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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.