Mechanism of organic matter assimilation and its role in sulfide saturation of oxidized magmatic ore-forming system: insights from C-S-Sr-Nd isotopes of the Tulaergen deposit in NW China

doi:10.1007/s00126-021-01087-8

GIG OpenIR

	Xue, Shengchao 1; Wang, Qingfei 1; Deng, Jun 1; Wang, Yanning 1; Peng, Touping 2
	Mechanism of organic matter assimilation and its role in sulfide saturation of oxidized magmatic ore-forming system: insights from C-S-Sr-Nd isotopes of the Tulaergen deposit in NW China
刊名	MINERALIUM DEPOSITA
ISSN号	0026-4598
	2022-01-21
页码	19
DOI	10.1007/s00126-021-01087-8
语种	英语
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
摘要	Organic matter assimilation-induced reduction is thought to play a critical role in the formation of magmatic sulfide deposits if the parental magmas are too oxidized to form Ni-Cu deposits, but the mechanism for addition of organic matter to the magma and its global significance are unclear. The Tulaergen deposit, which was formed at 280 +/- 4 Ma, is one of the several major magmatic Ni-Cu sulfide deposits in the Central Asian Orogenic Belt in western China and is associated with oxidized magmas derived from a subduction-modified mantle. Three types of carbonaceous phases are recognized in the sulfide-bearing ultramafic rocks, (i) graphite enclosed in olivine grains, (ii) graphite enclosed in apatite or sulfide, and (iii) solid bitumen in veinlets among silicates. The graphite inclusions are more common than the bitumen veins. Solid bitumen is also found in the Carboniferous volcano-sedimentary rocks which host the deposit. Based on the different modes of occurrences, we interpret that the graphite formed in the magmatic stage and bitumen during the post-magmatic stage. Non-carbonate carbon extracted from the sulfide-bearing ultramafic rocks has delta C-13 values from - 27.6 to - 22.9 parts per thousand, significantly lower than mantle values (- 7 to - 5 parts per thousand), but similar to those of volcano-sedimentary rocks (- 27.5 to - 24.0 parts per thousand). The anomalous C isotopic ratios are attributed to addition of organic matter via dehydration of crustal rocks during magma emplacement. Bulk assimilation of country rocks estimated using Sr-Nd isotopes is only < 5 wt.%, suggesting that the organic matter was incorporated into the magma via selective assimilation. The addition of organic matter to the magma resulted in a sudden decrease of oxygen fugacity of the magma, thereby triggering sulfide over-saturation in the magma. No correlation is observed between delta C-13 values and estimated magmatic oxygen fugacities (f(O2)) for the Tulaergen deposit, which could be due to highly variable delta C-13 values in the contaminants. The delta S-34 values of sulfide ores are from - 1.3 to 3.8 parts per thousand, within the range (- 2.6 to 4.5 parts per thousand) of pyrite grains in the volcano-sedimentary rocks, suggesting that the country rocks could have supplied some sulfur to the magma. Our results propose that selective assimilation of organic matter, even for low abundance organic carbon in country rocks, could play a key role in causing sulfide saturation in highly oxidized mafic magma.
关键词	Organic matter Selective assimilation Magma reduction Sulfide saturation Tulaergen deposit
WOS记录号	WOS:000745365900001
收录类别	SCI
引用统计
文献类型	期刊论文
条目标识符	http://ir.gig.ac.cn/handle/344008/66152
通讯作者	Wang, Qingfei
作者单位	1.China Univ Geosci, State Key Lab Geol Proc & Mineral Resources, Beijing 100083, Peoples R China 2.Chinese Acad Sci, Guangzhou Inst Geochem, State Key Lab Isotope Geochem, Guangzhou 510640, Peoples R China
推荐引用方式 GB/T 7714	Xue, Shengchao,Wang, Qingfei,Deng, Jun,et al. Mechanism of organic matter assimilation and its role in sulfide saturation of oxidized magmatic ore-forming system: insights from C-S-Sr-Nd isotopes of the Tulaergen deposit in NW China[J]. MINERALIUM DEPOSITA,2022:19.
APA	Xue, Shengchao,Wang, Qingfei,Deng, Jun,Wang, Yanning,&Peng, Touping.(2022).Mechanism of organic matter assimilation and its role in sulfide saturation of oxidized magmatic ore-forming system: insights from C-S-Sr-Nd isotopes of the Tulaergen deposit in NW China.MINERALIUM DEPOSITA,19.
MLA	Xue, Shengchao,et al."Mechanism of organic matter assimilation and its role in sulfide saturation of oxidized magmatic ore-forming system: insights from C-S-Sr-Nd isotopes of the Tulaergen deposit in NW China".MINERALIUM DEPOSITA (2022):19.