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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