Unique Tsumeb Namibia Part II
PART II
No other ore deposit has had three oxide zones. As we explained in Part One, Tsumeb is a unique ore deposit because it has three separate oxide zones, and has produced several uncommon species. When mining started there, back in the early 1900s, the initial ores were rich in secondary minerals formed as weathering had attacked the primary copper and lead sulfide ores. This initial oxide zone, which extended some 1,000 feet down, produced some of the world’s finest azurite specimens; including the amazing “Bird’s Nest” azurite described in Part One, which may be the world’s finest azurite.
Later, Tsumeb’s three oxide zones produced huge quantities of secondary minerals, many of them rare, or unusual. Each oxide zone has its differences, which made Tsumeb famous, and certainly surprised the engineers as mining passed through the upper oxide zone, into the sulfides, and encountered another oxide zone. When they started running into a second oxide zone, with the sulfides, they were surprised. They were well below the near-surface oxide ore zone by a matter of hundreds of feet. Once they mined through the second oxide zone they eventually got back into sulfides. This was too deep to have been attacked by surface waters from above, and mining continued through the second oxide zone into sulfide ores again. Remarkably, a third oxide zone was breached. Clearly, they were mining something unique and very complex.
It took years before they figured out the cause of these unexpected oxide zones. In Part One, we explained this happened because of faulting, especially what they called the Great Fault system, which includes the North and South Break zones. These allowed surface waters to reach deep into the ore body and create the second and third oxide zone. What makes these lower oxide zones more interesting is the primary metals including rare elements like germanium, gallium, and rare earths.
With three oxide zones producing colorful, sometimes rare, and well crystallized secondary mineral species, Tsumeb became exceedingly popular among dealers. Note, the oxide and primary sulfide zones were interwoven because of repeated faulting as the Great Fault system and the oxide zones extended into the sulfides at differing levels.
The upper oxide zone is well known for superb azurites along with different types of malachite.
Pseudomorphs, after azurite crystallized malachite on calcite, native copper and cuprite were found. Tsumeb is a copper-lead deposit, so secondary copper and lead minerals were found throughout the ore body but concentrated in the oxide zones.
In the early days of mining, the company was not strict about miners collecting. In fact, sometimes they let miners go underground to collect during off duty instead of paying them overtime. This is how the great Bird’s Nest azurite was found in the 1940s, on the 800 level.
The second oxide zone is noted for the great amount of cerussite and dioptase it produced. I can recall the Tucson Show in the 1970s having huge quantities of these two species from Tsumeb. In fact, when I wrote the Fifty-Year History of the Tucson Show
I noted this deluge of specimens of dioptase and cerussite in the 1970s. I even named 1971 “the Year of Dioprase.” In a following year, I titled it “the Year of Cerussite.” These were described in Part I of this article. I actually tried to get a count of the number of flats on dealer tables one year. I came up with a count of over fifty flats, but there were many more.
Of the huge quantities of cerussite mined were twinned and ranged in size from under an inch to