[meteorite-list] Serra Pelada Meteorite Fall is Official

From: Galactic Stone & Ironworks <meteoritemike_at_meteoritecentral.com>
Date: Mon, 4 Sep 2017 10:28:13 -0400
Message-ID: <CAKBPJW-mnwJRKUa7eG_y6MnGFnW8qe-o1j3wBum2BaHgWP_0yA_at_mail.gmail.com>

The Serra Pelada meteorite fall is now approved.

Link - https://www.lpi.usra.edu/meteor/metbull.php?code=65794

Serra Pelada 5?57.135?S, 49?39.238?W
Para, Brazil
Confirmed fall: 2017 June 29
Classification: HED achondrite (Eucrite)

History: (A. L. R. Moutinho, D. Rios, M. Cardoso Rocha, W. Carvalho) A
fireball appeared over the southeastern region of Par? state, Brazil,
on June 29, 2017, around 10:35 local time (UTC-3). It was traveling in
an apparent NE to SW direction. Loud detonations were heard in towns
including Marab?, Eldorado dos Caraj?s and Paraopebas. People from
these towns thought it could have been an airplane crash. In the the
village of Serra Pelada (a famous gold-mining location), some students
and a watchman, Mr. Manuel da Silva, of Rita Lima de Souza school
heard a series of four to six detonations and a few mins later
witnessed a rock falling on a roadside near the school. A smoke trail
was observed and also some dust caused by the impact. The rock was
broken by the impact, collected and shared among local people just
after the fall. A geologist from Serra Pelada, Marcilio Cardoso Rocha,
was contacted, and he made preliminary analysis and sent a sample to
MNRJ for study and classification.

Physical characteristics: One stone was recovered. Its original size
is difficult to determine because it was broken during impact and
shared among local people, but it had been ~40 cm along the major axis
and around 6 kg.

Petrography: (M.E. Zucolotto and C.V.N. Villa?a, UFRJ) Optical
petrographic examination of a thin section shows a brecciated texture
with many clasts set in a fine-grained matrix and a fusion crust
~50-200 ?m thick. Some clasts contains both ophitic, subophitic
texture and are surrounded by pulverized rocks of the same phase. Some
clasts are separated by impact shock melt veins. The size of the
plagioclase needles and pyroxene varies between the different clasts
and exhibit about 700 ?m in the coarse-grained clasts and less than 70
?m in the fine-grained clasts. All the different clasts are from the
same compositional group but of different metamorphic type, therefore
it is a genomict breccia. Accessory minerals are silica, ilmenite,
chromite, troilite, and Fe-metal (low Ni). Mineral grains show the
effects of shock as undulatory extinction and mosaicism , some sparse
melt pockets and impact melt veins but no maskelynite. Minor phases
include ilmenite, with silica, iron sulfide, and Fe,Ni metal.

Geochemistry: (A. Tosi, UFRJ and D. Rios, GPA/UFBA) Microprobe
examination of a polished mount shows at least six lithologies with a
very similar pyroxene and plagioclase composition. Low-Ca pyroxene
Fs52.5?2.6Wo11.3?1.7, Fe/Mn 31.8?1, n=37; Ca-rich Pyroxenes
Fs31.0?0.5Wo39.4?0.5 plagioclase An87.6?5.8Ab12.2?3.4, n=20. (mean
value from EMPA with 20 ?m beam) SiO2=47.5?0.1, TiO2=0.45?0.15,
Al2O3=10.6?0.4, FeO=23.7?1.8, MnO=0.91?0.09, MgO=7.5?1.2, CaO=8.3?1.1,
Na2O=0.5?0.1 (all wt%).

Classification: Achondrite (eucrite, genomict breccia); medium shock
(no maskelynite), no weathering.

Specimens: MNRJ 50 g; masses with anonymous owners

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Received on Mon 04 Sep 2017 10:28:13 AM PDT