Short Paper No. 18
DEPARTMENT OF LANDS AND MINES
By A. C. SKERL, Ph.D., A.R.S.M.; and
F. OATES, M.B.E., B.Sc., A.R.S.M.,
DAR ES SALAAM
PRINTED BY THE GOVERNMENT PRINTER
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Short Paper No. 18
DEPARTMENT OF LANDS AND MINES
The Geology of the North
By A. C. SKERL and F. OATES
DEPARTMENT OF LANDS AND MINES
THE HONOURABLE THE DIRECTOR,
DEPARTMENT OF LANDS AND MINES,
DAR ES SALAAM.
I have the honour to transmit, herewith, a geological map and description
of the North Ilunga Area of the Lupa Goldfield by Dr Skerl, permission to
publish the same as a short paper of the Geological Survey having been kindly
accorded by Messrs Tanganyika Diamonds and Gold Development Company,
Limited. Your sanction is now sought to allow this to appear as suggested
together with the accompanying petrological appendix by Mr Oates.
2. The map is the outcome of Dr Skerl's field work alone, while the paper
was written later when the petrological appendix was available. Delay in
assembly and presentation of the results has been caused by the necessity of
interchange of correspondence with Dr Skerl, who is now in the Philippine
3. It may be as well to recall that the foundations of Lupa geology were
laid by Dr Grantham's work carried on at intervals between 1928 and 1932,
that is, at a relatively early period in the history of this Survey when much
less was known of the geology of the Territory as a whole. Furthermore,
at that time necessity dictated that the first regional mapping should have been
performed on terrain now acknowledged to be almost unique in its geological
complexity. Although complete solution of the many academic and economic
geological problems of the field cannot be said to be even in sight, the detailed
work in restricted areas by geologists in the employment of the larger mining
companies has already made important contributions to our knowledge of Lupa
geology. This detailed work has demonstrated that the only hope of unravelling
the tangled skein of igneous sequence is to map the field on a scale very much
greater than that normally employed for regional work-say, on 1: 25,000
instead of 1: 250,000.
UNIVERSITY OF FLORIft LAF.R L
4. Needless to say such an ambitious programme cannot be envisaged under
the present financial conditions of the Territory, but until the Lupa problem
has been tackled in the manner suggested, disagreement and speculation in
regard to the interpretation of its geology is bound to be rife, consequently
this Survey welcomes the publication of the views of authoritative co-workers.
I have the honour to be, Sir,
Your obedient servant,
F. B. WADE
25th March 1938. Chief Geologist
PART I.-PRELIMINARY REMARKS :
Introduction .. .. .. ... ... .. ... ... 5
Situation ... ... ... ... ... ... ... .. ... 5
Physical Features ... ... ... ... ... ... ... 5
Field Procedure ... ... ... .. ... ... ... ... 7
General Geology : ... .. ... .. ... ... 7
Rock Types: ... ... ... ... .. ... ... 8
1. The Meta-diorite Suite ... ... ... ... ... ... 8
2. The Ilunga Felsitic Series ... ... ... ... ... 9
3. The Newer Granites: ... ... ...... ... ... 9
(i) The grey granites ... ... ... ... ... ... 9
(ii) The Ilunga granite ... ... ... ... ... ... 10
Minor Rock Types: ... ... ... ... ... .. ... 11
1. M icro-aplogranite ... ... ... .. ... ... ... 11
2. Banded Ironstone and Associated Basic Rocks ... ... 11
3. Para-gneisses ... ... ... ... ... ... ... 11
4: D olerites ... ... ... ... .. .. .. ... 12
5. Iron Oxide ... ... ... ... ... ... ... ... 12
Distribution and Structure of the Rock Types ... ... ... 12
Petrogenesis .. .. .. ... ... ... ... 12
Quartz Veins ... .. .. ... ... ... ... 14
PART III.-PETROLOGICAL APPENDIX : ... ... ... ... ... 15
1. Ilunga Granite ... ... ... .. ... ... ... 15
2. Grey Granite ... ... ... .. ... ... ... 16
3. Ilunga Felsites ... ... ... ... ... ... 17
4. Micro-aplogranites ... ... ... ... ... ... 19
5. Aplogranites ... ... ... .... ... 19
6. Ultramafic Rocks with Noritic Affinities ... ... ... 20
7. Appinites and Meta-basites ... ... ... ... ... 22
8. Dolerites ... ... ... 26
9. Altered Ultramafic Rocks ... ... ... ... ... 27
10. Tonalite-porphyry ... ... ... ... ... ... ... 27
11. Plagioclasite ... ... ... ... ... ... ... 27
12. Hematite-quartzite ... ... ... ... ... ... 27
13. Feldspathic Quartzite ... ... ... ... ... ... 28
14. Iron Oxide of Magmatic Origin ... ... ... ... ... 28
15. Doubtful Rock Types ... ... ... ... ... ... 29
16. List and Description of Photomicrographs ... ... ... 32
17. List of Specimens and their Localities ... ... ... ... 32
BIBLIOGRAPHY ... ... ... ... ... ... ... ... 35
LIST OF PUBLICATIONS AND MAPS.
GEOLOGICAL MAP OF NORTH ILUNGA AREA (Scale 1: 50,000). In pocket at back.
PART I.-PRELIMINARY REMARKS
The western part of the Lupa goldfield is bounded on the north by the
imposing Ilunga range, beyond which few prospectors had been previous to
1936, and before which date, therefore, little was known concerning the
geology or mineral possibilities of this extension of the field. In December
1936, as senior geologist of Tanganyika Diamonds and Gold Development
Company, Limited, the author was asked to determine the mineral potentiali-
ties of the country north of the Ilunga range. A rapid reconnaissance covering
an area of five hundred square miles was made before geological conditions
were discovered suitable for the occurrence of auriferous veins, and shortly
afterwards a "strike" was made. The onset of the heavy rains made systematic
prospection of the whole area impracticable, and accordingly the most promising
section was pegged under exclusive prospecting licence before postponement
of field work until the dry season.
The following account is based on an intensive campaign of prospecting and
geological mapping carried out over ninety square miles of country by the
writer (A.C.S.) with the able assistance of three prospectors, Messrs A. M.
Cogill, F. Fritz and R. Klapprott, and a surveyor, Mr A. E. Turnbull, during
a period of two months, from the 15th June to the 15th August 1936. The field
work has now been supplemented by a laboratory study of numerous rock
specimens by Mr F. Oates, the Government ,Chemist and Petrologist, which
is included in full as an appendix.
The area has proved of great interest geologically and the detailed mapping
has led the writer to draw conclusions new to the literature of the Lupa
The area examined lies on the northern side of the Ilunga range with its
south-eastern corner at the foot of Sinipala Hill. Thence the southern boundary
runs due east along the whole length of the lower slopes of the Ilunga range,
coinciding approximately with the northern boundary of the Lupa Controlled
Area, and then crosses the Luika River to the eastern boundary of the
S.E.P.L.* No. 62. The northern boundary is six miles north of the southern
boundary and trends east-west. The insertion on the geological map (in cover
at back) shows the position of the area relative to the Lupa goldfield.
The comparatively small area now being described belongs to the "pene-
plain area" of Grantham's three topographical divisions (1932, p. 3). It is
largely flat to undulating but with isolated hills to the south-west and the crest
of the Ilunga range on the southern boundary rising approximately 1,000 feet
above the general level. To the north, but just outside the area, an east-west
line of hills forms a dissected counterpart of the Ilunga range. At one time
a large portion of the country between the two sets of hills consisted of swamp
land but it has been effectively drained by the late Tertiary and Quaternary
Rukwa rift faulting.
*S.E.P.L. indicates special exclusive prospecting licence.
The whole of the drainage is into the Luika River, which flows through
the western half of the area from north to south. The rift faulting has led to
the rejuvenation of this river with effects that can be seen over the entire
district. Thus the channels of the tributaries are often deep and unusually
rocky whilst large expanses of old swamp land are rapidly becoming denuded
of their soil and the underlying rock exposed. The area would be devoid of
outcrops and therefore useless to prospect but for this cleansing effect of the
The principal tributary of the Luika River is the Nkulwisi, which in turn
is fed by the Kwango and Mitao streams, all three flowing in a westerly
direction for the greater part of their courses. An examination of the accom-
panying geological map will show that the watercourses have a strong tendency
to follow shear lines and contacts between the different rocks.
The major rivers flow for the greater part of the year and should prove
suitable as sources of water supply for mining purposes.
The area is now readily accessible from the government highways, and bush
roads are easily made to connect up the various prospects. A variety of both
hard and soft timber is available for all purposes; large trees are confined to
areas that still retain the deep mantle of soil of the old peneplain surface
whilst thorn trees and coarse grass characterize the black clay of the old
At present, game such as elephant, various large antelope, giraffe, and
occasional lion and leopard, still roam through the district. Tsetse fly are
abundant throughout the area, but, although very annoying, they are not
infected with sleeping sickness germs and so are harmless to human beings.
The following description of the method of exploration that was adopted
is given in the belief that it will be of interest and help to geologists and
prospectors working elsewhere in the Territory. The area was prospected and
mapped by means of straight-line compass traversing between control lines
First, a central, east-west base line was started from the eastern end of the
area and kept ahead of the prospectors throughout the work. North and south
boundary lines were also laid out at approximately three miles from the centre
line with occasional north-south tie-lines. These three lines were surveyed
with a 4-5-inch prismatic stand-compass and a 100-foot land-surveyor's chain,
corresponding stations being numbered off at intervals of one-tenth of a mile.
Careful back-sighting as well as fore-sighting was found essential when laying
out base lines owing to the strong local irregular magnetic variations from
the normal of the district (6W.). Camp was always placed on the centre line
and shifted along four miles at every move.
Traverses were run between the corresponding stations on the centre line
and on the north and south boundaries, a pocket prismatic compass being used
for direction and a bicycle wheel with a cyclometer attached, to measure the
distances. The prospectors had three natives on each side of them carrying
four-pound hammers and spaced at intervals of 100 feet so that practically all
vein outcrops and boulders of any size could be found. The incentive provided
by a bonus system of reward ensured the active co-operation of the natives.
Samples were chipped off the outcrops and boulders in as thorough a manner
as possible and sent by lorry in bi-weekly batches to the company's assay office
The writer as geologist-in-charge traversed on an average every third to
fourth line ahead of the prospectors and so acted as a guide in the identification
of rock types, etc.
Detailed traverse notes were kept so that the position of all rock outcrops,
samples and topographical features could be plotted daily on a field map to
the scale of 1: 10,000. This map was subsequently reduced to the scale of
1: 25,000 for the purpose of a company report and now a further reduction
has been made to 1 : 50,000 to accompany this short paper.
About 1,500 samples, representing nearly 1,000 quartz veins, were taken
during a period of two months, resulting in the location of ten gold prospects,
of which at least one holds out the promise of being large enough to warrant
its exploitation by the company. The estimated total cost of the two months'
operations was 500.
The previous descriptions in the Geological Survey publications of the
geology of the Lupa goldfield apply broadly to the north Ilunga area but the
greater detail of the field work carried out in this restricted region has led to
important conclusions, which would appear to justify the publication of this
account. The difficulties in mapping and interpreting type variations in the
district, due to the changes in texture and to the varying degrees of meta-
morphism, assimilation and hybridization, have been pointed out by Teale and
Oates (Teale, Eades and Oates, 1935, p. 14). In a later section of the present
paper, under the heading of "Petrogenesis," an hypothesis is presented which
co-ordinates the observations and tentative views of previous workers in the
Lupa goldfield. At this point it will merely be stated briefly that the north
Ilunga area is regarded as a striking example of anatexis.
Over the main portion of the goldfield, rocks of sedimentary origin appear
to be absent. This statement also applies to all but a limited part of the north
Ilunga area where para-gneisses occur that are described later (pages 11 and 28).
Granite-gneiss was found extensively to the north during the reconnaissance
survey of the surrounding country but none was mapped in the area under
discussion although a gneissic variety of the newer granites (see below) was
found in the northern part. Since granite-gneiss is often considered to be the
country rock for many of the veins in the goldfield, its absence from this area
where veins are so abundant constitutes a major point of difference.*
The principal rock types to be described are classified under three head-
1. The Meta-diorite Suite.
2. The Ilunga Felsitic Series.
3. The Newer Granites.
1. THE META-DIORITE SUITE.
The writer is indebted to Dr D. Gallagher, Geologist to East African
Goldfields, Limited, for bringing to his notice the results of his microscopical
studies of the varied types mapped as "Diorites" by the Geological Survey
and for suggesting the more fitting name "Meta-diorite."t
The centre of the north Ilunga area is occupied by a mass of meta-diorite
at least fifteen miles long and three miles wide, thus constituting the largest
body of this general type known in the Lupa region. In addition there are
numerous scattered occurrences as shown on the map. In the field the meta-
diorites are characterized by their essential make-up of hornblende and feldspar,
but the grain-size and relative proportion of these minerals are extremely
variable. Thus the rock may be so fine-grained as to possess a micro-texture,
or so coarse as to contain crystals as much as an inch and a half long. Again,
the rock may be largely feldspar with a little quartz and wisps of mafic
minerals simulating an aplogranite; or, at the other extreme, may consist
purely of hornblende, as hornblendite. A striking variety, towards the ultra-
mafic end of the suite yet containing accessory feldspar, has been described by
"Granite-gneiss" of the Geological Survey maps comprises both acidic and basic varieties,
the latter including much material that is classed as "meta-diorite" in the present paper.
t "Meta-. A prefix used before the names of igneous rocks to signify that the mineral and
chemical composition of the latter have been modified by alteration." (Holmes, "The Nomen-
clature of Petrology," 1920). The term is usually restricted to those rocks in which the changes
metamorphismm and metasomatism) have not completely effaced the identity of the parent.
In a private communication to one of us (r.o.), when referring to certain altered Lupa rocks
believed by Grantham to be of doleritic origin (the "basic gneiss," see T.T. Geological Survey
Department Bull. 3, p. 12, 1932), Dr Gallagher made use of the term "meta-diorite" since he
believed that originally they were diorites in the sense that they had crystallized from a magma
of that composition under plutonic conditions and had subsequently suffered alteration.
Dr Skerl has extended the use of the term to cover all the appinitic suite, which may be in
part the meta-diorite of Gallagher (equivalent to the "basic gneiss" of Grantham) in situ, and
in part intrusive dyke rocks of mixed origin. It is mainly to the latter class that the term
dioritee" was applied by Grantham (op. cit., pp, 18, 19),
Oates as "Appinite" (1935, op. cit., p. 31). These extreme variations may
sometimes be seen in one outcrop, presenting a problem in petrogenesis that
will be referred to again later (see pages 12, 13 and 24-26).
A microscopical examination of the appinitic rocks shows that in general
the same minerals and structures are common to all. There is also a suggestion
of gradation towards ultramafic types, on the one hand, and towards more
felsic types on the other. Locally within the meta-diorite masses foliated rocks
are found which the writer believes correspond with the "Epidiorites" des-
cribed by the Geological Survey (1935, op. cit., pp. 41-2). It is thought that
the re-constitution of such rocks has led to the formation of the meta-diorite
suite, the variations being partly attributable to the differences of composition
of the original rock (e.g., basic volcanics and lava flows) and partly to the
degree of mixing and reaction with magmatically introduced granitic material.
In discussing the relation of the newer granites to the hornblendic rocks, Teale
and Oates (1935, p. 28) have already suggested that "it would appear that
the complicated suite of rocks has come into being as a result of an intrusion
of pre-existing basic and ultrabasic rocks by various phases of the younger
This conception will be extended in the discussion on petrogenesis (see
pages 12 and 13).
2. THE ILUNGA FELSITIC SERIES.
These rocks have already been described in detail by Grantham (1932,
pp. 14-15), and the evidence in the north Ilunga area is in agreement with his
conclusions as quoted by Oates (1935, pp. 23-24). The normal type is a
purplish-pink rock of micro-granitic texture, and as such is readily mapped,
but the hydrothermally altered contact varieties near the Ilunga granite (see
pages 17 and 30) area are frequently puzzling.
In micro-section one specimen (SK.40) is described as consisting of sporadic
micro-porphyroclasts of undulose quartz in a micro-felsitic groundmass con-
taining numerous minute grains of iron oxide, small flakes and threads of
chlorite and granules of epidote. Another specimen (SK.48) is greyish with
ragged micro-phenocrysts of oligoclase, partly granulitized areas of quartz and
sparse hornblende in a similar groundmass, in which much greyish-brown
epidote and comminuted hornblende show distinct alignment.
A number of specimens (SK.39, 46, 51, 53, 61, 76 and 85) are purplish-
pink rocks similar in texture and appearance to a micro-aplogranite. They
are referred to at greater length in the petrological appendix.
3. THE NEWER GRANITES.
Although the newer granites are separated into two distinct types named
the "grey granite" and the "Ilunga granite" respectively, it is maintained
that they are of the same geological age and represent different faces of the
same granitic intrusive period, the differences being due to the environment
during anatexis. That is to say, at least part of the granite originated as
assimilated material, the variation in the composition and amount of which
has given rise to the separate granitic types.
(i) The grey granite.-Normally this is an even-grained, medium-textured
granite with a plentiful speckling of finely divided biotite. Occasionally it is
found as a gneissose granite, but its origin can be inferred from the transitional
types seen in the field. This granite is remarkable for the extent to which it
has been contaminated near its contact with the meta-diorite, the first sign
of which in micro-section is the chloritization of the biotite and the cloudiness
of the feldspar, whilst nearer the contact hornblende begins to appear, along
with a porphyritic generation of feldspars, which are usually pink and up to
one inch long. Not uncommonly xenoliths of re-crystallized basic material can
There is no clearly defined contact but instead a hybrid zone up to 1,000
feet wide consisting of an intimate mixture of basic and acidic material in
all proportions and often strongly sheared. Both this zone and the porphyritic
granite are highly epidotized, sometimes to such an extent as to yield an
epidosite. Outcrops showing these variations due to contamination and
hybridization are well exposed by the Nkulwisi River where it flows along
the northern margin of the main meta-diorite mass. In the field the gradual
transition of a normal, fresh-looking, grey biotite-granite into hornblendic
varieties with pink porphyritic feldspars was taken as positive evidence for
regarding Grantham's Saza granite (1932, pp. 17-18) as a variation of this
granite. The following account of the microscopic features supports this
The average composition of the grey granite is adamellitic, but granodioritic
and tonalitic facies exist. The adamellitic facies shows an assemblage of
allotriomorphic clear microcline and quartz, and subhedral turbid plagioclase.
The quartz is somewhat granulitized and, where not, has slight undulose
extinction. The mafic minerals and accessories are not associated in clots, the
biotite occurring sporadically in rather large partly chloritized flakes and sphene
being the most prominent accessory. Epidote is generally present, either as
quite large independent crystals or as the alteration product within the
plagioclase. Myrmekitic intergrowths are common.
In the granodioritic facies the feldspar consists principally of basic oligoclase
with a marked tendency towards idiomorphism; it is strongly zoned with a
slightly turbid centre and a clear periphery; unaltered microcline is quite
subordinate and the mafic minerals consist of chloritized biotite and of epidote.
When deficient in quartz the rock approaches a tonalite in composition.
A specimen (SK.112) of a marginal facies of the grey granite consisting of
coarse, pinkish, dominantly feldspathic rock was observed in micro-section
to contain approximately equal proportions of clear microcline and turbid
albiclase. The specimen contains a xenolith similar in microscopic characters
to one appearing in a rather mafic specimen (SK.114) of the grey granite.
This example serves to illustrate the variation of the proportion of ferro-
magnesian minerals in the grey granite.
(ii) The Ilunga granite.-In the field this granite has, in contrast to the
preceding type, consistent megascopic features over wide areas. It is a some-
what coarse-grained rock with pink feldspar and faintly opalescent quartz,
although the latter in some specimens tends to be inconspicuous, probably
owing to extreme granulitization. There is usually a suggestion of foliation,
which the dark minerals in the form of finely crystalline clots tend to
In micro-section large plates of perthitic microcline with subordinate plates
of albite are seen to occur in a granular allotriomorphic assemblage of the
same minerals with the quartz displaying a variation of granulitization to
lenticular aggregates. The mafic minerals and accessories occur as straggling
clots consisting of a sodic hornblende, biotite of an unusual reddish-yellow or
golden-yellow colour, iron oxide, sphene, zircon, epidote and orthite. The
dynamic effects seen in thin section are granulitization, shattering, micro-
faulting of albite and lobate penetration of feldspar by granular quartz. The
perthite is of striking appearance since the intergrown lattices under
crossed-nicols show blotchy and spindle-shaped forms. The patchy or vein-like
appearance of the albite within the microcline plates in some types of inter-
growth suggests strongly that it has resulted by a hydrothermal replacement
process. Myrmekitic intergrowths are rare.
As has already been tentatively suggested by Oates (1935, pp. 22 and 24),
the gneissose microcline-granite described by Grantham (1932, pp. 15-16)
appears to be a more foliated variety of the Ilunga granite. In the present area
all degress of foliation of the Ilunga granite may be seen in the field and the
descriptions of the microscopic examinations of the more sheared specimens
do not differ greatly from those of Grantham for the gneissose microcline-
granite. In contrast to the grey granite there is little hybridization along the
contact of the Ilunga granite and where present it is limited to a narrow zone
of a few feet.
MINOR ROCK TYPES
These include types too limited in the size of their occurrence to be
indicated on the map.
Throughout the area mapped but most frequently in the main meta-diorite
mass, occur dykes of a pinkish leucocratic quartz-feldspar rock (SK.43, 45),
which appears to be an end phase of the grey granite and is the nearest approach
to a porphyry or aplite dyke facies of the granite.
In micro-section the type consists of allotriomorphic clear microcline and
quartz, the latter showing myrmekitic intergrowths with subordinate turbid
plagioclase. The mafic minerals consist of sporadic shreds of biotite and
2. BANDED IRONSTONE AND ASSOCIATED BASIC ROCKS.
Highly ferruginous quartzitic rock, sometimes strongly contorted, has been
found as "float" along the southern section of the area. In some instances
it appears to be an altered amphibolite and in one micro-section a pale green,
non-pleochroic amphibole was noted. On the south side of Kango Hill it occurs
with a fine-grained, dark grey, serpentinized ultrabasic rock in various stages
of schistosity and showing minute glistening specks of magnetite. In micro-
section this rock is seen to consist largely of serpentine with a little sericitic
or talcose material occurring patchily, and abundant irregularly shaped grains
of released iron oxide. An additional association in this case consists of
boulders of highly limonitic vein quartz containing visible gold, which is a
further corroboration of the statements: "There is a fairly constant association
of the ironstones with hornblendic and talcose rocks," and "Quartz reefs
commonly occur in proximity to these rocks." It also duplicates: ". one
case, south of Heslam's, where a specimen of ferruginous 'float' assaying 21-6
pennyweights of gold per short ton was found." (Teale, 1935, p. 18.)
An interesting patch of quartz-feldspar-gneisses and calcareous quartz-
schists occur within the hybrid zone of the grey granite along the north margin
of the main meta-diorite mass. These are probably the remains of sedimentary
or volcanic rocks which have escaped the prevailing granitization. A micro-
scopic section of the "gneiss" shows that it is a feldspathic quartzite consisting
of sub-rounded quartz and acidic plagioclase, chloritic and micaceous flakes,
and abundant apatite, zircon and iron oxide.
A large variety of dolerites is found here as elsewhere in the field. They are
mostly normal in megascopic appearance although one striking occurrence
contains feldspar phenocrysts up to one inch in length.
5. IRON OXIDE.
Along a zone approximating to the axis of the main meta-diorite mass are
found numerous outcrops of massive titaniferous iron oxide occurring as dykes
up to 500 feet long by three feet wide and appearing to be magmatic injections
of one of the ultrabasic constituents of the meta-diorite country rock.
An analysis of this material at Dodoma (SK.72) showed it to contain about
15-2 per cent of titania (see also pages 28 and 29).
DISTRIBUTION AND STRUCTURE OF THE ROCK TYPES
The whole of the north Ilunga area is dominated by an east-west structural
"grain" as shown by the intense shearing, the distribution of the various rock
types and the alignment of the numerous quartz veins. The shearing reaches
its greatest intensity along the hybrid zone between the grey granite and the
meta-diorite. The main meta-diorite mass, forming the central core of the
area, trends a few degrees north of west, passing at both ends beyond the
limits of the mapped portion so that it must be at least fifteen miles long with
a greatest width of three miles. The curiously shaped large expanse of meta-
diorite to the north appears to be the remains of a partially assimilated mass
fringed by the contaminated porphyritic granite.
The Ilunga granite has invaded the southern and western portions of the
central meta-diorite in a series of tongues so that the resulting pattern on the
present surface recalls that of many goldfields where granite apophyses have
invaded "greenstones." In the ensuing section, however, it will be shown that
the petrogenesis is more complicated than this statement suggests.
The possibilities and effects of assimilation and re-constitution are men-
tioned in several places in the Geological Survey publications, and the evidence
in the north Ilunga area strongly suggests that these are paramount factors in
the formation of the rocks. Whilst statements concerning these phenomena
are of necessity conjectural, their discussion helps towards the understanding
of the relationship between a number of otherwise unrelated rocks in the north
Ilunga area, and, by comparison, in the Lupa goldfield as a whole. To the
writer (A.C.S.) the area presents large-scale examples of what results when
neighboring rock masses of opposite chemical characters, namely acidic and
basic, are subjected to great heat and pressure over long periods of time.
During an earlier period in the geological history of this district, perhaps
during Cambrian times, it is surmised that there existed an old granitic land
surface over which spread basic and acidic lavas. These three general rock
classes are assumed to have been the parents of the granite-gneiss, meta-
diorites, and Ilunga felsites respectively in the Lupa region. Feldspathic sand-
stones and arkoses formed from the denudation of the old granite have survived
to a limited extent as the para-gneisses described above, whilst the local
decomposition and weathering of the basic lavas soon after their formation
produced ferruginous laterites, which ultimately became banded ironstones in
the manner described by Dunn (1935).
In the course of time the volcanic rocks were folded and then buried deeply
by later formations. The depth of burial increased until the formations
considered entered a deep zone of the earth's crust where the conditions were
such as to cause plasticity or even fusion. Thus the old granite would in
general revert to magma and similarly the acidic volcanics would also yield
a magma, the composition of which would depend on that of the original rock.
At the contacts between rocks of different chemical composition reactions
would take place modifying the new magmas, whilst hybrids would result from
the penetration of mobile fractions of the molten products into the still solid
neighboring rock. Probably this latter process was aided considerably by
filter-pressing engendered by the intense lateral pressure, the results of which
are seen in the constant east-west shearing of the north Ilunga area. During
the vast ensuing period of denudation the modified formations rose in a relative
sense within the earth's crust, the gradual lowering of temperature causing
general solidification with production of the rock assemblage now laid bare.
The conditions postulated would be inimical to the formation of porphyries,
and it is significant to note their complete absence in the area under considera-
tion. Narrow tongues and dyke-like bodies of granite are seen in the meta-
diorites, but never porphyries, which result only from the rapid cooling of
a comparatively small volume of granitic magma.
The major changes undergone by the original rocks were:-
(i) Acid Volcanics.-Where the conditions were insufficient to produce
fusion, re-crystallization gave rise to the Ilunga felsitics, but, where melting
took place the Ilunga granite resulted, and, with more intense shearing, the
gneissose microcline-granite was formed. This is the explanation offered for
the similarity between these three rocks and also for Grantham finding the
first two so confusingly alike in some areas that he mapped them as one
(1932, p. 16).
(ii) Basic Volcanics.-Heat and differential pressure without actual fusion
produced the nondescript epidiorites, etc., of the central meta-diorite area,
whilst complete melting led to the production of the wide range of types that
this general term connotes. No doubt differentiation also played a part in these
(iii) Granite.-The melting of the old granite and its contamination along
the contacts with the basic rocks produced types rich in biotite and horblende,
whilst away from the contacts the granite simply recrystallized under pressure
as granite-gneiss. As suggested above, the formation of the noteworthy sheared
hybrid zone along the northern margin of the main meta-diorite mass was
probably aided by a concentration of the shearing stresses forcing the molten
fraction into the neighboring rock.
In the case of the Ilunga granite, hybrids become noticeable only where
there has been intense shearing along the contact. The interdigitating contact
of the Ilunga granite and the meta-diorites is regarded as representing folding
that took place during burial.
The numerous quartz veins are thought to have been formed from the silica
squeezed out of the melted granite and even to represent veins re-formed from
previously existing veins in the original rocks. This latter theory was advanced
by Malcolm Maclaren (1908) for many of the auriferous veins in the schist
areas of the world. 13
There are three distinct belts of quartz veins stretching across the area
from east to west and following the general structural direction.
(i) The first is along the sheared marginal hybrid zone on the north side
of the central meta-diorite. Individual veins are short, never more than three
hundred feet long and usually much less, but the en echelon arrangement
often confers a considerable effective strike. The quartz is typically glassy,
often mineralized with limonite from the oxidation of pyrites, and copper is
sometimes present as sulphide or carbonate but the gold content of these veins
is never higher than 1-5 pennyweight per ton.
The calcareous quartz-schist of the para-gneiss described above has been
mineralized in one place by a copper sulphide dissemination, and a lenticular
patch was found in it about six feet long by one foot wide by three feet deep
of quartz highly mineralized with chalcopyrite and galena but no gold.
(ii) The second belt, which is much wider than the foregoing since it
covers the main mass of meta-diorite, has numerous small quartz veins usually
striking east-west. The quartz is granular and glassy with limonite after pyrites.
Sometimes magnetite is present but never copper minerals. Here again only low
values of up to one pennyweight of gold per ton have been obtained.
(iii) The third and economically important zone since it is auriferous lies
along the southern section of the area. Here there are hundreds of veins most
of which have an east-west strike. These, in the eastern half of the zone, are
always small, e.g., lenses up to 300 feet long and two feet wide but frequently
grouped together en echelon. Towards the west, however, they become much
larger, and several veins are exposed for over 500 feet with an average width
of four feet. Here also east-west strikes with en echelon grouping is the rule.
There are two distinct types of quartz in this southern belt, sometimes
occurring separately but more commonly together in the vein. That occurring
more abundantly is a sheared cherty quartz usually highly mineralized with
pyrite or its oxidation product, limonite, when it has a honeycomb appearance.
The other type is dark grey and unsheared and is not so well mineralized.
Normal translucent white quartz occurs only occasionally.
,Copper mineralization in the form of chalcopyrite and malachite was seen
in two places only, in both of which there were short but wide north-south
reefs. The first is situated at right angles to a strong east-west reef in the
centre of the belt and is unique in being mineralized with specularite as well
as with copper and iron sulphides. The other is two miles further west where
Mr A. E. Bousfield has a gold prospect on a vertical north-south shear zone
highly mineralized with chalcopyrite and pyrite.
-Towards the western end of the belt molybdenite* was found in small quan-
tities in two veins. This mineral is of especial interest since it occurs at theLuika
mine of East African Goldfields, Limited, where it is taken as an indication
of high gold values. In the present case, however, it is not associated with gold.
All the veins occupy shear zones either in the isolated masses of meta-
diorite near the sourthen margin of the main meta-diorite mass or in the
surrounding Ilunga granite, but normally never further than a quarter of a
mile from a contact. By far the greater number of veins have east-west strikes
although a few important ones strike nearly north-south as mentioned above.
It is of significance to note that the rich Rukwa vein, several miles to the
west, lies along this southern belt of gold-bearing veins.
*Presence of molybdenum was confirmed in the Geological Survey laboratory by the potassium
Xanthate test. 14
PART III.-PETROLOGICAL APPENDIX
The rocks about to be described were collected by Dr Skerl in the north
Ilunga area while carrying out geological mapping for Messrs Tanganyika-
Diamonds and Gold Development Company, Limited. The specimens, together
with a geological map of the area on a scale of 1 : 25,000 and key to localities
of specimens were supplied to the writer, who has not, however, visited the
area in question. It should therefore be understood that the following notes
are concerned principally with the microscopical examination of the thin
sections prepared from the rocks collected, and with their classification and
petrographic affinities rather than with the larger aspects of petrogenesis.
Some of the specimens are referable to types established by previous
mapping in other part of the Lupa, but there are many, the affinities of
which are by no means clear. It is proposed first of all to describe those rocks
that belong to the former category or else form definite types, so as to establish
a firm basis of reference when discussing the hybridized and metamorphosed
1. ILUNGA GRANITE.
Megascopically, the Ilunga granite is a rather coarse-grained rock, with
pink feldspar and faintly opalescent quartz. In some specimens the quartz,
owing perhaps to extreme granulitization, is not so conspicuous. The dark
minerals are present in finely crystalline clots and show some suggestion of
alignment. Even in those specimens deficient in dark minerals there is usually
some indication of schistosity.
In micro-section the features presented are extremely characteristic. Large
plates of perthite or perthitic microcline with subordinate plates of albite
showing fine lamellar twinning occur in a granular, allotriomorphic, micro-
cline-albite assemblage (SK.93, 107). Quartz showing a varying degree of
granulitization to lenticular aggregates (SK.108, 110) is relatively abundant.
The mafic minerals and accessories occur in straggling clots consisting of a
sodic-looking hornblende, biotite of an unusual reddish-yellow or golden-brown
colour (SK.93, 113), iron oxide, sphene, zircon, epidote, orthite. SK.111 has
iron oxide bordered with sphene and abundant euhedra of zircon and pleochroic
reddish-brown orthite (SK.111). Most slides show a considerable amount of
dynamic effects; there is much granulitization, shattering, micro-faulting
of albite, and lobate penetration of feldspar by granular quartz (SK.103). The
perthite is of striking appearance, the intergrown space-lattices under crossed
nicols commonly showing blotchy or spindle-shaped forms (SK.93, 110). The
relationship of the albite to the potash feldspar is somewhat variable and the
different types of intergrowth would seem to have developed in different ways.
Normally the perthitic plates have a blotchy or fusiform appearance, the
optically parallel wavy spindles of albite extinguishing in a different position
from the optically parallel untwinned potash feldspar. A core of albite is
sometimes present connected with a fusiform intergrowth at the border
(SK.110, plate I, figure 1). In this type of intergrowth, which appears to have
been controlled by the crystallographic directions within the crystal plate, the
albite is usually more turbid than the potash feldspar and may or may not
display lamellar twinning. In other types of intergrowth there is extensive
replacement of microcline by albite, in which large areas of slightly turbid
albite with lamellar twinning faintly apparent enclose irregularly shaped
residual patches of microcline (SK.113). Where replacement is less complete
the microcline plates are crossed at random by albitic veinlets (SK.107, 108).
In a third type a mottled appearance, as shown in SK.18, plate II, figure 7,
is produced, neither mineral showing twinning effects. Myrmekitic inter-
growths are by no means conspicuous although crenulate encroachments of
albite upon microcline (SK.113) are not uncommon.
SK.103 is megascopically quite dissimilar to typical Ilunga granite, being
a rather bright-red or reddish-purple fine-grained rock in which a few dark
green streaky mafic clots are to be seen. Under the microscope, however, it is
revealed as Ilunga type by the lenticular remnants of the perthitic feldspar so
characteristic of the less altered rock. It has been powerfully sheared; the
feldspar lenses are peripherally granulitized, and parallel with their direction
of elongation are bands of highly granulitized quartzo-feldspathic material.
There has been much shattering revealed by micro-faulting of plagioclase,
granulitization to quartz mosaic and development of micro-zones of shear. The
mafic minerals consist of scarce chloritized biotite, often forming vein-like
shreds. Finely divided dust-like hematite is common and appears to be confined
to the feldspar, the quartz, by contrast, being quite clear. It is figured under
crossed nicols in plate I, figure 2.
The grey mesotype granitoid rocks SK.18 and 21, which megascopically
are very similar, possess curious microscopic features to some extent linking
them with the Ilunga granite. In SK.18 (plate II, figure 7) there are
conspicuous clots consisting of granules and relict structure of skeletal iron ore
surrounded by successive rims of hornblende, quartz-mosaic, and finely
granular epidote. The relict structures are of amphibolic and pyroxenic
cleavage and indicate incomplete digestion of partly amphibolized basic
material. The feldspar is largely albitized and under crossed nicols presents
the peculiar mottled appearance already referred to. Similar structures, though
recognizable, are less pronounced in SK.21, in which the mafic and accessory
minerals, including golden-brown biotite, blue-green hornblende and abundant
zircon, are indistinguishable from those present in typical Ilunga granite.
2. GREY GRANITE.*
Megascopically, this is a grey, non-schistose granite of medium grain with
a plentiful speckling of evenly distributed, finely divided biotite. Porphyritic
feldspars of pale pink or pale mauve tinge are sporadically distributed in some
of the specimens, absent in others.
In micro-section, the difference between this and the Ilunga type is equally
apparent. Its average composition is that of an adamellite, but granodioritic
and even tonalitic facies exist. Specimens corresponding with granite or
adamellite are SK.80 (plate I, figure 3), 81, 100; they are allotriomorphic
assemblages of clear microcline, subhedral turbid plagioclase and quartz. The
last sometimes shows a little granulitization, and, where ungranulitized, slight
undulose extinction, but the strain effects are not nearly so marked as in the
Ilunga granite. Mafics and accessories are not associated together in clots;
*Referred to by Dr Skerl as "Grey Ilunga Granite."
tAdamellite is here taken to mean a granite in which plagioclase (irrespective of its basicity)
varies from one-third to two-thirds of the total feldspar. By tonalite is understood a granitic
rock composed of quartz, oligoclase-andesine, and rather abundant biotite and/or hornblende.
Tonalite is therefore practically synonymous with quartz-diorite. The term granodiorite is here
applied to rocks intermediate in basicity between adamellite and tonalite in which some potash
biotite in rather large partly chloritized flakes occurs sporadically, and sphene
is the most prominent accessory. Epidote is generally present, either as quite
large independent crystals or as products of alteration within the plagioclase.
Myrmekitic intergrowths are common.
SK.82, 84 appear to belong to this group but the twinning in the micro-
cline is largely obliterated. SK.54 is a fine-grained, rather streaky type, which
from its microscopic characters would seem to belong here also.
In the granodioritic facies the feldspar consists principally of basic oligoclase
with a strong tendency towards idiomorphism; it is strongly zoned and usually
slightly turbid in the centre with a clear periphery. In SK.118 clear microcline
is quite subordinate and the mafics consist of chloritized biotite and epidote.
In SK.105 (plate I, figure 4) only one occurrence of microcline was observed in
the micro-slide, where a small portion of the fresh mineral formed a patch in
a large euhedron of plagioclase. Biotite, sometimes associated with epidote,
in isolated flakes, not clots, is abundant, and quartz is deficient. This rock
approaches a tonalite in composition. SK.106 is similar to SK.118, perhaps
containing more microcline and less biotite. No hornblende was seen in any
of the members of this group save SK.88, which thus corresponds to the Saza
granite (Grantham, 1932, pp. 17-18).
Specimen SK.112 consists of a coarse, pinkish granitic rock showing contact
with a mesotype, fine-grained rock possessing schistosity. In micro-section
the coarse portion of the specimen has approximately equal proportions of
clear microcline and turbid albiclase. Mafic minerals consist of chloritized
biotite and yellowish-green epidote. There is seen occasional patchy inter-
growth of microcline with plagioclase but the former is never perthitic though
it may show slight albitic veining. These characters are more akin to the
Saza type than to Ilunga, and indicate that the rock to which they belong
should have been classified for purposes of mapping with "Ilunga Grey
Granite," rather than with "Ilunga Granite." The mesotype, schistose
portion consists of a granular assemblage of hornblende, biotite, epidote, basic
oligoclase, and quartz and is very similar to a small (one-inch) xenolith con-
tained in SK.114, which appears to be a rather mafic variety of the grey
granite. In both the mesotype portion of SK.112 and the xenolith of SK.114
there is an abundance of sphene, apatite and epidote, all these indications
suggesting that the former is a xenolith and not a dyke.
Specimen SK.89, a fine-grained, pale pinkish-grey granite, proves in micro-
section to be a grano-dioritic facies of the grey granite. Specimens SK.6, 83,
109 also belong here. Hydrothermal alteration products (chlorite, epidote and
calcite) are present in these, especially SK.83, while SK.109 contains large
euhedra of orthite surrounded by yellow epidote.
3. ILUNGA FELSITIC SERIES.
According to Grantham (1932, pp. 14-15) these comprise acidic volcanic
rocks and their ashy derivatives, which have been hybridized or granitized
around their margins. These marginal altered types ". .. were it not for -their
enormous volume, many cubic miles would certainly be classed as foliated
aplites." Grantham goes on to say: "The Ilunga granite, was first thought to
be fine-grained owing to confusion with the felsitic hybrid .", and this
attitude of mind was later experienced by Teale and Oates (1935, pp. 21-24)
in regard to the equivalent rock types on the eastern side of the field. Petro-
logical work carried out in both areas shows that the Ilunga felsitics and
Ilunga granite are closely associated and that there is a probable anatectic
gradation of the former into the latter through a range of hybrid or migmatitic
types (Grantham, op. cit., p. 15 ; Oates, op. cit., p. 22).
It follows from the above that pitfalls exist in regard to more than usually
subtle distinctions of lithology. Isolated outcrops of aplitic appearance, the field
relations of which are obscured by drift, may represent inliers of the felsitics,
while similar "aplitic" schlieren in streaky gneissose granite of doubtful
affinities may represent sheared felsitic remains in migmatite. Such outcrops
may well have been recorded in the past as aplitee dykes," and magmatic
consanguinity with the newer granites inferred. The tendency to confusion in
these matters can only be effectually counteracted by mapping the geology to
a much larger scale than that normally employed by this Survey and by
subjecting field identifications to careful petrographical control. Unfortunately
both these correctives are wellnigh impossible to apply under the special
conditions obtaining in this country.
Of the dozen or more specimens dealt with under this heading, the affinities
of the greater number are clearly with the felsitics. The remainder are micros-
copically indistinguishable from ordinary micro-aplogranites but are included
here by reason of their known field association with types mapped as Ilunga
Three specimens are felsites in the accepted sense of the word save for the
fact that their groundmass is micro-crystalline rather than cryptocrystalline.
SK.40 is a purplish, aphanitic rock consisting microscopically of sporadic
micro-porphyroclasts of undulose quartz in a micro-crystalline groundmass in
which are numerous minute grains of iron oxide, small flakes and threads of
chlorite and granules of epidote. SK.48, of similar grain-size, is medium-
greyish in colour and consists of ragged micro-phenocrysts of oligoclase, partly
granulitized quartz and hornblende. Much greyish-brown epidote and subordi-
nate pale green hornblende show distinct alignment. In SK.67 the grain-size
is slightly coarser, a suggestion of parallel trachytoid arrangement of albite
laths being discernible. A good deal of pale greenish sericitic material and
granular iron oxide is present.
SK.39, 46, 76, 85 are purplish-pink rocks of micro-granitic texture, some-
times showing penetration in hand-specimen by epidote veins. They consist
essentially of allotriomorphic microcline, albite and undulose quartz with few
dark minerals. SK.85 contains rather abundant euhedra of magnetite and dusty
iron oxide. Flakes of biotite and granules of epidote are sparsely distributed,
and among accessories zircon in rounded grains is not uncommon.
SK.61 from megascopic and microscopic characters might have been
grouped with the four specimens mentioned in the preceding paragraph but
for the fact that it is said to be associated with the grey granite.
SK.60 is a cream-coloured fine-grained rock showing pale pink and pale
greenish streakiness. Its field associations are with the Ilunga felsitics. In
micro-section a tendency towards augen structure is observed. The dominant
feldspar is somewhat micaized albite but an appreciable proportion of clear
microcline is present. Much of the feldspar shows the crenulated margins
characteristic of the migmatitic types. Quartz is undulose or marginally or
completely granulitized and some epidote is present in small granules and
granular aggregates. This should be compared with SK.44 and 58 described
under the ensuing heading.
SK.51 and 53 are purplish-brown, fine-grained leucocratic rocks from
Ilunga granite country .adjoining a transition to grey granite. In micro-section
the former resembles SK.85 with margins of the quartz and feldspar granules
accentuated by development along them of pleochroic micaceous material or
dusty iron oxide, and noteworthy content of iron oxide and zircon grains.
SK.53 is a finer-grained type than the preceding and microscopically not unlike
it save that it carries sporadic flakes of golden-brown biotite like that charac-
terizing the Ilunga granite. SK.42 (painted-on locality chipped off in transit)
is very like the two preceding, megascopically as well as microscopically, but
carries sporadic rhombdodecahedra of reddish-brown garnet up to 1-5mm. in
None of the above exhibits the curious micrographic intergrowths not
uncommonly encountered among the hybridized representatives of this group.
Certain types are included under this heading because (a) the geological
mapping shows that they are associated with grey granite rather than with
Ilunga granite, (b) they show no microscopic characters that would serve to
link them conclusively with the Ilunga felsitics or their hybridized represen-
SK.43, 45, 56 are pale pinkish-cream-coloured leucocratic rocks somewhat
coarser in grain than those described under the previous heading. In micro-
section an allotriomorphic assemblage of rather turbid albite and clear
microcline and quartz is seen, there being a notable deficiency of ferro-
magnesian minerals save for a sparse shred here and there of biotite and
epidote. In the first two albite is dominant; in the third the more abundant
clear microcline shows replacement by albite and marginal encroachment of
myrmekite. The field associations of these rocks are apparently with the grey
Finally, two rocks, SK.44, 58, not unlike SK.60 (see under previous
heading) megascopically, are included here since they apparently occur in grey
granite country. In micro-section both rocks display parallel alignment of the
constituents, elongated folia of coarse mosaic-quartz alternating with folia of
finer more feldspathic mosaic. This foliated structure is well seen in ordinary
light since the feldspar is slightly turbid and the quartz perfectly clear. In
SK.44, the feldspar is acidic plagioclase, much of which occurs in ragged,
patchily turbid micro-phenocrysts. In SK.58 the feldspar contains a fair
proportion of microcline and does not occur in micro-phenocrysts. Both slides
show sparse greenish to yellowish-brown shreds of biotite and sporadic develop-
ment of muscovite.
Although the origin and history of these rocks remain doubtful, it is
considered that they do not represent a normal aplitic dyke phase of the grey
Megascopically, SK.95 (see plate I, figure 5) is a pink leucocratic rock with
pale green epidote staining. In micro-section it is seen to consist of allotrio-
morphic microcline, albite and quartz with a notable absence of ferromagnesian
minerals. The grain-size is much coarser than any of the micro-aplogranites
just described. The albite shows micro-faulting and the quartz, undulose
extinction principally in proximity to veins of epidote, which enclose shattered
fragments of quartz and feldspar. The albite is in an unusually fresh condition.
The position of this rock is not shown on the map but the field, designation was
"Ilunga granite." The microscopic characters do not support this but the rock
might represent a late differentiate of the Ilunga granite.
SK.116 is a coarse-grained leucocratic rock resembling a pegmatite and
consisting of salmon-pink feldspar and white opaque quartz. Microscopic
features at first sight appear like those of SK.95 on account of the precisely
similar veins of epidote enclosing shattered fragments of quartz and feldspar.
An important difference is that microcline, in large plates, some of which carry
small perthitic inclusions, is the dominant feldspar and has crystallized before
the albite. There is more than a suggestion that the albite, which forms small
anhedral rather turbid plates, has actually replaced the microcline metasomatic-
ally. The albite forms ill-defined veins penetrating the microcline and pene-
trated in turn by the epidote. The field relations of this rock appear to be with
the grey granite.
6. ULTRAMAFIC ROCKS WITH NORITIC AFFINITIES.
These comprise several specimens that were mapped by Dr Skerl as
appinite. They are all dark-greenish-grey, medium-grained rocks containing
very little felsic material. They are distinct from the suite of appinites and
meta-basites, though, in view of what follows, it is not improbable that they
represent a starting point and early stage in appinite formation.
The freshest representative of this class is SK.35 (see plate II, figure 10).
Megascopically it is heterogeneous, displaying an irregular junction between
a platy ultramafic portion with little or no feldspar and a portion with distinct
felsic speckling. SK.20, from the same locality, is like the more mafic portion
of the preceding. SK.22, from about two miles to the east of the first locality,
forms a link between SK.28 and 31, which are more coarsely platy and
hornblendic. All these specimens are from the junction of grey granite with
"meta-diorite,"* and all save SK.22 are from the same locality.
Microscopical characters.-In micro-section the more mafic portion of
SK.35 is seen to consist of predominant amphibole, subordinate pyroxene, and
about 10-15 per cent of mesostatial basic plagioclase and clear quartz. Much
of the pyroxene is hypersthene, with distinct pale green to pale pink
pleochroism, altered along cleavage planes to cryptocrystalline, greenish-grey
uralitic material. Some clinopyroxene showing similar alteration is also present.
The feldspar, which is labradorite of medium basicity, is mostly clear but
may show patchy alteration to cloudy products. The dark cloudy product is
optically non-reactive but a lighter-coloured turbid material is cryptocrystalline
and has a medium to low birefringence. Progressive amphibolization has
resulted in considerable development of hornblende, some of which is pale
and some greenish-brown in large plates containing partly resorbed remains
of hypersthene. Where hornblende has developed strong crystal boundaries,
these were observed to be in juxtaposition with secondary minerals (e.g.
calcite, quartz or hydrothermally altered plagioclase). A little reddish-yellow
to reddish-brown biotite is associated with the larger hornblende porphyroblasts.
Portions of the pyroxene contain regularly arranged minute rods of iron oxide,
and here and there small clots of the same material have segregated.
The less mafic portion of SK.35 contains about 15-20 per cent of plagioclase
and there is less amphibolization than in the other portion of the specimen.
A little quartz occurs in the more amphibolized portions of the rock and forms
*See footnote on page 8 and remarks on page 22, heading 7.
large clear plates rarely showing faint undulose extinction. Calcite, like the
quartz, occurs in large anhedra moulded on hornblende. This rock is a norite,
in part amphibolized and hydrothermally altered.
Specimen SK.20 has very similar microscopic characters to the more
amphibolized portion of the preceding. Similar large (0-2-inch) porphyroblasts
of hornblende, brownish-green towards the centre and fading towards the
margins, poikilitically enclose small, partly resorbed euhedra of orthopyroxene.
The hornblende porphyroblasts tend to possess indefinite or irregular margins
as though they had, encroached on the surrounding material. Most of the
pyroxene is a monoclinic variety; some orthopyroxene is present but the
hypersthenic pleochroism is faint or absent. Cores of orthopyroxene in clino-
pyroxene are not uncommon. Plagioclase is less abundant than in SK.35 and
shows extensive alteration to a rather coarse aggregate of ragged secondary mica
and patches of dark-grey-brown, optically unreactive, undetermined material.
In SK.22 the alteration of the hypersthene along cleavages is more intense
and a tendency is displayed for the alteration to spread inwards. More pale
amphibole is present than in the two previous specimens and encroaches
extensively on the pyroxene. No recognizable plagioclase remains, the alter-
ation product thereof being similar to that just described. Some alteration
of the pyroxene to a pale green, non-pleochroic, low birefringent, serpentinous
material is evident. Similar schillerization effects to those in SK.35 are
displayed. No quartz or calcite were observed.
Specimen SK.28 represents a further stage in amphibolization of a rock
that must originally have been similar to SK.35. Recognizable remains of both
ortho- and clino-pyroxene can be seen but pale amphibole is now the dominant
mineral constituent. No quartz nor calcite are to be seen. The interstitial
felsic material has been altered by saussuritization* to a cryptocrystalline felt,
similar to that characterizing the suite af appinites and meta-basites, and
some clinochlore is present.
Specimen SK.31 appears to consist essentially of pale dingy amphibole,
traversed by a vein of yellowish-green epidote.
The noritic rocks thus show progressive amphibolization and saussuritiza-
tion, these effects having apparently resulted through subjection of the rock
to combined thermal and thermo-aqueous conditions. The alteration is sporadic,
different degrees thereof being exemplified in different parts of one hand-
specimen. The co-existence in one micro-section of clear primary labradorite
with calcite, saussurite and apparently secondary quartz is a somewhat remark-
able feature. There appears to be no doubt that the hornblende is truly
porphyroblastic; in the slides described above crystals up to three-sixteenths of
an inch in size were observed and in the hand-specimen of SK.28 a size of half
an inch is not uncommon. This indicates that large crystals of hornblende
are capable of developing under thermal metamorphic conditions and a link
is established thereby with SK.4, a typical appinite with closely set -inch
to 1-inch hornblende crystals, which, incidentally, is closely associated in the
field with the noritic rocks.
*A term applied to processes whereby the plagioclase feldspars of dolerites and other igneous
rocks become altered by the breakdown of the solid solutions of albite and anorthite into
a dense aggregate of saussurite. This material originally thought to be a specific mineral, is
composed essentially of albite (or oligoclase) and zoisite (or epidote), together with variable
amounts of calcite, seribite, and calcium-aluminium silicates other than those of the epidote
group. The alteration is specially characteristic of gabbros and greenstones (epidiorite and
diabase), and is accompanied as a rule by uralitization and chloritization. It may be due to
auto-, contact-, or low-grade dynamic metamorphism. (Holmes, 1920.)
7. APPINITES AND META-BASITES.
In a footnote on p. 8 some remarks have been made for the sake of
clarity in regard to the controversial use of the prefix "meta" by various workers
in the Lupa field. The present writer (F.O.) intends to apply it in the sense
defined by Holmes, e.g. meta-diorite, an altered diorite, meta-dolerite, an
altered dolerite, meta-gabbro, an altered gabbro, and so on. When occasion
arises to refer collectively to altered basic rocks, the tenn meta-basite will be
used. The inverted commas with "meta-diorite" indicates that the term is
used in the same sense as on the geological map, i.e. in a contrary sense to
that just stated.
The appinitic specimens are melanocratic, dominantly hornblendic rocks,
which megascopically resemble the Dodoma appinites described by Oates
(Wade and Oates, 1938, pp. 38-40). Two of them (SK. 4, 32) are from the
contact of grey granite with "meta-diorite", while SK.37 is from "meta-
diorite" but near a contact with Ilunga granite. Specimens SK.29 and 34 are
clearly related to the preceding but are without diopside; they are from a
similar situation to SK.37. Specimen SK.4 is a coarse-grained, homogeneous
rock of striking appearance with '-inch stout crystals of dark-green hornblende
closely set in a lighter greyish-green groundmass; it is typical of the appinites
that have been observed by this Survey to possess a dyke-like habit, although,
as will be shown later, this fact does not conclusively prove that it owes its
present mineral constitution to crystallization from a magma. The striking
porphyroblastic structure is not so perfectly developed in the other appinitic
specimens although their affinity to SK.4 is unmistakable. SK.29 is a remark-
able specimen consisting of coarse-grained appinite passing quite sharply,
though without a chilled margin, into a rock of similar composition but finer
grain, not unlike a dioritic lamprophyre.
Specimens SK.23, 26, 30, 36 are melanocratic, rather fine-grained basic
rocks, without conspicuous porphyroblastic development of hornblende. They
are variably though sparsely speckled with felsic material. In micro-section,
although evidently largely re-constituted, a palimpsest remains indicating
probable development from dolerite. They are amphibolized and albitized and
show a numerous assortment of secondary minerals due to hydrothermal
alteration. The general term meta-basite fits these rocks very well. All are from
within "meta-diorite" or near its contact with Ilunga granite.
SK.19 and 49 are distinctly more dioritic in appearance than any of the
specimens described under this heading and are from marginal situations close
to grey granite. Microscopically they are seen to be meta-basites but are of
coarser texture and appear to have been derived from gabbro rather than
Comparative microscopical study of the above groups indicates the presence
in all of them of somewhat similar minerals and structures, and this statement
may be extended to include the amphibolized noritic rocks described under the
previous heading. The nature of the changes that have involved the production
of these minerals and structures is believed to be partly metamorphic and
partly metasomatic. The appinitic specimens are characterized by the
homogeneous structure and anomalous mineral composition peculiar to this
class of rocks; their mode of origin is not yet fully understood and will be
discussed at greater length after the petrography of the rocks in question has
been more fully examined.
Appinites.-In the typical appinites, SK. 4, 32, 37 (see plate II, figure 9),
the large green hornblendic porphyroblasts contain poikilitically enclosed,
partly resorbed, colourless diopside, and show straight-line crystal boundaries
where in contact with saussuritized plagioclase, and irregular boundaries where
salients have encroached on the diopside. Between the hornblendic crystals
are smaller euhedra of diopside and hornblende in a felt-like saussuritic ground-
mass. Amidst the saussurite some cloudy albitic plagioclase may be recognized.
Apatite in stout crystals is a prominent accessory, sphene being less common.
Epidote is not conspicuous save in SK. 37.
Also appinitic is SK.34, which, however, consists principally of hornblende
without diopside and the usual proportion of cloudy groundmass with here and
there clear remnants of cloudy oligoclase. A particularly interesting specimen
from the same locality is SK.29, which consists of a coarse-grained portion
similar to SK.34 and a much finer-grained portion. In micro-section the finer-
grained portion is seen to consist of numerous irregularly shaped euhedra of
hornblende, with some suggestion of parallel alingment, evenly distributed
in the typical saussuritic groundmass (see plate II, figure 8). Stout crystals
of apatite are conspicuous accessories in the groundmass. This material has no
resemblance to dolerite, which was the field term assigned, and might be
described as a dioritic lamprophyre. A micro-section from the coarser portion
of the same specimen revealed identical minerals and structure on a larger
scale. Not all the feldspar is saussuritized for a large plate of relatively clear
material was seen with refractive index appreciably lower than that of Canada
balsam. This appears to be albite, though the lamellar twinning, possibly as a
result of incipient alteration, has been largely obliterated. Calcite in veinlets
and clearly recognizable crystal grains is common and accessory apatite and
sphene are prominent. Another slide of the fine-grained portion shows veinlets
of granular epidote.
The relationship of the fine-grained to the coarse-grained portion of SK. 29
is obscure. Neither megascopic nor microscopic characters provide a clear
explanation on this point. The fine-grained material appears to be rather more
felsic than the coarse-grained, platy, dominantly hornblendic rock in contact
with it; it may represent a cognate inclusion or even a schliere or vein due
to auto-injection. On the other hand, exactly the reverse may be true and the
fine-grained portion may be the parent from which the coarse-grained rock has
formed by re-constitution. In the absence of fuller field observations this must
remain an open question.
No microcline was seen in any of these specimens though it is the pre-
dominant feldspar in the Dodoma appinites and is not uncommon in those
from other parts of the Lupa.
Meta-basites.-Specimens SK.23, 26, 30, 36 are more felsic than the
appinites, the mafic constituents being in some cases as low as about forty
per cent. Little tendency is displayed for development of porphyroblastic horn-
blende. In SK. 23 the feldspar is largely saussuritized and a good deal of
penninite after biotite is present in addition to hornblende and epidote. A
little residual basic primary plagioclase remains but albitization has been
extensive. Clear quartz fills interestices between laths of albitized plagioclase
and to some extent also replaces it metasomatically. The borders of cloudy
plagioclase, where in contact with hornblende, show reactional development
of granular epidote.
In SK. 26 slightly altered oligoclase is the principal constituent. Hornblende
forms irregularly shaped plates with the bright blue-green tinge of hastingsite
here and there developed. Epitote is abundant and penninite, pyrite and iron
oxide are common.
Relict doleritic structure is especially evident in SK. 30 in which
saussuritized plagioclase occurs in large subhedral shapes or else in small
euhedra enclosed in secondary hornblende. Quartz, probably of secondary
origin, is an important constituent and occurs in large angular plates moulded
on the feldspar shapes. Specimen SKI.36 resembles the preceding
megascopically as well as microscopically-both contain chlorite-the former
penninite, the latter clinochlore.
More dioritic in megascopic appearance are SK.19 and 49, both of which
are speckled dark-green and cream-coloured and somewhat uneven in texture.
In SK.19 felsics exceed mafics, the latter consisting of large crystals of horn-
blende, some of which show almost complete alteration to a flaky aggregate
of clinochlore. Rarely the hornblende has a small core of residual clino-
pyroxene. Interstitially to the platy hornblende is the usual felt-like
saussurite in which are to be seen large anhedral grains or coarse mosaics of
undulose quartz. The isolated quartz grains are commonly sharply angular
owing to their having filled interstices between intersecting coarse feldspar
laths (now completely saussuritized). Within the general saussuritic ground-
mass there is considerable development of epidote and clinochlore, both of
which have a straggling veinlike habit. SK.49 has rather more mafics;
brownish-green hornblende is well developed but other paler aphiboles are also
present, sometimes in parallel intergrowth with the darker variety. There is
much development of coarse zoisite and epidote within the saussurite, and here
and there may be seen saussuritized feldspar laths, which have been almost
completely replaced by coarsely granular aggregates of epidote and zoisite
with retention of the original crystal shape of the feldspar.
The following outstanding features become apparent from the microscopical
study of the rocks described under headings 6 and 7 :-
(a) The abundance and diversity of hydrothermal minerals present.
(b) The tendency for regression of pyroxene to amphibole and for
porphyroblastic hornblende to develop.
(c) The constant occurrence of secondary albite and occasional
appearance of sodic amphibole.
(d) The universal development of the saussuritized, felt-like ground-
(e) The introduction of secondary quartz.
(f) The prevalence of reaction structures such as zonal alteration round
crystals, and resorption of diopside enclosed in porphyroblastic hornblende.
(g) The paramorphism or metasomatic replacement of certain minerals
by vein development and lateral extension thereof along cleavage planes.
(h) The existence of fine-grained and coarse-grained varieties of
appinite in unknown relationship in one hand-specimen.
Some remarks regarding the petrogenesis of the appinites will not, perhaps,
be out of place. An origin for appinites by differentiation of a hornblende-
granite overcharged with doleritic inclusions has been postulated by Grantham
(1932, p. 22), who further states that ". one is forced to consider the
possibility of gradation from them* through the perknites to peridotites."
"Spessartites" in original text-now known as appinites.
From the context, the implication here is clearly that the utramafic rocks
mentioned and the appinites are all differentiation products of the same
The present work shows that ultramafic norites as well as meta-dolerites
must be considered as possible starting points in the derivation of appinites.
Evidence has been adduced to show that porphyroblasts of hornblende tended
to grow to a large size under favourable metamorphic conditions and that such
amphibolization may have begun by sporadic and patchy growth in a fresh
norite and have progressed until the noritic character of the rock was scarcely
apparent. One is therefore compelled to consider the possibility that the
perknites, the monomineralic hornblendic rocks, as well as the appinites
themselves may have resulted through processes of metasomatic alteration in
situ. Such an origin may well be attributed to the small shapeless masses
referred to by Grantham (1932, p. 19) as margining the main mass of the Saza
As applicable to the rocks under discussion, a conception of their origin
due to post-magmatic replacement by hydrothermal solutions is entertained
by the present writer (F.O.), who regards the ultramafic norite as one (at
least) of the starting points whence the appinites have been derived. The
processes operative, though dominantly metasomatic, may be conceived as
lying on the borderland of hybridization since the fluids responsible for the
alteration are believed to constitute a late magma-fraction. Such fluids would
doubtless have been of a highly reactive and tenuous nature and would have
consisted largely of water charged with soda, alumina, silica, lime, carbon
dioxide and various "mineralizers". The general absence of potash feldspar
and prevalence of albite and epidote in the metasomatized rocks are consistent
with the hydrothermal idea, since under such conditions both potash feldspar
and oligoclase would be unstable, the potash tending to be fixed earlier as
mica, and the oligoclase to dissociate with formation of albite and epidote.
(Gilluly, 1933). The source of the hydrothermal magma-fraction is entirely
speculative, but from the fact that all the rocks that have been described
above are from the contacts of newer granite with the older basic rocks, the
granite may reasonably be considered to have provided it. The course of
crystallization of the granite may be supposed to have led to the production
of a final ichor of the nature already described and to its expression by orogenic
forces from the parent body along crush zones in the earlier solidified apophyses
and along contacts of neighboring rocks with consequent far-reaching meta-
A controversial point is encountered in attempting to explain the dyke-
like habit of the appinites occurring at a distance from the marginal masses
and referred to by Grantham (1932, p. 19) as "offshoots" thereof. The field
experience of this Survey shows that the typical homogeneous appinite consist-
ing of large stout crystals of dark green hornblende regularly and closely
distributed in a fine-grained, greenish-grey groundmass .is confined chiefly to
the dyke-like occurrences and is rarely seen in the marginal masses. This leads
one to suppose that the type appinite has either (a) been injected after
differentiation of a locally basified portion of a granitic magma and has
crystallized thereafter in its present form; or (b) been metasomatized to its
present form after instrusion; or (c) become sufficiently mobile during the
process of metasomatism in situ to have been injected a considerable distance
as a fluid or partly fluid, syntectically generated magma.
The first of these suppositions corresponds to that due to Grantham and
referred to above. It is to some extent discounted by the anomalous mineral
composition of the appinites and the evidence of the widespread operation of
metasomatic processes afforded by their microscopical examination. A serious
objection must likewise be stated against the second alternative. Thus, the
dykes are some distance from the supposed source of the metasomatizing fluids
and any radical change of the nature involved would argue that the radius of
metasomatic alteration must have been unaccountably great. Furthermore,
comparable alteration of the surrounding rocks, which in the circumstances
might be confidently looked for, has not been observed.
There remains, then, the third alternative offered, which alone appears
deserving of serious consideration. There seems to be no doubt that an appinitic
magma or quasi-magma possessing some degree of mobility can exist, for, in
addition to the somewhat inconclusive evidence afforded by the fine-grained
and coarse-grained portions of specimen SK.29, a case is on record of a fine-
grained appinite occurring in association with a much coarser-grained variety.
It is not unreasonable to suppose, then, that beneath the zone of active meta-
somatism, where the magmatic fluids were soaking into the solid basic rocks,
the temperature may have risen sufficiently for magma to have been generated
syntectically and for auto-injection to have resulted. Little can be said as to the
actual mechanism of the intrusive process but it may be imagined that the
intense hydrothermal reactivity of the environment and its presumed richness
in "mineralizers" would have tended to maintain the mesostasis, at least,
in a sufficiently fluid condition to permit injection. The absence of streakiness
or fluxion structure in the rocks rules out the possibility of a uniform
"pastiness" of consistency. Indeed, the intimate association of fine and coarse
appinites seems sufficient evidence that under certain conditions complete
liquefaction must have taken place. In these circumstances a range of mobility
commensurate with that demanded by the field evidence may fairly be
Finally, it may be remarked that in the somewhat uncommon cases where
the appinitic mesostasis displays none of the cloudiness attributable to
autometamorphism, it is probable that migration had proceeded beyond the
SK.16 and 50, which are closely similar megascopically, are medium-
grained types with sporadic waxy-looking pale greenish feldspar phenocrysts.
SK.7 is darker and finer-grained.
In micro-section SK.16 is seen to be a sub-ophitic, plagioclase-rich, coarse-
grained variety with pale, purplish-brown pyroxene and black-rimmed and
altered olivine, the last containing much released iron oxide. Some accessory
biotite is present. The feldspar shows some kaolinization but is fresh enough
to be recognizable as basic andesine. The pyroxene shows slight alteration to
uralitic and chloritic material. Unusual in an olivine-bearing rock is the
presence of a few small interstitial grains of quartz. SK.7 is a more mafic
variety of the preceding with intersertal texture.
SK.50 is more highly altered than the two preceding specimens and differs
from them in being without olivine. The pyroxene has the same purplish
tinge as that in SK.16 and the texture is sub-ophitic. All the minerals are
more or less altered; the feldspars are penetrated along parting planes by
greenish uralitic veinlets and show turbid or opaque patches due to development
of finely divided dominantly zoisitic alteration products. The mode of alteration
of the pyroxene is principally to a pale green uralitic aggregate, in which there
is sparse development of somewhat brighter green chloritic material and bright
blue-green hastingsite. The slide shows a lighter-coloured feldspathic
segregation in which saussuritization is extensive and large areas of granular
9. ALTERED ULTRAMAFIC ROCKS.
SK.24 and 73 are the only representatives and both occur near the margin
of the area mapped as "meta-diorite". Megascopically the former is a dark-
greyish rock showing abundant minute glistening specks of iron oxide; in
micro-section it is seen to consist largely of serpentine with a little talcose
material occurring patchily in association with the abundant irregularly shaped
grains of secondary iron oxide.
SK.73 is a dark-green, fine-grained, entirely re-constituted' rock with
numerous well developed octahedra of magnetite; in micro-section it is seen
to consist essentially of pale green pleochroic flakes of fibrous clinochlore with
a good deal of magnetite, appearing as irregular and often elongated shapes,
and prominent shapeless grains of apatite. Although no trace of relict structure
remains, an original igneous and ultramafic nature is indicated by this
specimen, which bears the impress of hydrothermal metamorphism.
There is only one representative SK.1, megascopically a dark-greyish fine-
grained rock with numerous small equidimensional feldspar phenocrysts. In
micro-section the stumpy strongly zoned fresh phenocrysts consist of oligoclase,
rather closely set in a groundmass consisting of smaller euhedra of plagioclase
(usually with micropegmatitic fringes); quartz; much acicular olivaceous
biotite; and sporadic grains of iron oxide. Clots of biotite are common and
associated therewith are grains of epidote and sphene. The biotite contains
minute zircons surrounded by well defined haloes. The affinities of this rock
The only specimen is SK.63, a grey medium-grained granular leucocratic
rock, the only mineral seen with the naked eye besides plagioclase being a
little pale greenish epidote. In micro-section it consists of acidic labradorite
in shapeless plates with here and there clots of pale epidote associated with a
little pale-green clinochlore and much dingy brown opaque material. A little
sphene-bordered iron oxide occurs sporadically.
This specimen is from the centre of the "meta-diorite" area, and probably
represents a leuco-differentiate of a gabbro.
SK.70 is a reddish rock, which in micro-section consists of shattered,
lenticular quartz with perhaps five or ten per cent of iron oxide. SK.71 is a
finely banded rock containing enough iron oxide to be called an iron ore.
Megascopically, it is penetrated by a small vein of quartz in which pyrite can
be seen. In micro-section the abundant iron oxide is seen to be arranged in
bands amounting perhaps to 40 per cent of the rock. The remainder consists
of quartz mosaic and a pale green non-pleochroic variety of amphibole. Well
rounded grains of apatite are common.
These specimens are similar to the "Ironstones" described by Grantham
(1932, pp. 11-12). Their mode of origin is uncertain.
13. FELDSPATHIC QUARTZITE.
The single specimen of this class is SK.69 from the "hybrid zone" shown
on the map. Megascopically it is a grey and brownish-pink banded, rather
fine-grained rock of distinctly sedimentary appearance. Its sedimentary origin
is confirmed by microscopical examination in thin section, which reveals an
equigranular assemblage of acidic plagioclase (chiefly albite) and quartz, usually
with crenulate interlocking margins, both of which show clear external rings
of secondary growth in optical continuity. The plagioclase is cloudy owing to
micaization; the quartz, with numerous minute inclusions, less so, and there
is a tendency for the cloudiness in both minerals to assume a regular disposition
at the peripheries of the original grains. The shape of the original grains and
the extent of secondary growth is thus readily apparent by ordinary trans-
mitted light. The quartz and feldspar are crowded with minute grains of diverse
minerals amongst which were seen sericite, calcite, red hematite, biotite,
greenish chlorite, and abundant brownish, sub-opaque, optically inert material.
Apatite and zircon in large rounded grains constitute a marked feature; their
rounded nature and abundance afford clear evidence of sorting and abrading
effects of stream action. There is also a tendency for the apatite, zircon and
iron oxide to be arranged along well defined sedimentation planes, which are
marked by megascopic banding. The bedding planes are cut almost at right
angles by veinlets of brownish optically indeterminate material, interspersed
with chlorite. A good deal of leucoxene is associated with the iron oxide.
Micro-sections from other parts of the same specimen showed more
extensive development of albite,. the grains being larger and more irregular
in shape. Infiltration of calcite and uralite along bedding planes was also noted.
This specimen is of great interest in that it affords evidence of remains of
sedimentary rocks now almost entirely engulfed by the prevailing alkalic
metasomatism. The abundant development of.secondary albite and the absence
of potash feldspar suggest that, in this case also, hydrothermal solutions have
been responsible for the alteration (cf. p. 25). Originally a sandstone, the
rock displays a considerable degree of feldspathization, which, however, is
insufficient to destroy its identity. There has been general induration owing to
peripheral "fritting" of the sandstone grains, and although parts of the
specimen are highly albitized,-wholesale recrystallization has not taken place
nor have the original bedding planes been obliterated.
14. IRON OXIDE OF MAGMATIC ORIGIN.
Specimen SK.72 is the iron oxide to which reference is made on p. 12. It
consists of massive oxides of iron with small encysted fragments of several
undetermined varieties of silicate minerals. Megascopically the specimen
consists of a dark violet-black (like indelible pencil) constituent with a high
metallic lustre in a finely granular, iron-grey and duller groundmass. Small
fragments of the specimen are unattractable by an ordinary magnet but part
of the finely pulverized material is so attracted. Chemical analysis indicates
that about fifteen per cent of titania is present and that chromium is absent.
A polished plane section examined by vertically incident reflected light
displayed octahedral or Widmanstitten structure, brought out by an eutectoidic
intergrowth of the two constituents mentioned above. In the grey groundmass
are seen somewhat darker, violet-tinged strips intersecting to form a triangular
lattice-work. This pattern is caused by the intercepts, on the plane of the
section, of the darker mineral, which has crystallized along the octahedral
cleavage planes of the other constituent of the eutectoid. Besides this regularly
arranged intergrowth, irregular areas show a sharp contact with the ground-
mass. The streak of the darker mineral is blackish, that of the groundmass
a dark brick-red.
It is hardly necessary to say that we are here dealing with a magmatic
effect though the exact mode of origin of the intergrown oxides is less clear.
The older view that they represent aneutectic in the strict sense and are due
to early crystallization or segregation has been discredited. It would now
appear that iron ores of this type are of late crystallization and are more
correctly described as magmatic injections. The characteristic intergrowth is
believed by Osborne (1928) "to be due to the unmixing of once-homogeneous
solid solutions, following a decrease in solubility because of a fall in temperature
below that which obtained at the time of formation of the ore." The fixation
of all the titania as ilmenite (FeO.TiO2), the violet-tinged mineral, has in
this instance led to an impoverishment in the FeO molecule and consequent
formation of some hematite. This hematite appears to be intimately com-
mingled with the magnetite and it is suggested that it may exist in a state
of solid solution.
15. DOUBTFUL ROCK TYPES.
Under this heading are included various groups of rocks from contact
(i) Crushed and silicified oligoclase-rich trondhjemites from contacts of newer
granites and "meta-diorite"
Specimens SK.6, 25, 79, 94, 98, 101, 115 are megascopically variable and
their essential similarity is recognizable only under the microscope. A few,
like SK.115, are granitoid in appearance, others, like SK.25, are greyish-white
leucocratic rocks in which the mineral structure is not readily apparent to the
naked eye. Microscopical examination shows that little relationship exists
between megascopic appearance and degree of crushing; actually SK.115 is
more highly crushed than SK.25 though the megascopic appearance suggests
that the reverse is the case. Microscopically, these rocks are all trondhjemitic
and consist essentially of large, subhedral, micaized plates of oligoclase and
quartz with a variable content of biotite and epidote. The biotite is usually
chloritized; it is least altered in SK.79 where the larger flakes making up the
clots contain sagenitic rutile. Microcline is generally absent; where present, it
is inconspicuous save in SK.6, in which, though subordinate to oligoclase,
it forms large plates relatively free from micaization but with twinning effects
effaced. In all these rocks there has been crushing and silicification with
deformation of the plagioclase crystals, which display bending and micro-
faulting, and in SK.64 and 79 complete rupture. The quartz shows a variable
degree of granulitization, and from its penetration of plagioclase along cleavage
directions it appears to have been in part, at least, injected. Presence of calcite
and epidote is general. All these rocks, save SK.6 (the microcline-bearing
specimen) are from the contact of Ilunga granite with "meta-diorite."
Specimen SK.64, a highly shattered plagioclase-quartz-epidote rock, said
by Dr Skerl to be an aplite, and shown by the map to lie within "meta-
diorite," appears to belong to this group though a good deal of the plagioclase
appears to be albite. The constancy of the trondhjemitic type at these contacts
is noteworthy. 29
(ii) Miscellaneous mixed types from contacts of newer granites and "meta-
diorite" not includable in group (i)
Another group of rocks from the above-mentioned contact situations com-
prise SK.9, 52, 65, 90, 91, 92. Unlike the preceding group their similarity
is megascopic rather than microscopic. They are dark green rocks with a
variable degree of red streakiness. The first five are of somewhat heterogeneous
texture while the last consists of large, regularly distributed, red porphyritic
crystals in a dark green groundmass. Specimens SK.52, 68, 90, 92 are from
contacts of grey granite, the rest from contacts of Ilunga granite.
SK.52 is not unlike the members of the preceding group (i) but there has
been greater contamination by mafic material from the neighboring basic
rocks now represented by chlorite, iron oxide and leucoxene, and brown
calciferous material. The rest of the rock is made up of micaized oligoclase and
quartz. SK.65, 90 and 91 are tonalitic hybrids, consisting of cloudy oligoclase
with about twenty to forty, per cent of hornblende and subordinate chloritized
biotite and a relatively small amount, up to fifteen per cent, of mesostatial
microcline and quartz. Among the accessory minerals sphene is very conspicu-
ous, apatite moderately so. Specimen SK.9 is highly crushed and has been
carbonatized and chloritized. It contains oligoclase similar in appearance to
that in group (i). The red porphyritic crystals in SK.92 consist of microcline
and may be upwards of one inch in size. The micaized oligoclase is subordinate
in quantity to the microcline. Biotite and hornblende make up about ten per
cent of the rock, both showing chloritization. Among accessory minerals sphene
and magnetite are conspicuous and much yellow epidote is associated with the
Specimen SK.68, from within the main zone of shear existing between the
northern margin of the main "meta-diorite" mass and the grey granite, is not
unlike the preceding but shows strong schistosity.
At contacts of grey granite with "meta-diorite" a greater range of types
appears, than is afforded by group (i). Thus, at the basic end we have rocks
approaching diorite in composition while the more acidic members not
infrequently contain microcline as well as plagioclase.
(iii) Migmatites from junctions of newer granite with Ilunga felsite
Megascopically these are somewhat nondescript rocks ranging from those
of granitic appearance to fine-grained more felsitic types. Specimen SK.62,
which may be taken as typical of this group, is a patchy, greenish-grey and
white, fine-grained silicic rock, the hand-specimen showing one or two lenticles
of the bluish opalescent quartz so typical of the Ilunga granite. In micro-
section, ragged phenocrysts of perthite, microcline and micaized albite occur
in a variably granulitized siliceous groundmass. Large lenticles of quartz
showing intense strain effects and peripheral or complete granulitization are
conspicuous. The dark minerals, consisting of biotite, chlorite and epidote
interspersed with the usual accessories, display streaky alignment.
Specimen SK.99, megascopically a dull, pinkish-brown rock of granitic
appearance, shows lenticular or augen structure in thin section. The augen
consists of albitized microcline, of the type of perthite showing blotchiness
under crossed nicols (see under heading 1, page 15), or of micaized acidic
plagioclase. The interspaces consist of granulitized quartz, and veins of
injection quartz showing strong undulose extinction cut across the principal
direction of shear. The dark minerals comprise streaky aggregates of biotite,
1 mm X Wools
I mm. ordinary light
chlorite and epidote with the usual accessories. The plagioclase crystals are
crowded with small inclusions due to hydrothermal alteration, amongst which
secondary mica, epidote and calcite are the most prominent.
Specimen SK.117, called by Dr Skerl a micro-aplogranite, appears on
microscopic grounds to be allied to the preceding. Specimen SK.96, a pinkish
carbonatized rock with pronounced directional structure, and SK.47, rather
like SK.62 in megascopic appearance, may also be included in this group. In
the last two, albite, now largely micaized, is the dominant feldspar and appears
to be secondary after microcline.
(w) Rocks of unknown affinities
SK.104.-Field relations show this to be a ten-foot dyke of Ilunga granite
intruding diorite. Megascopically it is not unlike Ilunga granite but the quartz
is not of the usual bluish opalescent tinge. The rock is somewhat sheared.
Microscopically there is very little resemblance : the feldspar is cloudy and
although potash feldspar exceeds acidic plagioclase, the microcline twinning
is largely effaced and no perthitic intergrowths are seen. One plate of potash
feldspar shows well developed carlsbad twinning. Mafic minerals consist of
rather sparse chloritized biotite and iron oxide. As in the Ilunga granite, orthite
S.K.87.-This is a greenish-pink, unsheared granitic rock from grey granite
terrain. Microscopically, it shows points of resemblance with SK.104, parti-
cularly in regard to the peculiar brown cloudy appearance of the feldspar, the
sparse chloritized biotite and the presence of orthite. Somewhat more plagio-
clase appears to be present and a curious feature is the development of
micropegmatitic fringes at contacts of plagioclase with the rather scanty
SK.86.-This pink rock resembles the Ilunga granite megascopically save
that its quartz is not bluish and opalescent. It is from an area mapped as grey
granite. Microscopically it is not unlike Ilunga granite but is practically devoid
of mafic minerals, consisting almost entirely of perthite and sheared quartz.
SK.102.-A medium-grained, pale-brownish granitic rock, the locality of
which appears to be doubtful. Microscopic characters suggest Ilunga granite
SK.38.-No locality was supplied for this specimen. Microscopically it
resembles SK.59 from Ilunga granite and Ilunga felsite contact, which is
highly crushed and sericitized without discernible relict structure.
SK.55, 57, 97.-Megascopically these are white and greenish-grey sheared
rocks not unlike SK.62 (see above under (iii)). The first is from the zone of
shear north of the main mass of "meta-diorite," the others are from contact
of "meta-diorite" with Ilunga granite. Microscopically they are very similar
feldspar-quartz-biotite rocks, all showing signs of hydrothermal alteration.
SK.41.-Megascopically this is a pink carbonatized rock showing well
defined lustre-mottling. Microscopically this feature is seen to be due to
development of abundant secondary calcite, which is metasomatically replacing
the original felsic rock material and displays optically parallel orientation over
the whole of the thin section examined. The grain-size of this secondary calcite
appears to be of the order of one inch or thereabouts. The original rock was
apparently a marginal type of Ilunga granite adjoining Ilunga felsite, for
remnants of what were once large perthitic feldspar crystals can be seen in
process of replacement by calcite.
SK.66.-This rock was referred to by Dr Skerl as a "contact hybrid" and
is from the main shear zone. Microscopically it is a foliated rock consisting of
predominant hornblende with subordinate acidic plagioclase in process of
alteration to granular epidote. Abundant sphene is present usually surrounding
SK.33.-This is an epidotized meta-gabbro from the "meta-diorite" area.
No feldspar remains, the rock having been entirely reconstituted to hornblende,
epidote and zoisite.
16. LIST AND DESCRIPTION OF PHOTOMICROGRAPHS.
1. SK.110 (X nicols). Ilunga granite. a=albite, o=orthoclase, q=quartz.
2. SK.103 (X nicols). Sheared Ilunga granite, showing one of the perthitic
3. SK.80 (X nicols). Grey granite (adamellitic facess. nm=microcline,
p=turbid, acidic plagioclase, q=quartz, b=partly chloritized biotite.
4. SK.105 (X nicols). Grey granite (tonalitic facies). o=oligoclase, q=quartz,
b= biotite, m = magnetite.
5. SK.95 (X nicols). Epidotized aplogranite. v=epidote vein enclosing frag-
ments of quartz and feldspar, p=micro-faulted plagioclase, m=microcline,
e = epidote.
6. SK.1 (ordinary light). Tonalite-porphyry. o=oligoclase, b=biotite, e=
epidote (the dark wisps are mainly biotite), q = quartz.
7. SK.18 (X nicols). The microscopic characters of this rock suggest affinities
with the Ilunga granite. In the mottled area shown in S.W. quadrant the
lighter portions are albite, the darker, orthoclase. The black areas in the
S.E. quadrant are the mafic clots and reaction zones, which are imperfectly
8. SK.29 (ordinary light). A fine-grained schliere, dyke or inclusion in meta-
diorite which may be described as a spessartitic lamprophyre. Micropheno-
crysts of hornblende (h) are closely crowded in a carbonatized and
sericitized feldspathic matrix.
9. SK.37 (ordinary light). Appinite. h=horhblende, d=diopside core, f=car-
10. SK.35 (ordinary light). Norite. hp=hypersthene, p=labradorite.
11. SK.7 (ordinary light). Olivine-dolerite. p=labradorite, a=pale purplish-
brown augite, o=olivine.
12., SK.69 (X nicols). An indurated feldspathic sandstone showing incipient
granitization. The granular structure is brought out by the X nicols but
the details of the constituent minerals are obscured by streaks, wisps and
veins of semi-opaque ferruginous and chloritic material.
17. LIST OF SPECIMENS AND THEIR LOCALITIES.
SNOTE.-A complete list of the specimens is given below. The localities had
been painted on the rocks and in some cases were obliterated. Where so, this
is stated. Localities are given in most cases as perpendicular offsets north or
south of three E.-W. lines designated N. C. S (north, centre, south) respec-
tively. The first two of these are straight lines but the south line, as may be
I 1 mm.Xnicols
S1 mm ordinary light
seen from the map. is not quite straight. From east to west stations are
numbered along the centre line from 0 to 200, every tenth station, representing
an interval of one mile, being marked. Thus 0-51m. N. of C. 66 means an
offset of 0-51 mile north of station 66 on the centre line. Stations on the south
line may be found by its intersection with vertical projections from correspond-
ing stations on the centre line.
1 ... 0-62m. N. of S. 79
2 ... Locality not supplied
3 ... 0-3m. N. of S. 67
4 ... 0-3m. N. of C. 40
5 ... 1.0m. N. of C. 88
6 ... 2-93m. N. of C. 29
7 ... 0-85m. N. of C. 62
8 ... 2.7m. S. of N. 38
9 ... 1-71m. S. of C. 151
10 ... 0-7m. N. of S. 154
11 ... 0-51m. N. of C. 66
,12 ... 2-93m. S of C. 124
13 ... Bousfield's E.P.L.,
N.-S. reef, ore at 50ft.
14 ... 2-98m. S. of C. 124,
15 ... 1-lm. N. of
(rest is obliterated).
16 ... 0-12m. S. of C. line,
17 ... Bousfield's E.P.L.,
N.-S. reef, ore at 50ft.
18 ... 1-77m. N. of S. 115
19 ... 0.71m. N. of C. 45
20 ... 0-75m. S. of N. 38
21 ... 1-44m. S. of C. 124
22 ... 1-6m. N. of C. 124
23 ... 0-1m. S. of C. line, Luika R.
24 ... 2-29m. S. of C. 110
25 ... 0-25m. S. of C. 186
26 ... 2-65m. S. of C. 59
27 ... 2-2m. S. of C. 110
28 ... 0-75m. S. of N. 38
29 ... 0.1m. N. of S. 188
30 ... 0.1m.N. of S. 127
31 ... 0-75m. S. of N. 38
32 ... I,
33 ... 0-45m. S. of C. 62
34 ... 0-1m. N. of S. 188
35 ... 0.75m. S. of N. 38
36 ... 2.1m. S. of C. 157
37 ... Station S. 147
38 ... 'Locality not supplied
39 ... 1.95m. S. of C. 163
40 ... 1-7m. S. of C. 157
41 ... 0-5m. N. of S. 127
1-52m. N. of C. 49
2-61m. N. of S. 42
1-2m. N. of C. 29
0-83m. N. of S. 172
1-98m. S. of C. 133
2-42m. S. of C. 124
Station N. 112
Station N. 71
0-lm. N. of S. 68
0-75m. N. of C. 39
0-95m. N. of S. 67
2-85m. N. of C. 20
1-0m. N. of C. 89
Station N. 128
2-12m. S. of C. 124
1-5m. N. of C. 89
0-58m. N. of S. 127
2-2m. S. of C. 124
4-52m. N. of C. 49
2-23m. S. of C. 117
0-23m. S. of C. 82
0-32m. S. of C. 29
1-7Im. S. of C. 165
0-51m. N. of C. 66
2-12m. S. of C. 139
0-87m. N. of C. 63
1-0m. N. of C. 84
S. side of Kango Hill
0-85m. N. of S. 90
Station C. 90
1-95m. S. of C. 109
from shaft on N.-S. vein.
Locality not supplied
2-0m. N. of C. 20
1-63m. S. of C. 94
Station N. 100
2-32m. S. of N. 38
2-66m. N. of C. 20
0-8m. N. of S. 20
0-65m. S. of N. 32
2-06m. N. of S. 127
0-1m. N. of S. 20
87 ... Station N. 32
88 ... 1-03m. S. of
89 ... 0-56m. N. of C. 49
90 ... 2-1m. S. of N. 6 (a figure
91 ... 1-56m. S. of C. 124
92 ... 2-23m. S. of N. 38
93 ... 0-4m. N. of S. 148
94 ... 2-34m. S. of C. 74
95 ... Station N. 138, Luika R.
96 ... 1-95m. S. of C. 133
97 ... 1-95m. N. of S. 79
98 ... 2-4m. S. of C. 74
99 ....0-1m. N. of S. 30
100 ... 2-7m. N. of C. 20
101 ... 1-75m. S. of C. 88
102 ... Station C. 75
3-08m. S. of C. 124
0-15m. S. of C. line at
intersection with Luika R.
2-5m. N. of C. 20
1-31m. S. of C. 29
2-42m. S. of C. 157
1-7m. S. of C. 117
Station N. 118
Station S. 119
2-23m. S. of N. 48
2-18m. S. of C. 163
2-2m. S. of N. 38
2-35m. S. of C. 74
1-0m. N. of C. 60
1-1m. N. of S. 121
0-88m. N. of S. 20
Specimens that have not been microscopically studied are as follows :-
2 ... A dark, fine-grained basic rock.
3 ... Oxidized, pyritic quartz.
5 ... Oxidized quartz with galena and copper staining.
10 ... Vein quartz with partly oxidized pyrite and molybdenite.
11 ... Quartz with malachite.
12 ... Quartz with hematite.
13 ... Mineralized quartz with "peacock" copper ore.
14 ... Quartz with malachite staining.
15 ... Oxidized pyritic quartz with finely divided visible gold.
17 ... Pyritic quartz with "peacock" copper staining.
27 ... Oxidized ore with visible gold.
74 ... Rich, oxidized, highly cupriferous gold ore.
75 ... Quartz vein with native sulphur after iron pyrites.
77 ... Acicular crystals of school in quartz.
1908. MACLAREN, MALCOLM. "Gold, its Geological Occurrence and Geographical
1920. HOLMES, A. "The Nomenclature of Petrology." London.
1928. OSBORNE, F. F. "Certain Magmatic Titaniferous Iron Ores and their
Origin." Economic Geology, vol. XXIII, Nos. 7 and 8, pp. 724-761 and
895-922. Lancaster, Pa., U.S.A.
1932. GRANTHAM, D. R. "Lupa Goldfield." Bulletin, Tanganyika Territory Geolo-
gical Survey Department, No. 3. Dar es Salaam.
1933. GILLULY, J. "Replacement Origin of the Albite Granite near Sparta,
Oregon." U.S.A. Dept. of the Interior, Geological Survey Professional
Paper 175-C. Washington.
1935. DUNN, J. A. "The Origin of Iron Ores in Singhbum, India." Economic
Geology, vol. 30, No. 7, pp. 643-654. Lancaster, Pa., U.S.A.
1935. TEALE, E. O., EADES, N. W. and OATES, F. "The Eastern Lupa Goldfield."
Bulletin, Tanganyika Territory Geological Survey Department, No. 8.
Dar es Salaam.
1938. WADE, F. B. and OATES, F. "An Explanation of Degree Sheet No. 52
(Dodoma)." Short Paper, Tanganyika Territory Department of Lands and
Mines, Geological Division, No. 17. Dar es Salaam.
TANGANYIKA TERRITORY DEPARTMENT OF LANDS AND MINES
LIST OF GEOLOGICAL PUBLICATIONS
Available on application to the Chief Geologist, Geological Division of the Department
of Lands and Mines, Dodama, Tanganyika Territory.
(Postal Orders should accompany indents).
ANNUAL REPORTS Shs Cts
Annual Report, 1928 ... ... ... ... ... ... 4/-
Annual Report, 1929 .. ... ... ... ... ... ... ... 4/-
Annual Report, 1930 ... ... ... ... ... ... ... ... 2/50
Annual Report, 1931 ... ... ... ... ... ... ... .. 2/50
Annual Report, 1932 ... .. ... ... ... ... ... ... 2/50
Annual Report, 1933 ... ..... ... ... ... ... 2/50
Annual Report, 1934 .. ... ... ... ... ... ... ... 2/50 -/15
Annual Report, 1935 ... ... .. ... ... ... ... ... 1/50 -/15
Annual Report, 1936 ... ... ... ... ... ... ... 1/50 -/15
Annual Report, 1937 ... ... ... ... ... ... ... ... 1/50 -/10
(N.B.-Annual Reports contain geological information not published elsewhere).
No. 2: "Report on the Geology of the Ruhuhu Coalfield (Being a Preliminary
Geological Survey of the Karroo Rocks East of Lake Nyasa)." By G. M.
Stockley. Contains "Technical Report on the Coal Samples." By F.
Oates, 68 pp., plates, 3 maps, 1 fig., 1931 ... ... ... ... ... 5/- /25
No. 3: "Lupa Goldfield." By D. R. Grantham, 34 pp., 2 maps, 1932 ... Out of print
No. 4: "The Limestone Deposits of Tanganyika." By F. Oates, 120 pp., 3
maps, 4 figs., 1933 ... ... ... ... ... ... ... ... 5/- -35
No. 5: "The Hydrology of Lake Tanganyika." By C. Gillman (Chief
Engineer, Tanganyika Railways), 27 pp., 2 figs., 1933 ... ... ... 3/- -/10
No. 6: (Revised): "Provisional Geological Map of Tanganyika with Explana-
tory Notes." By E. O. Teale (Director), 50 pp., 3 maps, 1 fig., 1936 ... 4/- -!20
No. 7: "Outline of the Geology of the Musoma District." By G. M. Stockley,
64 pp., 4 maps, 3 figs., 1935 ... ... ... ... ... ... ... 4/- -/20
No. 8: "The Eastern Lupa Goldfield." By E. 0. Teale (Director) and N. W.
Eades. Petrographical Notes by F. Oates, 61 pp., 3 maps, 1935 ... 5/- -/30
No. 9: "A Stratigraphical Classification and Table of Tanganyika Territory."
By F. B. Wade (Chief Geologist), 62 pp., 1 table ... ... ... ... 4/- -/20
No. 10: "Explanation of the Geology, Degree Sheet No. 1 (KaragweTinfields)."
By G. M. Stockley and G. J. Williams ... ... ... ... ... 5/. -/40
No. 11: "Explanation of the Geology, Degree Sheet No. 29 (Singida)." By
N. W. Eades and W. H. Reeve ... ... ... ... ... ... In the press
No. 12: "Explanation of the Geology, Degree Sheet No. 18 (Shinyanga)." By
G. J. Williams and N. W. Eades ... ... ... .. ... ... In preparation
No. 13: "The Kimberlite Province and Associated Diamond Deposits
of Tanganyika Territory." By G. J. Williams ... ... ... ... In preparation
No. 14: "Explanation of the Geology, Degree Sheet No. 17 (Kahama)" ... Projected
No. 5: "Water Supplies for Cattle along the Kondoa-Irangi-Handeni Stock
Route." By F. B. Wade, 24 pp., 1 map, 7 plates, 1930 ... ... ... 2/- -110
No. 6: "A Note of the Geology of the Country around Tendaguru, Lindi
District." By John Parkinson (by permission of the Trustees of the British
Museum), 16 pp., 7 figs., 1930 ... ... ... ... ... ... ... 2/- -/10
No. 7: "Notes on the Mineral Deposits in the Newala-Lindi Area." By G. M.
Stockley. With "Petrological and Mineral Notes on Certain Associated
Rocks." By F. Oates, 34 pp., 2 maps, 1931 ... ... ... ... 2/- -/10
No. 8: "Some Salt Lakes of the Northern Rift Zone." By Douglas Orr and
D. R. Grantham, 23 pp., 3 maps, 1931 ... ... ... ... 4/- -/15
No. 9: "Shinyanga Diamond Fields." By E. 0. Teale (Director), 39 pp.,
3 maps, 1931 ... ... ... ... ... ... ... ... ... 4/- -/20
No. 10: "The Kimberlite and Associated Occurrences of the Iramba Plateau;"
By E. 0, Teale (Director), 10 pp., 1 map, 1932 .. ... ...... 2/- -/10
No. 11: "The Eastern Extension of the Lupa Goldfield." ByD. R. Grantham,
9 pp., 1933 ... ... ... ... ... ... ... ... ...
No. 12: "The Saragura and Associated Gold Occurrences of the Mwanza
Area." By F. B. Wade, with Petrographical Notes by F. Oates, 44 pp.,
2 maps, 2 figs., 1934 ... ... ... ... ... ... ...
No. 13: "Geology of the South and South-Eastern Regions of the Musoma
District." By G. M. Stockley, 48 pp., 3 maps, 1936 ... ... .
No. 14: "Hints on the Cyanidation of Gold Ores-Recommendations for the
small-scale Operator." By J. H. Harris, 30 pp., 6 figs., 1936 ...
No. 15: "Geology of Iramba Plateau." By N. W. Eades, 36 pp., 1 map,
1 fig., 1936 ... ... ... ... ... ...
No. 16: "Hints on Prospecting and Working Alluvial Deposits." By F. B.
Wade, 24 pp., 9 figs., 1937 ... ... ... ... ...
No. 17: "Explanation of the Geology, Degree Sheet No. 52 (Dodoma)." By
F. B. Wade and F. Oates, 59 pp., 3 maps, 1 fig ..
No. 18: "The North Ilunga Area, Lupa Goldfield." By F. Oates and A. C.
Skerl ... ... ... ... ... ... ...
No. 19: "Geology of the Country around Mpwapwa." By B. N. Temperley,
61 pp., 1 map, 6 plates... ... ... ... ... ... ...
No. 20: "The Geology of Parts of the Tabora, Kigoma and Ufipa Districts,
North-West Lake Rukwa." Ry G. M. Stockley ... ...
No. 21: "Preliminary Report on the Geology and Gold Occurrences in the
Kahama Region." By D. R. Grantham .. ... ... ...
No. 22: "Geology of Uruwira Goldfied." By G. M. Stockley ... ...
1. Notes on the Sampling and Testing of Mineral Deposits, 4 pp. (Roneoscript),
1933 ... ... ... ... ... ... ... .. ... ...
2. Advice to Intending Reef Prospectors, by E. O. Teale, 8 pp., 1933
(Reprinted, 1938) ... ... ... ... ......
3. Mining Publicity Pamphlet (Revised), 50 pp., Geological map, 1938 ...
4. Precautions against Gold Theft in Mill Design and Practice, by J. H. Harris,
12 pp., 1936 ... ...
5. Notes on Methods of Searching for Water and the Development of Permanent
Wells for Native Villagers, by F. B. Wade and L. F. F. W. Streit, 1935
6. Hints on Amalgamation of Gold, by J. H. Harris, 4 pp., 1937 ...
7. The Microscope as an aid in the Metallurgical Testing of Gold Ores, by
Frank Oates, 8 pp., 1937 ... ... ...
Out of print
LIST OF MAPS PUBLISHED BY THE GEOLOGICAL SURVEY DIVISION
White Blue Blue
Map entitled Scale Linen Linen Paper
Prints Prints Prints
Geological Maps: Shs Shs Shs
D.F. 30. Kigugwe Area... ... ... ... ... 1:50,000 4/- 3/- 1/-
G.S. 58. South-West Highlands (Preliminary) ... 1: 300,000 8/- 6/- 21-
G.S. 59. Tabora to Speke Gulf ... ... ... 1: 500,000 6/- 4/50 2/-
G.S. 107. Ruhuhu Coalfields, printed in colours ... 1 300.000 3/- each
G.S. 122. Lupa Goldfields, printed in colours ... 1: 100,000 3/- each
G.S. 147. Reef Map of Lupa Goldfields ... ... 1:125,000 5/- each
G.S. 148. South-West Mwanza Area, printed in colours 1: 250,000 3/- each
G.S. 150. Eastern Extension Lupa Goldfields, printed
in colours ... ... ... ... ... 1:100,000 5/- each
G.S. 151. Guide Map to Lupa Goldfields ... ... 1: 250,000 2/- each
G.S. 158. Southern Musoma Goldfield ... ... ... 1: 125,000 3/- each
G.S. 159. Eastern Musoma Goldfield ... ... ... 1: 125,000 5/- each
Geological Sketch Maps:
G.S. 44. Kasulu and part Ujiji District, printed on
paper ... ... ......
G.S. 45. Portion of Kibondo District, printed on
paper ... ... ...
G.S. 46. S. Biharamulo and N. Kibondo District,
printed on paper ... .. ... ...
G.S. 115. Dodoma Area ... ... ... .
G.S. 120. Kingongolero Area .. ... ... ...
G.S. 121. Rufiji-Nandanga-Luwegu Traverse ... .
G.S. 124. Karema-Uvinza Traverse ... ... ..
G.S. 125. Lupa River Traverse Makampi-Punga ...
1' to 1 mile