Errachidia 004        32°2.418’N, 4°4.092’W

Errachidia, Morocco

Find: 2020

Classification: Primitive achondrite (Winonaite)

History: Found in 2020 by Mustapha Oulkouch and other finders in a strewnfield centered within the isolated rural community of Oued Naam. Later purchased by Sean Mahoney in February 2020.

Physical characteristics: Many small stones and fragments covered with a weathered fusion crust. 75% of the stones contain low amounts of visible metal; the remaining 25% contain high amounts of visible metal.

Petrography: (D. Sheikh, FSU) This sample features two distinct lithologies: 1) A low-metal lithology (<10 vol% metal) displaying a predominantly granoblastic texture composed of forsterite, enstatite, augite, and sodic plagioclase (Silicate grain size Av. 110±50 µm) with the mineral grain boundaries meeting at approximately 120° triple junctions. Kamacite and troilite are finely scattered throughout the interior as either veinlets or individual grains; some have been altered to form Fe-oxides. No chondrules were observed. 2) A high-metal lithology (up to 80 vol% metal) displaying a well-developed Widmanstätten pattern containing kamacite, taenite, plessite, and accessory troilite and schreibersite (kamacite band width Av. 2 mm, range 1-3 mm), and containing angular silicate inclusions of sodic plagioclase (some containing melt inclusions), augite, and enstatite (Silicate grain size Av. 350±50 µm). No chondrules were observed.

Geochemistry: Low-metal lithology: Forsterite (Fa_0.8±0.3, range Fa_0.4-1.4, FeO/MnO=2±1, n=30), Enstatite (Fs_4.3±0.6 Wo_1.7±0.2, range Fs_1.6-4.9 Wo_0.8-2.0, FeO/MnO=4±1, n=22), Augite (Fs_2.0±0.4 Wo_45.0±1.0, range Fs_1.2-2.6 Wo_44.1-46.7, Na₂O=0.7±0.2 wt%, Cr₂O₃=1.1±0.6 wt%, FeO/MnO=3±1, n=7), Sodic Plagioclase (An_10.8±0.8 Or_4.0±1.6, range An_10.2-11.4 Or_2.8-5.1); High-metal lithology: Sodic Plagioclase (An_12.2±2.6 Or_3.9±0.6, range An_9.7-19.5 Or_1.9-5.3), Augite (Fs_2.4±0.3 Wo_43.0±1.1, range Fs_1.8-3.0 Wo_39.9-45.7, Na₂O=0.9±0.1 wt%, Cr₂O₃=1.5±0.1 wt%, FeO/MnO=3±1, n=19), Enstatite (Fs_4.5±0.5 Wo_1.8±0.3, range Fs_3.9-5.7 Wo_1.4-2.2, FeO/MnO=4±1, n=8). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, Low-metal lithology: (δ¹⁷O 2.296, 3.022, 2.588; δ¹⁸O 5.276, 6.655, 5.843; Δ¹⁷O -0.489, -0.491, -0.497 per mil), High-metal lithology: (δ¹⁷O 3.940, 2.666, 2.577; δ¹⁸O 8.197, 6.019, 5.881; Δ¹⁷O -0.388, -0.512, -0.528 per mil). ICP-MS data of metal separates from high-metal lithology, using sample of North Chile (Filomena) as standard (C. Herd and P. Hill, UAb): Ni = 7.4, Co = 0.30 (both wt%); Ir = 5.9, Ga = 28, Ge = 123, As = 10.1, Ru = 5.0, Re = 0.5, Os = 13.6, Pt = 9.5, Cu = 180, Au = 0.85 (all μg/g).

Classification: Primitive achondrite (Winonaite). The unusual occurrence of two distinct lithologies within this sample suggests a transitional classification between an endmember winonaite (low-metal lithology) and a silicate-rich IAB-complex iron (high-metal lithology). This is supported by the oxygen isotopes, texture, and mineral abundances and compositions for both distinct lithologies, and the siderophile element abundances of metal separates from the high-metal lithology.

Specimens: 25.2 g type specimen and two polished thin sections (one of each lithology) at UNM; 397 g high-metal and 905 g low-metal with Sean Mahoney, 65 g high-metal and 50 g low-metal with Juan Aviles Poblador, 215 g high-metal and 85 g low-metal with Kyle Josefy, 800 g low-metal with Mark Lyon, 61 g high-metal and 61 g low-metal with Topher Spinnato.