Well, from these pics it looks to me that it is authentic albeit in poor condition having been buried and losing the prongs.
The type is officers first pattern (as opposed to other ranks / enlisted ranks) and the metal should be plated tombak (brass) with two prongs, one just under the eagles wing on either side. Every one of these I have seen has been made in two pieces usually with the eagle attached to the wreath by two further prongs on the wings bent over and soldered to the back of the wreath or by two rivets through the wreath one at the back of each wing.
The OR/Enlisted type was the same motif but in a more rounded shape and made in one piece. These were aluminium with the prongs made of brass and crimped in.
The officers 2nd pattern was the same shape as the OR/Enlisted type but again stamped in plated brass like the 1st type.
Here are images of the three variations from my collection;
1. Officers 1st type.
2. Officers 2nd type (this one has a third "double" or split prong behind the swastika but not of this type all have this).
3. OR/Enlisted aluminium type.
These badges were also worn by the fire brigade who were nominated as "Fire police" and the same patterns in gold colour were worn by the Wasserschutzpolizei or "Marine (ie waterways) Police"
I hope this helps