NA TURE 



457 



THURSDAY, AUGUST 3, 1916. 



ORE-DEPOSITS. 



The Deposits of the Useful Minerals and Rocks: 

 their Origin, Form, and Content. By Dr. F. 

 Beyschlag, Prof. J. H. L. Vogt, and Dr. P. 

 Krusch. Translated by S. J. Truscott. Vol. ii., 

 pp. xxi-f 515-1262. (London: Macmillan and 

 Co., Ltd., 1916.) Price 205. net. 

 ^PHE first volume of this treatise was reviewed 

 J" in Nature for January 28, 191 5 (vol. xciv., 

 p. 583). The second volume completes the work 

 so far as ore-deposits are concerned. The third 

 volume does not appear as yet to have been pub- 

 lished in Germany. Ore-deposits are classified 

 according to their mode of origin as follows : 

 magmatic segregations, contact-deposits, lodes, 

 and ore-beds. The first volume dealt with the 

 first two of these groups and with tin-lodes and 

 quicksilver deposits belonging to the third. The 

 second volume deals with lodes of gold and silver ; 

 lead, silver, and zinc ; uranium ; antimony ; iron ; 

 manganese; copper; pyrites and arsenopyrites ; 

 nickel and cobalt. It concludes with an account 

 of those ores which occur as beds in sedimentary 

 deposits. Each section is preceded by a biblio- 

 graphy. 



Gold-silver lodes are first described. The 

 largest and richest of these occur in geologically 

 young and chiefly Tertiary districts. The most 

 striking examples are found in the Andes of 

 Chile, Bolivia, and Peru, in the mount^qin ranges 

 of Mexico, in the Great Basin of the United States, 

 in the Sierra Nevada, and in the Rocky Moun- 

 tains. Similar lodes are met with in Japan, in 

 Sumatra, in Borneo, and in the Philippines. 

 Examples occur in Europe in the Carpathians and 

 in south-eastern Spain, where, as in the localities 

 already mentioned, Tertiary igneous rocks 

 abound ; but not in the -Alps and Pyrenees, where 

 such rocks are absent. The evidence from dis- 

 tribution alone that they are in some way con- 

 nected with vast outpourings of igneous rock — 

 especially andesite and dacite — is therefore very 

 strong, but it does not stand alone ; other reasons 

 are given, and finally the conclusion is reached 

 that the young gold-silver lodes were formed by 

 heated waters circulating towards the close of the 

 eruptive activity in the district in which they 

 occur, and that " these waters, together with their 

 metal content, were derived directly from the 

 eruptive magma." The view expressed in the 

 sentence just quoted will certainly not be generally 

 accepted if it must be taken to imply that the 

 water is not of meteoric origin. Having dealt 

 with the common characteristics and discussed 

 the mode of origin of this important and widely 

 distributed group of lodes the authors proceed 

 to describe special cases. These local descriptions 

 are illustrated by maps and diagrams, and in the 

 more important cases contain particulars as to the 

 development of the industry and of the amount 

 and value of the ore raised. Take, for example, 

 the case of Western Australia. The Kalgoorlie 

 NO. 2440, VOL. 97] 



field was discovered at the beginning of the 

 'nineties. The economic conditions at the start 

 were most unfavourable, supplies had to be ob- 

 tained from Perth, more than 300 miles away, 

 and water cost 2^d. a gallon. But in a few 

 years all was changed. A railway was con- 

 structed between the two places, and also a pipe 

 line capable of delivering 5,000,000 gallons 

 of water per day. In 1909 Western Australia 

 produced 1,595,263 oz. of fine gold, about one- 

 fourteenth of the world's production, and not 

 quite one-half of the total production of Austral- 

 asia. Between 1903 and 1909, the last date for 

 which figures were available when the book was 

 written, there had been a continuous decline, 

 which the authors attribute to decrease of value 

 with depth. The corresponding figures for 1913, as 

 quoted in Whitaker's Almanack, are 1,314,043 oz., 

 so that the decline is still going on. 



This goldfield has been examined by Dr. 

 Krusch. The lodes are intimately associated with 

 amphibolites, some of which . are schistose and 

 others massive. Although no evidence is given 

 that any of the surrounding rocks are of Tertiary 

 age, the authors refer the lodes to the younger 

 series on account of their nature. They are de- 

 scribed as veined zones consisting of a large 

 number of small fissure-filings from which intense 

 impregnation and replacement of the country 

 rock have proceeded. The lode material con- 

 sists chiefly of quartz containing auriferous 

 pyrites with gold — and other tellurides in variable 

 quantities. All the lodes are more or less decom- 

 posed near the surface, and where the gold is 

 chiefly associated with sulphides two well-marked 

 depth-zones occur : an oxidation zone from which 

 most of the gold has been leached, and an abnor- 

 mally rich cementation zone. On the other hand, 

 where the gold is chiefly in the form of telluride 

 no cementation zone exists, and the oxidation zone 

 carries free gold exclusively. 



The book then deals with the old gold lodes. 

 These are not, as a rule, associated with eruptive 

 rocks, quartz is by far the most abundant ganglie 

 mineral, and the country rock is rarely impreg- 

 nated with metal, as is so frequently the case with 

 the young gold-silver lodes. That quartz-veins 

 carrying gold are more abundant and lodes of the 

 Comstock type less abundant in the pre-Tertiary 

 than in the Tertiary rocks is unquestionable, but 

 it may be doubted whether, on this account, it is 

 desirable to introduce age as a factor into the 

 classification of ore-deposits. The gold-quartz 

 lodes of California, Ballarat, the Barberton district 

 of the Transvaal, and other areas are then de- 

 scribed. The wonderful de{X>sit of Mount Morgan 

 is considered in this connection, and the various 

 theories that have been advanced to account for it 

 are discussed. The authors favour Rickard's view 

 that it represents a highly altered part of a shat- 

 tered country which has been saturated with 

 mineral solutions and in part replaced by auri- 

 ferous quartz; or, in other words, that it is one 

 of the rare cases of a metasomatic gold-deposit. 



Space prevents us from following the authors 

 in their descriptions of the other metalliferous 



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