MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK IIQ 
The ore-zone is at least 100 feet wide, striking north 30° east and 
dipping almost vertically. The deposit is banded and disseminated ; 
grading from almost solid magnetite, mixed with pyrite and pyrrho- 
tite, in the center, to lean ore toward the walls, and finally into light- 
colored, syenitic rocks, quartz-bearing in places, and highly pegma- 
titic in an irregular manner in other places. 
The lean ore is essentially a magnetite-rich syenite, with a proto- 
clastic structure (see plate 8, figure 4) involving granulation of the 
margins of the feldspar grains, bending of grains, wedge twin- 
ning and strain effects; all primary deformation phenomena due 
to movement before complete solidification was effected. The mag- 
netite in the lean ore is interstitially distributed, cutting and in part 
replacing the ferromagnesian minerals and the feldspars, and is 
clearly of very late magmatic stage. Koeberlin*** recognized the 
general relationships and correctly assigned the magnetite to the very 
closing stages of crystallization. 
The ore has been described in a report by John Birkinbine and 
W. B. Kunhardt*®’ as consisting of compact, moderately fine 
grained magnetite, in a gangue composed mainly of quartz, horn- 
blende, feldspar, apatite and mica, and more or less pyrite and 
pyrrhotite. 
Hoffman (op. cit.) stated that exploratory work had blocked out 
at least $,c00,000 tons of ore, while a fair examination of the prop- 
erty showed “ not less than three times that amount in the mines.” 
According to N. S. Shaler *°° the deposit is 4000 feet in length, 
75 feet in width, and 1500 feet in depth. On this basis Shaler esti- 
mated 50,000,000 tons of ore, 75 per cent of which is minable! 
Almost as optimistic is the estimate of F. W. Gordon *® who stated 
“extensive workings and explorations show the deposit of ore to be 
one of the greatest in magnitude that has ever been developed in 
America . . . and warrant an estimate of the quantity of ore 
in easy reach to be not less than 30,000,000 tons.” 
These estimates are undoubtedly far in excess of the truth, as the 
really workable ore is not over 10 or 15 feet wide; some of the 
leaner ore could now be recovered by modern methods of magnetic 
concentration, but the optimistic estimates of Hoffman, Shaler and 
Gordon will undoubtedly never be realized. 
164 Koeberlin, F. R. The Brewster Iron-bearing District of New York; 
Econ. Geol., v. iv, D. 713-54. 1900. 
165 Cited by W. H. Hoffman, Trans. A. I. M. E., 20: 602. 18601. 
166 Cited by W. H. Hoffman, op. cit. 
167 Cited by W. H. Hoffman, op. cit. 
