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Passage 44

  According to a recent theory, Archean-age gold-quartz vein1 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 dehydration3 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 alluvial4 gold that were easily traced by simple prospecting5 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 unravel6 the subsurface geology of an area and pinpoint7 the position of  buried minerals. Methods widely used today include(20)analysis of aerial images that yield a broad geological  overview8; 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) envelop9 mineralization. However,none of these high-technology methods are of any value if the sites to which they are applied10 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 theories35) 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.

  1. The author is primarily concerned with
   (A) advocating a return to an older methodology
   (B) explaining the importance of a recent theory
   (C) enumerating11 differences between two widely used methods
   (D) describing events leading to a discovery
   (E) challenging the assumptions on which a theory is based

  2. 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

  3. 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 analyze12 rocks over a broad area
   (E) Limiting exploration to sites where alluvial gold has previously13 been found

  4. Which of the following statements about discoveries of gold deposits is supported by information in the  passage?
  (A) The number of gold discoveries made annually14 hasincreased between the time of the original gold rushesand the present.
  (B) New discoveries of gold deposits are likely to be the result of exploration techniques designed to locate buried mineralization.
  (C) It is unlikely that newly discovered gold deposits willever yield as much as did those deposits discoveredduring the original gold rushes.
  (D) Modern explorers are divided on the question of theutility of simple prospecting methods as a source ofnew discoveries of gold deposits.
   (E) Models based on the theory that gold originated from magmatic fluids have already led to new discoveries of gold deposits.

  5. 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 granite2
   (D) A gold deposit that has shed alluvial gold
   (E) A gold deposit that exhibits chemical halos

  6. 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 valid15 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.
   (E) It suggests that simple prospecting methods still have a higher success rate in the discovery of gold deposits than do more modern methods.

  7. 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.

  8. 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) Ⅰonly
   (B) Ⅱ only
   (C) Ⅰand Ⅱ only
   (D) Ⅰ and Ⅲ only
   (E) Ⅰ,Ⅱ and Ⅲ


1 vein fi9w0     
  • The girl is not in the vein for singing today.那女孩今天没有心情唱歌。
  • The doctor injects glucose into the patient's vein.医生把葡萄糖注射入病人的静脉。
2 granite Kyqyu     
  • They squared a block of granite.他们把一块花岗岩加工成四方形。
  • The granite overlies the older rocks.花岗岩躺在磨损的岩石上面。
3 dehydration UYkzX     
  • He died from severe dehydration.他死于严重脱水。
  • The eyes are often retracted from dehydration.眼睛常因脱水而凹陷。
4 alluvial ALxyp     
  • Alluvial soils usually grow the best crops.淤积土壤通常能长出最好的庄稼。
  • A usually triangular alluvial deposit at the mouth of a river.三角洲河口常见的三角形沉淀淤积地带。
5 prospecting kkZzpG     
  • The prospecting team ploughed their way through the snow. 探险队排雪前进。
  • The prospecting team has traversed the length and breadth of the land. 勘探队踏遍了祖国的山山水水。
6 unravel Ajzwo     
  • He was good with his hands and could unravel a knot or untangle yarn that others wouldn't even attempt.他的手很灵巧,其他人甚至都不敢尝试的一些难解的绳结或缠在一起的纱线,他都能解开。
  • This is the attitude that led him to unravel a mystery that long puzzled Chinese historians.正是这种态度使他解决了长期以来使中国历史学家们大惑不解的谜。
7 pinpoint xNExL     
  • It is difficult to pinpoint when water problems of the modern age began.很难准确地指出,现代用水的问题是什么时候出现的。
  • I could pinpoint his precise location on a map.我能在地图上指明他的准确位置。
8 overview 8mrz1L     
  • The opening chapter gives a brief historical overview of transport.第一章是运输史的简要回顾。
  • The seminar aims to provide an overview on new media publishing.研讨会旨在综览新兴的媒体出版。
9 envelop Momxd     
  • All combine to form a layer of mist to envelop this region.织成一层烟雾又笼罩着这个地区。
  • The dust cloud will envelop the planet within weeks.产生的尘云将会笼罩整个星球长达几周。
10 applied Tz2zXA     
  • She plans to take a course in applied linguistics.她打算学习应用语言学课程。
  • This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。
11 enumerating 5e395b32707b51ec56714161485900fd     
v.列举,枚举,数( enumerate的现在分词 )
  • There is no enumerating the evils of dishonesty here. 欺诈的罪恶在这里难以(无法)一一列举。 来自互联网
  • What she used to be most adept at was enumerating. 从前,她最拿手的是数落。 来自互联网
12 analyze RwUzm     
vt.分析,解析 (=analyse)
  • We should analyze the cause and effect of this event.我们应该分析这场事变的因果。
  • The teacher tried to analyze the cause of our failure.老师设法分析我们失败的原因。
13 previously bkzzzC     
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
14 annually VzYzNO     
  • Many migratory birds visit this lake annually.许多候鸟每年到这个湖上作短期逗留。
  • They celebrate their wedding anniversary annually.他们每年庆祝一番结婚纪念日。
15 valid eiCwm     
  • His claim to own the house is valid.他主张对此屋的所有权有效。
  • Do you have valid reasons for your absence?你的缺席有正当理由吗?
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