Circular black pendant with gold accents/gold mining equip enclosed in glass?

After Mom passed in March of this year, I inherited all of hers and her Mother's jewelry. There is a bit of fine jewelry, but more fascinating is the large amount of costume jewelry. 90% of the costume jewelry belonged to my Grandmother.

She was born in early 1900's, so any amount of jewelry that would have likely been accumulated from 30's to 70's (late). She died in early 80's. She seemed to LOVE brooches, Canadian Maple leaves, etc.

This is the circular black pendant with gold items (flakes and gold mining equipment?) I have only found the pendant thus far for the black one.

NOTE: Efesgirl...NO fingers in these pics! ;)