A Gold is a valuable piece in checkmate.

White in hand: nothing
  9  8  7  6  5  4  3  2  1
+---------------------------+
| *  *  *  * wK  *  *  *  * |a
| *  *  *  *  *  *  *  *  * |b
| *  *  *  *  *  *  *  *  * |c
| *  *  *  *  *  *  *  *  * |d
| *  *  *  *  *  *  *  *  * |e
| *  *  *  *  *  *  *  *  * |f
| *  *  *  *  *  *  *  *  * |g
| *  *  *  *  *  *  *  *  * |h
| *  *  *  *  *  *  *  *  * |i
+---------------------------+
Black in hand: G S 
Diagram 1.

S*5c

Instead of using a Gold, you should narrow the King's escape by dropping a Silver first.

With nothing in hand, White cannot escape from mate. If K-4a or K-6a, a Gold dropped at the head of the King will finish the game.

If you drop a Gold instead of a Silver on 5c, there will follow: K-6a, S*6b, K-7b... You'll let the King escape.

Suppose you have no Golds in hand in Diagram 1, you will need three Silvers to finish:

S*5c       K-4a
S*3c  Brinkmate -a(Diagram 2)

White in hand: nothing
  9  8  7  6  5  4  3  2  1
+---------------------------+
| *  *  *  *  * wK  *  *  * |a
| *  *  *  *  *  *  *  *  * |b
| *  *  *  * bS  * bS  *  * |c
| *  *  *  *  *  *  *  *  * |d
| *  *  *  *  *  *  *  *  * |e
| *  *  *  *  *  *  *  *  * |f
| *  *  *  *  *  *  *  *  * |g
| *  *  *  *  *  *  *  *  * |h
| *  *  *  *  *  *  *  *  * |i
+---------------------------+
Black in hand: S 
Diagram 2.

Lastly, the following diagram shows a tsume problem. This will pretty much recapitulate what I said above.

White in hand:
  9  8  7  6  5  4  3  2  1
+---------------------------+
| *  *  *  *  *  * bS  *  * |a
| *  *  *  *  *  *  *  * wK |b
| *  *  *  *  *  *  * wP  * |c
| *  *  *  *  *  *  *  * wP |d
| *  *  *  *  *  *  *  *  * |e
| *  *  *  *  *  *  *  *  * |f
| *  *  *  *  *  *  *  *  * |g
| *  *  *  *  *  *  *  *  * |h
| *  *  *  *  *  *  *  *  * |i
+---------------------------+
Black in hand: R G 
Diagram 3. A three-move tsume problem.

Solution: R*1a,  Kx1a,  G*2b