The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

ORES OF TIN AND TUNGSTEN 75 which completely decomposed the silicates, removing the aluminium as fluoride, leaving the silica as grains of quartz, and etching the quartz-phenocrysts of the porphyry. The residual quartz sank as the alumina was removed in solution, and the sand acquired its bedded structure. The White Face consisted of quartz-porphyry, which was altered into concretionary and radial growths of topaz during the in- troduction of the cassiterite; its residue, owing to the absence of pyrites, is a white clay, which includes prosopite (CaF,, 2A1(F, OH),) due to the decomposition of topaz. The pseudo-sedimentary nature of the residual deposits of Mt. Bischoff has been fully described by H. Herman (Proc. Austral. 1.M.E., 1914, p. 301). Lodes of quartz with coarse cassiterite occur at Mt. Bischoff, but have been of secondary importance. GERMANY, MaLavsia, AND NiGErRIA—The German tin- field at Zinnwald includes a * stockwork ” or impregnation of thin veins along the upper part of a granite intrusion ; its Cassiterite is associated with topaz and tourmaline, and is doubtless due to pneumatolytic solutions which spread through the crust of granite instead of forming a deep lode as at Dolcoath or large ore-body as at Mt. Bischoff. In recent years the largest supplies of tin have come from the Malay States, which with Siam, Southern Burma, and the islands of Billiton and Banka, yielded in 1925 60 per cent. of the world’s supply. The tin-fields consist of granite, in places injected into schist and limestone. The tin is associated with tourmaline and was introduced by Pneumatolysis, It occurs in thin veins, which are often crowded as a stockwork. The tin, however, rarely pays to work except where it has been concentrated by river action into alluvial placers, some of which are below sea-level, or by settlement in situ from decomposed and partially removed country rock. Some of the deposits are pseudo- bedded like the Brown Face of Mt. Bischoff. In some places, 3s at Kinta, the tin has been left in situ by the decay of altered schist and solution of limestone (W. R. Jones, 0.%.G.S., Lexi, 1917, p. 177). One lode, the Lahat Pipe, in limestone, Was worked to the depth of 314 feet. Some pegmatite veins contain nodules of cassiterite (Cameron, Ming. Mag. XXX, 1923, p. 276).

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