GC1MJXA White Bronze (Earthcache) in Indiana, United States created by bluegillfisherman

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GC1MJXA ▼

A cache by bluegillfisherman Message this owner

Hidden : 2/10/2009

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Geocache Description:

This Earthcache will give you a look into the formation, history, mining, production and major uses of zinc. Then we shall move on to a novel and historic use of the metal in it's pure form.

History

Centuries before zinc was discovered in the metallic form, its ores were used for making brass, and zinc compounds were used for healing wounds and sore eyes. Brass was produced by the Romans in the time of Augustus (20 B.C. - 14 A.D.). By 1374, zinc was recognized in India as a new metal and at Zawar, India, both zinc metal and zinc oxide were produced from the 12th to the 16th century. From India, zinc manufacture moved to China in the 17th century. Zinc was recognized as a separate metal in Europe in 1546. In 1743, the first European zinc smelter was established at Bristol in the United Kingdom.

Zinc Ores

Metal ores are generally oxides, sulfides, silicates, or "native" metals that are not commonly concentrated in the Earths crust, or "noble" metals. The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.
Ores containing zinc are widespread geologically and geographically and many ore bodies are still awaiting development when sufficient demand occurs. Ore veins are vertical to near vertical mineralized zones. They can be thinner than one inch or as wide as fifty feet. They are usually associated with “mineral districts” – multi-county areas with the widespread injection of minerals from deep within the Earths crust.

Usually zinc ores are found in association with those of lead, copper, gold, silver as well as other metals. Rarely is the ore, as mined, rich enough to be used directly by smelters; it needs to be concentrated. Typically zinc ores contain 3% to more than 10% zinc and zinc concentrates will contain 55% zinc.
Among several mineral ores,(ie: smithsonite, hemimorphite, zincite, & wurtzite), a mineral called sphalerite is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains some iron. When iron content is high it is an opaque black variety,

marmatite. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, and fluorite. Sphalerite is found in hydrothermal sulfide ore veins of any rock class, sedimentary, igneous, or metamorphic.

Zinc ore types, in detail, are:
a. Volcanic-hosted massive sulphides
VHMS deposits are a type of metal sulfide ore deposit, mainly copper-zinc-lead which are associated with and created by volcanic associated hydrothermal events in submarine environments. They are predominantly stratiform accumulations of sulfide minerals that precipitate from hydrothermal fluids on or below the seafloor in a wide range of ancient and modern geological settings. VHMS deposits occur in greenstone belt, island arc and back-arc settings that range in age from Archean to recent. A characteristic feature is district scale clustering with numerous low-tonnage occurrences and a small number of giants.

b. Sediment-hosted massive sulphides (SEDEX)
SEDEX (Sedimentary Exhalitive) deposits represent some of the world's largest accumulations of zinc. Stratiform and stratabound mineralization is associated with reduced host sequences in a variety of clastic sedimentary basin settings, with endowment peaks in the Mesoproterozoic and late Paleozoic. These settings include intracratonic rift basins and passive margins.
SEDEX ores imply they also formed as a result of hydrothermal fluid exhalation into sedimentary basins. This is not necessarily the case as these deposits are formed from metal-rich basinal brines that can either discharge onto the seafloor or flow through permeable horizons within the sedimentary rock package. The ore bodies occur as a set of stacked stratiform lenses separated by weakly mineralized meta-sedimentary rocks. The larger sediment-hosted deposits contain high percent levels of zinc and lead and by-product silver.

c. Mississippi Valley Type ("MVT") carbonate hosted deposits
MVT deposits are a varied family of epigenetic zinc mineralization styles hosted predominantly by dolostone sequences of Paleozoic-Mesozoic age. Undeformed orogenic foreland carbonate platforms are the favored tectonic settings. Areas are varied and include shale pinch-outs, limestone-dolomite transitions, solution collapse breccias, reef complexes, faults and basement topography.
The source of metals within carbonate-hosted lead-zinc ore deposits is the host carbonate sequence where diagenetic recystallisation of low-temperature calcite into a higher-temperature aragonite form prompts adsorbed zinc to be metamorphically ejected from the carbonate minerals. The zinc then enters the formational solutions and typically forms a chelated bond with hydrocarbons. The low-temperature hydrothermal solution formed by diagenetic recrystallization of the carbonates then migrates into stratigraphic highs, such as folds, and typically also concentrates in fault zones at the margins of basement grabens.

d. Intrusion-related zinc ore deposits
Intrusion-related copper-gold and zinc systems form a spectrum of significant deposits that range from classic porphyry copper-gold deposits to the more recently recognized zinc systems. The style and geochemistry of individual systems can be related to a complex interplay between emplacement depth, magma chemistry, host rock composition, structural setting and the influence of exotic fluids.

e. "Broken Hill" type ore deposits
Broken Hill-type deposits are a poorly understood and often-controversial category of sediment hosted metamorphosed massive sulphides. Known deposits occur in Paleo-Mesoproterozoic amphibolite to granulite facies metamorphic belts. Due to complex metamorphic, metasomatic and structural overprints it is difficult to define pre-metamorphic relationships. Despite these difficulties, the high-grade and excellent metallurgical performance of BHT deposits makes them attractive.

Mining

The Red Dog Mine, in Alaska, is the world's largest single producer of zinc and has the world's largest zinc reserves. Red Dog Mine accounts for 10% of the world's zinc production. It supplies 75% of the total United States production.The ores are hosted in black shales of the Kuna formation of Carboniferous age. The ore deposit is classically described as Sedex or shale-hosted base metal deposit.
Zinc ores are being mined in more than 50 countries with Australia, Canada, China, Peru and the U.S.A. being the leading producers. Owing to the nature of the ore veins, most zinc mines are underground but some newer mines are of the open pit type. In terms of production volume, open pit mines account for as much as 15% with underground mines producing 64%. 21% of mine production comes from the combination of underground and open pit mining.

Production

The raw material used for the production of zinc is zinc concentrate, which is the result of a flotation process after the ore has been mined and milled. The zinc ore contains 1-15% zinc whereas the concentrate typically contains approx. 55% zinc, 6.5% iron and 32% sulfur together with other elements at much lower levels.
The process begins with the roasting of the concentrate. At a temperature of around 950°C, oxidization of the zinc, iron and sulfur occurs. The iron and zinc oxides that, after the roasting process, have been reduced to powder form, are leached with dilute sulphuric acid. The solution is neutralized and the precipitates, i.e. metallic co-products together with any unwanted contaminants, are removed by filtration.
The refined solution is then electrolyzed in a cell fitted with a lead anode and an aluminum cathode. The cathode is immersed in the solution for 48 hours during which time the zinc is deposited on the aluminum cathode from which it is subsequently stripped.
The final process takes place in the foundry where the zinc takes its final form, either as a metal with a purity of 99.95% or as an alloy together with copper, aluminum or magnesium. The zinc is cast into various forms (normally ingots or plates)with weights from 9 kg to 4 tons.

Major uses:

Zinc is the fourth most widely used metal after iron, aluminum, and copper. Zincs major use is for corrosion protection coatings on steel (galvanized metal); as die castings, as an alloying metal added to countless other metals, as chemical compounds in rubber, ceramics, paints, and agriculture, and in pharmaceuticals & cosmetics. It's also a necessary element for proper growth and development of humans, animals, and plants.
Note: Todays U.S. one cent coin is 97.5% zinc, with the remaining metal being the copper plating.

A Historic use:

" White Bronze"

Monumental Bronze Company, of Bridgeport, Ct; made zinc grave markers and large monuments & statues from 1874 to 1914.
The term "White Bronze" was used only to make the monuments sound more appealing. It wasn't bronze at all. Zinc in its pure form was used. Monumental Bronze Company (and it's subsidiaries) was the only company to have ever manufactured monuments & grave markers with zinc. All the casting was done in Bridgeport, although most assembly of the final product was done by the subsidiaries.

The company’s original records show that its soldiers and sailors statues are standing on village and city greens in 31 states. Ranging in size from .5 to 5 meters in height, grave markers were sold and shipped nationwide.
These monuments have lived up to the sales agents promises of durability, and superiority to their stone counterparts(sandstones & marbles), and have remained in excellent condition for over a century. After 100 to 135 years, every word, name, and date is as clear and legible as the day it was cast.

One weakness that has damaged these zinc monuments is caused by the pressure from their own weight. Zinc has a tendency to creep, or bend when it's exposed to pressure over time. This creeping action may also cause tiny cracks on some of the monuments. Obviously, smaller markers do not exhibit this problem. Proper seating/mounting on concrete bases was important to reduce creep & corrosion from prolonged contact with the soils.

"Creep"....outward bending of base

In an attempt to boost sales, in 1879, Monumental Bronze Company changed the "finish" on the metal so it would more closely resemble stone. Sandblasting roughened the surface and speeded up the natural formation of protective oxide coating. Also, on many styles, the base was cast to resemble cut stone. Now, pre 1879 monuments are smooth with a grayish color. Post 1879's have a rough surface and are bluish-silver in color.

The company ceased to cast memorials in 1914 when the plant was taken over by the U.S. Government for the wartime manufacture of gun mounts and munitions, and from 1930-1939, failed to even advertise anything about their company. Although Monumental Bronze formally ceased to exist in 1939, company secretary C.A. Baldwin continued to cast the interchangeable name plates for the existing memorials under the new name of Memorial Bronze Company.

The "heyday" for these unique grave markers was short-lived. ~ 1880-1900 were the peak years for production. Having withstood the elements for over a century, it appears these rare zinc monuments will be with us for another one, and likely beyond.

To log this EarthCache:
Park at the above coordinates and locate the nearby zinc memorial:
In an email, answer the following.
1. How does the metals surface texture feel?
2. Is it pre, or post 1879?
3. Does it exhibit "creep", and are there any cracks in the metal near base?

Please post no photos that may disclose the requested information.

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White Bronze EarthCache

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