CHAPTER VII 
ORES OF LEAD, ZINC, AND SILVER 
Leap—Irs Uses, etc.—Lead (Pb; at. wt, common lead, 
207, uranium lead, 206 ; sp. gr., common lead, 11-33, uranium 
lead, 11-27; melting-point, 620° F.) is one of the six metals 
that was used by prehistoric man ; it is easy to work, being 
soft, ductile, and malleable. Among its valuable properties 
are its flow under pressure while’ cold, melting at a low tem- 
perature, and insolubility in concentrated sulphuric and 
hydrochloric acids. It is a constituent of some alloys in- 
cluding pewter, and being the heaviest of common metals 
is used for bullets. In 1025 40 per cent. of the supply was 
used by the electrical industry and 25 per cent. for paints. 
British lead mining was at its zenith in 1856 with 353 mines 
at work, and an output of 73,129 tons of lead and 61,400 
oz. of silver. The price of lead was then £32 a ton. The 
price fell, after the opening of lead mines in the United States, 
Mexico, and Australia, to as low as £13 16s. per ton in 1896. 
The United States has in recent years supplied 40 per cent., 
Mexico 11 per .cent., Spain 10 per cent., and Australia 10 
per cent. of the world’s output. The British Isles in 1924 
produced only 10,863 tons, mainly from eight mines. The 
declining yield of the six chief mining fields has led to the 
price rising to £40 per ton in 1924, but it has fallen again to 
£28 in 1927. Native lead is rare, as it is slowly oxidized, 
but it has been often recorded from torn shot found in gravels. 
The chief lead mineral is galena (PbS), which is usually 
associated with blende (ZnS), and nearlv alwavs contains 
silver as argentite (Ag,S). 
CrassiFicatioNn oF OrRes—The primary lodes occur along 
faults and fractures. Those due to the filling of fissures are 
often well crustified. Many lodes that are productive in 
ab