Nautilus Confirms Marketable Concentrate From Solwara 1 Ore

Nautilus Minerals Inc. has received results for metallurgical testwork completed on its Solwara 1 deposit. The results confirm that conventional flotation processing of Solwara 1 ore can produce a clean and high-grade copper concentrate. The low bond ball millwork index and simple flotation requirements also indicate low capital and operating cost potential of Solwara 1 ore treatment.

David Heydon, Nautilus’s chief executive officer, commented: “Building on the preliminary results reported in February, 2008, we can now confirm that a high-quality copper concentrate with grades of better than 28 per cent copper can be produced using standard flotation techniques with copper recoveries of more than 85 per cent. The concentrates produced are ‘clean’ with low levels of deleterious elements which demonstrate we have a marketable product.”

The metallurgical testwork, comprising mineragraphy, comminution and flotation, was carried out by AMMTEC laboratories in Perth, Western Australia. It was carried out on 10 composite samples recovered from 1.2 tonnes of Solwara 1 drill core collected during the 2007 drilling campaign at the company’s Solwara 1 project, located in the territorial waters of Papua New Guinea (PNG), as documented in the resource report completed by Golder Associates Pty. Ltd., released on Feb. 1, 2008.

The metallurgical test program was developed to provide data to design a flotation process. Several key points have been concluded from this metallurgical testwork:

Over 95 per cent of the copper occurs as the mineral chalcopyrite. The gangue consists of pyrite, barite, anhydrite and minor silicate minerals, all of which are readily separated from chalcopyrite using standard flotation techniques. Grinding and flotation tests indicate effective liberation with a likely primary grind size of 80 per cent — 55 microns and regrind size of 80 per cent — 25 microns. The comminution data tabulated attached indicate that the ore has an average bond ball millwork index of about 11 kilowatt-hours per tonne. The attached flotation results obtained using standard conditions indicate that copper concentrate grades greater than 28 per cent should be achieved at copper recoveries in excess of 85 per cent.The impurity element arsenic is held predominantly in the mineral arsenopyrite. Testwork indicates that the arsenopyrite is readily liberated from the chalcopyrite and pyrite and flotation produces marketable concentrates with arsenic contents below the penalty level. The copper concentrates contain significant gold contents and in some cases payable levels of silver. Greater than 90 per cent of the gold reports to sulphides either to a copper or a pyrite concentrate. Further work defining gold and silver deportment is in progress.

• Over 95 per cent of the copper occurs as the mineral chalcopyrite.
• The gangue consists of pyrite, barite, anhydrite and minor silicate minerals, all of which are readily separated from chalcopyrite using standard flotation techniques.
• Grinding and flotation tests indicate effective liberation with a likely primary grind size of 80 per cent — 55 microns and regrind size of 80 per cent — 25 microns.
• The comminution data tabulated attached indicate that the ore has an average bond ball millwork index of about 11 kilowatt-hours per tonne.
• The attached flotation results obtained using standard conditions indicate that copper concentrate grades greater than 28 per cent should be achieved at copper recoveries in excess of 85 per cent.
• The impurity element arsenic is held predominantly in the mineral arsenopyrite. Testwork indicates that the arsenopyrite is readily liberated from the chalcopyrite and pyrite and flotation produces marketable concentrates with arsenic contents below the penalty level.
• The copper concentrates contain significant gold contents and in some cases payable levels of silver.
• Greater than 90 per cent of the gold reports to sulphides either to a copper or a pyrite concentrate. Further work defining gold and silver deportment is in progress.

SOLWARA 1 PROJECT COMMINUTION DATA

Bond Bond

rod ball Bond Bond

Approximate mill- mill- abra- impact

percentage work work sion crusha-

of index index index bility

Sample No. Description resource (kWh/t) (kWh/t) (Ai) (kWh/t)

Ore type 1 Mineralized sediment 14 11.1 11.3 0.0881 3.9

Ore type 2 Vuggy massive sulphide 53 9.2 11.9 0.1188 3.4

Ore type 3 Massive sulphide 22 11.4 10.8 0.1559 3.9

Ore type 4 Brecciated massive 7 11.9 12.3 0.1524 3.8

sulphide

SOLWARA 1 COPPER FLOTATION TEST RESULTS

Copper Gold Gold

recov- grade recov-

Copper ery to of ery to

Approximate concen- copper copper copper

percentage trate concen- concen- concen-

of grade trate trate trate

Sample No. Description resource (% Cu) (%) (g/t) (%)

Ore type 1 Mineralized sediment 14 31.4 90.9 10.4 31.1

Ore type 2 Vuggy massive sulphide 53 30.1 87 7.86 23.4

Ore type 3 Massive sulphide 22 32.7 83.9 3.64 17.9

Ore type 4 Brecciated massive 7 25 89.9 3.75 14.2

sulphide

Ore type 9 Chimney — low zinc 30.1 92.6 20.5 31.9

3

Ore type 10 Chimney — high zinc 28.6 85 11.3 20.8

The metallurgical and mineralogical results reported in this announcement have been compiled under the supervision of Peter Munro, a full-time employee of Mineralurgy Pty. Ltd. and Dr. N.W. (Bill) Johnson, a consultant for Mineralurgy Pty. Ltd. Both are corporate members of the Australasian Institute of Mining and Metallurgy, with over 35 years experience in mining and metallurgical process engineering and are deemed to be qualified persons. Both members have consented to their names being used in this release.