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 I. Introduction

Collection:: Economics Books

ECONOMIC GEOLOGY for the solutions may have impregnated the wall rock with the lode minerals. Lodes consist of earthy minerals or veinstones, of metallic constituents, and of fragments of country rock. The com- monest veinstone is quartz. Next in importance is calcite, which is especially abundant in limestones. Fluorite, barite, and dolomite are frequent in volcanic regions, and in deep- seated lodes. Less common are the felspars, rhodonite (a pyroxene composed of silicate of manganese, MnSiO,), and garnets. Tourmaline, usually in the black variety known as schorl, and topaz are common in lodes that have been formed by superheated acids. Mica of economic value occurs under similar conditions. The metallic constituents sometimes form a minute proportion of the lode; but they give it its special character and value. The metals are sometimes native, but are usually present as compounds, chiefly sul- phides, oxides, and carbonates. The fragments of country in the lode may have fallen into the fissure, or have been torn from the walls by the faulting, or be parts that resisted replacement by the lode-forming waters, Large masses of sountry rock in a lode are known as horses. That terms is sometimes applied to the country between two arms of a branching vein, and also to beds of sandstone which have filled stream channels in coal. The term * horse” is con- veniently restricted, in connection with alode, to the original meaning of a mass of country which is completely surrounded by the lode. The veinstones and rock debris found in a lode are some- times grouped together as * gangue,” a French form of the German word ** gang” which means the whole lode. The rock debris in a lode is known in Australia as muliock ; the term has been rejected as miner's slang, but as it was similarly used by Chaucer, that objection is invalid. Some lodes consist of a fault-breccia of mullock, with the inter- spaces filled with veinstones and metalliferous constituents, True brecciated lodes have been broken into fragments by faulting or pressure after their formation, Tae Term Reer—There is much confusion between the terms reef and lode due to a reversal of the meaning of reef. Owing to the heaviness of the metallic grains the richest layer in an alluvial mine js usually at the base. When all

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