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

yO ECONOMIC GEOLOGY G. W. Card’s microscopic examination of the ores, and R. J. Frecheville showed (1898) that the lodes had been formed along crushed zones. Some bands were still regarded as slates of sedimentary origin until shown by C. O. G. Larcombe (Geol. Kalgoorlie, 1913, pp. 77-82) to be sheared fine-grained varieties of the country, which is mainly quartz-andesite and granophyric dacite. Some altered tuffs show that the rocks were in part volcanic. The lodes are of three types. In the N.E. of the field the Oroya-Brownhill lode is a curved sheet of quartz, which has been called a saddle-lode. The Associated Northern Mine is due to impregnation where dacite (quartz andesite) is faulted against tuffs (Fig. 14). The third type, as in the Great Boulder Proprietary (Fig. 15) and Lake View Consols mines, consists of branch- ing quartz-veins and sheaves of ore- lenticles in sheared country, which is slate-like aphanite and quartz-andesite. The sheared bands have been altered by hot water into quartz-sericite-car- bonate rocks, with epidote and chlorite. The carbonates were formed by de- scending meteoric waters and were followed by silicification and shearing with the formation of secondary plagio- clase; later the felspars and ferro- magnesian minerals were converted to an aggregate of quartz, sericite, epidote, and chlorite. That the gold was prob- ably introduced by deep-seated waters before these changes is shown by the abundance of telluride. Further N. in West Australia are gold mines of a simpler character, associated with quartz-veins and banded iron- stones, and connected with granitic and basic intrusions.

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