It's mentioned in "Ausrüstung der HJ" from January 15, 1934 on page 97.
Garry filed this
book here.
It was also shown in "Uniformen der HJ", the issues from 1933 and 1934, page 2.
Further it was also included in the "Verordnungsblatt der RJF-HJ" from September
18, 1933.
It is noted to be an oval black patch with crossed spade (Spaten- left) and
axe (Kreuzhacke- right) with a height of 6.0 cm and wide 4.0 cm. All parts
of the white silk embroidery were detailed mentions in size.
In my handbook page 350 I showed a photograph and mentioned the patch
disappared in late 1934 while these units silently were incorporated within
the general HJ. July 31, 1937 the remaining pioneer units were incorporated
within the nachrichten-HJ (Vbl.RJF from July 31, 1937, page 197)