New Tsumeb Update 04 June 2021

4 June 2021

THE Mindat online database currently lists 350 valid minerals from the Tsumeb district, for which Tsumeb is the type locality to 72.

Ore deposits occur all over the world, brought about by the gradual concentration of elements through all manner of geological processes. Elements assemble to form orebodies and once these surpass various economic criteria, they can be mined. Probably the majority of mines produce only a very limited suite of mineral species but through quirks of nature, certain deposits have evolved over geological time to host magnificent assemblages, even forming new species never found anywhere else on our planet before. Tsumeb is one such place and certainly ranks amongst the top ten mineral locations on Earth in most mineralogist’s and collector’s books.

In 1893, following the initial examination of the surface outcrop named the “Green Hill”, it was instantly apparent this orebody was very special, being primarily rich in copper, lead, zinc and silver, but also in secondary minerals in the near-surface oxidation zone. This is the zone where oxygen-rich atmospheric water can circulate and react with the primary ores, so producing more exotic mineral species. Normally, once a mine is developed to below this zone, the ore reverts to simple primary species marking the end of interesting specimens. This was thought to be the case at Tsumeb and so mining continued with little hope of any new interesting or remarkable discoveries.

Tsumeb’s vast array of secondary mineral species would not have formed if it were not for the three vertical zones of oxidation that occurred in the mineralised pipe structure, named the 1st, 2nd and 3rd Oxidation Zones. Although the ‘plumbing’ of the 1,700 m deep ore pipe is complex, basically the orebody is intersected at depth by a low angle fault/shear zone named the North Break Zone (NBZ) which over time has conveyed ground water and hence oxygen to depths not otherwise possible. And so the happy serendipity of the Tsumeb deposit was sealed and there, deep underground, sat untold mineral treasures waiting for man to discover. We live in a golden age when the minerals recovered from this deposit are still available to collect, an age which inevitable be finite.

So, just what is on offer today? We have a few rarities and many gorgeous aesthetic pieces. Staring with a choice thumbnail, a splendid Ludlockite forming excellent dense sprays of rich deep reddish-apricot acicular crystals to over 1 cm on a mixed Chalcocite and Germanite matrix. Ludlockite is a rare iron-lead arsenite. In the very rare department, do look at the Melanotekite on Leadhillite. Melanotekite is a lead silicate and forms several micro-circular yellow brown patches on the highly reflective Leadhillite surface. The Melanotekite has been confirmed by EDS analysis at the Royal Ontario Museum, whose ‘Study Card’ accompanies the specimen.

Although Calcite is ubiquitous throughout the Tsumeb orebody, the specimen of copper-rich Calcite we have is very rare and very special. Cuprian Calcite, sometimes referred to as Cuprocalcite, was discovered in the 2nd Oxidation Zone during 1977 as very pale pastel-green Calcite rhombs with a sugary surface texture. This was named the “Ice-cream Pocket” and is now the stuff of Tsumeb legend. This magnificent miniature of delicate pale peppermint green Calcite forms a domed mound of stacked and offset-stepped rhombohedral crystals on a small matrix of platy white Calcite.

Another favourite is a Cobaltoan Smithsonite of delicate rose to candyfloss pink forming a rose petal-like bed of curved bladed crystals. Individual blades are finely frosted, generating a semi-matt to slightly silky lustre and texture. Another Tsumeb classic is Calcite with Dioptase inclusions. We have a small cabinet specimen in which the included Dioptase is surrounded by an outer band of pure Calcite forming a rhombic shaped frames in which the Dioptase is displayed.

Other excellent specimens worth pondering over include a well-formed tightly clustered group of Schneiderhöhnite crystals; a powder to turquoise blue Rosasite with olive to leaf green Olivenite crystals and an unusual well crystallised Siderite with Goethite on Germanite. We have not even mentioned the Tsumcorite, Azurite with Arsentsumebite, Mimetite with Bayldonite on Dolomite or Azurite partly pseudomorphing to Malachite. All wonderful specimens worth reading a bit more about.

Even if you don’t collect Tsumeb there is no denying this is one of nature’s mineralogical marvels, a very special finite volume of the Earth’s crust which has produced a seemingly infinite supply of incredible minerals. We hope you enjoy today’s update and, if you are a Tsumeb collector, encounter an addition worthy of your collection.

Here is what you have to look forward to in next week's update:

Saturday 12th June - British (Summer Open Day)

                                         

If you'd like to see a video of any of the specimens listed above then please contact us at orders@crystalclassics.co.uk and we'll be happy to assist you. We endeavour to respond to all enquires within 24 hours during weekdays, however at the weekend it might take us a little longer to respond.

 

The Crystal Classics Summer Open Day will be taking place on Saturday, June 12.

Our beautiful showroom in East Coker, Somerset will be open from 10am to 5pm and will be packed with thousands of fine and rare minerals. There will be many specimens from new, recently purchased collections as well as many fresh Fluorite finds from our mines in Weardale, County Durham.

A delicious breakfast and lunch will also be provided by The Village Cafe which is located next door to our offices.

To book your place please email Debbie at debbie@crystalclassics.co.uk or by phone 01935 862 673 to register your interest.

COVID-19 guidelines will be in place during the day and the following is expected of all visitors:

- Face masks must be worn at all times
- Social distancing must be carried out
- You must wash your hands upon entry to the showroom (in addition there will be several hand sanitiser dispensers provided throughout the building)

It promises to be a great day and we look forward to welcoming you all.

 

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MINERAL WISH LIST

We also offer an additional service that enables you, as our customer, to contact us via orders@crystalclassics.co.uk with your mineral wish list to enhance your current collection, but are unable to find the right specimens on our website. We have 1000's of specimens in our general stock that do not appear online.

Author: JH
Categories: Updates

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