||The Phalaborwa Complex (RSA)
The alkaline Phalaborwa Complex contains the Palabora Mine. The mine is situated about 550 km north-east of Johannesburg in the lowveld plains of Northern Transvaal. At an altidude of 400m the climate is subtropical and the wildlife is plentiful. It is not uncommon to see elephants browsing within 1 km of the open pit (once even in it!). The original carbonate outcrop was a large hill known as Loolekop. The surface of the hill was once littered with primitive workings excavated by local tribesmen. Primitive smelting was carried out in the surrounding hills.1
The Arabs and possibly even the Phoenicians before them, traded for slaves, gold, ivory and copper in Africa. The Portuguese were amoungst the Europeans to penetrate into the interior. The copper and iron deposits of Loolekop were also known to the Dutch East India Company. Although a conciderable amount of copper was produced over the centuries, very few artifacts have been discovered. The only copper articles known are about 20 strangly shaped ingots locally known as the "marale" (singular: "lirale") and a few dozen armlets. The mirale consisted of a cylindrical bar 1,5cm thick and 45cm long with a flat cone-shaped end piece. In the town of Phalaborwa several interliked armlets where unearthed in a house foundation about 25cm below the surface. These contained 97,8% copper and 1,65% iron.2
During the stripping of the surface of Loodekop in 1964 early underground mines where exposed. Some of the ancient shafts where up to 20 m deep and some only 38cm wide. The walls of these shafts where smoke-stained and charoal fragments from the floors of two stopes indicated an age of 1000-1200 years.3
In 1934 the first modern mining started with the extraction of apatite for the use as fertiliser. The remoteness of the area lead to the termination of the first mining ventures. Interest however remained and 1946 a well known South African geologist Dr. Hans Merensky started an intensive prospecting on Loolekop to establish the existence of economic deposits of apatite in the foskorite rock. In the early 1950s the area was discovered to be radioactive - the uranium content was however not economic for mining. In the process of this prospecting a very large low grade copper sulphide ore body was discoverd which proved to be potentially exploitable. A joint venture between Rio Tinto Zinnc and Newmont Mining followed and resulted in the formation of the Palabora Mining Company in 1956. During 1957 to 1962 the ore body was proved and a pilot plant operation was built. In 1966 production commenced in one of the largest open pit copper mines of the world.4
The Phalaborwa Complex consists of a central bony of ultrabasic rocks surrounded by numerous plugs of syenite and is 2030 (+- 18) million years old. The pyroxenite body (which probably represents the remains of a volcanic vent) encloses three areas of ultrabasic pegmatite. Copper with the co-products of silver, gold, phosphate, iron ore, vermiculite, zirconia and uranium are extracted from the rocks.5
The Complex is unique when comared to other African alkaline complexes, because its carbonatite components contain copper ore. Magnetite, uraninite-thorianite and baddeleyite are subsidiary pruduct of the copper mining. The ultramafic rocks of the complex also contain economic deposits of apatite and vermiculite. Large numbers of younger dolerite dykes intrude and cut all of the rocks of the complex, and it is in these that zeolitic mineralisation occurs.6
The Phalaborwa Complex covers an area of 1950 hectares and it consists mainly of a phlogopite- and apatite rich pyroxenite. This pyroxenite is intruded successively by a series of more differentiated rocks - foskorite, and olivine- magnetite- apatite- phlogophite rock and finally a central intrustion of sövite (transgressive carbonatite). The sövite intrusion shows an intimate relationship with foskorite. The sövite (50 hectares at the surface) is composed of calcite and magnetite with minor amounts of dolomite, apatite, chalcopyrite, bornite and various silicates. Furthermore uraninite-thorianite and baddeleyite are imortant accessory minerals. The sövite is being mined by large scale opencast methods mainly for copper with uranium, zirconium and minute amounts of platinum as by-products. The foskorite is mined for the extraction of phosphate. The resources of apatite from the foskorite and the pyroxenite are enormous.7
Over 50 minerals (excluding trace minerals) are reported from the Palabora Mine. The minerals can be devided into those that are associates the the many cross-cutting dolerite (diabase) dykes and those that are associated with intrusive rocks of the Complex. In particular the lining cavities in the dykes have produced some of the most attractive zeolitic specimens yet reported from South Africa. The dykes vary in width form a few cm to 50m. The zeolite mineralisation occurs mainly in the fractures and joints as chalky coatings, but in the wider fractures, and in particular in the faulted areas crystals occur. In March 1982, in the Main dyke on bench 24 of the Palabora open pit, a series of open cavities completely lined with well-crystallised mineral were discovered. Specimens from the upper portions of the Main dyke are particularly attractive, especialy those with silky white mesolite crytals projecting from clear fluorapophyllite crystsals set in a matrix of green prehnite. Later specimens from deeper down show a wider variety of zeolites.8
The first locality consisted of a shear zone, some 1,8m wide, and composed of brecciated dyke material which was cemented with prehenite and fluorapophyllite. The northern side of the zone was bounded by an open cavity lined with crystallised fluorapophyllite and spiky mesolite, with larger amber pseudocubic calcite crytals up to 15cm on edge. The southern boundary consisted of a series of interconnected cavities lined with hundreds of snow-white mesolite crystals up to 2cm long. In the central brecciated zone small cavities lined with crystallised prehnite, transparent pseudocubic crystals of fluorapophyllite, and occasionally calcite crystals, were found.9
In the Main dyke crystals of analcime to 4mm and heulandite to 1mm occured in open joints. Species of particular interest included soft pectolite balls associated with natrolite in long thin prismatic crystals to 2cm. Thomsonite assiciated with fluorapophyllite occured on one boulder. Prehnite, mesolite, calcite, datolite, laumonite and chabazite have also been found.10
In the Ramp dyke a different suite of zeolitic minerals ws found. The minerals included pectolite (in both fibrous and free-standing crystals) and stilbite as small crystals often in association with scolecite and fluorapophyllite.11
The carboatite is generally of limited interest regarding specimens. An exception is a very localised area on the eastern boundary where small cavities have been found associated with foscorite xenoliths within the carbonatite.12
The micaeous pyroxenite contains economic deposits of vermiculite and apatite. These are however of little interest to the collector. Palabora probably represents one of the best localities worldwide for the rare species zirkelite. Large apple-green diopside crystals and books of phlogopite are also of interest. The diopside crystals reach over 1m in length, but cannot be removed intact from the enclosing matrix. Many crystals of euhedral baddeleyite (1-2cm), which were embedded in the carbonatite, have been recovered. The largest single specimen known mesesures 3x10cm. Other minerals such as bright orange-red euphedral chondrodite crystals up to 5mm, hghly lustrous octahedral magnetite of 1-2cm on edge, fluoborite and the rare mineral iowaite are also found. The iowaite occurs as micro crystals up to 5mm. The mineral is very dark-green to brown-green to black and has a micaceous apperance.13
The minerals from the Palabora Mine come from local geologists.
"Minerals of South Africa" by Bruce Cairncross and Roger Dixon:
1: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 110.
2: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 110f.
3: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111.
4: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111.
5: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111.
6: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111.
7: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111f.
8: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 112f.
9: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 113.
10: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 113.
11: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 114.
12: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 114.
13: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 114.
Back to Home