Page 22 - Handbook of Gold Exploration and Evaluation

Nature and history of gold 5

1.1 Basic requirements for the formation of any ore deposit. The degree of
element concentration during ore formation is a critical factor (modified from
McQueen, 1997).

millerite), by its strong metallic lustre and characteristic tint. Gold does not react
with oxygen to form stable oxides, the principal oxidation states being +1 and
+3. The most common compounds are AuCl 3 and the chlorauric acid HAuCl 4 .
Both are built up around the Au +3 metal ion. The main physical properties of
metallic gold are listed in Table 1.3.

Table 1.3 The main properties of gold

Chemical symbol Au
Atomic number 79
Atomic weight 197
Crystal form Cubic
Colour Golden yellow to silver white rarely orange red
Melting point 1064.43 ëC (1948 ëF)
ÿ6
Thermal expansion 14.2 10 /ëC
Diaphansity Opaque
Seawater abundance 4 to 8 10 ÿ6 ppm*
Hardness 2.5 to 3.0
Density 19.3 (when pure)
Magnetic susceptibility Low
Resistivity 2.2 10 ÿ8
Ductility High
Lustre Metallic
Tensile strength 138 megapascals when annealed
Crustal abundance 0.005 ppm
Volatility Commences well below melting point

* The oceans contain about1,350 million cubic kilometres of water and a seawater abundance of
0.000006ppm (average value) represents a gold resource of about 8,200 cubic kilometres of fine
gold.