Savana Mining Gold & Diamond Wash Plant For Sale
39 in. dia. x 15′ length
6 x 8 ft. ore feed hopper.
6.6 ft. long scrubber section.
(2) screen sections for dual classification.
Water manifold and internal drum spray bar.
Chain driven by a SEW Gear Motor.
Drum supported by heavy duty caster wheels.
Includes sluice box.
30 to 50 tons per hour.
Portable with dual axles
Includes Two Pan American Mineral Jigs with underflow sluices
Size: 45 In. X 45 In. Duplex.
Max Capacity 30 Tons/Hour.
116 cycles per minute.
2.2kw SEW Gear Drive Motor.
Can be supplied refurbished.
Includes Hy-G Gold Centrifuge Concentrator (see featured Image)
Owners are upgrading to a bigger Savana Mining Equipment plant www.savanamining.com and will consider selling individual pieces and/or leasing. Plant is located in Kono, Sierra Leone. Owner will help with logistics. A great opportunity to buy a proven plant for a fraction of it’s normal cost.
175,000 USD Refurbished
A few minutes into my conversation with Wyatt Yeager and I realized that he could stand with any of these daredevils. Yet, nothing prepared me for the real Wyatt Yeager.
As a Texan and the daughter of a cattle rancher, my family album is peppered with photos of men – and a couple of women – with their arm slung over the dusty saddle of a horse, deep in the wilds of Montana, Wyoming, Alaska, the Amazon, or Mexico. Such exploits ceased to amaze me by the age of five as I had my picture taken virtually every weekend with a 10-foot alligator or a gigantic fish pulled in from the Gulf. A few minutes into my conversation with Wyatt Yeager and I realized that he could stand with any of these daredevils. Yet, nothing prepared me for the real Wyatt Yeager. Far from being a “geologist type,” Yeager is an eclectic breed of tweed and fearless, aptly named after the historic cowboy, Wyatt Earp.
Yeager will be the first to tell you that diamond-mining exploration is nothing like the iconic Indiana Jones depiction of the intrepid gentleman hero, jewel in hand and angry natives at his back, poised on the edge of the precipice between extinction and extravagant wealth. However, a few minutes into our conversation and I’ve uncovered that he’s escaped from riots, been stabbed in Venezuela, bitten by piranhas, and met people who have never seen a white man before.
Nicknamed “The Wolf” by his colleagues, Yeager is an undisputed wunderkind. “In my late teens, I became obsessed with diamond exploration and mining after finding a few small stones in our California alluvial mining operation,” he informed me when asked how he chose such a profession. Arguably, “Diamond Mining 101” is not listed as a college credit course. However, Yeager refers to himself as an “explorationist” – one who, by trade, explores and mines for diamonds in Africa and South America.
Turns out, the small stones he unearthed in California fueled a passion that has yet to diminish. Yeager reveals how his upbringing prepared him for the diamond trade, “I was raised working the Alaskan, Central American, and Californian goldfields with my grandfather and father who were both consulting engineers and mine owners.” With a family that originally came west to the California Gold Rush of 1849 and then later to the diamond fields of South Africa, it would seem that mining is in his blood.
On the subject of his work, Yeager contends, “I consider myself to be a part of the old school colonial exploration crowd.” By this, Yeager means that he differs from the upcoming geology grads who would rather sit behind a computer screen and interpret maps and geologic reports. At 36, Yeager is considered the youngest and one of the last to be doing real “old fashioned” exploration work with a pick and shovel. As he fiddles with his pen, he shares how fortunate he was to grow up in the mining industry, trained by the “old cranky geologists.” You can tell he relishes fieldwork and would consider it a punishment to be tied to a computer.
Those interactions with the old school South African geologists must have made an impression on him. Yeager’s quest for a diamond pipe has led him far from technology and deep into some of the most inhospitable places on Earth-places that even the bravest men might give a wide berth. Even following his travels as a blue dot trail on a map is scary. During his early twenties, Yeager found himself neck deep in the piranha-infested waters of the Venezuela jungle. However, this was more than a short-term reconnaissance. Yeager, who is also an academically trained anthropologist, had a knack for ingratiating himself with the native people, building a hospital and a school in the remote areas he inhabited as he searched for diamonds. More compelling, he seems to have won the loyalty of even the most seasoned of warriors and adventurers as he moved through Venezuela to Africa and beyond, which says more about the man than he will ever say about himself.
Throughout our interview, Yeager is humble. I’ve seen this before in men such as Yeager. They rarely open up because even their average exploits are so mind-blowing that they sound far-fetched to the rest of us regular folks. I know that with a little (or a lot) of Cognac and some goading, I’ll have the outline of a great adventure novel. When I ask for facts and stories about his life, Yeager shrugs; he suggests other people, other interviews as a source of information. I’m left digging for more information on diamonds because that is something that he will talk about.
It turns out that Yeager has his eye on the United States for his next project. Though he still chases diamond prospects in Africa and Brazil, gold in Mali and Sierra Leone, and sapphires in Tanzania, it is here that he has begun his latest search for “exceptional” diamonds. Yeager states, “I’m known as “fixer” in the field. For years I continually have been contracted to fix, run and make other companies mining operations profitable. After all these years, I want to take the time to work on my own operations.” The increasing demand for diamonds, coupled with the slowing production rates has raised the stakes for discovery. And why not? We’ve seen oil wells blossoming once more in the United States-more than even the Saudis have to offer. Why not diamonds, then? There have been very few new diamond sites uncovered globally in recent years. In fact, Yeager foresees deposits in the United States that may create a paradigm shift in global diamond production.
Having escaped civil wars, stabbing, ambushes, and angry natives, the United States looks tame in even its roughest, most remote regions. If diamonds can be unearthed here, Yeager is the man to do it. Like the Indiana Jones of legend, Yeager has an academic and mathematical acumen coupled with the spirit of a risk-taker that has fueled his success. As a valued advisor for programs throughout Africa and South America, Yeager established a new standard for diamond exploration and mining techniques. He’s known for creating engineering and fabricating mineral recovery equipment that’s considered some of the best in the field of mining.
Yeager’s extensive field experience, combined with his technical knowledge may make him the first of his kind to open diamond mining up in the United States. Like the wildcatters of old, Yeager may well be on his way to legend. One thing is certain though, given enough Cognac and a recording device, he could easily cash in as the newest contender to Clive Cussler.
Learn more about Wyatt Yeager’s Interview by contacting email@example.com
Article Source: http://EzineArticles.com/8925047
Wyatt Yeager is perhaps best known for his involvement in the discovery of new diamond fields in Venezuela. His 2005 alluvial exploration program in the La Paragua river system of the Gran Sabana ignited a diamond rush that continues to this day.
I rarely put adds on the blog but when I saw this Precision 10″ gold dredge for sale in Montana I made an exception to the rule. If you’re a commercial dredger than you are extremely familiar with Precision Dredges which are considered the workhorse of the industry. A Precision 10 inch gold dredge is a very rare find and this unit is in immaculate condition. I personally own a Precision 10″ dredge, it being the first unit I modified for diamond recovery in Venezuela. Here is a link to the Precision Dredge website:
Here are the specifications for the unit from the seller.
Powered by (2) 40hp Volkswagen Engines, 2 PH-2 precision pumps primed by manifold vacuum, Air supply 2 twin piston compressors, floats 6 aluminum covered foam filled floats 8’x length 14″ thick x 27″ wide. Sluice 42″ wide x 15 ‘ long riffles break down into 3 sections. Suction system nozzle system consists of 6 nozzles each pump supplying 3 nozzles the taper section is 8’ long and tapers from 10 1/4 to 10 1/2 x 28 wide. 2- 6 gallon gas tanks gas consumption approx. 1 1/4 gallons per hour per motor. square tube frame breaks down into 3 sections. Total dredge weight approx. 2500 lbs. Motors run very good don’t use oil and both pumps were fitted with new bearings and resealed with less than 20 hours on them, Trailer is included. Been in storage since 2011.
If interested send me an Email and I will put you in touch with the owners.
Read more and Doug Bierend’s Article – Here
There is no such thing as a diamond dredge. There is no such thing as a gemstone dredge.
I can see your eyebrows lifting at these bold statements but if you are about to spend a significant amount of your mineral recovery equipment budget on a “diamond dredge” you should do a little more research. The first point we should mention is that a gold dredge cannot recover diamonds and colored gemstones efficiently. A typical venturi gold dredge has an accidental gemstone recovery rate of about 5-10%. I say accidental because that is what happens, a diamond can be caught when a rogue settling zone occurs in a sluice riffle and the diamond is buried beneath heavy material. In fact, anyone can test their own dredge’s recovery efficiency with a handful of different sized diamond tracers. Diamond tracers are an engineered polymer cube with the exact specific gravity of a diamond. Mining companies including my own do tracer tests on a daily basis to verify that their diamond recovery equipment is operating at peak performance. Your world will change when you watch your 1,5,10,15 and 20 carat tracers simply flow out of your 100,000 USD diamond dredge.
But please don’t just take my word for it! Ask questions and start discussions with geologists, mineralogists, mining engineers and real gemstone mining companies.
Questions for Wyatt Yeager concerning diamond dredging:
Q: I was looking to purchase a diamond dredge for Guyana and after reading your blog I scribbled down some notes to ask the company about recovery. The company stated, “Our riffles are higher than normal riffles, our sluice box is longer than normal and we have screens running over those riffles to help keep the stones in.” Does this arrangement work?
A: I can’t tell you how many times I have heard this jargon, either the manufacturer has no clue what they are talking about or are just spinning a yarn. This is a serious red flag especially having personally dredged Guyana and imagining these concepts applied to the Guyana alluvial sands and average .10 carat stones. A riffle no matter how high, shape or their spacing will not recover diamonds. Feel free to call me concerning the sand buildup in your dredge and why a diamond won’t settle through that sand layer into the riffle. (It is a bit too much to type)
Q: Can I convert my gold dredge into a diamond dredge?
A: Yes and no. I realize this sounds somewhat vague but here are the reasons why. I’m assuming your dredge uses a venturi suction system which is great for gold but since a dredge sluice cannot capture diamonds they need to be conveyed to the proper diamond recovery system. A venturi jet can only truly lift material 1-2 feet above the water line so unfortunately you really can’t pump your gravel into a recovery vessel whether it is a barge behind your dredge or a system on land. What you can do is have your venturi jet lift the gravel to the surface while a smaller 4” GRAVEL pump lifts to the recovery machinery on your barge or to the shore. (Email me if you need me to explain the difference between gravel pumps and venturi type systems) In my opinion if you are interested in modifying your dredge I would just build new. It will save you time and money to have a properly outfitted system no matter what the cost.
Q: Can I coat my dredge sluice in grease to capture diamonds?
A: Not really because the method you are referring to is not that simple. A grease belt or table uses clean water that stays a constant 70 F with a slow feed of grit free gravel. Diamond grease has to stay warm to be “tacky” to catch the stones. A dredge sluice is too fast, cold and dirty with big cobbles and gravel knocking out any stones that might have been captured by chance.
Q: You state that a dredge riffle cannot capture diamonds so how is it done and what are these people trying to sell me?
A: Your question is by far the largest enquiry I receive on a daily basis. You should come meet me for coffee so I can explain in depth but I can give the short answer in this Email. There are basically only TWO ways to go about diamond dredging. After extracting the gravel from the river or ocean it can be conveyed to a floating recovery plant or a land-based recovery plant. What people are trying to sell you is a hyped up version of a hobbyist gold dredge and advertising them as diamond dredges. It gives the industry a bad name and causes complete confusion hence, why I started the blog www.diamonddredge.com . A proper diamond dredge should essentially be outfitted with two main components; a gravel pump and a mineral jig recovery unit. If you visit my blog you can see descriptions and pictures of these components.
Alluvial diamond mining companies know the last true reserve of diamonds is to be found nestled deep in the remote rivers of Africa and South America. For years, Wyatt Yeager of Precision Dredges has been engineering and designing a series of dredges that enable miners to reach these hidden gems. Read more…
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.
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).
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 – firstname.lastname@example.org
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).
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.
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 – email@example.com
This is why many fail in the business.
Cost of Mining One Plot
Using one CAT Dozer D8, one CAT Excavator 320, one Dump Truck and one Wash Plant, and assuming there is no break-down of machinery throughout the operation, the cost of mining one plot of 200 feet x 200 feet will be as follows:
(1) Site clearing by D8 Dozer for 14 days x $1,000 per day = $14,000
(2) Fuel for D8 for 14 days x 70g per day = 980 gallons x $4.12 = $4,037
(3) Extraction by Excavator for 100 days x $850 per day = $85,000
(4) Fuel for Excavator = 100 x 45g per day = 4,500 x $4.12 = $18,540
(5) Dump Truck for 100 days x $250 per day = $25,000
(6) Fuel for Truck 25g x 100 days = 2,500 gallons x $4.12 = $10,300
(7) Wash Plant for 150 days x $500 per day = $75,000
(8) Fuel for Wash Plant 30g x 150 days = 4,500 gallons x $4.12 = $18,540
(9) Labor $10,000
Total Cost: $14,000 + 4,037 + 85,000 + 18,540 + 25,000 + 10,300 + 75,000 + 18,540 + 10,000 = $260,417 + Misc. expenses x 5% = 13,020 = $273,437
(i) Extraction and washing of gravel occur simultaneously but our experience is that washing continues long after the end of extraction. This explains why our estimate for washing is 150 days as against 100 for extraction.
(ii) Estimates are based on breakdown-free operations throughout. If breakdowns occur, the timing of operations could alter.
(iii) If additional machinery (excavators and front-end loaders) were provided, the extraction period could be shortened substantially but not necessarily the quantum and cost of inputs like fuel, lubricants, etc.
(iv) All calculations are based on one shift work per day of 8 hours. If two shifts are used, again period could be halved. Period could be reduced even more substantially if additional machinery is provided.
(v) The more plots mined the better. Ideally, additional machinery and double shift work make a huge difference.
(vi) Management cost is not included in these estimates.
Congratulations to our neighbors!!!!
This 153-carat diamond, valued at over $6 million, is one of the finest diamonds to be found in Sierra Leone in the last 10 years. It is rated a D+, which is the topmost in terms of color, and only matched or surpassed in price by rare diamonds such as blue or pink diamonds (National Minerals Agency, Sierra Leone, via Facebook).
Freetown (AFP) – Sierra Leone said on Saturday it had discovered a diamond worth $6.2 million, declaring it one of the most precious finds of the past decade.
The stone, dug up last week in the eastern district of Kono, was measured at 153 carats, making it significantly bigger than the largest find of 2013, a 125-carat diamond unearthed in the same area, the state-run National Minerals Agency said.
“This 153.44-carat diamond is one of the finest diamonds to be found in Sierra Leone in the last 10 years,” the agency said in a statement.
It was graded as D+ on the D-to-Z diamond colour scale, meaning that it has almost no yellow tint caused by nitrogen impurities, and the agency said it “could only be matched or surpassed by fancy diamonds such as blue or pink in terms of price”.
“The diamond is a cleavage in terms of shape and the clarity is of very high quality,” the statement added.
“In other words, this is a premium stone as a result of its colour and clarity, and had it been an octahedron-shaped stone, it could have almost doubled the price of $6 million.”
SURAT: Indian diamond jewellery consumers have been a big disappointment for the world’s biggest diamond mining company De Beers in 2013.
According to the annual report by Anglo American owner of De Beers, the Indian diamond jewellery market has not performed up to its mark in 2013, while the US and China have continued to show positive growth with strong holiday season sales. Read more…
Antwerp was the place in the 80’s.
06 February 2014
The Antwerp diamond business community, including the Antwerp World Diamond Centre (AWDC), HRD Antwerp NV, and Antwerp City Hall, has launched Antwerp’s very own quality label, “Antwerp Most Brilliant,” which was awarded on January 29 to the first six Antwerp jewelers during a ceremony at Antwerp City Hall. Antwerp’s Most Brilliant holders must meet 32 quality requirements, thus indicating that they “live up to Antwerp’s reputation as a diamond centre of excellence.”
“We congratulate the AWDC, HRD Antwerp and the City of Antwerp, in particular the alderman for the diamond industry, Ludo van Campenhout, on making the Antwerp Most Brilliant label a reality,” said World Diamond Mark Foundation Chairman Alex Popov.
“The goals of the Antwerp Most Brilliant (AMB) campaign and program very much mesh with the World Diamond Mark (WDM) program, not only in its pursuit to promote diamonds and diamond jewelry among consumers, but also by the strict code of practices holders of the AMB need to adhere to. I am confident that we will find a way to integrate AMB holders into the global WDM program,” Popov said.
The WDM’s global objective is to ensure the health and future growth of the diamond and jewelry industry in the luxury market sector. It is based on three fundamental principles: the education of jewelry retailers about diamonds; confidence building among consumers with the WDM accreditation program; and the creation of a generic marketing program to promote diamonds and diamond jewelry, based on the Authorized Diamond Dealer concept.
BHP Names Cutt to Succeed Yeager as Petroleum Unit President
I know that there are people out there that have an interest in the equipment we use in diamond and gem cutting. So I am putting this page together to show the equipment we use. Along with some explanations as to what the photos show and how the equipment is used.
The Rough and Sawing
It all starts with the rough, small parcel of approximately 22cts.
The cutter examines the rough and marks it for sawing.
17.85 ct marked for sawing
The diamond saw.
A diamond being sawed. The diamond saw is a very thin copper blade coated with diamond dust, its the orientation of the diamond in its cutting direction against the saw blade that allows the diamond to be sawn. The cutting direction is perpendicular to the dodecahedral grain.
17.85ct sawed in half.
The girdling process is the shaping of the diamond into its finished shape. This process goes against the grain of the diamond and is done with the utmost care. The girdle of the diamond can also be faceted to get its final shape.
This is the girdling machine, this is a single head unit that has the ability to off set the diamond, this allows the cutter to center the diamond as well as make other elliptical shapes.
Here you see the girdling process, the diamond cemented on the dop spins at approximately 500 rpm, with a diamond being held in a girdling stick that does the shaping. When your finished shaping the diamond it then goes to the cutting bench.
The Diamond Cutting Bench
This diamond cutting bench is constructed of angle iron, with a 1″ steel table. The bench has to be substantial in order to spin the 12″ cast iron lap at approximately 2500 rpms, without vibration. Diamond cutting is a grinding process, the tools that are shown here allow the cutter to hold the diamond in position against the lap to grind and polish the facets into place.
Here is the cast iron lap with three stones running on it. The rings you see on the lap are cutting and polishing rings, the outer wide ring is for polishing and the inner thin rings are for cutting.
My Diamond Cutting Bench at work. The tangs and dops you see around the bench are used to hold the diamonds while being cut.
The Tangs and Dops
These two tangs are for holding the diamond in the bottom position, which allows the cutter to place the 8 main pavilion facets. The top tang is manual positioning and the bottom tang is automatic positioning
Here you see the diamond set in the bottom tang and being measured for accurate angle.
Here you see the diamonds on the left being cut in bottom position. Note that the dop is holding the diamond by the girdle edge. The diamond on the right is being cut in top position or crown. Note that the diamond is being held with pressure on the table of the diamond.
The top tang is for cutting the girdle of the diamond and the bottom tang is for cutting the crown of the diamond.
Here we are measuring the angle of the crown main facet.
These tangs are used with dops the are on copper stalks, to make an adjustment with a dop on a copper stalk you simply bend the wire. On our other dop and tangs we make an adjustment by turning a knob on the dop. The top tang is for cutting and polishing the table or making the culet. The wooden tang is the first tang used in diamond cutting, and used a variety of dops to do the cutting.
Here are a variety of dops used with the tangs that take copper stalks. Starting top left is a bottom dop, top dop, brass table dop, table dop and a girdle dop. A cutter needs the variety of dops to cut a diamond, there are also dops for certain shapes of diamonds. The dops for pear, marquise and emerald cuts have different holding ability to help produce the finished shape.
These are the measuring devices that we use to produce the finished diamond. Starting at the top left we have a girdle marker this allows all facets to meet at the same point in the girdle, a 90 degree guage, a 41 degree gauge, an emerald cut gauge, star emerald cut gauge (38 to 45), crown star gauge (30 to 37), bottom gauge (41 to 42), and the butterfly bottom gauge (39 to 42).
All this equipment is used to produce one thing and that’s BEAUTY.
Send mail to firstname.lastname@example.org with questions or comments.
Colored diamonds are unique even in a world of uniqueness. By doing just a little research on the internet and other places, you can verify the fact that colored diamonds have increased in value on average more than 15% every year. Some very unusual stones have increased in value much more than 40%. Unlike most products, the supply of colored diamonds is very limited and the largest mine for colored diamonds, the Argyle mine in Australia has less than 10 years of viability. Unfortunately for colored diamond lovers, there has not been one significant diamond mine discovery in more than twenty years that has a large production of colored diamonds.
Every colored diamond has its own distinctive shade of color regardless of its hue or carat weight. For those who invested in colored diamonds in the past, they have seen increases in value of 15-25% year after year. We can expect the same or greater increase in value in the years ahead. This is especially true for the pink, purple, red, and violet diamonds that Argyle is famous for. As the two powerhouse economies of China and India emerge, the global demand for diamonds is set to continue rising. The yearly demand from India and China is expected to rise more than 20% each year for the next 5 years, catching up with America as a major importer of polished stones (De Beers).
The Asian cultures have always appreciated colored gemstones. Now Asian collectors have an added incentive as they have realized that colored diamonds are a vehicle to protect and increase wealth. Colored diamonds have increased in value without failure for more than 30 years. With a dwindling supply and an increasing demand it is logical that we shall continue to see strong ROI in this area.
Colored diamonds are a great investment, made better when the gemologist is connected to the right suppliers. It is a well known fact: The money in diamonds is made in the buying. Interestingly, when it comes to unusual and rare diamonds, the retail stores and labs rely on dealers who have access to these diamonds to tell them the value. There are less than fifteen dealers in the world who have the skills and knowledge to accurately evaluate these rare and beautiful stones.
Appraisal companies will look for “comps” and will ask for direction to evaluate a stone. For two examples of excellent ‘comps’ see below two recent sales. One is for a 24 Ct Fancy Intense Pink Diamond VVS2 and the other for a 1.57 Fancy Red Diamond. The fancy pink sold to a London diamond dealer for $46,000,000 and the 1.57 is listed to sell from a dealer for $3,000,000. (By typing in the basic information you can find detailed accounts of the transaction on Google).
Sotheby’s Geneva Sella 24.78 ct Pink Diamond for $46M to Graff. New Owner Names his Diamond ‘The Graff Pink’
Nov 16, 2010 4:10 PM By Jeff Miller
RAPAPORT… Sotheby’s Geneva realized a world auction record price for any diamond and any jewel when it sold an exceptionally rare 24.78-carat, VVS2, fancy intense pink diamond of the purest, vibrant hue for $46,158,674 (CHF 45,442,500). Four bidders competed for the pink diamond, but the winning bid went to Laurence Graff. Shortly after the sale, Graff named the diamond “The Graff Pink” and stated, “It is the most fabulous diamond I’ve seen in the history of my career and I’m delighted to have bought it.”
Commenting on the sale of the pink diamond, David Bennett, chairman of Sotheby’s Europe and the Middle East jewelry department, said, “Tonight’s spectacular result demonstrates that truly extraordinary objects will bring truly extraordinary prices. This outstanding pink diamond combined exceptional color and purity with a classic emerald-cut and fully deserves the exceptional price of $46,158,674.It was simply one of the most desirable diamonds I have seen during my 35-year-career at Sotheby’s.”
This diamond came to the market from a private collection, and has not appeared on the open market since it was purchased some 60 years ago from Harry Winston.
The Geneva sale also set a record total for Sotheby’s at $105,051,728 (CHF 103,421,800), a figure well above presale expectations of CHF 65.8 million to CHF 95.3 million. The sale of Magnificent Jewels was 82 percent sold by lot. Top prices were achieved for important white diamonds, rare colored stones, jewels with important provenance and exceptional signed pieces.
The second top lot of the sale realized $2,814,163 for a 4.59-carat, pear-shaped fancy intense pink
diamond ring, followed by a 20.16-carat diamond ring by Graff, which sold for $2,757,281. The fourth top lot was an important diamond ring by Harry Winston featuring a 20.18-carat emerald-cut center stone flanked by tapered baguette diamond shoulders, which sold for $2,472,868. A diamond necklace and brooch signed by Adler rounded out the top five lots at $2,359,103, and featured a graduated line of 39 brilliant-cut diamonds.
An article from the July-August 2011 edition of JCK magazine. (JCK is a major trade magazine for the diamonds industry)
Best Investment Stones Red and Purple Diamonds
If recent auction records set by extraordinary diamonds have taught us anything, it’s that remarkable gems are a good investment. So imagine the excitement of New York City–based Global Diamond Group when it showcased two extremely rare natural color diamonds at LUXURY at JCK: a 1.57 ct. oval-modified, brilliant-cut, fancy red stone, set in a platinum ring with a halo of colorless diamonds, and a loose 3.02 ct. cut-cornered, rectangular- modified brilliant fancy intense purple diamond. Both stones—which hail from Africa—are the utter definition of incomparable. In fact, the rocks flat-out stumped many passersby, some of whom asked if they were rubies. “After they heard the price, they had no more questions,” a company rep told JCK, pegging the cost of the fancy red diamond ring at roughly $3 million …wholesale. (The diamonds nabbed the interest of two American buyers in particular.) Bonus: Both stones come with an analysis by famed diamantaire and author Steven Hofer. —JH
According to powerhouse mining company Petra diamonds; “Most mines are past peak performance; mining firms are actually cutting back in production to extend the life time of their mines. Over the past
25 years more than 12,000 kimberlite deposits have been discovered throughout the world and less than 1% has contained enough diamonds to become economically viable.”
Bloomberg states; “Out of 170 diamond mining companies there are only 25 in production.”
Evy Hambro, manager of the $6.7 billion World Mining Fund in London for Merrill Lynch. Has said; “Diamonds have the best fundamental. The gap between supply and demand is much greater compared to other commodities.” (Bloomberg)
“If we continue to diamond mine at this rate we shall run out within 20 years”. Gareth Penny, ex Managing Director of De Beers was quoted in 2010.
“Diamonds could very well outperform base metals in the coming years” According to the brilliant Andrew Ferguson, manager of the $313 million fund at New City Investment Managers in London. “Given the
huge increases in demand and the imbalances in supply, I expect good returns.” (Bloomberg)
The world’s largest producer of yellow diamonds is reported to be the Ellendale mine in Australia. It has an annual production of less than 21,000 carats of fancy yellow diamonds. The total carat weight of intense and vivid yellows is unpublished, but is considerably less. (Telegraph)
One of the world’s leading jewelers, Tiffany & Co in 2010 agreed to a 25% price increase for yellow stones from their supplier in order to incorporate yellow diamonds in their own jewelry range. (Tiffany & Co).
The Pan-American Mineral Jig: Building a Duplex Round Jig Courtesy of Savana Mining Equipment
The modern mineral jig or gravity concentrators have their foundation firmly rooted in ancient history and are considered to be one of the oldest mechanical device designed specifically to recover heavy minerals from lighter gangue material. During the development of the Wilfley table in the 1890’s to the innovative and successful flotation techniques of the 1940’s mineral jigs fell in popularity. The earliest mention of jigging was by Agricola in his famous 1556 printing of De Re Metallica. He noted that circular sieves were submerged in water while the operator utilized an up and down pumping action to pulse the material through the screen itself. Currently, almost 500 years later this hand jigging method is still employed and is the standard method for most alluvial diamond mining prospecting and final concentrate cleanup in Africa and South America. You can see modern hand jigging machines such as the Bushman Jig or “Diggers Dream” popular in South Africa.
Over the past 150 years many variants of the mineral jig were created but it is the author’s opinion that the last 50 years has seen an increase in the actual engineering of highly efficient jigs. Mineral jig principles and theory are widely published in mineral processing journals and throughout the internet so I will not bother discussing the science behind gravity concentration. Excellent information can be found on page 204.
What the information lacks is the instruction and knowledge pertaining to the operation of jigs. In the mineral processing world the jig is one of my favorite pieces of recovery equipment. In my operations the combination of jigs and the dredge is a match made in heaven.
After WWII jigs fell out of favor (in the metallic mining scene, not gemstones) for the simple reason that flotation techniques were all the rage. It was a simple process with a high recovery ratio. Of course during those years they didn’t know or didn’t care about the harmful chemicals used in the flotation process. After 30 years of stricter environmental laws causing increased awareness and costs in the process, usage of flotation cells sharply declined. Thus, the reemergence of interest in the jig around the 1960’s in places like Malaysia, the Yukon and Brazil. In fact the creation of the circular or round jig for the Malaysian tin fields brought recovery and profit to an all-time high. Every mine operator should love jigs. Why do you ask? Because jigs are user friendly, cheap, environmentally approved and have a recovery of up to 95%. This article deals with the creation and use of mineral jigs for the recovery of diamonds and other gemstones.
I thought it would be interesting to show a pictorial timeline of a Pan-American style circular jig being fabricated for the famous alluvial diamond fields in Kono, Sierra Leone. I would like to thank Savana Mining Equipment for sharing their photos.
You can watch the round jig being tested here:
Although I had seen the fabrication of various mineral jigs in our plant, the first time I watched a jig unit in action was in 1983. We visited a friends mining operation in the Yukon and he was using a 6’ diameter circular jig unit as a final stage in his gold recovery system. During the early 80’s circular jigs were very rare and only a few operators understood the recovery difference between a circular and a normal square unit. I found it fascinating to lay my hand on the pulsing jig bed and watch it slowly disappear into the gravel with each stroke just like a piece of gold or a diamond. Since that moment it has dominated my career as a mining equipment designer. I have been working on various aspects of jig design and application to the present day. Mineral jigs fascinate me; it is this aspect that fuels my desire to continue working with them. The jig is a simplistic machine that incorporates a highly complex stratification process but yet remains cheap and user friendly. After almost 20 years using and designing jigs I am now finishing the process of building the very best jig I know how for recovery aboard dredges and ocean going vessels.
Over the past 40 years my family has used every style of jig imaginable. For diamond recovery we prefer the circular jig over the standard 42×42 square jig. Round jigs sacrifice a tiny bit of throughput compared to the square jig but the recovery factors of the circular jig make up for it. We actually use a combination of both types of jig shapes in some of our operations. The circular jig has also proved an essential design aspect when a jig is needed for mounting on a dredge platform that rides on river current or ocean waves. Over time we have preferred to use a hydraulic action seen here:
For more information on the sawtooth pulse pattern read page 18 here
Occasionally I will add to this article when different questions come in. Here are a few simplified images of what the typical Dorr-Oliver based jig looks like.
I would like to note that the only piece of equipment in my opinion that might rival the jig in alluvial stone recovery is the diamond stir pan popular in South Africa but that’s another article.
Please feel free to email with any questions or comments you might have and please, don’t let friends buy Chinese made mining equipment 😉
Wyatt Yeager Msc
I have to say that I am pleasantly surprised after watching the first three episodes of Gem Hunt http://www.travelchannel.com/tv-shows/gem-hunt produced by the Travel Channel. I really can’t stand to watch the mock drama of most of the current mining shows so I was happy to see more “truth” of the business with the Gem Hunt crew. Don’t get me wrong there is a little bit of drama but nothing you won’t be able to stomach. If you haven’t tuned in essentially you have a trio of people with different backgrounds trying to buy gemstones as close to the source as possible to turn a profit later. I get nostalgic having sat in the same cafes and dealt with the same dealers as the Gem Hunt folks. What they show is pretty close to what happens in a gem deal. Any buyers out there want to chime in with your experiences or views about the show?
Over the past two years we have been inundated with Emails and calls concerning dredging in the Bering Sea. With the obvious media attention and current economic situation, Alaska is a hard place to ignore especially if you are a displaced California miner. The Bering Sea beach placers can be a lucrative prospect with the biggest downside being an average 30 day season due to weather and ocean conditions. We have compiled our field notes, experience and equipment design from the past 40 years of Alaskan dredging to aid you.
I’m going to make the assumption that you are a competent dredger and that you have a working knowledge of dredges. Outfitting a dredging operation for Alaska can be a daunting task. You most likely have studied numerous geologic reports, read everything online that you could find and of course watched the television reality shows. But the question remains. What do I need to be successful? Before we get into the fine details you should ask yourself a few questions:
1) Can I risk the time and capital of a project of this scope?
2) Am I physically and mentally healthy to endure the extremely hard and tedious labor?
3) Do I have the tenacity and perseverance to continue with the project even if the mineral find is small?
4) Last but most important, am I undertaking this venture as a mining operation or a get rich quick scheme?
If you answered “yes” to the above mentioned questions than you have made the rational decision to go ahead a form a realistic mining plan. To fully try and help you, I must approach the exploration plan as if it was researched by our company. Notice I used the term “exploration plan” instead of mining plan. The biggest mistake we see are individuals who choose to stay in one spot hoping to eventually hit the pay streak. In the Bering Sea if you don’t see gold after running one ton of material move on to the next location. This venture is a business, therefore run it like a business. Common business sense while dredging dictates that every 12” of overburden you take off you lose $100 per hour in doing so. Four feet of sand overburden equals $400 loss. Dredging the Alaskan offshore placer deposits is a straight forward concept. The more gravel you process in the right area, the more gold you will produce. When planning your operation the key component is logistics, logistics, logistics. Our dredging operations take us to some of the most remote regions of Africa and the Amazon. Logistics can be a nightmare and must be planned for. Nome and the Alaskan frontier are no different. If you are prepared to invest a substantial amount of money in your project than it makes sense to fly to Nome and observe a dredging season before you place a single dredge in the water. You should diligently research the price of diesel, living costs including food, transport and berthing fees. Ask questions of the seasoned miners and pay close attention to how many working weather days occur.
The dredge component of your operation can either be the most daunting challenge or the easiest. In our opinion, when designing or buying a dredge keep it simple. Electronics, motors, gadgets and lack of spares are the major factors in dredge shutdown. If you are using an open platform dredge without an enclosure keep your electronics to a minimum. The smallest hose we would use is an 8” diameter hose with a 10” being the norm. In the ocean we are not so much concerned about the rock size but the suction lift of the hose. The 8-10” hose readily sucks the gravel with less of the need for using a pry bar, compared to the smaller 6” hose. The downside to using bigger hoses is the restriction in flex. Effort is needed to move the bigger hoses underwater but can be helped by attaching your hose to floating buoys or by putting your hose through inflated inner tubes to lessen the weight
Although it is the standard recovery system for Nome, sluices are not the choice for optimum recovery. If you can imagine for a moment the typical gold recovery circuit and the ideal recovery conditions it would be similar to a land based recovery model. As the material enters into the scrubber it is effectively cleaned and sized. The concept is to have your cleaned fractions go to the proper recovery system. For instance you would not want your ½ inch material mixed with your ? inch material going into your mineral jigs, sluices or centrifuge. The different sized material would collide and interrupt the settling pattern of the gold we are trying for. Yet, this is precisely the methods currently used. The ideal recovery solution at sea would be for the material to:
- slow down after exit from the taper
- settle and classify itself
- transfer to individual recovery zones
The concept might sound impossible especially with the rolling sea conditions, absence of mineral jigs or centrifuges and a small dredge platform but fortunately we have implemented these basic recovery techniques and so far are they working well.
Essentially how the system works is as the material exits the taper it should flow over a static double deck screener. We use a top screen of ¼ inch and a bottom screen of ? inch. The screener is set an angle so the oversize material flows out with gravity. Each screen has a collection chute so the fractions go to separate holding bins. At this point the dredger has a choice to either collect and save the fines to process on land or to process on deck. On deck processing is the preferred method since most dredgers don’t have the floatation capacity and space to hold two tons of material. Since the fines are small we have a small submersible slurry pump in each bin that conveys the material to the proper recovery unit. Depending on the size of your dredge the recovery units can be volume controlled sluices or for us we use a system of small lidded jigs and a centrifuge. By all means our dredges are not starter units. I am currently designing a similar on-deck dredge processing unit for South America so I will hopefully have a few pictures of the fabrication process to share.