I'm not sure about all of that. If you panned on private property you would of course need the owners permission and they could ask that you split with them what you find. I don't know that an assay office would necessarily ask where you got it. They, from what I understand, will be testing to see what quality you have, 14, 18, 24 carot. Or if you brought ore they estimate how much per ton or something like that. I have never sold any of my gold because I only prospect for recreation not professionally. Laws are different state to state. In some states you can pan in the streams, sluice with a permit and cannot dredge anywhere. Some states you can dredge with a permit, non needed to sluice or pan. Contact the state to find out what you can do and what permits are needed. The laws can change. The Gold prospectors association of America goldprospectors.org can tell you much more. If you go to their site, click on events, then Alaska and watch the video. You will see me , first in the mess hall with my granddaughter and then a lot of my husband and her fishing him in purple and black jacket her in green sweatshirt, then her and I (me in red sweater) shovelling into highbanker. Another Gold Prospecting show that is on from time to time on the outdoor channel has an interview with her and I when we were in Alaska. I also like California prospecting.