THE 
MOURNAL OF GEOLOGY 
VANOARY —FPEBROARY 1913 
THE SECONDARY ENRICHMENT OF SILVER ORES 
HC. COOKE 
INTRODUCTION 
The past half-century has been a period of rapid development 
of mines and mining, both in America and ‘in other countries, and 
as a consequence, the basal facts regarding the occurrence of ores 
are now comparatively well understood. The geologic causes for 
the location of ore-bodies in certain zones or horizons are in 
many cases known, and many former theories are generally 
accepted as facts. The transportation of ores by aqueous 
solutions, the origin of some of these solutions in cooling igneous 
magmas, and the secondary enrichment of many ore-bodies through 
the agency of meteoric waters; such are some of the ideas which 
have withstood prolonged criticism and have become established 
tenets of geologic faith. But beyond basal facts, adduced almost 
solely from field evidence, our knowledge of the mechanism of ore 
depositions is somewhat vague and unsatisfactory. Only prolonged 
investigation along chemical and physico-chemical lines will render 
possible a reasonably accurate understanding of the complex com- 
position of ore-bearing solutions, of the reactions of these solutions 
with the wall rocks, of the causes for the deposition of minerals 
from them, and of many other problems connected with the depo- 
sition of ores. 
At the present time the problems most important and most 
Vol. XXI, No. 1 I 
