42 GOLD AND TIN DEPOSITS OF SOUTHERN APPALACHIANS. 
of columbium, with possibly some tantalum. It is probable that these rare elements were 
confused with tungsten in the early analyses. 
The material which is mined as tin ore consists of the pegmatite rock, with its content of 
cassiterite. Within the limits of the ore shoots this mineral is in general fairly evenly 
distributed through the rock. PI. Ill, A, reproduces a photograph of a specimen from the 
Henry Carpenter property near Long Shoals, Lincoln County, and gives a good idea of 
the common appearance of the ore. The black spots are the cassiterite. This particular 
specimen is rather rich, containing probably 10 per cent of cassiterite, which corresponds 
to about 7 per cent of metallic tin. PI. Ill, B, is a photomicrograph of this ore. In a 
small dike in the Faires mine near the village of Kings Mountain the cassiterite is distributed 
as shown in fig. 4. The dark portion is cassiterite and the larger light areas are muscovite, 
the remainder being a finely granular mixture of quartz, muscovite, and a little feldspar. 
In the quartz-muscovite variety of pegmatite, cassiterite seems to be more common in the 
mica-rich rocks than in those which contain more feldspar. Very little tin has been found 
in the spodumene-bearing dikes. 
Much of the ore from depths to which superficial alteration has barely extended is coated 
along cracks and seams with black manganese oxide, probably pyrolusite, which has 
doubtless resulted from the decomposition of lithiophilite. This manganese mineral is in] 
many places deposited on and between the foils of the muscovite. It is scattered in patches 
over the surface of the ore, and when viewed at some distance is easily mistaken for cas- 
siterite. The quartz-mica pegmatite is stained somewhat brown on weathering and becomes 
more friable. The microcline pegmatite readily decomposes into a white, soft kaobn, con- 
taining small gritty grains of quartz. In this soft matrix the cassiterite remains practically 
unchanged and can easily be picked out with the fingers. Some crystals thus obtained 
have a roughened surface, as if they had been slightly etched. Whether this is actually 
the explanation or not is unknown. 
GENESIS OF THE DEPOSITS. 
From the standpoint of the geologist the point which is perhaps of greatest interest con-] 
cerning the ore deposits of a region is their origin. To the miner as well this subject should be 
of interest, since it is of great importance. An understanding of the manner in which 
the ore was formed and reached its present position is almost certain to throw light on its 
probable richness in unexplored places, the probability of its continuing with depth, and 
other vital questions which confront the mining man in the development of a new region. 
Throughout the world the most common occurrence' of lode tin, that is, tin ore mined from 
the rock in place, is in veins, which usually cut granitic rocks. These veins generally have a 
gangue of quartz and are characterized by the presence of fluorine, boron, tungsten, lithium, 
and arsenic minerals associated with the cassiterite. Prominent among these minerals are 
topaz, fluorite, tourmaline, wolframite, scheelite, lepidolite, zinnwaldite, and arsenopyrite. 
These materials are regarded as representing the final emanations from the granitic magmas. 
It is supposed that these comparatively rare elements are more and more segregated and 
concentrated as the solidification of the granite goes on, and at last, when fissures form, they 
are carried up in the form of vapors and solutions at high temperature and are deposited with 
quartz in the veins. Although these are usually veins of filling, occupying fissures on 
crevices, alteration and metasomatic replacement of the wall rock has in nearly all cases been 
considerable. The quartz of the granite has been little affected, but the feldspar and mica 
have bi'en attacked, being partially converted into a mica which is usually lithia bearing, 
either lepidolite or zinnwaldite, and partially replaced by one or more of the foregoing 
minerals and by cassiterite. The resulting rock, composed largely of quartz and mica, is 
designated greisen. This term can never be applied to any but an altered rock, a product of 
this particular kind of vein metamorphism. 
In contrast with this usual occurrence of tin in veins is the occurrence of cassiterite as a 
primary or original mineral of igneous rocks, usually pegmatite. Tin has thus been found 
in pegmatite in the Vegetable Creek district of New South Wales and in the Black Hills of 
