San Juan 009             ~25°30′S 69°50′W

Area San Juan, Comuna Taltal, Provincia Tocopilla, región Antofagasta, Chile

Find: 23 July 2007

Type: CO3

History: A single stone was found in a deflation surface of the San Juan area, in the Atacama Desert, northern Chile, by the 2007 CEREGE-Universidad de Chile scientific expedition (Millarca Valenzuela, Jerome Gattacceca and Clement Suavet). This is the first carbonaceous chondrite found in the Chilean territory.

Physical characteristics: (J. Gattacceca, CEREGE) A single stone of 45.56 g without fusion crust and a smooth dark brown outer surface. The interior has the same dark brown color. Grain density is 3.25 g/cc. Log χ = 4.69 indicate maximum metallic Fe-Ni content of 8.9 wt%.

Petrography (M. Valenzuela U. Chile, M. Bourot-Denise MNHNP, J. Gattacceca, C. Suavet CEREGE): Sharply defined type I chondrules are dominant (~50% vol) and range in size from few tens of microns to 1 mm, with average ~200 μm. Type II chondrules are scarce (~2% vol), CAIs and AOIs account for ~5 vol% of the meteorite, dark matrix is ~30% vol, and the rest correspond to olivine, pyroxene fragments (~8% vol) and opaques phases (5% vol) as nodules of Fe-Ni and troilite and possible magnetite.

Mineral compositions and geochemistry: Olivine ranges from Fa_0,27 to Fa_57,4 (mean value Fa_17.3, n = 29). Low-Ca pyroxene is Fs_0.76–3.39 (mean value Fs_1.68, n = 19). Terrestial age obtained by ¹⁴C measurements (UAz Accel. MS laboratory, T. Jull, M. Leclerc, M. Valenzuela) is less than 1.3 ka. The average of two oxygen isotope analyses of acid-washed 1.5 mg bulk samples (C. Suavet, C. Sonzogni, A. Alexandre, J. Gattacceca, CEREGE) is δ¹⁷O = −7.98‰, δ¹⁸O = −4.78‰, and Δ¹⁷O = −5.49‰.

Type specimens: 38 g and one polished-thin section are on deposit at U.Chile, 4 g and one polished section at CEREGE, and one polished section at MNHNP.

Classification: Carbonaceous chondrite (CO3). The meteorite is basically unshocked (S1) and has minor weathering.