Preparing & Cleaning Mounts for analysis at the Arizona LaserChron Center (Prepared by Alex Pullen & Martin Pepper, Oct 09)

Step 1: Preparation

Always start by cleaning the work area. Contamination is the enemy.

What you will need for step 1 (Fig 1): • 8.5 inch x 11 inch photocopy paper • 4 inch x 4 inch ceramic tile (smooth surface), available from hardware stores • Fine-point tweezers (we use #7 Dumont titanium forceps, http://www.finescience.com)

Fig. 1 Items needed to start mounting your sample • • •

Spray bottle ethyl alcohol Computer cleaning duster air can Double-sided tape. We generally use 2 inch wide mounting tape (3M #410M, Model S-6761, http://www.uline.com).

• • •

Mounting tube for detrital samples (aluminum or brass, we can send you one) Mounting shield for igneous (composed of 4 glass slide covers to form an open box Sample. At this point zircon separates should consist of >90% zircon. Some barite or rutile is acceptable, however absolutely no pyrite. Less than 90% zircon at this point = return to mineral separation.

Step 2: Mounting (make sure you make a map showing sample names!) Making detrital zircon mounts: 1. In addition to cleaning the picking area, clean the forceps and aluminum (or brass) mounting tube with alcohol, then dust off with air canister. 2. Put strip of tape on clean tile; press down hard on the tape as it is unrolled onto the tile. Make sure it is smooth. 3. Peel back tape film with clean forceps (Fig. 2). 4. Add mounting tube near the center of the tape. Do not press down too hard (Fig. 3A and B). Add tape to cover one opening of the mounting tube if two separate detrital samples are to be added to the same mount (two samples per mount is not recommend by Arizona LaserChron). Figure 2: Clean forceps peeling back tape film.

Figure 3: A) Aluminum mounting tube, B) mounting tube centered on tape.

5. Put all zircons into folded sheet of weighing paper 6. Slide back-and-forth to mix grains thoroughly 7. Pour a subset of thoroughly mixed grains (just enough sample to cover the sticky tape inside the mounting tube) into another folded weighing paper. 8. Pour zircons into openings at the top of the mounting tube (Fig. 4A). * If zircons have a wide range in sizes (i.e. 20 to 250 microns across) use a clean scoop to pour in zircons to ensure all sizes are represented (Fig. 4B). Dip the scoop down through the sample in the weighing paper to insure the widest range in sizes is represented.

Figure 4: A) using folded weighing paper to pour in zircons onto tape (good for samples with little range in grain size distributions B) using clean scoop to pour zircons into mounting tube. 9. Label tile with sample name(s). 10. Tilt tile slightly, tap and rotate it several times to distribute grains on tape. 11. Hold tile upside-down above weighing paper and trash can to recover unstuck zircons (Fig. 5). Figure 5: dumping excess zircons back into weighing paper.

12. Use a shearing motion to remove mount tube (Fig. 6) (do not pass tube over apposing samples and risk contamination if more than one sample is added to a mount. Figure 6: removing mounting tube safely.

13. Using clean forceps, add SL (6 to 7 chips) and R33 (3 grains) standards to the open area between sample piles (Fig. 7).

Figure 7: adding standards to mount.

14. Using forceps, push standards down into tape so that they will be fully exposed on polished surface. 15. Gently flatten down unknowns so that most crystal faces are against the tape. 16. Label tile with standards add (in addition to the sample labels) 17. Make a schematic map. 18. Add ring form. 19. Add epoxy (see Mixing Epoxy, or cover with tape if epoxy will be added later. 20. Clean-up. Making igneous zircon mounts:

1. In addition to cleaning the picking area, clean the forceps with alcohol and glass shield, then dust off with air canister. 2. Put strip of tape on clean tile; press down hard on the tape as it is unrolled onto the tile. Make sure it is smooth. 3. Peel back tape film with clean forceps (Fig. 2). 4. Using clean forceps, add 6 to 9 thin chips of the SL2 standard to the center of the tape (Fig. 8, step 1). 5. Cover standard chips and areas where other samples will go with the glass shield. Add first sample (~50 grains) using clean forceps and label within the mount using zircon grains (Fig. 8, step 2). Gently flatten down sample zircons so that most crystal faces are against the tape. 6. Rotate shield 90 degrees covering standard chips and Sample 1. Add second sample (using clean forceps) and label within the mount using zircons grains (Fig. 8, step 3). Gently flatten down sample zircons so that most crystal faces are against the tape. 7. Repeat procedure for Samples 3 and 4 (Fig. 8, step 4 and 5). 8. Add secondary standard (e.g. R33) (Fig. 8, step 6). 9. Add ring form (Fig. 8, step 6).

Figure 8, steps 1 through 6. 10. Add epoxy (see Mixing Epoxy, or cover with tape if epoxy will be added later. 11. Clean-up. Step 3: Mixing Epoxy

Option I: The Stir You will need: • Clean counter • Disposable (50 or 100 mL) beakers • Two disposable pipettes • Epoxy: Buehler Epo-Thin (we use Buehler #20-8142-016 & 20-8140-032, from http://www.buehler.com) • Piece of copier paper • Inexpensive balance Epoxy procedure: 1. Put copier paper and empty beaker on balance. 2. Zero balance. 3. Pour in as much epoxy resin as you need (from the larger bottle). 4. Use one clean pipette to add hardener (from the smaller bottle) in a ratio of 4:10 (hardener to resin) (Fig. 9).

Figure 9: Adding hardener to beaker

5. Slowly mix epoxy using bulb end of the second disposable pipette. Circle pipette 10 times one direction, then 10 times to the opposite until mixed. Try not to incorporate bubbles from the surface while mixing. Epoxy will appear to take on a Vaseline looking texture and then return to clear again when mixed (Fig. 10A, B, and C).

Figure 10 A, B, and C: Mixing the epoxy. Stirring slowing will ensure no bubbles. 6. To pour, hold tile at a ~60 degree angle (Fig. 11A). Dribble in the epoxy until it starts to cover the zircon grains. Slowly lay the tile flat again, allow the epoxy to flow around grains as to not trap air bubbles (Fig. 11B).

Figure 11A and B: Pouring epoxy and slowly lowering tile back to horizontal. 7. Once flat, fill ring form to half with epoxy. 8. Mount will be ready for polishing after ~24 hours at room temperature. 9. Clean-up Option II: The Swirl You will need: • Clean counter • Two Disposable (50 or 100 mL) beakers • One disposable pipettes • Epoxy: Buehler Epo-Thin (we use Buehler #20-8142-016 & 20-8140-032, from http://www.buehler.com) • Piece of copier paper • Inexpensive balance

Epoxy procedure: 1. Clean counter top. 2. Need two beakers, epoxy resin and hardener, balance calculator, pipette (large-disposable). 3. Turn on balance, set copier paper and empty beaker on balance. 4. Zero balance with empty beaker. 5. Pour epoxy resin (large bottle) into beaker (only as much as you need, 12 grams will be enough for ~4 mounts). 6. Multiply weight of epoxy by 0.4 (actually 100:39 resin to hardened), add this amount of hardener. 7. Use pipette to add hardener (small bottle). 8. Swirl beaker for 15 seconds. 9. Pour into second beaker and swirl for 15 seconds (Fig. 12). 10. Pour back and forth between two beakers 5 times, swirling each time. 11. Mixture should be clear, void of any Vaseline looking textures. 12. Pour into mount ring, holding tile at an angle, gently lower (Fig. 11A & B). 13. Fill ring to half. 14. Clean up everything (use alcohol to dissolve epoxy). 15. Mount will be ready for polishing after ~24 hours at room temperature. Figure 12: pouring epoxy between beakers to mix

Step 4: Polishing

You will need (Fig. 13): • Flat surface • Wet or dry sandpaper of 2500 grit • 9 micron lapping film (we use Precision Surfaces PSI-1609-6) • 5 micron lapping film (we use Precision Surfaces PSI-1605-6) • Distilled or MQ water

Figure 13: polishing items Polishing Procedure: 1. Remove mount from tile, its all in the thumbs (Fig. 14). 2. Label mount using scribe. Add mount number, sample number, and owner’s name to the sample side of the ring form (Fig. 15). Figure 14: removing the mount

Figure 15: labeling mount with electric scribe

3. Add water to 2500 grit sandpaper on flat surface. Polish mount with light pressure in figure 8 pattern (Fig. 16A). Check depth of polish periodically.

Figure 16: A) figure 8 pattern on wet 2500 grit sandpaper, B) figure 8 pattern on lapping film. 4. The goal is to polish 1/3 of the way into most of the grains without sanding away the smallest grains. Epoxy partially covering grains forms halos around. Halos will move towards the edge of the grains as more material is sanded away and is a good indicator of depth (Fig. 17A, B, and C).

Figure 17: A) Reflected light microscope image of unpolished mount, B) partially polished mount with striations forming of polished areas, and C) halos move towards the edges of the grains as material is removed 5. When polished to a satisfactory depth move onto 9 micron (Fig. 16B) and then 5 micron lapping films to bring up the polish. 50 passes on each film should be sufficient. 6. Clean-up area.

Step 5: Make Map of Final Sample Surface You will need to make an image of the sample surface at sufficient detail that individual grains can be identified. Step 6: Cleaning Mount: 1. Wash mount thoroughly with soap and water to remove sanding debris. 2. Rinse thoroughly with tap water. 3. Immerse in cleaning solution (2% HNO3 and 1% HCl) and buzz in ultrasonic for a few minutes. 4. Drain cleaning solution into acid waste barrel (not down drain!). 5. Rinse with tap water. 6. Put on gloves and spray mount with isopropyl alcohol (into trash can is OK). This is to displace water and to remove oils. 7. Wipe surface with Kimwipe to remove alcohol and leave dry surface. 8. Do not touch sample surface with bare fingers after cleaning.