PLACER GOLD OF THE BARKERVILLE AREA. 557

by Emmons,” Brokaw," and others, chlorine in the nascent state is
a most important and efficient solvent of gold. Chlorine-bearing
minerals have not been recognized in the veins, and there seems to
be no reason for suspecting their presence. Except for the pos-
sibility of the presence of chlor-apatite in the schists, quartzites
and dike rocks of the area, the only other sources of chlorine that
might be available would be the rain water, or salt (NaCl) de-
rived from the limestones of either sedimentary series. Oxida-
tion of the pyrite and arsenopyrite would afford a supply of sul-
phuric acid which is essential to the solution of gold. Man-
ganiferous carbonate, which on oxidation affords manganese di-
oxide, an important agency in the solution of gold, occurs abun-
dantly in the veins. In this connection, it is interesting to note
that on Burns Mountains near Stanley, from which the largest
recorded pieces of quartz gold have been derived, a deposit of
bog manganese was found from which a random sample gave on
analysis 21.7 per cent. manganese. This manganese was no
doubt derived from the alteration of the carbonates.

Minute quantities of the above-mentioned constituents might
produce solvents for gold in amounts large enough to produce the
results that have been accomplished, when it is noted that these
changes occupied a long period of time during which the country
was being reduced toa plain. Semi-arid conditions, as is possibly
indicated by the general absence of wood in the ancient gravels,
would also be favorable for gold enrichment, as they would permit
of deep weathering and a marked oscillation of the ground-water
level.

Agents for the precipitation of the gold are abundantly present
in the form of pyrite, ankerite, and carbonaceous material in the
veins. According to Brokaw ** the carbonates, calcite, siderite,
and rhodochrosite, rapidly precipitate gold from chloride solu-

“Emmons, W. H., “ The Enrichment of Ore Deposits,’’ U. S. G. S., Bull. 625,
1917, Ppp. 305-308.

* Brokaw, A. D., “The Solution of Gold in the Surface Alterations of Ore
Bodies,” Jour. Geol., vol. 18, 1910, pp. 321-326.

* Brokaw, A. D., “ The Secondary Precipitation of Gold in Ore Bodies,” Jour.
Geol., vol. 21, 1913, p. 256.