10 
The composition of these original metalliferous solutions and 
the precipitation of the metals from them during their migration, 
by changes in temperature and pressure, by interaction with other 
solutions derived from elsewhere, or by interaction with the solid 
minerals with which they come in contact, all these are matters 
demanding the closest study. Only when they are thoroughly 
investigated and understood will the present unscientific and waste- 
ful methods of prospecting and development give place to thorough- 
ly scientific and therefore economical methods. 
One of the earliest theories of the origin of gold deposits, and 
one which still prevails almost universally is that the gold was 
originally a very minor constituent of a molten magma, the solidi- 
fication of which resulted in a concentration of practically the 
whole of the metal in the form of gold chloride in a comparatively 
small volume of water. This solution rising under pressure into 
cavities in the zone of anamorphism and katamorpliism met there 
with reducing agents, particularly with the carbon of fossil vege- 
table matter, which produced a separation of the metal. If this 
be so the richer portion of the gold deposit should be found adjacent 
to carbonaceous portions of the wall rocks, and the worthless por- 
tions of a gold deposit adjacent to those portions lacking in carbon,. 
This theory appears to be borne out by facts in some few cases, 
e.g ., at Bendigo, and has resulted in a scientific direction of pros- 
pecting operations in certain districts. 
The study, however, of the majority of Western Australian 
gold deposits, and of many in other parts of the world, shows this 
theory to be completely inapplicable in the majority of cases. In 
a description of the Kalgoorlie deposits published in 1912, I first 
promulgated the theory that the gold in the primary solutions of 
magmatic origin was present not in the form of chloride but in the 
form of the suJphaurate anion, (AuS 8 ). Simultaneously and in- 
dependently a similar suggestion was put forward by Professor 
Lenlier of California to explain the primary introduction of gold 
into some of the rich veins of that State. The main facts upon 
which this theory was based by myself are briefly : — 
1. The invariable association of free gold and pyrite and 
the very frequent quantitative substitution of the 
latter for previously existing iron silicates : 
2. The association at Kalgoorlie, Ora Banda and elsewhere 
of free gold with tellurides of gold, silver, and other 
metals soluble as sulphosalts : 
3. The frequent absence of any concentration of gold in the 
immediate neighbourhood of bands of graphitic 
material, whilst the contrary would be the case if 
gold had arrived in the form of solutions of auric 
chloride and auric cation ; 
