Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

quadrangle (tables 1 and 3) were from chilled margins of the dikes, which tend to be less
altered. These two analyses show unusual chemical characteristics, and significant
differences indicate the dikes have variable chemistry. Both samples have very high LOI
(3 to 5 percent) indicating abundant volatile water, probably related to strong
hydrothermal alteration. Samples 05-03 and 05-680 are classified as latite and dacite,
respectively, on the basis of the chemical classification of De la Roche and others (1980).
Thus, the chemical characteristics of the andesite dikes show significant chemical
variability most likely related to different degrees of contamination and/or magma
Table 3. Whole-rock chemical comparison of Tertiary () andesite hybrid dikes with
average rhyolite and andesibasalt. [Commercial analyses by ALS-Chemex, Sparks,
Nevada]
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Rhyolite Ta-1 Ta-2 Andesibasalt
SiO 2 71.66 54.01 60.91 53.44
Al 2 O 3 13.80 15.04 15.06 16.93
Fe 2 O 3 1.57 8.02 1 5.47 1 3.75
FeO 1.16 - - 5.58
CaO 1.38 3.88 3.18 8.36
MgO 0.47 5.02 2.83 4.76
Na 2 O 3.81 3.12 4.10 3.04
K 2 O 3.89 4.01 3.17 1.24
TiO 2 0.32 1.11 0.77 1.19
MnO 0.06 0.13 0.10 0.15
P 2 O 5 0.10 0.54 0.35 0.23
H 2 O + 1.29 4.72 2 3.32 2 0.86
H2O - 0.65 - - 0.52
TOTAL 100.16 99.60 99.26 100.05
Rhyolite - Average rhyolite- CLAIR database, 293 analyses (De la
Roche and others, 1980)
Ta-1 05-03 Tertiary () andesite hybrid dike (latitic)
Ta-2 05-680 Tertiary () andesite hybrid dike (dacitic)
Andesibasalt - Average andesibasalt- CLAIR database, 918 analyses (De
la Roche and others, 1980)
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1 Total Fe as Fe 2 O 3
2 Reported as LOI- Loss On Ignition (volatiles)
107