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gold as well) show negative pseudomorphs of pyrite or cubical depressions
from which the iron sulphide has been leached. Much fine gold occurs
in the porous, honeycombed quartz from which pyrite has been removed,
and specimens of the quartz from Burns mountain were seen by the writers
from which finely crystalline gold could be removed by shaking or tapping
the specimen.! Both of these cases are illustrations of the efficacy of pyrite
as a precipitant of gold from solution in this area. Gold has also been found
pr ais with the characteristic rusty negative casts left by the solution
of siderite.

The occurrence of free gold: (1) as very fine crystalline dust in the
negative casts of pyrite crystals and in the rusty fractures near the surface;
(2) as cement in fractured quartz; and (3) as fairly large crystals and
crystal groups, throws some light on the manner of its growth. These three
types of gold are crystalline, and show distinct evidence of having been
deposited from solution. No evidence has yet been found to prove in what
condition the gold exists in the sulphides—whether in the native form as
very fine disseminations, in chemical combination, or in solid solution—
but the fact that wherever found it is either in actual crystal forms or with
a crystalline structure indicates strongly that it must occur in the sulphides
in a state in which, on the removal of the sulphides, it is readily subject to
solution from which it is later deposited.2 The gradations in size between
the fine, free gold and the larger mass suggest continuous growth of the
gold by the addition of material from gold solutions. The occurrence of
the cement gold is undoubted proof of the operation of the processes of
solution and deposition of gold ending up with the healing of the fractures.
Where a rich supply of gold in its original form, as in some of the arsenopy-
rite, is available, there seems to be no reason why the continuous oxidation
of the mispickel and the removal of part of the gold in solution should
not result in the gradual growth of fairly large single masses of cement
gold.

A satisfactory hypothesis of the origin of large crystalline masses and
definite crystals of gold in the veins is based on the reasonable assumption
that the main part of the enrichment took place prior to peneplanation,
while the country was still somewhat rugged and semi-arid. Under these
conditions the belt of oxidation above the groundwater-table would have
had a considerable vertical extent, perhaps 100 feet or even more. On
the oxidation of the sulphides and the solution of the carbonates, solvents
would be provided for the fine gold. This gold, once in solution, would
travel vertically downwards until reducing conditions were met with at the
level of ground water or beneath it, and these would be deposited in cry-
stalline form. This set of conditions would provide a relatively thick
gathering ground for the gold solvents, and, on the other hand, a restricted
locality in which deposition would take place. Were the level of the
groundwater-table to remain constant until all the gold were leached from
the suggested thickness of 100 feet above the water-table, the result would

1Rickard, T, A,: cites a similar case in ‘‘The Formation of Bonanzas in the Upper Portions of Gold-veins’’;
Genesis of Ore Deposits, Am. Inst. Min. Eng., 1901, p. 737. x E t
*In this connexion certain experiments by Liversidge are interesting, in which he produced filaments of gold
ee moss—and tree—gold by roasting auriferous mispickel; Proc. Roy. Soc., N.S.W., vol. XXVII, p.1
1892).