新東方GMAT培訓(xùn)價(jià)格

【新東方GMAT培訓(xùn)價(jià)格】　According to a recent theory, Archean-age gold-quartz vein systems were formed over two billion years ago from magnetic 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 (alluvial gold: 砂金) that were easily traced by simple prospecting (prospecting: n.探礦) 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.