Precious Metals In The Northern Cordillera

Author : Mark E. Griffin
Publisher :
ISBN 13 :
Total Pages : 170 pages
Book Rating : 4.:/5 (113 download)

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Download or read book Precious Metal Deposits Associated with Alkaline Rocks, North American Cordillera North of 41 Degrees N. written by Mark E. Griffin and published by . This book was released on 1984 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Alkaline igneous rocks are the source, and host, a varlety of mineral deposits including: (1) epithermal Au and Ag deposits, (2) porphyry copper deposits with significant concentrations of Ag, Au, and Pt-metals, and (3) submarine exhalative base- and precious-metal deposits. These deposits occur throughout the North American Cordillera within isolated intrusives and related volcanics which have been emplaced in the crust through a variety of mechanisms. Experimental evidence suggests that these alkaline rocks are derived from an alkali basalt parent which has formed from partial melting of the upper mantle. ALKY is a petrochemical data base containing information on 3992 chemically analyzed alkaline and related rocks from the North American Cordillera. ALKY was created to evaluate classification schemes, genetic models, and geochemical prospectins techniques for alkaline rock-related mineral deposits. Based upon our data six rock assemblages can be recognized with respect to their associated mineral deposits and petrologic and chemical similarities. Of these, the felsic syenite assemblage holds the greatest potential for discovery of alkaline rock-related epithermal gold deposits. Statistical tests show a background value for gold in epithermal systems of 1 - 3 ppb, and Au:Ag ratios being 1:=10. Epithermal Ag deposits appear to be confined to the associated subalkaline rocks in these systems suggesting that the alkaline rock may have only been the heat engine which melted the crustal rocks. Chemical criteria for recognition of areas wlth a high exploration potential for the discovery of alkaline rock-related precious metal deposits include: (1) wt % SiO2 45, unless wt % CO2> 5; (2) high Au (> 10 ppb); (3) wt % Na2O + wt % K2O> 10; (4) K2O> Na20; (5)Fe2O3> FeO; (6) high Te, Ba/Rb; (7) locally high Tl, F, Nb and Ag"--Document.