1.5. Water Table (Wilfley Table)
Table of contents
Attention
NOTE: It is important during all steps to avoid touching the surface of the table with your fingers. Oils from your fingers could make grains stick to the table and be detrimental to proper separation.
1.5.1. Set Up
Move plastic sheet up and over the water spigots so it’s out of the way.
Using a damp paper towel, wipe the table area around the water table to prevent any contamination of your sample. Place the trash bag full of sample that has been processed by the disc mill on the table next to the machine.
Turn on both spigots on top of the water table to begin the flow of water, and turn on the switch to activate the shaking of the table.
Apply a bit of dish soap to the handled brush and using mainly right-to-left motions, scrub the surface of the table. Be sure to also wash the sides and front lip of the table, as well as underside of the black water tray at the top. This step not only ensures there are no contaminants, but also will help water flow evenly over the surface by keeping surface tension of the water to a minimum.
Allow the table to run for about 5 minutes to ensure all the soap is rinsed away. Any areas that are not rinsing off from the normal flow of water should be rinsed using the squirt bottle.
Make sure the metal collection trays are completely clean, and wash them with dish soap and a sponge if there is any chance of there being grains left behind in them. Focus on the corners, as this is where grains are likely to be caught.
Place the metal collection trays under the water table, and use bits of aluminum foil to cover the seams between them, so sample will not fall into the cracks.
Adjust the flow of water so that it seems to be evenly flowing from all parts of the black water tray at the top. Things to look for that indicate good flow are: minimal splashing from the spigots into the black water tray, similarly sized waves of water moving down the riffles of the table, and evenly distributed dripping water from the bottom of the black water tray. This is something you will get a better feel for as you process more samples.
1.5.2. Sample Processing
Deposit small bits of sample (a few tablespoons) at a time in the area indicated in the image below, and wait to see where your sample flows on the table. There should be a small line of sample running down the “steps” on the left side of the riffles. You should see the majority of the finer grains being swept away by about halfway across the table. Being too aggressive with the flow of water will result in a small yield of zircon at the end of processing. The image here shows how the distribution of sample on the table should look while you’re running it. The flow of water may be adjusted if necessary, but do not adjust any of the gates in the black water tray. Again, recognizing a good flow of water is something learned by experience. As you get further into your sample, you should see a large majority of it ending up in the middle two collection trays, and a steady trickle off the table into the left-most tray.
Tip
As your sample is running, if spaces develop where water is not flowing on the table, use the squirt bottle to break the water tension and to allow flow to continue. You may also use the squirt bottle to gently nudge sample off the left end of the table into the left-most collection tray if it starts to build up.
Once your entire sample is run, build two aluminum foil trays or “boats”. Label them with your sample name, and designate one as “heavy” and one as “light”. Let the water table run during this time to allow it to clear the remainder of your sample.
Use the squirt bottle to nudge along sample that may be stuck in the right side of the table, or any other areas where you see sample is stuck. Move the stuck sample to a point where the motion of the water table can take over and sort the sample.
Remove the left-most collection tray. This is your “heavy” tray, as this is where the most dense or “heaviest” minerals will have collected. (Including zircon!)
Pour out most of the water, careful not to lose any sample into the sediment tray below the water table. Then pour the sample and residual water into your “heavy” aluminum tray. Use the squirt bottle to free all the sample from the metal collection tray.
Carefully pour out as much excess water as you can, and then move the “heavy” tray to the heat lamp to dry.
Repeat the same process for the next metal collection tray over, which is your “light” tray. Leave this in the oven to dry overnight at 100°C. (The next day, or once this “light” tray is completely dry, collect it in a zip-loc bag with your sample name, and the word “Light”. You will want to save this, as some of the zircon in your sample will be in this bag, just in case you’ll need it in the future.)
The sample in the last two trays may be disposed of. Pour out the excess water and empty them into the trash. You may need to rinse and repeat several times to remove all of the grains.
1.5.3. Clean Up
If there is any reddish-brown discoloration on the water table, this is from the iron oxides in your sample. To remove it, turn off the water and the table, and deposit a small amount of the phosphoric acid powder onto the discolored areas. Use the handled brush to work the powder into the area and to dissolve it in the residual water. Resume the flow of water and turn on the shaking again to allow it to rinse.
Scrub the table in the same way described in step 4 to thoroughly clean the table.
While the water table is rinsing, use dish soap and a sponge to thoroughly clean the metal collection trays, focusing again on the corners. Leave the trays to drip dry on the shelf.
Using compressed air, COMPLETELY dry the water table, including the black water tray and sides of the table.
Once completely dry, replace the plastic dust cover on the table.
High-Five yourself.