Offshore Minerals Fact Sheet

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Introduction

The offshore minerals industry in Australia is relatively small with only two offshore dredging operations. They are:

  • sand for construction purposes in Moreton Bay near Brisbane; and
  • lime sand for cement manufacture south of Fremantle.

There are many offshore mineral occurrences in Australia but only one mineral resource has been quantified, a tin deposit in Ringarooma Bay, Tasmania. Beach sand replenishment also has occurred in some coastal areas of Australia such as on some beaches near Adelaide.

The available information on offshore minerals comes from limited exploration by private companies and from reconnaissance surveys undertaken by Australian Government and State geoscience agencies.

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Marine

Coastal waters, or those within the three nautical mile limit, fall within the jurisdiction of State and Northern Territory Governments. Exploration and mining activities in coastal waters are administered by relevant State and Northern Territory Mining Acts, or, if enacted, offshore minerals legislation. However, Local Governments play a significant role in the planning and management of coasts and coastal waters.

The Commonwealth Offshore Minerals Act 1994 provides the statutory framework for the exploration for and production of minerals over the continental shelf three nautical miles beyond the territorial baseline of the States and Territories. The outer limit of Australian territory is the outer edge of the continental shelf. However, the limit of the continental shelf sometimes is defined by the 200 nautical mile limit or Exclusive Economic Zone. Applications for a mineral exploration licence are made to the designated authority, usually the State or Territory Minister responsible for mining. The Joint Authority consists of the responsible State or Territory Minister and the responsible Australian Government Minister. The Joint Authority is responsible for major decision relating to licences.

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Offshore Mineral Occurrences and Deposits

Construction Materials

In New South Wales, sand resources are known to exist between Wollongong and Newcastle. The Sydney Coastal Councils Group is seeking to have these resources made available to replenish sand eroded from beaches. In recent times companies such as Metromix Pty Ltd and Sydney Marine Sand Pty Ltd have had applications for exploration licences rejected by the New South Wales Government. Marine sand is periodically extracted from the entrance to Narrabeen Lagoon in northern Sydney for use at nearby Collaroy Beach to mitigate extensive erosion which takes place during severe storms.

In South Australia in the early 1990s, sand deposits south of Hallett Cove a trailer suction dredge was used to replenish nearby beaches. This reduced the amount of sand trucked to replenish Adelaide's southern beaches.

In Queensland the Gold Coast City Council started beach replenishment in the mid1970s, initially taking sand from estuarine sources. In the late 1980s the council partly replenished the southern Gold Coast beaches with large scale offshore dredging and sand pumping. Offshore mining in Moreton Bay of fine grained siliceous marine sand ceased several years ago after operating for 28 years. However, studies are underway into a proposal to extract 20 million cubic metres of sand from the Moreton Bay Marine Park for a major expansion of Brisbane Airport.

In Western Australia, Cockburn Cement Ltd has dredged shell sand from Owen Anchorage in Cockburn Sound since 1972. Shell sand is primarily calcium carbonate and is used in the production of lime and cement. Under an agreement with the State Government, Cockburn Cement can extract shell sand within an 8km radius offshore from a point on Coogee Beach until 2011, with rights to extend the operation until 2021.

Mineral Sands

Since the early 1970s a number of companies have explored the inner shelf area for economic mineral sand deposits in northern New South Wales and southern Queensland, but without success. In the early 1990s there was some exploration drilling between The Entrance and the New South Wales/Queensland border and, although heavy mineral concentrations were encountered, none was considered economic. Offshore exploration for mineral sands also has been conducted along parts of the Queensland coast from the New South Wales border to north of Rockhampton.

Heavy mineral concentrations are located off King Island and in Ringarooma Bay in Tasmania and in Geographic Bay and Hardy Inlet on Western Australia's southern coast. Heavy minerals also occur in northern Western Australia between the Robe River Mouth in the Pilbara and Secure Bay in the Kimberley.

Tin

Concentrations of tin occur in Ringarooma Bay in north east Tasmania. Van Dieman Mines plc is investigating the viability of mining onshore and offshore deposits of tin bearing alluvial resources with associated gem and heavy mineral sands. Offshore the company has reported that around 200 million cubic metres of an alluvial tin resource has been identified.

Offshore accumulations of tin also have been identified off King Island and Cape Barren Island in Tasmania. Some offshore exploration for tin and tantalum also has been undertaken in Bynoe Harbour in the Northern Territory.

Diamonds and other alluvials

The Kimberley area of Western Australia is one of the world's major diamond producing provinces. Over the past two decades several companies have explored for diamonds in river channel and deeper sediments in the Kimberley near shore and in coastal areas which extend into Commonwealth waters. Exploration in the Cambridge Gulf/Bonaparte Basin area has focussed on palaeochannels on the inner shelf which form the continuation of the major river systems onshore. Diamonds have been discovered at the mouth of the Berkeley and Ord Rivers but none have been discovered in waters under Commonwealth jurisdiction.

Minor amounts of gold are known offshore from Wynyard in Tasmania and offshore from Bermagui and Narooma in New South Wales.

Offshore Phospherite

Offshore phosphorite can be quite extensive at water depths of 200 to 450 metres, particularly off northern New South Wales. However, these deposits, are characteristically thin, of low grade and often high in iron making their economic potential low.

Extensions of onshore mineralisation

Probably the most common form of offshore exploration and mining occurs as an extension to mining onshore deposits. Examples of where mineralisation is known to extend offshore from onshore deposits, or where exploration has been carried out offshore for such extensions are:

  • Coal. At Newcastle in New South Wales, offshore seams have been mined by underground methods from onshore. The Gippsland Basin off the coast of Victoria has brown coal deposits.
  • Scheelite (tungsten). At King Island off Tasmania, mineralisation occurs in basement rocks of the continental shelf surrounding the island.
  • Manganese. At Groote Eylandt off the eastern Northern Terrritory rich manganese beds in the Lower Cretaceous are known to extend off the island.
  • Iron ore. At Cockatoo Island and Koolan Island off Western Australia iron ore extending under the sea floor is being mined using seawalls.

Ferromanganese Nodules and Crusts

In general terms, deep sea ferromanganese nodules and crusts containing copper, nickel, cobalt and manganese are regarded as long term resources. Manganese nodule fields are common south and west of Australia. Ferromanganese crust and nodule deposits also have been reported on the continental margin south and west of Tasmania and manganese nodules have been recorded in the Tasman Sea south east of Sydney.

The most prospective manganese nodule field is in the Cape Leeuwin region of south west Australia which has about 900,000 square km of closely packed nodules, mostly in international waters. The prevailing weather conditions would make recovery of these nodules very difficult. Water depths in the area vary from 4,300 metres to 5,300 metres. Ferromanganese deposits occur in the Christmas Island region as small nodules on seamount slopes and abyssal plains and as thick crusts on volcanic seamounts. The economic potential of the deep sea nodules in the Christmas Island Exclusive Economic Zone is negligible. West of Tasmania and on the South Tasman Rise, rocky outcrops in water depths of 1,500 metres to 4,500 metres are commonly coated with ferromanganese crusts up to 20 centimetres thick. Manganese nodules, which are often associated with the crusts, are roughly spherical and exceptionally large in places, sometimes reaching up to 12 centimetres in diameter.

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