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About oro

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    Costa Rica
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    placer mining
  1. I need some advice - I am going to batch leach some milled ore samples and plan on using AC to capture the values. Instead of stripping the AC I was wondering if it can be smelted, maybe with a bit of litharge as a collector and some borax to slag off contaminants. I understand the carbon can be “ashed” in an electric muffle furnace at 650 celsius for 6-8 hours (I don’t have a muffle furnace) and thinking a gas furnace or torch (which I do have) might create too much wind and either volatilize the microscopic gold particles and/or blow the particles and ash out of the pan - hence the smelting question. I’m talking about a handful of AC per batch.
  2. Hey Flint, thanks for that. By the way, I love your stuff (frozen tundra tunneling / drifting)... wish I was half as tough as you my friend! Gravel pump - I wonder most about a dredging application to transfer a mixed size aggregate slurry, sharp or rounded rock, cobble, sand, broken bedrock etc.. could be for river dredging or for a pit bottom recovery application, to sweep off the bedrock after the excavator. The examples of pumping head ore I posted all appear to be of comparitively small size aggregate ores, sand and clay - some appear to use a screen (grizzly) at the intake nozzle so as not to pass larger rock. I haven't come across a working example of moving mixed size and larger aggregate but I wrote to Mark Keene about a video I saw on Youtube (see link below) and he said the 6" gravel pump would pass a 5.5” sphere, didn't mention if that was a continuous duty task but I assume the design is for river dredging (?)…I think it was a prototype but he said the’ve used these pumps for years. Gold dredgers on the Amazon use 12” gravel pumps mounted on huge barges, but again, it seems mostly for silt and sandy ores. I inquired about some inexpensive gravel pumps in South America (made in Brazil) and the manufacturer made a recommendation for 10 sets of wear parts (side plates and impellers) as well as an extra case or two - so that tells you something about the expected wear! (hence the rubber lined US built pumps). The advantage of a gravel pump is the ability to transfer a slurry straight up in the air and out over a distance to a recovery plant, but like you say needs big horse power…but also notice the engine / pump doesn’t need to be located near the intake…the Keene design claims 100’-150’ of lift using a pony pump and a jet to maintain prime for the 6” gravel pump coupled to a 100 hp diesel engine. Is it just me or is this not a very cool way to move head ore to a recovery plant. It's potentially a substantial cost savings in heavy equipment, maybe no need for a trommel because you could use a vibrating screen deck instead, the pump having a macerator effect to help bust up and dissolve clays. Maybe I should start another post titled “mining with a gravel pump" and see if it gets more attention than this one. I would love to learn more and what applications have proven to be practical. From Mark Keen: Jeff We do not carry the pumps shown in the links below. We use a Wemco model CE pump. We have used these for mining for over 50 years and have had very good performance reliability. The thing that we like is the 4” pump can pass up to a 3.5 sphere and the 6” pump can pass up to 5.5” sphere. Just the pump alone sell for just under 10K 6" gravel pump. http://www.youtube.com/watch?v=rb1KdeU1Ju4 http://www.youtube.com/watch?v=kBwCiFQbDpo
  3. When the excavator cannot scrape or dig into harder bedrock, what are other practical methods to recover the gold laying on top of and wedged into the bedrock? I suppose by suction using a gravel pump but have not actually seen this in use. Venturi suction like what is used on a typical suction dredge won’t work in a deep hole. A gravel pump however will transport the slurry vertically and out a distance to a wash plant. They make gravel pumps as small as 4”, popular in Brazil. Gold miners in South America use 8” 10” 12” gravel pumps as a primary feed method to a rustic sluice, mostly for head ore that makes a sandy / clay slurry, pumping from excavated pits. It’s impressive actually, very practical and definitely a cheap way to move ore to a recovery plant! In some cases the ground water supply from natural filtration maintains a certain water level in the pit along with some makeup water from another source. They also use high pressure pumps to hydraulic excavate and move material in the pit. Does anyone have experience with gravel pumps? Here’s some youtube links of the South Americans (note that environmental impact is of little concern!)
  4. Basically I'm looking to buy a simple device (geophysical, not drill) to keep on hand, for simple estimates of depth to bedrock. I see simple devices for seismometers (earthquake) and for ground resistivity (electrical contractors) for other applications but my particular interest is for occasional measurement of depth to bedrock.
  5. Any placer miner these days knows there are several state of the art geophysical methods used in mineral exploration (gas and oil too), that determine a variety of characteristics of the subsurface in 2D and 3D outputs - by measuring resistivity, gravity, magnetism and other features such as depth to bedrock and contour, water table, sediment / gravel layers etc. - seismic units and ground penetrating radar to locate “anomalies”. The problem is these technologies are still expensive and out of reach of most small commercial scale placer miners and seem to require a high level of learning and deployment. But I sometimes think / dream about a simple device that would measure just one thing - depth to bedrock. I see some of the commercial seismic survey systems use a simple sledge hammer activator (striking plate) to send out a seismic wave which is picked up by a daisy chain of geo-phones and sent to a computer to record, analyze and display the data and images. I also see simple seismic detector devices to measure earthquakes for sale for under $500 (Infiltec / Amazon). I would think coupling the same sledge hammer activator to a simple seismic detector designed to measure one thing (depth to bedrock) would be feasible and inexpensive. Maybe even without a laptop / expensive software but rather a single digital output / display. Is this only in my dreams or does a device like this exist? I recently got a quote from Geotmetrics for an entry level seismic survey system… 25k + 5k for onsite training. So, I dream on. I’ve done a bit of placer sample drilling and it’s not cheap either. Maybe there are other ideas / methods for an inexpensive geophysical method to determine depth to bedrock. Any suggestions?