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

ORES OF LEAD, ZINC, AND SILVER 111 only than Potosi in Bolivia and two fields in Mexico. The ores at Cobalt are associated with four pre-Palzozoic series. The lowest, the Keewatin Series, consists mainly of a basic Pillow-lava which is associated with cherts, jaspers, and iron ores, which form ‘the ironstone formation.’ Above the Keewatin is the Timiskaming Series of conglomerates and quartzites. The third division, the Cobalt, consists of quartzites and conglomerates. The fourth is the Nipissing diabase, 5 widespread sill which is in places 1000 feet thick. The veinstones are chiefly calcite and dolomite with duartz, barite, and fluorite. Native silver is associated With numerous silver, cobalt, and nickel sulphides and com- Pounds with arsenic and antimony. The chief minerals Present are argentite (AgsS), dyscrasite (Ag,Sh), pyrargyrite (AgsSbs,), smaltite (CoAs,), and cobaltite (CoAsS), with any rarer species. The mines are of three types. The characteristic type, which has yielded 90 per cent. of the silver, is of veins in the lower part of the Cobalt sediments, below the diabase sill, The veins are near the diabase, the greatest distance being 550 feet in some of the Cobalt rocks, and 350 feet in the Keewatin lavas. The second type is that of the Timiskam- 'ng Mine, where the diabase is intrusive into the Keewatin 0d the veins occur in both. The third type, the Keeley Mine In South Lorraine, is in the Keewatin above the dia. dase, Into which the main vein continues though it is there Poor in ore, According to the generally accepted explanation the metals were originally disseminated through the diabase, from which they have been leached either by its own magmatic water or by surface waters which were heated by it. This theory ‘has serious difficulties + (1) the characteristic “Onstituents—silver, cobalt, nickel, arsenic, and antimony— Are Not apparent in the normal diabase, which shows no signs of leaching or of solution channels; (2) most of the diabase 'S not accompanied by ore, which is almost confined to one Srea of 8 square miles ; (3) the Cobalt ores resemble those of mony where the country is gneiss and not diabase; (4) Imilar ore at Cobalt occurs in diabase, in the Cobalt sedi- ons, and in the cherts and lavas of the Keewatin; (5) the 5 1s dependent on the mechanical and not on the chemical ects of the Intrusion, for the veins were formed after the

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