Campo del Cielo

Campo del Cielo refers to a group of iron meteorites and to the area in Argentina where they were found. The site straddles the provinces of Chaco and Santiago del Estero, north-northwest of Buenos Aires, Argentina. It is half that distance, north-east, to Paraguay's capital, Asunción. The crater field covers and contains at least 26 craters, the largest being .
The craters' age is estimated as four to five thousand years. Containing iron masses, they were reported in 1576, but were already well known to local aboriginal inhabitants. The craters and their surrounds contain many fragments of an iron meteorite. The total weight of the pieces recovered is about 100 tonnes, making the meteorite possibly the greatest recovery.
The largest two fragments, the 30.8-ton "Gancedo" and 28.8-ton "El Chaco", are among the heaviest single-piece meteorite masses recovered on Earth, along with the 60-ton Hoba and a 31-ton fragment of the Cape York meteorite.
History.
In 1576, the governor of a province in Northern Argentina commissioned the military to search for a huge mass of iron, which he had heard that natives used for their weapons who claimed that the mass had fallen from the sky in a place they called "Piguem Nonralta" which the Spanish translated as "Campo del Cielo" ("Field of heaven (or the sky)"). The expedition found a large mass of metal protruding out of the soil. They assumed it was an iron mine and brought back a few samples, which were described as being of unusual purity. The governor documented the expedition and deposited the report in the Archivo General de Indias in Seville, but it was quickly forgotten and later local reports merely repeated the Native legends.
Following the legends, in 1774 Don Bartolomé Francisco de Maguna rediscovered the iron mass which he called "el Mesón de Fierro" ("the Table of Iron"). Maguna thought the mass was the tip of an iron vein. The next expedition, led by Rubin de Celis in 1783, used explosives to clear the ground around the mass and found that it was probably a single stone. Celis estimated its mass as 15 tonnes and abandoned it as worthless. He himself did not believe that the stone had fallen from the sky and assumed that it had formed by a volcanic eruption. However, he sent the samples to the Royal Society of London and published his report in the "Philosophical Transactions of the Royal Society". Those samples were later analyzed and found to contain 90% iron and 10% nickel and assigned to a meteoritic origin.
Later, many iron pieces were found in the area weighing from a few milligrams to 34 tonnes. A mass of about 1 tonne known as "Otumpa" was found in 1803. A portion of this mass was taken to Buenos Aires in 1813, then donated to the British Museum. Other large fragments are summarized in the table below. The mass called "el Taco" was originally , but the largest remaining fragment weighs .
The second-largest mass of 28,840 kg named "El Chaco" was found in 1969 down using a metal detector. It was extracted in 1980 and estimated to weigh around 37 tonnes. This stone was at the time the second heaviest meteorite after the Hoba in Namibia of about 60 tonnes. The total mass of the Campo del Cielo fragments found so far exceeds 60 tonnes, making it the heaviest set of such finds on Earth.
In 1990 a local Argentine highway police officer foiled a plot by Robert Haag to steal "El Chaco"; having gone abroad it was returned to Campo del Cielo and is now protected by provincial law.
In 2015, police arrested four alleged smugglers trying to steal more than a ton of protected meteorites.
In 2016, the largest-known meteorite of the record-tonnage strewn field was unearthed. Named the Gancedo meteorite after the nearby town of Gancedo which lent equipment to aid in the extraction, this nickel-iron meteorite has a mass of 30,800 kg. Originally, it was thought to weigh less than "El Chaco". Due to a suspected lack of precision when "El Chaco" was weighed in 1980, the latter was then reweighed with the same instruments and it was discovered that it only had a mass of 28,840 kg, thus less than Gancedo.
The meteorite impact, age and composition.
A crater field of at least 26 craters was found in the area, with the largest being . The field covered an area of with an associated strewn area of smaller meteorites extending farther by about . At least two of the craters contained thousands of small iron pieces. Such an unusual distribution suggests that a large body entered the Earth's atmosphere and broke into pieces which fell to the ground. The size of the main body is estimated as larger than 4 meters in diameter. The fragments contain an unusually high density of inclusions for an iron meteorite, which might have facilitated the disintegration of the original meteorite. Samples of charred wood were taken from beneath the meteorite fragments and analyzed for carbon-14 composition. The results indicate the date of the fall to be around 4,200–4,700 years ago, or 2,200–2,700 years BC. The age is estimated to be 4.5 billion years old, formed as part of the development of our solar system.
The average composition of the Campo del Cielo meteorites is 6.67% Ni, 0.43% Co, 0.25% P, 87 ppm Ga, 407 ppm Ge, and 3.6 ppm Ir, with the remaining 92.6% being iron.