370 17·Gold been found in California and even larger ones in Transylvania as depicted in Plate 17.1.Chunks up to 90 kg in weight have been supposedly encountered in Australia.Most of the time,however, quartz rocks contain gold in concentrations of one-hundredth of a percent or less.Gold has been traditionally "harvested"from river beds into which it was washed after the rocks have been eroded by wind and water.The technique of panning is com- monly used.(Due to its high density,gold sinks to the bottom of a slurry of water and rocks.)Small nuggets or flakes of gold have been,and still can be,picked up in streams near surface veins or alluvial deposits.In antiquity,gold-containing mud was passed through sheep skin whose wool was subsequently burned to ob- tain gold dust.The Sumerians 6000 years ago already crushed gold-bearing quartz applying massive stone hammers.Eventu- ally,"surface"gold became scarce and man had to resort to un- derground mining.This was done particularly since about 600 B.C.in the Mediterranean region,as well as in Asia Minor,West- ern and Eastern Europe,Africa,and Asia.It was made possible through advances in ventilation and later by better drainage of the ground water.In antiquity,Egypt was the land richest in gold (and poorest in silver).It derived its gold from the desert region on the Red Sea and from Nubia.(Nub in the Egyptian language means gold.)The Greeks and Romans used scores of slaves and convicts as mine workers who labored under deplorable condi- tions.Rome got most of its gold from Spain.Looting of the gold holdings of other countries likewise filled her treasury. During the Middle Ages,the miners were liberated from slav- ery and became free agents who offered their services to the high- est paying governments.Gold mining,melting,and casting pretty much paralleled similar endeavors developed for copper pro- duction,as described in Chapter 1.This can be understood by knowing that the melting point of gold (1063C)is even 20C lower than that of copper. Discoveries of gold in certain regions of the world led to large migrations of people to these places.Examples are the great gold rush to California in 1849,or to New Zealand in 1861 (which doubled that country's population in six years).The city of Jo- hannesburg in South Africa was founded as a result of a gold rush in 1886,and Canada's Yukon Territory had a similar influx during 1897/98. Over the centuries several chemical methods have been devel- oped to separate gold from its admixtures.Among them is the cyanide leaching process,in which gold from crushed rocks is dissolved by NaCN in the presence of oxygen.Subsequently,the impurities are separated by treating the resulting solution,forbeen found in California and even larger ones in Transylvania as depicted in Plate 17.1. Chunks up to 90 kg in weight have been supposedly encountered in Australia. Most of the time, however, quartz rocks contain gold in concentrations of one-hundredth of a percent or less. Gold has been traditionally “harvested” from river beds into which it was washed after the rocks have been eroded by wind and water. The technique of panning is com￾monly used. (Due to its high density, gold sinks to the bottom of a slurry of water and rocks.) Small nuggets or flakes of gold have been, and still can be, picked up in streams near surface veins or alluvial deposits. In antiquity, gold-containing mud was passed through sheep skin whose wool was subsequently burned to ob￾tain gold dust. The Sumerians 6000 years ago already crushed gold-bearing quartz applying massive stone hammers. Eventu￾ally, “surface” gold became scarce and man had to resort to un￾derground mining. This was done particularly since about 600 B.C. in the Mediterranean region, as well as in Asia Minor, West￾ern and Eastern Europe, Africa, and Asia. It was made possible through advances in ventilation and later by better drainage of the ground water. In antiquity, Egypt was the land richest in gold (and poorest in silver). It derived its gold from the desert region on the Red Sea and from Nubia. (Nub in the Egyptian language means gold.) The Greeks and Romans used scores of slaves and convicts as mine workers who labored under deplorable condi￾tions. Rome got most of its gold from Spain. Looting of the gold holdings of other countries likewise filled her treasury. During the Middle Ages, the miners were liberated from slav￾ery and became free agents who offered their services to the high￾est paying governments. Gold mining, melting, and casting pretty much paralleled similar endeavors developed for copper pro￾duction, as described in Chapter 1. This can be understood by knowing that the melting point of gold (1063°C) is even 20°C lower than that of copper. Discoveries of gold in certain regions of the world led to large migrations of people to these places. Examples are the great gold rush to California in 1849, or to New Zealand in 1861 (which doubled that country’s population in six years). The city of Jo￾hannesburg in South Africa was founded as a result of a gold rush in 1886, and Canada’s Yukon Territory had a similar influx during 1897/98. Over the centuries several chemical methods have been devel￾oped to separate gold from its admixtures. Among them is the cyanide leaching process, in which gold from crushed rocks is dissolved by NaCN in the presence of oxygen. Subsequently, the impurities are separated by treating the resulting solution, for 370 17 • Gold