Silicon Smelters is located in the Limpopo province South Africa,
8kms South of Polokwane and 360kms North of Johannesburg.
The first mining operations started in the 1950’s at
Witkop (“white hill”) and consisted of blasting,
extracting and crushing quartz.
Silicon Smelters is the largest operation of its kind in the
western world. 183,000 ton per year.
The general public are not allowed to enter this quartzite
mining area. I did some research and find an outcrop (koppie) not
far from Witkop with 3 different rocks. 1. quartzite, 2. sandstone,
3. sedimentary rocks.
There is a service road that goes to the cell tower, at
additional waypoints use the coods for turn. The last section of
the cement road is steep but a nice concrete road. You can park
your vehicle next to the tower. Big concrete parking area. On the
same koppie (outcrop) is two traditional caches. (GC16GVQ) by
Jakkals en Eendjie and (GC1RF3Y) by hennieventer.
This site is part of The Pietersburg greenstone belt and
contains the Eersteling, Mt. Maré, Mt. Robert and Roodepoort
goldfields, with the first two having been exploited until recently
at the Eersteling and Zandrivier mines. The Witkop silica deposit,
just south of Polokwane, is a greenstone hosted quartz vein, mined
by Silicon Smelters and used to produce silicon metal. As this
deposit is almost exhausted, other silica deposits are increasingly
used to supply raw material for this plant. Two significant silica
deposits are known in the east of the province, near Gravelotte and
Phalaborwa.
Greenstone belt diagram
Quartzite is most of the time a hard metamorphic rock which was
originally sandstone. Sandstone is converted into quartzite through
heating and pressure usually related to tectonic compression within
orogenic belts.
Pure quartzite is usually white to grey, though quartzites often
occur in various shades of pink and red due to varying amounts of
iron oxide (Fe2O3). Other colors, such as yellow and orange, are
due to other mineral impurities.
When sandstone is metamorphosed to quartzite, the individual quartz
grains recrystallize along with the former cementing material to
form an interlocking mosaic of quartz crystals. Most or all of the
original texture and sedimentary structures of the sandstone are
erased by the metamorphism. Minor amounts of former cementing
materials, iron oxide, carbonate and clay, often migrate during
recrystallization and metamorphosis. This causes streaks and lenses
to form within the quartzite.
Metamorphic rock
Metamorphic rock is the result of the transformation of an
existing rock type, the protolith, in a process called
metamorphism, which means "change in form". The protolith is
subjected to heat and pressure (temperatures greater than 150 to
200 °C and pressures of 1500 bars[1]) causing profound physical
and/or chemical change. The protolith may be sedimentary rock,
igneous rock or another older metamorphic rock. Metamorphic rocks
make up a large part of the Earth's crust and are classified by
texture and by chemical and mineral assemblage (metamorphic faces).
They may be formed simply by being deep beneath the Earth's
surface, subjected to high temperatures and the great pressure of
the rock layers above it. They can form from tectonic processes
such as continental collisions, which cause horizontal pressure,
friction and distortion. They are also formed when rock is heated
up by the intrusion of hot molten rock called magma from the
Earth's interior.
The study of metamorphic rocks (now exposed at the Earth's surface
following erosion and uplift) provides us with very valuable
information about the temperatures and pressures that occur at
great depths within the Earth's crust.
Some examples of metamorphic rocks are gneiss, slate, marble,
schist, and quartzite.
A good example of the metamorphosis process
Orthoquartzite is very pure quartz sandstone composed of usually
well rounded quartz grains cemented by silica. Orthoquartzite is
often 99% SiO2 with only very minor amounts of iron oxide and trace
resistant minerals such as zircon, rutile and magnetite. Although
few fossils are normally present, the original texture and
sedimentary structures are preserved. The term is often misused,
and should be used for only tightly-cemented metamorphic
quartzites, not quartz-cemented quartz arenites[3]. The typical
distinction between the two (since each is a gradation into the
other) is a proper quartzite is so highly cemented, diagentically
altered, and metamorphosed that it will fracture and break across
grain boundaries, not around them.
Quartzite is very resistant to chemical weathering and often forms
ridges and resistant hilltops. The nearly pure silica content of
the rock provides little to form soil from and therefore the
quartzite ridges are often bare or covered only with a very thin
soil and little vegetation.
Quartzite koppie (outcrop) and ridge viewed
from cache coods.
Quartzite is a decorative stone and may be used to cover walls,
as roofing tiles, as flooring, and stair steps. Crushed quartzite
is sometimes used in road construction and for railway ballast.
High purity quartzite is used to produce ferrosilicon, industrial
silica sand, silicon metal and silicon carbide.
Sedimentary rock
Sedimentary rock is a type of rock that is formed by
sedimentation of material at the Earth's surface and within bodies
of water. Sedimentation is the collective name for processes that
cause mineral and/or organic particles (detritus) to settle and
accumulate or minerals to precipitate from a solution. Particles
that form a sedimentary rock by accumulating are called sediment.
Before being deposited, sediment was formed by weathering and
erosion in a source area, and then transported to the place of
deposition by water, wind, mass movement or glaciers.
The sedimentary rock cover of the continents of the Earth's
crust is extensive, but the total contribution of sedimentary rocks
is estimated to be only 5% of the total volume of the crust.
Sedimentary rocks are only a thin veneer over a crust consisting
mainly of igneous and metamorphic rocks.
Sandstone
The formation of sandstone involves two principal stages. First, a
layer or layers of sand accumulates as the result of sedimentation,
either from water (as in a river, lake, or sea) or from air (as in
a desert). Typically, sedimentation occurs by the sand settling out
from suspension; i.e., ceasing to be rolled or bounced along the
bottom of a body of water (e.g., seas or rivers) or ground surface
(e.g., in a desert or erg).
Finally, once it has accumulated, the sand becomes sandstone
when it is compacted by pressure of overlying deposits and cemented
by the precipitation of minerals within the pore spaces between
sand grains.
The most common cementing materials are silica and calcium
carbonate, which are often derived either from dissolution or from
alteration of the sand after it was buried. Colors will usually be
tan or yellow (from a blend of the clear quartz with the dark amber
feldspar content of the sand). A predominant additional colorant in
the Limpopo province is iron oxide, which imparts reddish tints
ranging from pink to dark red (terracotta), with additional
manganese imparting a purplish hue. Red sandstones are also seen in
the Southwest and West of England and Wales, as well as central
Europe and Mongolia. The regularity of the latter favors use as a
source for masonry, either as a primary building material or as a
facing stone, over other construction.
Must involve visitors undertaking some educational task that
relates to the Earth science at the site. This could involve
measuring or estimating the size of some feature or aspect of
the
site, collecting and recording data (such as time of a tidal
bore),
or sending an e-mail to the cache owner with the answer to
Earth
science related questions they obtained by reading an
information
display. While photographs may be requested, they do not take
the
place of other logging requirements. Taking a photograph alone
or
asking people to do internet research does NOT meet these
logging
guidelines. Requests for specific content in the photograph
(must
include the visitor's face, for example) will be considered
an
additional logging requirement and must be optional. Cache
owners
may not delete the cache seeker's log based solely on
optional
tasks.
To Log your earthcache find, please do the
following (answers by email please, not in your log): You can go
ahead and log your find then email the answers to me within 7 days,
if not your log will be deleted.
Click on hennieventer top of the page and
Send Message
Questions:
1. When examine the 3 different rock types. What are common in
all of them?
2.Looking at the Sedimentary rocks (pointing up). In witch
direction did the tilt happen?
3. At additional waypoints ROCKS (Big quartzite rocks) How many
different shade of colours can you identify in the white quartzite
rocks?
4.Looking at the sandstone at coordinates, the lines is layers
of sand that accumulate as the result of sedimentation. To your
understanding doing this earthcache how did this layers of sand
became a rock?
5. Find a piece of sand stone, Look at the grain size. Describe
in your own words the texture.
6. Take a photo with your GPS at any of the 3 types of rock.
Place photo with your log.
I have used sources available to me by visiting the site, the
Polokwane library, internet, research, and asking questions to get
information for this earth cache.
I am not a geologist. Since Earth caching is educational I also
leant a lot through the research. Hope you will enjoy this
Earthcache
