chapter one - amazon s3...the zambian copperbelt (figure 2) lies within the north-directed...
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PETROLOGY STRUCTURAL GEOLOGY AND THE INFLUENCE OF THE LUFUBU ON THE ORE FORMATION AT MUFULIRA MINE Page 1
CHAPTER ONE
INTRODUCTION
1.1 Background
The copper deposits at Mufulira are distinguished from many deposits in the Copperbelt by their
characteristic of being comprised of three stacked orebodies. These three orebodies are named
A, B and C which coincides with the sedimentary packet within which they are each hosted. Of
these, the C ores are the most areally extensive followed by the B and then the A ores. The ore
generally occurs within basins between Basement ridges, but in places is found to drape over
these ridges (Brandt, et al., 1961). The areas of the Mufulira deposit have been named, from
East to West, the Eastern, Central and Western Basins respectively, which are separated from
each other by Basement highs. No economical ores occur within the Basement rocks at
Mufulira, however, some low grade Chalcopyrite is known to occur in veins within the Basement
highs. Historically, the A ores have been the highest grade, but to-date these have been of
limited areal extent.
The Eastern basin ores are of the greatest aggregate thickness, particularly since the A and B ores
are dominantly restricted to this region. The effect of the Basement topography is evident in the
thickness of the C ores. Where the A and B ores extend over the highs, they appear less affected
by any presence of Basement topography.
In general, the distribution of the ore in all three orebodies is stratigraphically controlled, in that
the distribution of economical ores coincides with the stratigraphic limits of the host facies.
The ore sulfides occur dominantly within the interstices between sedimentary mineral grains as
disseminations, blebs and irregular masses. The ores show a preference for medium- to fine-
grained quartzite host rocks, and are less prevalent in finer-grained siltstones and mostly do not
occur within dolomitic rocks rich in biotite or chlorite. The ores are comprised of the sulfides
chalcocite, bornite, chalcopyrite and pyrite which are often concentrated along bedding planes.
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In May 2011, the Department of Geology at Mopani Copper Mine in Mufulira identified the
need to carry out an investigation in the Basement formation of the deeps area (below 1340
meter level) within the central part known as Muf-central. This is a new work area that has never
been investigated. In mapping and doing the investigation within the Basement, mineralisation in
the overlying C ore body would be projected and predicted. This report seeks to address this
need and to outline the findings of the work carried out between 9th June and 9
th August 2011.
1.2 Objectives of the project
The main objectives of the study include the following:
To determine the petrology and structural geology of the Basement rocks also known as
the Lufubu system.
To investigate how the Basement formation relates with the ore formations.
To outline the Basement – footwall contact.
To explain the presence of the vein hosted mineralisation within the Basement.
This was going to be achieved by doing an intensive underground mapping exercise which was
going to help with the structural geology of the Basement. Sampling of the Basement rocks for
the purpose of making thin sections and assaying so that grades within the Basement could be
determined. To achieve this work, literature review was also done which helped in understanding
the mine area.
1.3 Location and access
The study area is located in the town of Mufulira which, lies within the Copperbelt Province of
Zambia which is in the Southern part of Africa as shown in figure 1 below. From Lusaka the
capital city of Zambia, Mufulira is accessed by the Great North Road, via Ndola. It precisely 385
km from the Lusaka.
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Figure 1: Showing the Location of the study area in Southern Africa, Zambia. After Cailteux et
al. (1994),
1.4 Mine history of Mufulira Mine Mufulira Mine is in the Nkana Concession, in the Rhodesian, or southern part of the Central
African Copperbelt (Fig. 1). When Anton Gray visited the current mine location, in August,
1927, several trenches and shallow pits had been dug. No documentation was done by earlier
small scale miners who first discovered copper.
In June 1928, the first drill-hole on the property, put down by the Rhodesian Selection Trust,
was completed. This hole encountered ore at a depth of about 100 meters, and since then twenty-
nine holes have been drilled in ore, the deepest of which struck the lode at 1000 meters. These
holes covered a strike length of two kilometers, and indicated ore bodies of 116 000 000 tons,
averaging 4.4 per cent copper. In 1934 mining was commenced upon the sinking of the shaft.
1.5 Previous work A number of workers have worked and reported quiet a lot about Mufulira Mine. Mendelson
(1961) described the Geology of the Zambian Copperbelt and his book is one of the major
STUDY
AREA
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references on the Zambian Copperbelt as he spent much of his time in this region. In 1993,
Mineral Resources Development Limited (MRDL) made a visit to the Zambian Copperbelt and
the Mufulira Mine. While being shown representative sequences of drill core, MRDL geologist
Borden Putnam noted algal features which were going unrecognized and unlogged. MRDL was
prompted to initiate a study to review the geological concept-model for the Mufulira deposit to
investigate the presence of algal and other shallow-water facies in the district, and to determine
their relationship to ore. Ultimately, it was hoped that the study would target areas for
exploration.
In 1982 WG Garlick carried out an investigation on the erosion of the folded copper rich arenite
and the filling of a rolled-up algal mat. The following were the conclusions of the study.
1. Deposition of algal sediment was probably very slow, but preservation of algal flaps,
protruding above the sediment-water interface during formation of the cylinder was probably due
to the non oxidizing nature of the marine water, i.e., anoxic conditions.
2. Precipitation of copper sulfide was spasmodic, possibly correlated with intermittent inflow of
copper-bearing terrestrial waters into the lagoon. The copper sulfide is syngenetic although the
present mineral composition is a result of diagenesis and metamorphism. The intermittent inflow
of copper-bearing water resulted in superposed layers of sediment with greatly varied copper
content as finely disseminated sulfides from under 1 percent copper to over 10 percent, but
dissemination as long any individual layer are as consistent as the distribution of the detrital
grains of quartz and feldspar.
3. The mineralization of the richer copper sulfide Layers apparently had a cementing effect, so
that these were disrupted and injected by low-grade carbonaceous dikelets. Extensive continuity
of the richer and poorer layers, even when only a few millimeters thick, is typical of the
sediments outside the cylinder and indicates co-precipitation of sulfides with sedimentation.
1.6 Present work The present work which was carried out at Mufulira Mine involved desk study which gave the
basic information of the Mine and the work which was done, also consultations from supervisors
to come up with meaningful information on the project.
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During underground visits, investigation of the Basement – footwall contact was carried out at
the five levels that is 1357ml, 1373ml, 1390ml, 1407ml and 1440ml.
Underground mapping was done to get structural information ranging from shear zones, veins,
joints and to investigate areas of mineralisation within the Basement rocks. Mineralised samples
from the calcite-quartz veins which occurred within the Basement rocks were assayed for the
purpose of obtaining grades. Sampling was also done for the purpose of making thin sections
which helped in understanding the lithologies of the mine.
Following the underground mapping exercise, data was plotted on plans and section and a
Digitized Terrain Model (DTM) was made using Surpac Minex, a mining and geological model.
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CHAPTER TWO
GEOLOGY OF THE COPPERBELT
This encompasses the Regional Tectonic Setting of the Zambian Copperbelt and the stratigraphic
succession from the Basement Complex to the Katangan Sequence.
2.1 Regional Tectonic setting
The Zambian Copperbelt (Figure 2) lies within the north-directed thrust-and-fold arc The
Lufilian Arc which is central African Arcuate Belt and is bounded by Bangweulu Block in the
North East, Irumide Belt in the East and Zambezi Belt in the south. It is more than 150 km wide
and stretches for about 700 km from Mwinilunga in the west (Brock, 1961; Steven, 2000) to the
Bangweulu Block. The Copperbelt is situated along an 700km long structural trend of the folded
and thrusted Katangan sediments called the Lufilian arc (Figure 2), extending from Angola in the
west, through to Congo D. R and Zambia in the east. Most of the Zambian copper mines are
concentrated in the last 200km of this fold arc. The NW-SE trending Kafue anticline is the
dominant structural feature of the Copperbelt as shown in figure 2. The Katangan sediments are
contained in the two syncline structures flanking this anticline on the east and west (see figure 3
below).
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Figure 2: Tectonic Setting of the Copperbelt (modified after Porada, 1989).
The Copperbelt consist of the Basement Complex which is overlain by Neo-Proterozoic
sediments of the Katangan Supergroup, which host the bulk of stratiform copper-cobalt deposits
of Zambia.
The Katangan rocks were subjected to low-grade regional metamorphism of the higher
greenschist facies. The metamorphic grade increases southwards across the Copperbelt. The
overall effect of the metamorphism was the recrystallization of the constituent minerals and a
destruction of sedimentary textures. The regional picture is of metamorphic temperatures in the
order of about 200˚C - 400˚C with about 6 Kbars pressure (Bowen and Gunatilaka, 1977).
The Katangan supracrustal sedimentary succession is 5–10 km thick and commonly sub-divided
into three major lithostratigraphic units (Francois, 1974, 1995); Roan, Nguba (formerly Lower
Kundelungu) and Kundelungu (formerly Upper Kundelungu) Groups. Most of the Zambian
Copperbelt copper mineral deposits occur in the Lower Roan in proximity to Basement domes
and especially the Kafue Anticline.
STUDY AREA
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The Copperbelt has two main sedimentary basins. These are the Roan-Muliashi Basin at
Luanshya that contains the Roan, Muliashi and Baluba Orebodies and the other basin is actually
an aggregate of several interconnected synclines. The Lower Roan is seen to stretch continuously
from south of Kalulushi through the mines at Chibuluma, Nkana, Chambishi, round to Mimbula,
Nchanga, and Chililabombwe (Mendelson 1961).
2.2 STRATIGRAPHIC SUCCESSION OF THE COPPERBELT
2.2.1 Basement Complex
The Basement Complex rocks formed the land surface on which the sediments of the Katanga
Supergroup were deposited and possibly supplied some of the sedimentary material to form the
Katanga Supergroup. The Basement Complex is the oldest Unit and consists of the pre-Katangan
Lufubu Group, the Muva Group and the older granites and comprises the core of the structurally
important Kafue Anticline (Mendelsohn, 1961). The Kibaran orogenic phase caused a
compression of the Muva sediments into long northeasterly trending folds (Mendelsohn,
1961).The Lufubu Schists which were intruded by granites form part of the Basement Complex
composed of mainly mica schist and quartzites. There are a number of large granite masses in the
Basement varying widely in colour, textures, structure, composition and general relationship to
other rocks which were intruded (Mendelsohn, 1961). The Nchanga red granite is composed of
biotite, quartz, microcline, plagioclase, garnet, epidote and chalcopyrite mineralisation. The
Basement quartzite is a greenish Chloritic quartzite grey-green in colour. The Muva Supergroup
lies unconformably on the Lufubu Schists Group and its intrusive granite is considered to have
been subjected to deformation during the Kibaran-Irumide Orogeny, which is dated 1310 million
years (Cahen, 1974).
The figure 3 below shows the Geology of the copperbelt. The stratigraphic succession is from the
Basement Complex to the Nguba group (formerly Kundelungu) as indicated in the legend.
Mineralisation occurs on either sides of the Kafue anticline in the lower roan.
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Figure 3: Geological map of the Zambian Copperbelt showing rocks of the Basement Complex
and the Katanga sequences. ( After Mineral Resource Development., 1993)
2.2.2 Katanga Supergroup
The Katanga sediments overlie the Basement Complex with an irregular unconformity and reach
up to 10,000m in thickness. The lower part of the Katanga is well exposed in the Roan, while the
poorly mineralised upper formations are mainly confined to the central parts of the synclinal
basins (Bowen and Gunatilaka, 1977).
The first sediments were terrestrial talus screes, boulder conglomerates and aeolian sands. These
were followed by near shore sediments of a northeastward transgressing sea, consisting of beach
gravels, deltaic sands, and local algal bioherms passing seaward into sands and muds. The
copper-cobalt sulphide deposits are restricted to these near shore sediments.
Most of the Lower Roan arenites and argillites contain carbonates and sulphates. The Lower
Roan sediments gradually pass into the dolomite-rich Upper Roan and the carbonaceous shales
of the Mwashia, then a 150m thick fluvioglacial conglomerate of granite, quartz, quartzite, and
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dolomite with some shale fragments in a massive argillaceous matrix representing the base of the
Nguba. The Nguba is overlain by the Kakontwe Limestone and Dolomite, which is in turn
overlain by 500m thick shale. These are separated by a Tillite marking the boundary between the
Nguba and the Kundelungu.
2.2.2 (a) Roan Group
The Roan Group is the lower unit of the Katanga succession and is divided into the Lower Roan
and the Upper Roan Groups. The Roan Group unconformably overlies the Basement and
represents the first phase of the initial uplift and rifting which resulted in the deposition of
texturally immature proximally derived coarse conglomerates at the base. This was followed by a
marine transgression and sedimentation of sub-arkosic sandstones, and rare siltstones deposited
in fluvial, alluvial fan, aeolian and fan-delta environments. Shallow marine sediments which are
a mixed carbonate platform-hypersaline lagoon evaporate environment, traditionally demarcate
the boundary between the Lower Roan and the Upper Roan Group by the predominance of
carbonate strata (e.g. Gray, 1932; Mendelsohn, 1961). The Upper Roan Group is characterized
by laterally extensive, meter-scale, upward fining cycles of sandstone, siltstone, shales, dolomite,
algal dolomite and local nodular anhydrite.
2.2.2 (b) Nguba Group
Deposition of the Nguba Group (formerly Lower Kundelungu) commenced with a Glaciogenic
diamictite (the Grand Conglomérate) approximately 10 to 100 meters. In the upward deepening
sequence and overlying the Conglomérate are dolostones, shales, siltstones carbonates, and
mudstones. The Nguba is exposed in the core of the Lufukwe Anticline and probably correlates
with the 750Ma sturtian glacial deposits (Kampunzu et al., 2005).
2.2.2 (c) Kundelungu Group
Overlying Nguba is the Kundelungu Group (formely Upper Kundelungu) that commences with a
wide spread tectonically induced conglomerate of up to 50 m thick (`Petit Conglomerate‘)
containing abundant fragments of Kankotwe Limestone in the Copperbelt region. This was
previously been interpreted as a glacio-marine or glacio-fluvial deposit, but is now regarded as a
unit of tectonically triggered mud-flow deposit (Cahen, 1978). This conglomerate is followed by
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sandstones, siltstones, and shale with a few tens of meters thick of limestone near the base. The
Kundelungu subgroup terminates with a distinctive purple arkose.
The table 1 below shows the summary of the stratigraphy of the Basement complex and the
Katanga succession of the Zambian Copperbelt.
Table 1: Generalized Stratigraphic Sequence of the Basement Complex and the Katanga in the
Zambian Copperbelt.
ERA SUPER GP GROUP SUBGROUP FORMATION ROCK UNITS
NEO-PROTEROZOIC
KATANGA
KUDELUNGU
KUNDELUNGU
(U KUDELUNGU)
BIANONGULAGOMBELA
Argilaceous/Arkose Sst
Dol Stst,Tillites (Petit Conglomerate)
NGUBA
(L KUNDELUNGU)
BUNKEYAKAKONTWE
MUOMBE
Dolomitic Shales, Pelites,
Kakontwe Lst ,Dolomite and Shales
Tillites(Grand Conglom)
MWASHIA
Carbonaceous Shales,
Siltstone, DolomiteGabbroic sills
ROAN
UPPER ROAN KILILABOMBWE(BANCROFT)
Dolomite, Quartzite, Argillite
Shales and Dolomites Siltstone and Siltstone
LOWER ROANKITWE
MINDOLO
Laminated Argillaceous,
Siltstone, Dolostones, Shales, Course Arkoses,
Argillaceous Siltstone,
Bedded Quartzites Conglomerate at the base
BASEMENT
COMPLEX
MUVARUDACEOUS QUARTZITE
SCHIST
Quartzite
ConglomerateSchist
BASEMENT LUFUBU SCHISTGRANITE
Micaceous Quartzite,
SchistGranites and Amphibolites
Modified after Cailteux J.L.H. (2004)
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CHAPTER THREE
3.0 GEOLOGY OF THE MUFULIRA MINE AREA This encompasses the geology of the Mufulira Mina Area, from the Basement Complex to the
Katangan Sequence and the Kirilabombwe fold structure.
3.1 General Geology
The rocks of the Mufulira Mine area belong to the Katanga Supergroup, They occur on the
eastern limb of Kafue Anticline. They range from the Basement Complex the lowest unit which
is unconformably overlain by Roan Group, Nguba and Kundelungu sediments as shown in figure
6. The surface geology of Mufulira Mine area is shown in figure 5 below. The rocks are mainly
arenaceous in nature but some, especially in the higher stratigraphic successions above the Ore
body, are predominately dolomitic with interbedded shale and argillite units.
Figure 4: Geological Map of Mufulira Mine Area showing rocks of the Basement Complex and
the Katanga sequences.
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3.2 STRATIGRAPHY
3.2.1 Basement Complex
The Basement Complex comprises schists, quartzites and granites intrusions. The quartzites are
chararcterised by a strong presence of chlorite which is responsible for the greenish colour
observed in the Basement quartzites. Also present is the Muliashi Porphyry which has large
round microcline porphyroblasts simulating pebbles in a quartzite matrix of oligoclase, biotite
and epidote. The schists are dark in colour with micas visible in a hand specimen. They are also
characterized by the presence of high biotite content.
3.2.2 KATANGA SUPERGROUP
3.2.2.1 Lower Roan group
The Lower Roan lies unconformably on the Basement complex and consists of the Footwall Unit
quartzite and Hangingwall Units. The formations which belong to this Group are the banded shale
and dolomites, arenaceous to conglomeratic lithologies, quartzites, conglomerates, argillites and
impure dolomitic quartzite.
A. Footwall Formation
This formation forms the base of the Lower Roan Group and comprises the Basal Conglomerate,
feldspathic Quartzite, the Banded Shale and argillaceous quartzite. This unit is 50 to 100 ft thick. It
is interrupted by lenses of grit and sandstone. The unit is also characterized by the presence of
crossbeds.
B. “C” quartzite This is the basal part of the ore sequence, and is on average 6 to 19m thick, comprised of
quartzite, which is locally varies in colour from a very dark grey colour on the western end of the
strata to very light grey colour on the eastern end. The dark colour is attributed to large amounts
of introduced carbon rich clays+pyrite±magnetite. This unit is rarely cross-bedded. The
dominant sulfide is chalcopyrite and overall this lens averages approximately 3 percent Cu. In
the study area it covers a strike length of 400km
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C. Hangingwall Formations of the “C” ore body Just overlying the ―C‖ ore is the ―Mudseam‖: This thin dolomitic siltstone separates the C and B
beds and ranges to 1.5m in thickness, but is usually only about 0.5m thick, and is an excellent
marker bed. Overlying the dolomitic siltstone are banded units. These are the banded shales and
dolomites and the banded shales and quartzites. They are subsequently overlain by the inter B/C
quartzite.
D. The “B” quartzite.
This quartzite is 9 to 20m thick and resembles the C and D. The unit varies from having none to
being totally greywacke. These have been abundance of bornite and have average grades less
than the A lens. B and C ore lenses are locally contiguous.
E. Hangingwall formations of the “B” ore body
The lower dolomite is the first formation in the hanging wall of the ―B‖ quartzite. This is
proceeded by the shale, locally refered to as the ―Massive shale‖. The shale is overlain by the
banded shales and quartzites. The inter A/B beds end the hanging wall units of the ―B‖ orebody.
All these unit are between 7.6 to 20m thick. The inter A/B beds are sporadically to poorly
mineralized and are locally dominated by chalcocite especially near the base of the A unit.
F. The “A” quartzite
This is the least extensive and the uppermost orebody at Mufulira mine. The quartzite is 9 to
23.7m thick and resembles the B, C and D quartzites. This unit contains numerous cavities,
developed after dissolution of anhydrite. The contact with the overlying unit is poorly defined. It
is dominated by chalcocite and grade to approximately 10 percent Cu in the chalcocite-rich
areas.
G. Hangingwall of the “A” quartzite The ―A‖ quartzite is overlain by the lower argillaceous quartzite. The rest of the units which
make up the rest of the lower roan formations are the 90‘ dolomite, the grity quartzite and finally
the highly competent glassy quartzite.
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3.2.2.2 Upper Roan group Upper Roan Subgroup is dominated by chemically precipitated and clastically reworked (mainly
dolomitic) carbonate rocks and evaporites (anhydrite and gypsum), with few siliciclastic rocks.
At Mufulira mine evaporates are interbeded with dolomites, thus referred to as ―Intermediate
Dolomite and anhydrites‖. This is the major aquifer at the mine. Overlying the aquifer are shale
and finally the upper dolomite.
3.2.2.3 The Nguba group
The Nguioyhuba Group rests on an erosional unconformity on Upper Roan Group rocks, and
passes conformably into the Grand Conglomerate in places (Cahen, 1978; Wendorff, 2002b). It
consists mainly of carbonates and shales, but contains a thin pyroclastic unit with associated
stratiform banded magnetite/haematite iron formations, which form a regional stratigraphic
marker (Lefebvre, 1978, 1975; Cailteux et al., 2005).
3.2.2.4 Kundelungu group The Nguba is overlain by Kundelungu which is a second sequence of diamictite (Petit
Conglomerate) and is then overlain by carbonates, siltstones, mudstones following in the
sequence. Stratiform breccias, Petit Conglomerate, is regarded as a tectonic conglomerate, and
related to nappe emplacement along former evaporitic horizons during Lufilian deformation
(François, 1974; Cailteux and Kampunzu, 1999) upon which the youngest Kundelungu strata
were deposited.
The stratigraphic succession of Mufulira mine area is as shown in the table 2. The succession is
from the Basement to the Lower Roan and then the Upper Roan. These three major units in the
stratigraphy have their lithological units as described in chapter 3.
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Table 2: Stratigraphic Succession of Mufulira Mine‘s lower roan formation.
Special project by Hastings
Lupapulo.
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3.3 Structure of the orebody The orebodies at Mufulira mine as alluded to earlier are a stratiform type of deposit. The mine falls
in the syncline known as the Mufulira synclinorium. The orebodies have a northwest southeast
trend and dip at 450 to the northeast. There is folding observed through 62/63 boundary. Logging of
drill hole has shown that both the sub Kantanga and ore formations are folded together. See fig 6.
Figure 5: shows the folding in section through 62/63 boundary.
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CHAPTER FOUR
4.1 METHODOLOGY
The study methodology included the incorporation of existing information from the mine in
Mufulira, researches and papers written by previous workers. The information on the geology of
Mufulira mine area acted as the base for the study and was part of the desk study. Mining
methods used at the study area as well as mining terminology were also adopted.
Underground mapping was done in areas of exposure. The major areas of interest were areas
where the Basement units and the Basement footwall contact were well exposed. Such areas
included haulages, footwall drive and most important the cross cuts from the Basement to the ore
formations. It was in these crosscuts that the Basement footwall contact was mapped.
Underground mapping involved measuring of dips joints, veins, mapping of the footwall
Basement contacts and sampling. Samples were collected and these were mainly the muva
quartzite and the Lufubu schist for the purpose of studying the petrology of the Basement rocks.
The ‗C‘ ore body was also sampled along strike. This was for the purpose of studying the mica
content along the ‗C‘ so as to establish a trend which would help in understanding the possible
direction of the paleo currents which deposited the ―C‖ quartzite.
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CHAPTER FIVE
5.1STRUCTURAL GEOLOGY
5.1.1 The pre-Katanga surface
The structural geology of the Basement rocks was studied firstly by determining the surface of
the Lufubu rocks in the pre-Katanga times. This was done by mapping the Basement-footwall
contact and plotting the information on the mine plans and sections. A model was then made
using the software (Surpac). The results of this work were that the pre-Katanga surface was very
ragged and hilly. A ridge seems to be prominent down dip and is responsible for the paleo-highs
that characterize the pre-Katanga surface.
Figure 6: (A) The digitized model showing the pre-Katanga surface.
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Figure 6: (B) The digitized model showing the pre-Katanga surface and the developments at
different sub levels of mining.
5.1.2 Veins Veins were mapped within the Basement rocks. These were calcite-quartz veins and were
observed mainly within the areas where the Lufubu schist was present. The veins were very
prominent and hosted some chalcopyrite in places. In the study area, they remained restricted to
the Basement rocks. However, away from the study area, in the eastern direction, the veins were
seen to cut across the footwall formation into the mineralised lithologies. This was particularly in
block 62.
Within the Basement paleo highs, the veins were observed to be smaller and more systematic as
compared to the paleo lows. The veins in this area could have been formed as a result of the
deformation that could have affected the pre-Katanga rocks. They form near S shaped vein lets in
an en-echelon manner. Veins formed in such a manner are indicators of a sense of shear
66m
Hastings 2011
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deformation. (See figure 8) This is as a result of brittle ductile deformation.
Figure 7: Calcite quartz veins at 1407 meter level (blocks 56/57 boundary) and a hand specimen
(insert) showing Chalcopyrite mineralisation at 0.8% Total Copper.
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Figure 8: Shear sense indicator veins at 1423 meter level (block 56)
5.1.3 Joints Joints were mapped within the Basement formation. They appeared to have been concentrated in
55 and 56 blocks. The dip and dip directions of the joints were measured and the data plotted on
a stereo net. There were a total of four sets with two sets being major while the other two sets
were minor sets. For the major sets, the first was dipping to the east with an average dip angle of
400, the second major set with a SE-NW trend and dipping to the northeast at about 50
0. The
minor sets dip to the SE and the SW at very shallow angles.
The Lufilian arc is known to have suffered intense shearing, folding and thrusting. The
deformation episodes responsible for such deformations could have caused the formation of the
joints.
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Figure 9: (A) A plot of fisher concentration of the Joints showing two major sets (Circled), and
(B) A stereoplot of the poles for the Joints.
A
B
I
II
III
IV
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Figure 10: (A) Showing surfaces of Discontinuities in the Basement quartzite in situ. (B) A
surface of discontinuity hosting micas in the Basement quartzite (core).
From the analysis of the joints underground, it was observed that one set was intersecting another
set. This implies that the set which appeared to have been intersecting another set is the younger
one. From the fisher concentration in figure 9 (A), the younger joint set of the two sets is actually
set II. The joints in set II appeared to be intersecting the joints in set I as observed during my
studies of the joints underground. Set II joints generally had a steeper angle of dip and were
fewer than the joints of set I.
The observed East-West trend in the joint sets II and III could be attributed to the extensional D2
deformation suffered by the external fold thrust belt of the Lufilian arc. According to Daly 1986,
the structures of the fold thrust belt were a result of two kinematic phases. An early D1 east-
northeast directed and a later D2 northerly directed phase. I therefore wish to attribute the trend
of the joint sets II and III to the later D2 deformation event. This is because of the observed
perpendicular relationship between the trend of the joints and the direction of the extensional
forces that caused the thrusting and folding. While sets I and IV could have been caused by D1
ENE directed extensional forces referred to by Daly (1986).
A B
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CHAPTER SIX
6.0 THE RELATIONSHIP BETWEEN THE BASEMENT PELEO HIGHS AND THE
MINERALISATION IN THE “C” QUARTZITE. The relationship between the Lufubu Basement and the immediate overlying Katanga beds, the
―C‖ quartzite (―C‖ ore body) can be analysed in terms of the mineral distribution within the ―C‖
ore body and the structure of the copper bearing ―C‖ ore body. It must be noted at this point that
the Basement formation does not show any influence on the upper two orebodies, that is the ―B‖
quartzite and the ―A‖ quartzite.
6.1 The structural relationship
The influence of the Lufubu rocks on the overlying Katanga beds is evidenced by the structural
orientation of the Katanga beds where the Lufubu Basement paleo highs occur. Generally the
beds overlying the hills of the Basement were observed to be thinner in this zone (55 and 56
block). In the region were the Basements rocks are in contact with the ―C‖ mineralisation the
footwall quartzite is observed to be missing. Where it occurs, it equally a very thin layer of rock
This is most likely to be as a result of non deposition of the foot wall formation. Down the south
east flank of the Basement high, the ―C‖ quartzite once again thickens. On average, the thickness
of the ―C‖ orebody where the highs occur is about 2 meters. This is in contrast with the thickness
of the same orebody away from the Basement highs which averages at 11 meters.
Due to the structural influence of the Basement on the ―C‖ orebody, it was observed that the
strike of the ―C‖ quartzite was not persistent along the known general strike of the ore bodies .
This is purely as a result of the doming effect on the overlying ―C‖ orebody. See figure 12.
6.2 The mineralogical relationship
Mineralogicallly, the Basement highs are of economic importance. Where they occur,
mineralisation was observed to be of poor grade. At Mufulira‘s Mopani Copper Mine, the cut off
grade for the ore is 2%. However the mineralisation of the ―C‖ in these zones averages around
1.5%, which is below the cut off grade. The study showed that the total copper mineralisation
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down the right flank of the paleo high within the ―C‖ quartzite is greater than the mineralisation
elsewhere within the ore body. It was 3.5% total copper on average. See figure 12 below.
6.2.1 Distribution of mineralisation in the “C” quartzite.
Where the Basement highs come in contact with the ―C‖ quartzite, as shown in figure 11 below,
there seems to be generally a pyritic zone occurring in the zone above the hill. This is generally
surrounded by a concentric zone of chalcopyrite and bornite.
Figure 11: Distribution of sulphide mineralisation across the paleo highs in section. (After Brandt
1962)
The mineralization is often asymmetrically distributed across the ridges, suggesting the ridges
acted as a barrier to flow of the ore forming fluids. Where local perpendicular offsets in the
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ridges occur, the mineralization may drape over the ridges and extend down-flank on the other
side.
Figure 12: A plan showing the thickness, mineralisation and the effect of the paleo high on the
strike of the ―C‖ ore body.
Two different
strike directions
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CHAPTER SEVEN
7.0 THE PETROLOGY OF THE BASEMENT ROCKS The study area was characterised by the presence of Schists and Quartzites. Away from the study
area, granites have been reported west of the mine also called Muf-west.
The Lufubu schists and the intrusive granitoids are unconformably overlain by quartzites and
schists of the Muva Supergroup (Garlick, 1961b). The Muva metasediments have a maximum
age of 1941 ± 40 Ma, which is the age of the youngest detrital zircon dated by Rainaud et al.
(2003) from these sediments. Jackson (1932) called the Lufubu schists of the Mufulira area the
‗‗Basement Schist Series‘‘, consisting of garnetiferous chlorite schists, quartz-mica schists and
biotite gneisses, which he regarded as being metasedimentary in origin and Archaean in age.
Mendelsohn (1961b) described the Lufubu schists as mica schists, quartzites and gneisses with
minor metamorphosed carbonates, conglomerates, subgraywackes and arkoses, extensively
intruded by granites. He regarded the majority of the Lufubu schists as metasediments with the
possibility of some minor metavolcanics. Unconformably overlying the Lufubu schists are the
Muva metasediments, which consist of deformed quartzites, metaconglomerates and metapelitic
schists.
A sample of the Lufubu schist was collected from the Mufulira Mine by Rainauld et al (2005),
on the eastern flank of the Kafue anticline. This was a blastoporphyritic metavolcanic derived
from a hornblende-quartz porphyry in which they observed that the fine-grained matrix and
amphibole-phenocrysts are replaced by intergrowths of epidote, biotite, chlorite, quartz
magnetite and sphene. They also did whole-rock geochemistry on the Lufubu schists from the
Mwambashi B prospect in the Chambishi basin, Baluba Mine near Luanshya, the Kafue River
south of Mufulira and from Kinsenda in the DRC. Samples were analysed for both major and
trace elements and were examined petrographically for their mineralogical and textural
characteristics. All samples exhibited porphyritic textures with fine-grained matrices of
metamorphic sericite. Lufubu schist compositions are presented in a Zr/TiO2 vs Nb/Y diagram
(Winchester and Floyd, 1977) which showed that these rocks plot in the andesite/rhyodacite–
dacite/trachyandesite/alkali basalt domain (see figure 13). The sample suite had characteristics
consistent with a metavolcanic origin. The same samples were further analysed and results
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plotted in the AFM geochemical discrimination diagram of Irvine and Baragar (1971). All
analyses showed enrichments in the alkalis Na2O+K2O compared to FeO, and they plot in the
calc-alkaline field (see figure 14). Because these rocks may have suffered mobility of major
elements during metamorphism, the AFM plot can only be used to suggest that the data are
consistent with the Lufubu schists being mainly calc-alkaline metavolcanic rocks. The Lufubu
schist metavolcanic rocks, together with subordinate metasedimentary rocks such as quartzites
and marbles, are regarded as having formed in a subduction related magmatic arc.
Fig.13 Zr/TiO2 vs Nb/Y geochemical classification diagram (Winchester and Floyd, 1977) for
the Lufubu schists. Filled squares Lufubu schists from Mufulira; filled circles—Lufubu schists
from Kafue River, south of Mufulira; diamond—Lufubu schists from Kinsenda;
Fig14. AFM diagram (Irvine and Baragar, 1971) of the Lufubu schists. Filled squares—Lufubu
schists from Mufulira; filled circles—Lufubu schists from Kafue River, south of Mufulira;
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diamond—Lufubu schists from Kinsenda; empty square—BN53/1 from the Mwambashi B
prospect in the Chambishi basin; half filled squares—host rocks of the Samba
7.1 Petrography
7.1.1 The Basement Quartzite
The hand specimen of the Basement quartzite shows a dark gray fine grained and well
compacted rock type. It is characterised by bands of green minerals in places and within the fine
grained matrix. Notable in the hand specimen are quartz grains, muscovite flakes and chlorite.
The petrographic analysis done on the Lufubu rocks at the University of Zambia‘s school of
mines laboratory showed that the quartzite samples collected from the Basement is composed of
quartz, chlorite, epidote, and sericite. I therefore wish to call it a chloritic quartzite. See fig 15
below.
Plate 1: A photomicrograph of the Basement Quartzite.
Chlo
ri
Qt
z
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Figure 15: The quartzite in the core rack showing a large green band of chlorite.
7.1.2 The Basement schist (Lufubu schist)
The Lufubu schist is a very dark, fine grained and poorly foliated rock. It is characterised by
biotite, muscovite, epidote, chlorite, quartz and sericite.
This is similar to the findings of Rainauld et al 2005. I do not fully agree with Jackson (1932)
who described the Lufubu schist as a ganertferous chlorite schist and quartz mica schist. The
amount of chlorite in the schist is not as much to warrant the name chlorite schist. There is more
of biotite than chlorite as can be observed in plate 3. The chlorite is more in abundance in the
quartzite than in the schist.
A green chloritic band
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Plate 2: A photomicrograph showing Chlorite, Epidote, Sericite and Quartz in the Lufubu schist.
Plate 3: A photomicrograph showing Biotite and Chlorite in the Lufubu schist.
Ser
Qzt
Chl
Opaque minerals
Bio
Chl
Opaque
minerals
Epidote
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Plate 4: A photomicrograph showing Biotite, Muscovite Chlorite and Sericite in the Lufubu
schist.
7.1.3 Metamorphism in the Basement rocks
From the mineral assemblages discussed above, it becomes imperative to analyse the
metamorphism of the Basement rocks.
Regional metamorphism affected the Lufilian arc. It increases in grade from lower Greenschist
facies to higher greenschist facies over most of the mine areas, then to the lower epidote-
amphibolite facies to the southwest of the fold belt.
The Basement was previously subjected locally to higher temperatures and pressures than the
overlying Katanga sediments, yet evidence of high grade metamorphism are rare. Mendelson
1961 recognised that the Basement had undergone long lasting pervasive retrograde
metamorphism during the folding of the cover. Biotite and Sericite are both characteristic of the
Lufubu and Muva argillaceous.
Characterising the Lufubu schist at Mufulira mine as shown in plates 2, 3 and 4 above are the
minerals biotite, muscovite, sericite, chlorite and epidote. From this mineral assemblage it can be
Muscovite
Sericite
Bio
Qzt C
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concluded that the rocks were deformed to Greenschist facies. The greenschist facies is at
medium pressure and temperature. The facies is named for the typical schistose texture of the
rocks and green colour of the minerals chlorite, epidote and actinolite. Characteristic mineral
assemblages are:
chlorite + albite + epidote ± actinolite, quartz
7.1.4 Metamorphic veins and the mineralisation During folding, the more competent lithologies were fractured and the openings were filled by
minerals crystallising from connate and metamorphic fluids squeezed from the adjacent wall
rock. In the study area, the veins are characterised by the presence of anhydrides the minerals
quartz and calcite as shown in figure 8 (A) of chapter 5. Apart from the two major minerals, the
veins were observed to host copper mineralisation in the form of Chalcopyrite. When assayed for
copper, the total copper content from one of the samples collected at 1407ml gave 0.8% copper.
Therefore it can be concluded that the mineralisation in the Basement‘s veins is not of economic
significance.
Generally there is variation in the mineral content of the veins according to the grade of
metamorphism. In the study area, feldspar is practically absent. Albite crystals have been
recorded in less than a dozen veins. Anhydrite, calcite and quartz are the common in all veins,
and in terms of copper mineralisation in the veins, bornite and chalcopyrite are ubiquitous.
7.1.5 Geotechnical
Geotechnically, the Basement rocks have a good competence. They have an average RQD of
86.6%. this was established from the core which was drilled during the drilling for geotechnical
data of a pilot hole near the location of the planed new shaft. The only major detriment which i
thought could be hazard was the presence of platy minerals in the discontinuities. Micas were
observed to occur within the joint of the Basement quartzite. These can easily cause slope failure
depending on the angle of slope, as blocks of rocks are susceptible to sliding at steep angles of
dip for discontinuities. See figure 16 showing core of the basement rocks in core racks. Micas
are very visible and distinguishable in these discontinuities.
http://en.wikipedia.org/wiki/Schisthttp://en.wikipedia.org/wiki/Texture_%28geology%29http://en.wikipedia.org/wiki/Chlorite_grouphttp://en.wikipedia.org/wiki/Epidotehttp://en.wikipedia.org/wiki/Actinolitehttp://en.wikipedia.org/wiki/Chloritehttp://en.wikipedia.org/wiki/Albitehttp://en.wikipedia.org/wiki/Epidotehttp://en.wikipedia.org/wiki/Actinolitehttp://en.wikipedia.org/wiki/Quartz
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Figure 16: Showing discontinuities lined by micas in the quartzites.
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CHAPTER 8
8.0 DISCUSSION AND CONCLUSION The pre Katanga topography is of great significance to the study of the pattern of mineralisation
in the Katanga beds of the Mufulira synclinorium. It determined the characteristics of the strata
which were to be eventually deposited on it and the distribution of the copper in the same.
This exercise brought out the nature of the surface of deposition of the Katanga beds. From the
mapping exercise which was followed by digitization of the results, it was eminent that the pre
Katanga surface was ragged and uneven. This came to light after having carried out a detailed
mapping of the Basement-footwall quartzite contact within the study area. The model which was
produced in the mining and geology software (Surpac minex) helped to visualize the possible
topography before the deposition of the Katanga beds. With that established, the study was
focused on the Katanga beds which were deposited on the ragged Basement. Where the
topography was high, it was observed that the footwall quartzite was either extremely thin (
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accumulating down the hills could have been affected by compaction over the hills forcing them
to migtrae down the hills.
Owing to the fact an unconformity occurs between the Katanga sediments and the Basement
rocks, it is possible that the pre Katanga surface could have suffered normal geological processes
prior to the deposition of the Katanga beds. The observed veins in the peak regions of the
Basement rocks could have been pre Cambrian fractures which characterized the Basement
rocks. The open fractures could have allowed circulating metal bearing fluids to fill them. The
circulating non metal bearing fluids rendered a high possibility of weathering of these schists.
Upon the introduction of the metal bearing fluids to the weathered schists, part of the minerals
accumulated in these fractures as veins.
However a more plausible theory by Fleischer R., 1967 is one postulating that the tectonic
forces that affected the sediments over the hills could have caused great stress during folding. In
the process the more rigid rocks of the Basement could have fractured in the peak regions. The
produced waters of metamorphism and connate waters could have carried some minerals with
them into the fractured areas. The rest of the copper bearing fluids could have migrated downhill,
accounting for the accumulation of the copper at the SE flank of the hills. The quartz calcite
veins observed in the peak areas of the Lufubu rocks could have formed that way. Inside these
openings, the environment was a low pressure and alkaline environment. This is the only
possibility for the deposition of the calcium carbonate crystals. Otherwise the precipitation of
calcium carbonate would not occur.
The petrographic studies have shown that rocks were affected by a greenschist facies
metamorphic grade. This is characterized by the minerals chlorite, albite and epidote for volcanic
rocks. Thin sections of the rocks sampled reveal the presence of the minerals chlorite, biotite,
epidote, sericite and muscovite. The metamorphic grade observed is in conformity to the findings
of many other workers who have worked in the Lufilian arc. The establishment of the protolith
of the Basement rocks was beyond the scope of this exercise. However findings by Rainauld et al
(2005), were that the Basement schists are of calc alkaline volcanic rocks in origin.
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The change in the strike of the ―C‖ quartzite where the Basement highs occurs is an important
factor in the day to day mining operations. The knowledge of the location of the highs can help
in planning of future developments. A mining geologist can easily predict any future changes in
the strike of the ore body as mining progresses from the highs. Since over the Basement highs
mineralisation is of poor grade, exploration in these areas would not have to be intensified as a
way of saving resources and time. Of great importance to Mopani Copper Mine (MCM) are
capital projects involving haulages and declines. The development of these projects is carried out
in the Basement rocks as they are deemed competent and of high RQD. The immediate overlying
lithology the footwall quartzite is arkosic. This means that it is susceptible to weathering as
feldspars are readily attacked by water. Therefore the footwall quartzite is not ideal for
placement of capital projects. So the establishment of the Basement-footwall contact is vital for
the mine, as this will ensure that the capital projects of the mine are confined to the right
lithology which happens to be the Basement formation. This is a direct application of the results
of this work.
8.1 Conclusion. This influence of the Basement rocks on the ore formation of Mufulira mine is such that the
ridges also known as Basement highs have impoverished the overlying ―C‖ quartzite. The grades
are sub economic and as such not mined out. The strike of the ―C‖ quartzite is equally altered
where the highs occur. The Basement rocks are of calc alkaline volcanic origin and
metamorphosed to the greenschist facies.
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Wendorff, M., 2002b. Stratigraphy of the Fungurume Group—evolving foreland basin
succession in the Lufilian fold-thrust belt, Neoproterozoic- Lower Palaeozoic, Democratic
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ZCCM and Mineral Resource Development Limited, 1995. Geological Concept Model-Mufulira
Mine.
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PETROLOGY STRUCTURAL GEOLOGY AND THE INFLUENCE OF THE LUFUBU ON THE ORE FORMATION AT MUFULIRA MINE Page 42
APPENDIX A
No Range of Core Recovery RQD (%)
1 103.40-106.40 3.05 97.0
2 106.40-109.40 3.00 86.7
3 109.40-112.40 3.02 96.0
4 112.40-115.40 3.00 87.7
5 115.40-118.40 3.02 81.7
6 118.40-121.40 2.53 71.0
7 121.40-124.40 2.94 99.7
8 124.40-127.40 3.00 96.0
9 127.40-130.40 3.05 92.7
10 130.40-133.40 3.04 97.0
11 133.40-136.40 3.05 100.0
12 136.40-139.40 2.96 87.0
13 139.40-142.40 3.00 30.3
14 142.40-145.40 2.96 59.7
15 145.40-148.40 3.00 92.0
16 148.40-151.40 2.98 96.0
17 151.40-154.40 2.93 93.7
18 154.40-157.40 3.08 90.0
19 157.40-160.40 2.93 90.0
20 160.40-163.40 2.96 72.0
21 163.40-166.40 2.92 81.0
22 166.40-169.40 2.62 64.3
23 169.40-172.40 1.00 64.3
24 172.40-175.40 2.90 24.3
25 175.40-176.40 0.85 72.3
26 176.40-177.40 1.22 56.0
27 177.40-180.40 2.96 100.0
28 180.40-183.40 2.68 99.7
29 183.40-186.40 3.00 99.3
30 186.40-189.40 2.90 80.3
31 189.40-192.40 3.00 78.3
32 192.40-195.40 3.00 93.0
33 195.40-198.40 2.92 83.3
34 198.40-201.40 2.98 91.0
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PETROLOGY STRUCTURAL GEOLOGY AND THE INFLUENCE OF THE LUFUBU ON THE ORE FORMATION AT MUFULIRA MINE Page 43
35 201.40-204.40 3.00 93.3
36 204.40-207.40 2.90 76.7
37 207.40-210.40 3.00 92.3
38 210.40-213.40 2.96 98.0
39 213.40-216.40 3.02 100.0
40 216.40-219.40 2.86 87.3
41 219.40-222.40 3.00 95.3
42 222.40-225.40 2.98 87.7
43 225.40-228.40 3.00 83.3
44 228.40-231.40 2.83 90.0
45 231.40-234.40 3.11 95.3
46 234.40-237.40 3.00 98.7
47 237.40-240.40 3.00 83.3
48 240.40-243.40 2.86 84.7
49 243.40-246.40 3.00 82.7
50 246.40-249.40 3.00 58.7
51 249.40-252.40 2.92 83.0
52 252.40-255.40 2.93 98.0
53 255.40-258.40 2.94 85.3
54 258.40-261.40 3.00 86.3
55 261.40-264.40 3.00 85.7
56 264.40-267.40 3.00 91.7
57 267.40-270.40 3.00 93.3
58 270.40-273.40 3.00 95.3
59 273.40-276.40 2.94 92.7
60 276.40-279.40 2.93 92.0
61 279.40-282.40 2.90 83.3
62 282.40-285.40 2.87 88.7
63 285.40-288.40 2.95 95.3
64 288.40-291.40 3.03 100.0
65 291.40-294.40 2.92 91.0
66 294.40-297.40 2.97 82.7
67 297.40-300.40 3.05 95.0
68 300.40-303.40 2.87 92.7
69 303.40-306.40 3.03 88.3
70 306.40-309.40 2.94 97.0
71 309.40-312.40 2.72 83.3
72 312.40-315.40 3.28 97.7
73 315.40-318.40 3.00 84.7
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PETROLOGY STRUCTURAL GEOLOGY AND THE INFLUENCE OF THE LUFUBU ON THE ORE FORMATION AT MUFULIRA MINE Page 44
74 318.40-321.40 3.00 95.7
75 321.40-324.40 2.88 85.7
76 324.40-327.40 2.89 98.0
77 327.40-330.40 2.88 65.3
78 330.40-331.40 0.84 26.0
79 331.40-333.40 2.27 87.5
80 333.40-336.40 2.93 94.3
81 336.40-337.90 1.63 99.4
82 337.90-339.40 1.33 88.0
83 339.40-342.40 2.84 95.3
84 342.40-345.40 3.11 100.0
85 345.40-348.40 2.94 97.0
86 348.40-351.40 2.95 85.0
87 351.40-354.40 3.00 97.0
88 354.40-357.40 3.00 88.0
89 357.40-360.40 2.92 88.3
90 360.40-363.40 3.00 100.0
91 363.40-366.40 3.00 98.0
92 366.40-369.40 3.00 93.3
93 369.40-372.40 3.00 94.7
94 372.40-375.40 2.85 80.0