Abstract

The Himalayan mineral field includes over 50 quartz-vein type Sb-Au deposits, and placer Au deposits. The poorly documented Laqiong deposit is a typical example of quartz-vein type Sb-Au mineralisation in Tethys Himalayan sequence. The orebody are controlled by shallow north-dipping normal faults and north–south trending faults. Magmatic zircons extracted from muscovitic leucocratic monzogranite from the southern part of the Laqiong mine area yield a Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry U-Pb ⁴⁰Ar/³⁹Ar age of ca. 14？Ma from hydrothermal sericite in auriferous sulphide-quartz veins. The ε_Hf(t) values for the magmatic zircon rims range from ？5.4 to ？1.9, corresponding to two-stage Hf model ages of 1403–1214？Ma. Quartz from the mineralised veins has δ¹⁸O_H2O-SMOW values varying from +4.97 to +9.59‰ and δD_H2O-SMOW values ranging from ？119.7 to ？108.1‰. The δ¹³C_V-PDB values for calcite from the ore Stage III range from ？6.9 to ？5.3‰, and calcite from Stage IV are ？3.5 to ？1.7‰. The δ¹⁸O_V-SMOW values for calcite from Stage III are +20.3 to +20.6‰ and for Stage IV are ？6.3 to ？4.9‰. The stibnite and pyrite samples have ²⁰⁸Pb/²⁰⁴Pb ratios of 38.158 to 39.02, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.554 to 15.698, and ²⁰⁶Pb/²⁰⁴Pb ratios of 17.819 to 18.681, and bulk and in-situ δ³⁴S_V-CDT values for stibnite, arsenopyrite and pyrite range from ？1.1 to +2.3‰. The calcite from the orebodies are enriched in MREE and depleted in LREE and HREE. Fieldwork, petrological, and geochemical data collected during our study leads to the following salient findings: the mineralising fluid is a mix of magmatic and meteoric fluids; and the deposit is closely related to the emplacement of Miocene granites originating from a thickened continental crust.

Keywords: Laqiong Sb-Au deposit; U-Pb zircon age; Ar-Ar age; C–H–O–Pb–S isotope; Tethys-Himalayan zone

https://doi.org/10.1016/j.gr.2019.02.010