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

32 ECONOMIC GEOLOGY gold so thoroughly that it was the finest that has been found and contained 998 parts of gold in 1000. The microscopic structure of the quartz gives no support to the geyser theory. The mine (Fig. 16) is on an ancient volcano, as observed by the author in 1909, as the quartzite proved to be quartz- porphyry and the slates to be volcanic tuffs and altered spherulitic basalt with crusts of variolite. The formation of the mine began during the Paleozoic (Newman and Camp- bell Brown, Tr. Austral. I. M.E., xv, 1911, p. 443) with the injection of a complex series of dykes, followed by the in- trusion of diorite which so weakened the crust that the igneous rock reached the surface and established a volcano. Its base was intruded by a second series of dykes and after the volcano became extinct, the rocks were saturated by FO. WW, F Fig. 16.—SECTION ACROSS THE MounT Morgan MINE, QUEENSLAND, The ore-body (O.B.) traverses mainly variolitic diabase (V) which is asso- ciated with a band of limestone and quartz-porphyry (dotted), To the west is an area of old granite covered by Desert Sandstone with placer gold (X) indicating the pre-Cretaceous age of the ore-deposits. 0.C. is the open cut; black lines, diabase dykes. F.O. former outline of the hill. waters which deposited sulphides of iron and copper rich in gold. The plutonic origin of these waters is indicated by the presence of tin oxide, cassiterite. A large mass of pyrites was deposited by replacement beside the volcanic pipe. The country was worn down to a peneplane on which was deposited the Upper Cretaceous Desert Sandstone, which contains placer gold from the mine. As the country was lowered by denudation, surface waters dissolved silica, gold, and iron oxide and re-deposited them as the rich gossan. The upper part contained 3 oz. of gold to the ton; the lower part of the open-cut was enriched to 6 oz. to the ton, below which the grade fell to 14 oz. Pyrite was deposited below the enriched oxidized belt, but the copper was carried lower and deposited in the underlying pyritic ore-body beside the

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