PROCESSES OF ALTERATION. 
189 
METASOMATIC CHANGES IN LATITE-PHONOLITE. 
The altered phases of the latite-phonolites are best studied at the Golden 
Cycle and Vindicator mines. Pyrite and dolomite are the minerals most abundantly 
introduced, but the alteration is not always uniform, so that in some specimens 
either of these two minerals may be lacking. There is usually a development of 
sericite and adularia. 
The discussion may best begin by a description of the altered latite-phonolite 
of the dike along the Independence lode in Stratton’s Independence mine, collected 
in the Washington shaft by Cross. The analysis of the rock was made by W. F. 
Hillebrand in 1894, but has hitherto been unpublished. The rock is a yellowish-gray, 
fine-grained porphyritic latite-phonolite, with close relationship to the phonolites. 
There is a tendency to platy structure, emphasized by numerous small cavities of 
dissolution coated with crusts of fluorite, adularia, pyrite, and a soft material which 
seems to be a mixture of sericite and kaolin. Throughout the rock are small specks 
of fluorite and pyrite. Under the microscope the large phenocrysts of orthoclase 
are little altered; the groundmass consists of narrow laths of generally unaltered 
orthoclase, between which lies an interstitial mass of fine sericite fibers clearly 
replacing the analcite, sodalite, or nepheline which, in the fresh rocks, are apt to 
occupy this position. Small crystals of pyrite are distributed throughout. Spaces 
of dissolution are plentiful and are filled with adularia, while the central part is 
occupied by fluorite. In one place fibers of sericite project into the adularia. No 
biotite, amphibole, or pyroxene are visible, and these minerals have no doubt been 
thoroughly decomposed. Neither are there any carbonates in this rock, though 
other specimens of the same dike collected by us contain a considerable amount of 
these minerals replacing ferromagnesian silicates. 
Analyses of altered and fresh latite-phonolites. 
[Analysts, W. F. Hillebrand (A. and B), W. T. Schaller (C.).] 
A. 
B. 
c. 
A. 
B. ! c. 
56. 74 
59.38 
57.91 
P 2 Ch. 
.25 
.08 
20.30 
19. 47 
so 3 . 
.37 . 
1.06 
1.60 
Cl. 
7° 
FeO. . 
1.19 
F. 
Undeter- 
MgO . 
.23 
.36 
.33 
mined. 
S. 
1.12 
CaO. 
.57 
1.96 
.81 
MnO. 
None. 
.15 . 
Na 2 0. 
.62 
7.80 
. 45 
1 BaO. 
.19 
. 13 
K 2 0. 
13.30 
5.83 
13.35 
SrO. 
Trace. 
.03 . 
H 2 0- . 
.33 
.11 
Li 2 0. 
Trace. 
Trace. 
h 2 o+. 
1.15 
.69 
FeS 2 . 
4.65 
Ti0 2 . 
.58 
.58 
ZrD 2 . 
.07 
.10 
co 2 . 
. 66 
100.10 
100.05 . 
A. Altered latite-phonolite, Washington shaft, Stratton’s Independence mine. 
B. Fresh latite-phonolite, west slope Bull Cliff (Petrographic reference collection No. 624). 
C. Altered latite-phonolite, level 11, vein No. 3, Vindicator mine (Cripple Creek collection No. 687). 
13001— No. 54—06-14 
