70 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE. [buli,.182. 
The internal structure of the fissure fillings, such as banding and 
comb structure, and the size and shape of pay shoots, while, strictly 
speaking, embraced under the head of lode structure, will be more 
conveniently described in the following sections on the ores of the 
lodes. 
THE ORES OF THE LODES. 
MINERALOGY OF THE ORES. 
GANGUE MINERALS. 
Under this head are included those mineral constituents of the lodes 
which commonly make up the matrix Of or are intimately associated 
with the metallic ore minerals. The term is a somewhat relative one. 
Thus pyrite is often a matrix for free gold, and has sometimes been 
treated, with chalcopyrite, etc., as a gangue mineral. 1 But in the 
present report the term gangue will be restricted to the so-called non- 
metallic minerals, 2 chiefly oxides, carbonates, sulphates, and silicates, 
while the compounds of the heavj^ metals, largely sulphides, sulphar- 
senites, sulpharsenates, sulphantimonites, or suiphobismuthites. all 
commonly possessing metallic luster, will be treated as ore minerals, 
although they may not in all cases be valuable. This is but following 
the convenient distinction laid down by such classical writers on ore 
deposits as Von Cotta and Von Groddeck, and is in accordance with 
the usage of Lindgren, 3 Phillips, 4 and others. 
In the brief resume of physical properties given with each mineral, 
the aim has been simply to give those features of color, form, etc., 
which will enable one to recognize the minerals as the}' occur in this 
particular quadrangle. The same minerals occurring in other regions 
may differ in the properties named. 
Quartz. — Si0 2 . Rhombohedral. Massive, or in hexagonal prisms 
terminated by rhombohedrons. Usually white or colorless. Hardness, 
7. Specific gravity, 2.6. 
This, as a rule, exhibits the usual character of vein quartz common 
in most mining districts. It varies from semiopaque, milk-white vari- 
eties to those which are vitreous and transparent. The latter occur 
in the Camp Bird and Tomboy lodes carrying free gold, usually in 
minute particles. In the Tomboy the occurrence of the gold in 
quartz of that particular vitreous appearance which is elsewhere coma 
inonty regarded as a sign of worthless vein matter has been com- 
mented upon by Purington. 5 The quartz of the veins is generally 
massive, and in thin section under the microscope is seen to be com! 
1 Mining industries of the Telluride quadrangle, Colorado, by C. W. Purington: Eighteenth, 
Ann. Rept. U. S. Geol. Survey, Pt. Ill, 1898, p. 781. 
2 Von Groddeck, Lagerstatten der Erze, p. 58, Leipzig, 1879. 
3 Gold-quartz veins of Nevada City and Grass Valley districts: Seventeenth Ann. Rept. U. S. 
Geol. Survey, Pt. II, 1896, pp. 114-119. 
4 Treatise on Ore Deposits, 2d ed., pp. 1-2 and 85, London, 1896. 
5 Loc. cit., p. 840. 
