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Mining 101
MINING INTRODUCTION
Posted on March 1, 2014 by Wyatt Yeager
9.1 PRIMITIVE EXTRACTION by Vitor Pacheco
I include under mining all human activities concerned with the extraction of inert natural materials. As such, the use of stone for construction, is mining. At the beginning, perhaps the easiest was the excavation in relatively soft sandstones, to enlarge the original caves where the people dwelt (fig. 89). Also, rock blocks shaped by natural jointing were used originally possibly only for religious purposes (fig. 163B), but later they started building wall protections and houses by “dry packing” carefully selected well shaped blocks.
Figure 163B – Stonehenge, one of the earliest human utilisation of stone.
As technology progressed people realized that they could improve on the natural jointing by using very simple chisels for digging grooves along predetermined lines, in order to create an artificial joint through which the rock would fracture, as shown in figure 164.
This granite block is located within the Moorish castle at Sintra (Fig. 165), which was built not very much earlier than 1100 AD.
Figure 165 – Wall of the Moorish castle where the block is located (Sintra, Portugal).
Another, interesting example, is the extraction of rock salt in a deposit near Rio Maior, in Portugal. Its extraction method is quite unique. The deposit is located in a rather large but enclosed aquifer within a limestone succession containing a salt diapir. The water of this aquifer dilutes the rock salt, reaching a concentration seven times larger than the one of the Atlantic at the coast approximately 30km W of this deposit. Thus, instead of having to mine the rock salt underground, the saturated water is simply drawn from a well (fig. 166)
Figure 166 – Well into waterlogged rock salt deposit (Rio Maior, Portugal)
and the much cleaner salt is collected from the salt pans around it (fig. 166A). Supposedly, the extraction of this salt was initiated in 1177.
Figure 166A – Salt pans for recovering the dissolved rock salt (Rio Maior, Portugal).
Finally, laterite occurs in regions with high precipitation. India is a great example, with their well known monsoons. There, I saw laterite being mined (item 6.6.3, fig. 124) by cutting it in blocks (fig. 167) for the construction of houses. These blocks are rather large, about 0.5 x 0.2 x 0.1 metres but apparently they are not too heavy, so they can be handled reasonably easily. Also, I was told that no cementing material is needed since, with time and the local enormous rain fall, the iron in the laterite is mobilized and the blocks seal themselves.
Figure 167 – Laterite construction blocks (Orissa, India).
9.2 SIMPLE EXTRACTION
With the present technology, inert materials can be extracted in many sophisticated ways. Here I just refer to some which have been extracted since time immemorial and even today are extracted in a relatively simple manner. River sand dredging (fig. 168) is one of them. This job that in the old days was done entirely manually is now done in a totally mechanized procedure.
Figure 168 – Sand dredging (Douro River, Portugal).
Note that this sand is not extracted to permit navigation, but rather for construction. A consequence of this huge and continuous suction of sand, is the rejuvenation of the river, thus increasing enormously its erosional power, with disastrous consequences on the river bed, bridges across, etc. To me this is a very short sighted approach because sand of the same quality can be obtained by minor additional processing of the fines that develop at stone crushers, which otherwise have to be discarded as waste and occupy unnecessary space requiring additional costs for the final rehabilitation.
Going now for alluvial mining, this was done in the good old days by panning but now, even though done more mechanically, it can still be considered a one man operation, with very few helpers. The example I show, is for diamonds along the Orange River, in South Africa (item 6.4.1, fig. 99). Figure 169, shows a rather simple but effective mechanical method of grading the clasts,
Figure 169 – Mechanical grading of the river gravel (Ulco Area, Orange River, South Africa).
and figure 170 shows the owner of the enterprise doing the final sorting. It was impressive how fast his hand moved and I do not think many diamonds were missed.
Figure 170 – Final hand sorting for diamonds (Ulco Area, Orange River, South Africa).
Now for another one man operation, we go to a gold rich quartz vein operation in Zimbabwe. In fact, in this case it was a partnership of two persons. Here we do not need a grader but rather a crushing unit, stamping mill (figure 171),
Figure 171 – One man gold mine operation, ore stamping mill (Bulawayo region, Zimbabwe).
which is also rather simple and very effective. Figure 172, shows a vibrating table which sorts the heavy material. Note the pale, rather thick streak of material at the top of the table. Unfortunately this streak is not just gold but rather predominately pyrite with minor gold specks. For the final separation they were still using mercury which makes an amalgam with the gold, and then the mercury is “boiled out”.
Figure 172 – Vibrating table (Bulawayo region, Zimbabwe)
9.3 OPEN CAST
As the name indicates, open cast means mining on the surface. Of these, the simplest are the extraction of stone for construction and since there is construction everywhere, stone quarries also exist everywhere. Here I only want to show not so much the importance of the health regulations but rather, their implementation. Figure 173 shows an entirely dustless loading operation in a granite quarry in South Africa,
Figure 173 – Dustless dump loading operation in a quarry (Halfwayhouse, South Africa).
and figure 174 shows a limestone quarry in Portugal with so much dust, that one has difficulty in distinguishing the crusher unit on the right hand side. Probably, because Portugal belongs to the EU, its mining laws are actually more strict than those in South Africa but, obviously in Portugal there is no apparent law implementation, because the photo was taken from a moderately important road with considerable traffic of all sorts.
figure 174 – Quarry without any dust prevention (Serra de Janeares, Portugal)
Quarry dust is prevented by continuously spraying the haul roads, the blast heaps, as well as all the crushing units. That is, all the sectors where dust may develop. The only dust observable in a South African quarry is that caused by the blast (fig. 175).
Figure 175 – Blasting in progress (Ulco, South Africa).
For obvious reasons, this regulation is extremely important and, in Portugal, where water is abundant, it is not even expensive to apply. On the other hand this is not so in many parts of South Africa like Ulco, which has a very arid climate and consequently where water is difficult to obtain. Even than however, for sake of the health of the employees, the quarries are maintained dust free.
Going still further, Ulco is not a stone quarry, but rather a cement and lime factory which means, another potential sector of large quantities of dust development. Figure 176 shows the Ulco factory and quarry from the air and practically no dust is noticeable, even though as the surrounding vegetation indicates, the local climate is rather arid.
Figure 176 – Ulco from the air, with the township on the right, the quarry in the middle, and the factory complex on the left (South Africa).
Still to do with construction and ornamental stone we go now to the extraction of marble. The interesting aspect here is that technology has already managed do away with blasting which used to cause a lot of wastage due to cracking of the rock, even under very cautious controlled blasting. The method now use is a wire line impregnated with diamond chips. Figure 177 shows the control unit and careful observation shows two wires, which are the two sides of a closed wire loop. On the other side there is a pulley located in such a fashion that the wire is in continuous contact with the marble to be cut. In other words it is the same principle as a jig saw.
I can not resist to go back to the problem of heritage misusage. The background of figure 177 is completely filled with waste dumps, that is another example of shortsightedness, since nature is a human heritage to be preserved and not to be abused.
Figure 177 – Wire cutter in a marble quarry (Porto Alegre region, Portugal).
9.4 UNDERGROUND
Naturally mining is cheaper at the surface than underground. Hence, mining will only go underground if the desired material can no longer be extracted from the surface, or if that material does not outcrop.
9.4.1 Marble Mining Underground
I visited this quarry or mine, I’m not sure what to call it, in November of 1998. It is apparent that the exploitation is still within day light. In fact it is a case of cutting inwards from a central open pit. Going underground, reduces the need to remove the thick overburden constituted by very weathered and broken marble, thus reducing waste processing. One can have an idea on how close the surface is because the surface weathering is still noticeable on the upper section of the central portion, which is a structural support pillar. Also, it is apparent that the marble is of a very high quality. However, even with all these possible cost advantages, I wonder if the venture is still going. I do not have much faith in it.
Figure 178 – Underground mining of marble (Porto Alegre region, Portugal).
This picture also shows how well the wire cutting (fig 177) system mentioned above, works.
Chrome Mine at Boula, India
The chrome mine at Boula, is a good example of a mine which started at the surface, but due to the space constraints with depth, it had to opt and go underground (fig. 178).
Figure 179 – Boula chrome mine (Orissa, India)
Three chrome rich zones exist in this mine. The richest, originally mined at the pit on the left is named Shankar. To the right within a shallower pit, is the next chrome rich zone, named Laxmi and to the right of that, outside of the picture, there is the third chrome rich zone named Durga. The Shankar section is the deepest portion of the open cast development, at the far end of which, the small little building is the engine house for the hauling of ore along an inclined shaft. On the right within the Laxmi pit we have the more obvious headgear of a vertical shaft. It is via these two shafts that the underground mining is done.
This mine has interesting features that deserve mentioning. Notice at the centre, of picture 179, the flat portion at the higher point separating the Shankar from the Laxmi pits. That is where the ore is sorted (fig. 180)
Figure 180 – Hand ore sorting (Chrome mine, Boula, India)
and piled (fig. 181). Female laborers do the sorting by hand and they are also the ones who, manually and meticulously, pack the the ore on an exactly dimensioned four sided prism. This is a natural consequence of cheap labour. Note that a mechanical ore sorting machine would be far too expensive, making this venture not viable. In the same way, the packed ore does not need to be weighed, saving on the expense of such a machine. The volume is measured by tape and the tonnage is calculated using the predetermined SG of the packed ore.
Figure 181 – Manually packed ore pile (Chrome mine, Boula, India)
Now, the naming of the ore zones; figure 179 is facing S and the picture was taken from a ridge formed by a fault zone with an apparent uplift to the N. On the N side of the fault, that is, behind the photographer, only one ore zone exists which was named Ganga. I find the reasoning behind the naming fascinating. If I understood it correctly, Shankar is a very important god whose wife is Laxmi, and they have a daughter called Durga. In other words, the thickest and best developed ore zone gets the name of an important god, next to it but not as well developed, is his wife and the smallest of the ore zones is the daughter. More, supposedly Ganga is Shankar’s lover. The affair must not be obvious so Ganga is separated by a fault, but she is important and so she is at a higher level than Laxmi and Durga.
9.4.3 Kimberly Diamond Pipe
The Kimberly pipe (fig. 17 ) is the one which started the diamond rush in South Africa and gave the name to the rock that forms it (kimberlite). This is another example of surface mining having to go underground due to lack of space. By 1875, within the 38 acres encompassing the outcrop area of the pipe, there were hundreds of independent miners working in their separate claims as can be observed in figure 181B, showing not only the web made by the numerous cables of the active individual rock hoists, but also the depth at which they were already working.
Figure 181B – The historical Kimberley Pipe in South Africa: A – Photo taken in 1875, showing the existing individual rock hoists (photo obtained in the Kimberley Museum “sold in the aid of the Red Cross”.
The corresponding statistics shown in figure 182, give a rather nice summary.
Figure 182 – Diagrammatic section and statistics of the Kimberley diamond pipe (South Africa).
9.4.4 Witwatersrand Mining
I think this is the best example of the influence of mining on the surface morphology and on the important differences between surface and underground mining. Figure 183 shows Johannesburg from the air, seen from the South. Notice in the background all the large buildings, followed in the mid ground by an area with practically no buildings showing two rather barren ares, one close to the left extremity, which is a remaining waste dump. The one, nearer to the middle and with a considerably larger area is a slimes dam. In front of the slimes dam there is a reasonably sized lake. This central area is where the gold bearing sedimentary horizons of the Witwatersrand Supergroup outcrop. When this picture was taken in 1984, most of that ground still belonged to the mining houses.
Rehabilitation wise, to my knowledge the majority of the material forming the waste dumps, being predominantly very hard quartzite, was reprocessed as gravel. As for the slimes dams, that was a very difficult problem. The gold ore was crushed to a very fine mesh and the gold was removed using cyanide. This means that the slimes dams are constituted by a very fined grained totally sterile material. On windy days, Johannesburg was often covered by a dust of very fine quartz particles. The solution encountered was to cover these large slimes dams with thick layers of fertile soil and vegetate them as quickly as possible.
Figure 183 – Johannesburg from the air (South Africa).
These gold bearing sediments dip southwards at about 25º and the mining started going underground by about where the lake is. In other words, the houses in the foreground of the picture were built over ground that was mined pretty close to the surface. That is why, by municipal law, no houses of more than one floor were allowed on that sector.
Nowadays all the Witwatersrand gold mines are underground and their head gears are characteristic of the region (fig. 184).
Figure 184 – Winklehaak Gold Mine no 1 shaft and reduction works, Evander, SA
The haulage levels are approximately 30 vertical metres apart and the staff as well as the materials are transported by very fast lifts with stations at every level (fig. 185).
Figure 185 – Underground lift station, East Driefontein Gold Mine (Carletonville South Africa).
All the development of the haulages used to be done by drilling and blasting (fig. 186),
Figure 186- Underground drilling team (East Driefontein Gold Mine, Carletonville South Africa).
but by the time I left, 1975, boring machines were staring to be used in main haulages and raises (fig. 187).
Figure 187 – Raise borer hole (East Driefontein Gold Mine, Carletonville South Africa).
Stopes are the section of the mine from where the ore is extracted. Since we are dealing with a sedimentary horizon, mine-wise speaking, it has a limited thickness but an unlimited length and width. Thus wherever the grade is economical that layer of the rock sequence is entirely removed. Figure 188 shows a stope face with the ore exposed.
Figure 188 – Stope face (East Driefontein Gold Mine, Carletonville South Africa).
To use rock pillars, is to reduce the amount of extractable ore. Thus they used wood log mats (fig. 189). The picture shows two pillars already in place and in the middle a loose pile of mats.
Figure 189 – Sotpe pillar support (East Driefontein Gold Mine, Carletonville South Africa).
Finally, observation of my assistant, Zé (fig. 188), shows how hot it is in those mines. This picture was taken at about 1800m below surface and the rock temperature was close to 50ºC. Work is only possible because refrigeration is used in the ventilation.
Wyatt Yeager - wyattyeager@gmail.com
Diamond Prospecting
PROSPECTING
Posted on March 1, 2014 by Wyatt Yeager
8.1 GRASS ROOTS by Vitor Pacheco
Grass roots exploration is the general term for the very initial stage of prospecting that starts from a zero base, that is, neither geological maps, nor aerial photos are available, and often not even topographic maps. Of these, my first experience was in Mozambique in 1972, when communication with the outside world was a very precarious land line and some times, when we were lucky, a fax, both by means of the post office at the nearest village, which was about 150 km away.
I do not think it appropriate here, to go into the prospecting work itself which consists of mapping, sampling, drilling, data synthesizing and interpretation. However, under advanced prospecting I will show some photos referring to sampling which, I think, takes most of the geological time.
8.1.1 Transport
In areas of grass roots exploration, most of the times even the main roads are simple tracks across the veld. Hence a tough reliable 4 wheel drive vehicle is fundamental as this example, still in Mozambique and which was my baptism of bundu bashing, indicates.Figure 143 shows the end of my successful attempt of taking my lovely car out of a river side mud bog. I was alone, and it took me 4 hours to get it out.
Figure 143 – Bogged down in deep Africa (Porto Amélia District, Mozambique).
Just for comparison purposes I also show the same kind of experience, but in Portugal in 1996 (fig. 144). This time it was easy, we only had to call the farmer to bring his tractor and pull us out. So, not only was this in a different continent, but also 24 years later.
Figure 144 – Bogged down in paradise (Alentejo, Portugal).
What I want to make clear is that if I had the fancy comfortable white car in Africa, even today, it would take me perhaps weeks to get it out, if at all. This because today’s sophisticated jeeps have so many complicated electronic gismos that one needs to have a highly qualified, not just mechanic, but a well equipped garage within easy reach.
Unfortunately I’m considered too old by the powers that be, to continue prospecting. One thing is for sure though, if I did go, the jeep I would choose is the Indian manufactured Mahindra (fig. 145). It is incredibly robust and has a totally old fashioned simple, reliable engine that will go anywhere and the only assistance it needs is regular greasing and any simple mechanic assistant to deal with minor difficulties.
Just as an interesting memory of the stay in India, notice the jeep’s front decorations with the string of flowers and the painted swastikas. This is a must to make sure the car is accepted by the gods.
Figure 145 – One of our local 4-wheel drive vehicles (Orissa, India).
8.1.2 Accommodations
Even in many remote parts of Africa it is often possible to organise a side farm building or similar locations to use as living and working quarters. When that is not possible, as in my stay in Angola, one has to organize camping facilities which must have a minimum of practicality and comfort. My full staff (fig. 146) consisted of one local geologist, one local person of the correct tribe and political affiliations, one overall organizer, two security guards (hence the guns), one cook with an assistant and two laborers. I was fortunate to find a very reliable and professional person, Vete Willy, who not only built our camp but also kept it going, always in impeccable conditions. He is not in the picture because, other than me, he was the only one capable of using the camera.
Figure 146 – My Angolan prospecting staff and me in the vicinity of our camp at Bentiaba.
I was working for a medium sized mining company but, not so far away, there was the camp of a very large mining group, who also had to organize a camp and whose chief geologist I became acquainted with. Since I have pictures of both camps it is interesting to put them side by side. The dimension difference is impressive. Two of my whole camps (fig. 147)
Figure 147 – The entrance to my prospecting camp (Bentiaba, Angola).
would fit within the entrance area of the other camp (fig. 148). Or putting it another way, when there are funds, much more can be done in a much shorter period, and in much more efficient working conditions.
Figure 148 – Large mining group entrance to their camping site and chief geologist’s caravan (Caama region, Angola)
The fleet difference is also striking. Figure 149 shows my two cars,
Figure 149 – My camp, and whole vehicle fleet, my tent and the office (Bentiaba, Angola).
and figure 150 shows part of the, let us call opposition, fleet. Also shown in my camp is my tent in the foreground and the office tent in the middle ground. Naturally this little office was strictly for rough work. We did have a comfortable house and office at the nearest town.
Figure 150 – Partial vehicle fleet of the opposition (Caama region, Angola).
Going now to the eating facilities, the comparison continues to be striking. Not only is there a great difference in space, but also the accommodation and the furniture. My little dining hut (fig. 151) was built with the minimum of the essentials.
Figure 151 – The dining room of my camp (Bentiaba, Angola).
The other one even had a TV, with its dish aerial at the left edge of figure 152 . One must be fair though, I did have a satellite phone and it worked pretty well. It was not as bad as in Mozambique but, after all, I was in Angola in 1997/8, that is, 26 years later.
Figure 152 – The dining facilities of the opposition (Caama region, Angola).
Finally, the ablution facilities. Our toilet (fig. 153) was the long drop method and to reduce unpleasant smells it was sufficiently far away, outside the camp area and on the correct side of the prevaling winds.
Figure 153 – My camp’s toilet facilities (Bentiaba, Angola).
Notice that the opposition even had a water pump so that one could have a nice cleansing shower at the end of the day (fig. 154). In my case, to wash we had to go to the nearby river and use the remaining water pools during the dry season. I will never forget though, the most enjoyable showers I had. During the rainy season it practically rained every day, and often late in the afternoon, that is, at the correct time to clean all the work day dirt and sweat. I would undress in my tent, come out with the soap and use the rain as a shower. It was divinely refreshing and it lasted long enough for me to complete the job. It is definitely a lovely memory.
Figure 154 – The oppositions ablutions area (Caama region, Angola).
8.2 ADVANCED PROSPECTING
After basic geological mapping, trenching is often used, especially over areas with poor or no outcrop. Additional geological mapping is done along them and, when applicable, tentative initial trench sampling will also be considered (fig. 155).
Figure 155 – Trenching along very weathered strata (Trás-os-Montes, Portugal)
Nowadays, after detailed mapping as well as soil, trench and rock outcrop sampling, if the indications are positive a drilling programme will be planned. In the old days short underground adits into the hill sides would be cut or, in flatter areas they would sink small shafts from which adits would be cut, generally along strike. Since geologists are eternal optimists, it is very frequent to encounter such old mine workings in many present day prospecting sites. The assumption is always that whoever was there before did not look well enough, or most likely, the price of the metal concerned was not high enough to make the venture viable at that stage. Obviously, these old workings are always very closely scrutinized since they will add valuable data at practically no additional cost (fig 156).
Figure 156 – Preparing to go down a prospecting shaft (Alentejo, Portugal).
Returning to the rock outcrop sampling, it is most advantageous where the outcrop is good and very continuos, since it is much cheaper than drilling. In the old days the sampling was done by chipping the rock with a chisel and hammer but now there are diamond circular saws that do not need water to cool and make the exercise much simpler and faster, although a bit dusty and hence the masks in figure 157.
Figure 157 – Sampling team at work (Boula, India).
Figure 158 shows the sample groove and respective number.
Figure 158 – Sample groove and respective number (Boula, India).
So, all is well and a drilling programme is planned and budgeted. It is now fundamental to prepare a yard to store the drilling core and also a sample preparation laboratory where the samples can be cut crushed quartered, a portion sent to an assaying laboratory and the remainder kept for potential future use (fig. 159). Naturally this sample laboratory must have all the necessary equipment to prevent contamination. For the more basic prospecting facilities the core is simply split and half is sent away.
Figure 159 – Initial stage of preparation of future core shed, left, and sample preparation lab, right (Boula, India).
Returning to the core yard, for an effective and thorough study of the diamond drill core, especially in new areas, not only must each hole be meticulously geologically logged, but perhaps even more important, the core of as many of the holes available as possible must be laid side by side, to assist in the correlation of all the existing stratigraphic features, in order to develop a local and/or regional succession. Hence, the larger the yard, the easier it is. Figure 160 is the core yard where I was fortunate enough, at a very early period of my career, to be present during the early stages of the drilling programme in the Bush Veld Igneous Complex and assist a senior colleague. His very good stratigraphic experience permitted the identification of all the individual stratigraphic units immediately above and below the Marensky Reef (item 2.3 Magmatic Differentiation), so necessary for a successful final synthesis.
Figure 160 – Very well planned Core shed and yard (Springs, South Africa).
Prospecting is not done only to find new ore resources but, just as important, it is necessary when, for example, in an already working mine, there is the possibility of exploiting an additional metal which was previously considered waste. In that case, the waste dumps of the original extraction, must be reevaluated to ascertain if it contains enough of the second metal to be re-qualified as ore. This is what happened at the chrome mines at Boula in India, where platinum was though to have sufficient grade to be exploited as well (fig. 161).
The little markers seen all over the chromite waste dump, actually form a well delineated sampling grid. It is possible that the sampling method selected, which only used chips cut from every piece of rock within the delineated square might be misleading, but that is how it was done. Also, prospecting within a working mine must continue throughout its life time to maintain a detailed advanced knowledge of the location and grade of the ore ahead of the working faces.
Figure 161 – Chrome mine waste dump sampled for platinum (white tags on little metal rods) (Boula, India).
Finally an important point about the reliability of sampling. Even though the two following figures are actually mine stope sampling for grade control, it is important to make it absolutely clear that sampling must strictly adhere to a specified grid. The yellow lines are actually the markings of each sample. When I left the gold mines the hammer and chisel chipping method was still being used. Careful examination of figure 162 shows very nice looking buckshot pyrite just to the left of the sampling line, which means good gold values, but no buckshot at the actual sampling location. If the sampling position is moved to include the buckshot, we are no longer dealing with a sample but rather with a bias grab specimen.
Figure 162 – Underground single sampling for gold in the Witwatersrand, South Africa.
In figure 163 we are dealing with an ore horizon consisting of various conglomerate bands separated by quartzite, termed internal waste because, as it should be expected, it never carried any gold. In the present case, for a detailed study and considering the abrupt changes in thickness of the conglomerates the sampling zone consists of four adjoining sections.
Figure 163 – Underground detailed sampling for gold in the Witwatersrand Mines, South Africa
Wyatt Yeager – wyattyeager@gmail.com
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