Characteristics of Ore-Forming Fluids in Himalayan Au-Sb-Pb-Zn Polymetallic Belt: Constraints from H-O Isotopes

The Tethys Himalayan metallogenic belt contains dozens of gold, gold-antimony and lead-zinc polymetallic ore deposits with variable sizes. Some Be-Rb-Sn-W polymetallic deposits in the gneiss dome have been found in recent mineral explorations. A 2-stage gold-antimony-lead-zinc mineralization in the orogenic belt has been recognized, one of which is the orogenic gold deposit represented by the Bangbu and Mayum gold deposit. These deposits were formed at 59-45 Ma, belonging to the main collision stage of the India-Asia continental collision. The others are hydrothermal-type gold-antimony-lead-zinc deposits represented by the Jienagepu gold deposit, Cheqiongzhuobu vein-type antimony deposit, Zhaxikang lead-zinc polymetallic vein-type deposit and Jisong lead-zinc deposit. The formation of the deposits is concentrated in the post-collision orogenic stage of 21-12 Ma. A large number of fluid inclusion researches indicate that the ore-forming fluids of Himalayan gold-antimony-lead-zinc metallogenic belt are mainly medium-low temperature (less than 300 °C) and medium-low salinity fluid (<10% NaCleqv). This paper presented a total of 169 H-O isotopic data of quartz, sericite and rhodochrosite that have been published and newly obtained from experiments. It is found that these isotopic compositions constitute three endmembers in the δ18OH2O-δDV-SMOW phase diagram. The endmember A (the Cheqiongzhuobu-type) has characteristics of very low δ18OH2O value (<-13‰) and low δDV-SMOW value (<-111‰, which is close to the Modern Rainwater Line(MRL), and completely falls into the H-O isotope range of Tibet geothermal water. The endmember B (the Shalagang-type) shows the lowest δDV-SMOW value (lowest to -172‰) and higher δ18OH2O (up to 12‰) value than A, that falls within range of the Formation Water. The endmember C constitutes very high δDV-SMOW value (up to -43‰) and a medium δ18OH2O value, which has two typical representative types of the Bangbu-type and the Langkazi-type. The Bangbu-type has the same oxygen isotope range(6‰-13‰) as that of orogenic gold deposit. However, the Langkazi-type shows same oxygen isotope range with the Original Magma Water(OMW). The ore-forming fluids hydrogen and oxygen isotopes of most deposits in Himalayan collisional belt fall among endmembers A, B and C, indicating that most of ore-forming fluids are not of a single fluid source, but have the characteristics of fluid mixing with multiple sources. © 2019, Editorial Department of Earth Science. All right reserved.