Malachite & Molybdenite
This specimen contains easily visible molybdenite, malachite and quartz with less visible amounts of chalcopyrite, and bornite.
Molybdenite is the main ore mineral for molybdenum. It is very soft and has a similar appearance to graphite. It can be used as a lubricant due to the weak bonding between layers within its crystal structure.
Malachite is formed when copper containing minerals are weathered. This sample likely had visible bornite and chalcopyrite before weathering into the distinct green malachite colour found on the outside of the specimen.
Bornite and chalcopyrite are important copper ore minerals found in many different types of copper deposit. Bornite 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.
This sample comes from the Bethlehem copper porphyry deposit in the Central Interior. The deposit is about 15 km west of the small town of Logan Lake, and about 80 km southwest of Kamloops.
The Bethlehem deposit is one of the deposits that make up the Highland Valley Copper mine, which also includes the Lornex, Highmont and Valley deposits. Early prospectors found copper mineralization in the Highland Valley area in the late 1800s and started hand mining at the Snowstorm and Iona zones of the Bethlehem deposit in 1907, when a wagon trail was built to nearby Ashcroft and the Fraser Canyon railway line. Large-scale open pit mining started at Bethlehem in 1962 and continued until the early 1980s, when production shifted to the other deposits, which are still being mined today. The large Valley pit and operations are visible from a lookout on Highway 97C.
The main ore minerals at the Bethlehem deposit were bornite and chalcopyrite, which are present in this sample. The ore minerals are mainly in very narrow veins, often only a few millimetres wide. Chalcopyrite is also found as fine “disseminations”, or speckles, throughout the host granodiorite rock. Pyrite is also common at Bethlehem, mainly towards the outer edges of the deposit. The other ore mineral mined at Bethlehem was molybdenite, another sulphide mineral and the main ore for molybdenum, which also occurs in narrow veins with quartz and is present in this sample.
From 1962 to 1982, production at the Bethlehem mine totalled 96,324,510 tonnes of ore that yielded 99,826,893 grams silver, 1,279,833 grams gold, 398,112,545 kilograms copper and 851,048 kilograms molybdenum.
Store: Association for Mineral Exploration (AME)
Accession #: AME-21b
Primary Mineral: Molybdenite & Malachite
Secondary Mineral: Chalcopyrite, Bornite, & Quartz
Site Locality: Close to Logan Lake, B.C.
Location: Highland Valley, B.C.
Special Features: n/a