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 factors.
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.
According to the passage, methods of exploring for gold that are widely used today are based on which of the following facts?
文章提到矿藏一般都深埋在地下这个事实当前版本由 KK立志71党 更新于2017-07-29 11:09:20 感谢由 KK立志71党 对此题目的解答所做出的贡献。
第三段开头讲到challenges是unravel那些buried的金子，然后承接着这句开始讲挖金的methods.所以AB选项molten和on the surface是不对的。
DE选项的only不仅过于极端而且选项内容未在第三段提及到。埋在地下是找不到具体的地点不等于hard to reach,D错误。
B是讲述一开始容易开采的矿。 而问题问的是定位第三段第一第二句话： The challenge in exploration is therefore to unravel the subsurface geology of an area and pinpoint the position of buried minerals. 现在广泛应用的方法是针对藏在地下的矿藏。
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. 答案在第二段结尾和第三段开头。 The challenge in exploration is therefore to unravel the subsurface geology of an area and pinpoint the position of buried minerals. 错因：还是没有读懂文章的意思。比较重要的这一段，讲述了文章整个的背景逻辑，没有搞懂，导致整篇文章浑浑噩噩。