112 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
some of which are an inch in diameter. This altered rock has a con- 
choidal fracture. The microscope shows the rock to be composed of 
interlocking quartz grains in which there is some finely divided mate- 
rial, possibly of a clayey nature. The areas once occupied by feldspar 
phenocrysts contain a slightly higher percentage of this turbid sub- 
stance, while some sagenitic webs of rutile indicate the former pres- 
ence of biotite. Associated with the silicified porphyry are white 
kaolinized facies which are locally stained red or purplish by iron 
oxides. Numerous other areas of silicified porphyry have been located 
by prospectors, but at none was gold visible to the eye. although many 
panned gold. The boundary between the silicified and unsilicified 
porphyry is usually sharp. Strong iron stains and some dendrites of 
manganese dioxide are associated with the gold. The iron stains 
probably point to pyrite as the original source of tin 4 ore, an inference 
strengthened by the presence of gypsum. This mineral is rather 
closely associated with the on-, in some places filling cavities in it and 
in others filling joint and fracture planes in the country rock. The 
gypsum occurring in the country rock is fibrous, the fibers being set i 
at right angles to the walls. The residual soil near ore deposits is 
locally cemented by gypsum. Gypsum was probably formed by the 
interaction of iron sulphate, set i'v^ by the oxidation of pyrite, and 
of calcium-bearing solutions derived from the decomposition of the 
plagioclase of the monzonite porphyry. Quartz veinlets cut the sili- 
cified porphyry, but these are reported to carry no values. Certain 
clear phenocryst-like quartz areas indicate that silicification contin- 
ued after the removal of the phenocrysts usual in monzonite porphyry. 
In the deepest shafts the silicified porphyry holds its width, although 
up to the time of this examination the values were low except at tin 
surface. At the Gold Reed mine good values have been obtained in a 
kaolinitic substance found in the cavities of the silicified porphyry at 
the 100-foot lewl. 
Iron pyrite has been encountered on the 150-foot level at the Gold 
llvvd mine, disseminated in unsilicified monzonite porphyry. Its 
assay value is low. Several thin veins of pyrite occur on the lowei j 
levels of the Diamond No. 2. These veins are banded and vugs occui 
here and there in the center. This pyrite is said to assay $35 in golc j 
per ton. 
The silicified monzonite porphyry has been considerably faultec 
and slickensides and breccias are common. At the Gold Reed min< 
the faulting has been very complex, and wedge-shaped cavities 
which reach a maximum length of ."> feci, appear to be <\w^ to fault 
ing. At the Chief Kawich mine the faults strike X. 50° W., paralle 
to the silicified-porphyry boundary, and dip 80° SW. At the Dia I 
mond No. 2 the faults dip i:» E. The step-like offsets in the silici 
fied porphyry on which the Chief Kawich and the Gold Reed mine 
