SEDIMENTARY FORMATIONS. 
27 
Mineralogical composition of fresh and altered Homestake limestones, calculated from 
' chemical composition. 
Fresh lime- 
stones. 
Altered limestones. 
Average 
of com- 
mon type 
of altered 
limestone 
(H,I,J). 
Mineral. 
A. 
1 
B. 
H.o 
I. J. 
K. 
N. 
( alcite 
78.30 
4.90 
2.64 
72.40 
2.58 
0.50 
24.77 
18.78 
1.40 
11.61 
1.50 
15.55 
20.52 
3.90 
3.09 
6.30 
19.00 
4.32 
70.80 
3.10 
7.92 
21.10 
"'34.'i4' 
1.93 
Kaolin 
Chert 
Actinolite 
13. 16 
8.86 
11.52 
Diopside 
2.16 
15.57 
5.24 
.86 
1.94 
9.02 
5.19 
Serpentine 
4.97 
11.20 
6.76 
3.14 
5.66 
Andradite 
4.78 
5.96 1 
6.03 
8.65 
9.86 
.50 
"'i'.ob' 
l.n 
2.62 
3.48 
Wollastonite 
" 16.77 " 
4.76 
16.24 
8.34 
1.31 
3.13 
36.15 
8.89 
2. 62 
5. 10 
6.81 
3.89 
3.93 
7. 66 
9. 60 
2.63 
Albite 
23.02 
5.74 
1.12 
.56 
.69 
3.74 
3.48 
5.92 
2.55 
Magnetite 
1. 16 
2.03 
i 
1.00 
.62 
.31 
.31 
4. 96 
1.24 
.41 
Pyrite 
• 12 
.16 
.84 
.59 
Water 
1.54 
.81 
2.21 
.59 
2.32 
3.53 
1.52 
Siderite 
.20 
99.23 1 
97.17 
99.09 
98.52 
99.82 
99.31 
99.14 
99.18 
a Contains glass which has been calculated in terms of minerals. 
Introduction of ore. — The introduction of ore took place after the 
development of the silicated contact phase, as is demonstrated by 
its occurrence in fissures that intersect this phase. The sili- 
cated contact phase is found also along parts of the contact whore 
ore is absent. The introduction of ore-bearing solutions effected 
further metamorphism of the limestone of approximately the same 
sort, nearly all of the minerals found at the barren contacts being 
duplicated w r ithin and adjacent to the ore itself. (See analyses 
above.) Apatite, amphibole, biotite, pyrite, and garnet are more 
abundant in association with the ores than elsewhere in the contact 
phase, while albite and orthoclase appear in the contact phase and 
not in the ores. Beyond this it has not been found possible to sepa- 
rate the metamorphic effect of the ore-bearing solutions, aside from 
its deposition of ore, from the earlier contact effect of the andesite, 
although it is thought likely that additional careful field work with 
this object in view might lead to the discovery of further criteria for 
their separation. The replacement of the limestone by ore is dis- 
cussed in connection with the origin of the ore (pp. 75-79). 
Normal contact 'phase. — The following paragraphs are devoted to 
the silicated contact phase, which is described as a unit, without 
regard to the extent to which it has been developed under the influ- 
ence of the first contact of the andesite or under the influence of later 
ore-bearing solutions, although the former is unquestionably dominant. 
