THE ORE DEPOSITS OF SOUTH AFRICA 
 
THE ORE DEPOSITS 
 
 OF 
 
 SOUTH AFRICA 
 
 WITH A CHAPTER ON 
 
 HINTS TO PROSPECTORS. 
 
 BY 
 
 J. P. JOHNSON, 
 // 
 
 of Council of Geological Society of South Africa, 
 Certificated Mine Surveyor of the Transvaal, 
 Kiiif/'* Prizeman in Metallurgy. 
 
 PAHT 1. 
 
 BASE METALS. 
 
 WITH 1) Lid HAMS. 
 
 NEW YOEK: 
 
 THE NOEMAN W. HENLEY PUBLISHING CO., 
 132, NASSAU STREET. 
 
 LONDON: 
 
 CROSBY LOCKWOOD AND SON, 
 1908. 
 
Postal & Cable Address, Box 6231. 
 
 J. P. JOHNSON, 
 
 mining Geologist 
 = and engineer, = 
 
 Mines Sampled, Surveyed, and Valued. 
 
 33, Permanent Buildings, Harrison Street, 
 JOHANNESBURG. 
 
PREFACE. 
 
 THIS little volume is intended to meet a demand among 
 those technically connected with the mining industry, for a 
 co-ordinated and condensed account of the ore-deposits at pre- 
 sent known in South Africa. 
 
 It is also intended as a guide to the prospector. Only an 
 elementary knowledge of geology and some mining experience 
 are necessary in order to understand it. With these qualifica- 
 tions, it will materially assist him in his search for metallifer- 
 ous mineral occurrences and, so far as simple ores are con- 
 cerned, should enable him to form some idea of the possibili- 
 ties of any he may find. Regarding complex ores he will, of 
 course, need metallurgical advice in addition. 
 
 Throughout this book the stratigraphy of the country is 
 ignored, the principles of ore deposition being independent of 
 it. Moreover, it is already dealt with in Hatch and Corstor- 
 phine's "Geology of South Africa." 
 
 Unless otherwise stated the writer has seen the occurrences 
 described. 
 
 P.O. Box 6231, JOHANNESBURG, 
 August, 1908. 
 
CONTENTS. 
 
 PAGE 
 
 CHAPTER I. INTRODUCTION ... 1 
 
 PRIMARY ORES .. ... ... ... 1 
 
 SECONDARY ORES ... ... ... ... 8 
 
 SULPHIDE SEGREGATIONS . . ... ... 4 
 
 DYKE SEGREGATIONS AND PEGMATITES ... 5 
 
 CLASSIFICATION OF ORE-OCCURRENCES ... 6 
 
 CLASSIFICATION OF IGNEOUS ROCKS ... ... 7 
 
 CHAPTER II. TlTANIFEROUS AND CHROMIFEROUS IRON OxiDES 9 
 
 CHAPTER III. NICKEI 12 
 
 CHAPTER IV. COPPER 18 
 
 CHAPTER V. COBALT 28 
 
 CHAPTER VI. TIN 30 
 
 CHAPTER VIL MOLYBDENUM... 38 
 
 CHAPTER VIII.- TUNGSTEN 40 
 
 CHAPTER IX.- LEAD 41 
 
 CHAPTER X.- MERCURY ... 46 
 
 CHAPTER XI. ANTIMONY ... 47 
 
 CHAPTER XII.-lRON 49 
 
 CHAPTER XIII HINTS TO PROSPECTORS ... ... 50 
 
 ANTIMONY ... ... ... ... 51 
 
 ARSENIC ... ... ... ... ... 52 
 
 CADMIUM... ... ... ... ... 52 
 
 CHROMIUM ... ... ... 52 
 
 COBALT AND NICKEL 53 
 
 COPPER ... ... ... ... ... 53 
 
 LEAD ... ... ... ... ... 54 
 
 MANGANESE 54 
 
 MERCURY... ... ... ... ... 55 
 
 MOLYBDENUM ... ... ... ... 55 
 
 TANTALUM 55 
 
 THORIUM 55 
 
 TIN 56 
 
 TUNGSTEN 56 
 
 URANIUM... ... ... ... ... 56 
 
 VANADIUM 57 
 
 ZINC ... 57 
 
The Ore-Deposits of South Africa, 
 
 CHAPTER I. 
 
 INTRODUCTION. 
 
 Ax understanding of the genesis of an ore occurrence is 
 essential before any exploitation of it is attempted, since it 
 alone enables one to answer the all-important questions, 
 whether it will continue in depth and whether its value will 
 increase or decrease. Our knowledge of the processes of ore- 
 formation is now sufficiently advanced to enable us, in the 
 majority of cases, to answer these questions with confidence, 
 though in other instances it is still impossible to do so. 
 
 PRIMARY ORES. 
 
 The investigations of the last few years into the genesis of 
 ore-occurrences have resulted in the almost universal accept- 
 ance of the theory that they have a magmatic origin, that the 
 deep-seated magmas contain water and dissolved metals which , 
 upon the ascent of the magma into a zone of lessening pres- 
 sure, escape, penetrate the overlying rocks, and even reach 
 the surface as thermal springs. The immediately resulting 
 ore-occurrences are, in order of formation : (1) Segregations 
 within the magma ; (2) Impregnations at or near the point 
 where the volatile substances left the magma ; and (3) 
 Deposits by waters condensed at greater distances from the 
 magma on their way to the surface. No better illustration of 
 this theory could be instanced than the great Bushveld lac- 
 colith, which is probably unique among plutonic masses in the 
 
2 /i\; ^ij^Jt.Jwi Dejjositv of South Africa. 
 
 extent to which its structure has been revealed by denudation , 
 and in the slight amount of distortion to which it has been 
 subjected by subsequent earth movements. This igneous com- 
 plex consists of a dominant granite core which passes along 
 its circumference, through syenites and gabbrodiorites, into 
 pyroxenite containing ore-bodies of the first class, namely, 
 segregations of titaniferous and chromiferous iron oxides. The 
 rock masses overlying the central granite portion, as well as 
 the upper, and earlier solidified, part of the granite itself, are 
 impregnated with tin and copper minerals, constituting ores 
 
 FIG. 1. 
 Section at Blaafjeld, Scandinavia (after Voyt). 
 
 Syenite with 2 per cent, of ilmenite, containing basic pegmatite with 40 
 per cent, of ilmenite and segregated masses of ilmenite. 
 
 of the second class. While the copper-lead-zinc veins in the 
 surrounding strata afford excellent examples of the third class. 
 The kinship between a metalliferous segregation in pyroxenite 
 and a metalliferous deposit in a fissure is, no doubt, very dis- 
 tant, but it is nevertheless real. 
 
 In considering the sequence of these ore-occurrences it 
 should be borne in mind that the exterior of the intruded 
 magma will solidify before the interior ; that the molten por- 
 tion of the latter, with its periodically escaping residual water 
 and dissolved metals, would recede more and more from the 
 surface as the whole gradually cooled ; and that what was in 
 
Introduction. 3 
 
 :li< earlier stages a zone of gaseous impregnation might at a 
 later period become a zone of deposition from solution. 
 Further, it is probable that at different levels in the super- 
 incumbent rocks penetrated by the ascending vapours and solu- 
 tions, different chemical reactions take place according to the 
 pressure and also to the constitution of the rock, involving the 
 precipitation of different groups of minerals. 
 
 SECONDARY ORES. 
 
 At, and within a comparatively short distance of, the sur- 
 face, ore-bodies are subject to the disintegrating influences of 
 the atmosphere and of descending surface waters. This dis- 
 integration, which is chiefly due to the presence of oxidizable 
 minerals, usually extends more or less completely down to the 
 level of the ground w r ater, and its intensity is dependent on 
 the amount of these oxidizable minerals present. In most 
 ore-bodies the original valuable minerals are sulphides w r hich 
 are all readily oxidized, and many of these are converted into 
 soluble compounds, which are carried down by the descending 
 waters and reprecipitated at the bottom of the porous zone of 
 oxidation, in the form of carbonates, chlorides, oxides and 
 silicates. In some cases the compounds in solution, on reach- 
 ing the unoxidized zone, are reconverted into sulphides. 
 
 Thus three zones are frequently encountered in opening up 
 such ore-bodies, namely, (A) A barren zone of disintegrated 
 rock, termed the gossan, (B) A high-grade layer of oxidized or 
 sulphide ore, know r n as the zone of secondary enrichment, and, 
 (C) The main body of primary low-grade sulphide ore. Fig. 2 
 shows an actual example. 
 
 In other ore-bodies where the valuable mineral cassiterite 
 for instance is insoluble, no such chemical concentration 
 takes place, but rich detrital accumulations may result from 
 their denudation. 
 
 Most of the metalliferous occurrences being mined at the 
 present day are secondary ore-bodies of the above kinds. 
 
4 Ore Deposits of South Africa. 
 
 SULPHIDE SEGREGATIONS. 
 
 In view of the fact of magmatic differentiation there is noth- 
 ing astonishing in finding segregations of the oxides, ilmenite, 
 magnetite and chromite, since all are common constituents of 
 basic igneous rocks. Now in Scandinavia, Canada and South 
 Africa, sulphide aggregates (pyrrhotite, pyrite and chalcopy- 
 rite, containing a small percentage of nickel and cobalt) have 
 been discovered with such strikingly similar associations, that 
 
 FIG. 2. 
 
 Section through Utah and Boston Copper Mines, Binyham, U.S. (after 
 
 Ingalh). 
 
 (c) Quartz -porphyry dyke impregnated with primary sulphide (chalcopy- 
 rite). Copper contents about 1 per cent, (a) Leached zone stained brown 
 with iron oxide and mottled with green and blue copper carbonates. Unpay- 
 able. Thickness 30 to 150 feet, (b) Zone of secondary sulphide (chalcocite) 
 enrichment. Copper contents 2 per cent. Thickness 100 to 300 feet. 
 
 they are regarded by many, with good reason, as magmatic 
 segregations also. Others, however, maintain that they are 
 merely ordinary impregnations. There seems to be one point 
 of difference, namely, that while the oxide segregations, though 
 usually near the margin, are always distinctly within the 
 
Introduction. 5 
 
 igneous rock, the sulphide aggregates, on the other hand, are 
 right at the contact of country and intrusive rock, while this 
 last is much altered there. The feature certainly lends some 
 support to the argument of the objectors. In both cases the 
 igneous rock is similar and a gradual passage can be seen 
 between it and the metalliferous masses. The absence of 
 undoubted original sulphides in igneous rocks presents another 
 obstacle to this interpretation of the occurrence. Oxidizing 
 conditions were obviously the rule in fused magmas. At the 
 same time there may have been exceptions. It has been 
 suggested, for instance, that the escape of sulphurous gas 
 through the still molten rock along the contact converted the 
 contained metals into sulphides. The remarkable identity of 
 the occurrences in such widely separated parts of the world, 
 taken in conjunction with their undeniable resemblance to 
 undoubted oxide segregations, makes it highly probable that 
 they are, indeed, segregations also. 
 
 DIKE SEGREGATIONS AND PEGMATITES. 
 
 Dykes are offshoots from deep-seated magmas that have 
 welled -up fault planes during periods of disturbance. They 
 are similar in composition to the portion of the magma from 
 which they come. Magmatic segregations of metalliferous 
 minerals are hence sometimes met with in the form of dykes. 
 
 Those very coarse-grained aggregates of quartz and felspar, 
 or of felspar and pyroxene, with or without accessory minerals, 
 known as pegmatites, which are so frequently met with in 
 granite and gabbrodiorite areas, and which are chiefly noted 
 as the source of commercial mica, have long been the subject of 
 speculation. Though generally regarded as modifications of 
 the main body, it is maintained by many that pegmatites, 
 whether in the form of irregular masses or of vein-like dykes, 
 are not differentiations of the magma, but have crystallized 
 under high pressure from the superheated aqueous solutions 
 that remained after its solidification. In other words, that 
 
6 Ore Deposits of South Africa. 
 
 they occupy a position intermediate between igneous masses 
 and mineral veins. 
 
 If the conception of the genesis of ore occurrences pre- 
 viously described be correct, it is clear that many substances 
 are more soluble in such residual waters than in the magma 
 itself. Examples of these are tourmaline, fluorite, cassiterite 
 and allied minerals. Now many acid pegmatites actually con- 
 tain these minerals while their very coarse crystallization is 
 such as would result from the slow cooling necessary if the 
 above contention be correct. 
 
 In view of the similarity in constitution between granites 
 and certain mineral veins, for instance, those of the Eooi Berg, 
 this is certainly an attractive theory. The possibility of the 
 tourmaline, fluorite, cassiterite, etc., in the pegmatites, being 
 of a secondary nature, however, must not be overlooked. In 
 fact, a great deal of w T ork will have to be done before this 
 explanation of the origin of pegmatites can be proved or dis- 
 proved. 
 
 CLASSIFICATION OF ORE-OCCURRENCES. 
 
 A number of classifications of ore-occurrences have been 
 proposed in recent years, but none of them can be said to be 
 satisfactory from the point of view of the mining man. In the 
 following classification the writer has attempted to remedy 
 this defect. The object of classification in scientific and tech- 
 nical subjects is to enable the student to more readily obtain a 
 firm grasp of his subject and of the interrelation of its several 
 branches. In the imparting of knowledge it may be compared 
 to organization (as opposed to muddle) in other branches of 
 human endeavour. Such a classification must present a broad 
 view unobscured by minor details, and is necessarily, to a 
 certain extent, arbitrary. Actually no hard and fast line can 
 be drawn between the different types of ore-occurrences. In 
 such a classification, too, the main sub-divisions at least should 
 be of a kind that would be recognizable in the field ^vithout 
 
Introduction. 7 
 
 recourse to laboratory investigations. The following is the 
 proposed scheme in brief ; the relation of the sub-divisions to 
 the terms Eeef and Lode being indicated also. By ore is 
 meant any metalliferous mineral or rock of present or prospec- 
 tive economic value. 
 
 A. Magmatic Segregations. 
 
 B. Irregular Impregnations. 
 
 C. Regular Impregnations of a Stratum. 
 
 D. of a Dyke. 
 
 E. ,, ,, along contact with 
 
 Reefs. 
 
 a Dyke. 
 
 VLodes. 
 
 F. ,, ,, of the walls of a 
 
 fissure. 
 
 G. Regular Gratifications* (in fissures) 
 H. Irregular Gratifications (in pockets). 
 I. Detrital Accumulations. 
 
 The great majority of ore-occurrences fall under the head- 
 ing of Impregnations and Crustifications. Impregnations are 
 those in which the metalliferous and accompanying minerals 
 are disseminated throughout a pre-existing rock. Crustifica- 
 tions are those in which the metalliferous and accompanying 
 (" gangue ") minerals occupy cavities in a rock. 
 
 CLASSIFICATION OF IGNEOUS ROCKS. 
 
 The classification of the igneous rocks here employed is 
 that recommended for field use by the authors of the Quantita- 
 tive Classification of the Igneous Rocks. It is a classification 
 based entirely on megascopic characters which, however, in a 
 broad way reflect their chemico-mineralogical constitution. 
 The mining geologist seldom requires to define an igneous 
 rock more exactly, and when it is necessary to do so, a descrip- 
 tion of its microscopical characters will serve the purpose. 
 
 * Crustifications " Fillings of Fissures and other Cavities," Posepny, 
 Genets of Ore Deposits, p. 12 ^1905;. 
 
8 Ore Deposits of South Africa. 
 
 The primary sub-division is into phanerites and aphanites. 
 Phanerites are those whose constituent minerals are sufficiently 
 large to be visible to the unaided eye. Aphanites are those 
 whose constituent minerals are too small to be visible to the 
 naked eye. Those rocks, intermediate between phanerites 
 and aphanites, which consist of megascopic minerals dis- 
 tributed throughout a groundmass of microscopic constituents 
 are termed porphyries. 
 
 The major bulk of the phanerites may be referred to three 
 groups,' (1) Granite, those composed essentially of quartz and 
 felspar, (2) Syenite, those composed essentially of felspar and 
 amphiboles or pyroxenes, the former being dominant, and 
 (3) Gabbrodiorite , those composed essentially of pyroxene or 
 amphibole and felspar, the latter being subordinate. 
 
 In addition to these are the rare felspar-less phanerites 
 which are named according to the dominant constituent 
 mineral, e.g., Amphibolite, Pyroxenite, Peridotite, etc. 
 
 Since quartz and the felspars are light in colour and the 
 pyroxenes and amphiboles are dark, it is usually possible to 
 infer the end of the scale to which an aphanite inclines. 
 Hence, this factor whether acid or basic should be men- 
 tioned. 
 
 The porphyries are further qualified as Quartz-porphyries, 
 Felspar-porphyries, Pyroxene-porphyries, etc., according to 
 the mineral megascopically developed. 
 
CHAPTER II. 
 
 TITANIFEROUS AND CHROMIFEROUS IRON OXIDES. 
 
 BUSH VELD LACCOLITH (A*). 
 
 SEGREGATIONS of titaniferous and chromiferous iron oxides 
 occur in the basic margin of the Bushveld laccolith, and 
 although not at present of commercial value as iron ores, since 
 both the titanium and chromium, in the quantities in whicli 
 they occur in these ore-bodies, cause serious difficulties in their 
 treatment, t must yet sooner or later come within the range of 
 payability, either through scientific investigation overcoming 
 the difficulties or through the exhaustion of the more easily 
 treated ores. 
 
 Enormous bodies of the titaniferous ore have been located 
 all along the periphery of the laccolith. The mineral is mainly 
 magnetite, the titanium being present either as a chemical 
 combination in place of some of the iron, or else as a mechani- 
 cal mixture in the form of ilmenite or rutile. 
 
 The chromite bodies, though probably possessing an equally 
 long distribution are not so large. They have been well 
 studied along the southern and eastern margins of the lac- 
 colith by Hall and Humphrey, while, more recently, Schoch 
 has a'lso added to our knowledge of them. They are associated 
 with very basic members of the marginal rocks, among which 
 types rich in pyroxenes and poor in felspars are common. The 
 ore occurs in fairly well denned sheets with a dip and strike 
 
 * The letters in brackets indicate the position of the ore-occurrence in 
 the scheme of classification. In this case for example (A) = Magmatic 
 Segregation. 
 
 t Although both titanium and chromium impart desirable properties to 
 steel when added in certain small proportions. 
 
10 Ore Deposits of South Africa. 
 
 roughly parallel to that of the periphery of the laccolith. In 
 thickness they range from five feet downwards, and usually 
 maintain a fairly uniform width for some distance. 
 
 In its purest form the ore consists of a black lustrous fine- 
 grained aggregate of chromite, which easily weathers to a 
 friable rock and becomes readily disintegrated into a heavy 
 dark-coloured sand. As the ore becomes less pure pyroxenes 
 appear, and the gradual transition can be traced from black, 
 heavy chromite-ore to less heavy and dark-coloured pyroxenite, 
 containing scattered grains of chromite, and thence into gab- 
 brodiorite. 
 
 A little platinum is associated with the chromite. 
 
 The southern belt stretches from north-west of the village 
 of Eustenburg to the Crocodile River, a distance of about 
 twenty-eight miles. The farms on which the chromite has 
 been located are : Boschkopje, Boschfontein, the Rustenburg 
 Commonage, Waterval, Arnoldstad, Kronendal, Rietfontein, 
 Kaffirskraal, Dekroon, Brakspruit, Spruitf ontein , Rooikopjes, 
 and others. The eastern belt stretches north-westwards from 
 the Steelpoort River, and chromite has been located on the fol- 
 lowing farms : Hendricksplaats, Mooihoek, Mondagshol, Twy- 
 felaar, Zwartkopjes, Klipfontein, Mooijalijk, Brakfontein, 
 Winterveld, and Jactslust. 
 
 When the proportion of chromium is high and that of iron 
 low, this ore is much valued for its chromic oxide. To find a 
 market it must contain not less than fifty per cent. Ore of 
 that standard fetches about 65s. a ton, while better qualities 
 command a premium. The laccolith occurrences hitherto dis- 
 covered do not come up to the market requirements. 
 
 SELUKWE (A). 
 
 Mennell states that chromite bodies are found in several 
 places along the great peridotite intrusion that runs from near 
 Fort Impatene to the Zambesi, notably in the Hartley and 
 Lomagundi districts. Mining is carried on in a hill of 
 
Titaniferons and Cliromiferous Iron Oxides. 11 
 
 chromite at Selukwe. This occurrence is about a mile from 
 the peridotite, but may be in an offshoot from it. The writer 
 has not seen this ore-body. The following outputs have been 
 registered : In 1905, 276 tons; in 1906, 3,371 tons, and in 
 1907, 8,017 tons. 
 
CHAPTER III. 
 
 NICKEL. 
 1NSIZWA (A). 
 
 Tms nickel occurrence is of special interest in that it be- 
 longs to the class of magmatic sulphide segregations. 
 
 The Insizwa range is situated near Mount Ay lilt. It is 
 composed of a big gabbrodiorite laccolith intruded into a series 
 of sandstones and shales. The igneous rock has been exposed 
 by denudation all over the upper portion of the range, the 
 sedimentary formation on which it rests constituting the lower 
 slopes. The shales are much altered and indurated at the con- 
 tact. 
 
 The mineral is pyrrhotite, with which is mixed a little 
 chalcopyrite, and, in very subordinate quantity, pyrite. The 
 nickel content averages about seven per cent. Traces of cobalt 
 are also occasionally present. 
 
 The sulphides are disseminated throughout the marginal 
 portion of the gabbrodiorite, and increase in quantity towards 
 the contact where they form lenticular aggregates, and also 
 slightly impregnate the wall rock. 
 
 This mode of occurrence of the ore is strictly homologous 
 with that of the well known Scandinavian and Canadian bodies, 
 while the. comparative freshness of the igneous rock in this 
 instance seems for the first time to place sulphide segregation 
 beyond doubt. 
 
 The occurrence is at present only in the prospecting stage, 
 but there can be no doubt that sooner or later it will become of 
 economic importance. 
 
CHAPTEE IV. 
 
 COPPER. 
 OOKIEP (A). 
 
 THE Ookiep and neighbouring mines are situated in Little 
 Namaqualand. 
 
 The writer has not seen them, the following account being 
 derived from a paper* by Kuntz : 
 
 The surrounding district is occupied by granite and associ- 
 ated schists. This formation is traversed by five parallel west 
 and east lines of crush along which dykes of gabbrodiorite have 
 risen. It is in these dykes that the copper occurs. 
 
 The dykes outcrop prominently. In some cases they are 
 traceable for miles without break, but in others are in evidence 
 only from point to point, with big gaps between. 
 
 The copper-bearing minerals, chiefly bornite and chalcopy- 
 rite, are disseminated in minute quantities throughout the 
 whole of the gabbrodiorite, and in spots almost entirely replace 
 it. 
 
 While the entire mass of the gabbrodiorite thus contains 
 traces of copper and rich patches occur here and there through- 
 out, it is only in a few places that it is of a payable nature. 
 In these places the ore occurs in the form of very large and 
 high-grade pockets. 
 
 Kuntz considers that these pockets have been formed at 
 points where the dykes are intersected by later faults. 
 
 On the most southern line are situated the abandoned mines 
 of Spektakel and Springbok, from which large quantities of 
 
 * J. Kuntz, Transactions Geological Society of South Africa, VII., p. 70- 
 72 (1904). 
 
14 Ore Deposits of South Africa. 
 
 high-grade ore were obtained, together with the less produc- 
 tive workings of Koperberg. 
 
 On the second line occur the mines of Nababeep, Ookiep, 
 and Narap. A plan and section, reproduced herewith (fig. 3), 
 of the Ookiep pocket is given by Kuntz in his p&per. Its shape 
 is oblong, with a peculiar prolongation along the cross break. 
 
 1 
 
 FIG. 3. 
 
 Plan and section of Ookiep Copper Nine (after Kuntz). 
 
 Its extent from west to east is nearly a thousand feet, its 
 greatest width is about two hundred feet, and its greatest 
 thickness (vertical) three hundred feet. 
 
 The Nababeep is a similar enormous ore-body, while Narap 
 is only a small pocket and has been abandoned. 
 
Copper. 15 
 
 On the fourth line lies the Tweefontein mine, which is 
 probably the most instructive to the geologist. Kuntz also 
 gives a plan and section of this mine, while Ronaldson* has 
 figured a further section, reproduced herewith (fig. 4), made 
 at a later date. It consists of three pockets. Ore-bodies No. 
 
 TWEEFONTEIM 
 
 MINE. 
 
 Cross Section- of 
 Ort-body JK1 
 
 FIG. 4. 
 Section through Tweefontein Copper Mine (after Ronaldson). 
 
 1 and No. 2 are situated about 700 feet apart on the strike, 
 both outcropping at the surface but at different elevations. 
 Ore-body No. 3 immediately underlies No. 2. The dimen- 
 sions of these pockets, in the order given, are : Greatest 
 
 * J. H. Ronaldson, Trans. Geol. Soc. S. Africa, VIII., p. 165 (1905). 
 
16 Ore Deposits of South Africa. 
 
 length, 540, 550, and 760 feet; greatest depth, 240, 225, 800; 
 and greatest width, 75, 50, and 60 feet. 
 
 On the remaining two lines are a number of abandoned 
 mines and prospects. 
 
 At the surface the copper sulphides are, of course, mainly 
 changed to malachite and azurite, while the red and black 
 oxides, cuprite and tenorite, and the green silicate, chrysocolla, 
 as well as copper itself, occur in small quantity. 
 
 Kuntz considers the copper sulphide to be an original con- 
 stituent of the dykes, in other words, that the dykes are 
 intruded portions of a magmatic sulphide segregation, the pay- 
 able pockets being secondary enrichments. 
 
 The following figures have been compiled* of the output of 
 this field : 
 
 From the opening of the mines in 1852 to the end of 1862 : 
 Springbok, Spektakel, and Ookiep produced 18,999 long tons. 
 From 1862 to, 1882 (20 years) Ookiep produced 164,025, 
 Spektakel 14,765, and Trial Mines 1,057. The average cop- 
 per content of this ore was 29 '5 per cent. 
 
 From the beginning of 1883 to the end of 1904 the produc- 
 tion in long tons was : 
 
 Ookiep 534,626, averaging 20'20 per cent, copper 
 
 Spektakel , ... 19,636 ,, 31/85 
 
 Springbok ... 332 ,, 30'50 
 
 Nababeep ... 114,332 ,, 6'16 
 
 Ookiep, E. ... 19,022 ,, 5'02 
 
 Xoperberg ... 6,087 ,, 9'49 
 
 Narap 1,326 ,, 13'05 
 
 Twfeefontein ... 138,683 ,, 25*40 
 
 Flat Mine ... 5,000 ,, 20*00 
 
 Hester Maria ... 3,500 ,, 20'00 
 
 As many of the above percentages of copper contents are 
 those of the ore subsequent to concentration, it is impossible to 
 
 * T. Quentrall and J. H. Konaldson, Report to Government, Capetown 
 (1905). 
 
Copper. 17 
 
 arrive, approximately even, at the average value of the ore 
 mined and raised, but much of it from Springbok, Spektakel, 
 and Ookiep mines has been abnormally rich. 
 
 MESSINA (F). 
 
 The Messina copper belt is situated in the west angle 
 between the Zand River and the south bank of the Limpopo. 
 It is nearly twenty miles in length and extends in a north- 
 easterly direction from the "farm" Oostenryk, through 
 Papenbril, Vogelsang, Berkenrode (on which the Messina mine 
 is located) and Uitenpas, to Artonvilla. It consists of a line 
 of crush in the schistose granite country, impregnated with 
 copper minerals and contains a number of well-defined fissures, 
 the walls of which have been impregnated and here and there 
 completely replaced by lenticular bodies of copper sulphide. 
 The whole belt is riddled with old Kaffir workings w r hich reach 
 a depth of seventy feet and are situated on lenses of rich ore. 
 They are probably the most extensive of their kind in South 
 Africa, and many thousand tons of copper must have been 
 extracted from them. 
 
 The Messina is the only mine so far opened up on this belt. 
 Most of the development has been done on the two main lodes 
 whose strike is indicated by the two chief lines of old workings 
 shown in the accompanying plan (fig. 5). The northern of 
 these lodes has been opened up for a length of 800 feet, and 
 the southern for 500 feet, the maximum depth being 200 and 
 300 feet respectively. The accompanying longitudinal sec- 
 tions (fig. 6) through them, showing the bodies of rich ore 
 (20 per cent, copper) so far encountered and stoped out, and 
 those extracted at the surface by the old workers, well illustrate 
 the mode of occurrence. The mineral encountered so far 
 is almost entirely chalcocite, there being very little bornite 
 or chalcopyrite and hardly any of the oxidation products 
 
 (malachite, etc.) which, however, probably constituted the ore 
 
 c 
 
18 Ore Deposits of South Africa. 
 
 o 
 
 o 
 
 I 
 
 FIG. 5. 
 
 o/ Old Workings at Messina Copper Mine (after Callerwood}. 
 A few are not shown, being hidden by modern dumps. 
 
Copper. 
 
 19 
 
 ^ 
 
 
 i 
 
 
 I 
 
20 Ore Deposits of South Africa. 
 
 extracted from the old workings. The richer ore contains a 
 few ounces of silver to the ton and traces of gold. 
 
 The development has clearly not yet reached the bottom 
 of the zone of secondary sulphide enrichment, which in this 
 case extends practically to the surface. 
 
 The following amounts of picked ore containing 61 per- 
 cent, copper have been shinned: In 1906, 585 tons; 1907, 
 1,242 tons; 1908, January-June inclusive, 370 tons. 
 
 SWAKOP-KUISEB (E). 
 
 A number of copper occurrences have been located in the 
 schist country between the Swakop and Kuiseb Rivers. The 
 writer has not visited them, but they have been well described 
 in a paper* by Voit, from which the following notes have been 
 extracted : 
 
 The most extensive occurrences are those at the Hope, 
 Gorap, and Matchless mines. All these are situated in close 
 proximity to a belt of schistose amphibolite which strikes 
 through the district in a north-easterly direction and which 
 seems to be connected with the origin of the ore-bodies. 
 Voit's paper is illustrated by plans and sections of these. 
 
 At the Gorap mine the copper occurrences are situated 
 within a huge lenticule of mica -schist enclosed by the amphi- 
 bolite. In this mica-schist is an interbedded string of 
 quartzite lenticules with a length of strike of about three miles. 
 It is in the hanging wall of these quartzite lenticules that the 
 copper impregnations occur. 
 
 The ore is chalcopyrite and chalcocite, which give way at 
 the surface to a reddish-brown mixture of cuprite and iron- 
 stone mottled here and there with the green and blue copper 
 carbonates. Volborthite also occurs in yellow to green earthy 
 masses. 
 
 At the Hope mine the copper occurrence is very similar. 
 There are two parallel quartzite lenticules interbedded with 
 
 * F. W. Voit, Trans. Geol. Soc. S. Africa, VII., p. 77-94 (1904). 
 
Copper. -2\ 
 
 
 the Dlica-sciiial. .between these arc three zones, having a 
 
 length of about '2(50 feet and a width of about one foot, impreg- 
 nated with copper-ore. 
 
 At the Matchless mine, which is about 130 miles away 
 from the Hope, two bands of amphibohte enclose a belt of 
 mica-schist and schistose granite. In these schists is a large 
 lenticule of quartzite on the hanging wall of which the im- 
 pregnations of copper ore occur. The mineral is chiefly chal- 
 copyrite, which is changed at the surface to green copper car- 
 bonate and brown iron-oxide, but solid layers of bornite and 
 chalcocite are also present. 
 
 Voit remarks that ' ' the ores occur in compact masses 
 chiefly at the surface and for a short depth down only, whilst 
 at a greater depth, where the bedding was able to offer a 
 greater resistance to the circulation of waters, these ores 
 gradually thin out to narrow seams, and finally pass into finely 
 disseminated impregnations." From which it is clear that the 
 payable 1 ore is a secondary concentration of a low-grade im- 
 pregnation. 
 
 EDMUND I AN (F). 
 
 The Edmundian mine is situated about 190 miles by rail 
 from Beira, about seven miles west of Macequece, and about 
 ten miles east of Umtali. It lies near the top of a low range of 
 mountains rising up from the north side of the Beira-Mashona- 
 land railway, with which it is connected by a good w r agon 
 road of about two miles in length, with a steady downward 
 uiade. The mode of occurrence of the ore has been well 
 described* by Brackenbury. It consists of lenticular bodies 
 of chalcopyrite, with a little pyrrhotite, and, in the upper por- 
 tion of the mine, their oxidation products, distributed in the 
 form of vertical shoots throughout a zone of fracture in amphi- 
 
 * C. Brackenbury, Trans. Institution of Mining and Metallurgy, XV.' 
 p. 633-642 (1906). 
 
22 Ore Deposits of South Africa. 
 
 bolic and chloritic schists. The rich shoots often attain a 
 thickness of over three feet of solid sulphide, narrowing down 
 laterally to veins a few inches wide, which in turn split up 
 into little stringers and finally into disseminations along the 
 course of the lode. 
 
 UMKONDO (C). 
 
 This is a promising proposition situated some 115 miles 
 east of Victoria by wagon road, about ten miles west of the 
 Sabi River, and some 130 miles south and slightly west of 
 Umtali. 
 
 Its site was indicated by the presence of numerous old 
 workings, which extend over a length of about 1,500 feet, and 
 are in places over 300 feet wide. The old workers not only 
 made large open-cast excavations, as much as 60 feet in depth, 
 but also sank small shafts, and in places sloped out the ore 
 right down to the water level. 
 
 The copper occurs in a sedimentary formation, consisting 
 of much altered shales and sandstones overlying granite, 
 apparently unconformably, and intersected by numerous gab- 
 brodiorite dykes. 
 
 Brackenbury, who gives a very able and detailed descrip- 
 tion of this occurrence, concludes that the copper has been 
 subsequently introduced into these beds along zones of frac- 
 ture, and that although the ore in some cases occurs as a 
 bedded deposit, it is not likely to be found in this form at any 
 great distances from these zones of disturbance. He also con- 
 nects the ore-bodies with the gabbrodiorite intrusions. 
 
 The present water level has been found to be less than one 
 hundred feet below r the surface, but the sulphides do not 
 appear until some distance below this. 
 
 In the zone of oxidation the ore is mainly green and blue 
 carbonate in the form of incrustations and little seams in the 
 bedding planes of the shales and in the fractures in the 
 
Copper. 23 
 
 quavtzite, bat also occurs as an impure grey oxide in the shape 
 of hard nodules in the shale up to several inches in diameter. 
 
 ALASKA (B). 
 
 This is a promising prospect , situated some 90 miles north- 
 west of Salisbury, about thirty miles west of the Ayrshire mine 
 and only some thirteen miles from the Eldorado mine. 
 
 It is remarkable for the great size of its old workings, 
 which are perhaps the largest in the country between the Lim- 
 popo and Zambesi Elvers. They extend in an almost un- 
 broken line for about 1,700 feet, with an extreme width of 660 
 feet, and they have been proved to go down in some places to a 
 depth of at least 70 feet. 
 
 The occurrence has been well described by Brackenbury 
 in the paper already cited. The copper so far exposed is 
 mainly in the form of the green carbonate, malachite, the sul- 
 phide zone not yet having been reached. It is disseminated 
 throughout siliceous and calcareous schists. 
 
 PALABORA (B). 
 
 The Palabora kopjes are situated some forty miles east of 
 Leydsdorp and are celebrated as the source from which the 
 Kafirs of the surrounding districts formerly obtained their iron 
 and copper ores. I visited the locality in 1907, and since then 
 a detailed account of the old workings has been published by 
 Mellor.* The kopjes, with one exception, to which the name 
 Lulu has been given, are of granite, and stand out conspicu- 
 ously from the surrounding flat or slightly undulating bush- 
 country. Lulu kop is composed of a white metamorphosed 
 limestone or marble, and it is in this that the ore-bodies and 
 old workings are mostly situated. 
 
 Magnetite is distributed almost everywhere throughout the 
 
 * E. T. Mellor, Report Geological Survey, Pretoria, p. 44-49 (1907). 
 
24 Ore Deposits of South Africa. 
 
 limestone, occurring in grains, crystals and masses, up to six 
 feet or more in diameter. ]t is especially abundant along cur- 
 tain bands in the limestone. 
 
 Chalcopyrite is found in places disseminated in small 
 quantity throughout the limestone while its alteration pro- 
 ducts, malachite and azurite, are more abundant, though only 
 constituting a very small proportion of the rock. 
 
 The old workings extend over the whole area of the kop 
 and are mostly shallow pits which have been sunk on pockets 
 of ore. 
 
 Nothing of a payable nature is exposed, but indications of 
 copper are so abundant, not only in the limestone, but in the 
 adjacent granite, that the locality must be regarded as worthy 
 of a more complete examination than it has yet received. 
 
 WILLOWS (G). 
 
 The Willows occurrence is situated east of Pretoria. It 
 consists of a series of parallel lodes true fissure-fillings out- 
 cropping in clay-slates. 
 
 The ore consists of chalcopyrite , pyrite, and tetrahedrite 
 in a gangue of siderite. In the oxidized zone where the ore 
 contained a big percentage of silver, malachite and azurite 
 largely replaced the sulphides. 
 
 A great deal of work was done on this occurrence in the 
 early days when it was regarded as a silver mine, and it is 
 said that something like a quarter of a million's worth of ore 
 was shipped from it. 
 
 Development work has lately been restarted after a long 
 period of idleness. 
 
 VALLEY (G). 
 
 The Valley mine is located 85 miles south-east of Bulawayo 
 and is primarily a gold proposition, but produces copper as a 
 bye-product. 
 
Copper. -Jo 
 
 It is on a quart/ nrf situated near the junction of the 
 granite and schists, and is heavily charged with pyrite, 
 nyrrhotite and chalcopyrite. 
 
 In the middle of 1906 a smelter was erected to treat the 
 sulphide concentrates, the resulting matte being shipped. The 
 following outputs have been declared, the quantities referring 
 to the amount of copper in the matte : 1906, 76 tons, value 
 -5,765 ; 1907, 115 tons, value 9,625 ; 1908, January to June 
 inclusive, 40 tons, value 2,327. 
 
 SUBENI (G). 
 
 Eunning through the farms Nonpareil, Goudhoek, and 
 Fairview, about a day's journey south-east of Vryheid, is a 
 large prominently outcropping quart/ reef, situated near, and 
 running parallel to, the junction of granite and schists. 
 
 The Subeni prospect is located on Goudhoek and consists 
 of a metalliferous shoot in the quart/ reef. The minerals con- 
 sist of chalcopyrite and bornite with a very little chalcocite. 
 
 Shafts have also been put down in this reef on Nonpareil 
 and Fairview, but nothing of a promising nature has been dis- 
 covered at those places. 
 
 OTAVI (H). 
 
 The Otavi Mountains are situated in northern Damara- 
 land. The writer has not seen the copper and lead deposits 
 there, the following account being extracted from a paper* by 
 Kuntz. The mountains are composed entirely of limestone. 
 
 " As in all limestone formations, so also here a great 
 number of caves exist as a consequence of the action of water. 
 Some of them are empty, some filled with water, and others 
 filled with a sandstone-like mass, which contains the copper 
 ore in small and large pieces of different shapes 
 
 ' The enormous copper deposits at Otavi, Guchab, 
 Tschumeb, etc., are simply fillings of such caves. 
 
 * J. Kuntx, Trans. Geol. Soc. S. Africa, VII., p. 75-76 (1904). 
 
26 Ore Deposits of South Africa. 
 
 "At Gross-Ota vi, dark and light grey limestone can be 
 seen cropping out in layers, striking east and west, and dip- 
 ping steeply to the south. This rock is spangled with large 
 and small pockets of copper ore of irregular shape, and from 
 the size of a pea to that of a cubic yard. The pockets again 
 are connected with each other by a network of irregular run- 
 ning veins, as the accompanying sketch shows. The extent 
 of this cavernous zone is about 80 by 200 yards, the ore con- 
 sisting chiefly of chalcocite, seldom bornite and chalcopyrite. 
 There is also a great quantity of galenite. 
 
 ' The occurrences at Klein-Ota vi and Guchab are of the 
 same nature, but show more compact bodies of ore. 
 
 ' What Gross-Otavi is on a small scale, Tschumeb is 
 on a much larger scale. The extent of the outcrop is about 
 200 yards in the direction of the east and west strike, and 40 
 yards vertically. The dip is steeply to the south, and the ore- 
 deposit seems to have the same dip, as proved by the prospect- 
 ing shafts, following, apparently, an easier decomposable bed 
 within the limestone. 
 
 ' The most northerly part of this body is . to a great extent , 
 replaced by copper and lead ore, whilst in the southern part 
 the ore occurs breccia-like, as at Gross-Otavi, showing that 
 the character and origin of the deposits are the same in both 
 places. 
 
 " As in the footwall, so in the hanging-wall beds of lime- 
 stone, numerous small clefts and cracks are filled with copper 
 ore. 
 
 " On the eastern part of the outcrop the ore consists chiefly 
 of galenite, the copper ore being in the minority. Towards 
 the west the galenite diminishes, but does not disappear 
 entirely, while the chalcocite is the chief ore there. Bornite 
 and chalcopyrite exist only in small quantities." 
 
 The genesis of these ore-bodies seems uncertain, though 
 it is clear they are secondary enrichments. 
 
 During the financial year 1907-8 (April to March inclu- 
 
Copper. 27 
 
 sivc) there were shipped from Tschumeb 15,000 tons of ore 
 with an average content of 0'035 per cent, silver, 19 per cent, 
 copper, and -23 per cent. lead. Also 1,000 tons of matte con- 
 taining 0'040 per cent, of silver, 38 per cent, of copper, and 
 19 per cent, of lead, and 700 tons of 95 per cent, lead contain- 
 ing 0'090 per cent, of silver. 
 
 From Gnchab 1,800 tons of ore containing 33 per cent, of 
 copper and 0'040 per cent, of silver were shipped. 
 
 During the first quarter of the current financial year (April 
 to June, 1908) about 6,500 tons of ore, 900 tons of matte and 
 800 tons of lead were shipped. 
 
CHAPTEK V. 
 
 COBALT. 
 KRUISRIVIER AND EENZAMHE1D (E AND D). 
 
 THE well-known Kruisrivier cobalt lode in the Selons 
 Valley has often been described* and was visited by the writer 
 in 1907. The mineral is smaltite, which occurs, as shown in 
 the accompanying section (fig. 7), as an impregnation at or 
 near the junction of a series of felspathic quartzites with a 
 gabbrodiorite intrusion. 
 
 
 FIG. 7. 
 Section through Kruisrivier Cobalt Lode (after Mellor). 
 
 In the best exposure, about two feet from and parallel to 
 the junction, there is a thin interbedded vein of smaltite crys- 
 tals on either side of which the quartzite is impregnated with 
 
 * E. J. Dunn, Quarterly Journal Geological Society of London, XXXIII.' 
 p 883 .18771. 
 
 K. Oehmichen, Zeitschrift fur Practische Geologie, p. 271-274 (1899). 
 
 B. Beck, Trans Geol Soc. S. Africa, X., p. 10 (1907). 
 
 E. T. Mellor, Eeport Geol. Survey, Pretoria, p. 70-71 (1907). 
 
Cobalt. 29 
 
 the same mineral. The qnartzitc in this zone contains 
 numerous cherty patches and has a generally altered and 
 indurated appearance. 
 
 On the adjoining farm, Laatstedrift, there is a further 
 occurrence of the smaltite, the impregnated rock there being 
 the gabbrodiorite. 
 
 At the surface the smaltite is changed into the peach-red 
 and black oxidation products, erythrite and transvaalite. Both 
 contain a notable quantity of gold, up to four ounces per ton. 
 
 On Eenzamheid, about a mile south of Balmoral station, 
 on the Pretoria-Delagoa Bay railway, there is an analogous 
 occurrence of cobalt ore, which, however, the writer has not 
 seen. It has been described by several observers.* The 
 smaltite, together with a little quartz and molybdenite, occurs 
 as an impregnation in a series of parallel basic dykes that 
 penetrate a highly indurated shale and are probably offshoots 
 from a big neighbouring gabbrodiorite intrusion. A small pro- 
 portion of nickel is present in the smaltite. 
 
 * D. Dorftel, Trans. Geol. Soc. S Africa, VI (1903). 
 C. B. Horwood, Trans. Geol. Soc. S. Africa, VII. (1904) 
 
CHAPTEE VI. 
 
 TIN. 
 ROOI BERG (B, C AND F). 
 
 THE Eooi Berg, which give their name to this field, are a 
 group of hills rising out of the flat or gently undulating country 
 about 40 miles due west of the village of Warmbaths. The 
 ore occurrences are situated mainly on the northern slopes of 
 the Kooi Berg and their western extension, on the farms 
 Haartebeestpoort, Blauwbank, Haartebeestfontein, Olieven- 
 bosch, and Onverwacht, and have been well described by 
 Eecknagel.* 
 
 The whoje of the area is covered with a sedimentary forma- 
 tion consisting of felspathic quartzites, shales and thin con- 
 glomerates, surrounded by, and resting on, granite, which is 
 intrusive into it. 
 
 Over the whole north-western half of this area, the forma- 
 tion is practically undisturbed, and strikes from north-west to 
 south-east, w r ith a dip of 5 to 10 degrees to the north-east. 
 Over the eastern portion of this area, that is, on the northern 
 slopes of the Eooi Berg, the formation is equally free from 
 dislocations, but strikes mainly east and west, with a southerly 
 dip of about 30 degrees. The thickness of this sedimentary 
 formation is very considerable, amounting to several thousand 
 feet. 
 
 Overlying the sedimentary formation are a series of felspar- 
 porphyry flows, which constitute the main mass of the Eooi 
 Berg. 
 
 * K. Kecknagel, Trans Geol. Soc. S. Africa, XI. (1908). 
 
Tin. 31 
 
 Throughout the whole area the felspathic quartzites con- 
 tain impregnations of tounnalino. The impregnations vary 
 from very small isolated irregular patches to belts which follow 
 the same stratum uninterruptedly for long distances. With 
 the tourmaline which is predominant are associated the follow- 
 ing other secondary minerals, in decreasing order of abund- 
 ance, quartz, felspar (orthoclase) , and sidero-calcite. Cassi- 
 terite is usually present, but only in very small quantities. 
 Pyrite is abundant, but chalcopyrite is rare. 
 
 The main tin occurrence is situated on. Haartebeestfontein 
 and Olievenbosch, and differs somewhat from the prevalent 
 type. It may be described as a gigantic stockwork, in which 
 the tiny cracks, veinlets and impregnations of the stockwork 
 proper are represented by fissures and lodes accompanied by 
 impregnations of corresponding magnitude. It owes its redis- 
 covery to the existence over the whole of its outcrop some 70 
 acres of very extensive old workings. 
 
 These lodes strike in all directions, but at least two parallel 
 systems can be distinguished among them, one containing 
 lodes with an approximately north-south strike, and the other 
 whose lodes strike w^est-north-west. 
 
 It is very difficult to describe in a few words the various 
 types of lodes encountered, as there is scarcely any type unre- 
 presented. There are fissures of small width, mere cracks 
 with no vein filling except some clay ; there are similar fissures 
 with irregular pockets of vein minerals attached ; there are 
 lodes with one well-defined wall, showing brecciated structure 
 and enclosing vughs of large dimensions ; and there are lodes 
 which show both walls well defined over long distances. The 
 task of conveying a proper idea of the various types is made 
 even more difficult by the fact that in most of the lodes various 
 types are represented. 
 
 The filling of the lodes consists in part of decomposed 
 country rock and clay, but mainly of the following gangue 
 minerals (in order of decreasing abundance), tourmaline, 
 
32 Ore Deposits of South Africa. 
 
 quartz, sidcro-calcite, and orthoclase. As an accessory gangiiL- 
 mineral found in small quantity only fluorite may be men- 
 tioned. These gangue minerals enclose, besides cassiterite as 
 the main metallic mineral, smaller quantities of pyrite, specu- 
 larite, chalcopyrite , galenite, sphalerite, and, as a rarity, gold. 
 The most frequent gangue mineral, and, in many places, the 
 only one, is tourmaline ; it occurs mostly in a fibrous state, and 
 very often forms spherulitic aggregates which, in places, are 
 the only filling of wide veins. In some of the lodes the tour- 
 maline crystals form, with quartz or sidero-calcite, a dense 
 felt-like mixture which, only under the microscope, reveals its 
 true nature. Orthoclase, mostly pink in colour, forms the 1 
 gangue mineral in several lodes, at least in part, and usually 
 appears quite fresh to the unaided eye, but in places can be 
 seen changing into yellowish-green sericite. 
 
 The cassiterite occurs either by itself, forming crystalline 
 masses of smaller extent within the lodes, or associated with 
 either of the gangue minerals, forming coarse to fine-grained 
 mixtures, or as impregnations in the country rock. 
 
 It is established that most of the fissures and lodes must 
 have been originally mere cracks, and that open fissures were 
 the exception. The present apparent filling of gangue 
 minerals is merely a replacement of the sides of these cracks. 
 It is further established that a rerupturing of many fissures 
 has taken place afterwards, as the brecciated lodes include 
 fragments of pre-existing "filling." These cracks were the 
 main channels through which the impregnating agents oper- 
 ated. The secondary minerals introduced completely replaced 
 the rock immediately adjoining the cracks, but, further away. 
 were merely disseminated throughout it, and finally ceased to 
 penetrate at all. It is interesting to note that where these im- 
 pregnations followed the bedding planes a banded arrangement 
 of the secondary minerals is often met with. 
 
 As to the forces that produced the original cracks, no satis- 
 factory explanation has yet been offered. It is certainly most 
 
Tin. 33 
 
 uncommon to find an area of sedimentary formation, practi- 
 cally free from dislocation, fissured to such a degree. The 
 only dislocation of any extent is that which separates eastern 
 and western are as above described, and which strikes north- 
 east through Blauwbank, but this is three miles away from the 
 fissured area. In looking for possible causes of the fissuring, 
 the theory of torsional movement suggests itself as a feasible 
 explanation. 
 
 WEYNEK. 
 
 The Weynek tin lodes are situated on the farm of that 
 name about four miles from the great Rooi Berg stockwork 
 already described. They are in the same felspathic quartzites 
 but the mode of occurrence of the ore is very different. They, 
 also, owe their rediscovery to the presence of old workings on 
 them. 
 
 There are two main parallel lodes. Their mean dip is, 
 approximately, at right angles to that of the felspathic 
 quartzites, but their course here and there follows the bedding 
 planes for short distances. 
 
 The filling of these lodes is a clayey substance of uncer- 
 tain nature. The cassiterite, with which is associated the 
 oxidation products of chalcopyrite , is disseminated throughout 
 this filling. No tourmaline is present. 
 
 The genesis of the ore occurrence is, no doubt, the same 
 as tha-t of the Eooi Berg, and the lode stuff was probably 
 originally very similar, but has subsequently suffered decom- 
 position owing to local causes. 
 
 DOORNHOEK (B AND F). 
 
 The farm Doornhoek* is situated north-east of Nylstroom. 
 The tin-ore occurs partly as an irregular impregnation in the 
 granite, but chiefly as an impregnation along fissures in the 
 overlying felspar-porphyry flows. 
 
 * J. P. Johnson, South African Mining Journal, VI., p. 571 (1908). 
 
 D 
 
34 Ore Deposits of South Africa. 
 
 The main ore-body, which has been traced for a distance 
 of several hundred yards, is coincident with a fissure crossing 
 the felspar-porphyry and consists of an impregnation of the 
 crushed rock forming the walls. Five main prospecting shafts 
 have been sunk on this to an average depth of about fifty feet, 
 the distance between the two extreme end shafts, measuring 
 along the lode, being 1,250 feet. The average width of this 
 lode is about eighteen inches, and the values go as high as 30 
 per cent, tin, and average 10. It is intersected in various 
 directions by numerous small cassiterite-bearing veins. 
 
 This lode is the centre of a highly stanniferous area of the 
 nature of a stock work. Numerous parallel veins intersect the 
 surrounding rock in all directions. 
 
 The cassiterite and associated secondary minerals (tour- 
 maline, quartz, sericite and fluorite), while megascopic in the 
 granite, are in a very fine state of division in the lodes, being 
 there rarely distinguishable to the naked eye. 
 
 POTGIETERSRUST (B). 
 
 The Potgietersrust tin-field* is located in the mountainous 
 country between the Magalakwin River and its tributary the 
 Sterk. The country rock is granite. Throughout the whole 
 of this area irregular impregnations of cassiterite and associ- 
 ated secondary minerals are met with, but the payable occur- 
 rences so far dicovered are confined to a zone of fissuring run- 
 ning through the farms Solomonstempel, Sterkwater, Groen- 
 fontein, Eoodepoort, and Zaaiplaats. 
 
 Running north and south through Groenfontein and ex- 
 tending into Roodepoort on the one hand and Sterkwater on 
 the other, is a pegmatitic quartz-vein, dipping at a low angle 
 to the west, and containing massive fluorite and sericite, 
 together with much coarsely crystalline cassiterite. 
 
 The granite adjoining this quartz-vein on the east is 
 * J. P. Johnson, Trans. Geol. Soc. S. Africa, X., p. 115-119 (1907). 
 
Tin. 35 
 
 sparsely impregnated with small crystals of cassiterite for a 
 width of about forty yards. Megascopically this impregnated 
 granite shows little evidence of alteration. Apart from the 
 cassiterite, specks of yellow to green sericite and an occa- 
 sional crystal of violet-blue fluorite, alone differentiate it from 
 the adjoining rock. 
 
 East of this belt of impregnated granite and arranged in 
 a line roughly parallel to it, are small patches of similarly 
 impregnated granite and groups of peculiar cylindrical pipes. 
 These extend into Zaaiplaats on the north and Solomons- 
 tempel on the south. 
 
 The cylindrical pipes, as a rule, consist of a core of altered 
 granite thickly studded with crystals of cassiterite, usually, but 
 not always, surrounded by a sharply defined ring consisting of 
 spherulites (about a centimetre in diameter) of black tourma- 
 line closely packed in a white quartz matrix. Outside this is 
 a halo of granite characterized by specks of yellowish green 
 sericite which gradually merges into the unaltered rock. 
 
 The extent to w r hich the granite is altered in these pipes 
 is very variable in one and the same pipe. As a rule the 
 greater part of the rock still retains its granitic texture, and 
 to the naked eye seems to have suffered little alteration beyond 
 the replacement of some of the constituents by sericite, 
 fluorite and cassiterite. Much, in some cases the major por- 
 tion, has, on the other hand, suffered such complete alteration 
 as to be megascopically nothing more than a friable dirty 
 green (sericitic) rock speckled with cassiterite. Between 
 these two extremes every gradation can be observed. Under 
 the microscope the sericite is seen to be an alteration product 
 of the felspars. 
 
 Accessory secondary minerals occurring in the pipes are 
 molybdenite, pyrite, chalcopyrite (and hence malachite), 
 arsenopyrite, and galenite. Grains of copper were also found 
 in one of the pipes on Zaaiplaats embedded in the tourmaline 
 spherulites at a depth of 130 feet. 
 
36 Ore Deposits of South Africa. 
 
 The pipes are found to take an irregularly inclined course 
 in depth and sometimes join together. They mostly dip to 
 the west. 
 
 The payable tin-ore is practically confined to these chim- 
 neys. According to Merensky* about 250 tons of ore yielding 
 an average of 30 per cent, of tin were recovered from one pipe 
 alone. 
 
 The output of ore and concentrates from this field has been 
 as follows :1906, 61 tons, value 3,928; 1907, 1,296 tons, 
 value 36,435; 1908, January to June inclusive, 712 tons, 
 value 43,754. 
 
 WELBELOOND. 
 
 This is an interesting prospect situated on the farm Welbe- 
 loond on the eastern flank of the Tyger Berg. The ore- 
 occurrence, which I have not seen, and for a description of 
 which I am indebted to Mr. Mills-Davies, consists of small 
 quartz veins carrying coarse cassiterite, which traverse a long 
 low kopje of slates and quartzites not far from an intrusive 
 granite contact. 
 
 EMBABAAN (I). 
 
 The detrital accumulations of cassiterite in the Embabaan 
 valley have been regularly worked since 1892, but it is only 
 from 1905 that records of the output have been kept. 
 
 The cassiterite is derived from irregular impregnations 
 in the surrounding granite. Associated with the cassiterite 
 in small quantities and having the same source are the rare 
 and interesting minerals, aeschynite, euxenite, and monazite. 
 
 The following outputs of concentrates have been regis- 
 tered : Year ending 30th June, 1906, 229 tons; 1907, 270 
 tons; 1908, 512 tons. 
 
 * H. Merensky, Trans. Geol. Soc. S. Africa, XL, p. 35-39 (1908). 
 
Tin. 37 
 
 LANGVERWACHT (I). 
 
 Detrital accumulations of cassiterite were worked in the 
 creek on the farm Langverwacht , about twelve miles from 
 Cape Town, during 1906 and 1907, when about 300 tons of 
 concentrates were shipped. The cassiterite is derived from 
 irregular impregnations in the surrounding granite. 
 
CHAPTEE VII. 
 
 MOLYBDENUM. 
 APPINGADAM (B). 
 
 THE molybdenum occurrence* on Appingadam is situated 
 at the foot of the north end of the kopjes on the left bank of 
 the Sterk River and occupies an irregularly shaped area. 
 The country rock around this area is granite plentifully 
 sprinkled with spherulites of tourmaline, though, so far as 
 can be detected by the unaided eye, otherwise unaltered. 
 Within this area the granite shows additional alteration of 
 varying intensity. The first manifestations are the increase 
 in the number of tourmaline spherulites and the addition of 
 sericite and fluorite. Then molybdenite and cassiterite (w r hich 
 however is here rare) appear. With the increase in quantity 
 of these secondary minerals the granite gradually loses its 
 original character. Finally, in certain centres of intense 
 alteration peculiar types of rock have been produced which 
 bear no resemblance to the original. Their constituent 
 minerals occur both in evenly granular aggregates and as 
 irregular mixtures. They comprise tourmaline-quartz rock, 
 sericite-quartz rock, sericite-molybdenite rock, molybdenite- 
 arsenopyrite-quartz rock, and arsenopyrite-fluorite rock. 
 Sphalerite also occurs in irregular masses. These rock types, 
 of course, pass one into the other, and it is possible to get hand 
 specimens containing all the minerals mentioned together. 
 
 Molybdenite in the form of scales, often hexagonal, is the 
 dominant metallic mineral. The yellow oxidation product, 
 molybdite, also occurs. 
 
 * J. P. Johnson, Trans. Geol. Soc. S. Africa, X., p. 115-119 (1907). 
 
Molybdenum. 39 
 
 An interesting feature of this altered area is the presence 
 of groups of giant spherulites of tourmaline, some as much as 
 four decimetres in diameter, in which the slender needles of 
 the ordinary sized spherulite are replaced by stout columns. 
 Tourmaline also occurs as short, thick crystals associated with 
 quartz in small irregular bodies. 
 
 To find a market molybdenum-ore must contain not less 
 than 45 per cent, of the metal, and must be free from other 
 metallic minerals, especially copper. Picked sulphide, practi- 
 cally free from gangue, will command from 16 to 19 shillings 
 per unit per cent, of molybdenum per ton. 
 
 H OUT EN BE K (B). 
 
 On the farm Houtenbek, north-east of Pretoria, there are 
 two interesting occurrences* which, although not of economic 
 importance, are deserving of mention here. The country rock 
 is granite. 
 
 One is a band, two feet in width, consisting of almost pure 
 arsenopyrite, some fluorite, and large leaves of molybdenite. 
 
 The other is a similar band showing arsenopyrite, fluorite, 
 and large crystals of monazite, all closely intergrown. The 
 monazite is greenish-grey to dark red in colour. Some of the 
 ore was reported to have an average yield of 5 per cent, of 
 thorium. 
 
 H. Merensky, Trans. Geol. Soc. S. Africa, XI., p. 31 (1908). 
 
CHAPTEE VIII. 
 
 TUNGSTEN. 
 RICHARDSON (B). 
 
 The Richardson mine is situated at Essexvale, near Bula- 
 wayo. 
 
 The mineral is wolframite with a little scheelite, and occurs 
 together with chlorite, quartz, tourmaline, fluorite and topaz, 
 as an impregnation in fine-grained granite. 
 
 In 1906 17 tons, and in 1907 12 tons, of picked ore were 
 produced. The figures of output for the first six months of 
 this year are not available. 
 
 SCHEELITE-KING (G). 
 
 The Scheelite-King mine is situated near the Umswege 
 River, on the Gaturna side of the Hartley district. 
 
 The mineral is scheelite, and occurs in a quartz reef in 
 schistose granite, w T hich is much epidotized in the vicinity. 
 
 During 1907 38 tons of picked ore were produced. Mining 
 is being continued there, but no declaration of output has yet 
 been made for this year. 
 
 I am indebted to Mr. Mennell for the information relating 
 to the above occurrences which I have not seen. 
 
CHAPTER IX. 
 
 LEAD. 
 DWARSFONTEIN (G). 
 
 THE Dwarsfontein occurrence is situated about forty miles 
 south-east of Pretoria. It is a vertical lode outcropping in 
 clay-slates. 
 
 The ore consists of galenite, with subordinate chalcopyrite , 
 pyrite, and tetrahedrite, in a gangue of siderite. In the oxi- 
 dized zone where the ore contained a big percentage of silver, 
 cemssite and malachite largely replaced the sulphides. 
 
 As a rarity, translucent red crystals of the lead chromate, 
 crocoite, are met with. 
 
 A great deal of work was done on this occurrence in the 
 early days when it was regarded as a silver mine. From 1891 
 to 1893 inclusive, 50,000 was realized from the sale of ore, 
 concentrates, and metal. 
 
 Work has lately been restarted. A small amount of galenite 
 was contributed to the Pretoria district output (given under 
 Edendale) for the first six months of this year. 
 
 ROODEKRANZ (G). 
 
 The Roodekranz occurrence is situated sixteen miles south- 
 west of Pretoria. It is a lode in the dolomite formation con- 
 taining galenite and quartz. 
 
 It made small contributions to the Pretoria district output 
 during 1906 and 1907. 
 
 PENHALONGA (G). 
 
 The Penhalonga mine is located on the slopes of the range 
 of hills of the same name, some 10J miles north of Umtali. It 
 
42 Ore Deposits of South Africa. 
 
 is primarily a gold proposition, but produces lead as a bye- 
 product. A short description of it has been published by 
 Townsend.*. 
 
 The ore occurrence is a vertical quartz reef heavily charged 
 with argentiferous galenite, running in and parallel to a series 
 of schists, and has been traced for a distance of 14,000 feet. 
 There are numerous old workings on it. 
 
 At present some 3,500 feet of the lode is being exploited. 
 This portion is divided into two sections by a longitudinal 
 fault. The western section is 1,500 feet in length and the 
 eastern section is 2,000 feet in length, a barren stretch of 700 
 feet separating the two. The lowest drive is some 900 feet 
 below the outcrop. 
 
 The ore-body consists of quartz lenticules intercalated with 
 small bands of schist. Its width varies from 25 to 50 feet, of 
 which 8 to 20 have proved to be worth working. The quartz 
 contains in addition to the galenite a small amount of zinc, 
 iron and copper sulphide. The oxidized zone is characterized 
 by a considerable quantity of the chromate of lead, crocoite. 
 
 In the eastern section there is a parallel band of quartz 
 lenticules lying 150 feet to the south, which, however, has not 
 been found in the western section. 
 
 Galenite concentrates have been shipped for several years. 
 From January to June, 1908, inclusive, concentrates contain- 
 ing 510 tons of lead valued at ,6,292 were produced. 
 
 U1TLOOP-PJETFONTEIN (F). 
 
 This occurrence! is situated in the granite ridge which 
 forms the boundary between the farms Uitloop and Eietfon- 
 tein, north of Potgietersrust , and although not of economic 
 importance is of special interest in that it presents the unusual 
 
 * H. P. Townsend, Journal S. African Assoc. Engineers, XIIL, p. 132-140 
 (1908). 
 
 f J. P. Johnson, Trans. Geol. Soc. S. Africa, X., p. 115-119 (1907). 
 
Lead. 43 
 
 feature of being- genetically similar to the tin, molybdenum 
 and tungsten impregnations already described. 
 
 The main occurrence is in a narrow but sharply denned 
 belt of altered granite which strikes approximately north and 
 south and dips at a big angle to the west. This is traceable 
 for some distance. 
 
 The section is as follows : 
 (a) Hanging Wall. 
 
 (6) Mottled Red and Yellowish-green Rock. Altered 
 granite. Granitic structure mostly retained but 
 partly obscure. 1 ft. 
 
 (c) Bluish-white Chert-like Rock. Traversed by a 
 
 network of fluorite veinlets containing galenite. 
 Altered granite. Traces of granitic structure 
 retained in places. Specks of red felspar 
 throughout. 2 ft. 
 
 (d) Foot Wall. 
 
 A short distance to the west of this a similar occurrence 
 runs parallel and has been exposed in a pit, but at the time of 
 my visit had not been traced far. It is not so sharply de- 
 marcated from the enclosing rock as in the main occurrence. 
 It shows veinlets of chert and galenite-bearing fluorite travers- 
 ing a narrow belt of the granite which is not megascopically 
 much altered. 
 
 A microscopical examination shows the ore-body to be a 
 line of crush in the granite, along which the galenite and asso- 
 ciated secondary minerals have been deposited by vapours at 
 the expense of the felspars. 
 
 EDENDALE (G). 
 
 The Edendale lead and zinc mines are located on the farm 
 of the same name, some seventeen miles north-east of Pre- 
 toria. Both are situated on a lode in quartzites and shales. 
 
 This lode consists of a belt of fissuring of very variable 
 width. It has been traced for a distance of about 2,000 yards 
 
44 Ore Deposits of South Africa. 
 
 and opened up at one point to a depth of 700 feet. It dips 
 against the strata at an angle of about 75 degrees. 
 
 The metalliferous minerals consist of galenite and 
 sphalerite with very subordinate chalcopyrite, and occurs in 
 the form of lenticular bodies and disseminations throughout 
 the lode. The galenite contains about 14 ounces of silver to 
 the ton, and constitutes about ten per cent, of the ore. The 
 sphalerite is less abundant. The two minerals are seldom 
 mixed. 
 
 At the surface the sulphides are largely replaced by the 
 oxidation products cerussite and smithsonite. In smaller 
 quantity also occur the red oxide of lead, minium, in opaque 
 earthy crusts, and translucent yellowish-white crystals of the 
 lead sulphate, anglesite. 
 
 These mines have been responsible for nearly the whole of 
 the lead-ore output from the Pretoria district, which is as fol- 
 lows :1904, 389 tons, value '2,863; 1905, 768 tons, value 
 3,756; 1906, 1,103 tons, value 14,473; 1907, 1,014 tons, 
 value 12,513; 1908, January to June, inclusive, 682 tons, 
 value 6,328. During 1906 and 1907, Eoodekranz and, 
 during 1908, Dwarsfontein, contributed to the above amounts. 
 
 In 1907, 40 tons of zinc ore, valued at 365, were also 
 sold. 
 
 There is a similar but smaller occurrence on the adjoining 
 farms Leuwkloof and Breeder stroom , some 28 miles south- 
 west of Pretoria. A small quantity of galenite included in the 
 above figures was mined from there in 1907 and during the 
 first six months of 1908. 
 
 OTTOSHOOP (H). 
 
 The Ottoshoop lead and zinc occurrences are analogous to 
 the Otavi copper-lead deposits, being fillings of irregular cavi- 
 ties in dolomite, 
 
 The ore consists of galenite and sphalerite in a gangue of 
 calcite, fluorite and quartz. A little chalcopyrite is sometimes 
 
Lead. 45 
 
 associated with the sphalerite. The immediately adjoining 
 rock is charged with tremolite. 
 
 Pockets have been located on the farms, Zendelingspost, 
 Bufl'elshoek, Witkop, Naauwpoort, Strydfontein, Kuilfontein, 
 Khenosterhoek, and Doornhoek. 
 
 The main occurrence at Witkop w r ell illustrates these 
 deposits. There a horizontal section of a characteristic 
 chamber of ore is exposed at the surface. It is approximately 
 circular in outline, and has a diameter of about fifty yards. 
 Within this area the solid dolomite is replaced by angular 
 blocks embedded in a matrix of calcite, fluorite, and quartz 
 containing masses amd disseminations of galenite and 
 sphalerite. The galenite is argentiferous. The immediately 
 surrounding dolomite and the included blocks of same, are 
 charged with tremolite. 
 
 At the surface the sulphides are often changed to cerussite, 
 smithsonite, and hemimorphite. Minium and angiesite are 
 also present in subordinate quantity. More rarely greenockite 
 occurs in greenish yellow crusts. 
 
 The output of ore from this district has been : 1907*, 
 334 tons of lead ore, value 3,930, and 318 tons of zinc ore, 
 value 2,851; 1908, January to June inclusive, 723 tons of 
 lead ore, value 5,173, and 249 tons of zinc ore, value 1,715. 
 
 * Previous records unobtainable. Some ore was mined at Rhenosterhoek 
 in the early days. 
 
CHAPTEE X. 
 
 MEECUEY. 
 LOUW'S GREEK (F). 
 
 THIS occurrence is about ten miles south of Malelane Sta- 
 tion, on the Pretoria-Delagoa Bay Railway, and on the fur- 
 ther side of the range of hills between the railway and Louw's 
 Creek, which it overlooks. 
 
 The writer has not seen the ore-body and is indebted to 
 Mr. Draper for the information contained in this note. 
 
 The mineral is cinnabar. It occurs disseminated through- 
 out a belt of crushed quartzite from four to five feet wide and 
 about 400 yards long. The mercury content over this width 
 and length is from 2 to 3 per cent. 
 
 Numerous prospecting shafts have been put down on it, 
 but an adit driven lower down the hill-side to intersect the 
 deposit in depth, failed to locate it. 
 
CHAPTEK XI. 
 
 ANTIMONY. 
 MURCHISON RANGE (C). 
 
 THE Murchison Eange* is made up of picturesque lines of 
 kopjes lying between the Selati and Groot-Letaba Eivers. It 
 affords a pleasing contrast to the monotonously flat or slightly 
 undulating bush-country with which it is flanked. Geologi- 
 cally it consists of a narrow belt of schists, bounded on either 
 side by granite. 
 
 These schists in common with their representatives in other 
 parts of the country contain numerous auriferous quartz-veins, 
 fahlbands and general impregnations of a lenticular nature, 
 which conform both in strike and dip with the adjacent beds. 
 Sawyer has published an account of them in his book on ' ' The 
 Murchison Eange" (1892), while Wilson-Moore t , and, more 
 recently, Merenskyt, have also made contributions to our 
 knowledge of them. 
 
 The antimony deposits occur in the string of kopjes which 
 extend in a north-easterly direction from north of Leydsdorp 
 for a distance of about thirty miles. These kopjes are con- 
 stituted of a definite horizon in the schists, and are made up 
 of much altered and compressed chloritic quartzites and quartz 
 and clay slates, which dip at a big angle to the north. The 
 antimony occurs as the sulphide, stibnite, in lenticular veins 
 which can be traced at intervals throughout the whole length 
 of these kopjes and which seem to occupy the same minor 
 stratigraphical position. 
 
 * J. P. Johnson, The Antimony Deposits of the Murchison Range (1907)" 
 f Wilson-Moore, Trans. Geol. Soc. S. Africa, I., p. 51-62 (1895). 
 I H. Merenskv, Trans. Geol. Soc. S. Africa, VIII., p. 42-46 (1905). 
 
48 Ore Deposits of South Africa. 
 
 The richest sections of the antimony reef which I saw are 
 at the Gravelotte and Caledonian properties, but very little 
 work has been done on them, and that only in the oxidized 
 zone. There, large lenticules of pure mineral are a prominent 
 feature, while gangue is absent unless an occasional small 
 quartz vein can be considered as such. 
 
 Only at the Free-State mine has the antimony reef been 
 opened up in depth. There the stibnite occurs disseminated 
 throughout a calcareous gangue, which, under the microscope, 
 is seen to be mainly made up of calcite and dolomite with a 
 little green sericite and some secondary quartz. 
 
 It seems not unlikely, therefore, that these antimony de- 
 posits are impregnations of a bed of metamorphosed lime- 
 stone.* 
 
 At the Castle kopjes there is a large quartz vein which was 
 exceedingly rich in visible gold in places and w-hich sometimes 
 contains a little stibnite. 
 
 At the surface the stibnite is altered into a yellow oxide, 
 probably cervantite, and the hydroxide, stibiconite. 
 
 The antimony reef contains a notable quantity of gold and 
 silver. 
 
 The individual kopjes of the antimony line are separated 
 from one another by transverse faults, the beds trending 
 sharply round to the south at the east end of each kopje, and 
 to the north at the western end. 
 
 * Mellor in a later account (Report Geol. Survey, Pretoria, 1907) regards 
 the antimony reef as a true lode. 
 
CHAPTEE XII. 
 IRON (I). 
 
 The prominent part played by the peculiar banded silica - 
 iron oxide rocks and magnetite-hematite-quartz slates, among 
 the older sedimentary formations of South Africa make it 
 probable that many valuable ore-bodies will be found where 
 the conditions have been favourable to the growth of secondary 
 enrichments. The iron w T as probably originally deposited in 
 the form of hydrate at the time of the laying down of the beds, 
 and though, strictly speaking, largely of the nature of a chemi- 
 cal precipitate, may, for convenience, be regarded as a mem- 
 ber of the class of Detrital Accumulations. 
 
 FIG. 8. 
 
 Section through the Timeball Rang^ntar Pretoria, showing the Magnetite 
 Beds (after Hall Steart). 
 
 In the quartzite of the Timeball Kange, near Pretoria, 
 there are two beds (fig. 8) highly charged with magnetite, in 
 one of which the magnetite is considerably in excess of the 
 quartz and constitutes a good iron ore. 
 
 The iron content of the different sedimentary ores, when 
 theoretically pure, a condition, however, which, in nature, 
 is never attained in bulk, are : Magnetite (Fe 3 4 ) 72 per 
 cent., hematite, and its variety specularite (Fe 2 3 ), 70 per 
 cent., limonite (2Fe 2 3 . 3H 2 0), 60 per cent., and siderite 
 (Fe C0 3 ) 48 per cent. The most serious impurities usually 
 met with are sulphur and phosphorus, which are present in the 
 form of pyrite and apatite, and must not exceed certain 
 minute proportions. 
 
 E 
 
CHAPTEE XIII. 
 HINTS TO PROSPECTORS. 
 
 SOUTH AFRICA affords a fine field for prospectors. The 
 number of competent prospectors in the country could prob- 
 ably be counted on the fingers of one hand, a circumstance, 
 however, which one can only expect. A combination of 
 mining experience and geological knowledge are the essential 
 qualifications of competent prospectors, and those possessing 
 them are seldom inclined to expend their talents in a direc- 
 tion where reward is so uncertain. For all that there are 
 prospectors. 
 
 There are also many mining men possessing the necessary 
 grounding, who now and then can, and are prepared to, spend 
 a little time and money in trying their luck. To these 
 amateur prospectors a few hints will be useful. 
 
 The use of the pan in detecting the presence of gold or 
 other heavy minerals occurring in a finely divided state will 
 already be familiar to them. In searching for coarse, heavy 
 minerals in loose debris, such as detrital cassiterite, a sieve 
 will be found more useful. By placing some of the debris 
 inside and jigging it in water, the heavier minerals will be 
 made to sink to the bottom, while on sharply inverting on 
 the ground the contents will be spread out with the heavy 
 minerals on top. These can then be readily examined. 
 
 They should also make themselves thoroughly acquainted 
 with the blowpipe methods of determining minerals and with 
 the use of the more readily applicable reagents. These 
 methods are described in all text-books on minerals, and can- 
 not be detailed here. Proficiency in the laboratory is essential 
 
Hints to Prospectors. 51 
 
 before their aid is employed in the field, as many of them are 
 not so easy in practice as they seem to be on paper. By ex- 
 perimenting with mixtures of minerals they will be put on 
 their guard against the weaknesses of these methods under 
 certain conditions. For instance, small percentages of a 
 mineral yielding a very strong coloration may obscure the 
 presence of large percentages of one giving only a feeble 
 coloration. 
 
 Amateur prospectors as denned by the writer will already 
 be familiar with the commoner rock-forming minerals. The 
 economically valuable metalliferous minerals, with the excep- 
 tion of certain iron compounds, however, do not come under 
 that heading. The writer has, therefore, prepared the fol- 
 lowing comparative description of their more obvious features. 
 This is not intended to supersede the use of a text-book on 
 minerals, but merely to narrow down the range of enquiry. 
 It must be remembered that numerous other minerals will 
 answer to many of the descriptions given here, though they 
 are less likely to occur in any abundance, and it must be re- 
 membered that the most precious minerals are worthless unless 
 present in sufficient quantity. Having located the mineral in 
 the following scheme they should, unless a decisive result 
 such as the production of a recognisable metallic bead shall 
 have been obtained, turn to their text-book and put it through 
 the remaining tests, which will either confirm the prelimin- 
 ary identification, or else prove it to be merely a similar but 
 worthless mineral. 
 
 ANTIMONY. 
 
 Stibnite. Sulphide (Sb 2 S 3 ). A brittle metallic grey 
 mineral. Distinguishable from galenite by its fusibility in an 
 ordinary flame. 
 
 Antimony is used in the manufacture of certain bearing 
 and type alloys. Its property of imparting expansion in 
 changing from the liquid to the solid state and hence of pro- 
 
52 Ore Deposits of South Africa. 
 
 ducing a sharp cast, makes it specially useful for the latter 
 purpose. The demand, however, is limited. 
 
 ARSENIC. 
 
 Arsenopyrite (Mispickel). Sulpharsenide of Iron (Fe 
 As S). A heavy whitish metallic grey mineral. Resembles 
 smaltite-chloantite. It is the main source of arsenic which, 
 however, is also v obtained as a bye-product in the treatment of 
 the cobalt-nickel arsenides. In common with these last 
 minerals it readily yields the characteristic arsenical (garlic- 
 like) odour on roasting on charcoal. 
 
 CADMIUM. 
 
 Greenockite. Sulphide (Cd S). A yellow translucent 
 mineral. It is a common associate of the sulphide of zinc, 
 sphalerite, but has not hitherto been known to occur in suffi- 
 cient quantity to constitute an ore. The cadmium, however, 
 is recoverable as a bye-product in the production of zinc. 
 
 Cadmium is mainly employed in the manufacture of solder 
 alloys. Its possession of the quality of lowering the melting 
 point of the metals with which it combines, makes it specially 
 useful for that purpose. The demand, however, is limited. 
 
 CHROMIUM. 
 
 Chromite. Oxide of chromium and iron (Fe Cr 2 O 4 ). An 
 opaque black, sometimes brownish, mineral. Distinguishable 
 from magnetite by not being attracted by the hand magnet, by 
 its brown (as opposed to black) streak and by the test for 
 chromium. Fuse the mineral with salt of phosphorus when 
 any chromium present will impart a dirty green colour which 
 changes on cooling to a clear glass. 
 
 The principal uses of chromium at present are the pre- 
 paration of chromium salts, employed in tanning and textile 
 w r orks, the manufacture of chrome-brick for basic furnace 
 linings, and of ferro-chrome alloys for use in the manufacture 
 of certain steels. 
 
1<> Prospector*. 53 
 
 COBALT AND MCKEL. 
 
 Smaltite-Chloantite. Arsenides of cobalt and nickel 
 [(Co Ni) As 2 ] respectively, the one grading into the other. 
 A heavy whitish metallic grey mineral. Distinguishable from 
 arsenopyrite* by the test for cobalt or nickel. By fusing with 
 borax, after first roasting, any cobalt present will impart a 
 deep blue colour to it. Nickel will give, when using the 
 oxidizing portion of the flame, a violet colour which changes 
 to reddish-brown on cooling. 
 
 Cobaltite and Gcrsdorffite. Sulpharsenides of cobalt 
 (Co As S) and nickel (Ni As S) respectively, are exactly simi- 
 lar to the above in external characters. 
 
 Niccolitc. Arsenide (Ni As). A heavy reddish metallic 
 yellow mineral, much resembling pyrrhotite, which, however, 
 will attract a compass needle, and bornite, which may be dis- 
 tinguished by the test for copper. It usually contains a little 
 cobalt and sometimes sulphur or antimony in place of some 
 of the arsenic. 
 
 Garnierite. Hydrous silicate of magnesium and nickel. 
 An earthy apple-green mineral of very variable composition. 
 Not known in South Africa, but may be looked for in serpen- 
 tine areas. Very large bodies occur in that rock near Noumea, 
 New Caledonia, where it is mixed extensively. 
 
 COPPER. 
 
 Chalcocite. Sulphide (Cu 2 S). A heavy, brittle, blackish 
 metallic grey mineral. Contains 80 per cent, copper. 
 
 Bornite. Sulphide (Cu 3 Fe S 3 ). A yellowish to reddish 
 metallic brown mineral. Contains from 50 to 70 per cent, 
 copper. Occupies an intermediate position between chalco- 
 cite and chalcopyrite, and is usually intimately mixed with 
 varying proportions of these minerals, hence its variable cop- 
 
 * Arsenopyrite itself, however, sometimes contains small quantities of 
 hese metals, as also does pyrrhotite, pyrite and chalcopyrite in certain occur- 
 rences See under Nickel-ore occurrences. 
 
54 Ore Deposits of South Africa. 
 
 per content in mass. Distinguishable from both these, when 
 isolated, by the colour on a fresh fracture. Readily tarnishes 
 to metallic red and blue tints. 
 
 Chalcopyrite. Sulphide (Cu Fe S 2 ). A metallic yellow 
 mineral. Contains 35 per cent, copper. 
 
 Tetrahedrite. Sulphantimonide (Cu 8 Sb 2 S 7 ). A brittle 
 blackish metallic grey mineral. Often argentiferous. Has 
 some resemblance to chalcocite, but may be distinguished by 
 the emission of dense white inodorous antimonial fumes on 
 roasting on charcoal. The tetrahedral crystals of this mineral 
 afford a ready basis for identification. 
 
 Malachite and Azurite. The green and blue carbonates, 
 respectively, resulting from the alteration of the sulphides. 
 Sometimes occur in translucent crystals, but more often as an 
 opaque earth. They form important ore-deposits. 
 
 All the copper minerals will yield a metallic globule under 
 the blowpipe on charcoal the sulphides with soda after roast- 
 ing and the carbonates without. 
 
 LEAD. 
 
 Galenite (Galena). Sulphide (PbS). A heavy brittle 
 metallic grey mineral. Eesembles stibnite and argentite. 
 Usually contains a varying quantity of silver. 
 
 Cerussite. Carbonate (Pb C O 3 ). A heavy translucent 
 white mineral, often tinted brown, blue or green. An im- 
 portant ore of lead resulting from alteration of galenite. 
 
 Both minerals yield a lead globule under the blowpipe on 
 charcoal. 
 
 MANGANESE. 
 
 Pyrolusite. Oxide (Mn O 2 ). A blackish metallic grey 
 mineral. 
 
 Psilomelane and Wad. Hydrous alteration products of 
 pyrolusite which often form important ore-deposits. Eange 
 from a hard greyish-black to a soft brownish-black mineral. 
 
Hints to Prospectors. 55 
 
 These minerals may be distinguished from most similar 
 ones by the test for manganese. Fuse with soda when any 
 manganese present will impart a green colour to it. Wolfra- 
 mite and tantalite will yield the same manganese reaction, but 
 
 arc much heavier. 
 
 MERCURY. 
 
 Cinnabar. Sulphide (HgS). A very heavy translucent 
 red mineral. Heated in a glass tube it gives off sulphurous 
 fumes and mercury which, with careful manipulation, can be 
 made to condense on the sides. 
 
 MOLYBDENUM. 
 
 Molybdenite. Sulphide (MoS 2 ). A flexible metallic grey 
 mineral. Distinguishable from graphite by dissolving in nitric 
 acid with the formation of a w r hitish grey residue (Mo0 3 ). 
 Also readily gives off SO 2 under blowpipe. 
 
 Molybdenum is mainly employed in the manufacture of 
 certain steels, to which it imparts desirable properties. 
 
 TANTALUM. 
 
 Tantalite. Tantalate of iron and manganese [(Fe, Mn) 
 Ta 2 4 ]. A heavy opaque blackish-grey mineral. Eesembles 
 cassiterite. Distinguishable from wolframite by infusibility 
 under blowpipe alone. Not known to occur in South Africa, 
 but may be looked for with tin-ore occurrences. 
 
 Tantalum is used for the filaments of certain electric lamps. 
 The demand is very limited. 
 
 THORjfJM, 
 
 Monazite. Phosphate of the Rare Metals (Ce, La, Di, 
 Y, Er and Th). Thorium contents very variable. A trans- 
 lucent yellowish-brown to hyacinth-red mineral. 
 
 Moistened with sulphuric acid and ignited on a platinum 
 
56 Ore Deposits of South Africa. 
 
 wire, it affords the reaction for phosphoric acid a bluish-green 
 flame coloration. 
 
 Thorium is used for the manufacture of gas mantles. The 
 demand is very limited. 
 
 TIN. 
 
 Cassiterite. Oxide (SnO). A heavy opaque black, some- 
 times translucent brown, mineral. Resembles some varieties 
 of wolframite, rutile, sphalerite, tourmaline and garnet. Dis- 
 tinguishable from wolframite by infusibility under blowpipe 
 alone. From the others by its high specific gravity. From 
 all by yielding a bead of tin when fused with soda on char- 
 coal.* 
 
 TUNGSTEN. 
 
 Wolframite. Tungstate of Iron and Manganese [(Fe, 
 Mn) W O 4 ] . A heavy opaque greyish-black or brownish-black 
 mineral. Resembles cassiterite and tantalite. 
 
 Scheelite. Tungstate of Calcium (Ca W O 4 ). A heavy 
 translucent white and yellow mineral, often brownish, 
 greenish and reddish. 
 
 Tungsten is used in the manufacture of certain steels, to 
 which it imparts desirable properties. 
 
 URANIUM. 
 
 Uraninite (Pitchblende). A very heavy opaque greyish, 
 greenish, and brownish-black substance of variable composi- 
 tion, probably including two or three different mineral species. 
 Interesting as the chief source from wliich radium is obtained. 
 
 Uranium has been used experimentally in the manufacture 
 of certain steels to which it imparts desirable qualities, but it 
 is at present too costly for that purpose. 
 
 * This, however, is not readily obtained When megascopic by wrapping 
 in a piece of zinc foil and dropping into hydrochloric acid, cassiterite can be 
 reduced externally to metal which will reveal its characteristic colour on 
 rubbing. 
 
57 
 
 VANADIUM. 
 
 Yanadinite. A chloro-vanadate of lead (3Pb 3 V 2 8 . Pb 
 Clo). A heavy translucent red mineral. Yields a globule of 
 lead under the blowpipe on charcoal. Distinguishable from 
 crocoite and minium (which are also a different tint of red) 
 by the chlorine test. Heat in salt of phosphorus bead with 
 copper oxide, when, if chlorine is present, it is immediately 
 surrounded by a purple flame. 
 
 Vanadium is mostly used in the manufacture of certain 
 steels to which it imparts desirable properties. Vanadinite 
 is a frequently occurring accessory mineral in lead ores and 
 was formerly concentrated from lead ores carrying 4 to 5 per 
 cent, in the Iberian peninsula. The discovery of a large 
 occurrence of rich vanadium sulphide (patronite) in South 
 America, has, however, for the time being, deprived that 
 source of commercial value. 
 
 ZINC. 
 
 Sphalerite (or Zincblende). Sulphide (ZnS). A brittle 
 translucent yellowish to blackish-brown mineral. 
 
 Smitlisonite. Carbonate (ZnCo 3 ). A brittle translucent 
 white, often greyish, greenish and brownish, sometimes green, 
 blue and brown, mineral. 
 
 Hemimorphite (Calamine). Hydrous silicate (H 2 Zn Si 
 O 5 ). A brittle translucent w^hite mineral sometimes with a 
 bluish or greenish tint, also yellow to brown. 
 
 Smitlisonite and Hemimorphite are alteration products of 
 sphalerite, but often form important ore-deposits. Under the 
 blowpipe on charcoal, they give an incrustation which is yel- 
 low while hot and white when cold, and which, when heated 
 again, after moistening with cobalt solution, becomes a fine 
 green. Smitlisonite may be distinguished from the others by 
 the carbonate reaction.* 
 
 * Effervescence in acids. 
 
58 
 
 Ore Deposits of South Africa. 
 
Hints to Prospectors. 
 
 59 
 
 5 
 ^ S 
 
 I -I 
 
60 Ore Deposits of South Africa. 
 
 It is hardly necessary to remind the reader that most 
 minerals exhibit a wide range of variation in regard to their 
 colour. Only that most frequently met with is mentioned in 
 the above comparative descriptions. Also that minerals that 
 are usually translucent may often be transparent or opaque. 
 
 When prospecting for the insoluble minerals search 
 should always first be made among the detrital accumulations 
 in the bottom of creeks or in the natural riffles of river beds. 
 On finding any there, they may be traced to their source by 
 panning or sieving at intervals in the direction from which 
 they have apparently drifted. In prospecting for the more 
 readily decomposable minerals, stains of the colour of the 
 oxidation products of the various metalliferous minerals should 
 be looked for, especially along gossan-like (rusty) outcrops. 
 
 Worthless but more abundant and more noticeable 
 minerals often serve as indications of the presence of valuable 
 minerals. Tourmaline, for instance, nearly always points to 
 the presence of cassiterite. The commoner associates of the 
 valuable minerals recorded in the preceding pages, should be 
 specially noted. 
 
 Any old workings that may be discovered should be 
 examined, though it should be borne in mind that the Kafirs 
 very often excavated small patches of ore that would not pay 
 a European to exploit. 
 
 Farther, having located a reef, they must not be dis- 
 couraged if, after tracing it for a little distance, they find its 
 continuation shifted by a dyke or fault. The dislocation pro- 
 duced by them is seldom of serious extent. A little per- 
 severance will usually pick up the reef again on the other side. 
 
 Finally, it may be observed (1) that occurrences of tin and 
 its genetically allied metals should be looked for in the vicinity 
 of intrusive granite contacts, (2) that gold deposits are mostly 
 found among the schistose rocks, and (3) that the neighbour- 
 hood of big gabbrodiorite intrusions is frequently prolific in 
 other metalliferous minerals. 
 
Ilintx to Pfospcctors, 61 
 
 If would-be prospectors will ponder over this last state- 
 ment for a little while, and at the same time call to mind the 
 various types of ore occurrences described in the preceding 
 pages, and the working hypothesis by which they are co- 
 ordinated, they will soon realize the importance to them of au 
 understanding of the principles outlined in the introduction. 
 
BY THE SAME AUTHOR. 
 
 THE STONE IMPLEMENTS OF 
 SOUTH AFRICA. 
 
 SECOND EDITION. 
 REVISED and ENLARGED. 
 
 WITH ILLUSTRATIONS. 
 Price 10 -. 
 
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 39, PATERNOSTER ROW, LONDON. 
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 THE GEOLOGY OF THE ROBERTS- 
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 THE 
 
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 UNIVERSITY OF CALIFORNIA LIBRARY