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Geological report on the Field reconnaissance of Stawes Investments Iron ore Claims in the Nyuni Mountains (Masvingo Greenstone Belt) Report by:-
MineFind Geological Consultancy July 2011
Executive Summary Stawes Investments hereinafter referred to as “the company” is a wholly owned Zimbabwean company that holds 21 Iron ore claims measuring 25 hectares each grouped into three blocks of 125Ha, 125Ha and 275Ha in the Nyuni Mountains of the Masvingo greenstone belt. The company’s vision is to go into full scale exploration of the iron ore claims with planned subsequent mining of the iron ore should the exploration programme result in the delineation and quantifying of an iron ore reserve. The claims are located in one of the most exciting locations in terms of iron ore potential. Stawes Investments is thus positioning itself into becoming one of the major players in the iron and steel industry should their exploration programme be successful in the event that a suitable investor has been found to partner the company in this very promising project. The company has tasked MineFind geological Consultancy hereinafter referred to as “the consultant” to carry out a reconnaissance geological survey. Introduction Iron ore in Zimbabwe is largely found in Archean and Proterozoic belts largely known as greenstone belts except for occurrences such as Dorowa and Gungwa in Rushinga. Stawes Investments holds an area of approximately 525 hectares divided into 21 claims measuring about 25 hectares each in the Masvingo greenstone belt. The claims cover part of the Nyuni Mountains which lie about 40km northeast of the city of Masvingo in South central Zimbabwe. Iron ore occurrence has been known in the area for a long time and Rio Tinto Mineral Search of Africa Limited in June 1958 carried out a short investigation of the iron ore occurrence (Wilson, 1964). A haematitic orebody is known to occur on one of the ridges striking east to west about 250m above the surrounding plain within the banded iron formations (BIF). This orebody belongs to Steelmakers (Pvt) Ltd, a Kwekwe based iron and Steel manufacturing company and is pegged as part of their claims. The company’s claims surround the Steelmakers claims on the northwestern, western and southern sides (Fig. 2) covering part of the peak of Nyuni Mountain, areas which are covered by banded ironstone.
Stawes Investments intends to know the iron ore potential of the banded iron formations (BIF) that lie within their claims and to evaluate the quantities of iron ore that could be held within their claims. This reconnaissance report was produced following 5 days of reconnaissance work undertaken by MineFind Consultancy geologists. The reconnaissance work involved geological mapping of the area as well as chip sampling of outcrops for analytical work to determine the iron contents of the banded iron formation. Access and Infrastructure The claims are located about 40km northeast of Masvingo adjacent to Lake Mutirikwi on its Northeastern shoreline. Access to the claims is by driving for about 35km along the Masvingo-Mutare highway past the Mutirikwi River bridge. A dust road leading to Zano communal area is followed for about 6km to the Steelmakers mine, from where the claims can be accessed by foot. The area is served by 11kv power line going to the Steelmakers mine, telephone lines and water is a short distance from Lake Mutirikwi which has not been known to run dry in history
Fig. 1 Geological map of Zimbabwe showing the approximate location of the claims within the Masvingo greenstone belt. Regional Geology Stawes Investments claims lie in the Precambrian Masvingo greenstone belt. The greenstone belt comprises of rocks that range from the Sebakwian, through the Bulawayan to the Shamvaian system of rocks. The oldest rocks in the region of the claims area are the undifferentiated greenstones of the Upper Bulawayan system which lie southeast of the Nyuni Mountain range separated with both the younger phyllites to the North and the granite to the south by unconformity.
Approximate location of Stawes Inv. claims
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Fig. 2 Regional geological map of the claims showing the banded iron formation (BIF) in brown. Stawes claims are shown in red. Adapted from Wilson 1964. Geological survey Bulletin No. 58. The crests and ridges of most of the mountains within the Nyuni range are made up of ironstone while the slopes and surrounding plains are largely phyllites and pelitic schist. The banded iron formations which belong to the Upper Shamvaian series of the greenstone belt are among the oldest rocks in comparison to the phyllites, pelitic schists and granites. In the Northwest approximately 6km from the Nyuni trigonometrical beacon is Nenga fault which runs northeast. Immediately to the north of the Nenga fault lies a section covered by felsites and rhyolites which are separated by the fault from the southern occurring phyllites.
The south of the area is largely covered by granitic intrusions which are shown in pink in (Fig. 2). A small granitic intrusion approximately 3km in length by 2km lies northeast of the range. The rocks in the claims area have suffered extensive folding both on a large and very small scale which is very evident in the banded ironstones. The banding in the BIF ranges in thickness from as little as 1mm to as wide as 8mm in places. In the ridge which hosts the Steelmakers mine, there has been a near complete replacement of silica by iron oxide forming an elliptical haematite orebody which averages 61% Fe (total). The orebody has been known to contain lenses of phyllite and talc schist especially at the ends. Local Geology and mapping work An area of approximately 600 hectares (6km2) was mapped around the claims over a 4 day period. This area includes the Steelmakers claims which shall however not be discussed in this report in detail as it is out of the company’s claims. The mapping was done with traverses running across the general strike of the banded iron formation and spaced 1km apart. The mapping work included walking across the strike of the rocks, identification of visible rock outcrops, position marking using GPS as well as structural mapping using compass. The geology of the claims is fairly complex for an area of such magnitude. The banded iron formation in most cases forms the crests of ridges and the peaks of mountains. It ranges in hand specimen from ferruginous quartzite (Fig. 3) which can be hardly called BIF through to high iron content rocks that even lack the “banding” but are almost entirely pure iron ore. The quartzite sometimes shows surface enrichment of iron but upon breaking shows very little amounts of iron. In some cases the bands are quite clear and the thickness of the individual bands range from 1mm to 8mm with the iron rich bands standing out on weathered faces while the paler siliceous bands tend to weather out more. In the areas around the Steelmakers mine, some sections of the BIF show appreciable amounts of limonite.Fig. 3 Geological map of the company’s claims area. Note :- Topography is omitted.
Fig. 3 Ferruginous quartzite with low iron content. The large piece above which hammer is placed is quartzite that shows surface enrichment of iron. The country rock on the other hand ranges from quartzite to phyllite with some places even having talc schist. In the hills next to Glen livet hotel, the country rock is largely quartzite. The phyllite which forms most of the country rock as one progresses east is graphitic in many places. The area is heavily folded with the two major belts of BIF in the claims being two limbs of an anticline (Wilson, 1964) that has its limbs steeply dipping southeast. Some tight folding is apparent (Fig. 4) in most of the BIF especially at the summits of most of the mountains.
Fig. 4 Tightly folded banded iron formation on the summit of the mountain north of Glen livet hotel. Chip sampling work and analytical results A total of 16 rock chip samples were collected from the banded iron formation outcrops which showed high iron content in hand specimen for further analysis during the mapping exercise. Some of the samples were taken off the traverse lines in order to concentrate on areas that showed high iron potential. The samples were bagged and labeled accordingly with the GPS coordinates of their locations logged. The samples were analysed by the consultant and the results are shown in Table 1.
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Table 1. Analytical results of the samples collected in the Stawes claims area. Sample No. Easting Northing Fe (%) Loss on Ignition Magnetite (%) Phosphorous (%)
Not tested Fe too low
Not tested Fe too low
Not tested Fe too low
Not tested Fe too low
Not tested Fe too low
Not tested Fe too low
Not tested Fe too low
The mapping work delineated 2 high grade orebodies with the first one estimated to be about 360m long and 80m wide. The sampling results confirmed the results of the mapping work with a high grade iron orebody being delineated with an average iron content of 66.7% Fe. (This is the first time that this particular orebody has been discovered as far as MineFind Consultancy understands). A second and larger orebody was delineated nearby and its dimensions are about 800m long and 120m to 150m wide with an average of 61%Fe. The BIF to the west of the delineated high grade orebodies is enriched BIF which has not been analysed but has the potential in hand specimen of giving iron content as high as 45%-60% Fe. One small area slightly out of Stawes claims to the extreme southeast also showed some high grade results averaging 61.3% Fe and 0.09% phosphorous. Discussion
The Stawes Investments claims are covered by huge tracts of banded iron formation and the 4 day reconnaissance work was done on a very large scale with traverses spaced not less than 1km. This regional scale of work showed some interesting
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prospects in terms of iron ore given that two high grade orebodies could be delineated within such a short amount of time.
Fig. 5 The delineated orebodies in Stawes claims shown in blue. Note the extent of BIF outside the claims.
The BIF in the claims has been learnt to be of variable iron content with some of it being replacement type BIF where the silica was partially or completely replaced by iron while in some places it is enriched BIF with appreciable amounts of iron ore. The topography of the area is very rough which limited the scope of work that could be done given the time constraints. However the claims show huge potential given that the short amount of work led to partial delineation two high grade orebodies that sit on the East-West striking limb of the Nyuni mountain anticline. The general strike of the BIF outcrops within the orebody is 2500 with a general dip of 600. The surface area covered by the first orebody is estimated at 32 000m2 and a depth of 40m estimated as the orebody sits of partly eroded slopes and occurs over an altitude difference of more than 60m. Given
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these two estimates, the orebody could contain in excess of 4million tonnes of high grade iron ore with more than 65%. (It should be noted that these figures are estimates based on surface mapping and six rock chip samples and should not be considered accurate as no sub-surface and bulk sampling work was done). The area covered by the second orebody is estimated around 97 000m2 and a conservative depth of 30m is assumed working with the altitudes over which the orebody if exposed. This second orebody has the potential to contain in excess of 10million tonnes grading 60-61%. The total surface area of the company’s claims covered by banded iron formation is estimated at over 128 hectares, a substantially huge area. The area from which samples 1, 10 and 11 came from also deserves special note although it lies slightly out of the company’s claims. The “discovery” of some potential orebodies within the claims given the small amount of work done there suggests that the claims may hold more than the now known orebodies. The area is relatively huge considering the punishing terrain and as such there is still potential that the consultant might have missed other ore bodies within the area owing to time limits. The surface area covered by BIF in the Nyuni range is above 4 700 000m2 with the average crests and ridges rising more than 300m from the surrounding plains. This figure gives an estimated 1.4billion cubic metre of BIF, with variable amounts of iron ore. Most of the BIF in the range is enriched BIF which according to the consultant has some appreciable potential to hold huge iron ore resources. The area immediately west of the delineated orebodies has enriched BIF resources that span more than a kilometer long and 300m wide with average height of more than 300m against the surrounding plains. The BIF has a sub-vertical to vertical dip and is part of a series of anticlines and synclines which define the whole range. This area was not sampled but in hand specimen the BIF showed decent amounts of iron ore which were estimated to have the potential to give up to 50% Fe should they be analysed. This area alone to the west could have could have iron resources that could run beyond 100million tonnes. (These figures are estimates based on field observations assuming that the BIF extends the entire depth of the range.). Taking the Recommendations Following the short amount of work done in the Stawes Investment claims which yielded positive results and led to the partial delineation of relatively large orebodies within the claims, it is recommended that:-
1) Follow up work be done in the area where the orebodies have been delineated to properly map their boundaries as well as do systematic sampling over the entire orebodies.
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2) A detailed geological mapping exercise be carried out of the entire claims area and slightly beyond in order to fully understand the geology and structural geology of the area as well as delineate any areas of high iron content (orebodies).
3) A Systematic grid sampling programme be undertaken, starting with rock chip sampling followed by pitting and trenching to obtain bulk samples for further analysis.
4) Following the results of the above procedures, a drilling exercise be undertaken employing Reverse Circulation (RC) drilling to determine the behavior of the orebodies as well as to measure and quantify the iron content and grades of the orebodies.
5) Further land be acquired by Stawes adjacent to the current claims to increase the area into which exploration can be done as the range holds very high potential.
Conclusion Stawes Investments holds claims that have been shown to have iron ore. An orebodies of approximately 32 000m2 and 97 000m2 were discovered within the claims and the potential for discovery of other orebodies in the areas that could not be covered owing to time constraints. The claims still hold huge potential to and they require a decent amount of work to evaluate the true value of the resources locked in the range. Much of the enriched BIF that has been spoken of can be improved in terms of Fe content by onsite beneficiation which can increase the resource content. The areas that lie adjacent to Stawes investments claims also hold a lot of potential and it is recommended that should a suitable investor be found by Stawes, then the areas around can be bought off and thereby increase the resource base. References Wilson J. F (1964). The Geology of the Country around Fort Victoria (Masvingo). Southern Rhodesia (Zimbabwe) Geological Survey Bulletin No. 58