TY - JOUR

T1 - Immiscible hydrous Fe-Ca-P melt and the origin of iron oxide-apatite ore deposits

AU - Hou, Tong

AU - Charlier, Bernard

AU - Holtz, François

AU - Veksler, Ilya

AU - Zhang, Zhaochong

AU - Thomas, Rainer

AU - Namur, Olivier

N1 - Funding Information: Stefan Linsler, Julian Feige, and Chao Zhang are thanked for their help during experiments, sample preparation, and microprobe analyses. Don Lindsley is thanked for his kind help with the identification of oxide minerals. T.H. acknowledges support by the China Nature Foundation of Sciences (41502052 and 2016YFC0600502), a Marie Curie Individual Fellowship within the Horizon 2020-Research and Innovation Framework Programme (656923), and the "Fundamental Research Funds for the Central Universities (2652015054)". B.C. is a Research Associate of the Belgian Fund for Scientific Research-FNRS. O.N. was supported by an Emmy Noether grant (DFG NA1171/1-1). This work was partly supported by DFG grant KO1723/20-1 and Chinese 973 program (2012CB416806).

PY - 2018/4/12

Y1 - 2018/4/12

N2 - The origin of iron oxide-apatite deposits is controversial. Silicate liquid immiscibility and separation of an iron-rich melt has been invoked, but Fe-Ca-P-rich and Si-poor melts similar in composition to the ore have never been observed in natural or synthetic magmatic systems. Here we report experiments on intermediate magmas that develop liquid immiscibility at 100 MPa, 1000-1040 °C, and oxygen fugacity conditions (fO 2) of ∆FMQ = 0.5-3.3 (FMQ = fayalite-magnetite-quartz equilibrium). Some of the immiscible melts are highly enriched in iron and phosphorous ± calcium, and strongly depleted in silicon (<5 wt.% SiO 2). These Si-poor melts are in equilibrium with a rhyolitic conjugate and are produced under oxidized conditions (~FMQ + 3.3), high water activity (aH 2O ≥ 0.7), and in fluorine-bearing systems (1 wt.%). Our results show that increasing aH 2O and fO 2 enlarges the two-liquid field thus allowing the Fe-Ca-P melt to separate easily from host silicic magma and produce iron oxide-apatite ores.

AB - The origin of iron oxide-apatite deposits is controversial. Silicate liquid immiscibility and separation of an iron-rich melt has been invoked, but Fe-Ca-P-rich and Si-poor melts similar in composition to the ore have never been observed in natural or synthetic magmatic systems. Here we report experiments on intermediate magmas that develop liquid immiscibility at 100 MPa, 1000-1040 °C, and oxygen fugacity conditions (fO 2) of ∆FMQ = 0.5-3.3 (FMQ = fayalite-magnetite-quartz equilibrium). Some of the immiscible melts are highly enriched in iron and phosphorous ± calcium, and strongly depleted in silicon (<5 wt.% SiO 2). These Si-poor melts are in equilibrium with a rhyolitic conjugate and are produced under oxidized conditions (~FMQ + 3.3), high water activity (aH 2O ≥ 0.7), and in fluorine-bearing systems (1 wt.%). Our results show that increasing aH 2O and fO 2 enlarges the two-liquid field thus allowing the Fe-Ca-P melt to separate easily from host silicic magma and produce iron oxide-apatite ores.

UR - http://www.scopus.com/inward/record.url?scp=85045525015&partnerID=8YFLogxK

U2 - 10.1038/s41467-018-03761-4

DO - 10.1038/s41467-018-03761-4

M3 - Article

C2 - 29650951

AN - SCOPUS:85045525015

VL - 9

JO - Nature Communications

JF - Nature Communications

SN - 2041-1723

M1 - 1415

ER -