Chalcopyrite, Molybdenite, Pyrite & Quartz
Chalcopyrite is the most common ore mineral for copper and is a sulphide of iron and copper. Chalco comes from the Greek word chalko, meaning copper. Chalcopyrite is commonly found in sulphide deposits in most ore-forming environments. A characteristic deep brass yellow colour and iridescent green-to-purple weathering surfaces distinguish chalcopyrite from gold and sulphides such as pyrite.
Soft silvery-grey molybdenite is the main ore mineral for molybdenum. Molybdenum, often just called ‘moly’, is used to make alloys with other metals like iron. Adding molybdenum to steel makes it stronger, harder and more resistant to corrosion. It also has a very high melting temperature, so is very useful when added to alloys to make aircraft parts and industrial motors, which need to withstand high temperatures.
Pyrite is a common iron sulphide mineral found in many different geological settings. It has a brassy-yellow metallic colour that has caused many people to mistake it for gold, giving it the name “Fool’s gold”. Pyrite and gold can be quite easily distinguished from one another: pyrite is less yellow and much lighter and harder than gold, which can be scratched with a pocket knife. Pyrite often forms perfect cubes, which can grow to quite large sizes, because of its crystal structure. The word pyrite comes from the Greek word ‘pyr’ meaning fire, because it will spark if hit with other metal or stone objects.
Quartz is the second most abundant mineral on Earth, occurring in many different types of rocks. Although usually clear or milky white in colour, quartz can be found in a variety of colours because of impurities in the crystal structure. Pure quartz is made up of silicon and oxygen only, but atoms of other elements, like iron or titanium, often make their way into the quartz crystal structure. Some varieties of quartz, like purple amethyst, are considered to be semi-precious gemstones and have been used since ancient times to make jewellery and decorative objects.
This sample is from the Gibraltar mine in the Cariboo region of central BC, around 60 km north of Williams Lake. The mine is the second largest open pit mine in Canada.
The Gibraltar mine contains five main ore bodies: Gibraltar East, Gibraltar West, Gibraltar North, Granite Lake and Pollyanna. Production started in 1972 and continued until 1998, when metal prices dropped and the owner at the time, Boliden Resources, put the mine into care and maintenance. In 1999, Taseko Mines Ltd bought the mine and re-opened it in 2004. Production continues today.
The Gibraltar ore bodies are copper-molybdenum porphyry deposits, which are large, low-grade, high-tonnage deposits associated with granitic intrusions. Mineralization consists of veins of chalcopyrite with or without quartz, and molybdenite with quartz. The veins are mainly concentrated in areas that have been faulted and deformed.
The mine currently produces an average of 138 million pounds of copper at grades of 0.26% copper and 0.008% molybdenum.
Store: Association for Mineral Exploration (AME)
Accession #: AME 991
Primary Mineral: Chalcopyrite, Molybdenite, Pyrite, & Quartz
Secondary Mineral: –
Site Locality: Gibraltar Mine
Location: Cariboo Region, Central British Columbia
Special Features: n/a