Beitrag
Geochemistry, texture, and mineralogy of the supergene iron oxide deposits from the Binaloud zone, NE Iran
Najafzadeh Tehrani, Parvin; Calagari, Ali Asghar; Velasco, Francisco; Yusta, Iñaki
Neues Jahrbuch für Mineralogie - Abhandlungen Band 195 Heft 3 (2018), p. 211 - 225
veröffentlicht: Dec 18, 2018
Manuskript akzeptiert: Sep 14, 2018
finale Ms. Revision erhalten: Jul 18, 2018
Manuskript-Revision angefordert: Feb 19, 2018
Manuskript erhalten: Mar 2, 2017
ArtNo. ESP154019503003, Preis: 29.00 €
Abstract
The studied supergene iron oxide ore deposits in the Binaloud zone are located in two areas, in southwest of Mashhad (Pivehzhan) and northwest of Neyshabour (Shahin) NE Iran. These deposits are hosted by carbonate rocks of Devonian age in Pivehzhan area and by sedimentary carbonate rocks of lower Cretaceous age in Shahin area. The main oxide ore minerals are hematite and goethite accompanied by trace amounts of remaining sulfides and magnetite. Field relationships and mineralogical and geochemical studies of the ores show that these deposits were formed by almost complete oxidation of hitherto poorly understood sulfide-magnetite deposits. Ore minerals occur as lenses, veins/veinlets, and filling of pore spaces, vugs, cavities, and fractures, which supergene products replacing the pre-existing sulfide ore body with the enclosing carbonate rocks and, accordingly, they adopt the morphology of the pre-existing deposits. Textural examination revealed extensive replacement of all the hypogene ore minerals (pyrite, pyrrhotite, magnetite) by goethite and hematite exhibiting botryoidal-colloform aggregates and cellular and boxwork textures of supergene origin. The exceptional preservation of minute remains of magnetite and pyrite prove the intensity of leaching of the primary deposits. Chemical analyses of the ores show very high Fe2O3 contents (up to 79 wt.%) and MnO (up to ca. 3–4 wt.%) with lesser amounts of Zn, Pb, Cu, Co, and Ni, which inherited character of these elements from the alteration of metal base pyrite-rich ores hosted in carbonate rocks. Alteration and ferruginization indices (AI and FI) of altered and mineralized rocks prove the intensity of weathering and the extension of the gossanization processes in all the studied areas (i.e., they show mature gossan profiles). These characteristics indicate that the observed iron enrichment was caused by supergene leaching (weathering) through downward circulation of surface waters.
Schlagworte
Hematite • Goethite • Supergene iron deposit • Binaloud • Iran