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Genesis of exceptionally scandium-rich clinopyroxene in magnetite ore at El Laco: Implications for the formation of iron oxide-apatite (IOA) deposits.

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Title: Genesis of exceptionally scandium-rich clinopyroxene in magnetite ore at El Laco: Implications for the formation of iron oxide-apatite (IOA) deposits.
Authors: Xie, Qiuhong1 (AUTHOR) qhxie01@163.com, Zhang, Zhaochong2 (AUTHOR), Simon, Adam3 (AUTHOR), Campos, Eduardo4 (AUTHOR), Hou, Tong2 (AUTHOR), Zhu, Xiangkun1 (AUTHOR), Wang, Yu5 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. May2026, Vol. 420, p175-189. 15p.
Subjects: Pyroxene, Magnetite, Ore genesis (Mineralogy), Inclusions (Mineralogy & petrology), Ore deposits
Geographic Terms: Chile
Abstract: As an important global sources of iron, the origin of iron oxide-apatite (IOA) deposits, whether magmatic or hydrothermal, has been a matter of persistent scholarly debate. To explore this issue, we conducted a detailed study of clinopyroxene in ore-hosting andesite, high-temperature hydrothermally altered andesite, and veined magnetite-apatite-clinopyroxene ore from the enigmatic Pliocene El Laco iron deposit in northern Chile, which is recognized as the youngest and best-preserved IOA deposit in the world. New data presented here show that clinopyroxene in magnetite-apatite-clinopyroxene ore at El Laco exhibits exceptionally high Sc concentrations, reaching up to 1476 μg/g (average 476 ± 666 μg/g, 2SD). These data contrast sharply with clinopyroxene from the host andesite and the high-temperature alkali-calcic hydrothermally altered andesite, which exhibit Sc concentrations of 72–174 μg/g (average 128 ± 46 μg/g, 2SD) and predominantly <10 μg/g (average 0.5 ± 0.7 μg/g for clinopyroxene in early-stage alkali-calcic altered andesite and 4.3 ± 20 μg/g for pristine clinopyroxene in late-stage alkali-calcic altered andesite), respectively. In combination with comprehensive statistical analyses of Sc concentrations in clinopyroxene from global magmatic and hydrothermal systems, and the occurrence of abundant fluorapatite and anhydrite ± magnetite inclusions in fluorapatite from veined magnetite-apatite-clinopyroxene ore at El Laco, we propose that the extremely Sc-enriched clinopyroxene, along with its host magnetite ore, precipitated at magmatic temperatures from a magmatic-hydrothermal fluid wherein Sc was dissolved and transported as Sc-sulfate and Sc-fluoride complexes. Notably, magnetite-apatite-clinopyroxene ore and the pervasive alkali-calcic alteration at El Laco likely formed from paragenetically distinct pulses of magmatic-hydrothermal fluids evolved from a common underlying magma plumbing system. This study provides compelling evidence for a magmatic-hydrothermal origin for IOA deposits, invoking multiple pulses of magmatic-hydrothermal fluids, and suggests that IOA deposits could be prospective targets for Sc exploration. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:As an important global sources of iron, the origin of iron oxide-apatite (IOA) deposits, whether magmatic or hydrothermal, has been a matter of persistent scholarly debate. To explore this issue, we conducted a detailed study of clinopyroxene in ore-hosting andesite, high-temperature hydrothermally altered andesite, and veined magnetite-apatite-clinopyroxene ore from the enigmatic Pliocene El Laco iron deposit in northern Chile, which is recognized as the youngest and best-preserved IOA deposit in the world. New data presented here show that clinopyroxene in magnetite-apatite-clinopyroxene ore at El Laco exhibits exceptionally high Sc concentrations, reaching up to 1476 μg/g (average 476 ± 666 μg/g, 2SD). These data contrast sharply with clinopyroxene from the host andesite and the high-temperature alkali-calcic hydrothermally altered andesite, which exhibit Sc concentrations of 72–174 μg/g (average 128 ± 46 μg/g, 2SD) and predominantly <10 μg/g (average 0.5 ± 0.7 μg/g for clinopyroxene in early-stage alkali-calcic altered andesite and 4.3 ± 20 μg/g for pristine clinopyroxene in late-stage alkali-calcic altered andesite), respectively. In combination with comprehensive statistical analyses of Sc concentrations in clinopyroxene from global magmatic and hydrothermal systems, and the occurrence of abundant fluorapatite and anhydrite ± magnetite inclusions in fluorapatite from veined magnetite-apatite-clinopyroxene ore at El Laco, we propose that the extremely Sc-enriched clinopyroxene, along with its host magnetite ore, precipitated at magmatic temperatures from a magmatic-hydrothermal fluid wherein Sc was dissolved and transported as Sc-sulfate and Sc-fluoride complexes. Notably, magnetite-apatite-clinopyroxene ore and the pervasive alkali-calcic alteration at El Laco likely formed from paragenetically distinct pulses of magmatic-hydrothermal fluids evolved from a common underlying magma plumbing system. This study provides compelling evidence for a magmatic-hydrothermal origin for IOA deposits, invoking multiple pulses of magmatic-hydrothermal fluids, and suggests that IOA deposits could be prospective targets for Sc exploration. [ABSTRACT FROM AUTHOR]
ISSN:00167037
DOI:10.1016/j.gca.2026.04.003