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

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

[18 ECONOMIC GEOLOGY occurred beside the lower margin of the gabbro. Solutions working upward then formed the ores by partial replacement of the gabbro, and the deposition of veins and nodules of sulphides in all the rocks along the fracture planes. The ore was developed in the granite and fractured gabbro (Creighton Mine), in the greenstones (Victoria Mine), in the quartz-diorite (Copper Cliff), and in the quartzites (Frood Mine) ; in the Alexo Mine, 140 miles from Sudbury, similar ore was formed in serpentine. The hydrothermal formation of these nickel ores is shown not only by their microscopic structure, but by their occurrence where planes of fracture and shearing admitted the solutions after the intrusion of the quartz-diorite, the last of the four igneous rocks in the mining field. The ore is due to magmatic water—not to magmatic segregation. New Careponta—New Caledonia is the second nickel field as regards output. The nickel is in garnierite (Hp(NiMg)SiO,), and in the green variety has replaced the iron in the serpentine, and in the brown variety the mag- nesium. The ore occurs to the depths of 25 to 35 feet, and is a shallow formation ; it is partly in crusts which have to be broken off the serpentine masses, and sometimes as veins along the joints. The source of the nickel is unknown; it was probably not a primary constituent of the original peri- dotite, as so much of the serpentine is barren. Gap Mine—The origin of nickel ores by segregation in basic igneous rock has been suggested for various fields, of which the Gap Mine at Lancaster, Pennsylvania, is of special historic interest. A band of nickel ore there occurs along part of the edge of an intrusive amphibolite. For long this mine was inaccessible, but it has been re-examined by T. C. Phemister (Fourn. Geol., xxxii, 1924, pp. 496-510), who has shown that the ore was not formed by differentiation in the igneous rock ; for the sulphides cut across the silicates, and like the associated siderite, are later than the amphi- bolite ; the ore was formed by replacement along many small fractures. In Floyd County, S.W. Virginia, a dyke said to be norite, contains nickel-bearing pyrhotite and is intrusive in syenite ; microscopic examination (Watson, Tr. Amer. I. M.E., xxxviii, 1908, p. 695) shows that the sulphides are in cracks in the

Access restriction

Copyright

fullscreen: The Elements of economic geology

Monograph

Chapter

Table of contents

Download

Monograph

Chapter

This page

Image fragment

Citation links

Citation recommendation