I am not into gold mining yet, however, someday I would like to get into it so I have been dabbling into esrearch and talking to old-timers about techniques.
The key with the miners carpet (as I can find out) is that it is a substrate for the heavy gold to sink into and not get washed out. Most of the miner's carpet that I saw online when I did a search kinda looks like a brillo-pad. The fibers are all tangled together and provide alot nooks and crannies for the gold to wedge into and stay. All the astroturf I have seen is a bunch of "blades" that stand up and all run somewhat perpendicular to the ground. While it would probably catch some gold, I think the efficiency of it would be low and alot of the fines would just pass on through.
One of my friends has done gold mining (panning, sliucing, etc.) as a hobby for most of his life. He tells me his favorite technique is to fill a cookie sheet with old bacon grease and put that in the bottom of the stream. The heavy gold sinks into the grease and the lighter sands and sediment flow right on over it. After a couple of weeks or so, he dips the pan into a pot of hot water and melts the bacon grease down. The grease floats to the top, the gold sinks to the bottom. Now, is he pulling my leg - or is this true? I don't know, but the whole theory of most gold panning is that gold is heavier and settles to the bottom.