

Page Index
Introduction
History of Zinc
Uses of Zinc
Zinc Pricing
Lead and Zinc Geology and
Exploration
Introduction
The base metal zinc (symbol Zn)
is a lustrous (light-reflective) bluish-white metal,
ordinarily brittle and crystalline. Zinc becomes
malleable and ductile when heated to between 110 and
150? Celsius.
Although not abundant in nature,
zinc has several key commercial applications. It is
primarily used as a protective coating material in
transportation, construction, and electrical
equipment. Zinc is also an essential animal
nutrient.
Zinc is most readily found in the
ores sphalerite, zincite, calamine, and smithsonite,
and is often mined in conjunction with lead, silver,
copper, and cadmium.
The world's biggest zinc
producers are Canada, China, Australia, Peru,
Mexico, Ireland, and the United States.
For further information on zinc,
visit the
International Zinc Association.
History of Zinc
Zinc has been in use since
ancient times. An alloy containing 87 percent zinc
was discovered in prehistoric ruins in Transylvania;
bronze objects containing zinc, discovered in the
Middle East, are estimated to be 3,000 years old.
The Babylonians smelted copper
alloys containing tin and zinc in the third century
BC. Zinc was used to make mirrors and coins in China
around 600 AD. Both the Greek and Roman
civilizations actively used zinc to produce brass.
Metallic zinc was produced in 13th-century India by
reducing the calamine ore with organic substances
like wool.
As explorers forged early trade
routes, zinc's applications became well known
throughout Europe and the New World. Zinc enjoyed a
revival upon discovery in Europe in 1746 by Andreas
Sigismund Marggraf.
Uses of Zinc
Zinc has many personal and
industrial uses.
Human bones, teeth, and the
immune and reproductive systems all require the
fortifying power of zinc - the recommended daily
zinc intake is between nine and 15 mg, and is
derived from beef, liver, cheese, eggs, milk, and
yoghurt.
Zinc is found in insulin, a
treatment for diabetes, while creams and lotions
made with zinc oxide are used to treat wounds,
infections, and various skin disorders. Zinc is also
found in sunblocks.
Zinc is essential in the
preparation of alloys like brass and German silver;
and it is sometimes utilized in making bronze. The
metal is used for the negative plates in certain
electric batteries, and in roofing and gutters in
building construction.
Zinc castings turn up in
everything from electronic devices to children's
toys. Modern cars contain about 40 pounds of zinc
each, much of it found in steel body panels. In
addition to zinc oxide, other important zinc
compounds include zinc chloride, used in adhesives
and cements and to preserve wood, and zinc sulfide,
which is used to make television screens and X-ray
apparatus.
Zinc Pricing
Zinc is traded daily on the
London Metal Exchange. The price is set each day at
two separate sessions. First session: 12:10 p.m. and
12:50 p.m. Second session: 3:25 p.m. and 4:05 p.m.
Lead and Zinc Geology and
Exploration
Because the base metals lead and
zinc are most often found together in mineral
deposits, that is how this section will consider
them.
Principal lead-zinc deposit types
include carbonate-hosted Mississippi Valley (MV)
ores, sandstone-hosted ores, shale-hosted (or SEDEX)
deposits, and volcanogenic (VMS) deposits.
Of sedimentary ores, the MV
deposits have provided considerable past production
of lead and zinc mined throughout the world. These
deposits occur along the edges of large sedimentary
basins in all parts of the world, are typically
hosted by carbonate (dolostone) rocks, and form very
large ore districts with numerous individual
deposits within these camps. The former Pine Point
district, NWT and the Viburum lead-zinc ore trend in
Missouri are two notable examples. Data for
individual deposits is highly variable, but an
approximate range for MV deposits is from five to
ten percent combined lead-zinc and one to 10 million
tons. As with other zinc-lead deposits, sphalerite
and galena are the main ore minerals.
Canada's north serves as a good
example of carbonate-hosted ores. Here a total of
300 million tons have been mined from the Pine Point
deposits, Polaris and Nanisvik. Together, these
mines average two percent lead and 6.9 percent zinc.
Recent exploration successes for carbonate lead-zinc
deposits include Platinova's (1993) discovery in NE
Greenland of a 55 million ton deposit grading 12
percent zinc and one percent lead, and Rhonda Mining
Corp.'s (1996) discovery of the Esker deposit in the
NWT, Coronation Gulf area. High-grade lenses of up
to 8.6 percent zinc and 2.3 percent lead occur
within a lower-grade geological resource estimated
to be approximately 100 million tons.
For the shale-hosted (SEDEX) type
of lead-zinc ore, examples in Canada include the
giant Sullivan Mine in British Columbia and the
deposits of the Yukon's Anvil district. In
Australia, Mount Isa and the metamorphosed Broken
Hill deposit are important economic examples
belonging to this class.
SEDEX deposits consist of layers
of massive sulfide interbedded with layers of
sedimentary rock (shales, mudstones, and
argillites). The massive sulfides are composed of
alternating layers of iron sulfide (pyrite or
pyrrhotite), with lesser amounts of sphalerite,
galena, and layers of clastic sediments. The
calculated average size and grade of SEDEX deposits
is in the order of 45 million tons grading 6.8
percent zinc, 3.5 per cent lead, and 1.45 ounces/ton
silver. Deposit size, however, can be quite large -
up to several hundred million tons with grades up to
18 percent zinc and nine percent lead. SEDEX
deposits are, therefore, important exploration
targets, in spite of the fact that they are
relatively rare and have metallurgical recovery
problems due to the fine-grained nature of the
sulfides.
Volcanogenic massive sulfide
deposits (VMS) comprise the third significant
category for world production of lead and zinc
concentrates. This class of mineral deposit differs
from the above by being associated with rhyolitic to
basaltic flows and fragmental volcanics. The
sulfides occur as more or less stratabound lenses
with an underlying, commonly discordant zone of
disseminated sulfides (stockwork or stringer zones)
in highly altered rocks. The ores are polymetallic
and of two major types: copper-zinc or zinc-lead
(minor copper). Precious metals, along with tin,
cadmium, bismuth, and selenium, can be recoverable
byproducts with the base metals.
Examples of the lead-zinc type
include the Brunswick Mine, New Brunswick, and the
ores from the Buchans Camp, Newfoundland, while Kidd
Creek Mine in Ontario and the numerous deposits in
the Noranda camp typify the copper-zinc-type. While
a few deposits are huge (greater than 100 million
tons), 80 percent of VMS deposits fall in the range
of one to 10 million tons. In the Bathurst camp
(lead-zinc type) the average grade and tonnage of 29
deposits is 5.43 percent zinc, 2.17 percent lead,
0.56 percent copper, and 1.74 ounces per ton silver.
For the copper-zinc type, the average grade and
tonnage of 52 deposits in the Abitibi belt is 10
million tons grading 1.47 percent copper, 3.43
percent zinc, 0.07 percent lead, and about one ounce
per ton silver. By the mid-1980s, over 1,000 VMS
deposits had been discovered and the search for this
economically important source of metals continues
unabated.
Sandstone-hosted lead-zinc
deposits are much less common. Well-known examples
include the Laisvall, Vassbo, and Dorotea deposits
in Sweden, Largentiere in France, and
Maubach-Mechernich in Germany. In Canada, the Yava
mine in Nova Scotia was mined for a short period in
the 1980s. Deposits of this type have ranged in size
from very small prospects to 225 million tons. These
deposits are lead-rich (2-5 percent) and generally
contain insignificantly amounts of zinc (0.2-0.8
percent). The deposits are only of local
significance (e.g. in Sweden) and exploration is
virtually non-existent. |