90 
MINING GEOLOGY 
Government report on the ores, by Lindgren, Graton and Gordon, 
categorically asserts that, “The ore is the result of contact meta¬ 
morphism of the limestone by the monzonite dikes.” 
The monzonite dikes with which the ores are claimed to be 
genetically associated are numerous on the mesa. While some of 
them traverse the country as huge, cyclopean walls for distances 
of a dozen miles or more, others are only a few feet in width 
and do not rise above the ground. How extensively such insig¬ 
nificant eruptives could metamorphose and mineralize the adja¬ 
cent limestones may be left to the imagination. On perfectly 
fresh contacts the metamorphism effects seem almost nil, and min¬ 
eralization is also inappreciable. Moreover, the occurrence of 
these ores is not always confined to the sides of the dikes. There 
are magnetite ores in the same region which lie in fault-planes in 
which no eruptive rock is in evidence. 
These intrusive sheets are doubtless regular fault dikes, a phe¬ 
nomenon quite common throughout this region. Although the 
Figure 9, Pre-Cretacic Dike and Ore Bodies on Chupadera Mesa 
limestones are sharply turned up against the dikes on either side the 
structure is in no sense an anticlinal one, as the Lindgren report 
claims. 
At the Dios Springs group of deposits, near the north end of 
the Mesa, a score of miles from Willard, on the New Mexico Cen- 
