218

worn; Nos. 2, 3, 4 are well worn. The nuggets when polished and etched
show definitely a crystalline structure (Plate IX A) and it is probable, as.
has been found in other regions,! that nearly all the placer gold, as well as
the vein gold, is crystalline, and only a small part concretionary. One
nugget (No. 1, Plate IX A) is composite and consists of a large crystal
occupying the middle part, with additional crystal growths at both ends.
All the nuggets show cavities and inclusions. Two of the nuggets, Nos.
3 and 4, apparently contain gold of different fineness, one part being higher
in silver than the other part. This is shown by the fact that when the
surface is etched with aqua regia one part turns a persistent grey, whereas:
other parts remain bright. The contact between the two kinds of gold
is an irregular, but sharply defined line (Plate IX B). The bright gold is
not due to leaching of the silver content of part of the gold in the nugget,
for, in places, particles of bright gold are completely enclosed in the greyish
gold. A narrow band of bright gold around the outside of the nuggets,
however, is probably due to leaching of the silver content. Assays of
two pieces cut from a nugget were made by the Mines Branch, Department
of Mines, Canada. The nugget was first treated with aqua regia to
remove the outside part. Two pieces weighing about one-tenth gramme
were then cut from the nugget in such a way that one piece contained a
greater quantity of the bright-coloured gold than the other piece, but,
because of the intimate relationship of the two kinds of gold, no definite
separation could be made. The polished surface of the nugget, when
slightly etched, showed, distinctly, patches of bright and dark-coloured
gold; when thoroughly etched the whole surface turned dark, owing to the
formation of a surface film of silver chloride, the nugget being high in silver.
The results of the assays showed that one piece of the nugget contained
80-04 per cent gold and 18-33 per cent silver, and the other 81-37 per
cent gold and 17-38 per cent silver. Though the evidence is not as definite
as might be wished, it seems probable that some of the nuggets were formed
by deposition from different kinds of gold solutions, and, therefore, by a
process of gradual accretion.

The cavities and inclusion in the nuggets are probably partly due,
as pointed out above, to modification of the shapes of the nuggets by the
action of the streams. Some of the cavities are probably due to removal
by solution of pyrite in the gold, this action having taken place, largely,
during the time of formation of the nugeet.

The placer gold varies in fineness from about 775 to about 950. The
vein gold is said to vary in fineness from 850 to 9102. The marked difference
in fineness of the gold of different creeks is probably mainly due to differ-
ences in the character of the vein gold, from which the placer gold was
derived, and only slightly to the leaching of the silver content, for it is
evident that the nuggets have been only slightly leached. There is no
evidence that the placer gold is, as a rule, of greater fineness than the vein
gold.

1Liversidge, Jour. Roy. Soc., N.S.W., vol. XXVIII, p. 343 ; Ibid, cx ; ibi
SOR TIT 0 vo p (1893); Ibid, vol. XX XT, p. 79 (1897); ibid, vol.

Atkin, A.J. R.: ‘‘Some Further Consideration f the G is of th i vi
dhaiViony Colao es Tee eae of the Genesis of the Gold Deposits of Barkerville, B.C., and