Source teacing and He-Ar-S isotopic compositions of ore-forming fluid in the Zhengguang large gold deposit, Heilongjiang Province

This paper is the result of geological survey engineering.

Objective Zhengguang gold deposit in Heilongjiang Province is located in the Ordovician Duobaoshan island arc belt on the northwest side of Nenjiang—Heihe NE trending fault zone in the eastern margin of Xing'an block. By study of the ore samples in the main metallogenic period, we aim to explore the source of ore-forming fluids.

Methods Nine ore samples from the main metallogenic stage were selected for systematic study of the He, Ar and S isotopic compositions.

Results The results show that the ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios for fluid inclusions of pyrite and galena in the gold-bearing quartz veins are 1.95×10^-6-5.03×10^-6 and 349.1-453.9, respectively. The mantle-derived He accounting for 13.17%-44.67%, averagely 27.58%, indicating that the metallogenic fluid is mainly atmospheric precipitation, with the composition of mantle fluid as well, reflecting that the mineralization of gold deposit is closely related to mantle activity. The δ³⁴S of minerals is-1.2‰ --3.9‰, averagely -2.33‰, probably from deep mantle fluid, also with the addition of crustal fluid.

Conclusions The oceanic crust subducted toward Xing'an block, with mantle wedge metasomatized by the subducted fluid, and resulted in partial melting and fluid rising to the shallow surface mixed with the downward precipitation to form the metallogenic fluids. The decrease of temperature and pressure and fluid boiling lead to the change of physical and chemical conditions of the metallogenic fluids and precipitate metallogenic materials.