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  Mesosiderite A-1

TKW: 3.83 metric tons. Fall not observed. Found 1861 in Antofagasta, Chile

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Holger writes:

More than one hundred fragments of Vaca Muerta have been found, spread over a 11.5 by 2.1 km fall ellipse some 60 km South-East of the Chilean coastal town Taltal. Further to our tally in 2012, 3869 kg, visitors have made finds at old and new positions. One entire fragment of 158 kg is rumored to have been excavated in December 2016; its position is not known.

The documented history goes back to Ignacio Domeyko's discovery in 1861 which, two years later, led Gustav Rose to name a new class of meteorites, 'mesosiderites'. Prior indigenous knowledge seems likely: small amounts of flint debitage were found near one of the largest masses. Iron, be it of terrestrial or meteoric origin, is, however, not known in Chilean, archaeological context.

Before his execution by gunshot, 1843, the local resident Rafael Aracena - a member of the Chango population and a convicted murderer - may have sold some meteorites, as were they rich silver-ore. By the mid-to-late 19th century, a small mining industry arose at Vaca Muerta, breaking several meteorites up - perhaps using glazed gun-powder lit by long fuses -, and in one case concealing a bag of fine pieces underground. How much was removed from the field is not known; it may well have been several tons. More on this in my book from 2012.

Find of No. 18: The fragment discussed here, was found on January 8, 1988, during an expedition with Claudio Canut de Bon, junior and senior, and Harri Lindgren. The desert was barren and without sign of human activity to perhaps more than 100 meters (Photo 2, 3 and 4); the mass had thus not been seen by the 19th century prospectors - nor, for that matter, anybody else. It weighed 32.6 kg, in addition to 487 gram of shales.

Following an exchange deal with La Serena University, the mass was sent Copenhagen's Tycho Brahe Planetarium, where cracked fragments from the underside were removed, and the full mass sandblasted. Four holes were drilled into the mass, so that it could be firmly bolted to the wall of the exposition area. Here, it was exposed to handling by visitors (Photo 5). This gave cause for some concern, and after about four years, it was transferred to the nearby Geological Museum, sandblasted once more, and put on display - this time behind glass. Asger Ken Pedersen and John T. Wasson kindly brokered this transfer.

A phone call from my old employer: By 2015, an idea emerged that a meteorite of no specific type should be put on display at the European Southern Observatory's forthcoming planetarium in Garching. I was asked for advice, and suggested to Henning Haack (Geological Museum), that one of the Vaca Muerta masses, which I had brought to Denmark (all with official Chilean permission), could be used. In addition to VM 18, the largest are VM 16 (7.8 kg), VM 68 (13.1 kg). I stayed out of the ensuing negotiations, but at some point it was decided that VM 18 should be 'sacrificed', i.e. cut through the middle, one half for Garching, one for Copenhagen. After Henning's departure, the transfer was completed by Martin Bizzarro and Zina Fihl.

The task of cutting was entrusted to Joachim Karl of Frankfurt am Main. By the first days of 2016, the initial cut had been completed, and soon after, two slices, each about 4.5 mm thick, were detached. The two end-pieces weigh about 12.5 kg each. Polishing was done at a separate workshop. Photo 6 and 7 show the first cut; Photo 8, one of the slices.

The end-piece destined for ESO reached Garching by the end of February 2018 (Photo 9). A few days later, it was photographed by Mahdi Zamani, while I looked on. Contrary to tradition, we decided to use diffuse light, hence preserving dynamic range and clarity of the silicatic matrix, but leaving nuggets dark (Eventually, a specular image can be taken, to pinpoint precisely which parts are metallic, which not). A mosaic of more than two dozen images covered the full surface and were stitched together, to form a 54,948 by 45,620 pixel image. Its scale is 5.3 micrometers per pixel. Photos 10 to 14 show some noteworthy inclusions. The numbers below refer to numbering within the pictures.

No. 1 - 17: Fe/Ni-nodules, filamentary structures in nodules, tetrataenite (FeNi) rim (at some places: double-walled). Some apparent bulges may be instrumental (grinding, polishing).

No. 18 - 21: bagel-shaped rings of tetrataenite.

No. 22 - 25: troilite (FeS) inclusions in nuggets.

No. 26 - 27: mostly fractured olivine and other inclusions.

No. 28: rust.

No. 29 - 30: ”?” and unknown (perhaps contamination).

Holger Pedersen, April 28, 2018.

REFERENCES:

H. Pedersen, C. Canut de Bon, H. Lindgren: Vaca Muerta mesosiderite strewn-field, Meteoritics vol.27, pp 126-135 (1992). See also John T. Wasson's editorial on p.125.

H. Pedersen: Road-map to the Indian's Treasure: On the Chilean meteorite Vaca Muerta and its early mistake for Silver. Books on Demand, Norderstedt, Germany, 312 pages (2012).

FIGURE CAPTIONS:

Photo 1: The polished face of VM 18 at the European Southern Observatory's planetarium ”Supernova”, which opens today in Garching, near Munich, Germany. Credit: ESO / Holger Pedersen (holger@nbi.dk) / M. Zamani.

For access to the 54,948 by 45,620 pixel image, click here and then click the 'zoomable' link.

Photo 2 and 3: the discovery of VM 18. Copyright: H. Pedersen.

Photo 4: the discovery, one hour earlier, of nearby VM 16 (7.8 kg + 3.0 kg weathered fragments). Copyright: H. Pedersen.

Photo 5: a sideway view of VM 18, published in Berlingske Tidende (newspaper), on July 26, 1991. The hinted terrestrial age, 3500 years, is no longer a preferred value; it can be much shorter. The picture must predate the installation on the wall of the Tycho Brahe Planetarium (inaugurated on October 31, 1989).

Photo 6: after the first cut.

Photo 7: after the first cut.

Photo 8: one of the two slices. This photo, and the two previous, have undergone approximate correction for perspective.

Photo 9: at arrival in Garching.

Photo 10 - 14: some noteworthy inclusions.