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 I. Introduction

Collection:: Economics Books

THE SCOPE OF ECONOMIC GEOLOGY 11 saddles.” Adjacent lodes may dip in opposite directions like the two limbs of a saddle-lode that has lost its cap; and if the two lodes were the flaps of a saddle other saddle- lodes would be expected below. False-saddles may be due to the occurrence of a bedded vein near a rake vein ; either of them may be the main lode and the other the branch. The search for an underground repetition of this structure should be made along the major lode, and not along the plane Pisecting the angle between the two lodes (Fig. 6). Lodes sometimes bifurcate into approximately equal divisions, but they more often give off branches or spurs {cf. Figs. I, 6). The branches may be small and are then known as ** stringers.” Those on the hanging-wall of a lode are often described ag © leaders '* or * feeders,” on the view that they fed the lode; those on the footwall are called * droppers.” In some fields that have been broken by intersecting fractures the quartz-veins form an irregular network; the veins may divide and reunite, or disappear irregularly. Lodes are often formed along fissures, as they are channels for the passage of metalliferous solutions. As the solutions cool they deposit some of their constituents on the walls of the fissure; crystals thus formed are often prismatic, and they grow crowded and parallel like the teeth of a comb; each sheet with this * comb structure” is known as a crust. The successive crusts may be of different materials, and may fill the fissure or leave only a thin median space known as the vugg. Crustified lodes are formed by the gradual infilling of a fissure from solutions. The fissure may be tnlarged by repeated earth-movements, and thus a thick lode may be formed of numerous crusts. They may be Symmetrical on the two sides, but, especially in the case of moderately inclined lodes, the one side may be thicker, and have more crusts than the other. The Three Princes Lode at Freiburg in Saxony at one part consisted of twenty crusts, which in order from the outside were blende, quartz, fluor, blende, barite, pyrites, barite, fluor, pyrites, and calcite, with a central vugg. This sequence indicated repeated variations in the temperature and composition of the solu- tions which deposited the lode, A lode is not always sharply marked off from the country,

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