December 2002

• New report highlights petroleum reserves increase
• Geophysical Airborne Data Release
• Mordor Pound: the geology of Lord Sauron's 'Australian home'
• Three decades of diamond exploration on one map

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New report highlights petroleum reserves increase

Australia's commercial and non-commercial gas and condensate reserves have continued to increase as a result of further discoveries and revision of gas and condensate reserves, announced the Parliamentary Secretary to the Minister for Industry, Tourism and Resources, Warren Entsch in a recent media release.

Oil and Gas Resources of Australia 2001, published by Geoscience Australia, shows that current gas reserves increased in 2001 to 141 trillion cubic feet, 23 per cent over 2000 reserves.

Reserves of crude oil and condensate currently amount to 4084 million barrels - an increase of 6.7 per cent from 2000 despite sustained levels of production and a decline of five per cent in crude oil reserves. This is due to increases in reserves of condensate in gas fields.

"These significant increases in our commercial and non-commercial gas reserves are attributable to continuing large gas discoveries and revisions to the reserves of existing fields particularly off north west Australia in the Carnarvon and Browse Basins," Mr Entsch said

"In addition, further gas discoveries made in 2001 and the first nine months of this year will also significantly add to our gas reserves and provide further security for Australia's gas supplies and for further LNG exports," he said.

However, Mr Entsch sounded a note of caution. "While there have been some large gas discoveries made, recent discoveries of crude oil are insufficient to maintain production in the medium term," he said.

"A reduction of nearly 37 per cent in crude oil and condensate production is expected by 2005 and possibly 55 per cent by 2015, however, this shortfall situation could change in the near future if we were to discover a significant new oil province."

The Oil and Gas Resources of Australia 2001 contains a record of oil and gas expenditure, exploration, reserves, undiscovered resources, development, production and supporting information and statistics. It also includes a forecast of Australia's crude oil and condensate production from 2002 to 2015, an estimate of undiscovered oil and gas potential, and sustainability indicators for petroleum resources.

Copies of Oil and Gas Resources of Australia 2001 and additional large copies of the Petroleum Exploration and Development Titles Map and Key can be purchased from the Geoscience Australia Sales Centre.

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Airborne geophysical data release

A new set of airborne geophysical data covering the West Musgrave region of Western Australia became available on 16 December. The survey covers parts of the Scott and Cooper 1:250 000 sheet areas. The area is actively being explored for base metals following recent discoveries of nickel-copper sulphides.

Geoscience Australia reduces exploration risk and encourages investment through targeted geoscientific surveys and research to locate prospective areas. Minerals are Australia's largest export earner, with most mines located in regional and rural Australia.

The West Musgrave airborne geophysical data include new survey data flown by Fugro Airborne Surveys for Geological Survey of Western Australia and Geoscience Australia in 2002, as well as existing private company survey data flown by Kevron Geophysics over the Jamieson Range in 1998.

The new survey produced 45 000-line km of geophysical data, flown between August and September 2002.

• The data is available on CD-ROM at a cost of $99 per CD or alternatively colour plots at 1:250 000 scale are available at $27.50 per plot.
• To purchase the data, please contact Geoscience Australia Sales Centre.

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Mordor Pound: the geology of Lord Sauron's 'Australian home'

Mordor, J.R.R. Tolkien'' imaginary land of the dark Lord Sauron, actually exists in Australia.

The Mordor Pound bears an uncanny resemblance to J.R.R. Tolkein''s land of Mordor from his novel "Lord of the Rings".

Mordor Pound lies 70 km north-east of Alice Springs, in Australia's Northern Territory. Such was the resemblance between the landscapes that geologist Alan Langworthy renamed the land form which was previously called Spring Pound to Mordor Pound in the 1970s.

Since Langworthy and his colleagues initially mapped the area for the Bureau of Mineral Resources (now called Geoscience Australia), Mordor Pound and the surrounding Arunta Region have been providing clues about how the Red Centre formed hundreds of millions of years ago for geological detectives from Geoscience Australia and the Northern Territory Geological Survey.

What is a Pound?

The Mordor Pound is an example of a landscape feature referred to as a 'Pound' in Australia. The term 'Pound' appears to have been derived from the late Old English term for a stone enclosure to shelter or accommodate livestock.

In Australia, Pounds are deep valleys that are enclosed by cliffs. They form when the soft rocks in the valley floor erode more easily than the harder rocks which form the cliffs.

Mordor Pound is a spectacular example of a rectangular pound that is enclosed by high cliffs.

Other examples of Pounds in Australia include: the Wilpena Pound in South Australia and the Ormiston Pound west of Alice Springs in the Northern Territory.

What do rocks in the Mordor Pound tell us about the geology of central Australia?

The valley floor of Mordor Pound is made up of igneous rocks that are formed by the cooling of magma, or molten rock, below the surface of the earth. Compared to the surrounding sandstone cliffs, these rocks are soft, which is the reason Mordor Pound formed.

In the image you can see the dark rocks in the floor of Mordor Pound which are composed of iron and magnesium-rich minerals with no quartz. One of these minerals, phlogopite, which is a magnesium-rich mica, commonly has a bronze, shimmering effect. The combination of the dark colour along with the shimmering effect gives the rocks of Mordor Pound the feel of a "dark land where the shadows lie" as the Land of Mordor was described in the Lord of the Rings. One of the highest hills made of these unusual dark rocks was christened 'Mt Doom' by Langworthy.

The discovery that rocks in Mordor Pound are about 1130 million years old provides a clue that the Red Centre was connected to North America a billion years ago. The Mordor Pound rocks are important as they are one of the northernmost examples of rocks of this age. These rocks form a belt of rocks to the south in the Musgrave area of South Australia and the Northern Territory.

Similar aged rocks form a belt of rocks, known as the 'Grenville Front', that extends from eastern Canada to Arizona in the south-western United States through to the Musgrave region.

Many geologists consider that Australia was connected to North America up until about 600-700 million years ago, when the Australia-North America super-continent, called Rodinia by geologists, was split, or rifted apart by subterranean forces to start forming the Pacific Ocean.

The map is a reconstruction of Rodinia showing the inferred relationship between Australia and North America about 600-700 million years ago. It is based on the reconstruction presented by Karlstrom et al. (2001), Precambrian Research, v. 111, p. 5-30.

How old is old?

An age of 1130 million years is not particularly old by Australian standards. The oldest rocks in Australia are more than 3700 million years and occur in Western Australia. Over half the rocks in Australia are more than 1000 million years old. The map on the right shows the distribution of rock ages in Australia. The earth itself was formed about 4500 million years ago.

To put these vast ages into perspective, think of a calendar year matched to the Earth's history of 4500 million years, as seen in the geologic calendar below. This calendar shows important events in the history of the Red Centre (in red), Australia and the Earth.

A single day on this calendar corresponds to 12.5 million years. One hour corresponds to 520 000 years, and one second to 145 years.

According to this 'calendar clock', the earliest fossil evidence of life (blue-green algae) appeared on Earth in late March (about 3500 million years ago).

Many of the rocks covering the vast areas of central Australia were formed in mid-August (1850-1750 million years ago).

The unusual igneous rocks of the Mordor Pound formed on about 3 October (1130 million years ago).

A wide variety of life forms, including jellyfish, worms, trilobites and animals with backbones, burst onto the scene around 19 November (545 million years ago).

Dinosaurs first roamed the Earth on 14 December (225 million years ago) and became extinct on 27 December (65 million years ago).

Early 'Man' (Homo sapiens) did not appear on Earth until about 11.25 p.m. on 31 December (300 000 years ago).

Aboriginal people were painting in rock shelters at 11.58 p.m. on 31 December (20 000 years ago), and explorer John McDougall Stuart traversed the Red Centre (in 1860) one second before the end of the calendar year.

How do scientists measure the ages of rocks?

How can scientists be so confident about measuring the ages of rocks?

Some philosophies regard all time and the Earth as eternal, with no beginning and no ending. Others consider that there was a definite starting point: for example, the 17th century Archbishop Ussher in Ireland counted back through the Biblical and Hebrew records to suggest that the Earth was created in 4004 BC. Since Ussher's calculations, scientists and philosophers have estimated the age of rocks and the Earth using a number of methods - some accurate, some not.

The scientific breakthrough came in 1896 when the French physicist Becquerel discovered that minerals containing the element uranium emit radiation. The radioactive breakdown of uranium yields a stable end product-lead, and the steady rate of lead accumulation from uranium decay enables the ages of uranium-bearing minerals and rocks to be measured using the lead accumulation clock.

In the dark igneous rocks of Mordor Pound, uranium and lead accumulations in a mineral called zircon (pictured at right) have allowed geologists at Geoscience Australia to confidently measure their ages.

The uranium-lead dating of rocks is done in Canberra at the 'SHRIMP' (Sensitive High-Resolution Ion Microprobe laboratory), a joint facility of the Australian National University and Geoscience Australia.

Why is Mordor of interest to exploration companies?

During the past three decades, the igneous rocks of Mordor Pound have generated considerable exploration interest for nickel, copper, chromium, gold, platinum-group elements, diamonds, mica, uranium, and rare-earth elements. This extensive list of commodities reflects the wide range of compositions of the rocks. Trace to minor amounts of these commodities have been found by mining companies, but no economic resources have been delineated to date.

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Three decades of diamond exploration on one map

A new 1:5m scale map showing Australian diamond deposits was released recently by Geoscience Australia at a special one-day seminar on mineral exploration in Perth.

The map, titled Australian Diamond Deposits, Kimberlites and Related Rocks, shows Australia's operating diamond mines, historic alluvial mines and selected occurrences of diamond, as well as more than 500 intrusions of kimberlites and related rocks, a small number of which carry diamond in sub-economic amounts. Most of these bodies have come to light over the last 30 years in the course of diamond exploration by companies and this information has been generously provided for incorporation on the map.

In 2001, through the world-class Argyle mine in Western Australia, Australia produced 22 percent of the world's supply of natural diamonds by weight.

The map should be of interest to companies exploring for diamonds, government departments and researchers. It is available from the Geoscience Australia Sales Centre.