Can anyone help me date this old photograph?

I am hoping that the community may be able to help me determine an approximate date for an old photograph that my hubby and I have had for years. It features a group of men and is marked "Engineering Staff - Randfontein South". It appears to be from around 1920-ish but could be earlier. See pic below. Click here for a larger version.

Thank you in advance - Vicky - avrall0007@gmail.com