By Gisela Hinder

The Skorpion Zinc deposit is a complex, non-sulphide zinc orebody situated in a paleo-channel fill overlying rocks of the Port Nolloth Zone of the Gariep Belt about 20 km north-west of the little mining town Rosh Pinah, Karas Region, Namibia.
The Skorpion Zinc mine is the 8th largest Zinc Mine in the world and a world-class integrated mining and refinery operation. Skorpion Zinc's annual capacity is 150 000 tons of Special High Grade zinc.
The zinc-oxide is mainly hosted by arkoses (siliciclastics) and subordinately by quartz sericite schists (volcanic siliciclastics). Other rock types associated with the orebody include limestone, mafic volcanics and a sheared volcanic siliciclastic, dividing the orebody in half. The orebody is wide near the surface and becomes narrower with depth. Two main ore limbs make up the orebody. The western limb is associated with copper and extends much deeper than the eastern limb, which is associated with calcium.

The oxide orebody is believed to have formed in a paleo-channel due to supergene alteration of a sulphide-rich primary body situated west and underneath the current non-sulphide orebody. Zinc grades are highest at the orebody-limestone contact as well as in vugs and where the orebody is interfingered with limestone. This poses a challenge in mining such ore shoots and beneficiating the ore with minimum calcium. The mine life of the present deposit extends to 2016–2017 with some additional work to be done to convert resources into reserves.

Major ore minerals include a zinc smectite, sauconite, smithsonite and hemimorphite. Other occurring zinc minerals are tarbuttite, scholzite, chalcophanite, hydrozincite and hydrohetearolite.
The oxide ore at Skorpion mine produced a vast amount of interesting oxide and phosphate minerals in the past and has surprised us again. A new mineral for Skorpion has been discovered and analyzed as churchite Y with a chemistry of (Y, Er)PO4 - 2H2O, a hydrated yttrium erbium phosphate. 


White churchite Y balls growing on romanechite.
Photos taken by Dr H Malzahn

Some years ago an unknown mineral was found at Skorpion Mine which could not be identified. This unknown mineral had tiny colourless needle-like crystals of monoclinic symmetry. Micro-chemical tests showed calcium, zinc, phosphate and carbonate as major components, thus indicating the presence of a possibly completely new mineral. Subsequent single-crystal X-ray studies and microprobe analyses confirmed this material to be a new species. The new mineral was named skorpionite after the deposit’s locality. Skorpionite occurs as a fine crystal growth in the ore, growing mainly on green tarbuttite.

But back to the new discovery. Churchite-(Y), also known as just churchite and weinschenkite, is a fairly scarce rare earth phosphate. A rare earth mineral is one that contains any of the so-called rare earth metals/elements. In this case, it is yttrium and erbium, two industrially valuable metals that are the two rare earth elements in churchite-(Y). The (Y) is for the yttrium which is more significant than the erbium in the chemistry of churchite-(Y). The mineral churchite-(Nd) contains the element neodymium, another rare earth element. Churchite was first discovered in Bavaria Germany in the late 1800s and occurs in another few mines in the world. For Skorpion Mine it represents a new find. Churchite occurs here as little white balls formed by concentric growing minute needles, sitting on hetearolite or romanchite and in some places on a thin quartz crystal layer. The usual size of the little balls is about 3 mm but can reach up to 8 mm in cases. 


White churchite Y balls growing on romanechite
Photos taken by G Hinder

Some other examples of recently found minerals originating from the more copper rich ore body mentioned in the text above are malachite, herbertsmithite and zincolibethenite.


Turquoise green zincolibethenite balls (5 mm)
covered by a thin chalcedony layer


Green malachite stars (1 cm) sitting on hetearolite


Calcite crystals growing on green
malachite on a zincolibethenite crust
(Specimen size 6 x 4 cm)


Emerald green shiny herbertsmithite balls (1-2 mm)
on a zincolibethenite crust

Photos taken by Dr H Malzahn