Bornite

With garnet and quartz

Bornite is an important copper ore mineral found in many different types of copper deposit. It is also known as peacock ore because of its iridescent purple-blue-green tarnish. Fresh bornite, however, is copper red. Bornite commonly occurs with other copper sulphide minerals such as chalcocite and weathers, or “oxidizes”, to malachite.

Garnet occurs in many different colours and crystal shapes, but is commonly found as deep red dodecahedra. The term garnet actually refers to a group of minerals that have very similar crystal structures but contain different elements that affect the colour of the mineral. Garnets rich in chromium (e.g. demantoid or tsavorite garnets) are green-coloured, whereas garnets rich in iron or magnesium (e.g. almandine or pyrope garnets) tend to be red, pink or reddish-brown. Garnets are hard and have a glassy to resinous lustre. They form in metamorphic and igneous rocks but because of their hardness are persevered during the weathering processes and can accumulate in sediments as well.

Quartz is the second most abundant mineral on Earth, present in many different types of rocks. Although usually clear or milky white in colour, quartz is found in a variety of colours due to impurities in the crystal structure. Pure quartz consists of silicon and oxygen only, but atoms of other elements often make their way into the quartz crystal structure, colouring the crystals. Some varieties of quartz, like purple amethyst and yellow citrine, are considered to be semi-precious gemstones and have been used since ancient times to make jewellery and decorative objects. Well-formed (euhedral) crystals of quartz have a hexagonal cross section and are highly collectible.

This sample was collected on Gribbell Island on the north coast of BC. As well as bornite, the sample also contains quartz and garnet.

A small copper showing was discovered and staked at the southern tip of the island in the early 1900s. Several short mining adits, all less than 220 m long, were driven into the bedrock and about 35 tons of ore were extracted between 1900 and 1906. Some further exploration work was carried out in the 1960s and early 1970s but the amount of ore present is too small to be considered economically viable or significant.

On Gribbell Island, the copper ore minerals bornite, chalcocite and covellite are found in a small copper skarn deposit. Skarn deposits form around the contacts between carbonate sediment host rocks, often transformed into marbles and schists, and a magmatic intrusion. Common gangue (waste) minerals found in skarns include garnet and quartz, as seen in this sample.

Gribbell Island is now part of the Great Bear Rainforest, a protected area of 6.4 million hectares that was recognized by the BC government in 2016. The island is home to a population of rare Kermode bears, also known as spirit bears because of their unusual white fur. 

Specimen Information

Store: Pacific Museum of the Earth, University of British Columbia

Collection: Sutton-Thompson Collection

Accession #: S74-4302

Primary Mineral: Bornite

Secondary Mineral: Garnet and Quartz

Site Locality: –

Location: Gribbell Island, British Columbia

Special Features: n/a

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