Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A fundamental role of carbonate–sulfate melts in the formation of iron oxide–apatite deposits


Genetic models for iron oxide–apatite deposits are controversial and span a spectrum from orthomagmatic to hydrothermal endmembers. This lack of consensus is rooted in uncertainties as to the nature and origin of ore-forming fluids in these systems. Here, we present a fluid-inclusion study of mineralizing fluids at two iron oxide–apatite deposits (Buena Vista, Nevada and Iron Springs, Utah). We found that the inclusions in both systems comprise both aqueous brine and ubiquitous iron-rich carbonate–sulfate melts. These melts were found throughout the paragenesis of both deposits and show a tremendous capacity to transport ferric iron. Hence, we argue that orthomagmatic fluids played a role in mineralization at both Buena Vista and Iron Springs, and that the main ore-forming fluid was an iron-rich carbonate–sulfate melt formed by the assimilation and anatexis of evaporite-bearing carbonate rocks. The geological conditions that give rise to carbonate–sulfate melts are also a common feature of other classic iron oxide–apatite systems worldwide. Hence, we argue that the process of assimilation, anatexis and immiscibility of carbonate–sulfate melts is fundamental to iron oxide–apatite formation and provides a common link between iron oxide–apatite systems in different geological settings.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Fluid and melt inclusions in apatite and actinolite from Buena Vista and Iron Springs.
Fig. 2: Phases within polycrystalline (melt) inclusions from Buena Vista.
Fig. 3: Melting of polycrystalline inclusions.
Fig. 4: Schematic cross-section showing IOA formation via anatectic carbonate melting.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and its Supplementary Information files. We are unable to make the data available in a publicly accessible repository at this time.


  1. Barton, M. D. in Geochemistry of Mineral Deposits (ed. Scott, S. D.) 515–541 (Elsevier, 2014).

  2. Tornos, F., Velasco, F. & Hanchar, J. M. The magmatic–hydrothermal evolution of the El Laco deposit (Chile) and its implications for the genesis of magnetite–apatite deposits. Econ. Geol. 112, 1595–1628 (2017).

    Google Scholar 

  3. Westhues, A., Hanchar, J. M., LeMessurier, M. J. & Whitehouse, M. J. Evidence for hydrothermal alteration and source regions the Kiruna iron oxide–apatite ore (northern Sweden) from zircon Hf and O isotopes. Geology 45, 571–574 (2017).

    Google Scholar 

  4. Tornos, F., Velasco, F. & Hanchar, J. M. Iron-rich melts, magmatic magnetite, and superheated hydrothermal systems: the El Laco deposit, Chile. Geology 44, 427–430 (2016).

    Google Scholar 

  5. Velasco, F., Tornos, F. & Hanchar, J. M. Immiscible iron- and silica-rich melts and magnetite geochemistry at the El Laco volcano (northern Chile): evidence for a magmatic origin for the magnetite deposits. Ore Geol. Rev. 79, 346–366 (2016).

    Google Scholar 

  6. Simon, A. et al. in Metals, Minerals, and Society (eds Antonio, M. et al.) 89–114 (Society of Economic Geologists, 2018).

  7. Ovalle, J. T. et al. Formation of massive iron deposits linked to explosive volcanic eruptions. Sci. Rep. 8, 14855 (2018).

    Google Scholar 

  8. Dare, S. A. S., Barnes, S. & Beaudoin, G. Did the massive magnetite ‘lava flows’ of El Laco (Chile) form by magmatic or hydrothermal processes? New constraints from magnetite composition by LA-ICP-MS. Miner. Depos. 50, 607–617 (2015).

    Google Scholar 

  9. Jonsson, E. et al. Magmatic origin of giant ‘Kiruna-type’ apatite–iron-oxide ores in central Sweden. Sci. Rep. 3, 1644 (2013).

    Google Scholar 

  10. Nyström, J. O. & Henríquez, F. Magmatic features of iron ores of the Kiruna type in Chile and Sweden: ore textures and magnetite geochemistry. Econ. Geol. 89, 820–839 (1994).

    Google Scholar 

  11. Barton, M. D. & Johnson, D. A. Evaporitic source model for igneous-related Fe oxide–(REE–Cu–Au–U) mineralization. Geology 24, 259–262 (1996).

    Google Scholar 

  12. Li, W., Audétat, A. & Zhang, J. The role of evaporites in the formation of magnetite–apatite deposits along the Middle and Lower Yangtze River, China: evidence from LA–ICP–MS analysis of fluid inclusions. Ore Geol. Rev. 67, 264–278 (2015).

    Google Scholar 

  13. Oliver, N. H. S. et al. Modeling the role of sodic alteration in the genesis of iron oxide–copper–gold deposits, eastern Mount Isa Block, Australia. Econ. Geol. 99, 1145–1176 (2004).

    Google Scholar 

  14. Hofstra, A. H. et al. Mineral thermometry and fluid inclusion studies of the Pea Ridge iron oxide–apatite–rare earth element deposit, Mesoproterozoic St. Francois Mountains terrane, Southeast Missouri, USA. Econ. Geol. 111, 1985–2016 (2016).

    Google Scholar 

  15. Hou, T. et al. Immiscible hydrous Fe–Ca–P melt and the origin of iron oxide–apatite ore deposits. Nat. Commun. 9, 1415 (2018).

    Google Scholar 

  16. Chen, H., Clark, A. H. & Kyser, T. K. The Marcona magnetite deposit, Ica, south-central Peru: a product of hydrous, iron oxide-rich melts? Econ. Geol. 105, 1441–1456 (2010).

    Google Scholar 

  17. Veksler, I. V. et al. Liquid immiscibility and the evolution of basaltic magma. J. Petrol. 48, 2187–2210 (2007).

    Google Scholar 

  18. Veksler, I. V. Extreme iron enrichment and liquid immiscibility in mafic intrusions: experimental evidence revisited. Lithos 111, 72–82 (2009).

    Google Scholar 

  19. Lindsley, D. & Epler, N. Do Fe–Ti-oxide magmas exist? Probably not! Am. Miner. 102, 2157–2169 (2017).

    Google Scholar 

  20. Johnson, D. A. & Barton, M. D. in Part I. Contrasting Styles of Intrusions-Associated Hydrothermal Systems (eds John H. Dilles et al.) 127–144 (Society of Economic Geologists, 2000).

  21. Johnson, D. A. Studies of Iron-Oxide (Cu–REE–Au–Co–Ag–Ni–U) Mineralization and Associated Sodic Alteration in the Great Basin. PhD dissertation, Univ. Arizona (2000).

  22. Rowley, P. D. & Barker, D. S. in Guidebook to Mineral Deposits of Southwestern Utah (ed. Shawe, D. R.) 49–58 (Utah Geological Association, 1978).

  23. Whiting, D. L., Grover, J. D. Jr. & Benson, W. R. in Engineering and Environmental Geology of Southwestern Utah (ed. Harty, K. M.) 287–313 (Utah Geological Association, 1992).

  24. Bullock, K. C. Iron Deposits of Utah Bulletin 88 (Utah Geological and Mineralogical Survey, 1970).

  25. Speed, R. C. Geologic Map of the Humboldt Lopolith and Surrounding Terrane, Nevada Map and Chart Series MC-14 (Geological Society of America, 1976).

  26. Gregory, H. E. & Moore, E. C. The Kaiparowits Region, a Geographic and Geologic Reconnaissance of Parts of Utah and Arizona Professional Paper 164 (USGS, 1931).

  27. Jones, A. P., Genge, M. & Carmody, L. Carbonate melts and carbonatites. Rev. Mineral. Geochem. 75, 289–322 (2013).

    Google Scholar 

  28. Eiler, J. M. Oxygen isotope variations of basaltic lavas and upper mantle rocks. Rev. Mineral. Geochem. 43, 319–364 (2001).

    Google Scholar 

  29. Wyllie, P. J. & Tuttle, O. F. The system CaO–CO2–H2O and the origin of carbonatites. J. Petrol. 1, 1–46 (1960).

    Google Scholar 

  30. Lentz, D. R. Carbonatite genesis: a reexamination of the role of intrusion-related pneumatolytic skarn processes in limestone melting. Geology 27, 335–338 (1999).

    Google Scholar 

  31. Durand, C., Baumgartner, L. P. & Marquer, D. Low melting temperature for calcite at 100 bars on the join CaCO3–H2O—some geological implications. Terra Nova 27, 364–369 (2015).

    Google Scholar 

  32. Floess, D., Baumgartner, L. P. & Vonlanthen, P. An observational and thermodynamic investigation of carbonate partial melting. Earth Planet. Sci. Lett. 409, 147–156 (2015).

    Google Scholar 

  33. Wenzel, T., Baumgartner, L. P., Brügmann, G. E., Konnikov, E. G. & Kislov, E. V. Partial melting and assimilation of dolomitic xenoliths by mafic magma: the Ioko–Dovyren intrusion (North Baikal region, Russia). J. Petrol. 43, 2049–2074 (2002).

    Google Scholar 

  34. Fulignati, P., Kamenetsky, V. S., Marianelli, P., Sbrana, A. & Mernagh, T. P. Melt inclusion record of immiscibility between silicate, hydrosaline, and carbonate melts: applications to skarn genesis at Mount Vesuvius. Geology 29, 1043–1046 (2001).

    Google Scholar 

  35. Rocco, T., Freda, C., Gaeta, M., Mollo, S. & Dallai, L. Magma chambers emplaced in carbonate substrate: petrogenesis of skarn and cumulate rocks and implications for CO2 degassing in volcanic areas. J. Petrol. 53, 2307–2332 (2012).

    Google Scholar 

  36. Ganino, C., Arndt, N. T., Chauvel, C., Jean, A. & Athurion, C. Melting of carbonate wall rocks and formation of the heterogeneous aureole of the Panzhihua intrusion. Geosci. Front. 4, 535–546 (2013).

    Google Scholar 

  37. Gozzi, F. et al. Primary magmatic calcite reveals origin from crustal carbonate. Lithos 190, 191–203 (2014).

    Google Scholar 

  38. Carter, L. B. & Dasgupta, R. Effect of melt composition on crustal carbonate assimilation: implications for the transition from calcite consumption to skarnification and associated CO2 degassing. Geochem. Geophys. Geosyst. 17, 3893–3916 (2016).

    Google Scholar 

  39. Giuliani, A. et al. Nature of alkali–carbonate fluids in the sub-continental lithospheric mantle. Geology 40, 967–970 (2012).

    Google Scholar 

  40. Hsu, H. S., DeVan, J. H. & Howell, M. Corrosion of iron in molten carbonates at 650 °C. J. Electrochem. Soc. 134, 3038–3043 (1987).

    Google Scholar 

  41. Yardley, B. W. D. Metal concentrations in crustal fluids and their relationship to ore formation. Econ. Geol. 100, 613–632 (2005).

    Google Scholar 

  42. Moore, F. & Modabberi, S. Origin of Choghart iron oxide deposit, Bafq mining district, central Iran: new isotopic and geochemical evidence. J. Sci. 14, 259–269 (2003).

    Google Scholar 

  43. Matthews, S. J., Marquillas, R. A., Kemp, A. J., Grange, F. K. & Gardeweg, M. C. Active skarn formation beneath Lascar Volcano, northern Chile: a petrographic and geochemical study of xenoliths in eruption products. J. Metamorph. Geol. 14, 509–530 (1996).

    Google Scholar 

  44. Harmon, R. et al. Regional O-, Sr-, and Pb-isotope relationships in late Cenozoic calc-alkaline lavas of the Andean Cordillera. J. Geol. Soc. 141, 803–822 (1984).

    Google Scholar 

  45. Baker, T. et al. Mixed messages in iron oxide–copper–gold systems of the Cloncurry district, Australia: insights from PIXE analysis of halogens and copper in fluid inclusions. Miner. Depos. 43, 599–608 (2008).

    Google Scholar 

  46. Broman, C., Nyström, J. O., Henriquez, F. & Elfman, M. Fluid inclusions in magnetite–apatite ore from a cooling magmatic system at El Laco, Chile. GFF 121, 253–267 (1999).

    Google Scholar 

  47. Mungall, J. E., Long, K., Brenan, J. M., Smythe, D. & Nuslund, H. R. Immiscible shoshonitic and Fe–P-oxide melts preserved in unconsolidated tephra at El Laco volcano, Chile. Geology 46, 255–258 (2018).

    Google Scholar 

  48. Giebel, R. J., Marks, M. A. W., Gauert, C. D. K. & Markl, G. A model for the formation of carbonatite–phoscorite assemblages based on the compositional variations of mica and apatite from the Palabora Carbonatite Complex, South Africa. Lithos 324-325, 89–104 (2019).

    Google Scholar 

  49. Anenburg, M., Burnham, A. D. & Mavrogenes, J. A. REE redistribution textures in altered fluorapatite: symplectites veins, and phosphate–silicate–carbonate assemblages from the Nolans Bore P–REE–Th deposit, Northern Territory, Australia. Can. Mineral. 56, 331–354 (2018).

    Google Scholar 

  50. Lentz, D. R. in Mineralized Intrusion-Related Skarn Systems (ed. Lentz, D. R.) 519–657 (Mineralogical Association of Canada, 1998).

  51. Goldstein, R. H. & Reynolds, T. J. Systematics of Fluid Inclusions in Diagenetic Minerals (SEPM Society for Sedimentary Geology, 1993).

  52. Lafuente, B., Downs, R. T., Yang, H. & Stone, N. in Highlights in Mineralogical Crystallography (eds Armbruster, T. & Danisi, R. M) 1–29 (De Gruyter, 2016).

  53. Palmer, D. A. S. & Williams-Jones, A. S. Genesis of the carbonatite-hosted fluorite deposit at Amba Dogar, India: evidence from fluid inclusions, stable isotopes, and whole rock-mineral geochemistry. Econ. Geol. 91, 934–950 (1996).

    Google Scholar 

  54. Kontak, D. Analysis of evaporate mounds as a complement to fluid-inclusion thermometric data: case studies from granitic environments in Nova Scotia and Peru. Can. Mineral. 42, 1315–1329 (2004).

    Google Scholar 

  55. Kenderes, S. M. & Appold, M. S. Fluorine concentrations of ore fluids in the Illinois-Kentucky district: evidence from SEM–EDS analysis of fluid inclusion decrepitates. Geochim. Cosmochim. Acta 210, 132–151 (2017).

    Google Scholar 

  56. McCrea, J. M. On the isotopic chemistry of carbonates and paleotemperature scale. J. Chem. Phys. 18, 849–857 (1950).

    Google Scholar 

Download references


We thank M. Barton and E. Seedorff for introducing us to the Buena Vista deposit. We thank N. Gerein for help with the SEM analysis, E. Soignard, E. Walton and Y. Klyukin for help with Raman analysis, J. Cline, S. Jowitt and D. Barkoff for help with microthermometry and A. Degrado for help with video editing. We thank A. Hofstra and J. Brenan for detailed and constructive comments that helped us improve the paper. This work was supported by NSERC through a Discovery grant to M.S.-M. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US government.

Author information

Authors and Affiliations



W.M.B. conducted the analyses, interpreted the data and wrote the manuscript. M.S.-M. conceived and designed the study, interpreted the data and wrote the manuscript. K.L. and L.L. contributed to the isotopic analyses and interpretations. F.K.M. and E.M. contributed to the analyses, interpreted the data and wrote the manuscript.

Corresponding author

Correspondence to Matthew Steele-MacInnis.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Primary Handling Editor: Rebecca Neely.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary results, including Figs. 1–22 and Tables 1–6.

Supplementary Video 1

Video recording at room temperature, of the same polycrystalline inclusion shown in Figure S5, showing the movement of a vapor bubble in aqueous liquid in the inclusion. Movement can be observed in the area denoted by the red arrow and circle, and unambiguously demonstrates the presence of aqueous liquid and vapor in the polycrystalline inclusion.

Supplementary Video 2

Video recording of a polycrystalline inclusion from the Buena Vista system during heating from room temperature to >700 °C (temperature shown in lower left), showing the melting behavior. Notice that at T > 518 °C, several bubbles within the inclusion begin to deform in shape and gradually migrate. At T > 597 °C, a meniscus between solid and liquid migrates inward from the inclusion walls. The inclusion is mostly molten above 700 °C, although at least one small opaque grain is still evident in the upper left-hand corner of the inclusion at the highest temperature recorded in this video (731 °C).

Supplementary Video 3

Video recording of an aqueous inclusion from the Buena Vista system during low-temperature microthermometry. Notice the change in the size and position of the vapor bubble during heating above ~–70 °C; followed by increase in size of the vapor bubble heating from –50 to –43 °C. Obvious melting takes place from –43 through >0 °C, and in particular, a distinct melting event takes place at +9.2 to +10.2 °C, which is interpreted as melting of salt hydrate, likely a carbonate or sulfate.

Supplementary Video 4

Video recording of a polycrystalline inclusion from Iron Springs during heating from room temperature to 898 °C (temperature shown in upper right), showing the melting behavior. The onset of melting in this inclusion can be seen at ~190 °C and the majority of the inclusion abruptly melts at >750 °C, followed by the shrinking of the opaque phase which persists to higher temperatures.

Supplementary Video 5

Video recording of an aqueous inclusion from Iron Springs during low-temperature microthermometry. Notice the change in size and shape of the vapor bubble above ~ -82 °C with the onset of ice melting. At -24 °C, ice abruptly melts and the halite crystal begins to shrink with the formation of granular salt hydrate. At ~4 °C, another abrupt melting event occurs, interpreted as melting of salt hydrate, likely a carbonate or sulfate.

Supplementary Video 6

Video recording of an aqueous inclusion from Iron Springs during low-temperature microthermometry. Note the disappearance of the halite crystal at -36 °C and its sudden reappearance following hydrate melting at +12 °C.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Bain, W.M., Steele-MacInnis, M., Li, K. et al. A fundamental role of carbonate–sulfate melts in the formation of iron oxide–apatite deposits. Nat. Geosci. 13, 751–757 (2020).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing