The author is primarily concerned with______ [br] According to the passage, the

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问题 The author is primarily concerned with______ [br] According to the passage, the widely held view of Archean- age gold-quartz vein systems is that such systems______

选项 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

答案 A

解析 The best answer is A. In lines 5-6 the author mentions “the widely held view that the (Archean-age gold-quartz vein) systems were deposited from metamorphic fluids.” This view is said to be contrary to the recent theory that these systems originated in molten granitelike bodies, so choice B is not correct. Alluvial deposits are mentioned in the passage as having aided simple prospecting methods, but such deposits are not said to have formed that Archean-age gold-quartz vein systems (choice C). According to the author, “most deposits not yet discovered have gone undetected because they are buried and have no surface expression” (lines 14-16, so choice D is not correct. And choice E is incorrect because the author says that chemical tests can aid the discovery of gold deposits if they are conducted in areas where mineralization is likely to have taken place (lines 23-27).

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