Page 30 - Curriculum Visions Dynamic Book

Silver and silver ores
Silver is a rare element, being 68th in the elements of the earth’s crust. Because it reacts poorly, it is sometimes found as native (pure) silver metal. This allowed the Egyptians, for example, to use silver nearly 5000 years ago. Similar native deposits, called lodes, have been
Hydrothermal veins and native deposits
Native metals are found only
in places that were once so hot that the metals existed in molten form. It is quite common to find deposits of all of the coinage metals together. This is because
found in the Americas. This attracted Spanish they are all products of hot
colonists in the 17th and 18th centuries, and the
discovery of the Comstock Lode in Nevada in the
19th century caused a silver rush. source chambers, full of liquid
magma chambers begin to cool and many of the constituents crystallise out. At the same time, hot acidic liquids are produced that flow out from the magma into fissures in the surrounding
Outside these rare native deposits, silver
is more commonly found as silver sulphide.
Much silver is also found associated with end of the volcanic activity the
other metals such as zinc and copper, and is recovered as a byproduct of refining these more plentiful metals.
Layers of sedimentary rocks are pushed up by the rising magma.
Hydrothermal veins in which
minerals are concentrated. rock. Here the hot solutions
liquids created during intense volcanic activity.
Deep below volcanoes lie their
rock (called magma) that has forced its way up from deep within the Earth’s crust. At the
cool and the various dissolved compounds solidify in fissures called veins.
Veins contain a variety of minerals, including metal compounds and native metals. These are the rich “lodes”
that prospectors have sought through the centuries.
Less concentrated deposits have been produced by sedimentary processes, and the ores, though much more extensive, are far less rich in metal.
 This diagram shows how hydrothermal
veins are related to the magma source, which subsequently cools to granite rock. Erosion often strips the surface rocks away, leaving deposits in a ring pattern around the granite.
Rocks around the hot magma chamber are metamorphosed, or changed.
Magma from below the Earth’s crust initially heats the surrounding rocks
but eventually cools to form granite.
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