1914] 



Lawson: 



Ore Deposition by Meteoric Waters 



239 



and along the contact of the porphyry and limestone, then there would be a 

 mingling of the solutions and localized chemical activity in the vicinity of the 

 fault and porphyry, "36 



Not a word about magmatic waters ! And yet a most typical 

 occurrence of contact ores in the instructive southwest. 



Ransome's argument in favor of recognizing the role that may be 

 played by meteoric waters in a synclinal trough abutting upon a hot 

 intrusive mass is admirably set forth, but only as a possibility. To 

 me it is a result which flows inevitably from the simple premises of 

 structure, the recognition of ground-water and the hot mass. 



Clifton-Morenci. — In the Clifton-Morenci district, so well described 

 by Lindgren, 37 the dominant structural features are due to intrusion 

 and faulting rather than to folding. The sedimentary series consists 

 of quartzite, limestones, and shales ranging from the Cambrian to the 

 Cretaceous resting on an eroded surface of granite. Both granite and 

 sedimentary strata have been invaded by a mass of granite porphyry. 

 The chief areas of sedimentary rocks and the porphyry occupy a 

 sunken tract between two granite buttresses. In this sunken territory 

 lies the principal ore-bearing ground. 



' ' The two principal granite areas, Coronado and Copper King Mountains, 

 occupy positions of resistant buttresses between which the fractured sediments 

 have settled. In the porphyry stock there are undoubtedly many faults which 

 have not been recognized. 



"The fault planes divide the sediments into blocks of varying extent and 

 shape; these are nearly always monoclinal and have gentle dips prevailing to 

 the west and north, rarely to the south and east; they average about 12°, while 

 dips of more than 30° are very seldom encountered, "as 



This sunken tract would afford the most favorable conditions for 

 the convergence of meteoric waters upon the central porphyry mass. 

 Near Morenci the strata are synclinally sagged and the syncline is cut 

 off by the porphyry. 39 The ore is partly in the metamorphic contact 

 zone of the sedimentary strata and partly in fissures both in the 

 adjacent porphyry and also in the sediments. Where these fissures 

 cut the limestone the walls are altered in a manner analogous to the 

 contact metamorphism. 



36 Op. tit., pp. 152, 153. 



M Op. tit. 



as Op. tit., p. 89. 



39 Op. tit., pi. I, sect. D-I). 



