June 15, 191 1] 



NATURE 



531 



ill particular. The examination of its trade relations, how- 

 ever, may entail a visit to the neighbouring Trobriands. 

 If it prove possible, he will also proceed so far afield as 

 Rossell Island, where certain ethnological problems of 

 peculiar interest await solution. 



SOME AMERICAN ORE DEPOSITS.' 

 "MEW MEXICO has one of the longest mining histori^.s 

 of the western United States, for its semi-civilised 

 aborigines, the Pueblo Indians, mined gold and turquoise 

 before the arrival of the first white explorer in 1534. The 

 Jesuit missions converted the Indians to Christianity, and 

 then sweated them as miners until they were goaded into 

 revolt, and the .Spaniards were only readmitted on condi- 

 tion that their industrial operations were confined to agri- 

 culture. Mining was only resumed with the discovery of 

 the copper-bearing sandstones at the close of the eighteenth 

 century. Placer mining was started in 1828 ; the modern 

 era of active mining was begun about 1866 upon the silver- 

 lead ores, followed during the present century by the 

 opening of mines of copper, lead, and zinc. The Stale 

 contains large deposits of bituminous coal of Cretaceous 

 age. 



The geology of the country has a long and scattered 

 literature. A general survey of its metalliferous mining 

 fields was made in 1905 by Dr. W. Lindgren, Louis C. 

 Graton, and C. H. Gordon, and a preliminary account of 

 their results was issued as a Bulletin (^No. 285) by the 

 United States Geological Survey in 1906. The volume 

 containing the detailed account of their researches consists 

 of a general summary of the economic geology, followed 

 by descriptions of the separate fields and mines. The work 

 will no doubt remain for years the standard authority on 

 the mines of New Mexico, and will repay stuay by all 

 students of ore deposits. It contains, moreover, instructive 

 evidence on some problems of general geology. The volume 

 is illustrated by instructive topographic maps, mine plans, 

 and plates ; a geological map of the State, however incom- 

 plete, would have been very useful. 



New Mexico has a base of Archaean crystalline rocks 

 covered unconformably by Cambrian quartzites. The 

 northern part of the State shows the stratigraphical gap 

 so characteristic of the Rocky Mountain sequence, for the 

 Cambrians are followed by the Carboniferous ; but the inter- 

 mediate Pateozoic systems are represented in the Southern 

 districts. The Mesozoic series, usually complete in the 

 Rocky Mountains, is imperfect, as the Jurassic is sparsely 

 represented. The Carboniferous beds include marine lime- 

 stones, followed by " Red Beds," some of which belong 

 to the Trias. The Cretaceous system includes 6000 feet 

 of marine beds ; their deposition was followed by active 

 earth movements, and the intrusion of sheets and laccolites 

 of granodiorites which lifted the overlying Cretaceous rocks 

 into domes. Igneous activity was renewed in the middle 

 Cainozoic, when wide lava flows were erupted from 

 numerous volcanic vents ; at the close of the Cainozoic 

 came a third period of igneous activity, and the outpouring 

 of vast sheets of basalt. The last eruptions were of very 

 recent date. 



The " metal deposits," as the Monograph calls them, for 

 the term metallisation is replacing mineralisation, though 

 both assume similar limitations — are divided by the authors 

 into six groups. The oldest series, the ores in the pre- 

 Cambrian rocks, contain gold and copper, and were de- 

 veloped as fahlbands in shear-zones. 



The second group of ores arc contact-formations around 

 the laccolites. The evidence offered by the mines as to the 

 range of the contact metamorphisni is of much interest. 

 The shales are altered for a very narrow width, but the 

 limestones may be completely changed for half a mile. 

 The authors are emphatic that the metasomatic are more 

 important than the paramorphic changes, and that the 

 addition of silica, iron, and sulphides from without ■■^ 



1 " The Ore Depos=ti of New Mexico." By W. Lindgen, C. C. (1 

 and C. H. Gordon. I'p. 16'. 



"Maneanese Or*- Depo.sits of the United .Stiitcs," with Recti">n» on 

 Foreign Deposits, Chemi«try. and Uses. By E. C. Harden. Pp. jpS. 



" Some Ore Deposits in Maie and Milan Mine, New Hamoshiic." By 

 W. H. Knimon<!. Pp. 62. (Washineton : Government Printing Offic, 

 iqio ) (U. .S. Geological Suivey-Btilletins 43a, 427. and Professional 

 Papers 68). 



NO. 2172, VOL. 86] 



" positively proved." The fresh materials are attributed to 

 emanations from the intrusive magmas. The limitation of 

 contact metamorphisin " simply to a rearrangement of 

 molecules in a single bed is absolutely contrary to the 

 facts." That these ores were not introduced in' solution 

 after the intrusive rock had cooled is shown bv the unaltered 

 condition of its border. 



The igneous rocks belong to that granodiorite- and 

 quartz-monzonite series which is so often associated with 

 ore deposits. The rocks are granular, although they 

 solidified at the comparatively shallow depth of sometimes 

 only 2000 feet. The toughness of their cover appears to 

 have prevented their reaching the surface. 



The third series of ores are veins connected with the 

 granodiorite intrusions. They are usually pyritic gold- 

 quartz fissure-veins. The veinstones include albite, tourma- 

 line, and fluorite, and the ores often include much blende. 

 They are usually normal fissure veins, one of which is 

 illustrated by a fine coloured plate of part of the vein. 

 Such figures are very useful. The regular trend of the 

 veins is doubtless due to compression during the intrusion 

 of the igneous rocks. 



Ore bodies and veins due to the replacement of lime- 

 stone form a fourth group. They are associated with the 

 igneous rocks, but occur some distance froin the contact. 

 The chief ores are of silver, lead, and zinc ; the two chief 

 minerals are galena and calcite. The most famous of these 

 deposits is the ore-body known as the Bridal-Chamber, a 

 mass of almost pure kerargyrite found in limestone beneath 

 a cap of andesite. The authors regard the ore as older 

 than the andesite, and as formed above a hidden intrusion 

 of porphyry. 



The fifth group of ores are veins connected with the 

 Cainozoic volcanic rocks. They occur in shoots where the 

 lavas have been propylitised, and have no doubt been 

 formed by the action of hot mineral waters at a slight 

 depth below the surface. 



In connection with these veins the authors describe an 

 interesting fluorite vein formed in gneiss by the hot springs 

 at Ojo Caliente. The vein contains barite, limonite, oxide 

 of manganese, silver, and gold. The richest examples 

 assayed contained $75 of silver and $30 of gold to the ton. 

 The mineral waters, owing to their predominant sodium 

 carbonate and chloride, are described as of well-defined 

 volcanic affinities (p. 71), and they supply an interesting 

 addition to the known mineral veins formed by existing hot 

 springs. 



The last group of minerals are copper ores, usually chal- 

 cocite, in the Red Sandstones. The ores are epigenetic. but 

 their distribution shows no relation to that of any igneous 

 rocks ; they contain no gold and very little silver. .'\ 

 coloured plate of these ores includes one in which the 

 chalcocite has replaced coal. In the San Miguel Mine tree 

 trunks 60 feet by 2 J feet in diameter have been almost 

 completely replaced by glance. The widespread occurrence 

 of copper in Red Sandstones of late Palaeozoic and Triassir 

 age has given rise to considerable discussion, and is a very 

 suggestive fact. Dr. Lindgren discussec; the origin of 

 these ores, and rejects the theories of iIk ii precipitation 

 from solution or formation by adsorption : and he concludes 

 that they are due to minute traces of copper, some of 

 which may have been sedimentary, by meteoric waters 

 containing chlorides and sulphate. Mr. Graton offers a 

 somewhat different explanation owing to the lack of evi- 

 dence of descending acid solutions. He regards the chalco- 

 cite as introduced by ascending alkaline carbonates con- 

 taining metallic sulphides in solution. .As in the historic 

 case of Mansfeld, the ores in the .Sandstones appears to b'* 

 most abundant above the richest copper-bearing veins in the 

 underlying rocks, a fact which is in favour of Mr. Graton 's 

 view. 



Mr. E. C. Harden 's bulletin on the manganese deposits 

 gives a summary of the known manganese deposits in the 

 United .States, and brings up to date Penrose's well-known 

 inograph. The author's personal observations were made 

 ring a tour from January to April. 1008. The informa- 

 tion then collected is supplemented from the literature and 

 by chapters on the manganese deposits of other countries 

 and on the chemistry and uses of the metal. The man- 

 ganese ores of the United .States lx>long to four main 

 series. . The first includes residii.nl peroxides left by the 



