Highlands is currently in dispute with 80% owner, PanAust, a subsidiary of China's Guangdong Rising Asset Management (GRAM).
PanAust is trying to roll the board of Highlands, while Highlands has criticised PanAust for a Frieda River feasibility study it describes as "sub-optimal".
On Friday, Highlands noted it had received an addendum to the feasibility study, incorporating new data and information, including increased resources and reserves, an amended open pit design and mine plan, and updated production schedule.
The additional information has resulted in an increase in the internal rate of return from 10.8% to 11.4%, and a lift in the post-tax net present value from $US820 million to $1.13 billion.
The updated economics are solely from the new information, with no changes to consumables or metal prices.
The study, released last year, used a copper price of $3.30 per pound and a gold price of $1455 an ounce.
Highlands managing director Craig Lennon said the company was pleased to receive the additional information.
"However, the addendum does not address certain fundamental deficiencies in the initial study, particularly regarding the proposed integrated storage facility and hydro dam," he said.
"The provision of the addendum vindicates our view that the initial study undertaken by GRAM was not complete, and we continue to assert that further work is required by GRAM to complete the feasibility study properly, including refining the development plan."
PanAust is working towards a final investment decision for Frieda River after submitting the environmental impact assessment just before Christmas.
Frieda River is one of the world's largest undeveloped copper resources and has capital costs of $US3.6 billion for a 40 million tonne per annum open pit operation to produce an average 175,000 tonnes of copper and 250,000 ounces of gold per annum over an initial 17-year life.
The Horse-Ivaal-Trukai, Ekwai and Koki (HITEK) mineral resource at Frieda River is estimated at over 2.7 billion tonnes at an average grade of 0.42% copper and 0.23 grams per tonne gold for about 12Mt of copper and 19 million ounces of gold.
Last week Highlands said it had appointed Cutfield Freeman and Co to explore options to maximise the value of its 20% stake in the project, which could include a potential sale.
Highlands said it had not made a formal decision to sell the stake and the process was at an early stage.
PanAust has a pre-emptive right over the stake and a 13.9% stake in Highlands.
Last month, Highlands received a requisition notice from PanAust, seeking to remove four of its five non-executive directors, including chairman Ken MacDonald and newly appointed director Ron Douglas and replace them with its own nominees.
However, PanAust said its nominees would be independent.
"The reasons for PanAust seeking to change the composition of the Highlands board include to implement a new strategy and direction for Highlands with a view to increasing shareholder value in circumstances where the Highlands' share price has decreased significantly over the last five years," the company said.
Highlands has called a vote for May 18 in Port Moresby, the same day as its annual general meeting.