ATOMIC ENERGY BOARD

PEGMATITE DEPOSITS IN THE REPUBLIC OF SOUTH AFRICA

by

J.W.VON BACKSTROM

PELINDABA , PRETORIA r REPUBLIC OF SOUTH AFRICA $ MARCH 1973 PEL 227

ATOMIC ENERGY BOARD

PEGMATITE DEPOSITS IN THE REPUBLIC OF SOUTH AFRICA

by

J.W. VON BACKSTROM*

* Geology Division

PELINDABA POSTAL ADDRESS March, 1973 Private Bag X256, PRETORIA

ISBN 0 86960 419 8 CONTENTS

Page Page 1. INTRODUCTION - - - 4 3.3.6 Noumas No. 2 .. ~ .. - ~ « .. ~ .. ~ ~ .. 14 1.1 Previous Work .. 5 3.3.7 Norrabees « - - ~ ~ .. ~ ...... 14 2. GENERAL DESCRIPTION - 5 3.3.8 Sleight's Mine •- ...... 15 2.1 Structural Features • - 5 3.3.9 Spodumene Kop No. 1 ~ .. 15 2.2 Distribution •• 6 3.3.10 Spodumene Kop No. 2 - ~ ~ ...... SYNOPSIS 15 3.3.11 Swartberg •• ~ ...... | 3. THE PEGMATITE BELT OF THE NORTH­ 0 WESTERN CAPE PROVINCE ~ 6 Interest in pegmatites centres on minerals containing beryllium, lithium, bismuth, 3.3.12 Witkop 16 3.1 Gordonia ~ ~ - - 6 3.3.13 Groendoorn River Gorge- ...... i tantalum, niobium and the rare-earths, which have proven or indicated usefulness in the 0 3.1.1 Bak River 6 development of nuclear power. Information concerning the occurrence, mode of emplace­ 3.3.13.1 Groendoorn Nc. 1 - - •• - ~ - ~ ~ ~ 16 3#1»2 Jdpié »••••••* •* »• •» •• •• •• •• •• •* •• •• •• / ment and source of the pegmatites, together with the modus operandi for their exploration, 3.3.13.2 Groendoorn No. 2 ~~~~~.. ~~~ 17 3.1.3 Mostertshoek - 7 assessment of grades and estimate of reserves are given. 3.3.13.3 Groendoorn No. 3 ~ •• .. ~ -. ~ .. ~ .. 17 3.1.4 Murasie ~ •• - 7 3.3.13.4 Groendoorn No. 4 ...... yj 3.1.5 Riemvasmaak •• •• - - 7 4. PEGMATITE DEPOSITS IN THE 3.1.6 Baviaanskrantz •• - - 7 TRANSVAAL • 3.2 Kenhardt ~ — 8 4.1 Piet Retief Area - ~ « 18 ~ .. .. 18 3.2.1 Angelierspan 8 4.1.1 Witkop - 3.2.2 Blomerus 8 4.1.2 Assegai - •• - 18 3.2.3 Crietf *• •• — 8 4.2 Letaba Area - 18 3.2.4 Jack No. 1 8 4.2.1 Gravelotte 18 *• •» •* 1Q 3.2.5 Kombaers Brand (Jack No. 2 and No. 3)~ 9 4.2. Palakop 19 3.2.6 Konkonsies - - 9 4.3 Pietersburg Area 3.2.7 Middelpos 9 4.4 Other Areas .. ~ .. 20 3.2.8 Noriseep .. io 5. CLASSIFICATION OF PEGMATITES • 20 5.1 Homogeneous Pegmatites 20 SAME VAT TING 3.2.9 N'Rougas Noord (Straussheim No. 1 and No. 2) 10 5.2 Inbornogeneous Pegmatites •• •• 21 3.2.10 Oup 10 5.2.1 Zonal pegmatites 21 Belangstelling in pegmatiete word toegeskryf aril die teenwoordigheid van miner ale 3.2.11 Oupvlakte 11 5.2.2 Fracture fillings 21 soos berillium, litium, bismut, tantaal, niobium en die seldsame aardes wat werklike en 3.2.12 Uitdraai and Meyer 11 5.2.3 Replacement bodies • 22 moontlike toekomstige toepassings net in die ontwikkeling van kernkrag, Inligting oor die 3.3 Namaqualand 11 5.3 Segregations 22 voorkoms, inplasing en oorsprong van pegmatiete tea am e met die modus operandi vir 3.3.1 Groenhoekies 12 6. MODE OF EMPLACEMENT 22 hulle eksplorasie, bepaling van ertgehaltes en beraming var reserwes word gegee. 3.3.2 Area west of Jakkalswater 13 7. SOURCE OF PEGMATITES 23 3.3.3 Kokerboomrand 13 8. EXPLORATION 24 3.3.4 Mount Stoffel 13 9. ASSESSMENT OF GRADE 25 3.3.5 Noumas No. 1 13 10. ESTIMATE OF RESERVES 27 PEL 227 - 4

1. INTRODUCTION the same pegmatite. Exploitation of these ores and minerals PEL 227 - 5 sometimes results in supplies of beryl becoming available. between the mineralogic types of pegmatite and the compo­ 2. GENERAL DESCRIPTION According to Landes (1933) the word "pegmatite" was sition of the enclosing wall rock. Sheet-mica-bearing peg­ 2.1 Structural Features coined by Haiïy in the early years of the 19th century as a Pegmatite bodies are notoriously complex in their matites have been cited as one example of this. There is no descriptive term for rocks with a graphic texture. Today the shape, size and continuity, their disposition being controlled The pegmatites vary greatly in size, shape and attitude. doubt that most of the productive sheet-mica-bearing peg­ use of the term has been extended to include all types of by the structure of the older rocks into which they have been They range in size from less than half a metre to more than matites of the country occur in mica schists and mica- exceptionally coarse-grained plutonic rocks, whether graphic intruded. In addition, the distribution of economic minerals two kilometres in length, and from more than 100 metres to bearing quartzites, and the idea that the mica conte.it is due or not. within them is normally very erratic, and in most cases a a fraction of a centimetre in width. They occur as thin lenses in some way to incorporation and redeposition of aluminous Although the term pegmatite conveys adefinitemeaning, very considerable tonnage of rock must be moved for I and dykes, and as sheetlike and irregular bodies. Lenticular material from schists is an attractive one. It should be it is difficult to define it briefly and accurately. The defi­ relatively small recovery of mineral. bodies commonly fill fractures and joints that cut the poorly- pointed out, however, that in some districts much of the nition given by Andersen (1931) adequately describes the This means that the operator must be reasonably to-well-developed foliation in the various types of granite, mica in the wall rock has clearly been derived from the occurrences: "Pegmatites are mineral associations crys­ familiar with the behaviour of pegmatites if there is to be gneiss, granodiorite and granulite, whereas irregular forms pegmatites. It should also be pointed out that sheet-mica- tallized in situ, decidedly more coarse-grained than similar a fair chance of the operations proving economic. In the case of pegmatite are usually emplaced parallel to the foliation bearing pegmatites do occur in other types of rock, particu­ mineral associations in the form of ordinary rocks, and of companies exploiting large and important deposes, ade­ of the country rock. The pegmatites are between vertical1, larly in hornblende schists and in igneous rocks. differing from these in having a more irregular faoric of the quate geological and engineering assistance is available and and horizontal in inclination; those with a high di,> pre­ mineral aggregates." such operations are strictly controlled. In the case of the dominate. Pegmatites occurring as a dyke swarm have 1.1 Previous Work The term pegmatoid has been suggested to denote very individual miner or prospector, the position is very different, uniform characteristics, being clearcut, parallel-sided, coarse-grained f acies of igneous rocks which have a peg- and, in most cases, such operators lack even an elementary Mountain (1931) and Behrend (1933) were the first to transgressivc dykes dipping at steep angles. The mineral mafiric habit but which differ from pegmatite proper inasmuch knowledge of geoiogy and find difficulty in acquiring even describe uranium-bearing minerals encountered in certain assemblage consists essentially of quartz, potash feldspars as the graphic texture is absent (Rice, 1955). some understanding of pegmatite behaviour. This is particu­ pegmatites present along the Bak River, which closely follows and soda feldspars and mica. Zoning in the ore-bearing peg­ South Africa is of considerable importance in terms of larly the case where Africans have now started to work such rhe common boundary between the Republic and South West matites is usually well-developed and commonly repetitive pegmatites, if not on account of thesizeof individual occur­ deposits on their own account, many pegmatites being too Africa, near where it joins the Orange River in Gordonia. on each side of a core most frequently consisting of massive rences, then at least because of the very large areas over sparsely mineralized to warrant European exploitation, but The first detailed description of Namaqualand peg­ quartz. which they are developed. Although we have some knowledge being nevertheless capable of yielding an adequate return matites was given by Gevers et al (1937). More than two There is a marked relationship between the mode of of their structure and mineralization, it is true to say that within the African economy. decades elapsed before the remarkably similar pegmatites occurrence and the structural characteristics of the enclosing we do not know much about the potential reserves of the Most pegmatites consist of quartz and microclir.e, of Gordonia and Kenhardt were described by Poldervaart rock. In competent rocks such as weakly folded gneiss, economically valuable minerals present in our pegmatites. with or without albite, orthoclase,muscovite and tourmaline. and Von Backstrom (1949), Von Backstrom (1964) and Hugo granite and quartzite, the pegmatites occupy fractures that Furthermore, the possibilities of mining of pegmatites in a Associated with the pegmatites are dikes and veins of aplite. (1970). Later further contributions to the knowledge of the commonly transect foliation and/or bedding. In schists, on way that will not just operate on a shallow basis (taking out These generally predate the pegmatites. Strung out along the pegmatites from Namaqualand was made by De Jager(1964) the other hand, pegmatites are invariably conformable with the minerals commanding a price at the moment) but will larger pegmatite dikes are lenticular bodies of colourless, and (1967) and Von Backstrom and De Villiers (1972). the foliation. Exceptions are common, and the contacts of ensure the extraction of all the valuable minerals in an white, pink or smoky quartz, surrounded by alteration zones Because an important phase of the Atomic Energy some pegmatites are in part concordant and in part dis­ economic fashion, have still to be thoroughly probed. characterized by pneumatolytic minerals. Mineralization is Research and Development Programme for South Africa cordant although most pegmatites follow the strike of the Modern industry calls for the use of many minerals chiefly associated with these later quartz bodies, and their concerns the materials that have proven or indicated useful­ foliation. Many of the pegmatites studied exhibit structural which are found mainly in pegmatites. For this reason a pneumatolytic aureoles. Characteristic mineral of these ness in the development of nuclear power, officers of the relations indicating volume-by-volume replacement of the greatly increased interest in the possible economic potential zones are kaolin, sericite, spessartite, tourmaline,fluorite, Atomic Energy Board have compiled monographs on nuclear host rocks, but thegreat majority have made room by dilation. of such deposits has developed. Thus it is that an important epidote, biotite and beryl. Rare-earth minerals include reactor materials (Nel, 1965), beryl (Nel, 1965), lithium Most pegmatites however are confined bodies without visible phase of the Atomic Energy Research and Development allanite, euxenite, monazite, uraninite, scheelite and wolf ra- (Nel, 1968), niobium and tantalum (Von Backstrom and Nel, avenues of supply from conventional sources (mother Programme for .South Africa concerns the materials which mite. 1968), and rare-earths (Von Backstrom, 1969). magmas), but they may be explained by migration of material have a proven, or apparent, usefulness in the development There are many contrasts in mineralogy, texture and The present monograph is the outcome of a desire to along microscopic and submlcroscopic paths in the host of nuclear power. structure among groups of pegmatites in different regions, present a convenient summary of information concernir.g rocks of activated ions, atoms and molecules. As in most parts of the world, zoned pegmatites have and even between groups within a single region. Differenceé pegmatites in South Africa. It is based on the atrhor's own Although the contact between pegmatite and enclosing so far been the only source of an important group of nuclear in physical conditions of formation, and differences in degree observations over more rhan three decades, but he is also rock appear macroscopically sharp in the great majority materials produced in Southern Africa. Beryl generally of reaction of pegmatitic solutions with wall rocks, are keenly aware of the debt he owes to authors referred to in of cases, the microscope often reveals a diff use contact with occurs together with ores of one or more of the metals undoubtedly responsible for some of the contrasts between the text and their contributions are hereby greatfully an interchange of mineral grains now known to be common lithium, niobium (columbium), tantalum, rare-earths, bis­ groups of pegmatites. acknowledged. to both pegmatite and host rock. Where shared minerals are muth and tin, and with sheet mica and ceramic feldspar in It has been suggested that there is a relationship PEL 227 - 6 large enough this phenomena is detectable by the unaided have been cursorily examined and their positions plotted by eye and referred to as wall-rock alteration. Hugo on regional geological maps prepared by Von Backstrom There are also examples where the host rocks are and De Villiers (1972). A similar belt in the west occupies ccmpletely soaked with pegmatitic material and are intimately the rugged mountainous tract south of the Orange River in intergrown and welded together. Space-problem considera­ Namaqualand, between Onseepkans and the Richtersveld, is tions leads to the surmise that pegmatite has completely about 200 km in length and has been described by Von replaced the host rock. Some pegmatites are merely Backstrom and De Villiers (1972). clusters of feldspar porphyroblasts in gneiss or schist, and The pegmatites in the western and eastern sections of all gradations can be found into larger pegmatite bodies. the pegmatite belt are the main source of nuclear materials Crumpling and plastic distortion of schists and gneisses produced in the northwestern Cape Province. In the central adjacent to pegmatite bodies are common and have been section, between Goodhouse and Onseepkans, pegmatites taken to indicate forceful injection. Plastic deformation of are fewer and not so striking, and have been less productive. solid rocks by a fluid melt is, however, difficult to visualize, A fair percentage of the nuclear materials in the whole unless crystallization forces and tectonic strain during and area has come from diggings by both European and non- after emplacement of the pegmatites are held responsible. European nomads collecting material from surf ace exposures and shallow excavations. As a rule, work on these pegmatites 2.2 Distribution was abandoned after rich pockets had been picked out. Such minerals have also been, or are still being mined deeper In the Republic of South Africa, pegmatites occur mainly down in several pegmatites by small concerns. The rest of as relatively small sporadic deposits that are connected the production has come from pegmatites mined principally with intrusions of Precambrian granites. Besides those in for other metallic or non-metallic minerals. In many cases granite, pegmatites are also found in srhist and other it is most likely that, had proper prospecting and mining metamorphic rocks invaded by these granites. On the other methods been applied, further payable concentrations would hand, there are some pegmatites in gneiss, schist or other have been discovered at depth in the pegmatites. ultrametamorphosed rocks which have no visible connection with granite intrusives, but which developed instead by the concentration of elements in rocks during the metamorphism 3.1 Gordonia or grankization of the host rock. Rocks of the Basement Complex containing pegmatites The areas in the Republic within which pegmatites are exposed over the greater part of the area. West of the occur, or are likely to be present, are shown on figure 1, Molopo River they are capped by younger resistant quartzite published originally by Nel (1965). Valuable nuclear materials of the Kuibis Series which belongs to the Nama System. have been produced from pegmatites derived from the The most prominent mineralized pegmatites are pre­ Gordonia, Kenhardt, Namaqualand, Piet Petief and Letaba sent in the Bokvasmaak Native Reserve, the eas'em part of districts. which is known as Riemvasmaak and the western part as Bokseputs. Some occur in the deeply incised valleys of the 3. THE PEGMATITE BELT OF THE NORTHWESTERN Bak River and are known as the Bak River, Japie and CAPE PROVINCE Murasie pegmatites. Others, known as Riemvasmaak and Geographically, the pegmatite belt in the northwestern Mostertshoék, occur north and east of the Riemvasmaak Cape Province can be referred to as two sections, viz. the settlement, respectively. eastern and western (fig. 1). The eastern section extends from Putsonderwater in the east to Onseepkans in the west and incorporates the deposits of Kenhardt, Gordonia and 3.1.1 Bak River Bushmanland described by Hugo (1970). These deposits The Bak River pegmatite is situated on the eastern occur along a more or less continuous belt, approximately slope of the Bak River, roughly 9 km south of the Bokseputs 25 km wide and 250 km long, estimated to contain more than settlement. It is roughly 30 metres long and betveen 10 and 50 000 large and small pegmatites. Of these some 12 000 30 metres wide. It forms an irregualr body with a discordant V^'/A P*t*ntoai ormm: or* is known h OTW~9tOYinq peqmoéhwt mty ponátéry

FiAl PEL 227 - 7 offshoot, and exhibits a complicated structural relationship large bifurcating Riemvasmaak pegmatite, 60 metres long with the enclosing country rock. This pegmatite has been and 3 metres wide, is exposed in red porphyroblastic biotite described in detail by Mountain (1931) and Behrend (1933). gneiss on the steep slope of a small spur jutting out from The first age determination carried out on uraninite in the hill on which the northwestern corner beacon of the farm South Africa was undertaken by Holmes (1934) and gave a Waterval is located. The contact with the country rock is result of 950 million years. The sample was recovered from knife sharp. The pegmatite contains a number of pink-to- the pegmatite under discussion. white cores of quartz, enclosing crystals of tourmaline and Some gadolinite and allanite was produced in the period feldspar. These cores are set in massive pegmatite com­ 1952-1959, but the pegmatite is now largely worked out and prising mainly graphically intergrown quartz andmicrocline- no further trace of uraninite could be found. perthite. Strung out along the contact with the quartz core are lenses of biotite containing pink feldspar and feldspar 3.1.2 Japie intergrown with tourmaline, some of which are more than 8 cm long and up to 5 cm in diamete:\ The Japie pegmatite lies 5 km northeast of the con­ Rare-earth minerals, mainl} gadolinite, have replaced fluence of the Bak and Orange Rivers, on the south slope of microcline-perthite close to and along contacts with the core a very steep hill. The east-west striking, oval-shaped botiy, and the biotite. Masses averaging from 1 cm to 3 cm in dips almost vertically and plunges east. It is about 80 metres diameter are sporadically developed. The largest aggregate long and between 10 and 20 metres wide. It is well zoned and discovered to date weighed 7 kg and had a diameter of 30 cm. contains anhedral crystals of gadolinite, zircon and fergu- About 140 kg of gadolinite were produced during 1945 from sonite. About 7 tonnes of gadolinite and a considerable a small mineralized portion of the main pegmatite body, quantity of fergusonite was produced during the period 1956- estimated to contain about 0,1 per cent rare-earth minerals. 1958.

3.1.6 Baviaanskrantz 3.1.3 Mostertshoek Two very similar pegmatites of significance occur Mostertshoek is situated about 10 km east of Riemvas­ 8 km from Kakamas below Baviaanskrantz, immediately maak Mission. This is a zonally arranged intrusive body adjacent to the main tarred road to Keimoes. They are about 1 000 metres long and between 7 and 30 metres wide, mineralogically similar and lie in juxtaposition. The one from which more than 225 tonnes of beryl have been pro­ nearer the road is a thin, vertical, hook-shaped dyke, about duced. It consists of a quartz-perthite core in contact with 170 metres long and seldom more than 15 metres wide. The a zone consisting of albite, cleavelandite, quartz, muscovite, bottom of this dyke was reached in an excavation about 80 beryl, schorl and columbite-tantalite. metres from its eastern end, indicating that it plunges to the east. The second pegmatite, a tabular-shaped body 3.1.4 Murasie varying in width between 17 and 30 metres and dipping at a At Murasie five thin, tabular, parallel pegmatites dip low angle, lies on the concave side of the pegmatite dyke. 40° south and form a low hill 9 km south of Bokseputs A trench on its eastern side cuts down through its core and settlement. A prospecting trench, 500 metres long reveals underlying zones to reach its bottom at a depth of 8 metres. the well-developed zonal structure ofthese pegmatites which The core of both pegmarires consists of quartz and comprise a quartz core, an Intermediate zone of perthite, perthite. Following the core isamedium-to-coarse-grained and a wall-zone of graphic granite consisting of quartz, intermediate zone composed of cleavelandite, quartz, topaz plagioclase and biotite. Allanite and gadolinite are present and muscovite, with accessory beryl, fluorspar, tourmaline in the penhite zone and a few tonnes of each mineral have and rarely monazite, zircon (cyrtolite), gadolinite and bis­ been produced. muth. The wall zone is fine-grained and consists essentially of quartz, plagioclase and muscovite with subordinate pen e. 3.1.5 Riemvaar«aak Bodies consisting of muscovite, greisen and interstitial

Approximately 3 km north of Riemvasmaak Mission the cleavelandite, between the core and intermwliate zone, PEL 227 - 8 PEL 227 - 9

replace both, but preferably the quartz of the core. No 64 km east of Kenhardt on the road to Putsonderwater. crystals of beryl are confined to the contact between the core common. Prospecting trenches revealed the presence of minerals of economic significance are found in these re­ Prospecting and mining operations, commenced in 1962, and intermediate zones which consist of quartz, albite, beryl in at least seven pegmatites, the mean width of which placement bodies. exposed the pegmatite over an area 33 metres by 13 metres. muscovite,. beryl, apatite and lithia mica. is 5 metres and the length from 30 to 50 metres. Some beryl Both pegmatites were mined for feldspar and, for a The pegmatite dips at an angle of 30 degrees to the northeast. crystals with diameters of a metre and a half or more were short time, together produced approximately 225 tonnes It has a central core of perthite and quartz on the foot-wall 3.2.5 Kombaers Brand (Jack No. 2 and No. 3) found. About 55 tonnes of beryl were recovered. monthly. Only nine tonnes of beryl have been recovered side of which there are the following three zones: The Jack No. 2 pegmatite lies near the eastern boundary The internal structure of these pegmatites, and the distribution of beryl and other metalliferous minerals in since mining for feldspar began in 1960. This mining was (i) An inner thin medium-grained to coarse-grained inter­ of Kombaers Brand, about 1,5 km south of the Mottels River, them, could not be ascertained because of waste rock having terminated in 1962. mediate zone consisting mainly of cleavelandite, sugary where it forms a low hill almost completely covered by soil been dumped in the excavations. albite and muscovite, with beryl, columbite and apatite as and quartz-feldspar rubble on top, but well exposed over 3.2 Kenhardt accessories. The beryl, varying in colour from rose pink to 120 metres along the northern slope of the hill. 3.2.7 Middelpos 3.2.1 Angelierspan light green, invariably occurs as anhedral lumps and masses, The pegmatite has been well exposed in two large sometimes weighing as much as nine tonnes. A white variety Angelierspan lies 88 km southeast of Kenhardt, and excavations which reveal the distinct zonal build, steep dip Two very prominent pegmatites occur 25 km from of this mineral is commonly intergrown with nests of colum­ 3 km northeast of the farmhouse. The pegmatite has been to the east and low plunge to the north of the body. Along the Kakamas on the road to Kenhardt. Beryl production has been bite. exposed in an excavation about 20 by 10 metres in size, and core zone, beryl was well developed, and at least two masses mainly from two large pegmatites about 5 to 7 km to the east (ii) An outer intermediate zone of plagioclase, quartz and % dips 40 degrees west. It is largely covered by superficial of beryl in excess of 20 ts. nes each have been recovered. of the homestead. One of them, an almost horizontal sheet muscovite, which is also present on the hanging-wall side. material such as soil, rubble and surface limestone and its A number of small replacement bodies of cleavelandite about 230 metres long and 70 metres wide (known as No. 1 Except for small crystals of beryl which occur sporadically trace can be followed for over 70 metres. admixed withgreisen and carrying columbite-tantalite, are pegmatite), forms the summit of a 30-metre-high hill. An in this zone, no other mineral of economic importance is Although only the hanging wall is exposed, three zones present but did not lead to any production. inclined borehole near the southern end of the pegmatite encountered. are clearly distinguishable. The beryl-rich core zone is The Jack No. 3 pegmatite lies approximately 5 km due passed through its bottom at a depth of about 15 metres. (iii) A fine-grained to medium-grainec1 wall zone consisting from 1 to 2 metres thick and composed of perthite, plagio- south of Jack No. 2, also on Kombaers Brand and close to The core of the pegmatite varies in width from 7 metres essentially of graphic granite, quartz, plagioclase and mus­ clase, quartz, muscovite and beryl. its eastern boundary. It outcrops over 230 metres, is between in the south to about 40 metres in the north and consists covite. Much of the beryl near the surface of the ground was 16 and 66 metres wide and dips 15° east. Only the northern mainly of rose quartz and perthite. Along its western side rendered useless by weathering and impregnation of surface Replacement bodies of light-purple lithia mica, cleave­ portion has been mined for beryl. a zone 2 to 8 metres wide, consisting of quartz, perthite and limestone. However, prospecting was rewarded by striking landite and quartz occur between the core and the inner Against the ce-tral quartz-perthite core of the peg­ muscovite, is exposed over a distance of about 60 metres. a single mass of beryl weighing 63 tonnes. Yellowish-green intermediate zone on the foot-wall side. These bodies mostly matite, a thin (30 - 120 cm) intermediate zone consisting of Beryl is recovered from this zone throughout which its beryl crystals up to half a metre in diameter occur, along replace the core minerals, except that in the main excavation cleavelandite, muscovite and quartz, with accessory beryl, crystals, none of them large, are evenly distributed. The with tourmaline, in a groundmass of feldspar, quartz, lepido- the biggest ones cut through the overhanging core to come was seen on the foot-wall side in one of the excavations. main excavation, which at present is about 12 metres deep, lite and muscovite. During the period 1950-1953, about 135 into contact with the intermediate zones on both the hanging- Elsewhere along the core there is a second intermediate is near the northern end of the zone. Although this zone also tonnes of beryl were produced from this pegmatite. wall and foot-wall sides. zone of plagioclase, quartz and muscovite with accessory occurs around the eastern margin of the core, prospecting About 45 tonnes of beryl have been produced, the beryl, apatite and tourmaline. Directly against the core, on trenches failed to locate any beryl deposits there. The colour 3.2.2 Blomerus average BeO content of the product being 12,1 per cent. In its hanging-wall side, there were several anhedral masses of of the beryl varies from greenish yellow to blue, the latter beryl of which some weighed well over 20 tonnes. Certain of variety bordering on acquamarine. The average BeO content This pegmatite on Steynsputs lies close to the home­ addition, a few hundred kilograms of columbite ore, with an these masses were found to penetrate 2 to 3 metres into the of the beryl is more than 12percent.About 200 tonnes of beryl stead on the portion of the farm known as Sidi Berani. This average composition of 52 per cent Cb-Cg and 21 per cent Ta were recovered as a core. Fifty tonnes of beryl, having an average BeO content have been produced from the pegmatite. squat-shaped body is about 150 metres long and between 100 2°5' by-product. The lithia mica of 12 per cent, have been taken from this pegmatite since and 200 metres wide. This pegmatite consists mainly of a contains, on average, 2,5 per cent LICL. The other pegmatite, situated on the northern slope of central part of quartz and perthite, with an outer zone com­ production started early in 1934. a long hill six kilometres east of No. 1 pegmatite, dips posed essentially of perthite and plagioclase graphically 3.2.4 Jack No. 1 southwards at an angle of 85 degrees. It has a somewhat o 3.2.6 Konkonsies assymetrical zonal stru ure. Towards the foot-wall side of intergiown with quartz and some subordinate muscovite. It There are a number of pegmatites named Jack. Jack the pegmatite, the centralquartz core is succeeded by a zone is characterized by the presence of the radioactive: minerals No. 1 denotes a group of more or less parallel pegmatites A number of zonal pegmatites on Konkonsies, situated composed of mica, tourmaline, plagioclase, quartz and beryl. euxenite, gadolinite and xenorime. on the central portion of Jacomyn's Pan, about 9,5 km due about 6km north of Pofruder, are beryl-bearing, and some This zone is about 7 metres wide and was opened up over a south of the homestead on Crieff, where they form the 200 tonnes of beryl were recovered from three excavations. distance of nearly 70 metres. Mining was stopped at a depth 3.2.3 Crieff crest of a low ridge immediately south of the Mottels River. One large aggregate mass of beryl recovered weighed 40 of 13 metres because of the danger from dislocated quartz tonnes and was taken from an excavation about 10 km north­ The Crieff pegmatite, originally almost entirely covered The pegmatites are all well zoned, as can be seen in lumps of the core. About 120 tonnes of beryl were recovered. west of the homestead. On Vaalputs, a portion of Nouzees, by soil, lies about 13 km south of the homestead on Crieff, a the 80-metre-long trench made across their strike. The The quality of the beryl obtained was good, analyses of 25 km southeast of Pof adder, scattered eluvial beryl is fairly portion of the farm Jacomyn's Pa.., and is situated about largest pegmatite is 100 metres in length. Large embedded PEL 227-U PEL 227 - 10 and, in places, more than 20 metres wide, which strikes in boundary with Uitdraai, is found a pegmatite of irregular representative samples indicating an average BeO content No. lpegmatiteoutcropsoveradisianceof about 400 metres. a northerly direction, dips 40° to the west and plunges 30° to shape, known as Steenkamp. It is 200 metres long and between of 12 to 13 per cent. No beryl was found in the hanging-wall Except for one trench across the entire width of the peg­ the south. Like all other mineralized pegmatites in the 20 and 50 metres wide. It has been well exposed in a number side of the pegmatite. matite, excavations are confined to the zones on the foot- vicinity it has a huge quartz-perthite core. Towards the foot of workings which reveal its vertical stand and zoned struc­ wall side of the core. wall of the pegmatite the core is succeeded in turn by a ture extremely well. The large central quartz core is sur­ 3.2.8 Noriseep Beryl, together with other accessory minerals apatite, coarse-grained intermediate zone composed of plagioclase rounded by an intermediate zone consisting of albite, perthite, triplite, spodumene and black tourmaline, occurs in a thin East of Onseepkans on Noriseep, beryl occurs in two (mainly albite), quartz and muscovite, then by a fine-to- quartz, and muscovite, with some accessory beryl, zircon, zone on the foot-wall margin of a relatively thin core of zoned pegmatites of which one, on the northern slope of a medium-grained indistinguishable border-zone and wall-zone triplite and columbite-tantalite. This pegmatite produced an quartz and perthite. Idiomorphic crystals of spodumene, 60 metre high hill, has a total length of about 600 merres. consisting of quartz and plagioclase, with subordinate mus­ appreciable tonnage of beryl during the period 1952-1955 lcm to 10 cm in diameter and sometimes more than 2 metres The pegmatite has a northwesterly dip of 70 degrees. Beryl covite, tourmaline and magnetite. Indications are that these but no exact records were kept. long, normally occur close to the core whereas the apatite, crystals - rarely more than 25 cm in diameter - occur zones are less well developed in the hanging-wall. The wall beryl and triplite are concentrated in the outer parts of the frequently throughout a 3 to6-metre-wide intermediate zone zone of the pegmatite contains scattered xenoliths of biotite 3.2.12 Uitdraai and Meyer zone. The beryl forms small, yellow to green idiomorphic between a 1 to 3-metre-wide border zone of quartz-feldspar- gneiss. crystals. This zone is followed outwards by a zone a few On the farm Uitdraai there are two pegmatites w irthy mica rock and the central core composed of quartz and Certain areas in the intermediate zone, which locally centimetres to several metres wide and composed essentially of mention. The first, termed Stofberg, is close to the com­ perthite which has a mean width of 5 metres. The production is very rich in pale-green to greenish-yellow beryl, may of sugary albite and cleavelandite, with accessory fine-grained mon boundary with Styrkraal. It is about 450 metres long, 6 of beryl from this pegmatite in the latter part of 1959 contain as much as two per cent beryl crystals ranging from garnet, apatite, muscovite and quartz, through which small metres wide, dips vertically and plunges 30°wast. It is well avaraged 6 tonnes per week. Analyses of representative 1 to 5 cm in diameter. Beryl crystals, sometimes more than idiomorphic crystals of cassiterite and black tourmaline are zoned with a huge quartz core and an intermediate zone con­ samples gave 12,6 percent BeO. Only a few crystals of one metre in diameter, are usually found near the core or irregularly disseminated; a medium-grained to coarse­ sisting of albite, quartz, muscovite, cleavelandite and beryl. beryl were found in prospecting trenches in the hanging-wail they may even be disposed in the outer parts of the core. grained zone more than 10 metres wide composed of plagio- About 30 tonnes of beryl and 3 tonnes of columbite-tantalite side of the pegmatite. Eluvial beryl occurred on the slope At places in the intermediate zure, clusters of small beryl clase, quartz, perthite and tourmaline containing nests of were recovered, more especially from the western part of facing the hanging-wall. crystals occur in nests of muscovite-quartz-cleavelandite muscovite; and an outermost 1 cm to 8 cm thickfine-grained the body. The second pegamtite - 6 km east of the first one - greisen from which it is very difficult to separate the small zone of quartz, plagioclase and muscovite with accessory The second pegmatite, known as Meyer, lies about 3 km strikes from east to west and is exposed over a distance of beryl crystals by hand-sorting. tourmaline. Of thos zones, the last two are also present in south of the homestead on Uitdraai. It is approximately 300 about 500 metres. Beryl crystals, seldom more than five The total amount of beryl produced from this pegmatite the hanging-wall side of the core, although less well developed, metres long and between 10 and 30 metres wide. It dips centimetres wide, occur in "nests" of muscovite, feldspar is not known, but it must have been considerable. The peg­ The Straussheim No. 2 pegmatiteforms a low hill, about steeply southwest and is well zoned. The central quartz- and quartz. The production of beryl from this pegmatite in matite, which was mined on a large scale, is still of im­ half a mile south of the Straussheim No. 1 pegmatite. It has perthite core is surrounded by an intermediate zone of albite, 1959 seldom exceeded four tonnes per month. portant economic significance as it has not been worked a dyke-like shape and can be followed along its W 30° N quartz, muscovite and huge crystals of beryl. During the Farther to the east there are a considerable number of out and because it probably extends southwards underneath strike for a distance of about 245 metres. It is not more than period 1957 - 1959 about 70 tonnes of beryl with an average large beryl-bearing pegmatites on thefarms Oup, Oupvlakte, surface rubble to connect up with an outcrop of pegmatite 45 metres wide and stands either vertical or dips in a BeO content of over 12% was produced. Styrkraal and Uitdraai. which lies in its line of strike. southerly direction at a very steep angle. The intermediate Approximately 1,5 km to the south there is a similar zone of the pegmatite is composed mainly of cleavelandite, 3.3 Namaqualand large mineralized pegmatite forming a tabular body about sugary albite, quartz and muscovite with accessory schorl, Since before 1914, pegmatites in this part of the country 3.2.9 N'Rougas Noord (Straussheim No. 1 and No. 2) 400 metres long and between 30 and 50 metres broad, known beryl, cassiterite, apatite and spodumene. The spodumene, have been extensively prospected in the search for various as Oup No. 2. It dips with a low angle to the east, strikes About 35 km north of Kenhardt, on the portion of N'Rou­ with cleavelandite, occurs close to the contact of the zone minerals. From about 1929, when beryl was included in this north-south and plunges south. gas Noord known as Straussheim, there are several very with the massive milky-white quartz core, whereas the beryl search, these pegmatites have been the source of the bulk prominent pegmatites. The first pegmatite, designated and cassiterite appear at or near the contact with the wall The major portion of the pegmatite outcrop consists of of the beryl produced in the Republic of South Africa. Straussheim No. 1, forms a hill known locally as Mica Kop, zone of the pegmatite. The crystals of spodumene, varying in a large core of quartz. It has an attendant coarse-grained In Namaqualand a multitude of homogsneous and hetero­ so named by people who originally prospected it for mica size from a fraction to more than 25 cm in diameter, are intermediate zone consisting of quartz, muscovite and albite geneous pegmatites occur within a well-defined zone, about during the period 1890 to 1900. Since the beginning of 1952 stated to be rather abundant close to the core. with accessory beryl. This wall zone is fine-grained to this pegmatite and two other large pegmatites in its vicinity medium-grained and consists of plagioclase, perthite and 18 kilometres wide, which extends westwards from the farms were intermittently mined for beryl. In all, several hundred muscovite. This pegmatite was rich in beryl and contained Ramans Drift and Horn, east of Goodhouse,viaHenkries and 3.2.10 Oup tonnes of beryl were produced. Beryl production virtually many large crystals along the quartz core contact with the Kokerboom rand to Groendoorn where it disappears under the ceased when the Straussheim mine started producing cassi- A pegmatite known as the Oup No. 1 pegmatite is one of outer zones. Neint Nababeep Plateau. The bulk of the deposits of economic terite. the major sources of beryl on this farm. Situated close to importance are to be found in pegmatites within the zone, Varying in width between 15 to 100 metres and dipping the Styrkraal boundary, about 30 km east of Onseepkans, this 3.2.11 Oupvlakte which are mainly distributed in the metamorphosed Wilgen- at a rather steep angle to the southwest, the Straussheim pegmatite is a dyke-like body, about 400 metres in length On the western part of Oupvlakte, near the common houtdrlft and Kaaien Series of the Kheis System, and in the PEL 227 - 12 PEL 227 - 13

grey granite Archaen gneiss of the area. associated with bismuth, bismuthinite, lepidolite, columbite- muscovite and a little lepidolite and lithiophylite, occur in a southwards, plunges to the north and dips about 70° to the In the rugged scenery of this region the numerous peg­ tantalite and uranium ochre in some of the pegmatites. pegmatite east of the Uranoop River. In some trenches the west. In its exposed length of about 50 metres, the pegmatite matites are conspicuously exposed en mountain slopes and Spodumene, lepidolire, lithiophylite and triphylite are spodumene accounted for nearly 40 per cent of the rock. varies in width between 8 and 12 metres. The core of massive on the sides of deep gorges. As usual, the pegmatites are widely distributed in the Namaqualand pegmatites, but it is milky-white quartz, and subsidiary microclinef-perthite is characterized by irregularity in shape, dimension and con­ only spodumene which is present in appreciable and economi­ 3.3.2 Area west of Jakkalswater successively followed outwards by an intermediate zone cally important quantities at a number of localities. The other tinuity along strike. They form either steeply dipping dykes Away from the Uranoop River, in the country west and consisting of quartz, cleavelandite, spodumene and accessory three minerals occur in comparatively minor amounts. No­ or massive bodies of low inclination, the former usually northwest of Jakkalswater, numerous homogeneous and in- beryl, muscovite, and columbite-tantalite, and a wall zone of where has lepidolite been seen to occur in large masses with more regular outlines than the latter. They range in size homogeneous pegmatites, many of which contain beryl, are quartz, plagioclase and muscovite, with accessory micro­ comparable to those in the Karibib pegmatites of South West from veinlets measurable in centimetres to some bodies distributed in four separate areas, namely (a) a stretch cline-perthite, beryl, spodumene and garnet. At the contact Africa. The lepidolite is frequently found as irregular masses, more than two kilometres in length and 50 metres in width. roughly 8 km long between Diepnik and Noumas; (b) a stretch between the core and intermediate zones there are smah books, scaly granular bodies diluted to varying degrees of The larger pegmatites, however, are mostly less than 70 of about 8 km between Oiepnik and Klipbokkoppie and beyond; replacement bodies of lithia mica greisen. The pegmatite albite and quartz, or as an alteration product of spodumene, metres long and 20 metres wide. Pinch and swell structures (c) a stretch of about 4 km some 3 km southwest of the tri­ has been mined down to a depth of about 12 metres. while minor quantities of lithiophylite and triphylite in lumps are mostly encountered in non-dyke-like bodies. In some gonometrical beacon of Swartenbonthoutkop; and (d) roughly Beryl, spodumene, mica and columbite-tantalite have weighing up to about three kilogrammes are associated in localities there is a variable ramifying network of smaller 5 km further west, an area along both sides of the Kowiep or been produced from Kokerboom No. 2 pegmatite which is a some pegmatites with spodumene, lepidolite or bismuth. dykes and completely irregular pegmatite bodies between Groendoorn River. massive 70 by 10 metre body that has been mined down to a large pegmatites of dyke-like habit. Such a network is well Although spodumene theoretically contains 8,4 per depth of 8 metres. Beryl has been produced from a number of the peg­ depicted on the dark slopes of Mount Stoffel, forming the cent lithia, the spodumene as produced from the pegmatites matites in the Diepnik-Klipbokkoppie area. The pegmatites southern wall of the Pegmatite Valley near Henkries. normally contains 4 to 7 per cent lithia. This variation in the on both sides of the Kowiep or Groendoorn River area were 3.3.4 Mount Stoffel The pegmatites, like those in the eastern part of the lithia content of the spodumene is due to the replacement of originally prospected and worked for tungsten ore, mainly The dark slopes of Mount Stoffel, forming the southern pegmatitic belt, consist typically of ordinary coarse-grained the lithia by soda and potash, to partial alteration of the scheelite, because in or associated with this ore are quartz- side of the Pegmatite Valley which branches off the Henkries quartz and feldspar. Other constituents that frequently appear mineral to non-lithium materials, or to the presence of tourmaline bodies or veins which contain variable quantities Valley, are characterized by a ramifying network of numerous are muscovite as well as small amounts of black tourmaline impurities. of this ore. white pegmatites. One of the pegmatites, a coarse massive and red garnet. Xenoliths of country rock are present in 3.3.1 Groenhoekies The largest beryl-bearing pegmatite, which is situated body about 550 to 630 metres long and in places 30 metres some pegmatites. The ore-bearing pegmatites are generally on the western slope of the gorge and which has a central wide, was found, in an excavation near the bottom of the heterogeneous or inhomogeneous. The more important base Some of the many beryl-bearing pegmatites on the quartz core of about 3 metres in width, forms a dyke 200 valley, to contain long crystals of spodumene. The spodumene metallic minerals, of which one or more are present in a western side of the Uranoop River, between 6 and 8 km north­ metres long that dips at an angle of 50 degrees to the west. is stated to be decomposed and not abundant. Towards the pegmatite, are beryl, the lithium minerals spodumene and east of the Kokerboom pegmatite, contain spodumene. The Beryl, in the usual quartz-muscovite-feldspar zone, was high black cone of Mount Stoffel, and about a kilometre up lepidolite, tantalite, columbite, bismuth metal, bismurhi.iite name Groenhoekies has been given to the apophysis of a large, mined over a distance of 50 metres along the foot-wall side the steep southern side of the Valley, there is another coarse and their oxidation products such as bismite and bismutite, poorly zoned pegmatite. Striking northwest and dipping of the pegmatite. About 50 tonnes of beryl were produced pegmatite, irregular in shape and measuring about 27 by and the tungsten mineral scheelite. Occasional minor amounts steeply to the southwest, the body is exposed over a distance during the period 1953 -1954. Operations ceased when the 23 metres. A zone of very coarse feldspar and quart" in the have also been recorded of other minerals of little or no of 100 metres and varies in width between 7 and 25 metres. hanging wall became too dangerous. Only small quantities upper portion of the pegmatite contains masses two to three economic value, such as lithiophylite,triphylite, molybdenite A two to three-metre-thick zone of cleavelandite, quartz and of beryl were produced from other pegmatites in the gorge, metres wide, of lepidolite, muscovite in the form of greisen and uranium ochre. spodumene, with accessory beryl, tantalite-columbite and mainly as a result of poor development and lack of proper and large sheets, and prismatic crystals of spodumene, 30 cm Generally, beryl occurs as isolated crystals ranging in triplite, had been quarried to a depth of 8 metres in 1965. mining equipment. During 1960 the production in this area in length, which are associated with quartz. Within the greisen size from minute grains to very large crystals and irregular The zone is between the large quartz and microcline-perthite was at the rate of about 18 tonnes per annum, the mining there are also occasional blebs of bismuth ore and, in a aggregates roughly a metre in width. Often up to a dozen or core, and the graphic granite wall zone comprising quartz, activities being limited to prospecting and opening up of new 30cm-wide patch, numerous small plates of tantalite. more crystals occur sporadically in clusters. Clusters of plagioclase, microcline-perthite, beryl and garnet of the quarries. more than twenty crystals, however, are rare and usually pegmatite on the hanging-wall side of its core. 3.3.5 Noumas No. 1 the crystals are just a lew centimetres in diameter. Most of Hast of Groenhoekies, at Uranoop, just across the 3.3.3 Kokerboomrand the beryl is of good quality, the BeO content of representative Lranoop Ri"er, there are al3o beryllium-bearing pegmatites, The Noumas pegmatite lies about halfway between samples from the Goodhouse and Jakkalswater areas, for in one of which the presence of spodumene has been noted. Appreciable quantities of spodumeneoccurinanumber Steinkopf and Vioolsdrift, approximately 10 kilometres due instance, being 10 to 13 per cent. Beryl crystals or aggregate Another occurrence of spodumene in a beryl-bearing peg­ of prospects near Kokerboomrand, about 8 km northwest of west of the main road connecting these two settlements. in the pegmatites are generally found in quartz, feldspar or matite is found at a place called Fankie, farther down the Jakkalswater. One of these prospects, a pegmatite known as The pegmatite body is narrow and dyke-like, and is greisen. Prospectors generally look for a concent I at ion of course and on the eastern side of the Uranoop River. In the the Kokerboom No. 1 pegmatite, lies flush with the ground discordantly em placed in granodioritic grey gneiss. Lying ore minerals in pegmatites that show white, pinkish or smoky south, halfway between Uranoop and Jakkalswater, abundant about J,6 km east from where the road to Noumas branches for Its greater part on the western slope of the Blesberg, quartz, and associated muscovite greisen. The beryl is crystals of spodumene up to ametre long, together with albite, off from the main road to Vioolsdrif. The pegmatite strikes the difference in elevation between the highest and lowest PEL 227 - 15 PEL 227 - 14 almost one metre in diameter and weighing as much as 3 zones of lithia greisen, and occurs also as an alteration pro­ 3.C.6 Noumas No. 2 exposed parts of the pegmatite is approximately 160 metres. tonnes, were found close to the contact of the intermediate duct of spodumene. Lithiophylite is found as small crystal Its length is just over 1100 metres, and in wid*h it varies Immediately to the north of the Noumas No. 1 pegma­ zone with the core which consists of microcline-perthite aggregates or lumps, the surfaces of which are frequently between 10 and 45 metres. The body strikes northwest, and tite, several zoned «homogeneous pegmatites are found lying crystals embedded in massive white quartz. altered into a brownish-black, ferriferous manganese dioxide. dips at angles between 50 and 80 degrees to the southwest. parallel to it. The most important of these beryl-bearing Several replacement bodies consisting of lithia mica, The pegmatite known as Spodumene Kop No. 1 is about At the northwestern extremity the pegmatite disappears bodies is the Noumas No. 2 pegmatite which has been mined greisen, tourmaline, cleavelandite and poli» cite, occur along 7 km east of Norrabees No. I pegmatite. It forms the top of a underneath sand, while at its southwestern extremity it for this mineral. the contact between the core and the intermediate zone. hill, is approximately 70 metres long by 12 metres wide and digitates into three separate dykes which terminate within The body is about 270 metres long and between 12 and About 1100 tonnes of spodumene and 35 tonnes of beryl have dips at a steep angle to the south. Its excellent zonal structure a short distance. The pegmatite has been described by De 30 metres wide. It dips almost vertically and plunges to the been produced since 1955 on an intermittent basis. Details is revealed in a huge prospecting trench. The fine-grained Jager (1964). northwest. of the size, structure and degree of mineralization of the to medium-grained wall zone, consisting of plagioclase, The northwestern part of the pegmatite has been exten­ Two zones were distinguished, viz. a core and wall other spodumene-bearing pegmatites of the area are not quartz and muscovite, with accessory beryl, schorl and garnet sively mined by way of several open quarries. These open- zone. The core, consisting of quartz and microcline-perthite, known. is followed inwards by an intermediate zone to a milky-white casts reveal the regular, though somewhat asymmetrical, is best developed in the northwestern part of the body. The quartz core, best developed at the pegmatite's extremeties. internal zonal structureof the body. Thefollowing zones were "ore is enveloped by a wall zone of quartz, albite (mostly 3.3.8 Sleight's Mine The constituents of the intermediate zone are: spodumene, identified; wall, intermediate, core and replacement. cieavelandite), muscovite with accessory beryl, bismuth The largest aggregate mass of beryl so far discovered cleavelandite and quartz; bismuth minerals, triplite, streng- A fine-grained border zone between one and 15 cm wide minerals and tantalite-columbite. This zone occurs pre­ in the western part of the pegmatite belt and weighing about ite, columbite, lithiophylite and a little uranophane are found is present on both the foot and hanging-wall contacts of the dominantly on the northern side of the core where most of 16 tonnes was removed in 1929 from a coarse-grained peg­ as accessories. Abundant prisms of spodumene, some 2 pegmatite. It consists of plagioclase, quartz and muscovite, the mining operations have taken place. matite west of the Uranoop River and 3 km northwest of metres long, 25 cm wide and 5 to 7 cm thick, and occurring with accessory garnet. A few replacement bodies, consisting essentially of Jakkalswater. This pegmatite, the site of the former Sleight's mostly in feldspar, were exposed in a pit on the northern A wall zone is also present on both the hanging-wall and muscovite greisen and never more than 3 metres in diameter, mine, is irregularly shaped and extends about 90 metres slope near the summit of the hill; lumps of lithiophylite up foot-wall sides of the pegmatite. It varies in thickness from are found scattered along the contact between the core and from its southeastern end up to the top of a koppie, whence to 20 by 18 by 13 cm, occurring with strengite in replace­ one to more than 10 metres. The main constituents of this wall zone. it is exposed for another 135 metres. The pegmatite consists ment patches of greisen, or associated with spodumene. zone are muscovite, quartz, plagioclase, microcline-perthite of white potash feldspar, plagioclase, quartz (generally white were also seen in this pit. Spodumene crystals, one metre with accessory beryl, bismuth minerals, apatite,triplite and 3.3.7 Norrabees but occasionally smokey or pinkish in colour) and muscovite. long, 23 cm wide and 5 cm or more thick and enclosed in garnet. Muscovite books, the diameters of which sometimes white, glassy quartz, were observed in another pit a little Norrabees, also known as Durrabees, situated in the Potash feldspar forms large masses in pans of the pegmatite. reach one metre, are generally found on the contact with the farther down the mountain slope. Near the surface the Steinkopf Reserve, is about 24 km northeast of Jakkalswater Muscovite, either in small or large amounts, is ubiquitous; border zone. Mica production, which averages 100 tonnes spodumene is mostly altered to a dense earthy material. and about 3 km east of the Uranoop River. The pegmatites muscovite greisen is often concentrated in large pockets, per month, were produced from quarries opened up on this numbered Norrabees 1, 2, 3, 4, 5, and 6 are the more im­ especially near irregular bodies of quartz in feldspar. Small zone on the hanging-wall side. 3.3.10 Spodumene Kop No. 2 portant ones among a swarm of inhomogeneous pegmatites, crystals of red garnet are of common occurrence and in An intermediate zone between one and eight metres places there are xenoliths of sheared biotite granite. Acces­ in the Norrabees area, containing spodumene and beryl. This pegmatite lies about 3km east of theVioolsdrift- wide and consisting of spodumene, albite (cleavelandite) and sory minerals are beryl, lepidolite, lepidolite greisen, black The Norrabees No. 1 pegmatite is situated on the Steinkopf main road, approximately 7 km north of thetumoff quartz, with accessory beryl and tantalite-columbite, is tourmaline, spodumene and colombite-tantalite. In 1935, southern slope of a hill and is exposed over a total distance to Noumas. found between the wall zone and the inner zone or core. This 3 000 tonnes of the pegmatite rock was broken on this site, of more than 100 metres. It varies in width between 7 and The body is dyke-like, about 270 km long, and more zone is best developed on the foot-wall side of the pegmatite but only 1,5 tonnes of beryl were recovered. than 17 km wide in some places. It strikes in a northwesterly where it dips at an angle of about 30° underneath the core. 25 metres and dips steeply to the southwest. Before it was direction and dips 45° to the southwest. The zone has been mined for its spodumene, beryl and tanta­ mined, the pegmatite was largely concealed by wall rocks; 3,3.9 Spodumene Kop No. 1 Two zones, a core and a wall zone, were distinguished. lite-columbite content. it seems possible that the pegmatite is one of considerable The core consists of anhedral, milky-white quartz and length and depth. It has been opened up in a quarry measuring On the western side of the Henkries Valley appreciable A well-developed core consisting of quartz, spodumene 60 by 27 metres, extending down to about 28 metres at the large blocklike subhedral crystals of microcline-perthite. quantities of spodumene are contained in certain beryl- and albite, with accessory beryl, is present in the central deepest point. The intermediate and core zone of the peg­ bearing pegmatites which form part of the swarm of peg­ The feldspar, which is suitable for use in the ceramic in­ part of the pegmatite. The core is followed by a mediiM?- dustry, was mined in the past. matite are enclosed by a wall zone of between 2 and 8 metres, matites occurring around Spodumene Kop and Mount StoffeL grained to coarse-grained wall zone of quartz, muscovite, Several replacement bodies consisting of lithia mica consisting of quartz, plagioclase, biotite and muscovite, with Some of the spodumene-bearing pegmatites were prospected accessory beryl and garnet. The constituents of the inter­ microcline-perthite and albite, with accessory spodumene. and cleavelandite, with accessory tantalite-columbite, micro- or mined mainly for beryl, columbite and bismuth minerals. mediate zone are cleavelandite, spodumene, and quartz, with lite, thorite, orangite and gummite are found scattered along Occurrences of lepidolite and lithiophylite found in them are The core was mined for its spodumene content. The average accessory bery] and bismuth minerals. Spodumene and quartz thought to be of little or no economic significance. The the foot-wall side contact between the wall zone and the predominate in places, whi le f lsewhere in the zone spodumene lepidolite forms books, irregular pockets and replacement spoduiiiene zone. The diameters of these bodies range from diameter of the spulumene crystals is approximately 10 cm. and cleavelandite are more prevalent. Spodumene logs, one to more than 10 metres. PEL 227 - 16 PEL 227 - 17

3.3.11 Swartberg the gorge from Noumas and Steinkopf are mere tracks traver­ serves of the minerals to a depth of 20 metres are approxi­ excavation. Muscovite books are small and very scattered sing extremely rough country and are barely passable in a On the northwestern slope of a conspicuous hill at the mately as follows:- and there is some beryl, but grades are too low to justify four-wheel-drive vehicle. eastern side of the entrance to the Henkries Valley, is a Spodumene = 34 tonnes exploitation. To a depth of 20 metres, 30 000 tonnes of zoned The pegmatites in the gorge occur in the same broad pegmatite one kilometre long and 12 to 18 metres wide. It Amblygonite = 5 tonnes material have been estimated, and for the entire body, belt as those between Steinkopf and Goodhouse, described strikes approximately east-west and dips at an angle between Muscovite = 200 tonnes 130 000 tonnes of pegmatite. in the previous section. There are literally thousands of 30° and 50° to the south. The constituents of the main mass Beryl = 23 tonnes pegmatites which have the same general characteristics as of the pegmatite (which is not well zoned) are quartz, plagio- 3.3.13.4 Groendoorn No. 4 those described previously. Only a very small proportion clase and subordinate muscovite. Beryl, spodumene and 3.3.13.2 Groendoorn No. 2 This pegmatite is situated about one kilometre north­ contain valuable minerals in cxtractable quantities, beryl columbite are accessory minerals. Scattered crystals of west of No. 3 pegmatite and forms four separate outcrops occurs in most of the larger-zoned pegmatites, together This pegmatite measures approximately 130 by 30 beryl occur over the greater part of the pegmatite, whereas which appear to be connected at depth. It is a small body. with lithium minerals, muscovite and feldspar. metres and is situated about 80 metres due north of Green- spodumene is apparently confined to the eastern end of the doom No. 1 on tue steep slope of a ravine where it forms a The largest exposure measures 30 by 13 metres and dips pegmatite, ihe spodumene forms euhedral crystals up to at about 70 degrees. It is estimated to contain 10 000 tonnes 3.3.13.1 Groendoorn No. 1 conspicuous knoll - the central core of white quartz - which 15 cm and more in diameter. Mining operations being carried of pegmatitic material down to a depth of 20 metres. For is partly surrounded by a wall zone consisting of undiffe­ out on the pegmatite are stated to have yielded 50 tonnes of This pegmatite is situated within half a kilometre of the whole pegmatite the volume would be approximately 2\ rentiated pegmatite composed of quartz, plagioclase and mus­ beryl and some 6 tonnes of columbite-tantalite. the homestead on the steep eastern slope of the gorge. The times this «mount. covite, in varying proportions ar

f flakes of tantalite-columbite occur sporadically and a small The wall zone which is present onthe uot-wall side of probably absent from the whole pegmatite. Had either of these conspicuous, with the result that one might underestimate crystal of pyrochlore was also seen. the body consists mainly of graphic granite (both plagioclase been present in reasonable quantities the pegmatite could the quantity present. The core zone is also composite and is similar in com­ and microcline-perthite are present) with some muscovite have had much greater potential. Muscovite is fairly abundant in the wall zone and con­ and garnet. position to the wail zone. The commercially valuable minerals stitutes approximately 3 per cent of thfBZone. Unfortunately in the core zone are beryl, spodumene, amblygonite, tantalite- The intermediate zone contains plagioclase (usually 3.3.13.3 Groendoorn No. 3 a considerable proportion of the books have structure "A", columbite and muscovite. The latter is coarse, and books up sugary albite) and quartz with accessory beryl, columbite- and would therefore not be suitable for the production of to 25 cm in diameter were observed. Beryl is more abundant This pegmatite is located on the western flank of the rantalite, bismuth minerals and schorl. This zone has been sheet mica. All the spodumene is altered to sericite and can

r than in the wall zone but the crystals are generally less than Groendoorn River Valley, opposite numbers 1 and 2, and is mined . or beryl and coiumbite-tantalite on thenorthernside therefore not be relied upon as a by-product. 5 cm in diamerer. about one kilometre from the homestead. It strikes NIOW, of the body by means of a long cross-cutting trench. The dips 60° west, is dyke-like, is 235 metres in length and production was, however, discouraging. .Several irregular pits and excavations, the deepest of 4. PEGMATITE DEPOSITS IN THE TRANSVAAL between 7 and 20 metres in width and has pinch and swell The core, which consists of quartz and microcline- which is 10 metres, have been dug into the core zone. It is structures. Pegmatites occur at various places in the Archaean perthite, constitutes the central and largest position of the estimated that approximately 1500 tonnes of material has The southern part of the dyke is differentiated and has Complex of granite, gneissic and metamorphosed rocks which pegmatite outcrop. been removed from them. If it is assumed that the pegmatite a distinct microcline-perthite core surrounded by a com­ underlie the Eastern Transvaal Lowveld, the higher ground maintains its width and composition down to a depth of 20 posite wall zone. The longer northern section is the equiva­ between Pietersburg and Louis Trichardt, and the Lpwveld 3.3.13 Groendoorn River Gorge metres, then the quantity of pegmatite material amounts to lent of the composite wall zone and extends from wall to wall. north and west of the Soutpaneberg Range. Apart from a The four main mineralised pegmatites in thegorgeare 150 000 ronnes. Of this quantity the core zone would con­ Although fairly large, only a small section of the peg­ report that beryl has been discovered in a pegmatite on the situated on Viooisdrift South, 50 km northwest of .Sreinkopf stitute approximately one tenth. If the grade figures given matite contains minerals of commercial value. Amblygonite farm Carolina 76 about 50 km northwest of Thabazimbi,it is and were described by De Jager (1967). Roads leading into above are applied to this volume of core zone, then the re­ constitutes about 0,1 per cent of the assemblage in the main not known whether there are any other occurrences of beryl- PEL 227 - 18

bearing or mineralized pegmatite in the large granite area tains no quartz core. In addition to the minerals listed for PEL 227 - 19 in this part of the Western Transvaal. the Witkop pegmatite, it also contains some monazite and Emeralds were produced on the farms Willie and Barbara, place in the coarse-grained zones. chrysoberyl. and they occur on the adjoining property and in the Germania Except for one or two places, e.g. the Kubannek Quarry, 4.1 Piet Retief Area Hills to the south. Associated with the emerald in the schist the beryl and tantalite deposits are too small and scattered 4.1.1 Witkop 4.2 Letaba Area and pegmatite are apati*^, black tourmaline, molybdenite to be mined economically. Cassiterite, apatite and tourmaline The southernmost known occurrence of a pegm atite con­ 4.2.1 Gravelotte and its oxidation products, and pyrite, but none of these are accessories in these pegmatites. taining beryl in the broad tract of Archaean rocks in the Beryl-bearing pegmatites are not known to occur in the minerals is present in payable quantities. Non-transparent Approximately 140 tonnes of beryl and 12 tonnes of Eastern Transvaal is on the farm Witkop507IT, about 15 km granite or other rocks of the Archaean Complex between beryl has also been reported from the emerald-bearing schist tantalite-columbite have been produced since 1934 in the west of ^iet Retief. The pegmatite, which is a lenticular Piet Retief and the Letaba District some320kmto the north. and the parent pegmatite, but it is not clear whether there Palakop area. body 900 metres long with a maximum width of 100 metres, The pegmatites in the Letaba District, expecially those in the has been any production of beryl from these sources. The spodumene deposits are much more promising. is emplaced into basic schist. It is poorly zoned but has a area around Gravelotte, and more specifically those on Since 1927, production of emeralds has been inter­ In places the spodumene constitutes about 10 per cent of the definite quartz core. Replacement bodies up to 3 metres, Leeuwspruit 18 and Selati Ranch 143, are the source of most mittent. During the nine years 1929 to 1937, the total amount pegmatite and further investigation would perhaps be justified. mostly of weathered beryl, spodumene and feldspar have of small emerald crystals produced was 664 585 carats which of the beryl produced in the Transvaal. Generally, beryl Aggregates of good quality kyanite are present in a been found. Inclusions of schist are common in the pegmatite. were sold for R162 204. happens to be present only in pegmatite occurring either in quartz pegmatite southwest of Palakop. To determine the The following minerals are present: Quartz, feldspar, The pegmatites which occur around Mica Railway Sta­ schist or granite along or close to the contacts of these rocks. extent of this deposit, further prospecting is, however, muscovite, tourmaline, spodumene, beryl, lithiophilite, tion, south of Gravelotte, do not appear to be particularly necessary. columbite-tantalite and garnet. The extent to which both For many years, tantalite-columbite was sporadically well zoned. Only mica and feldspar are produced from these spodumene and feldspar have been weathered has rendered produced from a tourmaline-bearing pegmatite in granite- pegmatites although some of them are known to contain both 4.3 Pietersburg Area them useless for exploitation. In the quarry, 60 metres long gneiss on Leeuspruit 18, about 50 km east of Gravelotte, beryl and columbite; the quantities of these may, however, by 20 metre., wide by 18 metres deep, the core is not ex­ before it was realized that the pegm atite also contains beryl. The presence of beryl in pegmatite has been observed be insufficient for profitable recovery. posed and its relation to the mineralized zones could not be The beryl, mistaken for quartz by the producers of the on a number of farms around Pietersburg. Of these occur­ ascertained. It would appear, however, that the largest tantalite-columbite, was dumped as waste until, through the rences those in pegmatites on Verbrandehoek, 65 km east, 4.2.2 Palakop concentration of beryl and columbite occurs in the hanging years, a considerable tonnage of beryl had accumulated. On and Kalkfontein, 25 km north of Pietersburg, as well as those wall of the inclined quartz core. its identity having been established, more than a hundred The Palakop pegmatites have been described by Wilke in pegmatites on several other farms southwest of the town tonnes of beryl were collected from the dumps within a few (1963) and the following abstract is culled from his descrip­ The owner of the farm, who previously worked the peg­ may, if. thoroughly explored, prove to be of commercial weeks and were exported. Eluvium composed ci debris pro­ tion: matite, recovered 97 tonnes of beryl and 29 tonnes of colum­ value. duced by the weathering of the pegmatite was also found to bite from an estimated 29000 tonnes of ore, which probably Palakop is situated in the Lowveld of the northeastern Massive cream-coloured blocks of quartz lie strewn be rich in beryl. Subsequently, the pegmatite itself has been included material from a layer of eluvium. Recovery was by Transvaal, about 55 km northeast of Mooketsi, and forms over part of a field about 450 metres west of the homestead worked for beryl. hand cobbing. I'and-cubbing operations were continued by part of the Sutherland Range. The tantalite-columbite de­ on the farm Verbrandehoek 983. Large beryl crystals occur Space Metals from July 1963 to June 1964 and 25 tonnes of Other strikes have been reported in the area to the posits in this area have been known since 1934. in a few of the quartz blocks which were evidently derived beryl and 130 kg of columbite were recovered from 12000 south and southwest, and it is quite possible that there are Elongated pegmatite bodies, ranging from a few centi­ from a fair-sized body of pegmatite that may contain suf­ tonnes mined. A study of the information obtained from bulk still occurrences which have escaped notice so far. The metres to about 180 km in diameter, occur in metamorphosed, ficiently abundant beryl to be mined profitably. The strike sampling and hand cobbing indicated that, where tested, the potential field in this part of the country, which has already steeply dipping amphibole schist of the Swaziland System. and extent of the pegmatite, however, could not be deter­ developed into a major producer of beryl in South Africa, pegmatite contains an average of 0,25 per cent of beryl and The injection of the pegmatites and some later diabase dykes mined, due to lack of exposures. Closer to the homestead is large. 0,03 per cent of columbite per ton of ore. Two boreholes was controlled by the foliation of the schist, giving rise to a few beryl crystals were also found in another but smaller intersected the pegmatite body at a depth of about 90 metres Beryl crystals, many of which have the colour and other a lit-par-lit injection pattern. pegmatite which is possibly a remnant of a pegmatite of below surface where it was narrower than at the surface. qualities of true emeralds, are found at several localities a Three types of pegmatite occur which are characteriz­ larger dimensions. A rough calculation indicated that there are at least 3000000 few kilometres southeast and east of Gravelotte. The emerald ed by the following minerals: (i) beryl, columbite-tantalite, There are several pegmatites running parallel to a tonnes of pegmatite material. occurs almost invariably in biotite schist at or near the edges cassiterite and apatite, (ii) spodumene and (ill) kyanite. diabase dyke on the farm Kalkfontein 615. Two of these peg­ of pegmatite bodies. The average size of the emerald crystals, Zoning took place, and the pegmatites consist mainly matites on the northern side of the dyke are zoned. The 4.1.2 Assegai most of which are of inferior quality, is small and their of a thin, fine-grained contact zone, a medium-grained wall larger of the two, 15 metres wide and 60 metres long, con­ distribution is limited. Nevertheless, crystals are found in zone and a coarse-grained innermost zone. Core zones con­ tains occasional beryl crystals up to 15 cm in diameter in A smaller pegmatite occurs on Assegai 143 HT, the which there are portions of pure transparent emerald from sisting of quartz and microcline-perthite occur only in a few a quartz-feldspar-mica zone along the poorly developed farm adjoining Witkop 507 IT. It strikes northeast-southwest, which stones up to 10 carats can be cut. Exceedingly fine small pegmatites in the central part of Palakop. In the beryl- quartz-perthite core of the pegmatite. The other, a smaller parallel to the foliation of the schistose country rock. The stones suitable for cutting into facetted gems, some of which pegmatite, is exposed in a prospecting trench. Its interme­ pegmatite is about 90 metres long, 5 metres wide and con­ bearing pegmatites the wall zone constitutes the greatest have realized up to R200 per carat, have been recovered. part of the body, whereas in the spodumene-bearingpegma­ diate zone consists of quartz, cleavelandite, and exploitable tites the innermost zone predominates. Mineralization took quantities of spodumene. Although beryl was not seen In this PEL 227 - 20 PEL 227 - 21 pegmatite, further prospecting may reveal its presence be­ on the farm Kalkfontein mentioned above, beryl, according fusion. They consist essentially of uniform mixtures of distributed pods of coarser grain-size. cause the association of beryl with spodumene and other to old records, was known to occur near Soekmekaar, but quartz, potash feldspar, a litt'e plagioclase and muscovite In the sodium-rich and lithium-rich pegmatites, beryl lithium minerals in pegmatites is a fairly common feature. more precise information concerning this occurrence does and, in some localities, accessory magnetite, ilmenite, may occur in very fine-grained form with the'sugary* albite Numerous pegmatite veins from less than 3 cm to aLout not seem to be available. apatite and zircon. On rare occasions, a little spessartite of the wall zone where it is seldom visible to the naked eye. one metre wide crisscross the gneissic Archaean granite is present. None of these pegmatites has yielded any minerals It may be accompanied here by tin or tantalite. Secondly, it exposed on rising ground or hillocks, and aiong stream 4.4 Other Areac of economic importance. may occur towards the inner side of themicrocline-bearing courses on the farms Boschfontein 736, Syferfontein 733, intermediate zone, in a range of grain sizes from fine to Another two areas in the Transvaal underlain by Holspruit 732, Rietfontein 731 and Rotterdam 12 and, close 5.2 Inhcmogenec s Pegmatites coarse, generally up to 15 cm in diameter but occasionally Archaean rocks merit closer investigation. They are the to Pietersburg, on Koppiesfontein 686. In some places these as giants up to 3 metres or more. In the lithium pegmatites, Lowveld north and west of the Soutpansberg and, farther to All three kinds of structural and lithologic units within small pegmatite bodies occur so close together that the rock heryl may also be present within the lithium units, particu­ the south, the low country west of Thabazimbi. In the former inhomogeneous pegmatites, listed by Cameron (1955), viz. could be described as a pegmatitic granite. The pegmatites, larly as very fine-grained to medium-grained, shapeless and area beryl is stated to have been collected on the farm Kit­ zonal pegmatites, fracture fillings and replacement bodies, consisting of quartz, feldspar and muscovite, are usually often transparent crystals within fine-grained lepidolite, chener 504. According to the latest report on pegmatites on have been recognized. fine-grained and homogeneous. Clusters and single little where it may be accompanied by microlite. In general, it this farm, the chances of finding payable deposits of beryl Zonal pegmatites are by far the most important, both crystals of beryl are frequently scattered through them, does not occur in the pure units of petalite, amblygonite or there are considered to be very remote. There have been quantitatively and economically. Since very little exploration particularly those pegmatites that contain garnet and mag­ spodurn ene-quartz. rumours that bervl also occurs on a neighbouring farm, has been done, one is largely dependent on natural exposures netite. Over the larger part of the area the granite is hidden In the posiassium-rich pegm atites, the beryl is generally Kempshell 497, situated a few kilometres northwest of Mopane. which present only limited scope for investigation. under covering of coarse-grained sand of quartz and feldspar. absent from the wall zone and is normally confined to the The possibility of beryl occurring in the terrain west of the The quartz and feldspar could have been derived from the junction between the intermediate zone of larger microcline Soutpansberg might be worth investigating because this min­ 5.2.1 Zonal pegmatites disintegration of pegmatites concealed by the cover. The crystals and the quartz core, where it may form medium to eral has been exploited in Bechuanaland, just across the numerous pegmatites in this area, and the manner in which Most zonal pegmatites appear to have been formed by very coarse crystals, with an apparent absence of any fine­ border at Martinsdrif. small beryl crystals are distributed in them, may be an the crystallization of magmatic fluids within dilations in the grained beryl. The occurrence of beryl appears to depend on Apart from a report that beryl has been discovered in indication of the presence of low-grade disseminated de­ country rock. Crystallization proceeded from the walls in­ the development of the quartz core, being absent in those a pegmatite on the farm Carolina 76, about 50 km northwest posits of beryl in the granite and its pegmatites, and in the ward, producing a definite pattern of zones which *s common sections of the strike where the core is not developed. In of Thabazimbi, nothing is known of this or any other occur­ coarse quartz-feldspar sand. to most pegmatites. pegmatites where the quartz is limited to small patches rence, of pegmatites in the large granite area in this part of About 19 kilometres from Mooketsi Station, on the farm In this simplified pattern there is a narrow border within a core of perthite crystals, beryl may occur at the the Western Transvaal. A search in this areafor mineralized Welgevonden 886 which is situated on the divide between the zone, a few cm wide, at the contact with the country rocks. junction of the aibite and perthite zones. pegmatites may, however, be worthwhile. Lowveld and the Pietersburg Highveld Region, beryl had been This is usually composed of quartz, with aibite, rnustuviue collected in the past from a prospecting pit in a 10-metre- and tourmaline. Adjacent to this is a wall zone, consisting 5.2.2 Fracture fillings 5. CLASSIFICATION wide pegmatite. The pegmatite, exposed on the eastern end predominantly of aibite, frequently fine-grained or'sugary', Fracture fillings are relatively scarce. The most im­ of a ridge of Archaean granite, forms irregular outcrops Cameron (1955) has shown that the zonal classification with quartz and muscovice. The intermediate zone is charac­ portant occurrences are on Zoovoorby, and on Bok Island in over a distance of roughly 1,6 km. It dips 55 degrees to the first propounded by himself and co-workers can be applied terized by an increase of microcline-perthite which becomes the Orange River opposite Keimoes. On Zoovoorby a large southwest. The pegmatite has a coarse-grained-to-rnassive with success to the pegmatites of the northwestern Cape dominant in the potassium-rich pegmatites, sometimes occur­ vertical dyke of pegmatite, intrusive into quartz-rich granu- core of quartz and a border zone of medium-grained graphic Province and of South West Africa. ring as large crystals up to a metre or more in diameter. lite, is traversed by a 30 cm wide quartz-feldspar vein granite. Owing to the pegmatite being largely covered by Following Cameron, Jahns, McNair and Page (1949), Finally, there is the development of quartz in the core. striking in the same direction. It contains aggregates of debris and soil, and because of a reddish veneer on its ex­ these pegm atites have been grouped into the following classes: The chief modification to this simplified sequence ilmenite (up to 15 cm long), "blows" and irregular masses posures, little could be gleaned about its mineralogy and (a) Homogeneous pegmatites occurs in the lithium-rich pegmatites in which further in­ of chrysocolla, bomite and chalcocite, and small amounts of internal structure. Beryl occurs irregularly along the length (b) Inhomogeneous pegmatites termediate zones are developed adjacent to the quartz core. opal, epidote, turquoise, calcite and azurite. Although pros­ of the pegmatite. In the prospecting pit, where beryl was (i) Zonal pegmatites These zones are usually albite-rich cleavelandite, mostly of pected, the deposit is too small for economic exploitation. collected from the core zone, the crystals were seen to show (ii) Fracture fillings the lamellar variety, and contain discontinuous units of one a tendency to group together in clusters. Such clusters are (iii) Replacement bodies or other of the lithium minerals, lepidolite or spodumene. On Bok Island (Keimoes), fracture filling consists of up to 50cm wide; some individual crystals are 8 cm in dia­ (c) Segregations The crosscutting nature of many of these units suggests a thin veins of quartz and scheelite emplaced in pegmatite. meter. late-stage, and probably replacement, origin. The scheelite grains vary in size from specks visible only A methodical search for beryl deposits in pegmatites 5.1 Homogeneous Pegmatites Beryl may occur in any of the zones of a zoned pegma­ under an ultraviolet lamp to lumps a few cm in diameter. In more than 30 pegmatites studied, the quartz-scheelite veins and adjacent rocks should include the widespread area occu­ These pegmatites are the predominant type. They can tite, but is generally restricted to one or two. Within the never exceed a metre in length and 5 cm in width, and pro­ pied by rocks of the Archaean Complex between Pietersburg best be studied in the area adjoining the section of the Kaka- zones it may be evenly distributed, particularly when of bably represent the late phase of the pegmatite intrusions. and the Soutpansberg. Besides the beryl-bearing pegmatites mas Settlement known as Burger, where they occur in pro- fine grain, but it is more commonly restricted to randomly PEL 227 - 22 PEL 227 - 23 5.2.3 Replacement bodies growths of feldspar and quartz appear sporadically. The while others exhibit evidence for more tnan one mode of persed. This was favoured by the slip planes which, being grains of quartz and potash feldspar crystals are up to a The recognition of replacement bodies in pegmatite emplacement. low-pressure areas, naturally channelized the fluids. The few millimetres in diameter. Occasional large crystals of proved to be ^ considerable importance in the search for The following evidence, gleaned from field studies, extent of soaking of the country rocks was too low to result the latter are one centimetre in length. These are set in a radioactive minerals during 1944 - 1945 in the northwestern favours displacement as advocated by Chadwick (1958), as in extensive f eldsparthization, giving rise to gneisses, etc. medium-grained to coarse-grained, allotriomorphic, granu­ Cape Province, since identification of such minerals was opposed to replacement: lar mass of the abovenamed minerals in which the potash often difficult in the field. Radioactive minerals were, without 7. SOURCE OF PEGMATITES feldspar is replacing the quartz. 1. The pegmatites occur as veins and tabular bodies, with exception, associated with white or pink replacement bodies The segregations of pegmatite are traversed here and clean margins crosscutting all the other rock types The development of pegmatite has, over the last 100 of quartz and perthite strung out as lenses along the centres there by minute tongues of micaceous material and feldspar except dolerite. years, been attributed to a number of different processes or close to the wall zones of individual pegmatites. which can be traced towards and right up to the contacts 2. Detailed studies showed that where marker beds, such or to a combination of one or more of such processes, chief The rare-earth radioactive minerals are individual with the adamellite. These tongues, or veins, consist of one as aplites or dykes in the country rock, are obliquely amongst them being injection, segregation, secretion, re- crystals, crystal aggregates or small lumps, set in a base of the following: sericite; partly turbid oligoclase; sericite, transected by veins of pegmatite, they are invariably crystallization and replacement. of feldspar, and are invariably associated with fluorspar, biotite, spinel and magnetite. offset, indicating faulting movement, i.e. displacement. It is not the intention of the present author to review dark mica and tourmaline. Along contacts with pegmatitic segregations, the 3. In thin, tabular bodies of pegmatite following the strike all these different theories, but rather to state tha such Rare-earth minerals in small quantities are relatively adamellite is invariably a hybrid consisting of relatively of the country rock, removal of the pegmatite would in diverse conclusions, derived by so many competent ob­ abundant in limited areas. Immediately west of Kakamas, small amounts of plagioclase, abundant quartz and minor some instances allow the host rock to be fitted together servers for similar but genetically distinct rocks, are in­ 65 occurrences were recorded within approximately 50 km-, amounts of potash feldspar, orthopy roxene, biotite and opaque perfectly, suggesting that they had been forcibly parted dicative of several probable modes of origin. with the help of a Geiger-Muller counter. ore. No hornblende, a typical mineral of the normal adamel­ and no intervening material had been removed. No satisfactory explanation of the genetic relationship According :o radiation-intensity measurements, 48 of lite, was observed. 4. At some localities, marked beds or identifiable zones in of the pegmatite of the northwestern Cape Province has been the Kakamas pegmatites contained gadolinite, eight euxenite, Segregations similar to those on Geel Kop can be seen the country rocks wrap around emplaced bodies of peg­ given. Its origin (and age) is intimately bound up with that two monazite, two allanite and five mixed euxenite-gadolinite. on Warm Zand. They are seldom more than 25 cm in dia­ matite in such a fashion that no part of the stratigraphic of the so-called Namaqualand Granite-gneiss Complex de­ The euxenite group includes all the minerals fairly high in meter and are best developed in limbs of folds where they sequence is interrupted or terminated abruptly. Such scribed by Gevers, Partridge and Joubert (1937). This com­ L^Og and contains, on average, about 6 per cent of this oxide, are mterbedded with sediments. distorted country rock, moulded around a pegmatite, is plex is now known to consit of granites of magmatic origin while the allanite and gadolinite average only 0,4 to 0,5 per evidence for displacement of the former by the latter. as well as of reconstituted sedimentary and granitoid rocks. cent. The latter consist of autochthonous granite, ranging in miner- 6. MODE OF EMPLACEMENT The classic view is that residual magma, enriched in alogical composition from tonalite to granite - individual 5.3 Segregations Various mechanisms of emplacement have been pro­ volatile and rare elements, are intruded along fissures in bodies varying greatly in size - and exhibiting much mig- posed for specific pegmatites or groups of pegmatites. These the surrounding rocks. The temperature was high enough for Pegmatitic segregations and normal pegmatites were matite. Such rocks have been described by Jansen (1960), include: vhe magma to remain in a liquid condition for a long time. originally not distinguished in thefield. They were considered De Villiers and Sohnge (1959) and Poldervaart and Von (i) invasion of fluid, either essentially magmatic or Through orogenic movements, the magma is kneaded into to have a common origin and to be derived from the same Backstrom (1949), apart from Gevers, but the origin of the aqueous; the surrounding rock, forming larger and smaller bodies original magma. The segregations are now believed to be pegmatite cannot be related to any of these intrusives. (ii) forcible intrusion of country rock; not connected on the surface, the adjaceni rock at the same much older and are probably not all of the same age. Accor­ (iii) permissive draining into structural openings; time developing schistosity parallel to the sides of the The most logical explanation for the origin of pegma­ ding to Poldervaart and Von Backstrom (1949, p. 491 -492), (iv) segregations in magmas; pegmatite body. tites, to all intents and purposes the same over such a vast segregations in the grey gneiss originated during the Gariep (v) metasomatic replacement; The formation of pegmatites of the northwestern Cape area, is to postulate that they were formed during the same Orogeny. Pegmatitic segregations, enclosed in adamellite (vi) metamorphic differentiation; Province are favoured by the following conditions: orogenesis. on Geel Kop and traversed by minute veins of adamellitic (vii) concretion (crystals growing outward from a centre There are examples where the hosi rocks are com­ material, must either predate or belong to the adamellite in a solid medium, pushing aside the wall rocks); High temperatures were maintained over a period of pletely soaked with pegmatitic material and are intimately cycle of igneous activity. This raifips the question as to (viii) secretion (diffusion of particles to openings, where time when intermittent shearing stress resulted in the de­ intergrown and welded together. Space-problem considera­ whether pegmatitic fluids segregated from the adamellite they crystallize into open space). velopment of slip planes. These slip planes formed favourable tions lead to the surmise that pegmatite has completely re­ magma, and whether more than one phase of pegmatite in­ Of these, fractional crystallization of pegmatitic fluid structural locales into which alkali-alumina-silica fluids placed the host rock. Some pegmatites are merely clusters trusion is represented. Against this possibility is the fact inward into a chamber to which no pegmatitic solutions were preferentially migrated and crystallized as pegmatites. High of feldspar porphyroblasts in gneiss or schist, and all gra­ that, in appearance, mineral composition and mode of occur­ added, has the most adherents. temperatures prevailing throughout this period maintained dations can be found even up to large pegmatite bodies. rence, all the pegmatites are closely allied. Chadwick (1958) lists a Targe number of criteria for the high diffusion rates, and the Intermittent shearing stress In the segregations on Geel Kop, strained quartz and classifying the emplacing process. Certain lines of evidence opened the slip planes, permitting further immigration of Crumpling and plastic distortion of schists and gneisses untwinned potash feldspar are the main minerals. Minor are, however, interpreted differently by different investi­ fluids and development of zoned and composite pegmatites, adjacent to pegmatite bodies are common, and have been amounts of strongly zoned plagioclase and graphic inter- gators. Also, few pegmatites exhibit truly diagnostic features where earlier units show evidence of replacement by later taken to indicate forceful injection. Plastic deformation of units. Migrating fluids were channelized rather than dls- solid rocks by a fluid melt is, however, difficult to visualize, PEL 227 - 24 PEL 227-25 only deposits containing coarse crystals and masses are of unless crystallization forces and tectonic strain during and plant. 4. Likewise, intergrowths of amblygonite with quartz, or current economic interest. after emplacement of the pegmatites are held responsible. 7. A detailed economic survey of the markets and prices of plagioclase muscovite with quartz, beryl with quartz and The metals tantalum and columbium are derived mainly Many of the pegmatites studied exhibit structural re­ the minerals occurring in pegmatite deposits, with special plagioclase, and columbite-tantalite with quartz or plagio­ from members of the tantalite-columbite series and, to an lations which indicate volume-by-volume replacement of the emphasis on the availability of water, the great distance clase (where hand methods are ineffective for recovering appreciable extent, from microlite which occurs as finely host rocks, whereas others have made room by dilation. that these deposits axe from railheads, and the rugged the minerals sought), will have to be investigated and disseminated crystals in replacement bodies of lepidolite. The pegmatites are confined bodies without visible country in which they occur. successful ore-dressing techniques established. avenues of supply from conventional sources (mother mag­ In most of the pegmatites the distribution of valuable Detailed geological maps have been prepared which 5. The presence of iron in potash feldspar may subject the mas), but may be explained by migration along microscopic minerals is governed by the zonal structure, the analyses of show the size and shape of both the pegmatite bodies and product to penalties and, where some of the iron is pre­ and submicroscopic paths in the host rocks of activated ions, which can be used to guide prospecting, exploration, develop­ the component internal units of most of the major pegmatites sent in the form of dendrites (as at Noumas), it will be atoms and molecules. ment and estimation of tonnage and grade. It is well-nigh exploited; only these warrant further investigation. Con­ extremely difficult to separate; it may, on the other hand, impossible, however, to delineate such zonal structures from tacts between pegmatite units are for the most part grada- be present below the permissible limit, since the dendrites 8. EXPLORATION outcrops alone, even under very favourable circumstances. tionaL Most zones are continuous throughout the pegmatite form a thin veneer on the rocks. The zoning only becomes apparent where large artificial Comparatively little is known about South African peg­ bodies and reflect to some degree the shape of the pegmatite exposures have become available for study due to exploitation. 9. ASSESSMENT OF GRADE matites because the operators have, over the years, of body. Outer zones are shaped more like the pegmatite as a Elsewhere drilling and trenching will have to be undertaken necessity had to work at shallow levels, and could take out whole than are the inner zones, and more regular in thick­ Estimating grade and reserves requires that the type in an attempt to acquire these data. Even where zonal struc­ only those minerals for which there was a market at that ness. An appreciable number of zones are hood-shaped and of pegmatite and the size, shape and internal structure be tures can be established it will still be very difficult to particular time. The great majority of pegmatites are too are approximately parallel to the crest of the pegmatite. determined by detailed geological mapping and careful estimate tonnage and reserves, owing to the erratic dis­ small for mining except on a very small scale in shallow Distribution of minerals within most zones is fairly mineralogical study. tribution of valuable minerals within the zones themselves. opencast workings. There is little systematic preparation uniform, though small blocks of rock may be very rich or Since no single mineral assemblage or zone can be selected The mineral distribution is closely allied to the size, for mining, if any, and only a very general knowledge of as the sole source of beryl or any other valuable mineral, very poor in certain minerals. Mineral proportions may shape and internal structure of the containing pegmatite body, general exploration. Because no technically trained personnel the entire pegmatite will have to be considered a potential also change. The richest parts of some zones form offshoots and manifests itself as a series of successive shells, roughly are employed, no estimates of grade or reserves are made. ore body. that plunge in the same direction as the pegmatites. concentric about a number of innermost cores, developed In general, the pegmatite mining operations range in A coordinated programme is required, both for pros­ laterally along the strike of the pegmatite. Contacts between The question of whether any pegmatite, or adjacent size from one-man enterprises to small companies with a pecting and assessment in the field, and for research into pegmatite units are for the most part gractional. The thick­ groups of pegmatites, can be operated on a sufficiently large limited capital investment, and the mines are very small in the methods of the simultaneous recovery of all minerals ness of some zones is fairly uniform, whilst that of others scale to support the establishment of a venture based on relation to mines in other sectors of the mineral industry. present in pegmatites, the idea being to establish a centrally changes gradually rather than abruptly and irregular ly. mass wall-to-wall mining, followed by milling operations The mining method is simply a process of following the ore located processing plant to treat material from several de­ designed to recover all useful minerals from the ore, can­ Distribution of minerals within most of the zones is along narrow zones where the structure is simple, to a posits and to recover as many products as possible. not be answered without further research being undertaken subject to continual changes, small blocks of rock being very limited depth of 5 to 8 metres. These zones are seldom The following should, however, be borne in mind: on the following aspects: rich, or conversely very lean, in certain minerals. This is more than 1 to 2 metres wide. A limited number of work­ 1. Potash feldspar containing more than negligible quantities especially the case close to the contacts of large xenollths of men are employed, using little mechanical equipment. 1. Whether diamond drilling can be used to determine the of intergrown tourmaline, garnet or biotite, is valueless country rock in the pegmatite or where the contact between Pegmatites are the chief source of commercial feld­ grades of the different minerals of potential economic for ceramic use. Portions of the Noumas microcline are pegmatite and country rock becomes either steeper or flatter spar, scrap and punch mica, beryllium, tantalum-columbium, value in the pegmatites. intergrown with garnet, but can probably be avoided by to form the so-called "rolls". These xenoliths can be scores and lithium and bismuth minerals, produced respectively 2. Ths distribution of valuable minerals in the pegmatites. selective mining which in its turn complicates the con­ of metres in length, both laterally and vertically, but are, from microcline-perthite, muscovite, beryl, tantalite-colum- 3. The mineralogical characteristics of such minerals and cept of wall-to-wall mining of the entire pegmatite. more often than not, less than 3 metres in width. Concen­ bite (and microlite), spodumene, native bismuth, bismuthinite their variation in the different zones of the pegmatite. 2. Intergrowths of plagioclase with potash feldspar lower the trations of pegmatite minerals of commercial value are and other bismuth minerals. Thepegmatites have also yielded 4. The reserves of the different associated industrial value of the latter. At Noumas, albite (cleavelandite) is associated with these inclusions of country rock, following small amounts of uranium/thorium and rare-earth minerals, minerals which would help to pay the cost of mining the found intergrown with microcline-perthite and will prob­ an essentially regular and orderly pattern. There is a general copper ores, lithium and calcium phosphates and kaolin, rarer but higher priced minerals such as columbite- ably be difficult to separate out, quite apart from the cost systematic arrangement of lithologic units parallel to the but not on a commercial scale. tantalite and beryl. factor involved, contacts of the xenoliths, and where these are of limited size Feldspar and mica are by-products derived from the 5. The mineralogical and structural changes that occur at 3. Graphic intergrowths of potash feldspar and quartz con­ a decided concentric build has been achieved. Moreover, the mining of spodumene, beryl and tantalite-columbite, and depth in these pegmatites. stitute the wall zone of most pegmatites and can form shape and distribution of many of these units reflect the hence the general output normally varies according to market 6. Development of efficient ore-dressing techniques for the an appreciable part of the pegmatite as a whole. Where general shape or structure of the inclusion, irrespective of conditions. The spodumene and beryl are recovered from recovery of feldspar, tantalite-columbite, spodumene, the concentrating method is hand cobbing, the quartz that of the host pegmatite body. • the host pegmatite by rough cobbing and hand sorting, thus sphene, beryl and other valuable minerals in a single cannot be separated. Replacement bodies form at the expense of pre-existing PEL 227 - 26 pegmatite, primarily along the contact ofdifferentlithologic be made for differences in specific gravity, and the percent­ PEL 227 - 27 and structural units. They range from thin, discontinuous age of mineral by weight can be determined. veins to almost complete pseudomorphs of zones several As in other types of sampling, it is necessary to con­ TABLE 1: PREDICTED GRADE COMPARED WITH PRODUCTION FIGURES Micro- tens of metres thick. They may be tabular, vein-like or sider grain size and evenness of distribution in determining Musco­ Lepi­ Spodu­ Tanta-I Uthlo- Zones '.uartz J Albite cline- Beryl Apatite Garnet Totals vite dolite mene Ute nojrllite Bismuth irregular units, and extend across boundaries between two how large an area should be measured. For the fine-grained perthite or more adjacent zones. portions, microscopic counts were considered but were found A. Wall zone 36.7 2S.9 17,3 11.4 1.5 0.7 0,6 1.5 0.1 1.2 0,02 0.5 100.3 Quartz, sodic albite and lepidolite are the most common to be impracticable because the optical properties of quartz, B. Hood zone 29.2 - 65,3 5,5 -- O.l - 0.2 - -- 100.3 plagioclase and beryl are too similar to make these minerals C. Interme­ constituents of pegmatite replacement units. Much of the diate zone albite occurs as cleavelandite, the remainder as fine-grained readily distinguishable in small grains during the process of a) Foot Wall 38,4 17.5 4.5 7.6 3.1 23.0 5.6 0.3 0.1 0.2 100.2 to medium-grained crystalline aggregates. Most of the other counting. b) Hanging Wall 55,6 9.4 11.4 6.2 11.8 5.6 -- 0.5 - 100.0 common pegmatite minerals, and nearly all the economically Experience has shown, however, that for rocks with an D. Replacement zone 13,3 19.3 9.2 6.1 48.0 4.1 -- 0.2 100.1 2 important types, are closely associated with replacement average grain size of 5 cm or less, 10 m are normally ade­ E. Hood zone & 2 7.2 58.0 9,0 -- 0.6 0.2 0.2 1 -- 1U0.2 bodies which are thereforeof major importance. Spodumene, quate; for an average grain size of 15 cm, 100 m should be Wall zone 25.2 F. Core zone 21.4 - 68.0 2.4 5,6 1.9 --- 0,5 -- 99.8 beryl and tantalite-columbite are significantly developed. measured, and for 30cm, 500m2 suffice. A+B+C+D+E+F 31,4 11,8 33.4 6.9 9.2 5,0 1.0 0.3 0.2 0.6 0.02 0.1 »°.7 Geological techniques have been applied with increasing In the field, measurements of mineral intercepts were Production 4.3 0.2 0,02 success, in overseas countries, to the economic analyses of made along linear traverses spaced a metre apart. Several Figures 5.0 1.0 1 pegmatites since the start of World War II. Results obtained sets of these traverses covered each exposure of the pegma­ in South Dakota, United States of America, by Staatz et al tite both on the surface and in the excavation. The respective (1963) indicated that grain measurements are at least as intercepts were converted to volume proportions of minerals position of the zones at points where no exposure is pro­ that, generally speaking, estimates of reserves of valuable accurate as channel or bulk sampling, provided the crystals and then to weight proportions. vided by mine workings or boreholes, the presence of xer.o- minerals in pegmatite deposits are not as unreliable as is exceed one centimetre in diameter. Where zones, or both structural and lithologic units liths of all sizes which may occur sporadically throughout commonly believed. South African literature contains no reference to were unequally exposed, the measurements were accordingly thï pegmatite, major variations in grain sizes within cer­ To enable an estimate to be made of the ore reserves methods of grain measurements made to evaluate grade of weighted in computing the average content of each mineral. tain zones where crystals are either too large or too small of a pegamtite, a certain amount of preliminary dvelopment ore in pegmatites. None of the minor accessory minerals in the pegmatite in relation to the norm for that particular zone, incorrect must have been undertaken. From this development and Because the word grade is used in several different was considered in the measurements which were confined to relative length of traverses to be applied in each to ensure previous exploratory work on the deposit, a good deal of in­ senses in pegmatite mining and in commerce, it is necessary quartz, albite, microcline-perthite, muscovite, lepidolite, a reasonably small analytical or precision error, and t.ie formation should have become available regarding the geo­ to define this term more precisely for the purpose of the spodumene, beryl, apatite, tantalite, lirhinnhyllire, bismuth almost complete removal of certain minerals in certain logy of the occurrence, the amount and comparative value present investigation. and garnet. zones because of mining activities. of which will vary considerably from one pegmatite to the The grade or mineral content of a pegmatite deposit, Grades for the different minerals of the different zones Since the basic data are not exact, and often speculative, other. It should give a good idea of the limits of the ore along as determined by grain measurements on representative were determined separately since they are subject to wide it is questionable whether great refinements in calculation and across the strike and of the average width and structure faces, expresses the total percentage of mineral present. variations. Results are given in Table 1, where they are also are warranted. However, it seems probable that reasonably of the ore body down to the depth reached, and should furnish It can thus be directly applied to express the grade of poten­ compared with the production figures for the period Septem­ close approximations have been attained for the more fully sufficient geological data to permit an approximate forecast tial reserves. ber 1961 -September 1964. exposed deposits. Counts of different but geologically com­ to be made of the persistence, or otherwise, of the deposit Grade can also be expressed by a single figure for Although care was exercised to ensure that the faces parable parts of a given deposit, when matched against one in depth. each or a number of pegmatites in terms of rand per tonne sampled were as representative as possible, accessible ex­ another, show satisfactory agreement. In the northwestern Cape Province and Namaqualand, of rock. Such a figure will, however, still have to be used in posure in some parts of the mine are virtually non-existent, From the practical standpoint, the significant figures mica, feldspar, spodumene, beryl, microlite, bismuth and conjunction with percentage figures which remain the same because they were either mined out completely or stripped for grade are those given for the full thickness of the peg­ tantalite-columbite could only be profitably extracted by for each deposit or part of a deposit, whereas grade ex­ of all valuable minerals. At such localities selection of re­ matite, although the valuable minerals are concentrated in selective mining of recognizable rock units within which pressed in terms of rand value will vary with price changes. presentative faces is difficult, if not impossible. different zones, because wall-to-wall mining is to be con­ concentrations of these economically desirable pegmatite The determination of grade from grain measurements For minerals such as tantalite-columbite and bismuth, sidered, and not selective mining. minerals occur sporadically. The shape and distribution of is an adaptation of the Rosiwal Method of micrometric analy­ which are too fine-grained or disseminated to be measured many of these units reflect the general shape or structure of ses applied macroscopically, and consists of measuring the satisfactorily, grab samples were taken at a number of 10. ESTIMATE OF RESERVES the host pegmatite. intercepts of grain boundaries on lines at fixed intervals of working faces and pulverized. The panned concentrates ob­ an exposure. tained were then weighed to obtain representative values. It is still widely believed that an appraisal of the grade The estimation of pegmatite reserves rests on the The total area of the rock exposure and area of the The chief sources of error in the figures are the possible and reserves of pegmatites in advance of mining can only be prediction of the size and shape of such zones, as well as mineral can be used to obtain volume, or corrections can occurrences of major irregularities in the sub-surface dis- made in a most general way. Intensive studies of the eco­ of the pegmatite as a whole. The wall, intermediate (of which nomic geology of pegmatites during recent years indicate there may be more than one), core and replacement zones PEL 227 - 29

PEL 227 - 28 REFERENCES are all potential ore bearers, whilst the chill, or border and In the case of pegmatkcr «vhich are largely under­ Andersen, O. 1931: Jansen, H. 1960: hood zones, are invariably barren. Laboratory investigations developed, certain assumptions have to be made regarding Discussions of certain phases of the genesis of peg­ The geology of the Bitterfontein area, Cape Province: matites. Norsk, geol. Tiddskr., 12, p. 1 - 55. Expl. Sht. 253, geol. Surv. S. Africa. have shown that it would be advantageous to employ portable the continuity and grade of the ore between exposed and pilot plants for the recovery of certain minerals such as sampled openings, and extensions of ore beyond exposed ore Behrend, F. 1933: Landes, K.K. 1933: spodumene, columbite-tantalite and microlite, which would faces. In making these assumptions the geologist must inter­ Uranerz fuhrende Pegmatitgange in Siidafrika undihre Origin and classification of pegmatites: Amer. Min. Geochemie: Arch. Lagerst Forsch., 54. 10, p. 355 - 411. -iiio help to obtain more reliable grade figures for each pret the data available, as the accuracy of the final results individual zone. These tests comprise heavy-media separa­ will depend to a large extent upon his experience and the Cameron, E.N., Jahns, R.H., McNair, A.H. and Page L.R. Mountain, E.D. 1931: tion, pneumatic tabling and electromagnetic separation. soundness of his judgement. Forecasts will be based on the 1949: Pegmatites of the Cape Province: Rec. Albany Mus., Internal structure of granitic pegmatites: Economic 4, p. 122 - 144. Estimates of ore reserves are bas^d upon the results geology, the amount of payable development and the grade of Geology Publishing Company, Urbana. the ore. As all these are subject to change and variation, it of exploration and development, and on the samples there­ Nel, L.T. 1965: is apparent that the estimation of ore reserves can never Cameron, E.N. 1955: from. Nuclear reactor materials: PEL-74,Geol. Div. Atomic Concepts of the internal structure of granitic pegma­ For individual pegmatites, the ore reserves for each be a precise and accurate procedure. It follows that serious Energy Board, S. Afr. tites and their applications to certain pegmatites in South body are the developed and partially developed ore having mistakes of interpretation are possible. This is especially West Africa: Trans, geol. Soc. S.Afr., 58, p. 45 - 70. Nel, L.T. 1965: an assay above the lower limit of payability, and are express­ the case should too much reliance be placed on the results Chadwick, R.A. 1958: Beryllium ore deposits in the Republic and South West ed in tonnes at the mean assay content for the different obtained from boreholes alone, which may penetrate enriched Mechanisms of pegmatite emplacement: Bull. geol. Soc. Africa: PEL-136, Geol. Div. Atomic Energy Board, S. Afr. or low-grade material which is not representative of the ore minerals recovered. Amer.,69, p. 803 - 836. At present very little is known of potential pegmatite body as a whole. Nel, L.T. 1968: Coetzee, F. 1964: reserves in ground already leased, and next to nothing in Once the volume of the ore within the explored area has Ore deposits of lithium in the Republic of South Africa: Pegmatietvoorkomste op Witkop 507 IT en Assegai PEL-174, Geol. Div. Atomic Energy Board, S. Afr. tracts outside leased areas. The Geological Survey has been ascertained, the tonnage is derived from the volume 143 HT, wes van Piet Retief. Ann. geol. Surv. S. Afr., 3, carried out considerable regional and detailed mapping of by applying a cubic-metre-per-tonne factor which varies p. 127 - 132. Poldervaart, A. and von Backstrom, J.W. 1949: certain pegmatite fields, but, with one or two exceptions, for different ores, depending upon the specific gravity and De Jager, D.H. 1964: A study of an area at Kakamas: Trans, geol. Soc. S. an advanced stage of ore development has not been reached; proportion of each of the constituent ore and gangue minerals, The geology of the Noumas (Blesberg)pegmatitemine, Afr., 52. nor is enough known concerning ore grades to justify esti­ and the density (or, conversely, the porosity) of the mineral Namaqualand, Unpublished Rep. geol. Surv. S. Afr. complex. A conversion factor of 3 cubic metres of pegma­ mations of reserves. De Jager, D.H. 1967: Von Backstrom, J.W. and Nel, L.T. 1968: It is realized that in most pegmatite deposits it will tite ore per tonne has been applied to the pegmatites. Report on some pegmatites of the Kowiep (Groendoorn) Niobium and Tantalum Mineral Deposits in the Republic of South Africa: PEL-177, Geol. Div. Atomic Energy Board, hardly be safe to estimate any ore reserves beyond those Of the more than 12 000 pegmatites examined in the River gorge and ore in the Richtersveld, Namaqualand: Unpublished Rep. geol. Surv. S. Afr. S. Afr. exr- 3d or closely blocked-out by thorough prospecting and northwestern Cape Province and Namaqualand, 30 were ait»*, ing. Yet, even an order of magnitude is far better than mapped in detail. Estimates based on the techniques de­ De Villiers, J. and Sohnge, P.G. 1959: Von Backstrom, J.W. 1969: scribed above, and applied to the 12 largest pegmatites in The geology of the Richtersveld: Mem. geol. Surv. S. wild guessing. It is contended that reasonably reliable es­ Rare-earth mineral deposits in the Republic of South Afr., 48. timates are possible if detailed geological mapping, pros­ Namaqualand, indicated that there are approximately 4,5 Africa: PEL-193, Geol. Div. Atomic Energy Board, S. Afr. pecting and core drilling are carried out in order to deter­ million tonnes of pegmatite material present for every 30 Gevers, T.W., Partridge, F.C. and Joubert, G.K. 1937: mine parameters such as shape, vertical range and type of metres in depth. Estimated resources of beryl, lithium and The pegmatite area south of the Orange River in Nama­ Vor. Backstrom, J.W. and de Villiers, J. 1973: qualand: Mem. geol. Surv. S. Afr., 31. mineralization, contacts between different units, plunge, tantalite-columbite, at the given grades for every 30 metres The geology of the Orange River Valley between On- seepkans and the Richtersveld. Expl. Sht., 2817D Viools- regional dip and irregularities such as rolls and large in­ thickness of ore, are shown in the following table: Holmes, A. 1934: drif, 2818C and D. Goodhouse, and 2819C Onseepkans. Geol. clusions or xenoliths. Even though contacts between different The Gordonia uraninite and the Upper Precambrian Surv. S. Afr. Estimated Grade 6 Mineral Tonnes (x 10^ Value in Rand (x 10 ) rocks of Southern Africa: Amer. J. Sc. 27, p. 343 - 353. units may, for the most part, begradational,the occurrence Per Cent of a diagnostic mineral (or group of minerals) and the per- Beryl 22 7 Hugo, P.J. 1970: Von Backstrom, J.W. 1964: The geology of an area around Keimoes, Cape Province: entage or ratio of individual minerals or differences in Spodumene 2 32 1 The pegmatites of the Kenhardt and Gordonia districts, Tantalite- 0,1 2,2 20 Cape Province: Mem. geol. Surv. S. Afr. 58. Mem. 53. Geol. Surv. S. Afr. re^ure, invariably still define the limits of, as well as the columbite variation in, the types of mineralization. It is essential to endeavour to develop some technique Though small blocks of rock may be very rich or very to establish the degree of mineralization of a pegmatite prior lean in certain minerals, distribution of minerals within to its exploitation. Some workon analytical methods to estab­ most zones is fairly uniform. Thus, the content of any reason­ lish grade has been undertaken by the National Institute for ably large block of rock, at least several hundred tonnes in Metallurgy but core samples of chill and other zones of peg­ weight, is normally about tHe same as the average content matites are required in order to develop and test statistical of the entire zone. methods and techniques. ISBN 0 86960 419 8