Origin and Nature of Parental Magma and Sulfide Segregation of the Baixintan Magmatic Ni–Cu Sulfide Deposit, Southern Central Asian Orogenic Belt (CAOB), NW China: Insights from Mineral Chemistry of Chromite and Silicate Minerals

Autor: Chao Chen, Bingke Sun, Banxiao Ruan, Mingyang Liao
Jazyk: angličtina
Rok vydání: 2020
Předmět:
Zdroj: Minerals
Volume 10
Issue 12
Minerals, Vol 10, Iss 1050, p 1050 (2020)
ISSN: 2075-163X
DOI: 10.3390/min10121050
Popis: The mineral chemistry of chromite and silicate minerals in the Baixintan magmatic Ni-Cu sulfide deposit in the Northern Tianshan, southern Central Asian Orogenic Belt (CAOB) are reported here. Two types of chromite were identified in mafic-ultramafic rocks. Type I chromite occurs as inclusions encased in olivine and has a primary and magmatic origin and homogeneous composition with Cr# values (49&ndash
66). It is characterized by high Ti contents (0.33&ndash
1.52 wt%) and small quantities of ZnO (0&ndash
0.21 wt%), MnO (0.28&ndash
0.45 wt%), and NiO (0.06&ndash
0.24 wt%) contents. In contrast, type II chromite with interstitial phase and larger compositional variations has significantly higher TiO2 (up to 6.2 wt%) and FeOt contents (up to 69.3 wt%) and slightly lower Al2O3 (minimum 3.0 wt%) and MgO contents (minimum 0.53 wt%). It is considered to crystallize from a more evolved and fractionated melt and suffers from post-magmatic alteration, such as serpentinization and chloritization. The olivine has forsterite values (Fo) varying from 76.8 to 85.6. The parental magma is characterized by high temperature (1389 °
C), high pressure (3.8 Gpa), and high Mg content (11.4 wt%) with oxidized (FMQ + 1.6) and hydrous nature based on compositions of primary chromite and olivine&ndash
chromite pairs. The intrusion originated from high-degree partial melting of depleted mantle that had been modified by crustal components and metasomatized by subduction fluid in a post-orogenic extensional setting. Two stages of sulfide segregation have been recognized. Early segregation led to the depletion of platinum group elements (PGE), and disseminated sulfide mineralization was the product of later segregation. The assimilation of crustal Si and S components played more important roles on sulfide segregation rather than fractional crystallization.
Databáze: OpenAIRE
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