Tin: Describing the Chief Methods of Mining, Dressing, and Smelting It Abroad; With Notes Upon Arsenic, Bismuth, and Wolfram (Classic Reprint)

Excerpt from Tin: Describing the Chief Methods of Mining, Dressing, and Smelting It Abroad; With Notes Upon Arsenic, Bismuth, and Wolfram

Near the former place, which has given its name to the entire district, the mineral (cassiterite) occurs in deposits of two distinct sorts; in the one case impregnated through a mass of rock (locally known as zwitter) that measures about 1312 feet across its outcrop in the other, associated with hematite, quartz, and other gangue, in a number of small but regular fissures, averaging rarely more than 8 inches in width. These latter form a complete network of veins through the same formation of zwitter alluded to, which is enriched wherever they traverse it, although the veins themselves now hold but a comparatively small amount of tin. On passing into the adjoining porphyritic granite, most of them, however, appear to become richer, and are frequently found with a parting of red clay; whilst, on the other hand, they cease to be productive, where they enter the next adjacent eruptive masses of quartz-porphyry and syenite-porphyry, which so imperceptibly merge into one another, that no distinct line of demarcation can be traced between them.

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