Abstract
Magmatic fluids and leaching of rocks are regarded as the two sources of magmatic hydrothermal deposits, but their relative contributions to the metals in the deposits are still unclear. In this study, we combine major elements and Fe isotopes in two sets of rocks from the Han-Xing iron skarn deposit in China to constrain the iron sources. The positive correlation between the δ56Fe and ∑Fe2O3/TiO2 of altered diorites (∑Fe2O3 refers to the total iron) demonstrates that heavy Fe isotopes are preferentially leached from diorites during hydrothermal alteration. However, except for the pyrite, all the rocks and minerals formed in the skarn deposit are enriched in the light Fe isotope relative to the fresh/less altered diorites. Therefore, besides the leaching of rocks, the Fe isotopically light magmatic fluid also provides a large quantity of iron for this deposit. Based on the mass balance calculation, we conclude that iron from magmatic fluid is almost 2.6 times as large as that from the leaching of rocks. This is the first study to estimate the relative proportions of iron sources for Fe deposits by using Fe isotopes. Here, we propose that the high δ56Fe of magmatic intrusions combining the positive correlation between their ∑Fe2O3/TiO2 and δ56Fe could be taken as a fingerprint of exsolution or interaction with magmatic fluids, which contributes to the exploration of magmatic hydrothermal ore deposits.
Highlights
IntroductionOne of the main prerequisites for the genetic modeling and exploration strategies of metallic mineral deposits is the understanding of their metal source and the mechanism of concentration
One of the main prerequisites for the genetic modeling and exploration strategies of metallic mineral deposits is the understanding of their metal source and the mechanism of concentration.Magmatic hydrothermal ore deposits are the most common metalliferous ore deposits and provide much of the Cu, Mo, Au, W and Fe for the needs of modern society [1]
Based on the discussion above, we propose a scenario for the origin of the Han-Xing iron skarn deposit as follows
Summary
One of the main prerequisites for the genetic modeling and exploration strategies of metallic mineral deposits is the understanding of their metal source and the mechanism of concentration. H and O isotopes of hydrothermal minerals and fluid inclusions in skarn deposits often display mixing between magmatic and meteoric water, whereas S isotopes often show the dominance of magmatic sulfur with minor sedimentary sulfur [9] None of these isotopes can provide direct and explicit information about the metal source. It is worth to note that the lithology of intrusive rocks in the Han-Xing iron skarn ore cluster is diverse (ranging from the intermediate-basic hornblende diorite to the intermediate-acidic quartz diorite) Whether these rocks have the same fractionation features during the skarn-type alteration is still unknown. We analyzed two sets of rocks (different intrusive rocks) from the Han-Xing iron skarn ore cluster for their major elements and Fe isotopes to understand iron isotope fractionation and to evaluate the relative proportion of the two metal sources mentioned above. Each set includes intrusive rocks, skarn, ores and limestone, to cover a whole spectrum of rock types for skarn deposits
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