260 ALBERT D. BROKAW 
deposits. Analyses of calcite often show small amounts of ferrous 
carbonate, ranging in some cases up to 6 per cent. Im sixteen 
analyses reported by Doelter’ only three showed no ferrous iron, 
and the average for the sixteen was 1.33 per cent, reported as FeO. 
Magnetite and olivine were selected as fairly simple ferrous 
compounds, and were allowed to stand in contact with a 0.5 per cent 
gold solution for 60 days. Neither one showed any precipitation 
of gold. 
IV. MANGANOUS COMPOUNDS 
a) Manganous salts in solution—The fact that manganous 
salts, under certain conditions, can precipitate gold from solution 
and at the same time be oxidized to the insoluble manganese 
dioxide, seems to have escaped the attention of chemists. At 
least the writer has searched through chemical literature in vain 
for information on the subject. Wells? has called attention to the 
increased ease of oxidation of manganous salts in alkaline solutions, 
but the application to precipitation of gold has not been made. 
The interesting occurrences of gold and manganese dioxide 
in a number of localities, notably in the San Juan,3 Crede,* Park 
City’ and Red Clifi® led to the suspicion that under the proper 
conditions manganous salts might act as the precipitating agent 
according to some such reaction as the following: 
2AuCl,+3MnSO,+12H.0O=2Au+3Mn0O,+6HC1+3H.SO, 
Since this is the reverse of the reaction believed to be responsible 
for the solution of gold in the surface alteration of ore bodies, it 
is to be expected that it proceeds in this direction only under certain 
conditions, and the following series of experiments was undertaken 
with a view to ascertaining these conditions. 
Gold chloride solutions of varying concentration were mixed 
with manganous sulphate solutions with concentrations ranging 
tC. Doelter, Handbuch der Mineral-Chemie, 1, 274-75. (Dresden, 1911.) 
2 Cited by W. H. Emmons, Trans. Am. Inst. Min. Eng., XLII, 29 (1911). 
3 Ransome, U.S. Geol. Survey, Bull. No. 182, p. 101 (see also Emmons, op. cit., 31). 
4 Emmons and Larsen, U.S. Geol. Survey, Bull. No. 530. 
5 U.S. Geol. Survey, Professional Paper No. 77, p. 103. 
6S. F. Emmons, cited by W. H. Emmons, of. cit. 
