The Laqiong Sb-Au deposit: Implications for polymetallic mineral systems in the Tethys-Himalayan zone of southern Tibet, China

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 granite from the southern part of the Laqiong mine area yield a Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry U-Pb age of 14 ± 1 Ma (n = 12, MSWD = 0.9) that is similar to the 40Ar/39Ar age of ca. 14 Ma from hydrothermal sericite in auriferous sulphide-quartz veins. The εHf(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 δ18OH2O-SMOW values varying from +4.97 to +9.59‰ and δDH2O-SMOW values ranging from −119.7 to −108.1‰. The δ13CV-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 δ18OV-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 δ34SV-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.