet ween various Bronze
(C) show the need for using high smelting
(D) illustrate the uniformity of lead isotope
(E) explain the success of copper isotope
composition analysis 6. Select the sentence in the passage that the author
rejects copper as the ―ideal choice‖.
7. It can be inferred from the passage that the use
of flux in processing copper ore can alter the
lead isotope composition of the resulting metal
(A) there is a smaller concentration of lead in
the flux than in the copper ore
(B) the concentration of lead in the flux is
equivalent to that of the lead in the ore
(C) some of the lead in the flux evaporates
(D) any lead in the flux has the same isotopic
composition as the lead in the ore
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This document was uploaded on 09/16/2013.
- Fall '13