Gold formation

Because gold is very stable over a wide range of conditions, it is very widespread in the earth’s crust. While its overall concentration is very low (about 5 milligrams per ton of rock), rich concentrations of gold, forming ore deposits, are known throughout the world. The well-known saying amongst prospectors that "gold is where you find it" suggests its occurrence is unpredictable, but it is now known that certain geological environments favor gold’s formation.

A popular misconception is that natural gold has cooled from a molten state. In fact, gold is transported though the Earth’s crust dissolved in warm to hot salty water. These fluids are generated in huge volumes deep in the Earth’s crust as water-bearing minerals dehydrate during metamorphism. Any gold present in the rocks being heated and squeezed is sweated out and goes into solution as complex ions. In this form, dissolved gold, along with other elements such as silicon, iron and sulphur, migrates wherever fractures in the rocks allow the fluids to pass. 

This direction is generally upwards, to cooler regions at lower pressures nearer the Earth’ssurface. Under these conditions, the gold eventually becomes insoluble and begins to crystallise, most often enveloped by masses of white silicon dioxide, known as quartz. This association of gold and quartz forms one of the most common types of "primary gold deposits".

Veins and reefs of gold-bearing quartz can occur in many types of rock, for example around granites, in volcanic rocks or in regions of black slate, but in most cases these host rocks are not the immediate source of the gold.

Gold deposits have formed at many different times during Earth’s history. For example, those in Western Australia are believed to have formed about 2400 million years ago, during a period of intense metamorphism and intrusion of igneous rocks. The gold-bearing quartz reefs in Victoria are significantly younger, about 400 million years, but also owe their origin to a period of intense metamorphism in the region. As chemical weathering and erosion gradually break down the host rocks and lower the land surface, the quartz and gold veins are eventually exposed to the atmosphere. The veins provide far more resistance to chemical attack than the surrounding rocks, so that mechanical weathering is required to fragment the quartz, thereby releasing the gold. Because they are relatively heavy, particles of gold are more difficult to move and so become naturally concentrated in the soil or in adjacent gullies or streambeds. These concentrations are known as alluvial or placer deposits and have yielded incredible riches on some goldfields, such as those in California and central Victoria.

Alluvial deposits take many forms, including sands and gravels in the beds of modern-day streams, in old river valleys buried under lava flows or perched on hilltops due to uplift of the land surface. The terms shallow and deep leads are used in Victoria for gold-bearing gravels covered by younger sedimentary layers or lava flows. These were especially important in the Ballarat district. Because of its resistance to chemical attack, gold can be recycled from one type of alluvial deposit to another. Because gold is very stable over a wide range of conditions, it is very widespread in the earth’s crust. While its overall concentration is very low (about 5 milligrams per ton of rock), rich concentrations of gold, forming ore deposits, are known throughout the world. The well-known saying amongst prospectors that "gold is where you find it" suggests its occurrence is unpredictable, but it is now known that certain geological environments favor gold’s formation.

A popular misconception is that natural gold has cooled from a molten state. In fact, gold is transported though the Earth’s crust dissolved in warm to hot salty water. These fluids are generated in huge volumes deep in the Earth’s crust as water-bearing minerals dehydrate during metamorphism. Any gold present in the rocks being heated and squeezed is sweated out and goes into solution as complex ions. In this form, dissolved gold, along with other elements such as silicon, iron and sulphur, migrates wherever fractures in the rocks allow the fluids to pass. This direction is generally upwards, to cooler regions at lower pressures nearer the Earth’s surface. Under these conditions, the gold eventually becomes insoluble and begins to crystallise, most often enveloped by masses of white silicon dioxide, known as quartz. This association of gold and quartz forms one of the most common types of "primary gold deposits".

Veins and reefs of gold-bearing quartz can occur in many types of rock, for example around granites, in volcanic rocks or in regions of black slate, but in most cases these host rocks are not the immediate source of the gold. Gold deposits have formed at many different times during Earth’s history. For example, those in Western Australia are believed to have formed about 2400 million years ago, during a period of intense metamorphism and intrusion of igneous rocks. The gold-bearing quartz reefs in Victoria are significantly younger, about 400 million years, but also owe their origin to a period of intense metamorphism in the region.

As chemical weathering and erosion gradually break down the host rocks and lower the land surface, the quartz and gold veins are eventually exposed to the atmosphere. The veins provide far more resistance to chemical attack than the surrounding rocks, so that mechanical weathering is required to fragment the quartz, thereby releasing the gold. Because they are relatively heavy, particles of gold are more difficult to move and so become naturally concentrated in the soil or in adjacent gullies or streambeds. These concentrations are known as alluvial or placer deposits and have yielded incredible riches on some goldfields, such as those in California and central Victoria.

Alluvial deposits take many forms, including sands and gravels in the beds of modern-day streams, in old river valleys buried under lava flows or perched on hilltops due to uplift of the land surface. The terms shallow and deep leads are used in Victoria for gold-bearing gravels covered by younger sedimentary layers or lava flows. These were especially important in the Ballarat district. Because of its resistance to chemical attack, gold can be recycled from one type of alluvial deposit to another

Economic history of South Africa

Prior to the arrival of European settlers in the fifteenth century the economy of what was to become South Africa was dominated by subsistence farming and hunting. In the north, central and east of the country tribes of Bantu peoples occupied land on a communal basis under tribal chiefdoms. It was an overwhelmingly pastoral economy and wealth was measured in the number of cattle men (not women) held. Population growth had created a land pressure that had seen the tribes move steadily from the origins in central east Africa.

Processed GOLD (AU)

                                                                                                                UNPROCESSED GOLD(AU)

A BRIEF HISTORY OF GOLD IN SOUTH AFRICA

European prospectors found the first alluvial gold deposits at Eersteling (Limpopo Province) between 1840 and 1870, but the first major gold rush in South Africa, however, started on 5 February 1873 at MacMac, a mere 5 km from Pilgrims Rest as the crow flies. The big strike however, was when Alec "Wheelbarrow" Patterson discovered gold in the Pilgrim's Creek in 1873. He could not keep his find secret and soon another prospector, William Trafford, found gold in the Pilgrim's Creek. Legend has it that he shouted with joy "Now at last, a pilgrim is at rest!"

He registered his claim at the gold commissioner's office, MacMac, resulting in a major gold rush on 22 September 1873, when Pilgrim's Rest was officially proclaimed a gold field.

Not even a year later, 1500 diggers worked 4000 claims around the streams of Pilgrim's Creek.  By 1876 most of the tents were replaced by permanent structures, and many made their "gold" from the various businesses supplying the diggers with necessary provisions. Gold was also discovered in the De Kaap Valley in January 1874 and some diggers moved from Pilgrim's Rest to this area to try their luck. Small deposits were found at Kaapsehoop and Berlin but it was only with the discovery of alluvial and reef gold by August Robert, alias French Bob in 1882, that the Barberton Goldfields were established. Gold was mined and melted in ancient times in Southern Africa to a limited extent. Artifacts made of gold were excavated from sites such as Mapungubwe (now a world heritage site in the Limpopo Province), Klipwal (near Piet Retief) and Thulamala in the northern part of the Kruger National Park.

Gold was smelted by means of a furnace, which was probably similar to the iron and copper smelting furnaces excavated elsewhere in southern Africa, and was utilised for personal adornment as well as a means of barter for glass beads from Egypt, ceramics from China and cloth from Phoenicia. By 1898 the gold production of the Witwatersrand exceeded that of the entire United States of America. Gold is still to this day, the basis of the South African economy. George Harrison discovered by chance, the Great Rand Reef (Johannesburg) in 1886.  The first diggers moved in, and by September of that year, 3000 prospectors were working the area. In 1893, Peter Marais discovered more gold deposits on the Witwatersrand. The geologists Harry and Fred Struben were convinced of rich deposits, and erected a five-stamp battery on top of the area which became the largest gold-bearing reef in the world!

Formation of jointz in Rockz

Joints are formed within rockz, especialy sedimentary rocks due to variety of process. Joints may sometimes formed due to temperature variation, seismic forces, loading conditions of rocks, etc. Joints are structural formations which are formed in rocks due to development of cracks without a considerable displacent.

To stay in rural areas is advantageous who can believe that this stractural formation har been found in RURAL area like GUYUNI, HA-MAKUYA. There is still lot of geological data and information which is gona be published here. Thanks.

UNIVEN GEOLOGY FIELD TRIP TO BARBERTON

BARBERTON GREENSTONE BELT

BARBERTON GREEN-STONE BELT

THE Barberton Greenstone Belt occurs in an area known as the Barberton
Mountain Land - a rugged tract of country in the Lowveld region of Mpumalanga Province and Swaziland. This Archean green-stone belt represents one of the oldest and best pre-served volcano-sedimentary successions not only in South Africa, but in the entire world. It consists of a wide variety of volcanic and sedimentary rock types, collectively referred to as the Swaziland Supergroup.

The volcano-sedimentary Onverwacht Group, at the base of the succession, attains a thickness of approximately 15 km and is subdivided into six formations. The lower three formations (Tjakastad Subgroup) consist mainly of mafic and ultramafic volcanic rocks (komatiites, komatiitic basalts, high-magnesium basalts and tholeiitic basalts) that were erupted approximately 3500 million years ago into an ancient oceanic environment (similar to present-day ocean-floor domains). A persistent sedimentary horizon, termed the Middle Marker, then occurs, followed by the three upper formations (Geluk Subgroup) that are made up principally of repeated cycles of volcanic, volcaniclastict and sedimentary rocks. The volcanic rocks (the modem-day equivalents of which are found in oceanic island arcs) consist mainly of tholeiitic basalts and felsic pyroclastic rocks and agglomerates, together with cherts. Lesser amounts ofkomatiite, basaltic komatiite, carbonaceous shale and chert, and siderite-rich carbonate beds are also present. 

Some of the sedimentary rocks represent ocean-floor muds and debris deposited between volcanic eruptions. The carbonaceous shales and chert have been found to contain primitive microfossils indicating that early forms of life were in existence as far back in time as 3500 million years ago. A number of layered ultramafic complexes occur as igneous intrusions in the Onverwacht Group. In many of these, chrysotile asbestos has been mined in the past, and it is still being mined at the Msauli Mine southeast of Barberton and at Havelock Mine in northwest Swaziland. Overlying the Onverwacht Group and occupying the central core of the Barberton Greenstone Belt are two distinctly different groups of sedimentary rocks. The oldest is the Fig Tree Group, consisting of shales, greywackes (impure sandstones), banded iron formations, and cherts, as well as subordinate volcanic rock types. Again, some of the cherts and shales are carbonaceous and contain primitive microfossils. 

The Fig Tree rocks were deposited in relatively deep water, and the sediments were derived from the erosion of oceanic islands (island arcs), which developed probably as a result of some form of primitive plate tectonic processes. In contrast, the overlying Moodies Group sediments display evidence of having been deposited by fluvial systems into relatively shallow-water continental environments. The rock succession consists mainly of conglomerates, quartzites, sandstones, shales, banded iron formations, and minor volcanic interlayers. Some sediments appear to have been deposited in areas affected by tidal influences (such as occur in river deltas at the edges of continents). The entire Swaziland Supergroup succession has undergone multiple stages of deformation, which produced large- and small-scale folds and faults, the latter providing ideal channel ways for migrating hydrothermal solutions carrying gold and sulphide minerals. Numerous gold workings exist in the area, gold having been discovered in 1882 (alluvial gold in the Jamestown Schist Belt north of Barberton) and in 1884 in quartz veins in the hills around the town of Barberton. Some of the mines founded over 100 years ago (Sheba, New Consort, Fairview) are still being worked to this day. 

The deformation that affected the rocks of the Barberton Greenstone Belt was largely the result of the intrusion of numerous granite bodies. Several stages of granite emplacement have been recognized, beginning with trondhjemite and tonalite (mainly sodium-rich granites) intrusions, which range from 3500 to 3200 million years in age. Later, potash-rich granites were intruded and formed large batholiths, some being over 40 km in diameter. These occur north and south of the Barberton Greenstone Belt (and in Swaziland), and were intruded approximately 3100 million years ago. A final stage of granite emplacement followed and ended with the intrusion of smaller- scale, potassium-rich granite (Mpangeni) and syenite (Boesmanskop) plutons ranging from 3100 to 2700 million years in age. All the granites interacted with the earlier-formed greenstones and produced a variety of metavolcanic and metasedimentary rock types, particularly near the granite-greenstone contacts where heat from the intrusions was greatest. Fluids produced by the heating of the greenstones moved through the rocks and along faults and fractures, and were responsible for the localisation of gold mineralisation. 

The entire Barberton Greenstone Belt was later covered by rocks of the Transvaal Supergroup (about 2500 million years ago). This resulted in the Barberton rocks being protected until about 50 million years ago when, follow- ing the break-up of Gondwana, the rivers on the east side of southern Africa began to cut back to where the present-day Drakensberg Escarpment is now situated. The Barberton Mountain Land has provided geologists with a unique opportunity to study the early history of the Earth and the evolution of the primitive crust, as well as of early life on our planet. The sites that have been selected here represent but a small number of illustrations portraying the wide-ranging character of one of the world's best-preserved Archaean granite- greenstone terranes.

BARBERTON

Prehistoric

The Barberton Mountain Range, 2001 image from NASA's Landsat 7
satelliteThe mountains around Barberton are the oldest in the world
dating back 3.5 Billion years, and these mountains include some of the
oldest exposed rocks on the planet (only rocks from the Isua
greenstone belt in Western Greenland are older). These volcanic rocks,
which scientists call the Barberton Greenstone Belt, have given up
direct evidence of conditions of life on the surface of the very early
earth.

In the satellite image, the bare rocks of mountain peaks appear as a
pale gray-green, accentuated by the sharp relief of sunlit slopes and
their shadows. Deeper shades of green indicate vegetation, including
some vegetation on the lower slopes.

In the mountain valleys, bright
green areas suggest well-watered grassy areas and crops. Deeper green
areas are probably forests. The series of bright green circles north
of the town of Barberton result from center-pivot irrigation systems.
The area north and west of Barberton appears slightly pale and fuzzy
compared to the rest of this image, probably the result of low-lying
haze.
The first form of life on earth, a bacterial micro fossil
Archaeospheroides barbertonis was discovered here and has been
identified as being 3.2 billion years old.

Gold
19 June 1984, Participants in the Barberton Centenary Trek make their
way through the Kaap Valley en route to Barberton for the 100 year
celebration.In 1881 gold in the Barberton area was discovered by Tom
McLachlan who found alluvial gold at Jamestown.

However due to the
location (the hot lowveld region was rife with malaria) no-one wanted
to go there until Auguste Roberts (French Bob) discovered gold in
Concession Creek in 20 June 1883. This discovery resulted in a gold
rush to the area.
On 21 June 1884, Graham Barber wrote a letter to the State Secretary
to inform him that he and his two cousins Fred and Harry discovered
payable gold on state land where the Umvoti Creek entered the De Kaap
valley.

The State Secretary then asked the Magistrate in Lydenburg to
investigate the matter and for David Wilson, the Gold Commissioner, to
submit a report. Wilson investigated on 24 July 1884 and declared the
township of Barberton.
At first it was just a simple mining camp but grew when Edwin Bray, a
prospector discovered gold in the hills above Barberton in 1885 and
with 14 partners started the Sheba Reef Gold Mining Company.

Large amounts of money flowed into Barberton and the first Stock
Exchange to operate in the then Transvaal opened its doors. More
buildings were erected, billiard saloons and music halls established.
The Criterion and Royal Standard hotels were opened.
Barberton flourished for only a brief period and soon the inhabitants.

GEOLOGICAL FORMATION KNOWN AS MALTESE CROSS

The "Maltese Cross", a well-known rock formation in the Cedarberg
Mountains, Western Cape Province, South Africa. These hard sandstones
have been shaped into tall pillars and other fantastic forms by
weathering along the vertical cracks in the rock.

SEDIMENTARY FORMATION

The "Finger of God", also known as Mukorob, a rock pillar in southern
Namibia, photographed in 1979. A 34 metre column of sandstone rests on
softer mudstone, which has eroded away to a narrow neck. The pillar
eventually blew down in a storm on 4 December 1988.