The Elements of economic geology

Bibliographic data

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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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

135 ECONOMIC GEOLOGY which have thrown the limestones against shale; the ore is bounded on one side by the fault and passes on the other into limestone with such an irregular boundary that, according fo the miner's expression, the ore and rock have “grown together.” In places the ore encloses masses of limestone and beds of shale in their original position, and casts of fossil shells. These hematites are therefore due to replacement, but whether by ascending solutions connected with the late Carboniferous and early Permian or the Kainozoic igneous activity, or to descending solutions of post-Triassic age, has been long debated. Pebbles of haematite in the breccias at the local base of the Permain have been regarded as evidence that the ores are earlier than Middle Permian. The evidence is however in favour of the view that the ores were derived from the Permian and Triassic red rocks by water which percolated downward and deposited the iron in the lime- stones, the hematite in the breccias being replaced pebbles. Bilbao—The iron mines of Bilbao in Northern Spain are famous for their high-grade hematite, which being low in sulphur and phosphorus was especially adapted for the Bessemer process, and was largely used in British iron-works. The mines were opened about 1865; their development was delayed by the Carlist War from 1872 to 1876, after which active mining began. The output increased rapidly and attained its maximum of nearly six million tons in 1899 ; there has since been a steady decline, interrupted by the War, until 1925 when the output was two million tons. The price of the ore before the War averaged about 11s. a ton. It rose during the War to 18s. 6d., but has fallen since to about 8s. About a third of the present output is spathic iron which is less profitable, as it has to be calcined from carbonate into oxide at a cost of about 3s. a ton, and calcined ore has a lower price than natural oxide, The cost of mining has moreover increased with depth, and with the narrowing of the ore. The Bilbao iron mines occur (Fig. 41) in an anticline of Lower Cretaceous beds, which trends approximately from W.N.W to ES.E. Its arch had been faulted parallel to the strike, and across it from N.N.W. to S.5.E. The faults have dropped blocks of limestone against the underlying sandstones, and the ore occurs in the down-faulted blocks.

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