220 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
source of chlorides in the waters. As chlorides are found among the volatile sub¬ 
stances emitted during eruptions, it seems most probable that the magma of any 
rock which now contains chlorine contained more of it before the pressure in the 
magma was reduced by movement to a higher level in the earth's crust, and that 
chlorine, mingled with magmatic water, was one of the constituents which escaped. 
SULPHATES. 
• That sulphates were present in the waters is indicated by the almost universal 
occurrence'of celestite or sulphate of strontium in the veins (pp. 124, 125), as well as 
by the more sparing development of barite. Celestite is fairly soluble in water, the 
proportions given varying from 6,895 to 10,101 parts of water (at 15° C.) for 1 part 
of celestite. It is, however, much more soluble in water containing sodium chloride, 
1 part of the sulphate dissolving in 457 parts of water with 15 per cent NaCl. rt 
Celestite is very much more soluble than barite, of which 1 part dissolves in 429,700 
parts of water. 
The presence of celestite rather than barite in the veins is a very unusual 
occurrence in mineral veins, although known in a few cases from France and Hun¬ 
gary. The granites and phonolites, as well as the basic dikes of Cripple Creek, 
contain a very small amount of baryta, varying from a trace up to 0.18 per cent, 
and practically only a trace of strontia, occasionally rising to 0.07 per cent. On 
the other hand, the majority of the latite-phonolites and the syenite are much richer 
in both constituents. Six analyses of these show from 0.13 to 0.24 per cent baryta 
(average of the six, 0.19 per cent BaO) and from 0.03 to 0.21 per cent strontia 
(average of the six, 0.12 per cent SrO). Strontia is here present in much larger 
quantities than is usual in rocks, and the proportion is exceeded only in certain 
leucite and analcite rocks, monchiquites, tinguaites, and sjrnites from Montana and 
Wyoming. 6 The average percentage of baryta in rocks, as calculated by Clarke, 
is 0.11 per cent baryta and 0.04 per cent strontia/ The latter figure is probably 
higher than the actual average. 
Strontia exists, moreover, in many thermal spring waters in amounts exceeding 
those of baryta. Salts of strontium are known from many spring deposits, such as 
Vichy, Carlsbad, and Hammam-Meskoutine, and celestite is deposited by the hot 
springs of Bourbon-1' Archambault/ From the data given there is, therefore, some 
reason to suppose that the strontia may have been leached from some of the intrusive 
rocks at Cripple Creek, but as celestite occurs in the veins throughout the district, 
irrespective of the particular wall rock, it follows that this leaching has probably 
not taken place within the zone opened by mining, but perhaps rather in intrusive 
latite-phonolite and syenite at greater depths. 
Calcium sulphate is not found as a primary constituent of the veins, but the peculiar 
occurrence of large masses of gypsum associated with pyrite and fluorite at the Deer- 
horn mine (p. 284) leads to the belief that waters rich in sulphates of the alkaline 
earths appeared as one of the latest phases of thermal activity. The closest analogy 
a See Comey’s Dictionary of Solubilities. 
b Clarke, F. W., Analyses of rocks: Bull. U. S. Geol. Survey No. 228, 1904. 
cOp. cit., p. 17. 
d Daubree, A., Les eaux souterraines a l’epoque actuelle, vol. 2, 1887, p. 18. 
