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Page: of 12
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"From reliable information regarding recent developments,
it is evident that the North Star shaft, at a depth of 6300 feet
on the northeasterly dipping vein, has intersected the westdipping Pennsylvania ledge. The 6000-foot east drift from the
North Star shaft is also reported to have encountered this vein.
As far as can be ascertained, the exploratory work undertaken
by the North Star Company has to date (1918) failed to find a
continuation of the Nortn Star vein beyond the Pennsylvania
vein, but it is said that the latter vein continues downward on
its regular dip. The Pennsylvania vein has also been developed
southward by the North Star Company, who have also recently
purchased the Bonivert ground of 100 acres lying south of the
Pennsylvania-W. Y. O.D. claims belonging to the Empire Company. The Empire Company, a year or SO ago, acquired the
property of the Golden Treasure Mining Company, which is
bounded on the west by the bonivert ground, on the west and
north by the W. Y. ©. D., on the east by the Cassidy-Nevada
claim, and on the south by the property of the Bullion Con-solidated; and within the past few months have purchased the
Berriman holdings comprising 160 acres of agricultural land.
This property is bounded on the north by the Bonivert property of the North Star Company, on the east by the Bullion,
and on the west by a narrow strip of agricultural ground separating it from the Omaha claim of the Empire West group.
The Berriman property lies about one mile north of the Allison Ranch Mine. The foregoing facts lead tothe conclusion that the
Pennsylvania-W. Y. O. D. fissvre is one of the main fissures
of the district, and that the Allison Ranch vein is the southerly
continuation of this fissure system.
"The veins lying in the hanging wall side of the Allison
Ranch are the southerly continuation of the Omaha fissure
system, which belongs to the west-dipping, northand southstriking general group that includes the Pennsylvania and the
parallel Empire veins.
"The general conclusion is that all the fissures of the
Grass Valley district have been formed during the same geologic period by compressive stresses exerted from different
directions.
"The total displacement or upward movement of the hanging wall (reverse or overthrust faults) which has taken place
along the main fissures is comparatively small, with the p> ~
sible exception of the Eureka-Idaho fracture. Extensive sheeting
of the granodiorite and other igneous rocks has occurred,
resulting in not only parallel veins, but in the formation of
minor fractures between the main lines of faulting. Thus the
compressive stresses have a relieved by this sheeting,
and the movement nas not beenéxcessive along any one fissure
or line of weakness, For this reason the veins of the Grass
Valley district are narrow or small, when compared with the
veins along the Mother Lode, Little mechanical alteration of
the rock wall has taken place, and the fresh country rock lies
very close to the vein, with little ‘gouge’ separating them. ..
"As a rule the fissures in the diabase porphyrite seem to
be less definitely confined to one plane than are the same fissures after passing into the granodiorite; in other words, the
veins have more branches and are also slightly larger than in
the granodiorite. The contacts of the various rocks have not
been lines of weakness and therefore have had little influence
on the fissure systems. The notable exception to this is the
Eureka-Idaho, where the fissure follows the contact of the serHistory of Nev
Published ir
W.B. Lardner
pentine and gabbro-diabase, Here the upward movement of the
hanging wall has been comparatively large, and the mechanical
and hydro-thermal alteration has been more extensive than elsewhere in the district.
"Post-mineral faulting and. sheeting has taken place, and
most of the veins of the district show evidence of slight displacements or bending by these barren cross seams, which
have a general strike of east-northeast and a steep dip. These
seams now act as water-courses for the circulation of vadose
or surface waters."
VEIN SYSTEMS
"The vein systems are the result of the filling of the
previously described fissure systems by quartz, carrying gold
and auriferous sulphides, . . .The slipping of one irregular
and undulating wall of the fissure on the other resulted in
open spaces forming in the fissures, through which circulated hot solutions carrying silica, hydrogen sulphide, carbon
dioxide, and gold and other metallic minerals. These thermal
waters were in all probability surface waters which penetrated