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GEOGRAPHICAL AXD GEOLOGICAL DESCRIPTION OF GOLD BELTS. 19
having an eminently lenticular structure. They are often garnetiferous and contain also many of the rarer accessory minerals, such as zircon, monazite, xenotime, etc. These gneisses are considered to have been igneous granites and diorites, subsequently rendered schistose by dynamo-metamorphism. The general strike of the schistosity is jS". 10° 25° W., and the dip 20°-25° ]ST.E. To the northwest of South Muddy creek and Vein mountain, however, the strike is generally X. E. and the dip S. E. This is the case also in the northern part of the general belt, in Caldwell county.
Isolated masses of pyroxenite and amphibolite occur as rounded inclusions or blebs, from less than 1 to nearly 100 feet in diameter, in the gneiss. They are looked upon as basic segregations from the original igneous magma out of which the gneisses were formed. They alter to talc and serpentine.
Pegmatites are of frequent occurrence in the gneisses, and like them their structure is usually lenticular. At several points there are indications of pegmatite dikes. Granite dikes occur in the South mountain region; and in the northern part of the belt, in Caldwell county, a very persistent and continuous dike of aphanitic olivine diabase has been observed. Brown mountain, in the northern part of Burke county, is made of granite.
THE QUARTZ-VEINS.
The auriferous quartz-veins of the South mountain belt form a system of parallel fissures of remarkable regularity, striking X. 60°-70° E. and dipping 70°-S0° N.W. Their thickness varies from that of a knifeedge to 4 feet. The great majority are from less than 1 to 3 inches in thickness, lying in zones of scores of small veins; the larger ones (1 to 4 feet) are few and far between. Xormal faulting has been observed in a few instances. The ore is quartz, usually of a milky white color, generally saccharoidal and seldom vitreous or glassy. It is often stained brown and is cellular from decomposed sulphurets. The sulphurets are pyrite, galena, chalcopyrite, and zinc-blende. All observations go to show that the vein-matter is formed from ascending mineralized solutions. There is no evidence of the replacement of the country rock by ore.
In the South mountain region proper there are five parallel lines or zones along which these quartz-veins appear to be concentrated:
1. The jlorganton zone, passing through Morganton, along Little Silver creek and through the Neighbor's place to Xorth Muddy creek.
2. The Huntsville zone, passing over the southern end of Huntsvillo mountain.
3. The Pilot mountain zone, passing over Halls knob, Whites knob,
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