Geology, Fluid Inclusion, Stable Isotope And Molybdenite Re-Os Age Constraints On The Genesis Of The Dahu Au-Mo Deposit, Xiaoqinling Region, China

The Dahu Au-Mo deposit is located in The Xiaoqinlin region which is in the Qinling Mountains of eastern Shaanxi and western Henan provinces in central China. This region forms a part of the southern margin of the Archean North China craton. According to microscopic and field observations, the mineralization are divided into four stages, an initial quartz–K-feldspar–molybdenite stage, a second quartz–molybdenite–gold stage, a third quartz–galena–chalcopyrite–gold stage and a final carbonate stage. Two main alteration zones are distinguished, including an inner K-feldspar alteration zone and an outer sericite alteration zone. Two different types of fluid inclusions have been distinguished. Type 1 H₂O-CO₂ inclusions and Type 2 H₂O inclusions. Type 1 H₂O-CO₂ inclusions are the most common type of inclusions and with multiphase ( aqueous liquid +liquidCO₂±vapor CO₂±solid ) at room temperature. H₂O-CO₂ inclusions can be further divided into four sub-types(1A,1B,1C,1D) according to the volume percent of the carbonic phase at room temperature. According to microthermometric data, the ore-forming temperature and pressure range from 198～440°C and 1055～3463 bars respectively. Fluid immiscibility occurred during gold and molybdenite precipitated. Theδ¹⁸OSMOW values for quartz range from 10.2‰to 11.9‰, theseδ¹⁸OSMOW values are calculated to be in equilibrium with ore fluids of between 3.1‰and 6.5‰. TheδD values for fluid inclusion waters range from -117‰to -54‰,theδD values results from bulk extraction of fluid inclusions may reflect a mixture of primary and later secondary meteoric inclusion waters. The ore fluids are mainly derived from mantle but also include some crustal components. Mo is proposed to be derived from crust. Compared with other gold deposits, the local crustal budget of Mo and relatively high ore-forming temperature lead to the enrichment of Mo in the Dahu deposit. This deposit was formed at 207～233Ma, corresponding to the localised extensional setting during the timing of peak collision in the Qinling orogenic belt...