Meteoritical Bulletin: Entry for Errachidia 004

Writeup from MB 110:

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±0.6Wo_1.7±0.2, range Fs_1.6-4.9Wo_0.8-2.0, FeO/MnO=4±1, n=22), Augite (Fs_2.0±0.4Wo_45.0±1.0, range Fs_1.2-2.6Wo_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±0.8Or_4.0±1.6, range An_10.2-11.4Or_2.8-5.1); High-metal lithology: Sodic Plagioclase (An_12.2±2.6Or_3.9±0.6, range An_9.7-19.5Or_1.9-5.3), Augite (Fs_2.4±0.3Wo_43.0±1.1, range Fs_1.8-3.0Wo_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±0.5Wo_1.8±0.3, range Fs_3.9-5.7Wo_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.

Errachidia 004: reclassification

(D. Sheikh, Cascadia): Although winonaites can display various textures and compositions, Errachidia 004 is unique compared to other winonaites in that it represents a polymict assemblage of various different winonaite lithologies, e.g., ultramafic and basaltic (Sheikh, 2021). Although the low metal lithology displays the commonly observed ultramafic assemblage characteristic of most winonaites, the high metal lithology displays an overall basaltic texture and unique variation in mineral modal abundance, with some pieces consisting of >50 vol. % plagioclase and no olivine (as similarly observed in recently classified NWA 15487). Other lithologies, with >70 vol. % Fe-Ni metal, are "transitional" between metal-bearing winonaites and silicate-bearing IAB iron meteorites. In some cases, high- and low-metal lithologies are juxtaposed against each other. Overall, Errachidia 004 is unique among winonaites and should be designated as anomalous.