PLACER GOLD OF THE BARKERVILLE AREA. 555

during the summer of 1922. Hopper-shaped faces indicative of
rapid growth are common.

One crystal aggregate consisting of about a dozen dodecahe-
drons with hopper-shaped faces, having an arborescent arrange-
ment and almost entirely enclosed in a mass of limonite, was ob-
tained by the authors. The mass was about the size of a bean,
and when found, only about three minute corners of the gold
penetrated the envelope of limonite.

Hypidiomorphic crystals of gold are common. Angular pieces
or fragments of quartz are frequently associated with the gold
and much of the quartz is iron-stained. Spongy masses with a
high degree of porosity are not uncommon, while many specimens
consist of a fine-textured quartz-breccia, the fragments of which
are held together by a cement or fracture-filling of gold. Leaf-
like gold is also common, and appears under the microscope
as if the leaves or flakes had just been removed from between
walls of some other mineral whose rough fractures are preserved
in relief on the sides of the leaves. Many of the pieces of gold
have a fine columnar or wire structure apparently due to incipient
crystallization.

Origin of the Vein Gold—The outstanding characteristics of
the vein gold are (a) its occurrence in the form of leaves or vein-
lets—acting as cement in fractured quartz; (b) its occurrence
as crystals; (c) its limitation to those portions of the veins charac-
terized by limonite.

These characteristics definitely correlate the free gold with
oxidizing conditions and with deposition in those parts of the
veins which are highly fractured and cavernous. Well-developed
crystals and crystal aggregates, such as that of the group of
dodecahedrons mentioned above, could develop only in open
spaces, or in spaces filled with the soft products of rock decay,
where they had the opportunity of taking on definite bounding
faces without interference from adjacent hard minerals. Vein-
like gold, which is so common both by itself and as a cement in the

* Maclaren, J. M., “ Gold, its Geological Occurrence and Geographical Distribu-
tion,” London, 1908, p. 19.

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