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

[16 ECONOMIC GEOLOGY pp. 95-285), by T. C. Phemister (Ign. Rocks, Sudbury, Ontario Dept. of Mines, xxxiv, 1926, pp. 1-61), and Jas. Park (Econ. Geol., xx, 1925, p. 504). They point out that in addition to the sulphides having been formed after the silicates, the majority of the ore bodies are not in the gabbro, though near it, that the ores were introduced long after the intrusion of the gabbro, and that they occur in the sedimentary as well as in the igneous rocks. Phemister has shown that the micropegmatite altered both the overlying Trout Lake Conglomerate and the underlying gabbro, and that the most basic part of the gabbro is not at its lower side, as required by the igneous theory of the ore, but near the top. The igneous formation of the ore rests on the claim that it occurs within the basic rock. Yet of the marginal ore-bodies, the lower part of the largest, the Creighton, is wholly within the granite, which was itself intrusive into the gabbro and was followed by the intrusion of quartz-diorite dykes; and the ores were deposited later than these dykes, and are only associated with the gabbro along its shattered margin. The upper part of the Crean Hill ore-body is in granite and the lower part is along the contact between that rock and gabbro. The Victoria Mine occurs near the edge of the gabbro, but the ore is entirely in greenstone and quartzite (Fig. 36). The Levack Mine is in gneiss. The Garson Mine consists of parallel veins of ore in greenstone and schist, and partly along the contact between gabbro and greenstone. Of the off-set beds the famous deposit at Copper Cliff is a kind of pipe-lode and, according to Phemister, is an altered shattered quartz-diorite, of the same age as the last intrusions at the Creighton Mine; it has been cemented to a breccia by the sulphides. The Worthington Mine is in similar rock that has been sheared and impregnated by ore. The Frood Mine is also a sheared brecciated band along a fault, and the ore in it occurs in all the rocks, igneous and sedimentary, traversed by the fault. In the Murray Mine the ore is the cement to blocks of gabbro. The field evidence agrees therefore as to the formation of the ores with their microscopic structure. After the deposi- tion of the sedimentary Animikie rocks the country was invaded by a sheet of gabbro, which was followed by an intrusion of micro-pegmatite, the junction, as pointed out

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