Assimilation of sulfate and carbonaceous rocks: Experimental study, thermodynamic modeling and application to the Noril’sk-Talnakh region (Russia)

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. sulfate and organic matter-rich sedimentary rocks has been proposed as a possible mechanism for the origin of these exceptional sulfide deposits but the interaction process and the reaction paths have never been fully investigated. Here we clarify, by both experimental petrology and thermodynamic modeling, how sulfate and organic matter assimilation occur in mafic-ultramafic magmas, affecting magma composition, crystallization and sulfide saturation.Interaction experiments were conducted at conditions relevant to the emplacement of Noril'sk type intrusions (1200 °C, ~80 MPa) to simulate the assimilation of sulfate and/or organic compounds by ultramafic magmas. We used a picrite from Noril'sk1 intrusion, and coal and anhydrite from the area as starting materials. The experimental results show that the incorporation of anhydrite into the magma occurs by chemical dissolution in the melt, which increases the magma's sulfur content, but suppresses sulfide saturation and reduces olivine crystallization. Extreme assimilation leads to sulfate saturation in the magma and high dissolved sulfur contents of 0.9±0.1 wt.% S. Conversely, coal assimilation promotes sulfide segregation and magma crystallization, while decreasing the dissolved H 2 O content of the melt and increasing the amount of coexisting fluid phase.We also employed gas-melt thermodynamic calculations to quantify the effect of these assimilations on the redox conditions and the S content of the magma, and investigate the role of temperature, pressure, and initial gas content of the magma in the assimilation process. We quantify how sulfate assimilation strongly oxidizes the magma and increases its S content; both effects are intensified by 2 increasing pressure (from 50 to 100 MPa in this study), decreasing temperature (from 1350 to 1200 °C in this study), and decreasing amounts of fluid phase initially coexisting with the magma (from 2 to 0 wt.%). The interaction with organic matter (CH in this study) induces a strong reduction of the magma, even for extremely low degrees of assimilation (few tenths of wt. %), and the dehydration of the melt.We therefore suggest that in the Noril'sk-Talnakh district (1) additional S was supplied to mantle derived magmas by the assimilation of evaporitic rocks, and was transported during magma ascent in the form of dissolved, oxidized S; (2) a substantial reduction of the magma inducing sulfide segregation and important crystallization then occurred due to the interaction with carbonaceous sediments. This mechanism can potentially produce massive sulfide deposits by imp...

Melt inclusions track melt evolution and degassing of Etnean magmas in the last 15 ka

“…This assimilation enriches the melt in S and to a lesser extent in CaO, while decreases its silica content (Figs. SI6a-b), and strongly oxidizes the magma (Iacono-Marziano et al 2017). Being this a local process that depends on the physical path followed by each magma upon its ascent, and also on its temperature and ascent rate, sulfate assimilation could therefore account for (i) the changes in the redox conditions (and the resulting different timings and amounts of spinel crystallization) observed between the different eruptions (section 4.1.4, Fig.…”

A Raman calibration for the quantification of SO42−groups dissolved in silicate glasses: Application to natural melt inclusions

“…FiGure 5. Parts per million of S6+ determined from Raman calibration as a function of parts per million of S determined from EPMA measurements from Gennaro (2017) and Iacono-Marziano et al (2017) for basalt melt inclusions collected from Etna lava flows and basalt glasses synthesized at high pressure (80-200 MPa) and fO2 conditions below QFM+1.5 (see Appendix1 Table 1). Raman measurements are in favor of an unaccounted amount of S attributed to S2-species.…”

Mineral Chemistry, S-Pb-O Isotopes, and S/Se Ratios of the Niubiziliang Ni-(Cu) Sulfide Deposit in North Qaidam Orogenic Belt, NW China: Constraints on the Parental Magma Composition, Evolution, and Sulfur Saturation Mechanism

“…Crustal assimilation and contamination and fractional crystallization typically occur simultaneously during the evolution and emplacement of magma [53], and the crustal assimilation and contamination, which often occur during the formation of a large-scale Ni-Cu deposit, are considered to be some of the key factors in the formation of a magmatic Ni-Cu sulfur deposit (Voisey's Bay [4], Jinchuan [5], Noril'sk [9], and Xiarihamu [54]). First of all, the presence of many xenoliths in the Niubiziliang complex indicates that crustal contamination inevitably occurs during the emplacement of magma.…”

“…Many investigations have indicated that sulfide liquation led to a sharp loss of Ni content in magma under sulfur saturation, and thus the olivine also showed a loss of Ni [3,9]. In other words, the Ni content of olivine was significantly controlled by sulfide liquation, and the Ni deficit in olivine was determined by the volume ratio of olivine to sulfide, in magma.…”

“…A key factor in the formation of magmatic sulfide deposits is the saturation of sulfur in magma, causing immiscibility between the silicate magma and sulfides, and enrichment in chalcophile elements in the sulfide melt [3]. Sulfur saturation in magma can generally be achieved by any combination of the following processes: (a) Rapid cooling, such as the sulfides at the bottom of the Bushveld complex [67]; (b) magma mixing, such as the Merensky Reef in Bushveld [68]; (c) fractional crystallization, such as the sulfides in chromitites in Bushveld, and the Hongqiling, Huangshan, and Kalatongke deposits [6]; (d) the addition of external sulfur, such as the Voisey's Bay, Duluth, Tianyu, and Baishiquan deposits [7]; and (e) the addition of crustal compositions, such as the Noril'sk, Huangshannan, and Kalatongke deposits [9]. It should be pointed out that the addition of external sulfur and crustal compositions are attributed to the crustal assimilation and contamination, which play a key role in Ni-Cu sulfide deposit formation and often occur during the formation of large-super large Ni-Cu deposits (Voisey's Bay [4], Jinchuan [5], Noril'sk [9], and Xiarihamu [54]).…”