The story of the formation, discovery and mining of the ore-bodies at Northparkes is a long one! It began approximately 450 million years ago, during the Ordovician period of geological history, and it continues at the present time.
The Northparkes ore-bodies lie within a belt of volcanic rocks that was erupted during a time period of a few million years, approximately 450 million years ago.
These rocks were probably formed in a region similar to the south-west Pacific Ocean today, where volcanic islands have been built up over thousands or millions of years by volcanic eruptions out of the sea.
Lopevi, a volcano in Vanuatu, SW Pacific
Heat from deep inside the earth caused rocks in the earth's interior to partly melt, forming blobs of hot, thick liquid called magma. The magma rose up through the earth and as it rose, it slowly cooled over millions of years. Cooling caused crystals of minerals to grow in the magma, forming huge bodies of solid pink to brick-red rock called porphyry.
The crystallising magmas contained tiny amounts of sulfur, copper, gold and silver which crystallised as ore minerals in the porphyry, and in the surrounding volcanic rocks, deep within the earth. The crystallisation of these ore minerals formed the Northparkes ore bodies.
Rock that is mined because it contains valuable and useful minerals is called ore. The main ore minerals are copper-iron-sulfur minerals called bornite (Cu5FeS4) and chalcopyrite (chemical formula = CuFeS2). As well as small amounts of gold and silver, bornite contains about 63% copper (by weight), 11% iron and 26% sulfur and chalcopyrite contains about 35% copper, 30% iron and 35% sulfur.
The photo shows a piece ore-bearing rock from Northparkes. The pinkish parts are the porphyry and the thick grey bands are veins of quartz, and are about 2cm wide. In the middle of the veins the gold-coloured grains are chalcopyrite, one of the main ore minerals at the mine.
Over millions of years, the land was uplifted above sea level, and eroded by wind and water, until eventually the chalcopyrite-rich ore bodies were brought close to the surface.
Gold was discovered in the Parkes district in 1862, but the gold rush only lasted five years until 1867.
In 1976 a company called Geopeko became interested in the Northparkes area because it had similar rock formations to other areas which were known to contain valuable minerals. Geopeko began drilling along the sides of public roads and discovered the Endeavour 22 deposit a year later. Further deposits (Endeavour 26, 27 and 48) have been discovered since.
Rocks taken as "drill core" from the Earth's crust during drilling at Northparkes.
A geologist examines the drill core looking for signs of ore mineralisation.
The company North Limited began mine construction in 1993, and the first gold was produced in May 1994, followed by copper concentrate production in September 1995.
