It contained an image of an old painting showing a busy sea port in the mid-1800s, along with an inquiry from a British auctioneer asking if it could be of Port Chalmers.
"As soon as I saw the lamps and the wharf with the paddle steamer, I knew straight away that it was Port Chalmers," the Port Chalmers Historical Society president said.
"You can recognise the hill shape from above Careys Bay going down towards Aramoana."
There were photos in the Port Chalmers Museum catalogues which showed a remarkably similar scene of the harbour, taken from George St.
"It matched up with the painting."
Mr McCormack was thrilled the previously unknown work had surfaced, as it showed a rare piece of New Zealand history.
The painting is to go under the hammer at Cheffins Fine Art Auctioneers in Cambridge on June 22, and has been described as "an exceptionally rare and early view of the first British settlement at Otago Harbour, New Zealand".
Mr McCormack said he would love to bid on it and have it at the Port Chalmers Museum, but the museum did not have funds for such a purchase.
Dunedin Public Art Gallery director Cam McCracken said the gallery did not have an appetite for the painting at this stage.
The artwork has an estimated value of more than $2900, but is expected to sell for much more, despite it needing restoration work.
Cheffins spokeswoman Patricia Durdikova said the painting had been in the same family for generations.
She believed the painting might be one of the earliest depictions of Otago Harbour to come to auction.
"Bearing in mind the British only settled at the harbour in 1844, this is an important historical document."
