William Heinemann reprinted THE DIAMOND HUNTERS a few times: in 1971 (same year as the first printing), 1975, 1980, 1987, and 1989 for a Uniform Edition.
I found the signed copy below on eBay and it is not in my collection.
I have owned and sold numerous signed copies of THE DIAMOND HUNTERS. All below are first printings.
Doubleday never reprinted its first edition or published any later editions, so all copies are first printings of the first edition.
Many copies of this edition were remainder-sprayed by Doubleday. It is tough to find a copy in collectible condition that has not been remaindered. I have owned copies with remainder spray on the bottom page edges of the book. Below is an example of what remainder spray looks like on Doubleday copies of GOLD MINE, DIAMOND HUNTERS, and EAGLE IN THE SKY, with THE SUNBIRD in the middle without remainder spray.