GOLD - Barberton Exploration Project
Tsodilo Resources Ltd (the 'Company') holds a 70% interest in its South African subsidiary Idada Trading 361 (Pty) Ltd. ("Idada"). The remaining 30% is held by Idada's Black Economic Empowerment (BEE) partner Identity Resources (Pty) Ltd.
In May of 2015, Idada was granted Prospecting Right MP30/5/1/1/3/2/10471PR subject to certain subsequent conditions being met. Those conditions were met in the 3rdQuarter of 2015. The PR lies near Barberton in the Mpumalanga Province of South Africa, immediately west of eManzana (Badplaas). The PR occurs some 360 km east of Johannesburg and is near the border with Swaziland (Fig. 1). It is some 9032 hectares (90.3 km2
) in surface area and is underlain by the well-known Barberton Greenstone Belt ("herein BGB") famous for its long history of Gold mining and prospecting.
Barberton is situated in the De Kaal Valley at the southeastern edge of De Kaap Valley pluton and is fringed by the Makhonjwa Mountains (Barberton Mountain Land). The Barberton area has a long and colorful history of gold production producing an estimated 360 tonnes of Au between 1884 and 2012 (Anhaesser, 2012), worth over $13 trillion USD at today's gold prices (2015). However, it is noted that around 70% of this was extracted from four main mines Sheba, New Consort, Fairview and Agnes.
Figure 1. Location of the Companies Prospecting Rights.
The Barberton area and the northwestern part of Swaziland, around Piggs Peak, have been mined for gold for over 130 years, and it seems likely that this will continue for many years to come. However gold deposits in greenstone belts such as the BGB are known to be difficult to find and evaluate as gold is by nature patchy and variable in grade. Therefore, factors such as the price of gold and understanding the geological controls of mineralization will be key factors for continued gold exploration. The company is well placed to take advantage of modern exploration techniques such as more detailed geophysical studies to potentially unlock previously unknown gold prospects.
Big game hunters such as renowned elephant hunter Henry Hartley reported seeing ancient gold diggings in the Tati region of South Africa around 1860's. Webster, (2001 reported famously a story of Henry Hartley; that while Henry was on an elephant hunt with his sons, rather than shooing a troublesome lion with a rifle shoot, which would have scared off the elephants also, Hartley managed to get the lion to leave the hunt vicinity by stalking behind the lion then jumping up making a loud roaring noise whilst shaking his large beard.
Henry Hartley took German exploration geologist and cartographer Carl Mauch to see the Tati ancient gold workings in 1867. Mauch returned in 1868 and confirmed these ancient gold diggings to the Transvaal Argus as "an enormous gold field". Which were then somewhat over billed by newspapers in Europe as "rediscovering King Solomons Mines" (Anhaeusser, 2012; Webster, 2001). This and further gold discoveries that same year in the Olifants River area, well to the north of the Barberton area, are credited with the onset of the first South African gold rush.
In 1873, gold was discovered approximately 100km north-north-west of Barberton in the Pilgrims Rest area in the alluvials as well as in Transvaal Supergroup rocks (stratiform gold-quartz-carbonate sulphide veins in dolomite). Following this 35 km north-west of Barberton in 1882, gold was discovered in the Black Reef Quartzite Formation near Kaapsehoop. Then in that same year gold was discovered below the escarpment in the Noordkaap River Valley. But due to the unfavorable health conditions (malaria and sleeping sickness) in the valley several prospectors moved to higher ground and found alluvial gold in 1883 in Concession Creek. This led to the discovery of the Pioneer Reef just south-west of what became Barberton - the first payable reef gold in the mountain land. This discovery opened the flood gates and the Barberton area became a true gold rush location with the Barberton Town itself being founded in 1884 (Fig 2).
With now many Gold prospectors roaming the hills around the town many new discoveries were soon made. There was a colorful early history to the discovery of the gold discoveries in the Archean volcano-sedimentary succession of the BGB, which straddles South Africa and Swaziland. Over 350 gold workings or prospects were eventually recorded. Of these 44 became mines with each producing more than 311kg (10,000 oz) of gold. However, over 70% of the total gold produced in the Barberton area came from four main producers -- Sheba (Fig 3), Fairview, New Consort, and Agnes mines, with grades of 7 to 14 g/t and in some places as high as 30 g/t. The total production of the Barberton Goldfield since inception to 2012 is estimated to have been 360 t (12,698,626 Oz).
For more details and a comprehensive historical account of the Barberton discoveries see Anhaeusser (2012), and Ward and Wilson (1998).
Figure 2. A view along Pilgrims Street in the nascent town or Barberton ca. 1885. In the background is the valley of Rimer's creek in which gold was discovered by James Rimer and the brothers Fred and Harry Barber and their cousin Graham, after whom the town was named. Sourced from Anhaesser 2012.
Figure 3. A view looking east down Sheba Creek showing some of the mining activity associated with the Shea Gold Mining Company and other properties in the area from around 1890. For reference the Golden Quarry is on the hill slope on the top left of the photograph. Sourced from Anhaesser 2012.
Gold has been the focus of most activity and exploration in the Barberton region; however other historical mineral discoveries in the area contribute to the BGB being regarded as a favorable mineral exploration region. These other minerals discoveries include significant chrysotile asbestos, iron ore, magnesite, talc and barite deposits.
Gold mining continues around Barberton at present day encapsulating a period of over 130 years of uninterrupted gold mining. There are still new discoveries being made today as well as re-evaluating historical deposits and their tailings as techniques of mining and extraction improve, hence increasing the life of mines and re-starting older ones. These developments as well as recent discoveries such as nickel-sulfide mineralization close to the Scotia Talc mine at Bon Accord suggest that mining activities in the Barberton are set to continue well into the foreseeable future.
Geologically, the BGB in the Makhonjwa Mountains of South Africa and Swaziland has probably received more attention than any other region in South Africa. The BGB is an exceptional example of mid-Archean (3.2-3.6 Billion years old) supracrustal rock sequences (terrane) in which virtually all aspects of the early earth evolution have been studied (de Wit, 2011). The Onverwacht Suite represent the early Earth in Archean times comprising predominantly volcanic rocks and intrusions formed between 3.5 -- 3.3 Ga (Fumes et al., 2014). Similar rocks but slightly older include the Isua Greenstone Belt (3.8 -- 3.7 Ga) in Greenland (Nutman et al., 2007), the Nuvvuagittuq Greenstone Belt (4.3 to 3.7 Ga) in Quebec Canada (Cates and Mojzsis, 2007; O'Neil et al., 2012) although the older dates still remain controversial and disputed (Cates et al., 2013), and the Acasta Gneiss in the Northwest Territories Canada that have reportedly a metamorphic age of around 4.0 Ga (Bowing and Williams, 1999). However, the Barberton rocks are the best preserved rocks of this type and are therefore represent the most interesting for research into the Earths earliest history (de Wit, 1992, 2011). Which is why the International Continental Scientific Drilling Program (ICDP) in 2011 drilled 5 holes to a combined total core length of 2,874.3 meters into the rocks in the Barberton Greenstone Belt for their project called "Barberton Drilling Project: Peering into the Cradle of Life (BARB)", to collect samples which would help the research teams studies into the earliest environments of life formation on Earth (reference - http://barberton.icdp-online.org
The BGB is located on the Kapvaal Craton of Southern Africa and is made up of a sequence of volcanic and sedimentary rocks which are surrounded by granitoid plutons, and it is the type locality for the volcanic extrusive ultra-mafic rock known as komatiite. Komatiites were first recognized by Viljoen & Viljoen (1969) in the Barberton greenstone belt, South Africa. The features that marked these rocks out as distinctive was their high Mg content but also their large, skeletal, platy, bladed or acicular grains of olivine, which Viljoen & Viljoen (1969) called 'crystalline quench texture' and later referred to as 'spinifex textures'. It is believed that the BGB is an ancient island arc system made up of mafic to ultra-mafic volcanic, sedimentary, and shallow intrusive rocks. The deeper level granitoid plutonic unit's dome up under the BGB sequence and give the belt a sequence of anticlines and synclines.
The BGB is divided into the following three main lithostratigraphic units:
- At the base is the oldest Onverwacht Group, made up dominantly of mafic and ultra-mafic volcanics including komatiites and is around 10km thick.
- Next is the Fig Tree Group and defines a transition between interlayered volcanic derived sedimentary materials and land derived sedimentary sequences.
- Above this is the Moodies Group which is a combination of sandstone and conglomerates originating from the erosion of the underlying units and uplifted plutonic rocks.
As mentioned above the structure of the BGB is dominated by a series of anticlines and synclines that plunge to the core of the belt. The gold mineralization in the BGB are mainly linked to structural influences that have been repeatedly activated in the greenstone belt. The episodic stages of heating related to the granitoid emplacement augmented these structural influences, causing greenschist to amphibolite grade metamorphism, but also importantly introduced gold rich fluid migration into the brittle to ductile fractures and shear zones. These were best developed on the north-west flank of the BGB in the deformed sediments of the Fig Tree and Moodies Groups in close proximity to the Sheba, Lily and Barbrook faults (Anhaesseur, 2012), (Figs.4, 5 and 6).
Figure 4. Simplified structural map of the Jamestown and Sheba Hills area of the BGB. The red lines show faults, where the most important regional faults are labeled. The black lines show the structural fabric of the lithology including regional anticlines and synclines. The three main gold producing mines (Sheba, Fairview and New Consort are also shown for reference. It is noted that more than 80% of the gold produced in the Barberton Mountains has come from deposits in this region. Taken from Anhaesseur (2012).
Figure 5. Geological map of the BGB taken from Anhaesseur (2012) highlighting the major lithologies and faults. The circles show the locations of gold mines, where most gold mines occur on the northwest flank of the belt, or near contacts with the surrounding granites.
The combination of structural traps due to tectonic events and the introduction of gold-bearing fluids associated with the emplacement of the granitoids around 3.5 to 2.75 Ga were instrumental in the mineralization model. The development of the gold deposits in the BGB are therefore linked spatially and temporal to the major structures within the host sequences and the intrusion of the granitoids.
There are three main ore types within the BGB (Anhaesseur, 2012), these are:
- Unoxidised, complex sulphide ore, which is the main gold ore type seen and from which most of the gold is produced.
- Gold-bearing quartz veins and shears, common throughout the area, and which also contain sulphide minerals.
- Weathered ore occurring in the upper zones and which have been oxidized by near surface processes.
The gold bearing Type 1 unoxidised sulphide mineral complexes is a refractory ore (minerals are stable at high temperatures) and hence this ore was treated with acids to separate the gold from the gangue. Acid dissolution gold yields were historically low, but were improved over time by numerous advances in metallurgical treatment processes, such as roasting. These advances increased the gold recoveries over the years. Notably including a recent advanced ore pre-treatment known as BIOX(r) process, which uses bacterial action to breakdown the sulphide minerals via accelerated oxidation and exposes the gold for more complete leaching.
The geological map shown in figure 6 (de Ronde and de Wit, 1994) is similar to that of figure 5 but highlights the major faults and shear zones (in red), such as the important Saddleback Fault/Inyoka Shear Zone and Moodies Fault, the southwesterly extensions of the Sheba and Barbrook faults (Figs. 4 and 6), and its southwestward continuation in the form of the Inyoni Shear Zone (Fig. 6).
Figure 6. Shows the geology of the BGB and its associated escarpment unconformity. The red lines represent major structural faults and sheer zones which are so important for the development of the gold deposits for which the area is so famous. Map is modified after De Ronde et al. 1994.
A detailed Ariel Magnetic Geophysical survey was carried out by the International Continental Scientific Drilling Program (ICDP) (reference - http://barberton.icdp-online.org
) prior to the commencement of their Barberton Drilling Project in July 2011. This survey was conducted by GyroLAG and used their revolutionary Kriek IIB gyrocopter that allows for stable low speed flying resulting in higher resolution magnetometer readings (Woods, 2012). This helped the ICDP identify hidden structures and faults that were unknown prior to the survey and helped refine the Barberton Drilling Projects drill hole locations away from these structures.
This data was presented at Geosynthesis 2011, an integrated Earth Sciences Conference and Exhibition, held in Cape Town in August 2011. The data was also published in the October 2012 edition of the Popular Mechanics magazine (Woods, 2012). An image showing results of this Arial Magnetic survey is presented in figure 7. The prospecting right which was granted to Idada, covers the central-western part of this survey (Fig. 7).
The ICDP Barberton Drilling Project subsequently drilled 2,874.3m of drill core from 5 diamond drill holes the results of which will help reconstruct the environments where life first emerged and evolved in Archean times some 3.5-3.2 billion years ago.
The importance of structures in relation to the location of gold deposits in the BGB has already been highlighted above. The fact that the data from the Airborne survey has suggested that the Saddleback-lnyoka Shear Zone, also the southwesterly extension of the Barbrook and Sheba faults (Figs 4 and 6), continuous to the northwest rather than turning south has been interpreted by the Company as anomalous and led to the application for ground over this new geological data (Fig. 7). Since many of these structures are intimately related to gold deposits and when the major Saddleback-lnyoka Shear Zone continuous west-north-westwards (Fig. 7, white line) rather than southwards as was previously modeled (Fig. 7, black line), it makes the area covered by the Prospecting Right highly prospective. The GyroLag geophysical survey suggests that the Saddleback-lnyoka Shear Zone system, now striking towards the west-north-west, separates the Nelshoogte Gneiss from the Badplaas Gneiss.
The adjoining Nelshoogte granitoid pluton (Fig. 6) has been dated to be 3,212 ± 1 million years old (Anhaeusser, 2001). This age is within the window of 3,500 and 2,750 million years that is associated with the gold-bearing fluids generated during the emplacement in the area (Anhaeusser, 2012).
Figure 7. The total magnetic intensity map of the GyroLag magnetic survey. The outline of Idada's prospecting right is shown by a thin black. The thick black line is the classical interpretation of the Inyoni Shear Zone being a southerly continuation of the Saddleback-lnyoka Shear Zone system. The new data rather suggests that the Saddleback-lnyoka Shear Zone system continues towards the west-north--west as shown by the thick white line.
The proposed exploration program will be subdivided into four main phases:
- A desktop study of all published and available geological, geochemical and geophysical data will be done and incorporated into the Company's GIS database. This will be used as a basis for Idada's field activities.
- Field mapping of the main rock exposure will be conducted in order to map the area of interest as accurate as possible.
- A detailed geophysical ground magnetic survey will be conducted using the Company's owned and latest Magnetometers to pin point the position of the major shear zone and this will be modeled to position borehole locations for optimum intersection of these structures.
- Finally several diamond holes (NQ) will be drilled to intersect, map and sample the major structures separating the two previously mentioned gneissic terrains.
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