Chap. XXXV. ] jabalpur district. 81 3 
It depends on the degree of completeness to which the replace- 
ment has been carried as to whether the ore is of commercial value cv 
not. When the replacement has not been pushed far enough the ore is 
apt to be very siliceous owing to the large proportion of the grains of 
quartz that have escaped replacement. When, however, the replace- 
ment has been pushed to its utmost limit, an ore may be produced that 
is practically free from quartz. This is well illustrated by the analyses 
given below. The pyrolusites they represent are from four different 
localities, and have all been formed at the surface by the replacement 
of quartzites. It will be noticed that in the sample from Gosalpur the 
process of replacement has been pushed nearly to completion, so that 
there is now only 1"85% of silica left, whilst the percentage of manga- 
nese has risen to 56"80. In the Mansakra sample the replacement has 
been carried nearly as far, but replacement by iron in the form of 
limonite has accounted for a somewhat larger proportion of the change 
than has replacement by manganese. In the Paharewa and Mangeli 
sample the replacement is much less complete, 17";: 0% of silica being 
left in the former case and ir35% in the latter. Here also about half 
of the replacement has been effected by iron and about half by man- 
ganese, although the presence of iron in such large amount would not 
have been suspected from the physical aspects of the ore. These two 
latter samples showed residual sihceous matter in quantity, whilst even 
the Gosalpur sample showed occasional quartz. 
Numbf;!- of sample. 
63 ' 
68 
A.6 
A. 16 
Locality. 
Mansakra. 
Paharewa. 
Mangeli. 
Gosa ipur. 
Character of the ore. 
Pyrolusite 
with 
limonite. 
Pyrolusite. 
Pyrolusite 
with psilome- 
lane and limo- 
nite. 
Pyrolu- 
site. 
MnOj 
MnO ..... 
Fe.Oj . . • . . 
Bab 
SiO, (combined) 
SiO;; (free) .... 
PjO', 
As,,6, 
HjO (combined) 
Moistmre at 100° C. . 
34-92 
2-46 
44-96 
trace 
2-13 
2-27 
0-50 
0-44 
37- 07 
1- 53 
38- 06 
2- 48 
14-82 
0-31 
012 
37-90 
213 
37-42 
010 
5- 35 
6- 00 
0-655 
7 - 00 
0-60 
88-58 
1- 03 
2- 28 
1-61 
1- 75 
010 
0 355 
nil 
2- 60 
0-40 
