My experiments with volcanoesJaggar, Thomas Augustus
Science
My experiments with volcanoes
Jaggar, Thomas Augustus
Geologists -- Biography; Volcanoes
I was employed to examine the Quartette Gold Mine, and the geologic
mystery of the origin of a million dollars in dirt between a level
200 feet down and another at a depth of 500 feet. The million dollars
was along a crushed, slipped, so-called vein, where a fault followed
the upright bedding of just such gneisses, granite dikes, and schists
as had made Crooks Complex in the Bradshaws. Where gold was richest,
minerals were richest--beautiful orange-colored wulfenite, green
chrysocolla, blue azurite, onyx, quartz, and calcite. Everywhere were
quantities of gouge, or crushed clays, from grinding walls. Native gold
particles were distributed through all this.
The schists were filled with lava fissure fillings, and the mine
was where this pattern of bands was interrupted by a very ancient
greenstone or basalt body. Hot fluids of the volcanic period, deep
underground, had accompanied fault slipping or fracture where the ore
was, the vertical fault parallel to the upright layers and across the
greenstone contact.
Ore and gold particles were directly related to fracture, to the fault
slipping on an upright crack of one mountain block against another,
to the hot vapors depositing the mineral collection, and to renewed
crushing and sliding on the mountain blocks. This was during or
following some part of the volcanic period when all the cracks were
injected with andesite lavas, or what the miners call porphyry. The
origin of the minerals was in lead and copper sulfides which lie deeper
down.
A hundred miles to the northeast is the Grand Canyon, and all around
are granite mountains, just as in Arizona. These Searchlight schists
are the same Algonkian ancient strata, recrystallized and granitized,
that make the inner gorge of the canyon, and are traversed up cracks
by volcano-making lavas, such as dot the north bank of the canyon
with crater cones. Above in the canyon are the horizontal strata from
Cambrian up to the Coal Measures and beyond. The vast maze of castles
and turrets is a net of branch valleys of the Colorado, trenching
through these old seabed deposits.
Including Searchlight ore, the whole history going backward is top
country desert, deep trench, strata piled in rivers and sea bottoms for
500 million years, and lastly faulting and cracking that squirted steam
and made gold minerals over and over again during the last 100 million
years. There were at least a dozen revolutions that lifted and lowered
mountain ranges and continents for 2,000 million years, and the remains
of iron-eating bacteria and of seaweeds and other living things that
go back for 1,500 million years. Through it all are granite injections
as a process, as a mystery, going over the whole range of years in
different ages, and meaning what?
Public-domain text, read in full here on John Shaqi.
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