92 ANALYSES OF ROCKS AND MINERALS, 1880-1908. 
10. ELKHORN MINING DISTRICT. 
Rocks collected by W. H. Weed. Described in detail by J. 8. Barrell in 22d Ann., 
pt. 2, p.511. Analyses by H. N. Stokes, record No. 1858. 
A. Gabbro, west side of Black Butte. Hessose. Contains labradorite, augite, horn- 
blende, biotite, and magnetite, with a little quartz and zircon. P. R. C. 351. 
B. Andesite, Elkhorn Mountain. Harzose. Contains plagioclase, hornblende, bio- 
tite, and pyroxene. P. R. C. 413. : 
C. Hornblende andesite porphyry, southwestern part of the district. Contains pla- 
gioclase and hornblende phenocrysts in a groundmass of hornblende. Pyrite, pyrrho- 
tite, and perhaps magnetite are also present. P. R. C. 412. 
D. Quartztmonzonite, Elkhorn. Harzose. Contains labradorite, orthoclase, quartz, 
biotite, hornblende, augite, magnetite, apatite, and titanite. P. R. C. 407. 
E. Aplite, north of Black Butte, middle ofintrusion. Toscanose-tehamose. P.R.C. 
410. 
F. Like E, eastern side of intrusion. E and F contain soda-orthoclase and quartz, 
with a little:plagioclase and occasional crystals of magnetite and biotite. P. R.C. 411. 
A B Cc D. E F 
SiO oi xa spose ways eee eerpoeenecemne sn eenansitacreesotine 47.44} 59.64] 54.50] 6431) 76.26 74.61 
ADO 9... socmicccre ce ered sees Beeatemaue eee 18. 21 16.64] 17.97] 15.44] 12.94 13. 36 
POO secre cisisissce sels 5.37 2. 33 8.55 2. 43 69 83 
FeO. 6.05 4.35 NWeeseanse 2. 58 13 36 
MgO 5. 53 2.10 3. 37 2.21 17 35 
CaO. 9. 98 4. 59 9. 36 4.22 1.10 1.35 
NaO.. --| 2.58 3.31 2.34 2.71 2.73 2, 49 
KO cre sponte se Etemioe antes SeaeeRermeneE see Sal 1.17 4.16 1. 62 4.09 5.26 5.70 
HF OF 86 LOO? cya are ciesercescenie nrctanseieis so rays cigR emo ieee sialall +13 14 14 .19 Feld 19 
H20 above 100° --| 1.08 69 -96 .79 - 43 42 
i102... 1.38 1.08 +94 +71 11 ll 
P20s. 68 49 31 . 22 06 06 
Bevce a.03| @.01 63 | trace} ¢@.01 trace 
MnO 06 | trace | trace | trace! trace trace 
OE Os ics ds ses yeaaya is eistodeaese Sietadslslonaiae Dacca mine ene eeaaA 08 05 -05 | trace | none trace 
BA Ouse echoes Ota Tae syed shane hagdysisintsateisiamne neice 08 10 +06 07 07 10 
Dis bras esydecbed ld hbiabiereieciaie karbincrecdi oS ats ines Onin trace | trace | trace | trace | trace trace 
99.85 | 99.68 | 100.80 | 99.97 | 100.13 99. 93 
@ May be present either as S or SO3. 
Cr2O3, NiO, COz are all absent. 
The following rocks were also analyzed for Weed, who supplies the petrographic 
data: : 
G. Grossularite hornfels. Contains diopside, grossularite, calcite, and quartz. 
H. Lime-enriched gabbro. Contains labradorite, pyroxene, and scapolite. Anal- 
yses G, H, by W. T. Schaller, record No. 2158. 
I. Grossularite hornstone, a modified marble. Contains calcite, chlorite, grossula- 
rite, and augite. 
J. Mica diorite, the normal batholith rock. Contains labradorite, soda orthoclase, 
quartz, biotite, hornblende, augite, magnetite, and apatite. Analyses I, J, by E.C. 
Sullivan, record No. 2195. In these the TiO, and P.O; were not separated from the 
alumina. 
