154 ANALYSES OF ROOKS, U. S. GEOLOGICAL SURVEY. 
10. ELKHORN MINING DISTRICT. 
[no. 228. 
Rocks collected by W. H. Weed. Described in detail by J. S. Bar-i 
rell in 22d Ann., Part 11^ p. 511. Analyses by H. N. Stokes, record 
No. 1858. 
A. Gabbro, west side of Black Butte. ITessose. Contains labra- 
dorite, augite, hornblende, biotite, and magnetite, with a little quartz 
and zircon. P. R. C. 351. 
B. Andesite, Elkhorn Mountain. Adamellose. Contains plagioclase, 
hornblende, biotite, and pyroxene. P. R. C. 113. 
C. Hornblende-andesite porphyry, southwestern part of the district. 
Contains plagioclase and hornblende phenoerysts in a groundmass of 
hornblende. Pyrite, pyrrhotite, and perhaps magnetite are also 
present. P. R. C. 112. 
D. Quartz-monzonite, Elkhorn. Harzose. Contains labradorite, 
orthoclase, quartz, biotite, hornblende, augite, magnetite, apatite, and 
titanite. P. R. C. 107. 
E. Aplite, north of Black Butte, middle of intrusion. Toscanosd 
tehamose. P. R. C. 110. 
F. Like E, eastern side of intrusion. E and F contain sodaj 
orthoclase and quartz, with a little plagioclase and occasional crystals 
of magnetite and biotite. P. R. C. 111. 
Si0 2 
A1 2 :S 
Fe 2 :i 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 at 100° .... 
H 2 above 100° 
Ti0 2 
?A 
s 
MnO 
SrO 
BaO 
LLO 
47.44 
18.21 
5.37 
6.05 
5.53 
9.98 
2.58 
1.17 
.13 
1.08 
1.38 
.68 
«. 03 
.06 
.08 
.08 
trace 
99.85 
59. 64 
10. 04 
2.33 
4. 35 
2.10 
4.5!) 
3.31 
4.16 
.14 
.69 
1.08 
.49 
".01 
trace 
.05 
.10 
trace 
99.68 
54.50 
17.97 
S. 55 
3.37 
9.36 
2.34 
1.62 
.14 
.96 
.94 
.31 
.63 
trace 
.05 
.06 
trace 
100. 80 
64.31 
15. 44 
2.43 
2.58 
2.21 
4.22 
2.71 
4.09 
.19 
.79 
.71 
22 
trace 
trace 
trace 
.07 
trace 
99. 
E. 
76. 26 
12.94 
.69 
.13 
.17 
1.10 
2.73 
5.26 
.17 
.43 
.11 
.06 
«. 01 
trace 
none 
.07 
trace 
100. 13 
74.61 
13.36 
.83 
.36 
.35 
1.35 
2.49 
5. 70 
.19 
.42 
.11 
.06 
trace 
trace 
trace 1 
.10 
trace 
99. 93 
« May be present either as S or SO :! 
Cr 2 3 , NiO, CO, are all absent. 
