Petrogenesis of the Sanchahe skarn type iron-gold deposit in Laiwu area, western Shandong: Evidences from zircon U-Pb geochronology and geochemistry

This paper is the result of mineral exploration engineering.

Objective Laiwu Sanchahe iron-gold deposit is the first skarn type iron-gold deposit (without copper) discovered in western Shandong. Previous research on the Sanchahe deposit is weak. The purpose of this paper is to discuss the age of ore-forming pluton, magma sources, petrogenesis and tectonic setting.

Methods We carried out LA-ICP-MS zircon U-Pb dating, major and trace elements analysis.

Results Zircon U-Pb age of pyroxene diorite is (138.4 ±1.2) Ma in the Early Cretaceous. Pyroxene diorite is calc-alkalic (Rittmann index σ = 2.20-2.54) and characterized by high Mg^# and high contents of Na₂O, Sc, Cr, Co and Ni, which demonstrates that it has geochemical affinity with mantle-derived magma. It is enriched in LREE and depleted in HREE, with no obvious Eu anomaly, and shows enrichment in Cs, Ba, Sr and depletition in high field strength elements (Nb, Ta, Zr), indicating involvement of some crustal materials.

Conclusions Geochemical features of pyroxene diorite combined with geochronological data imply that it may be generated by partial melting of the enriched lithospheric mantle which had been metasomatized by the ancient crust materials of the North China Craton, and formed in the strong extensional tectonic background of lithospheric thinning, which may be caused by the retreat of the subducting Paleo-Pacific plate.