Base Metals

 

Zinc-Copper volcanogenic massive sulfide (VMS) deposits have been observed as they form at mid-ocean ridges. Chimneys formed at the ridges have as much as 29 weight % zinc and 6 weight % copper in sulfide minerals (pyrrhotite, pyrite, sphalerite, and chalcopyrite). The minerals are dissolved in fluids at temperatures as high as 380 C flowing at 1-5 m/sec.

The minerals precipitate as the hot solution comes in contact with cold sea water. Photography courtesy of Woods Hole Oceanographic Institution and members of the Adventure dive (Principle Investigators: D. Fornari, R. Haymon, K. Von Damm, M. Perfit, M. Lilley, and R. Lutz).

 

 

Lead, zinc, and cooper are found in VMS deposits. The deposits form in deep ocean water by the precipitation of sulfide minerals released by submarine volcanoes.

 

Volcanic fluids and hot seawater move through the volcanic rocks and leach metals. The deposits are associated with lava flows, breccia, water-deposited tuffs, cherts, sulfates, and limestones. VMS deposits are usually associated with quartz, anhydrite, gypsum, and barite. This photo shows pyrite in silicified tuff from a VMS deposit in eastern Java, Indonesia. The sample contains 0.55 ppm gold.

There are three types of VMS deposits:

  Zinc-Copper Lead-Zinc-Copper Copper-Pyrite
Host rock basalt to rhyolite rhyolite basalt or ultramafic lava
Age Archean Proterozoic-Paleozoic Mesozoic
Ore minerals sp, ch, py ga, sp, py, some ch ch, py
Associated metals gold, silver silver, some gold gold
Famous Occurrences greenstones of Canada, Australia Sudbury and Bathurst Canada Kuroko, Japan Cyprus
Setting spreading centers back-arc basins spreading centers
Minerals: sp = sphalerite ch = chalcopyrite py = pyrite and ga = galena.

 

Kuroko-style VMS deposits are found in dacite-rhyolite domes that erupted in the deep water of back-arc (behind the main volcanic arc) basins. Kuroko deposits are zoned from copper-rich near the center, to zinc-rich, to lead-rich at the outer edges of the deposit. The fluids that form Kuroko deposits have twice the salinity of average ocean water and temperatures of 250-300 C. This cross-section of a typical Kuroko deposit is from Sato (1974) and Franklin and others (1981). Modern-day VMS deposits of the Kuroko-style have been observed as they form in the back-arc basin of the Okinawa Trough (Halbach and others, 1989).

The deposit at Bathurst in Canada is an example of lead-zinc-copper VMS. Hydrothermal solutions associated with Keweenawan flood basalts have produced copper deposits in the Lake Superior area. Between 1845 and 1968, over 13 billion pounds of copper and 16 million ounces of silver were produced from the Keweenawan district.

The porphry (not VMS) mine at El Abra in Chile will produce 500 million pounds of copper annually.

 

Uses for Copper, Lead, and Zinc

Copper was used as long ago as 8000 BC for tools, weapons, and ornaments. The discovery of bronze (copper and tin alloy) about 3500 BC marked the onset of the Bronze Age. Romans used lead for the plumbing and sewage systems. In Modern times, the electrical conductivity, ductility, and resistance to corrosion of copper, lead, and zinc, make them very useful in alloys. Copper is used for electrical applications (50%), general and industrial engineering applications (20%), building and construction (15%), transportation (11%) and other applications. Lead is used in storage batteries, paints, dyes, explosives, insecticides, and rubber products.

Zinc is used in galvanized steel, protective coatings for steel, and die casting. Zinc compounds are used for luminous dials, cosmetics, plastics, rubber products, soaps, and inks.

World Supply of Copper

In 1991, 9,167,000 tons of copper was produced. Chile (19.8%), USA (17.8 %), and the CIS (9.8%) are the main producers. USA, Japan, and the CIS are the main consumers.