ransome] DEPOSITS OF RED MOUNTAIN REGION. 215 
in it as fine veinlets and irregular bunches, and the mass generally 
contains much finely disseminated pyrite. The nature of this altera- 
tion has already been fulty described on pages 124-131. 
The Silverton breccia is cut by numerous dikes, sills, and irregular 
intrusive masses of andesite. Intrusive plug-like masses of mon- 
zonite-porphyry, carrying conspicuous phenocrysts of orthoclase and 
quartz in a fine gray groundmass, are also common. Such a mass is 
exposed at the roadside between the Yankee Girl and Guston mines. . 
The general character and distribution of the typical Red Mountain 
ore deposits have already been discussed (pp. 103-104:), and it is only 
necessary in this place to proceed directly to the detailed descriptions 
of the various mines. 
Yankee Girl mine. — The Yankee Girl ore body was discovered in 
the autumn of 1881 by John Robinson. 1 In 1882 it was being opened 
by 1 wo shafts, each about 50 feet deep. At that depth the ore is said to 
have been about 9 feet wide, consisting chiefly of galena with bunches 
of chalcopyrite, and carrying as much as SO ounces of silver and 05 
per cent of lead. The ore body was rapidly opened up and proved 
large and rich. In 1883, with a thousand feet of drifts and shafts, 
about 3,000 tons of ore were extracted, with an average value of nearly 
$150 per ton. The product for this year is given in the Mint report 
as $400,000, and the ore is said to have carried a high percentage of 
lead. In 1884, according to the same authority, the mine was pro- 
ducing about 40 tons a day, which, at *15<> per ton, would be something 
over $2,000,000 for the year. This, however, is obviously an excessive 
estimate. In L 88 7 the output is not known, but was probably much 
less than #200,000. In L890 ii is credited with $1,352,994, the silver, 
as usual, being given at its coinage value and no return being made for 
copper or lead. In L891 the product is given as $601,465 in gold and 
silver, and in L892 it had fallen to $95,445. Of this amount $5,200 
was in gold, $48,333 in silver (coinage value), $3,632 in lead, and 
$38,280 in copper. Thus these fragmentary records show that in the 
course of ten years' working the ore changed, within a vertical dis- 
tance of 1,000 feet, from one carrying chiefly galena to one rich in 
copper. 
This has probably been the most widely known and most produc- 
tive mine in the Red Mountain district, although closely rivaled by 
the Guston. But it was an expensive mine to operate on account of 
the irregular form of its large ore bodies, the abundance and corrosive 
activity of its waters, and the necessity of hoisting and pumping 
through deep shafts. These adverse conditions, in conjunction with 
a falling off in the value of the ore and the decline in silver, finally 
caused the mine to shut down about 1896. 
The Yankee Girl ore body lies in Silverton breccia (possibly extend- 
1 T. A. Rickard (Trans. Am. Inst. Min. Eng., Vol. XXVI, 1896, p. 842) states that the discovery 
was made in August, 1882, by Andrew Meldrum. This is apparently erroneous. 
