Zinc and Zinc Compounds

Galena and lead receive most of the attention when it comes to mining in southwestern Wisconsin but, zinc was also found the same deposits as galena. In the 1860’s after most lead mines had been closed, several mines were still extracting zinc. For a short period of time Mineral Point, Wisconsin had the world’s largest zinc processing mill. In the 1970’s, a large deposit of zinc sulfide was discovered near Crandon, Wisconsin. The proposed mine was very controversial as residents cited concerns about pollution and environmental damage. After several years of debate the proposal for the mine was dropped because of resident’s opposition and concerns over the mine’s profitability.

Figure 1 - Black Smoker

Source: Unknown

The ionic compound or mineral that zinc is obtained from is sphalerite. This mineral was formed about the same time the copper and iron formations were produced in the Lake Superior region. At the time the area under an ocean and there was a great deal of volcanic activity. The zinc formations were formed near “black smokers”. Today “black smokers” are found in rift areas on the sea floor where the continents are pulling away from each other. The black smokers form because water that seeps down through the ocean floor is heated and dissolves sulfide minerals like zinc sulfide, copper sulfide, or iron sulfide. As soon as the hot water hits the cold ocean water the sulfide minerals precipitate producing what looks like “black smoke”. These sulfide minerals eventually deposit around the smoker and eventually become the zinc deposits that can be mined after millions of years. Geologists suspect other sulfide mineral deposits may exist in north-central Wisconsin because several hundred million years ago this area was located on the edge of a continental plate. Today, black smokers are found at the bottom of the ocean along the plate boundaries where the continental plates are either pulling apart or colliding with one another.