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The Kamativi pegmatite tin mine, which also contains resources of Tantalum, Nobium, Tungsten, Lithium and Beryllium, is located ~52 km east of Hwange, ~135 km ESE of Livingstone and 400 km west of Harare in western Zimbabwe (#Location: 18° 19' 37"S, 27° 2' 32"E).
The Kamativi Mine lies within the Central African Tin Belt, and was historically the largest tin producer in that belt. Ancient Phoenician workings dating back some 2000 years are known at Kamativi. The deposits were re-discovered during the early 1920s with the first significant production derived from alluvial gravels commencing in 1936 from small prospector workings.
Following the second World War, Consolidated Goldfields tested the area, but decided the property did not warrant further consideration. The manager of this testing program privately persuaded the Oakes Trust, a Bermuda based family, to finance further testing. Subsequently, in 1952, Billiton was brought into the venture as a partner. Mining commenced in the mid 1950s. In 1974, following the Shell takeover of Billiton, that company withdrew from Kamativi. Their interest in Kamativi Tin Mines Ltd was bought by the Rhodesian State owned Industrial Development Corporation, the IDC. The mine continued production, until closed in 1995 as a result of prolonged low tin prices.
This summary is based on a detailed technical visit in 1978 and information provided during discussions by Dr K.C. Taupitz, the Group Consulting Geologist, of the IDC.
Regional and District Setting
Kamativi is one of a series of tin and tungstem deposits distributed intermittently through central Africa, from western Zimbabwe in the south, through Zambia and southern DRC to southwestern Uganda.
In the south of the belt, in Zimbabwe, the Proterozoic sequence overlies the Archaean granite-greenstone basement of the Zimbabwe craton, and commences with the Deweras-Lomagundi Groups. The Deweras Group is overall older than the Lomagundi, although in sections they interfinger. The Deweras Group comprises mafic volcanic rocks (dated at 2150 Ma), arkoses, schists, phyllites and dolomites, while the Lomagundi Group is limestone, meta-siltstone and shales. These are succeeded by the Piriwiri Group, a sequence of well bedded, intercalated, dirty quartzite and shale, overlain by arkosic sandstone. The Piriwiri Group is now a succession of micaceous quartzite, biotite schist and granitic gneiss and is cut by 2.0 Ga granitoids.
The sequence within the Kamativi district is as follows, from the base:
Malaputese Group - This is the local equivalent to the Dewaris-Lomagundi groups, and comprises mafic volcanic rocks and black quartzite, with limestone rich bands associated with the volcanic rocks. The black quartzite varies from a quartzitic muscovite schist to a muscovite-quartzite. Few pegmatites are found within this sequence. The Malaputese becomes more metamorphosed towards the base of the Piriwiri where it is known as the Gn 1 gneiss.
Piriwiri Group, which comprises:
• Iuvantue Formation - mostly a graphite schist.
• Tshontonda Formation - an interbedded schistose-quartzite, biotite-schist sequence at the base of, and grading upwards into, the Kamativi Formation. Like the Kamativi Formation it is finely bedded with frequent repeated intercalations of the major components. It is characterised by beds carrying fine tourmaline laminations. Within this there is a 20 to 30 m wide band carrying from 0.1 to 0.2% WO3. The remainder of the Formation carries anomalous levels in general <100 ppm WO3. The thickness of the unit is not known.
• Kamativi Formation - which comprises intercalated schistose-quartzite and biotite-schist representing an original quartzite, silty-quartzite and shale unit. In general these schists have around 10% tourmaline. Every 0.3 to 2 m there are bands from 10 to 30 cm thick which comprise 40% tourmaline as 0.5 to 1.0 mm thick laminae (or foliations). The more siliceous parts of the sequence have about 10% biotite within fine white quartzite (about 0.5 to 1 mm in grain size) with up to 20 to 25% tourmaline bands in places. The mica schist ranges from a micaceous quartzite to a massive biotite schist with very little free quartz. In places the biotite schist and quartzite are intercalated as 1 to 10 cm thick beds, while elsewhere relatively clear quartzite members of up to 5 m in thickness are obvious. The Kamativi Formation carries around 200 ppm Sn throughout, with tantalum being high near the base.
• TG Gneiss - overlies and partly interfingers with the Kamativi Formation to the south-west. It comprises a light coloured granitic rock with black spots and needles of tourmaline throughout. It is chemically similar, but different in appearance, to the Gn 2 gneiss.
• Gn 2 Gneiss - also known as the 'migmatite zone', is a metamorphosed arkosic sandstone. In general, it is a pink granitic gneiss composed of well foliated 3 mm thick pink feldspar, quartz and fine biotite. Thin biotite and biotitic bands are distributed throughout the rock, often reflecting inferred sedimentary structures. These biotite bands are from 1 to 10 mm thick and constitute up to 10% of the rock over irregularly spaced 30 cm intervals. In some sections, Kamativi Formation type facies rocks are again developed within the Gn 2 gneiss. Much of the Gn 2 gneisses also have well developed tourmaline laminae, although high tin values are only found locally. The contact between the Gn 2 and Kamativi Formation is gradational over a 100 m interval.
The North East Granite - a very grey, medium grained, porphyritic intrusive, apparently of palingenetic origin. It is dated at 2100 to 2000 Ma.
Pegmatoids - The pegmatoids are developed roughly parallel to strike and have been folded with the enclosing sequence. They are in general tourmaline rich and barren, ie. they only carry 200 ppm Sn, the same as the enclosing Kamativi Formation schists. They range from 50 cm white veins, with 20 cm wide enveloping margins of coarse mica and feldspars as 2 to 3 cm wide crystals, to thin 2 to 3 cm thick veins of mixed 1 cm crystals of quartz, feldspar and mica. The larger pegmatoids comprise up to 5 to 6 m wide graphic intergrowths of coarse feldspar (3 to 4 cm) quartz (1 x 2 cm) and tourmaline (2 x 1 cm), cut by white mica bands. Some of these pegmatoids are mineralised in the tungsten zone. In this region, mineralisation is developed in later quartz ladder veins crossing the main pegmatoid. The pegmatoids are dated at 1.9 to 1.6 Ga in age.
Mineralised Pegmatites - These are dated at 990 Ma. They are described in detail below.
Sijarira Series - Deposition of the Sijarira commenced in the Neoproterozoic and may have continued into the Lower Palaeozoic. It comprises red grits, quartzite, sandstone, fanglomerate and siltstone, and unconformably overlies the Piriwiri and Malaputese Groups.
Karoo Supergroup - The Karoo comprises cratonic clastics and coal measures, with associated basic volcanic rocks. They are from Permian to Lower Jurassic in age.
Tertiary to Recent Kalahari Sands - which mask the older rocks to the west.
Mine Geology and Mineralisation
The Kamativi pegmatites occur as large, shallow dipping, sheet like bodies, in shape resembling a series of inverted saucers. The pegmatite bodies themselves are large and lenticular with no apparent feeders, and vary from stringers and thin bodies less than 1 m thick, to lodes in excess of 30 m thick. Contacts with the host sequence are very abrupt and show negligible reaction haloes. The pegmatites dip outwards at from 10 to 20°, often splitting down dip into two or more branches which tend to gradually pinch out. The flat lying pegmatites are largely restricted to areas of vortex folding between the blocks of 2.1 Ga granite. In contrast however, in the areas of more regular deformation, the pegmatites are more steeply dipping and linear, and parallel to schistosity.
Cassiterite is the only ore mineral currently extracted. Most pegmatites in the area carry less than 0.08% Sn while a number have around 0.2% and a few have in excess of 0.4% Sn. The latter are usually found in the thinner pinch-out zones on the margin of the larger pegmatites.
The mineralised pegmatites appear to have been developed in three main stages, namely:
i). A coarse K feldspar-quartz-spodumene stage made up of 2 to 5 cm wide crystals. The feldspars are in general cream with, in some areas, pink varieties.
ii). A fine grained (aplitic in appearance) albite-quartz-lithium muscovite stage. This is an alteration stage imposed on the earlier phase, partially modifying it. The resultant texture has bands of fine albitised pegmatite with other bands of un-altered, coarsely crystalline material. Occasional coarse crystals are dotted through the albitised zone. The albitised zones vary in colour giving well defined bands from 1 to 50 cm thick.
iii). A quartz-lithium muscovite stage. Quartz crystals and aggregates are usually from 1 to 2 cm wide with 1 cm pale green books of muscovite. This phase is usually present on the margins or selvage zone of the pegmatite, although bands from 1 to 10 cm thick are found through the body also, cutting across the albitised zones.
Each of the two later stages and the initial pegmatite formation has been repeated a number of times. The cassiterite mineralisation appears to have been introduced with the albitisation. Cassiterite does occur in the first coarse stage, except in cracks adjacent to albitised zones. The pegmatites have beryl developed throughout with an average grade of around 0.5% Be2O3.
Columbo-tantalite is found in two forms; i). in the albite stage it is present as fine intergrowths (less than 1 mm) with cassiterite, and ii). in the coarsely micaceous quartz-mica stage it is present as individual platy crystals from 4 to 5 mm in diameter. Tantalite occurs in the ratio Ta2O5:Sn of 1:30.
As mentioned previously, the Kamativi Formation carries around 200 ppm Sn throughout in association with tourmaline rich beds. In places, there are pods of tourmaline-biotite-quartzite with up to 60% tourmaline as bands from 0.5 to 2 mm thick. These pods are as much as 5 m thick and persist for a few tens to a few hundreds of metres along strike. They commonly average around 400 ppm Sn. The tourmaline layers usually contain the elevated tin levels which are in part due to tin held within the lattice of the associated biotite. These levels, apart from minimal cassiterite, are usually not due to the presence of heavy minerals. The tourmaline itself is also high in tin and base metals.
Muscovite is found within the host rocks on the pegmatite margins. It occurs as flakes from 2 to 4 mm across developed at a high angle to the foliation of the biotite schist. The biotites of the Kamativi Formation carry around 1000 to 2000 ppm Sn. The muscovite in the sequence however only has of the order of 200 ppm. It is believed that the development of muscovite from biotite during pegmatite formation liberated tin which was then concentrated in the pegmatite. To produce the required tin grade in the pegmatites the muscovitisation of the degree observed would need to have been developed over a 300 m interval outwards from the pegmatite (ie. on one side or 150 m on either side). This is of the order of what is observed.
Within particular mineralised pegmatites the grade x thickness product is remarkably constant ie. if a 1 m thick pegmatite with 0.5% Sn thickens to 5 m the grade will be of the order of 0.1% Sn.
The grade x thickness product does show variations locally. If these variations are contoured it is found that they parallel the bedding of the host sequence with high patches corresponding to particular tourmaline rich beds.
Upon crossing from the Kamativi Formation to the low tin background Gn 2 gneiss the tin level within pegmatites usually drops from say 0.4% to <0.1% Sn in less than 30 m. On the basis of a large number of samples the pegmatites overall have a very similar composition to the overall chemistry of the 'intruded' sequence.
Pegmatite thicknesses are quite variable, but in general the larger bodies are greater than 10 m thick while the major bodies are from 20 to 30 m thick over areas of up to 0.5 km2 or more. The margins of individual pegmatites are not usually parallel. The lower margin often has a stepped appearance with sections being flat over intervals of 20 to 30 m, then suddenly steepening to 20 to 30° over a 10 to 15 m length before flattening again. These steps are apparently controlled by small (pre-pegmatite) cross fault structures.
Old fault structures also often control the lateral margins of the pegmatite bodies. One body will terminate near one of these faults or shear zones while another (not a faulted continuation of the same body) will be seen to commence at a different level on the other side.
Each of the different pegmatite bodies in the area has a slightly different character. The following examples were visited:
• Bottom Lode of 'Section 7', which is relatively evenly mineralised throughout. At one point it attains a thickness of 30 m, although 250 m to one side it is only 50 cm thick. In the opposite direction it maintains a thickness in excess of 20 m for 1 km until over an interval of 200 m it pinches out. In the direction perpendicular to this, it also persists for about 1 km with an average thickness also of around 20 m. Over the whole area the grade averages 0.2% Sn.
• Section 4 - The main ‘Section 4’ pegmatite is a large, thick, low grade body, some 2 km across and several tens of metres in thickness. On its rims there are three thin en echelon lensoid developments. These are, or were, of the order of 150 x 200 m in area and 0.5 to 3 m in thickness with grades of up to 0.4% Sn. Although they had a lower grade x thickness product than the main pegmatites because they were thin, the grade was sufficiently high to exploit. A number of thin, steeply dipping, off-shoots branch off the bottom of the large flat lying pegmatite. Some of these are mineable.
• Souchon Lode - This lode branches off the upper side of the Top Lode in ‘Section 7’, which in turn branches off the top of the Bottom Lode. This body has a high spodumene content, usually around 16%. It has a barren upper half with less than 0.1% Sn, while the lower section is usually around 0.25%. It ranges from 2 to 10 m in thickness.
• Chingahari Section - This pegmatite type either has a very good grade, i.e., >0.4% Sn or is very poor having <0.1% Sn. Its margins are very irregular and undulose, often having wave like surfaces with amplitudes of 1 to 2 m and a wavelength of 2 m. Within a stope the thickness can vary from 3 m to 0.5 m in 20 m laterally. It usually has a well developed hanging wall quartz lithium mica selvage around 20 cm thick which carries around 50% of the cassiterite in the pegmatite that is in places as coarse as 2 x 4 cm. Elsewhere the cassiterite in the albitic phase is around 1 mm in diameter.
Mining, Treatment and Testing
Pegmatites were located by vertical BX diamond drilling, which was employed to indicate the presence of mineralised pegmatites whose potential was then assessed by experience and intuition on the basis of the core grade and appearance. The drilling grid employed varies, depending on the nature of the body. The next stage of proving involves underground development. Drives are put into the upper margin of the pegmatite and cross cuts run off at 30 m intervals along that margin. These drives are channel sampled and a grid of vertical GXU diamond holes drilled to the base of the pegmatite on the basis of 1 hole per 20 000 tonnes of ore. From this, accurate reserves and grades are determined.
Mining is mainly by an underground benching method. Ground conditions are good and very little rock bolting is necessary.
Reserves, Resources and Production
Annual mining rate in 1977-78 - ~0.75 Mt @ 0.18 to 0.20% Sn, with a 75% recovery for 1100 t of contained Sn. Lowest grade mined of 0.115% Sn. Recovery varied with grade. For 0.20 and 0.22% Sn head grades, recovery was 78 and 80% respectively.
In 1978, the 'blocked out reserve' was ~80 Mt @ 0.20% Sn. Total estimated 'resources' were of the order of 150 Mt at similar grades.
According to the Zimbabwe Regional Investment Agency website (visited June 2016), at the suspension of operations in 1995,
Ore reserves were - 28.143 Mt @ 0.179% Sn, including 4.435 Mt @ 0.195% Sn amenable to open pit mining.
Mineral resources were - 21.504 Mt @ 0.124% Sn.
Total production over the mine's 58 year life had been 27 Mt @ 0.169% Sn to recover 37 000 t of tin and 3000 t of Ta2O5.
The remaining reserve also apparently contains 6951 t of Ta2O5; 14 398 t of Nb2O5; 19 859 t of WO3; 106 741 t of Spodumene [LiAlSi2O6] and 27 306 t of Beryl [(Be3Al2Si6O18)].
The most recent source geological information used to prepare this summary was dated: 1978.
This description is a summary from published sources, the chief of which are listed below.
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